Queue Back-Pressure Random Access in Multihop Wireless Networks: Optimality and Stability

A model for wireless networks with slotted-Aloha-type random access and with multihop flow routes is considered. The goal is to devise distributed algorithms for utility-optimal end-to-end throughput allocation and queueing stability. A class of queue back-pressure random access algorithms (QBRAs), in which actual queue lengths of the flows in each node´s close neighborhood are used to determine the nodes´ channel access probabilities, is studied. This is in contrast to some previously proposed algorithms, which are based on deterministic optimization formulations and are oblivious to actual queues. QBRA is also substantially different from the well-studied ldquoMaxWeightrdquo type scheduling algorithms, even though both use the concept of back-pressure. For the model with infinite backlog at each flow source, it is shown that QBRA, combined with simple congestion control local to each source, leads to optimal end-to-end throughput allocation within the network saturation throughput region achievable by random access, without end-to-end message passing. This scheme is generalized to the case with minimum flow rate constraints. For the model with stochastic exogenous arrivals, it is shown that QBRA ensures stability of the queues as long as nominal loads of the nodes are within the saturation throughput region. Simulation comparison of QBRA and the queue oblivious random-access algorithms, shows that QBRA reduces end-to-end delays.