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远程移动水声通信关键技术研究
中文摘要

当今世界,海洋以其巨大的资源潜力和重要的战略地位受到人们越来越高的重视,远程移动水声通信技术在海洋开发和水下安全方面具有重要的作用与意义,近年来成为水声通信领域的研究热点。水声通信作为涉及物理、通信、信号处理、传感器等技术的综合学科,存在诸多理论及技术难关需要攻克。远程水声信道多途时延扩展大、信噪比低,要在移动条件下实现稳健且高效的远程水下信息传输,更加具有挑战性。本文针对远程移动水声通信中面临的几个难题,对相应的关键技术进行了理论分析、仿真和试验验证。论文的主要研究内容如下: 1.针对远程移动水声通信中计算大点数帧同步,所需存储资源与计算资源过多,实现实时处理困难的问题,提出了一种帧同步分块算法,在不影响同步性能的前提下,降低了计算的空间复杂度和时间复杂度,有利于信号的实时处理。 2.针对远程移动水声通信中低信噪比下难以有效跟踪时变多普勒因子的问题,提出了一种基于正交扩频调制的联合处理算法,利用扩频码良好的时频分辨能力,对时变多普勒进行逐符号跟踪估计,同时完成对扩频码码片的捕获跟踪,借助扩频增益获得在低信噪比下的可靠性能。仿真和海试表明,该算法在远程移动水声通信中低信噪比的环境下,可以有效估计和跟踪时变多普勒因子。 3.针对移动水声通信中正交多载波信号对多普勒因子较为敏感的问题,提出一种基于压缩感知的多普勒跟踪与快速补偿算法,根据水声信道时域稀疏特性,借助压缩感知技术对信道估计结果进行稀疏度评估,选择稀疏度最佳的信道响应对应的多普勒估计对信号进行快速补偿。仿真和结果表明,该算法有效的克服了传统多普勒算法难以跟踪时变多普勒的缺点,在一定的信噪比条件和多普勒范围内,估计误差优于对比算法;同时快速补偿算法显著降低了计算量,更适于信号实时处理;通过对导频进行复用,避免占用额外的频带资源,提高了通信效率。 4.研究了适用于正交多载波扩频的信道匹配技术,提出了一种无导频信道估计(Pilot-Free Channel Estimation,PFCE)算法,充分利用浅海水声信道的稀疏特性,解决了传统算法需要添加导频冗余来初步估计信道而带来的通信效率下降的问题。仿真分析和湖试结果表明,PFCE算法可以在不添加导频信息的条件下可达到与对比算法接近的性能。 5.针对远程移动水声通信中通信带宽受限导致通信速率较低的问题,研究了混沌通信的原理和特点,将混沌与正交多通道扩频调制相结合,提出了一种混沌混合扩频(Chaotic Hybrid Spread Spectrum,CHSS)调制技术,利用混沌信号良好的互相关特性,降低了混合扩频的通道间干扰,在提高通信速率的同时保证了系统的误码率性能;为进一步提高扩频通信的通信效率,结合正交多载波调制和频域M元扩频技术,提出一种新的正交多载波M元混沌调相扩频(M-ary Chaotic Phase Modulation Orthogonal Multi-carder Spread Spectrum,M-ary CPM-OMCSS)水声通信方式,在保证通信误码性能的同时极大的提高了通信效率。 6.研究了北极及中高纬度冰下声传播的物理特性,分析了传播特性对冰下水声通信的影响,在此基础上对中国第七次北极科考首次极地冰下水声通信试验的数据进行了处理与分析,分析结果验证了北极冰下水声通信的可能性,为今后北极及中高纬度海域冰下水声通信的进一步研究与试验提供了研究基础。 关键词:水声通信;多普勒估计与补偿;混沌通信;信道估计;冰下通信

英文摘要

At present, the ocean receives more and more attention due to its great resource potential and important strategic position. The technology of long range mobile underwater acoustic communication is of great significance for ocean development and underwater security, and has become a research hotspot in the field of underwater acoustic communication recently. As an integrated discipline which combines physics, communication, signal processing and sensor technology, the underwater acoustic communication still has plenty of problems both on theory and technology to overcome. With a greater multipath delay spread and lower signal to noise ratio of long range underwater acoustic channel, it's more challengeable to achieve the stable and high efficient long range underwater information transmission. This paper provides the theoretical analysis, simulation and experiment verification for several problems facing in the long range mobile underwater acoustic communication. The main research content of this paper is summarized as follows: 1.In consideration of the long-range mobile real-time underwater acoustic communication, the paper proposes a block frame synchronization algorithm. This algorithm is able to decrease the space and time complexity of the frame synchronization without performance loss. 2.Toovercome the disadvantages of conventional Doppler estimation under low signal to noise ratio, a joint processing algorithm based on orthogonal spectrum spread modulation is proposed to track the time-variant Doppler in long range mobile underwater acoustic communication. The algorithm utilizes the excellent time-frequency resolution of spreading code to track the Doppler factor of each symbol, and realizes the chip phase estimation. The reliable performance under low signal to noise ratio is achieved due to the spectrum spread gain. Simulation results and sea-trial results are provided, demonstrating that the proposed algorithm can effectively track the time-variant Doppler factor symbol by symbol in the long range mobile communication. 3.Multicarriersignals are sensitive to the Doppler factor in mobile underwater acoustic communication. To overcome such disadvantage, a novel algorithm based on compressive sensing is proposed to track and rapidly compensate the time-variant Doppler. The algorithm utilizes the compressive sensing technology to evaluate the sparseness of the channel estimation. Then the correct Doppler factor is achieved and eliminated by seeking the sparest channel impulse response. Results performed by Monte Carlo simulation and sea-trial data are provided, demonstrating that the proposed algorithm can effectively track and rapidly compensate the time-variant Doppler factor, overwhelming the comparing method in the range of specific signal to noise ratio and Doppler factor. Besides, the compensation algorithm significantly decreases the computational complexity which is helpful to real-time processing. What’s more, the method improves the communication efficiency by avoiding occupying extra spectrum. 4.Thechannel matching technologies are studied, and a pilot-free channel estimation algorithm is proposed. This algorithm utilizes the sparseness of underwater acoustic channel. The results obtained by Monte Carlo simulation and lake-trial are provided, demonstrating that the proposed algorithm can realize a reliable equalization and effectively improves the efficiency of underwater acoustic communication without losing the robustness. 5.Thecommunication rate in the long-rang mobile underwater communication is usually very low due to the limited bandwidth. To improve the communication efficiency, the principle and characteristic of chaotic communication are studied. A chaotic hybrid spread spectrum modulation method which combines the multi-channel spectrum spread modulation and chaotic modulation is proposed. This new method utilizes the excellent cross-correlation property to decrease the inter-carrier interference, thus enhances the communication rate without losing much BER performance. To further increase the efficiency of spread spectrum communication, we proposed a novel M-ary chaotic phase modulation orthogonal multi-carrier spread spectrum method. This modulation algorithm significantly increase the communication efficiency without losing much BER performance. 6.The physical property of acoustic propagation in the Arctic as well as middle and high latitudes are studied. The influence of propagation property on underwater acoustic communication under ice is analyzed. By processing and analyzing the data from China’s first arctic underwater acoustic communication trial in the seventh Arctic scientific exploration, and the possibility of underwater acoustic communication under the Arctic ice is verified. Besides, the results provide a research foundation for further research and experiment on the underwater acoustic communication under ice in the Arctic as well as middle and high latitudes region. Keywords: Underwater Acoustic Communication, Doppler Estimation and Compensation, Chaotic Communication, Channel Estimation, Under Ice Communication

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