Quantize-and-Forward Strategy for Interleave-Division Multiple-Access Relay Channel

The quantize-and-forward (QF) strategy for the half-duplex interleave-division multiple-access relay channel (ID-MARC) is investigated in this paper with multiple users, single relay, and single destination. Different from the orthogonal MARC, multiple users in such an ID-MARC are distinguished by different interleavers. For the case that the relay node cannot recover the initial bits correctly, a denoising mutual-information preserving quantizer (DMIPQ) is proposed, which can remove the noise from the received signal while preserving the useful information. A suboptimal searching algorithm is designed to reduce the complexity of DMIPQ. The approximation of DMIPQ is further discussed to get an analytical solution. It is shown that the approximate DMIPQ is equivalent to the minimum mean square error (MMSE) Lloyd-max quantizer. Numerical results illustrate that the proposed DMIPQ outperforms the MMSE Lloyd-max quantizer. It can be also shown that the bit error rate of the ID-MARC (BER) with DMIPQ is close to its compress-and-forward (CF) bounds.