Efficient combining technique with a low-complexity detect-and-forward relay for cooperative diversity scheme

This paper studies what is the right relay protocol strategy for a low density parity check (LDPC) cooperative diversity scheme. In this scheme, an improved maximum likelihood detection (MLD) featuring Log-likelihood (LLR) combining technique is also introduced. A basic cooperative diversity scheme of a source node (S), a relay node (R) and a common destination node (D) is considered. This scheme employs a low-complexity relaying scheme which detects the signals (i.e. hard-decision) and forwards (DAF) to the destination node. A popular decode-and-forward (DF) relay protocol and soft-forwarding (SF) protocol are also investigated for comparison. Simulation and analytical results demonstrate that the knowledge of S-R link quality doesn´t contribute to the improvement to the proposed scheme. Nonetheless, the proposed scheme still achieves a fairly remarkable result. This improvement is achieved by using only a cheap DAF relaying protocol which is well-suited for resource limited conditions, for instance, in sensor networks. The results are validated through a simulation work and compared with maximum ratio combiner (MRC) and cooperative-MRC (C-MRC).