The Research On Access Node Congestion Control Algorithm In Wireless LAN

With the advances and mature in wireless technology, more and more userschoose wireless internet. WLAN has been widely used in various fields of our life.However, WLAN also exists many problems as a new technology. WLAN exists ageneral problem that bandwidth and flow rate do not match with wired network. Withthe instability of wireless channel, high error, high latency, etc, WLAN access nodeAP can easily become network bottleneck. If the access node AP accumulates a largenumber of data packets, and does not forward in time, this will cause networkcongestion. Serious congestion conditions may lead to network paralysis. Socongestion problem in WLAN has gotten more and more attention.To achieve congestion control, strategies mainly include queue schedulingalgorithm and queue management in WLAN access node AP. Queue schedulingclassify data packets into different queue based on demand, according to priority levelof queue with a reasonable order forwards the packet to destination node toimplement congestion control. Queue management is grouped into the cache,groups are discarded properly before cache overflow in order to prevent thehappening of congestion. Two strategies can alleviate congestion to some extent. Thispaper considers from above two aspects and proposes queue scheduling algorithmand active queue management algorithm for WLAN.Firstly, this paper introduces the basic characteristics of WLAN, analyzes thereasons of congestion in wireless network and introduces existing queue schedulingalgorithm and active queue management algorithm.Secondly, in order to solve unfair problem of variable-length packet schedulingin wireless network, this paper puts forward a scheduling algorithm on the basis of afair distribution of resources between users based on WRR algorithm, the algorithmcan be based on the average packet length dynamic change of weights, weightschange considering the fairness of small data flow. And using a two state Markovsimulates the error of wireless, which express this algorithm alleviating the blockingqueue head problem effectively. Packet with channel state is unavailable when channel state variable can be used to give the appropriate compensation, to ensurelong-term fairness among users. The simulation experiment shows that improvedalgorithm not only ensures the fairness, but also improves the system throughput.Once again, RED algorithm was improved, which makes it a good suitable forWLAN. The date packets in the cache are divided into different queue according tothe destination and class of service. And different levels of data packets are discardedaccording to a different probability. According to average queue length judges thedegree of congestion. Select a queue which first packet waited the longest time whenimmediately congestion, randomly discard a packet in the queue. The packets areretention in better channel conditions, the packet is discarded in poor channelconditions. This will not only control the network congestion, but also improve theoverall throughput of the network.Finally, improved RED algorithm and proposed AFWRR algorithm areestablished in the same system model to simulate experiments. The two algorithmsare used in combination, can achieve effective congestion control and resourceallocation in WLAN AP node. The proposed algorithm has a better performancecompared with other algorithms in terms of throughput, packet loss rate, the averagelength of queue.