Dipole group delay time

For wideband communication systems, the differential group delay time may be a critical parameter. Dipole type elements are frequently used in arrays at the low end of the microwave band; the group delay of a dipole is calculated for frequencies in the vicinity of a half wavelength. The calculation is based on the zero order impedance and a formula developed previously for computer use.     

Discrete time techniques for time delay estimation

Basic aspects of time delay estimation (TDE) based on sampled signals are investigated. The direct cross-correlation method is analyzed and compared to the average square difference function (ASDF) and the (addition only based) average magnitude difference function (AMDF) estimators, Their relative accuracy is theoretically evaluated, and previous empirical results are explained. It is shown that both the ASDF- and the AMDF-based estimators outperform the direct cross-correlation based estimator for medium-high signal-to-noise ratios. Moreover, the AMDF-based estimator, which avoids any multiplications, significantly reduces the computational complexity of the estimation procedure while offering only a moderate performance loss with respect to the ASDF based estimator     

Method of measuring time delay

The propagation time of a linear system, defined as the group delay at zero frequency, is given by the time centroid of its response to unit impulse. Based on this, a method of measurement is described which is independent of the shape of either the input or output time functions.     

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.     

Guided-wave optical time delay network

A hybrid optical time delay unit using lithium niobate switches and precisely produced fiber loops is described. Three prototypes of the device were fabricated and characterized. The measured optical extinction ratio between time slots is typically /spl Lt/25 dB. On average, delay values are within 0.7% of their design values. The device is a 6-b (64 time slot) delay unit with 44 picosecond per increment.     

Bounds of age replacement time

An age replacement policy with a planned replacement time t₀ is considered. Five approximations which give upper or lower bounds of an optimum time t₀¹ and are computed more easily than t₀¹ are derived. A numerical example shows, when the failure time has a Weibull distribution, that some approximations are fairly good.     

Performance characterization of components with group delay fluctuations

A variety of components in optical communication systems exhibit group delay fluctuations, which degrade the quality of transmitted signals. In this letter, we present a method to derive two independent figures-of-merit, based on the measured group delay, which accurately determine the system performance degradation caused by any type of group delay fluctuations in a component. These two parameters can be used to estimate the performance of concatenated components and are, therefore, suited for component specifications.     

Frequency selective adaptive time delay estimation

A frequency-selective algorithm for time delay estimation between two channel data is proposed, and its performance is studied. The adaptive stochastic gradient scheme provides a direct estimate of the time delay. It has a low numerical complexity, and it is an alternative to data prefiltering and time delay estimation when the source and noise components have different spectral characteristics     

Dispersion compensation by differential time delay

A technique for optical pre- or postdistortion in order to compensate for fiber dispersion is discussed theoretically, The dispersion compensation device is based on differential time delay for the upper and the lower sideband of the modulated signal. The proposed scheme is primarily intended for high bit rate (>10 Gbit/s) time division multiplexed transmission, and in an ideal case the transmitting distance could be enhanced by a factor of 4 in a dispersive limited system. With more realistic demands on the dispersion compensation device, the gained distance is in the order of 2.5     

Load frequency control incorporating time delay

This letter discusses a load frequency control scheme incorporating the computation delay time in the control law. When there is a computation delay in determining feedback gains, the incorporation of the time delay is necessary for the improvement of dynamic responses. The influences of the delay time on the responses are investigated using a two-area load frequency model.     

Control of linear systems with time delay

Luenberger's procedure for the design of controllers of linear systems with inaccessible state vectors is extended to deal with time-delay systems.     

Pure time delay of an analogue signal

A method of delaying an analogue signal is described. The method has applications in the simulation of transport lags on an analogue computer.     

Stability of control systems with time delay

To find the approximate stability limit on the forward gain in control systems with small time delay, this note suggests approximating the exponential in the characteristic equation by the first few terms of its series and using the Routh?Hurwitz criterion. This approximation avoids all the time-consuming graphical work and gives a somewhat pessimistic maximum bound for the gain constant.     

On time delay estimation of epileptic EEG

The present study deals with comparative evaluation of various methods for time delay estimations applied to multichannel seizure EEG. The different methods included block algorithms, both in time and frequency domains (such as general crosscorrelation, FFT, AR), and a new method for time delay estimation based on adaptive least-squares filtering. The various time delay estimators were tested on simulated signals and on real multichannel EEG recorded from rats having generalized seizures with focal onset. The adaptive least-squares filtering method (the lattice-ladder type) has been found to be the most efficient for time delay estimation     

DSL系统时域均衡训练中一种新的时延优化算法

在数字用户线(DSL)系统中,每个符号在进行传输时要加入循环前缀(CP)以消除符号间干扰。理论上,CP的长度等于信道冲激响应的记忆长度,较长的CP大大降低了DSL系统的数据传输效率。为了避免使用较长CP,通常在接收端采用时域均衡缩短信道冲激响应长度。但是,信道冲激响应最优缩短算法的复杂度很高,为此,提出了一种实用的时延优化算法,该算法将信道的冲激响应与矩形序列进行卷积,用得到的序列进行时延估计,使得算法的复杂度大幅下降,满足了系统的实时性要求,并且缩短信噪比的损失很小。     

Group delay measurements of optical components near 800 nm

Phase-locked interferometry was used to measure the group delay of several optical components in the spectral region 700-850 nm. The dispersive and absorptive properties of several different types of linear filters were measured. Measurements of the absorption and dispersion of several linear, causal optical filters show that a generalized Kramers-Kronig relation does not exist for many commonly used filters. This result emphasizes the importance of making direct measurements of the dispersive properties of filters, since the dispersion of a linear filter cannot always be determined from a measurement of its absorption. Data are presented for a birefringent filter, dielectric mirror, Gires-Tournois interferometer, and titanium-doped sapphire     

Preventive replacement in systems with dependent components

A multicomponent series system includes a component which deteriorates over time, changing its operating characteristics and, consequently, increasing the failure rates of neighboring components. Preventive replacement of the deteriorating component can be beneficial. Replacement policies that include inspecting the deteriorating component at system failure instances and replacing it if the deterioration exceeds a critical level, or continuously monitoring the deteriorating component are considered. The system is modeled as a Markov chain solved by an efficient algorithm that exploits the system structure. For a two-component system, a closed-form equation gives the critical level for the minimum-average-cost failure-replacement policy. For the general case, replacement policies are evaluated by mean cost rate and by the ratio of the reduction in the number of failures to the number of preventive replacements     

Passive time delay estimation in non-Gaussian noise

This article deals with the structure of the maximum-likelihood (ML) estimator for time delay with arbitrary signal and noise statistics. At high signal-to-noise ratios (SNRs), the ML estimation performs a nonlinear operation on the delayed difference of the two received waveshapes. The required nonlinearity depends only on the noise statistics. At low SNR, a closed-form simple expression for the ML, which depends only on the noise statistics and on the second-order statistics of the signal, is provided. With statistically independent noise processes, the estimator correlates two vectors generated by separate nonlinear operations on the two received waveshapes