Multiuser Detection and Diversity Combining for Wireless CDMA Systems

Multipath fading presents a major limitation for the performance of wireless CDMA systems. Multipath propagation alone enhances multiple-access interference, while fading on propagation paths induces near-far problem. Multiuser detection has the capability of eliminating near-far problem and providing a capacity increase in CDMA systems, while diversity reception combats the fading effects of the channel. We investigate multiuser receivers which combine explicit antenna diversity, RAKE multi-path diversity and multipath decorrelating detection. Both coherent reception with maximal-ratio combining and differentially coherent reception with equal-gain combining are analyzed. The results demonstrate significant performance improvement over the conventional RAKE techniques. In the case of limited receiver complexity antenna diversity is shown to be effective in reducing residual multiple-access interference.