Mobile Underwater Sensor Networks Research Articles

Coordinated target localization and tracking with node scheduling for a network of autonomous underwater vehicles

Underwater mobile sensor networks (UMSNs) have the advantages of large area coverage, flexible network structure, and good local resolution. Particularly, spatial diversity can be exploited through node mobility to get more target information. To take those advantages in the context of regional cooperative target localization and tracking, a joint node scheduling and acoustic model fusion method is proposed for an UMSN consisting of multiple autonomous underwater vehicles (AUVs). First, a target tracking algorithm framework based on the random finite set theory is established. To take the acoustic environment into account, the a priori acoustic field and target distribution information are combined to evaluate the detection probability. A path-planning scheme with node scheduling is then developed based on the information gain to optimize the detection performance. To achieve effective node scheduling, three reward functions with different information gains respectively derived from the Rényi divergence and Fisher information matrix are proposed and compared. The rationale and the performance of the developed method are verified via simulations. A simplified version of the approach is also tested in field experiments with three AUVs, verifying the effectiveness of node scheduling in a realistic scenario.

Self-Organized Ad Hoc Mobile (SOAM) Underwater Sensor Networks

The need of underwater wireless sensor networks (UWSNs) having mobile sensor nodes has been there for a long time in form of underwater warfare or explorations by autonomous underwater vehicles (AUVs) or remote unmanned vehicles (ROVs). There are very few protocols for ad hoc mobile UWSNs (AMUWSNs). Designing a protocol for AMUWSN is quite challenging because of continuous random movement of the sensor nodes. In addition to random movement, the challenges to design a routing protocol for AMUWSN are more demanding than terrestrial ad hoc networks due to acoustic communications, which has large propagation delay in water. In this article, we present a self-organized ad hoc mobile (SOAM) routing protocol for AMUWSN. The sensor nodes may need to communicate with each other to the gateway (GW). The protocol, which we also refer to as SOAM, is a reactive, self-configuring, and self-organizing cluster-based routing protocol that uses received signal strength (RSS) for distance estimation. A beacon (BCN) packet will be sent by the GW, which will traverse through all the cluster heads (CHs) to form forwarding paths between the GW and the CHs. The ordinary sensor nodes (OSNs) will select the CHs every time they intend to forward a packet based on the BCN and they will receive from CHs. The formation of the forwarding path between the GW and the CHs and the selection CHs by OSN is explained in <xref ref-type="sec" rid="sec4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Section IV</xref> .

An energy-balanced head nodes selection scheme for underwater mobile sensor networks

Underwater sensor networks system is a promising technology for smart ocean monitoring applications. To address the imbalance problem of network overhead and limited energy of underwater sensor nodes, this paper presents a CH–SH Selection and Sink Path-planning (CSSP) scheme to collect vast amount of data from heterogeneous sensor nodes. The scheme firstly establishes a three-layer network structure model for underwater mobile sensor networks (UMSN) based on multi-mode communication mechanism and provides energy-balanced head nodes (cluster head and sub-cluster head nodes) selection algorithm based on particle swarm iterative optimization. Then, the optimal global-path-plan of mobile sink is proposed to visit all the head nodes to collect data, reduce the multi-hop underwater acoustic transmission distance of relay nodes, and avoid the energy hole problem. Lastly, the upper-layer multi-hop network of UMSN is designed to remotely control local-path-plan over mobile sink, in order to implement joint planning of global and local paths of mobile sink. Simulation results verified that the proposed CSSP scheme outperformed 11%, 16% and 22% over three typical protocols in terms of nodes energy consumption, CSSP was 9%, 12% and 19% lower than three typical protocols in terms of SD of energy consumption, packet delivery ratio of CSSP was 8%, 10% and 12% higher than three typical protocols. The scheme could significantly balance energy and reduce packet loss rate.

An efficient self‐deployment methodology for maximized coverage of mobile underwater sensor networks

SummaryA well‐optimized and well‐performed communication network protocol is necessary to build successful underwater acoustic sensor networks (UWASNs). But for wired and wireless communication, medium access control (MAC) has a great effect on network performance and optimization. But unlike land‐based MAC protocols, underwater MAC protocols come with various challenges and issues like high propagation delay, limited bandwidth for communication signals, large attenuation in network signals, and the high noise level in signals. It is very challenging to build a well‐optimized underwater MAC protocol. Also, in UWASN, sensor nodes are generally divided into sub‐network parts to reduce the propagation delay of data signals. But this creates the problem of non‐uniform traffic load in sensor nodes. So, considering these issues, dynamic hold time MAC (DHT‐MAC) protocol is proposed here. In this protocol, depending on the distance from the central node, sensor nodes are divided into two sub‐network zones (parent node and child node). Depending on the traffic load and propagation delay, the child nodes can change their respective parent nodes dynamically. Advantage of the proposed method is that, if any of the parent nodes stops working, the child node will connect to the nearest parent node. When collecting the data signals, it has been observed that child nodes have a light traffic load compared to parent nodes. So dynamic cooperative transmission MAC (DCT‐MAC) protocol which is a contention‐based MAC protocol has been used in child nodes and as parent nodes have high traffic load, reservation‐based MAC protocol has been used.

AquaE-lite Hybrid-Solar-Cell Receiver-Modality for Energy-Autonomous Terrestrial and Underwater Internet-of-Things

Our goal is to develop an energy-autonomous solar cell receiver that can be integrated with a variety of smart devices to implement the Internet of Things in next-generation applications. This paper details efforts to develop such a prototype, called AquaE-lite. Owing to the capability of detecting low-intensity optical signals, 20-m and 30-m long-distance lighting and optical wireless communication with data rates of 1.6 Mbit/s and 1.2 Mbit/s have been achieved on a laboratory testbed, respectively. Moreover, field trials on an outdoor solar cell testbed and in the turbid water of a harbor by the Red Sea have been conducted. Under bright sunlight, energy autonomy and 1.2-Mbit/s optical wireless communication over a transmission distance of 15 m have been implemented, which demonstrated that AquaE-lite with an elaborate receiver circuit has excellent performance in energy harvesting and resistance to background noise. In a more challenging underwater environment, 1.2-Mbit/s signals were successfully received over a transmission distance of 2 m. It indicates that energy-autonomous AquaE-lite with large detection area has promising prospects in future underwater mobile sensor networks to significantly relieve the requirement of pointing, acquisition and tracking while resolving the energy issues.

Energy efficiency maximization algorithm for underwater Mobile sensor networks

Modern Underwater Wireless Sensor Networks (UWSN) would provide big administrations with numerous underwater surveying and technical applications, working in the unstable submerged deep-water conditions. A huge obstacle in these networks is the lifetime limit. The submerged correspondence frameworks mostly employ acoustic communication today. Acoustic interchange communication offers longer ranges that are yet limited by three variables: restricted and subordinate data transmission, time-differing multi-way engendering and low speed of sound. In this paper, an AUV (Autonomous Underwater Vehicle)-assisted acoustic correspondence convention, specifically Energy Efficiency Maximization Algorithm (EEMA) has been proposed to minimize the energy consumption. Underwater sensor networks depend on the hub ceaseless operation, the restricted correspondence transmission capacity and the hub lifetime, which entails difficulties in the operation of USWN. The proposed system will enhance the lifetime by lessening the number of bounces amid sensor transmissions, which fundamentally lessens time utilization and lifetime. Dynamic AUV ways and dynamic gateway assignments will enhance lifetime – proficiency balance proportion in the submerged system. To decrease the system energy utilization with an acceptable conveyance proportion is recommended. The Experimental results show that the proposed methodology has improved the level of energy compared with related techniques.

Multi-AUV Aided Cooperative 3D-localization for Underwater Sensor Networks

Background: Effective 3D-localization in mobile underwater sensor networks is still an active research topic. Due to the sparse characteristic of underwater sensor networks, AUVs (Autonomous Underwater Vehicles) with precise positioning abilities will benefit cooperative localization. It has important significance to study accurate localization methods. Methods: In this paper, a cooperative and distributed 3D-localization algorithm for sparse underwater sensor networks is proposed. The proposed algorithm combines with the advantages of both recursive location estimation of reference nodes and the outstanding self-positioning ability of mobile AUV. Moreover, our design utilizes MMSE (Minimum Mean Squared Error) based recursive location estimation method in 2D horizontal plane projected from 3D region and then revises positions of un-localized sensor nodes through multiple measurements of Time of Arrival (ToA) with mobile AUVs. Results: Simulation results verify that the proposed cooperative 3D-localization scheme can improve performance in terms of localization coverage ratio, average localization error and localization confidence level. Conclusion: The research can improve localization accuracy and coverage ratio for whole underwater sensor networks.

A Two-Stage Localization Scheme with Partition Handling for Data Tagging in Underwater Acoustic Sensor Networks.

Knowledge about the geographic coordinates of underwater sensor nodes is of primary importance for many applications and protocols of under water sensor networks (UWSNs) thus making localization of sensor nodes a crucial part of underwater network design. In case of mobile underwater sensor network, location estimation becomes challenging not only due to the need for periodic tracking of nodes, but also due to network partitioning caused by the pseudo-random mobility of nodes. Our proposed technique accomplishes the task of localization in two stages: (1) relative localization of sensor nodes with respect to a reference node at regular intervals during sensing operation. (2) Offline absolute localization of sensor nodes using absolute coordinates of the reference node and relative locations estimated during stage 1. As our protocol deals with mobile underwater sensor networks that may introduce network partitioning, we also propose a partition handling routine to deal with network partitions to achieve high localization coverage. The major design goal of our work is to maximize localization coverage while keeping communication overhead minimum, thus achieving better energy efficiency. Major contributions of this paper are: (1) Two energy efficient relative localization techniques, and (2) A partition handling strategy that ensures localization of partitioned nodes.

ProLo: Localization via Projection for Three-Dimensional Mobile Underwater Sensor Networks.

We study the problem of three-dimensional localization of the underwater mobile sensor networks using only range measurements without GPS devices. This problem is challenging because sensor nodes often drift with unknown water currents. Consequently, the moving direction and speed of a sensor node cannot be predicted. Moreover, the motion devices of the sensor nodes are not accurate in underwater environments. Therefore, we propose an adaptive localization scheme, ProLo, taking these uncertainties into consideration. This scheme applies the rigidity theory and maintains a virtual rigid structure through projection. We have proved the correctness of this three-dimensional localization scheme and also validated it using simulation. The results demonstrate that ProLo is promising for real mobile underwater sensor networks with various noises and errors.

A Cluster Based Localization Scheme with Partition Handling for Mobile Underwater Acoustic Sensor Networks.

Many applications of underwater sensor networks (UWSNs), such as target tracking, reconnaissance and surveillance, and marine life monitoring require information about the geographic locations of the sensed data. This makes the localization of sensor nodes a crucial part of such underwater sensing missions. In the case of mobile UWSNs, the problem becomes challenging, not only due to a need for the periodic tracking of nodes, but also due to network partitioning as a result of the pseudo-random mobility of nodes. In this work, we propose an energy efficient solution for localizing nodes in partitioned networks. Energy consumption is minimized by clustering unlocalized partitioned nodes and allowing only clusterheads to carry out a major part of the localization procedure on behalf of the whole cluster. Moreover, we introduce a retransmission control scheme that reduces energy consumption by controlling unnecessary transmission. The major design goal of our work is to maximize localization coverage while keeping communication overheads at a minimum, thus achieving better energy efficiency. The major contributions of this paper include a clustering technique for localizing partitioned nodes and a retransmission control strategy that reduces unnecessary transmissions.

Topology Control for Energy-Efficient Localization in Mobile Underwater Sensor Networks Using Stackelberg Game

The characteristics of mobile underwater sensor networks (UWSNs), such as low communication bandwidth, large propagation delay, and sparse deployment, pose challenging issues for successful localization of sensor nodes. In addition, sensor nodes in UWSNs are usually powered by batteries whose replacements introduce high cost and complexity. Thus, the critical problem in UWSNs is to enable each sensor node to find enough anchor nodes in order to localize itself, with minimum energy costs. In this paper, an energy-efficient localization algorithm (EELA) is proposed to analyze the decentralized interactions among sensor nodes and anchor nodes. A single-leader-multi-follower Stackelberg game is utilized to formulate the topology control problem of sensor nodes and anchor nodes by exploiting their available communication opportunities. In this game, the sensor node acts as a leader taking into account factors such as “two-hop” anchor nodes and energy consumption, while anchor nodes act as multiple followers, considering their ability to localize sensor nodes and their energy consumption. We prove that both players select best responses and reach a socially optimal Stackelberg-Nash Equilibrium. Simulation results demonstrate that the proposed EELA improves the performance of localization in UWSNs significantly, and in particular, the energy cost of sensor nodes. Compared to the baseline schemes, the energy consumption per node is about 48% lower in EELA, while providing a desirable localization coverage, under reasonable error, and delay.

APE-Sync: An Adaptive Power Efficient Time Synchronization for Mobile Underwater Sensor Networks

Time synchronization is a cooperative work's foundation among underwater sensor networks' nodes; it takes a crucial role in the application and the study of underwater sensor networks. Several time synchronization protocols have been presented for terrestrial radio networks, but they cannot be instantly utilized to real-time underwater sensor networks due to the slow propagation speed of the underwater acoustic signals, the mobility among sensor nodes, and the energy limitation in the underwater wireless sensor networks. In this paper, we propose an adaptive power-efficient time synchronization for mobile underwater sensor networks, called APE-Sync. The proposed scheme takes into account the time-varying clock skew and combines the Doppler-Enhanced synchronization protocol (DE-Sync) and the Kalman filter tracking the clock skew to achieve time synchronization. The proposed scheme also helps in reducing the energy consumption of the nodes by guaranteeing accurate time synchronization. The simulation results are presented, which show that APE-Sync outperforms existent time synchronization schemes in both power efficiency and precision.

SenseVault: A Three-tier Framework for Securing Mobile Underwater Sensor Networks

The unique characteristics of underwater channels, such as the mobility of sensor nodes, require robust and efficient security mechanisms for secure and efficient data collection in mobile underwater sensor networks (UWSNs). In this paper, we propose a novel three-tier framework for securing data collections in mobile UWSNs, called SenseVault. First, to support both the authentication of intra-cluster nodes and the authentication of inter-cluster nodes, we propose a cubic cluster formation approach to adapt to dynamic environments with flexible split and merge operations, and use cryptographic hash functions to derive secret keys for the authentication of nodes moving among the clusters. Second, we design a lightweight node revocation and authentication key update mechanism based on higher-order polynomial. To provide strong resilience against misbehavior of the compromised cluster head, we further introduce a Tripartite Cooperation Update (TCU) scheme by leveraging the cooperation among surface stations, safe neighboring cluster heads, and safe intra-cluster members. Third, we propose a deterministic quantization approach, called Virtual Phase Shift (VPS) for the secure generation of secret keys at the physical layer. Extensive experimental results demonstrate the effectiveness of the proposed framework under different scenarios.

Energy-efficient localization and target tracking via underwater mobile sensor networks

Underwater mobile sensor networks (UMSNs) with free-floating sensors are more suitable for understanding the immense underwater environment. Target tracking, whose performance depends on sensor localization accuracy, is one of the broad applications of UMSNs. However, in UMSNs, sensors move with environmental forces, so their positions change continuously, which poses a challenge on the accuracy of sensor localization and target tracking. We propose a high-accuracy localization with mobility prediction (HLMP) algorithm to acquire relatively accurate sensor location estimates. The HLMP algorithm exploits sensor mobility characteristics and the multi-step Levinson-Durbin algorithm to predict future positions. Furthermore, we present a simultaneous localization and target tracking (SLAT) algorithm to update sensor locations based on measurements during the process of target tracking. Simulation results demonstrate that the HLMP algorithm can improve localization accuracy significantly with low energy consumption and that the SLAT algorithm can further decrease the sensor localization error. In addition, results prove that a better localization accuracy will synchronously improve the target tracking performance.

DE-Sync: A Doppler-Enhanced Time Synchronization for Mobile Underwater Sensor Networks.

Time synchronization is the foundation of cooperative work among nodes of underwater sensor networks; it takes a critical role in the research and application of underwater sensor networks. Although numerous time synchronization protocols have been proposed for terrestrial wireless sensor networks, they cannot be directly applied to underwater sensor networks. This is because most of them typically assume that the propagation delay among sensor nodes is negligible, which is not the case in underwater sensor networks. Time synchronization is mainly affected by a long propagation delay among sensor nodes due to the low propagation speed of acoustic signals. Furthermore, sensor nodes in underwater tend to experience some degree of mobility due to wind or ocean current, or some other nodes are on self-propelled vehicles, such as autonomous underwater vehicles (AUVs). In this paper, we propose a Doppler-enhanced time synchronization scheme for mobile underwater sensor networks, called DE-Sync. Our new scheme considers the effect of the clock skew during the process of estimating the Doppler scale factor and directly substitutes the Doppler scale factor into linear regression to achieve the estimation of the clock skew and offset. Simulation results show that DE-Sync outperforms existing time synchronization protocols in both accuracy and energy efficiency.

Dynamic Collaboration Between Networked Robots and Clouds in Resource-Constrained Environments

Underwater mobile sensor networks such as Autonomous Underwater Vehicles (AUVs) or robots are envisioned to enable applications for oceanographic data collection, environmental and pollution monitoring, offshore exploration, and distributed tactical surveillance. These applications require running compute- and data-intensive algorithms that go beyond the capabilities of the individual AUVs that are involved in a mission. To execute these task-parallel algorithms in resource- and time-constrained environments, dynamic and reliable collaboration between local networked robots (e.g., AUVs) and remote public Clouds is needed. To this end, the heterogeneous sensing, computing, communication, and storage capabilities of local and remote resources are exploited to form a “loosely coupled” mobile Cloud, and a novel resource provisioning engine that dynamically takes decisions on “what” and “where” the tasks should be executed in the mobile Cloud is introduced. Comparison of benefits of collaboration between local and Cloud resources with purely local and centralized approaches are presented through exhaustive computer simulations.

Adaptive Decentralized Control of Mobile Underwater Sensor Networks and Robots for Modeling Underwater Phenomena

Understanding the dynamics of bodies of water and their impact on the global environment requires sensing information over the full volume of water. In this article, we develop a gradient-based decentralized controller that dynamically adjusts the depth of a network of underwater sensors to optimize sensing for computing maximally detailed volumetric models. We prove that the controller converges to a local minimum and show how the controller can be extended to work with hybrid robot and sensor network systems. We implement the controller on an underwater sensor network with depth adjustment capabilities. Through simulations and in-situ experiments, we verify the functionality and performance of the system and algorithm.

DA-Sync: A Doppler-Assisted Time-Synchronization Scheme for Mobile Underwater Sensor Networks

Time synchronization plays a critical role in distributed network systems. In this paper, we investigate the time synchronization problem in the context of underwater sensor networks (UWSNs). Although many time-synchronization protocols have been proposed for terrestrial wireless sensor networks, none of them can be directly applied to UWSNs. This is because most of these protocols do not consider long propagation delays and sensor node mobility, which are important attributes in UWSNs. In addition, UWSNs usually have high requirements in energy efficiency. To solve these new challenges, innovative time synchronization solutions are demanded. In this paper, we propose a pairwise, cross-layer, time-synchronization scheme for mobile underwater sensor networks, called DA-Sync. The scheme proposes a framework to estimate the doppler shift caused by mobility, more precisely through accounting the impact of the skew. To refine the relative velocity estimation, and consequently to enhance the synchronization accuracy, the Kalman filter is employed. Further, the clock skew and offset are calibrated by two runs of linear regression. Simulation results show that DA-Sync outperforms the existing synchronization schemes in both accuracy and energy efficiency.

VAPR: Void-Aware Pressure Routing for Underwater Sensor Networks

Underwater mobile sensor networks have recently been proposed as a way to explore and observe the ocean, providing 4D (space and time) monitoring of underwater environments. We consider a specialized geographic routing problem called pressure routing that directs a packet to any sonobuoy on the surface based on depth information available from on-board pressure gauges. The main challenge of pressure routing in sparse underwater networks has been the efficient handling of 3D voids. In this respect, it was recently proven that the greedy stateless perimeter routing method, very popular in 2D networks, cannot be extended to void recovery in 3D networks. Available heuristics for 3D void recovery require expensive flooding. In this paper, we propose a Void-Aware Pressure Routing (VAPR) protocol that uses sequence number, hop count and depth information embedded in periodic beacons to set up next-hop direction and to build a directional trail to the closest sonobuoy. Using this trail, opportunistic directional forwarding can be efficiently performed even in the presence of voids. The contribution of this paper is twofold: a robust soft-state routing protocol that supports opportunistic directional forwarding; and a new framework to attain loop freedom in static and mobile underwater networks to guarantee packet delivery. Extensive simulation results show that VAPR outperforms existing solutions.

Mobi-Sync: Efficient Time Synchronization for Mobile Underwater Sensor Networks

Time synchronization is an important requirement for many services provided by distributed networks. A lot of time synchronization protocols have been proposed for terrestrial Wireless Sensor Networks (WSNs). However, none of them can be directly applied to Underwater Sensor Networks (UWSNs). A synchronization algorithm for UWSNs must consider additional factors such as long propagation delays from the use of acoustic communication and sensor node mobility. These unique challenges make the accuracy of synchronization procedures for UWSNs even more critical. Time synchronization solutions specifically designed for UWSNs are needed to satisfy these new requirements. This paper proposes Mobi-Sync, a novel time synchronization scheme for mobile underwater sensor networks. Mobi-Sync distinguishes itself from previous approaches for terrestrial WSN by considering spatial correlation among the mobility patterns of neighboring UWSNs nodes. This enables Mobi-Sync to accurately estimate the long dynamic propagation delays. Simulation results show that Mobi-Sync outperforms existing schemes in both accuracy and energy efficiency.