Congestion Control And Scheduling Algorithm Based On IEEE 802.11s Standard

With the competition in telecommunications industry, wireless access networks have developed fast, more and more wireless access technologies have been proposed. Wireless mesh network is such a new wireless access technology, which is a distributed peer network. So the data is easy to accumulate at access point, and this will cause network congestion resulting in serious problem on network performance. Congestion problems of wireless mesh network are concerned by people and it is urgent to design a good congestion algorithm to solve network problems.One of draft standards on wireless mesh network is IEEE 802.11s, which has been paid much attention, and has a prospect. Congestion control mechanism on MAC has been lead in this draft standard. This paper proposed an improved algorithm based on this draft standard for both efficiency and equity. So far the proposed improved algorithms based on this draft standard are all belong to ENC, which are not considered connection with congestion control and priority level very well. Besides they do not combined with other algorithms such as scheduling algorithm to solve congestion problems. This paper does some research on these two problems.First of all, the paper describes the reasons for network congestion and analysis the performance of congestion control mechanism and currently status of congestion control algorithm on wireless mesh network of draft standard IEEE 802.11s.Secondly, this paper proposed improved algorithm based on draft standard of IEEE 802.11s, and there are two aspects to improve. At first, price theory is introduced to wireless mesh networks and pricing theory-based congestion control algorithm has been proposed. Then improved leap forward virtual clock algorithm has been introduced to the wireless distributed environment.Pricing theory-based congestion control algorithm introduces the price theory in economics to congestion control. Congested node calculates price by the design of the pricing function and write it in to congestion control requirement behavior frame according to congestion levels and business priorities and sent them to the transmitter. Transmitter controls local rate by using the information in congestion control requirement behavior frame. According to draft standards IEEE 802.11s, modifying the parameters on physical layer is forbidden so rate control is based on contention window on MAC layer. By adjusting contention window it can influence access probability of data so the rate of transmitter can be changed.Improved leap forward virtual clock algorithm improves centralized environment algorithm to make sure that it can be used on wireless mesh networks. There are two aspects to improve, one is to propose a compensation queue to store packets which can not been sent resulting from instability network channel. The other is to control priority of transmission queue by adjusting the contention window based on draft standard IEEE 802.11s and adjust the contention window by congestion window and business priorities based on pricing theory-based congestion control algorithm.Finally, two improved algorithms were compared in simulation in NS-2. By compared with other algorithms in throughput, packet loss rate, fairness index and smoothness index two algorithms proposed in the paper is good in both fairness and effectiveness. The performance of improved leap forward virtual clock algorithm is not destroyed seriously in especial wireless environment which has high bit error rate.