MIMO-OFDM系統(tǒng)的聯(lián)合頻偏與信道估計(jì)技術(shù)研究
發(fā)布時(shí)間：2019-06-20 04:03
【摘要】：正交頻分復(fù)用(Orthogonal Frequency Division Multiplexing, OFDM)技術(shù)能夠有效地對(duì)抗多徑衰落,同時(shí)具有較高的頻譜效率,因此是寬帶移動(dòng)通信系統(tǒng)最佳的調(diào)制和多址接入候選方案。多輸入多輸出(Multiple-Input Multiple-Output, MIMO)技術(shù)能夠有效地利用多徑來提高系統(tǒng)容量(復(fù)用增益)或鏈路可靠性(分集增益),是極大提高通信系統(tǒng)頻譜效率的有效手段。而兩者聯(lián)合而成的MIMO-OFDM技術(shù),集兩者之長于一身,已成為時(shí)下熱門移動(dòng)通信系統(tǒng)的標(biāo)準(zhǔn)配置。 作為多載波系統(tǒng),OFDM對(duì)載波頻率偏移(Carrier Frequency Offset, CFO)非常敏感。由多普勒頻移和收發(fā)端晶振不匹配引起的CFO,會(huì)破壞子載波間的正交性,造成子載波間干擾,導(dǎo)致系統(tǒng)性能嚴(yán)重惡化。同時(shí),為了實(shí)現(xiàn)相干解調(diào),準(zhǔn)確的信道沖激響應(yīng)(Channel Impulse Response, CIR)信息也是不可或缺的。在通信系統(tǒng)中,這兩個(gè)未知參數(shù)經(jīng)常是同時(shí)存在并耦合在一起的,因此研究聯(lián)合CFO和CIR估計(jì)算法具有現(xiàn)實(shí)意義。 針對(duì)時(shí)不變頻選衰落信道MIMO-OFDM系統(tǒng),論文在前人研究的基礎(chǔ)之上,提出了一種“多天線、多徑”模型；基于此模型,推導(dǎo)了最大似然聯(lián)合估計(jì)和相應(yīng)的CRLB限：接著為了降低估計(jì)的復(fù)雜度,論文研究了基于期望最大化型算法(Expectation-Maximization,EM)的迭代聯(lián)合估計(jì),仿真的結(jié)果表明EM型算法能夠有效地逼近克拉美羅下限(Cramer-Rao Lower Bound, CRLB);最后,論文針對(duì)稀疏信道環(huán)境,采用子空間匹配(Subspace Pursuit, SP)壓縮感知算法,修正了信道估計(jì)部分的方法,仿真的結(jié)果表明修正后的迭代聯(lián)合估計(jì)具有更好的估計(jì)性能和更低的迭代復(fù)雜度。 針對(duì)時(shí)變頻選衰落信道MIMO-OFDM系統(tǒng),論文分析了時(shí)變信道的統(tǒng)計(jì)特性,給出了時(shí)變信道表示方法——基擴(kuò)展模型(Basis Expansion Model, BEM),并仿真比較了幾種常見BEM的表示性能；然后在前人研究的基礎(chǔ)之上,論文先研究了SISO-OFDM系統(tǒng)的系統(tǒng)模型,并分別給出了頻域和時(shí)域兩種聯(lián)合估計(jì)方法；最后針對(duì)MIMO-OFDM系統(tǒng),論文提出了一種“多天線、多徑、時(shí)變”模型,從前面的時(shí)域聯(lián)合估計(jì)方法中拓展出基于最大似然準(zhǔn)則和最大后驗(yàn)準(zhǔn)則的兩種估計(jì)方法,仿真結(jié)果表明基于時(shí)變相關(guān)特性的最大后驗(yàn)方法具有更好的估計(jì)性能。 最后,簡單梳理了本文的研究思路和取得的成果,并針對(duì)不足之處,探討了以后的研究方向和改進(jìn)思路。
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology can effectively combat multi-path fading and has high spectral efficiency, so it is the best modulation and multiple access candidate scheme for broadband mobile communication systems. Multi-input multiple-output (Multiple-Input Multiple-Output, MIMO) technology can effectively use multi-path to improve system capacity (reuse gain) or link reliability (diversity gain). It is an effective means to greatly improve the spectral efficiency of communication systems. The MIMO-OFDM technology, which combines the two technologies, has become the standard configuration of popular mobile communication systems. As a multi-carrier system, OFDM is very sensitive to carrier frequency offset (Carrier Frequency Offset, CFO). The CFO, caused by Doppler frequency shift and crystal oscillator mismatch at the transceiver will destroy the orthogonality between subcarriers and cause inter-carrier interference, resulting in a serious deterioration of system performance. At the same time, in order to realize coherent demodulation, accurate channel impulse response (Channel Impulse Response, CIR) information is also indispensable. In communication systems, these two unknown parameters often exist at the same time and are coupled together, so it is of practical significance to study the joint CFO and CIR estimation algorithms. Based on the previous research, a "multi-antenna, multi-path" model for time-invariant frequency selective fading channel MIMO-OFDM system is proposed in this paper. Based on this model, the maximum likelihood joint estimation and the corresponding CRLB limit are derived. Then, in order to reduce the complexity of the estimation, the iterative joint estimation based on the expected maximization algorithm (Expectation-Maximization,EM) is studied. The simulation results show that the EMtype algorithm can effectively approach the Cramer-Rao Lower Bound, CRLB); lower limit (Cramer-Rao Lower Bound, CRLB);). Finally, the subspace matching (Subspace Pursuit, SP) compression sensing algorithm is used to modify the channel estimation method for sparse channel environment. The simulation results show that the modified iterative joint estimation has better estimation performance and lower iterative complexity. For time-varying frequency-selective fading channel MIMO-OFDM systems, the statistical characteristics of time-varying channels are analyzed, and the base spread model (Basis Expansion Model, BEM), which is a time-varying channel representation method, is given and the representation performance of several common BEM is simulated and compared. Then, on the basis of previous studies, the system model of SISO-OFDM system is studied, and two joint estimation methods in frequency domain and time domain are given respectively. Finally, for MIMO-OFDM system, a "multi-antenna, multi-path, time-varying" model is proposed, and two estimation methods based on maximum likelihood criterion and maximum posterior criterion are extended from the previous joint time-domain estimation methods. The simulation results show that the maximum posterior method based on time-varying correlation characteristics has better estimation performance. Finally, the research ideas and achievements of this paper are briefly combed, and the future research direction and improvement ideas are discussed in view of the shortcomings.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN929.53
本文編號(hào)：2502908
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology can effectively combat multi-path fading and has high spectral efficiency, so it is the best modulation and multiple access candidate scheme for broadband mobile communication systems. Multi-input multiple-output (Multiple-Input Multiple-Output, MIMO) technology can effectively use multi-path to improve system capacity (reuse gain) or link reliability (diversity gain). It is an effective means to greatly improve the spectral efficiency of communication systems. The MIMO-OFDM technology, which combines the two technologies, has become the standard configuration of popular mobile communication systems. As a multi-carrier system, OFDM is very sensitive to carrier frequency offset (Carrier Frequency Offset, CFO). The CFO, caused by Doppler frequency shift and crystal oscillator mismatch at the transceiver will destroy the orthogonality between subcarriers and cause inter-carrier interference, resulting in a serious deterioration of system performance. At the same time, in order to realize coherent demodulation, accurate channel impulse response (Channel Impulse Response, CIR) information is also indispensable. In communication systems, these two unknown parameters often exist at the same time and are coupled together, so it is of practical significance to study the joint CFO and CIR estimation algorithms. Based on the previous research, a "multi-antenna, multi-path" model for time-invariant frequency selective fading channel MIMO-OFDM system is proposed in this paper. Based on this model, the maximum likelihood joint estimation and the corresponding CRLB limit are derived. Then, in order to reduce the complexity of the estimation, the iterative joint estimation based on the expected maximization algorithm (Expectation-Maximization,EM) is studied. The simulation results show that the EMtype algorithm can effectively approach the Cramer-Rao Lower Bound, CRLB); lower limit (Cramer-Rao Lower Bound, CRLB);). Finally, the subspace matching (Subspace Pursuit, SP) compression sensing algorithm is used to modify the channel estimation method for sparse channel environment. The simulation results show that the modified iterative joint estimation has better estimation performance and lower iterative complexity. For time-varying frequency-selective fading channel MIMO-OFDM systems, the statistical characteristics of time-varying channels are analyzed, and the base spread model (Basis Expansion Model, BEM), which is a time-varying channel representation method, is given and the representation performance of several common BEM is simulated and compared. Then, on the basis of previous studies, the system model of SISO-OFDM system is studied, and two joint estimation methods in frequency domain and time domain are given respectively. Finally, for MIMO-OFDM system, a "multi-antenna, multi-path, time-varying" model is proposed, and two estimation methods based on maximum likelihood criterion and maximum posterior criterion are extended from the previous joint time-domain estimation methods. The simulation results show that the maximum posterior method based on time-varying correlation characteristics has better estimation performance. Finally, the research ideas and achievements of this paper are briefly combed, and the future research direction and improvement ideas are discussed in view of the shortcomings.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN929.53
【共引文獻(xiàn)】
相關(guān)期刊論文 前2條
1 張靜;羅漢文;金榮洪;;Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems[J];Journal of Shanghai University(English Edition);2009年06期
2 張靜;羅漢文;金榮洪;;多天線系統(tǒng)符號(hào)和載頻同步的混合粒子濾波[J];上海交通大學(xué)學(xué)報(bào);2010年02期
相關(guān)博士學(xué)位論文 前2條
1 張曉瀛;OFDM及MIMO系統(tǒng)中的迭代接收技術(shù)研究[D];國防科學(xué)技術(shù)大學(xué);2008年
2 景源;MIMO-OFDM無線通信系統(tǒng)中信道估計(jì)和頻率同步的研究[D];大連理工大學(xué);2010年
相關(guān)碩士學(xué)位論文 前1條
1 何凡;MU-MIMO-OFDM上行鏈路中載波頻偏同步技術(shù)研究[D];復(fù)旦大學(xué);2012年
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