Abstract: We studied several fundamental key issues of localization in underwater sensor networks(UWSNs) , then proposed an multi-frequency active localization method ( MFALM) based on the time difference on arrival (TDOA) for UWSNs. The method, which is event driven, divides all the nodes into three groups: buoy nodes, relay nodes, and ordinary nodes. To guarantee the low-power and effectiveness of communication, the nodes communicate with each other by two types of frequencies ; low frequency and high frequency, the former is used in long distance communication, while the latter is used in short distance. In addition, package formats for communication between nodes were defined, which make the packages short and can reduce the costs of sensor nodes in localization. Analysis shows that our method, which has the characteristics of event driven, reduced packages and multi-frequency, has low communication cost and can extend the network lifetime.

Key words: Wireless sensor network,Underwater localization, TDoA