Research Of Frame Synchronization Technology And MAC Protocol For Underwater Acoustic Sensor Networks

Underwater Acoustic Wireless Sensor Networks(UAWSNs)have important practical value and can be applied in the marine environment measurement,tsunami early warning,marine military defense and other fields.UAWSNs are extensions of wireless sensor networks(WSNs)in underwater environments.The underwater acoustic channel of UAWSNs is much more complicated than the terrestrial wireless channel.Traditional network protocols of WSNs often cannot be directly applied to UAWSNs.Under UAVSNs,underwater acoustic signals have low transmission rates,long transmission delays,narrow available bandwidth,and severe multipath effects.Mobile underwater acoustic communication is accompanied by severe Doppler effects.In order to ensure the reliability of underwater acoustic communication frame synchronization,an LFM underwater acoustic communication frame synchronization mechanism based on segmented FFT is proposed.First,the underwater acoustic frame synchronization signal is segmented.The length of each segment must ensure that a single LFM signal can also be divided into several segments.Then perform FFT operation on each small segment to obtain the maximum amplitude value and corresponding frequency value of the FFT result of each segment.The position of the synchronous LFM signal is determined by fitting the results of the standard LFM signal segmented FFT operation.Finally,the underwater sound data collected from Jingye Lake of Tianjin University is used to verify the synchronization effect of the frame synchronization mechanism of the LFM underwater acoustic communication proposed in this paper.In order to reduce network conflicts,a UAGSNs MAC protocol based on Orthogonal Frequency Division Multiple Access(OFDMA)subcarrier pre-grouping(OSPG-MAC protocol)is proposed.The OFDMA subcarriers are divided into fixed subcarrier groups in advance,and the subcarriers are allocated in the form of subcarrier groups to reduce the amount of information carried by the control packet,thereby reducing the length of the control packet,improving the accuracy of channel listening,and reducing network conflicts.In order to reduce the complexity of OFDMA resource allocation,a joint power and subcarrier allocation algorithm suitable for the OSPGMAC protocol is proposed,which is called the OSPG-MAC algorithm.Simulation results show that the OSPG-MAC protocol proposed in this paper can effectively extend the network life and reduce network conflicts,and the OSPG-MAC algorithm can effectively reduce the complexity of OFDMA resource allocation.