Energy-Balanced Unequal Layering Clustering in Underwater Acoustic Sensor Networks

Nowadays, with the recent advances of wireless underwater communication and acoustic sensor devices technology, we are witnessing a surge in the exploration and exploitation of the ocean’s abundant natural resources. Accordingly, to fulfill the requirements of the exploration of the ocean, researchers have focused their work toward the design of methods and algorithms for the underwater acoustic sensor networks (UASNs). Although considerable research effort has been devoted to the development of a variety of UASN-based applications, very limited work has addressed the algorithmic design and analysis for UASN. To this end, we propose to provide a comprehensive design, development, and analysis of algorithms and protocols for UASNs. We discuss each of the fundamental UASN building blocks, such as (i) underwater acoustic communication channel modeling, (ii) sustainable coverage and target detection, (iii) Medium Access Control (MAC-layer design and time synchronization, (iv) localization algorithms design, and (v) underwater routing protocol. Then, we illustrate the different protocols from each category and compare their benefits and drawbacks. Finally, we discuss a few potential directions for future research related to the design of future generations of UASNs.

Underwater acoustic sensor networks (UASNs) have become a popular research topic, with research challenges focused on underwater communication techniques. By incorporating long end-to-end latency, high energy consumption and dynamic network topology in UASNs, many intelligent routing protocols have been proposed to solve the problem. However, shortcomings still exist, and comprehensive routing protocols are urgently needed. In this paper, we propose an adaptive Deep Q-Network-based energy- and latency-aware routing protocol (DQELR) to prolong network lifetimes in UASNs. In the DQELR, a Deep Q-Network algorithm with both off-policy and on-policy methods is adopted to make globally optimal routing decisions. Based on both the energy and depth states of nodes at different communication stages, nodes with the maximum Q-value can be selected as forwarders adaptively considering both energy and latency. A hybrid of the broadcast and unicast communication mechanisms is also designed to reduce network overhead. In addition, network topology changes can be addressed through an on-policy method that makes a new routing decision when the current route becomes corrupted. With less energy consumption and strict latency limitations, the DQELR can prolong network lifetimes in UASNs. Simulation results show that the DQELR can achieve a superior network lifetime with better latency and energy efficiency performances relative to other general schemes applied in UASNs.

A time synchronization algorithm for hidden mobile node (HMB), which can only receive signals, joining an existing synchronized underwater Acoustic (UWA) sensor network (UASN) is proposed. In order to obtain the location of the HMB or communicate with it, the local time of the HMB should synchronize with the UASN. However, the propagation delay in UWA channels could not be ignored compared to electromagnetic radio channels. In the proposed algorithm, the HMB do the uniform linear motion in a certain direction, and the clock drift could be solved. After the derivation of the solution equations and the MATLAB simulation, it was proved that this algorithm is useful to reduce time error and improve the node localization accuracy in specific underwater circumstance.

Underwater acoustic sensor network with terrestrial wireless sensor network characteristics distinct, underwater acoustic sensor network uses sound waves to be transmitted, resulting in underwater network with high propagation delay characteristics, if applied directly to land-based routing mechanism water network, will give rise to a number of problems. Therefore, this paper designed for underwater network environment routing protocols, thereby reducing the underwater acoustic sensor network to send packets to the end-to-end delay and for collaborative work on underwater acoustic transmission sensor network, encountered the challenges of high propagation delay characteristics discussed. This paper presents the work last sleep period, coordinated and collaborative collection of neighbor information transfer protocol. Through simulation, this paper found that the proposed routing protocol SCTP, the delay in the point to point, network transmission performance and power consumption of a significant improvement in performance.Keywordscooperative transmissionroutingenergy holeunderwater sensor networks

The properties of underwater acoustic channel are quite different from those of terrestrial wireless sensor networks, which brings many challenges to design an efficient media access control (MAC) protocol for underwater acoustic sensor networks (UWASNs). In order to overcome the long propagation delay and the funneling effect of UWASNs, a MAC protocol, named path-oriented code assignment (POCA) CDMA MAC (POCA-CDMA-MAC) protocol, is proposed in the paper. In the proposed protocol, a round-robin method and the CDMA technology are used to make the sink receive packets from multiple neighbors at the same time. Unlike other CDMA-based protocols using the transmitter-oriented code assignment (TOCA) or the receiver-oriented code assignment (ROCA), the POCA is used in the CDMA technology. Since the number of the path is much less than the number of nodes, the length of the spreading code used in systems with POCA is greatly shorter than those of the spreading code used in systems with TOCA or ROCA. Simulation results show that compared to existing MAC protocols for UWASNs, the proposed MAC protocol achieves a higher throughput, and a lower end-to-end delay.

The underwater acoustic sensor network (UASN) is a specific deployment of Internet-of-Things (IoT) technology in the underwater environment, since energy constraints limit the lifetime of UASNs, effectively balancing the energy consumption of acoustic sensor nodes in UASNs is important to maximize the amount of information collected and to prolong the network lifetime. Node clustering is widely regarded as one of the most important energy-efficient schemes for UASNs. However, most existing clustering schemes focus on the cooperation-based election of cluster headers (CHs) in a centralized manner. Due to the limited energy capacity, acoustic sensor nodes are designed to save their own energy, hindering the realization of such cooperation. To address this issue in this article, game theory is applied to UASNs to balance network energy consumption and model acoustic sensor nodes as rational and selfish players. Specifically, a game-theory-based clustering (GTC) scheme for UASNs is developed. In the CH election phase, each node makes a decision in pursuit of a greater payoff based on the Nash equilibrium. An incentive mechanism is invented to induce nodes to make more beneficial collective decisions and plays a role in the CH rotation to effectively balance the energy consumption. Meanwhile, the network area is divided into nonuniform sectors to ensure the energy consumption of the CH is more evenly distributed. Simulation results show that the proposed GTC scheme can effectively balance network energy consumption and extend the network lifetime.

Underwater acoustic sensor networks (UASN) based on the advances in underwater data collection and observing systems may play an important role in oceanographic research. UASN typically comprises of sensor nodes that are deployed in sufficiently large numbers for data collection, monitoring and surveillance, where sensor nodes are also energy limited without easy way to replenish power unfortunately. Due to severely limited energy constraints of nodes and poor transmission feature in the harsh oceanic environment, how to conserve energy while maintaining network coverage has been one of the most difficult problems. As one special kind of UASN, Buoys based sensor networks (BSN) proposed by ourselves comprises a mass of buoy-based vertical detection chains, which are regard as surface buoy nodes in one planar sea level. Compared with UASN, BSN can extend coverage distance and improve wireless transmission rate, therefore, it is one more promising method to perform oceanic three-dimensional exploration. This paper investigates the utility of a Connected Dominating Set (CDS) based coverage control algorithm for buoys based sensor networks. Traditional CDS-based algorithm maintains a connected virtual backbone of awaking nodes to enable necessary information delivery. Surface buoy nodes belonging to CDS virtual backbone remain awake until the next new round, whereas non-CDS buoy nodes go to low-powered sleep mode. However, how to maintain network coverage of BSN has not been considered. Surface buoy nodes are more sparsely deployed because of their much higher prices, therefore, wireless communication links are prone to break and regions of interest (ROI) are prone to blind monitoring since lack of accurate placement. This paper used CDS-based coverage control algorithm to decide buoys scheduling policy so as to guarantee network reliability and robustness.

The autonomous underwater vehicle (AUV) aided mobile data collection is an effective method for reducing the energy consumption of the underwater acoustic (UWA) sensor networks. In this paper, we propose an AUV-aided path-planning scheme using cooperative transmission mechanism for a medium-scale UWA sensor network. In the proposed scheme, we analyze not only the energy consumption, but also the task duration and path-planning cost comprehensively for practical applications. We analyze four different path-planning schemes in terms of energy consumption of UWA sensor nodes and travel cost of AUV. The simulation results show that the lawn mower path-planning scheme has lower energy consumption of UWA sensor networks. But the circle path-planning scheme has lower working time and path energy consumption of AUV. Therefore, in view of different needs, we should make a comprehensive selection.

In Underwater Acoustic Sensor Network (UASN), routing and propagation delay is affected in each node by various water column environmental factors such as temperature, salinity, depth, gases, divergent and rotational wind. High sound velocity increases the transmission rate of the packets and the high dissolved gases in the water increases the sound velocity. High dissolved gases and sound velocity environment in the water column provides high transmission rates among UASN nodes. In this paper, the Modified Mackenzie Sound equation calculates the sound velocity in each node for energy-efficient routing. Golden Ratio Optimization Method (GROM) and Gaussian Process Regression (GPR) predicts propagation delay of each node in UASN using temperature, salinity, depth, dissolved gases dataset. Dissolved gases, rotational and divergent winds, and stress plays a major problem in UASN, which increases propagation delay and energy consumption. Predicted values from GPR and GROM leads to node selection and Corona Virus Optimization Algorithm (CVOA) routing is performed on the selected nodes. The proposed GPR-CVOA and GROM-CVOA algorithm solves the problem of propagation delay and consumes less energy in nodes, based on appropriate tolerant delays in transmitting packets among nodes during high rotational and divergent winds. From simulation results, CVOA Algorithm performs better than traditional DF and LION algorithms.

As an extension of wireless sensor network in underwater environment, underwater acoustic sensor networks (UASNs) have caused widespread concern of academia. In UASNs, the efficiency and reliability of data transmission are very challenging due to the complex underwater environment in variety of ocean applications, such as monitoring abnormal submarine oil pipelines. Motivated by the importance of energy consumption in many deployments of UASNs, we therefore propose an energy-efficient data transmission scheme in this paper, called energy-efficiency grid routing based on 3D cubes (EGRCs) in UASNs, considering the complex properties of underwater medium, such as 3D changing topology, high propagation delay, node mobility and density, as well as rotation mechanism of cluster-head nodes. First, the whole network model is regarded as a 3D cube from the grid point of view, and this 3D cube is divided into many small cubes, where a cube is seen as a cluster. In the 3D cube, all the sensor nodes are duty-cycled in the media access control layer. Second, in order to make energy efficient and extend network lifetime, the EGRC shapes an energy consumption model considering residual energy and location of sensor nodes to select the optimal cluster-heads. Moreover, the EGRC utilizes residual energy, locations, and end-to-end delay for searching for the next-hop node to maintain the reliability of data transmission. Simulation validations of the proposed algorithm are carried out to show the effectiveness of EGRC, which performs better than the representative algorithms in terms of energy efficiency, reliability, and end-to-end delay.

Underwater acoustic sensor network is an important part of the ocean Internet of Things. For the problem that the energy of sensor nodes is limited and the nodes are prone to random failure due to the complex ocean environment, this paper presents an energy saving and fault tolerant topology for underwater acoustic sensor network. Firstly, the energy consumption of underwater acoustic sensor network is analyzed based on the characteristics of water acoustic communication. And the communication radius of each node is analyzed by considered the underwater communication delay and the node energy. Secondly, the classic scale-free structure which can tolerant random node failure is introduced into the underwater acoustic sensor network. Then the fault topology of underwater acoustic sensor network is generated. Finally, the performance of the generated underwater acoustic sensor network topology is verified by simulation experiments. The experimental results show that the generated topology has the scale-free property which can effectively tolerate the failure of random nodes and can prolong the network lifetime.

In recent years, a typical representation of the next-generation Internet architecture, named data networking (NDN), and a critical form of the underwater Internet of Things (IoT), underwater acoustic sensor networks (UASNs), have attracted widespread attention in academia. Meanwhile, since the battery energy of the sensor node is limited and the battery is difficult to replace or recharge in underwater environments, extending the networks' lifetime has become a key issue in UASNs. In this paper, we try to deploy a UASN on NDN architecture and explore the energy consumption of the NDN-based UASN under shallow water and deep water conditions based on the relay network topology. A simulation is carried out to compare the delay performance of NDN-based and IP-based UASNs and validate the result. It is believed that the study could provide a theoretical criterion for the selection of the direct or relay path to optimize energy consumption in the future deployment of NDN-based UASNs.

Constrained surface-level gateway placement for underwater acoustic wireless sensor networks

Underwater acoustic wireless sensor networks are crucial for underwater monitoring, underwater development and national defense applications. In order to solve the problems of long propagation, high mobility, limited bandwidth, multipath and Doppler effect in underwater acoustic sensor networks, this paper proposes an energy-efficient and reliable underwater routing protocol. This protocol leverages the link quality information of each node for data transmission. When selecting the optimal relay, it evaluates not only the transmission success rate between the node and the next-hop node but also considers the link quality of the next-hop node and its neighboring nodes. This approach effectively reduces the likelihood of nodes encountering communication gaps. Moreover, the protocol incorporates the concept of relay node persistence, significantly reducing the frequency of handshakes between nodes and conserving energy. Ultimately, the efficacy of EERP was verified through MATLAB simulation analysis.

Underwater communication uses sonar waves instead of electromagnetic waves, results in low data rate as compared to ground communication. The constraints of underwater communication are large propagation delay, low bandwidth and low data rate results in degradation efficiency. As ultra-wide band (UWB) signals have high penetration capability through the obstacle, so underwater communication channel can be modified as UWB Saleh-Valenzuela (S-V) model. Here, an underwater positioning scheme is proposed with the use of UWB channel. Theoretical performance analysis of positioning scheme in underwater acoustic sensor network is simulated using MATLAB. The applications of this technique can be applied to various underwater acoustic (UWA) sensor networks (SNs).