Qos Improvement In Mac Layer For Multimedia Transmission Over Wlan

IEEE802.11 is a widely accepted standard for WLAN system which has been supported by most international manufacturers and gained biggish quotient in the world market. In recent years the support of the real-time multimedia service in the wireless channel is the trend of the communication system. Thus the requirement of QoS supporting schemes in WLAN is critical. The IEEE Task Group E was formed and defining QoS enhancements for the IEEE802.11 MAC layer by introducing and Enhanced Distributed Coordination Function (EDCF). The EDCF provides prioritization enhancement of the IEEE802.11 Distributed Coordination Function (DCF).In this paper an Enhanced Distributed Coordination Function (EDCF) performance and its improvement is shown by proposing and evaluating a packet retransmission algorithm which is called Age-Dependent Backoff (ADB).[1]The ADB algorithm dynamically varies the persistent factor associated with the contention window, based on VoIP packed queue age and lifetime. ADB maintains the backward compatibility property of EDCF and involves relatively easy implementation at low cost. A hybrid design framework is proposed to improve the quality of video streaming. This framework consist Forward Error Correction (FEC) and Priority Mapping Mechanism. [1]The QoS performance is shown by simulations when supporting VoIP traffics and H.264 video streams. The existing QoS mechanisms and some viewpoints of the author are generalized. Some viewpoints of the author, in the case of a complex network environment, to provide high-quality voice services should consider using the scheduling based on the medium access method. On the one hand, the scheduling approach is easy-to-centralized control and access control; [1] On the other hand the scheduling approach in the video communication can be used for the transmission of important video frames.Extensive simulation results obtained using NS2 software show that EDCF with ADB retransmission algorithm provides low value for latency and drop rate for voice traffic, and verify FEC with QoS Priority Mapping impact of video transmission.