The Effect of Channel Fading on Providing Quality

Transferring real-time traffic such as voice and video over wireless LAN network (WLAN) requires stringent delay and jitter requirements. One of the methods to provide QoS in this standard is Enhanced Distributed Channel Access (EDCA) which benefits form the concept of traffic categories. However, EDCA is a contention based method; therefore it can not guarantee strict QoS required by real-time services without proper network control mechanisms. One of the challenging problems in wireless networks is the failure of transmitting media due to fading. Normally the node does not differentiate between the media access collision and the channel failure. The performance of this method in case of fading channel has not yet been evaluated. In this paper, we analyze the effect of loss and delay caused by fading channel on EDCA performance. Then, we propose a modification to the media access scheme to elevate the performance against channel failures. Moreover an adjustment for the maximum number of retransmissions is proposed to maintain the delay and jitter requirements of the real-time traffic. The performances of the proposed methods are evaluated by simulations.