Lower phase estimation bounds for CDMA systems in AWGN and Rayleigh fading channels

The Cramer-Rao lower bound (CRLB) and minimum mean-square error (MMSE) lower bound on the variance of phase estimation in CDMA receivers in AWGN and slow and fast Rayleigh fading conditions are presented. The bounds are useful as benchmark information for implementation of channel estimator algorithms needed for coherent combining in CDMA receivers. Analytical results indicate that increasing the signal-to-noise ratio or/and averaging period for phase estimation improves the performance. Hence, the phase error can be reduced to avoid significant degradation in bit error rate of the system. However, for fast fading there is a high error floor on the phase estimation (about 50 degrees of rms phase error) regardless of how high the signal-to-noise ratio is made. This presents a challenge of achieving acceptable bit error rate performance for users who are moving at very fast speeds.