Cross-layer Combining of Queuing with Adaptive Modulation and Coding over Wireless Links

Assuming there are always sufficient data waiting to be transmitted, adaptive modulation and coding (AMC) at the physical layer have been traditionally designed separately from higher layers. However, this assumption is not always valid when queuing effects are taken into account at the data link layer. In this paper, we analyze the performance of a wireless system with finite-length queuing and AMC. We characterize the queuing service process induced by AMC, and derive the recursion of the queue state. We then construct a finite state Markov chain (FSMC) with a state pair containing both the queue and the queue server state, and compute its stationary distribution. The latter enables us to derive closed-form expressions for the packet loss rate and the average throughput. Guided by our performance analysis, we also introduce a cross-layer design, which optimizes the target packet error rate in AMC at the physical layer, to minimize the packet loss rate and maximize the average throughput, when combined with a finitelength queue at the data link layer.