OFDM扩频技术在水声通信中的应用研究

发布时间：2018-06-07 20:25

本文选题：水声通信 + 正交频分复用　；参考：《哈尔滨工程大学》2014年硕士论文

【摘要】：伴随着海洋事业的壮大,水下通信业务繁忙,发展网络化水声通信刻不容缓。其中,水下网络多用户通信已逐渐成为水声通信研究的热点。扩频(Spread-Spectrum,SS)技术作为一种抗干扰和抗衰落能力强的通信技术,发射功率低、可靠性高、保密性好,具有广泛的应用。正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术是一种抗频率选择性衰落能力强、频谱利用率高、传输速率高的通信技术,将其与扩频技术相结合应用于水下通信,能大大增加系统的抗干扰和抗衰落能力,对于水下多用户通信的发展具有深远意义。本文主要研究OFDM扩频技术在水声通信中的应用。论文最初对扩频技术、OFDM技术的基本原理进行了理论分析,并研究了扩频与OFDM结合的三种方式,分析了频域扩频MC-CDMA、正交MCDS-CDMA和多音DS-CDMA的实现过程,通过仿真验证了频域扩频的优越性,该扩频方式充分利用了频率分集增益,抗多径衰落能力更好。扩频通信技术抗多径干扰能力强,适用于较低信噪比条件,并且具有很好地组网能力。本文在实现直接序列扩频与OFDM结合的基础上,研究了循环移位扩频OFDM技术和组合扩频OFDM技术,这两种技术拥有更高的通信速率。仿真验证了无循环前缀的OFDM扩频系统仍可以保持高效可靠的解码。在水声通信中,空间的变化对水声信道冲激响应函数影响甚大,这使得不同空间位置上的水声信道的冲激响应函数具备弱相关性。利用水声信道的这一物理特性,将时间反转镜技术用于多用户水声通信中,以聚焦期望用户,屏蔽非期望用户实现空分多址。本文构建基于时间反转镜技术的OFDM扩频多用户水声通信系统,实现了多个用户的可靠通信。然后提出差分OFDM扩频技术,差分技术在接收端采用差分相干解调的方法,削弱水声衰落信道引起的性能下降问题,不需要相干解调和信道估计,提高系统的频带利用率,降低系统的复杂度和计算量,将其结合OFDM扩频技术应用于多用水声通信中,能建立稳健的通信系统。本文对所研究的算法进行了计算机仿真实验和水池试验验证,结果表明:扩频技术与OFDM技术相结合提高了水声通信系统的性能,实现了高质量点对点水声通信和多用户水声通信。
[Abstract]:With the development of ocean business, underwater communication business is busy, so it is urgent to develop network underwater acoustic communication. Among them, underwater network multi-user communication has gradually become the hot spot of underwater acoustic communication research. As a kind of communication technology with strong anti-interference and anti-fading ability, spread spectrum SS (spread Spectrum) technology has a wide range of applications, such as low transmission power, high reliability and good confidentiality. Orthogonal Frequency Division Multiplexing (OFDM) is a kind of communication technology with strong anti-frequency selective fading ability, high spectral efficiency and high transmission rate. It can greatly increase the anti-interference and anti-fading ability of the system, and has far-reaching significance for the development of underwater multi-user communication. This paper mainly studies the application of OFDM spread spectrum technology in underwater acoustic communication. At the beginning of this paper, the basic principle of spread spectrum technology and OFDM technology is theoretically analyzed, and three ways of combining spread spectrum with OFDM are studied, and the realization process of spread spectrum MC-CDMA, orthogonal MCDS-CDMA and multi-tone DS-CDMA in frequency domain is analyzed. The superiority of spread spectrum in frequency domain is verified by simulation. The spread spectrum method makes full use of frequency diversity gain and has better anti-multipath fading ability. Spread spectrum communication technology has strong ability to resist multipath interference, is suitable for low signal-to-noise ratio (SNR), and has good networking ability. Based on the combination of direct sequence spread spectrum (DSSS) and OFDM, the cyclic shift spread spectrum OFDM technology and the combined spread spectrum OFDM technology are studied in this paper. These two technologies have higher communication rate. Simulation results show that OFDM spread spectrum system without cyclic prefix can still be decoded efficiently and reliably. In underwater acoustic communication, spatial variation has a great influence on the impulse response function of underwater acoustic channel, which makes the impulse response function of underwater acoustic channel have weak correlation. Based on this physical property of underwater acoustic channel, the time reversal mirror technique is used in multi-user underwater acoustic communication to focus on the desired users and shield the non-expected users to realize space-division multiple access (SDMA). In this paper, the OFDM spread spectrum multi-user underwater acoustic communication system based on time reversal mirror is constructed, and the reliable communication of multiple users is realized. Then the differential OFDM spread spectrum technique is proposed, which adopts differential coherent demodulation at the receiver to weaken the performance degradation problem caused by underwater acoustic fading channel, without the need of coherent demodulation and channel estimation, so as to improve the frequency band efficiency of the system. In order to reduce the complexity and computational complexity of the system, a robust communication system can be established by applying OFDM spread spectrum technology to multi-purpose underwater acoustic communication. In this paper, computer simulation experiments and tank experiments are carried out to verify the proposed algorithm. The results show that the performance of underwater acoustic communication system is improved by the combination of spread spectrum technology and OFDM technology. High-quality point-to-point underwater acoustic communication and multi-user underwater acoustic communication are realized.
【学位授予单位】：哈尔滨工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.3;TN929.53

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