一种基于频域加窗的OFDM信道估计算法

该文分析了实际OFDM系统时域信道估计中的信道冲激响应(CIR)泄漏问题。提出了一种新的OFDM时域信道估计算法,利用频域加窗降低CIR泄漏,对CIR进行过门限判决,最大限度删除CIR中的噪声。在非整数采样多径衰落信道下与已有的OFDM时域信道估计算法进行了仿真对比,证明该算法有效降低了信道估计MSE值,改善了系统BER性能。     

快时变OFDM系统中非采样间隔信道的信道估计

摘要：在快时变环境下的OFDM（orthogonal frequency division multiplexing,正交频分复用）系统中,针对非采样间隔信道CIR（channel impulse response,信道冲击响应）能量泄漏和ICI（inter-carrier interference,子载波间干扰）的问题,提出了一种基于分数抽头信道近似的复指数基扩展联合反馈离散傅里叶变换信道估计算法。该算法首先根据基于分数抽头信道近似的复指数基扩展模型计算信道参数,再根据该信道参数计算出快时变环境下OFDM系统的ICI系数,然后将初次消除ICI的信号作为反馈进行离散傅里叶变换,进一步消除噪声和ICI。该算法在一定程度上抑制了CIR能量泄漏,消除了ICI和噪声,有效地近似了实际信道。仿真结果表明,该算法在误比特率和信道均方误差方面均有明显提高。     

60GHz通信系统中一种IQ不平衡补偿算法

基于SC-FDE(单载波频域均衡)和OFDM(正交频分复用)的60GHz通信系统,对联合信道估计的IQ不平衡补偿算法进行了研究。通过最小化CRE(信道残余能量),在未知IQ不平衡参数时可得CIR(信道冲击响应)的最优解。一旦得到IQ不平衡参数,CIR的估计可以通过简单的替换计算来获得。因此,该算法可将信道与IQ不平衡分离开来进行灵活的补偿,且对训练序列没有任何限制。仿真结果表明,无论是60GHz LOS(视距)还是NLOS(非视距)信道,使用该方法均可得到很好的性能。     

非理想信道估计下的软输出MMSE V-BLAST检测算法

针对信道编码MIMO系统,该文推导出了实际信道估计下的软输出MMSE V-BLAST检测算法,该算法同时考虑了信道估计误差和判决误差传播的影响。仿真结果显示该文所提算法在几乎没有增加复杂度的情况下,可以极大地降低残余误码平层,获得显著的性能增益;所提算法对信道估计误差方差的估计可靠性不敏感,因而具有实际应用价值。     

4G无线网络的信道估计算法研究

MIMO-OFDM是4G的关键技术之一,在实际中需知该系统信道状态（CSI）,所以信道估计显得尤为重要。文章从该系统基本原理出发,对目前已有的三大类信道估计算法进行了概括并进行了优劣比较。     

一种基于基扩展模型的OFDM频域快时变信道估计方法

现有的OFDM系统快时变信道估计方法均为时域估计方法,假定信道为整数倍采样信道,利用理想的等间隔均匀导频恢复信道时域响应函数,进而采用基扩展模型拟合并估计其时变特性。而实际的信道通常为非整数倍采样信道,频带内可用的导频也并非假定的理想模式。此时,恢复的信道时域响应出现能量泄漏,导致算法性能大大受限。本文提出一种频域快时变信道估计方法,利用信道频域时变传输函数辅助估计,从而估计得到信道频域响应矩阵。该方法在频域实现,性能不受信道时域响应能量泄露影响。仿真实验从误码率、均方误差两方面分别验证了该方法的有效性。     

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。     

基于整体最小二乘的联合信道估计及OFDM信号检测算法

针对现有的联合信道估计及OFDM信号检测算法性能不高的问题,该文提出一种基于整体最小二乘的联合信道估计及OFDM信号检测算法。该算法首先通过导频估计初始的信道信息,在此基础上不断地采用整体最小二乘进行OFDM信号检测及信道估计,有效缓解迭代模型误差的影响,加快了算法迭代的收敛速度,提高了信道估计的精度,从而降低了OFDM系统的误码率。该文推导的信道估计克拉美罗界及仿真结果均表明所提出的算法在时变信道环境下优于现有的联合信道估计及OFDM信号检测算法。     

一种低复杂度自适应信道估计方案

针对最小平方估计方法精度有限的问题,该文提出一种自适应信道估计方案。该方案首先采用矩阵对角化的思想对最小均方误差估计方法进行改进,使得其在保持估计精度的同时大幅度降低计算复杂度。然后根据自适应的理论提出一种新的方案,该估计方案能够根据当前信道状况自适应地选择合适的算法进行信道估计,显示了较高的灵活性。仿真结果表明,该方案可以在计算复杂度较低的情况下进一步改善系统的误码率和均方误差,具有良好的实际应用价值。     

二维RAKE接收机中一种新的信道矢量估计算法

在二维RAKE接收机中，通常仅用导频信道来估计信道矢量，当导频功率较低时，估计误差较大。本文提出一种新的信道矢量估计算法，该算法采用导频信道与业务信道联合估计技术，通过分集组合两个信道的估计结果，使信道矢量的估计精度得到了提高，仿真结果表明，该算法能有效地降低系统的误码率。     

Channel Estimation for Cyclic Postfixed OFDM

A novel channel estimation algorithm is presented in this paper for the recently proposed cyclic postfix based on orthogonal frequency division multiplexing （OFDM） systems. Phase equalization with the erasure decision is used to reduce both the channel estimation error and the computational complexity. Simulation results show that the proposed channel estimation algorithm can effectively estimate the channel impulse response （CIR） and the performance of the proposed phase equalization with erasure decision is comparable with the minimal mean square error （MMSE） equalization, but it offers less computational complexity.     

Statistical Estimation of Fast Varying Channels for Cellular Mobile Telecommunications Systems

The time variant environment in fast channels severely impacts on the performances of classical equalization techniques. A method is proposed here to circumvent this problem, particularly in the severe channel with fast behaviour. To improve the Bit Error Rate (BER) at the receiver, a new approach is proposed for the channel impulse response (CIR) estimation in the Enhanced Data rates for GSM Evolution (EDGE)cellular system. The computation of the CIR h(t) (finite impulse response filter) is performed by using the Least Squares algorithm. Then, a statistical estimation of the CIR is achieved to update the coefficients of the equalizer filter. Computer simulation results show that statistical estimation (CIR re-estimation) provides significant improvement with 250 km/h vehiclespeed (RA250): the bit error rate (BER) is 20% lowered for data bits far from the middle of the burst.     

Fast Time-Varying Dispersive Channel Estimation and Equalization for an 8-PSK Cellular System

In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evolution (EDGE) system with fast time-varying and frequency-selective fading channels is presented. Via a mathematical derivation and simulation results, the channel impulse response (CIR) of the fast fading channel is modeled as a linear function of time during a radio burst in the EDGE system. Therefore, a least-squares-based method is proposed along with the modified burst structure for time-varying channel estimation. Given that the pilot-symbol blocks are located at the front and the end of the data block, the LS-based method is able to estimate the parameters of the time-varying CIR accurately using a linear interpolation. The proposed time-varying estimation algorithm does not cause an error floor that existed in the adaptive algorithms due to a nonideal channel tracking. Besides, the time-varying CIR in the EDGE system is not in its minimum-phase form, as is required for low-complexity reduced-state equalization methods. In order to maintain a good system performance, a Cholesky-decomposition method is introduced in front of the reduced-state equalizer to transform the time-varying CIR into its minimum-phase equivalent form. Via simulation results, it is shown that the proposed algorithm is very well suited for the time-varying channel estimation and equalization, and a good bit-error-rate performance is achieved even at high Doppler frequencies up to 300 Hz with a low complexity.     

基于TD-SCDMA系统的快速频率估计算法

提出了一种应用于TD-SCDMA系统中的快速频率估计算法.这种算法利用训练序列估计信道冲击响应,恢复不受信道干扰的发送信号;然后利用最大似然估计算法和二分数值估计算法,估计出较为准确的频率偏移值.仿真表明,该算法比常用的频率估计算法具有更低的复杂度,而且在高斯白噪(AWGN)和多径衰落环境下,均能够对TD-SCDMA系统中的频率偏移获得较为准确的估计结果.     

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.     

Time-domain channel estimator based on cyclic correlation for OFDM systems with guard interval

Channel impulse response （CIR） can be estimated on the basis of cyclic correlation in time-domain for orthogonal frequency division multiplexing （OFDM） systems, This article proposes a generalized channel estimation method to reduce the estimation error by taking the average of different CIRs. Channel impulse responses are derived according to the different starting points of cyclic correlation. In addition, an effective CIR length estimation algorithm is also presented. The whole proposed methods are more effective to OFDM systems, especialiy to those with longer cyclic prefix. The analysis and the simulation results verify that the mean square error performance is 4-5 dB better than the conventional schemes under the same conditions.     

一种短波信道自适应均衡算法的研究

基于逐幸存路径处理(PSP)的思想,研究了一种减少状态序列估计(RSSE)的短波信道自适应均衡算法.该算法首先通过训练序列估计信道的参数,然后利用RLS算法对信道参数和输入数据的估计值同时进行逐幸存路径地更新.数值仿真表明,在短波信道环境下,RSSE-PSP算法在减小计算复杂度的同时最大限度地保持了性能增益,其性能明显优于其他均衡算法.