Layered compress-and-forward cooperation in wireless multicast with M-ary PAM transmissions

We consider a relay-aided wireless multicast channel in which all transmissions are constrained to be drawn from M-ary PAM constellations. In order to deal with heterogeneous channel conditions at different receivers, we propose a practical layered compress-and-forward (CF) scheme that utilizes scalar quantization concatenated with Slepian-Wolf coding. Exploiting the inherent unequal protection provided to different bit-planes of an M-ary PAM constellation, the layering is accomplished through an intelligent mapping of the quantization bits to the relay's transmission symbols. This allows users to adapt by extracting as many CF cooperation layers as allowed by the channel conditions. By analyzing information theoretic performance, we find that the proposed scheme performs significantly better than the traditional unlayered CF for a wide variety of channel conditions; our best results indicate a performance gap of 1.1 dB between the two.