Performance Analysis of Multiple Input Multiple Output Systems With Antenna Selection

Abstract

Over the last decade, the massive demand for high data-rate wireless applications has motivated the study and design of new communication technologies. Among all of them, multi-antenna schemes have been shown to provide remarkable benefits in terms of bit error rate (BER) performance. Multiple input multiple output (MIMO) systems are popular due to its ability to improve performance and mitigate fading in a wireless communication system without increasing bandwidth and reducing data rate [1]-[4]. However, there are some bottlenecks, for example, limited spacing between adjacent antennas at mobile station, requirement of costly RF chains and power spreading between antennas. Antenna selection (AS) is an attractive approach to alleviate these requirements of MIMO system without loss of diversity gain. Selecting a subset of antennas at the transmitter or the receiver is called transmit antenna selection (TAS) or receive antenna selection (RAS), respectively. A joint transmit receive antenna selection (JTRAS) scheme considers selection at both the ends. In the literature, optimum TAS [5][8], optimum RAS [11][12], and optimum JTRAS schemes [13][14] have been proposed and analyzed. In frequency division duplex (FDD), AS at the transmitter requires a feedback link from the receiver. The receiver selects the antenna based on the available channel state information (CSI) and send the selected indices back to transmitter. However, the complexity of AS algorithm at receiver and number of feedback bits increases the overhead of the system. Therefore, some sub-opt AS schemes with less feedback bits and complexity are given in [6].In this thesis, we consider a MIMO system equipped with N (N ≥ 2) transmit antennas and at most two receive antennas in down-link applications. We limit the number of receive antennas to two, since a mobile station can only mount one or two antennas due to space, complexity, and cost limitations [15]. We consider three different cases. Case 1: We consider two transmit antennas out of N with one receive antenna, denoted as (N, 2; 1) sub-optimum TAS scheme. We keep one antenna fixed and select the best among the remaining N − 1 antennas. We use Alamouti transmit diversity (ATD) and derive the exact closed form expression for the pdf of SNR and then obtain the outage probability and SER for BPSK, MPSK and MQAM constellations. We also address the issue of feedback bit requirement. We compare the considered case with other schemes in literature with respect to BER, outage probability and feedback bit requirement. Case 2: We consider two transmit antennas out of N and one receive antenna out of two, denoted as (N, 2; 2, 1) sub-optimum JTRAS scheme. For each receive antenna we select two transmit antennas and then we select the receive antenna. At the transmitter we keep one antenna as fixed and select the best among the remaining N−1 antennas. At the receiver we select the best antenna out of two antennas. We use ATD and derive the exact closed form expression for the pdf of SNR and then obtain the outage probability and BER for BPSK constellation. We show (N, 2; 1) sub-optimum TAS/ATD as its special case. We also address the issue of feedback bit requirement. We compare the considered case with other schemes in literature with respect to BER, outage probability and feedback bit requirement. Case3: In first two cases we consider perfect AS, but due to time varying channel and imperfection in feedback link, we cannot carry out instantaneous AS. So in [16]-[19] the case of imperfect AS is considered. We consider a (N, 2; 1) sub-optimum TAS/ATD system with imperfect TAS. We carry out simulations to study the effect of imperfect TAS on BER performance. We compare the considered case with other schemes in the literature with respect to BER performance.