Comparison of biphase spreading to quadriphase spreading in DS CDMA systems that employ long PN sequences

Efficient series that are used to calculate the bit error probabilities for biphase spread and quadriphase spread, BPSK modulated, asynchronous DS CDMA systems are derived. These series are then used to investigate the degradation in the performance of both systems due to synchronization errors. The analysis requires the characteristic functions of the multiple access interference and of the self interference and these functions have been expressed in terms of the special functions of mathematical physics. It is found that both systems have comparable performance when synchronization errors are considered. Thus, as far as the system capacity is concerned, quadriphase spreading does not offer any advantage relative to the simpler biphase spread system.