Iterative Cochannel Interference Suppression for the Downlink of a Binary Block Coded Multiuser System

Iterative methods for interference suppression in a block coded multiuser system are considered. In particular, the error performance of a two-user system with a short BCH code and iterative belief propagation (BP) decoding over the associated Tanner graph is evaluated. Two possible combinations of a BP-based iterative decoder and a soft interference suppressor (IS) are studied: (1) joint IS-BP, in which the soft-outputs from the BP decoder at each iteration are used as inputs to the IS, and this soft information is exchanged until some number of IS-BP iterations are executed; and (2) serial concatenated IS-BP, with the IS and BP decoder working independently, the IS delivering soft-inputs to the BP decoder, who performs a number of decoding iterations prior to delivery of soft-outputs back to the IS. Results of both hard and soft output exchange are given. An early detection scheme is studied, with the goal of reducing the complexity of the iterative receiver with a small impact in bit error rate (BER) performance.