Research Of QoS Of MAC In Wireless Local Area Network

The wireless LAN is the combination product of computer network and wireless communication technology in the 1990's, it provides the access to network via wireless channel, and then it could be a potential method for future telecommunication: mobility, personality and multimedia application, it also comes to be an efficient broad-band wireless access mechanism. Wireless LAN only involves two layers, physical layer and medium access control layer, which are the lowest layers of open system interconnection. The specification of MAC includes medium access method, authentication, encrption and so on. DCF is the basical medium access mechanism, which is based on CSMA/CA(channel sense multiple access/collision avoidance). The traditional wireless LAN can only provide the "best effort" service, those time-sensitive traffics such as video and audio require better quality of service, but it is because wireless LAN has the high mobility, high bit error rate and channel access scheme based on contention mode, to realize QoS mechanism becomes difficult and challenging.This paper first analyses the mechanism and architecture of quality of service and then investigates the performance of IEEE802.11 MAC layer. By analyzing the throughout, time-delay, time-jitter and fairness, the paper presents a new EDF mechanism called P-DCF based on time-delay. P-DCF is a way of realizing the QoS by the different inter-frame slot(IFS) which is put up in the IEEE802.11 standard. P-DCF reguards the expiration time of packet as a critical paramete, which is used to decide the priority of packet. The priority of real time service changes exponentially with the expiration time, but that of 'best-effort' service changes linearly with the expiration time, so the packet of real time service will be send first and time delay can be guaranteed. Theoretic and simulative analysis shows that P-DCF can satisfy the requirement of time-delay and is better than the traditional basic DCF, so the P-DCF can realize the differentiated service based on time-delay.