Performance of Selection Diversity for a DS CDMA System with Synchronization Errors

An eecient series that is used to calculate the probability of error for a BPSK modulated DS CDMA system with chip timing and carrier phase errors in a slowly fading, multipath channel is derived. The receiver is assumed to be a coherent RAKE receiver that employs selection diversity. The error probability derivations require the characteristic functions of the intersymbol interference and the multiple access interference and these functions have been expressed in terms of the connuent hypergeometric function. The series is then used to assess the reduction in the system capacity due to diierent levels of synchronization errors. Systems of 1.25MHz, 5MHz and 10MHz are considered for diierent number of diversity branches. Direct-sequence code division multiple access (DS CDMA), which was primarily used in military communications until the late 80's, has recently been the center of attention in cellular radio communications. This is mainly due to the recent developments in the eld which increased the capacity of a CDMA system to a comparable level to the capacities of TDMA and FDMA systems 1]. In mobile radio environments, the received signals are subjected to multipath fading which severely degrades the system performance. If the system bandwidth is higher than the coherence bandwidth of the channel, fading tends to be frequency selective 2]. In this case, the multipath components in the received signal are resolvable with a resolution in the time delay of T c , the chip duration. With CDMA techniques , the resolvable paths can be demodulated individually by a RAKE receiver and the information obtained from each branch can be combined in a certain way to minimize the interference and further mitigate the fading 3]. We have previously developed an exact, innnite series expression for the calculation of error probabilities for a DS CDMA system that uses coherent reception in an AWGN channel without resorting to a Gaussian approximation for the interference 4]. In this paper, extending on the procedure of 4], we present a performance analysis for a DS CDMA system in a slowly fading multipath environment. We assume that the system uses coherent reception using RAKE receivers that employ selection diversity. As in 4], we do not neglect the presence of synchronization errors in the system but rather investigate the degradation in the system capacity due to such errors. An outline of the paper is as follows. The system-fading and multipath model is described in Section II. …