【摘要】：正交頻分復用(OFDM)因為其具有較高的頻帶利用率、較強的抵抗頻率選擇性衰落等特點而被廣泛應用于目前移動通信領(lǐng)域,成為了第四代通信系統(tǒng)的核心技術(shù)之一。然而目前OFDM技術(shù)仍舊面臨許多技術(shù)問題。眾所周知,依據(jù)奈奎斯特采樣定律,對OFDM系統(tǒng)中數(shù)字信號問題的處理需要極高的采樣率,然而目前的前端模數(shù)轉(zhuǎn)換器(ADC)較難滿足其要求。因此我們迫切需要尋求一種新的方法用于解決OFDM系統(tǒng)中數(shù)字化信號的處理問題。近幾年來壓縮感知理論為該問題提供了一種有效的解決方案,它可以同時實現(xiàn)信號的采樣和壓縮,然后通過特定的重構(gòu)算法從少量的信息中準確地恢復出原始信號,可大大降低了通信系統(tǒng)系統(tǒng)的采樣率和硬件成本。首先本文為了改善OFDM通信系統(tǒng)的性能,在深入分析了 OFDM通信系統(tǒng)的信道特征基礎(chǔ)上,結(jié)合OFDM系統(tǒng)信道估計技術(shù)的特點,將經(jīng)過加窗優(yōu)化的自適應匹配追蹤算法應用到通信系統(tǒng)的信道估計中,抑制了由于信道截斷造成的沖擊響應泄露現(xiàn)象,有效消除了沖擊響應泄露所產(chǎn)生的噪聲,保證了信道的稀疏性,并在此基礎(chǔ)上進一步構(gòu)造了基于窗函數(shù)的觀測矩陣,然后將自適應匹配追蹤算法用于信道的恢復中。本文算法可在未知信道稀疏度的條件下,通過自適應步長合理地調(diào)整候選集中原子的個數(shù),進而較為精確的估計出信道的沖擊響應。仿真結(jié)果表明,與目前信道估計算法相比,本文所提算法能夠進一步改善信道估計的性能,有較好的實際應用以及推廣價值。其次,本文針對目前OFDM系統(tǒng)中窄帶干擾檢測所存在的問題,在對壓縮感知理論及其重構(gòu)算法深入研究的基礎(chǔ)上,利用基于自適應壓縮感知理論的自適應匹配追蹤算法解決通信系統(tǒng)的窄帶干擾檢測問題,該方法可在窄帶干擾稀疏度未知的情況下,通過選擇合適的補償自動地調(diào)整候選集中原子的個數(shù),在低于奈奎斯特采樣率下,快速實現(xiàn)單個及多個窄帶干擾信號檢測。仿真結(jié)果表明,與現(xiàn)有的干擾檢測算法相比,本文算法能夠有效地實現(xiàn)窄帶干擾檢測且運行速度較快快,有效地改善OFDM通信系統(tǒng)的性能。
[Abstract]:Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in the field of mobile communication due to its high bandwidth efficiency and strong resistance to frequency selective fading. It has become one of the core technologies of the fourth generation communication system. However, OFDM still faces many technical problems. It is well known that according to Nyquist's sampling law, the processing of digital signal in OFDM system requires a very high sampling rate. However, the current front-end analog-to-digital converter (ADC) is difficult to meet its requirements. Therefore, we urgently need to find a new method to solve the problem of digital signal processing in OFDM system. In recent years, the theory of compression perception provides an effective solution to this problem. It can simultaneously sample and compress signals, and then recover the original signal accurately from a small amount of information by a specific reconstruction algorithm. It can greatly reduce the sampling rate and hardware cost of the communication system. Firstly, in order to improve the performance of OFDM communication system, based on the in-depth analysis of the channel characteristics of OFDM communication system, combined with the characteristics of OFDM system channel estimation technology, A windowed adaptive matching tracking algorithm is applied to the channel estimation of communication systems. The leakage of impulse response caused by channel truncation is suppressed and the noise caused by the leakage of impulse response is effectively eliminated. The sparsity of the channel is ensured, and the observation matrix based on the window function is further constructed, and then the adaptive matching tracking algorithm is applied to the channel recovery. Under the condition of unknown channel sparsity, the proposed algorithm can reasonably adjust the number of atoms in the candidate set by adaptive step size, and then estimate the impulse response of the channel accurately. The simulation results show that the proposed algorithm can further improve the performance of channel estimation compared with the current channel estimation algorithm and has good practical application and popularization value. Secondly, aiming at the existing problems of narrowband interference detection in OFDM systems, this paper deeply studies the theory of compression sensing and its reconstruction algorithm. An adaptive matching tracking algorithm based on adaptive compression sensing theory is used to solve the problem of narrowband interference detection in communication systems. This method can be used to detect narrowband interference when the sparse degree of narrowband interference is unknown. By selecting the appropriate compensation to automatically adjust the number of atoms in the candidate set, the detection of single and multiple narrowband interference signals can be realized quickly under the Nyquist sampling rate. The simulation results show that compared with the existing interference detection algorithms, the proposed algorithm can effectively realize narrowband interference detection and run faster, and improve the performance of OFDM communication system effectively.
【學位授予單位】：哈爾濱工程大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.53

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