Research Of QoS Mechanism Of VoWLAN

Voice over WLAN (VoWLAN) is a noval application which is the integration of Wireless Local Area Network (WLAN) and Voice over Internet Protocol (VoIP) technology. It has become the focus of telecom vendors and operators for its cost-efficiency. However, VoWLAN still faces significant challenges, among which QoS (Quality of Service) is the primary one. Based on the cooperation project of BUPT-ERICSSON joint lab, "Research of QoS of Voice over WLAN and WLAN-3G Integrated Network", the QoS problem of VoWLAN is studied, and enhancing algorithms are proposed in this paper. The author is one of the main algorithm proposers; undertake the theory analysis work, and participate in the simulation work.This paper studies the MAC (Medium Access Control) mechamism of 802.11 and 802.11e, analyzes their four problems, namely unfairness, high collision rate, low channel efficiency, and unstrict priority differentiation. Based on the analysis and comparation of existing QoS enhancement methods, this paper proposes a novel "Waiting-time Dependent Backoff (WDB)" algorithm for 802.11, and its extention, EWDB (Enhanced WDB) for 802.11e. WDB takes into consideration of the time requimients of voice, and introduces WT (Waiting Time) as the control factor of BT (Backoff Time) window. WDB alleviates the above problems, so it can dramatically reduce delay jitter and collision probability; reduce end-to-end delay, while maintain acceptable drop rate, which is validated by simulation. EWDB inherits the basic idea of WDB as well as the class differentiation mechanism of EDCF. It applies different BT ructions to voice, video and data, which could improve delay and jitter of voice and video, as well as data throughput, thus synthetically improve multimedia QoS.The trend of VoWLAN is to integrate with 3G network. So WLAN-3G integerated network, and its vertical handoff problem is briefly introduced in the end of this paper, and some primary ideas of design target are proposed.