OFDM系统中基于导频的时变信道估计

该文对OFDM系统中基于导频的时变信道估计进行了研究,采用分组导频对一个OFDM符号间隔内某些时刻的信道冲击响应值进行估计,提出一种利用低通插值估计一个符号间隔内其他时刻的信道值的方法。仿真结果表明该文采用的低通插值方法所得到的估计均方误差要小于用线性插值或直接用信道模型产生的系数进行插值所得到的估计均方误差。     

宽带移动通信系统中基于梳状导频的信道估计

本文主要研究了OFDM系统中基于梳状导频的空时信道估计方法,并提出一种新的信道估计算法,即实现了空时二维信道估计。基于梳状导频的空时信道估计的算法分为两步:第一步是利用导频信号对导频位置的信道进行估计,第二步是信道插值,得到所有频域位置的信道信息。同时还研究了基于LS准则的信号估计以及基于线性插值的信道插值。     

船舶物联网中基于莱斯信道的导频插值估计算法

随着船舶物联网技术的快速发展,船舶信息系统相对落后的局面将得到极大改善。目前,水上移动业务中的船舶自动识别系统正逐步升级为VDE系统,这为船舶物联网提供强大技术保障。提出了一种基于VDE系统莱斯信道的导频估计算法,使得误比特率极大下降,提高船舶物联网系统性能。根据VDE信道参数的特性,该导频估计算法采用了多种插值算法进行比较,包括线性差值和高次的多项式插值。仿真结果表明,线性插值虽然复杂度低,但降低慢衰落效果比其他高次的多项式插值算法更加明显。     

OFDM系统中插值技术的研究与实现

导频辅助信道估计法是OFDM（Orthogonal Frequency Division Multiplexing）系统中的主要信道估计方法,使用LS方法估计导频点处的信道响应,然后使用插值法可以获得信道的全响应.本文详细介绍了各种插值算法,包括线性插值算法、高斯插值算法和基于DFT的插值算法.所有涉及到的插值算法的应用背景是数字地面电视系统（DVB-T,Digital Video Broadcasting-Terrestrial）.应用于测试系统,我们将对比分析三种算法的均方误差性能和运行时间性能.     

CDMA系统中对应于线性插值信道估计的最佳扩频因子

线性插值信道估计是一种适用于CDMA系统的简单而有效的信道估计方法。这种方法的性能受到信道的时变特性和接收机端噪声的影响。本文通过研究发现，在插值密度相同的情况下，导频符号信道估计克服噪声的能力和扩频增益(SE，spreading factor)成正比，而线性插值的跟踪时变信道的能力和扩频增益成反比。这样，在信道的变化剧烈程度一定的情况下，必然有使估计性能达到最优的最佳扩频因子。本文考查了在采用线性插值信道估计的CDMA系统中，当插值密度和车速一定时，不同扩频因子带来的系统的性能差别。仿真结果表明，对于给定车速，系统存在着最佳扩频因子，并且随着车速的变化而不同。     

TD-LTE-A上行信道估计中基于加权的插值算法

TD-LTE-A上行信道估计中的线性插值算法只利用数据两端的两个导频位置的信道响应进行插值,不能很好拟合信道响应。针对此问题,提出了基于加权平均的插值算法。该算法以线性插值算法为基础,首先利用连续3个导频位置的信道响应进行线性插值得到数据位置的两个初步插值结果,再在此基础上引入权值α,最后对初步插值结果进行加权得到数据位置的信道响应。在EPA环境下的MATLAB仿真结果表明,相对于线性插值算法,基于加权的插值算法在不过度增加计算复杂度的情况下能降低系统的误比特率。     

几种插值算法在OFDM水声通信系统中的应用研究

介绍了四种信道估计插值算法,在较为理想的水文条件下,用实际水池实验验证了线性插值法等四种插值算法用于基于导频信道估计的OFDM水声通信是切实可行的,并比较了四种插值算法对通信效果的影响.     

基于导频和多项式模型的信道估计

本文提出一种基于导频辅助、多项式近似和信号重建的信道估计通用方法,适用于高速移动环境.假定无线信道响应具有多项式特性,用两个或多个时隙的导频符号,估计出该时间段内任意符号时刻上的信道响应值.用仿真方法研究了WCDMA上行链路性能与移动台速度的关系、最佳多项式阶数和最佳时隙数,并与WMSA方法进行了比较.     

OFDM信道估计中插值算法的性能研究

由于无线电波信号在移动通信信道的传输过程中很容易受到多径和衰落效应的影响,所以就需要采用信道估计技术来跟踪信道响应的变化。在估计出导频子信道的频响后,频域内就需用插值算法做相应的内插运算,才可以得到数据子信道的频域响应。论文介绍了四种插值算法,包括常值插值、线性插值、拉格朗日插值和牛顿插值,并通过matlab仿真发现了几种算法的优缺点。     

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。     

基于特定导频OFDM信道估计的研究

在OFDM系统中,准确的信道估计是对抗瑞利衰落信道中信道干扰的关键。提出了一种对OFDM信道估计的新方法,利用CR Spline函数的插值方法,设计一个特定的导频结构,从而导出信道估计的CR Spline函数形式,用该函数近似信道衰落包络。实验结果表明,仅用少量导频就可以近似出信道特性,并具有良好的平滑性。计算机仿真证明了提出算法的有效性。     

Time-Varying and Frequency-Selective Channel Estimation with Unequally Spaced Pilot Symbols

In this paper, an accurate and computationally efficient algorithm is proposed for estimating time-varying and frequency-selective fading channel with unequally spaced pilot symbols. By employing the time-varying coefficient polynomial interpolation method, it is proved that the time-varying channel impulse response can be estimated by the product of a constant matrix and the fading information at pilot symbol positions. Furthermore, a least square off-line training algorithm is presented to optimally calculate the constant matrix, taking into consideration of the statistics of channel fading and noise. The new algorithm can also be applied for estimating flat fading channel with equally spaced pilot symbols as a special case. Simulation results indicate that our new channel estimation algorithm leads to small mean square error for fading estimation and provides bit error rate performance close to that of the perfect channel estimation.     

数字并行接收机在时变信道下的信道估计与均衡方法

为了适应高速宽带无线通信的需要,本文在一种高速数字并行接收机(APRX)结构的基础上,提出了一种时变信道下的信道估计和均衡方法。使用伪随机(pseudo-randomnumber,PN)序列相关进行信道估计,将所得到的信道频率响应粗估计按照一个DFT块的长度在一帧内进行线性内插得到信道频率响应细估计,将其用来在频域进行信道均衡。这种结构能适应高速率传输的要求,并且能有效地对抗时间和频率选择性衰落。仿真结果表明,在多径衰落信道下,APRX已经无法工作,而本文提出的数字并行接收机的信道估计和均衡方法有较好的性能,并且该方法实现简单,便于应用。     

基于多项式内插的MIMO时间-频率双选择性信道的信道估计

数据的高速率传输以及终端的高速移动,导致无线通信信道具有时间选择性与频率选择性两个特征。该文主要研究了数据分组传输方式下,基于导频符号辅助调制(PSAM)的多输入多输出(MIMO)时间-频率双选择性信道的信道估计问题。首先,将时间-频率双选择性MIMO信道,建模为一个随时间变化的多项式内插信道模型;然后,根据信道Doppler衰落速率、多项式模型中的误差项,确定出模型的阶数以及整个数据块的长度;最后,基于该多项式内插信道模型,提出了采用PSAM的MIMO双选择性信道估计方法。实验结果表明该算法在时间-频率双选择性衰落信道下具有较好的性能。     

基于宽深超分辨率网络的信道估计方法

在正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM) 系统中由于快衰落导致信道特征不连续,常规的信道插值方法无法准确反应导频与整个信道之间的关联性。针对这一问题,提出了一种基于宽深超分辨率（Wide Deep Super-resolution,WDSR）网络的信道估计方法,把导频值通过最小二乘估计（Least Squares,LS）初步插值,再通过WDSR网络再次放大重构整个信道的响应。将信道估计插值上采样替换成初步插值和图像超分辨率上采样两步。仿真结果表明,与超分辨率卷积神经网络(Super-resolution Convolutional Neural Network,SRCNN)信道估计算法相比,在不同种类的信道以及导频数下WDSR信道估计方法均方误差性能提升约4.6 dB。     

Improved Frequency Domain Channel Estimation and Equalization for MIMO Wireless Communications

This paper introduces an improved frequency domain channel estimation method based on interpolation vectors for single carrier frequency domain equalization (SC-FDE) with the multiple-input multiple-output (MIMO) scheme. The proposed algorithm is derived by employing the least squares (LS) criterion, and a specified application for the wide sense stationary uncorrelated scattering (WSSUS) Rayleigh fading channel is presented. The channel frequency domain responses estimated at two adjacent pilot blocks are used to track the time-variant channel information, which can effectively improve the accuracy of channel estimation without significantly increasing complexity. Maximum mean square error (MMSE) frequency domain equalization based on the estimated channel is employed in the receiver to recover transmitted signals. This paper also investigates a training sequence design method for multiple transmit antennas and a noise variance estimation method. Numerical simulation results show that the proposed methods can perform very well for fading channels with long multipath delay and high Doppler spread.     

WCDMA中一种新的信道估计方法

本文介绍了第三代移动通信标准WCDMA(FDD)中基于时分复用的导引符号辅助瑞利衰落信道下的信道估计.提出了一种新的利用两个连续时隙的导引符号估计出的信道参数进行最小二乘意义下二次曲线内插的信道参数估计方法.仿真表明本方法能有效地估计出时隙中数据段的信道参数,尤其在高速及变速运动情况下,Rake接收机的性能得到了显著的改善.     

Effect of Channel Estimation Error on Bit Error Probability in OFDM Systems over Rayleigh and Ricean Fading Channels

A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sine interpolator with Hamming windowing and a Wiener interpolator, are compared.     

A time-domain estimation method of rapidly time-varying channels for OFDM-based LTE-R systems

This paper addresses the performance of fast doubly selective fading channel estimation combined with Inter-Carrier Interference (ICI) cancellation for Long Term Evolution (LTE) communication platform in the High Speed Railway (HSR) environment. We consider the Channel Impulse Response (CIR) coefficients with a critical Doppler frequency shift and multi-path fading that were taken from the WINNER II channel model and the D2a propagation scenario, where the conditions of HSR are analyzed. As multi-path fading increases and the channel varies in the order of the symbol period, we first propose a novel approach for designing a pilot symbol structure in the time domain. Then, we describe the deployment of the proposed pilot symbol structure to estimate the channel in the time domain. Channel information corresponding to the data positions is obtained by linear interpolation. In each OFDM symbol, the slope and the initial value for establishing an interpolation function are estimated to adapt to the time variation of the channel. An accurate estimate of channel state information is used for the purpose of ICI cancellation. The simulation results show that the channel estimated by our proposed method can follow the real channel well, even in a very high Doppler frequency. The estimation method in terms of Mean Squared Error (MSE) significantly outperforms the state-of-the-art methods. The combination of our channel estimator with several interference cancelers provides a considerably better system performance than that achieved when frequency channel estimation is used.     

Channel estimation techniques based on pilot arrangement in OFDM systems

Channel estimation techniques for OFDM systems based on a pilot arrangement are investigated. Channel estimation based on a comb type pilot arrangement is studied through different algorithms for both estimating the channel at pilot frequencies and interpolating the channel. Channel estimation at pilot frequencies is based on LS and LMS methods while channel interpolation is done using linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Time-domain interpolation is obtained by passing to the time domain by means of IDFT (inverse discrete Fourier transform), zero padding and going back to the frequency domain by DFT (discrete Fourier transform). In addition, channel estimation based on a block type pilot arrangement is performed by sending pilots in every sub-channel and using this estimation for a specific number of following symbols. We have also implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots. We have compared the performances of all schemes by measuring bit error rates with 16QAM, QPSK, DQPSK and BPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.