Adaptive Polling Algorithm for Reducing Polling Delay and Increasing Utilization for High Density Subscribers in WiMAX Wireless Networks

The IEEE 802.16 standard is proposed to support QoS-aware transmission of real-time service in WMANs, where the wireless transmission range can be up to 30 miles. WiMAX adopts the polling access control for a base station (BS) to poll subscriber stations (SSs) in turn and it will increase polling delay when there is a lot of number of SSs within the BS. The disadvantage of long polling delay may not guarantee the QoS requirement of real-time service and cause long waiting time while not in unicast polling. Therefore, in this paper we propose an adaptive polling approach to switch the polling mode while continuous supporting rtPS. The proposed approach consists of two phases. First, two hysteresises of number of SSs and residual bandwidth are adopted to determine the polling mode between the unicast and multicast polling modes. Second, a novel quasi-rtPS service (QrtPS) that provides an average delay of real-time traffic instead of the maximum delay of rtPS is proposed to take over the rtPS service when the BS is in multicast polling. Numerical results demonstrate that the proposed approach outperforms the IEEE 802.16 standard in average delay and utilization significantly. Moreover, the average delay of different contention slots and the number of groups within a BS are also evaluated for multicast polling