Application of Density Evolution in Turbo-MUD Design for Overloaded Coded CDMA Systems

An original turbo multiuser detector for overloaded coded DS-CDMA systems is presented and studied: the performance of the proposed system is tested by Monte Carlo simulations and by means of the density evolution theory. The proposed turbo-MUD receiver is based on the use a combination of a linear MMSE detector in the first stages and an interference cancellation scheme in the successive ones. The inputs of both receivers are the soft information from a bank of turbo decoders. The performance of the proposed receiver can be effectively predicted in overloaded communication systems by means of density evolution technique: the use of this technique also permits us to evaluate the proper number of MMSE iterations, making easier the design of the receiver.