Performance of multiuser diversity reception in nonselective Rayleigh fading CDMA channels

The optimal multiuser receiver for synchronous CDMA fading channels consists of an adaptive estimator of the fading distortion and the detector that utilizes so-obtained estimates. High complexity of the optimal detector motivates the use of a decorrelating detector, whose performance is significantly improved through diversity. The estimates of the complex fading processes are utilized both for maximal-ratio combining and carrier recovery. To analyze the impact of channel estimation errors on the receiver performance, error probability of coherent decorrelating receiver is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimation as well as fading-induced error probability floor. The coherent receiver performance is compared to that of a differentially coherent receiver with equal gain combining