The Research Of The Optimization Problems Of MAC Layer Protocol In Wireless Mesh Network

Wireless Mesh networks are also referred to as "multi-hop network", which is a new network technology that completely different with the traditional wireless networks. With the continuous development of computer network technology, people have paid more attention to the wireless network. In this paper we mainly study the optimization problem of MAC layer protocol of Wireless Mesh Networks (WMN).The research of wireless mesh networks is divided into two parts, one is the optimization of DCF mechanism of the MAC layer itself and the other is the optimization of traffic control.As a new transmission pattern, network coding can greatly improve the throughput of wireless networks; it can be divided into intra-flow encoding and inter-flow encoding pattern. However, the wireless network coding protocol has been realized mainly based on the ideal network conditions or the network packet loss rate is very low; while in the actual wireless network, packet loss is inevitable, and the research shows that the actual packet loss rate is about 30% or above for wireless network.In this paper, we firstly propose a new backoff mechanism for WMN by introducing the link status of the network to calculate the backoff time, and then propose a new type of linear encoding and dual-decoding strategy for wireless network based on the more and more popular network coding research.The original DCF binary backoff algorithm of MAC layer for 802.11 protocols exist some problems, which can not dynamically adapt to the network environment changes. So we use the new delay backoff algorithm, that is to concern the link status and delay time when calculate the backoff time, using this method can make the data frame transmission dynamically adjust to the network link status and avoid the congestion and waste of resources.The previous proposed network coding protocols are not suitable for the WMN which has higher packet loss rate. In this paper we propose a new linear coding program and dual-decoding program for WMN. In the encode process, we use the random linear coding strategy to take full advantages of the redundancy coding package, and combine network coding and opportunity forward strategy to create more encoding opportunities; and in the decoding process, we adopt the double-decoding strategy to improve the decoding success rate. Firstly the node decode the packets using the original packets in the OVERHEARD queue, then it will decode using packets in the code cache when the first decode failed, the node will discard this packets and handle the next one if the second decode process still failed,.Finally, through the theoretical analysis and NS2 simulation by comparing the throughput and decoding success rate performance, we can prove the effectiveness of the new linear encoding and double-decoding scheme for high packet loss rate wireless mesh network.