Multiuser detection in single-path fading channels

The performance analysis of maximum likelihood sequence and decorrelating multiuser detectors is developed for the single-path Rayleigh fading channel. The received signal in this multipoint-to-point channel is additively composed of white Gaussian noise and independently faded waveforms from a finite number of asynchronous users. The optimum sequence detector consists of a bank of single-user matched filters followed by a dynamic programming algorithm, has a demodulation complexity per symbol which is exponential in the number of users, and requires the knowledge of the system as well of the fading parameters. The decorrelating detector has a complexity which is polynomial in the number of users, and does not require knowledge of the signal amplitudes, which are assumed to vary slowly relative to the symbol rate. The single-user error rates are presented for both detectors and compared to conventional detection and isolated transmission, and the notion of asymptotic multiuser efficiency is developed for this channel. In contrast to conventional detection; which suffers from near-far effects due to Rayleigh fading, it is shown that the aforementioned multiuser detectors exhibit performance which rivals that of isolated transmission for sufficiently small thermal noise power. The results of the analysis are illustrated with numerical examples and indicate that the near-far problem may be alleviated by a more sophisticated receiver design