Simple-to-evaluate and accurate bit error probabilities are given for binary DS-CDMA communications over independent Rayleigh faded multipath channels while Rake type of receivers are used. By extending the simplified improved Gaussian approximation (SIGA) of Holtzman for multipath channels, we show the accurate results based on SIGA and compare those with widely used standard Gaussian approximation (SGA). By considering flat and exponentially decaying power delay profiles (PDP) of the multipath channel, we investigate the effect of spreading bandwidth and the number of combined paths on the multiple access performance of the system. In other words, we investigate the validity of SGA of multiple access interference (MAI) as compared to the more accurate SIGA for multipath channel while all Rake (ARake) and selective Rake (SRake) receivers are employed. We show that the SGA is accurate 1) for ARake while the spreading is low and 2) for SRake until some number of combined paths, beyond which it becomes optimistic. Additionally, we show that the effect of MAI is much less pronounced in an SRake while the number of combined paths is small. The multiple access performance of the receivers and the validity of SGA also depend on the shape of the PDP.
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