Simplified MAP-MUD for Active User CDMA

Abstract

In CDMA systems with variable number of users, the decoder consists of two stages. The first stage is the active user identification and the second one is the multi-user detection. Most of the proposed active user identification methods fail to work in overloaded CDMA systems (when the number of users is more than the spreading factor). In this paper we propose a joint active user identification and multi-user detection for binary input CDMA systems using the Viterbi algorithm. We will show that the proposed identification/detection method is Maximum A posteriori Probability (MAP) and outperforms the pervious results. In addition, some suboptimum decoders will be proposed that have lower computational complexities but lower performances.