Performance of multi-level modulation in MMSE receiver based CDMA systems

This paper studies the effect of using higher order modulation formats in the performance of minimum mean-squared error (MMSE) receiver based direct-sequence (DS) code-division multiple access (CDMA) systems in terms of the bit error rate (BER) at different loading levels in additive white Gaussian noise (AWGN) and slow fading channels. The performance of BPSK, QPSK, and 16 QAM modulation formats are compared and analytical and simulation results are presented in terms of the symbol error rates for these different modulation formats. A comparison of the rejection of the near-far effects for each modulation scheme is also presented. Under a high loading level, 16 QAM outperforms QPSK and BPSK for identical bandwidth and information rate while at a moderate loading levels, QPSK represents the best option.