Improvement of Fairness by PCRQ scheduling in Multihop Wireless Ad hoc Networks

The IEEE 802.11 MAC protocol for medium access control in wireless Local Area Networks (LANs) is the de facto standard for wireless ad hoc networks, however, it does not perform well in terms of delay, throughput, and specially, fairness in multihop wireless ad hoc networks. Many researches have been published in this area. Among them, a modification of the IEEE 802.11 MAC protocol was proposed to achieve per-node fairness, but the modification of the MAC layer requires a change of hardware, so, it is difficult to implement. Moreover, it still faces up per-flow unfairness problem. As another solution, the Round Robin (RR) scheduling was introduced to overcome the per-flow unfairness problem caused by the First In First Out (FIFO) scheduling. Those solutions are based on the assumption that the MAC layer gives the ideal fairness of bandwidth allocation, but IEEE 802.11 MAC protocol fails to ensure the MAC layer fairness in multihop ad hoc network. We address why the RR scheduling cannot achieve good fairness if the MAC layer does not give the ideal fairness. In this paper, we propose a new scheduling method, Probabilistic Control on Round robin Queue (PCRQ) scheduling, aiming to achieve per-flow fairness in multihop ad hoc networks. In our PCRQ scheduling, a new link layer scheduling is proposed without assuming the fairness of the MAC layer. We use the RR queues in the link layer, and propose three algorithms to control the number of input packets to the queue, the turn of reading queues, and the number of output packets from the queue. Our PCRQ scheduling can improve the MAC layer fairness by these algorithms in the link layer. It does not modify the 802.11 MAC layer protocols. In addition to per-flow fairness, our PCRQ scheduling archives positive impact in terms of the effective buffer resource and delay time. We evaluate the efficiency of our PCRQ scheduling with NS-2 by comparing with the FIFO and RR schedulings on various topologies of multihop ad hoc networks.