Media Access Control Algorithm In Wireless Mesh Networks

Providing quality of service guarantee for broadband multimedia services is one of next-generation wireless communication development essential targets. Wireless Mesh Network is designed for this goal. In Wireless Mesh Networks, communication between nodes and telecommunication infrastructures adopts multi-hop that is nodes access networks through the relay from neighboring nodes. This manner provides users with a flexible, convenience and broader Internet access. Media access control is precisely a coordination mechanism used to allocate channel resources and maximize the system resources utilization. Therefore, this thesis does some reach about problems of media access control in Wireless Mesh Networks.Aiming at the short-term priority problem in Wireless Mesh Networks, a medium access control algorithm with QoS guarantee is proposed. The main idea of the algorithm as fellow: each station timely detects the contention level. When the contention level is higher than a triggered threshold, it dynamically suspends the transmissions of low-priority traffic in order to prevent that low-priority traffic keep attempting to access the channel and collide with high-priority traffic, and provide more opportunities of channel access for high-priority traffic. When the updated contention level is lower than an ending threshold, it then goes back to normal EDCA operation. By doing this operation, the proposed algorithm can alleviate "short-term priority" problem at high loads and provide QoS guarantee for real-time traffics. Simulation results show that comparing with the IEEE 802.11e EDCA, this algorithm not only greatly improved the throughput of real-time traffic and transmission quality, but also increased the total throughput 5.1%.Based on the IEEE 802.11e EDCA, we analyzed the priority reversal phenomenon of network under heavy loads. Combined with transmission features of real-time traffic, a media access control algorithm based on dynamic priority strategy is proposed. The procedure of the algorithm as fellow: each station timely detects the contention level by calculating the collision probability. When the contention level is higher than a predefined threshold, it calculates the queue length of AC1. To judge load level of voice traffic by comparing the calculated AC1 queue length value with two different kinds of thresholds. According to the compared results, low-priority traffic and key frames of video traffic are dynamically adjusted, which improves the channel utilization and provide QoS guarantee for high-priority traffic. Simulation results show that comparing with the IEEE 802.11e EDCA, this strategy greatly improves the throughput of real-time traffic and transmission quality, also increases the total throughput 9.1%, and eventually alleviates the "priority reversal".