Delay-limited throughput of cooperative multiple access channels with hybrid-ARQ

This paper considers a two-user, quasi-static multiple access channel with hybrid-automatic repeat request (HARQ) and user cooperation. The protocol uses incremental redundancy HARQ packet transmission from both users until at least one userpsilas packet is successfully decoded. If one userpsilas packet is successful before the other, the successful user begins to act as a relay for the other user until packet success or until a maximum number of HARQ rounds L, where L represents the packet delay constraint. The performance of this cooperative multiple access channel is evaluated using the delay-limited throughput, defined as a measure of the throughput of an arbitrary packet, as well as the conventional long-term average throughput. The throughput metrics depend on each userpsilas individual outage probability, which is approximately equal to the userpsilas packet error probability as a function of the number of HARQ rounds. Compared to no user cooperation, this cooperative protocol provides significantly higher throughputs, with increasing gains for more stringent quality-of-service (QoS) constraints.