Multi-hop Underwater Acoustic Networks Research Articles

Space/Frequency-Division-Based Full-Duplex Data Transmission Method for Multihop Underwater Acoustic Communication Networks

Underwater acoustic communication networks (UACNs) have been widely utilized in recent years because of the growing interest in interactive information in the deep ocean. Compared with traditional radio wireless networks, UACNs are characterized by complex and dynamic 3-D network topology and longer signal propagation delay. Therefore, recent studies on UACNs usually apply dynamic routes in data communication to adapt to complex UACN structure. However, the approaches are hardly adequate for UACN scenarios with high-traffic requirements. This is because dynamic routing methods, such as opportunistic routing, usually require external contention costs to control the routing paths, which leads to decreased network throughput. Accordingly, this article focuses on enabling high-speed acoustic communications for underwater application scenarios with high-traffic requirements, and proposes an underwater data transmission method using the multichannel full-duplex (FD) communication technique. The proposed method applies the underwater orthogonal frequency division multiple access (OFDM) technique, that uses collision-free channels to relay data in multihop routes for simultaneous transmission and reception. Unlike the traditional communication methods of UACNs with dynamic routing, the proposed one uses static routes when transporting data over hop-by-hop paths to achieve stable and uninterrupted FD communication. The approach also includes a directional forwarding-based route request method and an elimination-based channel evaluation proposal, which purpose to reduce the overheads from exploring routes and enable collision-free FD communications. The performance analysis of the proposed method is under simulated conditions of high-traffic UACN scenarios, and the results show that it has superior performance compare to the classical underwater data transmission methods.

Underwater Acoustic Sensor Network Data Optimization with Enhanced Void Avoidance and Routing Protocol

Deployment of a multi-hop underwater acoustic sensor network (UASN) in a larger region presents innovative challenges in reliable data communications and survivability of network because of the limited underwater interaction range or bandwidth and the limited energy of underwater sensor nodes. UASNs are becoming very significant in ocean exploration applications, like underwater device maintenance, ocean monitoring, ocean resource management, pollution detection, and so on. To overcome those difficulties and attains the purpose of maximizing data delivery ratio and minimizing energy consumption of underwater SNs, routing becomes necessary. In UASN, as the routing protocol will guarantee effective and reliable data communication from the source node to the destination, routing protocol model was an alluring topic for researchers. There were several routing techniques devised recently. This manuscript presents an underwater acoustic sensor network data optimization with enhanced void avoidance and routing (UASN-DAEVAR) protocol. The presented UASN-DAEVAR technique aims to present an effective data transmission process using proficient routing protocols. In the presented UASN-DAEVAR technique, a red deer algorithm (RDA) is employed in this study. In addition, the UASN-DAEVAR technique computes optimal routes in the UASN. To exhibit the effectual results of the UASN-DAEVAR technique, a wide spread experimental analysis is made. The experimental outcomes represented the enhancements of the UASN-DAEVAR model.

Energy-Efficient Markov-Based Lifetime Enhancement Approach for Underwater Acoustic Sensor Network

The multihop underwater acoustic sensor network (M-UASN) collects oceanographic data at different depths. Due to the harsh underwater environment, the route is a major research problem. In this article, the routing path from source to sink is adapted by the vector-based forwarding (VBF) protocol. In VBF, based on the vector size, the packets are transmitted within the pipe from hop to hop. The limitation is that every node inside the pipe vector receives the same packets. That results in a waste of battery energy and, in turn, reduces the lifetime of the acoustic node. To enhance, in this article, it is divided into two parts. The first part is that the first hop nodes from the source are optimally divided into subsets such that all the second hop nodes will receive packets from each subset. This optimal route cover subset is identified with an evolutionary memetic algorithm. The election of subset is done through a voltage reference model, and the battery voltage is modeled mathematically and the role of the nodes is given based on the voltage profile and Markov probability approach. This method enhances the lifetime of the underwater acoustic network when compared with the VBF algorithm. The proposed model also provides improved throughput and equal load sharing. The results are compared with VBF, quality-of-service aware evolutionary routing protocol (QERP), and multiobjective optimized opportunistic routing (BMOOR).

Optimizing the number of relays for energy efficient multi-hop covert underwater acoustic cooperative networks

Multi-hop underwater acoustic (UWA) cooperative networks can effectively reduce the energy consumption of the system, yet the covertness of communication is also greatly reduced since a spatial diversity gain can be obtained by both the intended receiver and the intercept detector. In this paper, we investigate how to select the optimal number of relays for multi-hop UWA cooperative networks, by considering both the low probability of detection (PD) and energy consumption. We derive the relationship between PD and the number of relays and then analyze the relationship between energy consumption and the number of relays for the system. To address the joint PD and energy consumption optimal problem, we define the energy consumption rate for multi-hop UWA systems by normalizing the energy consumed in single-hop UWA systems at the same source-to-destination distance. Then, we derive the range number of relays under the given PD and energy consumption rate. Moreover, we construct the objective function and derive the optimal number of relays by jointly addressing PD and the energy consumption rate. Finally, we simulate and analyze the impact of several parameters on PD and energy consumption, including the signal-to-noise ratio, working distance, position angle of interceptor and data length. The simulation results show that the number of relays for multi-hop covert UWA cooperative networks can take the value between 2 and 6 under a given condition, which can meet the covert communication requirement with a PD < 0.5, while the system energy consumption is relatively low.

Maximizing secrecy rate of an orthogonal frequency division multiplexing‐based multihop underwater acoustic sensor network

AbstractIn this article, we consider an eavesdropping attack on a multihop, underwater acoustic sensor network that consists of M + 1 underwater sensors which report their sensed data via orthogonal frequency division multiplexing (OFDM) scheme to a sink node on the water surface. Furthermore, due to the presence of a passive malicious node in nearby vicinity, the multihop underwater acoustic (UWA) channel between a sensor node and the sink node is prone to eavesdropping attack on each hop. Therefore, the problem at hand is to do (helper/relay) node selection (for data forwarding onto the next hop) as well as power allocation (across the OFDM subcarriers) in a way that the secrecy rate is maximized at each hop. To this end, this problem of node selection and power allocation (NSPA) is formulated as a mixed binary‐integer optimization program, which is then optimally solved via decomposition approach, and by exploiting duality theory along with the Karush‐Kuhn‐Tucker conditions. We also provide a computationally efficient, suboptimal solution to the NSPA problem, where we reformulate it as a mixed‐integer linear program and solve it via decomposition and geometric approach. Moreover, when the UWA channel is multipath (and not just line‐of‐sight), we investigate an additional, machine learning‐based approach to solve the NSPA problem. Finally, we compute the computational complexity of all the three proposed schemes (optimal, suboptimal, and learning‐based), and do extensive simulations to compare their performance against each other and against the baseline schemes (which allocate equal power to all the subcarriers and do depth‐based node selection). In a nutshell, this work proposes various (optimal and suboptimal) methods for providing information‐theoretic security at the physical layer of the protocol stack through resource allocation.

Energy Efficiency of Multi-Hop Underwater Acoustic Networks Using Fountain Codes

Ensuring low energy consumption is a crucial issue in underwater communications, since battery replacement may be difficult and expensive in these scenarios. We analyze in this paper the energy consumption of a multi-hop underwater acoustic network (UWAN) employing fountain codes. Moreover, in order to reduce this energy consumption we optimize the modulation order assuming differential phase-shift keying ( $M$ -DPSK), as well as the number of hops. We investigate the required number of fountain-encoded packets for different modulation orders. Our results show that, by optimizing the modulation order, the number of hops and the number of fountain packets, we can obtain important energy savings, especially for long distances. In addition, with the proposed scheme the energy consumption decreases significantly compared to the case without fountain codes, reaching up to 40% of savings.

Time Reversal Based MAC for Multi-Hop Underwater Acoustic Networks

Constrained-energy underwater acoustic nodes are typically connected via a multi-hop underwater acoustic network (MHUAN) to cover a broad marine region. Recently, protocols for efficiently connecting such nodes have received considerable attention. In this paper, we show that the time reversal (TR) process plays an important role in the medium access control (MAC) because of its physical capability to exploit the multi-path energy from the richly scattering underwater environment, as well as to focus the signal energy in both spatial and temporal domains. In MHUANs, with severe multi-path propagation at the physical layer, the active TR process spatially focuses the signals to the location of the intended receiver; this significantly diminishes the interference among parallel links. We propose an active TR-based MAC protocol for MHUANs, with the aim of minimizing collision and maximizing channel utilization simultaneously. Furthermore, by considering the impact of the cross-correlation between different links on the TR-based medium access, we derive the threshold of the link cross-correlation to resolve collision caused by the high cross-correlation between realistic links. We perform simulations using the OPNET and BELLHOP environments, and show that the proposed TR-based MAC results in significantly improved throughput, decreased delay, and reduced data drop ratio in MHUANs.

Software-Defined Underwater Acoustic Modems: Historical Review and the NILUS Approach

Flexible/adaptive acoustic modems that are reprogrammable/reconfigurable at all layers of the communication stack, either by a user or by means of autonomous decisions, are considered as an important enabler for interoperability and cognitive networking in the underwater domain. In this paper, we review the existing literature on software-defined acoustic modems (SDAMs) for underwater communications and networking, considering past and ongoing academic efforts, as well as industrial developments and European collaborations centered on software-defined modem structures and functionalities. We then zoom in on relevant R&D efforts currently taking place in a defense cooperation between The Netherlands and Norway, targeting the design of a software-defined modem for the NILUS MK 2 sensor node. This modem is built using general-purpose (GP) computing architectures running open-source operating system and tools, thereby making a further step toward software-defined open-architecture underwater acoustic modems. The first field tests of the NILUS MK 2 node in multihop underwater acoustic networks are presented, showing satisfactory performance in shallow and open waters.

A Double Rate Localization Algorithm with One Anchor for Multi-Hop Underwater Acoustic Networks.

Localization is a basic issue for underwater acoustic networks (UANs). Currently, most localization algorithms only perform well in one-hop networks or need more anchors which are not suitable for the underwater environment. In this paper, we proposed a double rate localization algorithm with one anchor for multi-hop underwater acoustic networks (DRL). The algorithm firstly presents a double rate scheme which separates the localization procedure into two modes to increase the ranging accuracy in multi-hop UANs while maintaining the transmission rate. Then an optimal selection scheme of reference nodes was proposed to reduce the influence of references’ topology on localization performance. The proposed DRL algorithm can be used in the multi-hop UANs to increase the localization accuracy and reduce the usage of anchor nodes. The simulation and experimental results demonstrated that the proposed DRL algorithm has a better localization performance than the previous algorithms in many aspects such as accuracy and communication cost, and is more suitable to the underwater environment.

Dolphins First: Dolphin-Aware Communications in Multi-Hop Underwater Cognitive Acoustic Networks

Acoustic communication is the most versatile and widely used technology for underwater wireless networks. However, the frequencies used by current acoustic modems are heavily overlapped with the cetacean communication frequencies, where the man-made noise of underwater acoustic communications may have harmful or even fatal impact on those lovely marine mammals, e.g., dolphins. To pursue the environmental friendly design for sustainable underwater monitoring and exploration, specifically, to avoid the man-made interference to dolphins, in this paper, we propose a cognitive acoustic transmission scheme, called dolphin-aware data transmission (DAD-Tx), in multi-hop underwater acoustic networks. Different from the collaborative sensing approach and the simplified modeling of dolphins’ activities in existing literature, we employ a probabilistic method to capture the stochastic characteristics of dolphins’ communications, and mathematically describe the dolphin-aware constraint. Under dolphin-awareness and wireless acoustic transmission constraints, we further formulate the DAD-Tx optimization problem aiming to maximize the end-to-end throughput. Since the formulated problem contains probabilistic constraint and is NP-hard, we leverage Bernstein approximation and develop a three-phase solution procedure with heuristic algorithms for feasible solutions. Simulation results show the effectiveness of the proposed scheme in terms of both network performance and dolphin awareness.

A Distributed Scheduling Algorithm for Underwater Acoustic Networks With Large Propagation Delays

Underwater acoustic (UWA) networks are a key form of communications for human exploration and activities in the oceanographic space of the earth. A fundamental issue of UWA communications is large propagation delays due to water medium, which has posed a grand challenge in UWA network protocol design. Conventional wisdom of addressing this issue is to live with this disadvantage by inserting a guard interval to introduce immunity to propagation delays. Recent advances in interference alignment (IA) open up a new direction to address this issue and promise a great potential to improve network throughput by exploiting large propagation delays. In this paper, we investigate propagation delay-based IA (PD-IA) in multi-hop UWA networks. We first develop a set of simple constraints to characterize PD-IA feasible region at the physical layer. Based on the set of PD-IA constraints, we develop a distributed PD-IA scheduling algorithm to greedily maximize interference overlapping possibilities in a multi-hop UWA network. Simulation results show that the proposed PD-IA algorithm yields higher throughput than an idealized benchmark algorithm without propagation delays, indicating that large propagation delays are not adversarial but beneficial for network throughput performance.

Optimizing the Number of Hops and Retransmissions for Energy Efficient Multi-Hop Underwater Acoustic Communications

Energy efficient underwater communications systems design is a crucial task, once battery replacement may be barely feasible in this scenario. As acoustic underwater channels are usually harsher than terrestrial wireless channels, decreasing the transmission distance through a multi-hop approach is very appealing. In this sense, in this paper, we analyze how much energy is required to successfully transfer an information bit over a multi-hop underwater acoustic network while considering the optimum number of hops, retransmissions, code rate, and signal-to-noise ratio. We also investigate the impact of delay constraints in the total energy consumption, by allowing limited or unlimited retransmissions. Our results show that great energy savings can be obtained when the above-mentioned parameters are jointly optimized for a given link distance. Moreover, even though the impact of multiple hops is more beneficial, allowing for a small number of retransmissions lead to important energy savings. Finally, we compare the obtained results with a terrestrial wireless communications case, showing that an adequate modeling of the underwater scenario is imperative for an energy efficient design, once the optimal number of hops for terrestrial wireless may considerably differ from that for underwater communications.

A High-throughput routing metric for multi-hop Underwater Acoustic Networks

In most wireless network architectures, a routing metric plays an important role for a routing protocol to select suitable paths (or, links) for communications. An inefficient routing metric may increase overall transmission cost per packet by selecting lossy links and thereby may lead to poor throughput. Underwater Acoustic Networks (UANs), where most of the nodes operate on battery power, prefer topology-based routing metrics over active probing based routing metrics. Considering this fact, in this paper, we investigate the performance of various topology-based routing metrics over UAN-architecture. We then apply the acquired knowledge to design a new routing metric called Cubic Min to Avg Signal-to-Noise Ratio (CMAS), which is capable of selecting high-throughput links. We evaluate the performance of the proposed metric with other available topology-based routing metrics in underwater scenario. Simulation results demonstrate that the proposed metric attains significantly higher throughput than that of the other compared metrics.

Analyzing the performance of Aloha in string multi-hop underwater acoustic sensor networks

Abstract In this article, we intend to investigate the performance of channel access protocols in multi-hop underwater acoustic sensor networks, which are characterized by long propagation delays and limited channel bandwidth. An analytical model specifically designed for contention-based protocols in multi-hop underwater acoustic networks is identified and validated. The model is based on an underwater network model, called string topology network model, which provides a method for computing the expected network throughput and the probability of packets’ delivery to the gateway from an arbitrary sensor. This study demonstrates an improvement of an existing model, in which a node is implicitly assumed to be able to transmit two packets at the same time, which is not realistic due to the half-duplex character of underwater acoustic channels. Based on our findings, we propose a modified analytical model and evaluate it using NS-3 simulator. Results show that our analytical model is more precise than the existing one.

AURP: An AUV-Aided Underwater Routing Protocol for Underwater Acoustic Sensor Networks

Deploying a multi-hop underwater acoustic sensor network (UASN) in a large area brings about new challenges in reliable data transmissions and survivability of network due to the limited underwater communication range/bandwidth and the limited energy of underwater sensor nodes. In order to address those challenges and achieve the objectives of maximization of data delivery ratio and minimization of energy consumption of underwater sensor nodes, this paper proposes a new underwater routing scheme, namely AURP (AUV-aided underwater routing protocol), which uses not only heterogeneous acoustic communication channels but also controlled mobility of multiple autonomous underwater vehicles (AUVs). In AURP, the total data transmissions are minimized by using AUVs as relay nodes, which collect sensed data from gateway nodes and then forward to the sink. Moreover, controlled mobility of AUVs makes it possible to apply a short-range high data rate underwater channel for transmissions of a large amount of data. To the best to our knowledge, this work is the first attempt to employ multiple AUVs as relay nodes in a multi-hop UASN to improve the network performance in terms of data delivery ratio and energy consumption. Simulations, which are incorporated with a realistic underwater acoustic communication channel model, are carried out to evaluate the performance of the proposed scheme, and the results indicate that a high delivery ratio and low energy consumption can be achieved.

Analysis of a Linear Multihop Underwater Acoustic Network

In this paper, a multihop underwater acoustic line network, which consists of a series of equal-distance hops connected by relay transceivers in a tandem, is considered. Messages are originated as coded packets from a source node at one end, relayed sequentially hop by hop (decoded and re-encoded), and finally received by a destination node at the other end of the network. Several key characteristics of underwater acoustic channels, namely, frequency-dependent signal attenuation and noise, interhop interference, half-duplex modem constraint, and large propagation delay, are taken into account in the analysis. Simple transmission protocols with spatial reuse and periodic transmit/receive schedule are considered. Performance bounds and scheduling design are developed to satisfy the half-duplex constraint on relay transceivers in the presence of long propagation delay. To efficiently cope with frequency-dependent channel characteristic and interhop interference, the power spectral density (PSD) of the signaling is analytically optimized in a way analogous to water filling. Furthermore, the problem of determining the minimum number of hops to support a prespecified rate and reliability with and without a maximum coded packet length constraint is examined. Finally, numerical results are presented to illustrate the analysis.

RIPT: A Receiver-Initiated Reservation-Based Protocol for Underwater Acoustic Networks

Although there are many MAC protocols that have been proposed for terrestrial wireless networks with a wide variety of aspects, these protocols cannot be applied directly in underwater acoustic networks due to the channel's uniqueness of having low data rate and long propagation delay. In order to achieve a high throughput, both characteristics must be taken into account in the MAC design. We propose a random access MAC protocol for multi-hop underwater acoustic networks based on receiver reservation, which we shall call the Receiverinitiated Packet Train (RIPT) protocol. It is a handshakingbased protocol that addresses the channel's long propagation delay characteristic by utilizing receiver-initiated reservations, as well as by coordinating packets from multiple neighboring nodes to arrive in a packet train manner at the receiver. Our simulation results have confirmed that the RIPT protocol can achieve our goal of having high and stable throughput performance while maintaining low collision rate.