MIMO OFDM系统中同步和信道的联合估计

提出了一种MIMO OFDM系统的定时恢复、频率同步和信道估计的联合算法。为了减少算法的复杂度，算法分两步完成：首先利用接收信号的自相关函数进行粗同步和信道估计，得到时延和频偏的粗估计，然后在粗估计基础上采用最大似然准则进行精确的同步和信道估计。仿真结果表明，该算法能够达到很好的效果，系统误码率接近已知信道响应时的情况。     

基于改进帧结构设计的无人机集群信道均衡

针对无人机集群链路单载波频域均衡(Single Carrier Frequency Domain Equalization,SC-FDE)系统信号同步与信道估计模块相互独立、系统开销大、信道估计精度不高的问题,提出了一种基于Schmidl&Cox的改进数据帧结构设计,使用同一训练序列实现信号同步和信道估计,降低了系统开销;利用快速傅里叶变换的周期性及线性性质,将多次复杂频域信道估计转换为时域降噪处理,得到更精确的信道频域响应估计.通过引入NH(Neumann-Hoffman)序列,解决了Schmidl&Cox定时方法存在峰值平台的问题,定时测度函数尖锐,方差性能较好.利用Matlab软件对设计算法进行了仿真验证,结果表明,在不增加系统开销的情况下,所提算法在相同信噪比下比传统均衡算法误码率更低,在误码率为1×10-5时有2～3 dB的性能增益,系统开销由0.28降为0.2,实现复杂度低.     

OFDM传输系统同步方案简介

本文研究数字地面电视DVB-T的OFDM传输系统接收端的同步。根据OFDM的原理特点和DVB-T标准,设计同步方案。该方案采用多载波(OFDM)系统时域插在循环保护间隔携带的冗余信息进行粗符号和分数频率偏移估计。该方案利用OFDM系统时域插入的保护间隔前缀所携带的冗余信息,进行粗符号同步和分数频率偏移估计。FFT后,再利用频域插入的连续导频进行整数频偏估计,及利用分散导频通过估计信道冲击响应,实现精符号同步。仿真表明,同步设计在加性高斯白噪声信道能达到最佳性能,在慢衰落Rayleigh信道下也有较好的性能。     

OFDM传输系统同步方案简介

本文研究数字地面电视DVB-T的OFDM传输系统接收端的同步。根据OFDM的原理特点和DVB-T标准，设计同步方案。该方案采用多载波（OFDM）系统进域插在循环保护间隔携带的冗余信息进行粗符号和分数频率偏移估计。该方案利用OFDM系统时域插入的保护间隔前缀所携带冗余信息，进行粗符号同步和分数频率偏移估计。FFT后，再利用频域插入的连续导频进行整数频偏估计，及利用分数导频通过估计信道冲击响应，实现精符号同步。仿真表明，同步设计在加性高斯白嗓声信道能达到最佳性能，在慢衰落Rayleigh信道下也有较好的性能。     

TD-SCDMA系统中低代价信道估计方法的改进

TD-SCDMA系统中运用B.Steiner估计器是一种低代价的信道估计器，其估计精度受信道中加性噪声的影响，导致估计值与真实值相比误差较大，影响系统性能。本文提出一种门限处理方法，对Steiner估计器得到的信道响应进行改进，削弱噪声影响。模拟实验表明，改进的信道响应更接近真实值，能提高系统性能。并且，这种后处理方法简单，易于实现，很小或几乎不增加系统的运算。     

新的盲信道估计算法

研究了各种盲信道估计算法.提出一种关于信道的假设,并在此基础上提出一种新的盲信道估计算法.新算法能够同时估计出信号和信道.新算法基于MMSE准则,利用m进制通信系统中,在接收端和发射端都已知信号模式且模式个数有限(K=log2m)的特点,结合预置于算法的信道模型,得到信道模型和信号模式的估计.然后依据MMSE准则得到信道和信号的最佳估计.最后给出仿真结果,仿真表明:新的盲信道估计方法能够精确估计实际信道的等效冲击响应,并能够进行有效通信.     

基于小波多阶阈值去噪的LWT-OFDM系统信道估计

为了消除LWT-OFDM系统受无线信道多样化的影响,增强LWT-OFDM系统信道估计的效率和准确性,提出了基于小波多阶阈值去噪的信道估计算法.该算法在LS信道估计的基础上,首先通过小波提升变换对得到的信道冲击响应进行快速分解,再采用多阶的阈值函数精确的消除噪声.通过在高斯信道和多径信道下的仿真表明,本文算法相对于其它四种基于导频的信道估计算法,提高了LWT-OFDM系统的误码率性能和MSE性能.     

基于kumar快速算法的信道估计

信道估计是无线通信系统的一项关键技术,快速信道估计能够提高通信信号处理的实时性.文章提出了一种通过构建特殊训练序列得到Toeplitz矩阵方程,并利用kumar快速算法来求解方程从而估计出信道冲击响应的方法,仿真结果表明,可以有效地降低信道估计过程中的运算复杂度.     

TDS-OFDM系统中信道估计方法的研究

信道估计是通信领域的一个研究热点,它是进行相关检测、解调、均衡的基础。针对DMB-T系统中的时域同步信道估计进行了研究,在算法级对其进行了详细的分析并提出了改进得到更优的性能。提出的算法采用PN序列的相关技术得到信道估计,通过比较不同的相关方法所得到的信道,确定最终输出的信道冲激响应。     

MIMO-OFDM系统中一种改进的信道估计方法

信道的准确估计是提高MIMO-OFDM系统性能的关键.在最优导频时域信道估计的基础上,提出了一种较低复杂度的改进算法,利用时变信道的自回归(AR)模型构造卡尔曼滤波器对估计出的时域信道响应进行滤波,提高信道时域响应的估计精度.仿真结果表明,在慢时变信道环境下,改进方法可以进一步提高信道估计的精度,同时保持了较低的复杂度.     

Joint Synchronization and Channel Estimation for OFDM Systems

1Introduction Orthogonal Frequency Division Multiplexing(OFDM) has become a popular technique for transmis-sion of signals over wireless channels . OFDMhas beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting ( DAB) , Digital Video Broadcasting(DVB-T) ,the IEEE 802 .11a[1]Local Area Network(LAN) standard and high performance LAN type 2(HIPERLAN/2)[2]standard. OFDMis also being pur-sued for Dedicated Short-Range Communications(DSRC) for road side to …     

A combined timing and frequency synchronization and channel estimation for OFDM

This letter addresses training-signal-based combined timing and frequency synchronization and channel estimation for orthogonal frequency-division multiplexing systems. The proposed scheme consists of two stages. At the first stage, coarse timing and frequency-offset estimates are obtained. Based on these estimates, a (coarse) channel response estimate is obtained. The timing and frequency-offset estimates at the second stage are obtained by maximum-likelihood (ML) realization based on a sliding observation vector. Then ML channel estimation is performed. A means of complexity reduction by an adaptive scheme is also presented. The simulation results show that the proposed combined approach performs quite well, and circumvents the problem of mismatch among individual synchronization tasks.     

分布式MIMO-OFDM系统的同步捕获算法

该文提出了一种分布式多输入多输出正交频分复用(MIMO-OFDM)系统初始信号检测和同步捕获算法。该算法设计了导频符号,采用谱分析方法实现可靠的初始信号检测、粗定时和粗频偏估计,并在快速傅里叶变换(FFT)之后进行精确地频偏和定时估计。仿真结果表明,该算法在低信噪比多径瑞利信道条件下具有很好的性能。     

基于循环移位前导序列的OFDM载波同步方法

提出一种基于循环移位前导序列的正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）系统载波同步方法，该方法根据离散傅里叶变换（Discrete Fourier Transform，DFT）的时移性质，构造循环移位前导序列，并设计了两个频偏估计器。由估计器1完成粗同步，而精同步采用两个估计器的最优线性组合完成。在多径信道下优化估计器的设计，消除了均方误差中出现的地板效应。新算法与传统算法相比，估计范围大，运算精度高，且估计范围和精度可灵活调节。同时分析并得出了本估计方法的Cramer—Rao下限。仿真结果表明，新算法降低了均方误差和误码率，有效提高了系统性能。     

Joint estimation of symbol timing and carrier frequency offset of OFDM signals over fast time-varying multipath channels

In this paper, we present a novel joint algorithm to estimate the symbol timing and carrier frequency offsets of wireless orthogonal frequency division multiplexing (OFDM) signals. To jointly estimate synchronization parameters using the maximum likelihood (ML) criterion, researchers have derived conventional models only from additive white Gaussian noise (AWGN) or single-path fading channels. We develop a general ML estimation algorithm that can accurately calculate symbol timing and carrier frequency offsets over a fast time-varying multipath channel. To reduce overall estimation complexity, the proposed scheme consists of two estimation stages: coarse and fine synchronizations. A low complexity coarse synchronization based on the least-squares (LS) method can rapidly estimate the rough symbol timing and carrier frequency offsets over a fast time-varying multipath channel. The subsequent ML fine synchronization can then obtain accurate final results based on the previous coarse synchronization. Simulations demonstrate that the coarse-to-fine method provides a good tradeoff between estimation accuracy and computational complexity.     

卫星5G通信抗干扰时频同步算法

为了提高卫星通信系统的抗干扰和抗频偏能力,提出了一种在5G物理层波形中融入扩频技术的传输波形设计方案和辅同步信号（Secondary Synchroniztion Singnal,SSS）辅助主同步信号（Primary Synchronization Signal,PSS）多步联合抗干扰时频同步算法。该算法的实现分为3步：首先采用SSS辅助PSS二维时间同步得到粗同步点;然后根据粗同步点进行整数倍和小数倍频偏估计与补偿,其中小数倍频偏估计分为PSS扫频粗频偏估计和SSS辅助PSS互相关精频偏估计;最后对频偏补偿后的接收序列再次进行精时间同步和频偏补偿。仿真结果表明,所提设计方案和同步算法可以抗干信比为12 dB的干扰,并且在低信噪比下的性能优于传统算法。     

Frequency Offset Estimation by Multi-Band Averaging Method: A New Approach for MB-OFDM Based Ultra-Wideband Communication System

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).     

Fast Synchronization and Channel Estimation for OFDM Systems

A joint synchronization and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) system. In the proposed scheme, the integer frequency offset, fine timing offset and channel estimation are estimated based on the characteristics of the chirp signals. The main contributions of the paper are: the more robust ability to find the actual first path instead of the strongest path on the assumption of repeated chirp waveforms in the timing synchronization approach, and the lower computational complexity with high performance in the channel estimation approach. Moreover, we analyze the performance of the proposed method and check it via Monte Carlo simulations. The simulation results show that the proposed method can achieve good performance for both synchronization and channel estimation in frequency selective channels.     

Joint carrier frequency synchronization and channel estimation for OFDM systems via the EM algorithm

A joint carrier frequency synchronization and channel estimation scheme is proposed for orthogonal frequency-division multiplexing (OFDM) system. In the proposed scheme, carrier frequency synchronization and channel estimation are performed iteratively via the expectation-maximization (EM) algorithm using an OFDM preamble symbol. Moreover, we analytically investigate the effect of frequency offset error on the mean square error (MSE) performance of channel estimator. Simulation results present that the proposed scheme achieves almost ideal performance for both channel and frequency offset estimation.