Performance issues of multiple-relay cooperation

In this paper, we investigate the impact of the deployment of a second relay node in a cooperative communication scheme. The relay nodes relay packets from a number of users to a destination node. We assume that the two relays do not have packets of their own and the users have saturated queues and random access to the medium with slotted time. We obtain analytical expressions for the arrival and service rates of the queues of the two relays and the stability conditions. We also study a model of the system, in which the users are divided into two clusters, and show its advantages in terms of aggregate and per user throughput. We quantify the above, analytically and through simulations, for different number of users and we indicate the conditions under which the deployment of a second relay in the system provides significant advantages.