Bandpass Signal Sampling and Coherent Detection

Coherent detectors in radar and communications receivers are generally implemented in the form of two parallel baseband channels which form in-phase (I) and quadrature (Q) components of a received RF/IF signal. Phase errors of several degrees due to imperfect matching of these separate channels limit the performance achievable from signal processors such as moving target indicators (MTI), coherent integrators, Doppler filters, antenna array processors, and coherent sidelobe cancellers. Thus methods in which a single analog to digital (A/D) converter samples and digitizes the IF signal directly, eliminating the need for IF to baseband conversion, have been of recent interest and are the subject of this paper. To obtain accurate coherent detection from IF samples taken near the Nyquist rate requires interpolation based upon a number of stored samples. An algorithm derived from sampling theory is defined and used to demonstrate accurate reconstruction of the original IF signal from digitized samples. In-phase and quadrature components of the signal are shown to be available from processed samples with demonstrated phase errors less than 0.2°.     

Multichannel Recovery of Quadrature Components of Bandpass Signals

The problem of sampling signals maintaining the theoretically minimum (average) sampling rate and allowing a separate interpolation is considered from a general point of view. The formulation will follow a recently published method for multichannel sampling; this way there is the advantage of working with functions depending only on the frequency and not on time and frequency as in other approaches. This simplifies the general expressions and the determination of separation conditions. Under the assumption of nonsingularity of certain matrices, we obtain the necessary and sufficient conditions for a separate interpolation and discuss them. Finally, an especially important case is considered as an example.     

A digital quadrature demodulation system

Existing digital quadrature demodulation techniques sample the input at either 2B Hz or 4B Hz, select the even samples as the in-phase (I), and interpolate the odd samples to give the quadrature (Q), output. The signal bandwidth is B. We propose a demodulation system to produce I and Q samples at arbitrary sampling rate greater than 2B Hz. The system eliminates the IF downconversion step with a special sampling scheme. The even samples correspond to the I component, while the Q components are the filtered output. The filter can be a lowpass or least squares (LS) filter. The lowpass filter design is based on trade-offs between the filter length and the degree of oversampling. It produces similar results as previous work when the sampling rate is 2B Hz or 4B Hz. Unlike existing methods which assume the input is white, a LS filter, on the other hand, can make use of input signal characteristics to achieve a better result. The higher the correlation in the input the larger the improvement. The cost for LS filtering is a coefficient update step if the input is time varying. A scheme to cancel dc offset from analog to digital (A/D) converters is also given     

Time jitter analysis for quadrature sampling

Time jitter in the quadrature sampling processes is modeled and the performance of an adaptive cancellation system in the presence of such time jitter is analyzed. It is shown that the decorrelation due to time jitter depends on the magnitude of the jitter, the sampling scheme used, the bandwidth of the signal and the intermediate frequency (IF) preceding the analog-to-digital (A/D) conversion stages. The performance of a sidelobe cancellation system in the presence of time jitter, for several sampling approaches, is evaluated numerically as well as simulated. The results show that the direct quadrature sampling scheme with a lower IF provides superior performance for an adaptive cancellation system     

动态数据建模中时间序列采样间隔的研究

动态数据建模认为,平稳连续随机过程是白噪声激励相应的线性时不变连续时间系统的输出,为便于计算机处理,需要确定对连续随机过程进行采样的采样间隔,通常人们采用仙农采样定理来对待。文中阐述了对动态数据建模中时间序列采样的问题,用多项式插值的采样理论进行了研究,指出在动态数据建模中,若要使从连续时间随机过程到离散时间序列的统计特性得到保持,采样频率应大于系统最大极点自然频率的6倍。     

Phase-Lock Loop Jump Phenomenon in the Presence of Two Signals

Jump phenomena are known to exist in many non-linear systems [I], [2], [3]. The non-linear analysis presented in this paper explains and predicts the conditions for the jump phenomenon that is observed in a phase-locked loop (PLL) preceded by an automatic gain control (AGC). The jump phenomenon occurs when the frequency separation AM of two sinusoids at the input to the AGC is greater than the bandwidth B of the linearized PLL. If the loop is initially locked to the stronger signal, the weaker signal will frequency-modulate the PLL voltage-controlled oscillator (VCO) with a modulation frequency AI. The amplitude S2 of the weaker signal al can be increased until it becomes greater than the amplitude Si of the signal being tracked, without causing the loop to lose lock; i. e., the VCO continues to track the original signal. However, if the ratio of the amplitudes S2 S1 = R is increased above some critical value RC > 1, the loop will lose lock on the original signal, and jump to track the interfering signal. If the frequency separation is at least twice the PLL bandwidth, a good approximation for this critical ratio is Rc ? ?w/B.     

The Effect of Integrator Pole Position on the Performance of an Adaptive Array

The LMS adaptive array requires an integrator in each weight feedback control loop. In practice the integrator is often replaced by a low-pass filter, i.e., by a filter with a single pole at s = - ? (where s is complex frequency). The effect of this pole position on array performance is examined. It is shown that to obtain optimal performance from the array, ? must be less than k?2, where k is the loop gain and ?2 is the thermal noise power per element. When at exceeds k?2, the output signal-to-inter ference-plus-noise ratio from the array is degraded for intermediate values of interference power.     

On Truncation Error Bounds for Sampling Representations of Band-Limited Signals

All sampling representations of band-limited signals involve infinite sums. The truncation error associated with a given representation is defined as the difference between the signal and an approximating sum utilizing a finite number of terms. In this paper truncation error is expressed as a contour integral for Lagrange interpolation, general Hermite interpolation, the Shannon series (cardinal series), the Fogel derivative series, and multidimensional sampling expansions. Truncation error bounds are obtained under various constraints on the signal magnitude, spectral smoothness, and energy content.     

径向基函数在三维Euler方程数值计算中的应用

基于三维Euler方程,对非结构四面体网格给出了一种基于紧支径向基函数重构的ENO型有限体积格式,方法的主要思想是先对每一个四面体单元构造插值径向基函数,而在计算交界面的流通量采用高斯积分公式以保证格式的整体精度,时间离散采用三阶TVD Runge-Kutta方法。最后用该格式对一些典型算例进行了数值模拟,结果表明该方法计算速度快,对间断有很好的分辨能力。     

一种非结构网格上基于径向基函数重构的ENO格式

基于二维Euler方程,对非结构三角形网格给出了一种基于紧支径向基函数重构的ENO型有限体积格式,方法的主要思想是先对每一个三角形单元构造插值径向基函数,而在计算交界面的流通量采用两点高斯积分公式以保证格式的整体精度。时间离散采用三阶TVD Runge—Kutta方法。最后用该格式对一些典型算例进行了数值模拟,结果表明该方法计算速度快,对间断有很好的分辨能力。     

台阶流模型流场的局部DQ-Lagrange求解方法

以Lagrange多项式作为Differential Quadrature(DQ)方法的基函数,应用局部DQ-Lagrange方法对Navier-Stokes方程进行了数值求解,建立了基于局部迎风DQ-Lagrange方法的复杂台阶流流场求解模型.并在此研究基础上,提出了本质和自然边界条件的处理方法.分析了支持域的选择、边界条件处理方法、迎风机制等对求解精度的影响.结果表明:支持域较大时,Lagrange高阶插值易出现振荡现象,可以采用局部替代全局的插值方法;迎风支持域的加入可以提高求解精度;建模时速度支持域的选择应该大于压力支持域.      

A new quadrature sampling and processing approach

A quadrature sampling and array signal processing technique that differs from earlier approaches in that is processes the data before the Hilbert transformation is presented. A fast Fourier transformation (FFT) technique that performs the discrete Fourier transformation (DFT) on the sampled data directly without Hilbert transformation is proposed for frequency-domain signal processing. For array signal processing, the proposed approach does not perform Hilbert transformation prior to signal combining. It features high processing speed, low distortion, and hardware simplicity. Error analyses, performance evaluation, and computer simulation results are included     

Quadrature Sampling with High Dynamic Range

Many radio and sonar systems require signal outputs in complex low-pass form. To achieve this, it is possible to use uniform sampling of the bandpass signal, together with computation of the quadrature component by way of a Hilbert transform. The bandpass to low-pass translation is accomplished by undersampling. A hardware implementation is described which achieves 70 dB spurious-free dynamic range and a bandwidth of 30 kHz.     

The Correction of I and Q Errors in a Coherent Processor

A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor [1] by means of coefficients which are derived from measurements of a test signal. The residual errors after correction depend upon the signal-to-noise ratio (S/N) of the test signal and the degree of filtering used in deriving the correction coefficients.     

Curiosity’s Mars Hand Lens Imager (MAHLI) Investigation

The Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) investigation will use a 2-megapixel color camera with a focusable macro lens aboard the rover, Curiosity, to investigate the stratigraphy and grain-scale texture, structure, mineralogy, and morphology of geologic materials in northwestern Gale crater. Of particular interest is the stratigraphic record of a ～5?km thick layered rock sequence exposed on the slopes of Aeolis Mons (also known as Mount Sharp). The instrument consists of three parts, a?camera head mounted on the turret at the end of a robotic arm, an electronics and data storage assembly located inside the rover body, and a calibration target mounted on the robotic arm shoulder azimuth actuator housing. MAHLI can acquire in-focus images at working distances from ～2.1?cm to infinity. At the minimum working distance, image pixel scale is ～14?μm per pixel and very coarse silt grains can be resolved. At the working distance of the Mars Exploration Rover Microscopic Imager cameras aboard Spirit and Opportunity, MAHLI’s resolution is comparable at ～30?μm per pixel. Onboard capabilities include autofocus, auto-exposure, sub-framing, video imaging, Bayer pattern color interpolation, lossy and lossless compression, focus merging of up to 8 focus stack images, white light and longwave ultraviolet (365 nm) illumination of nearby subjects, and 8 gigabytes of non-volatile memory data storage.     

网格之间流场信息传递的高精度方法和验证

理论分析了插值方法引入误差的原因,提出一种利用时间推进方法和移动网格技术实现网格之间流场信息传递的思想,并构造计算方法。在介绍新的信息传递算法原理的基础上,根据三维情况下传递过程需要满足的时间推进步长稳定性条件,推导出最小推进步数的要求。最后,通过对激波诱导物体运动的非定常流动模拟,比较了信息传递算法和线性插值、加权最小二乘插值方法,计算结果表明,与插值方法相比,信息传递过程没有引入误差,能有效抑制非物理振荡,保持流场计算精度。     

On the Performance of Some Sequential Multiple-Decision Procedures

The performance of several sequential procedures for the following multiple-decision problem is investigated. Samples from k random processes (or populations) are available, k at a time (one from each process), to a receiver or data processor. One process contains a signal; the other k - 1 are statistically identical noise. The receiver is to select the odd process (locate the signal), with prescribed probability of error. The optimal receiver makes the selection in minimum average time. Analytical and Monte Carlo computations were performed under the hypothesis that the processes sampled are Rayleigh; however, a method for extrapolating results to other cases is given. The parameter k is allowed to vary from 2 to 1000.     

基于谱插值和奇异值差分谱的滚动轴承静电监测信号去噪方法

采用静电传感器进行滚动轴承故障监测实验研究.针对滚动轴承静电监测中各种强噪声、故障特征难以提取的问题,提出了基于谱插值和奇异值差分谱的联合去噪方法.首先采用谱插值抑制工频干扰,然后将所得信号构造Hankel矩阵,求取奇异值差分谱并自动确定有用分量个数,最后重构信号.仿真和实验结果表明:仅采用奇异值差分谱或者小波去噪方法,无法从含有强工频干扰的信号中提取有用成分;所提出的方法相比较谱插值和小波去噪方法能够凸显早期故障特征频率.     

总体均值估计量最小方差的改进

在简单随机抽样中,样本均值是总体均值的无偏估计.其他复杂的抽样方法常以简单随机抽样为基础,对于相同的样本容量条件下不同的抽样方法来说,总体均值估计量的方差就成为衡量各种抽样方法的有效程度的重要标志.对文[1]中给出的求有限总体均值估计量最小方差的几种方法进行了讨论,并对其求解方法进行了改进.     

基于CFD方法对微型扑翼翼型设计的研究

基于CFD方法从扑翼设计的角度出发对扑翼的外形进行深入的研究.使用基于广义无限插值理论的代数网格生成方法开发适合扑翼运动的三维结构N-S动网格,并应用有限体积法结合双时间推进技术求解预处理后的低速三维非定常N-S方程,完成了对低速扑翼绕流的数值模拟.通过与文献算例的比较验证了本文方法的可靠性和正确性.在此基础上,对文献[8]中介绍的一种混合翼型的相关参数变化对扑翼气动特性的影响开展了深入的研究.