BER Analysis of Quasi-Orthogonal Codes in Quasi-Synchronous CDMA Communication

Abstract

Code division multiple access (CDMA) schemes and combination of CDMA with OFDM have been considered as attractive multiple access schemes in the second-generation (2G), third-generation (3G) and future broadband wireless systems. In this paper, we studied the performance of DS-CDMA signals with quasi-orthogonal codes namely balanced gold codes and m-sequences in presence of timing synchronization error. The synchronization error considered is smaller than the chip duration. We evaluate the maximum synchronization error that can be tolerated so that complete error-free despreading is guaranteed for the two quasi-orthogonal codes in the absence of additive white Gaussian noise and channel impairments. This provides insight in the synchronization demands for QS-CDMA systems. Also system capacity (the total bit rate which can be transmitted) subject to this synchronization error has been calculated for the two codes. It has been found that m-sequence provide maximum tolerable synchronization error and system capacity as compared to balanced gold code. We have also presented the BER analysis for QS-CDMA. The BER performance of the two quasi-orthogonal sequences at different values of synchronization error is also studied. Monte-Carlo simulations have been carried out to verify analysis with the simulation results.