Adaptive Modulation-Based TCP-Aware Uplink Scheduling in IEEE 802.16 Networks

In this paper we propose polling based uplink scheduling schemes for TCP based applications in a multipoint- to-point fixed broadband IEEE 802.16 network. Our schemes adapt the transmission rates between subscriber stations (SSs) and the base station (BS) dynamically using adaptive modulation. We ensure fairness among the SSs via a credit-based approach in which an SS that misses a chance to transmit due to bad channel gets more weightage when the channel favors scheduling. We also propose a method to compute an optimal polling interval that aims to maximize slot utilization and TCP throughput. We demonstrate through exhaustive simulations that the proposed schedulers maximize link utilization, provide long-term fairness and minimize contraction of TCP congestion window. Implementation of the proposed schemes requires a cross-layer based feedback protocol stack at the BS and SSs.