摘要正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）技术具有较强的对抗多径干扰的能力和高的频谱效率，已被多项国际标准采用为关键技术，是未来无线通信系统的必备技术之一。尽管如此，但是基于OFDM技术的无线通信系统对由模拟器件的非理想特性引起的同相正交（In-phase and Quadrature-phase, IQ）支路不平衡十分敏感。IQ不平衡会导致系统性能的下降。因此，如何有效地抑制IQ不平衡成为OFDM 系统研究中一个非常重要的方向，成为学术界和工业界关注的焦点之一。64920

本文的主要工作如下：（1）利用频域最小二乘（Least Square，LS）算法、时域最小二乘算法、基于特殊导频（Special Pilot Pattern，SPP）的估计算法和高斯消元（Gaussian Elimination，GE）算法对信道参量进行估计；（2）利用频域最小二乘算法、时域反馈补偿算法和高斯消元算法对信道IQ不平衡进行补偿；（3）进行仿真，对各种算法的性能进行分析比较。仿真结果表明：（1）时域最小二乘估计算法和高斯消元估计算法的性能较好，它们都只需要两个训练符号就能实现逼近理想信道估计的性能，但高斯消元算法复杂度较低，而频域最小二乘估计算法是以增加训练符号数量为代价进行信道估计，它至少需要16个训练符号才能实现逼近理想信道估计的性能；（2）相比于其他两种算法，高斯消元补偿算法具有复杂度低、高信噪比下性能更好等优点，是一种实用的补偿算法。

毕业论文关键词  正交频分复用  频域  时域  IQ不平衡 信道估计  补偿

毕业设计说明书（论文）外文摘要

Title  Channel Estimation and Compensation Schemes for OFDM Systems with IQ Imbalances                                     

Abstract Orthogonal frequency pision multiplexing (OFDM), with the advantages of high frequency spectrum efficiency and being able to overcome frequency-selective fading, has been adopted by a number of international criteria as key technology and  becomes one of the mandatory technologies for the future wireless communication systems. Although having those advantages, OFDM systems are quite sensitive to the in-phase and quadrature-phase (IQ) imbalances caused by the imperfection of analog components. Thus, the investigation of IQ imbalance mitigation becomes a  very important research direction in OFDM, and it has attracted the focus of academia and industry.

The main contents are as follows: (1) investigate four channel estimators  including frequency-domain (FD) least-square (LS), time-domain (TD) LS ，special pilot pattern(SPP)-based channel estimation and Gaussian eliminate (GE) channel estimation to estimate channel parameters; (2) Study several compensation algorithms: FD-LS, pre-FFT compensation and GE compensation algorithms to compensate for IQ imbalance. (3) Output the BER  performance of channel estimation and compensation algorithms.The simulation result shows that: (1) TDLS and GE are better than FD-LS in terms of BER  performance when two training pilot OFDM symbols are used. They just require two training symbols to achieve the ideal estimation performance as that of FD-LS with sixteen symbols, while the GE estimation has lower complexity. (2) Compared with the other two compensation algorithms, the GE compensation is an efficient one, which has the advantage of lower complexity and better performance at high SNR.

Keywords  OFDM  IQ Imbalance  frequency-domain  time-domain  channel estimation  compensation

目  次

1  绪论 1

1．1  无线通信的发展概况