On Stability and Throughput for Multiple Access with Cooperation

In the wireless two-user multiple-access system with a single destination, the characterization of the stability region and the throughput region is revisited in the context of a packet-based “networklevel” cooperation among the two users. Cooperation is achieved through the relaying of packets by the user with a better user-destination channel. Through queueing-theoretic techniques, the stability and throughput regions are characterized and compared under a centralized scheduled access and a random access scheme respectively. We conclude that the throughput region depends on the scheduling policies at the relay node, and may or may not be equal to the stability region, which is shown to be independent of the scheduling policies. By contrast, in the non-cooperative random access system, the stability region and the throughput region are proved to be identical. Another significant outcome is that the cooperative stability region under random access does not necessarily outer bound the non-cooperative stability region. Furthermore, when network coding is applied at the relay node as an alternative to simple retransmission, we show that there is no improvement either in the stability region or in the throughput region over plain store-and-forward routing.