OFDM系统信道估计几种插值算法综述

阐述了OFDM系统信道估计的基本原理,介绍了OFDM系统在快衰落信道下的几种插值算法,并通过仿真比较他们的优缺点。     

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。     

一种改进的DFT-S-OFDM系统信道估计方法

本文首先给出了DFT-S—OFDM上行链路系统的一个简单发射机框图，然后基于该框图对系统进行了简单描述，给出了基于LS准则的信道估计方法和为了进一步提高估计精度基于时域维纳滤波处理的信道估计方法。仿真结果表明，在未编码16QAM-DFT-S-OFDM系统中，基于时域维纳滤波处理的估计可以达到与导频基于LMMSE准则的信道估计方法相同的估计性能，但这种方法一般要比后者有低的复杂度。     

一种新的CDMA2000信道估计方法

文章分析了非连续导频情况下CDMA2000反向信道结构，针对CMDA2000反向信道中导频信道与功控子信道时分复用情况，提出了一种基于判决反馈的信道估计方法。最后用COSSAP软件对此方法进行了仿真，仿真结果表明该方法能有效的估计出插入功控比特导频情况下的信道参数。     

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。     

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。     

LTE系统中基于改进样条插值的信道估计方法

上行控制信道(PUCCH)格式1/1a/1b在长期演进(LTE)系统中承载重要的控制信令,其信道估计对系统性能有着重要影响.普通循环前缀(CP)时,PUCCH格式1/1a/1b要利用时隙内3个连续排放的导频进行插值需要考虑二阶插值或者三次样条插值.为了使其在TD-LTE测试仪表系统中得到高效实现,分析了两种插值算法,并...     

CDMA2000导频辅助的信道估计方法研究

文章分析了非连续导频情况下CDMA2000反向信道结构，针对CDMA2000反向信道中导频信道与功控子信道时分复用情况，研究了四种信道估计方法，分别是重复使用、判断校正及其改进方法、最小二乘插值。最后用COSSAP软件对这四种方法的性能进行了比较，仿真结果表明改进的判别校正和最小二乘插值方法能有效的估计出插入功控比特导频情况下的信道参数。     

宽带CDMA系统中的一种新的自适应信道估计方法

该文提出了采用实测的信道自相关系数作为权重的信道估计处理方法,并给出其误差性能的数学表达式,同时给出了经典的滑动平均信道估计方法的误差性能的数学表达式。理论分析及仿真结果表明所提的方法能自动适应移动信道的时变模型及衰落速率,具有有效地抑制噪声的优点;同时克服了滑动平均估计方法的估计长度对估计准确性影响较大的缺点,在移动速度固定及移动速度变化很大的环境下都具有稳定的误差性能;尤其在移动速度变化很大的环境下具有比滑动平均估计方法更低的估计方差,大大提高了RAKE接收机的性能。     

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。     

Performance Comparison of Multiuser Detectors with Channel Estimation for Flat Rayleigh Fading CDMA Channels

Since the conventional detector performs poorly in bandwidth-efficient Code Division Multiple Access (CDMA) systems, several multiuser detectors were proposed recently. In this paper, we compare performance of the decorrelator, the two-stage detector (2S), and the decision-feedback detector (DF) for the Rayleigh flat fading synchronous CDMA channel. First, assuming perfect channel estimation, we show that the 2S and the DF have much lower bit error rate (BER) than the decorrelator, and prove that the ideal DF has unity Asymptotic Multiuser Efficiency (AME). Furthermore, we evaluate the performance of these detectors in the presence of channel mismatch. We model the Rayleigh flat fading channel as the second order Auto Regressive (AR) process, and use the Kalman filter as the channel estimator. The lower bounds on the BER of the 2S and the DF are derived. The analytical results and the simulations show that the estimation error accumulated due to cancellation of other users limits the performance of the 2S and the DF. Therefore, in the presence of channel mismatch, the decorrelator offers comparable or even better performance than more complex decision-feedback and two-stage detectors.     

WCDMA下行链路信道估计算法的性能分析及比较

在WCDMA／FDD第三代移动通信系统中，下行链路的信道估计有基于公共导频信道（CPICH）和基于时分复用导频符号两种方式。本文就分别基于这两种方式的信道估计算法进行了性能的分析和比较，并给出实现模型及仿真结果。     

两种星载高分辨宽测绘带SAR系统通道相位误差估计方法

 本文针对星载方位多通道高分辨宽测绘带(HRWS)合成孔径雷达(SAR)系统,提出了两种通道相位误差估计方法:信号子空间比较法和天线方向图法.信号子空间比较法基于信号特征向量张成的空间(即信号子空间)与真实导向矢量张成的空间相同这一特性,得到各通道间的相对相位误差,该方法适用范围广,估计精度高,对系统要求低,且运算量小.天线方向图法结合天线方向图,直接估计通道相位误差,无须特征分解,无须矩阵求逆,运算量小,主要适用于均匀分布的场景.最后利用实测地基数据验证了两种方法的有效性.     

WRAN系统中基于自适应内插的信道估计算法

提出了一种基于自适应复系数内插的信道估计算法,改善了无线区域网络（WRAN）系统对抗动态多径时延的能力。WRAN是第一个采用认知无线电技术改善频谱效率的宽带接入标准,系统在下行链路中采用了正交频分复用（OFDM）调制技术,而信道估计技术对于采用相干解调的OFDM系统十分重要。传统的OFDM信道频域响应（CFR）估计算法通常采用实系数频域内插的方式,在对抗WRAN系统长多径时延信道时,不能有效地工作。该文在研究实系数FIR内插变换域响应的基础上,提出了一种复系数内插算法。为了同时适用于短时延信道,提出了一种低复杂度、自适应匹配信道最大多径时延的算法。通过仿真,验证了该算法能够对抗更大的多径时延,提高信道估计的精度,改善系统误码性能。      

基于三次Hermite插值的OFDM信道估计

主要研究基于导频的正交频分复用（OFDM）信道估计的插值方法,提出三次Hermite插值信道估计算法,目的是利用该插值算法在不同信噪比的环境下,缩短运算时间和降低误码率（BER）。通过Matlab仿真实验说明,该算法相对于传统的信道估计算法具有较良好的性能。相对于改进的二项插值,具有较低的BER,相对于三次样条插值算法,具有运算时间较短、大信噪比环境下BER较低的优点。     

Detection of Channel Variations to Improve Channel Estimation Methods

In current digital communication systems, channel information is typically acquired by supervised approaches that use pilot symbols included in the transmit frames. Given that pilot symbols do not convey user data, they penalize throughput spectral efficiency, and transmit energy consumption of the system. Unsupervised channel estimation algorithms could be used to mitigate the aforementioned drawbacks although they present higher computational complexity than that offered by supervised ones. This paper proposes a simple decision method suitable for slowly varying channels to determine whether the channel has suffered a significant variation, which requires to estimate the matrix of the recently changed channel. Otherwise, a previous estimate is used to recover the transmitted symbols. The main advantage of this method is that the decision criterion is only based on information acquired during the time frame synchronization, which is carried out at the receiver. We show that the proposed criterion provides a considerable improvement of computational complexity for both supervised and unsupervised methods, without incurring in a penalization in terms of symbol error ratio. Specifically, we consider systems that make use of the popular Alamouti code. Performance evaluation is accomplished by means of simulated channels as well as making use of indoor wireless channels measured using a testbed.     

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.     

Channel Estimation by Using Short Training Sequences in CDMA Systems

Multiuser detection techniques are known to be effective to counter the presence of multiuser interference in code division multiple access channels. Multiuser detectors can provide excellent performance only when the channel impulse responses of all the users are precisely known. Hence, channel estimation becomes a challenging issue in mobile communication systems. In this paper, we address the problem of efficient maximum likelihood mobile radio channel estimation at high channel efficiency that requires a short training sequence along with the known spreading sequence. The proposed system can be employed in both the uplink and downlink of a heavily loaded multiuser CDMA system. The extension of the approach with unknown users' delays are also proposed. We present results that show the success of this method in recovering the transmitted bits with a relatively small number of preamble bits. Ahmet Rizaner was born in Larnaca, Cyprus, on January 31, 1974. He received the B.S. and M.S. degrees in Electrical and Electronics Engineering from the Eastern Mediterranean University, Famagusta, North Cyprus, in 1996 and 1998, respectively. He completed his PhD. degree in Electrical and Electronic Engineering in Eastern Mediterranean University and joined Eastern Mediterranean University as a lecturer in 2004. He is lecturing in the School of Computing and Technology. His main research interests include CDMA communications, adaptive channel estimation, and multiuser detection techniques. Hasan Amca was born in 1961 in Nicosia-Cyprus. He graduated from the Higher Technological Institute in Magosa-Cyprus (which is renamed later as Eastern Mediterranean University). He joined EMU in 1985 after receiving a M.Sc. (Digital Signal Processing) degree from the University of Essex in England (1985). He took his Ph.D. (Mobile Communications) from the University of Bradford where he was on a Commonwealth scholarship. He has been teaching in the Electrical and Electronic Engineering Department of Eastern Mediterranean University since 1993 where he also served as the vice chairman from Spring 1998 to Spring 2000. He has been appointed as the Director of the School of Computing and Technology of the EMU since Spring 2000. His research interests include Multi User Detection of CDMA signals, Adaptive Equalisation, Multi Carrier Systems, Mobile Radio Systems and Networks, Internet and Information Technology Applications in Education. Kadri Hacıoğlu was born in Nicosia, Cyprus. He received the B.Sc., M.Sc., and Ph.D. degrees in electrical and electronic engineering from the Middle East Technical University, Ankara, Turkey, in 1980, 1984, and 1990, respectively. After his two-year military service, in 1992, he joined the faculty of Eastern Mediterranean University, Magosa, North Cyprus, as an Assistant Professor, and became an Associate Professor in 1997. While there, he taught several classes on electronics, digital communications, speech processing and neural networks. During this time, he conducted research on applying fuzzy logic, neural networks, and genetic algorithms to signal processing and communications problems. From 1998 to 2000, he was a Visiting Professor in the Department of Computer Science, University of Colorado, Boulder. Here, he taught classes on neural networks and continued his research. Since 2000, he has been a Research Associate at the Center for Spoken Language Research, University of Colorado. He has authored or coauthored numerous papers and supervised a dozen M.Sc./Ph.D. theses. His current research interests are concept-based language modeling, speech understanding, natural language generation, and search methods in speech recognition/understanding. He also does research on multiuser detection and equalization in CDMA systems. Ali Hakan Ulusoy was born in Eskişehir, Turkey, on June 3, 1974. He graduated from the double major program of the department of Electrical and Electronic Engineering and department of Physics in Eastern Mediterranean University as the first rank student of Faculty of Engineering in 1996. He received his M.S. degree in Electrical and Electronic Engineering in Eastern Mediterranean University in 1998. He completed his PhD. degree in Electrical and Electronic Engineering in Eastern Mediterranean University and joined Eastern Mediterranean University as a lecturer in 2004. He is lecturing in the School of Computing and Technology. His current research interests include receiver design, multi-user detection techniques, blind and trained channel estimation in Code Division Multiple Access (CDMA).     

CDMA移动通信系统中的信道盲与半盲估计

介绍了应用于异步CDMA移动通信系统中的信道盲估计技术的原理,信道盲估计主要分为子空间分解、相关拟合和最大似然三种方法。分析了各自的特点,然后讨论了在部分发送数据已知条件下的半盲信道估计技术。