Multipacket MAC for multiple antenna systems: a cross-layer approach

In multiple access wireless channels mechanisms for an efficient management of the channel usage are of special interest. Particularly, in multiple access systems with multiple transmit and receive antenna, many antenna selection algorithms that exploit instantaneous channel information have been presented in the literature. On the other hand, MAC protocols control the access to the channel by evaluating average performance parameters such as throughput and delay. Both approaches, namely PHY layer and MAC layer approaches, present advantages and drawbacks. Far from being competitive, we argue that such approaches are complementary. Therefore, we present a unified view of both, PHY and MAC layer visions for a multiple input multiple output (MIMO) multiple access channel. First, we evaluate the impact in terms of throughput of a PHY layer scheduling strategy. Second, a multipacket MAC algorithm is presented. Finally, we show the benefits of a PHY-MAC cross-layer optimization and present mathematical expressions to evaluate them. We also present our cross-layer design as an extension of multiuser diversity for the multi-user detector case.