Abstract
A major limiting factor in the performance of multiple-input-multiple-output (MIMO) code division multiple access (CDMA) systems is multiple access interference (MAI) which can reduce the system’s capacity and increase its bit error rate (BER). Thus, a statistical characterization of the MAI is vital in analyzing the performance of such systems. Since the statistical analysis of MAI in MIMO-CDMA systems is quite involved, especially when these systems are fading, existing works in the literature, such as successive interference cancellation (SIC) or parallel interference cancellation (PIC), employ suboptimal approaches to detect the subscriber without involving the need for MAI statistics. The knowledge of both MAI and noise statistics plays a vital role in various applications such as the design of an optimum receiver based on maximum likelihood (ML) detection, evaluation of the probability of bit error, calculation of the system’s capacity, evaluation of the outage probability, estimation of the channel’s impulse response using methods including the minimum mean-square-error (MMSE), the maximum likelihood(ML), and the maximum a posteriori probability (MAP) criterion. To the best of our knowledge, there is no existing work that explicitly evaluates the statistics of the MAI-plus-noise in MIMO fading channels. This constitutes the prime objective of our proposed study here. In this work, we derive the expressions for the probability density function (PDF) of MAI and MAI-plus-noise in MIMO-CDMA systems in the presence of both Rayleigh fading channels and additive white Gaussian noise. Moreover, we evaluate the probability of the bit error rate in the presence of optimum reception using a ML receiver. Our theoretical findings can provide a reliable basis for both system design and various performance analyses of such systems. Our simulation results show that the theoretical findings are very well substantiated.
Highlights
In spite of their numerous advantages, MIMO-code division multiple access (CDMA) systems suffer from a major drawback in multiple access interference (MAI) which can reduce their capacity and increase their bit error rate (BER), resulting in a degraded system performance
7.1 Investigation on MAI statistics we aim to investigate the effect of different parameters on the probability density function (PDF) of the MAI and MAI-plusnoise, namely the effect of the number of transmitting and receiving antennas, length of the pseudo-randomnoise (PN) sequence used, and the number of users in the system
8 Conclusions In this work, a thorough statistical analysis of MAI and MAI-plus-noise in MIMO-CDMA systems has been performed in the presence of Rayleigh fading channel. the major contribution of this work is the statistical characterization of MAI without relying on any Gaussian assumption as is usually reported in the literature
Summary
In spite of their numerous advantages, MIMO-CDMA systems suffer from a major drawback in MAI which can reduce their capacity and increase their BER, resulting in a degraded system performance. A statistical analysis of MAI becomes a very important factor in the performance analysis of these systems. In CDMA systems, each user is assigned a unique spreading code. These orthogonal codes should ideally provide perfect isolation from other subscribers so as to maintain error-free communication among all users. Most of the reported research work is done on characterization of single-input single-output (SISO) CDMA systems and is based only on approximations, such as the standard Gaussian approximation (SGA) [1], improved Gaussian approximation (IGA) [2] and simplified IGA (SIGA) [3].
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