基于节点区分的IEEE802.11e无线局域网中的VoIP容量分析与优化

摘要

基于因特网协议的语音(VoIP)是无线局域网(WLAN)的一个具有广阔前景的应用,但VoIP容量在WLAN中却受到了较大的限制.为了增强对VoIP等实时业务的支持,IEEE 802.11e EDCA协议提供了竞争窗口(CW)、仲裁帧间间隔(AIFS)和传输机会(TXOP)3个参数来实现对业务流的区分,但没有考虑如何优化这些参数以达到对WLAN中的接入点和终端节点进行区分服务,而WLAN中的接入点却恰恰是制约其VoIP容量的一个重要因素.提出了一个语音容量分析模型,引入了协议的3个参数以区分接入点和终端节点,并考虑到语音流的ON-OFF模型和语音流的上行与下行时延约束.基于给出的分析模型,分别进行了单参数独立区分与多参数联合区分优化分析,在不同的语音编码与语音间隔情况下,定量地给出了利用CW,AIFS和TXOP进行独立区分时和联合区分时的优化值,从而达到提高VoIP容量的目的.仿真结果表明,利用这些参数的优化值为接入点和终端节点提供区分服务是正确的和有效的.%A new service called voice over Internet Protocol (VoIP) is becoming a promising application in wireless local network (WLAN). However, VoIP capacity is also limited because of the WLAN environment. To support VoIP service over WLAN, IEEE 802. Lle EDCA adjusts three parameters ( contention window ( CW ) , arbitration inter-frame space ( AIFS ) , transmission opportunity (TXOP)) to provide a differentiation service (DS) for application flows. However, it is not considered how to optimize those parameters to provide a DS for the access point (AP) and the terminal nodes, although the AP undergoes the higher traffic load and becomes the bottleneck for the VoIP capacity improvement. In this paper, this topic will be handled. A new analytical model is proposed for the VoIP capacity over WLAN. This analytical model, which reflects the ON-OFF model of voice flows and delay bound of voice uplink and downlink flows, can be utilized to differentiate the AP and terminal nodes using the three parameters. Based on the analytical model, two differentiation schemes, called separate differentiation (SD) and joint differentiation (JD) , are analyzed in which the SD utilizes one arbitrary parameter and the JD uses two arbitrary parameters to provide differentiation service. As a result, with aid of the analytical model > the optimal values of CW, AIFS and TXOP of two differentiation schemes can be obtained for improving the VoIP capacity according to the different voice codes and different voice packetization intervals. Finally, simulation results confirm that the analytical model is accurate and effective for the optimization of VoIP capacity.