Effective Capacity Analysis for Multi-Rate Relay Channels Exploiting Adaptive Cooperative Diversity

Aiming at improving the QoS performance over fading channels, this paper presents an analysis of the effective capacity for a relay-assisted communication system which utilizes a cooperative packet retransmission protocol at the link-layer in conjunction with AMC-based multi-rate transmission at the physical layer. In the considered model, a source (S) node employs AMC to transmit delay-constrained packet traffic to the destination (D) node. To achieve adaptive cooperative diversity, a relay node, also equipped with AMC, forwards the packet received from node S to node D if it was able to decode the source packet correctly and node D requested a packet retransmission. For this protocol we derive a closed-form expression for the effective capacity of the queue service process at node S. Numerical results reveal that the proposed cooperative protocol can dramatically increase the effective capacity with respect to a direct transmission system with AMC.