In Underwater Wireless Sensor Networks (UWSNs), data should be transmitted to data centers reliably and efficiently. However, due to the harsh channel conditions, reliable data transmission is a challenge for large-scale UWSNs. Thus, opportunistic routing (OR) protocols with high reliability, strong robustness, low end-to-end delay, and high energy efficiency are widely applied. However, OR in UWSNs is vulnerable to routing attacks. For example, sinkhole attack nodes can attract traffic from surrounding nodes by forging information such as the distance to the sink node. In order to reduce the negative impact of malicious nodes on data transmission, we propose an intrusion detection scheme (IDS) based on the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering algorithm for OR (DOIDS) in this paper. DOIDS is based on small-sample IDS and is suitable for UWSNs with sparse node deployment. In DOIDS, the local monitoring mechanism is adopted. Every node in the network running DOIDS can select the trusted next hop. Firstly, according to the behavior characteristics of common routing attack nodes and unreliable underwater acoustic channel characteristics, DOIDS selected the energy consumption, forwarding, and link quality information of candidate nodes as the detection feature values. Then, the collected feature information is used to detect potential abnormal nodes through the DBSCAN clustering algorithm. Finally, a decision function is defined according to the time decay function to reduce the false detection rate of DOIDS. It makes a final judgment on whether the potential abnormal node is malicious. The simulation results show that the algorithm can effectively improve the detection accuracy rate (3% to 15% for different scenarios) and reduce the false positive rate, respectively.

/pdf/doids-an-intrusion-detection-scheme-based-on-dbscan-for-5xap38cy.pdf

DOIDS: An Intrusion Detection Scheme Based on DBSCAN for Opportunistic Routing in Underwater Wireless Sensor Networks

Traditionally, underwater acoustic modems and positioning systems were developed for military and Oil & Gas industries, that require deep water deployments and extremely reliable systems, focusing on high power expensive systems and leaving the use of low-cost devices only attractive for academic studies. Conversely, recent developments of low-cost unmanned vehicles, such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), suitable for shallow water coastal missions, and the need of sensors network deployments for measuring water quality and studying the effect of climate change in coastal areas, called to the need of low-cost and low-power acoustic modems and positioning systems that are gaining more and more momentum to date. The use of these devices can enable a wide set of applications, often based on low-cost AUV swarm formations, where an acoustic link between the vehicles is required to coordinate the mission, perform the maneuvers, and maintain the formation along the time. Moreover, they can make environmental wireless sensor deployment cost effective by substituting wired systems. Underwater positioning systems, usually used in large-scale operations, can be finally applied to small-scale application thanks to the reduction in costs, at the price of a lower transmission and positioning range and precision. While in open-sea application this performance reduction is a huge limitation, in river, lagoon, port and lake deployments this is not an issue, given that the extremely shallow water and the presence of many obstacles would deteriorate the acoustic signal anyway, not allowing long range transmissions even with expensive and sophisticated acoustic devices. In this paper, we review the recent developments of low-cost and low-power acoustic communication and positioning systems, both analyzing University prototypes and new commercial devices available in the market, identifying advantages and limitations of these devices, and we describe potential new applications that can be enabled by these systems.

/pdf/survey-on-low-cost-underwater-sensor-networks-from-niche-qvsc55le.pdf

Survey on Low-Cost Underwater Sensor Networks: From Niche Applications to Everyday Use

Underwater acoustic channels are characterized by long propagation delay, limited available bandwidth and high energy costs. These unique characteristics bring challenges to design media access control (MAC) protocol for underwater acoustic sensor networks (UASNs). Especially in data-collection-oriented UASNs, data generated at underwater nodes are transmitted hop-by-hop to the sink node. The traffic loads undertaken by nodes of different depths are different. However, most existing MAC protocols do not consider the traffic load imbalance in data-collection-oriented UASNs, resulting in unfairness in how the nodes transmit their own generated data. In this paper, we propose a novel traffic-aware fair MAC protocol for layered data-collection-oriented UASNs, called TF-MAC. TF-MAC accesses a medium by assigning time slots of different lengths to each layer via different traffic loads to achieve traffic fairness of nodes. To improve throughput and avoid collision in the network, an overlapping time slot division mechanism for different layers and multi-channel allocation scheme within each single layer is employed. Considering the time-varying traffic loads of the nodes, an adaptive packet length algorithm is proposed by taking advantage of the spatial-temporal uncertainty of underwater channels. A sea experiment was conducted to prove the spatial-temporal uncertainty of UASNs, which provides a feasibility basis for the proposed algorithm. Simulation results show that TF-MAC can greatly improve the network performance in terms of throughput, delay, energy consumption, and fairness in the layered data-collection-oriented UASNs.

https://www.mdpi.com/2072-4292/15/6/1501/pdf?version=1678285884

A Traffic-Aware Fair MAC Protocol for Layered Data Collection Oriented Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UASNs) face many security threats since they are deployed in open or even hostile environments. How to ensure the confidentiality of data transmission in the presence of eavesdroppers at unknown locations is an urgent problem. In this article, we first define the security coverage of the network. Then, a physical layer secure transmission scheme, named ST-CJ, which is based on self-assisting nodes with cooperative jamming signals, is proposed. With the allocated jamming transmission power, the proposed scheme takes advantage of the long propagation delays of underwater acoustic (UWA) signals to create collisions at the eavesdropper without affecting the reception of the legitimate user. In the ST-CJ, the transmission schedule and power level of each assisting node are jointly optimized. The goal is to maximize the coverage of the secure area in the network with minimal energy consumption. Both simulation and field test results demonstrate that the proposed scheme obviously reduces the interception ability of eavesdroppers, thus realizing the confidentiality of transmission.

A Secure Transmission Scheme With Energy-Efficient Cooperative Jamming for Underwater Acoustic Sensor Networks

Physical layer security (PLS) is one of the important methods to solve the security problems of Underwater Acoustic Sensor Networks (UASNs). In this paper, combining the characteristics of cooperative communication and cooperative jamming in PLS, we propose a Secure Relay Selection Scheme based on Cooperative Jamming for UASNs. On the one hand, according to the link quality and residual energy, one or several nodes are selected to forward information as relays. On the other hand, the scheme takes advantage of long propagation delay of the underwater acoustic channel and employs two different jamming ways: Self-Protection Jamming and Assistance Jamming, both of which can interfere with eavesdroppers without affecting the reception of legal users. The proposed scheme can increase the channel capacity of the legal channel by deploying relay nodes to forward the information and reduce the channel capacity of the eavesdropping channel by Self-Protection Jamming and Assistance Jamming. Simulation and field experiment results show that the proposed scheme can improve the PLS of the network. 

A secure relay selection scheme based on cooperative jamming for Underwater Acoustic Sensor Networks

Underwater acoustic communication (UAC) modem is an important infrastructure of underwater network construction. In recent years, with the performance improvement of the STM32 processor, the realization of reliable UAC through high-performance STM32 processor is conducive to reduce the system power consumption, cheapen the hardware cost, and ease the development difficulty. In this letter, we propose an embedded UAC system with the STM32H743 processor as the core and the peripheral sending/receiving circuit as the signal conditioning circuit module. The system can support a variety of modulation and demodulation methods, including single/multi-carrier frequency-shift keying and orthogonal frequency division multiplexing. Furthermore, in order to reduce the computational cost of the system, a fast and robust frame synchronization algorithm based on the segmented fast Fourier transform is applied. The sea trials show that the system can realize the reliable UAC transmission of 100 b/s–1 kb/s in the distance of 5–8 km in the shallow water area.

A General Embedded Underwater Acoustic Communication System Based on Advance STM32

A novel chalcogenide As2Se3 fiber based on a twin-tube structure is proposed and numerically studied for mid-infrared (MIR) single-polarization single-mode (SPSM) operation. The proposed fiber consists of two identical thin-wall tubes, which are located symmetrically inside the cladding. The simulation results show that the y-polarization fundamental mode (YPFM) can be well confined between the two tube walls near the fiber center, while all of the unwanted modes, including the x-polarization fundamental mode (XPFM) and all of the higher order modes (HOMs), are effectively suppressed due to huge confinement loss (CL). The SPSM operation can be maintained in the wavelength range from 3 to 10 μm, covering almost the entire transparency region of an As2Se3 fiber, with the maximum YPFM CL of 8.63 × 10−3 dB/m at 10 μm. To the best of our knowledge, this is the first MIR fiber that can keep SPSM operation over such a wide wavelength region. Furthermore, the mode area of YPFM is quite small (e.g., 10.82 μm2 at the wavelength of 6 μm), which is beneficial to realize high nonlinearity. Besides, the bending induced CL increment of YPFM at 10 μm is only 1 × 10−5 dB/m even when the fiber bending radius is 1 cm. Owing to the simple structure and outstanding properties, the proposed fiber has practical applications in MIR photonics and nonlinear fiber optics.

A Mid-Infrared Ultrawide-Bandwidth Single-Polarization Single-Mode Fiber Based on a Twin-Tube Structure

A highly birefringent and low-loss hollow-core anti-resonant fiber (HC-ARF) based on a hybrid guidance mechanism is proposed and investigated by using a finite element method. The hybrid guidance mechanism is caused by the anti-resonance effect and the total internal reflection effect. The proposed HC-ARF is obtained by employing twin symmetrical and mutually tangential elliptical arc anti-resonance layers (EA-ARLs) in a conventional 8-tube HC-ARF. Because of the anti-resonance mechanism and the total internal reflection mechanism in the EA-ARL, mode coupling appears between the core mode and the cladding mode. Simulation results indicate that the proposed HC-ARF can achieve birefringence as high as 10−2 in a near-infrared range of 1400 nm to 1600 nm and a low confinement loss (CL) of 7.74 × 10−4 dB/m (9.26 × 10−4 dB/m) for x- and y-polarization components of the fundamental mode (FM) at 1550 nm. In addition, the existence of the 8-tube anti-resonance structure in the cladding significantly suppresses the CL of the x-polarization component of the FM significantly, but the impact on the CL of the y-polarization FM can be ignored, which is determined mainly by the twin EA-ARLs. Furthermore, the performance of the birefringence and CL are also investigated by changing the values of other fiber structure parameters. Our proposed structure successfully shows the ability of the hybrid guidance mechanism in the application of CL manipulation of orthogonal polarization components.

/pdf/highly-birefringent-and-low-loss-hollow-core-anti-resonant-1at3u6m9.pdf

Xuan Liu

Papers

A General Embedded Underwater Acoustic Communication System Based on Advance STM32

A Traffic-Aware Fair MAC Protocol for Layered Data Collection Oriented Underwater Acoustic Sensor Networks

A Mid-Infrared Ultrawide-Bandwidth Single-Polarization Single-Mode Fiber Based on a Twin-Tube Structure

Highly Birefringent and Low-Loss Hollow-Core Anti-Resonant Fiber Based on a Hybrid Guidance Mechanism