Research And Optimization Of Wireless Mesh Network Protocol Based On Network Coding

The wireless mesh network(Wireless Mesh Network, WMN) is a multi hop routing network model which based on the P2 P technology. It has the high rate and high capacity. WMN belongs to the Ad hoc network, but compared to the Ad hoc network, its nodes have little mobility. WMN generally does not exist as an independent network, it always acts as the "last mile" access network to the Internet. At present, most commonly used routing protocols in WMN is directly from the use of Ad hoc network routing protocols, such as OLSR protocol and AODV protocol. These protocols' initial design intention is to suit the quick movement and self-organizing application scenarios. The protocol's features don't suit to the mesh network well, some problems existing during the network transmission such as low throughput and high transmission delay problem etc.To solve these problems, based on the OLSR protocol mechanism, this thesis proposed an improved protocol, quick mesh protocol on MAC layer, QMPML. And its transmission performance has been improved. The thesis also combined with the network coding techniques to optimize the protocol's throughput.A new method about the classification and characteristics of the wireless Mesh network was introduced by this thesis, and the OLSR routing protocol chosen by it as the research object, emphatically introduces the principle and mechanism of OLSR routing protocol. The OLSR protocol depends on the hop-counts routing, its wireless transmission is difficult to reflect the link quality between its nodes. A new mechanism which uses the link quality weights given by this thesis to search the routes. Combined with signal strength, each network node's operation status, the thesis also introduces the influence factor, makes the protocol reflects the link quality and nodes' condition better in the routing establishment and transmission. Based on the routing mechanism, it redesign the structure of Hello package, neighbor list, and then implement the QMPML protocol in the embedded device. The results of comparison test for two protocols in open source embedded platform Openwrt show that the QMPML protocol in terms of throughput, delay and other aspects are greatly improved.For wireless network's transmission bandwidth attenuation problem in the multi hop topology, the thesis depends the broadcast nature of wireless mesh networks and its time-varying characteristics, combined with network coding and opportunistic routing technology to the QMPML. The COPE principle was applied on the QMPML protocol. After prove its feasibility of decoding, it designs the encode data packet format, the encoding chance discover mechanism, and the coding and decoding process in transmission. The thesis also tests the throughput and delay performance and makes the simulation based on the platform of NS2. Results show that, in the network of small and medium-sized mesh network, after combined with the network coding, the protocol's throughput has been further improved.