A chip based multiuser detector for the downlink of a DS-CDMA system using a folded state-transition trellis

The maximum-likelihood sequence estimation (MLSE) multiuser detector has very good performance but at the expense of the exponentially increasing number of states. We propose a scheme that exploits the feature of power-equality in the downlink to reduce the number of states involved. By using all the possible discrete chip values as the states in the transition trellis diagram and operating the Viterbi algorithm at the chip level, the number of states is reduced from 2^K to K+1 where K is the number of users