Performance Analysis of Multiple-Chip-Rate CDMA Systems based on the Simplified Improved Gaussian Approximation

We consider very general code-division-multiple-access (CDMA) systems, namely multiple-chip-rate CDMA systems, where signals can be transmitted at different chip rates, carrier frequencies, processing gains, and transmitted powers to satisfy the given quality of service (QoS) requirements. Also, non-zero and possibly different carrier frequency offsets are assumed for different users. For these systems, a closed-form bit error rate (BER) expression is derived based on the simplified improved Gaussian approximation. Unlike the conventional simplified improved Gaussian approximation, however, we utilize the correlations between chip waveforms and their integrations rather than using the correlations between chip sequences in order to obtain the closed-form BER expression. Numerical results demonstrate that the proposed method provides much more accurate BER values compared to the standard Gaussian approximation