MAC-layer Time Fairness across Multiple Wireless LANs

Wireless LANs have been densely deployed in many urban areas. Contention among nearby WLANs is location-sensitive, which makes some hosts much more capable than others to obtain the channel for their transmissions. Another reality is that wireless hosts use different transmission rates to communicate with the access points due to attenuation of their signals. We show that location-sensitive contention aggravates the throughput anomaly caused by different transmission rates. It can cause throughput degradation and host starvation. This paper studies the intriguing interaction between location-sensitive contention and time fairness across contending WLANs. Achieving time fairness across multiple WLANs is a very difficult problem because the hosts may perceive very different channel conditions and they may not be able to communicate and coordinate their operations due to the disparity between the interference range and the transmission range. In this paper, we design a MAC-layer time fairness solution based on two novel techniques: channel occupancy adaptation, which applies AIMD on the channel occupancy of each flow, and queue spreading, which ensures that all hosts and only those hosts in a saturated channel detect congestion and reduce their channel occupancies in response. We show that these two techniques together approximate the generic adaptation algorithm for proportional fairness.