On the tradeoff between MAC-level performance metrics in MIMO ad hoc networks with imperfect channel estimation

Classic approaches to channel estimation in MIMO ad hoc networks focus on the accuracy of the estimation techniques as applied to point-to-point links. However, when considering more complex networks, a number of further issues arise that have a significant impact on the performance of channel estimation. More specifically, ad hoc networks usually feature many simultaneous non-orthogonal communications whose impact on channel estimation as well as on higher layers of the protocol stack has not yet been thoroughly studied. In this paper we present some results on the effects of multiuser transmissions on channel state information accuracy in MIMO ad hoc networks, and evaluate the impact of imperfect channel estimation on the performance of MAC protocols. In particular, we consider a cross-layer MAC which accounts for the structure and behavior of the underlying PHY to make decisions on channel access; we then show the interplay between PHY parameters (such as the length of the training sequences used for channel estimation or the number of antennas) and MAC-level performance metrics such as throughput, efficiency, and success ratio. Our results show that relevant tradeoffs arise in this context and allow, e.g., to tune the MAC layer behavior by controlling the channel estimation accuracy.