Optimum 2-D LOS MIMO Performance Using Omni-directional Antennas Attained through Genetic Algorithms

Abstract

mum 2-D LOS MIMO performance using omni-directional antennas attained through genetic algorithms, " Proceedings of the 6th Annual Communications Networks and Services ResearchConference (CNSR 2008), vol. 1, (Halifax, NS, Canada), pp. 331-338, May 5-8, 2008 This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by sending a blank email message to pubs-permissions@ieee.org.By choosing to view this document, you agree to all provisions of the copyright laws protecting it. Optimum 2-D LOS MIMO AbstractThe application of genetic algorithm (GA) optimization has been proven to be highly successful in the area of nonlinear optimizations. For a Multiple-Input, Multiple-Output (MIMO) wireless communication system, the optimum performance of the users with respect to the arrangement of antennas is a highly non-linear function which a genetic algorithm seems highly suited to. In this paper, a four-by-four MIMO system model is considered using a simplified 2-D LOS radio channel with additive white noise. Placing the users in a known arrangement, the optimum placement of the four antennas is determined through a genetic algorithm optimization using the average MSE of the four users as the fitness function. Initial results show a tendency towards an arrangement in which at least two antennas seen by the all transmitters are separated by a symbol wavelength. IntroductionRecent work in the area of wireless communications has shown that when antenna placements in a two-by-two MIMO system are on the order of a symbol wavelength rather than the carrier wavelength, significant improvements can be made with respect to performance [1], [2]. This has given rise to the term of Signaling Wavelength Antenna Placement (SWAP) Gain to describe the advantages. The premise of this finding is that when the antennas are spaced a symbol wavelength apart, the likelihood that the channels are correlated is minimal.Much of the MIMO work to date relies heavily on assuming a randomized multipath rich environment to realize the maximum gains from spatial diversity [3]. The fading characteristics are often modeled as Rayleigh distributions. However, in close range indoor situations, the line of sight (LOS) can often dominate the multipath components (modeled as Ricean distributions), minimizing the prospective gains from MIMO techniques. It is therefore necessary to examine MIMO performance in LOS situations. By strategically arranging the antennas in the system to take advantage of the SWAP Gain, an optimal placement exists that will maximize the performance of the MIMO system in a LOS situation.However, determining the optimum placement of the antennas is seen as a highly non-linear problem that depends on the number of antennas in the system, and distribution of the users in the three-dimensional wirel...

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