Performance Analysis of Code Division Multiple Access (COMA) Technique in Digital Communication Systems

Abstract

Transmission is considered for a synchronous Direct-Sequence Code­ Division Multiple-Access (DS-CDMA) system via nonlinear satellite channels, with BPSK and QPSK modulation schemes which lend to coherent demodulation. Multiuser detection strategies are derived and analyzed for several signal detection problems arising in Code-Division Multiple-Access channels. The channel model takes into consideration the TWTA satellite nonlinearity which affects the signal amplitude and phase by AM-AM and AM­ PM distortion, in addition to the background noise of the channel at the receiver, and multiple access interference for different munber of users shared on the same channel. Since the optimum detector requires high computational complexity that grows exponentially with the number of users, and the implementation of this detector will be very complex, so different types of suboptimum detectors are studied. Performance analysis of linear detectors represented by the conventional and the decorrelator detector are studied. Also, performance simulation is undertaken of the linear detectors and multistage detectors represented by the two-stage detector with conventional first stage, and the two-stage detector with decorrelator frrst stage. A comparative study between analytical and simulation results for linear detectors, as well as between the simulation results of these detectors are presented. In the case of linear detectors, the decision algorithm is performed by comparing the sufficient statistics to a threshold which yields to a computation complexity that is linearly growing with the number of users.