On the Improvement of Maximum Likelihood Detection in Multiple Relay Systems

Maximum Likelihood Detection (MLD) featuring Log-likelihood (LLR) combining technique has been introduced in earlier works to achieve diversity gains in block fading channels for one relay node. In this paper, we extend this strategy to multiple relay systems (MRS) and introduce a new method such that the computational complexity of MLD is further reduced. This method approximates bit LLR values from the symbol LLR, thereby reducing the computational burden at the destination. A cooperative relay scheme of a source node (S), multiple relay nodes (R) and a common destination node (D) is considered. This scheme utilizes a simple relaying protocol which detects the signals (i.e. hard-decision) and forwards (DAF) to the destination node. While LDPC codes do not achieve significant performance gain in Single Input Single Output (SISO) scheme over block fading channel, we suggest that with the proposed scheme, the gain is essentially significant under MRS platform. This improvement is achieved by using a cheap DAF relaying protocol which is well-suited for resource limited conditions, for instance, in wireless sensor networks (WSN). The results are validated through a simulation work and compared with maximum ratio combiner (MRC) and cooperative-MRC (C-MRC).