Research On TDMA MAC Protocol In Wireless Mesh Emergency Communication Network

Wireless mesh networks(WMN) is self-configured, self-organized and self-healing distributed mesh network architecture, which consist of some communication nodes with radio transceivers. Emergency communication network is a typical application of WMN, and plays significant role on the occasion of emergency rescue when facing major accident or natural calamities. However, the research and application of the medium access control(MAC) protocol of WMN mainly concentrates on the IEEE 802.11 s based scheduling protocol, which has some disadvantages such as inefficient radio resource utilization, long end-to-end delay and small hops supported. To address those problems, the paper focused on the time division multiple access(TDMA) based link scheduling protocols and proposed two MAC protocol, centralized WMN MAC protocol and distributed WMN MAC protocol, separately.Firstly, we proposed a centralized WMN MAC protocol for the small-sized WMN with less hops. In order to improve the efficiency of channel utilization, the proposed protocol adopted a compact time slot structure and fine time schedule scheme. There is a mesh base station(MBS) in each WMN, who determines the time assignment of the whole network according to the real-time traffic of both MBS and the other nodes. The channel is scheduled dynamically in unit of one physical layer symbol transmission time. The paper provided the frame structure and the major protocol process, such as the join/departure procedure, time synchronization, time assignment and frame error control. The proposed protocol is realized and validated in the field programmable gate array(FPGA) of the test bed.Because the control overhead and delay increases with the hops of centralized WMN MAC, this paper proposed a distributed WMN MAC for large-scale WMN with large hops. Different from the centralized WMN MAC, every node is equivalent in the distributed WMN MAC, and there is no base station to manage the channel assignment. Therefore, a distributed channel assignment algorithm is proposed, which assign the time slot dynamically according the two-hop neighbor relationship of each node. The complexity and overhead is unrelated with the network scale, and adapt quickly when the network topology changes. Finally, the proposed distributed WMN MAC is simulated in OPNET in three levels: network model, node model and process model. The simulation results prove the superiority of our protocol. It has higher capacity and smaller delay when compared with IEEE 802.11 s and fixed slot assignment algorithm.