Time Synchronization of Underwater Wireless Sensor Networks

Large propagation delay and node movement are considered to be two significant attributes that differentiate an underwater wireless sensor network (UWSN) from a ground wireless sensor network (WSN). The acoustic-based media dramatically narrows the bandwidth of communication of UWSN due to slow propagation speed. An underwater sensor node can move out of and into another node’s range frequently in an unstable underwater environment. In this chapter, the author will elaborate the study of investigating the property and the impact of these two attributes of UWSN. Then, this chapter will describe a prototype of a synchronization protocol which is suitable for UWSN considering the effects of both propagation delay and movement. With its protocol algorithm, no time synchronization is necessary if the time stamps of the received data packets are within the tolerance. In this fashion, the network underwater does not need to perform global time synchronizations frequently nor periodically, which reduces the time used to synchronize clocks among sensor nodes. Finally, this chapter will discuss simulation results which show the time cost for synchronization is linear to the data packets exchanged with this protocol.