On the performance anomaly in WiMAX networks

The WiMAX system carries a wide range of services in urban and rural environments supporting quality of service. A key element of the QoS framework is the scheduling algorithm adopted by the Base Station (BS). In this paper, we analyze the saturation throughput perceived by Mobile Stations in the cases of two BS scheduling algorithms: Deficit Round Robin (DRR) and time-based DRR. We demonstrate that theWiFi issue of ‘Performance Anomaly’ also occurs in WiMAX networks: when the BS uses scheduling approaches aimed at achieving throughputfairness, like DRR. Performance Anomaly means that when some Mobile Stations (MSs) use a very low bit rate, the throughput of MSs with a high bit rate is dramatically degraded. We propose time-based DRR as a viable solution to remove the Performance Anomaly. Time-based DRR is a simple modification of the DRR algorithm that achieves time-fairness. Its implementation is feasible in WiMAX. The analysis is carried out by means of analytical models supported by NS2 simulations. Two scenarios are considered: the first is suitably set up to highlight and understand the phenomenon of Performance Anomaly; the second examines the impact of Performance Anomaly on a system level focusing on a rural environment.