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Sampling technique allowing exclusion of antialiasing filter

ELECTRONICS LETTERS 2000年第4期36卷 297-298页

作者： Poberezhskiy, Y Poberezhskiy, G Datron World Commun Inc San Diego CA 92103 USA SiRF Technol Inc Los Angeles CA 90045 USA

It is shown that antialiasing filtering can be performed by a multichannel sample-and-hold amplifier with weighted integration, and a conventional antialiasing filter can be excluded when the weight function and number of channels are properly selected. This makes analogue-to-digital conversion less expensive and adaptable to Various conditions.

关键词： signal sampling ADC filtering theory filtering methods in signal processing sample and hold circuits multichannel sample/hold amplifier weight function weighted integration analogue-to-digital conversion analogue-digital conversion antialiasing filtering A/D and D/A convertors

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Directional diversity of HF signals received over high latitude paths, and the possibility of improved data throughput by means of spatial filtering

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IEE PROCEEDINGS-MICROWAVES ANTENNAS AND PROPAGATION 2000年第6期147卷 487-494页

作者： Warrington, EM Jackson, CA Lundborg, B Univ Leicester Dept Engn Leicester LE1 7RH Leics England Def Res Estab S-58111 Linkoping Sweden

The high latitude ionosphere is a dynamic propagation medium in which HF radio signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and in elevation. Furthermore, ionospheric movements at the reflection points impose Doppler shifts and Doppler spreads onto the signals. Large Doppler spreads and multipath propagation in which the delay spread is large are particularly prevalent at these northerly latitudes and can result in a significant degradation in the performance of digital communication systems. This investigation suggests that the application of spatial filtering from simple antenna arrays comprising pairs or triplets of antennas can significantly reduce the level of apparent Doppler spreading, frequently to levels at which modern, high speed modems are expected to operate satisfactorily. The investigation concentrated on Doppler spread since this was the most significant factor in the data employed in this study: however, it is noted that reductions in effective multipath delay spread are also possible.

关键词： array signal processing Antenna arrays spatial filtering delays Doppler shift diversity reception data communication ionospheric electromagnetic wave propagation modems filtering methods in signal processing Modems HF radio propagation data throughput Doppler shifts multipath propagation high latitude ionosphere Radiowave propagation high latitude paths digital communication systems antenna arrays Doppler spreads ionospheric disturbances high speed modems reflection points HF radio signals multipath delay spread reduction filtering theory ionospheric movements multipath channels spatial filters directional diversity Radio links and equipment delay spread

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Time-varying filtering of speech signals using linear prediction

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ELECTRONICS LETTERS 2000年第8期36卷 763-764页

作者： Stankovic, S Tilp, J Darmstadt Univ Technol Inst Commun Technol Darmstadt Germany

Time-varying filtering of noisy speech signals based on linear prediction (LP) is presented. The approach is rested on noisy speech signals apparent in hands-free telephone systems.

关键词： time-varying filters interference suppression Speech processing techniques filtering theory noisy speech signals filtering methods in signal processing prediction theory linear prediction Speech and audio signal processing hands-free telephone systems time-varying filtering signal processing theory speech enhancement

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Quantifying the convergence speed of LMS adaptive FIR filter with autoregressive inputs

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ELECTRONICS LETTERS 2000年第6期36卷 585-586页

作者： Homer, J Univ Queensland Dept Elect Engn & Comp Sci Brisbane Qld 4071 Australia

In general the least mean squares adaptive finite impulse response (FIR) filter converges more slowly with an increase in filter length and input signal correlation level. An explicit expression is presented relating the convergence speed of this adaptive filter to the FIR filter length and the correlation characteristics of autoregressive (AR) modelled input signals. The expression provides a simple means for justifying (or not) the cost of input signal whitening techniques within for example acoustic echo cancellation, in which very large FIR filter lengths and highly correlated AR modelled speech input signals occur.

关键词： LMS adaptive FIR filter digital filters Interpolation and function approximation (numerical analysis) autoregressive processes signal processing theory filtering theory filter length input signal correlation level correlation characteristics Digital filters finite impulse response filter echo suppression correlation theory FIR filters least mean squares type acoustic echo cancellation convergence speed convergence of numerical methods AR modelled input signals filtering methods in signal processing input signal whitening techniques adaptive filters autoregressive inputs least mean squares methods

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Convergence performance of adaptive lattice filters with nonlinear parameter updates

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IEE PROCEEDINGS-VISION IMAGE AND signal processing 2000年第3期147卷 238-246页

作者： Kumura, T Iiguni, Y Maeda, H Osaka Univ Grad Sch Engn Dept Commun Engn Suita Osaka 5650871 Japan

The convergence properties of adaptive lattice filters with nonlinear parameter updates have been analysed. The theoretical expressions for the con convergence rate and the asymptotic error variance of the PARCOR coefficient are derived. Using these expressions, the convergence performance in the absence of impulsive noise is investigated and compared with those of the linear-type and sign-type adaptive lattice filters. Furthermore, the mean parameter variation caused by an impulsive noise and the parameter recovery time are evaluated to comprehensively compare the convergence performances in the presence of impulsive noise.

关键词： adaptive filters Error analysis in numerical methods adaptive signal processing convergence properties impulsive noise transversal filter structure network parameters correlation methods impulse noise LMS algorithm sign-type adaptive lattice filters error analysis least mean square algorithm parameter recovery time filtering methods in signal processing partial correlation convergence performance nonlinear parameter updates mean parameter variation filtering theory convergence of numerical methods PARCOR coefficient lattice filters linear-type adaptive lattice filters asymptotic error variance signal processing theory convergence rate

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Explicit formulas for coefficients of maximally flat FIR low/highpass digital filters

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ELECTRONICS LETTERS 2000年第23期36卷 1918-1919页

作者： Khan, IR Ohba, R Hokkaido Univ Grad Sch Engn Div Appl Phys Sapporo Hokkaido 0608628 Japan

New designs of general low/high pass MAXFLAT filters are derived from an available design or halfband lowpass MAXFLAT filters, using a new relationship developed between the tap coefficients of general and halfband lowpass filters. The presented designs have explicit tap-coefficients formulas, are extremely simple and exactly meet the desired cutoff frequency.

关键词： high-pass filters explicit tap-coefficients formulas filtering theory FIR lowpass digital filters FIR highpass digital filters halfband lowpass filters filtering methods in signal processing cutoff frequency FIR filters Digital filters digital filters filter tap coefficients filter design maximally flat FIR filters signal processing theory low-pass filters

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Factorisation for subclass of symmetric-antisymmetric multifilter banks and its application to image coding

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ELECTRONICS LETTERS 2000年第6期36卷 516-518页

作者： Gao, XQ Gan, L Zou, CR Southeast Univ Dept Radio Engn Nanjing 210096 Peoples R China

A complete and minimal factorisation is proposed for an important subclass of symmetric-antisymmetric multiwavelet filter banks (SAMFBs). Based on this factorisation, optimal SAMFBs are designed for image coding under an optimisation criterion. Experimental results show that the SAMFBs significantly outperform the traditional 9-7 wavelet in terms of coding efficiency, especially for hard-to-compress images.

关键词： optimisation symmetric-antisymmetric multifilter banks coding efficiency filtering theory Image and video coding data compression hard-to-compress images filtering methods in signal processing Optimisation techniques optimisation criterion image coding minimal factorisation zerotree image coder multiwavelet filter banks signal processing theory image coding application Computer vision and image processing techniques

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Adaptive fault detection in real-time GPS positioning

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IEE PROCEEDINGS-RADAR SONAR AND NAVIGATION 2000年第5期147卷 254-258页

作者： Jang, CW Juang, JC Kung, FC Natl Cheng Kung Univ Dept Elect Engn Tainan 70101 Taiwan

The paper presents an adaptive scheme of a GPS (Global Positioning System) Kalman filter. The adaptive scheme is capable of estimating the covariance in response to the changing dynamics in GPS navigation. When augmenting a Kalman filter, the adaptive scheme may lead to a more accurate position update. Moreover, the estimation method can also be used in integrity monitoring to enhance the selection of threshold for fault erection. The proposed method is verified using simulated data.

关键词： adaptive estimation integrity monitoring fault detection position update Radionavigation and direction finding covariance Kalman filter real-time systems Global Positioning System adaptive scheme covariance matrices Other topics in statistics adaptive Kalman filters estimation method filtering methods in signal processing adaptive fault detection real-time GPS positioning Satellite communication systems

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Colour filtering using local density information

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ELECTRONICS LETTERS 2000年第18期36卷 1530-1531页

作者： Fotinos, A Fotopoulos, S Zigouris, E Univ Patras Elect Lab Patras 26110 Greece

A multichannel filtering technique is proposed based on local density estimation. The window data are ordered according to their distance from that of the maximum density, and the samples to be averaged are selected u... 详细信息

关键词： image processing estimation theory Optical, image and video signal processing filtering theory filtering methods in signal processing Computer vision and image processing techniques Fisher discriminant criterion multichannel filtering technique window data ordering colour filtering signal processing theory vector ordering technique local density estimation colour local density information

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Efficient non-intrusive divergence detection techniques in an in-service non-intrusive measurement device

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ELECTRONICS LETTERS 2000年第23期36卷 1980-1981页

作者： Ng, WP Elmirghani, JMH Broom, S Univ Wales Swansea Dept Elect & Elect Engn Swansea SA2 8PP W Glam Wales BT Labs BT Network & Syst Ipswich IP5 3RE Suffolk England

Efficient non-intrusive techniques that minimise divergence and enable optimal echo path modelling of noise-impaired speech telephony circuits are proposed. Original simulation results show a modelling misadjustment improvement of 28dB at an echo-to-noise ratio of 0dB over Is adaptation using conventional realtime least-mean-square digital adaptive filter systems.

关键词： Electromagnetic compatibility and interference optimal echo path modelling digital filters Interpolation and function approximation (numerical analysis) Telephony modelling misadjustment improvement real-time LMS adaptive filter systems in-service nonintrusive measurement device adaptive system identification noise-impaired speech telephony circuits nonintrusive divergence detection techniques echo suppression identification four-wire digital trunk echo speech intelligibility echo-to-noise ratio filtering methods in signal processing adaptive filters telephone interference least-mean-square digital adaptive filter least mean squares methods

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