Performance analysis of frequency synchronization in MIMO-OFDM systems with ST/MRC scheme

In this paper, the performance of frequency synchronization in a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system is analyzed for the purpose of carrier frequency offset (CFO) estimation and compensation. Speci?cally, a joint transmit antenna selection (ST) and receive maximum ratio combining (MRC) （ST/MRC） method is adopted, that is, only one transmit antenna with the highest channel power is selected while MRC is used at the receiver to maximize the sum of frequency synchronization metric. The mean square error (MSE) closed-form expressions of CFO estimation are derived for several antenna con?gurations. Simulations in both ?at and multipath fading channels validate the theoretical analysis.     

Analysis of chaotic synchronization of cascade coupled systems for phase-locked loop using wavelet analysis

A method for detection and study of chaotic synchronization of cascade coupled single ring continuous phase-locked-loop systems is based on the determination of the phase of chaotic signal using continuous wavelet transform and the subsequent monitoring of phases on time (frequency) scales. Morlet, Gauss, Shannon, and B-spline complex wavelets are studied. The results of mathematical simulation are presented. Signal-to-noise ratios that allow chaotic phase synchronization are estimated.     

半导体激光器外腔长连续调频特性的研究

研究了半导体激光器的外腔长连续调频特性，在外腔长λ／２变化范围内，激光频率与外腔长度呈线性变化关系，线性连续调频宽度小于外腔纵模频率间隔。外腔长调频率与激光管本征频率成正比，与外腔长度成反比。实验测量结果与理论分析相一致。     

Theoretical analysis of interbase-station synchronization systems

Discusses the performance, in terms of residual timing error, of the over-the-air autonomous decentralized interbase-station synchronization system. An exact solution for the uniform weights case and an approximate solution for the power weights case are obtained in closed form. The residual timing error, system stability, and system convergence performance are studied based on the closed-form solutions. It is shown that timing can converge very fast for the uniform weights case; the power weights case has lower residual timing error measured in terms of standard deviation than that of the uniform weights case when all transmitted power levels are the same     

Scattering analysis by the multiresolution time-domain method usingcompactly supported wavelet systems

We present a formulation of the multiresolution time-domain (MRTD) algorithm using scaling and one-level wavelet basis functions, for orthonormal Daubechies and biorthogonal Cohen-Daubechies-Feauveau (CDF) wavelet families. We address the issue of the analytic calculation of the MRTD coefficients. This allows us to point out the similarities and the differences between the MRTD schemes based on the aforementioned wavelet systems and to compare their performances in terms of dispersion error and computational efficiency. The remainder of the paper is dedicated to the implementation of the CDF-MRTD method for scattering problems. We discuss the approximations made in implementing material inhomogeneities and validate the method by numerical examples     

Noise characteristics of autodynes with frequency stabilization by means of an external high-Q cavity

The expressions describing the autodyne (AD) response are obtained with allowance for the internal noise of a frequency-stabilized microwave oscillator subjected to the action of its self-radiation reflected from an object. The results of analyzing the AD and noise characteristics of the stabilized oscillator built around the band-reflecting filter with resistive coupling are presented. The conditions leading to the appearance of the periodic non-stationarity of noise characteristics are established. It is demonstrated that frequency stabilization is ensured by a gain in dynamic range. The experimental data on unstabilized and stabilized hybrid-integral AD oscillators based on the two-mesa Gunn diode of 8-mm range are presented.     

A robust timing synchronization scheme in multiple antenna systems with Doppler frequency shifts

We propose a timing synchronization scheme for a dual antenna system in Rayleigh-fading environments. Instead of assuming the channel gain to be constant during the training duration, we consider the time-variant nature of the multiplicative distortions and formulate them with linear combinations of eigenfunctions. Then, we derive a formula to find the maximum-likelihood estimation of the channel timing and simulate the performance with both ideal and nonideal channel state information. The results show that this approach outperforms the conventional ones especially when the Doppler spread is severe.     

MIMO-OFDM系统载波同步的空间分集算法

在分析MIMO-OFDM系统载波频偏信号模型基础上,提出了基于单个OFDM前导子符号相关的MIMO-OFDM载波同步的空间分集算法,从链路级研究了易于实现的MIMO-OFDM系统载波同步算法,在无线多径Rayleigh信道COST207模型下,车速分别为10km/h 和120km/h时,给出了MIMO-OFDM系统载波同步分集算法的仿真结果.     

Low frequency modes and their link with summer monsoon activitydescribed by wavelet analysis throughout India

The purpose of this paper is to propose a method and its application to attempt investigating temporal-frequency characteristics of low frequency modes throughout India. This diagnostic method combines wavelet analysis (WT) interlaced by a factor D and empirical orthogonal function (EOF). It is shown that the stability related to WT is ensured by the adequate choice of factor D and the sampling frequency. Thus, the reconstruction of a time series from its wavelet coefficients becomes possible (i.e., “wavelet synthesis,” which can constitute a narrow bandpass). This method has been applied to daily pressure during summer monsoon activity for the year 1977. The results of analysis indicate a link between summer monsoon activity and both a 10-20-day and 25-50-day band. This link is expressed by the simultaneous occurrence of both modes throughout India with a different amplitude from one region to another expressed by the following factors. During summer monsoon onset, it is the 10-20-day mode that is predominant, while during the break, both modes have nearly the same amplitude. These modes have a maximum activity situated nearly at 23°N, 83°E     

Timing and frequency synchronization for the uplink of an OFDMA system

This paper deals with timing and frequency recovery for the uplink of an orthogonal frequency-division multiple access (OFDMA) system. The frequency estimator is derived from ad hoc reasoning, whereas the timing estimator is based on the maximum-likelihood criterion. Both schemes rely on the repetition of a fixed pilot symbol. Their main feature is that they provide feedforward estimates and allow synchronization in only two OFDM blocks. In contrast to other existing methods, they do not require that the subcarriers of a given user occupy adjacent positions in the signal bandwidth. This makes it possible to interleave subcarriers of different users so as to optimally exploit the frequency diversity of the channel. Theoretical analysis and computer simulations are used to assess the performance of the proposed synchronizers. It is found that the degradations due to residual frequency and timing errors are negligible at signal-to-noise ratios of practical interest.     

Modeling frequency-time synchronization systems that use signals of common sources

Article presents results of design and implementation of system model that uses signal of a common source to synchronize geographically distributed time and frequency standards (so-called general coverage algorithm). The use of various processing (mutual correlation and matched filtering) and estimation of time signal position methods as well as taking into consideration of multipath in channel are essential peculiarities of the model. The model may be used for estimating potential precision of a wide class of synchronization systems and the possibility of using various signals and processing techniques in such systems.     

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.     

短波跳频通信系统同步方法的研究分析

文章介绍了短波通信抗干扰的几种方法,分析了跳频同步技术的特点、技术原理及影响因素、同步技术实现过程;设计了一种并行搜索TOD同步字头法,这种方法同步速度快,适用于快速跳频系统。     

一种结合使能控制的采样钟同步实现方法

许多通信场景中调制信号不能完全满足过零特性,常用检测方法都不能直接应用,为了解决这个问题,采用了一种结合使能控制的采样钟同步方法。通过使能信号控制环路中的Gardner定时误差检测模块,达到环路收敛的目的。该方法既利用了通常的Gardner算法结构,具有低复杂度特性,又保证了环路可以可靠工作。在实验过程中给出了具体的工程实现流程,并通过仿真验证了该方法的有效性。     

一种带外同步输入的视频发生器模块的设计

阐述了一种主要用于检测视频同步信号的基于ISA总线的视频发生器模块的设计过程。本硬件电路板还可以通过PC机对同步的选择与图像的发送进行控制,并具有故障检测的功能,其中的视频同步信号生成电路以及视频图像数据地址生成电路采用了PLD器件,这样就可以很方便 地去改变视频制式,也便于调试。     

TD-LTE系统时频同步算法仿真及DSP实现

基于简化后的ML(最大似然)估计算法,提出一种适用于TD-LTE(时分长期演进)系统的时频同步算法,并在TMS320C64x DSP(数字信号处理器)中实现了该算法.仿真结果表明,该同步算法在不同的信道环境下都能较好地工作,具有稳定、计算复杂度低等优点.     

Rapid slot synchronization in the presence of large frequency offset and Doppler spread in WCDMA systems

Slot synchronization is the most challenging step for rapid cell search in intercell asynchronous code division multiple access systems such as wide-band code division multiple access (WCDMA). For rapid cell search, it is desirable to design the receiver robust to initial frequency offset and Doppler spread. In this letter, we consider combining schemes for rapid slot synchronization of WCDMA signals in such channel impairments. We propose an inner-slot differential combining scheme that exploits partial correlation of slot synchronization code, making the receiver tolerable to a large amount of initial frequency offset and Doppler spread. Unlike conventional differential combining schemes, the proposed scheme is also applicable to the use of transmit antenna diversity. The detection performance of the proposed combining scheme is analyzed with the use of transmit antenna diversity. Finally, the analytic results are verified by computer simulation.     

Joint optimization of time and frequency synchronization based on polynomial sequences for OFDM systems

In orthogonal frequency division multiplexing (OFDM) systems, time and frequency synchronization are two critical elements for guaranteeing the orthogonality of OFDM subcarriers. Conventionally, with the employment of pseudo-noise (PN) sequences in preamble design, the preamble information is not fully utilized in both symbol timing offset acquisition and carrier frequency offset estimation. In this article, a new synchronization algorithm is proposed for jointly optimizing the time and frequency synchronization. This algorithm uses polynomial sequences as synchronization preamble instead of PN sequences. Theoretical analysis and simulation results indicate that the proposed algorithm is much more accurate and reliable than other existing methods.     

Frame synchronization in the presence of frequency offset

A new frame synchronization technique, which is robust to carrier frequency and phase errors, is proposed for M-ary PSK systems. This technique is derived through modification of the procedure used for obtaining the maximum-likelihood (ML) rule in the paper by Gansman et al. (1997). The proposed rule is based on an operation called a double correlation which evaluates a correlation after properly multiplying the received signal with a sync pattern. It was shown through computer simulation that the proposed rule generally outperformed the existing rules when a frequency offset existed.     

Coherent transmission using an external waveguide Bragg reflector laser with direct frequency modulation

Single-frequency l.5?m semiconductor lasers, formed by butt-coupling of a regular Fabry?Perot laser to an external waveguide Bragg reflector, are shown to have very uniform frequency modulation characteristics under direct current modulation. The laser's frequency modulation characteristics, together with its narrow linewidth (? 1 MHz), make coherent transmission possible without external modulators. The laser performance was evaluated in a 417Mbit/s, 102 km, frequency-shift-keying coherent transmission experiment.