基于PN码的数据辅助前向位定时估计

突发信号一般采用前向结构的位定时估计。针对非数据辅助的前向位定时估计算法在低信噪比和小成形系数场合性能严重恶化的情形,本文提出了一种适用于PN码的数据辅助前向位定时估计算法。该算法利用突发信号帧头捕获过程中的相关值,通过插值运算估计出精确的位定时信息,仅需每符号2个样点的采样,实现简单,估计性能优良。即使在低信噪比和小成形系数场合,估计方差仍然非常逼近修正克拉美罗界（MCRB）。最后针对两种应用场合给出了算法的实现结构。      

基于数据辅助的低滚降定时同步算法

突发信号的定时同步通常采用非数据辅助的定时误差估计算法进行定时误差估计。非数据辅助的定时误差算法实现简单,然而在低滚降条件下,估计性能会产生严重恶化,对系统同步性能影响较大。文章针对突发信号在低信噪比、低滚降系数的条件下,对定时同步困难的问题进行了研究,提出了基于一种数据辅助的定时误差估计算法,利用突发捕获处理中的相关值,实现了定时误差的准确估计,并给出了定时同步实现结构。通过计算机仿真对算法进行了验证,仿真结果表明,文章算法在低滚降低信噪比条件下可实现良好的同步。     

DVB-S2 ACM技术中的信噪比估计

为了在DVB-S2系统自适应编码调制(ACM)技术中实现对信道信噪比的精确、高效估计,提出了一种基于子空间分解的数据辅助类信噪比估计算法。计算机仿真结果表明,在较宽的信噪比范围内,该算法的性能优于数据辅助类的最大似然估计算法和经典的基于子空间分解的ED算法,估计精度高,计算复杂度低,非常适合在DVB-S2系统ACM技术中应用。     

SNR Estimation for Adaptive Coding and Modulation Technique in DVB -S2

为了在DVB -S2系统自适应编码调制(ACM)技术中实现对信道信噪比的精确、高效估计,提出了一种基于子空间分解的数据辅助类信噪比估计算法.计算机仿真结果表明,在较宽的信噪比范围内,该算法的性能优于数据辅助类的最大似然估计算法和经典的基于子空间分解的ED算法,估计精度高,计算复杂度低,非常适合在DVB - S2系统ACM技术中应用.     

小BT突发GMSK信号定时恢复算法及性能分析

针对小带宽周期积(BT)的突发高斯频移键控(GMSK)信号解调中的定时问题,分析研究了2种非数据辅助定时估计方法,通过Matlab仿真比较了它们的性能和影响因素。仿真结果表明,在BT值较小的情况下,联合相位定时恢复算法能达到较好的定时性能,在Eb N0≥12 dB的条件下,定时方差小于1×10-3;而联合频偏定时估计算法在频偏大于1%的情况下性能基本不受影响,在工程实现中可根据应用要求进行算法选择。     

基于数据辅助的MPSK信号频域信噪比估计

为在载波频率精确恢复前提高多进制数字相位调制（MPSK）信号在低信噪比下的估计精度,提出了一种数据辅助的MPSK信号频域信噪比估计算法。算法在符号定时恢复和帧同步后提取同步段符号,相关运算后在频域进行信噪比估计。仿真结果表明,算法估计均值无偏,不受载波频率误差的影响,在符号长度为512、信噪比为-10 dB时,均方误差与克拉美罗界只有0.15 dB的偏差,特别适合于接收信号包含载波频率误差且要求低信噪比下具有较高信噪比估计性能的应用。     

DVB-RCS突发信号符号同步的近似常模算法研究

分析了DVB-RCS卫星网络中子站与主站进行交互的通信结构特点,得到了获取回传链路突发信号参数的方法。重点对相应突发信号的符号常模定时估计算法进行了推导和简化,结合系统结构特点设计了一种基于数据辅助的的近似常模算法。该算法复杂度低、达到要求定时精度使用符号数少。与其他前向型定时估计算法比较,理论分析和Monte Carlo仿真结果显示该算法在实际系统的突发参数下,均方根误差均更接近MCRB。     

MPSK信号的最大似然SNR估计方法

该文利用最大似然准则分别推导了对于MPSK信号的数据辅助SNR估计方法、判决指向SNR估计方法和一种新的盲信噪比估计方法。文章对这些算法的性能进行了分析和计算机仿真,并与其它一些SNR估计算法进行了比较。分析和仿真的结果显示数据辅助的SNR方法性能优越,很好地符合了信噪比估计性能下限(CRLB)。判决指向算法性能依赖于判决的准确程度,在高信噪比时性能较好;而在低信噪比条件时,特别是小于OdB以后其估计有较大偏差。新的盲SNR估计算法对于BPSK信号具有估计范围广、精度高和复杂度小的特点,但是当M增加时性能会明显下降。     

一种新的基于最大似然估计的迭代定时恢复算法

符号同步误差对LDPC译码性能会产生严重恶化,如何在低信噪比下,利用LDPC的编码增益来提高符号同步误差估计性能是本文的核心问题.基于最大似然(ML)准则,提出了似然函数导数归零的码辅助迭代符号同步算法,该算法以单一编码分组为单位进行迭代估计,不但可以应用于连续信道,同样适用于突发通信.仿真结果表明,本文提出算法的估计性能可以在信噪比很低的情况下逼近MCRB,在符号同步误差估计值快速收敛的同时,译码性能接近符号精确同步的理想情况.     

基于突发分组传输的OFDM同步算法研究

基于802.11a突发数据帧结构,分析了突发分组传输中OFDM同步算法的性能;对802.11a突发数据帧中的短训练符号结构作了改进,给出了相应的时频域估计算法;该算法有良好的定时相关特性,运算复杂度低,仿真结果表明该算法具有很好的定时和频偏估计性能.     

A new non-data-aided feedforward symbol timing estimator using twosamples per symbol

A new non-data-aided feedforward symbol timing estimator is proposed, which can apply to two samples per symbol. Numerical results show the proposed estimator is approximately unbiased. Computational complexity of the new estimator is even simpler than conventional estimators with two samples per symbol. Estimation accuracy of the new estimator is similar to that of the conventional estimator with four samples per symbol presented by Oerder and Meyr in 1988, which is the simplest among the estimators using four samples per symbol. While some conventional estimators have better estimation accuracy than the proposed, this estimator has an attractive advantage over the formers from an implementation point of view     

An alternative blind feedforward symbol timing estimator using two samples per symbol

Recently, S.J. Lee proposed a blind feedforward symbol timing estimator that exhibits low computational complexity and requires only two samples per symbol (see IEEE Commun. Lett., vol.6, p.205-7, 2002). We analyze Lee's estimator rigorously by exploiting efficiently the cyclostationary statistics present in the received oversampled signal; its asymptotic (large sample) bias and mean-square error (MSE) are derived in closed-form expression. A new blind feedforward timing estimator that requires only two samples per symbol and presents the same computational complexity as Lee's estimator is proposed. It is shown that the proposed new estimator is asymptotically unbiased and exhibits smaller MSE than Lee's estimator. Computer simulations are presented to illustrate the performance of the proposed new estimator with respect to Lee's estimator and existing conventional estimators.     

Unified analysis of a class of blind feedforward symbol timing estimators employing second-order statistics

In this letter, all the previously proposed digital blind feedforward symbol timing estimators employing second-order statistics are casted into a unified framework. The finite sample mean-square error (MSE) expression for this class of estimators is established. Simulation results are also presented to corroborate the analytical results. It is found that the feedforward conditional maximum likelihood (CML) estimator and the square law nonlinearity (SLN) estimator with a properly designed prefilter perform the best and their performances coincide with the asymptotic conditional Cramer-Rao bound (CCRB), which is the performance lower bound for the class of estimators under consideration.     

Symbol and superbaud timing recovery in multi-h continuous-phasemodulation

This paper is concerned with the estimation of two synchronization parameters that play a key role in multi-h continuous-phase modulation receivers-the ordinary symbol timing phase and the so-called superbaud timing phase. The recovery of symbol and superbaud timing is implemented by means of feedforward nondata-aided algorithms. The novelty of the proposed method is that it can be applied to any modulation format, either full or partial response, with binary or multilevel symbols and with arbitrary modulation indices     

滚降系数不匹配对MQAM解调性能影响

在非协作通信中,发送端的滚降系数对于接收方是未知的。为了能够对接收信号进行正确解调,接收方必须从观测数据中估计出这个参数。因此研究滚降系数误差对QAM系统的影响,具有重要意义。文中仿真分析了在接收端无处理和采用符号定时恢复两种情况下根升余弦滤波器滚降系数不匹配对接收性能的影响,测试结果表明此影响很小,在未知发端滚降系数的情况下,收端滚降系数设置为0.5～0.7,对接收性能的影响最小。这一结论在非协作通信中具有重要意义。     

一种新的每符号两个样点的前向定时估计算法

针对线性调制信号,提出一种新的每符号两个样点的非数据辅助的前向符号定时估计算法。算法的基本思想是：首先,将两倍符号速率的样点信号通过一个特定的抗混叠滤波器,使得输出信号经非线性变换后,在符号速率处不再混叠;然后,利用传统的平方律非线性等算法估计定时相位偏差。文中详细描述了算法的推导过程。最后的仿真数据表明,在计算复杂度相当的情况下,新算法的估计性能优于其他两种算法,并且对于信号及应用环境的适应性更强。     

Cramer-Rao Lower Bound for Non-Data-Aided SNR Estimation of Linear Modulation Schemes

Powerful parameter estimators exhibit a jitter variance which is fairly close to the Cramer-Rao lower bound (CRLB) as the theoretical limit. In contrast to symbol timing and carrier frequency/phase, not very much information is available from the open literature with respect to the signal-to-noise ratio (SNR), i. e., the CRLB has been reported only for the data- aided case and some simple M-PSK examples for non-data-aided estimation of the SNR. Motivated by this background, an efficient algorithm is presented which applies to any M-ary one/two- dimensional modulation scheme with axis/halfplane symmetry and a channel distorted by additive white Gaussian noise. Finally, the performance of different SNR estimators is compared to the derived bound.     

ML-based symbol timing and frequency offset estimation for OFDM systems with noncircular transmissions

This paper deals with the problem of joint symbol timing and carrier-frequency offset (CFO) estimation in orthogonal frequency-division multiplexing (OFDM) systems with noncircular (NC) transmissions. Maximum-likelihood (ML) estimators of symbol timing and CFO have been derived under the assumption of nondispersive channel and by modeling the OFDM signal vector as a circular complex Gaussian random vector (C-CGRV). The Gaussian assumption is reasonable when the number of subcarriers is sufficiently large. However, if the data symbols belong to an NC constellation, the received signal vector becomes an NC-CGRV, i.e., a CGRV whose relation matrix (defined as the statistical expectation of the product between the vector and its transpose) is not identically zero. Hence, in this case, previously mentioned estimators, termed MLC estimators, are not ML estimators. In this paper, by exploiting the joint probability density function for NC-CGRVs, ML estimators are derived. Moreover, since their implementation complexity is high, feasible computational algorithms are considered. Finally, refined symbol timing estimators, apt to counteract the degrading effects of intersymbol interference (ISI) in dispersive channels, are suggested. The performance of the derived estimators is assessed via computer simulation and compared with that of MLC estimators and that of modified MLC (MMLC) estimators exploiting only ISI-free samples of the cyclic prefix.     

Feedforward symbol timing recovery technique using two samples per symbol

In this paper, a new feedforward symbol timing recovery technique using timing estimation followed by interpolation is presented for digital receivers with two samples/symbol or higher sampling rate. A few timing estimation algorithms are proposed to estimate the timing offset accurately. The basic algorithm uses only the in-phase (I) or quadrature (Q) signal for timing detection, which applies to a BPSK communication system. It is shown that the basic algorithm, when applied in quadrature modulation systems where both I and Q signals are available, can be modified slightly to yield an improved estimation precision. The mean and variance of the resulting timing estimate are analyzed and simulated, supporting a satisfactory estimation performance. It is also shown that by applying a postprocessing scheme, such as the Kalman filter, the variance can be further reduced, resulting in a smoothed timing estimate. Some of the issues concerning the implementation of the proposed technique are also addressed.