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摘要正交频分复用(OFDM，Orthogonal frequency pision multiplexing)频谱利用率较高，抗多径干扰的能力较强，已经成为下一代无线移动通信的关键技术之一。与超外差接收机相比，零中频接收机价格低、功耗低，被广泛应用在 OFDM系统中。但是它却面临着受同相和正交相(In-phase and Quadrature-phase, IQ)不平衡影响的难题，这会导致无线通信系统的性能明显下降。本论文对发射端和接收端同时存在 IQ不平衡的 OFDM 系统进行了深入的研究，主要工作如下：(1) 利用频域最小二乘(Least Square, LS)信道估计算法、时域 LS 信道估计算法和高斯消元(Gaussian Eliminate, GE)的信道估计算法对信道参数进行估计。仿真和分析表明频域 LS 信道估计算法以增加训练序列为代价来提高估计性能，至少需要 16 个训练符号才能达到无 IQ失真的理想信道估计性能，而时域 LS 算法充分挖掘时域信道的特性，在第一种算法的基础上做出改进，高斯消元算法对导频信号做出特殊的设置，这两种算法只需 2 个训练符号即能达到较好的估计性能；(2)利用频域 LS算法和高斯消元算法对 IQ不平衡进行补偿， 仿真表明高斯消元补偿算法的复杂度低且性噪比损失较低。7076
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关键词 正交频分复用 IQ不平衡 频域 时域 信道估计 补偿
Title Channel Estimation and Compensation Schemes of OFDM Systems with IQ
Imbalances
Abstract
Orthogonal frequency pision multiplexing (OFDM) owns a high spectrum efficiency
and a good ability to combat multi-path interference and has been regarded as one of
the core technologies of the future wireless communications. Compared with the super
heterodyne receiver, the zero-IF receiver has lower price and lower power consumption
and has been widely used in OFDM systems. But it suffers from IQ imbalance which
can cause a significant degradation in the bit error rate (BER) performance of wireless
communication system. This paper focuses on the study of OFDM systems with IQ
imbalances at both the transmitter and receiver，the main work is as follow: 1) The
frequency-domain (FD) least-square (LS), the time-domain (TD) LS and the Gaussian
eliminate (GE) channel estimation are used to estimate the channel parameters. The
analysis and the simulation show: the FD-LS improves the estimation performance at
the expense of increasing the training symbols and it requires at least 16 training
symbols in order to achieve the performance of ideal IQ channel estimation; the TD-LS
fully exploits the characteristics of time-domain channel and make improvement on the
basis of the FD-LS and the GE designs special pilot signal. The TD-LS and GE require
only two training symbols to achieve an ideal channel estimation performance. 2) The
FD-LS and GE compensation algorithms are adopted to eliminate IQ imbalance and the
simulations show that the latter has lower complexity and lower SNR loss than the
former.
Keywords OFDM IQ Imbalance frequency-domain time-domain channel
estimation compensation.
目 次
1 绪论 .. 1
1.1无线通信概述 .. 1
1.2研究背景及意义 . 2
1.3 OFDM技术的发展及 IQ不平衡的原因 .. 2
1.4国内外研究现状 . 3
1.5论文结构和内容 . 4