Managing Contention with Medley
Feng Lu, Geoffrey M. Voelker, Alex C. Snoeren · IEEE Transactions on Mobile Computing · 2014
As WLANs achieve gigabit per second speeds, they will need to support users with a wide range of workloads, ranging from VoIP and Web clients to data backup, file transfers, and streaming high-definition video. Unfortunately, channel efficiency degrades severely in these scenarios under existing MAC protocols due to contention and back-off overheads. Moreover, small yet latency-sensitive flows suffer disproportionally as load increases. We present Medley, a system that leverages frequency-based contention to allocate subchannels in an OFDMA-based link layer in a delay-fair manner. In contrast to traditional CSMA schemes in which each node competes uniformly for the channel, Medley ensures that nodes with smaller service rates are served before those with heavier demand; the more bandwidth a node consumes, the larger its packet average delay will become. An initial implementation of Medley on a software defined radio platform demonstrates its feasibility in a small network, while more comprehensive simulation results show its benefits under a wider range of conditions. Medley delivers delay fairness while remaining over 94 percent efficient in the face of massive over-subscription.