PROBABILITY OF ERROR FOR DIVERSITY COMBINING IN DS CDMA SYSTEMS WITH SYNCHRONIZATION ERRORS

An efficient series that is used to calculate the probability of error for a BPSK modulated DS CDMA system with chip timing and carrier phas e errors in a slowly fading, multipath channel is derived. The receive r is assumed to be a coherent RAKE receiver. Three types of diversity schemes are considered: selection diversity, equal gain diversity comb ining and maximal ratio diversity combining. The error probability der ivation does not resort to the widely used Gaussian approximation for the intersymbol interference and multiple access interference and is v ery accurate. The derived series for probability of error calculations is used to assess the reduction in the system capacity due to differe nt levels of synchronization errors. For all three diversity combining schemes considered, the degradation in the system performance is expr essed as an effective reduction in the system processing gain. Systems of 1.25 MHz, 5 MHz and 10 MHz are considered for different number of diversity branches and it is shown that the percentage reduction in th e system capacity due to synchronization errors is approximately the s ame for all these systems.