Simulation of a Code Division Multiple Access Implicit Diversity Processor

Abstract

The aim of this thesis is to study and analysis Direct Sequence Division Multiple Access (DS-CDMA) systems with regard to the fading that occurs in a received signal due to multipath, trying to combat this fading by using special receiver named Rake receiver with affords inherent diversity to improve the strength of the received signal, hence reception quality. The choice of the channel model used for analysis is important since it has a decisive influence on the receiver performance. The most interesting performance measure of DS-CDMA systems, like other digital systems, is the bit error rate (BER). A simulation program has been built for DS-CDMA system using a Rake receiver for reception over a slow, frequency selective, Rayleigh multipath fading channel with additive white gaussain noise, a tapped delay model has been used to represent this channel. The system has been simulated using Borland C++ programming language. The results obtained show that DS-CDMA system becomes interference limited as the number of users increases. At high level of inter-user interference (large number of users) and at high level of multipath fading (no diversity) the addition of channel noise (AWGN) does not add considerable degradation on the system performance. A conventional Rake receiver with four fingers can provide significant improvement on the system performance by exploring multipath diversity.