A Study on Weighted Multiband Communication Method Based on Iterative Coding for Long Range Underwater Acoustic Communication

Recently, underwater acoustic communication is an essential technology for underwater communication in marine research, and its application field is expanding. In addition, with the development of military AUV capable of long-distance movement, there is an increasing need to develop a technology capable of reliably communicating over a long distance for efficient marine surveillance. In the long distance acoustic communication, as the transmission distance increases, the bandwidth decreases and the throughput efficiency decreases. Multiband transmission technique is an efficient method to improve the transmission distance and performance in long-range underwater acoustic communication. However, sometimes the performance of multiband is lower than that of single bands. This is because in the transceiver model using the conventional multiband transmission technique, signals of different frequency bands are combined with the same weight and input to the decoder, so that performance degradation of a specific frequency band affects the total band. Accordingly, this thesis propose a weighted multiband transceiver model to improve the performance of the multiband transceiver model. In the weighted multiband transceiver model, the transmitter uses a convolution code and a turbo code of 1/3 coding rate, and receiver uses a decision feedback equalizer to compensate for multipath distortion after compensating for frequency and phase offsets in each band. And, by applying the turbo equalization technique, the equalizer and the decoder is connected to each other to update the information iteratively to improve performance as the number of iteration increases. In addition, the threshold detector adds weights by setting threshold values through preamble BER(Bit Error Rate) of each band. The weighting method according to the threshold value for each band can improve the performance by reducing the influence of the band having low performance in the total band. Simulation results show that the performance improves as the number of bands increases when the multiband transmission technique is applied. The performance of the proposed weighted multiband transceiver model analyzed through short and 90 km long-range sea experiments. In the short-range sea experiment, it confirmed that the performance improved with the increase of the number of bands, and that the performance was improved by applying the proposed weighted multiband structure to the data with low performance when the number of bands was four. In addition, the 90 km long-range sea experiment applied a weighted multiband transceiver model for data that did not completely correct errors within 5 iterations in the conventional multiband. As a result, it confirmed that the performance is further improved when the weighted multiband is applied.List of Tables ii List of Figures iii Abstract iv 제 1 장 서론 1 제 2 장 수중음향통신에서 고려되는 전송 기법 3 2.1 채널 부호화 기법 4 2.2 단일밴드 전송 기법 6 2.3 다중밴드 전송 기법 9 제 3 장 가중화된 다중밴드 통신 12 3.1 임계값 및 가중치 설정 알고리즘 12 3.2 가중화된 다중밴드 기반의 송·수신구조 15 제 4 장 시뮬레이션 및 실험 결과 분석 17 4.1 시뮬레이션 17 4.2 단거리 해양 실험 20 4.3 장거리 해양 실험 26 제 5 장 결 론 35 참고문헌 37 감사의 글 40Maste

Multicarrier Spread Spectrum Communication Scheme for Cruising Sensor Network in Confined Underwater Space

A cruising sensor network works as an online monitoring system for industrial liquid environments such as oil tanks and nuclear storage ponds. The cruising sensor network consists of a few submerged nodes which can actuate themselves to execute tasks like “cruising.” This paper presents a multicarrier spread spectrum scheme, which is designed for communications between the nodes and the control station. Although underwater acoustic communication has been widely researched due to the growing demands from ocean development and marine research, communication in confined underwater space is an unexplored domain as most research focuses on communication in spacious water areas. The occasions that the cruising sensor network works in are confined. The main distinction in confined underwater spaces is the existence of strong multipath arrivals reflected by the boundaries, which can cause more severe intersymbol interference (ISI). We propose a communication scheme which applies spread spectrum in orthogonal frequency-division multiplexing (OFDM) to address severe frequency selective fading channels. This scheme can be robust in confined underwater channels when coupled with turbo code. The simulation and experimental results prove the feasibility and reliability of this scheme. It is demonstrated that significantly better performance is achieved than that of the conventional OFDM method