一种基于过采样的OFDM系统定时同步算法

针对基于辅助训练序列的OFDM符号定时同步,文章提出了一种基于过采样的定时同步相关算法。首先介绍了OFDM系统的传输模型,然后阐述了定时同步算法,包括已有的基于已知辅助数据的定时同步算法和基于过采样的已知辅助训练序列定时同步算法,最后对算法性能进行了仿真分析。     

基于信号频域特征实现位定时恢复

数字通信系统对接收信号进行采样时,如果存在位定时误差,则会严重影响通信系统的工作性能。而采样信号的变换域相位谱中包含位定时误差信息,只要有效地恢复该误差信息,即可以很好地实现通信系统的位定时同步。在此基础上,对频域检测位定时估值算法的原理和实现过程进行了较详细的描述和分析,最后,针对几种典型信号对算法的性能进行了仿真研究,仿真结果表明,该算法对几种典型信号都有效,具有较广泛的适应性。     

非相干直接序列扩频信号的定时估计

首先分析了定时恢复在非相干直接序列扩频中的必要性,然后利用滑动平均器将解扩后的非相干扩频信号等效为高倍采样的非扩频信号,最后选择了一种适合于非扩频信号定时估计的算法,并将该算法用于非相干扩频信号的定时估计。仿真表明,该算法性能满足非相干直接序列扩频信号对定时估计误差的要求。     

基于符号定时偏差补偿的过零点采样自干扰消除

针对系统存在符号定时偏差时造成自干扰信号过零点漂移,进而导致过零点采样自干扰消除方法性能失效问题,本文提出一种符号定时偏差补偿的信号过零点采样自干扰消除方法.首先,利用辅助信号设计与自逆多项式根存在原理得到计算过零点的数学模型.其次,通过分析两种不同符号定时偏差对接收信号的影响,采用差值法和相关函数法计算系统符号定时偏...     

适合短突发通信的定时同步算法仿真与FPGA实现

在突发通信系统中,快速、高效地完成定时同步对接收机正确接收有重要意义,针对短突发信号持续时间短、不连续的特点,讨论了一种前馈式内插结合数字滤波平方定时频域的定时同步算法。该算法不需要调整本地采样时钟,通过对当前突发信号的采样点进行插值获得最佳采样时刻的采样值,从而实现突发信号的符号定时同步。通过Matlab仿真,给出了不同信噪比条件下算法能适用的短突发最短符号长度以及算法的性能损失。最后给出了算法的FPGA实现方案。     

特征值极限分布的改进合作频谱感知

本文采用随机矩阵理论,分析和研究了多认知用户接收信号采样协方差矩阵的最小特征值的极限分布,针对基于最大最小特征值之差的合作频谱感知算法,提出了新的门限判决方法。此算法能有效克服噪声不确定度的影响,且不需预先知道授权用户信号的先验知识和噪声方差。仿真结果表明,与以前的感知算法相比,本文算法有更低的判决门限,在低信噪比、小采样时,在达到设定虚警概率的前提下,该算法能够获得更好的感知性能。      

采样定时偏差对无源雷达性能影响研究

外辐射源雷达利用第三方信号作为照射源来探测目标,参考通道中的信号重构和监测通道中的杂波抑制是外辐射源雷达信号处理流程中的关键部分。主要讨论了OFDM波形照射源信号,并从理论上分析了采样定时偏差在参考信号重构、时域杂波抑制和匹配接收性能的影响。理论分析和仿真表明,采样定时偏差的存在会减少重构后的参考信号和监测信号的相关性,降低时域杂波抑制性能以及匹配接收的目标信噪比。基于WiFi信号帧结构的特点,提出了一种对采样定时偏差估计和补偿的方法,并在实测数据中验证了该方法的有效性。     

LTE中一种改进的基于探测参考信号的定时估计算法

研究了LTE系统中探测参考信号(SRS)的定时同步方法。由于基本的滑动相关算法和传统的后向搜索算法不能有效地消除相关过程中旁瓣峰值的影响,不适用于SRS的定时同步。因此,针对SRS的时频结构特点,提出一种改进的后向搜索算法。该方法通过将本地序列与接收序列在时域上相关得到定时度量函数,并重新定义门限值,通过结合门限和新的搜索技术来确定第1径的位置,从而得到正确的定时采样点。仿真结果表明,所提方法的估计性能优于滑动相关算法和传统的后向搜索算法,有效地消除了旁瓣峰值的影响,提高了SRS的正确定时概率。相比传统的后向搜索算法,所提方法的估计性能提高了6倍左右。     

LTE系统中小区搜索定时同步算法研究

介绍了LTE系统主同步信号的产生,提出了一种新的符号定时同步算法。利用主同步信号在时域具有镜像对称的特性,结合分段相关同步算法的优点,以及对接收端信号进行累积处理的方法,有效地提高了算法的抗频偏性能和同步性能。同时,将3组本地PSS序列相加后在与接收信号序列进行互相关,有效地减小了算法的运算量并能快速实现下行定时同步。理论分析和仿真实验结果表明,所提出的算法在AWGN信道下具有良好的性能,能够满足LTE系统对同步性能的要求。     

一种基于过采样的单通道MPSK信号盲分离算法

针对单通道接收两个MPSK混合信号的盲分离问题,该文提出了一种基于过采样的盲分离新算法。该算法基于最优贝叶斯估计准则,利用粒子滤波对发送的符号和一些参数进行序贯估计,从而实现了混合信号的分离。算法通过对接收信号的过采样,利用了更多的接收波形信息,有效地抑制了噪声的影响。仿真实验表明,新算法具有良好的误码率性能。该文同时还从极大似然的角度,对分离算法的性能进行了分析,给出了算法的误码率性能界。     

Joint Estimation of Doubly Selective Channels and Carrier Frequency Offsets in High Mobility MIMO-OFDMA Uplink

In this paper, we address the joint estimation of doubly selective channels (DSCs) and carrier frequency offsets (CFOs) in multiple input multiple output orthogonal frequency division multiple access uplink with highly mobile users. Since the channel coefficients are rapidly varying over time and the base station has to perform the estimation task from the received composite signal, the exact solution to this joint estimation problem requires multidimensional search which is computationally intensive. We propose an iterative technique for the joint estimation of DSCs and CFOs based on space alternating generalized expectation maximization algorithm which will decompose the multidimensional optimization to many one dimensional searches. The proposed method works even in the presence of residual timing offsets and it does not require the knowledge of channel statistics at the receiver. Convergence properties of the proposed algorithm in terms of rate matrix is studied and analytically proved that the proposed joint estimation algorithm converges. Simulation studies illustrate that the proposed technique offers good performance even at very high mobile speeds.

     

A hybrid joint ML technique for CFO,timing offset,and channel estimations in an OFDMA uplink

In this paper, we propose a novel hybrid joint maximum‐likelihood estimator for carrier frequency offset (CFO), timing offset, and channel response of all users in the uplink of an orthogonal frequency division multiple access (OFDMA) system. The proposed estimation method significantly reduces complexity of this multiparameter, multidimensional optimization problem, using the concept of separation of the different user signals by means of newly defined projection operators. This projection technique is combined with the alternating projection method available in the literature to arrive at a new hybrid algorithm that offers significant performance advantages in terms of computational complexity and estimator performance. The joint estimation of the CFOs, timing offsets, and channel coefficients for all active users together at the base station of the OFDMA uplink is a rarely addressed task. The proposed method also offers the flexibility of application to any subcarrier assignment scheme used in OFDMA systems. Extensive simulation studies corroborate the advantages of the new hybrid method for all three estimation requirements in the multiuser OFDMA uplink. Copyright © 2012 John Wiley & Sons, Ltd.     

A new symbol timing and carrier frequency offset estimationalgorithm for noncoherent orthogonal M-CPFSK

We present a new joint symbol timing and carrier frequency offset estimation algorithm for noncoherent orthogonal continuous-phase M-ary frequency-shift keying (M-CPFSK). Our algorithm performs nondata-aided feedforward processing of finite-length observations, and it is suited for an all-digital modem implementation based on a DSP or an ASIC processor. The algorithm exploits phase continuity of M-CPFSK in order to generate both a spectral component at the carrier frequency offset and a timing error signal. This is obtained without nonlinear transformations of the received signal involving noise×noise products. Thus, our algorithm can operate at a very low input signal-to-noise ratio. We discuss the operating range of our algorithm, and we show that no additional overhead (training sequence) in excess of the standard overhead of FDMA/TDMA packet transmission is required to resolve timing and frequency ambiguities. Moreover, we show that by differentially preceding the transmitted symbols, it is possible to eliminate automatically frequency ambiguities, at the price of a slight increase in the bit-error rate. An approximate mean-square error analysis of the estimators and simulation results prove that our algorithm provides good performance, even with a relatively short observation block length and large carrier frequency offset. Computer simulations show also that our algorithm is extremely robust to phase noise. These features make our algorithm a good candidate for satellite FDMA/TDMA applications in the 20-30 GHz band, with a large number of users and bursty transmission     

Low complexity joint estimation of synchronization impairments in sparse channel for MIMO–OFDM system

Low complexity joint estimation of synchronization impairments and channel in a single-user MIMO–OFDM system is presented in this paper. Based on a system model that takes into account the effects of synchronization impairments such as carrier frequency offset, sampling frequency offset, and symbol timing error, and channel, a Maximum Likelihood (ML) algorithm for the joint estimation is proposed. To reduce the complexity of ML grid search, the number of received signal samples used for estimation need to be reduced. The conventional channel estimation techniques using Least-Squares (LS) or Maximum a posteriori (MAP) methods fail for the reduced sample under-determined system, which results in poor performance of the joint estimator. The proposed ML algorithm uses Compressed Sensing (CS) based channel estimation method in a sparse fading scenario, where the received samples used for estimation are less than that required for an LS or MAP based estimation. The performance of the estimation method is studied through numerical simulations, and it is observed that CS based joint estimator performs better than LS and MAP based joint estimator.     

一种突发模式下GMSK信号相干解调的方法

GMSK信号是一种连续相位调制方式,由于它具有较好的功率效率和频谱利用率,因此在无线通信领域得到广泛的应用。在此给出一种适合于数字化处理的突发GMSK调制信号的相干解调方式,利用基于FFT的载波频偏及符号时钟误差联合估计算法,实现前导字检测以及频偏和符号定时误差的估计和补偿。采用基于匹配滤波的前向位同步技术实现位同步,对存在残留频偏误差情况下该相干解调系统的解调性能进行了计算机仿真分析。仿真和实验表明,该解调方法具有良好的误码性能。     

Performance evaluation of a new BPSK-OFDM timing estimation algorithm

Previously, the timing estimation in OFDM system employs cyclic prefix has been presented with the assumption of independent identified distributed OFDM symbol. The information used to find the symbol synchronization depends on the length of cyclic prefix. Actually, the data in the BPSK-OFDM modulated symbol, transferred by inverse fast Fourier transform, is with a complex symmetry character. With this character, more information from the whole OFDM symbol could be provided for the symbol timing. In this paper, the proposed algorithm uses the autocorrelation of the received signal to obtain the symbol timing. The simulation of Beek’s algorithm and the proposed scheme are presented. The performances of these algorithms are evaluated based on the missing symbol probability and the estimator mean square error. The simulation results show that the proposed algorithm is suitable to achieve a better symbol synchronization.     

基于分数傅里叶变换的OFDM的联合定时和频率同步

In this paper a joint timing and frequency synchronization method based on Fractional Fourier Transform (FrFT) is proposed for Orthogonal Frequency-Division Multiplexing (OFDM) system. The combination of two chirp signals with opposite chirp rates are used as the training signal, the received training signal with timing and frequency offset is transformed by FrFT and the two peaks representing two chirps in FrFT domain are detected, then the position coordinates of the two peaks are precisely corrected and substituted into an equation group to calculate timing and frequency offset simultaneously. This method only needs one FrFT calculation to implement synchronization, the computational complexity is equal to that of FFT and less than that of correlation or maximum likelihood calculation of existing methods, and estimation range of frequency offset is large, greater than half the signal bandwidth, while the simulation results show that even at low SNR it can accurately estimate timing and frequency offset and the estimation error is less than that of existing methods.     

Joint linear timing and carrier phase estimation of DS-CDMAmultiuser communications

Previous work on multiuser synchronization assumed that either timing recovery or carrier phase recovery schemes were available. Therefore, a generalized joint linear timing and carrier-phase estimation scheme to effectively estimate both the received timings and carrier phases at the same time is of paramount interest. Based on the idea to linearly combine the sufficient statistics of timings and carrier phases, we introduce the generalized joint linear timing and carrier phase estimation scheme with commensurate complexity of the generalized linear timing estimator. To avoid the difficulty of the design by minimizing the mean-square error (MSE), a simple and novel design criterion for this generalized joint linear estimation is proposed. With a discrete timing assumption, we not only mathematically prove that the MSE of the proposed estimator converges to zero as noise vanishes for an arbitrary number of users, but also conduct simulations to verify it. On the other hand, for the general case with a continuous timing assumption, arguments and simulations are provided to confirm the effectiveness of our proposed estimator for an arbitrary number of users. We further show that such an efficient linear-complexity joint estimation scheme is effective in the near-far environment. Consequently, the nonpolynomial (NP) hard multiuser synchronization over additive white Gaussian noise (AWGN) channel is successfully solved     

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。     

On Timing Offset Estimation of OFDM

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