Multiple Poll Scheme for Improved QoS Using IEEE 802.11 PCF

IEEE 802.11 contains a mechanism for transmission of data with real time constraints known as point coordination function (PCF). This supplementary medium access protocol uses a centralized polling approach. Due to predicted inefficiency of PCF, IEEE 802.11e medium access control (MAC) is proposed as an emerging supplement to the IEEE 802.11 standard to support quality-of-service (QoS) over wireless local area network (WLAN). In this paper we evaluate the suitability of legacy PCF for the transmission of real time data by using an IEEE 802.11e type scheduler over IEEE 802.11. We show that the simple concept of "multiple polls to single station" aided by "delay bounded superframe size" is suitable for providing improved QoS without requiring any change in the existing protocol. The performance of the proposed scheme is evaluated through ns-2 simulator and then compared against the standard scheme in PCF. The simulation results confirm that multiple poll strategy enhances the PCF performance by increasing the overall system throughput and achieving more acceptable streaming quality in terms of frame losses and delays