Analysis of Two-Level-Polling System with Mixed Access Policies

The support for real-time services particularly with QoS guarantees is a challenge in design of MAC protocol for wireless local area networks (WLANs), several kinds of mixed polling mechanism have been enrolled in design of point coordination function (PCF) MAC protocol recently. In this paper, we propose a novel and efficient mixed polling system with two-level-polling scheme, which consists of a hub station and N common stations in a WLAN, and the hub station and N common stations have been provided with exhaustive service and limited-1 service in discrete time respectively. By the embedded Markov chain theory and the probability generating function method, our scheme gives closed form expressions for obtaining the mean queue length and the mean waiting time, and analytical results are verified through extensive simulations. The results of our system can be potentially used as a model for differentiating services to guarantee better QoS and system stability in IEEE 802.11 WLANs, and it has better efficiency and impartiality than that of the traditional polling system with only exhaustive or limited-1 service.