Adaptive control system utilising sampling techniques and Aitken's approximation

A model-reference adaptive control system is described, where adaption is performed by means of sampled signals. Aitken's method of iterative interpolation and extrapolation is employed to predict the performance of the continuous system at the sampling instants. The predicted-performance information is used to compute the strength of adaption impulses by sampled-data analysis techniques.     

Adaptive beam-space nulling of multipath signals

A beam-space adaptive nulling technique that has potential for applications in communication circuits degraded by multipath signals is described. The technique is based on a well-known vector relationship in beam space. A linear transformation is used to prevent the degradation of the desired signal reception. Results are presented from tests of the technique that were conducted using real multipath data. The data used in these tests were recorded using a 32-element sampled aperture antenna (SAMPAR). These measurements were carried out on an over-water path. The direct signal, i.e. the signal that propagates via the shortest path from the transmitter to the receiver antenna, is selected as the desired signal; its reception is enhanced by suppressing the unwanted signals, i.e. the multipath signals that propagate via a reflection from the surface of the water. Examples are given in which the wanted and unwanted signals are separated by less than a beamwidth     

A Level-Crossing Analog-to-Digital Converter With Triangular Dither

In this paper, a level-crossing analog-to-digital converter is described. It can convert audio bandwidth signals with high resolution using few threshold levels and digital interpolation. Samples are generated at nonuniform time intervals and then interpolated to produce uniformly spaced output samples. A periodic triangular dither signal added to the input ensures that low-amplitude or slowly varying signals are sampled and converted accurately. The dither is estimated and removed digitally before interpolation. Simulations show that greater than 10-bit resolution can be achieved with only seven comparators when using a sixth-order polynomial interpolator.     

基于信号频域特征实现位定时恢复

数字通信系统对接收信号进行采样时,如果存在位定时误差,则会严重影响通信系统的工作性能。而采样信号的变换域相位谱中包含位定时误差信息,只要有效地恢复该误差信息,即可以很好地实现通信系统的位定时同步。在此基础上,对频域检测位定时估值算法的原理和实现过程进行了较详细的描述和分析,最后,针对几种典型信号对算法的性能进行了仿真研究,仿真结果表明,该算法对几种典型信号都有效,具有较广泛的适应性。     

Demonstration of a Self-Synchronized Polyphase Sampling and Demultiplexing Scheme for Radio-Frequency Analog Signals

A novel self-synchronizing optoelectronics polyphase scheme for sampling and demultiplexing radio-frequency (RF) signals is demonstrated. One unique feature of this approach is that the optically sampled RF signal always remains in the electrical domain and thus eliminates the need for electrical-to-optical and back to electrical conversions. Furthermore, the simplicity and ease of construction of the scheme readily allows it to be scaled to obtain high sampling rates. As a proof of concept, a 100-MHz RF electrical signal sampled at the rate of 1.28 GS/s and then demultiplexed into four 320-MHz signals was experimentally demonstrated.     

Vector sampling expansion

The vector sampling expansion (VSE) is an extension of Papoulis' (1977) generalized sampling expansion (GSE) to the vector case. In VSE, N bandlimited signals, all with the same bandwidth B, are passed through a multi-input-multi-output (MIMO) linear time invariant system that generates M (M⩾N) output signals. The goal is to reconstruct the input signals from the samples of the output signals at a total sampling rate of N times the Nyquist rate, where the Nyquist rate is B/π samples per second. We find necessary and sufficient conditions for this reconstruction. A surprising necessary condition for the case where all output signals are uniformly sampled at the same rate (N/M times the Nyquist rate) is that the expansion factor M/N must be an integer. This condition is no longer necessary when each output signal is sampled at a different rate or sampled nonuniformly. This work also includes a noise sensitivity analysis of VSE systems. We define the noise amplification factor, which allows a quantitative comparison between VSE systems, and determine the optimal VSE systems     

基于低速采样的多正弦波信号频率估计

高频段信号由于受到A/D转换器和后续信号处理器件运算速度和成本的限制,其处理往往难以实现,为解决此问题,提出了一种新的基于低速采样的高频段多正弦波信号频率估计方法。首先将含有多个频率互异的多正弦波信号经过功分器分成两路信号,然后分别用不同的采样率对这两路信号进行低速采样,用傅立叶变换及基于改进的Rife算法与Quinn算法来估计两路信号低速采样后的频率,接下来利用中国余数定理对多个信号的频谱快速配对解模糊准确的估计出各个信号的频率。该方法在工程上易于实现,可同时实现低的采样速率与高精度估计,而且在较低信噪比的情况下仍可获得较高的估计精度。给出了该方法的具体步骤,通过计算机仿真试验验证了该方法的有效性。      

A Theory for Sampling Signals From a Union of Subspaces

One of the fundamental assumptions in traditional sampling theorems is that the signals to be sampled come from a single vector space (e.g., bandlimited functions). However, in many cases of practical interest the sampled signals actually live in a union of subspaces. Examples include piecewise polynomials, sparse representations, nonuniform splines, signals with unknown spectral support, overlapping echoes with unknown delay and amplitude, and so on. For these signals, traditional sampling schemes based on the single subspace assumption can be either inapplicable or highly inefficient. In this paper, we study a general sampling framework where sampled signals come from a known union of subspaces and the sampling operator is linear. Geometrically, the sampling operator can be viewed as projecting sampled signals into a lower dimensional space, while still preserving all the information. We derive necessary and sufficient conditions for invertible and stable sampling operators in this framework and show that these conditions are applicable in many cases. Furthermore, we find the minimum sampling requirements for several classes of signals, which indicates the power of the framework. The results in this paper can serve as a guideline for designing new algorithms for various applications in signal processing and inverse problems.     

Power spectrum of sampled signals distorted by jitter

A new approach has been used to obtain general expressions for the power spectrum of sampled signals distorted by jitter and noise resulting from jitter. A time-variant delay network is used as a model of jitter sources.     

基于伪非均匀采样的高精度时间间隔测量方法

为提高脉冲激光测距的精度,采用一种新的高精度时间间隔测量方法。在脉冲计数法的基础上,利用温补晶振生成与计时量化时钟同步同频率的参考正弦波信号,将提高时间间隔测量精度问题转化为初始相位估计;通过伪非均匀采样方法对参考正弦波信号采样,并针对研究中所采用的伪非均匀采样方法推导出相应的理论公式,然后利用最小二乘法对采样数据进行曲线拟合,将伪非均匀采样信号还原成被采样的参考信号,实现相位估计,从而实现高精度时间间隔测量。将本文方法应用于脉冲激光测距仪中,实验表明,测距仪的测距精度优于±5mm。     

Computer Modeling and Simulation of Communications Satellite Channels

Computer modeling of satellite communications channels is a valuable adjunct to analytical modeling and hardware simulation for predicting and verifying communications link performance. In the computer simulation approach, sampled signals are created in the computer and operated on by algorithms that simulate the effects of filtering, channel nonlinearities, interference, and noise. After passage through the simulated channel, the distorted signals are demodulated to determine the performance degradation introduced by the channel. This paper describes the approach used in simulating communications channels on the computer. Examples are given that apply to the communications satellite channel; however, the techniques described are applicable to general channel configurations.     

The time-domain electromagnetic interference measurement system

A novel real-time broad-band time-domain electromagnetic interference (TDEMI) measurement system for the 30-1000-MHz frequency range is described. The signals from the antenna are sampled, analog-to-digital (A/D) converted and digitally processed. The fast-Fourier transform (FFT), the Welch- and Bartlett periodograms are digitally computed. Compared with state-of-the-art EMI measurement systems, the novel described TDEMI system samples the complete phase and amplitude information of the EMI simultaneously over the whole frequency band under consideration. With the presented time domain measurement system the measurement time can be reduced by a factor of 10. The digital processing of EMI measurements allows emulation in real-time of the various modes of conventional analogous equipment, e.g., peak, average, rms and quasi-peak detector and also introduces new concepts of analysis, e.g., phase spectra, short-time spectra, statistical evaluation and FFT-based time-frequency analysis methods.     

高速数据采集卡在雷达信号采集和分析中的应用

随着电子器件的高速发展和计算机总线技术日趋成熟,数据采集的采样速率已经得以飞速发展,现今的A／D采样率已经达到10GS／s,通过A／D采样在中频对雷达进行信号处理变得完全可能。本文介绍一种基于PCI总线技术的数据采集卡,通过它完成对雷达回波信号的采集和存储。     

Designing better adaptive sampling algorithms for ECG Holtersystems

Let Ψ be any adaptive sampling algorithm that can run in real time on a tapeless multichannel electrocardiogram (ECG) Holter system. Simple methods which can significantly improve Ψ's fidelity are described and their results are compared in this paper. It is shown that by adding some simple tests to Ψ, the signals reconstructed by Ψ can be improved as much as 5.45 dB. It is also shown that under the same data rate, a good data compressor with slowly sampled input ECG is preferable to a bad data compressor with highly sampled input ECG     

波片相位延迟量的测量与快轴的标定

本文提出用空心轴步进电动机带动待测波片调制输出光强,单片机控制步进电动机并同步采样输出光强的光电信号,通过USB接口将采样的光电信号数字量传给上位机,上位机根据步机电动机的时钟脉冲和采样光电信号,求出波片相位延迟的方法。同时提出利用已知四分之波片快轴标定待测波片快轴的新方法。对该方法的不确定度进行了分析。设计制作了实验装置,测量结果表明,四分之波片相位延迟测量的不确定度小于2°。     

A novel frequency estimator for sampled Doppler signals

In multigate pulsed Doppler systems with serial processing the Doppler signals are retained in their sampled form. The time-discrete nature of the Doppler signals affects the procedure to estimate the average frequency of the Doppler signal. Based on computer simulation studies it is demonstrated that a time-discrete frequency estimator based on either the density of zero-crossings or the time average of the instantaneous frequency exhibit a large relative error under poor signal-to-noise conditions or in the case of relatively wide band signals. Especially, the frequency estimator based on the instantaneous frequency functions poorly for average Doppler frequencies close to the Nyquist frequency. However, restricting the detected instantaneous frequency to a specific interval around its average improves the estimator performance considerably, while it allows tracking of center frequencies beyond the Nyquist frequency. A hardware realization of this modified estimator as incorporated in a high-resolution multigate pulsed Doppler system is described. In vitro and in vivo registrations as assessed with this system demonstrate the ability of the system to track frequencies close to and beyond the Nyquist frequency.     

Spectral analysis of linear digital systems using BIFORE

A spectral analysis of linear digital systems using BIFORE is carried out. Expressions for power and amplitude spectra of the input and output signals are developed. The frequency-sequency structure of the power spectra, which are invariant to cyclic shift of the sampled data, is analysed.     

离散控制系统采样信号数学描述方法的讨论

计算机控制系统的广泛应用，使得离散系统的建模、分析以及设计在经典控制理论的教学中处于愈来愈重要的位置。本文针对学生在学习采样信号的数学表述方法时存在的疑问和困惑，指出现有的采样信号的数学表述方法本身，有其欠妥之处，容易造成学生的误解。论文同时给出了改进的采样信号的数学表述方法。教学实践表明：基于改进的采样信号表述方法授课，理论上更为严谨，学生易于理解、接受。     

多路A/D非均匀采样信号的数字谱分析

对多路 A/D采样过程中出现的一类非均匀、非理想采样信号进行了频谱分析 ,得到了此类信号的数字谱表达形式 ,并对非均匀采样周期信号的数字谱进行了深入的研究 ,得到了其数字谱完整的表达形式及其一些重要性质。     

A shortest data window algorithm for detecting the peak value ofsinusoidal signals

A digital algorithm for detecting the peak value of known-frequency sinusoidal signals is proposed. The algorithm detects the peak value of a sinusoidal signal exactly and uses only two successive sampled data points for each peak value calculation. Hence, its transient response is only a sampling period. Simulation results show that this algorithm is applicable to detecting the peak value of steady-state, varying, and decaying sinusoidal signals used in power system telecontrol. Therefore, this technique is very useful for digital systems in which the peak value of sinusoidal signals must be detected