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International standard bodies have specified an instrument capable of detecting and assessing the severity of lighting flicker, which is called a flickermeter. However, a deficiency with regard to flicker caused by high-frequency interharmonics has been reported in the recent literature. In this paper, another deficiency of the International Electrotechnical Commission (IEC) flickermeter with regard to low-frequency interharmonics, whose frequencies are below the difference between the fundamental frequency and the cutoff frequency of a bandpass filter of the IEC standard flickermeter, will be discussed and illustrated based on analysis and numerical experiments. A new approach based on down-up sampling in the discrete-time sample domain is also proposed to address the flicker-detection problem associated with interharmonics. We demonstrate the efficacy of the proposed method by a comparison with the current flickermeter standard in the presence of interharmonics. [ABSTRACT FROM AUTHOR]

This paper develops a signal processing, time-frequency analysis-based analytic solution to locate transient capacitor switching disturbances. The flow of transient disturbance energy caused by the capacitor switching is determined by the time and frequency localized phase difference. Cross time-frequency analysis provides time- and frequency-localized phase difference between the transient voltage and current disturbance waveforms which determine the direction of transient disturbance energy flow. The time and frequency localization properties of the proposed scheme allows one to expand the application to complicated power distribution systems without knowledge of system parameters, capacitor size, and configuration. The proposed scheme has been verified by the Electromagnetic Transients Program simulation for all possible spatial locations of the capacitor switching. [ABSTRACT FROM AUTHOR]

For reasonable power quality assessment of transient disturbances in electric power systems, new transient power quality indices are developed based on a signal processing technique, time-frequency analysis. Based on the time-frequency distribution of a transient disturbance, a set of time-frequency based power quality indices are developed. In this paper, the instantaneous disturbance energy ratio, normalized instantaneous disturbance energy ratio, instantaneous frequency, and instantaneous K-factor are suggested for transient power quality assessment. Time-frequency based power quality indices allow one to quantify the effects of transient disturbances with high-resolution and accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new high-resolution reflectometry technique that operates simultaneously in both the time and frequency domains. The approach rests upon time-frequency signal analysis and utilizes a chirp signal multiplied by a Gaussian time envelope. The Gaussian envelope provides time localization, while the chirp allows one to excite the system under test with a swept sinewave covering a frequency band of interest. This latter capability is of particular interest when testing communication cables and systems. Sensitivity in detecting the reflected signal is provided by a time-frequency cross-correlation function. The approach is verified by experimentally locating various types of faults, located at various distances, in RG 142 and RG 400 coaxial cables. [ABSTRACT FROM AUTHOR]

In conventional discrete multitone (DMT) systems, a multitap time-domain equalizer (TEQ) is used to shorten the channel length, so that the bandwidth efficiency reduction due to cyclic extension is relieved. The TEQ, however, tends to introduce spectral nulls which degrade the achievable signal-to-noise ratio at corresponding subchannels, thereby decreasing the bandwidth efficiency. Furthermore, computationally expensive joint TEQ initialization and optimal delay (introduced by TEQ) selection is necessary. In this paper, a novel subsymbol-equalization scheme is proposed, and is based on the observation that the high-bit-rate twisted-pair channels rarely contain a zero that is close to the unit circle. Although a delay of a fraction of a DMT symbol period is introduced, the proposed subsymbol-equalization scheme eliminates the necessity of both the channel shortening at the receiver and the cyclic extension at the transmitter. Simulation results demonstrate the computational efficiency (no TEQ) and the bandwidth efficiency of the proposed subsymbol-equalization scheme. [ABSTRACT FROM AUTHOR]

Recently, ultra wide-band (UWB) wireless communication technology, which provides high data transmission rates and is capable of linearly trading off between throughput and signal-to-noise ratio (SNR), has drawn much attention for short-range wireless networks. To fully exploit its desirable features and to minimize its interference with coexisting other systems requires knowledge of the SNRs at the receivers. In this paper, we propose an algorithm for estimating the pulse energy-to-noise ratio of an UWB signal through utilization of output samples from a correlator in the receiver and evaluate the performance of the proposed algorithm through computer simulation. A notable feature of the proposed algorithm is that it does not affect the effective throughput because the estimation process does not require any additional specific training signals. [ABSTRACT FROM AUTHOR]

This paper addresses a Volterra series representation of bilinear (or quadratic) time-frequency distributions that belong to Cohen's class, whereby the analogy of the bilinear class with a second-order double Volterra series is utilized. In addition, a different viewpoint for the bilinear kernel and a complementary interpretation concerning the quadratic time-frequency distributions are provided. [ABSTRACT FROM AUTHOR]

Presents the use of rule-based method and hidden Markov model (HMM) in classifying the power distribution line disturbances. Function of the rule-based method and HMM; Classification on the types of actual recorded power distribution disturbances by the methods; Classification rate of the methods for actual disturbance events tested.

Derives a fifth-order Volterra kernel estimation algorithm for a bandpass nonlinear system. Characteristics of circularly symmetric zero-mean complex-valued Gaussian random variable; Details on the modified Volterra kernel estimation algorithm for Phase Shift Keying; Simulation result and conclusion.

Part II. Details the construction of a wavelet-based neural classifier and an evaluation of its ability to recognize actual power quality disturbance data from several distribution feeders. Disturbance data set; Use of the voting scheme and the Dempster-Shafer theory of evidence in combining outputs of the multiple neural networks.

Part I. Applies advances in wavelet transformers, artificial neural networks, and the mathematical theory of evidence to the problem of automatic power quality disturbance waveform recognition. Pattern recognition for disturbance waveforms; Wavelet-based neural classifier; Learning vector quantization.

Presents a Volterra-based predistorter based on the indirect learning architecture. Categories of nonlinear compensators; Third-order Volterra series for a causal and finite-memory system; Simplified base band satellite telecommunication channel.

Presents a fast algorithm to compute the time-domain output of a third-order Volterra filter using fewer computational operations than the conventional time-domain multidimensional convolution approach. Input and output of higher order filters; Sectioning of input and output sequences in order to ensure the time-domain output corresponds to linear convolution.

Responds to comments on an article appearing in the January 2000 issue of 'IEEE Transactions on Power Delivery,' which dealt with recognition of power quality disturbance waveforms using wavelet-based neural classifiers. Implementation of multiresolution decomposition technique; Selection of a dyadic-orthonormal mother wavelet.

Responds to comments on an article appearing in the January 2000 issue of 'IEEE Transactions on Power Delivery,' which dealt with recognition of power quality disturbance waveforms using neural classifier. Failure to compare accuracy and productivity of proposed classifier on a large scale basis; Duration of impulsive transients.

We analyze the effect of time-selective fading on the information outage probability and diversity order of Alamouti transmit diversity with joint maximum likelihood, symbolwise linear maximum likelihood, zero forcing, and decision feedback detectors. In contrast to the existing bit error rate (BER) and bit error outage (BEO) analyses, we evaluate the information outage probabilities and corresponding asymptotic diversity orders for each detector. From the theoretical and simulation results, we demonstrate that, when the channel is time selective, the asymptotic diversity orders for the four detectors approach two, zero, one, and one, respectively. [ABSTRACT FROM AUTHOR]

By combining multiple-input-multiple-output (MIMO) communication with block transmission using a cyclic prefix (CP), MIMO block transmission systems can not only achieve high data rates but also simplify channel estimation and equalization. In this paper, to provide a bandwidth-efficient solution for channel estimation in MIMO block transmission systems with a CP, we present a framework for blind channel estimation based on a general non-redundant precoding. Using this framework, we propose a blind estimator exploiting a simplified non-redundant precoding that is robust against overestimates of a true MIMO channel order. Furthermore, in the case with the number of transmit antennas greater than that of receive antennas, we show under specific system conditions that the pro- posed blind algorithms can be used for estimation of the MIMO channel without oversampling the received signals. With the simplified precoding conditions established in this paper, the proposed method does not impose the strict identifiability conditions on the MIMO channel, which are required for the existing methods. Furthermore the proposed estimator achieves accurate channel estimation with a small number of symbol blocks. In addition, we derive a simplified precoder that is optimized in the sense of minimizing the impact of unknown additive noise. We discuss the tradeoff between channel estimation accuracy and bit error rate performance associated with the simplified precoder. Finally, we develop a technique for resolving the channel ambiguity in the proposed blind estimator to create a semi-blind channel estimator relying on only a few known symbols. [ABSTRACT FROM AUTHOR]

By combining multiple-input multiple-output (MIMO) communication with the orthogonal frequency division multiplexing (OFDM) modulation scheme, MIMO-OFDM systems can achieve high data rates over broadband wireless channels. In this paper, to provide a bandwidth-efficient solution for MIMO-OFDM channel estimation, we establish conditions for channel identifiability and present a blind channel estimation technique based on a subspace approach. The proposed method unifies and generalizes the existing subspace-based methods for blind channel estimation in single-input single-output OFDM systems to blind channel estimation for two different MIMO-OFDM systems distinguished according to the number of transmit and receive antennas. In particular, the proposed method obtains accurate channel estimation and fast convergence with insensitivity to overestimates of the true channel order. If virtual carriers (VCs) are available, the proposed method can work with no or insufficient cyclic prefix (CP), thereby potentially increasing channel utilization. Furthermore, it is shown under specific system conditions that the proposed method can be applied to MIMO-OFDM systems without CPs, regardless of the presence of VCs, and obtains an accurate channel estimate with a small number of OFDM symbols. Thus, this method improves the transmission bandwidth efficiency. Simulation results illustrate the mean-square error performance of the proposed method via numerical experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a new switched MIMO system where the MIMO includes both diversity-based MIMO and spatial multiplexing MIMO (SM-MIMO). The proposed scheme is a closed-loop system where the feedback bits are sent back to the transmitter to indicate the channel quality. The switching operation is employed among groups of a certain number of transmit antennas. For diversity-based MIMO systems, the switching operation aims to improve the link performance, while the goal of the switching for the SM-MIMO systems is to increase the data rate. The authors analyze and optimize the proposed systems and show that there is considerable benefit in terms of performance and practical use. [ABSTRACT FROM AUTHOR]

In theory, polyspectra can be applied to solve many important problems in signal processing and data analysis. In practice, however, one has been discouraged by the poor statistical properties of most polyspectral estimators. In this paper, we extend Thomson''s original multitaper power (and bispectral) estimator to polyspectra of arbitrary order, and to any orthonormal family of tapers. The multitaper polyspectral estimators we derive have favorable statistical properties, and they are well suited for the analysis of short data segments. We derive useful expressions for the first and second moments of the estimator. It is shown that a quantity we call the total polyspectral window is the core quantity for describing and understanding the statistical properties of the proposed estimators. Leakage can be a dominant effect in polyspectral estimation. We thus extend Thomson''s adaptive power spectral leakage reduction scheme, to polyspectral estimators of arbitrary order. Based on an extensive Monte Carlo simulation of the bispectrum for four different stochastic processes (one Gaussian, and three non-Gaussian), we conduct a comparison between four conventional bispectral estimators and two multitaper bispectral estimators. Our simulations show that the estimator of choice is the adaptive multitaper polyspectral estimator using discrete prolate spheroidal sequences. Finally, we apply the estimators to Volterra model system identification based on a real data set from an offshore platform experiment. The system identification requires polyspectra up to and including order four, and we show that the adaptive multitaper polyspectral estimator outperforms the conventional estimators with respect to modeling accuracy. [Copyright &y& Elsevier]

This paper develops a new large-signal transient load model to represent the composite power electronic load at a network bus. Traditional load models do not account for the transient responses of power electronic loads which occur at the onset and clearing of voltage sags. The new model is supported with actual utility fault response data and laboratory controlled tests. This paper shows that power electronic loads have a unique impact on generator rotor angle swings compared to those using conventional load models. [ABSTRACT FROM AUTHOR]

Space-time block codes (STBCs) from coordinate interleaved orthogonal designs (CIODs) offer several advantages including full-diversity and single-symbol decodability. In an effort to assess their performance in quasi-static frequency- nonselective i.i.d, Nakagami-m fading channels, we analyze the error rate, outage capacity, and information outage probability. First, based on an accurate closed-form formula for the average symbol pairwise error rate (SPER). we derive tight union upper and lower bounds on the symbol-error rate (SER). Second, we apply Gaussian and Gamma approximations to provide closed- form expressions for the outage capacity. Third, using high signal-to-noise ratio (SNR) and moment-matching approximation techniques, we also derive accurate closed-form approximations for the information outage probability (IP). Finally, we show that STBCs from CIODs provide fall-diversity by deriving SER-based and IOP-based asymptotic and instantaneous diversity orders, Monte-Carlo simulations show that the analytical results agree with simulation experiments. [ABSTRACT FROM AUTHOR]

In this paper, the effects of visual feedback and aging on postural sway systems and signals are investigated by analyzing the transient phase difference between "input" and "output" which correspond to center of pressure (COP) and center of mass (COM), respectively. In order to analyze the transient phase difference characteristics of COP and COM, a relatively new cross time-frequency analysis technique that provides time- and frequency-localized phase difference information is utilized. The feedback control process in the postural sway is interpreted in terms of a feedback compensator which is characterized in terms of a phase difference. Using the experimental results of the transient phase difference obtained from the cross time-frequency distribution, it is demonstrated that the postural control of young person are more stable and rely more on visual sensory feed- back to stabilize postural control compared to that of the elderly persons. [ABSTRACT FROM AUTHOR]

The influence of damage on the performance of the lifting surface of an aircraft has been an area of interest to the military for over half a century. Some of the earlier studies of this subject focused on the impact that structural damage resulting in the loss of lifting surface structural strength, stiffness, and mass might have on imparting catastrophic aeroelastic failures to the lifting surface. Discouraging mixed results arose over the next 30 years in these investigations that employed only structural damage models. As time passed, it was finally noticed that if the often neglected, usually second-order, drag term was now included (as aerodynamic damage often creates a high, unsteady, localized drag rise) in the earlier aeroelastic damaged-wing analyses, more encouraging results were obtained. That is, the realistic asymmetric damaged lifting surfaces flutter and divergence analysis did show lowered, and not raised, flutter and divergence speeds over that of the undamaged lifting surface. This occurred both in the presence of or in the absence of structural damage as in the case of icing or external wing stores. In essence, it was determined at this time that the resulting high and unsteady drag rise caused by the damage could do more than just cause an energy deficiency in the aircraft mission. It could, in fact, cause shorter term catastrophic or stiffness failure events in terms of reduced flutter and divergence speeds as well as give rise to limit cycle oscillations embedded within what was shown to be that part of the damaged-aircraft flight envelope free from classic flutter and divergence. The present experimental wind-tunnel study was carried out to confirm these past theoretical findings by employing a one-twelfth-scale F-111 aeroelastic model and (third-order) higher-order statistical signal processing to identify the frequency ordering that occurs in these additional damaged-induced limit cycle oscillations. These limit cycle oscillations were also found to exhibit the classic lock-in/lock-out phenomenon that occurs in the well-known F/A-16 and F/A-18 wing store induced limit cycle oscillations. [ABSTRACT FROM AUTHOR]