Joint-design of adaptive modulation and coding with adaptive ARQ for cooperative relay networks

This article investigates the efficacy of a joint-design of adaptive modulation and coding (AMC) at the physical (PHY) layer with an adaptive R^max-truncated selective-repeat automatic repeat request (ARQ) protocol at the medium access control (MAC) layer to maximize the throughput of cooperative amplify-and-forward (CAF) relay networks under prescribed delay and/or error performance constraints. Specifically, we generalize the existing design/results for cross-layer combining of AMC with truncated ARQ in non-cooperative diversity systems in three-folds: (i) extension of the cross-layer PHY/MAC design or optimization to cooperative diversity systems; (ii) generalization/unification of analytical expressions for various network performance metrics to generalized block fading channels with independent but non-identically distributed (i.n.d) fading statistics among the spatially distributed nodes; (iii) investigation of the effectiveness of joint-adaptation of the maximum retransmission limit R^max in ARQ protocol and cooperative diversity order N for delay-insensitive applications. Our numerical results reveal that the average throughput can be increased considerably by judiciously combining two additional degrees of freedom (N and R^max) that are available in CAF relay networks besides employing AMC at the PHY layer, especially in the most challenging low signal-to-noise ratio (SNR) regime.