Underwater Channel Environment Research Articles

Modulation recognition for underwater acoustic communication based on hybrid neural network and feature fusion

It is a huge challenge for underwater acoustic receivers to correctly identify modulation methods due to the complex underwater channel environment and severe noise interference. Combined with the lightweight network (SqueezeNet) and attention mechanism (SENet), a multi-attribute and multi-scale feature fusion model based on a hybrid neural network is proposed, which achieves efficient and accurate recognition for modulation modes. First, the wavelet time-frequency (WTF) spectrum, square power spectrum, and contour maps of cyclic spectrum are extracted as multi-attribute inputs for the network to reduce the impact of inherent defects in single attribute feature. Second, shallow and deep features based on the SqueezeNet model are obtained as multi-scale features, of which the key feature expression ability is enhanced by the SENet model to provide sufficient feature information for modulation recognition. The simulation experiments and sea trial data confirm that the suggested method demonstrates strong generalization capabilities and effectiveness when applied to underwater acoustic channels and environmental noise. In contrast to algorithms in existence, the method verifies superior recognition abilities.

Evaluation of WATERMARK Channel for Underwater Communication using Dual Tree Complex Wavelet Transform based Orthogonal Frequency Division Multiplexing Model

Underwater communication is one of the important research areas which involves design and development of communication systems that can demonstrate high data rate and low Bit Error Rate (BER). In this work three different modulation schemes are compared for their performances in terms of BER and Peak to Average Power Ratio (PAPR). The realistic channel model called WATERMARK is used as a benchmark to evaluate channel performances. The mathematical model is developed in MATLAB and channel environments such as Norway Oslo fjord (NOF1), Norway Continental Shelf (NCS1), Brest Commercial Harbour (BCH1), Kauai (KAU1, KAU2) are considered for modelling different underwater channels. The data symbols are modulated using Dual Tree Complex Wavelet Transform (DTCWT) Orthogonal Frequency Division Multiplexing (OFDM) model to generate multi subcarriers and are demodulated at the receiver considering underwater channel environments. The BER results are evaluated for channel depth less than 10m and 10-50m. An improvement of 2x10-2 in terms of BER is observed when compared with Fast Fourier Transform (FFT) based OFDM model.

Modulation Recognition of Underwater Acoustic Signals Using Deep Hybrid Neural Networks

It is a huge challenge for the receiver to correctly identify the modulation types due to the complex underwater channel environment and severe noise interference. Additionally, the real-time communications have strict requirements in terms of time. In order to solve this well-known issue, in this work, we combine the automatic feature extraction and learning ability of recurrent neural network (RNN) and convolutional neural network (CNN) for designing a modulation recognition model for underwater acoustic signals. The proposed model is based on deep hybrid neural networks called recurrent and convolutional neural network (R&CNN). As compared with the traditional modulation recognition techniques, this method achieves higher recognition accuracy without manual feature extraction. The experimental results show that the validation accuracy of the proposed R&CNN’s on the Trestle data set is 98.21%. Similarly, the validation accuracy of the proposed R&CNN’s on the South China Sea data set is 99.38%. The average recognition time is 7.164ms. As compared with the conventional deep learning methods, the proposed R&CNN not only has a higher recognition accuracy, but also greatly reduces the recognition time.

Underwater acoustic communication using nonlinear frequency modulation waveform with low side-lobe characteristics

In fluctuating underwater acoustic (UWA) communication, reducing the interference caused by multi-path propagation is important to get better performance. For this reason, Chirp Spread Spectrum (CSS), which has insensitive Doppler effect and having effective bandwidth, using Linear Frequency Modulation (LFM) waveform was used in UWA communication before. But LFM waveform has high auto-correlation function sidelobes it becomes interference and gets worse performance in reverberation environment. This presentation proposes an UWA communication using Generalized Sinusoidal Frequency Modulation (GSFM) waveform which is generalized form of sinusoidal FM. GSFM waveform usually attains much higher spectral efficiency and lower peak-to-average power ratio than LFM while maintaining same bandwidth and pulse duration. GSFM waveform has various types and we use two GSFM pulses that is a Forward type in time-frequency domain and a time reversing type of Forward type in this presentation. Each type represents binary values '0' and '1', respectively. Each of pulses occupy same band of frequency and each of GSFM pulses have nearly orthogonality. Simulation results in various underwater channel environments with noise will be presented. A Bellhop-based underwater channel model is used for simulation. The proposed method will be analyzed compared to the conventional CSS method with LFM waveform.

Analysis of underwater wireless optical communication system performance.

Because the underwater channel environment is complicated, it is difficult to do an actual experiment in the ocean to analyze the performance of underwater wireless optical communication (UWOC) systems. In this study, the spot-expansion characteristics and time-domain broadening characteristics of underwater wireless optical signals are simulated and analyzed by a Monte Carlo statistical method. Thus, what we believe is an improved underwater channel transmission-attenuation model and time-domain broadening model based on UWOC are proposed, so the transmission distance characteristics of the UWOC system are obtained by combining the system parameters, and the transmission-rate characteristics can be analyzed by using the Shannon-Hartley theorem. The results show that the transmission distance is linear with the receiver sensitivity, and the transmission rate decays exponentially with the transmission distance and is limited by the receiver sensitivity in the UWOC system.

Preliminary Study on the Characteristics of Laser Underwater Proximity Transmission

Due to the special circumstances of underwater channel environment, laser underwater communication technology is facing challenges. The characteristics of underwater channel have been simulated and tested in this paper. Firstly, the scattering model and Monte-Carlo simulation method based on Mie scattering are established. Secondly, the simulation test on the influence of laser transmission under different parameter conditions is carried out. Finally, the design of the laser signal receiving system and the laser underwater transmission experiment are designed. The method of reducing the signal to noise ratio is analyzed and put forward. The experimental research is also carried out to verify the correctness of the simulation results. The experimental results show that with the increase of transmission distance, the diameter and density of scattering particles, the time domain broadening, space broadening and energy absorption of the laser will reduce the received light energy transfer signal, the sine wave will be distorted and the transmission will be affected effectiveness.

Analysis of underwater acoustic communication channel environment in Kyungcheon Lake

Analysis of underwater acoustic communication channel environment in Kyungcheon Lake

Reinforcement learning-based link adaptation in long delayed underwater acoustic channel

In this paper, we apply reinforcement learning, a significant area of machine learning, to formulate an optimal self-learning strategy to interact in an unknown and dynamically variable underwater channel. The dynamic and volatile nature of the underwater channel environment makes it impossible to employ pre-knowledge. In order to select the optimal parameters to transfer data packets, by using reinforcement learning, this problem could be resolved, and better throughput could be achieved without any environmental pre-information. The slow sound velocity in an underwater scenario, means that the delay of transmitting packet acknowledgement back to sender from the receiver is material, deteriorating the convergence speed of the reinforcement learning algorithm. As reinforcement learning requires a timely acknowledgement feedback from the receiver, in this paper, we combine a juggling-like ARQ (Automatic Repeat Request) mechanism with reinforcement learning to minimize the long-delayed reward feedback problem. The simulation is accomplished by OPNET.

Experimental study of efficient multi-band underwater acoustic communication algorithm

In the underwater acoustic communication environment, multipath transfer characteristics or Doppler spread due to time and space changes such as seabed, sea level, and water depth affect the performance. The multi-band communication technique is effective in terms of performance and throughput efficiency because it can overcome selective frequency fading by allocating the same data to different frequency bands in the environment of rapidly changing channel transfer characteristic. In addition, the transmission distance can be further extended while overcoming various underwater channel environments. However, the multi-band configuration may have worse performance than the single-band one. It is because the performance degradation in a particular band affects the output from the entire bands, which is input into a decoder, thereby decreasing the overall performance. This problem can be solved through a receiving end that analyzes error rates of each band, sets threshold values, and allocates lower weights to inferior bands. In this paper, we proposed an algorithm to set the threshold value using the preamble error rate, which is known data to be transmitted and received. We have analyzed the efficiency of multi-band transmission scheme by applying 1–4 number of multi-bands using turbo pi code through actual underwater experiment.

Improving BER and data throughput using adaptive modulation level MC-CDMA technique in underwater wireless communication

Underwater communication has a wide range of applications like environmental monitoring to predict the natural disasters, underwater ex-ploration and military applications. The need for effective underwater communication is the high demand in the present scenario. The im-plementation of precise modulation technique is also important because the underwater channel environment is time variant due to various noises present in the underwater like natural and vehicle noise (mechanical noises). The bandwidth is also highly limited in underwater communication. The existing method is adaptive modulation based OFDM system. This method has low spectral efficiency, however, each symbol is modulated with different carriers. The proposed method is Adaptive Modulation Level MC-CDMA (Multi carrier Code Division Multiple Access). The CDMA techniques share the same carrier frequency to multiple number of users. It adapts the modulation scheme according to the present channel conditions in the underwater. The performance of the proposed system improves the Data Throughput and Bit Error Rate.

Underwater ship noise pattern detection and identification

The anthropogenic underwater noise event could be identified by spectral analysis and acoustic pattern pre-classification of previously measured noise sources. This paper discusses real-time applicable methods for separation of purely natural noise recordings when ships are absent from the data polluted by the ship noise. The natural noise periods are used for the statistical modeling of underwater channel environment and relative levels of marine ambient noise (Wenz curves). The anthropogenic noise periods allow us to identify the noise sources. Moreover, most of the ship identification methods require spectrum component processing and pre-determined ship classification, which could be based on this automatic separation results. The correlational and multiple criteria detection methods compared with cyclostationary feature detection and widely used energy detection. False alarm and misclassification minimization could be achieved by multiple sensor data fusion: weather and Automatic Identification System (AIS). The measured data were collected near the seafloor with an autonomous long-term passive acoustic recorder and were combined with ship passage information from the AIS. Three years of measurements include multiple individual ship observations with different speeds and directions. Analysis of the experimental results emphasizes the importance of pre-classification, especially in multiple target cases.The anthropogenic underwater noise event could be identified by spectral analysis and acoustic pattern pre-classification of previously measured noise sources. This paper discusses real-time applicable methods for separation of purely natural noise recordings when ships are absent from the data polluted by the ship noise. The natural noise periods are used for the statistical modeling of underwater channel environment and relative levels of marine ambient noise (Wenz curves). The anthropogenic noise periods allow us to identify the noise sources. Moreover, most of the ship identification methods require spectrum component processing and pre-determined ship classification, which could be based on this automatic separation results. The correlational and multiple criteria detection methods compared with cyclostationary feature detection and widely used energy detection. False alarm and misclassification minimization could be achieved by multiple sensor data fusion: weather and Automatic Identification System...

수중 채널환경에서 FMT-OFDM 시스템의 성능 향상을 위한 연구

수중 채널환경에서 FMT-OFDM 시스템의 성능 향상을 위한 연구

10kHz 반송파를 사용한 서해안 수중 채널환경 분석

This study was carried out near the waters of Jango port, Dangjin-gun, Chungcheongnam-do by utilizing 10kHz carrier frequency, for the purpose of measurement and analysis of underwater channel environment of the Western sea. For the measurement of horizontal channel environment, the separation distance between transmitter and receiver is made differently in the range between 10m and 4000m. Meanwhile, for the measurement of vertical channel environment, transmission and receiving side ships are fixed as contacted each other and measured differently depending on their depth of submergence. In this study, the Coherence Bandwidth and the Coherence Time were estimated by analyzing the Power delay profile of the real sea based on the measured data, and analyzing the doppler frequency through frequency conversion of received tone-signal, respectively. This study is expected to become a base study in carrying out the frame design for underwater communication to improve the communication and secure the reliability of communication in future underwater channel environment.

수중 채널 환경에서 전송량 증대를 위한 다중반송파 시스템에 관한 연구

Studies applying multiple carrier method such as OFDM(Orthogonal Frequency Division Multiplexing) or FMT(Filtered Multi-Tone) to Underwater acoustic communication(UAC) system are actively under way as UAC is utilized in the various fields and the demand of high speed data transmission increases. In the existing OFDM method, the use of virtual carrier, which is inserted not to affect the adjacent channel in the frequency domain, and the cyclic prefix, which is used to reduce the impact of Inter Symbol Interference and Inter Channel Interference, decrease the throughput. In particular, the length of cyclic prefix to be used becomes longer under water since underwater has a rapidly changing channel characteristic, and the data throughput diminishes because it has to allocate more subcarrier on virtual carrier. This study therefore suggests FMT-OFDM system, a combination of OFDM and FMT, for the purpose of enhanced throughput in the underwater channel environment. Besides, in this study, channel is modeled based on data measured in real sea and the performance is analyzed after setting system parameters. 논문 15-40-06-26 The Journal of Korean Institute of Communications and Information Sciences '15-06 Vol.40 No.06 http://dx.doi.org/10.7840/kics.2015.40.6.1193 1193 ※ 본 연구결과는 국토해양부의 “수중 광역 이동통신 시스템 기술개발” 과제에서 수행된 연구결과 중 일부임을 밝히며, 연구비 지원에 감사드립니다. First Author : Hoseo University Department of Information and Telecommunication Eng., minsang@hoseo.edu, 정회원 ° Corresponding Author : Hoseo University Department of Oceanic IT Eng., taehoim@hoseo.edu, 정회원 * Hoseo University Department of Information and Telecommunication Eng., 정회원 ** Sangmyung University Department of Information and Telecommunication Eng., 정회원 *** Korea Research Institute of Ships and Ocean Eng.(KRISO), 종신회원 논문번호:KICS2015-05-153, Received May 21, 2015; Revised June 16, 2015; Accepted June 16, 2015 The Journal of Korean Institute of Communications and Information Sciences '15-06 Vol.40 No.06 1194 그림 1. 실측데이터 측정지역 Fig. 1. Measurement area map I. 서 론 최근 해양 생태계 연구 및 자원탐사, 인명구조, 군 사적 목적 등 사람이 직접 작업할 수 없는 환경에서 AUV(Autonomous Unmmanded Vehicle)를 활용한 원격 작업이 증가함에 따라 수중음향통신 기술의 중요 성이 대두되고 있다 . 따라서 향후 수중에서도 원활한 원격 작업을 위해 음파를 사용한 고속의 데이터 서비 스가 요구될 것이며, 이러한 요구를 만족하기 위해 OFDM(Orthogonal Frequency Division Multiplexing) 과 FMT(Filtered Multi-Tone)와 같은 다중반송파 전 송방식을 수중에 적용하기 위한 연구가 활발히 진행 중이다 . 일반적으로 수중 채널 환경은 수온과 수심, 염분 등 의 영향으로 인하여 장소와 계절에 따라 급격하게 변 화하고, 수중생물 및 해면과 해저면, 해양 생물 등에 의해 발생하는 다중경로 페이딩의 영향으로 신호의 심볼 간 간섭이 증가하여 통신성능의 저하를 초래한 다. 따라서 극심한 채널변화를 갖는 수중 채널 환경에 서 단일반송파 전송방식을 사용하게 되면 주파수 선 택적 채널이 되어 이를 보상하기 위해 복잡한 등화기 의 설계가 필요하지만 다중반송파 방식을 사용하면 각 부반송파 단위로 데이터 심볼의 채널 등화를 수행 하기 때문에 간단한 등화기를 사용하여 심볼 복원이 가능해진다 . 그러나 실제 수중 채널 환경에서 상관대역폭은 불 과 수십~수백 Hz로 작기 때문에 OFDM을 적용하기 위해 각 부반송파의 대역폭을 상관대역폭보다 작게 설계하게 되면 부반송파의 개수증가로 FFT 사이즈가 증가하여 시스템의 복잡도가 증가하게 되고, 극심한 채널변화를 갖는 수중 채널 환경은 부반송파 간 인접 채널에 영향을 증가시키므로 인접 채널간의 영향을 줄이기 위해 사용하는 가상 부반송파(virtual carrier) 개수의 증가를 초래하여 데이터 전송량이 감소된다. 따라서 수중 채널 환경에서 신뢰성 있는 고속의 데이 터 통신 및 전송량 증대를 위해 기존의 OFDM 시스 템과 FMT 시스템을 결합한 FMT-OFDM 시스템을 제안한다. FMT-OFDM 시스템은 전체 사용 주파수 대역에서 multi-band를 생성하고 각 sub-band에 OFDM을 수행 하는 방식으로 OFDM 시스템과 부반송파의 개수는 동일하지만 sub-band 내의 OFDM 부반송파의 개수는 감소하여 FFT 사이즈를 감소시키고 FMT의 사용으로 부반송파 간의 인접 채널 간섭이 감소하므로 가상 부 반송파의 개수를 감소시켜 데이터 전송량을 증대시킬 수 있다. 본 논문의 II장에서는 측정환경 설명과 수중 채널 환경에 적합한 FMT-OFDM 시스템 연구를 위해 실해 역에서 측정한 데이터를 분석하였으며, III장에서는 FMT-OFDM 시스템의 구조도에 대해 설명한다. IV장 에서 FMT-OFDM 시스템의 성능 검증을 위한 시뮬레 이션 결과를 보이고, 끝으로 V장에서 본 논문의 결론 을 맺는다. II. 측정 환경 및 수중 채널 분석 그림 1은 측정데이터 측정 장소인 거제도 앞바다와 송신측과 수신측의 위치(35°1'48.43N 128°37'28.3 1E와 35°2'3.64N 128°38' 14.35E)를 나타낸 그 림이다. 그림 2에는 본 측정에 사용한 (a)선박과 (b)선박 내 부에 설치한 측정 장비, (c)송신 센서와 (d)수신센서가 보인다. 거제도 앞바다는 수심이 약 40m이며 송수신기의 입수 깊이는 해면 반사파와 해저면 반사파의 반사 거 리를 동일하도록 전체 수심의 중간 지점인 20m에 위 치시켰고 송수신 선박간의 거리에 따른 수중 채널 특 성의 변화를 알아보기 위해 선박과 수신 선박 간의 거 리를 100m에서 1500m까지 다르게 하여 데이터를 송 수신 하였다. 본 논문에서는 수중 채널 환경에 적합한 FMT-OFDM 시스템의 파라미터 선정과 채널 모델링 을 위해 실측데이터 분석을 하였으며, 측정데이터 분 석의 신뢰성을 높이기 위해 각 거리별로 9~15회 반복 하여 데이터를 수집하였다 . 송신신호는 BPSK 변조 방식을 사용하여 1023개의 PN 코드를 반복해서 전송 하였고, 데이터의 전송률은 5kbps였으며, 25kHz의 반 송주파수로 데이터를 전송하였다. 그림 3은 거제도 천 논문 / 수중 채널 환경에서 전송량 증대를 위한 다중반송파 시스템에 관한 연구 1195 (a) 선박 (b) 선박 내부의 측정장비

오차분포거리의 반복적 계산에 의한 결정궤환 알고리듬

As a criterion of information theoretic learning, the Euclidean distance (ED) of two error probability distribution functions (minimum ED of error, MEDE) has been adopted in nonlinear (decision feedback, DF) supervised equalizer algorithms and has shown significantly improved performance in severe channel distortion and impulsive noise environments. However, the MEDE-DF algorithm has the problem of heavy computational complexity. In this paper, the recursive ED for MEDE-DF algorithm is derived first, and then the feed-forward and feedback section gradients for weight update are estimated recursively. To prove the effectiveness of the recursive gradient estimation for the MEDE-DF algorithm, the number of multiplications are compared and MSE performance in impulsive noise and underwater communication environments is compared through computer simulation. The ratio of the number of multiplications between the proposed DF and the conventional MEDE-DF algorithm is revealed to be ) 4 N N + for the sample size N with the same MSE learning performance in the impulsive noise and underwater channel environment.

A Multi-hop OFDM Frame Structure for Short-Range Underwater Acoustic Communication Networks

In this paper, for the purpose of providing high data rate services, the multi-hop frame structure is designed for the underwater acoustic (UWA) short-range system which is proposed as a part of ocean surveillance and tracking network (OSTN). Under the measured underwater channel environment, the link-level system performance are also evaluated. Simulation results show not only the packet error rate (PER) comparisons, but the optimal modulation and coding scheme (MCS) levels for the orthogonal frequency division multiplexing (OFDM) based short-range UWA communications network.

수중채널 환경에서 센서 간의 간격에 의한 수신 신호의 상관 특성 분석

In this paper, we have analyzed the performance of space diversity technologies using experimental data in order to analyze the usability of space diversity techniques in underwater channel environments. After analyzing the experimental data we found out that high diversity gain should not be expected when using a stationary transmitter with a stationary receivers in swallow underwater channel. And we also find out that the distance between sensors should be at least 8 wavelengths apart to take advantage of diversity gain in underwater moving channel environments.