Noncoherent multistage multiuser detection of M-ary orthogonal signals

Abstract

In recent years, a great deal of research has been performed on methods of alleviating the performance degradations suffered by code division multiple access (CDMA) systems due to multiple access interference. The majority of work thus far has focused on the coherent case, spurred by the development of an optimal detector for asynchronous binary phase shift keying (BPSK) by Verdu. Much less work has been performed on noncoherent detection. There are, however, several reasons why noncoherent detection may be preferred for some applications. For instance, there may be difficulty tracking carrier phase over some channels due to oscillator phase instability, movement of the transmitter and receiver in a mobile environment, and multipath fading. In this paper, a multistage detector for noncoherent CDMA using M-ary orthogonal signals is proposed and analyzed. Using a decorrelating detector as its first stage, the detector iteratively estimates the multiple access interference affecting the desired signal, subtracts the estimated interference, and forms symbol estimates for each of K users. Numerical examples are provided to contrast the bit error rate performance of the decorrelating detector with previous detectors for the same signalling scheme.