Hard/soft detection with limited CSI for multi-hop systems

We consider a single-branch, mobile multihop relaying (MMR) network with limited channel state information (CSI) at the destination. The considered CSI signalling strategy reduces the signalling overhead at each relay by at least 50%. We show that this significant overhead reduction comes at the expense of no performance loss at all when hard maximum likelihood detection is carried out at the destination. Furthermore, we consider the use of the MMR system with concatenated channel codes to carry out soft maximum a posteriori (MAP) detection, and demonstrate that with channel codes employed the optimum detection rule becomes prohibitively complex to implement. We propose two approximate soft MAP detection schemes to make the detection feasible for the system, and demonstrate that the performance is either almost identical to or slightly degraded from the ideal case with full CSI at the destination.