On the Optimal Link Adaptation in Linear Relay Networks With Incremental Redundancy HARQ

In this letter, we investigate a joint power and rate optimization for a multihop relay network with incremental redundancy hybrid ARQ (HARQ-IR), where multiple relays are serially connected from a source to a destination. The optimization problem is to adjust both transmission rate and power of each node in order to maximize long-term average transmission rate (LATR) for given sum-power and delay constraints, which is unfortunately not mathematically tractable. Hence, we propose a sub-optimal algorithm to improve the LATR, which is computationally efficient and has comparable performance with the exhaustive search algorithm. Simulation results show that the proposed algorithm outperforms the conventional algorithms, including the HARQ-IR scheme with fixed power and rate and the Chase-combining HARQ scheme of which both power and rate are optimized for the same network.