Multiple-access relay system based on nested distributed turbo code

We propose a novel cooperative protocol with the joint channel and network code for the multiple-access relay channel with two sources, one relay, and one destination. In the proposed cooperation, by using a superposition technique, the relay node combines the information from both sources and forwards it to the destination, simultaneously. Although several superposition techniques have been proposed (e.g., superposition modulation, network coding), we will utilize a modified nested coding scheme which can be applied to iterative decoding. In the proposed relay system, the decoding operation at the destination node is adaptively changed according to the decoding results of each direct link (from source to destination channel), but the structures of sources and relay are not changed. If the one of the direct links is in failure, the system can be operated as just the distributed turbo coding proposed for the simplest relay channel with one source, one relay and one destination. Even if both direct links are in failure, the destination can still iteratively decode both sources´ data with three received signals from individual sources and relay. Simulation results reveal that the proposed system can significantly improve the performance.