Multiple-Access via Turbo Joint Equalization

This paper develops a receiver for a multiple access scenario obtained by simply overlaying transmitted signals from different users, with (essentially) the same carrier, same modulation format, etc., without the benefit of conventional multiple access signaling. A joint a posteriori probability detector is derived for co-received signals. The receiver structure follows the familiar general model for turbo processing, employing a soft-in-soft-out joint detector followed by error correction decoding, which feeds back soft information in the form of extrinsic probabilities. Since the receiver is intended to function with an existing transmission system with no modifications to the transmitter, channelization methods and/or interleavers which would normally be designed into a multi-access system are absent. The general structure is demonstrated using a system employing LDPC decoding and simulated performance results are presented.