Comparison of estimators for frequency offset

A model is proposed for errors that occur in estimating frequency offset between oscillators driving two clocks that are synchronized with a digital control loop. Three specific estimators are analyzed. One, the maximum-likelihood estimator, yields a minimum-mean-square estimate for Gaussian errors. A second offers convenient implementation and provides performance close to that of the maximum-likelihood estimator     

Performance analysis of blind carrier phase estimators for generalQAM constellations

Large quadrature amplitude modulation (QAM) constellations are currently used in throughput efficient high-speed communication applications such as digital TV. For such large signal constellations, carrier-phase synchronization is a crucial problem because for efficiency reasons, the carrier acquisition must often be performed blindly, without the use of training or pilot sequences. The goal of the paper is to provide thorough performance analysis of the blind carrier phase estimators that have been proposed in the literature and to assess their relative merits     

The effects of phase on high-resolution frequency estimators

Several different ways in which the initial phase differences between two closely spaced sinusoids manifests itself, e.g., in the singular values of the data matrix, the angles between signal vectors, and the Cramer-Rao bound, are described. A closed-form expression for the singular values of the data matrices used in subspace-based algorithms and an expression for the angle between the signal components are presented. Based on these expressions, conjectures are made regarding the effect of the relative phase difference between signal components on the resolving ability of subspace-based techniques. The behavior of the Cramer-Rao bound for the two-complex-sinusoid case is examined as a function of phase difference. Predictions are made as to the effect of this behavior on expected algorithm performance as a function of the phase difference. Empirical results that validate the prediction are provided     

Performance of quadratic time-frequency distributions as instantaneous frequency estimators

General performance analysis of the shift covariant class of quadratic time-frequency distributions (TFDs) as instantaneous frequency (IF) estimators, for an arbitrary frequency-modulated (FM) signal, is presented. Expressions for the estimation bias and variance are derived. This class of distributions behaves as an unbiased estimator in the case of monocomponent signals with a linear IF. However, when the IF is not a linear function of time, then the estimate is biased. Cases of white stationary and white nonstationary additive noises are considered. The well-known results for the Wigner distribution (WD) and linear FM signal, and the spectrogram of signals whose IF may be considered as a constant within the lag window, are presented as special cases. In addition, we have derived the variance expression for the spectrogram of a linear FM signal that is quite simple but highly signal dependent. This signal is considered in the cases of other commonly used distributions, such as the Born-Jordan and the Choi-Williams distributions. It has been shown that the reduced interference distributions outperform the WD but only in the case when the IF is constant or its variations are small. Analysis is extended to the IF estimation of signal components in the case of multicomponent signals. All theoretical results are statistically confirmed.     

Feedforward carrier frequency estimation with MSK-type signals

We propose a non-data-aided technique for the estimation of the carrier frequency offset in minimum-shift keying (MSK)-type modulations. The proposed algorithm has a feedforward structure and is suited for burst-mode transmissions. Computer simulations are used to assess its performance and make comparisons with other existing methods in terms of estimation accuracy and minimum operating signal-to-noise ratio (threshold). Numerical results are provided for modulation schemes of practical interest such as MSK and Gaussian MSK     

Minimum entropy approach for carrier frequency recovery

This paper introduces a new carrier frequency recovery approach. It can be applied before modulation classification and/or demodulation of the M-ary PSK signals. It relies on the entropy of the instantaneous phase probability density function, and uses the fact that it reaches minimum when the receiver is fine-tuned to the unknown carrier frequency. This estimator is applicable to algorithms requiring high accuracy without any a priori knowledge concerning modulation scheme, signal contents (bit-stream), or its timing parameters. Simulation results have proved the robustness of the algorithm: for low carrier to noise ratios (CNR), corresponding variances are proportional and close to Cramer-Rao lower bounds (CRLB). For CNR greater than 20 dB, they are constant and limited by the resolution of the algorithm.     

Simple empirical relationship between mobility and carrier concentration

Analysis of experimental data shows that a simple relationship connects the electron mobility with the donor concentration ND. At room temperature, the mobility is inversely proportional to 1+?(ND/1017) for a number of important semiconductors.     

Multiuser carrier frequency offsets estimation for OFDMA uplink with generalized carrier assignment scheme

The frequency synchronization issue of multiuser in the uplink of an orthogonal frequency-division multiple-access (OFDMA) system is investigated in this letter. We develop a subspace based blind carrier frequency offsets (CFOs) estimation algorithm for the base station (BS) equipped with uniform linear array (ULA). Due to the adoption of ULA at the BS and the narrowband signal assumption, CFOs of different users can be separated by their spatial information. Thus, unlike existing blind alternatives, which are subject to some specific carrier assignment schemes (CAS) or rely on null subcarriers, our proposed method can support generalized carrier assignment scheme (GCAS) and fully loaded systems, i.e., all subcarriers are available to users. Consequently, the dynamic channel assignment is available and the bandwidth efficiency is higher. Moreover, the closed-form directions of arrival (DOAs) of all active users are also obtained, which can be used in downlink beamforming in frequency division duplex (FDD) systems. Performance of the proposed scheme is evaluated by computer Monte Carlo simulations.     

一种基于频率校正的BPSK信号高精度载频估计算法

为了实现BPSK信号载频的高精度估计,提出一种基于频率校正的高精度BPSK信号载频估计算法。算法通过非线性变换将BPSK信号的载频估计问题转化为对点频信号的估计,再用DFT对点频信号进行粗估计,针对DFT估计频率分辨率差的问题,采用相位差校正法对DFT估计频率进行校正,从而实现BPSK信号载频的高精度估计。最后,通过性能分析和计算机仿真验证了算法的有效性,其结果表明:该算法在低信噪比情况下能获得较好的估计精度,在高信噪比情况下,估计精度大幅提高。     

稳健的OFDM系统载波频率捕获算法

本文提山了一种新的应用于OFDM系统的载波频偏捕获算法。算法利用训练帧结构的循环重复性特点，剥离信道的影响和定时偏差的影响，完成频偏的捕获。同时本文算法训练帧既可以在时域添加，也可以在频域添加，增加了算法的灵活性。仿真结果表明，算法具有稳健，精度较高，计算量较少等优点。     

OFDM burst frequency synchronization by single carrier trainingdata

We propose a burst frequency synchronization procedure which is based on the usage of single-carrier training data and orthogonal frequency division multiplexing (OFDM) payload modulation. The payload modulation format is similar to the one that is used in the DAB standard, whereas training data are chosen as simple CAZAC sequences. It is shown that the resulting modulation and transmission scheme is suitable for burst transmission and single-burst demodulation. Performance degradation due to synchronization errors is shown to be small     

Simple voltage-to-frequency convertor with increased frequency range

Conventional free-running multivibrators are frequently used as voltage-to-frequency convertors, although the fmax/fmin ratio of this circuit is rather small. A free-running multivibrator with complementary transistors has advantages concerning this ratio as well as regards some other convertor parameters.     

基于FPGA的简易频谱分析仪

观测信号频谱在科研中具有重大意义,在教学实验中也有利于学生更直观深入地了解信号特征。采用单片机C8051和FPGA,外加高速A／D转换器设计一种简易的频谱分析仪。该系统主要包括信号采集、频谱搬移、数字滤波、数字FFT和LCD显示。经测试,该系统能够分析信号带宽为0～5MHz,最低分辨率达到1Hz。而且信号频谱图能够很好地显示在LCD上。整个系统工作稳定,操作方便,且成本比其他频谱分析仪低很多。     

基于FPGA的简易频谱分析仪

观测信号频谱在科研中具有重大意义.在教学实验中也有利于学生更直观深入地了解信号特征.采用单片机C8051和FPGA.外加高速A/D转换器设计一种简易的频谱分析仪.该系统主要包括信号采集、频谱搬移、数字滤波、数字FFT和LCD显示.经测试.该系统能够分析信号带宽为0～5 MHz,最低分辨率达到1 Hz.而且信号频谱图能够很好地显示在LCD上.整个系统工作稳定,操作方便,且成本比其他频谱分析仪低很多.     

单载波频域均衡消除符号间干扰的研究

介绍了单载波频域均衡（SC-FDE）系统以及SC-FDE所常用的频域块最小均方（FBLMS）算法。为了进一步改进单载波频域均衡系统的性能，基于抽头泄漏的思想，通过增加抽头的泄漏进一步优化了FBLMS算法，并对基于优化算法的单载波频域均衡系统进行了计算机仿真模拟。其仿真结果表明：与常用算法相比较，该优化算法能有效提高均衡器的收敛速度和显著改善均衡器消除符号间干扰（ISI）的性能。     

基于FPGA的实时载波频率检测电路设计

为了实现窄带调制信号载波频率的快速准确获取并减少硬件资源消耗,基于FPGA设计一种综合哥兹柔(Goertzel)算法和能量重心估计算法的实时载波频率检测电路。首先,确定频率检测算法实现流程,在Matlab中进行了频谱和能量重心的仿真;接着提出一种低复杂度频率检测系统的硬件实现架构,以8个哥兹柔电路并行运行获取信号频谱,通过查找峰值谱线位置初步估计出信号频率;最后,采用能量重心估计法,精确估计出载波信号的频率。实验结果表明,设计的低复杂度实时频率检测硬件电路在资源消耗上仅为传统FFT方法的1 3,测频相对误差小于0.2%,2 048点频谱获取时间仅为103μs,易于硬件实现,可用于实时准确获取载波频率。     

一种新的大载波频偏估计算法

基于卫星通信快速、准确捕获载波频率的需求,提出了一种根据反余弦函数的大载波频偏估计算法。通过详细的理论推导和仿真验证,表明了该算法抗噪声能力强、频偏估计范围大、估计精度高以及易于实现的良好性能。     

Measuring the carrier frequency of single short-duration MWradio-wave pulses

A new method for measuring the carrier frequency of single microwave (MW) radiowave pulse is described, which is based on its transduction to a series of echo pulses using a transversal filter. The analysis of the radio-wave pulses exhibiting constant carrier frequency or frequency modulation is shown to be both theoretically and experimentally feasible with the help of a bulk acoustic-wave delay line. A frequency meter has been developed for single short-duration 2.5-10.5-GHz radiowave pulses, which was demonstrated to be operative under strong radio-interference conditions     

The sensitivity of downlink MC-DS-CDMA to carrier frequency offsets

We investigate the sensitivity of a downlink MC-DS-CDMA system to carrier frequency offsets. It is shown that the resulting interference power depends only on the ratio of the frequency offset to the carrier spacing. Hence, for given a frequency offset and system bandwidth, the MC-DS-CDMA performance degradation is independent of the spreading factor but increases with the number of carriers; equivalently, for given frequency offset and symbol rate, the performance degradation increases with the ratio of the number of carriers to the spreading factor     

Effect of carrier frequency offset on performance of MC-CDMAsystems

The bit error probability of the downlink of an MC-CDMA system is analysed taking into account the effect of a carrier frequency offset for Rayleigh and Rician fading channels. Derived results show that the performance of an MC-CDMA system is very sensitive even to a relatively small frequency offset