【摘要】：正交頻分復用（Orthogonal Frequency Division Multiplexing，OFDM）技術是一種對抗頻率選擇性衰落的有效技術，且具有較高頻帶利用率，由于水聲信道頻譜資源極為有限，為提高通信速率和頻帶利用率，將具有較高通信速率和頻帶利用率的OFDM技術應用于水下，具有現(xiàn)實意義。但其固有的缺點（例如大的峰值平均功率比（PAPR），相位噪聲以及子載波間干擾（ICI），易受多普勒頻偏和時變信道影響）又使得它在多普勒效應比較嚴重同時又具有多徑效應的水聲信道中性能急劇下降。因此尋求一種新的更好的水聲通信系統(tǒng)具有重要意義。 本文首先對水聲信道特性及其信道建模進行了綜述，進而分析了傳統(tǒng)的基于傅里葉變換的OFDM系統(tǒng)的基本原理與關鍵技術，總結了它的優(yōu)缺點，其中針對子載波的正交性容易遭到破壞而引起子載波間干擾的問題，研究了一種基于分數(shù)階傅里葉變換的OFDM系統(tǒng)，該系統(tǒng)選用一組頻帶相互重疊的LFM信號代替原來的正弦信號作為子載波進行信息調制，以分數(shù)階傅里葉變換作為調制解調方法來傳輸信息，同時通過信道估計與分數(shù)階傅里葉域的乘性濾波均衡器對輸出信號進行濾波均衡，以對抗水聲信道的多徑效應和多普勒效應。仿真表明，在水聲通信中，基于分數(shù)階傅里葉變換的OFDM系統(tǒng)性能優(yōu)于傳統(tǒng)的基于傅里葉變換的OFDM系統(tǒng)。
[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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.3

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