Buffer-Aided Relay Systems under Delay Constraints: Potentials and Challenges

Relay transmissions can help improve system coverage and throughput, and hence information- theoretic analysis of relay channels has been at the forefront of research for decades. While providing powerful results, information-theoretic studies generally assume no buffer at the relay, and the performance is limited by the worst conditions of the transmitting and receiving channels of the relay. Recently, it has been shown that the achievable throughput can be significantly improved with the introduction of a buffer-aided relay model. Specifically, buffer-aided relaying can provide significant gains in terms of throughput, diversity, and signal-to-noise ratio without delay constraints. This article considers buffer-aided relay systems under delay constraints specified by limitations on delay violation probability. The necessary research tools and several results on different relay networks including two-hop and three-node relay channels are discussed. Certain challenges associated with buffer-aided relaying under delay constraints and topics for future research are outlined.