The Ieee 802.11e Edca Plus The Contention Window Dynamic Backoff Algorithm

With the development of wireless network technology, the wireless local area nework which is based on the IEEE 802.11 standards has been rapidly and widespreadly applied in recent years. However, as a variety of new services has emerged on the network , the performance of the network will get higher demands that the different services have different requirements on throughput, bandwidth, latency, etc. EDCA(Enhanced Distributed Channel Access) is the extension of QoS support which is proposed by IEEE 802.11e working group and based on the IEEE802.11 DCF mechanism. The introduction of MAC-level QoS enables the wireless local area network begin to provide priority support for voice and video services, etc.However, due to the complexity of network conditions, the static setting of EDCA parameters can not provide optimal system performance, many papers have shown that EDCA performance is unsatisfactory at high load conditions due to the conflict in the network,and at low load condtitions it will cause the waste of idle slotimes. Therefore, the researches on the adaptive adjustment of protocol parameters to ensure the protocol performance under the different load conditions become the hot spots. Among them, the contention window has an important influence on the performance of the protocol, and many researchers are studying the improvements of adaptive adjustment mechanism based on the CW and the associated backoff algorithm. For example, Lamia Romdhani proposed the adaptive EDCF mechanism, Younggoo Kwon proposed the fast collision resolution mechanism, as well as Mohammad Malli proposed the adaptive fair EDCF mechanism.In this paper, we briefly describe the basic principles of IEEE 802.11e EDCA mechanism, which include the contention window and the related backoff algorithm, then we make a simple analysis and comparison of the different improvements in AEDCF, FCR, AFEDCF mechanisms. On this basis, we present an improvement mechanism D-EDCA which is based on the contention window, in accordance with the average collision rate in each update period, the network state is divided into three status: high-load condition, mid-load condition and low-load condition, in different states according to their network characteristics to take a different backoff algorithm, dynamically adjust the contention window size to improve the performance of EDCA. By way of simulating in different scenarios, we prove that the D-EDCA can improve the throughput and reduce the delay of voice and video services, in addition,it can adapt to the dynamically changing network conditions, and provide the further QoS.