Research On Time Synchronization Protocol For Underwater Sensor Networks

Underwater sensor networks have attracted more and more attention due to their huge application value,in the fields of marine resource monitoring and exploration,military work and disaster prediction.Time synchronization for sensors is quiet important for underwater localization,underwater scheduling mechanism and some MAC protocols.Therefore,time synchronization technology is one of the core technologies in the underwater sensor networks.It is well known that acoustic wave is the medium of information transmission in the water,whereas,the speed of acoustic wave in the water is about 1500m/s which makes the propagation delay very long.Furthermore,the phenomenon of signal attenuation and multipath interference is severe in the underwater communication environment.Therefore,the time synchronization protocol in most terrestrial wireless sensor networks is not suitable for underwater environment.At present,most of the existing time synchronization protocols is not suitable for large-scale underwater networks,however,a lot of marine work is based on lots of sensor nodes,thus study of the time synchronization in long delay large-scale underwater sensor networks is meaningful.I studied three typical underwater sensor networks time synchronization protocols which is TSHL,Tri-Message and DTSHL.TSHL is the first synchronization protocol that considerates the propagation delay and the clock skew.It's synchronization accuracy is high but because of sending large amounts of data it will cost a long period of time and a lot of energy.Tri-Message is a lightweight time synchronization protocol which correct the slave nodes' time by three information interactive between master and slave nodes.Thus,it will cost less time and energy than TSHL.Also,the synchronization accuracy of these two protocols is almost the same.DTSHL is a time synchronization protocol for underwater sensor networks with mobile nodes.Through four information interactive with master node slave nodes can compute the changing rate of propagation delay,and then estimate the propagation delay in time synchronization.Also,I studied the localization scheme LSHL and made a little improvement on it.The result showed that in terms of 20 underwater nodes the time and nodes' energy that was required of the fully broadcast time synchronization protocol the consumption of time and nodes' energy was about 1/5 of Tri-Message.And,the improved localization scheme was more efficient.