Channel estimation and symbol detection for multiuser CDMA receivers using HMMs

This paper addresses the problem of multiuser decoding in CDMA when interchip interference (ICI) is present. We present a hidden Markov model for the received signal, and derive the optimal adaptive filter for decoding each user, and estimating the unknown ICI. A suboptimal method is described which has computational complexity O(N²K), where K is the number of users, and N is the (fixed) spreading gain. The method achieves close-to-optimal performance. We use simulations to argue the effectiveness of the technique, with there being approximately 1 dB degradation from the single user bound