An admission control method for IEEE 802.11e contention access mechanism

Abstract

IEEE 802.11 Wireless Local Area Network (WLAN) is a shared medium communication network that transmits information over wireless links for all 802.11 stations in its transmission range. With the applications over 802.11 WLAN increasing, customers demand more and more new features and functions. The support of audio, video, real-time voice over IP and other multimedia applications over 802.11 WLAN with Quality of Service (QoS) requirements is the key for 802.11 WLAN to be successful in multimedia home networking and future wireless communications. Recently, the IEEE 802.11 task group e specified a distributed access approach, called Enhanced Distributed Channel Access (EDCA), which supports service differentiation in the Medium Access Control (MAC) layer. It ensures the packets sent by each mobile station can be differentiated by assigning different access parameters. However, no assurance can be given to higher priority traffic in terms of throughput and delay performance. The problem is especially apparent when the wireless channel is overloaded causing the bandwidth share of each flow to diminish. Admission control is the solution for the problem addressed above. In this research, a simple measurement based admission control method is proposed to enhance the QoS of EDCA network when it is heavily loaded. The proposed method can control the number of allowed wireless stations in the WLAN network without degrading the QoS (medium access delay and throughput) of the existing flows under a high load condition. Several QoS parameters such as delay and throughput are analyzed to investigate the performance of the proposed method. The simulation is done using Network Simulator ns-2 to study the QoS. The results have shown that the proposed method can protect the QoS of high priority applications and at the same time sacrificing the QoS of low priority flow at a moderate level.