An adaptive round robin scheduler for head-of-line-blocking problem in wireless LANs

Unlike wired networks, wireless networks are characterized by channel errors. In wireless LANs (WLANs), link-layer ARQ can be used for error recovery. However, this technique assumes packet losses are due to packet collisions. With FIFO queuing at the access point (AP), ARQ may give rise to a "head-of-line (HOL) blocking" phenomenon that severely degrades the throughput performance. We study a simple adaptive round robin (ARR) scheduler at the LLC (logical link control) layer as a solution to the HOL blocking problem. Salient features of ARR include: 1) an explicit estimate of the channel state is not required; 2) compatibility with the existing IEEE 802.11 MAC protocol; 3) ability to achieve near-optimal throughput; 4) flexibility for meeting various throughput-fairness objectives. Besides extensive simulations, we also give the analytical upper and lower bounds for WLAN throughput with ARR. Our analysis closely matches the simulation results.