样本容量对子孔径拼接检测精度影响的分析

应用数理统计理论及线性回归分析方法详细分析了在子孔径拼接检测中样本容量对测量精度的影响,通过计算确定了当子孔径拼接干涉检测中样本容量大于10 4时,即可保证检测精度,又能减小计算的复杂程度。     

Estimation of the mean radar reflectivity from a finite number ofcorrelated samples

The authors compare estimators of the mean radar reflectivity on images with different spectral properties. By working on complex data rather than detected images, they can take the speckle correlation into account and thus obtain more accurate estimates. A robust and computationally efficient approximation of the optimal estimator is proposed     

Clock jitter impact on the performance of general charge sampling amplifiers

In this paper we present the detailed performance analysis of general charge sampling amplifiers (CSAs) due to clock jitter impact. A simple analytical model for quick estimation of the signal-to-noise ratio by considering clock jitter alone as a noise source is proposed for a general CSA. The proposed analytical model is compared with a previously published more complex model and also with the well known voltage sampling. Simulation results showing the performance due to clock jitter impact of CSAs are also presented here to confirm the proposed analytical model. The potential advantages of clock jitter tolerances in charge sampling are discussed in detail.     

Performance of a finite capacity asynchronous multiplexer with modulated input

In this paper, a finite capacity multiplexer in ATM environments with modulated deterministic input sources is investigated. We consider three cases of input traffic: (1) a fixed number of deterministic cell-generating sources, (2) a fixed number of sources where each source is modulated by an ON-OFF process, and (3) a variable number of ON-OFF sources, modulated by a call arrival process in conjunction with a connection admission control scheme. The main performance measures in this study are the cell and call blocking probabilities. For case (1), we give a tight upper bound for the transient phase of the state process to reach stationary conditions. The state probabilities and the corresponding cell blocking probability are determined by means of an exact analysis. For cases (2) and (3), where we deal with more complex input traffic, the compound state process and the overall cell blocking probability are analyzed using a quasi-stationary approximation technique. This approximation is validated by means of simulations. The analysis presented is shown to be able to give reasonably accurate approximate results for ATM-multiplexer performance for cases in which conventional simulation and analytic methods already approach computing time and complexity boundaries.     

Representation of electromagnetic fields over arbitrary surfaces bya finite and nonredundant number of samples

It is shown that the electromagnetic (EM) field, radiated or scattered by bounded sources, can be accurately represented over a substantially arbitrary surface by a finite number of samples even when the observation domain is unbounded. The number of required samples is nonredundant and essentially coincident with the number of degrees of freedom of the field. This result relies on the extraction of a proper phase factor from the field expression and on the use of appropriate coordinates to parameterize the domain. It is demonstrated that the number of degrees of freedom is independent of the observation domain and depends only on the source geometry. The case of spheroidal sources and observation domains with rotational symmetry is analyzed in detail and the particular cases of spherical and planar sources are explicitly considered. For these geometries, precise and fast sampling algorithms of central type are presented, which allow an efficient recovery of EM fields from a nonredundant finite number of samples. Such algorithms are stable with respect to random errors affecting the data     

Feasibility study of parameter estimation of random sampling jitter using the bispectrum

An actual sampling process can be modeled as a random process, which consists of the regular (uniform) deterministic sampling process plus an error in the sampling times which constitutes a zero-mean noise (the jitter). In this paper we discuss the problem of estimating the jitter process. By assuming that the jitter process is an i.i.d. one, with standard deviation that is small compared to the regular sampling time, we show that the variance of the jitter process can be estimated from thenth order spectrum of the sampled data,n=2, 3, i.e., the jitter variance can be extracted from the 2nd-order spectrum or the 3rd-order spectrum (the bispectrum) of the sampled data, provided the continuous signal spectrum is known. However when the signal skewness exceeds a certain level, the potential performance of the bispectrum-based estimation is better than that of the spectrum-based estimation. Moreover, the former can also provide jitter variance estimates when the continuous signal spectrum is unknown while the latter cannot. This suggests that the bispectrum of the sampled data is potentially better for estimating any parameter of the sampling jitter process, once the signal skewness is sufficiently large.     

Effect of soliton interaction on timing jitter in communicationsystems

Timing jitter in soliton communication systems is studied, taking into account both soliton interaction and amplifier noise. Deviations from Gordon-Haus jitter for closely spaced solitons are observed. A new analytical model for the timing jitter is proposed. The model presented considers interaction in a random sequence of solitons and the effect of the amplified spontaneous emission noise added in each amplification stage. We obtain a good agreement between the new analytical model and simulation results for practical communication systems     

Step-like signal processing with distinct finite number of levels

An algorithm for filtering noisy step-like signals is proposed. This algorithm is based on the assumption of Gaussian contamination. In this procedure data within a moving window is divided into two almost equal clusters and a hypothesis tests (F-test) for differences in the means between two such clusters. Histograms analysis and/or our a priori knowledge about the number of discrete amplitudes in the ideal noise free signal provide information that is used to filter the signal further and produce a clean signal with the desired number of discrete amplitudes (levels). As an illustration the method is tested by simulation     

Simple measurement of eye diagram and BER using high-speed asynchronous sampling

This paper discusses eye diagram measurement using asynchronous sampling. Simple bit error rate (BER) estimation from eye diagrams is performed. The use of high-speed asynchronous optoelectrical (OE) sampling enables the monitoring of fixed timing Q-factors to be performed simply.     

Effect of distributed Raman amplification on timing jitter indispersion-managed lightwave systems

It is shown that the timing jitter of dispersion-managed soliton systems can be reduced by up to 40% by using a hybrid amplification scheme in which fiber losses are compensated by using erbium-doped fiber amplifiers in combination with backward pumped Raman gain. The jitter is smallest in the case of 100% Raman amplification, but considerable reduction occurs even for partial distributed amplification     

Rapid and precise read-out of terahertz sensor by high-speed asynchronous optical sampling

High-speed asynchronous optical sampling is used for the rapid and precise determination of transmission resonances of terahertz surface sensors based on asymmetric double split ring resonator arrays. The sensor response represented by a characteristic resonant frequency is determined to 0.66113 THz with an accuracy of ±325 MHz within 2 seconds of read-out time.     

Synthesis of hazard-free control circuits from asynchronous finite state machines specifications

We discuss a special class of state machine specifications called Asynchronous Finite State Machines (AFSM) which allows the specification and synthesis of hazard-free control circuits under the unbounded delay model. AFSM are useful for the specification of sequential behavior involving choices. In contrast, models such Signal Transition Graphs (STGs) are more amenable to the specification of deterministic concurrent behavior.AFSM specifications are transformed into STGs and then to State Graphs (SGs). At the SG level of representation, hazards can be identified as a type of violations of the Complete State Coding (CSC) property. Algorithms for obtaining SGs from AFSMs, and conditions for hazard-free implementation of SG derived from AFSM are discussed. A hazard-free synthesis technique from SG is described. A CAD prototype called CLASS (Cirrus Logic Asynchronous Synthesis System) has been built and used to successfully synthesize and verify the state machine benchmark from HP Laboroatories [1] and various other real applications.     

一种基于有限更新率的非带限信号采样方法

针对Shannon采样定理只能处理带限信号的缺陷,推导论证了一种基于有限更新率的非带限信号采样方法.该方法处理的是更新率有限的信号,先将信号经过一个采样核滤波,然后以不低于信号更新率的采样率对其采样,就可以借助抵消滤波器和范德蒙方程从采样点中重建出原信号.计算机仿真结果表明,该方法重建原信号的精确度较高,并且具有较好的抗噪声性能,信噪比为20dB时信号估计值的均方差只有10-5的数量级,完全能满足实际工程的需求.     

The reconstruction of a band-limited function and its Fouriertransform from a finite number of samples at arbitrary locations bysingular value decomposition

A method for the stable interpolation of a bandlimited function known at sample instants with arbitrary locations in the presence of noise is given. Singular value decomposition is used to provide a series expansion that, in contrast to the method of sampling functions, permits simple identification of vectors in the minimum-norm space poorly represented in the sample values. Three methods, Miller regularization, least squares estimation, and maximum a posteriori estimation, are given for obtaining regularized reconstructions when noise is present. The singular value decomposition (SVD) method is used to interrelate these methods. Examples illustrating the technique are given     

The bispectrum of sampled data. II. Monte-Carlo simulations ofdetection and estimation of the sampling jitter

For pt.I see IEEE Trans. Acoust. Speech, Signal Process., vol.41, no.1, p.296-312 (1993). The effect of jitter in sampling on the spectrum and bispectrum of the sampled data has been considered previously. Methods of detecting the presence of jitter in a uniform sampling process and of estimating its variance based on a test statistic calculated from the bispectrum estimates have been proposed. The present authors demonstrate, by means of Monte-Carlo simulations, how these results can be applied in an actual case. For this purpose, samples taken from a stationary band-limited process in sampling times given by a random jitter process are generated by computer. The authors then apply the jitter detection and estimation methods that have been developed in previous work and study how their performance depends on signal duration and on jitter variance. They examine the actual simulation results concerning detection probability, estimation bias, and estimation variance in comparison with the theoretical results. This comparison indicates that the bispectrum is a domain where jitter detection and estimation with high performance can be achieved, provided that a signal with sufficiently long duration and high skewness is available     

Tunable monolithic mode-locked lasers on InP with low timing jitter

Pulse trains with only 2 ps in width and low root-mean-square timing jitter of 220 fs are demonstrated from fine tunable monolithic 40-GHz laser integrated circuits on GaInAsP-InP. The repetition rate is tunable within 500 MHz by changing only the gain current and the absorber voltage. Simultaneously, the small pulsewidths are kept constant and the timing jitter remains below 300 fs. The determined time-bandwidth products between 0.37 and 0.5 are close to the transform limit and the fiber coupled optical power is /spl ges/1 mW. The fact that pulsewidth and timing jitter remain small over the whole repetition-rate tuning range constitutes an important step toward economic commercial applications, especially if frequency shifts caused by fabrication tolerances have to be compensated.     

Buffer analysis with finite number of tunable receivers in WDM passive star networks

This study develops a performance model as an expansion of the receiver collision analysis presented in [I.E. Pountourakis, Performance evaluation with receiver collisions analysis in very high-speed optical fiber local area networks using passive star topology, J. Lightwave Technol. 16 (12) (1998) 2303–2310] for WDM networks. By theoretical analysis we estimate the receiver collision phenomenon and evaluate the performance measures and the rejection probability at destination for finite number of tunable receivers. Receiver collision analysis makes the performance behavior more realistic and expands the original analysis.     

On the capacity of the Gaussian channel with a finite number ofinput levels

An analytic confirmation of an observation made by G. Ungerboeck (1965) that approximately optimal performance on a Gaussian channel with capacity C can be obtained with about 2^C+1 levels is given. In particular, the results imply that by using about 2^C-1 levels, a rate of nearly C-1 bit can be achieved, and that by using 2^C+1 levels a rate of about C-0.4 bits can be achieved     

Space-frequency sampling criteria for electromagnetic scattering of a finite object

The sampling criteria in the wavenumber space for generating the spatial impulse response of a finite target is described. A proper choice of canonical confinement for the target in space can greatly reduce the number of samples required to sufficiently characterize the target's spatial impulse response. Though a sampling lattice may be more efficient in the sense of a reduced number of measurement points per unit volume of hyperspace, it may be less effective when digital processing is involved. Specifically, the time-consuming interpolating step is required to put data presented in other types of sampling lattice into the proper type for the computer. Two-dimensional impulse responses reconstructed from cubic sampled data are compared with those using Mensa et al.'s method. The responses obtained also indicate good potential for image reconstruction via the spatial impulse response.     

The effect of timing jitter on MC-DS-CDMA

In this paper, we consider the effect of timing jitter on the performance of a multicarrier direct-sequence code-division multiple-access system for both uplink and downlink transmission, assuming orthogonal spreading sequences. Theoretical expressions are derived for the performance degradation caused by the timing jitter, in the presence of a multipath channel. Assuming an additive white Gaussian noise channel, perfect power control, and full load, it is shown that the performance degradation for the downlink transmission is independent of the number of subcarriers, of the spreading factor, and of the spectral contents of the jitter at the receiving mobile station, but only depends on the jitter variance. Under the same assumptions, we point out that, if the jitter spectra of all transmitting mobile stations are the same, the degradation on the uplink is the same as the degradation on the downlink.