Research On Time Synchronization And MAC Protocol Performance For Long Propogation Delay Networks

With the continuous development of human civilization, thelimitation of land resources has gradually emerged. Many powerfulcountries of the world have begun to transfer their strategic center ofgravity to the investigation and exploration of oceans and deep space andso on. However, there are some differences of the wirelesscommunication environment between the terrene and these two regions ofwhich the common denominator is both with a relatively large signalpropagation delay. Many algorithms on land cannot be directly appliedunder the long communication delay circumstance. In this paper wemainly focus on the underwater sensor network to analysis and researchon the time synchronization and synchronous MAC protocol.First, we propose an improved multi-hop time synchronizationalgorithm for underwater acoustic networks (IMSUAN) based onoverhearing mechanism and present the details of the three aspects ofimprovements of the algorithm. The first one is to establish a timesynchronization tree as low as possible. The second is to synchronizewith overhearing exchange packets from parent and neighboring nodesand the third is to filter the overheard inaccurate time-stamps packets. Wealso put forward the mathematical proof of the effectiveness of theoverhearing mechanism. Finally, we set up an OPNET simulationplatform to estimate the performance and overhead of IMSUANalgorithm in different network topologies.Secondly, based on the existing research results and timesynchronization algorithm, combined with network synchronization overhead analysis and synchronization accuracy, we conduct amathematical model to analyze the interval of the guard time of theTDMA protocol for the underwater sensor network. We also analyze thtepropagation jitter in the underwater network. Then, based on themathematical analysis above, we propose a single-hop dynamic TDMAaccess protocol which needs for the whole network synchronizationaccording to the spatial and temporal characteristics of the UANs. At last,we establish a OPNET simulation platform to compare it with the withthe traditional TDMA protocol, static TDMA protocol based on spatialand temporal characteristics and an asynchronous handshaking MACAUprotocol which doesn’t need for network synchronization under differentload conditions. The results show that the dynamic TDMA protocol has abetter network performance.Finally, we extend the single-hop TDMA protocol to multi-hopunderwater acoustic sensor networks and set an appropriate guard timeinterval for multi-hop TDMA protocol in multi-hop underwater sensornetworks based on the time synchronization accuracy of IMSUAN.Therefore we propose a TDMA time allocation algorithm for multi-hopunderwater acoustic sensor and add a dynamic allocation mechanism oftime slots based on network traffic. Then we carry out a simulation of theproposed dynamic multi-hop TDMA protocol, static multi-hop TDMAprotocol and MACAU asynchronous handshaking protocol in underwateracoustic sensor network using OPNET, with different types of datasources offered to the three MAC protocol. The simulation results showthat no matter in terms of equilibrium or non-equilibrium the offer load is,the dynamic multi-hop TDMA protocol, compared to the other two MACprotocols, has a better performance in throughput and end-to-end delay.