Multi-level coding and multi-stage decoding in MAC, broadcast, and relay channel

It is known that multi-level coding (MLC) with multi-stage decoding (MSD) approaches the point-to-point constellation constrained channel capacity subject to appropriate choice of code rates at each level. MLC/MSD in the context of multi-node networks has not been previously investigated, and is the subject of this paper. It is shown that MLC/MSD can approach the MAC capacity. Issues related to achieving non-corner points of the capacity region are discussed. A MLC-based superposition scheme for the degraded broadcast channel is discussed and an achievable region outlined. The half-duplex orthogonal degraded relay channel is studied under MLC/MSD. The achievable rate is calculated under two conditions: First we consider end-to-end layer-by-layer decoding, where each layer is decoded at the relay and destination only with help from previous layers. Then, we remove this constraint via a parity-forwarding approach at the relay, where the destination performs two multi-stage decoding operations: one corresponding to the relay-destination link and then one corresponding to the source-destination link. The achievable rate under parity forwarding is shown to be superior.