Exploiting Social Network Characteristics for Efficient Routing in Ocean Vessel Ad Hoc Networks Communication in the ocean vessel wireless ad hoc networks which currently rely on shorebased cellular stations, is expensive and can only be used near the coast. It is a big challenge for ocean vessels to achieve economic and largescope communications, due to the rare encounter opportunities and highly dynamic vessel mobilities. Previous works on routing algorithms for vessel wireless ad hoc networks did not take into account the social characteristics of ocean vessel networks. According to our empirical study on real trajectories of more than 7,000 ocean vessel recorded by the Vessel Monitoring System (VMS), we have made innovative observations. Firstly, there exist stable social connections among those vessels frequently encounter with each other. Moreover, stable social communities can be discovered for those ocean vessels with longterm connections. Inspired by the significant observations, two unicast routing approaches based on social society characteristics are proposed for wireless ocean vessel ad hoc networks, i.e., familiarity based routing (FBR) and community based routing (CBR). The key metric for message forwarding decision making of FBR is the expected multihop encounter probability of the potential forwarder with the message receiver. The expected multihop encounter probability is derived from the raised definition of familiarity, which measures the connection strengths between vessels. The proposed CBR forwards messages based on the metric of intercommunity betweenness centrality of a potential forwarder, which describes the bridge capability between two communities. Extensive tracedriven simulations based on real ocean vessel trajectories are performed and the evaluation results demonstrate the significant performance achieved by the proposed approaches. The transmission cost has been largely reduced with comparable delivery ratio and delay.

A Subregional MonitoringOriented Topology Control Strategy in UWSNs Underwater wireless sensor networks (UWSNs) have become crucial for many different applications, such as marine pastures, which needs stratified aquaculture according to the habitat and range of activities of marine organisms. This type of application poses a significant challenge to network topology because strengthening the monitoring of the living conditions and collecting underwater data on organisms in different regions is necessary. In this paper, a new concept of subregional monitoring is proposed, and subregions with frequent activities of marine organisms are taken as the key monitoring areas, i.e., the areas of interest (AOIs). Then, SFRG, an energybalanced and robust topology based on scalefree network and rigid graph theory, is proposed to strengthen the monitoring of the AOIs. The topology of a rigid graph is constructed in AOI, and the entire network is scalefree network with powerlaw degree distribution, when the rigid graph is regarded as a node. Furthermore, a transmission algorithm based on the SFRG is suggested to prolong the network lifetime. The algorithm guarantees that 90% of the received packets are from the AOIs. The simulation results demonstrate that the SFRG effectively prolongs the network lifetime and improves the network robustness, which provides a strong support in strengthening the monitoring of AOIs and balancing the energy consumption.