  The fairness of IEEE 802.11 wireless networks (including Wireless LAN and
Ad-hoc networks) is hard to predict and control because of the randomness and
complexity of the MAC contentions and dynamics. Moreover, asymmetric channel
conditions such as those caused by capture and channel errors often lead to
severe unfairness among stations. In this paper we propose a novel distributed
scheduling algorithm that we call VLS, for ``{\em variable-length
scheduling}'', that provides weighted fairness to all stations despite the
imperfections of the MAC layer and physical channels. Distinct features of VLS
include the use of variable transmission lengths based on distributed
observations, compatibility with 802.11's contention window algorithm,
opportunistic scheduling to achieve high throughput in time-varying wireless
environments, and flexibility and ease of implementation. Also, VLS makes the
throughput of each station more smooth, which is appealing to real-time
applications such as video and voice. Although the paper mostly assumes 802.11
protocol, the idea generally applies to wireless networks based on CSMA
(Carrier Sensing Multiple Access).
