Proceedings Volume 7349

Wireless Sensing and Processing IV

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Proceedings Volume 7349

Wireless Sensing and Processing IV

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Volume Details

Date Published: 28 April 2009
Contents: 6 Sessions, 20 Papers, 0 Presentations
Conference: SPIE Defense, Security, and Sensing 2009
Volume Number: 7349

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7349
  • Diversity and Multicarrier Techniques
  • Radio Frequency and Identification (RFID)
  • Implementation and Application
  • Modulation and Coding
  • Sensor Networks
Front Matter: Volume 7349
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Front Matter: Volume 7349
This PDF file contains the front matter associated with SPIE Proceedings Volume 7349, including the Title Page, Copyright information, table of Contents, Introduction (if any), and the Conference Committee listing.
Diversity and Multicarrier Techniques
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Optimization of MIMO unitary space-time codes
Xinjia Chen, Ernest Walker, Pradeep Bhattacharya, et al.
One category of Space-Time codes are constellations of unitary matrix in parametric form. Optimization is essential for seeking parameters of constellation with the largest diversity product. In this research, we demonstrate that diversity product is not a good measure of constellation quality as widely adopted in communication community. Moreover, we show that good codes may not need to have full diversity. We propose better criteria for measuring the quality of constellations, which are also very amenable for optimization and particularly suitable for the gradient search method. Furthermore, we propose a new approach for signal constellation design. Instead of ambiguously discriminating low and high SNR, our techniques target the range of block error rate which is acceptable and not extremely small. Although the computational complexity of code designing can be formidable, we have developed techniques which significantly improve the efficiency. We obtain space-time codes which significantly outperform existing ones.
Comparative performance evaluation of code-spread OFDM
Orthogonal Frequency Division Multiplexing (OFDM) is a popular technique used to combat frequency selective fading in multipath channels. When spectral nulls are present in the channel, they can severely degrade or cancel out several OFDM tones, resulting in an irreducible error rate. In Code-Spread OFDM (CS-OFDM), each sinewave carries a weighted sum of all the information symbols being transmitted in an OFDM block interval. In this paper, an MMSE estimator is derived for each symbol for a number of cases, including when the number of carriers is greater than the number of symbols. The performance of CS-OFDM is evaluated using Hadamard, Vandermonde, and Discrete Cosine spreading and compared to standard OFDM.
Space-time processing for OFDM using complementary Golay sequences
In this paper, a new method of space-time processing is proposed for Orthogonal Frequency Division Multiplexing (OFDM) using complementary pairs of Golay sequences. Space-time processing with complementary Golay sequences provides diversity at the transmitter which in turn helps improve performance in multipath fading channels without the need for channel knowledge at the transmitter. The autocorrelative properties of complementary Golay pairs allows multiple data signals at the transmitter to be perfectly separated at the receiver. Further, these properties significantly boost the signal energy at the receiver, leading to a higher SNR and thus better bit error performance. Building on work done in the field of orthogonal space-time block codes, the new Golay method is proposed and derived for both a 2×1 and 2×2 MIMO-OFDM system with a channel exhibiting Rayleigh fading; at the receiver, symbol estimation is effected via minimum mean-square estimation (MMSE).
Investigating the effects of filtering, clipping, and power amplification on the performance of OFDM waveforms
Orthogonal Frequency Division Multiplexing (OFDM) has become a very popular technique for digital data transmission on multipath fading channels due to its low computational complexity and simple equalization process. However, the multipath component of these types of channels causes a phenomenon known as frequency selective fading. This type of fading can severely degrade or completely eliminate the signal energy of many of the OFDM tones producing an irreducible error rate, even when no noise is present. Consequently, most OFDM systems operating in multipath fading environments utilize some form of forward error correction (FEC) and block interleaving. OFDM waveforms which utilize FEC are usually referred to as coded OFDM (COFDM). One of the main drawbacks of OFDM and COFDM waveforms is the very large peak envelope power to average power ratio (PAPR) which requires the use of very linear power amplifiers (PA) and a large power back-off into the PA. To reduce the PAPR, clipping is typically utilized. In addition, filtering must be applied to OFDM and COFDM waveforms in order to contain their spectral occupancy. This paper will investigate the effects of filtering, clipping and power amplification on the performance of OFDM and COFDM waveforms. The multipath fading channels used for testing will be based on the High Frequency (HF) channels due to their challenging nature.
Radio Frequency and Identification (RFID)
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Anti-collision protocols for RFID systems exploiting multi-antenna readers
In conventional RFID systems, only one tag can be identified at a time. Tag collisions occur if more than one tag simultaneously occupies the shared RF channel, resulting in low identification efficiency and long delay, particularly when the population of tags is large. In this paper, we propose two RFID anti-collision protocols, both are based on framed slotted ALOHA (FSA), to concurrently identify multiple tags by using a multi-antenna reader. The first one is Blind Identification Protocol, which relies on blind estimation of the channel between the activated tags and the reader and, as such, does not require redesign of the existing RFID tags. The second one is Orthogonal ID-aided Identification Protocol which estimates the channels with the use of temporary orthogonal IDs, which are randomly selected by the tags and are inserted at the head of each tag's reply signal. The use of orthogonal IDs facilitates both the detection of activated tags and the channel estimation. Unlike code division multiple access (CDMA) techniques which rely on the use of excessive bandwidth and require redesign of tags, the proposed protocols use multiple antennas at the reader to support concurrent identification of multiple tags without the requirement of additional bandwidth and no or minimal modifications to the existing tags. As a result, the proposed techniques yield significant improvement of the identification efficiency and reduction of the identification delay. We analyze, in an analytical framework, the identification efficiency of the proposed protocols, and the optimum frame size is derived.
Array processing for RFID tag localization exploiting multi-frequency signals
RFID is an increasingly valuable business and technology tool for electronically identifying, locating, and tracking products, assets, and personnel. As a result, precise positioning and tracking of RFID tags and readers have received considerable attention from both academic and industrial communities. Finding the position of RFID tags is considered an important task in various real-time locating systems (RTLS). As such, numerous RFID localization products have been developed for various applications. The majority of RFID positioning systems is based on the fusion of pieces of relevant information, such as the range and the direction-of-arrival (DOA). For example, trilateration can determine the tag position by using the range information of the tag estimated from three or more spatially separated reader antennas. Triangulation is another method to locate RFID tags that use the direction-of-arrival (DOA) information estimated at multiple spatially separated locations. The RFID tag positions can also be determined through hybrid techniques that combine the range and DOA information. The focus of this paper to study the design and performance of the localization of passive RFID tags using array processing techniques in a multipath environment, and exploiting multi-frequency CW signals. The latter are used to decorrelate the coherent multipath signals for effective DOA estimation and for the purpose of accurate range estimation. Accordingly, the spatial and frequency dimensionalities are fully utilized for robust and accurate positioning of RFID tags.
Implementation and Application
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1.25 GHz path loss prediction models for multifloored buildings
Ismail Fauzi Isnin, Martin Tomlinson, Mohammed Zaki Ahmed, et al.
In this paper, parameter statistics of path loss prediction models are presented for 1.25 GHz within multifloored buildings. Parameters are extracted from analyzed data which was collected from measurements within three buildings. Buildings were chosen with specific considerations such as building footprint shapes and internal design.For the consideration of building footprint, a building having rectangular footprint and a building having square footprint were chosen. Because of its internal design, the third building was chosen to represent buildings with an atrium. Results show that, buildings with square footprint caused higher path loss compared to rectangular footprint buildings. It is also found that, buildings with an atrium have the lowest path loss exponent and lowest floor attenuation factor among other considered buildings. A model for path loss prediction is proposed for multifloor buildings with its internal design allows lineof- sight (LOS) and non line-of-sight (NLOS), even though transmitter and receiver are not on the same floor. The model takes into consideration the factor of transmission type, whether it is LOS or NLOS. The proposed model has reduced the standard deviation of error prediction, which indicates better prediction accuracy is achieved.
Handheld emissions detector (HED): overview and development
George J. Valentino, David Schimmel
Nova Engineering, Cincinnati OH, a division of L-3 Communications (L-3 Nova), under the sponsorship of Program Manager Soldier Warrior (PM-SWAR), Fort Belvoir, VA, has developed a Soldier portable, light-weight, hand-held, geolocation sensor and processing system called the Handheld Emissions Detector (HED). The HED is a broadband custom receiver and processor that allows the user to easily sense, direction find, and locate a broad range of emitters in the user's surrounding area. Now in its second design iteration, the HED incorporates a set of COTS components that are complemented with L-3 Nova custom RF, power, digital, and mechanical components, plus custom embedded and application software. The HED user interfaces are designed to provide complex information in a readily-understandable form, thereby providing actionable results for operators. This paper provides, where possible, the top-level characteristics of the HED as well as the rationale behind its design philosophy along with its applications in both DOD and Commercial markets.
Near-field sensing using subspace techniques
Three techniques are studied for sensor array based pupil-plane imaging of point sources in the near field. Pupil plane imaging is a potential alternative in the absence of well-developed focal plane array technology. The techniques are sum and delay focusing, minimum variance distortionless response (MVDR) focusing and subspace focusing. While the first has been widely proposed for usage, it is demonstrated here that the other two provide better resolution. Between the MVDR and the subspace approaches, the latter potentially provides better performance in noise.
Modulation and Coding
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Structured low-density parity-check codes with bandwidth efficient modulation
Michael K. Cheng, Dariush Divsalar, Stephanie Duy
In this work, we study the performance of structured Low-Density Parity-Check (LDPC) Codes together with bandwidth efficient modulations. We consider protograph-based LDPC codes that facilitate high-speed hardware implementations and have minimum distances that grow linearly with block sizes. We cover various higherorder modulations such as 8-PSK, 16-APSK, and 16-QAM. During demodulation, a demapper transforms the received in-phase and quadrature samples into reliability information that feeds the binary LDPC decoder. We will compare various low-complexity demappers and provide simulation results for assorted coded-modulation combinations on the additive white Gaussian noise and independent Rayleigh fading channels.
Comparison of channel switching and reduced state trellis detection with coherent diversity combining for CPFSK
Techniques by which the receive performance of a Continuous-Phase-Frequency-Shift-Keying (CPFSK) UHF waveform can be improved in frequency-flat slow Rayleigh fading using receive spatial diversity are investigated. Through simulation, diversity techniques using limiter-discriminator-detection with post detection switching diversity is compared with techniques employing Maximum-Likelihood-Sequence-Estimation (MLSE) and Per- Survivor-Processing (PSP) for coherent maximum ratio combining.
Performance evaluation of CDMA, WDMA, DWDMA networks
The demand for bandwidth for applications in high-speed networks requires improved network topologies, throughput, and parallelism. Many techniques such as optical code-division multiple access (CDMA), wavelength division multiple access (WDMA) and dense WDMA (DWDMA), have shown considerable potential for high-speed network applications. This paper evaluates the performance of these techniques with respect to bandwidth utilization and delay under various scenarios. Simulation results showed that optical CDMA system emerges as the most efficient system because CDMA utilization is the highest when compared to the WDMA and DWDMA systems, and that CDMA is better for high offered loads compared to WDMA and DWDMA.
Swarm optimized UWB-PPM and protocol design for sensor network
In this paper, a swarm based ultra-wideband waveform and routing protocol is used for communicating messages in the form of short pulses in sensor based health care application. Due to the time sensitivity of the application, a cognitive protocol is applied to make decisions based on resource availability and quality-of-service. The combination of swarm based physical and routing layer protocol helps in achieving an energy, bandwidth and time efficient application. This paper compares the performance of cross layer protocol when exhaustive search and swarm based waveform design is used.
Some practicalities of popular error correcting codes on fading channels
For real world communication systems that operate in correlated fading channels, perfect channel state information is not always available. In the literature, performance curves for error correction codes are usually plotted from either closed form equations or simulations which assume perfect channel state information. While these methods of measuring the capabilities of error correcting codes do serve a theoretical purpose, they do not necessarily demonstrate how well a code will perform under non-ideal conditions. The goal of this paper will be to compare LDPC and Turbo codes and determine how well they perform when perfect channel state information is not available at the receiver. Bit error rate and some block error rate performances will be provided for the AWGN, Rayleigh and 1Hz 1ms multipath fading channel. The results of this paper may provide communication systems designers some useful insight into the actual performance of error correcting codes in real-world scenarios.
Sensor Networks
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Bio-inspired WSN architecture: event detection and loacalization in a fault tolerant WSN
Yosef Alayev, Thyagaraju Damarla
One can think of human body as a sensory network. In particular, skin has several neurons that provide the sense of touch with different sensitivities, and neurons for communicating the sensory signals to the brain. Even though skin might occasionally experience some lacerations, it performs remarkably well (fault tolerant) with the failure of some sensors. One of the challenges in collaborative wireless sensor networks (WSN) is fault tolerant detection and localization of targets. In this paper we present a biologically inspired architecture model for WSN. Diagnosis of sensors in WSN model presented here is derived from the concept of the immune system. We present an architecture for WSN for detection and localization of multiple targets inspired by human nervous system. We show that the advantages of such bio-inspired networks are reduced data for communication, self-diagnosis to detect faulty sensors in real-time and the ability to localize events. We present the results of our algorithms on simulation data.
Distributed radar network for real-time tracking of bullet trajectory
Yimin Zhang, Xin Li, Yuanwei Jin, et al.
Gunshot detection, sniper localization, and bullet trajectory prediction are of significant importance in military and homeland security applications. While the majority of existing work is based on acoustic and electro-optical sensors, this paper develops a framework of networked radar systems that uses distributed radar sensor networks to achieve the aforementioned objectives. The use of radio frequency radar systems allows the achievement of subtime- of-flight tracking response, enabling to response before the bullet reaches its target and, as such, effectively leading to the reduction of injuries and casualties in military and homeland security operations. The focus of this paper is to examine the MIMO radar concept with concurrent transmission of low-correlation waveforms from multiple radar sets to ensure wide surveillance coverage and maintain a high waveform repetition frequency for long coherent time interval required to achieve return signal concentration.
Mobility in free-space optics based wireless sensor networks
This paper proposes an FSO-based mobile sensor network that is not subject to RF interference common to wireless sensor networks. FSO-based mobile sensor networks can potentially be used in a battlefield where security of communication, including freedom from susceptibility to enemy-induced jamming, is important. The paper discusses the design of nodes containing multiple transceivers composed of LEDs and photo detectors. Results of initial experiments are included. The work reported in this paper is part of an ongoing investigation on mobile FSO networks, including the design of efficient protocols that can allow the mobile sensor nodes to function as a mesh network permitting information exchange among nodes directly and, possibly, through an intermediate node.
A new approach to architecture of sensor networks for mission-oriented applications
In this paper, a novel mission-oriented sensor network architecture for military applications is proposed involving multiple sensing missions with varying quality of information (QoI) requirements. A new concept of mission QoI satisfaction index indicating the degree of satisfaction for any mission in the network is introduced. Furthermore, the 5WH (why, when, where, what, who, how) principle on the operational context of information is extended to capture the changes of QoI satisfaction indexes for mission admission and completion. These allow modeling the whole network as a "black box". With system inputs including the QoI requirements of the existing and newly arriving missions and output the QoI satisfaction index, the new concept of sensor network capacity is introduced and mathematically described. The QoI-centric sensor network capacity is a key element of the proposed architecture and aids controlling of admission of newly arriving missions in accordance with the QoI needs of all (existing and newly admitted missions). Finally, the proposed architecture and its key design parameters are illustrated through an example of a sensor network deployed for detecting the presence of a hazardous, chemical material.
Histogram for ambiguity visualization and evaluation (HAVE)
Sparse interferometer array systems can be the cost-effective precision radio-frequency emitter directionfinding systems needed in military and civilian applications. High precision can be implemented by array extent, while low cost is supported because the array is sparse. However, in the design process ambiguities in the high dimensional array manifold space need to be evaluated, which typically can be mathematically or empirically daunting. Here we describe a method to collapse the high dimensional design space, using root-mean-squared phase differences for signals received at pairs of elements in the interferometer, to a twodimensional histogram for ambiguity visualization and evaluation (HAVE). The histogram facilitates design by presenting and locating interferometer ambiguities.