VoIP Performance Analysis And Research Over Wireless LAN

With the development of the wireless LAN technology and voice over IP (VoIP) technology, using wireless network to transmit voice over IP becomes a hot research direction in recent years. However, the service provided by IP network is the one which called'best effort'and the limited bandwidth of wireless network make voice over wireless LAN face many problems. Studying the capacity of VoIP users over WLAN has very important significance. This paper's research is carried out on this background.This paper's main work is to analze and verifies the capacity of voice traffic on DCF mechanism and PCF mechanism of WLAN. For the current common DCF mechanism, an improved scheme is proposed to improve the capacity of voice traffic over wireless LAN. In the theme we mainly work in following aspects.First of all, A simple introduction about the Wireless LAN (IEEE 802.11) standards and current research on WLAN technologies are given. The architecture of IEEE 802.11, the mode of operation, the MAC protocol, medium access mechanisms and so on are described in details. After that, the principle of VoIP communication is researched, and the brief introduction of VoIP key technology and QoS are given, which lay the foundation for later study.Secondly, on the base of analyzing the Markov chain transmission model of Giuseppe Bianchi, the effective throughput and the capacity about voice are investigated on the DCF mechanism according to the theoretical analysis and calculation. According to the transmission principle of PCF, the related mathematical model is established. Then, the effective throughput and the capacity about voice are investigated on the PCF mechanism by the theoretical analysis and calculation. After that, the theoretical capacity values of VoIP users are calculated by the above throughput and capacity formula, when VoIP users choose different voice encoding over IEEE 802.11b.Thirdly, OPNET Modeler is used to evaluate throughput and delay about VoIP over wireless LAN. The result shows that the simulation result and the theoretical value are close, which verifies the theoretical derivation.At last, with relevant literature, theoretical analysis and simulation experiment, main factors which limit the capacity of voice over wireless LAN are analyzed. Taking into account these factors, for the current common DCF mechanism, an improved scheme which called frame aggregation is proposed. Theoretical analysis and simulation experiment show that the improved scheme can effectively improve the capacity of voice traffic over wireless LAN.