时变条件下MIMO-OFDM系统中的信道估计算法

本文设计了时变多径衰落条件下MIMO-OFDM系统中一种新的信道估计算法.该算法结合递归EM算法和Kalman预测对时变信道进行跟踪.借助软球形译码器(List Sphere Decoder,LSD)产生的搜索列表,递归EM算法序贯遍历搜索列表中可能的符号组合来估计各个子载波上的信道频率响应;基于获得的信道频率响应估计,Kalman预测器利用衰落信道的时域二阶统计特性进一步跟踪信道时变.仿真结果表明:本文设计的算法可以有效跟踪信道时变,性能优于传统的软输入Kalman滤波算法.     

MIMO-OFDM系统中的子空间半盲信道估计

本文主要讨论了MIMO-OFDM系统中的一种半盲信道估计算法.该算法基于子空间分解技术,利用信号子空间和噪声子空间的正交性将两者分离.针对盲信道估计存在计算量大及收敛速度慢等缺点,本文充分利用少量的导频,给出了一种基于子空间跟踪技术的半盲MIMO-OFDM信道估计算法.仿真结果表明,该算法在保持盲信道估计算法性能的基础上,明显加快了收敛速度、降低了计算量.     

MIMO-OFDM系统信道估计技术的分析

介绍了MIMO—OFDM系统的信道估计技术，根据是否使用训练序列信息，信道估计可以分为导频辅助信道估计和盲信道估计，本文首先较全面地介绍了导频辅助信道估计技术，然后介绍了一种运用较多的基于子空间的盲信道估计技术，最后计算机仿真分析比较它们的性能。     

Diversity analysis for frequency-selective MIMO-OFDM systems with general spatial and temporal correlation model

In this paper, the effect of a general spatial and temporal fading correlation structure on the performance of coded multiple-input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems is studied. The analysis handles an arbitrary joint transmit-receive spatial correlation model, including the non-Kronecker model. An upper bound on the maximum achievable diversity order for frequency-selective MIMO-OFDM systems with general temporal and spatial correlation is derived. Furthermore, a space-time-frequency code design that can achieve the upper bound for any arbitrarily correlated channel scenario is provided. The general framework of the analysis includes space-frequency (SF)-coded systems as a special case. For the SF-coded MIMO-OFDM system, it is shown that any SF code designed to achieve full diversity in the independent fading channel can achieve full diversity in an arbitrary spatially correlated channel. The derived analytical results are consistent with those in the existing literature for special correlation structures. Extensive simulation results are provided to confirm the theoretical analysis.     

MIMO-OFDM系统信道最大似然估计研究

在深入分析MIMO-OFDM系统信道模型的基础上,提出了一种新的导频符号设计方案和采用最大似然比估计算法估计MIMO-OFDM信道,并分析了该算法的性能;计算机仿真结果表明在信道统计特性未知的条件下,采用所提出的导频符号设计方案效率高,估计性能优于RRE和LE等其他方法.     

Transmit beamforming for space-frequency coded MIMO-OFDM systems with spatial correlation feedback

This paper addresses the problem of joint optimization of transmit beamforming and space-frequency (SF) coding for MIMO-OFDM systems with spatial correlation feedback in broadband communications. This problem is challenging in the sense that the transmitter should be designed to beamform across multiple eigenspaces associated with the multipath environment simultaneously. With arbitrary transmit spatial correlation, the performance analysis for SF-coded MIMO-OFDM systems with beamforming is provided, and a general optimization problem for the beamforming design is formulated. Three suboptimal approaches to design the beamformer based on the derived design criteria are proposed: i) eigenvalue selection scheme; ii) eigenspace selection scheme; and iii) per-subcarrier approach based on decoding at each subcarrier. The proposed schemes take into account the multiple eigenspace information associated with the multipath-delay channel. Improvement in the performance over SF coding without beamforming is shown through simulations in terms of bit error rate. The eigenvalue selection scheme provides the best performance among the proposed algorithms. This scheme locates the subspace associated with the largest eigenvalues in the eigenspace of the covariance matrices. With the eigenvalue selection scheme, the performance improvement is about 3 dB over the SF coding without beamforming for highly correlated channels as shown in our simulations.     

一种MIMO-OFDM系统信道估计简化方法

提出了一种基于MMSE准则的MIMO-OFDM系统信道估计简化方法。该方法将信道估计问题转化为TBT线性方程求解问题,然后利用快速求解算法避免了复杂的矩阵求逆和矩阵相乘,大大降低了实现复杂度。仿真结果表明,相比于传统MMSE算法,该简化算法在降低复杂度的同时仅带来微弱的性能损失。     

分布式多入多出正交频分复用快衰落感知估计

针对分布式多输入多输出正交频分复用(MIMO-OFDM)快衰落系统,为了消除快衰落信道的干扰,提出一种分布式MIMO-OFDM系统快衰落信道估计方法.该方法利用分布式快衰落信道间的感知信息在空间、时延和多普勒频移上具有的互相关性,求取三维互相关联合稀疏信道模型.推导预相关随机导频测量矩阵,结合分布式压缩感知算法,以能量有效的方式,对快衰落稀疏信道参数进行联合压缩测量和重构,得到各分布式MIMO接收端任意的稀疏信道系数.理论分析与仿真结果都表明,该方法与传统的信道估计方法相比,可以明显提高系统频谱效率和误码率,减少计算复杂度.     

Pilot-symbol-aided channel estimation for OFDM in wireless systems

In this paper, we investigate pilot-symbol-aided parameter estimation for orthogonal frequency division multiplexing (OFDM) systems. We first derive a minimum mean-square error (MMSE) pilot-symbol-aided parameter estimator. Then, we discuss a robust implementation of the pilot-symbol-aided estimator that is insensitive to channel statistics. From the simulation results, the required signal-to-noise ratios (SNRs) for a 10% word error rate (WER) are 6.8 dB and 7.3 dB for the typical urban (TU) channels with 40 Hz and 200 Hz Doppler frequencies, respectively, and they are 8 dB and 8.3 dB for the hilly-terrain (HT) channels with 40 Hz and 200 Hz Doppler frequencies, respectively. Compared with the decision-directed parameter estimator, the pilot-symbol-aided estimator is highly robust to Doppler frequency for dispersive fading channels with noise impairment even though it has some performance degradation for systems with lower Doppler frequencies     

MIMO-OFDM快衰落信道的压缩感知估计方法

在快衰落多输入多输出(MIMO)-正交频分复用(OFDM)系统中,为了避免传统的信道估计方法中存在大量系数需要估计的问题,利用快衰落信道在角时延多普勒域可稀疏的特性,提出了基于压缩感知的MIMO-OFDM系统快衰落信道估计方法。根据压缩感知的受限等距特性(RIP),推导了一种少量导频随机结构测量矩阵,用于测量快衰落信道在角时延多普勒域稀疏系数。接收端可从这些少量的测量数据中以高概率重构出快衰落信道。理论分析与仿真结果都表明:该方法与传统的信道估计方法相比,所得到的系统数据传输效率及估计性能都有了明显提高。     

基于特殊训练序列的信道估计算法的研究

为降低MIMO—OFDM系统信道估计运算复杂度和提高估计精度，设计了一种特殊的训练序列，并给出了基于该训练序列的低复杂度算法，采用该方法避免了矩阵求逆运算，使运算大大简化，且在系统存在ISI时,采用本文给出的信道估计方法，信道的估计参数不会受到ISI的影响。仿真结果证明在存在ISI时，给出的信道估计与不存在ISI时性能相同，在高SNR时比传统方法其MSE高20dB。     

无线通信中的空时分组码及其性能分析

基于无线信道易受衰减和干扰影响的特点,介绍了用于瑞利衰落信道的空时分组码。给出了几种空时 分组码的编码和基于接收端线性处理的最大似然解码算法,建立了一个基站端和移动终端有若干个未线的系统模 型,分析其性能并进行仿真。仿真结果证明,通过空时分组码和多发射天线,可获得明显增益,且解码复杂度小。     

非理想信道估计下迫零接收的空间相关多输入多输出空分复用系统的误码率分析

分析了非理想信道估计和发射空间相关信道下,采用迫零接收的多输入多输出空分复用无线通信系统的误码率性能.基于随机矩阵理论,导出了闭合形式的M-PSK和M-QAM误码率近似解析表达式,并通过仿真验证了表达式的有效性.所获得的表达式形式简单、便于数值计算,可以用于系统性能评估.     

基于奇异值分解的MIMO-OFDM系统角域MAP信道估计算法

最大后验概率信道估计算法应用于多输入多输出-正交频分复用(MIMOOFDM)系统时需要大规模的矩阵求逆和乘积运算,且系统数据传输效率随发送天线数的增加明显降低.为克服这些问题,提出了一种基于奇异值分解的角域最大后验概率信道估计算法.该算法通过期望最大化把(MIMO)信道估计问题简化为一系列独立的单输入单输出(SISO)问题,并使用奇异值分解避免了大规模矩阵求逆和乘积运算;通过多个OFDM符号联合估计信道提高了系统数据传输效率及算法的估计性能.仿真实验验证了此算法的有效性.     

Walsh coded training signal aided time domain channel estimation for MIMO-OFDM systems

This letter proposes a novel Walsh coded training signal design and decoding method to estimate the channel response in MIMO-OFDM systems. The Walsh coded training signals, designed to be orthogonal in the time domain, facilitate the separation of the desired training signal from the received mixed signal and the estimation of the channel response. The proposed channel estimation method is directly applicable to practical MIMO-OFDM systems with null subcarriers and exhibits nearly the same performance as Li?s original channel estimator [5] at a much reduced computational complexity.     

MIMO—OFDM低延迟信道估计改进算法

为了克服多输入多输出正交频分复用（MIMO—OFDM）移动系统中采用空间复用技术的下行链路性能出现衰退现象,提出一种信道估计改进算法。它根据信道状态并通过一个决策指导方案为4×4 MIMO系统提供大约4bit／s／Hz的数据。通过使用LDPC短码,在LDPC译码器输出端采用MIMO—OFDM符号重建方法,达到提高估计精度的目的。在3GPP MIMO空间信道模型下进行了仿真验证,结果表明指定速率下的估计精度得到改善。     

MIMO-OFDM低延迟信道估计改进算法

为了克服多输入多输出正交频分复用(MIMO-OFDM)移动系统中采用空间复用技术的下行链路性能出现衰退现象,提出一种信道估计改进算法。它根据信道状态并通过一个决策指导方案为4×4 MIMO系统提供大约4bit/s/Hz的数据。通过使用LDPC短码,在LDPC译码器输出端采用MIMO-OFDM符号重建方法,达到提高估计精度的目的。在3GPP MIMO空间信道模型下进行了仿真验证,结果表明指定速率下的估计精度得到改善。     

MIMO-OFDM channel estimation method utilizing correlation in time domain for B3G-TDD uplink

This article proposes a simple pilot-aided channel estimation method based on correlation in time domain for multiple-input and multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. Pilot symbols in all transmit antennas are generated from different circular shifting of a certain sequence. Through once correlation, the receiver can obtain time-domain pulse responses for channel fading from all transmit antennas to a certain receive antenna, from which channel estimation in frequency domain can be obtained. Beyond 3G time-division duplex (B3G-TDD) uplink is introduced, and the channel estimation method is used in it. Theoretical analysis and simulation are both carried out. Mean square error (MSE) performance shows that the method can exhibit precise estimation. Complexity analysis proves it requires very low complexity. System simulation result shows that it guarantees the performance of B3G-TDD uplink very well.