MIMO-OFDM系统接收中信道估计技术研究

发布时间：2018-06-11 12:56

本文选题：多输入多输出 + 正交频分复用　；参考：《解放军信息工程大学》2014年硕士论文

【摘要】：多输入多输出(Multiple-Input Multiple-Output,MIMO)技术充分利用空间资源,能够为系统提供空间分集增益与空间复用增益,抵抗信道衰落,提高信道容量与频带利用率。此外,正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术作为一种高频带利用率的多载波调制技术,能够将频率选择性衰落信道转化为平坦衰落信道,克服多径传播对系统带来的不利影响。结合两者优势的MIMO-OFDM技术作为4G核心物理层的首选传输技术,受到了广泛地关注。同时,在MIMO-OFDM系统中,信道估计能够为接收端的相干检测提供重要的信道参数,对构建均衡器、校正畸变信号以及恢复发送序列具有至关重要的作用,直接影响着系统性能的好坏。因此,信道估计成为了MIMO-OFDM系统的研究热点。本文基于多输入多输出信道模型,以信道估计作为课题的研究方向,出于对高频谱效率以及高系统容量的追求,重点对盲信道估计技术进行了研究,主要工作与创新点归纳如下:1、在研究传统噪声子空间算法的基础上,对算法进行改进,提出了一种适用于MIMO-OFDM系统的子空间盲信道估计算法。该算法通过采用块矩阵方案减少了求解自相关矩阵所需的样本数,有效地降低了自相关矩阵与噪声子空间的扰动,提高了算法的收敛速度与估计精度。2、针对确定性子空间算法对信道阶数过估计比较敏感的缺点,本文基于频域滤波方法与子空间方法相结合,提出了一种具有阶数误差鲁棒的子空间算法。该算法利用频域子空间算法对信道进行估计,通过频域滤波算法进行降噪处理,提高估计精度。接着,为了进一步评价信道估计器的性能,推导了算法的最小约束克拉美罗界。理论分析与仿真结果表明,该算法对信道阶数的过估计具有很强的鲁棒性。3、针对MIMO-OFDM系统中频偏与信道联合估计问题进行了研究,综合考虑频偏估计与信道估计这两方面的因素,克服其单独估计无法使系统性能达到最优这一缺陷,提出了一种新的适用于MIMO-OFDM系统的半盲载波与信道联合估计算法。该算法通过将子空间方法与时域重复数据段的方法相结合,完成了MIMO-OFDM系统的载波同步与信道估计,并分析了载波频偏对系统性能的影响。实验仿真结果表明,所提算法具有较宽的频偏估计范围,在频率选择性衰落信道下能够取得优于其它同类算法的良好估计性能。
[Abstract]:Multiple-Input Multiple-OutputMimo (MIMO) technology can provide spatial diversity gain and spatial multiplexing gain, resist channel fading, and improve channel capacity and frequency band efficiency by making full use of space resources. In addition, orthogonal Frequency Division Multiplexing OFDM (OFDM) technology, as a high-frequency band efficient multicarrier modulation technique, can transform the frequency-selective fading channel into a flat fading channel to overcome the adverse effects of multipath propagation on the system. MIMO-OFDM, which combines the advantages of both, as the preferred transmission technology of 4G core physical layer, has received extensive attention. At the same time, in MIMO-OFDM systems, channel estimation can provide important channel parameters for coherent detection at the receiver, which plays an important role in constructing equalizer, correcting distorted signals and restoring transmission sequences. It directly affects the performance of the system. Therefore, channel estimation has become a hotspot in MIMO-OFDM systems. In this paper, based on the multi-input and multi-output channel model, the blind channel estimation technology is studied for the pursuit of high spectral efficiency and high system capacity. The main work and innovations are summarized as follows: 1. On the basis of studying the traditional noise subspace algorithm, this paper proposes a subspace blind channel estimation algorithm for MIMO-OFDM systems. The algorithm reduces the number of samples needed to solve the autocorrelation matrix by adopting the block matrix scheme, and effectively reduces the disturbance of the autocorrelation matrix and the noise subspace. The convergence speed and estimation accuracy of the algorithm are improved. Aiming at the shortcoming that the subspace algorithm is sensitive to the channel order overestimation, this paper combines the frequency domain filtering method with the subspace method. A robust subspace algorithm with order error is proposed. The frequency domain subspace algorithm is used to estimate the channel and the frequency domain filtering algorithm is used to reduce the noise to improve the estimation accuracy. Then, in order to further evaluate the performance of channel estimators, the minimum constrained Crameiro bound is derived. The theoretical analysis and simulation results show that the algorithm is robust to the over-estimation of channel order. The problem of joint estimation of intermediate frequency offset and channel in MIMO-OFDM system is studied. The two factors of frequency offset estimation and channel estimation are considered synthetically. To overcome the shortcoming that the system performance can not be optimized by single estimation, a new semi-blind joint carrier and channel estimation algorithm for MIMO-OFDM systems is proposed. By combining subspace method with time domain repeat data segment method, the carrier synchronization and channel estimation of MIMO-OFDM system are completed, and the influence of carrier frequency offset on system performance is analyzed. Experimental results show that the proposed algorithm has a wide range of frequency offset estimation and can achieve better estimation performance than other similar algorithms in frequency-selective fading channels.
【学位授予单位】：解放军信息工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN919.3

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