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- Theory and Technology for Digital Space
- Transmission and Network of Space Information
- Acquisition and Processing of Space Information
- Application System of Space Information
Theory and Technology for Digital Space
A high compression algorithm for stereo video stream of star field
Weifeng Liu,
Zengfu Wang
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In this paper, a zero-tree wavelet video coding algorithm with extremely high compression is presented. The algorithm is for the purpose of solving the compression problem of stereo star field video. It uses the perspective correlation, temporal correlation and spatial correlation between star-field images as cues for compression. With the algorithm we have realized the real-time compression of stereo video streams with high fidelity.
A new de-blocking algorithm in video coding system
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Block artifact deteriorates the video subjective visual quality, so it is needed to take measures to reduce the effect of block artifact. Unlike MPEG series coding system, H.264 does not use post-processing filter but adds loop-filter in motion vector compensation loop. The most essential points in loopfilter are strength- a value which indicates the strength of block artifact- and filtering operators. But loopfilter in H.264 is not so satisfactory, especially in low bitrate. A new loopfilter algorithm is proposed to improve the performance of filtering. The value of strength is evaluated by coding modes (intra and inter), estimated motion vector, flatness of image region and QP. There are 4 different filtering operators in total. Every operator which is a one-dimension filtering window corresponds a non-zero strength. The experiments show that subjective and objective quality of video can be improved remarkably.
A complete digital simulator for attitude control system design of nano-satellite
Long Han,
Xuecheng Jin,
Xingxing Liu,
et al.
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We have designed a complete digital system simulator for the purpose of spacecraft attitude control. The simulator is composed of several modules including real-time sensor image generation module, processing module, attitude estimate module, and attitude control module. Furthermore, we have developed some virtual reality elements for future work. It will provide some capabilities in real-time data visualization. The experimental results show that this work can help us to validate our attitude sensing and control algorithm in the case without any physical instruments, and can provide usable data for future implementation.
Modeling and analysis of characteristics of clutter for hybrid bistatic space-based radar
Hua Li,
Jun Tang,
Yingning Peng
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This paper sets up a new general clutter model for the hybrid bistatic space-based radar in which Unmanned Aerial Vehicle (UAV) is used as a passive receiver, and the transmitter is placed on the airplane or satellite. Clutter isorange contour and clutter ridge are simulated under a given geometry configuration based on this new model. Then we compare the angle-doppler relationship of clutter of the bistatic airborne radar with that of the hybrid bistatic space-based radar. We can see that the clutter characteristic of the hybrid bistatic system is highly sensitive to the high satellite velocity and the bistatic range, which is quite different from that of the bistatic airborne radar.
A novel BER model for turbo coding over Rayleigh channel
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The sensitivity of channel bit error rate (BER) to the turbo coding parameters (i.e., code rate, iterative number and interleave length, etc) and the wireless channel statistic enlightens us to model a BER for turbo coding over Rayleigh channel. The model presented in this paper synthetically considers and quantificationally analyzes the impacts of all the coding parameters and the wireless channel statistic on the BER, and then emphasizes a simple equation that relates the BER at the encoder to the relevant coding parameters. Based on this model, the BER performance can be estimated even before channel coding given certain coding parameters set and channel statistic. The simulation results show that the model can handle the actual values with high accuracy. The maximal average predictive error is around 0.07%. Moreover, the proposed model is very regular and simple, and can be extended to other cases. These characteristics will make it more useful in practice.
Simulation of wide-band radar echo of satellite in orbit
Xiaofeng Yuan,
Zhihe Xiao,
Hongmei Ren
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The technology of wide-band high resolution is very important to the space measuring radar because it is the foundation to the realization of imaging and identification to the space targets. In this paper, we design a modeling and simulating software to analyze wide-band radar echo of satellite in orbit. In the software, we are able to accurately predict orbital satellite motion[1] of two-body problem, and then we can get the wide-band radar echo of satellite. The intention of this simulation was to create a graphical user interface GUI, which consists of menus, push buttons, text boxes, plots and other interface devices that allow the GUI user to immediately see the impact of various changes. The analysis includes orbit determination and prediction position/velocity, radar cross section (RCS) and ISAR image of satellite in orbit.
Simulation of SAR's in-orbit performance
Bo Yang,
Jianping Yuan,
Xiaokui Yue
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Performances of SAR were measured by observation opportunities to specified targets and possible received reflected signal SNR (Signal-to-Noise Ratio), SCR (Signal-to-Clutter Ratio), integration time etc. Signal propagation model (rain loss, gaseous absorption loss etc) are considered and orbit propagation is integrated by analytical general perturbation method.
Approach of arbitrary clipping in volume rendering
Lan Lin,
Lijun Li,
Jianzhong Zhou,
et al.
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This paper proposes a new clipping method that is capable of using arbitrary geometries in volume rendering. With the assistance of pre-computed outer contour mesh, the method adopts Constructive Solid Geometry (CSG) for clipping, and uses 3D texture for the rendering of clipping surface. The outer contour mesh defines the boundary of the volume data, and improves the efficiency of clipping and rendering. Furthermore, CSG-based clipping method protects the topology of geometries. This method computes the texture coordinate in vertex shader to implement the 3D texture mapping, and achieves high frame rates based on the powerful programming graphics hardware.
Multi-agent-based space information interaction simulation model
Xiong Li,
Degang Liu,
Hua Cong
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Space information interaction process is so complex, distributed and intelligent that we have great difficulties in carrying through the advanced concept technology demonstration for it. To solve the problem, multi-agent-based modeling and simulation technology is applied to space warfare domain. By setting up the mapping from space warfare system's members to respective agents, the architecture of a distributed multi-agent system is designed and its control functions framework is discussed in this paper. As the farther analysis for the system's application, agent model is studied, and the inter-agent problems of task decomposition and task allocation are furthermore discussed. The established distributed simulation system model can be used to understand the external, complicated and intelligent space information interaction resources application activities and can afford advantage for realizing the dynamic space warfare action simulation.
The integration of gis and virtual reality for visualization of battlefield spatial information
Bo Ren,
Qing Jiang,
Li-jun Li,
et al.
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This paper explores the way in which GIS and virtual reality are closely integrated for visualization of battlefield spatial information in distributed interactive simulation system, analysis of battlefield preparation information and query of battlefield dynamic information. Based on this approach, a prototype distributed system is introduced which generates virtual battlefield environment.
An optimized infrastructure of VGE based on grid
Xian Wu,
Depeng Zhao,
Jianhua Gong,
et al.
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Virtual Geography Environment (VGE) is a multi-subject which includes Geographic Information System (GIS), Remote Sensing (RS), Virtual Reality (VR) and network etc. It is inevitable to include a lot of different structure, transdisciplinary and inter-organizations data. With the deep development of VGE, the VGE hopes to attain a primary goal, which deals with geographical data by integrating, storing, indexing, operating and analyzing to get kinds of decision-making information. It makes traditional network service lag behind the development of VGE, because there are some shortcomings in network technology at present such as limited bandwidth, a lot of data exchanging in different organizations, and hard to ensure resource sharing adequately. Grid, as the third generation network, brings new vigor to VGE. It gives a more progress to VGE by combing Grid. Grid-VGE, which abides by the standard of Open Grid Services Architecture (OGSA), takes services as core and constructing virtual database. It can achieve the functions such as integrating and sharing the different structure data, decomposing the task, using the disengaged resource fully and extending the services in VGE. After expounding the framework of Grid-VGE in detail and its pivotal technology, and application example will be given in the last.
Space information technologies: future agenda
Don M. Flournoy
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Satellites will operate more like wide area broadband computer networks in the 21st Century. Space-based information and communication technologies will therefore be a lot more accessible and functional for the individual user. These developments are the result of earth-based telecommunication and computing innovations being extended to space. The author predicts that the broadband Internet will eventually be available on demand to users of terrestrial networks wherever they are. Earth and space communication assets will be managed as a single network. Space networks will assure that online access is ubiquitous. No matter whether users are located in cities or in remote locations, they will always be within reach of a node on the Internet. Even today, scalable bandwidth can be delivered to active users when moving around in vehicles on the ground, or aboard ships at sea or in the air. Discussion of the innovative technologies produced by NASA's Advanced Communications Technology Satellite (1993-2004) demonstrates future capabilities of satellites that make them uniquely suited to serve as nodes on the broadband Internet.
Development of geo-spatial information science and technology -- with our practices in PolyU
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This paper addresses on our practices on the recent development in geo-spatial information technology. Specifically, these include a) spatial data capture technologies based on high resolution satellite imageries and laser scanning technology; b) modern GIS data modeling techniques - towards three-dimensional and dynamic data modeling solutions in GIS; c) spatial information distribution technology based on mobile computing and Internet technologies, and finally d) from certainty-based to uncertainty-based geo-spatial information science.
Subcatchment extraction and runoff simulation utilizing satellite remote sensing data
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In the fields of flood hazard prediction and water resource management, subcatchments and their parameters play very important roles because they are needed for almost all analyses and simulations related to rivers. However, they are prepared by field surveys in usual cases, so they have not yet been prepared for mountainous or deep forest areas difficult to survey, or they are not so accurate although they have been already prepared for those areas. In addition, such kinds of field surveys spend much time and costs, so it seems stalled to prepare subcatchments and their parameters with high accuracy in those areas. In this research, we developed the methods to extract subcatchments and their parameters from satellite remote sensing data. Our method to extract subcatchments needs only DEM obtained by satellite remote sensing, without any field surveys, so we can extract subcatchments anywhere if only DEM exists for there. Topographical parameters of extracted subcatchments are calculated also only from DEM. Using surface data obtained by multi band optical sensor, landcover is determined. These methods will enhance the preparation of subcatchments' parameters for mountainous or deep forest area. As a practical way to use of those extracted parameters, we developed a runoff simulation program too. It simulates draining discharges, using the extracted parameters above and some other parameters. By the simulation for past runoff, with fitting algorithm, it can correct parameters into more suitable.
Study of mobile satellite network based on GEO/LEO satellite constellation
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Mobile satellite network with Inter Satellite Links (ISLs), which consists of non-geostationary satellites, has the characteristic of network topology's variability. This is a great challenge to the design and management of mobile satellite network. This paper analyzes the characteristics of mobile satellite network, takes multimedia Quality of Service (QoS) as the chief object and presents a reference model based on Geostationary Earth Orbit (GEO)/ Low Earth Orbit (LEO) satellite constellation which adapts to the design and management of mobile satellite network. In the reference model, LEO satellites constitute service subnet with responsibility for the access, transmission and switch of the multimedia services for mobile users, while GEO satellites constitute management subnet taking on the centralized management to service subnet. Additionally ground control centre realizes the whole monitoring and control via management subnet. Comparing with terrestrial network, the above reference model physically separates management subnet from service subnet, which not only enhances the advantage of centralized management but also overcomes the shortcoming of low reliability in terrestrial network. Routing of mobile satellite network based on GEO/LEO satellite constellation is also discussed in this paper.
Simulation of target detection using a high range resolution radar
V. M. Orlenko
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The use of wideband radar signals is sometimes more preferable for solving not only the tasks of target resolution, recognition, measurement, and the illumination stealth, but the traditional task of detection too. The latter is due to the decreased fluctuations of echoes. However, if the signal has an excessively wide bandwidth, the losses of non-coherent integration increase and the threshold signals rise. We investigate the detection threshold signals for the targets of different sizes, for illumination signals of various bandwidths, and for detection of different type.
Transmission and Network of Space Information
An analysis of multimedia traffic transmission over OFDM wireless channel
Wenwu Meng,
Guangxi Zhu,
Xuemin Shen,
et al.
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With the rapid growth of wireless access to the Internet, there has been an increasing demand in providing high data rate real time traffic such as audio and video over wideband wireless channels. However, the transmitted multimedia traffic experience frequency-selective fading in wideband wireless channels. By dividing the wideband channel into several smaller sub-channels and sending multimedia traffic in parallel orthogonal sub-channels, which is widely known as orthogonal frequency division multiplexing (OFDM), the frequency-selective channel can be transformed into a set of frequency-flat channels. In this paper, we analyze the effect of sub-carrier assignment on the transmitted multimedia traffic. By increasing the number of sub-carriers, each sub-channel behaves practically as a quasic-static one, such that frequency-selective fading and intersymbol interference (ISI) can be alleviated. Sub-carrier assignment is thus important for multimedia applications. The multiplexing of sub-carriers is introduced to combat the variability of wireless channel, but the performance of wireless channel would also be degraded. We present a quality assessment of audio and video traffic over OFDM wireless channel based on sub-carrier assignment. Simulation results show that proper sub-carrier assignment could significantly reduce errors during high rate multimedia transmission.
Chaining of web services and its application in geographic information integration and visualization
Chuanbin Chen,
Qunyong Wu,
Chongcheng Chen,
et al.
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The rapid development of web services technology ushers Geographical Information Systems (GISs) into the era of geographic information web services (GIWS), which requires a scalable and extensible GISs model to deliver distributed geographic information and GISs functions integrated as independently-provided, interoperable services in a distributed computing environment. Several distributed services can be dynamically chained as a new service to accomplish a specific task. Such a model of service chaining is one of the most important research topics of next generation GISs. The paper highlights the issues of service chaining, the process of combining several distributed, interoperable GIWS dynamically to construct customized applications, and analyses characters of each pattern. Then, based on pattern of client-coordinated chaining, we design a service chaining which is developed in a J2EE development environment using web services technology, and construct a web services-oriented Geo-spatial data integration and visualization platform in order to integrate multi-sources and heterogeneous Geo-spatial data using Geography Markup Language (GML) and Geo-spatial data integration technology, and to visualize geographic information using Scalable Vector Graphics (SVG) and JavaScript technology. During the process of design, several GIWS are defined, and functions, interfaces and related methods of these services are discussed in detail. The paper focuses on the method for chaining distributed GIWS, the mechanism for geographic information dissemination and error handling. Finally, forest Geo-spatial Data which have two typical types of data E00 and Shapefile (SHP) was used to test the platform. The result indicates that using service chaining for multi-sources and heterogeneous Geo-spatial data integration and visualization can efficiently meet customized needs, but further research is needed for better application.
Strategy for solving jointless chain of large-volume transmission of multimedia information in space: application of dynamic information platform
Junfeng Li,
Jinjiang Liu
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Li junfeng, the inventor of the uninterrupted broad-band, large-volume Mobile Satellite Communication System(MSCS), directing the problem of jointless chain of large-volume transmission of multimedia information in space which the world wants to solve, put forward the strategy of applying the technology of dynamic information platform for solving it.
A cross-layer design in V-BLAST system with transmit correlation
Guangxi Zhu,
Xiaofeng Lu,
Liexin Peng,
et al.
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The combination of adaptive modulation (AM) at physical layer and truncated automatic repeat request at data link layer in V-BLAST system is considered in this paper. We deduce the spectral efficiency and the outage probability from our proposed design over frequency-flat Rayleigh channels in presence of transmit correlation. Numerical results reveal that the joint design of AM and truncated ARQ in V-BLAST system can achieve considerable spectral efficiency gain and outage probability reduction.
Core-based shared trees in LEO satellite networks
Lianzhen Cheng,
Jun Zhang,
Xuegui Song
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The satellite network is suitable to provide multicast services with broadcast capability, especially for the low earth orbit (LEO) satellite network due to its short round-trip delays. A new multicast routing algorithm called dynamic approximate center tree (DACT) is proposed specifically for LEO satellite networks in this paper. And a simple core placement method is presented to find the root for every multicast tree. Since processing packets in intermediate satellites consumes much time, paths from the core to other member nodes of a group are built using multicast routing algorithm (MRA) to reduce the number of branches, which tries to merge the links wherever possible. The DACT algorithm can be applied to many-to-many communications in LEO satellite networks. Also it supports dynamic group membership. Delay and tree cost performances of DACT algorithm are compared with those of other two schemes, whose core placement methods are named random core and diameter core (DC) respectively. Simulation results show that DACT produces the lowest mean delay and tree cost among the three methods.
A dynamic clustering algorithm in wireless sensor networks
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It is essential to prolong the lifetime of wireless sensor networks (WSN) via effective cooperation of its sensor nodes. Here, a dynamic clustering algorithm, named DCA, is presented to optimally and dynamically select the micro-sensor nodes to construct a dynamic sensor cluster at each time based on the integrated performance index including information acquirement and energy consumption. In distributed target tracking with WSN, the DCA can avoid the problem of "too frequent cluster head (CH) switches", save more than 80% energy and remain almost same tracking accuracy, compared with the information-driven sensor querying (IDSQ).
Relay-based routing protocol for space networks with predictable mobility
Zhi Zhang,
Guanzhong Dai,
Lixin Li,
et al.
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Future space scientific missions are envisioned to incorporate a large number of satellites and spacecrafts deployed in different orbits to network together into Space Networks. These networks have some unique characteristics such as limited resource of nodes, large latency and intermittent connectivity, which pose challenges to routing. In this paper, we propose a Relay-based Routing Protocol for Space Networks (RRPSN), which exploits the predictability of nodes motion to help deliver packets. Nodes use the link state and trajectory information received from other nodes to construct the routing tables where the next hop node is selected from the current as well as the future neighbors. Three key components of the protocol, including dissemination link information, modified Dijkstra's algorithm and packet processing are described in this paper. The computation complexity and overhead of the protocol is analyzed.
On-board-switch routing based on ant algorithm in satellite ATM networks
Zhongwen Yan
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In this paper, a routing algorithm used in On-Board-Switch units is proposed in satellite Asynchronous Transfer Mode (ATM) networks. The routing algorithm named Ant Algorithm based Switching Routing Algorithm (AASRA) is based on globally optimizing ant algorithm to solve congestion problems in satellite ATM networks. Compared with Link State routing algorithm mostly used in ATM switch units, better performances of AASRA are achieved.
A channel selection collision avoidance multiple access protocol for highly dynamic air-based self-organizing networks
Kai Liu,
Hantao Li,
Feng Liu
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A novel multichannel multiple access protocol, namely channel selection collision avoidance (CSCA) multiple access protocol, is presented for efficient channel sharing in highly dynamic air-based self-organizing networks. It flexibly employs request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and selects conflict-free traffic channel to accomplish the transmission of data packet. The acknowledgment (ACK) packet for the data packet transmission is replied to the sender over another common channel, which completely eliminates the influence of exposed terminal problem. The influence of hidden terminal problem is also greatly reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multiple channels. In addition, any communication pair within locality can take full advantage of multiple TCHs without collisions and spatial reuse of same channel are extended to other communication pair which is at least 2 hops away from them. Finally, simulation results validate the effectiveness of the proposed protocol.
FODA: a novel efficient multiple access protocol for highly dynamic self-organizing networks
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Based on the concept of contention reservation for polling transmission and collision prevention strategy for collision resolution, a fair on-demand access (FODA) protocol for supporting node mobility and multihop architecture in highly dynamic self-organizing networks is proposed. In the protocol, a distributed clustering network architecture formed by self-organizing algorithm and a main idea of reserving channel resources to get polling service are adopted, so that the hidden terminal (HT) and exposed terminal (ET) problems existed in traffic transmission due to multihop architecture and wireless transmission can be eliminated completely. In addition, an improved collision prevention scheme based on binary countdown algorithm (BCA), called fair collision prevention (FCP) algorithm, is proposed to greatly eliminate unfair phenomena existed in contention access of newly active ordinary nodes and completely resolve access collisions. Finally, the performance comparison of the FODA protocol with carrier sense multiple access with collision avoidance (CSMA/CA) and polling protocols by OPNET simulation are presented. Simulation results show that the FODA protocol can overcome the disadvantages of CSMA/CA and polling protocols, and achieve higher throughput, lower average message delay and less average message dropping rate.
Communication plan of GPS monitoring system based on the Internet
Xiangpeng Xing,
Zhenan Liu,
Yuanlu Bao
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In GPS monitoring system, wireless communications network is necessary to keep base station in contact with mobile stations. Public communications network and personal communications network can't work well all the time. In this article, an economical communications network that can be competent for communication of GPS monitoring system is introduced. Personal communications network is used in this GPS monitoring system. In order to enlarge the coverage area and to expand the capacity of the personal communications network, the concept of cellular radio system is introduced. Because only the non-adjacent cells can use the same frequency channel, handoff of mobile station is extremely important when it goes in another cell. The mobile station of the system will know its own longitude and latitude by receiving data from GPS satellites all the time, so it can change its working frequency channel according to its position. Internet, instead of personal communication cable, is used to connect the base stations. So the communications network has the advantage of public communications network and personal one.
A new QoS routing protocol for two-tier LEO/MEO satellite networks
Di Wu,
Qing Li
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The satellite network consumption is related to the amount of the hops of the selected path. The smaller the amount of the hops is, the lower the expense of the network resources is; otherwise, the expense of the network resources is higher. So a new dynamic QoS routing protocol (QRP) which can select path according to the current flow of the network and provide certain QoS (limitation of hops) is presented in this paper. It divides Low Earth Orbit (LEO) satellites into groups according to the footprint areas of the Medium Earth Orbit (MEO) satellites in each snapshot period. Based on the information sent by LEO satellites, MEO satellite managers form two topology views separately for each layer, and then send them to their LEO members. The LEO or MEO satellites select path for arrived requests based on the view they own. The snapshot and group decision method is detailed, and the performance of QRP is evaluated through simulations and compared with that of HSRP protocol.
SM_TCP: a new reliable multicast transport protocol for satellite IP networks
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A new reliable multicast transport protocol SM_TCP is proposed for satellite IP networks in this paper. In SM_TCP, the XOR scheme with the aid of on-board buffering and processing is used for error recovery and an optimal retransmission algorithm is designed, which can reduce the recovery time by half of the RTT and minimize the number of retransmissions. In order to avoid the unnecessary decrease of congestion window in the high BER satellite channels, the occupied buffer sizes at bottlenecks are measured in adjusting the congestion window, instead of depending on the packet loss information. The average session rate of TCP sessions and of multicast sessions passing through the satellite are also measured and compared in adjusting the congestion window, which contributes to bandwidth fairness. Analysis and simulation results show fairness with TCP flows and scalability.
Intelligent call admission control for multi-class services in mobile cellular networks
Yufeng Ma,
Xiulin Hu,
Yunyu Zhang
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Scarcity of the spectrum resource and mobility of users make quality of service (QoS) provision a critical issue in mobile cellular networks. This paper presents a fuzzy call admission control scheme to meet the requirement of the QoS. A performance measure is formed as a weighted linear function of new call and handoff call blocking probabilities of each service class. Simulation compares the proposed fuzzy scheme with complete sharing and guard channel policies. Simulation results show that fuzzy scheme has a better robust performance in terms of average blocking criterion.
Service discovery with routing protocols for MANETs
Xuemai Gu,
Shuo Shi
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Service discovery is becoming an important topic as its use throughout the Internet becomes more widespread. In Mobile Ad hoc Networks (MANETs), the routing protocol is very important because it is special network. To find a path for data, and destination nodes, nodes send packets to each node, creating substantial overhead traffic and consuming much time. Even though a variety of routing protocols have been developed for use in MANETs, they are insufficient for reducing overhead traffic and time. In this paper, we propose SDRP: a new service discovery protocol combined with routing policies in MANETs. The protocol is performed upon a distributed network. We describe a service by a unique ID number and use a group-cast routing policy in advertisement and request. The group-cast routing policy decreases the traffic in networks, and it is efficient to find destination node. In addition, the nodes included in the reply path also cache the advertisement information, and it means when each node finds a node next time, they can know where it is as soon as possible, so they minimize the time. Finally, we compare SDRP with both Flood and MAODV in terms of overload, and average delay. Simulation results show SDRP can spend less response time and accommodate even high mobility network environments.
Energy-efficient error-control schemes for on-chip networks
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On-chip networks (NoCs) for future Systems-on-chips (SoCs) will be required to consume as little energy as possible while satisfying other performance constraints. Meanwhile, NoCs has to deal with the increasing sensitivity of communication links to noise sources such as crosstalk or power supply noise. We focus on the communication reliability for NoCs from an energy-efficient viewpoint. Firstly, a new framework to implement error-control schemes is proposed. No encoders are needed for the communication switches of NoCs in this framework. Secondly, we model on-chip interconnect as noisy channels and evaluate the energy-efficiency of parallel error-detection codes through the experiments on two kinds of codes: PARITY code and Hamming code. The supply voltages Vdd are analyzed to meet the predefined reliability requirements. The results show that up to 15.4% power reduction can be achieved by parallel codes and it can make an appropriate trade-off between power, delay and wires.
A hierarchical QoS routing protocol for LEO and MEO satellite networks
Yunhui Zhou,
Fuchun Sun,
Bo Zhang,
et al.
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The rapid development of onboard processing (OBP) pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter-satellite links (ISLs), and Quality of Service (QoS) of the satellite networks cannot be reliably guaranteed because of great difficulties in processing of QoS service. In this paper, a two-layered LEO and MEO satellite network (LMSN) is presented. Based on the idea of time-slot division, a novel dynamic hierarchical and distributed QoS routing protocol (HDRP) is investigated, and an adaptive Bandwidth-constrained Minimum-Delay Path (BMDP) algorithm is developed to calculate routing tables efficiently by using the QoS metric information which is composed of delays and bandwidth. The performances of the LMSN and HDRP are also evaluated through simulations and theoretical analysis.
Design of chaotic sequences used for satellite spread spectrum communication system
Yong Chen,
Hangsheng Zhao
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In this paper, a chaos-based sequence generator with the multidimensional chaotic system is designed because the sequence generated by the unimodal map can be attacked easily. Some modifications are introduced to the n-dimensional nonlinear digital filters in order to improve the period and distribution property of the resulted sequence. The property of the generated chaotic sequences is similar to that of pseudo-noise (PN) sequences. Test results show that the generator produces sequences with a large code family, good randomness and high security. Chaotic sequences are thus very attractive for satellite spread spectrum systems.
Combined orbit determination satellite-network precision analysis based on whole network adjustment algorithm
Deyong Zhao,
Xiaogang Pan,
Haiyin Zhou,
et al.
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For LEO orbit determination based on Bi-satellite Positioning System (BPS), trajectory error of positioning satellites becomes bottle-neck which improves orbit precision of LEO, so we can take combined orbit determination strategy of BPS and user satellites (LEO) to ameliorate precision. This paper integrates whole network adjustment algorithm into satellite precise orbit determination technology, and brings forward multi-LEO combined orbit determination satellite- network conception based on BPS. Then this paper establishes combined orbit determination models and satellites orbit parameters estimation algorithm based on numerical integral fusion algorithm, and emphasizes on discussing partial parameters weighing adjustment data processing algorithm. Simulation computation results show that whole network adjustment algorithm can ameliorate combined orbit determination precision of satellite network effectively.
High performance packet switches for broadband satellite networks
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Buffered crossbar switches are now becoming very attractive for the high performance packet switches. An architecture that combines the VOQ architecture and internal buffers can eradicate the HOL problems and reducing the output contention. The architecture predominance and the internal distributed arbitration can fit the broadband satellite networks very well. We propose a new scheduling scheme named Rate Durative (RD), which a VOQ is served continuously at the same time considering its priority level under certain rules. Our scheme was shown to handle traffic more efficiently and better than previous schemes. In addition, this scheduling scheme also supports QoS very well
Downlink MIMO-OFDM system with adaptive resource allocation over Rayleigh fading space channel
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In this paper, we investigate adaptive resource allocation strategy for downlink multi-input-multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. We design a transmit scheme as a concatenation of dynamic sub-carriers and bit assignment, adaptive modulation and beam-forming. Our adaptive goal is margin adaptive optimization, which minimize the total transmission power subject to a target BER performance constraint on each sub-carrier, while meeting a constant bit rate. By use of Rayleigh fading model assumption, we introduce a new concept: the channel feedback coefficient, so as to compensate the error inducted by feedback channel. Simulation results show that the proposed resource allocation scheme outperforms the multi-user MIMO-OFDM with static allocation technique, and can lessen the performance loss caused by channel state information feedback error.
A new predistortion based on the double-mode adaptive technique for satellite communications
Henghui Wang,
Hao Zhang,
Wu Ye,
et al.
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Satellite communication channels are equipped with the Traveling Wave Tube (TWT) amplifiers which cause severe nonlinear distortions when they work near saturation. In this paper, a new predistorter is designed based on the double-mode adaptive technique. Firstly, a neural network is used to design the amplitude predistorter, and the error-filtering scheme is applied to improve the classical structure of adaptive control, hence the convergent process turns to be rapid by using the LMS algorithm. Secondly, a real polynomial is applied to identify the phase character of TWT, and then the negative polynomial is copied to the transmitted path. Simulation results show that the compensated system is characterized by the approximately ideal amplifier within the range of saturated input value.
A shortest path algorithm for satellite time-varying topological network
Tao Zhang,
Zhongkan Liu,
Jun Zhuang
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Mobile satellite network is a special time-varying network. It is different from the classical fixed network and other time-dependent networks which have been studied. Therefore some classical network theories, such as the shortest path algorithm, can not be applied to it availably. However, no study about its shortest path problem has been done. In this paper, based on the proposed model of satellite time-varying topological network, the classical shortest path algorithm of fixed network, such as the Dijkstra algorithm, is proved to be restrictive when it is applied in satellite network. Here, a novel shortest path algorithm for satellite time-varying topological network is given and optimized. Correlative simulation indicates that this algorithm can be effectively applied to the satellite time-varying topological network.
A novel handover scheme based on LEO/MEO double-layer satellite network
Bingcai Chen,
Tingxian Zhou,
Boxun Nie
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Due to the limited capacity of a single low earth orbit (LEO) satellite, the blocking probability of guaranteed handover (GH) algorithm increases rapidly in the case of high traffic load. In order to solve this problem, a novel handover scheme defined by multi-tier optimal layer selection is proposed. The scheme sufficiently takes into account the characteristics of the low/medium earth orbit (LEO/MEO) double-layer satellite network and the multimedia transmitted by such network, so it can effectively reduce the traffic load in the LEO which perform GH algorithm. The simulation results show that this approach integrated with GH algorithm used in LEO/MEO satellite network achieves a significant improvement in the QoS performance and practicability of the algorithm as compared to the single LEO layer network.
Research on time division multiplexing device in satellite communication
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Expatiate on method of transmitting data and voice in service channel; with the sync principle of time division system, it manages to transmit voice and data in one line and some schemes are designed. The hardware of one scheme is also made. The product's performance is good and can satisfy designing requirement after tested. The schemes given in this paper has merits of simple circuit, easy realization and stable work. So it has some use value.
Satellite TCP with on-board spoofing proxy
Jiong Liu,
Zhigang Cao,
Jinling Wang
Show abstract
The Transmission Control Protocol (TCP) which is widely used in the Internet, performs very well on wired networks. However, in the case of satellite channels, due to the delay and transmission errors, TCP performance degrades significantly. In this paper, a new idea of placing a TCP spoofing proxy on board the satellite is considered. A novel Satellite Transport Protocol (STP) which takes advantage of the special properties of the satellite channel is also proposed in this paper. By using simulation, as compared with traditional TCPs, we show that the on-board spoofing proxy integrated with the special transport protocol can significantly enhance throughput performance on the high bit-error rate (BER) satellite links, the time needed to transfer files and the bandwidth used in the reverse path are sharply reduced.
Study on statistical models for land mobile satellite channel
Show abstract
Mobile terminals in a mobile satellite communication system cause the radio propagation channel to vary with time. So it is necessary to study the channel models in order to estimate the behavior of satellite signal propagation. A lot of research work have been done on the L- and S- bands. With the development of gigabit data transmissions and multimedia applications in recent years, the Ka-band studies gain much attention. Non-geostationary satellites are also in research because of its low propagation delay and low path loss. The future satellite mobile communication systems would be integrated into the other terrestrial networks in order to enable global, seamless and ubiquitous communications. At the same time QoS-technologies are studied to satisfy users' different service classes, such as mobility and resource managements. All the above make a suitable efficient channel model face new challenges. This paper firstly introduces existed channel models and analyzes their respective characteristics. Then we focus on a general model presented by Xie YongJun, which is popular under any environment and describes difference through different parameter values. However we believe that it is better to take multi-state Markov model as category in order to adapt to different environments. So a general model based on Markov process is presented and necessary simulation is carried out.
Some fundamental considerations about the design of a broadband multimedia communication satellite system in China
Jin-Fei Tang,
Zhong-Wen Yan
Show abstract
China Academy of Space Technology (CAST) is currently making its first attempt to design the Chinese Broadband Multimedia Satellite Communication System. This satellite has many new features and this paper presents some fundamental ideas about its design. The general architecture and protocol stack of the system are outlined first. Some unique characters, such as service classes, beam coverage, frequency planning and multiple access, link budget analysis and radio resource management, are illustrated. It also describes the space and ground segment.
A low complexity multi-user detector for synchronous TH-PPM UWB systems
Fang Lu,
Zailu Huang
Show abstract
A novel low complexity multi-user detector for the TH-PPM UWB systems in synchronous AGWN channel is proposed in this paper. By exploiting the special signal structure of TH-PPM, using time diversity theory and utilizing the decision feedback method, the proposed detector is much lower computation complexity compared with the traditional receiver. Theoretical analysis and simulation results show that the proposed detector achieves better performance than the single user matched filter.
A flexible bandwidth reservation scheme for handover management in LEO satellite systems
Xiaoyan Wang,
Siliang Suo,
Yan Dong,
et al.
Show abstract
This paper proposes a new Flexible Bandwidth Reservation Scheme (FBRS) for handover management and call admission control in Low Earth Orbit (LEO) satellite systems. FBRS mainly aims to the QoS enhancement of multi-service systems. Compared with the other schemes, FBRS has a better performance in call dropping probability and call blocking probability. Moreover, considering the complexity and bandwidth utilization, FBRS outperforms the other schemes. An analytical model has been developed. Simulation results demonstrate the effectiveness of the proposed scheme.
GA based adaptive bandwidth allocation scheme for LEO satellite networks
Yan Dong,
Xiaoyan Wang,
Lin Huang,
et al.
Show abstract
In low earth orbit (LEO) satellite communication systems, frequent intra- and inter-satellite communication handoffs are caused by the high-speed relative motion between the Earth and the satellite. Then frequent handoffs lead to a great call dropping probability which is a main parameter for system's QoS. In this paper, a Genetic Algorithm (GA) based adaptive bandwidth allocation scheme is presented. Aiming at multi-services satellite systems, the scheme focus on the system's QoS which is expressed by the customers' satisfaction degree and handoff call dropping probability. The effectiveness of the scheme is proved by simulation results.
Performance evaluation and channel modeling of MIMO free space optical communication system
Show abstract
Free space optical communication systems represent one of the most promising approaches for addressing the emerging broadband access market, it can provide high bandwidth with no physical contact, but are hampered by signal fading effects due to particulate scattering caused by atmospheric turbulence. In this paper, we propose a new channel model of MIMO free space optical communication system. The physics meaning of this model is very clear, and its format is very simple. Mathematic results show that MIMO is a very effective way for intensity fluctuation reduction induced by turbulence, thus reduce the bit-error-rate of the system.
Performance analysis of LDPC coded OFDM for mobile communications via LEO satellites
Show abstract
This paper presents the performance analysis and optimization of LDPC coded OFDM system which provides high signal quality in LEO satellite communications. A three-state statistical channel model of LEO satellite channel is adopted including Rayleigh, Rician and shadowed Rician distributed submodels. The Irregular LDPC codes without loops of length 4 are optimized by the differential evolution algorithm under this LEO satellite channel. Simulations of BPSK, QPSK, 16QAM modulated systems are also conducted to analyze performances of theses systems.
The scheme for integration of satellite-based C4ISR system
Zhenyu Chen,
Yan Meng,
Yanhong Chen
Show abstract
This paper presents a technical scheme for the integrating of all types of strategic and tactical C4ISR systems through special satellite communication network and proposes information collection and distribution integrating networking scheme. The implementations of compatibility and interoperability of integrated system is described, and also anti-jamming features, covertness, and nuclear survivability are discussed.
Performance analysis of optical DPSK modulation for high speed satellite to ground laser communications
Show abstract
We here study the transmission performance of differential phase-shift keying (DPSK) modulation compared to the traditional On-Off keying (OOK) modulation in the potential high speed satellite to ground laser communication applications. By modeling the channel from the satellite to ground using widely accepted theoretical model and measured results, we estimate the scintillation-induced received power fluctuation. Through simulations, we show that DPSK systems using direct detection with balanced receivers has a clear advantages in performance over the OOK, especially under significant scintillation in the atmosphere.
An improvement of time-varying interference mitigation techniques through collaborative reception schemes
Bo Hu,
Xiulin Hu,
Xiaoyuan Yu
Show abstract
High power time-varying interference or jamming can severely disrupt wireless communication. Therefore, the technique of relevant interference mitigation is needed. Cooperative communication technique can organize a group of single-antenna systems in the same area at different locations as a distributed antenna array. Thus it can approximately achieve the diversity gain of regular multiple-antenna system. This paper is focused on cooperative communication for time-varying interference mitigation. Since some of traditional collaborative reception techniques have the constraint of requiring accurate estimation of SNR, an improvement of time-varying interference mitigation technique based on log-likelihood ratio (LLR) and jammer cancellation is proposed. The simulation results demonstrate that this new improved method enables communication in much more severe interference conditions.
A frequency-domain channel model and emulator for aeronautical communications
Xiaopeng Yang,
Jun Liang,
Kun Yao,
et al.
Show abstract
In this paper, we propose a frequency domain simulation structure for aeronautical wideband frequency-selective channel, which features ground-air and air-air wireless links. With appropriate channel parameters, the emulator can model the parking, taxi and en-route scenarios. The wideband frequency-selective channel consists of some parallel sub-channels in frequency domain, which are assumed to be independent to each other and have Rayleigh-distributed envelopes. The sub-channel models and emulators are based on a simple structure and characterized by flat fading. Through such decomposition approach, a frequency domain frequency-selective channel model can be achieved, which is suitable for an implementation of orthogonal frequency-division multiplexing (OFDM) or multi-carrier code-division multi-access (MC-CDMA) channel emulator on computer. Some appropriate emulator parameters have been proposed through channel sounding data collected for different scenarios. Particularly, in order to emulate the time-varying fading model well, the parameter sets are generated from time to time before the simulation with the same statistics.
BER performance analysis for broadband satellite communication system based on spectrum multiple connection
Yubin Xu,
Yongli Sun,
Xuejun Sha
Show abstract
In order to resolve the problem that RF devices with thinner band width such as heterodyne modulators largely limit the broadband signals transmitted, multiple connection of spectrum can be adopted as a valid measure. This method will inevitably increases bit error rate of the whole data transmission system. This paper aims to give parameter analysis on system BER recruitment.
An adaptive channel prediction algorithm based on fractal Brownian motion model
Gang Su,
Yingzhuang Liu,
Hao Chen
Show abstract
Adaptive channel prediction (ACP) technology is a promising tool for improving the spectral efficiency on time-varying mobile channels while keeping a predictable bit error rate (BER). In this paper, we describe the fractal Brownian motion (FBM) model and get the interior affiliation between the multi-path fading and FBM model by comparing various fractal characteristics of fading signals, especially the existence of self-similarity. The self-similarity of fractal characteristics indicates the existence of a nontrivial predictive structure, where the fractal dimension and variance are important parameters for describing the signal propagation. The wavelet synthesis algorithm based on FBM is proposed to reconstruct multi-path signals, yielding reasonably accurate replication at a cost of allowable calculating error. Simulation results indicate that the FBM model could predict wireless channel more accurately and effectively than those statistical models on the minimum SNR.
A method of links analysis for communication satellites
Xiaohui Hu,
Changwen Zheng,
Lihua Zuo,
et al.
Show abstract
One of the challenges of satellite networks is the development of specialized routing algorithms. The routing algorithms for satellite networks should adapt to the dynamic network topology in real time. In this paper, a time slices calculating algorithm is presented to study the dynamic topology of a double-layered satellite networks and analyze the timing which triggers the recalculation of the routing table and gives a minimum computational efficiency requirement for onboard routing algorithms.
FQPSK techniques for satellite and mobile radio communications systems
Yazhuo Li,
Jing Tang,
Xiaofeng Tao
Show abstract
A continuous phase modulation (CPM) and constant envelope modulation (CEM) alternative of Feher-Patented quadrature phase-shift keying (FQPSK) modulation technique is presented. It is found to provide good spectral efficiencies, power efficiencies, and bit error rate (BER) performance. The modulation schemes of FQPSK are described. The spectral efficiencies, BER performance are also compared with FQPSK and other modulation techniques which are widely used in current mobile and cordless radio standards. The results show that FQPSK modulated signal exhibits much less spectrum spreading than QPSK, OQPSK, and MSK, and the error probability performance of the FQPSK is superior to those in narrow-band nonlinear channels. Based on that, the system capacity and power dissipation are also analyzed for communication systems. It is found that the encoder or receiver for the FQPSK signal to be fully compatible with original I/Q modulated one. FQPSK technique is suitable for nonlinear channels, such as satellite and mobile communications systems reducing the AM/AM and AM/PM adverse effects. At last it is also attempted to extend the application in 3G (CDMA) and 4G (OFDM) mobile communications systems.
A novel cross-layer protocol design for planetary satellite network systems
Lixin Li,
Guanzhong Dai,
Zhi Zhang,
et al.
Show abstract
The Planetary Satellite Network consists of the satellites orbiting the planets to provide communication relay and navigation services to the surface elements, which are often spread out to form an Ad hoc network. However, the current TCP/IP layered protocols have very poor performance in the Planetary Satellite Network, which is characterized by extremely high propagation delays, link errors, asymmetrical bandwidth and blackouts. In this paper, a novel cross-layer protocol design that supports adaptability and optimization across multiple layers of the protocol stack is presented to solve the performance problem of the Planetary Satellite Network. This cross-layer feedback design on a Planetary Satellite device aims to optimize overall network performance by increasing local interaction among protocols, decreasing remote communications, and consequently saving network bandwidth, improving the QoS performance.
Design and implementation of the cluster control node for air ground tactical data link
Baowang Lian,
Feng Wang,
Yongsheng Wang
Show abstract
Aimed at the actual application of the air ground tactical data link, the multi point data transmit air ground tactical data link work model is presented in this paper. The cluster control node is an important part of the work model. The design requirements of the cluster control node are analyzed. A kind of design scheme of cluster control node for air ground tactical data link is presented based on the controller area network bus. The material implementation method is also given. That includes hardware and software design. A few key technology points in the implementation process are presented and discussed. The design thought and implementation method have been verified and proved in a certain actual communication control system.
A cross-layer design for admission control in satellite ATM networks
Rong Lu,
Zhigang Cao
Show abstract
In order to fully utilize satellite link resources, a connection admission control algorithm combined with the resources on-demand allocation (DA) protocol was developed for asynchronous transfer mode (ATM) over satellite communication networks. The algorithm was proposed through an approach of cross-layer design. It is based on a control theory model of the DA protocol and the effects of the protocol on the statistical attributes of the network traffic. Theoretical analysis and system simulations show that the proposed algorithm admits more connections than an algorithm that does not take into account the DA protocol. Thus, the algorithm can increase the admission ratio of traffic connections for satellite ATM networks and improve satellite link utilization.
A novel unicast routing algorithm for LEO satellite networks
Show abstract
One of research challenges in low earth orbit (LEO) satellite networks is to develop specialized and efficient routing algorithms. In this paper, a dynamic source routing algorithm (DSRA) for LEO satellite networks is presented to achieve short end-to-end delay and low computation overhead under the condition that a logical location concept is adopted to hide satellite mobility. In this algorithm, the path between source and destination with minimum propagation delay is designated by source satellite in packet header by an efficient metric < D0, n0; D1, n1; D2, n2 >. Then the packet is forwarded to its destination by intermediate nodes according to the metric. The performance of the algorithm is evaluated through simulation and its computation complexity is analyzed to validate algorithm efficiency.
Study of space wireless local area network application
Qingjun Zhang
Show abstract
This paper describes the standards about wireless local area network (WLAN), and discusses the applications in formatting satellite and the types of WLAN, and give one type of WLAN conception which is Bus/Token-Ring. Finally, it describes some key technologies of the space WLAN.
Improving space laser communication using adaptive optics system based on MEMS technology
Jun Li,
Haiqing Chen,
Guoping Yan,
et al.
Show abstract
Since a free space optics communication system cannot be free of atmosphere turbulence by nature, a micro-Adaptive Optics system based on Micro-Electro-Mechanical Systems technology is discussed, which meets the volume, weight, power consumption, price and heating/cooling requirements in this case. It not only compensates atmospheric turbulence, but also decreases the wavefront aberration resulted by random gravity, heat and component surface error during manufacturing to some degree. The laboratory experiments are also presented to reveal the benefit that such system can provide. Future possible improvements are addressed as well.
New method adaptive to geospatial information acquisition and share based on grid
Show abstract
As we all know, it is difficult and time-consuming to acquire and share multi-source geospatial information in grid computing environment, especially for the data of different geo-reference benchmark. Although middleware for data format transformation has been applied by many grid applications and GIS software systems, it remains difficult to on demand realize spatial data assembly jobs among various geo-reference benchmarks because of complex computation of rigorous coordinate transformation model. To address the problem, an efficient hierarchical quadtree structure referred as multi-level grids is designed and coded to express the multi-scale global geo-space. The geospatial objects located in a certain grid of multi-level grids may be expressed as an increment value which is relative to the grid central point and is constant in different geo-reference benchmark. A mediator responsible for geo-reference transformation function with multi-level grids has been developed and aligned with grid service. With help of the mediator, a map or query spatial data sets from individual source of different geo-references can be merged into an uniform composite result. Instead of complex data pre-processing prior to compatible spatial integration, the introduced method is adaptive to be integrated with grid-enable service.
Approach to spatial information security based on digital certificate
Shengri Cong,
Kai Zhang,
Baowen Chen
Show abstract
With the development of the online applications of geographic information systems (GIS) and the spatial information services, the spatial information security becomes more important. This work introduced digital certificates and authorization schemes into GIS to protect the crucial spatial information combining the techniques of the role-based access control (RBAC), the public key infrastructure (PKI) and the privilege management infrastructure (PMI). We investigated the spatial information granularity suited for sensitivity marking and digital certificate model that fits the need of GIS security based on the semantics analysis of spatial information. It implements a secure, flexible, fine-grained data access based on public technologies in GIS in the world.
Distributed cryptography and distributed transmission of space information
Shengli Liu,
Haijun Lu,
Fei Kang,
et al.
Show abstract
This paper presents the formal definition of distributed cryptography based on the notion of distributed characteristics of space and time, and also defines algorithm group and correlation of algorithm that describes the relationship of algorithms of space and algorithm of time. Then, based on the idea of distributed characteristics of space and time, this paper establishes a model of distributed transmission. The model gives a new method to solve security transmission of space information.
Optimizing radial basis function networks to recognize network attacks for intrusion detection
Wei Pan,
Weihua Li,
Haobin Shi,
et al.
Show abstract
A methodology for optimizing radial basis function (RBF) networks is proposed, which consists of the RBF network and the self-organizing map (SOM), aiming at improving the performance of the recognition and classification of novel attacks for intrusion detection. The optimal network architecture of the RBF network is determined automatically by the improved SOM algorithm, in which the centers and the number of hidden neurons are self-adjustable. The intrusion feature vectors are extracted from a benchmark dataset (the KDD-99) designed by DARPA. The experimental results demonstrate that the proposed approach to recognize network attacks performance especially in terms of both efficient and accuracy.
A novel packet classification algorithm for information security firewall
Show abstract
The exponential growth in optical link speed has stressed the performance of routers and firewall. Consequently, a new breed of microprocessors, called Network Processors (NP), are designed and fabricated specifically to effectively process packets on firewalls and routers. Packet classification is a major function in network processors to fit requirements of next-generation Internet. The paper presents a hardware-based packet classification algorithm for NP. The innovative aspect of the proposed algorithm is to use the NP's parallel character well enough. The algorithm use hash algorithm to make six-dimension classification be three-dimension classification. Compressing the size of classification fields are used for hash input while TCAM performs the lookup of the hash value and source IP. The memory of the algorithm is the total amount of memory needed to store the rules. The search speed of our algorithm is neither sensitive to the size of the rule table. It is only relate to the collision of the hash function. The performance of the proposed algorithm test result demonstrates that the proposed scheme is a sound approach that can be implemented on NP efficiently.
Design and implementation of an intrusion detection system based on IPv6 protocol
Bin Liu,
Zhitang Li,
Yao Li,
et al.
Show abstract
Network intrusion detection systems (NIDS) are important parts of network security architecture. Although many NIDS have been proposed, there is little effort to expand the current set of NIDS to support IPv6 protocol. This paper presents the design and implementation of a Network-based Intrusion Detection System that supports both IPv6 protocol and IPv4 protocol. It characters rules based logging to perform content pattern matching and detect a variety of attacks and probes from IPv4 and IPv6.There are four primary subsystems to make it up: packet capture, packet decoder, detection engine, and logging and alerting subsystem. A new approach to packet capture that combined NAPI with MMAP is proposed in this paper. The test results show that the efficiency of packet capture can be improved significantly by this method. Several new attack tools for IPv6 have been developed for intrusion detection evaluation. Test shows that more than 20 kinds of IPv6 attacks can be detected by this system and it also has a good performance under heavy traffic load.
An enhanced BLUE algorithm based on highest-rate-flow discards
Jiaolong Wei,
Jingjing Qian
Show abstract
Queue management and congestion control are important to the fairness of the Internet. We show analytically that the widely referenced queue management mechanism, RED and BLUE cannot achieve throughput assurance and proportional bandwidth sharing. Then we propose a new active queue management algorithm, called an enhanced BLUE algorithm based on highest-rate-flow discards (EBHFD). An EBHFD gateway detects incipient congestion, and notifies connections either by dropping packets or explicit congestion notification. We show that the performance of EBHFD is better than and comparable to that of BLUE in terms of fairness and better than RED in terms of queue length.
Acquisition and Processing of Space Information
Application of information processing technology about chaos theory
Chunyan Nie,
Yaowu Shi,
Wensuo Yi
Show abstract
The basic principle is introduced to measure weak sine signal using chaos theory. On this basis, criterion of measuring chaos phenomenon is provided. In this paper correlation detection method and modern spectrum estimation method is respectively combined with famous chaos system to constitute mixed measuring system to detect weak signal. At the same time the simulation system block and results are given. Simulation results show that the measuring accuracy to estimate sine signal is improved, which is one of effect methods to measure weak signals further more.
Low sampling frequency processing for ultra-wideband signals
Yonglun Wan,
Qiang Si,
Youxin Lu,
et al.
Show abstract
Ultra-wideband (UWB) signals are widely used in radar, navigation and satellite communications. It is rather difficult to process UWB signals. In this paper we adopt dechirp pulse compression method to process the received UWB linear frequency modulated (LFM) signals. UWB signals are converted into signals with frequency components that are proportional to the relative range between the target and the reference target. It means to select low-speed analog-to-digital converters (ADC) for sampling UWB signals. The simulation results show that LFM signal with 600MHz center frequency, 200MHz bandwidth and 30usec pulse width can be processed under 70MHz sampling frequency by means of the method.
An effective topological adjustment on vector maps for AVL
Yuanlu Bao,
Zhenan Liu,
Jin Qu
Show abstract
Advanced Vehicle Location (AVL) needs accurate vector maps. This paper presents a discrete topological transformation to get vector map nonlinear geo-adjustment. The new algorithm adjusts a sample point by a sample point. At the time of adjusting one point, the algorithm also automatically adjusts all its neighboring area points within a block/polygon area keeping their topology. If the selected sample point set has enough distribution, then the vector map will have an accurate adjustment for all map points because the total nodes on the map is very limited on the vector map. Example shows the effectiveness of the new method on vector map automatic geo-adjustment.
A new concept: critical number of looks for multilook processing method for InSAR noise suppression
Show abstract
Interferometric synthetic aperture radar(InSAR) is usually employed to provide altitude information of terrain. There are many factors to cause interferogram noise and the noise decreases height measurement accuracy of InSAR. In this paper, Multilook processing technique, which is used to reduce interferogram noise in InSAR, is studied. And a new concept - critical number of looks for multilook processing is proposed. The number of looks must be smaller than critical number of looks when multilook processing is applied to the interferogram noise suppression. The new concept benefits the multilook processing for InSAR noise suppression. With the knowledge of critical number of looks, the proper number of looks can be chosen for InSAR multilook processing to reduce the interferogram noise. The equations of range and azimuth critical numbers of looks are presented for both single baseline spaceborne InSAR and multibaseline spaceborne InSAR. The critical number of looks can be obtained from these equations. In the end, multilook processing with different numbers of looks is applied to InSAR simulated data and the results show the validity of critical number of looks in InSAR.
Interferometric baseline design and performance evaluation for 3-dimensional formation flying SAR satellite system
Show abstract
The orbital elements determination method for 3-demensional Formation-flying SAR satellites system is developed, basing on the closed form solution to the free orbit movements acquired from Kepler's equation. The quantificational relationship between the interferometric baseline, the orbital elements and formation configuration parameters is induced. The general baseline design approach is proposed, basing on the analysis of critical space baseline and critical time baseline. Typical configurations are selected for the L-band FF-SAR satellite systems, including circular configuration, circular horizontal projection configuration and linear horizontal projection. The efficiency of the baseline design technique is validated by the computer simulation results with measurement accuracy of terrain height and velocity.
Application of onboard radar to collision detection
Lei Han,
Lei Chen,
Bozhao Zhou
Show abstract
For the collision detection is based on the orbit prediction, the most dangerous debris is the one big enough to destroy the spacecraft but could not be tracked and catalogued by the ground-based surveillance net. The radar equipped on the large-scale spacecraft could track such kind of debris to supplement the space objects catalogue and propagate for the collision detection. The onboard radar has the shorter tracking duration than that of the ground-based radar. For an uncatalogued space object, the batch or least-squares estimation method should need the sufficient tracking data to meet the precision of the preliminary orbit. On the other hand, for a cataloged object, the known orbit information could be used to propagate the state vector at the time of each measurement and the sequential estimator or filter is employed to improve the priori orbit information. And the updating rate of the orbit information can be computed according to the orbital space-time relationship between the two objects. Then the new orbital information could modify the orbital propagation to detect the objects which would most probably collide with the spacecraft.
The estimate of ballistic trajectory and the analysis of its precision in space for early warning of medium or low orbit satellite
Han Long,
Zhenjie Li,
Dongyun Yi
Show abstract
In this paper, we studied the problem of estimating trajectory parameters of ballistic missile (BM) such as the first detected point and impact position, in space early warning of a single low orbit satellite, and provided corresponding precision analysis. The main idea is that through matching the observation trajectory data to the trajectory equation of free flight phase, first detected point and the main trajectory is determined. Simulation results review that those algorithms in this paper is efficient.
A processing method for rice crop inventory using multi-date ENVISAT-1 ASAR data
Feilong Ling,
Xiaoqin Wang,
Xiaoming Shi
Show abstract
Synthetic Aperture Radar (SAR) is anticipated to be the dominant high-resolution remote sensing data source for agricultural applications in tropical and subtropical regions due to its independent from cloud cover. ENVISAT-1 ASAR is the most advanced satellite radar-imaging instrument, its capabilities include beam steering for acquiring images with different incidence angles, duel polarization and wide swath coverage. Agricultural crop inventory based on remote sensed data will be improved greatly by ASAR's new capabilities. In this paper, a procedure has been developed using multi-date ASAR data for rice crop inventory. The procedure comprises two parts: data preprocessing and classification of multi-date data for rice field. In order to carry out the research, 6 scenes of ASAR images covering Fuzhou area year round of 2004 were used. PCI 9.1 is used for data preprocessing which includes data calibration, image co-registration, speckle suppression, orthorecitification and amplitude-to-dB conversion. Some novel methods are applied in this procedure such as correlation matching for image co-registration and multi-channel filtering for speckle suppression. Object-oriented classifier was used, compared with K-means supervised classifier and maximum likelihood classifier, and higher classification accuracy was achieved. By adopting the procedure presented in this paper, more than 90% classification accuracy for rice was achieved in Fuzhou city with multi-date Envisat ASAR data. This indicates that the procedure is feasible for rice crop inventory using multi-date ASAR data.
Impact analysis of residual code phase and carrier frequency error on GPS signal tracking and its improvement
Yunlong Zhu,
Dongkai Yang,
Qishan Zhang
Show abstract
In this paper, the com bining impact of residual code phase and carrier frequency error on correlation is discussed in detail. And the correlation expression is given according to the code phase and carrier frequency estimate error. A code phase discrimination method and a carrier frequency discrimination method are proposed based on the discussion mentioned above. The analysis and simulation indicate that the proposed methods can restrain the impact of carrier frequency error on code discrimination within a small range, and the impact on frequency discrimination from residual code phase error is also limited to be lower. Tracking precision is improved obviously.
Effect of low level atmospheric parameter on detection of remote aerial target by using ground-based microwave radiometer
Zubiao Xiong,
Yu Liu,
Yaoting Zhu,
et al.
Show abstract
It is necessary to study the attenuation model of atmosphere channel in order to detect remote aerial target by ground-based microwave radiometer. Firstly in this paper, according to the inhomogeneous vertical profile of atmospheric attenuation, a layered atmosphere is modeled between ground and the target to be detected. It is assumed that the atmosphere distributing is homogeneous in each layer, but unequal between the layers. Therefore, the microwave is refracted on the interface and its propagation path is a broken line. To ensure the accuracy of the model, hundreds of layers are occupied and the thickness of them increases exponentially from the ground. Then by using the United States Standard Atmosphere in 1976 and the MPM93 model, the theoretic values of the atmospheric opacity are computed. The results are compared with some experimental measured values. Based on the comparison, the validity and practicability of the layered atmosphere model is discussed. Finally, influence of operating frequency, elevation angle and altitude of radiometer on slant-path attenuation is analyzed, and some suggestions about these three parameters are provided.
Ambiguity resolution of double-difference GPS short baseline using genetic algorithm
Show abstract
The ambiguities must be resolved to their correct integer values in order to exploit the high accuracy of the carrier phase double-difference observables. The criterion used by ambiguity resolution technique is the selection of the integer combination that satisfies to the least squares adjustment. Integer ambiguity resolution could be regarded as a kind of global optimization search process. Genetic algorithm (GA) has the advantage to search the global optimum results in the robust and parallel way. Individual encoding is important to improve the efficiency of GA. This paper analyzed two encoding methods, which are binary code and real code, for GPS carrier phase double-difference short baseline ambiguity searching. Then the resolutions of the integer ambiguity using GA with binary and real code were compared. GA with binary code was used to determine the optimum integer estimation after float ambiguity solution resolved. However, due to non-integer nature of baseline vectors values, GA with real code was used to solve baseline vectors and double-difference ambiguity. Real encoding method made up for some deficiencies such as longer code lengthiness, larger solution space and longer time consumed in GA with binary code to non-integer solution. Numerical results showed that GA can be realized to resolve ambiguity resolution of DGPS with whether binary code or real code. The accuracy of both results was basically identical. On the premise of accurate float ambiguity solution, the convergence speed of GA with binary code was faster than that of GA with real code. The resolution of GA with real code was more robust and reliable because it did not depend on the accuracy of initial values.
The compensation method of high resolution range profile of the space radar target
Zhihe Xiao,
Chao Ning,
Hongmei Ren
Show abstract
The compensation method of high resolution range profile of radar targets was talked over in this paper. Based on the need of the wide band high resolution signal processing, this paper discussed the one dimensional high resolution range profile (HRRP) obtained by the linear frequency modulated (LFM) wave. Because of the effect of velocity of the target, the one dimensional range profile will be displaced and defocused. We suggested some new methods to alleviate the effect of velocity, and simulated with the point scattering source model and the measured data of target model.
Variable parameter log-polar transformation and analysis of its calculation quantity
Show abstract
Based on the classical log-polar transformation (LPT), the variable parameter log-polar transformation (VPLPT) is proposed. In the new algorithm, the size of uniform sampling central area is freely adjustable according to different vision task and its high resolution is reserved. The peripheral area is processed with log-polar transformation, which base can be adjusted. The calculation quantity of the two algorithms is analyzed respectively and compared with each other. The result shows the new algorithm's rapidity.
Average distance measurement model for pulse radar altimeter
Show abstract
A new theoretical model for measurement of average distance from radar to the arbitrary distributed rough surface is concerned in this paper. Reviewing the assumption of the Brown's model, the application restrictions of traditional algorithm based on the model is presented. Through constructing simplified model of the scattering surface, combining the radar equation, analyzing the quantitative relation between the amplitude of the waveform and scattering surface, the simplified expression of average distance measurement is obtained. Furthermore, the concept of average distance measurement model is emphasized and the improvement method is suggested.
A new algorithm of joint frequency offset and symbol timing acquisition for pi/4-DQPSK signals in low signal-to-noise ratios
Hangsheng Zhao,
Zhongmin Gan
Show abstract
A new algorithm of frequency offset and symbol timing acquiring is derived for π/4-DQPSK signals in low signal-to-noise ratios (SNR). Comparing with some conventional schemes, this algorithm can joint frequency offset acquisition and symbol timing acquisition and needs fewer preamble date. It can work quite well at 3 dB SNR. Even if SNR is zero, it also gives an acceptable performance.
Unified parametric ICA algorithm for hybrid sources and its stability analysis
Fasong Wang,
Hongwei Li,
Rui Li,
et al.
Show abstract
Independent component analysis (ICA) refers to extract independent signals from their linear mixtures without assuming prior knowledge of their mixing coefficients. The purpose of this paper is to develop a novel unified parametric ICA algorithm, which enable to separate hybrid source signals including symmetric and asymmetric sources with a self-adaptive score functions. It is derived from the parameterized asymmetric generalized Gaussian density (AGGD) model. The parameters of the score function in the algorithm can be chosen adaptively by estimating the high order statistics of the observed signals online. Stability analysis of the proposed AGGD-ICA learning algorithm is also discussed. Compared with conventional ICA algorithm, the method can separate a wide range of source signals using only one unified density model. Simulations confirm the effectiveness and performance of the proposed algorithm.
Blind estimation of pseudo-random sequences of non-cooperative direct sequence spread spectrum signals in flat-fading channels
Tian Bu,
Zhongzhao Zhang
Show abstract
A novel scheme is proposed to blindly estimate the pseudo-random sequences of direct sequence spread spectrum signals in a non-cooperative context, based on sequential Monte Carlo methodology and eigenvalue analysis technique, with additive white Gaussian noise in flat-fading channels. All the prior knowledge required is only the period of the pseudo-random sequence, which was well developed by the present authors. Because the fading process can be represented by a wavelet basis, the sequential Monte Carlo technique is employed to estimate the transmitted symbols. According to the period of the pseudo-random sequence, the received signals are divided into vectors. The autocorrelation matrix of each vector is accumulated into an estimation matrix, whose corresponding eigenvectors of two larger eigenvalues reconstruct the pseudo-random sequence. Simulation results are provided to demonstrate the good performance of the proposed blind estimation method.
Code acquisition with adaptive threshold for TH-UWB systems
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In this paper, we present a pseudonoise(PN) code acquisition scheme with adaptive threshold for Ultra Wideband(UWB) digital receivers, in which Time Hopping(TH) was introduced to allow for multi-user access(MA). The adaptive threshold setting is based on a so-called constant false alarm rate(CFAR) criterion, which will provide small probability of false alarm and large probability of signal detection compared with the fixed threshold algorithm. The noise and interference are estimated by integrating the total received signal power. The performance of the proposed acquisition scheme is analytically evaluated in terms of the detection probability Pd, the false alarm probability Pfa, the mean acquisition time TMA. Analysis in theory and numerical results show that the proposed scheme may actually perform somewhat better than the fixed threshold schemes.
Situation assessment for air combat based on the Bayesian networks technology
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This paper researches on the method of situation assessment for the air combat based on the Bayesian networks technology. It analyzes the events occur in the process of air combat, and presents a hybrid method of fuzzy sets and Bayesian networks to detect these events. Then, it presents a method to construct Bayesian networks using the events and then uses the networks to reason the purpose of enemy fighter pilots. Finally, it shows the method by an illustrative example.
Doubly weighted MUSIC algorithm for broadband DOA estimation using microphone arrays
Jingran Lin,
Qicong Peng,
Huaizong Shao
Show abstract
The performance of MUSIC (multiple signal classification) algorithm degrades substantially in practice due to array perturbations or the low SNR (signal-to-noise ratio). In this paper, we present a doubly weighted MUSIC algorithm that provides improved robustness for broadband DOA (direction-of-arrival) estimation using microphone arrays. Firstly, a weight matrix, imposed on the noise subspace of the spatial covariance matrix, is used in estimating DOA at each frequency bin. Secondly, another weight vector, based on the SNR at each bin, is imposed on the original estimates to calculate the final broadband DOA. The former decreases the standard deviation of the narrowband DOA estimation at each bin, which is caused by array perturbations, and the latter weakens the negative effect of those estimates at the low SNR bins on the final broadband DOA estimation. The two weighting operations together improve robustness of the broadband DOA estimation dramatically. Numerical examples show the effectiveness of the proposed method.
Fast implementation of long sequence wavelet transform based on partition
Bin Wu,
Xinhua Lv,
Xuejun Zhou
Show abstract
Based on the analysis of Mallat algorithm formulas, an improved wavelet transform implementation of high efficiency is proposed in this paper. Long sequence is partitioned into short ones by utilizing overlap-saving method. Cyclic convolution is proposed to be used in place of linear convolution in each section. Computer simulation shows that high accuracy and efficiency can be achieved by using this method. The speed of computation is greatly improved compared with Mallat algorithm involving linear convolution. This method is of good parallel property and is easy to be carried out in real-time by digital signal processor (DSP).
Reconfigurable 3D colour information acquisition system based on laser
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The new reconfigurable 3D laser colour information acquisition system has been developed to overcome the problems of the former three-dimensional laser color scanner (3DLCS). The system basic theory of measurement and whole structure are introduced. The hardware system architecture based on FPGA parallel processor has been designed and its work principle has been discussed. The key algorithms of extracting central line of laser stripe, head contour and central colour line from video image are accomplished by FPGA processor, then these important information is sent into host computer through PCI interface which accomplish advanced image processing, 3D reconstruction and 3D modeling. The key algorithms are described too. The system can acquire 3D and colour information of object in real time and the 3D images are displayed promptly on the screen of host computer. Finally, the experimental results of system are shown. By adopting ASIC and master-slave system architecture, it enhances the speed of obtaining 3D information of object greatly and overcome the computational bottleneck. The system performance is improved and the devices are low cost. In addition, it can implement special function and has good security and is applicable to many cases.
A stitching algorithm of remote sensing images from aviation swaying camera
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Stitching of images is the task of fusing a collection of images with smaller field of view (FOV) to obtain an image with a larger FOV. The need for this procedure is motivated by a variety of applications, especially including the application in the aviation remote sensing field. The paper puts emphasis on studying how to stitch the image set taken by the aviation swaying camera. In order to accomplish this task, we should know how the aviation camera sways. So the camera swaying model is presented firstly. The possible geometrical distortion of the image set can be known from the camera swaying model, and it includes two parts: the rotation and the perspective distortion. Aiming at the rotation distortion, we propose a novel image rotation method that can save the computation time. In this method, we rotate the four edge lines of the image utilizing the traditional rotation method. According to the relative position rotation invariability of any pair of points in an image, the other points except that on the four edge lines then can be rotated. The last step of the algorithm is the stitching which needs not only to search the optimal matching area between neighboring images but also to stitch the image set smoothly. The paper presents an extremum matching method based on the difference image, by which we can find the optimal matching areas between neighboring images in the image set. Through linearly changing the stitching weight of overlap areas, the image set can be stitched smoothly. The theoretical analysis and the experimental results have demonstrated the feasibility and validity of this stitching algorithm for the remote sensing images from the aviation swaying camera.
Classification of typical canopies over the Chong Ming eastern tidal flat from data fusion of ERS-2 SAR and Landsat ETM+
Show abstract
Based on analysis of the reflection spectra and backscattering characteristics of typical land canopies, the Chong Ming eastern tidal flat of the Yangtze River estuary, as a typical case, is chosen for study of data fusion from ERS-2 SAR and Landsat ETM+ observations. The ERS-2 SAR data are first filtered using the wavelet method and extraction of the image texture. And the Landsat ETM+ data is treated using the HIS transform. Two images are fused on the level of the characteristics class, and information extraction and classification of typical land canopies are discussed. The results are well validated by the ground truth from our field survey.
Moving target parameter estimation of SAR after two looks cancellation
Rongbing Gan,
Jianguo Wang,
Xiang Gao
Show abstract
Moving target detection of synthetic aperture radar (SAR) by two looks cancellation is studied. First, two looks are got by the first and second half of the synthetic aperture. After two looks cancellation, the moving targets are reserved and stationary targets are removed. After that, a Constant False Alarm Rate (CFAR) detector detects moving targets. The ground range velocity and cross-range velocity of moving target can be got by the position shift between the two looks. We developed a method to estimate the cross-range shift due to slant range moving. we estimate cross-range shift by Doppler frequency center. Wigner-Ville Distribution (WVD) is used to estimate the Doppler frequency center (DFC). Because the range position and cross range before correction is known, estimation of DFC is much easier and efficient. Finally experiments results show that our algorithms have good performance. With the algorithms we can estimate the moving target parameter accurately.
Subspace-based CFAR detection of vehicles from forests in SAR image
Yanfei Zhang,
Jian Guan,
Jie Wang,
et al.
Show abstract
Automatic detection of military vehicles hidden among forests in synthetic aperture radar (SAR) image is a challenging and difficult task because tree trunk clutter often appears as locally bright as obscured targets. We apply subspace-based detection methods to treat the problem as detecting subspace signals in structured subspace interference and broadband noise of unknown level. Specifically, tree trunk clutter is modeled as structured isotropic interferences with unknown amplitudes while dominant vehicle scatterers as anisotropic dihedral responses. Matched subspace detector (MSD) with constant false alarm rate (CFAR) property is derived. Experiments on both simulated and real foliage-penetrating (FOPEN) SAR image show that the proposed detection scheme has good detection performance even at low false alarm rates.
Target feature-enhanced of SAR image based on regularization of lk norm
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Target feature-enhanced processing of SAR image is meaningful to SAR ATR. One regularization method based on lk norm used for target feature-enhanced of SAR image is discussed in this paper. This method exploits the useful sparse prior information which is well consistent to the statistically property of SAR image, makes up the additional constraint condition, turns the problem of target feature-enhanced processing of SAR image into the simple-formed optimization problem. A fast iterative algorithm is proposed to solve the optimization problem. The Simulation results and computational results of measured data prove its validity.
An adaptive algorithm for removing the blocking artifacts in block-transform coded images
Show abstract
JPEG and MPEG compression standards adopt the macro block encoding approach, but this method can lead to annoying blocking effects-the artificial rectangular discontinuities in the decoded images. Many powerful postprocessing algorithms have been developed to remove the blocking effects. However, all but the simplest algorithms can be too complex for real-time applications, such as video decoding. We propose an adaptive and easy-to-implement algorithm that can removes the artificial discontinuities. This algorithm contains two steps, firstly, to perform a fast linear smoothing of the block edge's pixel by average value replacement strategy, the next one, by comparing the variance that is derived from the difference of the processed image with a reasonable threshold, to determine whether the first step should stop or not. Experiments have proved that this algorithm can quickly remove the artificial discontinuities without destroying the key information of the decoded images, it is robust to different images and transform strategy.
Investigation of image corner features matching algorithm based on heuristic local geometric constrained strategy
Ru An,
Huilin Wang,
Xuezhi Fen,
et al.
Show abstract
The main aim of the study is to improve the performance of image matching algorithm of Scene Matching Aided Navigation System. In the paper, corner-based image matching algorithm with automatic search of homonymous corner pairs is discussed. Gaussian Low-pass Filter with different kernels according to the spatial resolution of reference image and real-time image are applied to the image in preprocessing stage to remove noise, to get over spatial resolution difference between reference image and real-time image and to enhance the repeatability of corner detection. A novel fast corner detector, which is based on SUSAN and the geometric structure analysis, is designed to extract corner features. Normalized co-correlation algorithm is applied in search of homonymous corner pairs through a small window centering corners. A heuristic local geometrically constrained strategy is employed to remove mis-matched corner pairs in initial matching stage. In the end, matched corners, in combination with a suitable polynomial algorithm, are used to match and rectify images.
Analysis of DOA estimation spatial resolution using MUSIC algorithm
Yue Guo,
Hongyuan Wang,
Bin Luo
Show abstract
This paper presents a performance analysis of the spatial resolution of the direction of arrival (DOA) estimates attained by the multiple signal classification (MUSIC) algorithm for uncorrelated sources. The confidence interval of estimation angle which is much more intuitionistic will be considered as the new evaluation standard for the spatial resolution. Then, based on the statistic method, the qualitative analysis reveals the factors influencing the performance of the MUSIC algorithm. At last, quantitative simulations prove the theoretical analysis result exactly.
Airplane detection in remote sensing image with a circle-frequency filter
Hongping Cai,
Yi Su
Show abstract
This paper presents a new approach to detect airplanes in panchromatic remote-sensing images. A circle-frequency filter(CF- filter) is given to locate airplane centers from the background. The filter extracts candidate points of airplane centers first. Then through a simple clustering method, airplane centers can be located. 8 panchromatic images of 1.0m~4.0m resolution, including 65 airplanes, are tested with this approach. 59 airplanes are detected and 5 times are false alarmed.
Extraction of complex object contour
Famao Ye,
Lin Su,
Shukai Li,
et al.
Show abstract
In this paper an approach based on particle filtering to extract complex object contour from imagery is presented. To deal with sharp tips of complex object, we take an adaptive state transition model with adaptive change in contour direction and adaptive number of particles. We not only use the information of luminance gradient but also use the speed and the direct of the move to compute the likelihood. Experimental results show that the proposed approach is capable of locating the target object contour of sharp tips accurately in the interactive way.
The algorithm based on the texture of automatic cloud cover assessment
Show abstract
If the luminance of the cloud is high, we can identify the cloud by the luminance threshold. If the variance of the cloud is high, we can identify the cloud by the frequency information. If the difference in brightness between the light and dark cloud of a picture is big, they are difficultly identified. However, this type of the cloud has an obvious edge. This paper presents a new algorithm on base of texture to identify the cloud.
A remote sensing image ground control point matching algorithm based on feature corner and dynamic template
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An optimized point matching algorithm is introduced in this paper: the main idea is to extract ground control point by a new feature corner extraction method, then to search the sub-image unequdistantly with dynamic template during template matching calculation. The result of the experiment demonstrates that, the algorithm can extract valuable feature corners, it has more matching accuracy and efficiency, and it has more adaptability and applicable value.
A homogeneous ping-pang architecture for SAR real-time imaging
Jia Xu,
Yingning Peng,
Jun Li,
et al.
Show abstract
Based on the range-Doppler imaging algorithm, a novel homogeneous ping-pang architecture is proposed for synthetic aperture radar (SAR) real time imaging. Different from the normal heterogeneous pipeline architecture, almost the identical design on hardware and software is adopted by the two ping-pang nodes. Therefore, more scalable and efficient performance may be obtained for the proposed design with a balanced computational load, and it is especially suitable to be implemented via the commercial-off-the-shelf (COTS) platform.
An area change detection method of remote sensing image using historical land use graph
Show abstract
Kinds of historical vector graphs have been gradually accumulated by ground truth data or other reliable sources, but these data have not been fully adopted to detect change in remote sensing circle. In this paper we describe a novel change detection method. The key feature of the new method is the use of a piece of historical land using vector graph. By combing one satellite image and the vector graph after necessary geometric rectification, we could detect change region of the satellite image corresponding to patches in the vector graph. Through adopting coefficient of part change and coefficient of entire change, the study calculates statistics indexes of image corresponding to patches of vector graph with different coefficient groups and assesses the computing results by kappa matrix. According to analytical results, the coefficient of entire change is more important to the number of commission error than the coefficient of part change. This method is benefit to the reuse of historical vector graphs. As the image-processing work of this method is based on patches of historical vector graph, it helps to the development of different vector graphs.
Extraction of tree height from large viewing angle aerial images
Show abstract
Due to the complexity and non-regularity of tree shapes, traditional digital photogrammetry using stereo matching method is difficult to obtain the accurate tree height, This fact therefore limits the application of the aerial digital photogrammetry technology in the power line survey. This paper presents a method of tree height extraction from large viewing aerial image using the knowledge of segmented tree crown. This method is based on a rough digital surface model (DSM) of tree crowns and the exterior orientation of the image. The basic steps of this method is that the DSM is first used to find the region of interest in the image based on the exterior orientation, and then the edges of the distinct trees or branches are extracted using image segmentation technology. An algorithm that uses both the rough DSM height information and exterior orientation data to calculate the accurate heights of the segmented trees or branches is presented. The algorithm assumes that most of the trees are upright, and the projection in the large viewing angle images of the crown and branches can therefore be used to calculate their heights relative to the averaged DSM height. Hence, the accurate height of the trees around the rough DSM can be refined. Some experimental results are given with the image captured from multi-angular imaging system mounted on a helicopter in which a Position and Orientation System (POS) is onboard to record the exterior element of the cameras. The experimental results demonstrated that this algorithm can largely improve the accuracy of tree height extraction. The application in power line monitoring system is promising.
A mixture feature selection method for remote sensing image
Show abstract
The need for remote sensing image feature selection methods is discussed in this paper. A central problem in image classification and recognition is the redundancy of image features. To cope with many unnecessary and irrelevant features, we propose a mixture method based on principle component analysis (PCA) and rough set theory to alleviate this situation. The main contribution of this paper is to provide the method for remote sensing image classification with higher accuracy comparing to the single rough set theory and PCA method. Finally, some experimental results demonstrate that our proposed method is effective in feature selection for remote sensing image.
Improvement of orthogonal Fourier-Mellin moments
Bin Ye
Show abstract
Orthogonal Fourier-Mellin (OFM) moments have many desirable properties such as rotation invariance, robustness to noise, expression efficiency, fast computation and multi-level representation for describing the shapes of patterns, but there is a major drawback with OFM moments, they need to normalize an image to achieve scale invariance. This approach will take some errors since it involves the re-sampling and re-quantifying of digital images, and leads to inaccuracy of classifier. In this paper, we present an improved OFM moments, experiments show that the improved OFM moments not only have better rotation invariance, but also have scale invariance, the invariance of improved OFM moments have been greatly improved over the present methods.
Bayesian network classification for aster data based on wavelet transformation
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In this study, Bayesian networks are considered to be a classifier for the remote sensing image named Aster data, which involves 15 bands. Six bands, which have different spatial resolutions, are selected to be the attributes in Bayesian network classifier. The sample data from Aster image that is fused by wavelet transform is used to train Bayesian network classifier. Before the above-mentioned processing, the attributes from the transformed image should be normalized by some equal width schemes. Then the learning scheme process is used to acquire the structure of Bayesian networks from the training data set. The relationship of the attributes among all the constituents of the imagery data is mined through the Bayesian networks. To evaluate this classifier, a comprehensive study of the performance is investigated based on the training data set and the independent test data sets. The result shows that Bayesian network performs well on remote sensing imagery data.
Three dimensional reconstruction of irregular object with indigent texture based on structured light
Li Zheng,
Jianqing Zhang,
Zongqian Zhan
Show abstract
In this paper we describe three dimensional (3D) reconstruction of irregular object lack of texture based on structured light techniques. This system uses a CCD camera synchronized with the DLP projector captures the images, from which the 3D shape of the object is reconstructed. With the characteristic of the right image obtained from the projector and collinearity equations, the spacial point coordinates on the surface of the irregular object are obtained quickly by space intersection. As the grid table is rotating, the projector and the CCD camera are always fixed. Then all the point coordinates of different surfaces are computed in the same reference frame while the interior and exterior orientation elements of the CCD camera and projector are obtained in each different point of view. A CCD camera is also used to capture images for texture mapping. The untouched method based on close-range photogrammetry can be successfully adapted to reconstruct various kinds of shapes and some soft objects in the diverse areas.
Speckle reduction using module-maximum-based modification in wavelet domain
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Speckle noise in synthetic aperture radar (SAR) images is characterized as multiplicative random noise. To address SAR image speckle denoising, this paper proposes a new method which is based on the combination of statistical model of wavelet coefficients and modification to the coefficients according to module-maximum-based (significant coefficient) rule. In our method, wavelet coefficients of image are firstly modeled as mixture density of two Gaussian (MG) distributions with zero mean. In order to incorporate the spatial dependencies into the denoising procedure, hidden markov tree (HMT) model is explored and expectation maximization (EM) algorithm is proposed to estimate model parameters. Bayes minimum mean square error (Bayes MMSE) method is used to estimate the wavelet coefficients free of noise. The wavelet coefficients are updated according to a rule whether the coefficient is a significant one or not. 2D inverse DWT is performed on the updated coefficients to get denoised SAR image. Experimental Results using real SAR image demonstrate that the method can not only reduce the speckle but also preserve edges and radiometric scatter points. Equivalent Number of Look Enl shows that the proposed method yields very satisfactory results compared with other methods.
The application of the all phase contourlet on image denoising
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This paper proposes a new discrete transform called AP-Contourlet (All Phase Contourlet). Contourlet is a flexible and fixed transform for image representations of geometrical regularity. Because it has been concluded that APDCT (All Phase DCT) filter and APIDCT (All Phase IDCT) are excellent respectively in subband decomposition and image interpolation, this paper develops a novel mutliscale decomposition method based on the APDCT filter and APIDCT interpolators to replace Laplacian Pyramid at the fist step of contoulet. Experiments in denoising typical images have shown the performance of the proposed AP-contourlet is obviously superior to original contourlet both in vision and in signal to noise ratio (SNR).
A new image segmentation approach based on gradient
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In this paper, we first introduce the concept of thresholded image with constant total gray level, then based on the average gradient of this new kind thresholded image, we present a new image segmentation approach including binary and multithreshold segmentation. The basic idea of this approach is that the higher the mentioned average gradient is, the higher contrast between object and background is, thus the thresholds can be determined by maximizing the average gradient. The proposed approach is more consistent with the human vision perception compared to conventional approaches based on gray-level histogram. Experimental results show the effectiveness of this approach.
High precision geometric correction based on DEM data and GCP outlier detection for MODIS data
Shan Guo,
Weidong Sun
Show abstract
Terrain Height Error is one of the most important factors which influences the accuracy of direct system correction and has an obvious effect along the scanning direction. In this paper, taking Moderate-resolution Imaging Spectroradiometer (MODIS) data received from Earth Observing System (EOS) satellites as an example, and focusing on the high precision geolocation techniques of the moderate resolution optical satellite data, a high precision algorithm based on Digital Elevation Model (DEM) data and Ground Control Point (GCP) outlier detection is proposed to correct this kind of influences of Terrain Height Error. For more efficient and intelligent processing in practical applications, a group of GCPs should be used in the further geometric correction. But the correction result using GCPs is not so stabile, because it is often influenced by the data conditions. In this paper, a new idea based on local distortion similarity is proposed for the GCP outlier detection too. In this method, the distortion is described by a 2-D Gaussian distribution in the local area, and a decision rule is made to find out the abnormal GCPs according to the variance of the Gaussian distribution. Some experiment results using MODIS data show that the proposed algorithm based on DEM data and GCP outlier detection is feasible and valid. The final average location error of the new algorithm is about 0.13 pixels which is sufficient for many application requirements.
A new method for super-resolution reconstruction using wavelet transform
Shengwei Pei,
Haiyan Feng,
Minghui Du
Show abstract
In this paper, a super-resolution reconstruction algorithm based on Projection onto Convex Sets (POCS) and wavelets transform is proposed. A high resolution image, after wavelet transform, can be decomposed into two parts: approximate subband and detail subbands. Under some special conditions, the blurred low-resolution images can be thought as the wavelets transform approximate subbands of a high resolution image. Based on the above relationship, we can construct a series of convex sets and then apply the POCS method to recovering high resolution image based on the convex sets. After finite iterative computation, the desired high solution image can be obtained. The experimental results show that the algorithm has good performance in super-resolution reconstruction when the magnification is large enough.
Research on introducing a factor K self-adaptive smoothing algorithm in image processing
Qing Pan,
Guoping Yan,
Yang Kang
Show abstract
For an image accompanied by Gussian noise, image smoothing is usually achieved through adopting the classical Gaussian smoothing mask. This may sometimes blur the edges and other fine details. Noise removing and edges blurring are two conflicting requirements. And delta, as a key factor in the Gaussian function, can greatly affect noise removing, edges blurring and even brightness of an image after processing. In this paper, the theory of Gaussian smoothing in continuous domain is analyzed. With an adjustive factor K being introduced, an improvement on the Gaussian Smoothing algorithm is described. We try to find out the relation among the value of delta, the value of K and the result of image smoothing. Experiments confirm the proposed improvement. The relation gives us an indication that we should select appropriate values of delta and appropriate values of K according to the values of SNR in different regions of an image, then establish smoothing masks to obtain the best result of image smoothing. Some ideas about the new self-adaptive smoothing algorithm are presented simply. By employing the self-adaptive algorithm, the results of processing an image accompanied by Gaussian noise are shown. Finally we should conclude that we can obtain fine details remaining in some partial regions at the cost of a little reducing of the SNR character in the whole image after the algorithm being used.
An efficient algorithm for fast computation of orthogonal Fourier-Mellin moments
Bo Fu,
Jianzhong Zhou,
Jiqun Wen
Show abstract
Orthogonal Fourier-Mellin moments have better feature extraction capabilities and are more robust to image noise than the classical Zernike moments. However, orthogonal Fourier-Mellin moments have not been widely used as features in pattern recognition due to the computational complexity of the orthogonal Fourier-Mellin radial polynomials. This paper analyzes the deficiencies of the existing methods, and introduces an efficient recursive algorithm to compute the orthogonal Fourier-Mellin moments. The algorithm consists of a recurrence relation for Mellin orthogonal radial polynomials, which derived from the Jacobi polynomials for fast computation of orthogonal Fourier-Mellin moments. An experiment using binary image is designed to test the performance of the algorithm. The experimental result demonstrates that the computational speed of orthogonal Fourier-Mellin moments has been adequately improved over the present methods.
Wavelet pyramid structure based on integer wavelet transform
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This paper proposes a new data structure for GIS image data (wavelet pyramid structure) based on integer wavelet transform. With this structure, an original image is divided into an image of the lowest resolution and two groups of image detail coefficients. These coefficients are organized by a pyramid structure-wavelet pyramid structure. In comparison with R-trees, this structure can reduce data redundance and the original image can be restored perfectly and losslessly with this method.
Wavelet image compression based on bit-plane context and its application to remote sensing images
Qingyuan Wang,
Runhai Jiao,
Yuancheng Li,
et al.
Show abstract
A novel wavelet image compression scheme is proposed in this paper. The scheme is based on bit-plane context and adaptive arithmetic coding. Parent coefficient and parent neighboring coefficients of current coding coefficient are used to construct context models besides its neighboring coefficients. Higher order entropy is sufficiently employed. Experimental results show that the scheme is among the best image coders for natural images and remote sensing images.
Object-layering technology of video sequence with background restoration based on neural network
Yongqing Huo,
Qicong Peng
Show abstract
The object-layering technology of Video Sequence is very important in many fields. Commonly, video image can be decomposed into background and moving objects. In this paper, based on features of different objects of the scene video sequence, aimed at the background object, we study the object-layering technology with background restoration based on neural network. This technology adopts two-stage pattern recognition and estimation with weighted multiple frames, increasing the reliability of the object-layering and extremely suppressing the noise. The experiments show the technology discussed is effective.
Performance evaluation of integer to integer wavelet transform for synthetic aperture radar image compression
Wentong Xue,
Jianshe Song,
Lihai Yuan,
et al.
Show abstract
An efficient and novel imagery compression system for Synthetic Aperture Radar (SAR) which uses integer to integer wavelet transform and Modified Set Partitioning Embedded Block Coder (M-SPECK) has been presented in this paper. The presence of speckle noise, detailed texture, high dynamic range in SAR images, and even its vast data volume show the great differences of SAR imagery. Integer to integer wavelet transform is invertible in finite precision arithmetic, it maps integers to integers, and approximates linear wavelet transforms from which they are derived. Considering in terms of computational load, compression ratio and subjective visual quality metrics, several filter banks are compared together and some factors affecting the compression performance of the integer to integer wavelet transform are discussed in details. Then the optimal filter banks which are more appropriate for the SAR images compression are given. Information of high frequency has relatively larger proportion in SAR images compared with those of nature images. Measures to modify the quantizing thresholds in traditional SPECK are taken, which could be suitable to the contents of SAR imagery for the purpose of compression. Both the integer to integer wavelet transform and modified SPECK have the desirable feature of low computational complexity. Experimental results show its superiority over the traditional approaches in the condition of tradeoffs between compression efficiency and computational complexity.
A self-adaptive ant colony optimization approach for image segmentation
Jue Lu
Show abstract
Ant colony optimization, with good discretion, parallel, robustness and positive feedback, is well suited to image segmentation. But its search is random and has much computation for convergence. Constant evaporating coefficient leads to early convergence or stagnation. To improve it, the ideal of setting primary cluster center is proposed. Meanwhile, the algorithm is implemented in a small window so as to reduce its computation. The evaporating coefficient is also set to change with the number of ants which pass the allowable path in order to keep its good global convergence and stability. This method can segment an image accurately. Experimental results show it's an effective approach.
Fast algorithm of discrete Walsh-Haar transformation
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Walsh-Haar function system that was first intruoduced by us is a new kind of function systems, and has a good global/local property. This function system is called Walsh ordering function system since its generation kernel functions belong to Walsh ordering Walsh function system. We worked out a recursive property of the matrix corresponding to the first Walsh-Haar functions in Walsh-Haar function system, and we also proved that Walsh-Haar function system is perfect and orthogonal similar to Walsh function system and Haar function system. Thus, discrete Walsh-Haar transformation (DW-HT) is an orthogonal transformation that can be widely used in signal processing. In this paper, using the recursive property of the matrix and the fast algorithm of discrete Walsh transformation (DWT) in Walsh ordering, we have designed a fast algorithm of Walsh ordering DW-HT based on the bisection technique. The idea and method used in this paper can be used for designing fast algorithms of other ordering DW-HTs and other discrete orthogonal transformations.
A wavelet-based image matching scheme
XinRong Dai,
LuYi Chen
Show abstract
Among many image matching methods, Hausdorff distance scheme is the most effective one. On the basis of Hausdorff distance scheme, we present Hausdorff-wavelet image matching algorithm in this paper. First, the method makes full use of wavelet transform modulus maxima to select interesting point which has magnitude and orientation information, and makes position and orientation of image or object certain. Then matches the images via Hausdorff distance scheme. Under the same precision, this new method can speed up the process by reducing large amount of unnecessary operation. The new matching-image method can detect translation, and rotation, and shows excellent robustness against random noise and salt noise.
An algorithm for image information fusion based on CL multiwavelet
Show abstract
The purpose of image fusion is to merge information from multi-sensor and to improve abilities of information analysis and feature extraction. In this paper, a new image fusion algorithm based on discrete multiwavelet transform to fuse multi-sensor images is presented. The detailed discussions in the paper are focused on CL (Chui-Lian) multiwavelet, a two-wavelet and two-scaling function multiwavelet, and use it to accomplish image fusion processing. The CL multiwavelets have several advantages in comparison with scalar wavelets, so that it is employed to decompose and reconstruct images in this algorithm. When images are merged in multiwavelet space, different frequency ranges are processed differently. It can merge information from original images adequately and improve abilities of information analysis and feature extraction in remote sensing area. The experiments, including the fusion of registered Visible (VIS) \Infrared (IR) images are presented in this paper. Comparing with other image fusion methods, satisfactory result has been obtained by applying this method on both objective and subjective performance measure.
Multifeature distance map based fusion detection of small infrared targets with low contrast in image sequences
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Target detection techniques play an important role in automatic target recognition (ATR) systems because overall ATR performance depends closely on detection results. In this paper, a novel method for fusion detection of infrared weak targets based on multifeature distance map (MFDM) in image sequences is proposed. As for small weak targets, there are many features, such as local entropy, average gradient strength. These features depict the characteristics of small infrared targets and can be extracted. Multifeature-based fusion techniques are applied to detect such weak targets. The problem of detecting small targets is converted to search peak values in specified feature space where multifeature vectors space (MFVS) is considered. Distance map (DM) can be derived according to feature vectors and target detection is performed in DM. In order to accumulate energy of targets deeply and suppress background and clutters to a great extent, five distance maps obtained by corresponding five consecutive frames are utilized to fuse with average weight, which results in the fact that the contrast between targets and background including clutters are enlarged and that the feature peaks of targets are obvious different from background and clutters. After these steps, a contrast segmentation method is used to extract targets from complicated background on the fused DM. Actual infrared image sequences in background of sea and sky are applied to validate the proposed approach. Experimental results demonstrate the robustness of the proposed method with high performance.
Dim target detection in IR image sequences based on fractal and rough set theory
Xiaoke Yan,
Caicheng Shi,
Peikun He
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This paper addresses the problem of detecting small, moving, low amplitude in image sequences that also contain moving nuisance objects and background noise. Rough sets (RS) theory is applied in similarity relation instead of equivalence relation to solve clustering issue. We propose fractal-based texture analysis to describe texture coarseness and locally adaptive threshold technique to seek latent object point. Finally, according to temporal and spatial correlations between different frames, the singular points can be filtered. We demonstrate the effectiveness of the technique by applying it to real infrared image sequences containing targets of opportunity and evolving cloud clutter. The experimental results show that the algorithm can effectively increase detection probability and has robustness.
Recognition of spatial weak targets based on fractal geometry
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Recognition of the interesting targets is the key techniques of precise guided weapon systems. Because fractal dimension is an interesting textual feature of an image, it has been used in many pattern recognition applications including classification and segmentation. According to the fractal feature of man-made objects in infrared images, a new algorithm is presented to detect the airplanes in this paper. And then we can partition and identify the potential targets using this fractal algorithm. Simulations illustrate that the airplane is successfully identified with the algorithm. The algorithm only requires moderate operations, so it is easy to be implemented for automatic target detection in real-time systems. The results of the experiments show that the fractal dimension can efficiently reflect the object surface complexity or irregularity in images. The algorithm is a powerful tool in identifying airplanes from infrared images.
Infrared target recognition based on support vector machine
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Support vector machine (SVM) can effectively improve the algorithm's generalization capability. This paper proposes a support vector machine target recognition method based on the target infrared feature and edge invariant moments. The simulation result shows it is faster than others. The discrimination is higher than the K-nearby method's one.
Identification of false evidence using distance function and its application in target recognition
Yong Deng,
Huawei Guo,
Dong Sun
Show abstract
Dempster's rule of combination is a poor solution for the management of the conflict between the various information sources. It is proved that, if the false evidence can be correctly selected, Dempster's rule can deal with highly conflicting evidence combination efficiently. However, how to determine the false evidence is an open issue. In this paper, a novel method to identify the false evidence is proposed. First, the distance function between bodies of evidence is introduced to express the degree of conflict degree. Then, the confidence lever of each piece of evidence is obtained to reflect the reliability of each information source to some degree. By setting a threshold, the false evidence can be determined. The numerical example is shown to illustrate the efficiency of the presented approach.
Man-made target detection for imaging infrared terminal guidance missile considering turbulence degraded wave-fronts features
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Previous research employed natural background fractal features to detect man-made target for imaging infrared terminal guidance missile. The method is some effective but the optical turbulence is overlooked, which will disturb natural background intrinsic fractal. When the missile flies in atmosphere, there exits turbulent flow over the IR windows which will degrade the optical wave-fronts. In this paper, a new method considering degraded wave-fronts features is proposed for man-made moving target detection in natural background. To pre-process the infrared image and obtain the area in which target may exit, the image is divided into blocks and each block fractal dimension is calculated and compared. Then optical flow of the block is calculated from successive images to determine the moving target. The method is more applicable to actual missile fly environment, simulation results show that it reduces the optical flow calculation complexity and can detect the target availably.
Dynamic detection and identification for unstructured targets
Kun Zhao,
Fuyuan Peng,
Yiping Xu,
et al.
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In this study, a vision-based target detection method is developed for unstructured objects. Based on the extraction of "suspicious regions", similarity judgment and texture verification are combined for the detection. The proposed method is evaluated by several kinds of image sequence taken from both earth ground and deep sea environment. Experimental results demonstrate that the new method is valid for unstructured target detection and can real-timely obtain the target's information.
Independent moving target detection for aerial video surveillance
Dong Xu,
Jinwen An
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Due to complexities faced in the task of independent moving target detection from an airborne moving platform, simple methods like image stabilization followed by temporal differencing or change detection cannot be properly used unless distracting factors like 3D parallax motions, ego-motion compensation errors and image noise have been well disposed of. Instead of trying efforts to reduce these distractions, we proposed an attribute based salient extrema detection algorithm to extract the most salient extrema as targets from the residual motion image. Without the need for image filtering, the independent moving targets can be efficiently detected by valuating extrema saliency with respect to different morphological attributes. Experimental results show the effectiveness and flexibility of our algorithm.
Study on the detection of infrared small dim targets based on DMMFs
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This paper presents an effective method to detect small and dim infrared image target under complex background, which is performed in spatial domain. Roughly speaking, the new method contains two steps. The first step is further divided into two steps (called difference between maximum and minimum filters, DMMFs): firstly, an original image is filtered by maximum (max) and minimum (min) filters based on the considering max filter can enhance the target and preserve the background while min filter can eliminate the target and also preserve the background; and then the difference between these two results is obtained, therefore the target is enhanced and its background is suppressed at the same time. To obtain an accurate location of the target, the second step called post processing involves local feature mapping and projecting techniques. This DMMF method focuses on reducing the cost of computation, tracking the target in real-time, enhancing the SNR, and suppressing its background clutter. The simulation results show that the proposed algorithm is effective and practical.
Infrared image dim small target detection based on double energy accumulation
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Detection of dim moving small targets at low signal noise ratio is a very important issue and difficult problem in infrared searching and tracking system. Based on analysis of the character of infrared images, a new double energy accumulating method is proposed. Firstly, images are denoised by wavelet transformation with soft threshold. Then, object motion area is detected according to difference images and the target intensity is well enhanced by accumulating energy two times with addition and product operation. Finally, target candidates are separated from background by thresholding process with the selected threshold. Computer experiments are carried out with an infrared image sequence and the experimental results illustrate that the proposed method is effective and efficient.
Voronoi diagram and spatial clustering in the presence of obstacles
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Clustering in spatial data mining is to group similar objects based on their distance, connectivity, or their relative density in space. Clustering algorithms typically use the Euclidean distance. In the real world, there exist many physical obstacles such as rivers, lakes and highways, and their presence may affect the result of clustering substantially. In this paper, we study the problem of clustering in the presence of obstacles and propose spatial clustering by Voronoi distance in Voronoi diagram (Thiessen polygon). Voronoi diagram has lateral spatial adjacency character. Based on it, we can express the spatial lateral adjacency relation conveniently and solve the problem derived from spatial clustering in the presence of obstacles. The method has three steps. First, building the Voronoi diagram in the presence of obstacles. Second, defining the Voronoi distance. Based on Voronoi diagram, we propose the Voronoi distance. Giving two spatial objects, Pi and Pj, The Voronoi distance is defined that the minimum object Voronoi regions number between Pi and Pj in the Voronoi diagram. Third, we propose Following-Obstacle-Algorithm (FOA). FOA includes three steps: the initializing step, the querying step and the pruning step. By FOA, we can get the Voronoi distance between any two objects. By Voronoi diagram and the FOA, the spatial clustering in the presence of obstacles can be accomplished conveniently, and more precisely. We conduct various performance studies to show that the method is both efficient and effective.
Noisy image fusion of pixel level based on fuzzy neural network
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This paper presents one noisy image fusion scheme of pixel level based on fuzzy neural network. The simulation proves that the performance of fuzzy neural network is steady and convergent. By fuzzy pixel clustering of the competitive layer, the pixel level image fusion has been realized. The experiment and application verify that the presented method can fuse images with noise effectively.
Image fusion based on surface model
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This paper presents a novel two-dimensional surface model, the further development of facet model, to achieve image fusion through a "surface-then-fuse" information fusion architecture realized by an advanced approximation/derivative technique. Experiment confirms that surface model can improve the spatial quality and preserve the spectral characteristics of the original images both quantitatively and visually.
Fault-tolerant integrated navigation system based on neural network information fusion
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A fault-tolerant integrated navigation system based on neural network information fusion is designed. The neural network filter is used firstly to take the place of the traditional Kalman filter, then the fuzzy neural network is used to detect fault and the neurons for information fusion are used at last. The simulation results show that this approach is effective.
A study of PCA image fusion techniques on remote sensing
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We propose a PCA algorithm for image fusion between the infrared image and the visible image of the same night vision. The infrared image and the visible image are preprocessed with image Gaussian low-pass filter respectively, to smooth the images. The mathematical formulation of image fusion techniques is worked out in this paper. Included are block-based method, wavelet transform, wavelet packet and PCA. Experimental results show the effectiveness of the proposed method.
Study on visualization of spatial data mining and knowledge discovery
Shanlin Yang,
Yongsen Li,
Shuchu Zhang,
et al.
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Spatial data usually show as vector maps or raster images. The vector maps are composed of points, lines and polygons, while raster images are composed of grids. Spatial data have different character from common data, which makes it difficult to find knowledge from spatial database than from common database. Spatial Data Mining and Knowledge discovery (SDMKD) is considered as an advanced process to extract novel and interesting models from spatial database. However, visualization is a technique which can deal with substantive data and show this process as figures, images and charts by computers. But, SDMKD and visualization always keep separate and develop independently. A basic and important problem about visualization supporting SDMKD is seldom concerned. To make the process of SDMKD efficient and intuitional, this paper has a preliminary study on visualization of SDMKD through a mutual operation between the human and the computer. It realizes the visualization of data rebuilding and the process of data mining. Some techniques of visualization are used such as charts, maps, figures and images.
A framework for the uncertain spatial data mining
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On the basis of analyzing the uncertainties of spatial data mining (SDM), and in view of the limits of traditional spatial data mining, the framework for the uncertain spatial data mining has been founded. For which, four key problems have been probed and analyzed, including uncertainty simulation of spatial data with Monte Carlo method, measurement of spatial autocorrelation based on uncertain spatial positional data, discretization of continuous data based on neighberhood EM algorithm and quality assessment of results. Meanwhile, the experiments concerned have been performed using the geo-spatial datum gotten from 37 typified cites in China.
A discounting approach to evidence conflict management
Liang-zhou Chen,
Wen-kang Shi,
Yong Deng
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By combining several belief functions from distinct information sources, data fusion aims at obtaining a single Basic Probability Assignment (BPA) function. The classical Dempster's combining rule is the most popular rule of combinations, but it is a poor solution for the management of the evidence conflict at the normalization step. When deal with high conflict information it can even involve counter-intuitive results. A discount method to combine conflicting evidence based on evidence distance is presented; and the discount coefficient of the evidence in the system is also given. Numerical examples showed that the proposed method can provide reasonable results with good convergence efficiency.
An efficient communication strategy for mobile agent based distributed spatial data mining application
Guodong Han,
Jiazhen Wang
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An efficient communication strategy is proposed in this paper, which aims to improve the response time and availability of mobile agent based distributed spatial data mining applications. When dealing with decomposed complex data mining tasks or On-Line Analytical Processing (OLAP), mobile agents authorized by the specified user need to coordinate and cooperate with each other by employing given communication method to fulfill the subtasks delegated to them. Agent interactive behavior, e.g. messages passing, intermediate results exchanging and final results merging, must happen after the specified path is determined by executing given routing selection algorithm. Most of algorithms exploited currently run in time that grows approximately quadratic with the size of the input nodes where mobile agents migrate between. In order to gain enhanced communication performance by reducing the execution time of the decision algorithm, we propose an approach to reduce the number of nodes involved in the computation. In practice, hosts in the system are reorganized into groups in terms of the bandwidth between adjacent nodes. Then, we find an optimal node for each group with high bandwidth and powerful computing resources, which is managed by an agent dispatched by agent home node. With that, the communication pattern can be implemented at a higher level of abstraction and contribute to improving the overall performance of mobile agent based distributed spatial data mining applications.
Influence of formation flying satellites spatial state parameters estimate to velocity precision in ATI
Zhiyuan Wang,
Shiwei Fan,
Dongyun Yi,
et al.
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Based on the analysis of the characteristic parameters which have influence on the radical velocity precision, we establish two mathematical association models: One is between spatial state parameters estimate and characteristic parameters, another is between characteristic parameters and radical velocity precision. By simulation, characteristic parameters precision in different scenarios, error propagation matrix and the precision factors of measurement error propagation relation are obtained, and the influence of formation flying satellites spatial state parameters estimate to radical velocity precision is investigated finally.
Pseudolite-based multiple space-vehicles relative navigation for formation flying
Xiaokui Yue,
Jianping Yuan
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Precise relative navigation is a necessary and important technology for any operation of multiple space vehicles on-orbit formation flying together. Carrier-phase Differential GPS (CDGPS) positioning has been proven to be an accurate technique for relative positioning and attitude determining between multiple vehicles. But, the present satellite navigation system has no enough covering performance for some flying missions. For example, in high orbits, navigation satellite reception is often not sufficient to resolve position and attitude between all vehicles in the formation flying. One of the methods of taking advantage of satellite navigation system in such cases is to augment the available signals with additional signals from pseudolites. In fact, pseudolite is just a special transmitter, whose signals have many of the characteristics of the signals broadcast by the satellites of navigation system. Meanwhile, pseudolite can be placed on the ground, or in the MEO or GEO orbits. In this paper, an onboard pseudolite augmentation system of each vehicle for formation flying is studied, such as each vehicle can exchange navigation data with other vehicles. Such augmentation system can be used to improve the performance of satellite navigation system, e.g. GPS, GLONASS, and so on. Based on the correlative studies, some conclusion for the space application of pseudolite is given, including some idea about the arrangement of correlative ground experiments.
Minimal parameter solution of the quaternion differential equation
Ruihua Liu
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The efficiently calculate of the attitude matrix is an important subject in the Strap-down Inertial Navigation System (SINS), because the precision of its solution directly effects on the system performance. A new method of 3rd order minimal parameter solution for the orthogonal matrix differential equation is used to solve the quaternion differential equation of SINS in this paper, and the numerical simulation is done as well. From the simulation result, we can see that when the new algorithm is used, the precision of the solved attitude angles is two orders higher than the classical method, and the floating-point operations is only abort half of the old one.
EA/QFT robust control of target tracking system for space vehicle
Lan Chen,
Jinwen An
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Based on the model of gyro-stabilized platform which is a nonlinear system with high dimensions, an approach to robust control design for a multi-input/multi-output (MIMO) plant using eigenstructure assignment (EA) and quantitative feedback theory (QFT) is introduced. EA is used to decomposition of the MIMO system into decoupled SISO subsystems. Then the SISO QFT technique may be used to obtain robust stability under the given plant-parameter uncertainties. The simulation shows that the combined EA/QFT approach provides a more straightforward physical understanding of the design process and gives designers greater flexibility in making tradeoffs between system performance and controller complexity, and also shows that target tracking system has the good decoupling performance and high tracking precision even though space vehicle makes acute maneuver.
Strategy missile control system design using adaptive fuzzy control based on Popov stability criterion
Jianling Zhang,
Jinwen An,
Mina Wang
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This paper describes the application and simulation of an adaptive fuzzy controller for a missile model. The fuzzy control system is tested using different values of fuzzy controller correctional factor on a nonlinear missile model. It is shown that the self-tuning fuzzy controller is well suited for controlling the pitch loop of the missile control system with air turbulence and parameter variety. The research shows that the Popov stability criterion could successfully guarantee the stability of the fuzzy system. It provides a good method for the design of missile control system. Simulation results suggest significant benefits from fuzzy logic in control task for missile pitch loop control.
Trajectory measuring of ballistic missle with imaging infrared system based on knowledge
Junjie Zheng,
Xiaoke Yan,
Zhihua Jiang,
et al.
Show abstract
In order to demonstrate lock-on-after-launch (LOAL) capability, infrared trajectory measuring systems of the future require the ability to autonomously identify and track targets of interest, making use of strong correlation between neighboring-row and non-linear relationship between atmosphere temperature and height analysis etc, a background suppress method based-on knowledge for autonomously acquire and track an extended range target through its entire flight scenario is developed. At the same time we address a method of extracting regions of interest based-on experiential knowledge of detected object. Experiments with real targets show that the method can detect target effectively and reduce false alarm probability and the computational burden of processing the whole image.
Real-time attitude-independent sun-sensor/magnetometer calibration algorithm for micro-satellite
Fang Duan,
Jianye Liu,
Rongbing Li,
et al.
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Sun-sensor/Magnetometer has become the usual instruments combination for micro-satellite attitude determination with the low-weight/high-reliability character. Although these instruments have already been calibration strictly in ground testing, error items may appear during the launch and on-orbit running period. The magnetometer is affected not only by mechanical deformation but also by the disturbance of residual magnetic field of the satellite body. The sun-sensor is only affected by the mechanical deformation. A real-time on-orbit attitude-independent calibration method for sun-sensor/magnetometer is proposed. In the existing real-time attitude-independent magnetometer calibration algorithm, only the norm of the geomagnetic field is used as the measurement. In this paper the angel between the magnetic vector and the sun vector is introduced as another measurement, so that the system observability is reinforced, and it also enables the real-time calibration of the sun-sensor. The system state equation and measurement equation are constructed, and two kinds of filter are used to design the system sequently, Kalman filter and unscented Kalman filter(UKF). Although Kalman filter is widely used in many ways, its linearization process introduces some errors into the system. UKF is a non-linear filter which needn't the linearization process. Calibration algorithm using KF and UKF are researched in this paper, and the simulations are done on the basis of satellite simulation software Satellite Tool Kit(STK). The results show, the constructed recursive filtering algorithm in this paper realizes the real-time calibration of magnetometer/sun-sensor well, and UKF performs generally better than Kalman filter.
Design method for fault diagnosis of small satellites based on multi-level fuzzy neural network
Min Yao,
Min Zhao
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A design method based on multi-level fuzzy neural network for fault diagnosis is presented in this article which uses a multi-level method to diagnose small-satellites. In the first level, fuzzy clustering method is used to estimate which subsystem works abnormally. In this level only key parameters rather than all parameters of each subsystem are collected. In the second level, radial basis function neural network is used and most of the parameters of the faulty subsystem identified by the first level diagnosis will be considered. Then the specific component or part with fault can be confirmed. In the first level all the subsystems are integrated into one system and the small-satellite is regarded as a system to be diagnosed. Therefore, the result of the diagnosis is more accurate than traditional methods. Furthermore, in the first level only key parameters are collected and analyzed, so the complexity of the calculation can be reduced significantly. A simulation experiment for fault diagnosis on a small-satellite has been undertaken. The result indicates that in a small-satellite fault diagnosis, this multi-level method can significantly reduce the complexity of calculation in the process of the diagnosis.
Design and optimal control of on-orbit servicing trajectory for target vehicle in non-coplanar elliptical orbit
Wenyong Zhou,
Jianping Yuan,
Jianjun Luo
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Autonomous on-orbit servicing provides flexibility to space systems and has great value both in civil and in military. When a satellite performs on-orbit servicing tasks, flying around is the basic type of motion. This paper is concerned with the design and control problems of a chaser satellite flying around a target spacecraft in non-coplanar elliptical orbit for a long time. At first, a mathematical model used to design a long-term flying around trajectory is presented, which is applicable to the situation that the target spacecraft flies in an elliptical orbit. The conditions of the target at the centre of the flying around path are deduced. Considering the safety and task requirements, a long-term flying around trajectory is designed. Taking into account perturbations and navigation errors which can cause the trajectory unstable and mission impossible, a two-impulse control method is put forward. Genetic algorithm is used to minimize the cost function which considers fuel consumption and bias simultaneously. Some simulation works are carried out and the results indicate the flying around mathematical model and the trajectory control method can be used in the design and control of a long-term flying around trajectory.
Determination of satellite attitude based on virtual images
Xuecheng Jin,
Long Han,
Zengfu Wang
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One of the difficult problems in designing an attitude control system of nano-satellite for earth observation is to realize the high accuracy control of three-axis attitude stabilization when the nano-satellite orbits around the earth. In this paper, we present a virtual imaging based attitude determination method. The corresponding algorithm shares the images of the earth captured in real-time as the attitude sensing information, and uses the virtual imaging method based on coordinate transformation to obtain the attitude information.
Measurement method of frequency agile radar synthesis detection unit's frequency tracking accuracy
Jianhui Han,
Yonghua Jiang
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Frequency agile radar synthesis detection unit works in frequency hopping state in radio frequency (RF) band. For the limitation of the accuracy of instantaneous frequency measurement (IFM) technology, the frequency tracking accuracy can't be examined directly. The system design method proposed by the paper examines the frequency tracking accuracy of the frequency agile radar synthesis detection unit (FARSDU) at intermediate frequency. The method is realized in engineering and good performance has been got.
Image-based navigation and guidance for landing on small body
Shuang Li,
Zexu Zhang
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Due to long round-trip communication delay and low telemetry bit-rates, the traditional Guidance Navigation and Control (GNC) mode based on Deep Space Network (DSN) is no more suitable for landing spacecraft on small celestial bodies. This paper presents an image-based navigation and guidance scheme for future asteroid landing mission. Firstly, an autonomous navigation scheme based on feature detection and tracking technology is presented. Secondly, proportional plus derivative (PD) guidance control laws and Pulse-Width and Pulse-Frequency (PWPF) modulator are designed to track the desired descent trajectory and achieve landing on asteroids safely. Finally, the validity of the proposed scheme is confirmed by computer simulation.
Optimal trajectory generation for spacecraft formation flying reconfiguration
Chenguang Zhang,
Bin Li,
Darong Chen
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Multiple spacecraft formation flying has been identified as an enabling technology for many future space missions. In this paper, the generation of fuel optimal trajectories for spacecraft formation reconfiguration with finite thrust was investigated. The relative dynamics model of spacecraft in the formation was developed by employing the famous Clohessy-Wiltshire equations. Based on these equations, the generation of transferring trajectory for spacecraft was modeled as an optimal control problem with defined transferring time and known initial and terminal relative states. A direct method was applied to convert the trajectory optimization problem to a nonlinear programming problem. By this approach, the whole transferring trajectory was separated into several finite thrust arcs and non-thrust arcs. Then a collocation method based on Hermite interpolation was used to produce the constraints of thrust arcs, and the state transition matrix based on Clohessy-Wiltshire equations was applied to produce the constraints of non-thrust arcs. Meanwhile, to avoid collisions among spacecrafts during formation reconfiguration, an imaginary 3-dimensional sphere surrounding each spacecraft was introduced as a constraint of collision avoidance. The nonlinear programming problem was solved by sequential quadratic programming method. A numerical simulation of a formation reconfiguration with three spacecrafts was performed. The results showed that the present nonlinear programming method can be used to generate optimal trajectories for spacecrafts in the formation and the total fuel consumption of the whole formation is guaranteed.
Attitude determination for three-axis stabilized geostationary meteorological satellite image navigation
Yaguang Wu,
Zhigang Wang
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To achieve the high accuracy of attitude determination for three-axis stabilized geostationary meteorological satellite image navigation, a new approach combined gyro with star trackers is proposed, and a real-time algorithm for attitude estimation is designed. This algorithm begins with a prediction for angular rate model errors induced by gyro drifting error, and ends with the extended Kalman filtering (EKF) for attitude estimation of three-axis. A Matlab-based time domain simulation model is developed to evaluate the attitude determination performance. Simulation results demonstrate that the proposed algorithm has characteristics of high accuracy, rapid convergence and strong robustness.
Research and implementation of ground station software system with high automation
Peiyang Wang,
Jinshu Chen
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An experimental ground station (EGS) for the scientific experimental nano-satellite THNS-1 is developed. Great efforts are made to fulfill a highly automated, normally unmanned and low-cost EGS. The software system is designed with modularization, hierarchy and multi-mission concept. Monitor & control as well as scheduling of all resources have been centralized to track-management module and the remotely controlled ground station is normally unmanned. The azimuth/elevation (AZ/EL) parameters for antenna to track satellites are sent by computer after calculating in real time, which greatly reduces the cost of antenna system. Software control mode also solves the problem how the antenna tracks satellites continuously when a 2-axis antenna's elevation is near 90 degrees.
Optical flow based 3D motion estimation for autonomous landing of a UAV on deck
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3-D motion estimation method based on computer vision theory is employed to implement a vision guide algorithm for UAV in this paper. First, the image sequences of landing target are taken by the camera mounted on UAV with known focal length and the Lucas-Kanade method is adopted to estimate two successive frame optical flow; then a hierarchical approach is described to effectively decompose the nonlinearities of the 3-D motion estimation into two linear subsystems; finally 3-D motion and structure(depth) information of landing target relative to UAV is recovered without using features of landing target. Experiments using both computer simulated images and real video images demonstrate the correctness and effectiveness of our method.
Multivariable control system design using eigenstructure assignment based on LMI
Mei Wu,
Xiaogang Liu,
Lan Chen
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This paper describes a novel method of applying linear matrix inequalities (LMIs) to eigenstructure assignment (EA) approach for design of multivariable control system. Since the degree of freedom is available in EA using state or output feedback, respectively, numerous researchers have exercised this degree of freedom to make the system have good insensitively to perturbations in the system parameter matrices. We derive a series of equations to enhance system performance such as robust stability and parameter sensitivity according to left-over freedom in eigenvector and the solution of the lateral aircraft control system design is also derived using the proposed method, meanwhile, we find that this kind of design method can be classified into an optimization question and can be solved by inner point method using LMI. The implementation and verification of the control system is also presented. Simulation results on the aircraft demonstrate the good performance of the proposed control approach.
Robust guidance and control of lunar lander using model reference approach
Xing-Long Liu,
Guang-Ren Duan
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This paper deals with the soft landing of a lunar lander by the model reference. At first, according to the experimental result and human experience, we give an optimal trajectory for the lunar lander, from the perilune to the lunar surface, such that the lander has the least fuel consumption and the best security. Then, linearizing the optimal trajectory and the dynamical description of the lunar lander at some characteristic spots, we obtain two switched linear systems. Using the model reference approach, we design a switched state-feedback controller for the lunar lander such that tracking the optimal trajectory. But, for the derivation from the linearization, there exists a steady-state error between the optimal trajectory and the lunar lander. However, we choose suitable gain matrices to decrease the error as may as possible.
Robust Kalman filtering for relative state estimation of spacecraft-formation maintenance
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Relative state estimation is a key technology in the spacecraft formation flying area. Since there exists nonlinear perturbation and uncertainties in the dynamic model, it is necessary to use a robust filter to estimate the relative state. A robust Kalman filter is presented in this paper for discrete time-varying systems with uncertain nonlinear perturbation and uncertainties in the state, output and input matrices, and this filter is applied to solve the relative state estimation problem of spacecraft-formation maintenance. Simulation results show the high performance of the filter.
Observation trajectory design and control of on-orbit inspection satellite
Jian-jun Luo,
Wei-wei Tang,
Wen-yong Zhou,
et al.
Show abstract
An on-orbit inspection satellite is a kind of small multi-purpose servicing spacecraft, which can periodically flying around a target spacecraft. It is very useful in on-orbit remote observation, malfunctions detection and maintenance. Observation trajectory design and control is one of the key applied techniques of on-orbit inspection satellite. The on-orbit observation trajectory is formed by the close range visual relative motion between the target satellite and the inspection or chaser satellite. And, it can be divided into natural inspection motion and fast controlled inspection motion. In this paper, the velocity impulse control model for observation trajectory control was established at first; Then, how the typical observation trajectories, which include stationary observation trajectory, straight line oscillation observation trajectory, flyaround football observation trajectory and fast controlled flyaround observation trajectory, formed and their characteristics were analyzed; Finally, the major factors affecting the on-orbit observation trajectory were discussed and some useful conclusions were given. The results indicate that the natural flyaround football motion and the fast controlled flyaround motion are the two effective on-orbit inspection modes and the initial state error and impulse control error are the two dominant factors affecting the on-orbit observation trajectory.
Pursuit-evasion games for a team of UAVs under dynamic environment
Yingchun Chen,
Huan Qi,
Xia Liu
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Based on the interaction protocols of Contract Net and Subscribe-publish, a distributive pursuit-evasion algorithm is proposed for a team of pursuit UAVs to pursue an evasive UAV in a dynamic environment with threats. The pursuit UAVs fly to the suspicious area according to D* algorithm. If any threat is detected within the neighborhood of a UAV, it updates the map. If the evader is detected, the pursuit UAV (initiator) sends call-for-proposals messages to other pursuers. The other pursuers use D* algorithm to estimate their steps to reach the evader and submit their proposals. The initiator picks up the proposals for evaluation, chooses the nearest ones to join the pursuit team, sends accept-proposals to the selected agents and manages the team during the process of pursuit. If the evader is within the kill radius of some pursuit team members, the task is done; otherwise, D* algorithm is applied by each pursuit member to correct its path once the evader moves to a new position. Distributive in nature, it allows a UAV fleet to perform complex tasks in 3D space in a coordinated way. Simulation results show that the pursuit UAVs can dynamically form a pursuit team to catch evaders efficiently. It can be easily extended to cases of multiple pursuers versus multiple evaders.
Present status and perspectives about measurement technology of inter-satellite relative position and relative attitude
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Remote measurement, target searching and tracking missions being performed in space, bring new application for small satellites. To achieve relative navigation, attitude control and other important applications, inter-satellite relative position and relative attitude must be known. In this paper, the measurement procedures of relative position and relative attitude are given. The principles of some measurement means are discussed. The analysis of these means is presented. The modified laser ranging method is mentioned. It points out that the laser ranging method is the promising one among these methods. Achieving the continuous measurement of relative position and relative attitude in some stringent missions may require combination of various methods. And some characteristics of space environment are also discussed. The multipath effects of laser are analyzed and an available approach that can avoid these effects is provided. Finally, the outlook of the measurement of relative position and relative attitude is represented.
An investigation into precision 4-D guidance for long-range campaign weapons
Changqing Wang,
Jun Zhou,
Cheng Xu
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This paper presents the conception and the main task of the precision 4-D guidance technology. The 4-D control technology and the formatting control technology based on the precision 4-D guidance are introduced. The structure of the 4-D control system, the data structure of the 4-D guidance data, the schemes of the velocity control and the formatting control principle are discussed. A simulation of the penetration probability demonstrates the important meanings of developing the 4-D precision-guided weapons to improve the operation effectiveness of the long-range weapons.
A 2D radar imaging method of space debris based on Doppler information
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Shape and size estimation of space debris is an important issue of space debris observation. Generally speaking, space debris is prolate, and follows a simple roll rotation motion around the major axis. In virtue of its own shape and motion features, a two-dimensional radar imaging method of small space debris employing low resolution radar is proposed in this paper. The method recurs to time-frequency analysis technology to obtain the time-instantaneous Doppler distribution of all Scattering centers on the target, and then rearranges the distribution according to aspect angles to acquire target's cross range-aspect angle distribution, and finally reassigns respective points' power in the cross range-aspect angle distribution to gain target image. Furthermore, the paper analyzes the impact of reference center's uniform accelerated motion relative to radar on imaging, and presents corresponding solutions. Simulation results reveal the validity of the method, and target image has a resolution of approximate wave length.
Space debris environment monitoring fence: techniques and future directions
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Early warning of debris impact makes it necessary to detect and, if possible, catalog all threatening debris. Space debris environment monitoring fence is an attractive option for the requirement. This kind of fence can detect each object passing through its beam with no task planning. It has significant capabilities to detect new launchings, maneuvers and breakups. This paper depicts the necessity of monitoring space debris terrestrial environment and the merits of space debris environment monitoring fence. An overview of the world state of the fence research is present. The techniques of space debris environment monitoring using the fence are discussed, including determination the position and velocity vectors of detected objects from direction cosines, orbit determination by itself and by cooperating with auxiliary sensors, and correlation and cataloging of space objects. Methods of new launching, maneuver validation and detection of breakups are highlighted. The calibration of space debris environment monitoring fence is also described. The future directions of this kind of fence are analyzed in terms of operating frequency, operating concept and system configuration.
Wireless sensor networks solution for space environmental monitoring
Kezhong Liu,
Shu Wang,
Fuping Hu,
et al.
Show abstract
Wireless Sensor Networks (WSNs) is a novel technology in acquiring and processing information and has been an active research area in recent years. Because of the energy constraints of sensor nodes, such systems necessitate an energy-aware design to ensure the longevity of monitoring mission. In this paper, we present a remote space environmental monitoring system using wireless sensor networks. Some key technologies are investigated and discussed in detail. Firstly, the architecture of WSN is provided as well as the component structure of sensor nodes. Then, the key technologies including energy aware routing and localization scheme involved in the system are investigated. By simulation software OMNeT++, we include a performance study demonstrating the advantages of our approach based on simulation study. Simulation results show that the quality of localization is well bounded by the range of communication and the topology control is effective.
Interpretation of wetlands in Songnen Plain using MODIS data
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Wetland is a very important land resource and a natural resource, which has many functions like forest, cropland, and ocean, and has close relationship with human being. Northeast China has largest wetland distribution and richest wetland types in China. However, under economic interests driving, wetland in this area is exploited blindly, which causes wetland's functions and benefits decreasing. With the involvement of RS (Remote Sensing) and computer technology, we can monitor wetlands dynamically, which decreases labor intensity of field investigation. Although MODIS, loaded on Terra of new generation EOS, has a coarser spatial resolution than TM, it has higher spatial, temporal, and spectral resolution than AVHRR, which make it capabile to monitor wetland timely and dynamically. The article takes Songnen Plain as study area, uses multi-temporal MODIS-NDVI data to study wetland distribution, and makes validation of result. The research indicates that using multi-temporal MODIS-NDVI data is capable to get wetland distribution, and monitor wetland change effectively.
Image fusion method based on EMD method
Yan Tian,
Yubo Xie,
Caifang Zhang,
et al.
Show abstract
Image fusion is a technique to integrate different advantages of different images with the same scene. A method called empirical mode decomposition is introduced at first. For each pair of intrinsic mode functions, which are the components of two functions obtained by empirical mode decomposition, are fused by certain fusion rule. The final fusion result is acquired by the inverse empirical mode decomposition method. Experimental result shows that the proposed method is effective and promising.
DEM generation with PRISM/ALOS simulation data: a case study using airborne three-line scanner imagery
Tianen Chen,
Ryosuke Shibasaki,
Fumio Shinohara,
et al.
Show abstract
For natural landscape, area-based matching can be successfully applied because the elevation is undulating rather gently. On the other hands, urban areas with the mixture of artificial structures such as buildings and natural landscape, where the elevation tends to have steeper changes, conventional area-based matching may not be successful. Many computer vision papers demonstrated matching methods based on features such as edge and regions extracted from images have much better performance for artificial structures. 2.5 m ground resolution of PRISM, however, may not be enough to extract detailed features enough to represent artificial structures. This may suggest the combination of area-based and feature-based matching approach can be more appropriate for ALOS PRISM data. This paper presents the results of experiments on the combination of the two approaches using simulated PRISM image generated from air-borne image sensor, TLS (Three Line Scanner).
Application System of Space Information
Incorporate design of on-board network and inter-satellite network
Bin Li,
Zheng You,
Chenguang Zhang
Show abstract
In satellite, Data transferring is very important and must be reliable. This paper first introduced an on-board network based on Control Area Network (CAN). As a kind of field bus, CAN is simple and reliable, and has been tested by previous flights. In this paper, the CAN frame is redefined, including the identifier and message data, the addresses for source and destination as well as the frame types. On-board network provides datagram transmission and buffer transmission. Data gram transmission is used to carry out TTC functions, and buffer transmission is used to transfer mass data such as images. Inter-satellite network for satellite formation flying is not designed individually. It takes the advantage of TCP/IP model and inherits and extends on-board network protocols. The inter-satellite network includes a linkage layer, a network layer and a transport layer. There are 8 virtual channels for various space missions or requirements and 4 kinds of services to be selected. The network layer is designed to manage the whole net, calculate and select the route table and gather the network information, while the transport layer mainly routes data, which correspondingly makes it possible for communication between each two nodes. Structures of the linkage frame and transport layer data segment are similar, thus there is no complex packing and unpacking. At last, this paper gives the methods for data conversion between the on-board network and the inter-satellite network.
LEO satellite aided positioning of interference source
Jinjun Zheng,
Zhigang Cao
Show abstract
In order to resolve the problem of high precision in positioning ground interference sources by which someone attack geostationary satellites, we brought forward a new method called LEOAP (LEO Satellite Aided Positioning). Taking advantage of the longer base line and nearer distance which is brought through using low orbit satellite, we built a positioning model of LEOAP based on the measurement of differential Doppler parameters, with orbital parameters of satellite as parameters to be estimated. Results of simulation show that the precision of positioning aided by low orbit satellites at the height of 5000 km can reach 1 km, thus proving the correctness of LEOAP.
Timing and positioning of assisted-GPS receivers with rough time-tag
Guohui Gong,
Sikun Li
Show abstract
Precise timing is a significant issue for an assisted-GPS receiver, time-tag of better that 10 milliseconds accuracy has typically been a requirement, and a high speed wireless link is generally used to offer this time-tag. A method is proposed to determine position and correct local clock of an A-GPS receiver, using a coarse time-tag of 10 seconds accuracy. The method firstly measures ≥5 in-view satellites' C/A code phases, then searches along the time axis to find out the time point matching the measured C/A code phases mostly, and simultaneously determines the receiver position. In the following several hours, only 4 satellites are necessary for positioning, until the local clock error exceeds the permission. By this method, requirement of extra hardware or high speed wireless link is eliminated, thus effectively decreased the complexity and cost of the receiver and the wireless link.
Study on accuracy of long-range navigation of rendezvous
Liyan Zhang,
Faren Qi
Show abstract
To get precision long-range navigation can reach, we analyzed error factors influencing precision, put forward a method to calculate precision using simplified dynamical model together with quasi_mean element method and coariance method, we simulated based on mathematical model educed, and results showed that the method we introduced is feasible and position and velocity error can be controlled under 5Km and 3m/s separately under circumstances.
Constellation design and performance analysis for regional satellite navigation system in China area
Yuling Du,
Xuejun Zhang,
Zhigang Huang
Show abstract
Based on the idea of covering China area, a novel constellation is proposed, consisting of one geostationary satellite and five inclined elliptic orbit geosynchronous satellites in this paper. Through a number of simulation tests, the orbital elements of each satellite are designed concretely. Moreover, its coverage performance is also evaluated under some factors, such as the geometric dilution of precision (GDOP), orbital perturbation, space transmission loss and eclipse. What's more, this constellation is compared with other constellations. Finally, Simulation results show, in this constellation, the number of satellites is small, and the navigation precision is relatively high. Therefore, this is a kind of high performance and economic regional navigation system for China.
Method of combined satellite orbit determination by space-ground-based measurement data fusion based on sparse parameters
Haiyin Zhou,
Donghui Li,
Xiaogang Pan
Show abstract
This paper investigates the method of a user satellite and two observation satellites combined orbit determination. Based on the analysis of abundant practical measurement data and the lower-order dynamics model of user satellite and observation satellite, this paper establishes a sparse parameter expressing model of the user and the observation satellite orbit perturbation through the basis function. The paper then establishes an integrative parameters model, which employs the space-ground-based measurement data fusion to determine the user and observation combined satellite orbit. The corresponding parameters estimation method and algorithm are also designed. Finally, the paper employs the bias and covariance of the nonlinear model parameters estimation to amend the results of the user and observation satellite orbit determination. Simulations show that the algorithm can strongly improve the precision of the user and the observation satellite orbit determination, markedly reduce the complexity of computation and amount of calculation, and at the same time increase the stabilization and reliability of the orbit determination algorithm.
Airborne pseudolite aiding BeiDou system to improve positioning precision in low latitude areas
Weihua Ma,
Jianping Yuan,
Jianjun Luo
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The BeiDou System (BDS), which has three satellites in Geostationary Earth Orbit (GEO), is a regional satellite navigation system of China and its positioning performance is notorious in low latitude areas. The two mending plans using Airborne Pseudolite (APL) aiding BDS to improve navigation precision in such areas are put forward. Plan I uses three BDS satellites and one APS to supply navigation data and Plan II employs two BDS satellites, one APS and altimeter to work. Both of the plans adopt point positioning with code pseudo-range algorithm. Geometric Dilution of Precision (GDOP), which is calculated by Positioning Error Transfer Coefficient Matrix (PETCM), is used to evaluate the positioning performance of new plans. PETCM is predigested when user is in low latitude areas. The key elements of predigested PETCM that effect the Geometric Dilution of Precision (GDOP) are analyzed. The character of GDOP is forecasted easily with the predigested PETCM. The simulations show that the precision of plans are expected to be hundreds of meters except some region where the latitudes of user and APL are close to each other and Plan II is better than plan I. The phenomenal consists with the theoretical analysis.
Combined software GPS/Galileo receiver and applications
Xiaoli Liu,
Jingnan Liu,
Tao Li,
et al.
Show abstract
Modernized GPS and Galileo will be available to civil users at the end of this decade, thus there is a need for unified platform that can receive multi-frequency signal of GPS/Galileo to develop and test for growing variety of diverse applications. The unified platform for various applications will speed the design process and reduce its cost. Such a platform need an open architecture and design flexibility so that modifications and testing can be done conveniently and efficiently. The flexible, reconfigurable, combined and software based Global Navigation Satellite Systems (GNSS) receiver will allow development, test and measurement of a variety of receiver architectures. This paper proposes a structure of combined multi-frequency software GPS/Galileo receiver for future GNSS receiver, which can utilize the planned GPS and Galileo publicly available signals. The receiver consists of a hardware multi-frequency front end responsible for both capturing all planned civil satellite-based radio-navigation signals. A followed programmable processor performs signal correlation. The correlator output then goes on signal processing totally using software. The correlator can be implemented either completely in software or using Field Programmable Gate Array (FPGA) for real time processing. The software modules for signal processing are easily updated. Improvements in accuracy and integrity are also achieved by GPS/Galileo Receiver Autonomous Integrity Monitoring (RAIM). The combined software implementation of processing modules makes this system a truly versatile GNSS receiver suitable for various applications.
Data screening for kinematic orbit determination of LEOs
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The orbit determination (OD) accuracy of kinematic and reduced-dynamic method based on the spaceborne GPS data is strongly dependent on the quality and continuity of GPS observations, and the screening of the Low-Earth-Orbiter (LEO) GPS observations is substantially important. In this paper, an elaborate pre-screening procedure of zero-differenced spaceborne GPS observations was developed. This new efficient data-screening algorithm consists of two steps: in the first step, the "majority voting" method is used to locate the gross errors in zero-differenced GPS data; in the second step, the observation marked as gross error is corrected using the "Quasi-Accurate Detection of gross errors (QUAD)" method. In this step, an iterative least-square adjustment procedure is used to obtain residuals which are screened to detect bad observations thoroughly. For illustration of the feasibility and efficiency of the new algorithm, the processing of a numerical example of CHAMP satellite is presented in this paper.
Optimized strategy analysis on retrieval of GPS precipitable water vapor
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This paper mainly discusses how to determine the optimized strategy for retrieval of Precipitable Water Vapor (PWV) with high accuracy from tropospheric zenith wet delay using ground-based GPS receivers. GPS analytical network are constructed on the base of two observation sites in Antarctica in 1999 and several IGS sites. Tests are conducted to study the performance of different network sizes and different schemes parameters. A high-accuracy GPS processing software package GAMIT/GLOBK is utilized; multiple schemes are adopted for searching the optimized parameters for accurate PWV. After having running GAMIT/GLOBK of all test combination, the results are analyzed by Baseline Repeatability Rate(BRR) and bias between calculated GPS water vapor and actual water vapor. The primary achievements and conclusion are reached including the optimal IGS sites involved, network configurations, elevation cut-off angles, processing periods, knots position.
The key technique study of a kind of personal navigation oriented LBS system
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With the integration of GIS, IT technology and wireless communication techniques, LBS is fast developing and caused wide concern. Personal navigation is the critical application of LBS. It has higher requirement of data quality, positioning accuracy and multi-model services. The study discusses the key techniques of a personal navigation oriented LBS system. As an example for service platform of China Unicom, NAVISTAR especially emphasizes the importance of spatial data organization. Based-on CDMA1X network, it adopts gpsOne\MS-Assisted dynamic positioning technique, and puts forward a data organization solution to realize multi-scale representation.
GPS-based positioning for autonomous underwater vehicle
Wenling Huang,
Huajing Fang,
Yingchun Chen,
et al.
Show abstract
GPS-based positioning for AUV is a field of active researches, which integrates DGPS, radio sonobuoy, DSP, high speed data transmission technology with underwater telecommunication technogy. Many problems remain to be solved for GPS application to AUV because of the peculiarity of underwater environment. Some subjects in a GPS-based positioning system for AUV are reviewed in the paper. The development of underwater positioning and underwater GPS technology is introduced first. Secondly, the methods of underwater positioning are analyzed, followed with GPS-based AUV positioning algorithms. Thirdly, the origin of GPS error and its countermeasures are tudied. Finally, a conclusion is drawn that the GPS-based positioning system can provide high precesion positioning for 3D AUV in real time. It is promising in underwater applications. Some key technologies in underwater positioning are presented for future work.
The signal design of present satellite navigation system and its inspiration
Xiangwe Zhu,
Feixue Wang
Show abstract
Navigation signals are the basis of satellite navigation systems, which determine the navigation systems' performance (such as tracking accuracy, anti-interference capability etc.), and are determined by some constraints (such as radio frequency resources, construction cost, technology level etc.). The aim of signal design is to select "proper" signals considering these above factors and make tradeoffs between performance and constraints. This paper will summarize the signal structure evolution of present satellite navigation and conclude some principles and issues which will be greatly valuable to our 2nd satellite navigation system. There's four main satellite positioning systems presently, the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), the Europe Galileo satellite navigation system and the Chinese BD-1 satellite positioning system. Among these systems, the signal characteristics of GPS and Galileo are good reference to our 2nd satellite navigation system. The improvement of GPS signals is a main aspect of GPS modernization. The aim of GPS modernization is mainly to modernize its signal structure so as to improve the whole systems' performance. The signal structure of Galileo has been revised for several times, and its present signal is the results of long time signal design. From GPS modernization and Galileo signals status, we can summarize some key specifications of navigation signals and some technologies to support these specifications. Based on this, we'll discuss some problems which should be attentive in our country's 2nd satellite navigation system and give some suggestions. This paper is organized into five sections. The first section will give a brief introduction of present satellite navigation system and their main features. Section two will review the GPS and Galileo signals structure evolution, including GPS modernization, Galileo signals status and the comparison of two systems' signals. In the third section, the relationship between signal parameters and system performance will be analyzed, including RF signal characteristics, modulation type, ranging code (such as code type, length and rate) and navigation data. In section four we will discuss some inspiration and technologies concerning our 2nd satellite navigation system, such as the use of multiple frequency signals (ionospheric delay estimation and carrier ambiguity resolution), pilot tones & dataless channel, binary offset carrier (BOC) modulation, and so on. The last section is conclusion, in which the whole paper will be retrospected and some useful conclusion will be given.
The precise position and attitude resolution in MMS based on the integration of GPS/INS
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This paper proposes an approach to precise position and attitude solution for the land-based MMS using GPS and IMU data. Firstly, the synchronization of time and space in the system are discussed, which establishes the base of GPS/INS integration. Then, a new approach is proposed for performing GPS carrier-phase ambiguity resolution using single-epoch C/A code and dual frequency carrier phase data. Based on the inner correlation of dual frequency carrier phase, a new concept of error strip for double-differenced integer ambiguity in observation field is introduced. With the restriction of the strip, the ambiguities can be determined quickly using only single epoch data with the aid of IMU. The ambiguity solution is very efficient and robust even in rigorous situation, e.g. when the number of visible satellites is less than four. On the base of single epoch GPS ambiguity solution, a new coupling mode for double differential carrier phase GPS and INS is proposed. A multiplex Kalman filter is designed with one error state equation and two different observation equations of loose coupling and tight coupling. To verify the solution, great deals of experiments have been done using 1HZ GPS data and 100HZ IMU data of 1°/h precision level, whose results show that the GPS/INS integration can resolve the position and attitude of the vehicle with the error less than 0.2 meter and 0.1 degree separately.
An analytical method for real-time GPS attitude determination
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A new method of initialization about the real-time GPS attitude determination system is presented. The combination solutions of the dualistic, non-linear equations and the ambiguity function method promote the computation efficiency of the initialization. The paper discusses the ambiguity function method and describes the observation equation in terms of geometry. The analytical solution of the dual non-linear coupled equation is given, and the real-time data are processed. As a result, compared with the normal method, the new method is more effective and economical.
Designing a dynamic path guidance system based on electronic maps by using Q-learning
Liang Zou,
Jianmin Xu,
Lingxiang Zhu
Show abstract
Shortest path problem from one origin node to one destination node in non-FIFO (First In First Out) dynamic networks is an unsolved hard problem in dynamic path guidance system. A new approach based on Q-learning is adopted to solve the problem based on electronic maps in this paper. The approach uses geographical information on electronic maps to define Q-learning's value function. Q-learning algorithm's strategy train learning method and training process on path searching are presented. Finally based on Guangzhou City's electronic map, we randomly generate a dynamic network containing 20000 nodes, 40000 links and 144 time intervals, which do not satisfy FIFO to test the approach proposed in this paper. The approach is implemented with this dynamic network and its computational performance is analyzed experimentally. The experimental results prove the effectiveness of the approach.
Research on terrain analysis of mass DEM data based on grid computing
Jibo Xie,
Jianya Gong
Show abstract
With the development of spatial data acquisition technology, the surveying departments have acquired mass DEM Data at terabyte-scale. The current GIS software and computing methods can not meet the demand of analyzing and mining these mass data. A new kind of computing infrastructure is expected to support distributed access to and analysis of these datasets by potentially thousands of users. Grid computing has emerged as an important new field, distinguished from conventional distributed computing by its focus on large-scale resource sharing, innovative applications, and , in some cases, high-performance orientation. This paper focuses on the key problems of terrain analysis of mass DEM data based on grid computing and makes the following contributions. First, we review the current terrain analysis algorithms based on DEM data and analysis the parallel algorithms. Next, we proposed a DTA (Digital Terrain Analysis) grid and analyze the architecture and key problems of the DTA grid. Finally, the experiment system developed based on grid middleware is introduced.
Adaptive geovisualization of mobile map based on Voronoi neighborhoods
Renliang Zhao,
Chaode Yan,
Jun Chen,
et al.
Show abstract
Mobile map is an adaptive map or map-like geovisualisation on mobile information device (MID), which integrates related new techniques (e.g. mobile positioning, mobile computing, mobile communication, multimedia) and adapts to the actual context automatically. Mobile map has become a new application mode in moving environment. Geovisualisation of mobile map has different characteristics from others, so it can't directly copy the visualization mode from desktop maps. This paper analyzes the three main visualization problems and reasons, i.e. geoinformation unbalance between sheets, symbol fragments and unreasonable updating frequency, existing in present models. Based on the analysis, an adaptive geovisualisation model is proposed, which selects geo-objects, calculates adaptive scale, and updates map based on Voronoi neighborhoods. The principle and algorithm are introduced and described respectively. Finally, a test system based on our model is developed. The experiment result proves the new model is feasible and valid to overcome the three problems mentioned above.
The development model of a GIS application system
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How to deal with the relationship between GIS and normal management system is one of the most frequent problems that the developers meet when they are developing application system by using GIS. The reason is: the users have already had their own database or management information system before GIS, and the GIS developers always put all of the exiting data into the management of GIS but they always concentrated on GIS without concerning the different levels of the users. But, because the database function of many GIS softwares is very weak, it is difficult to achieve the task of managing normal database, which created some difficulties for developing the system. In addition, only a few functions of GIS have been used, even if all the exiting data have been put into GIS management. As a result, the cost of developing increased. Focusing on this problem, the authors proposed three developing models which combined management system with the advantages of GIS and based on analyzing users' demand in this paper. The authors also introduced the key techniques during developing this kind of application system in this paper.
Study on urban large-scale geo-database using high spatial resolution remote sensing image
Liangjie Yang,
Naixia Mou
Show abstract
Urban large-scale digital mapping demanded a greatly efficient and speedy surveying method. The traditional surveying process lagged behind because it had many shortcomings in mapping cost, mapping period, data storage and further usage. It is an effective way to use high spatial resolution remote sensing image to make large-scale urban maps. Firstly this paper discussed the relationship between mapping scale and image spatial resolution, analyzed the way of processing image about large-scale mapping, explained the data-abstracted method based on customized rules, intelligent symbols and automated topology. Secondly this paper expatiated on the core technology of geo-database based on large-scale digital maps and high spatial resolution image, argued how to establish and maintain a spatial database and how to serve the other different applications by the public interface. The remote sensing image, large-scale digital maps, intelligent symbols, map elements, map-framing indexes and social statistics data were stored into the same spatial database which further provided comprehensive data and the thematic maps for urban administration, urban plan, land management, digital city and Urban GIS. And then the spatio-temporal geo-database was established by the "versioning" which could manage different spatial and temporal data. So it was feasible to produce large-scale digital maps using high spatial resolution remote sensing image and construct spatio-temporal database using "versioning." Furthermore it is a necessary way to urban informational and intelligent administration.
An extended database system for handling spatiotemporal data
Baolin Yi
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With the rapid development of geographic information system (GIS), computer aided design (CAD), mobile computing and multimedia databases, spatiotemporal databases have been the focus of considerable research activities over a significant period. It becomes an enabling technology for important applications such as land use, real estate, transportation, environmental information systems, energy resource et al. In this paper we address research issues in spatiotemporal databases. We first proposed an integrated spatiotemporal data model, and then we provided novel threetier architecture for implementation where Meta tables to handle spatiotemporal data were extended. Finally, experiments confirm the effectiveness of our techniques under realistic settings.
The design of reconfigurable hardware platform on small satellite house-keeping computer based on SOC
Zhaobi Wei,
Zhiying Ma,
Jing Yan
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In this paper , the research of a reconfigurable hardware platform based on SOC according to the requirements of the hardware design of small satellite house-keeping computer is presented. Some special SOC chips of the platform for satellite house-keeping computer are well developed using electronic design automatic (EDA) technology, which are implemented on CPLD/FPGA. The platform can satisfy the requirement of static and dynamic reconstruction of the hardware of satellite house-keeping computer by using reusable function module and only changing the reconfiguration and job scheduling of reconfigurable hardware between them dispensing with hardware's alter. It can greatly increase the reliability, stability of the small satellite house-keeping computers and can shorten research periods by using the platform.
An all-digital demodulation scheme for DVB-S2
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In this paper, an all-digital demodulation scheme which is compliant with the second generation digital video broadcasting via satellites (DVB-S2) is presented. It works well for several modulation modes supported by DVB-S2 even under rather low signal-to-noise ratio (SNR). All algorithms adopted in this scheme have been described in detail and their computer simulation results have been shown. The symbol error rate (SER) performance from simulations is very close to the theoretical one.
Transmission-type stereo mapping micro-satellite payload and ground application system
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With the development of modern small satellite technology, it is potential and significant to use the new technology for the earth observation. The stereo mapping micro-satellite--"Experiment Satellite 1", designed and built by Harbin Institute of Technology, is taken as an example for discussion of the relevant technologies and corresponding principle of the satellite payload and its ground application system. The ground application system receives the stereo photographs data from the "Experiment Satellite 1" and then produces surveying products such as digital elevation map, digital orthoimage and digital topographic map, etc. "Experiment Satellite 1" is the first satellite where three-line-array CCD camera is used triumphantly in world for stereo mapping. It will have profound influence on the earth observation technique.
A new urban-plan system based on augmented reality
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This paper describes an Urban-Plan System based on augmented reality with tangible and interactive user interface. Virtual models, graphics generated by computer and physical materials have been used in whole urban-planning process. Participants can carry out their assignment collaboratively in direct and interactive manner and the final results can be browsed and modified in real-time. Augmented Reality enables users to achieve Urban-Plan more effectively and easily. One key object of our system is to enable users manipulate virtual models as they can do in real world. To achieve this, we must calculate the pose and position of camera relative to real world exactly. This paper uses computer vision technology and known marker to solve the above problem.
ARMAP: a novel geographic visualization system based on augmented reality
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Geographic visualization is a hot point in recent years. Many new methods for spatial information visualization have been developing. In this paper, we introduce a new Augmented Reality based geographic visualization system which has the properties of virtual- real combination and human-computer interaction. Registration is the key technique to realize the seamless combination of virtual and real objects. We mainly discuss the pattern and nature feature based registration algorithm used in our system.
Multipath effect suppression for instrument landing system based on MUSIC
Xiubin Zhao,
Yongsheng Wang,
Hengle Jiang,
et al.
Show abstract
The Decimeter-wavelength Instrument Landing System is designed to assure an exact and timely flight arrival on many airports. But its signal can often be distorted by reflections and scattering caused by objects which are illuminated by the radiating antennas, sometimes referred to be "multipath", which pose a great threat to the system's operation. In this paper, an improved receiver based on spatial spectrum estimation concepts is proposed for safer automatic landing procedures. The new approach is based on Direction of Arrival (DOA) estimation performed by the MUSIC algorithm and signal filter performed by beamforming algorithm. The superior performance of the proposed system with respect to currently employed techniques in the presence of unwanted interferences has been tested in extensive computer simulations.
Constellation design for low-earth orbit space-based radar for continuous coverage
Yong Wu,
Jun Tang,
Yingning Peng
Show abstract
The constellation magnitude is always the primary concern for a practical Space-base Radar (SBR) system, especially the ones using low-earth orbit (LEO). To control the constellation magnitude, the overlap between the sensor footprints should be minimized. In the special case of an asymmetric footprint in SBR scenario, we introduced a slope geometry to optimize the constellation of polar orbit, and the estimation of the magnitude is presented. An example constellation is given to confirm the analysis.
Agile multi-spot beams steering with a phase-only nematic liquid crystal spatial light modulator
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A 256×256 pixels commercial phase-only Liquid Crystal Spatial Light Modulator (LCSLM) is adopted to generate arbitrary spot patterns successfully. An improved Fourier iterative algorithm combining with pseudorandom phase encoding is proposed to satisfy the real-time processing requirement. The improved algorithm based on the (Gerchberg-Saxton) G-S algorithm with the initial phases generated by the pseudorandom phase encoding method. By employing the improved algorithm, the intensity error of a 4×4 spots array pattern is less than 7%.
Research on the key techniques of fiber optic gyroscopes in space applications
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The advantages and the characteristics of the fiber optic gyroscopes (FOGs) for the space application, compared with the traditional mechanical gyroscope and the laser gyroscope, have been mentioned. There are differences of the FOG designing between application in space and other conditions especially the radiation-resistant, low power cost and less weight of the FOG. The key techniques of the fiber optic gyros technology have been proposed and some test results have been discussed.
The study and implementation of embedded MPEG-4 image encoder for spacecraft
Lihua Zuo,
Qingxue Wu,
Zhuang Tian
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Images of astronauts must be transmitted to the earth in a low bit rate so as to lessen the tension of channel in spacecraft. In this paper, an approach to 384kbps Image Encoder for spacecraft is presented. With FPGA and special chips, a prototype which has a feature of lower time delays, better performance of motion estimation and higher resolution has been designed and implemented. This paper explores the motion compensation and texture coding as the basic coding structure, the MPEG-4 Image Encoder is coded in a content-based and object-based modern method, according to the thought of contour-texture. The coding module is the kernel component of the system that performs the DCT, quantification, motion texture coding, motion estimation and motion compensation, etc. Meanwhile, the digital video signals are compressed by this one. Pursuant to MPEG-4 standard, inter-frame coding and intra-frame DCT are adopted to reduce temporal and spatial redundancy. Variable length coding is also used to match the bit length and the signal frequency, in order to lower the bit rate further more. The bit rate ultimately reaches 384kbps. In special chips, data processing, transforming, coding, estimating and compensating are controlled by DSP which cooperates with FPGA. Error correction coding is also implemented by special chips under the control of DSP.
The research on command and guide/flight management system based on SIT
Gang Zhang,
Jianlin Bai
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Firstly, this paper describes and illustrates briefly the functions and structure of the Flight Management and Command Guidance System for Flight Test. Through space information technology, system can make use of GPS and data of every intelligence source well. Considering characteristic that the many kinds, many data and strong real time of intelligence processing, this thesis take twice swerve volley guide method for example, and introduces vector theory analyzing volley guide method and mathematical model of system Which will improve command guide capability. In Flight management, Using SIT to integrating flight information, according to aviation statute and requirement of flight task, systems organize planes in air management area to ensure flight safety, advance time using efficiency. The whole system has the important application value for all kinds of command guide and air management of aero craft.
An authentication framework for a hybrid satellite network with resource-constrained nodes
Ayan Roy-Chowdhury,
John S. Baras,
Michael Hadjitheodosiou
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The new phase of space exploration involves a growing number of human and robotic space missions to remote planets with varying communication and service requirements. Due to the critical nature of the missions, security is a very important requirement that needs to be addressed. Among primary security requirements are user authentication and message integrity that are needed to ensure that the data in the network is transmitted without unauthorized modifications between the source and destinations, and that data from only authorized network nodes are accepted by other nodes. In this paper we focus on the issue of user authentication and data integrity for a specific space network architecture supporting lunar exploration. We consider a hybrid network consisting of a terrestrial network on Earth, a network on the lunar surface, and a satellite constellation that connects the two surface networks. The lunar network comprises sensor nodes serviced by stationary gateways and mobile robotic vehicles with sensing capability, while the network on Earth is envisioned as a combination of private and public networks. The problem of authentication in this network is complex due to the presence of nodes with varying capabilities in terms of computation strength, storage and energy. The nodes on Earth and the gateways on the lunar surface would have higher computation and energy capabilities compared to the satellites and the sensor nodes. In this situation, an authentication protocol that is optimized to the strengths and limitations of the different classes of nodes would be most suited. We focus on a solution that will operate under the constraints of the space environment (delay, limited energy, limited processing capability at remote nodes). We present a framework for user authentication and data integrity based on an authentication algorithm that makes use of symmetric certificates and hash chains of keys used to compute Message Authentication Codes, to provide asymmetric authentication capabilities to the network nodes. nodes with more resources. We give a detailed description of the authentication protocol we develop for this network and provide an analysis of the security of the protocol by considering various types of passive and active attacks. We also highlight the savings incurred in terms of processing, storage and network bandwidth, which we get in using the proposed protocol in comparison to standard public-key authentication protocols.
A three dimensional modeling and simulation platform design for digital city
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Digital city is one of the important branches and regional layers of digital earth. The modeling and simulation of a city can visualize the city in the computer and therefore improve the management of the city. How to model and simulate the city in a three dimensional scale with the seamless link between spatial geometry and attribution has become the hot topic of experts from both virtual reality and geographical information system fields. This paper designs a platform of three dimension modeling and simulation for digital city. This platform consists of several modules such as Data Acquisition, Data Import & Export, Database Management, Model Edit & Reorganization, and Scene Create & Cruise. The most important input data resources used in this platform are DXF and 3DS, which are obtained and produced from the digital stereo photos taken by the Data Acquisition Module(Z-system). The Import & Export Module converts the DXF and 3DS data into OpenFlight format, and then by using the Model Edit & Reorganization Module, the converted models can be visually edited and reorganized so as to recreate more rational models with both spatial and attribute information stored in the Database Management Module. The Scene Create & Cruise Module selects models from the database to create three dimensional scenes of the city and provides the interactive cruise and information query in the scenes of the city. It is concluded that this platform integrates the technologies of geographical information system, virtual reality and database, and can play the role of the base of digital city onto which other application systems are joined.