Inadequacy of the Queue-Based Max-Weight Optimal Scheduler on Wireless Links with TCP Sources

The interaction between wireless optimized scheduling algorithms and TCP congestion control mechanisms can have adverse effects on the performance of the system. We focus on the queue based max-weight (QBMW) scheduler, a scheduling strategy which is known to be throughput-optimal under unregulated traffic sources. We use fluid modeling to describe the time evolution of the congestion window size and of the wireless buffer, and show by numerical results that under TCP traffic sources the QBMW scheduling policy leads to a very unfair outcome, in which some users may be completely shut off. We also evaluate and discuss the performance achieved by other scheduling policies: the proportional fair (PF) scheduler, and the queue age (QA) scheduler, which takes account of the age of the packets stored in the wireless buffers.