A Unified Approach to BER Analysis of Synchronous Downlink CDMA Systems with Random Signature Sequences in Fading Channe
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Research Article A Unified Approach to BER Analysis of Synchronous Downlink CDMA Systems with Random Signature Sequences in Fading Channels with Known Channel Phase M. Moinuddin, A. U. H. Sheikh, A. Zerguine, and M. Deriche Electrical Engineering Department, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia Correspondence should be addressed to A. Zerguine, [email protected] Received 19 March 2007; Revised 14 August 2007; Accepted 12 November 2007 Recommended by Sudharman K. Jayaweera A detailed analysis of the multiple access interference (MAI) for synchronous downlink CDMA systems is carried out for BPSK signals with random signature sequences in Nakagami-m fading environment with known channel phase. This analysis presents a unified approach as Nakagami-m fading is a general fading distribution that includes the Rayleigh, the one-sided Gaussian, the Nakagami-q, and the Rice distributions as special cases. Consequently, new explicit closed-form expressions for the probability density function (pdf ) of MAI and MAI plus noise are derived for Nakagami-m, Rayleigh, one-sided Gaussian, Nakagami-q, and Rician fading. Moreover, optimum coherent reception using maximum likelihood (ML) criterion is investigated based on the derived statistics of MAI plus noise and expressions for probability of bit error are obtained for these fading environments. Furthermore, a standard Gaussian approximation (SGA) is also developed for these fading environments to compare the performance of optimum receivers. Finally, extensive simulation work is carried out and shows that the theoretical predictions are very well substantiated. Copyright © 2008 M. Moinuddin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
It is well known that MAI is a limiting factor in the performance of multiuser CDMA systems, therefore, its characterization is of paramount importance in the performance analysis of these systems. To date, most of the research carried out in this regard has been based on approximate derivations, for example, standard Gaussian approximation (SGA) [1], improved Gaussian approximation (IGA) [2], and simplified IGA (SIGA) [3]. In [4], the conditional characteristic function of MAI and bounds on the error probability are derived for binary direct-sequence spread-spectrum multiple access (DS/SSMA) systems, while in [5], the average probability of error at the output of the correlation receiver was derived for both binary and quaternary synchronous and asynchronous DS/SSMA systems that employ random signature sequences. In [6], the pdf of MAI is derived for synchronous downlink CDMA systems in AWGN environment and the results are extended to MC-CDMA systems to determine the conditional pdf of MAI, inter-carrier interference (ICI) and noise
given the fading information and pdf of MAI plus ICI plus noise is derived,
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