Long-range Underwater Communication Research Articles

Frequency Shift Keying-Based Long-Range Underwater Communication for Consecutive Channel Estimation and Compensation Using Chirp Waveform Symbol Signals

Currently, the demand for long-range underwater communication (UWC) is increasing. Conventional long-range UWC studies utilize vertical line array (VLA) and equalization techniques such as TRM and DFE to mitigate the long multi-path delay. However, recently developed underwater platforms such as unmanned underwater vehicles (UUVs) utilize a single hydrophone, and it is hard to apply the conventional long-range UWC system to these platforms. This paper proposes frequency shifting-based modulation to overcome the large multi-path delay without any optimization or training symbol. Unlike FSK, the proposed modulation method transmits the data using linear frequency modulation (LFM). The proposed demodulation method estimates the multi-path delay using data-modulated LFM and utilizes the estimated multi-path to compensate for the subsequent data signal. Therefore, the proposed method has better BER performance than FSK, and it is demonstrated through a simulation and ocean experiment with a single hydrophone.

Design and simulation of acoustic vortex wave arrays for long-range underwater communication

The formation and propagation of acoustic vortex waves have been of increasing interest for multiple applications, namely, underwater acoustic communications. Several methods have been presented to form these vortices in underwater environments; however, their performance and propagation over long distances is largely unstudied. Understanding the long-distance propagation of these waves is vital to enhancing their usefulness as an added degree of freedom in underwater acoustic communications systems. In this work, the ray tracing algorithm of bellhop is used to investigate the design parameters of vortex wave transducer and receiver arrays consisting of multiple rings of independently controlled transducers and simulate their performance.

High-Data-Rate Long-Range Underwater Communications via Acoustic Reconfigurable Intelligent Surfaces

Despite decades-long development, underwater communication systems still cannot achieve high data rates and long communication ranges at the same time (i.e., beyond 1 Mb/s and 1 km). Currently, acoustic communication is the only choice to achieve long distances. However, the inherent low acoustic bandwidth results in extremely low data rates. In this article, the acoustic reconfigurable intelligent surface (RIS) system is proposed to realize high-data-rate long-range underwater communications. Although the EM-based RIS has been widely investigated in terrestrial scenarios in recent years, the underwater acoustic RIS is based on completely different physics principles. Hence, the EM-based terrestrial RISs do not work for underwater acoustic signals. More-over, the long acoustic wave propagation delay, the inherent wideband nature, and the water behavior all impose unique challenges in underwater RIS operation. Therefore, this article presents a new hardware design to realize acoustic RIS, based on which the underwater RIS operation protocols are developed to address the aforementioned challenges. The proposed acoustic RIS system can be considered as an underwater infrastructure that enables beamforming functionalities for all types of devices, especially small robots and low-cost sensors. The simulation results show that the proposed acoustic RIS system can efficiently reflect acoustic waves and dramatically increase communication data rates and distances.

Cancellation of dolphin sonar clicks in a communication signal based on adaptive time reversal processing.

In long-range underwater communication, conventional time reversal processing (CTRP) is used to mitigate the distortion caused by multipath and temporal spreading. However, signals produced by marine animals can contaminate communication signals. Impulsive signals, such as dolphin sonar clicks, have wide bandwidths and short pulse durations, making it difficult to isolate the communication signal. This letter proposes a method to cancel these sounds by estimating the Green's function of marine animal clicks and applying adaptive time reversal processing (ATRP). The effectiveness of the click nulling was verified by comparing the performances of CTRP and ATRP with seagoing experimental data.

Long-Range Underwater Communication Based on Time Reversal Processing Using Various Diversity Methods.

Time reversal processing (TRP) exploits signal diversity methods, namely, spatial, temporal, beam, and frequency, to mitigate the distortion caused by multipath time delay. Using the same experimental data, this study compares the performance of communication utilizing TRP based on various diversity methods. In October 2018, the biomimetic long-range acoustic communication experiment 2018 (BLAC18) was conducted in the East Sea, east of Pohang, Korea. During the experiment, communication signals modulated by binary phase-shift keying were transmitted over a range of 60 km, and a vertical line array of 16 elements (with an aperture of ∼42 m) was utilized. The BLAC18 analysis showed that the performance of each diversity method depends on the order of diversity. When the order of diversity was one, the beam diversity method with the beamformed signal yielded the best performance. For the maximum order of diversity, however, the spatial diversity method delivered the best performance, owing to the high channel variability and large number of receivers.

Bayesian Multidimensional Scaling for Location Awareness in Hybrid-Internet of Underwater Things

Localization of sensor nodes in the internet of underwater things (IoUT) is of considerable significance due to its various applications, such as navigation, data tagging, and detection of underwater objects. Therefore, in this paper, we propose a hybrid Bayesian multidimensional scaling (BMDS) based localization technique that can work on a fully hybrid IoUT network where the nodes can communicate using either optical, magnetic induction, and acoustic technologies. These communication technologies are already used for communication in the underwater environment; however, lacking localization solutions. Optical and magnetic induction communication achieves higher data rates for short communication. On the contrary, acoustic waves provide a low data rate for long-range underwater communication. The proposed method collectively uses optical, magnetic induction, and acoustic communication-based ranging to estimate the underwater sensor nodes' final locations. Moreover, we also analyze the proposed scheme by deriving the hybrid Cramer-Rao lower bound (H-CRLB). Simulation results provide a complete comparative analysis of the proposed method with the literature.

Cancellation of dolphin sonar click in communication signal

In long-range underwater communication, the conventional passive Time Reversal Processing (TRP) is widely used to mitigate the distortion due to the multipaths and temporal spreading. However, the signals produced by marine animals were present in the data acquired during the experiment, contaminating the communication signal and acted as an unwanted signal. In particular, because the impulsive signal such as a dolphin sonar click has a wide bandwidth and a short pulse duration, it is difficult to separate the communication signal from the impulsive signal. This overlapping problem affects critically the communication performance. In this study, we propose a method to successfully cancel click sound. The method involves combining the adaptive TRP and the estimation of Green’s function of click sound. The adaptive TRP was successfully used in canceling crosstalk between interferers in a multiuser environment. Also, the estimation of Green’s function utilized the characteristics of the impulsive signal with clear distinction between paths. The effect of spatially nulling click sounds without distorting the phase of the communication signal showed a remarkable improvement in communication performance in the seagoing experimental data of BLAC18.

Some startling effects of biologic factors on seafloor physical properties

Recently, the biological impact on marine geophysics has received much interest. The question now is What types of impacts, how intense, and how changing? How can these impacts be understood and quantified, and then enacted in our practical predictive systems? Two dramatic examples from NW Europe. The acoustic response of the sandy seabeds is being altered by dense populations of species such as the invasive Ensis (i.e., a change of seabed properties). The same species forms a baffle that alters the seafloor response to flows, causing sediment trapping (i.e., a change of processes). At the sea surface, massive drifting rafts of detached bladder algae change the acoustic response of the sea surface and can attenuate surface waves. The rafts have seasonal and longevity attributes and can be tracked remotely, so effects on long-range underwater communications may be manageable. The Volkswagenstiftung, Office of Naval Research, NATO, and others have understood the significance and started to finance meetings, projects, and expert teams. To improve prediction capabilities, especially before at-sea operations, a close cooperation of biology and physical sciences is necessary. This can be achieved by two parallel approaches: (1) make existing bio- and geo-information compatible and (2) design new combined bio-geo experiments.

Simulation and modeling of hydro acoustic communication channels with wide band attenuation and ambient noise

Acoustic waves are the preferred medium for long-range underwater communications. Increasing number of innovative methods for underwater communication using acoustic waves appears. Performance of underwater communications for the new methods needs to be evaluated through simulation. Simulation of underwater acoustic communications is challenging due to many impediments, including attenuation, multipath propagation, noise and Doppler spread. In this paper, a baseline time domain simulation model is extended to several frequency-domain models. The proposed frequency models, including two incoherent models and a coherent model, take multipath attenuation and ambient noise into account. An incoherent linear fitting model and a coherent model are simulated and compared with a theoretical reference and the baseline time model. The proposed incoherent models are also compared with one another. Simulation shows that the incoherent linear fitting model produces results similar to the multi-frequency-merge-path model, but requires less computation time. In addition, the proposed coherent model is compared with field experimental data. The coherent model with color noise, in the frequency domain, can match closely the bit error rates of the field experimental data.

Low-frequency source for very long-range underwater communication

Very long-range underwater acoustic communication (UAC) is crucial for long cruising (>1000 km) autonomous underwater vehicles (AUVs). Very long-range UAC source for AUV must exhibit high electro-acoustic efficiency (>60%) and compactness. This paper describes the Janus-Hammer Bell (JHB) transducer that has been designed for this purpose and meets those requirements. The transducer works on the 450-550 Hz bandwidth and reaches source level above 200 dB (ref. 1 μPa at 1 m) with 1 kW excitation and full immersion capability. JHB source has been used for communication experiments by the Japanese institute for marine technology (Japan Agency for Marine-Earth Science and Technology) achieving a baud rate of 100 bits/s at 1000 km.

Advanced Magnetostrictive Materials for Sonar Applications

Piezoelectric or magnetostrictive materials can be utilised as active materials for electroacoustic underwater transducers. Piezoceramic materials gained edge over the conventional magnetostrictive materials during 1940s due to their unique electro-acoustic properties. At present, inspite of passive sonars there is a need of low-frequency high-power active sonars for the Navy. This led toresearch for new activematerials with competing characteristics to that of the existing piezo transducers. The discovery of a giant magnetostrictive material, commercially known as Terfenol-D, led to a breakthrough in the development of a new generation of sonar transducers. Now, the materials (including composites) as well as sensors are commercially available. A new generation of transducers have emerged in ocean-related areas like acoustic tomography, longrange underwater communication, geophysical exploration, oil well exploration, etc. Indian Institute of Technology Madras, Chennai, has also developed the basic material technology a few years back. At present, in India, National Institute of Ocean Technology, Chennai, is developing underwater transducers utilising giant magnetostrictive materials as well as piezoelectric materials for marine applications like sub-bottom profiling (seafloor mapping) and long-range underwater communications. A prototype of a portable, low-frequency medium power transmitter operating over a wide-frequency range has been developed. The main advantage of this transducer is its simplicity in design. In this paper, (he recent developments in material processes, importance of device-oriented material characterisation, and transducer design aspects have been emphasised. Some results on the underwater performance of a wide-band transducer have also been presented. These materials also have ultrasonic applications, capable of revolutionising the processing industry.

Performance of a low-frequency, multi-resonant broadband Tonpilz transducer.

The underwater performance of a high-power multi-resonant Tonpilz transducer with a nearly flat frequency response and a power handling capability of 2 kW (peak) is reported here. A maximum transmitting voltage response (TVR) value of 156 dB re: 1 microPa/V at 1 m has been achieved at 3 kHz with a specially designed matching coil. A maximum receiving sensitivity (RS) of -164 dB re: 1 V/microPa at 3 kHz has been measured without using a matching coil. The horizontal half-power beam width of the transducer at 4 kHz is 101 degrees with a directivity index of 4 dB. This transmitter can be used for oceanographic applications such as subbottom profiling as well as long-range underwater communication.

State switched transducers: A new approach to high-power, low-frequency, underwater projectors

In order to produce high-amplitude, low-frequency signals, an underwater transducer must generate a relatively large volume displacement. Since water exerts a large reaction force back on the transducer, “conventional wisdom” dictates that such a transducer would have to be a high Q resonant device and thus not be broadband. However, a transducer does not have to be broadband in the conventional sense to meet the requirements of communication and sonar systems. A transducer that is capable of instantaneously switching between two discrete frequencies is adequate for communication and transmission of coded signals; one that is capable of switching among several frequencies could produce the chirp signals commonly used in active sonars. Ordinarily, a broadband transducer is needed to accomplish the frequency switching rapidly. A way around this difficulty is the “state-switched” source concept originally proposed by Walter Munk in 1980 which permits instantaneous frequency switching of a high Q resonant transducer while always maintaining the resonance state. The objective of this research has been to investigate this novel approach to the design of high-power, low-frequency, broadband transducers for use in long-range underwater communication, active sonar, and underwater research applications. This paper presents a practical realization of a “state-switched” source.

Performance of an adaptive multichanel combinerfor longrange underwater communications

The authors describe the implementation of LMS and RLS adaptive multichannel combiners for a 50 km underwater acoustic channel, and present experimental results on their performance. BPSK transmission was used and the phase constellation plots obtained show that both combiners achieve a significant improvement in SINR and BER over single elements.