OFDM系统中一种改进的最大似然同步迭代算法

在考虑多径衰落信道的影响下,改进了基于循环前缀的最大似然(ML)同步迭代算法,弥补了原ML迭代算法只在高斯白噪声信道背景下才能得到准确的定时和频率偏差估计的不足,实现了多径衰落信道下的同步估计.并在多径衰落信道下进行了仿真实验,结果表明改进迭代算法在具有较好的同步性能.     

cdma2000中基于分形滤波的信道估计方法

第三代移动通信标准cdma2000采用了基于平行连续导频信道辅助的信道估计体制.本文将分形理论引入多径衰落信道的描述,提出了一种利用分形滤波进行最小均方误差意义下信道参数估计的方法.仿真结果表明,本方法不仅对不同运动速度下的信道都能得到比较准确的估计,从而显著地改善Rake接收机的性能,而且可以自适应跟踪信道衰落的快慢变化.研究同时表明,与传统的随机模型相比,新的分形信道模型能更好地刻画多径衰落的行为.     

基于循环前缀的OFDM同步算法研究

针对传统基于循环前缀的定时同步算法在多径信道下定时估计精度明显下降的问题,在经典的定时同步算法最大似然估计算法的基础上,研究了一种整体相关的OFDM定时估计算法,最后结合两者提出了一种有效利用截短循环前缀进行定时估计的改进算法,避免了多径环境下ISI带来的定时估计误差。对算法进行了仿真,表明在高斯白噪声信道和多径衰落信道下改进的算法都具有较好的性能。     

一种新的基于参数信道模型的MIMO信道估计算法

针对频率选择性块衰落MIMO信道,该文提出一种改进的基于参数信道模型的信道估计方法。该方法首先通过修正后的TST-MUSIC算法估计多径的传播时延和角度。由时延和角度信息,得到一种基于参数信道模型的信道估计方法。仿真结果表明此种方法可以有效地减少参数估计的维数,其性能要远远优于非参数的最小二乘估计器。     

多径衰落信道的多重分形模型

本文研究多径衰落信号的多重分形性质,分析并指出了信号多重分形维数是描述无线信道传播特性的重要参数;计算了多径衰落信号的多重分形维数及其分形参数;在此基础上提出了一种新的无线信道模型;结合分形插值方法,对多径衰落信号的重构进行了研究.仿真结果表明,无线信道的多重分形模型与传统的统计模型相比更有效、更准确.     

适用于慢衰落信道的联合最大似然序列估计

为了克服移动通信中存在的多径衰落效应,基于Viterbi算法的最大似然序列估计需要不断跟踪信道参数的变化.在建立有限带宽信号的多径衰落信道传输模型的基础上,提出了一种适合于慢衰落信道特性的降阶联合信道跟踪与最大似然均衡算法D-PSP.该方法根据信道特性选择不同的降阶维数N,在保证数据正确接收率的条件下,不同程度的有效减小PSP算法的计算时间和存储空间.     

一种适用于多径衰落信道的OFDM系统同步算法

该文针对多径衰落信道的具体特点,提出了一种适用于无线衰落信道环境下的OFDM符号同步方法。此种方法利用前一帧估计的信道最大时延来调整相关窗长度,在最大程度上避开了多径的影响;并利用本帧信道估计得到的多径信息进一步完成符号精细同步。仿真证明,该方法比传统的方法有较大的性能改善,比较适合多径衰落信道环境下的符号定时同步。     

单载波频域均衡信道估计分析

针对高速率信息传输系统中多径衰落对单载波频域均衡(SC-FDE)信道估计造成的影响,在SC-FDE原理基础上,将无线通信中信噪比估计和SC-FDE中信道估计结合起来,对现有信噪比估计算法进行优化。分析和仿真结果表明,此方法能有效地改善多径衰落信道中信道估计的有效性,提高了频域均衡的效果,从而改善了SC-FDE系统的误码率(BER)性能。     

地空测控链路OFDM信道估计

针对无人飞行器大动态运动特点,提出利用地空测控窄带扩频链路的信道估计,辅助OFDM传输方式的下行宽带链路进行信道估计的方法。基于OFDM信道估计基带模型,设计了奇偶OFDM符号分组交错导频插入方式,设计了基于窄带链路多普勒频偏、多径时延信道估计的宽带链路信道估计算法。在大多普勒与多径传输信道下对算法误码率性能进行了仿真,验证了下行宽带链路具有较强的抗大多普勒、抗多径衰落的性能。     

OFDM系统中基于循环前缀的频偏估计算法

文章对几种常用的基于循环前缀(CP)的最大似然同步算法进行了分析,并对其频偏估计方差进行了比较;同时针对基于CP的同步算法在多径衰落信道下性能较差的情况,提出了一种改进的CP同步算法并进行了仿真,结果表明相比于原ML算法,文中算法在多径信道下可有效提高频偏估计性能.     

Adaptive joint beamforming and B‐MMSE detection for CDMA signal reception under multipath interference

The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency of a wireless system under multipath interference, especially in a fast‐fading channel. This paper studies the performance of an adaptive beamformer incorporated with a block‐wise minimum mean square error(B‐MMSE) detector, which works on a unique signal frame characterized by training sequence preamble and data blocks segmented by zero‐bits. Both beam‐former weights updating and B‐MMSE detection are carried out by either least mean square (LMS) or recursive least square (RLS) algorithm. The comparison of the two adaptive algorithms applied to both beamformer and B‐MMSE detector will be made in terms of convergence behaviour and estimation mean square error. Various multipath patterns are considered to test the receiver's responding rapidity to changing multipath interference. The performance of the adaptive B‐MMSE detector is also compared with that of non‐adaptive version (i.e. through direct matrix inversion). The final performance in error probability simulation reveals that the RLS/B‐MMSE scheme outperforms non‐adaptive B‐MMSE by 1–5 dB, depending on the multipath channel delay profiles of concern. The obtained results also suggest that adaptive beamformer should use RLS algorithm for its fast and robust convergence property; while the B‐MMSE filter can choose either LMS or RLS algorithm depending on antenna array size, multipath severity and implementation complexity. Copyright © 2004 John Wiley & Sons, Ltd.     

Channel estimation for OFDM transmission in multipath fadingchannels based on parametric channel modeling

We present an improved channel estimation algorithm for orthogonal frequency-division multiplexing mobile communication systems using pilot subcarriers. This algorithm is based on a parametric channel model where the channel frequency response is estimated using an L-path channel model. In the algorithm, we employ the ESPRIT (estimation of signal parameters by rotational invariance techniques) method to do the initial multipath time delays acquisition and propose an interpath interference cancellation delay locked loop to track the channel multipath time delays. With the multipath time delays information, a minimum mean square error estimator is derived to estimate the channel frequency response. It is demonstrated that the use of the parametric channel model can effectively reduce the signal subspace dimension of the channel correlation matrix for the sparse multipath fading channels and, consequently, improve the channel estimation performance     

A robust channel estimator for DS-CDMA systems under multipath fading channels

This paper addresses the problem of channel estimation for direct-sequence code-division multiple-access (DS-CDMA) systems with time-varying multipath fading channels. The multipath fading channels are modeled as autoregressive (AR) models. A method is first proposed to convert the time-varying regression model due to the time-varying nature of users' information symbols into a time-invariant one. Then, a polynomial approach is proposed to obtain the minimum mean square error (MMSE) estimator. The uncertainty of the channel model and decision errors of the DS-CDMA detector are taken into consideration in the design of the MMSE estimator. Compared with the Kalman estimator, the computational complexity of the proposed algorithm is much lower. The simulation results show that the proposed estimator provides a comparable estimation performance with the Kalman estimator and is robust for fast-fading channels.     

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.     

An improved blind adaptive MMSE receiver for fast fading DS-CDMAchannels

Blind adaptive minimum mean-squared errors (MMSE) receivers for multiuser direct-sequence code-division multiple access (DS-CDMA) systems that assume knowledge of the steering vector, i.e., the cross-correlation between the desired output and the input signal, are known for their robustness against channel fading as they do not attempt to explicitly track the channel of the user of interest. However, these receivers often have higher excess mean squared error and, hence, poorer performance than training-sequence based adaptive MMSE receivers. In this paper, an improved correlation matrix estimation scheme for blind adaptive MMSE receivers is provided. The new scheme takes advantage of the fact that the desired linear receiver can be expressed as a function of the interference correlation matrix only, rather than the total data correlation matrix. A theoretical analysis is performed for the flat fading case which predicts that the new estimation scheme will result in significant performance improvement. Blind adaptive MMSE receivers with the new estimation scheme appear to achieve performance comparable to the training-sequence based adaptive MMSE receivers. Detailed computer simulations for the fast multipath fading environment verify that the proposed scheme yields strong performance gains over previous methods     

SC-FDE系统中信道估计和均衡算法的研究和实现

为了克服多径信道下码间串扰带来的影响,本文对SC-FDE系统中的信道估计和均衡算法进行研究。首先分析了DFT插值算法原理,提出采用格雷互补序列估计信道频率响应的方法,然后对MMSE均衡估计参数进行了详细推导,最后通过Matlab对均衡算法中时域滤波进行仿真验证,结果表明该方法能够有效滤除噪声,提升多径信道下系统接收性能,具有一定的应用价值。     

基于粒子滤波的OFDM载波频偏和信道联合估计

一种基于粒子滤波(PF)的正交频分复用(OFDM)系统在慢衰落瑞利信道下联合信道估计和载波恢复的新方法被提出。该算法适用于多径时变信道模型以及等效离散时间信道模型。算法引入了在非线性系统参数估计和跟踪领域上十分有效的PF方法,将Kaman滤波与序贯蒙特卡罗采样(SMCS)相结合来估计信道衰落系数以及载波频偏(CFO)的后验概率密度,从而通过计算得到信道的响应函数,并在此基础上,利用MMSE均衡器消除码间串扰(ICI),进行码元估计。仿真结果表明了算法的有效性和优越性。     

Doubly Iterative Equalization of Continuous-Phase Modulation

In this paper, a doubly iterative receiver is proposed for joint turbo equalization, demodulation, and decoding of coded binary continuous-phase modulation (CPM) in multipath fading channels. The proposed receiver consists of three soft-input soft-output (SISO) blocks: a front-end soft-information-aided minimum mean square error (MMSE) equalizer followed by a CPM demodulator and a back-end channel decoder. The MMSE equalizer, combined with an a priori soft-interference canceler (SIC) and an a posteriori probability mapper, forms a SISO processor suitable for iterative processing that considers discrete-time CPM symbols which belong to a finite alphabet. The SISO CPM demodulator and the SISO channel decoder are both implemented by the a posteriori probability algorithm. The proposed doubly iterative receiver has a central demodulator coupled with both the front-end equalizer and the back-end channel decoder. A few back-end demodulation/decoding iterations are performed for each equalization iteration so as to improve the a priori information for the equalizer. As presented in the extrinsic information transfer (EXIT) chart analysis and simulation results for different multipath fading channels, this provides not only faster convergence to low bit error rates, but also lower computational complexity.