The estimation of time delay and Doppler stretch of widebandsignals

The problem of estimating the time delay and the Doppler stretch for wideband signals from a moving target is considered. The Cramer-Rao bound and the maximum likelihood (ML) method of estimation are derived. Due to the uncertainty of the reflection coefficient, the ML method may not be practicable. An alternative method involving the location of the peak of the wideband ambiguity function of the signal is suggested. The performance of the method is analysed, and, under high signal-to-noise ratios (SNRs), the method is asymptotically unbiased, and the variances of the estimates are closed to the Cramer-Rao bound for a large variety of signals. Optimum signals for the joint estimation of the time delay and the Doppler stretch under practical constraints are designed and, through computer simulations, their performance are shown to be superior to the commonly used signals     

Fast distributed multi-hop relative time synchronization protocol and estimators for wireless sensor networks

The challenging problem of time synchronization in wireless sensor networks is considered in this paper, where a new distributed protocol is proposed for both local and multi-hop synchronization. The receiver-to-receiver paradigm is used, which has the advantage of reducing the time-critical-path and thus improving the accuracy compared to common sender-to-receiver protocols. The protocol is fully distributed and does not rely on any fixed reference. The role of the reference is divided amongst all nodes, while timestamp exchange is integrated with synchronization signals (beacons). This enables fast acquisition of timestamps that are used as samples to estimate relative synchronization parameters. An appropriate model is used to derive maximum likelihood estimators (MLE) and the Cramer-Rao lower bounds (CRLB) for both the offset-only, and the joint offset/skew estimation. The model permits to directly estimating relative parameters without using or referring to a reference’ clock. The proposed protocol is extended to multi-hop environment, where local synchronization is performed proactively and the resulted estimates are transferred to the intermediate/end-point nodes on-demand, i.e. as soon as a multi-hop communication that needs synchronization is initiated. On-demand synchronization is targeted for multi-hop synchronization instead of the always-on global synchronization model, which avoids periodic and continuous propagation of synchronization signals beyond a single-hop. Extension of local MLE estimators is proposed to derive relative multi-hop estimators. The protocol is compared by simulation to some state-of-the-art protocols, and results show much faster convergence of the proposed protocol. The difference has been on the order of more than twice compared to CS-MNS, more than ten times compared to RBS, and more than twenty times compared to TPSN. Results also show scalability of the proposed protocol concerning the multi-hop synchronization. The error does not exceed few microseconds for as much as 10 hops in R4Syn, while in CS-MNS, and TPSN, it reaches few tens of microseconds. Implementation and tests of the protocol on real sensor motes confirm microsecond level precision even in multi-hop scenarios, and high stability (long lifetime) of the skew/offset model.     

Comparison of two methods for time delay estimation of sinusoids

This note concerns the time delay estimation of a sinusoid in the absence of noise. It is shown that the smoothed coherence transform (SCOT) method performs much better than the standard cross-correlation (SCC) method, in that the former greatly reduces the ambiguity in determining the peak of the related cross-correlation function.     

基才时间信息的快速检索方法探究

本文研究了利用时间信息实现快速检索视频文件的方法,视频文件的压缩编码标准采用的是H．264,该方法主要包括视频分析和视频检索两个部分的研究。在视频分析部分,对码流中的IDR帧（关键帧）进行抓取和获得其时间、位置、大小等信息。并将得到的时间等信息存入至数据库。该部分的重点是时间信息的获取,由于负责传输码流的RTP数据分组的时间戳记录了码流的时间信息,所以着重描述了获取并且记录RTP时间戳的过程。视频检索部分,利用时间等查询条件从数据库中进行视频检索。对所述方法进行研究。结果表明使用该方法能够快速查看某时刻视频内容．避免了检索视频时的重复处理。     

A new time delay estimator based on ETDE

In this paper, we address the problem of online subsample time delay estimation of narrowband signals of known center frequency. We propose a new so-called mixed modulated Lagrange explicit time delay estimation (MMLETDE) algorithm and study its performance through computer simulations. The MMLETDE is a modulated Lagrange ETDE, but the delay estimate adaptation process is based on the truncated sinc fractional delay filter algorithm. We provide theoretical derivations for our proposed estimator, a proof of its convergence performance, learning characteristics of its error performance surface, and an expression for its delay variance. Using simulations, we show that MMLETDE requires only a small filter order and has no noticeable estimation bias over a wide frequency range.     

一种基于时滞辨识的模糊Smith控制

利用信号处理中的互相关技术可以对声发射波之间的时间延迟进行测量的功能,实现对变化的时滞参数的跟踪,并将其同模糊控制以及Smith预估控制相结合,形成了一种基于时滞辨识的模糊Smith控制算法,对此算法进行仿真研究。仿真结果证明了此算法的有效性。     

On the Cramer- Rao bound for time delay and Doppler estimation (Corresp.)

Using a theorem due to Whittle, simple derivations of the Cramer-Rao lower bound are presented for some delay estimation problems related to a single source, multiple sources, and multipath. The problem of Doppler estimation is briefly discussed.     

Simultaneous measuring of Doppler frequency shift and group delay time by means of amplitude-modulated LFM-Signal

New method of the simultaneous measurement of the frequency dependencies of Doppler shift and group delay time of separate ionosphere modes by means of amplitude modulated chirp signal is presented in this paper. The algorithms for data processing are presented.     

基于分数时延滤波器的宽带数字信号时延的实现

阐述了基于分数时延滤波器的时延方法设计原理,对其中4种代表性的设计方法的时延性能进行了评估,给出宽带数字线性调频信号的时延仿真结果,该方法可用于宽带雷达数字信号处理。     

CMOS delay time model based on weighted peak current

The authors propose a new CMOS delay time model with the configuration ratio, the input slope and the load condition taken into account. This model is based on the optimally weighted switching peak current. The delay equations are computationally effective and the error is typically within 10% of SPICE results     

A high precision Doppler radar based on optical fiber delay loops

The proposed theory shows that, by using optical fiber delay lines or loops, it is no longer necessary to compress pulses with matched filters for optimum detection and it is possible to suppress interference from undesirable zones. The suppression leads to lessening of Doppler and range ambiguity. The theory further shows that it is feasible to measure Doppler beating with high precision based on a single pulse. Thus, with a single pulse, there is no Doppler and range ambiguity; interference from undesirable range zones due to Doppler range fold-over will no longer present; and the troublesome ground clutter problem would be greatly suppressed. The high precision Doppler beating provides a mechanism to reveal intrinsic characteristics of a target without time average blurring or masking. New information can be acquired on targets of interest for purpose of passive identification.     

A high-resolution time interpolator based on a delay locked loopand an RC delay line

An architecture for a time interpolation circuit with an rms error of ~25 ps has been developed in a 0.7-μm CMOS technology. It is based on a delay locked loop (DLL) driven by a 160-MHz reference clock and a passive RC delay line controlled by an autocalibration circuit. Start-up calibration of the RC delay line is performed using code density tests (CDT). The very small temperature/voltage dependence of R and C parameters and the self calibrating DLL results in a low-power, high-resolution time interpolation circuit in a standard digital CMOS technology     

Analysis of MUSIC-based delay estimators for direct-sequencecode-division multiple-access systems

Most receiver designs for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems exploit timing information to simultaneously detect the desired signal and suppress the interference. In this paper, a previously proposed MUSIC delay estimation algorithm is considered which requires no initial information and no exhaustive search of the delays. Based on a Taylor series expansion, approximations of the first and second moments of the delay estimation error are derived for this MUSIC algorithm. The analysis is alternative and further to that previously performed     

群时延的快速测量方法

群时延是射频器件测试中的一项重要待测指标。提出了一种新的群时延测量方法,改善了分辨率和准确性之间的矛盾,同时便于快速实现。本方法所得到的测量结果可用于对射频器件的频率响应特性进行校准,以消除信号通过射频器件时产生的幅度和相位失真,进而减小射频器件对通信和信号处理系统性能所产生的影响。仿真结果验证了提出的测量方法的有效性。     

Coherence and time delay estimation

This paper presents a tutorial review of work in coherence and time delay estimation. A review of coherence research and development is presented. A derivation of the ML estimator for time delay is presented together with an interpretation of that estimator as a special member of a class of generalized cross correlators. The performance of the estimator is given for both high and low signal-to-noise ratio cases. The proposed correlator is implemented and stimulated with synthetic data. The results are compared with performance predictions and found to be in good agreement.     

PWM methods to handle time delay in digital control of a UPS inverter

With the popularity of micro-processors, digital controllers are widely used in uninterruptible power supply (UPS) inverters. These digital control systems of UPS inverters require a time interval for sampling and computation, which sometimes affects the performance of inverters. In this paper, the problem of time delay in digital control of a UPS inverter is discussed. Then two novel pulsewidth modulation (PWM) methods, the two-polarity PWM method and the asymmetric PWM method, are proposed to handle the time-delay problem. Both of these PWM methods can achieve a wide range of duty ratio between 0.05-0.95, which is independent of inverter model. Furthermore, they are easy to implement using a digital micro-controller. Experimental results are presented in the paper to verify feasibility of the proposed PWM methods.     

In-variance of subspace based estimators

Subspace-based estimates, i.e., estimates obtained by exploiting the orthogonality between a sample subspace and a parameter-dependent subspace, have proved useful in many applications, including array processing and system identification. The purpose of this paper is to complement the already available theoretical results generally obtained in specific contexts. We discuss the generalization of the optimal weighted subspace fitting approach introduced by Viberg (1989) in the DOA estimation context; we exhibit some invariance properties of optimally weighted estimate, and we show the equivalence between subspace fitting and subspace matching     

一种基于动态时间弯曲距离的快速子序列匹配算法

动态时间弯曲距离在用于计算时间序列间的距离时是极其耗费时间的,尤其是处理较大规模的时间序列数据库中的子序列匹配问题时,时间消耗更是难以忍受。该文提出一种新的低边界距离,能够快速滤掉不满足结果条件的时间序列,以提高查询速度,并证明该低边界距离不会丢弃真实的结果。一种基于水平边界区域的索引技术被用于进一步提高查询效率。分别以真实数据集和人造数据集作为实验数据来测试该文所提出的算法的性能,结果表明该算法在数据库规模上和序列长度上都有良好的健壮性。     

基于自适应稀疏分解的探地雷达水平分层介质时延估计

传统的时延估计方法受瑞利限限制,一些基于子空间的方法可以达到高分辨或超分辨,然而,子空间方法需要处理的数据量大,计算复杂度高。提出一种新的基于自适应稀疏分解的探地雷达水平分层介质时延估计方法,自适应稀疏分解将传统的参数估计问题转化为字典学习问题。自适应稀疏分解从过完备字典中选取少量原子,其对应的时间参数即为所需估计的时延。与传统的基于子空间方法相比,该算法在低信噪比时具有更高的估计正确率,并且直接在时域进行,减少了计算复杂度。仿真及实测结果表明,该算法与MUSIC算法对比在时延估计方面具有更大的优势。