차동위상천이 방식을 갖는 저피탐 수중음향통신 시스템 설계

In recent years, underwater sensor networks can be used for environment monitoring, disaster prevention, and military surveillance. When acoustic waves are passed through the underwater, they are affected by attenuation, reflection of bottom and surface, scattering, ambient noise, and the Doppler effect caused by movement of the transmitter and the receiver. This thesis presents constructing transmitter and receiver by using a direct sequence spread spectrum techniques to DPSK (differential phase shift keying) scheme in underwater acoustic communication. Using direct sequence spread spectrum is helpful to overcome the jamming unlike other spread spectrum methods and has strong security between user. Since DPSK signal can be demodulated if the receiver knows only the phase difference between the adjacent bits, DPSK receiver structure has the advantage of being simplified. In the conventional receiver, two adjacent symbols of transmitted signal before despread are passed to the transition correlator that detects data by comparing maximum correlation outputs. At this time, the error for maximum value of the correlator output may increase because of low SNR (signal-to-noise ratio) or high Doppler shift frequency according to the underwater channel. In this thesis, a new method is proposed for accurate detection result. The proposed method uses the peaks’ width as well as the its magnitude among outputs produced by the correlator for BER performance enhancement. The performances of the proposed method was evaluated by simulation and sea trial data.List of Tables iii List of Figures iv Abstract v 제 1 장 서론 1 제 2 장 수중음향 채널 4 2.1 전달 손실 5 2.2 다중 경로 전달 6 2.3 도플러 효과 7 2.4 잡음 9 제 3 장 전이 상관기를 이용한 DPSK-DSSS 수신기 11 3.1 기존의 DPSK 송수신 방법 11 3.2 기존의 DPSK-DSSS 송수신 방법 13 3.2.1 직접 수열 대역확산 방식 13 3.2.2 기존의 DPSK-DSSS 송수신 방법 16 3.3 상관 폭 기반 DPSK-DSSS 수신 방법 제안 20 제 4 장 모의실험 및 해상실험 결과 24 4.1 모의실험 결과 24 4.1.1 DPSK-DSSS 수중음향통신 시스템 설계 25 4.1.2 VirTEX 모의실험 결과 27 4.2 해상실험 결과 30 제 5 장 결론 35 참고문헌 37Maste

Doppler estimation based on frequency average and recursive frame method for underwater acoustic communication

In recent years, underwater sensor networks can be used for environment monitoring, disaster prevention, and military surveillance. Unlike terrestrial communication, underwater acoustic communication utilizes sound waves. The sound speed is dependent on the water temperature and the salinity. The sound transmission path is changed by refraction according to the gradient of vertical sound velocity. When sound waves are passed through the underwater, they are affected by attenuation, reflection of bottom and surface, scattering, ambient noise, and the Doppler effect caused by movement of the transmitter and the receiver. Of these factors, the Doppler effect affects the correlation time of the channel related to the transmission efficiency. These influences thus cannot be neglected in the design of underwater acoustic communication systems. To increase transmission efficiency, estimation the changing Doppler frequency and compensation for distortion are needed. In this thesis, Doppler shift frequency estimation methods to use in the time varying channel proposed. Two kinds of methods are proposed. One is a Doppler estimation algorithm that has stable performance as a part of the communication system. From an overall communication system perspective, the other is a demodulation scheme that is different from the conventional communication system. The ambiguity function and decision-directed estimation are presented. Also, a more accurate Doppler estimation method that is based on decision-directed estimation is proposed, and a re-modulation method that can update the channel parameters for the equalizer operation and estimate the Doppler frequency during the data frame using two Doppler estimation techniques is proposed. A simulation based on the Bellhop modeling and sea experiment was carried out to compare the performance of the proposed method with a conventional non-recursive Doppler estimation. When the channel coding technique was not applied, the uncoded bit error rate performance of the proposed method was improved about maximum 50.3 % compared with conventional method.List of Tables iii List of Figures iv Abstract v 제 1 장 서론 1 제 2 장 수중음향 채널 4 2.1 수중음향 채널의 특성 4 2.1.1 전달 손실 5 2.1.2 다중 경로 전달 6 2.1.3 도플러 효과 7 2.1.4 잡음 8 2.2 수중음향 채널의 시변동성 8 2.2.1 시간영역 상관도 9 2.2.2 도플러 효과의 영향 12 제 3 장 도플러 추정을 위한 기법 14 3.1 기존의 도플러 추정 방법 14 3.1.1 모호 함수 기법 14 3.1.2 Decision-directed 추정 기법 16 3.2 제안된 도플러 추정 방법 17 3.2.1 주파수 평균 기반의 Decision-directed 추정 기법 18 3.2.2 재귀 프레임 변복조 19 제 4 장 모의실험 및 실험 결과 분석 23 4.1 모의실험 결과 23 4.2 호수실험 결과 26 4.3 해상실험 결과 29 제 5 장 결론 33 참고문헌 35 감사의 글 3

A study on FrFT receiver for frequency hopping spread spectrum with chirp signal

Unlike terrestrial communication, underwater acoustic communication utilizes sound waves. The sound speed is dependent on the water temperature and the salinity. The sound transmission path is changed by refraction according to the gradient of vertical sound velocity. When sound waves are passed through the underwater, they are affected by attenuation, reflection of bottom and surface, scattering, ambient noise, and the Doppler effect caused by movement of the transmitter and the receiver. Even due to the doppler effect, the received signal is expanded and compressed. Sometimes it is necessary to hide and protect our information from stranger. However, due to the characteristics of underwater acoustic communication using sound waves, the probability of detection is higher than that of terrestrial communication, and our information is easily intercepted. Therefore, it is necessary to study on the covert communication along with the reliable communication in the underwater acoustic channel. In this thesis, a covert underwater acoustic communication method that is robust to fading using a chirp signal combined with a frequency-hopping spread spectrum scheme is designed and demodulated to new type receiver. A fractional Fourier transform (FrFT), which estimates the slope of the signal frequency variation, is applied to the receiver to enable a robust and reliable symbol estimation with respect to the frequency and irregular phase variations. Using FrFT, the chirp signal can be distinguished and other frequencies can be treated as noise. Therefore, FrFT receiver is a different demodulation method compared to conventional correlator receiver. In addition, since the recursive symbol synchronization can be implemented using a chirp signal, compression and expansion effects due to the Doppler shift can be mitigated. Simulation and lake trials were performed to verify the performance of the proposed method.제 1 장 서론 1 제 2 장 수중음향 채널 특성 2.1 전달손실 6 2.2 다중 경로 전달 7 2.3 도플러 효과 8 2.4 잡음 9 제 3 장 처프 신호를 결합한 주파수 도약 방식과 FrFT 수신기 3.1 CSK 변조 방식과 주파수 도약 확산 스펙트럼 10 3.2 상관 함수를 이용한 기존의 수신 방법 13 3.3 FrFT를 이용한 수신 방법 제안 15 3.4 심볼 동기화를 위한 재귀 동기 보정 기법 23 제 4 장 모의실험 및 호수실험 결과 분석 4.1 모의실험 결과 25 4.2 호수실험 결과 29 제 5 장 결론 35 참고문헌 37Maste

Rake Receiver Based on BER of Training Sequence Duration in Low Probability of Detection for Underwater Acoustic Communication

In recent years, underwater sensor networks can be used for environment monitoring, disaster prevention, and military surveillance. When sound waves are passed through the underwater, they are affected by attenuation, reflection of bottom and surface, scattering, ambient noise, and the Doppler effect caused by movement of the transmitter and the receiver. In this thesis a type of channel and the channel parameters are investigated to calculate the counter-detection range in underwater acoustic communication channels. A rake receiver that uses the BER (bit error rate) analysis of train signals was proposed, which have the better performance than a conventional rake receiver. A conventional rake receiver selects the paths which are the matched filter output over threshold. Weights are allocated to selected paths in accordance with path gains. A proposed rake receiver uses the same method to a conventional rake receiver which is path selection, but that uses BER analysis of each path under threshold in the training sequence to assign weights. In accordance with training sequence BER the weights are allocated, the lower train BER the high weighting value. After the envelop of received signals are used in channel fading analysis, the channel types and channel parameters are investigated by curve fitting of the amplitude variability. After the ROC (receiver operating characteristic) curve are calculate by the channel types and channel parameters, as a result, counter-detection range are attained by calculating detection probability in accordance with false alarm probability. In the event of lake experiments the channel type is Rayleigh fading channel. Consequently ROC curve and counter-detection range are analyzed. A non-rake receiver, conventional rake receiver, and proposed rake receiver performance are evaluated in lake experiments. As a result, proposed rake receiver have the error free performance and conventional rake receiver have 12.5% BER performance.제 1 장 서론 1 제 2 장 수중음향 채널 및 탐지확률 3 2.1 수중음향 채널 특성 3 2.1.1 전달 손실 4 2.1.2 다중 경로 전달 5 2.1.3 도플러 효과 6 2.1.4 잡음 8 2.2 채널 페이딩 및 탐지확률 9 2.2.1 채널 페이딩에 따른 탐지확률 9 2.2.1.1 Non-fading 9 2.2.1.2 Gaussian fading 10 2.2.1.3 Log-normal fading 11 2.2.1.4 Rayleigh fading 12 2.2.2 곡선 적합 13 2.2.3 ROC 곡선 15 2.2.4 채널에 따른 탐지 거리 16 제 3 장 오차율 기반 레이크 수신기 19 3.1 기존의 레이크 수신 방법 20 3.2 제안된 레이크 수신 방법 24 제 4 장 모의실험 및 호수실험 결과 29 4.1 모의실험 결과 29 4.2 4월 호수실험 결과 35 4.3 5월 호수실험 결과 43 제 5 장 결론 51 참고문헌 53 감사의 글 5

ANN-Based Control of a Multiboat Group for the Deployment of an Underwater Sensor Network

Underwater sensor networks (USNs) can be used for several types of commercial and noncommercial applications. However, some constraints resulting from the nature of aquatic environments severely limit their use. Due to constraints such as large propagation latency, low-bandwidth capacity, and short-distance communications, a large number of USN nodes are deployed to provide reliability in most applications. In this study, an unattended deployment approach based on the use of an autonomous boat group is proposed. A map of the deployment zone and optimal locations of USN nodes are fed into the onboard computers of the boat group. After processing these data and determining paths to be followed, the boat group deploys sensor nodes at predetermined locations. During the deployment, the boat group is controlled by an artificial neural network- (ANN-) based control system for reducing path errors. A set of performance evaluations is given to prove efficiency of the proposed control system. Performance results show that the boat group can successfully follow a predefined path set and deploy USN nodes. The tradeoffs between energy consumptions, end-to-end delay, and number of hops between underwater relay nodes of energy-efficient USN are also examined. The results indicate that increasing the number of hops reduces the total energy consumption and the end-to-end delay