基于正交多载波调制技术的水声通信抗多普勒技术研究
发布时间：2018-08-11 21:29
【摘要】：正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）技术是一种对抗频率选择性衰落的有效技术，且具有较高频带利用率，由于水声信道频谱资源极为有限，为提高通信速率和频带利用率，将具有较高通信速率和频带利用率的OFDM技术应用于水下，具有现实意义。但其固有的缺点（例如大的峰值平均功率比（PAPR），相位噪声以及子载波间干扰（ICI），易受多普勒频偏和时变信道影响）又使得它在多普勒效应比较严重同时又具有多径效应的水声信道中性能急剧下降。因此寻求一种新的更好的水声通信系统具有重要意义。 本文首先对水声信道特性及其信道建模进行了综述，进而分析了传统的基于傅里叶变换的OFDM系统的基本原理与关键技术，总结了它的优缺点，其中针对子载波的正交性容易遭到破坏而引起子载波间干扰的问题，研究了一种基于分数阶傅里叶变换的OFDM系统，该系统选用一组频带相互重叠的LFM信号代替原来的正弦信号作为子载波进行信息调制，以分数阶傅里叶变换作为调制解调方法来传输信息，同时通过信道估计与分数阶傅里叶域的乘性滤波均衡器对输出信号进行滤波均衡，以对抗水声信道的多径效应和多普勒效应。仿真表明，在水声通信中，基于分数阶傅里叶变换的OFDM系统性能优于传统的基于傅里叶变换的OFDM系统。
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division) is an effective technique to counter frequency selective fading and has a high frequency band efficiency. Because of the limited spectrum resources of underwater acoustic channel, in order to improve the communication rate and frequency band efficiency, the orthogonal Frequency Division Multiplexing (OFDM) is an effective technique to combat frequency selective fading. It is of practical significance to apply OFDM technology with high communication rate and band efficiency to underwater. However, its inherent disadvantages (such as large peak-to-average power ratio (PAPR), phase noise and inter-carrier interference (ICI), are susceptible to Doppler frequency offset and time-varying channels) make it have more serious Doppler effect and multipath effect at the same time. The performance of the underwater acoustic channel drops sharply. Therefore, it is of great significance to seek a new and better underwater acoustic communication system. In this paper, the characteristics of underwater acoustic channel and its channel modeling are reviewed, and then the basic principles and key technologies of traditional OFDM system based on Fourier transform are analyzed, and its advantages and disadvantages are summarized. Aiming at the problem that the orthogonality of subcarriers is easy to be destroyed and the inter-subcarrier interference is caused, a OFDM system based on fractional Fourier transform is studied. Instead of the original sinusoidal signal, a group of overlapping LFM signals are used to modulate the information, and the fractional Fourier transform is used as the modulation and demodulation method to transmit the information. At the same time the output signal is equalized by channel estimation and multiplicative filter equalizer in fractional Fourier domain to counteract the multipath effect and Doppler effect of underwater acoustic channel. Simulation results show that the performance of OFDM system based on fractional Fourier transform is better than that of traditional OFDM system based on Fourier transform in underwater acoustic communication.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.3
本文编号：2178288
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division) is an effective technique to counter frequency selective fading and has a high frequency band efficiency. Because of the limited spectrum resources of underwater acoustic channel, in order to improve the communication rate and frequency band efficiency, the orthogonal Frequency Division Multiplexing (OFDM) is an effective technique to combat frequency selective fading. It is of practical significance to apply OFDM technology with high communication rate and band efficiency to underwater. However, its inherent disadvantages (such as large peak-to-average power ratio (PAPR), phase noise and inter-carrier interference (ICI), are susceptible to Doppler frequency offset and time-varying channels) make it have more serious Doppler effect and multipath effect at the same time. The performance of the underwater acoustic channel drops sharply. Therefore, it is of great significance to seek a new and better underwater acoustic communication system. In this paper, the characteristics of underwater acoustic channel and its channel modeling are reviewed, and then the basic principles and key technologies of traditional OFDM system based on Fourier transform are analyzed, and its advantages and disadvantages are summarized. Aiming at the problem that the orthogonality of subcarriers is easy to be destroyed and the inter-subcarrier interference is caused, a OFDM system based on fractional Fourier transform is studied. Instead of the original sinusoidal signal, a group of overlapping LFM signals are used to modulate the information, and the fractional Fourier transform is used as the modulation and demodulation method to transmit the information. At the same time the output signal is equalized by channel estimation and multiplicative filter equalizer in fractional Fourier domain to counteract the multipath effect and Doppler effect of underwater acoustic channel. Simulation results show that the performance of OFDM system based on fractional Fourier transform is better than that of traditional OFDM system based on Fourier transform in underwater acoustic communication.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.3
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