Direct formulation of the state equations: signal-flow-graph approach in time domain

In the t domain, the drawing of the signal-flow graph by inspection which is very useful in the direct formulation of the state equations of an active RLC network is discussed, and a method to obtain the state equations, based on the drawing of the signal-flow graph and on Mason's gain formula, is given.     

Algorithm for the evaluation of (sI-A)?1 B from signal-flow graphs not involving the complex variable s

A method of evaluating the Laplace transform of the state vector by a simple signal-flow graph of the state equations is presented. The coefficients of the numerator and denominator polynomials in Mason's gain formula are obtained from sub-graphs whose transmittances are real numbers.     

A Spectral Theory for Hybrid Modulation

Certain properties of periodic signals are defined in terms of the zeros and singularities of associated analytic functions of a complex time variablez. This algebraic approach is a generalization of analytic signal theory, and leads to the conception of hybrid modulation as the superposition of twoz-plane zero-singularity (ZS) patterns associated with amplitude- and angle-modulating signals, respectively. It is shown that important spectral properties of the modulated signal, such as band limitation, are explicit in the resultant pattern. Signal design is then interpreted in terms of ZS manipulation and placement. The theory is applied in a unified approach to compatible singlesideband (CSSB) modulation systems. It is shown that two types of proposed CSSB systems give rise to essentially nonband-limited output signals. The relation between conventional and single-sideband (SSB) angle modulation is also discussed in terms of their characteristic ZS patterns.     

A new generation of 90 Mb/s systems: bandwidth efficient, fieldtested 16-QAM

16-QAM (quadrature amplitude modulation) digital satellite broadcast equipment and satellite communications (SATCOM) systems that double the spectral efficiency of currently operational satellite links is described. It is shown that with this field-proven system, data transmission at a rate of 90 Mb/s (two multiplexed DS-3 signals) is feasible in a transmission bandwidth of 30 MHz. Extensive operational satellite tests performed over the T-303 satellite of AT&T demonstrated a BER <10^-10 and no errors for several days. The practical bandwidth efficiency of these SATCOM systems is 3 b/s/Hz, i.e. double the currently used 1.5 b/s/Hz QPSK (quadrature phase-shift keyed) systems. The doubling of the spectral efficiency is attained with advance modem (modulation-demodulation), adaptive equalization robust synchronization, high-power amplifier (HPA) linearization (predistortion), and low redundancy powerful forward-error-correction (FEC) subsystems. The systems may make possible the conversion of currently operational analog FM links into bandwidth efficient digital systems. In one 30 MHz satellite transponder three to four digitized high quality TV signals could be broadcast, or two standard rate DS-3 signals time-division multiplexed with a DS-1 rate signal and additional auxiliary data streams     

New formula for the signal-flow graph reduction

A new formula for the branch-gain computation of an equivalent signal-flow graph with reduced nodes is presented. This formula enables one to simplify a signal-flow graph by reducing an arbitrary number of nodes in one operation.     

Understanding linearity in wireless communication amplifiers

This paper investigates the linearity of active devices and amplifiers that have modulated input signals. We describe an implementation of a mathematical technique for calculating spectral regrowth due to the nonlinear amplification of modulated signals typically used in wireless communication systems. This technique only requires knowledge of the single-tone gain and phase data as a function of input power and can be applied to any modulated signal given (a) the device or amplifier characteristics do not change significantly over the bandwidth of the input signal and (b) the modulation frequencies are much less than the carrier frequency. Verification of the mathematical technique is presented using examples of measured and calculated spectra for π/4-differential quadrature phase shift keying (DQPSK) personal handy phone system (PHS) and code division multiple access (CDMA) Offset-QPSK personal communication system (PCS) modulation schemes. This calculation technique is essential in determining fundamental tradeoffs between device performance (linearity, output power, gain, and power-added efficiency) and device bias conditions and load impedance     

多相编码信号谱相关特征检测与参数估计

基于时域和频域2种循环谱密度估计方法,研究和总结了多相编码信号的循环谱特征及其与信号参数的关系。提出了一种没有先验知识条件下多相编码信号参数提取方法。首先介绍了多相编码信号的表示形式,然后使用循环谱密度函数估计方法分析了信号的循环谱特征,在此基础上提出了基于循环谱特征的信号参数提取方法。通过对6个典型多相编码信号参数提取相对误差的计算,验证了该算法的有效性。     

Frank码截获信号循环谱特征参数提取方法

基于时域和频域两种循环谱密度估计方法,研究和总结了Frank码信号的循环谱特征及其与信号参数的对应关系。提出了一种没有先验知识条件下Frank码截获信号参数提取方法。首先介绍了Frank码信号的表示形式,给出了信号主要参数之间的关系;然后使用时域和频域两种循环谱密度函数估计方法分析了信号的循环谱特征,得到了循环谱特征与信号参数之间的对应关系;在此基础上提出了基于循环谱特征的信号参数提取方法。通过对六个Frank码信号参数提取相对误差的计算,验证了该算法的有效性。     

A method for intermodulation noise calculations in a cabletelevision network with HD-MAC, PAL and FM radio signals

A statistical method for calculating intermodulation noise in CATV systems whose traffic can be characterized as a sum of a large number of independent signals is presented. The method is demonstrated by calculating the signal-to-intermodulation-noise ratio in the various channels of a prototype cable network supporting HD-MAC, PAL, and FM radio signals. The spectra of these individual signals are simplified in order to perform part of the calculation analytically. It is shown that the signal-to-intermodulation-noise ratio decreases when the total signal power is increased. This method can be used to calculate the necessary back-off of a cable network for a given frequency plan and to determine suitable plans for loading and controlling CATV networks     

Symbolic pole/zero calculation using SANTAFE

The aim of symbolic analysis is to gain insight into circuit behavior. To study the behavior of analog circuits, the locations of the poles and zeros have to be known. Unfortunately, no general method exists to calculate the poles and zeros symbolically for polynomials of degree greater than four from transfer functions in coefficient form. The CAD tool SANTAFE (Symbolic Analysis of Transfer Functions) applies the signal-flow graph method, which permits to keep the result in a factorized or partially factorized form. The graphic view provided by a signal-flow graph offers insight into the internal interactions between the circuit elements and, as will be demonstrated, enables the user to perform circuit knowledge-based approximations. A novel procedure based on symbolic Newton-iteration, accurately calculates high-order transfer functions in the desired pole/zero form. Another special routine, based on element weight ratios rather than numerical values, enables the simplification of large symbolic expressions without numerical values for each parameter. With the program SANTAFE, even large networks can be analyzed symbolically. This will be shown with an example of a wide band BiCMOS operational amplifier     

High-order voltage transfer function synthesis using CCII+ basedunity gain current amplifiers

Using the signal-flow graph approach, a general synthesis method for the realisation of high-order voltage transfer functions is presented and a current conveyor filter is obtained. The resulting filter contains a minimum number of capacitors, at most 2n+3 resistors, as well as n+2 current conveyors of plus type, all of which operate in current-mode     

Application of Coded Modulation to 1.544-Mbit/s Data-in-Voice Modems for FDM FM and SSB Analog Radio Systems

The technical issues relevant to providing high-quality digital service over analog radio using 1.544-Mbit/s DS-1 data-invoice modems operating through analog supergroup channels with 256-QAM modulation are reviewed. By means of a typical example, the desirability of increasing the fading margin when operating over FM radio systems is demonstrated. This motivates the consideration of coded modulation as a means of extending the threshold of the modem System, so that operation of the modem can be achieved in supergroup channels located higher in the radio baseband. It is found that trellis coded modulation provides better improvement of threshold performance than lattice coded modulation when the actual coding gain realized near the R0channel bound is used rather than the high signalto-noise-ratio (SNR)asymptotic coding gains. Using Ungerboeck's eight-state trellis code [3], a coding gain of approximately 2 dB is found for operation at 28 dB SNR (1 dB from the R0bound). Furthermore, it is found that even at this low operating SNR (where error events at the coded modulation receiver ouput can be long), high-rate, interleaved Reed-Solomon codes, used for burst noise protection at high SNR, still provide over 2 dB of additional coding gain.     

基于时间—顶点谱图小波变换的动态纹理分类方法

动态纹理在空间和时间上表现出“外观”和“运动”属性,为了有效结合这两种属性进行动态纹理分析,本文提出一种基于时间—顶点谱图小波变换与边缘分布协方差模型的动态纹理分类方法。该方法将动态纹理看成时间—顶点图信号,利用时间—顶点谱图Meyer小波变换对动态纹理进行多尺度分解,再对每个子带应用边缘分布协方差模型,由此得到带内相关性的特征协方差矩阵作为动态纹理特征进行分类。由于时间—顶点图信号的表示可以有效描述动态纹理像素间的空间关系及其沿时间的变化,同时谱图小波变换继承了图表示和小波变换的优势,因此利用时间—顶点谱图小波分解与边缘分布协方差模型,可得到有效的动态纹理特征。在标准动态纹理数据集上的分类实验结果表明,本文方法具有良好的分类性能。      

Comparison of advanced coding and modulation schemes for multicarrier satellite communication systems

Digital satellite communication systems use coherent quaternary PSK (QPSK) as the preferred modulation scheme. In recent years, however, the search for bandwidth and power-efficient digital modulation methods has become an active research area. In this paper the performances of combined coding and modulation schemes employing multilevel signal alphabets are considered, in the framework of a system model which reasonably approximates the INTELSAT SCPC system. The main goal of the research was to investigate whether the efficiency of coded modulation schemes and their savings in transmitted power could be maintained in a system environment dominated by interference more than by the additive white Gaussian noise. A second goal was to compare the performance of signals with constant envelope, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel QAM. In the paper, we propose a channel model which is reasonably close to the real system, and a method for performance evaluation leading to an estimate of the asymptotic power gain of the modulation systems. The channel model and the method are applied to the analysis of coded 16- and 32- PSK and QAM.     

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.     

Signal-flow-graph gain with respect to the general node of a graph

A new formula for the graph gain is given, which is more general than Mason's formula and enables the graph gain to be solved with respect to the general node of the graph that may also be the loop node.     

Modern spectral analysis techniques for blood flow velocity andspectral measurements with pulsed Doppler ultrasound

Four spectral analysis techniques were applied to pulsed Doppler ultrasonic quadrature signals to compare the relative merits of each technique for estimation of flow velocity and Doppler spectra. The four techniques were 1) the fast Fourier transform method, 2) the maximum likelihood method, 3) the Burg autoregressive algorithm, and 4) the modified covariance approach to autoregressive modeling. Both simulated signals and signals obtained from an in vitro flow system were studied. Optimal parameter values (e.g., model orders) were determined for each method, and the effects of signal-to-noise ratio and signal bandwidth were investigated. The modern spectral analysis techniques were shown to be superior to Fourier techniques in most circumstances, provided the model order was chosen appropriately. Robustness considerations tended to recommend the maximum likelihood method for both velocity and spectral estimation. Despite the restrictions of steady laminar flow, the results provide important basic information concerning the applicability of modern spectral analysis techniques to Doppler ultrasonic evaluation of arterial disease.     

LDPC-Coded Cooperation with Receive Multi-Antenna and Unknown CSI in the Destination

This paper studies a coded cooperation scheme with receive multi-antenna in the destination. A kind of simple-encoding irregular systematic low-density-parity-check (LDPC) codes is applied to the scheme. For Rayleigh block fading channels, in the unknown channel state information scenario, space-based adaptive least-mean square (LMS) transversal filters are adopted in the destination to realize receive diversity gain. The filtered signals from the source and relay are decoded by a joint “Min-Sum” iterative decoding algorithm. This algorithm agrees with the bilayer Tanner graph that can be used to fully characterize two distinct irregular systematic LDPC codes employed by the source and relay. Simulation results verify the effectiveness of the space-based adaptive LMS transversal filters in the coded cooperation scheme. Meanwhile, theoretical analysis and numerical simulation show that the proposed coded cooperation scheme can well combine cooperation diversity, multi-receive diversity and channel coding gains, and clearly outperforms the coded non-cooperation one under the same conditions.     

Key technologies for terabit/second WDM systems with high spectralefficiency of over 1 bit/s/Hz

To fully utilize a limited gain bandwidth of about 35 nm (4.4 THz) in an erbium-doped fiber amplifier, an increase in signal spectral efficiency is required. In this paper, we investigate the key technologies to achieve terabit/second wavelength-division multiplexing (WDM) systems with over 1 bit/s/Hz spectral efficiency. Optical duobinary signals, which have narrower optical spectra than conventional intensity modulation signals, were applied to such dense WDM systems. The measured minimum channel spacing for 20-Gbit/s optical duobinary signals was 32 GHz and a spectral efficiency of over 0.6 bit/s/Hz was reached. By using polarization interleave multiplexing, spectral efficiency was expected to reach 1.2 bit/s/Hz in an ideal case with no polarization dependencies along the transmission lines. In such ultradense WDM systems with narrower channel spacing, stabilizing the wavelengths of laser diodes is an important issue for achieving stable operation over long periods. To do this, we developed a simple and flexible wavelength stabilization system which uses a multiwavelength meter. The wavelengths for 116 channels with 35-GHz spacing were stabilized within ±150 MHz. The stabilization system is applicable to ultradense WDM signals with a spectral efficiency of over 1 bit/s/Hz by employing wavelength interleave multiplexing and an optical selector switch. On the basis of these investigations, we demonstrated a 2.6-Tbit/s (20 Gbit/s×132 channels) WDM transmission by using optical duobinary signals. In addition, 1.28-Tbit/s (20 Gbit/s×64 channels) WDM transmission with a high spectral efficiency of 1 bit/s/Hz was achieved by using polarization interleave multiplexing     

Taylor四相码频域旁瓣抑制数字滤波器的设计

本文分析了Taylor四相码信号的频谱结构,采用频域数字处理方法,研究了四相编码长码雷达信号距离旁瓣频域抑制滤波技术,提出一种适用于各种码长信号的旁瓣抑制滤波器(SSF)频域设计方法.并以127位Taylor四相码为例,对SSF处理的性能进行仿真分析和实验测试.当fd=0时,仿真与实测结果的主副比分别达到51dB和43dB.这表明采用这种方法所设计的T硝lor四相码信号SSF可以应用于现代雷达系统.