Linfeng Liu

A DEPLOYMENT ALGORITHM FOR UNDERWATER SENSOR NETWORKS IN OCEAN ENVIRONMENT

Underwater sensor networks will find many oceanic applications in near future, and the deployment problem in 3D sensor networks has not been paid enough attention at present. In order to maximize the network lifetime, a deployment algorithm (UDA) for underwater sensor networks in ocean environment is proposed. UDA can determine and select the best cluster shape, then partition the space into layers and clusters while maintaining full coverage and full connectivity. In addition, nodes closer to sinks are possible to bear a heavier data-relaying mission. UDA sets different node deployment densities at different layers in response to the potential relay discrepancy. The simulation results suggest UDA can choose the proper cluster shape to get the maximum underwater wireless sensor network lifetime approximately.

Topology control algorithm for underwater wireless sensor networks using GPS-free mobile sensor nodes

Underwater wireless sensor networks (UWSNs) have been developed for underwater applications, such as resource exploration, pollution monitoring, and tactical surveillance. The topology control techniques of UWSNs and terrestrial wireless sensor networks are significantly different because of the particularity of underwater environments and acoustic communication, such as mobility pattern, propagation delay and energy consumption. Due to multifarious factors of underwater environments, node mobility becomes a non-negligible issue. However, GPS may not be feasible because of the limitations of satellite coverage or obstructions in adverse underwater environments. In particular, anchored sensor nodes towed by wires are prone to offset around their static positions, causing each node to move within a spherical crown surface (spherical crown mobility pattern). Nevertheless, most previous studies have not focused on this specific mobility pattern. In the current paper, a mobility model for UWSNs nodes is constructed, and three representative topology control objectives are attained. A distributed radius determination algorithm is designed for the mobility-based topology control problem. Results of theoretic analysis prove that the proposed algorithm is convergent, and it has preferable approximate ratios and polynomial complexity. Performance of the algorithm is analyzed through simulation experiments, which indicate a well-constructed topology. Every objective can still be upgraded without the dynamic location information of mobile nodes.

A Complex Network Approach to Topology Control Problem in Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UASNs) have been developed for a set of underwater applications, including resource exploration, pollution monitoring, and tactical surveillance. Topology control techniques of UASNs are significantly different from those of terrestrial wireless sensor networks, due to the properties of underwater environments and acoustic communications. This research begins with a scale-free network model for calculating edge probability, which is used to generate initial topology randomly. Subsequently, a topology control strategy based on complex network theory (TCSCN) is put forward to construct a double clustering structure, where there are two kinds of cluster-heads to ensure connectivity and coverage, respectively. The performance of TCSCN is analyzed through simulation experiments that indicate a well-constructed topology, where (1,ξ)-Coverage and (1,ζ )-Connectivity can be achieved while optimizing energy consumption and propagation delay as much as possible.

A QoS-Based Topology Control Algorithm for Underwater Wireless Sensor Networks

The topology control techniques of underwater wireless sensor networks and terrestrial wireless sensor networks are significantly different because of the particularity of underwater environments and acoustic communication. In this paper, an underwater wireless sensor network model was constructed, and six universal topology control objectives were concluded. The QoS topology control problem was mapped into an ordinal potential game model, and a distributed strategy adjustment algorithm for nodes was designed accordingly. The strategy vector resulting from the algorithm converges to the Nash equilibrium; minor complexity and preferable approximate ratios can be represented by the algorithm as well. The performance of the algorithm was analyzed through simulation experiments which indicate a well-constructed topology. Every objective was upgraded when model parameters were set suitable.

Topology control models and solutions for signal irregularity in mobile underwater wireless sensor networks

Underwater wireless sensor networks (UWSNs) have been developed for a set of underwater applications, including resource exploration, pollution monitoring, and tactical surveillance. The topology control techniques of UWSNs and terrestrial wireless sensor networks are significantly different because of the particularity of underwater environments and acoustic communication. In underwater environments, signal irregularity phenomenon affecting network protocols is more prone to exhibit, and anchored sensor nodes towed by wires move within a spherical crown surface randomly. However, most previous efforts about topology control either have not been made on signal irregularity in mobile underwater wireless sensor networks, or the proposed irregularity models are too idealistic to reflect reality. The current study constructs a more authentic signal irregularity model, which can be degenerated into a variety of special cases easily, and three representative topology control objectives (( K S , β)-Coverage, ( K C , α)-Connectivity, and efficient consumption) are concluded. A topology control algorithm for signal irregularity (TCASI) is designed for this topology control problem. The results prove the convergence of TCASI and polynomial complexity as well. The performance of the algorithm is analyzed through simulation experiments that indicate a well-constructed topology, where (KS, β)-Coverage and (KC, α)-Connectivity can be achieved while optimizing energy consumption as much as possible.

A multi-hop localization algorithm in underwater wireless sensor networks

In mobile underwater environment, underwater wireless sensor networks (UWSNs) keep moving and dispersing due to water flowing and aquatic creatures touching, and thus some isolated nodes appear. This type of isolated nodes cannot obtain enough anchor nodes in their communication range, which makes self-localizations disabled. In order to solve this problem, a multi-hop localization scheme is proposed in this paper. Firstly, ordinary nodes between anchors and unknown nodes are set as routers to find the shortest paths by a greedy approach; secondly, the shortest paths are approximately fitted into a straight distance between two nodes; finally, the positions of unknown nodes can be calculated by trilateration. The proposed algorithm is simulated and is compared with other algorithms in terms of localization error, and the results are proven preferable.

On Exploring Data Forwarding Problem in Opportunistic Underwater Sensor Network Using Mobility-Irregular Vehicles

Data forwarding techniques in opportunistic underwater sensor networks (OUSNs) are significantly different from those of wireless sensor networks or delay-tolerant networks, due to the irregular mobility of nodes. To this end, an Opportunistic Forwarding Algorithm based on Irregular Mobility (OFAIM) is proposed hereby, which intermittently computes and chooses the appropriate paths of an end-to-end data session. In OFAIM, the contacting probabilities among nodes are estimated according to current nodes statuses. OFAIM is particularly suitable for heterogeneous networks composed of nodes with different communication and movement ranges. The performance of OFAIM is also analyzed through simulations, which indicate that OFAIM achieves a satisfactory delivery ratio (larger than 67% at the worst case) within a limited duration, while the message cost is largely reduced (the number of forwarding copies at every slot is restricted to two or three) compared with epidemic forwarding, motion vector forwarding, and predict and spread forwarding.

Multihops fitting approach for node localization in underwater wireless sensor networks

Nodes in underwater wireless sensor networks (UWSNs) keep moving and dispersing due to force of water flow and aquatic creatures touching, and thus some isolated unknown nodes emerge. This type of isolated unknown nodes cannot directly communicate with enough beacons in their neighborhoods, which makes localizations for them disabled or the localization error unbearable. To this end, a multihops fitting localization approach is proposed in this paper. Firstly, some intermediate nodes between beacons and unknown nodes are set as routers to construct paths via a greedy method; then, the multihop paths are approximately fitted into straight lines; finally, the positions of unknown nodes can be estimated by trilateration. The proposed algorithm is analyzed and simulated in terms of localization error and error variance, and the results are proven preferable.

Multisensor Data Fusion for Water Quality Evaluation Using Dempster-Shafer Evidence Theory

A multisensor data fusion approach for water quality evaluation using Dempster-Shafer evidence theory is presented. To evaluate water quality, each sensor measurement is considered as a piece of evidence. Based on the water quality parameters measured by sensor node, the mass function of water quality class is calculated. Evidence from each sensor is given a reliability discounting and then combined with the others by D-S rule. According to the decision rule which uses the fusion mass function values, the class of water quality can be determined. Finally, experiments are given to demonstrate that the proposed approach can evaluate water quality from uncertain sensor data and improve evaluation performance.

A Wireless Sensor Network Architecture for Diversiform Deployment Environments

Network architecture is the foundation of network system. Wireless sensor networks (WSN) are always concentrated some key technologies under specific applications, and some prototype systems are developed according to specific applications of environments, but the research on WSN architecture is relatively weak currently. WSN is a highly complex distributed system, the defects in traditional WSN architectures are firstly studied, then the typical requirement objectives of WSN are acquired by analysis, and a set of design principles for WSN model is concluded. Because the WSN is mostly intended for variable and inhospitable environments, where persistent and continuous energy supply is lacking, the environment adaptive and energy efficient capabilities are integrant for WSN architecture. According with other objectives scalability and service-customized, an environment adaptive, energy efficient, hierarchical structure and sub-facets functions architecture model of WSN (EAWNA) is proposed. Furthermore, the design methods, general characteristics and functions of every lay or every module are described and discussed. At last, from the abstract levels of component framework, EAWNA is described formally besides all component layers entities are defined. EAWNA has not only the double characteristics: environment adaptive and energy efficient, but also has the traits such as multi-dimensional scalability, service-customized, and cross-layer interaction. EAWNA model can supply a theoretical framework and a kind of unified description method for diversified protocols in WSN.