Space-Time Coded Buffer-Aided Relaying for Improving the Reliability of Cooperative Networks

Buffer-aided (BA) relay networks provide increased reliability and coverage in future wireless communications. This paper explores advanced transmission strategies to further enhance the performance of decode-and-forward (DF) cooperative networks with two relays. Unlike the existing DF BA relay selection solutions where the relays attempt independently to deliver the information message to the destination node, this work introduces a new methodology for leveraging the outage performance of the network by enabling space-time (ST) coded transmissions. Complementing BA relaying with ST coding is rendered possible by adjusting the transmission and reception policies at the relays and by equipping one of the relays with an additional buffer for storing duplicates of the packets delivered to the second relay. The introduced coordination between the relays allows them to collaboratively generate and transmit ST codewords over some time slots thus enhancing the quality of signal reception and improving the network’s reliability. The performance improvements of the proposed BA relaying technique are quantified by a Markov chain analysis for the sake of evaluating the achievable outage probability and average packet delay. We also present an asymptotic analysis that highlights the diversity gains compared to the benchmark schemes. Simulations over a generalized kappa-mu channel fading model demonstrate the capabilities of amalgamating BA relaying with tailored versions of ST coding techniques.