An Enhanced HCCA Based Adaptive Scheduler for Multimedia Traffic in IEEE 802.11e Wireless LAN

摘要

Designing a good Hybrid Coordination Function (HCF) scheduling algorithm in IEEE 802.11e wireless LAN is a challenging topic since the wireless channel is time varying and many multimedia applications have Variable Bit Rate (VBR) characteristics. Because of channel interference and streaming bursty or variable bit rate traffic, insufficiency occurs in the strict periodic Transmission Opportunity (TXOP) allocation scheme derived by the simple scheduler of HCF Controlled Channel Access (HCCA). This paper proposes design of an Enhanced HCCA based Adaptive Scheduler (EHAS) for multimedia traffic in IEEE 802.11e Wireless Local Area Network (WLAN). In the proposed scheme, a history of previous queue length estimations and packet loss rate estimations for each Traffic Stream (TS) is maintained by each Quality of Service aware Station (QSTA) and TXOP is allocated by predicting the future values of these factors. Based on the packet loss rate and the channel condition, the application data rate is adaptively adjusted. Through simulation it is shown that the proposed scheduler attains better throughput and channel utilization with reduced end-to-end delay, when compared with the existing scheduler for example Wireless Timed Token Protocol for HCCA (WTTP).