In this thesis, the performance and system capacity of quasi-synchronous CDMA system with QPSK and BPSK spreading scheme is considered for the satellite reverse link. We analyze the bit error rate(BER) performance over AWGN channel. We use OVSF code for multiple data rate system. The system capacity that meets adequate QoS requirements is subject to the number of OVSF code and BER performance. We suggest using BPSK spreading scheme to maximize system capacity instead of QPSK spreading scheme. When maximum timing jitter is less than half of chip duration, our result shows that the system capacity with QPSK spreading scheme is restricted by the number of OVSF code with small phase estimation error. Thus, BPSK spreading scheme is superior to QPSK spreading scheme in the sense of system capacity. Therefore, if the performance of phase estimator is good enough, BPSK spreading scheme can be used to maximize system capacity
