Tunable Terahertz Signal Generation by Chirped Pulse Photomixing

Tunable signal generation in the gigahertz to terahertz range was demonstrated by photomixing of a chirped optical pulse and its time-delayed replica. The chirped pulses were created by chromatically dispersing femtosecond pulses from a mode-locked fiber ring laser, and frequency tuning was achieved by adjusting the time delay and/or the amount of group velocity dispersion. It is shown that the signal phase is locked to the femtosecond-laser pulses and that an extinction ratio close to 100% can be obtained. Analytical calculations on the signal chirp introduced by higher order dispersion are also presented and compared with the experimental data     

GaAs CCD's with transparent (ITO) gates for imaging and optical signal processing

Sputtered indium tin oxide (ITO) film is used as the transparent Schottky gate material for GaAs CCD's. In addition the gigahertz clocking-rate capability of GaAs CCD's makes them attractive for high-speed optical signal processing applications. The operation of the GaAs CCD's with fixed-aperture mask over the transparent gates is reported here. Such structures are basic components of a GaAs CCD-based electrooptic processor (EOP).     

A Generalized Reverse Block Jacket Transform

Jacket matrices motivated by the center weight Hadamard matrices have played important roles in signal processing, communication, image compression, cryptography, etc. In this paper we propose a notation called block Jacket matrix which substitutes elements of the matrix into common matrices or even block matrices. Employing the well-known Pauli matrices which are very important in many subjects, block Jacket matrices with any size are investigated in detail, and some recursive relations for fast construction of the block Jacket matrices are obtained. Based on the general recursive relations, several special block Jacket matrices are constructed. To decompose high order block Jacket matrices, a fast decomposition algorithm for the factorable block Jacket matrices is suggested. After that some properties of the block Jacket matrices are investigated. Finally, several remarks are presented. These remarks are associated with comparisons between the Clifford algebra and the block Jacket matrices, generations of orthogonal and quasi-orthogonal sequences, and relations of the block Jacket matrices to the orthogonal transforms for signal processing. Since the Pauli matrices are actually infinitesimal generators of $SU(2)$ group, the proposed construction and decomposition algorithms for the block Jacket matrices are available in the signal processing, communication, quantum signal processing and information theory.      

一种基于StarFabric总线的通用信号处理平台设计

基于共享总线(CPCI或VME)的信号处理模块由于共享总线带宽逐渐成为提升信号处理系统性能的瓶颈,开关互连技术是新一代信号处理系统互连的趋势。给出了一种基于StarFabric总线的多DSP构成的通用信号处理平台设计,突破了这种设计瓶颈,能满足多种信号处理功能的需要。     

RF-Interferences Generate Chaotic GHz FM—Carrier for Communications

Following the principle of a highly nonlinear delay oscillator, we demonstrate the generation of an RF chaotic frequency modulated carrier, which could be used in chaos based communication systems. The nonlinear process is provided by the transfer function of an RF interferometer, modulating the amplitude of an FM signal; for this purpose, the path difference required for the interference process, as well as a long delay required for complex chaotic oscillation, are designed through the use of optical fibers. The RF signal used to produce interferences is transposed in the optical domain by a direct laser modulation with the gigahertz chaotic FM signal. The interference is obtained at fiber outputs terminated by photodiodes for backconversion of the RF signal into the electrical domain. Experimental results reporting the particular dynamical behavior of the nonlinear delay RF oscillator are presented, and also discussed in terms of chaos communication applications     

数字滤波器的设计和算法的实现

文章介绍用Ｉｎｔｅｌ公司新的８０Ｃ１９６ＵＮ单片机来设计数字滤波器。用此嵌入式数字信号处理器设计的滤波器的幅值、相位和响应较为精确,消除了多个或几个器件所引起的噪声,电压等误差。同时,文章还对Ｃ１９６ＵＮ硬件结构、软件设计及执行信号处理充集中的关键语句做了较好的概述。     

Walsh Functions in Image Processing, Feature Selection and Pattern Recognition

Walsh functions have become quite useful in the applications of image processing and feature selection. Due to their inherent efficiency of implementation, (they are a subset of the Reed Muller Codes and Hadamard matrices), they have become popular for coding, enhancement and other signal processing tasks. This paper will briefly describe applications in some of these areas with emphasis on a correlation analysis for justification purposes.     

Chaotic oscillations in Josephson tetrode

We numerically demonstrate the generation of chaos in a four-terminal superconductive device made of five Josephson weak-link junctions, which is referred to as "Josephson tetrode," for the applications of ultrafast random signal generations at frequencies of hundreds of gigahertz. In the Josephson tetrode, two junctions are series-connected and three junctions are parallel-connected. We calculate the dynamics of electrical voltages across the junctions when one of the normal resistances is varied. We confirm the generation of chaos by using a bifurcation diagram, three-dimensional attractors, and the Poincare sections. The bifurcation diagram can be interpreted as the quasi-periodicity-breakdown scenario to chaos. We clarify that the mechanism of the generation of chaos is a nonlinear frequency mixing among three independent voltages across the junctions. The condition of the generation of chaos can be predicted from the values of the coefficients in the equations of our model.     

基于LabVIEW的虚拟测试实验教学系统

测试系统以LabVIEW作为开发平台,研究内容包括:信号的产生、信号的分析处理以及案例分析。概述了系统的结构框架和主程序设计,以及PCI-9111HR数据采集卡的安装和虚拟信号发生器。叙述了信号分析处理部分的功能;最后通过了两个虚拟仪器实例证明,降低了实验成本,提高了利用率。     

Characteristics of chaotic masking in synchronized semiconductor lasers

Modulations imposed on a chaotic optical signal generated by a semiconductor laser can be suppressed by injecting the signal into another similar laser under conditions for chaos synchronization. This filter effect could be used to recover messages hidden in chaotic carriers for robust and secure communications. We use a numerical model to examine the filter properties and show that the filter can be described in terms of differences in characteristic transmission functions for imposed signal and chaotic carrier in the output of the synchronized laser. The filter effect is shown to be larger for lower frequencies and decreases as frequencies approach the relaxation oscillation frequency of the laser in the gigahertz regime, similar to the response of steady-state injection-locked lasers to small-signal modulation. The filter properties are confirmed in experiments using both single and multimode lasers.     

2位GaAs超高速模-数转换电路的设计与制作

模数(A-D)转换电路是信号处理系统中的一种关键性元件。本文结合现有GaAs起高速集成电路工艺,提出了一种2位GaAs A-D转换电路的设计方法,并制作出了单片形式的2位GaAs A/D转换电路。实验结果表明,该电路能正常工作在1Gs/s的转换速率下。它的转换时间小于1.0ns,电路功耗不高于340mW。这说明它在速度和功耗方面已展现出比Si双极电路更为广阔的发展前景。     

UWB Impulse Radio Receiver Based on Single Bit Quantization

Impulse Radio (IR) modulation is perceived to be a practical means of exploiting the multi-gigahertz bandwidth available for UWB links. However, the RMS delay spreading of indoor channels relative to the transmitted pulse width is typically very large such that several hundred signal samples are required to be quantized and processed for each received pulse. To realize a relatively low power low-complexity receiver of satisfactory performance in low signal to noise ratio environments, signal sampling based on single bit quantization is proposed which is readily realizable at gigahertz rates with modest power consumption. In this paper, the architecture and performance of a coherent IR receiver based on single bit quantization will be analyzed from the perspectives of Rake receiver processing, channel estimation and signal detection. This paper demonstrates that single bit quantization results in a modest manageable performance penalty relative to linear multi-bit sampling. This penalty is readily justifiable in light of the significant reduction in overall receiver complexity.     

Modeling complex via hole structures

Derives a physics-based circuit model for complex via hole structures in printed circuit boards. The via hole is modeled as a cascade of capacitance and inductance matrices. Capacitance values are computed using a three-dimensional electrostatic solver and inductance values are computed from a two-dimensional quasi-TEM solver. This model is valid at frequencies up to a few gigahertz for typical via hole geometries, where the return current follows a well defined path.     

基于MSP430的便携式数据采集器及信号发生器

为了实现便携式数据采集器和信号发生器,以及灵活的PC机控制、信号处理和显示结果的功能,采用MSP430F169作为主控芯片实现AD与DA转换,利用PDIUSBD12芯片大于10Mbps的传输率的优势,作为通信接口实现与PC机之间的数据传输,以实现信号波形产生和数据采集的收集。实验结果表明,利用低功耗的MSP430丰富的外围接口,不仅能够使用PC机的USB供电实现很好的波形的产生,而且能够将采集的信号波形通过PC机实现丰富的信号处理功能。     

Quadratic optimization for simultaneous matrix diagonalization

Simultaneous diagonalization of a set of matrices is a technique that has numerous applications in statistical signal processing and multivariate statistics. Although objective functions in a least-squares sense can be easily formulated, their minimization is not trivial, because constraints and fourth-order terms are usually involved. Most known optimization algorithms are, therefore, subject to certain restrictions on the class of problems: orthogonal transformations, sets of symmetric, Hermitian or positive definite matrices, to name a few. In this paper, we present a new algorithm called QDIAG that splits the overall optimization problem into a sequence of simpler second order subproblems. There are no restrictions imposed on the transformation matrix, which may be nonorthogonal, indefinite, or even rectangular, and there are no restrictions regarding the symmetry and definiteness of the matrices to be diagonalized, except for one of them. We apply the new method to second-order blind source separation and show that the algorithm converges fast and reliably. It allows for an implementation with a complexity independent of the number of matrices and, therefore, is particularly suitable for problems dealing with large sets of matrices.     

Fundamentals of Measurement in Terahertz Time-Domain Spectroscopy

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a main spectroscopic modality to fill the frequency range between a few hundred gigahertz to a few terahertz. This spectrum has been known as “terahertz gap” owing to limited accessibility by conventional electronic and optical techniques. Over the past two decades, THz-TDS has evolved substantially with enhanced compactness and stability. Since THz-TDS is becoming an industrial standard, the performance and precision of the system are of prime importance. This article provides an overview on terahertz metrology, including parameter estimation, signal processing, measurement characteristics, uncertainties, and calibrations. The overview serves as guidance for metrology and further developments of THz-TDS systems.     

Generation of fundamental soliton trains for high-bit-rate opticalfiber communication lines

The authors present a method for the generation of high-quality soliton trains at a high repetition rate of gigahertz to terahertz range. During nonlinear propagation of a continuous-wave (CW) dual-frequency signal through a fiber with effective amplification, a train of practically noninteracting fundamental solitons is formed. It is shown that the effective amplification can be achieved as in usual fibers with an actual amplification as well as in fibers with nonuniform parameters along the fiber axis. The method is demonstrated experimentally. Dual-frequency 25 ps pulses at λ=1.55 μm are reshaped into 0.2 THz combs of 0.49 ps solitons in fiber with slowly decreasing dispersion. It is also shown that stimulated Brillouin scattering (SBS) can prevent a CW soliton train transmission through optical fibers, and suggests a method for suppression of SBS     

Asymptotic Behavior of Random Vandermonde Matrices With Entries on the Unit Circle

Analytical methods for finding moments of random Vandermonde matrices with entries on the unit circle are developed. Vandermonde matrices play an important role in signal processing and wireless applications such as direction of arrival estimation, precoding, and sparse sampling theory, just to name a few. Within this framework, we extend classical freeness results on random matrices with independent and identically distributed (i.i.d.) entries and show that Vandermonde structured matrices can be treated in the same vein with different tools. We focus on various types of matrices, such as Vandermonde matrices with and without uniform phase distributions, as well as generalized Vandermonde matrices. In each case, we provide explicit expressions of the moments of the associated Gram matrix, as well as more advanced models involving the Vandermonde matrix. Comparisons with classical i.i.d. random matrix theory are provided, and deconvolution results are discussed. We review some applications of the results to the fields of signal processing and wireless communications.     

A performance comparison of measurement matrices in compressive sensing

Compressive sensing involves 3 main processes: signal sparse representation, linear encoding or measurement collection, and nonlinear decoding or sparse recovery. In the measurement process, a measurement matrix is used to sample only the components that best represent the signal. The choice of the measurement matrix has an important impact on the accuracy and the processing time of the sparse recovery process. Hence, the design of accurate measurement matrices is of vital importance in compressive sensing. Over the last decade, a number of measurement matrices have been proposed. Therefore, a detailed review of these measurement matrices and a comparison of their performances are strongly needed. This paper explains the foundation of compressive sensing and highlights the process of measurement by reviewing the existing measurement matrices. It provides a 3‐level classification and compares the performance of 8 measurement matrices belonging to 4 different types using 5 evaluation metrics: the recovery error, processing time, recovery time, covariance, and phase transition diagram. The theoretical performance comparison is validated with experimental results, and the results show that the Circulant, Toeplitz, and Hadamard matrices outperform the other measurement matrices.     

Line, Trunk, and Service Circuit Test System of ITT System 1240

This paper describes the implementation of the test system of the ITT System 1240 digital switch that was developed for line, trunk, and service circuit maintenance and diagnostics. At the core of the test system is a problem-oriented, remotely programmable, digital signal processor called the test signal analyzer (TSA). The TSA is a versatile signal generation and measurement tool, whose signal processing power is made readily available to the test engineer as a set of high-level functional instructions, rather than as a primitive register transfer language, or as inflexible test-specific instructions. Specifically, this paper briefly describes the TSA implementation, identifies the functions that are fundamental to any telecommunications test system, presents some of the digital signal processing algorithms, and gives a measurement example.