无线局域网中会话型语音业务的实现及效率

Realization and efficiency analysis of conversational voice services in wireless local area networks

为在无线局域网中支持高服务质量(QoS)要求的会话型语音业务,提出一种新的系统实现方案,给出了由无线终端、无线接入点、语音网关、因特网等组成的网络结构模型.无线局域网内部的协议栈自应用层到介质接入控制(MAC)层采用RTP/UDP/IP/LLC802.2/802.11e结构.在MAC层接入方面,提出一种基于IEEE 802.11e标准中混合协调方式(HCF)的改进型多点调度(Multipoll)方式.设计了调度帧结构和调度时序,推导了满足时延和带宽要求的准入协商、Multipoll和单点调度(Singlepoll)的调度效率公式.仿真结果表明,该方案可以实现会话型语音业务,保证其带宽、最大时延等QoS要求;Multipoll是比Singlepoll效率更高的调度方式.多用户条件下仿真所得的吞吐量与所推导公式的计算结果非常接近,表明推导的调度效率公式可用于系统吞吐量的精确估计.

A new system scheme was proposed to realize conversational voice services with high QoS requirements in wireless local area networks （WLAN）. This scheme contains a network model consisting of wireless terminals, wireless access point, voice gateway and internet, while the adopted protocol stack architecture of the wireless terminals inside WLAN is RTP / UDP / IP / LLCS02.2 / 802. lle, from application layer to medium access control （MAC） layer respectively. In MAC layer, an improved Multipoll based on hybrid coordination function （HCF） of standard IEEE 802. lle was presented by designing the polling mechanisms and the polling frame formats. The admission control policy was derived to satisfy delay and bandwidth requirements, and the polling efficiency formulae of Multipoll and Singlepoll were also derived. Simulation results show that the proposed system scheme can provide QoS guarantees, such as bandwidth and maximal packet delay, for conversational voice services; and that Multipoll is much more efficient than Singlepoll. The throughput performances obtained by simulation are very close to the analytical results, which means that the system throughput can be accurately estimated using the presented formulae.