Reconstruction of Nonuniformly Sampled Bandlimited Signals Using a Differentiator–Multiplier Cascade

This paper considers the problem of reconstructing a bandlimited signal from its nonuniform samples. Based on a discrete-time equivalent model for nonuniform sampling, we propose the differentiator–multiplier cascade, a multistage reconstruction system that recovers the uniform samples from the nonuniform samples. Rather than using optimally designed reconstruction filters, the system improves the reconstruction performance by cascading stages of linear-phase finite impulse response (FIR) filters and time-varying multipliers. Because the FIR filters are designed as differentiators, the system works for the general nonuniform sampling case and is not limited to periodic nonuniform sampling. To evaluate the reconstruction performance for a sinusoidal input signal, we derive the signal-to-noise-ratio at the output of each stage for the two-periodic and the general nonuniform sampling case. The main advantage of the system is that once the differentiators have been designed, they are implemented with fixed multipliers, and only some general multipliers have to be adapted when the sampling pattern changes; this reduces implementation costs substantially, especially in an application like time-interleaved analog-to-digital converters (TI-ADCs) where the timing mismatches among the ADCs may change during operation.      

Least-Squares and Minimax Design of Polynomial Impulse Response FIR Filters for Reconstruction of Two-Periodic Nonuniformly Sampled Signals

This paper proposes polynomial impulse response finite-impulse response filters for reconstruction of two-periodic nonuniformly sampled signals. The foremost advantages of using these reconstruction filters are that on-line filter design thereby is avoided and subfilters with fixed dedicated multipliers can be employed in an implementation. The overall implementation cost can in this way be reduced substantially in applications where the sampling pattern changes from time to time. The paper presents two different design techniques that yield optimum filters in the least-squares and minimax senses, respectively. Design examples are included that illustrate the benefits of the proposed filters     

SAR非均匀采样信号频谱重构

在常规星载SAR系统中,测绘带宽和分辨率之间存在矛盾,采用方位向多相位中心多波束模式可以很好地解决这个问题。但在方位向多相位中心多波束SAR系统中,要想实现宽幅成像,其方位向上回波的采样时刻大多是不均匀的。文中主要分析和研究如何重构非均匀采样信号的频谱。非均匀采样信号频谱重构的仿真结果证明了该重构算法的正确性。     

分数阶Fourier域上非均匀采样信号的频谱重构研究

 本文研究了分数阶Fourier变换域上非均匀采样信号的重构问题.首先得到周期非均匀采样信号经非均匀分数阶Fourier变换后的频谱表达式,研究了该分数阶频谱和信号连续分数阶频谱之间的关系,并基于该关系式提出了一种分数阶Fourier域周期非均匀采样信号的频谱重构算法;其次,讨论了分数阶Fourier变换域上更加一般情况下非均匀采样信号重构问题;最后,给出了周期非均匀采样信号频谱重构的仿真结果.     

一类非均匀采样信号的数字谱

本文对实际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,最后,给出了该理论的一个应用一分析数字合成周期信号的频谱及信噪比．     

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。     

分数阶Fourier域非均匀采样LFM信号的检测概率

为了减少分数阶Fourier域线性调频(LFM)信号处理的计算量,满足实时性要求,提出了一种新的非均匀采样方法.与传统的非均匀采样方法相比,该方法既解决了整个采样时段内由于过采样造成的数据冗余性,也消除了信号时变特征造成的局部冗余性.最后,应用该方法得到了非均匀采样LFM信号在分数阶Fourier变换域的频谱表达式,并对不同信噪比(SNR)条件下信号的检测概率进行了研究.结果表明,该方法具有较好的抗噪声能力.     

A Key Agreement Protocol Using Band-Limited Random Signals and Feedback

Key distribution is an essential element in cryptography. In this paper, the framework of a classical key agreement protocol using band-limited random signals and feedback is presented. The secrecy is derived from masking information by privately held random signals. Critical parameters of the protocol are identified. Raw performance of the system is presented. The secrecy can be enhanced by taking advantages of measures, such as reconciliation and privacy amplification, developed for classical and quantum key agreement protocols.     

混合信号系统非均匀抽样信号的分析和重构

混合信号系统的非均匀采样信号的重构算法是信号处理领域的一项重要研究内容。由于采样间隔是不均匀的,传统的Shannon采样定理己经不再适用,这就要求提出一些有效的算法来解决这个问题,已有的解决办法大多都是利用插值和迭代。通过使用一个多速率滤波器组,可以分析非均匀抽样信号的数字谱并且重建出均匀抽样序列,并通过计算机仿真验证了算法的正确性。该重构算法在工程实际中具有应用价值。     

二维带限信号正则重构和外推的快速算法

本文给出用离散正则化方法进行二维带限信号重构和外推的快速算法.其基本思想是将正则化方法与快速Fourier变换(FFT)结合起来,而正则参数的选取则基于偏差原理和作者提出的三阶收敛算法来实现,并进行数值了模拟.计算结果表明本文给出的新算法具有快速、稳定和抑制高频噪音干扰等优点.     

SAR方位向非均匀采样频谱重构算法及误差分析

SAR DPCMAB（方位向多相位中心多波束模式）能够提高方位向采样率,同时却带来非均匀采样的问题,通过频谱重构算法能够有效恢复原信号频谱。但是在SAR传感器运行过程中存在通道特性不一致、采样时刻偏差、噪声等干扰因素,导致重构后的信号出现频谱噪声,重构精度受到影响。文中通过对混叠干扰因素后的非均匀采样LFM信号进行频谱重构,分析各种干扰因素变化与重构误差的关系。通过仿真,得到了干扰条件下的重构频谱,并通过改变干扰条件进一步得到了频谱误差与干扰强度的关系曲线。仿真结果表明．超过一定阈值后,随着干扰强度的增加,重构频谱误差呈线性增长趋势,最终逼近重构前非均匀采样时的频谱误差。     

Stability and Constrained Control of a Class of Discrete-Time Fuzzy Positive Systems with Time-Varying Delays

This paper deals with the stability of nonlinear discrete-time positive systems with time-varying delays represented by the Takagi–Sugeno (T–S) fuzzy model. The time-varying delays in the systems can be unbounded. Sufficient conditions of stability which are not relevant to the magnitude of delays are derived by a solution trajectory. Based on the stability results, the problems of controller design via the parallel distributed compensation (PDC) scheme are solved. The control is under the positivity constraint, which means that the resulting closed-loop systems are not only stable, but also positive. Constrained control is also considered, further requiring that the state trajectory of the closed-loop system be bounded by a prescribed boundary if the initial condition is bounded by the same boundary. The stability results and control laws are formulated as linear matrix inequalities (LMIs) and linear programs (LPs). A numerical example and a real plant are studied to demonstrate the application of the proposed methods.     

Multichannel Sampling of Signals Band-Limited in Offset Linear Canonical Transform Domains

The aim of the multichannel sampling is the reconstruction of a band-limited signal f(t), from the samples of the responses of M linear time invariant systems, each sampled by the 1/Mth Nyquist rate. As the offset linear canonical transform (OLCT) has been found wide applications in signal processing and optics fields, it is necessary to consider the multichannel sampling based on offset linear canonical transform. In this paper, we develop a multichannel sampling theorem for signals band-limited in offset linear canonical transform domains. Moreover, by designing different OLCT filters, reconstruction formulas for uniform sampling from the signal, from the signal and its first derivative or its generalized Hilbert transform are obtained based on the derived multichannel sampling theorem. Since recurrent nonuniform sampling for the signal has valuable applications, reconstruction expression for recurrent nonuniform samples of the signal band-limited in the offset linear canonical transform domain is also obtained by using the derived multichannel sampling theorem and the properties of the offset linear canonical transform.     

Frequency and Offset Online Estimation of Sinusoidal Signals Based on High-Order Nonlinear Continuous Differentiator

Real-time parameter identification of si-nusoidal signals is an essential research topic due to its broad utilization in both theoretical studies and engineer-ing practice. A tracking differentiator based online estima-tion framework has been proposed to simultaneously iden-tify frequencies and offset of given multi-sinusoidal signal. Tracking differentiator is exploited in presented framework to track the time derivatives of measurements which are then utilized to estimate the frequencies and offset. We introduce a tracking differentiator called high-order non-linear continuous differentiator into the framework, giving birth to a new estimation algorithm. Comparative exper-iments on both single and two sinusoidal signal are sim-ulated, indicating the superiority of proposed method on both convergent speed and estimation accuracy.     

平移不变空间中信号的min-max插值重建方法

在一般平移不变子空间框架下讨论信号的有限非一致采样重建的问题.基于信号的子空间表示,本文给出一般信号在min-max插值准则下的最优插值方法以及相应的非迭代算法.该方法可以导出著名带限信号的Yen插值.数值实验表明所给方法能十分有效地重建信号.     

Time Delay Estimation by Cross-covariance Maximization of Quadrature Sampled Narrowband Signals

A numerically efficient algorithm for estimating the time delay from observations of a stationary narrowband signal and its delayed version is investigated. Quadrature sampling, a variant of bunched sampling, is applied to estimate samples of the quadrature components of the cross-covariance function of the two signals. The baseband magnitude squared of this function can be maximized for time delay estimation. Because the time delay is unknown, the baseband cross-covariance function cannot be interpolated from the estimated samples. Numerical maximization of the samples' magnitude squared and quadratic interpolation, however, results in a reasonable time delay estimate.     

Digital Separation and Reconstruction of NTSC Signals

A new digital method for separation and reconstruction of NTSC color TV signals is described. Digital conversion between an NTSC signal and its baseband component signals is performed at a sampling rate of(12/5)f_{sc} simeq 8.59MHz (fsc: the color subcarrier frequency), which is lower than the conventionally used3f_{sc}or4f_{sc}sampling rate. Since this lowered sampling rate satisfies the Nyquist condition for NTSC signals, the proposed digital method can provide an effective technique for the component coding of NTSC signals. Simulation results have shown that, with this method, no visible picture quality degradations can be observed for either the color bar signal or SMPTE Pictures.     

时变信道中CDMA信号的波达方向和直接扩频序列盲估计

本文研究CDMA信号的波达方向和直接扩频序列同时估计问题,在无任期任何波达方向信息的条件下,提出了利用用户特征序列定义一种新的目标函数,通过对目标函数寻优得到最佳权矢量,从而实现对波达方向和直接扩频序列进行估计,并利用改进的递归算法对权矢量进行实时更新,以适应移动通信无线环境的时变而导致信号的非平稳变化。该方法既适用于平稳信号,也适用于非平稳信号,仿真结果证实了该方法的有效性。