A Research Of MAC Protocol Based On TDMA In Ad Hoc Network

As a kind of rapidly changing technology in wireless mobile communication, Ad Hoc network has been increasingly concerned and studied by people because of its wide range of application scenarios. The MAC protocol is located on the second layer of the network protocol stack, which is the key point for sharing and accessing the limited channel resources. Generally, compared to the traditional MAC protocol based on competition and backoff mechanism, TDMA-MAC protocol is more suitable for Ad Hoc networks with better network performance.There are two main problems for TDMA-MAC protocol to solve. One is the clock synchronization, another is the slot allocation. TDMA-MAC protocol is a kind of time information-aware protocol and needs to promote the clock consistency of the whole network since the nodes in the network should maintain a consistent clock strictly. Meanwhile, the multi-hop feature in space of Ad Hoc network will lead to hidden and exposed terminal problems which can affect the effective transmission obviously. Therefore, TDMA-MAC protocol is also a kind of spatial information perception protocol. It should not only need to achieve conflict-free transmissions between nodes from different part of the network, but also give a full consideration to the slot spatial multiplexing rate inorder to let more nodes transmit simultaneously. Based on the above reasons, we mainly study the TDMA-MAC protocol in this paper from two aspects: clock synchronization and slot allocation.Firstly, based on the summary and analysis of existing clock synchronization protocols, we propose a distributed fast local clock synchronization protocol named LFSP. Each node can synchronize to the fastest clock reference of its one-hop neighborhood by the interactive synchronization process proposed in LFSP. Eventually, every node can achieve global synchronization in the way of local synchronization. Simulation results show that LFSP has a fast convergence and high accuracy of synchronization. Also, it is not sensitive to the size of the network.Secondly, in this paper, we aim at the blindness of slot allocation and the disadvantages of competition mechanism in FPRP, and then propose an improved broadcast protocol called E-FPRP. The protocol uses a multi-hop FCR algorithm to resolve reservation conflicts fastly and proposes a slot allocation mechanism based on traffic load. By setting up a number of simulation scenarios, we find that E-FPRP has significant performance advantages in slot spatial multiplexing rate, allocation fairness and the success ratio of node competition compared to FPRP. In addition, E-FPRP can not only improve the network throughput and packet delivery ratio, but also reduce the access delay by the on-demand allocation mechanism.Finally, we expand E-FPRP by proposing a new unicast protocol called SRPU because of the disadvantages of the broadcast schedule directly applied to unicast. And the protocol is both demonstrated from theoretical design and software simulation. Simulation results show that SRPU has a higher slot spatial multiplexing rate and effectively solves the transmission problems compared to E-FPRP. The simulation results also show that SRPU has significant advantages in terms of transmission performances such as throughput and access delay compared with CSMA/CA.