Researches In Multi-Channel Medium Access Control Scheme In Wireless Mesh Networks

Wireless Mesh Network (WMN) is a high-rate and high-capability distributed network. Because of its low expense characteristic, it is becoming one of the most promising broadband access networks. WMN can expand network coverage and increase network capacity. It is also an ideal technology to provide fast access to network, especially in network infrastructure hardly set up or facilities likely to be destroyed. There are variety of access methods and a wide range of wireless communication channel in WMN. Allocate and manage channel resources is important for optimization the performance of WMN. Multi-channel can make full use of physical network resources, increase the capacity of network. The thesis mainly research and design multi-channel Medium Access Control (MAC) schemes in WMN.The thesis puts emphasis on MAC protocols in WMN. After analyzing the common problems and limitations on the already existing multi-channel MAC schemes in WMN, it designs a multi-channel MAC protocol based on the single radio network and multi-radio network, respectively.Firstly, on the basis of combination of TDMA and FDMA, the thesis proposes a new random sequence of channel search based multi-radio MAC protocol, which is called RSS-MAC in the paper. In RSS-MAC, a communication cycle is divided into multiple windows, among which data transmission window is divided into multiple time slots. First of all, the nodes within the range of two-hop communication get a fair distribution of all the channel resources. During every communication cycle, the node which first gets successful competition of the channel is chosen as coordinator for the channel. The coordinator is responsible for the distribution of time slots for nodes which have applied for the channel based on their data traffic. The nodes which have not applied for time slots successfully search for other free channel resources according to their own random channel search sequence. It is worth mentioning that RSS-MAC supports broadcasting. The simulation results show that RSS-MAC has improved the utilization of the channel resources and realized a high network throughput.Secondly, we do some researches on channel assignment in multi-radio network. A new MAC scheme is proposed named MRMC-MAC, which solves the channel assignment in the case of network traffic relatively stable. MRMC-MAC includes default receiver channel allocation, distribution of the main switch-able channels, node communication and the update of the main switch-able channels. In MRMC-MAC, channel allocation is on the basis of a received load-based allocation algorithm. The received load is introduced as priority parameter in channel allocation, which ensures that the node with the heaviest received load has the most priority to get the channel with light load and the nodes with lighter received load share the same default receiver channel. Thus, the load between the channels can be balanced. In addition, the hidden terminal problem in multi-channel multi-radio network is analyzed, and some solutions to the hidden terminal problem are presented in the thesis.In the end, a simulation on MRMC-MAC is achieved using NCTUns 5.0 platform. The results show that network capacity has been greatly improved in MRMC-MAC.