Underwater acoustic communications and adaptive signal processing

This dissertation proposes three new algorithms for underwater acoustic wireless communications. One is a new tail-biting circular MAP decoder for full tail-biting convolution (FTBC) codes for very short data blocks intended for Internet of Underwater Things (IoUT). The proposed algorithm was evaluated by ocean experiments and computer simulations on both Physical (PHY) and Media access control (MAC) layers. The ocean experimental results show that without channel equalization, the full tail-biting convolution (FTBC) codes with short packet lengths not only can perform similarly to zero-tailing convolution (ZTC) codes in terms of bit error rate (BER) in the PHY layer. Computer simulation results show that the FTBC codes outperform the ZTC codes in terms of MAC layer metrics, such as collision rate and bandwidth utilization, in a massive network of battery powered IoUT devices. Second, this dissertation also proposes a new approach to utilizing the underwater acoustic (UWA) wireless communication signals acquired in a real-world experiment as a tool for evaluating new coding and modulation schemes in realistic doubly spread UWA channels. This new approach, called passband data reuse, provides detailed procedures for testing the signals under test (SUT) that change or add error correction coding, change bit to symbol mapping (baseband modulation) schemes from a set of original experimental data --Abstract, page iv

Federated Meta Learning Enhanced Acoustic Radio Cooperative Framework for Ocean of Things Underwater Acoustic Communications

Sixth-generation wireless communication (6G) will be an integrated architecture of "space, air, ground and sea". One of the most difficult part of this architecture is the underwater information acquisition which need to transmitt information cross the interface between water and air.In this senario, ocean of things (OoT) will play an important role, because it can serve as a hub connecting Internet of things (IoT) and Internet of underwater things (IoUT). OoT device not only can collect data through underwater methods, but also can utilize radio frequence over the air. For underwater communications, underwater acoustic communications (UWA COMMs) is the most effective way for OoT devices to exchange information, but it is always tormented by doppler shift and synchronization errors. In this paper, in order to overcome UWA tough conditions, a deep neural networks based receiver for underwater acoustic chirp communication, called C-DNN, is proposed. Moreover, to improve the performance of DL-model and solve the problem of model generalization, we also proposed a novel federated meta learning (FML) enhanced acoustic radio cooperative (ARC) framework, dubbed ARC/FML, to do transfer. Particularly, tractable expressions are derived for the convergence rate of FML in a wireless setting, accounting for effects from both scheduling ratio, local epoch and the data amount on a single node.From our analysis and simulation results, it is shown that, the proposed C-DNN can provide a better BER performance and lower complexity than classical matched filter (MF) in underwater acoustic communications scenario. The ARC/FML framework has good convergence under a variety of channels than federated learning (FL). In summary, the proposed ARC/FML for OoT is a promising scheme for information exchange across water and air

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

Low-complexity iterative receiver algorithms for multiple-input multiple-output underwater wireless communications

This dissertation proposes three low-complexity iterative receiver algorithms for multiple-input multiple-output (MIMO) underwater acoustic (UWA) communications. First is a bidirectional soft-decision feedback Turbo equalizer (Bi-SDFE) which harvests the time-reverse diversity in severe multipath MIMO channels. The Bi-SDFE outperforms the original soft-decision feedback Turbo equalizer (SDFE) while keeping its total computational complexity similar to that of the SDFE. Second, this dissertation proposes an efficient direct adaptation Turbo equalizer for MIMO UWA communications. Benefiting from the usage of soft-decision reference symbols for parameter adaptation as well as the iterative processing inside the adaptive equalizer, the proposed algorithm is efficient in four aspects: robust performance in tough channels, high spectral efficiency with short training overhead, time efficient with fast convergence and low complexity in hardware implementation. Third, a frequency-domain soft-decision block iterative equalizer combined with iterative channel estimation is proposed for the uncoded single carrier MIMO systems with high data efficiency. All the three new algorithms are evaluated by data recorded in real world ocean experiment or pool experiment. Finally, this dissertation also compares several Turbo equalizers in single-input single-output (SISO) UWA channels. Experimental results show that the channel estimation based Turbo equalizers are robust in SISO underwater transmission under harsh channel conditions --Abstract, page iv

Turbo Equalization for Single-Carrier Underwater Acoustic Communications

Recent research in underwater acoustic communications has taken advantage of MIMO technologies to achieve reliable communication with 10-100 times increase of data rate in comparison to traditional systems. The powerful turbo equalization and FEC coding techniques enable both single-carrier modulation and OFDM systems to combat triply selective UWA channels. This article reviews the time-domain and frequency-domain turbo equalizer schemes for MIMO SCM systems. Low-complexity techniques are presented with both turbo linear equalizers and turbo soft decision feedback equalizers in both the time and frequency domains. Although results are shown specifically for UWA channels, these turbo equalizer techniques are also suitable for terrestrial RF communication systems