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Underwater Acoustic Communications and Networks
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Underwater Acoustic Communications and Networks

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (30 April 2022) | Viewed by 58924

Special Issue Editor

Dr. Youngchol Choi

E-Mail Website
Guest Editor
Marine ICT Research Division, Korea Research Institute of Ships and Ocean engineering, 32 1312 beon-gil, Yuseong-daero, Yuseong-gu, Daejeon 305-343, Korea
Interests: underwater acoustic communication; network protocol; array signal processing; inverse scattering

Special Issue Information

Dear Colleagues,

Digital communication is one of the most important infrastructures in modern human activities. A lot of high-speed digital communication technologies, for example, 3G, LTE, and satellite communications, are available, except in the ocean, which accounts for 70% of the Earth. The lack of a communication infrastructure is one of the main reasons for restricting human activity in the ocean.

In general, acoustic waves are used for underwater wireless communications and networks. Underwater acoustic communications and networks should overcome (1) the limited data rate due to the narrow bandwidth and the extended multi-paths that change rapidly over time and (2) network throughput degradation induced by the long propagation delay of sound waves. Despite the ongoing efforts to improve the performance of underwater acoustic communications and network protocols, it is still a challenging area. This Special Issue solicits original research papers that address, but are not limited to, the following topics:

  • Underwater acoustic channel modeling
  • Information theoretic analysis of underwater wireless communications and networks
  • Underwater acoustic modem design
  • MIMO communications
  • Network architecture
  • Spatial reuse multiple access
  • MAC and routing protocols
  • Network localization
  • Transport protocols
  • Machine learning applications
  • Underwater mobile platforms (AUV, ROV, etc.)
  • Experimental verification

Dr. Youngchol Choi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (19 papers)

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Research

10 pages, 373 KiB  
Article
Performance Prediction of Underwater Acoustic Communications Based on Channel Impulse Responses
by Evan Lucas and Zhaohui Wang
Appl. Sci. 2022, 12(3), 1086; https://0-doi-org.brum.beds.ac.uk/10.3390/app12031086 - 20 Jan 2022
Cited by 4 | Viewed by 1848
Abstract
Predicting the channel quality for an underwater acoustic communication link is not a straightforward task. Previous approaches have focused on either physical observations of weather or engineered signal features, some of which require substantial processing to obtain. This work applies a convolutional neural [...] Read more.
Predicting the channel quality for an underwater acoustic communication link is not a straightforward task. Previous approaches have focused on either physical observations of weather or engineered signal features, some of which require substantial processing to obtain. This work applies a convolutional neural network to the channel impulse responses, allowing the network to learn the features that are useful in predicting the channel quality. Results obtained are comparable or better than conventional supervised learning models, depending on the dataset. The universality of the learned features is also demonstrated by strong prediction performance when transferring from a more complex underwater acoustic channel to a simpler one. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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20 pages, 6804 KiB  
Article
Hybrid Equivalent Circuit/Finite Element/Boundary Element Modeling for Effective Analysis of an Acoustic Transducer Array with Flexible Surrounding Structures
by Min-Jung Sim, Chinsuk Hong and Weui-Bong Jeong
Appl. Sci. 2021, 11(6), 2702; https://0-doi-org.brum.beds.ac.uk/10.3390/app11062702 - 17 Mar 2021
Cited by 1 | Viewed by 1669
Abstract
Transducer arrays are commonly analyzed by the finite element method (FEM) with high accuracy, but it is costly, particularly when having flexible surrounding structures. In this study, we developed an equivalent circuit (EC)-based model of an array of transducers with flexible surrounding structures [...] Read more.
Transducer arrays are commonly analyzed by the finite element method (FEM) with high accuracy, but it is costly, particularly when having flexible surrounding structures. In this study, we developed an equivalent circuit (EC)-based model of an array of transducers with flexible surrounding structures for effective analysis. The impedance matrix was first constructed by coupling the electrical, mechanical impedance, and the acoustic radiation impedance obtained by the EC method and finite element-boundary element (FE-BE) coupling method. The transfer matrix of far-field pressure to the transducer response was then constructed by the FE-BE coupling method, and finally the sound pressure of the external acoustic field was obtained. To verify the accuracy, the results of the proposed method were compared with those of the conventional FEM. To evaluate the efficiency of the proposed method, the reduction in the degrees of freedom (DOFs) of the proposed method from the conventional FEM analysis was investigated. The simulation results of the proposed method are highly accurate and efficient. The proposed method is expected to be useful for conceptual design. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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11 pages, 2436 KiB  
Article
Study on Time Reversal Maximum Ratio Combining in Underwater Acoustic Communications
by Anbang Zhao, Caigao Zeng, Juan Hui, Keren Wang and Kaiyu Tang
Appl. Sci. 2021, 11(4), 1509; https://0-doi-org.brum.beds.ac.uk/10.3390/app11041509 - 07 Feb 2021
Cited by 5 | Viewed by 1704
Abstract
Time reversal (TR) can achieve temporal and spatial focusing by exploiting spatial diversity in complex underwater environments with significant multipath. This property makes TR useful for underwater acoustic (UWA) communications. Conventional TR is realized by performing equal gain combining (EGC) on the single [...] Read more.
Time reversal (TR) can achieve temporal and spatial focusing by exploiting spatial diversity in complex underwater environments with significant multipath. This property makes TR useful for underwater acoustic (UWA) communications. Conventional TR is realized by performing equal gain combining (EGC) on the single element TR output signals of each element of the vertical receive array (VRA). However, in the actual environment, the signal-to-noise ratio (SNR) and the received noise power of each element are different, which leads to the reduction of the focusing gain. This paper proposes a time reversal maximum ratio combining (TR-MRC) method to process the received signals of the VRA, so that a higher output SNR can be obtained. The theoretical derivation of the TR-MRC weight coefficients indicates that the weight coefficients are only related to the input noise power of each element, and are not affected by the multipath structure. The correctness of the derivation is demonstrated with the experimental data of the long-range UWA communications conducted in the South China Sea. In addition, the experimental results illustrate that compared to the conventional TR, TR-MRC can provide better performance in terms of output SNR and bit error rate (BER) in UWA communications. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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19 pages, 3462 KiB  
Article
Time Reversal and Fractional Fourier Transform-Based Method for LFM Signal Detection in Underwater Multi-Path Channel
by Zhichen Zhang, Haiyan Wang and Haiyang Yao
Appl. Sci. 2021, 11(2), 583; https://0-doi-org.brum.beds.ac.uk/10.3390/app11020583 - 08 Jan 2021
Cited by 8 | Viewed by 2117
Abstract
Fractional Fourier transform (FrFT) is a useful tool to detect linear frequency modulated (LFM) signal. However, the detection performance of the FrFT-based method will deteriorate drastically in underwater multi-path environment. This paper proposes a novel method based on time-reversal and fractional Fourier transform [...] Read more.
Fractional Fourier transform (FrFT) is a useful tool to detect linear frequency modulated (LFM) signal. However, the detection performance of the FrFT-based method will deteriorate drastically in underwater multi-path environment. This paper proposes a novel method based on time-reversal and fractional Fourier transform (TR-FrFT) to solve this problem. We make use of the focusing ability of time-reversal to mitigate the influence of multi-path, and then improve the detection performance of FrFT. Simulated results show that, compared to FrFT, the difference between peak value and maximum pseudo-peak value of the signal processed by TR-FrFT is improved by 8.75 dB. Lake experiments results indicate that, the difference between peak value and maximum pseudo-peak value of the signal processed by TR-FrFT is improved by 7.6 dB. The detection performance curves of FrFT and TR-FrFT detectors with simulated data and lake experiments data verify the effectiveness of proposed method. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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23 pages, 5461 KiB  
Article
Underwater Wireless Sensor Networks: An Energy-Efficient Clustering Routing Protocol Based on Data Fusion and Genetic Algorithms
by Xingxing Xiao, Haining Huang and Wei Wang
Appl. Sci. 2021, 11(1), 312; https://0-doi-org.brum.beds.ac.uk/10.3390/app11010312 - 30 Dec 2020
Cited by 33 | Viewed by 3225
Abstract
Due to the limited battery energy of underwater wireless sensor nodes and the difficulty in replacing or recharging the battery underwater, it is of great significance to improve the energy efficiency of underwater wireless sensor networks (UWSNs). We propose a novel energy-efficient clustering [...] Read more.
Due to the limited battery energy of underwater wireless sensor nodes and the difficulty in replacing or recharging the battery underwater, it is of great significance to improve the energy efficiency of underwater wireless sensor networks (UWSNs). We propose a novel energy-efficient clustering routing protocol based on data fusion and genetic algorithms (GAs) for UWSNs. In the clustering routing protocol, the cluster head node (CHN) gathers the data from cluster member nodes (CMNs), aggregates the data through an improved back propagation neural network (BPNN), and transmits the aggregated data to a sink node (SN) through a multi-hop scheme. The effective multi-hop transmission path between the CHN and the SN is determined through the enhanced GA, thereby improving transmission efficiency and reducing energy consumption. This paper presents the GA based on a specific encoding scheme, a particular crossover operation, and an enhanced mutation operation. Additionally, the BPNN employed for data fusion is improved by adopting an optimized momentum method, which can reduce energy consumption through the elimination of data redundancy and the decrease of the amount of transferred data. Moreover, we introduce an optimized CHN selecting scheme considering residual energy and positions of nodes. The experiments demonstrate that our proposed protocol outperforms its competitors in terms of the energy expenditure, the network lifespan, and the packet loss rate. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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14 pages, 11100 KiB  
Article
Long-Range Acoustic Communication Using Differential Chirp Spread Spectrum
by Joohyoung Lee, Jeongha An, Hyung-in Ra and Kiman Kim
Appl. Sci. 2020, 10(24), 8835; https://0-doi-org.brum.beds.ac.uk/10.3390/app10248835 - 10 Dec 2020
Cited by 13 | Viewed by 2547
Abstract
Here, we propose a new modulation method using chirp spread spectrum (CSS) modulation to indicate the result of long-range acoustic communication (LRAC). CSS modulation had outstanding matched filter characteristics even though the channel was complex. The performance of the matched filter depends on [...] Read more.
Here, we propose a new modulation method using chirp spread spectrum (CSS) modulation to indicate the result of long-range acoustic communication (LRAC). CSS modulation had outstanding matched filter characteristics even though the channel was complex. The performance of the matched filter depends on the time–bandwidth product. We studied the method of using the same modulation method while increasing the amount of the time–bandwidth product. When differential encoding is applied, the de-modulation is made using the difference between the current symbol and the previous symbol. If the matched filter is applied using both the current and the previous symbol, such as the use of two symbols, the amount of the time–bandwidth product can be doubled, and this method can make the output of the matched filter larger. The proposed method was verified in lake and sea experiments, in which the experimental environment was analyzed and compared with the result using the channel impulse response (CIR) of the lake and sea. The lake experiment was conducted over a distance of about 100–300 m between the transmitter and receiver and at a depth of ~40 m. As a result of the communication, the conventional method’s bit error rate (BER) was 1.22×10−1, but the proposed method’s BER was 1.98×10−2. The sea experiment was conducted over a distance of ~90 km and at a depth of ~1 km, and the conventional method BER in this experiment was 1.83×10−4, while the proposed method’s BER was 0. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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12 pages, 1536 KiB  
Article
Deep Learning-Based Timing Offset Estimation for Deep-Sea Vertical Underwater Acoustic Communications
by Yanbo Wu, Yan Yao, Ning Wang and Min Zhu
Appl. Sci. 2020, 10(23), 8651; https://0-doi-org.brum.beds.ac.uk/10.3390/app10238651 - 03 Dec 2020
Cited by 3 | Viewed by 1743
Abstract
This study proposes a novel receiver structure for underwater vertical acoustic communication in which the bias in the correlation-based estimation for the timing offset is learned and then estimated by a deep neural network (DNN) to an accuracy that renders subsequent use of [...] Read more.
This study proposes a novel receiver structure for underwater vertical acoustic communication in which the bias in the correlation-based estimation for the timing offset is learned and then estimated by a deep neural network (DNN) to an accuracy that renders subsequent use of equalizers unnecessary. For a duration of 7 s, 15 timing offsets of the linear frequency modulation (LFM) signals obtained by the correlation were fed into the DNN. The model was based on the Pierson–Moskowitz (PM) random surface height model with a moderate wind speed and was further verified under various wind speeds and experimental waveforms. This receiver, embedded with the DNN model, demonstrated lower complexity and better performance than the adaptive equalizer-based receiver. The 5000 m depth deep-sea experimental data show the superiority of the proposed combination of DNN-based synchronization and the time-invariant equalizer. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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16 pages, 1185 KiB  
Article
Blind Modulation Identification of Underwater Acoustic MPSK Using Sparse Bayesian Learning and Expectation Maximization
by Tao Fang, Zhi Xia, Songzuo Liu, Xiongbiao Wu and Lanyue Zhang
Appl. Sci. 2020, 10(17), 5919; https://0-doi-org.brum.beds.ac.uk/10.3390/app10175919 - 26 Aug 2020
Cited by 2 | Viewed by 1903
Abstract
This paper presents a likelihood-based algorithm for identifying different phase shift keying (PSK) modulations, i.e., BPSK, QPSK, and 8PSK. This algorithm selects the modulation type that maximizes a loglikelihood function that is based on the known original constellation associated with the constellation of [...] Read more.
This paper presents a likelihood-based algorithm for identifying different phase shift keying (PSK) modulations, i.e., BPSK, QPSK, and 8PSK. This algorithm selects the modulation type that maximizes a loglikelihood function that is based on the known original constellation associated with the constellation of the received signals for the candidate modulation types. However, there are two problems in non-cooperative underwater acoustic Multiple Phase Shift Keying (MPSK) modulation identification based on the likelihood method. One is the original constellation, which as prior information is unknown. The other is the underwater acoustic multipath channel makes the constellation distort seriously. In this paper, we solved these problems by combining sparse bayesian learning (SBL) with expectation maximization (EM). The specific steps are as follows. Firstly, blind channel equalization can be achieved by channel impulse response (CIR), which is estimated by sparse bayesian learning in single input multi output (SIMO) underwater acoustic channel. Subsequently, we used expectation maximization to compensate amplitude attenuation and phase offset, as the original constellation of MPSK is unknown. Finally, modulation can be successfully identified by the Quasi Hybrid Likelihood Ratio Test (QHLRT). The simulation results show that the channel estimation method based on SBL can eliminate the influence of channel effectively, and the EM algorithm can make the received constellation converge to the preset constellation in the case of unknown original transmit constellation, which effectively solves these two problems. We use the proposed SBL-EM-QHLRT method to achieve an identification rate of more than 95% in underwater acoustic multipath channels with Signal to Noise Ratio (SNR) higher than 15 dB, which provides a new idea for modulation identification of non-cooperative underwater acoustic MPSK. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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18 pages, 4439 KiB  
Article
A Nonlinear Distortion Removal Based on Deep Neural Network for Underwater Acoustic OFDM Communication with the Mitigation of Peak to Average Power Ratio
by Xuefei Ma, Waleed Raza, Zhiqiang Wu, Muhammad Bilal, Ziqi Zhou and Amir Ali
Appl. Sci. 2020, 10(14), 4986; https://0-doi-org.brum.beds.ac.uk/10.3390/app10144986 - 20 Jul 2020
Cited by 12 | Viewed by 3343
Abstract
Machine learning and deep learning algorithms have proved to be a powerful tool for developing data-driven signal processing algorithms for challenging engineering problems. This paper studies the modern machine learning algorithm for modeling nonlinear devices like power amplifiers (PAs) for underwater acoustic (UWA) [...] Read more.
Machine learning and deep learning algorithms have proved to be a powerful tool for developing data-driven signal processing algorithms for challenging engineering problems. This paper studies the modern machine learning algorithm for modeling nonlinear devices like power amplifiers (PAs) for underwater acoustic (UWA) orthogonal frequency divisional multiplexing (OFDM) communication. The OFDM system has a high peak to average power ratio (PAPR) in the time domain because the subcarriers are added coherently via inverse fast Fourier transform (IFFT). This causes a higher bit error rate (BER) and degrades the performance of the PAs; hence, it reduces the power efficiency. For long-range underwater acoustic applications such as the long-term monitoring of the sea, the PA works in full consumption mode. Thus, it becomes a challenging task to minimize power consumption and unnecessary distortion. To mitigate this problem, a receiver-based nonlinearity distortion mitigation method is proposed, assuming that the transmitting side has enough computation power. We propose a novel approach to identify the nonlinear power model using a modern deep learning algorithm named frequentative decision feedback (FFB); PAPR performance is verified by the clipping method. The simulation results prove the better performance of the PA model with a BER with the shortest learning time. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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13 pages, 1582 KiB  
Article
Reliable OFDM Data Transmission with Pilot Tones and Error-Correction Coding in Shallow Underwater Acoustic Channel
by Iwona Kochanska
Appl. Sci. 2020, 10(6), 2173; https://0-doi-org.brum.beds.ac.uk/10.3390/app10062173 - 23 Mar 2020
Cited by 6 | Viewed by 3049
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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15 pages, 2777 KiB  
Article
Efficient On-Off Keying Underwater Acoustic Communication for Seafloor Observation Networks
by Yan Yao, Yanbo Wu, Min Zhu, Dong Li and Jun Tao
Appl. Sci. 2020, 10(6), 1986; https://0-doi-org.brum.beds.ac.uk/10.3390/app10061986 - 13 Mar 2020
Cited by 12 | Viewed by 3292
Abstract
In the cableless seafloor observation networks (SONs), the links among network nodes rely on underwater acoustic communication (UAC). Due to the energy constraint and the high-reliability requirement of the cableless SONs, the noncoherent UAC has been a preferred choice, even though a noncoherent [...] Read more.
In the cableless seafloor observation networks (SONs), the links among network nodes rely on underwater acoustic communication (UAC). Due to the energy constraint and the high-reliability requirement of the cableless SONs, the noncoherent UAC has been a preferred choice, even though a noncoherent UAC scheme generally suffers from low spectral efficiency. In this paper, we propose a high-spectral-efficiency noncoherent UAC transmission scheme which is implemented as an orthogonal frequency-division multiplexing (OFDM) system adopting the on-off keying (OOK) modulation. To simultaneously achieve high performance at a low energy consumption, an irregular recursive convolutional code (IrCC) is employed and an accumulator (ACC) is introduced to achieve a modulation with memory at the transmitter side. The ACC enables a turbo iteration between the soft demapper called the ACC-OOK demapper and the soft decoder on the receiver side, and also reduces the decoding error floor. To account for the unknown signal-to-noise ratio (SNR), an iterative threshold estimation (ITE) algorithm is proposed to determine a proper decision threshold for the ACC-OOK demapper. The IrCC is designed to match the extrinsic information transfer (EXIT) curve of the ACC-OOK demapper, lowering the SNR threshold of the aforementioned turbo iteration. Simulations and experimental results verify the superiority of the proposed noncoherent UAC scheme over conventional ones. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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11 pages, 537 KiB  
Article
Assessment of Wide-Sense Stationarity of an Underwater Acoustic Channel Based on a Pseudo-Random Binary Sequence Probe Signal
by Iwona Kochanska
Appl. Sci. 2020, 10(4), 1221; https://0-doi-org.brum.beds.ac.uk/10.3390/app10041221 - 11 Feb 2020
Cited by 5 | Viewed by 2040
Abstract
The performances of Underwater Acoustic Communication (UAC) systems are strongly related to the specific propagation conditions of the underwater channel. Designing the physical layer of a reliable data transmission system requires a knowledge of channel characteristics in terms of the specific parameters of [...] Read more.
The performances of Underwater Acoustic Communication (UAC) systems are strongly related to the specific propagation conditions of the underwater channel. Designing the physical layer of a reliable data transmission system requires a knowledge of channel characteristics in terms of the specific parameters of the stochastic model. The Wide-Sense Stationary Uncorrelated Scattering (WSSUS) assumption simplifies the stochastic description of the channel, and thus the estimation of its transmission parameters. However, shallow underwater channels may not meet the WSSUS assumption. This paper proposes a method for testing the Wide-Sense Stationary (WSS) part of the WSSUS feature of a UAC channel on the basis of the complex envelope of a received probe Pseudo-Random Binary Sequence (PRBS) signal. Two correlation coefficients are calculated that can be interpreted, together, as a measure that determines whether the channel is WSS or not. A similar wide-sense stationarity assessment can be performed on the basis of the Time-Varying Impulse Response (TVIR) of a UAC channel. However, the method proposed in this paper requires fewer computational operations in the receiver of a UAC system. PRBS signal transmission tests were conducted in the UAC channel simulator and in real conditions during an inland water experiment. The correlation coefficient values obtained using the method based on the envelope of a probe signal and the method of analysing the TVIR estimates are compared. The results are similar, and thus, it is possible to assess if the UAC channel can be modelled as a WSS stochastic process without the need for TVIR estimation. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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12 pages, 1498 KiB  
Article
Using Fast Frequency Hopping Technique to Improve Reliability of Underwater Communication System
by Jan H. Schmidt
Appl. Sci. 2020, 10(3), 1172; https://0-doi-org.brum.beds.ac.uk/10.3390/app10031172 - 10 Feb 2020
Cited by 21 | Viewed by 4267
Abstract
Acoustic underwater communication systems designed to work reliably in shallow coastal waters must overcome major limitations such as multipath propagation and the Doppler effect. These restrictions are the reason for the complexity of receivers being built, whose task is to decode a symbol [...] Read more.
Acoustic underwater communication systems designed to work reliably in shallow coastal waters must overcome major limitations such as multipath propagation and the Doppler effect. These restrictions are the reason for the complexity of receivers being built, whose task is to decode a symbol on the basis of the received signal. Additional complications are caused by the low propagation speed of the acoustic wave in the water and the relatively narrow bandwidth. Despite the continuous development of communication systems using coherent modulations, they are still not as reliable as is desirable for reliable data transmission applications. This article presents an acoustic underwater communication system that uses one of the varieties of the spread spectrum technique i.e., the fast frequency hopping technique (FFH). This technique takes advantage of binary frequency-shift keying (BFSK) with an incoherent detection method to ensure the implementation of a system whose main priority is reliable data transmission and secondary priority is the transmission rate. The compromised choice of parameters consisted of the selection between the narrow band of the hydroacoustic transducer and the maximum number of carrier frequency hops, which results from the need to take into account the effects of the Doppler effect. In turn, the number of hops and the symbol duration were selected adequately for the occurrence of multipath propagations of an acoustic wave. In addition, this article describes experimental communication tests carried out using a laboratory model of the FFH-BFSK data transmission system in the shallow water environment of Lake Wdzydze/Poland. The test results obtained for three channels of different lengths are discussed. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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20 pages, 5315 KiB  
Article
Bionic Morse Coding Mimicking Humpback Whale Song for Covert Underwater Communication
by Muhammad Bilal, Songzuo Liu, Gang Qiao, Lei Wan and Yan Tao
Appl. Sci. 2020, 10(1), 186; https://0-doi-org.brum.beds.ac.uk/10.3390/app10010186 - 25 Dec 2019
Cited by 17 | Viewed by 4842
Abstract
A novel method of bionic Morse coding mimicking humpback whale vocal is presented for covert underwater acoustic communication. The complex humpback whale song is translated as bionic Morse codes based on information entropy. The communication signal is made akin to the natural singing [...] Read more.
A novel method of bionic Morse coding mimicking humpback whale vocal is presented for covert underwater acoustic communication. The complex humpback whale song is translated as bionic Morse codes based on information entropy. The communication signal is made akin to the natural singing of male humpback whales. The intruder can detect the signal but will not be able to recognize the communication signal due to unified resemblance with the natural sound. This novel technique gives an excellent low probability of recognition characteristics. A flawless stealthy underwater acoustic communication has been established which has negligible chances of deciphered with high imperceptibility. Standard mimicry Morse codes have been developed for the characters of the English language and compared with Morse coding. Covert information of one character per second can be watermarked with perfect stealth and clandestine communication. This novel concept has been verified at transmission distance of five km and less than 10−3 Bit Error Rate (BER) is achieved at Signal to Noise Ratio (SNR) down to negative seven dB. Zero BER is attained by estimating the channel by a matching pursuit algorithm and equalizing the errors by virtual time reversal mirror technique. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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24 pages, 7272 KiB  
Article
Multi-Media and Multi-Band Based Adaptation Layer Techniques for Underwater Sensor Networks
by Delphin Raj K M, Sun-Ho Yum, Eunbi Ko, Soo-Young Shin, Jung-Il Namgung and Soo-Hyun Park
Appl. Sci. 2019, 9(15), 3187; https://0-doi-org.brum.beds.ac.uk/10.3390/app9153187 - 05 Aug 2019
Cited by 15 | Viewed by 4238
Abstract
In the last few decades, underwater communication systems have been widely used for the development of navy, military, business, and safety applications, etc. However, in underwater communication systems, there are several challenging issues, such as limitations in bandwidth, propagation delay, 3D topology, media [...] Read more.
In the last few decades, underwater communication systems have been widely used for the development of navy, military, business, and safety applications, etc. However, in underwater communication systems, there are several challenging issues, such as limitations in bandwidth, propagation delay, 3D topology, media access control, routing, resource utilization, and power constraints. Underwater communication systems work under severe channel conditions such as ambient noise, frequency selectivity, multi-path and Doppler shifts. In order to collect and transmit the data in effective ways, multi-media/multi-band-based adaptation layer technology is proposed in this paper. The underwater communication scenario comprises of Unmanned Underwater Vehicles (UUVs), Surface gateways, sensor nodes, etc. The transmission of data starts from sensor nodes to surface gateway in a hierarchical manner through multiple channels. In order to provide strong and reliable communication underwater, the adaptation layer uses a multi-band/multi-media approach for transferring data. Hence, in this paper, existing techniques for splitting the band such as Orthogonal Frequency-Division Multiple Access (OFDMA), Frequency-Division Multiple Access (FDMA), or Orthogonal Frequency-Division Multiplexing (OFDM) are used for splitting the frequency band, and the medium selection mechanism is proposed to carry the signal through different media such as Acoustic, Visible Light Communication (VLC), and Infrared (IR) signals in underwater. For the channel selection mechanism, two phases are involved: 1. Finding the distance of near and far nodes using Manhattan method, and 2. Medium selection and data transferring algorithm for choosing different media. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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18 pages, 3340 KiB  
Article
Singular Value Decomposition Channel Estimation in STBC MIMO-OFDM System
by Ruiguang Tang, Xiao Zhou and Chengyou Wang
Appl. Sci. 2019, 9(15), 3067; https://0-doi-org.brum.beds.ac.uk/10.3390/app9153067 - 29 Jul 2019
Cited by 12 | Viewed by 4935
Abstract
The multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technology is the combination of the OFDM and MIMO technologies, which could improve the system capacity and make efficient utilization of the frequency spectrum. This paper utilizes space-time block coding (STBC) to achieve diversity gains [...] Read more.
The multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technology is the combination of the OFDM and MIMO technologies, which could improve the system capacity and make efficient utilization of the frequency spectrum. This paper utilizes space-time block coding (STBC) to achieve diversity gains and combat the channel fading. However, channel estimation is an essential block for space-time block decoding (STBD). Many channel estimation methods are utilized for the single antenna OFDM system, but they cannot be directly applied to the multiple antennas system due to the interference from other antennas. In this paper, orthogonal pilot sequences are designed to suppress the interference of pilot symbols from other transmit antennas. This paper also derives a minimum mean square error (MMSE) channel estimation method in MIMO-OFDM systems. The MMSE method involves the inverse operation of the channel autocorrelation matrix, which has a large calculation complexity. To further reduce the complexity of the MMSE method, the singular value decomposition (SVD) is used to decompose the channel autocorrelation matrix, which avoids the inverse operation. Simulation results verify that the SVD channel estimation method with comb-type pilots and STBC can be effectively adapted to multipath propagation conditions. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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15 pages, 2015 KiB  
Article
Channel Estimation Based on IOTA Filter in OFDM/OQPSK and OFDM/OQAM Systems
by Xiao Zhou, Chengyou Wang and Ruiguang Tang
Appl. Sci. 2019, 9(7), 1454; https://0-doi-org.brum.beds.ac.uk/10.3390/app9071454 - 07 Apr 2019
Cited by 8 | Viewed by 3755
Abstract
In this paper, we present a study of bit error rate (BER) for orthogonal frequency division multiplexing/offset quadrature phase shift keying (OFDM/OQPSK) and OFDM/offset quadrature amplitude modulation (OQAM) systems with an isotropic orthogonal transfer algorithm (IOTA) filter. The novel noise suppression method based [...] Read more.
In this paper, we present a study of bit error rate (BER) for orthogonal frequency division multiplexing/offset quadrature phase shift keying (OFDM/OQPSK) and OFDM/offset quadrature amplitude modulation (OQAM) systems with an isotropic orthogonal transfer algorithm (IOTA) filter. The novel noise suppression method based on an IOTA filter is proposed to reduce the error of channel estimation caused by additive white Gaussian noise (AWGN). The OFDM/OQPSK and OFDM/OQAM systems do not insert the guard interval (GI) and pilots in the signal frames, thus they possess transmission efficiency. An analysis was carried out for convolutional coded OFDM/OQPSK and OFDM/OQAM systems in Rayleigh fading channels with generator polynomials and constraint lengths. Compared with conventional OFDM/QPSK and OFDM/QAM systems with the insertion of comb-type pilots, the proposed IOTA filter-based channel estimation method can provide significant energy per bit to time-varying noise power spectral density ratio gains over time and frequency-selective propagation Rayleigh fading channels in OFDM/OQPSK and OFDM/OQAM systems. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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17 pages, 1629 KiB  
Article
Factorial Design Analysis for Localization Algorithms
by Joaquin Mass-Sanchez, Erica Ruiz-Ibarra, Ana Gonzalez-Sanchez, Adolfo Espinoza-Ruiz and Joaquin Cortez-Gonzalez
Appl. Sci. 2018, 8(12), 2654; https://0-doi-org.brum.beds.ac.uk/10.3390/app8122654 - 17 Dec 2018
Cited by 5 | Viewed by 3438
Abstract
Localization is a fundamental problem in Wireless Sensor Networks, as it provides useful information regarding the detection of an event. There are different localization algorithms applied in single-hop or multi-hop networks; in both cases their performance depends on several factors involved in the [...] Read more.
Localization is a fundamental problem in Wireless Sensor Networks, as it provides useful information regarding the detection of an event. There are different localization algorithms applied in single-hop or multi-hop networks; in both cases their performance depends on several factors involved in the evaluation scenario such as node density, the number of reference nodes and the log-normal shadowing propagation model, determined by the path-loss exponent ( η ) and the noise level ( σ d B ) which impact on the accuracy and precision performance metrics of localization techniques. In this paper, we present a statistical analysis based on the 2 k factorial methodology to determine the key factors affecting the performance metrics of localization techniques in a single-hop network to concentrate on such parameters, thus reducing the amount of simulation time required. For this proposal, MATLAB simulations are carried out in different scenarios, i.e., extreme values are used for each of the factors of interest and the impact of the interaction among them in the performance metrics is observed. The simulation results show that the path-loss exponent ( η ) and noise level ( σ d B ) factors have the greatest impact on the accuracy and precision metrics evaluated in this study. Based on this statistical analysis, we recommend estimating the propagation model as close to reality as possible to consider it in the design of new localization techniques and thus improve their accuracy and precision metrics. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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17 pages, 1319 KiB  
Article
An Improved Kernelized Correlation Filter Algorithm for Underwater Target Tracking
by Xingmei Wang, Guoqiang Wang, Zhonghua Zhao, Yue Zhang and Binghua Duan
Appl. Sci. 2018, 8(11), 2154; https://0-doi-org.brum.beds.ac.uk/10.3390/app8112154 - 03 Nov 2018
Cited by 12 | Viewed by 2522
Abstract
To obtain accurate underwater target tracking results, an improved kernelized correlation filter (IKCF) algorithm is proposed to track the target in forward-looking sonar image sequences. Specifically, a base sample with a dynamically continuous scale is first applied to solve the poor performance of [...] Read more.
To obtain accurate underwater target tracking results, an improved kernelized correlation filter (IKCF) algorithm is proposed to track the target in forward-looking sonar image sequences. Specifically, a base sample with a dynamically continuous scale is first applied to solve the poor performance of fixed-scale filters. Then, in order to prevent the filter from drifting when the target disappears and appears again, an adaptive filter update strategy with the peak to sidelobe ratio (PSR) of the response diagram is developed to solve the following target tracking errors. Finally, the experimental results show that the proposed IKCF can obtain accurate tracking results for the underwater targets. Compared to other algorithms, the proposed IKCF has obvious superiority and effectiveness. Full article
(This article belongs to the Special Issue Underwater Acoustic Communications and Networks)
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