Acoustic Modem Research Articles

Underwater Adaptive Video Transmissions Using MIMO-Based Software-Defined Acoustic Modems

Achieving reliable acoustic wireless video transmissionsin the extreme and uncertain underwater environment is a challenge due to the limited bandwidth and the error-prone nature of the channel. Aiming at optimizing the received video quality and the user’s experience, an adaptive solution for underwater video transmissions is proposed that is specifically designed for Multi-Input Multi-Output (MIMO)-based Software-Defined Acoustic Modems (SDAMs). To keep the video distortion under an acceptable threshold and to keep the Physical-Layer Throughput (PLT) high, cross-layer techniques utilizing diversity-spatial multiplexing and Unequal Error Protection (UEP) are presented along with the scalable video compression at the application layer. Specifically, the scalability of the utilized SDAM with high processing capabilities is exploited in the proposed structure along with the temporal, spatial, and quality scalability of the Scalable Video Coding (SVC) H.264/MPEG-4 AVC compression standard. The transmitter broadcasts one video stream and realizes multicasting at different users. Experimental results at the Sonny Werblin Recreation Center, Rutgers University-NJ, are presented. Several scenarios for unknown channels at the transmitter are experimentally considered when the hydrophones are placed in different locations in the pool to achieve the required SVC-based video Quality of Service (QoS) and Quality of Experience (QoE) given the channel state information and the robustness of different SVC scalability. The video quality level is determined by the best communication link while the transmission scheme is decided based on the worst communication link, which guarantees that each user is able to receive the video with appropriate quality.

Time-delay high-order sliding mode control for trajectory tracking of autonomous underwater vehicles under disturbances

This paper presents a new generalized super-twisting algorithm (GSTA) controller with a time-delay estimator (TDE) for the tracking control of an autonomous underwater vehicle (AUV) under disturbances. For exploration tasks in confined areas, AUVs are typically equipped with sensors such as Doppler velocity logs (DVL) or acoustic modems to measure their position and speed. However, these sensors have a disadvantage in that their acquisition rates are low. This disadvantage, combined with the influence of external disturbances, directly influences position control because it requires partial knowledge of the system for proper operation. To solve this problem, the introduction of a TDE that estimates the vehicle hydrodynamics with delayed sensor information, and consequently, improves the controller performance is proposed. For controller validation, a stability analysis is presented, and two results are provided in the simulation. In the first test, the AUV is controlled to track a parameterized spiral-shaped path to validate the vehicle movement in the three directions of the plane (x,y,z). In the second test, the AUV performs path tracking in yaw and depth motions. In all numerical simulations, three types of disturbances/uncertainties are considered: (i) system parameters, (ii) sensor readings, and (iii) control.

A high‐resolution AUV navigation framework with integrated communication and tracking for under‐ice deployments

AbstractWe developed an environmentally adaptive under‐ice navigation framework that was deployed in the Arctic Beaufort Sea during the United States Navy Ice Exercise in March 2020 (ICEX20). This navigation framework contained two subsystems developed from the ground up: (1) an on‐board hydrodynamic model‐aided navigation (HydroMAN) engine, and (2) an environmentally and acoustically adaptive integrated communication and navigation network (ICNN) that provided acoustic navigation aiding to the former. The HydroMAN synthesized measurements from an inertial navigation system (INS), ice‐tracking Doppler velocity log (DVL), ICNN and pressure sensor into its self‐calibrating vehicle flight dynamic model to compute the navigation solution. The ICNN system, which consisted of four ice buoys outfitted with acoustic modems, trilaterated the vehicle position using the one‐way‐travel‐times (OWTT) of acoustic datagrams transmitted by the autonomous underwater vehicle (AUV) and received by the ice buoy network. The ICNN digested salinity and temperature information to provide model‐assisted real‐time OWTT range conversion to deliver accurate acoustic navigation updates to the HydroMAN. To decouple the contributions from the HydroMAN and ICNN subsystems towards a stable navigation solution, this article evaluates them separately: (1) HydroMAN was compared against DVL bottom‐track aided INS during pre‐ICEX20 engineering trials where both systems provided similar accuracy; (2) ICNN was evaluated by conducting a static experiment in the Arctic where the ICNN navigation updates were compared against GPS with ICNN error within low tens of meters. The joint HydroMAN‐ICNN framework was tested during ICEX20, which provided a nondiverging high‐resolution navigation solution—with the majority of error below 15 m—that facilitated a successful AUV recovery through a small ice hole after an 11 km untethered run in the upper and mid‐water column.

Diver‐Robot Communication Using Wearable Sensing: Remote Pool Experiments

Abstract Diver‐robot interaction is an exciting and recent field of study. There are different ways a diver and robot can interact, such as using tablets or detecting divers with cameras or sonars. A novel approach presented in this paper uses direct diver‐robot communication. To facilitate communication for humans, we use typical diver gestures, which are transmitted to a robot using a wearable glove and acoustic communications. Following previous work by the University of Zagreb and the University of Auckland, a collaboration to control an autonomous underwater vehicle based on a wearable diver glove has been made possible through the EU Marine Robots project. Under this project, Trans-National Access trials allow Laboratory for Underwater Systems and Technologies, University of Zagreb, to offer its robots and infrastructure to external partners. Initial trials with the University of Auckland, which were planned to take place on site, were transformed into remote access trials. This paper reports on these challenging trials and collaboration given the distance and time zone difference. The key point is to demonstrate the possibility of having a diver remotely controlling a robot using typical gestures recognized by a wearable glove and transmitted via acoustic modems (and the Internet for the remote connection).

Research on Co-Channel Interference Cancellation for Underwater Acoustic MIMO Communications

Multiple-input–multiple-output (MIMO) communication systems utilize multiple transmitters to send different pieces of information in parallel. This offers a promising way to communicate at a high data rate over bandwidth-limited underwater acoustic channels. However, underwater acoustic MIMO communication not only suffers from serious inter-symbol interference, but also critical co-channel interference (CoI), both of which degrade the communication performance. In this paper, we propose a new framework for underwater acoustic MIMO communications. The proposed framework consists of a CoI-cancellation-based channel estimation method and channel-estimation-based decision feedback equalizer (CE-DFE) with CoI cancellation functionalities for underwater acoustic MIMO communication. We introduce a new channel estimation model that projects the received signal to a specific subspace where the interference is free; therefore, the CoI is cancelled. We also introduce a CE-DFE with CoI cancellation by appending some filters from traditional CE-DFE. In addition, the traditional direct adaptive decision feedback equalization (DA-DFE) method and the proposed method are compared in terms of communication performance and computational complexity. Finally, the sea trial experiment demonstrates the effectiveness and merits of the proposed method. The proposed method achieves a more than 1 dB of output SNR over traditional DA-DFE, and is less sensitive to parameters. The proposed method provides a new approach to the design of robust underwater acoustic MODEM.

Fast indicators for robust acoustic communication and navigation in a double-ducted polar environment

A floating ice-buoy system equipped with GPS and acoustic modems provided communication and navigation to a Bluefin 21 Autonomous Underwater Vehicle (AUV) for under-ice operations in the Beaufort Sea, in March 2020. Acoustic modems were placed above and below the “Beaufort Lens,” at 30 and 90 m, where a data- and model-based autonomy selected which depth to use for transmitting messages to the AUV. Similarly, the AUV ran a depth adaptive path planning behavior to maintain acoustic communications with the ice buoy modems. The untethered mission showed a non-diverging navigation solution with the average error roughly 0.1% of the total 11 km traveled. This talk will summarize key metrics introduced for automated, on-the-fly processing of acoustic packets to navigate within a reliable acoustic channel and minimize navigation error. [Supported by Office of Naval Research.]

A Real-Time Underwater Acoustic Telemetry Receiver With Edge Computing for Studying Fish Behavior and Environmental Sensing

Underwater acoustic telemetry has emerged as a powerful tool for practical applications, including resource exploration, environmental monitoring, and aquatic animal tracking. However, current acoustic telemetry systems lack the capability to transmit the collected data continuously in real time, primarily because the acoustic networking bandwidth is limited. Retrieval of the recorded measurements from the deployed receivers usually must be manual, leading to long delays in data retrieval and processing, high operational costs associated with the required manpower, and safety risks for the operators. In addition, there is no efficient way to continuously assess the status of the acoustic telemetry system, including the acoustic transmitters and receivers. Here, we describe the design, implementation, and field validation of a cloud-based, real-time, underwater acoustic telemetry system with edge computing for estimating fish behavior and monitoring environmental parameters. The system incorporates microcontrollers for edge computing and connects to a cloud-based service that further post-processes the transmitted data stream to derive behavior and survival information of tagged animals. The developed system has been demonstrated to have significantly improved performance over the benchmark system because of the integration of edge computing, with a greatly reduced energy consumption of 0.014 W resulting in the energy used by the acoustic modem being reduced by over 300 times. This work opens up new design opportunities for future real-time and multifunctional underwater acoustic systems.

Underwater Acoustic Micromodem for Underwater Internet of Things

Underwater acoustic communication (UAC) networks are becoming a hot spot for research due to the growing demand for ocean development. Previous acoustic modems were mainly designed for the field of ocean engineering construction and scientific investigation, and consequently, with the characteristics of large size and high-power consumption, a low-cost, low-power consuming micromodem is proposed in this paper to satisfy the requirements of underwater Internet of Things (IoT). The STM32F767 processor is embedded in the micromodem as the core for fast digital signal processing. Furthermore, a convolutional code–block interleaving–frequency hopping–MFSK underwater communication scheme is also discussed to ensure the communication quality. Experimental results are shown to demonstrate our modem can realize the reliable UAC transmission of 200~300 bit/s at the distance of 500 m.

An Unmanned Underwater Vehicle Defence System

Nowadays, military threats are very close to us and cover terrestrial, aerial, and maritime attacks. This research defines a submarine defence system capable of monitoring and controlling a certain perimeter, based on submersible drones known as Unmanned Underwater Vehicles (UUV) and a grid of stations fixed to the seabed, which provides positioning acoustic signals as well as full-duplex digital communication using underwater acoustic modems. The novelty is the proposed 3D grid system with each Positioning Grid Element (PGE) being an Ultra-Short Baseline (USBL) low or medium operating range device and the processing

Ultra-Low-Cost and Ultra-Low-Power, Miniature Acoustic Modems Using Multipath Tolerant Spread-Spectrum Techniques

To enable long-term, large-scale, dense underwater sensor networks or Internet of Underwater Things (IoUT) this research investigates new novel waveforms and experimental prototypes for robust communications on ultra-low-cost and ultra-low-power, miniature acoustic modems. Spread-spectrum M-ary orthogonal signalling (MOS) is used with symbols constructed from subsequences of long pseudorandom codes. This decorrelates multipath signals, even when the time-spread spans many symbols, so they present as random noise. A highly cost-engineered and miniaturised prototype acoustic modem implementation was created, for the 24 kHz–32 kHz band, with low receive power consumption (12.5 mW) and transmit power of <1 W. Simulations show that the modulation scheme achieves 640 bit/s at −4.5 dB with AWGN or the equivalent level of multipath energy. Experimental validation of the hardware shows successful point-to-point communication at ranges of >3 km in lakes and >2 km in the sea including severe multipath. In lake testing of a 7-node, multi-hop, sensor network with TDA-MAC protocol, packet delivery was near 100% for all nodes. Trials of acoustic sensor nodes in the North Sea achieved 99.5% data delivery over a 3-month period and a wide range of sea conditions. Modulation and hardware have proven reliable in a variety of underwater environments. Competitive range and throughput with low cost and power are attractive for large-scale and long-term battery-operated networks. This research has delivered a viable and affordable communication technology for future IoUT applications.

UNDERWATER ACOUSTIC MODEM WITH HIGH PRECISION RANGING CAPABILITY BASED ON SECOND-LEVEL CESIUM ATOMIC CLOCK

Abstract. Equipped with a high-precision atomic clock can significantly improve the ranging accuracy of the underwater acoustic ranging system. However, the adverse characteristic of underwater acoustic channel (UAC) seriously deteriorates the ranging accuracy. In addition, as a timing device typically commercial cesium atomic clock is only designed to output second-level time reference, which cannot be applied to underwater ranging systems directly. To overcome this limitation, a new underwater acoustic modem with high precision ranging capability based on second-level cesium atomic clock is developed in this paper. The spread spectrum technology is chosen for highly reliable communication and the second-level commercial cesium atomic clock is used to ensure accurate clock synchronization. The proposed modem executes a predetermined ranging scheme based on spread spectrum technology. Specifically, at a certain specified second-level, the transmitter modem sends the ranging signal, and the receiver modem starts timing. Until the receiving modem detects the ranging signal, the propagation time is obtained and the single-item ranging capability is realized. The pool experiment shows the effectiveness of the modem, its ranging accuracy can reach cm level, and the average absolute error of ranging is 8 cm.

Performance Optimization of Underwater Communication Links at Different Ranges for AIS Relay to AUV

Autonomous Underwater Vehicles (AUVs) are becoming increasingly popular for large number of civil and military applications, such as environmental monitoring, oceanography, archaeology, or mine warfare. Operational safety issue still prevents the exploitation of the full potential of AUVs. Operations of AUVs are limited by constraints including the need to guarantee no collision with manned surface vehicles. To avoid collisions, a solution is to relay surface vessel positions to the AUVs by an underwater communication link. The communication must be optimized to establish a robust and reliable link at various range and depth. Commercial underwater acoustic modems are often dedicated for specific distances and bit rates with performances strongly dependent on the environmental conditions. For the considered application, the modem must be adaptive at the time and frequency selectivity of the channel which is varying according to the operation context. In this work, we propose an adaptive underwater acoustic waveform optimized to exploit at the best the time and frequency diversity the channel. To show the potential gain obtained by using diversity, the performance of the designed modem is evaluated using theoretical and realistic underwater channels. In addition, we propose a method for adapting the waveform based only on the knowledge of the transmission geometry. Finally, the proposed modem is tested to relay Automatic Identification Systems (AIS) picture of an area to AUVs.

Passive Acoustic Detection of Vessel Activity by Low-Energy Wireless Sensors

This paper presents the development of a low-energy passive acoustic vessel detector to work as part of a wireless underwater monitoring network. The vessel detection method is based on a low-energy implementation of Detection of Envelope Modulation On Noise (DEMON). Vessels produce a broad spectrum modulated noise during propeller cavitation, which the DEMON method aims to extract for the purposes of automated detection. The vessel detector design has different approaches with mixtures of analogue and digital processing, as well as continuous and duty-cycled sampling/processing. The detector re-purposes an existing acoustic modem platform to achieve a low-cost and long-deployment wireless sensor network. This integrated communication platform enables the detector to switch between detection/communication mode seamlessly within software. The vessel detector was deployed at depth for a total of 84 days in the North Sea, providing a large data set, which the results are based on. Open sea field trial results have shown detection of single and multiple vessels with a 94% corroboration rate with local Automatic Identification System (AIS) data. Results showed that additional information about the detected vessel such as the number of propeller blades can be extracted solely based on the detection data. The attention to energy efficiency led to an average power consumption of 11.4 mW, enabling long term deployments of up to 6 months using only four alkaline C cells. Additional battery packs and a modified enclosure could enable a longer deployment duration. As the detector was still deployed during the first UK lockdown, the impact of COVID-19 on North Sea fishing activity was captured. Future work includes deploying this technology en masse to operate as part of a network. This could afford the possibility of adding vessel tracking to the abilities of the vessel detection technology when deployed as a network of sensor nodes.

Survey of Acoustic Frequency Use for Underwater Acoustic Cognitive Technology

The available underwater acoustic spectrum is limited. Therefore, it is imperative to avoid frequency interference from overlapping frequencies of underwater acoustic equipment (UAE) for the co-existence of the UAE. Cognitive technology that senses idle spectrum and actively avoids frequency interference is an efficient method to facilitate the collision-free operation of multiple UAE with overlapping frequencies. Cognitive technology is adopted to identify the frequency usage of UAE to apply cognitive technology. To this end, we investigated two principle underwater acoustic sources: UAE and marine animals. The UAE is classified into five types: underwater acoustic modem, acoustic positioning system, multi-beam echo-sounder, side-scan sonar, and sub-bottom profiler. We analyzed the parameters of the frequency band, directivity, range, and depth, which play a critical role in the design of underwater acoustic cognitive technology. Moreover, the frequency band of several marine species was also examined. The mid-frequency band from 10 - 40 kHz was found to be the busiest. Lastly, this study provides useful insights into the design of underwater acoustic cognitive technologies, where it is essential to avoid interference among the UAE in this mid-frequency band.

Hybrid Tracking Controller for an ASV Providing Mission Support for an AUV

Autonomous underwater vehicles (AUVs) rely on surface support for communication with operators and position fixes to bound inertial navigation errors. By installing an acoustic modem on an autonomous surface vehicle (ASV), the ASV can carry out these tasks, replacing more expensive and less flexible manned research vessels. This paper proposes a hybrid tracking controller for an ASV providing mission support for an AUV. The proposed controller keeps the ASV in a donut-shaped safety domain about the AUV defined by the risk of collision (inner boundary) and the risk of communication loss (outer boundary). At the same time, the hybrid controller reduces power consumption and acoustic signal noise by going into standby mode when it is within the safety domain. Results from a simulation study and field trials are presented to demonstrate and validate the controller's performance. The results show that the controller performed well in the tested cases.

In Situ Performance Prediction of a Coherent Acoustic Modem in a Reverberant Environment

A channel sounding and communications experiment was performed in the Oslofjord, using eight bottom-mounted instrument units deployed in a network configuration. Five units were equipped with a software-defined 4–8-kHz acoustic modem, programmed to transmit probe signals and communication packets in a round-robin fashion. All transmitted waveforms were recorded by all units over 35 horizontal links and 5 vertical links. The channels reveal a reverberant environment with long and dense multipath arrival patterns. Measured power-delay profiles and delay-Doppler spread functions are used to predict receiver output signal-to-noise ratio (SNR) over a signaling period of 26 h. To this end, the channel quantities are first calibrated for the propagation loss. The prediction examines the effect of ambient noise, reverberation of previously transmitted packets, the packet’s own reverberation, and Doppler spread. The delay profile can be used under calm conditions, and results in a mean prediction error (averaged over all links) of about 3 dB, even hours after the measurement of the profiles. The mean error on individual links (averaged over time) is reduced to 1–2 dB by using up-to-date channel information. The relevance of predicting output SNR is finally illustrated by establishing a relationship between output SNR and the probabilities of bit and packet error.

FD-LTDA-MAC: Full-Duplex Unsynchronised Scheduling in Linear Underwater Acoustic Chain Networks

In-band full-duplex communication offers significant potential to enhance network performance. This paper presents the full-duplex linear transmit delay allocation MAC (FD-LTDA-MAC) protocol for full-duplex based underwater acoustic chain networks (FD-UACNs) for subsea pipeline monitoring. This incorporates a number of extensions to the LTDA-MAC protocol in order to fully exploit advantages of full-duplex communication to enhance the efficiency of underwater facility monitoring. The protocol uses a greedy optimisation algorithm to derive collision-free packet schedules for delivering data packets to the sink node of the underwater chain network. The purpose of this paper is to show the significant improvement that can be achieved in packet scheduling by exploiting temporal spectrum re-use of an underwater acoustic channel through full-duplex communication. Simulation results show that more efficient packet scheduling and reduced end-to-end packet delays can be achieved in large scale scenarios using FD-LTDA-MAC compared with LTDA-MAC and LTDA-MAC with full-duplex enabled nodes. It can provide much higher monitoring rates for long range underwater pipelines using low cost, mid range, low rate, and low power acoustic modems.

A step by step educational guide to designing and testing an underwater acoustic modem

We examine the design and systematic implementation of a receiver system for underwater acoustic communication. The system includes, but is not limited to, passband filter, down converter, matched filter, and detection logic. Our final implementation target is a frame-based system to minimize memory use and system latency. The matched filter uses the overlap-save method in frequency domain to reduce computational cost. Initially, the system is designed and tested for performance using the MATLAB platform in a non-real time vector-based implementation. The code is then restructured to a MATLAB frame-based model. The code contains several functions; each function performs a specific task and maintains its own histories as needed. Once the performance of the frame-based model is measured to be identical to the vector-based model, we systematically move each function to C + +. Each C + + function is individually substituted into the frame-based model using MEX files and verified for performance. Once all C + + functions are verified for performance, the entire C + + implementation is uploaded to the Popoto Modem™ real-time hardware and performs real-time transmission and reception in both air and underwater environments, with known and tested performance characteristics. [Work supported in part by NSF, Grant IIP-1500123, the INTERN program.]

Self-localization of buoyless fishing gear and other objects on the sea floor.

End lines used in commercial trap/pot fishing pose a significant entanglement risk to whales, sea turtles, and sharks. Removal of these ropes for buoyless fishing is being considered by the United States and Canadian governments, but a method to systematically locate the gear without an attached buoy is required. A method was developed for an acoustic modem to self-localize and broadcast its location to nearby ships to minimize gear conflict, optimize power consumption, and reduce lost gear. This method was implemented using a research modem that self-localized to within 5 m of its estimated location on the sea floor.

OMUS: Efficient Opportunistic Routing in Multi-Modal Underwater Sensor Networks

Underwater wireless sensor networks (UWSNs) have emerged as an enabling technology for aquatic monitoring. However, data delivery in UWSNs is challenging, due to the harsh aquatic environment and characteristics of the underwater acoustic channel. In recent years, underwater nodes with multi-modal communication capabilities have been proposed to create communication diversity and improve data delivery in UWSNs. Nevertheless, less attention has been devoted to the design of networking protocols leveraging multi-modal communication capabilities of underwater nodes. In this paper, we propose a novel stochastic model for the study of opportunistic routing (OR) in multi-modal UWSNs. We also design two candidate set selection heuristics, named OMUS-E and OMUS-D, for the joint selection of the most suitable acoustic modem for data transmission and next-hop forwarder candidate nodes at each hop, aimed to reduce the energy consumption and improve the network data delivery ratio in multi-modal UWSNs, respectively. Numerical results showed that both proposed heuristics reduced the energy consumption by 65%, 70%, and 75% as compared to the DBR, HydroCast, and GEDAR classical related work protocols, while maintaining a similar data delivery ratio. Furthermore, the proposed solutions outperformed the CAPTAIN routing protocol in terms of data delivery ratio, while maintaining comparable energy consumption.