Research On Seamless Handoff Technology For Wireless Mesh Network

With the rapid development of the wireless local area network (WLAN), tremendous convenience is provided to business enterprise and public. On the other hand, the wired infrastructure of WLAN is not suitable for the deployment extension. To increase WLAN coverage, a novel architecture of Wireless Mesh Network is proposed with safer access and broader area, which takes the advantages of wireless Ad hoc and WLAN. Traditional WLAN does not provide a good support for user mobility, then how to guarantee the quality of service in the ongoing mobile scenarios becomes a challenging research point for Wireless Mesh Network.In this thesis, handoff technology is introduced under the background of supporting multiple services, especially the real-time applications. Handoff mechanism in network layer with low latency and low packet loss rate is discussed and analyzed. Based on the traditional WLAN data link layer handoff and Mobile IP mechanisms, an improvement of handoff in Wireless Mesh Network has been proposed. According to the unique multi-hop property of Wireless Mesh Network, the flat routing procotol based handoff mechanism is presented with two specific implementations. In this mechanism, data link layer handoff between access points triggers routing activities inside the network, which can be thought of as network-layer handoff. Taking advantages of the special multi-hop property and omnidirectional wireless propagation, a new smooth handoff scheme based on neighbor caching is also provided. This scheme can greatly reduce the packet loss rate without any additional wireless transmission overhead. Seamless handoff in Wireless Mesh Network can be achieved by combining above schemes, and it can be also guaranteed that the handoff mechanisms are compatible with current protocol standards of WLAN.Compared with the traditional Mobile IP-based mechanisms, the simulation results show that fast handoff schemes based on flat routing procotol can effectively reduce handoff delay, which is between 40ms and 130ms; the new neighbor caching mechanism proposed in this thesis can greatly reduce the data packet loss rate with superior performance to the basic data packet caching scheme.