The performance seen by individual clients on a wireless local area network (WLAN) is heavily influenced by the manner in which wireless channel capacity is allocated. The popular MAC protocol DCF (Distributed Coordination Function) used in 802.11 networks provides equal long-term transmission opportunities to competing nodes when all nodes experience similar channel conditions. When similar-sized packets are also used, DCF leads to equal achieved throughputs (throughput-based fairness) among contending nodes. Because of varying indoor channel conditions, the 802.11 standard supports multiple data transmission rates to exploit the trade-off between data rate and bit error rate. This leads to considerable rate diversity, particularly when the network is congested. Under such conditions, throughput-based fairness can lead to drastically reduced aggregate throughput. In this paper, we argue the advantages of time-based fairness, in which each competing node receives an equal share of the wireless channel occupancy time. We demonstrate that this notion of fairness can lead to significant improvements in aggregate performance while still guaranteeing that no node receives worse channel access than it would in a single-rate WLAN. We also describe our algorithm, TBR (Time-based Regulator), which runs on the AP and works with any MAC protocol to provide time-based fairness by regulating packets. Through experiments, we show that our practical and backward compatible implementation of TBR in conjunction with an existing implementation of DCF achieves time-based fairness.

翻译：无线局域网（WLAN）中个体客户端所体验的性能，在很大程度上受无线信道容量分配方式的影响。802.11网络中广泛使用的MAC协议DCF（分布式协调功能）在所有节点经历相似信道条件时，为竞争节点提供平等的长期传输机会。当使用相似大小的数据包时，DCF会在竞争节点间实现相等的吞吐量（基于吞吐量的公平性）。由于室内信道条件的变化，802.11标准支持多种数据传输速率，以权衡数据速率与误码率之间的关系。这导致了显著的速率多样性，尤其在网络拥塞时。在此类条件下，基于吞吐量的公平性可能导致聚合吞吐量急剧下降。本文论证了基于时间的公平性的优势，即每个竞争节点获得相等的无线信道占用时间份额。我们证明，这种公平性概念可以在保证没有节点获得比其在单速率WLAN中更差信道接入的前提下，显著提升聚合性能。我们还描述了我们的算法TBR（基于时间的调节器），该算法运行在接入点（AP）上，可与任何MAC协议协同工作，通过调节数据包来提供基于时间的公平性。实验表明，我们实际且向后兼容的TBR实现与现有的DCF实现相结合，能够实现基于时间的公平性。