OPTIMUM DIVERSITY COMBINING RECEIVERS WITH DECISION-FEEDBACK EQUALIZATION FOR CELLULAR MOBILE RADIO WITH CCI

摘要

This paper analyzes and quantifies the performance of an optimum space diversity combining receiver with decision-feedback equalization (DFE) operating in a mobile radio environment with quadrature amplitude modulation (QAM) transmission, frequency-selective Rayleigh multipath fading, and cochannel interference (CCI). The optimum diversity receiver uses ideal matched filters and an infinite-length feedforward filter (FFF) for each cochannel source to perform CCI and precursive ISI suppression, while leaving the combined postcursive ISI to be mitigated by the subsequent feedback filter. Those filters are optimized jointly according to the minimum mean-square-error (MMSE) criterion. Our analysis accounts for pulse waveform, modulation and fading of the signal of interest, as well as the cochannel interference (CCI). Since the evaluation of the error probability is extremely complicated and time-exhaustive in simulation with residual ISI and CCI, the error probability for each fading channel is estimated fast and accurately using Gauss quadrature rules (GQR) which can approximate the probability density function of the combined intersymbol interference (ISI) and CCI. The comparison with the diversity receiver using linear equalizers is also provided. The results show a significant improvement in performance due to both diversity against fading and interference suppression. With the use of decision-feedback equalization, the effect of noise enhancement can be reduced while cancelling CCI, and thus improving the effective diversity order. The optimum results also provide space-time processing for interference suppression with an important performance benchmark.