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Proceedings Paper

Optimum placement of transmitters for indoor infrared wireless systems using modified recursive algorithm
Author(s): Arumugam Sivabalan; Joseph John
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Paper Abstract

Wireless indoor infrared systems have been widely considered as an alternative communication system, especially for wireless LAN. Optical wireless systems provide simple and flexible connectivity with the possibility of reuse of wavelengths in adjacent rooms. However, the performance of the optical wireless infrared (IR) systems is limited by several factors, such as the speed limitations of the opto-electronic devices, high path loss, multipath dispersion, receiver noise and the shot noise induced by natural and artificial light on the receiving photodiode. To overcome the high path loss introduced by the channel, we need to transmit more power. Allowable Exposure Limit (AEL) standard puts limit on the transmitter output power level. Instead of increasing the power of a single transmitter, an alternative solution is to use more than one transmitter with less transmitting power. Such an approach can satisfy the AEL standard and also achieve near-uniform power distribution in the indoor environment. The performance of such a system depends on the optimum choice of the number of transmitters in a room and also their placement. This paper gives simulation results of power distribution in a room with multiple transmitters located on the ceiling. To the best of our knowledge such a work has not been carried out so far. With the help of these results one can arrive at the optimum number of transmitters within a room and also their placement. To find an optimum placement of transmitters in the indoor infrared wireless system, an accurate knowledge of power distribution is required. The power distribution in the indoor channel mainly depends on the reflection characteristics of indoor surfaces. This power distribution can be completely characterized by the impulse response of the channel. Some of the existing algorithms to compute the impulse response are the recursive method, statistical approach, Monte Carlo calculation, Modified Monte Carlo Scheme, DUSTIN algorithm and Iterative Site-Based Modeling. All these models considered only the single transmitter environment. We propose a modified recursive algorithm to compute power distribution of an indoor IR channel with multiple transmitters. Using this algorithm, we computed the power distribution in a multiple transmitter environment. Our modified recursive algorithm was implemented on a Pentium-III PC, using Matlab 6.0. The transmitters were assumed to be ideal Lambertian sources, placed at the ceiling oriented towards the floor. We assumed the room to be empty. Reflection coefficient of all the indoor surfaces were assumed to be the same (=0.8). Our code was tested for the room size, and other conditions given by Barry (1993) for a single transmitter. We were able to get the same result as Barry, thus verifying our code. The room size taken for our simulation is 5x5x3m. The sources were assumed to emit equal powers, with a sum total of 1 watt. The position of transmitters considered fall into four configurations, viz., A, B, C and D, each with either four or five transmitters. The (x,y,z) positions of configuration A with four transmitters are (0,0,3),(0,5,3),(5,0,3) and (5,5,3). Configuration B with four transmitters were located at (1,1,3),(1,4,3),(4,1,3) and (4,4,3). Similarly, configuration C with four transmitters had locations (0.5,0.5,3),(0.5,4.5,3),(4.5,0.5,3) and (4.5, 4.5,3), while those of configuration D were at (0.75,0.75,3),(0.75,4.25,3),(4.25,0.75,3) and (4.25, 4.25,3). For all the above configurations with four transmitters, a fifth transmitter was also considered at the position (2.5,2.5,3). The simulation produced a contour plot of power distribution on the floor. For the single transmitter configuration (with 1 watt), the power distribution ranged from 0.5 to 3.5 micro watt. Compared to this, for the configuration B above with four transmitters, the power distribution range was only from 0.8 to 1.6 micro watt. We found this configuration to be the best placement with the lowest maximum-to-minimum power ratio.

Paper Details

Date Published:
Proc. SPIE 5282, Network Architectures, Management, and Applications, ; doi: 10.1117/12.519727
Show Author Affiliations
Arumugam Sivabalan, Indian Institute of Technology (India)
Joseph John, Indian Institute of Technology (India)

Published in SPIE Proceedings Vol. 5282:
Network Architectures, Management, and Applications
S. J. Ben Yoo; Kwok-wai Cheung; Yun-Chur Chung; Guangcheng Li, Editor(s)

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