一种改善802.11无线局域网语音传输性能的方法  

A Method for Improving Voice Transmission on IEEE 802.11 WLAN

作　　者：杨仁忠[1] 侯紫峰[2] 孙国滨[2] 

机构地区：[1]中科院计算所,北京100080 [2]联想研究院,北京100085

出　　处：《微电子学与计算机》2004年第5期85-89,100,共6页Microelectronics & Computer

摘　　要：IEEE802.11协议包括两种信道访问模式,即基于CSMA/CA的分布方式(DCF)和在此之上的集中控制方式(PCF)。对于语音如VoIP等实时应用来说,集中控制方式在一定程度上可以满足某些QoS需求,但是,PCF方式的无竞争周期(CFP)是接入点(AP)以竞争方式获得信道控制权并发送信标(Beacon)开始的,由于介质的繁忙,会延迟信标B的发送,这样会增大语音结点的传输抖动时间,并且使轮询序列后面的结点由于没有得到轮询而发生丢包的情况。为了改善这种情况,在每一个CFP周期开始之前,通过提前动态维护AP中的轮询序列的方法,可以克服上面存在的问题。该方法不用更改MAC协议,同时又保障了语音结点的QoS需求。仿真结果表明,更改后的PCF轮询机制在传输抖动和丢包率等方面比更改前都有明显的改善。The IEEE 802.11 wireless LAN protocol includes DCF and PCF wireless medium access models of operation. For real-time application such as voice over IP, the PCF model can meet some QoS needs. But the time which contend-free-period (CFP) begins is when an access point (AP) can control the medium access and transmit a beacon through contending with other stations. So when medium is busy, the beacon's transmission will be delayed and this will make the voice stations's jitter time longer and some stations which locate in poll list rear will lose packets for not polled. To deal with it, an improved method is proposed, that 's to say, before each CFP begins, we maintain the contents of the poll list dynamically in advance. This improved method doesn't modify the MAC protocol and also resolves the problem above. To verify this, a simulation is carried out and the results show that the jitter time and drop rate are reduced using the proposed method.

关 键 词：无线局域网 语音传输 

分 类 号：TP393.9[自动化与计算机技术—计算机应用技术]