Performance Of Underwater Acoustic Communication Research Articles

A review of underwater acoustic metamaterials for underwater acoustic equipment

Researchers use underwater acoustic equipment to explore the unknown ocean environment, which is one of the important means to understand and utilize the ocean. For underwater acoustic equipment, the application of underwater acoustic metamaterials is the premise to ensure and improve the performance of underwater acoustic communication, acoustic stealth, and sonar detection. Due to the limitations of mass density law and high hydrostatic pressure, traditional underwater acoustic materials cannot effectively absorb low-frequency sound waves and have low efficiency of elastic energy conversion. The sound absorption effect is poor under low frequency and high hydrostatic pressure. In recent years, with the development of acoustic metamaterials technology, all kinds of underwater acoustic metamaterials have also been proposed. Compared with sound waves propagating in the air, underwater sound is more difficult to control than air sound with the same frequency, so the design of underwater acoustic metamaterials is more complicated. This paper reviews the basic characteristics, development history of sound absorption, sound insulation decoupling, and underwater acoustic guided metamaterials, then the existing problems and the future development direction of underwater acoustic metamaterials are discussed.

Message Passing-Based Impulsive Noise Mitigation and Channel Estimation for Underwater Acoustic OFDM Communications

The impulsive noise and the time-varying channel are two major detrimental factors which greatly constrain the performance of underwater acoustic communications (UACs). Utilizing the joint sparsity of the impulsive noise and the channel impulse response, the paper proposes the generalized approximate message passing (GAMP)-based sparse Bayesian learning (SBL) frameworks for joint impulsive noise mitigation and channel estimation and tracking for orthogonal frequency division multiplexing (OFDM) UACs. Firstly, the SBL framework for the joint estimation is employed. To reduce the computational complexity, the GAMP is introduced into the expectation-maximization (EM) algorithm, and a low-complexity GAMP based SBL framework is formulated without performance degradation. To further estimate and track the impulsive noise and channel state information in the slow time-varying scenarios, we propose a novel GAMP-based temporal SBL framework. The factor graph and GAMP are used to achieve the approximated estimation for the posterior statistics of both the channel state information and the impulsive noise. The algorithm formulates the message passing scheduling for the EM algorithm to solve the joint multiple sparse signal recovery problem. Simulations and sea-trial results demonstrate that the proposed algorithms significantly improve the performance in terms of the mean square error of channel estimation, impulsive noise estimation, bit error rate and computational complexity compared with their corresponding SBL-based counterparts.

2E3-3 Underwater acoustic communication performance of space-frequency diversity applying maximum ration combining with maximum likelihood estimation in time varying fading channel by the movement of underwater vehicle

2E3-3 Underwater acoustic communication performance of space-frequency diversity applying maximum ration combining with maximum likelihood estimation in time varying fading channel by the movement of underwater vehicle

Model-based learning of underwater acoustic communication performance for marine robots

Accurate prediction of acoustic communication performance is an important capability for marine robots. In this paper, we propose a model-based learning methodology for the prediction of underwater acoustic communication performance. The learning algorithm consists of two steps: (i) estimation of the covariance matrix by evaluating candidate functions with estimated parameters using detrended measurements;and (ii) prediction of communication performance. Covariance estimation is addressed with a multi-stage iterative training method that produces unbiased and robust results with nested models. The efficiency of the framework is validated with simulations and experimental data from field trials. The field trials involved a manned surface vehicle and an autonomous underwater vehicle.

Variable observation window length blind equalization detector for underwater acoustic communication

Aiming at the influence of underwater acoustic channel (UAC) profile difference on the performance of underwater acoustic communication, a variable observation window length blind equalization detector (VOWL-BED) is proposed in this paper. Compared with the existing methods, the observation window length (OWL) of the proposed VOWL-BED can be dynamically regulated on the basis of a given UAC profile and finally converge to the optimum OWL. We have verified the feasibility of the OWL regulation. The simulation results also demonstrate that the VOWL-BED can achieve better performance than the conventional invariable OWL blind equalization detector (IOWL-BED).

Reliable OFDM Data Transmission with Pilot Tones and Error-Correction Coding in Shallow Underwater Acoustic Channel

The performance of Underwater Acoustic Communication (UAC) systems are strongly related to the specific propagation conditions of the underwater channel. Horizontal, shallow-water channels are characterised by extremely disadvantageous transmission properties, due to strong multipath propagation and refraction phenomena. The paper presents the results of communication tests performed during a shallow, inland-water experiment with the use of a laboratory model of a UAC system implementing the Orthogonal Frequency-Division Multiplexing (OFDM) technique. The physical layer of data transmission is partially configurable, enabling adaptation of the modulation and channel coding parameters to the specific propagation conditions. The communication tests were preceded by measurement of the UAC channel transmission properties. Based on the estimated transmission parameters, four configurations of OFDM modulation parameters were selected, and for each of them, communication tests were performed with the use of two Error-Correction Coding (ECC) techniques. In each case, the minimum coding rate was determined for which reliable data transmission with a Bit Error Rate (BER) of less than 10 − 4 is possible.

Underwater acoustic communication performance by signal to noise plus interference ratio in BLAC18

In underwater acoustic communications, inter-symbol interference (ISI) caused by multipath propagation of underwater channel degrades communication performance significantly. Various techniques, such as time reversal combining and decision feedback equalization, have been developed to eliminate the influence of the interference. However, few studies have assessed the performance with the signal-to-noise (SNR) of received communication signals. In practical underwater acoustic systems, the channel must be accurately estimated for the channel equalization and the SNR is involved in the accuracy of the channel estimation. The effect of interference is dominant at short distances, but the effect of noise becomes dominant as distance increases. In this study, SNR, signal-to-interference ratio, and signal-to-noise plus interference ratio (SINR) are estimated as a function of the distance, and communication performances are examined. Communication data from BLAC18, conducted in East Sea of Korea in 2018, are used to analyze the communication performances. In the experiment, communication signals with a carrier frequency of 2.5 kHz were transmitted and received at horizontal distances of 30, 60, and 90 km. Data analysis results shows that communication performance is most correlated with SINR. [Work supported by the ADD(UD170022DD).]

M-ary Cyclic Shift Keying Spread Spectrum Underwater Acoustic Communications Based on Virtual Time-Reversal Mirror.

Underwater acoustic communications are challenging because channels are complex, and acoustic waves when propagating in the ocean are subjected to a variety of interferences, such as noise, reflections, scattering and so on. Spread spectrum technique thus has been widely used in underwater acoustic communications for its strong anti-interference ability and good confidentiality. Underwater acoustic channels are typical coherent multipath channels, in which the inter-symbol interference seriously affects the performance of underwater acoustic communications. Time-reversal mirror technique utilizes this physical characteristic of underwater acoustic channels to restrain the inter-symbol interference by reconstructing multipath signals and reduce the influence of channel fading by spatial focusing. This paper presents an M-ary cyclic shift keying spread spectrum underwater acoustic communication scheme based on the virtual time-reversal mirror. Compared to the traditional spread spectrum techniques, this method is more robust, for it uses the M-ary cyclic shift keying spread spectrum to improve the communication rate and uses the virtual time-reversal mirror to ensure a low bit error rate. The performance of this method is verified by simulations and pool experiments.

Optimal Deployment of Vector Sensor Nodes in Underwater Acoustic Sensor Networks.

Underwater acoustic sensor networks have recently attracted considerable attention as demands on the Internet of Underwater Things (IoUT) increase. In terms of efficiency, it is important to achieve the maximum communication coverage using a limited number of sensor nodes while maintaining communication connectivity. In 2017, Kim and Choi proposed a new deployment algorithm using the communication performance surface, which is a geospatial information map representing the underwater acoustic communication performance of a targeted underwater area. In that work, each sensor node was a vertically separated hydrophone array, which measures acoustic pressure (a scalar quantity). Although an array receiver is an effective system to eliminate inter-symbol interference caused by multipath channel impulse responses in underwater communication environments, a large-scale receiver system degrades the spatial efficiency. In this paper, single-vector sensors measuring the particle velocity are used as underwater sensor nodes. A single-vector sensor can be considered to be a single-input multiple-output communication system because it measures the three directional components of particle velocity. Our simulation results show that the optimal deployment obtained using single-vector sensor nodes is more effective than that obtained using a hydrophone (three-channel vertical-pressure sensor) array.

An Underwater Time Reversal Communication Method Using Symbol-Based Doppler Compensation with a Single Sound Pressure Sensor

Due to the significant multipath and Doppler effects in the underwater acoustic (UWA) channel, the quality of the received signal is degraded, which seriously affects the performance of UWA communication. The paper proposes a time reversal UWA communication method combined with a symbol-based Doppler compensation (SBDC) technique to solve those problems. A single element time reversal mirror (TRM) is used to realize channel equalization and mitigate the inter-symbol interference (ISI) resulting from multipath propagation. The SBDC technique is subsequently used to compensate Doppler effects in the received signal, thereby reducing the bit error rate (BER) and improving the communication performance. In order to verify the performance of the proposed communication method, some simulations with real sounding channels were performed. Moreover, a field UWA communication experiment was conducted in the Songhua River (Harbin, China). The UWA communication experiment achieves nearly error-free performance with a communication rate of 100 bit/s in the bandwidth of 2 kHz. The results of the experiment demonstrate the feasibility and robustness of the proposed UWA communication method.

Optimal Deployment of Sensor Nodes Based on Performance Surface of Underwater Acoustic Communication.

The underwater acoustic sensor network (UWASN) is a system that exchanges data between numerous sensor nodes deployed in the sea. The UWASN uses an underwater acoustic communication technique to exchange data. Therefore, it is important to design a robust system that will function even in severely fluctuating underwater communication conditions, along with variations in the ocean environment. In this paper, a new algorithm to find the optimal deployment positions of underwater sensor nodes is proposed. The algorithm uses the communication performance surface, which is a map showing the underwater acoustic communication performance of a targeted area. A virtual force-particle swarm optimization algorithm is then used as an optimization technique to find the optimal deployment positions of the sensor nodes, using the performance surface information to estimate the communication radii of the sensor nodes in each generation. The algorithm is evaluated by comparing simulation results between two different seasons (summer and winter) for an area located off the eastern coast of Korea as the selected targeted area.

BER Performance Evaluation of Underwater Communication System with Spatial Diversity

Objectives: To use diversity technique to improve the Bit Error Rate (BER) performance of Underwater Acoustic Communication (UWAC). Methods/Analysis: Orthogonal Frequency Division Multiplexing (OFDM) is used in UWAC to effectively deal with the multipath propagation delay and also it produces high bitrate underwater communication. The three major factors that are considered in UWA propagation are attenuation, time varying multipath and low speed of sound. The noise that is considered in UWAC is ambient noise. Findings: To overcome the effect of multipath fading, diversity technique is used in UWC. Spatial diversity along with Maximal Ratio Combining (MRC) is found to be a better approach to improve the error performance. Novelty/Improvement: OFDM along with spatial diversity and MRC will mitigate the system against channel fading.

Redundancy allocation in time-varying channels with long propagation delays

In this paper, we propose an optimal redundancy allocation over a binary symmetric channel by using recent results on a tight approximation of codeword error probability in the finite blocklength regime. We evaluate the performance of the proposed algorithm over experimental data where slowly time-varying channel conditions were measured. The rationale of this study is to enhance the performance of underwater acoustic communications, for which low bit rates are available. The performance of the proposed scheme is compared with those obtained for a constant rate allocation and a rateless scheme. Results confirm that in the presence of a time-varying channel with long propagation delays, the utilization of a robust codeword is inefficient in terms of bandwidth used and energy per bit. However, as it results in a small number of retransmissions, it also guarantees short delivery delays. Furthermore, in the case where a lower reliability can be tolerated, the proposed scheme is more efficient and also has shorter delivery delays.

Algorithm and Experimental Verification of Underwater Acoustic Communication Based on Passive Time-Reversal Mirror

수중음향통신에서는 다중경로에 의한 지연확산 채널과 조류로 인한 자연적 유동 혹은 인위적인 플랫폼 이동 등으로 도플러 확산 채널이 발생한다. 이로 인하여 발생하는 인접 심볼 간 간섭을 제거하기 위하여 등화기가 사용되고 있으나 다중 경로 등의 음향 환경정보를 사용하고 있지 않다. 반면 수동형 시역전의 경우 한 방향 전파과정으로 산출한 채널응답특성의 수치적 정합필터를 통하여 자기 등화를 수행하게 되므로 등화기보다 비교적 단순한 알고리즘으로 간섭을 제거하는 특성을 갖는다. 본 논문에서는 2010년 동해에서 수행한 통신 실험의 실측 데이터에 수동형 시역전을 적용하여 다중경로로 인한 간섭을 제거하고, 통신성능이 향상됨을 보이고자 한다. 이를 검증하기 위하여 수동형 시역전의 적용 전/후의 신호 대 간섭 잡음비를 비교하고 분석한다. 또한 수동형 시역전과 적응형 등화기의 알고리즘을 각각 독립적으로 수행하여 비트오류율을 산출하고 이를 비교하여 수동형 시역전의 통신성능을 검증한다. The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

Influence of Underwater Channel Time-Variability on Communication Throughput Efficiency

Underwater acoustic channel has time-variability. Time varying channel which disturbs the continuous transmission of information data reduces the underwater acoustic communication performance. In this paper, we show the temporal coherence as time-variability of channel and indicate throughput efficiency in accordance with transmission time of information data. Then we analyzed influence of underwater channel time-variability on communication throughput efficiency. We confirmed that the throughput efficiency reduced when the time-variability of the channel increased via lake trial.

Relating the performance of time-reversal-based underwater acoustic communications in different shallow water environments

The performance of underwater acoustic communications, such as the output signal-to-noise ratio (OSNR), is generally dependent on the channel specifics, hence a channel model is normally required as the performance of the channel equalizer depends on the number of tap coefficients used (e.g., a sparse equalizer) which are different for different oceans having different multipath arrivals. This letter presents theoretical arguments, and experimental data from different oceans that suggest that the increase of OSNR with the number of diverse receivers (in terms of the effective number of receivers) and the decrease of OSNR with the channel-estimation error follow a universal relationship using the time-reversal or correlation-based equalizer, despite the fact that the channels have very different properties. The reason is due to the fact that the OSNR is a function of the q function, the auto-correlation of the received impulse responses summed over all receiver channels, and the q function is approximately the same for all shallow waters given a sufficient (≥4-6) number of receivers.

Investigation of the environmental factors affecting a horizontal underwater acoustic communication channel.

This study sought to characterize the long‐term performance of a horizontal underwater acoustic communication system using experimentation and channel simulation. A long‐term investigation was carried out off the coast of Western Australia in a depth of 100 m, simultaneously collecting environmental and modem communication performance data for over 16 days. Additionally, an underwater acoustic communication simulator based on the Bellhop propagation model was developed to provide performance predictions for the deployed modems. The signal‐to‐noise ratio was measured to be relatively high for the entire duration of the trial which helped classify environmental influences as being related to other parameters. Using multiple linear regression, it was determined that the sound speed profile, sea surface roughness, and signal‐to‐noise ratio contributed to the increased performance of underwater acoustic communication. This result was confirmed by implementing a simulation over the area of interest in a modeled...

A low-cost testbed of underwater mobile sensing network

Comprised by a swarm of acoustically linked and cooperative autonomous underwater vehicles (AUVs) with onboard sensors, an underwater mobile sensing network (UMSN) will be a complementary means to fixed observatory networks, e.g. seafloor observatory networks and moored buoy arrays. It has obvious advantages over a single large AUV in higher efficiency due to parallel observation, stronger robustness to vehicle failures and lower cost. Although an UMSN can be viewed as a counterpart of wireless mobile sensing networks for air and terrestrial applications, it is much more challenging due to poor performance of underwater acoustic communication, poor performance of underwater positioning and high degree of uncertainty in vehicle dynamics and underwater environment. In order to verify key technologies involved in an UMSN, e.g. cooperation of multi-AUVs based on acoustic communication, a low cost testbed has been developed for experimental study. The design of both hardware and software is introduced. Also the results of a functional test for verification of the effectiveness of the testbed are presented.

Using spatial coherence to improve the performance of underwater acoustic communications

Phase-shifted keying modulation schemes offer an efficient use of signal power for a given bandwidth in a communication channel. Successful communication often requires multichannel data (spatial diversity) to combat the signal fading due to random fluctuations in the channel. For each channel, a signal-to-noise ratio (SNR) of >10 dB is often required to estimate the channel impulse response for proper placement of the tap coefficients. Array beamforming can be used to improve the SNR, but when to use spatial diversity or beamforming is an issue long debated but not yet satisfactorily answered. It is shown with at-sea data that an effective use of beamforming versus spatial diversity depends on the phone spacing relative to the signal coherence. Beamforming requires the signals to be correlated between the sensors, whereas spatial diversity requires the opposite. Neither can fulfill the job of the other. By choosing phones according to spatial coherence and combining beamforming with diversity, bit error rates of the order of ∼0.001 were demonstrated using Advent 99 data over a period of ∼ 9 hours with an SNR as low as ∼1 dB at the phone level. [This work is supported by the Office of Naval Research and SACLANTCEN.]