基于DFT的OFDM系统信道估计改进算法

基于DFT的信道估计算法计算复杂度比MMSE算法低,性能比LS算法好.但是传统的基于DFT的信道估计只消除了信道冲击响应估计中循环前缀长度之外的噪声,循环前缀长度内的噪声并没有得到抑制,因此算法性能还有提高的空间.本文提出了一种改进的基于DFT的信道估计算法.算法首先估计出噪声方差,然后利用噪声方差设定一个门限,通过此门限对循环前缀内的信道时域冲击响应值进行阈值,进一步消除噪声的干扰.仿真证明,本文的改进信道估计算法性能优于原算法.     

改进的MB-OFDM UWB 信道估计算法

在MB-OFDM UWB 系统中,传统的信道估计方法没有充分利用信道长度这一信息,估计信道长度常大于实际长度,造成了性能损失。针对这一缺陷,提出一种新的信道估计算法。首先利用LS 算法估计出信道,然后通过信号能量估计(SEE)方法估计出信道长度。算法有效地降低了估计维数,因此提高了LS 算法的估计性能,同时对各算法的性能进行了分析比较。最后利用实验仿真证实了算法的有效性和分析的正确性。     

一种降低OFDM移动通信系统中LS信道估计均方误差的算法

在基于OFDM的移动通信系统中,针对LS信道估计时域结果的构成特点,同时结合无线信道冲激响应在时域为有限持续长度的特性,提出一种新的算法估计信道有效阶数,然后利用该估计值对LS信道估计时域结果进行加窗处理以减小LS算法中由噪声和子信道间干扰引起的均方误差:LS算法性能的提高及其对系统误符号性能的改善通过计算机仿真得以验证.     

一种基于信道缩短的MB-OFDM UWB稀疏信道估计算法

在MB-OFDMUWB系统中,利用UWB信道的稀疏簇特性,提出一种基于信道缩短的MB-UWB稀疏信道估计算法。首先利用信道缩短滤波器来消除由于循环前缀长度不足造成信道间干扰和码间干扰,然后基于信道缩短后的接收信号,利用UWB信道的稀疏性,探测出非零值抽头的位置,避免了无谓的零值抽头估计,改善了算法的性能。仿真结果表明:当循环前缀CP长度小于信道长度时,LS算法和DFT算法逐渐失效,而新算法可以获得较好的估计性能。     

基于导频和修正Kalman滤波的MIMO-OFDM信道估计方法

提出了一种适用于时间频率选择性衰落信道的MIMO-OFDM系统的组合信道估计方法。采用AR过程对信道进行建模,利用基于导频的低维Kalman滤波算法进行信道估计,并采用LS算法估计时变的信道衰减因子。Kalman滤波跟踪了信道的时域相关性,为了同时跟踪信道的频域相关性,采用了一种基于MMSE(minimum mean square error)的合并器对Kalman滤波算法进行修正。仿真表明,提出的这种组合算法降低了传统的Kalman滤波结构的复杂度,能够跟踪信道的时频变化,改进了基于LS准则的信道估计算法,并且与复杂的高维Kalman滤波算法的信道估计性能相当。     

一种MC-CDMA系统LS信道估计的改进算法

LS信道估计算法计算量小,实现简单,但是受噪声的影响信道估计精度低。为降低噪声对信道估计精度的影响,提出一种基于DFT的LS信道估计改进算法。该算法利用MC-CDMA中闲置的虚载波对信道噪声功率进行估计,通过将LS信道估计的时域响应限制在循环前缀长度内并进一步通过设置门限值忽略LS信道时域响应在循环前缀长度内的噪声分量和无效径响应,显著提高了信道估计精度。本文的算法运算量小,实现简单,信道估计精度高,仿真结果验证了算法的有效性。     

MC-CDMA系统中基于DFT的信道估计改进算法研究

LS信道估计算法运算量小,实现简单,但估计值对噪声影响敏感,算法精度低。为降低噪声对精度的影响,文章提出一种新的基于DFT的LS信道估计改进算法。该算法利用并行PN序列信号特性,通过时延点信息获取算法得到多径信道的时延点信息,并在改进的信道估计算法中利用此信息,最大程度地抑制噪声。仿真结果表明,与现有的基于DFT的LS改进算法相比,本算法可进一步提高估计精度,在低信噪比条件下性能更好。     

LTE系统中有关维纳滤波信道估计的性能分析

基于LTE系统下行信道中离散分布的导频符号,本文提出了一种时频维纳滤波信道估计方法。分别在频域和时域使用维纳滤波方法获得信道响应。这种方法有两种实现形式：一种是利用自相关矩阵计算导频部分的信道响应,再利用插值算法获得数据部分的信道响应,另一种是利用互相关矩阵直接计算导频和数据部分的信道响应。在瑞利衰落信道环境下进行MATLAB仿真,维纳滤波相比LS算法性能有很大提高,时频维纳滤波信道估计算法的性能优于LMMSE算法,自相关时频维纳滤波信道估计算法性能优于互相关时频维纳滤波信道估计算法。     

基于多项式模型的时频二维OFDM信道估计算法

本文提出了一种内插导频的时频二维信道估计算法,用于无线移动信道下的正交频分复用(OFDM)系统。该算法基于梳状内插的导频信号模型,采用多项式模型对信道进行拟合,从而能够精确的估计出信道信息。与时频二维维纳滤波以及自适应判决反馈的算法相比,该算法不需要预先知道信道相关矩阵以及信噪比等信道信息,简单易于实现,并且能够有效的抑制信道估计中的噪声干扰。仿真结果表明,在衰落环境下,该算法的信道估计最小方差(MSE)性能与最小二乘(LS)估计最小方差性能相比有显著提高。     

OFDM系统中信道估计算法研究与仿真

OFDM技术是现代通信领域的重要技术,而OFDM系统中的信道估计技术又是OFDM中的关键技术.文中对OFDM中信道估计算法进行了深入探讨,并给出了N04SE和LS两种经典算法在OFDM中的应用,并对这两种算法进行了仿真,对其性能进行了比较.     

Effects of imperfect channel sensing and estimation on the performance of cognitive radio systems

In realistic scenarios of cognitive radio (CR) systems, imperfect channel sensing may occur due to false alarms and miss detections. Channel estimation between the secondary user transmitter and another secondary user receiver is another challenge in CR systems, especially for frequency‐selective fading channels. In this context, this paper presents a study of the effects of imperfect channel sensing and channel estimation on the performance of CR systems. In particular, different methods of channel estimation are analyzed under channel sensing imperfections. Initially, a CR system model with channel sensing errors is described. Then, the expectation maximization (EM) algorithm is implemented in order to learn the channel fading coefficients. By exploiting the pilot symbols and the detected symbols at the secondary user receiver, we can estimate the channel coefficients. We further compare the proposed EM estimation algorithm with different estimation algorithms such as the least squares (LS) and linear minimum mean square error (LMMSE). The expressions of channel estimates and mean squared errors (MSE) are determined, and their dependencies on channel sensing uncertainty are investigated. Finally, to reduce the complexity of EM algorithm, a sub‐optimal algorithm is also proposed. The obtained results show that the proposed sub‐optimal algorithm provides a comparable bit error rate (BER) performance with that of the optimal one yet with less computational complexity.     

一种高速率的重叠复用传输系统及检测译码性能

该文研究了AWGN信道下重叠时分复用系统(OvTDM)及性能;在此基础上,研究了信道编码的OvTDM系统,并给出了最佳的检测译码算法-最大后验概率准则下的软入软出迭代算法。OvTDM系统与同频谱效率的QAM调制相比较,随着频谱效率的提高显示出性能增益。信道编码的OvTDM系统接收端在最大后验概率(MAP)准则下,检测与译码之间传递软信息进行迭代处理。仿真结果表明,软入软出迭代算法充分利用了符号重叠所自然形成的编码约束关系,获得了最大编码增益。     

MIMO-OFDM系统的低复杂度递推信道跟踪算法

该文针对时变多径信道下的MIMO-OFDM系统,基于变分贝叶斯原理,提出了一种新的联合信号检测和信道跟踪的低复杂度半盲贝叶斯迭代接收机。针对该接收机,基于递推变分期望最大化(RVBEM)算法,提出了一种RVBEM信道跟踪算法。由于RVBEM算法需要进行矩阵求逆,因此以该算法为基础推导得到了一种时频域联合递推的低复杂度信道跟踪(TF-LCRVBEM)算法。TF-LCRVBEM算法不仅完全避免了矩阵求逆运算,还通过合理的近似使得算法只具有线性复杂度。分析和仿真表明,在时变多径信道下,所提迭代接收机具有远优于传统接收机和接近理想接收机的性能。     

Least Square Channel Estimation for Two‐Way Relay MIMO OFDM Systems

This letter considers the channel estimation for two‐way relay MIMO OFDM systems. A least square (LS) channel estimation algorithm under block‐based training is proposed. The mean square error (MSE) of the LS channel estimate is computed, and the optimal training sequences with respect to this MSE are derived. Some numerical examples are presented to evaluate the performance of the proposed channel estimation method.     

Nondata-aided channel estimation for OFDM systems with space-frequency transmit diversity

This paper proposes a computationally efficient nondata-aided maximum a posteriori (MAP) channel-estimation algorithm focusing on the space-frequency (SF) transmit diversity orthogonal frequency division multiplexing (OFDM) transmission through frequency-selective channels. The proposed algorithm properly averages out the data sequence and requires a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and estimates the complex channel parameters of each subcarrier iteratively, using the expectation maximization (EM) method. To further reduce the computational complexity of the proposed MAP algorithm, the optimal truncation property of the KL expansion is exploited. The performance of the MAP channel estimator is studied based on the evaluation of the modified Cramer-Rao bound (CRB). Simulation results confirm the proposed theoretical analysis and illustrate that the proposed algorithm is capable of tracking fast fading and improving overall performance.     

OFDM系统基于矩阵开方的盲信道估计

该文提出一种基于矩阵开方(computing Roots of Matrices, RM)的盲信道估计算法和一种自适应矩阵开方(Adaptive computing Roots of Matrices, ARM)盲信道估计算法。RM算法利用信息符号的有限字符集特性,在时域上通过对一个Toeplitz下三角矩阵开方进行信道解卷积,得到信道估计的闭合解。该运算复杂度远低于现有的盲信道估计搜索算法,并且适用于信道阶数较大、搜索算法不能处理的情况。仿真结果表明RM信道估计性能接近于搜索算法的最佳性能,而ARM通过最陡下降迭代将代价函数最小化,可以进一步提高信道估计的准确性。     

Modified leaky LMS algorithm for channel estimation in DS-CDMAsystems

A simple adaptive least mean square (LMS) type algorithm for channel estimation is developed based on certain modifications to finite-impulse response (FIR) Wiener filtering. The proposed algorithm is nearly blind since it does not require any training sequence or channel statistics, and it can be implemented using only noise variance knowledge. A condition guaranteeing the convergence of the algorithm and theoretical mean square error (MSE) values are also derived. Computer simulation results demonstrate that the proposed algorithm can yield a smaller MSE than existing techniques, and that its performance is close to that of optimal Wiener filtering     

基于QR-RLS算法的OFDM系统盲自适应时域均衡器

在正交频分复用(OFDM)系统中,使用时域均衡器来消除由于循环前缀长度小于信道时延扩展长度而导致的符号间干扰。为了克服Merry算法收敛速度较慢的缺点,提出了一种适用于无线时变信道环境的改进的盲自适应时域均衡器。该算法利用QR-RLS算法实现均衡器抽头的迭代计算,改善了Merry算法的收敛速度和鲁棒性。理论分析和仿真结果表明,该算法收敛速度明显优于Merry算法,且性能接近MSSNR算法最优解。     

Joint MAP channel estimation and data detection for OFDM in presence of phase noise from free running and phase locked loop oscillator

This paper addresses a computationally compact and statistically optimal joint Maximum a Posteriori (MAP) algorithm for channel estimation and data detection in the presence of Phase Noise (PHN) in iterative Orthogonal Frequency Division Multiplexing (OFDM) receivers used for high speed and high spectral efficient wireless communication systems. The MAP cost function for joint estimation and detection is derived and optimized further with the proposed cyclic gradient descent optimization algorithm. The proposed joint estimation and detection algorithm relaxes the restriction of small PHN assumptions and utilizes the prior statistical knowledge of PHN spectral components to produce a statistically optimal solution. The frequency-domain estimation of Channel Transfer Function (CTF) in frequency selective fading makes the method simpler, compared with the estimation of Channel Impulse Response (CIR) in the time domain. Two different time-varying PHN models, produced by Free Running Oscillator (FRO) and Phase-Locked Loop (PLL) oscillator, are presented and compared for performance difference with proposed OFDM receiver. Simulation results for joint MAP channel estimation are compared with Cramer-Rao Lower Bound (CRLB), and the simulation results for joint MAP data detection are compared with “NO PHN” performance to demonstrate that the proposed joint MAP estimation and detection algorithm achieve near-optimum performance even under multipath channel fading.     

一种基于过采样的单通道MPSK信号盲分离算法

针对单通道接收两个MPSK混合信号的盲分离问题,该文提出了一种基于过采样的盲分离新算法。该算法基于最优贝叶斯估计准则,利用粒子滤波对发送的符号和一些参数进行序贯估计,从而实现了混合信号的分离。算法通过对接收信号的过采样,利用了更多的接收波形信息,有效地抑制了噪声的影响。仿真实验表明,新算法具有良好的误码率性能。该文同时还从极大似然的角度,对分离算法的性能进行了分析,给出了算法的误码率性能界。