MAP Multiuser detection with Soft Interference cancellation for UMTS TD-CDMA Receivers

A new multiuser detector (MUD) exploiting the MAP algorithm is proposed for channels affected by severe multipath and is then suitable for Time-Division Duplexing (TDD) CDMA receivers. After coherent combining the received multipaths, a multidimensional MAP nonlinearity is employed to compute step-by-step the A Posteriori Probabilities (APPs) of the transmitted data for each user separately and then their expected values conditional to the available observations. These are then employed for soft ISI and MAI removal from the received sequences so that the APPs can be more reliably re-computed. The procedure is iterated in a multistage structure until final decisions are taken. From the comparison with other existing techniques (interference cancellation, zero-forcing) the proposed Reduced MAP-MUD receiver exhibits better performance and equal or minor complexity.