Authors' Reply [to "Corrections and Comments to 'Model Reduction of Discrete Linear Systems Via Frequency-Domain Balanced Structure'"]

For original paper, see N. L. Prajapathy et al., ibid, vol. 54, no. 3, pp. 682-683, (2007). Reply to the comments on model reduction technique for discrete linear time invariant systems are presented. The proposed technique is based on a conceptual view point of the controllability and observability Grammians balancing of a system in an arbitrary frequency range. It can be considered as the generalization of the Moore's (1981) balance structure approach in a specific frequency range of operation. Two modified Lyapunov equations are derived for the proposed frequency domain balancing. The transfer function of the sixth-order Cheby-shev type 1 filter is considered. The Nyquist plots for the original filter as well as the reduced-order filters based on the Moore's balanced technique and the proposed method.     

可处理不稳定线性离散系统的平衡降阶方法

针对线性定常离散系统,本文将原定义于时域的能控性矩阵、能观性矩阵推广到频域上.研究表明:对于稳定系统,频域能控、能观矩阵等于时域能控、能观矩阵;但不稳定系统有频域能控、能观矩阵而无时域能控、能观矩阵.在此基础上,从频域角度提出了平衡实现的定义并导出一种新的线性离散系统平衡降阶方法,这种方法克服了传统Moore方法不能解决不稳定系统降阶问题的缺陷.本文详细给出了通过求解离散李亚普诺夫方程来计算频域能控、能观矩阵的过程,深入讨论了通过求解离散黎卡提方程来进行系统平衡降阶的新算法.一个关于离散不稳定系统的降阶算例显示:传统Moore方法完全失效,而本文的方法可行并得到满意的降阶效果.     

Generating compact, guaranteed passive reduced-order models of 3-D RLC interconnects

As very large scale integration (VLSI) circuit speeds and density continue to increase, the need to accurately model the effects of three-dimensional (3-D) interconnects has become essential for reliable chip and system design and verification. Since such models are commonly used inside standard circuit simulators for time or frequency domain computations, it is imperative that they be kept compact without compromising accuracy, and also retain relevant physical properties of the original system, such as passivity. In this paper, we describe an approach to generate accurate, compact, and guaranteed passive models of RLC interconnects and packaging structures. The procedure is based on a partial element equivalent circuit (PEEC)-like approach to modeling the impedance of interconnect structures accounting for both the charge accumulation on the surface of conductors and the current traveling in their interior. The resulting formulation, based on nodal or mixed nodal and mesh analysis, enables the application of existing model order reduction techniques. Compactness and passivity of the model are then ensured with a two-step reduction procedure where Krylov-subspace moment-matching methods are followed by a recently proposed, nearly optimal, passive truncated balanced realization-like algorithm. The proposed approach was used for extracting passive models for several industrial examples, whose accuracy was validated both in the frequency domain as well as against measured time-domain data.     

Damped sinusoidal signals parameter estimation in frequency domain

Parameter estimation of noisy damped sinusoidal signals in the frequency domain is presented in this paper. The advantage of the frequency domain approach is having the spectral energy concentrated in frequency domain samples. However, the least squares criterion for frequency estimation using frequency domain samples is nonlinear. A low complexity three-sample estimation algorithm (TSEA) for solving the nonlinear problem is proposed. Using the TSEA for initialization, a frequency domain nonlinear least squares (FD-NLS) estimation algorithm is then proposed. In the case of white Gaussian noise, it yields maximum likelihood estimates, verified by simulation results. A time domain NLS (TD-NLS) estimation algorithm is also proposed for comparison.The Cramer-Rao lower bound (CRLB) of the frequency domain estimation algorithms is derived. The theoretical analysis shows that the FD-NLS can yield a near-optimal performance with few energy-concentrated samples. On the other hand, the TD-NLS does not have the energy concentration property and requires more time domain samples to perform satisfactory estimation. Simulation results verify that the frequency domain estimation algorithms provide better tradeoff between computational complexity and estimation accuracy than time domain algorithms.     

一种基于平衡式对数域积分器的高阶滤波器

提出了一个新的工作在甲乙类状态的平衡式对数域积分器 ,用跨导线性原理分析得到其传递函数。基于该积分器电路 ,采用无源网络模拟法设计出一个 1 d B波纹的五阶切比雪夫对数域低通滤波器。PSpice仿真结果表明 ,这种新型对数域滤波器能在低电压条件下工作 ,并具有高频、宽调谐范围和低失真等特点。     

Polynomial-Based Interpolation Filters—Part I: Filter Synthesis

This paper introduces a generalized design method for polynomial-based interpolation filters. These filters can be implemented by using a modified Farrow structure, where the fixed finite impulse response (FIR) sub-filters possess either symmetrical or anti-symmetrical impulse responses. In the proposed approach, the piecewise polynomial impulse response of the interpolation filter is optimized directly in the frequency domain using either the minimax or least mean square criterion subject to the given time domain constraints. The length of the impulse response and the degree of the approximating polynomial in polynomial intervals can be arbitrarily selected. The optimization in the frequency domain makes the proposed design scheme more suitable for various digital signal processing applications and enables one to synthesize interpolation filters for arbitrary desired and weighting functions. Most importantly, the interpolation filters can be optimized in a manner similar to that of conventional linear-phase FIR filters.     

功率变流器传导干扰多通路频域模型研究

针对功率变流器传导电磁干扰建模与预测方法展开研究,提出了多通路并联的"干扰源-耦合通路"频域模型,研究了干扰源频谱及干扰耦合通路传递函数的建模提取方法.通过提取干扰源的端口频谱特性及干扰耦合通路的传递函数,直接在频域计算干扰噪声,具有建模方法简单,通用性强,不受具体电路结构限制的特点,可作为通用的频域建模方法应用于功率变流器传导电磁干扰建模与预测研究.通过具体实例,阐述了所提出的多通路频域模型的建模流程,验证了模型的准确性及其在变流器传导干扰建模、预测与噪声抑制过程中的指导意义.     

Motion estimation in the frequency domain using fuzzy c-planesclustering

A previous work explicitly models the discontinuous motion estimation problem in the frequency domain where the motion parameters are estimated using a harmonic retrieval approach. The vertical and horizontal components of the motion are independently estimated from the locations of the peaks of respective periodogram analyses and they are paired to obtain the motion vectors using a procedure proposed by Chen, Giannakis, Nandhakumar (see IEEE Trans. Image Processing, vol.7, p.1242-56, 1998). In this paper, we present a more efficient method that replaces the motion component pairing task and hence eliminates the problems of the pairing method described by Chen et al. The method described in this paper uses the fuzzy c-planes (FCP) clustering approach to fit planes to three-dimensional (3-D) frequency domain data obtained from the peaks of the periodograms. Experimental results are provided to demonstrate the effectiveness of the proposed method.     

基于双层扇形基片集成波导的双频平衡滤波器

提出了一种表面刻有一对互补开环谐振器(CSRR)的45°扇形基片集成波导谐振腔(SSIWR),设计并制作了一款结构紧凑且具有高选择性的双层双频平衡带通滤波器.分别利用具有带通特性的CSRR和谐振腔内的TM220模实现了差模双频响应;模式间的耦合以及缺陷地结构(DGS)的引入使得滤波器在通带附近产生4个传输零点,提高了带...     

Parametric Characteristic Analysis for Generalized Frequency Response Functions of Nonlinear Systems

In order to explicitly reveal the relationship between system frequency response functions and model parameters which define system nonlinearities, and consequently unveil a direct connection from model parameters to system frequency response characteristics, a parametric characteristic analysis approach is proposed for Volterra systems described by a nonlinear differential equation (NDE). The parametric characteristics of the generalized frequency response functions (GFRFs) for the NDE model are established, and some important properties are discussed, which can explicitly reveal what model parameters contribute and how these parameters affect the GFRFs. Based on the parametric characteristic analysis, it is demonstrated how the system frequency domain characteristics are related to the system time domain model parameters and how the output frequency response function can now be determined explicitly with a detailed polynomial structure. These new results provide a significant and novel insight into the analysis and design of nonlinear systems in the frequency domain. Several examples are included to illustrate the results.     

GMP-Based Channel Estimation for Single-Carrier Transmissions over Doubly Selective Channels

We present a graph-based channel estimation approach for SC-IFDE (single-carrier transmissions with iterative frequency domain equalization) without CP (cyclic prefix) over doubly selective channels using the recently developed Gaussian message passing (GMP) technique. A direct application of the GMP updating rules in the FFG (Forney-style factor graph) of the SC-IFDE system model incurs high complexity. Approximate updating rules are therefore developed to overcome this problem. The proposed GMP-based channel estimation approach has similar complexity as the low-complexity Kalman-filtering based frequency domain channel estimation approach in the literature, but significantly outperforms the latter due to its enhanced capability in capturing the time correlation information of doubly selective channels through bidirectional processing.     

A termination scheme for high-speed pulse propagation on a systemof tightly coupled coplanar strips

A realistic termination scheme is proposed for closely coupled N-conductor microstrips. The design aims to achieve satisfactorily low signal reflection and good fabrication feasibility for the planar MMIC (Monolithic Microwave Integrated Circuit) process. The matched termination network (MTN) for a lossless three-line coupled microstrip structure is presented. High-speed pulse transmission along terminated tightly coupled microstrip lines is analyzed using modal analysis in the frequency domain. Theoretical results for the propagating and reflected waveforms are obtained by applying the inverse discrete Fourier transform (IDFT) to the system responses. These responses are obtained by applying the theory of multiconductor transmission lines to a dispersive database which has been computed using the spectral-domain approach (SDA). The response of a six-line closely coupled microstrip circuit terminated by the proposed termination scheme is measured using the HP8510B network analyzer. The measured results show that the reflected signal is below -30 dB and the results are in good agreement with the theoretical waveforms     

BALANCED TRUNCATED MODELS OF C INTERCONNECT CIRCUITS AND THEIR SIMULATION

The Balanced Truncation Method (BTM) is applied to an even distributed RC interconnect case by using Wang's closed-forms of even distributed RC interconnect models. The results show that extremely high order RC interconnect can be high-accurately approximated by only third order balanced model. Related simulations are executed in both time domain and frequency domain. The results may be applied to VLSI interconnect model reduction and design.     

利用频谱信息改善时域电磁散射算法MOO的后时振荡现象

分析了MOO算法在后时低能区产生振荡的原因,提出了一种改善MOO算法计算时域电磁散射稳定性的方法.根据时、频域响应之间存在的傅立叶变换关系,及Laguerre多项式的时频域振荡特性,通过计算少量准确的频域数据替换掉时域数据经傅立叶变换后由于级数截断而产生的振荡频谱,并利用希尔伯特变换的内插技术进行数据平滑,对修正之后的频域数据进行逆傅立叶变换得到稳定的时域数据.通过对实际目标的仿真验证了方法的有效性.     

A Novel and Fast Algorithm for Solving Permutation in Convolutive BSS,Based on Real and Imaginary Decomposition

In this paper, a new fast method for solving the permutation problem in convolutive BSS is presented. Typically, by transferring signals to the frequency domain, the convolutive BSS problem is converted to an instantaneous BSS, and deconvolution takes place in each frequency bin. However, another major problem arises which is permutation ambiguity in the frequency domain. Solving the permutation ambiguity for N sources in frequency domain needs N! comparisons between adjacent frequency bins. This drastically increases the overall computational complexity of the convolutive BSS. In our new approach, the complex-valued signals are decomposed into real and imaginary parts in each frequency bin. We show that the ideal mixing matrix has to possess a simple and symmetric structure. Accordingly, the structure can be exploited for solving the permutation ambiguity in frequency domain. Although separation in subband is accomplished by the FastICA algorithm, the proposed method requires modification of the separation algorithm, and a new structure is imposed on the mixing matrix. After that signals are separated by means of the FastICA, the permutation correction takes place only by N comparisons, decreasing the computational complexity. Comparing to five competitive methods, we experimentally demonstrate that permutation ambiguity is resolved accurately by this very fast approach while substantially decreasing the order of calculations. In terms of the separation performance and signal quality, the proposed method is superior to four of the compared methods and almost similar to the best of them.     

Frequency domain pilot multiplexing technique for channel estimation of SC-FDE

A frequency domain pilot multiplexing technique for channel estimation of single-carrier frequency domain equalisation (SC-FDE) is proposed. The proposed scheme selects pilot positions to minimise the pre-imposed distortion caused by the loss of useful data tones. The corresponding receiver structure is also presented, where the pilot positions are blindly detected and the distorted data symbols are iteratively reconstructed. Simulation results show that the proposed system approaches the lower bound of SC-FDE.     

SEDP‐based detection of low‐rate DoS attacks

Low‐rate Denial of Service (LDoS) is a new type of TCP‐targeted attacks, which attempt to deny bandwidth to TCP flows while sending at sufficiently low‐average rate to elude detection of DoS defense system. Therefore, LDoS attacks are difficult to be detected by routers and counter‐DoS mechanisms. In this paper, an approach of detecting LDoS attacks is proposed by using the technology of signal processing based on the model of spectral energy distribution probability. The proposed approach calculates variances between the incoming traffic of normal TCP and attack flows to a server by using packet sampling sequence within a certain period. The network traffic is converted from the time domain to the frequency domain forming a spectral signal, and the distribution probability of spectral energy is estimated based on spectrum characteristics of rectangular pulses. This approach explores that the energy of LDoS attacks is mostly distributed in the main lobe width while that of normal TCP traffic is just concentrated near zero in frequency domain. Both the spectral energy of normal TCP traffic and LDoS attacks distributed in main lobe are calculated, and an energy threshold is set as decision value based on statistical results according to energy distribution properties. The existence of LDoS attacks is determined and detected by comparing calculated variances with the preset decision threshold value. Tests on the detection performance of the proposed approach were performed in NS‐2 simulation environment, and detection rate was obtained by Hypothesis test. Experiment results show that the proposed approach has higher detection accuracy and less computation consuming. Copyright © 2014 John Wiley & Sons, Ltd.     

基于抽取技术的二维密集频率估计方法

本文研究了有色噪声背景下的密集频率估计问题,提出了一种采用二维抽取技术估计密集频率的新方法.利用时域抽取增加频率间隔的能力,基于二维谐波信号模型,本方法对二维密集频率进行了有效的分离,并利用改进的二维矩阵束方法对分离后的二维密集频率进行了准确的估计.本文所提出的方法简单易行,解决了现有二维频率估计方法对密集频率估计失效的问题.仿真结果验证了本方法的有效性.     

An efficient two-step approach to integer frequency offset detection for OFDM systems

An efficient preamble structure for OFDM systems is proposed which inserts a short embedded repetition pattern (SERP) into conventional preamble structures allowing a two-step detection of the integer frequency offset (IFO). A coarse estimate of the IFO using the SERP is performed in the time domain prior to performing fine IFO detection in the frequency domain based on the original preamble structure. The complexity of the overall IFO detection procedure can be significantly reduced at a price of slight loss in SNR.     

单载波宽带MIMO系统广义近似消息传递Turbo频域均衡

针对编码单载波循环前缀(SC-CP)多输入多输出(MIMO)系统,该文采用消息传递算法研究软输入软输出MIMO频域均衡器(FDE)的设计问题。基于广义近似消息传递(GAMP)算法,该文提出一种新的低复杂度MIMO频域均衡方法。这种消息传递MIMO均衡方法的显著特点是既保留了SC-CP传输所产生的频域均衡的优点,同时又避免了传统MIMO FDE中逐频点MIMO矩阵求逆运算,所以具有随MIMO系统接收天线数增加而线性增长的计算复杂度。计算机仿真结果表明,与传统方案相比,该文提出的MIMO频域均衡算法具有明显的误码率(BER)性能优势。