Showing papers on "Quadrature mirror filter published in 1995"

An analog integrated polyphase filter for a high performance low-IF receiver

Abstract: An analog integrated asymmetric polyphase filter is a key building block for the development of a high performance fully integrated low-IF receiver. The asymmetric polyphase filter makes it possible to suppress the mirror signal not at HF, but after quadrature demodulation at a low IF. The most important parameters for the polyphase filter are a high dynamic range and a good mirror signal suppression. This paper reports on the realisation in a 1.2 /spl mu/m CMOS process of a 5th order Butterworth polyphase filter with a bandwidth of 220 kHz centered around 250 kHz. Its measured mirror signal suppression is 64 dB. The active-RC implementation renders a 94.2 dB dynamic range at the input.

Image coding using wavelet transforms and entropy-constrained trellis-coded quantization

Abstract: The discrete wavelet transform has recently emerged as a powerful technique for decomposing images into various multi-resolution approximations. Multi-resolution decomposition schemes have proven to be very effective for high-quality, low bit-rate image coding. In this work, we investigate the use of entropy-constrained trellis-coded quantization (ECTCQ) for encoding the wavelet coefficients of both monochrome and color images. ECTCQ is known as an effective scheme for quantizing memoryless sources with low to moderate complexity, The ECTCQ approach to data compression has led to some of the most effective source codes found to date for memoryless sources. Performance comparisons are made using the classical quadrature mirror filter bank of Johnston and nine-tap spline filters that were built from biorthogonal wavelet bases. We conclude that the encoded images obtained from the system employing nine-tap spline filters are marginally superior although at the expense of additional computational burden. Excellent peak-signal-to-noise ratios are obtained for encoding monochrome and color versions of the 512/spl times/512 "Lenna" image. Comparisons with other results from the literature reveal that the proposed wavelet coder is quite competitive. >

MDFT filter banks with perfect reconstruction

Abstract: The Modified DFT (MDFT) polyphase filter bank has been introduced. It has been shown that this filter bank is able to cancel adjacent channel alias spectra resulting in almost perfect reconstruction. Compared to cosine modulated filter banks, the MDFT filter bank offers advantages such as linear phase analysis and synthesis filters, complex valued signal processing with a different mapping into the subbands and low propagation delays. In this paper, it is shown that the MDFT filter bank structure provides a cancellation of all odd alias spectra. Furthermore, it is demonstrated that even perfect reconstruction can be obtained by an appropriate filter design.

Daubechies wavelets and Mathematica

Abstract: Analysis of time series data using wavelets provides both scale (frequency) and position information. In contrast, the Fourier transform provides frequency information only. We discuss the Daubechies formulation of wavelets, with reference to the WaveletTransform package that calculates the filter coefficients for any Daubechies basis to arbitrary precision. Examples of the wavelet transform applied to selected time series are presented to highlight the advantages of wavelets. We indicate an application of wavelets to sampled Barkhausen noise, a nonlinear phenomenon encountered in magnetic systems. The elements of the WaveletTransform package are discussed, with the emphasis being on the calculation of filter coefficients and their application to the discrete wavelet transform (DWT) and its inverse. With the construction of quadrature mirror filters, an efficient implementation of the DWT is possible and is similar in structure to the fast Fourier transform algorithm. © 1995 American Institute of Physics.

Efficient digital quadrature demodulator

Abstract: A digital quadrature demodulator for an intermediate frequency (IF) input signal with an analog-to-digital (A/D) converter having a sampling frequency fs and an input to which the IF input signal is applied where the IF input signal has a bandwith B

Optimization of filter banks using cyclostationary spectral analysis

Abstract: Generally, the output of a filter bank for a stationary input signal is not stationary but cyclostationary. In this paper, by using cyclostationary spectral analysis, the spectral correlation density of this output is derived. Using this result we derive a criterion to construct an optimal 2-band perfect reconstruction filter bank which minimizes the averaged mean squared reconstruction error when the high pass band signal is dropped. By adding constrains to the filter coefficients, the biorthogonal filter bank, the conjugate quadrature filter bank and the biorthogonal linear phase filter bank are respectively obtained. Some numerical results are also presented for optimal biorthogonal and PR linear phase filter banks which are compared in terms of some performance measures.

Factorization approach to unitary time-varying filter bank trees and wavelets

Abstract: A complete factorization of all optimal (in terms of quick transition) time-varying FIR unitary filter bank tree topologies is obtained. This has applications in adaptive subband coding, tiling of the time-frequency plane and the construction of orthonormal wavelet and wavelet packet bases for the half-line and interval. For an M-channel filter bank the factorization allows one to construct entry/exit filters that allow the filter bank to be used on finite signals without distortion at the boundaries. One of the advantages of the approach is that an efficient implementation algorithm comes with the factorization. The factorization can be used to generate filter bank tree-structures where the tree topology changes over time. Explicit formulas for the transition filters are obtained for arbitrary tree transitions. The results hold for tree structures where filter banks with any number of channels or filters of any length are used. Time-varying wavelet and wavelet packet bases are also constructed using these filter bank structures. the present construction of wavelets is unique in several ways: 1) the number of entry/exit functions is equal to the number of entry/exit filters of the corresponding filter bank; 2) these functions are defined as linear combinations of the scaling functions-other methods involve infinite product constructions; 3) the functions are trivially as regular as the wavelet bases from which they are constructed. >

Image encoding with triangulation wavelets

Abstract: We demonstrate some wavelet-based image processing applications of a class of simplicial grids arising in finite element computations and computer graphics. The cells of a triangular grid form the set of leaves of a binary tree and the nodes of a directed graph consisting of a single cycle. The leaf cycle of a uniform grid forms a pattern for pixel image scanning and for coherent computation of coefficients of splines and wavelets. A simple form of image encoding is accomplished with a 1D quadrature mirror filter whose coefficients represent an expansion of the image in terms of 2D Haar wavelets with triangular support. A combination the leaf cycle and an inherent quadtree structure allow efficient neighbor finding, grid refinement, tree pruning and storage. Pruning of the simplex tree yields a partially compressed image which requires no decoding, but rather may be rendered as a shaded triangulation. This structure and its generalization to n-dimensions form a convenient setting for wavelet analysis and computations based on simplicial grids.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Digitized quadrature modulator

Abstract: A digitized quadrature modulator receives an I-channel input digital signal and Q-channel input digital signal, and quadrature modulater the I-channel and Q-channel input digital signals by digital signal processing. The modulator has a digital filter (504) for shaping the spectrum of the I-channel and Q-channel input digital signals to provide I-channel and Q-channel output signals. The output signals have a predetermined phase shift between the I-channel and the Q-channel so as to compensate a phase difference based upon the quadrature modulation by the digital signal processing. Complementers (505a, 505b) for taking the complement of the I-channel and Q-channel output signals to provide I-channel and Q-channel complement signals. A multiplexer (505c) multiplexer the I-channel and Q-channel output signals from the digital filter and the I-channel and Q-channel complement signals from the complementers to provide a quadrature modulated output signal.

Image Encoding with Triangulation Wavelets

Abstract: We demonstrate some wavelet-based image processing applications of a class of simplicial grids arising in finite element computations and computer graphics. The cells of a triangular grid form the set of leaves of a binary tree and the nodes of a directed graph consisting of a single cycle. The leaf cycle of a uniform grid forms a pattern for pixel image scanning and for coherent computation of coefficients of splines and wavelets. A simple form of image encoding is accomplished with a one dimensional quadrature mirror filter whose coefficients represent an expansion of the image in terms of two dimensional Haar wavelets with triangular support. A combination the leaf cycle and an inherent quadtree structure allow efficient neighbor finding, grid refinement, tree pruning and storage. Pruning of the simplex tree yields a partially compressed image which requires no decoding, but rather may be rendered as a shaded triangulation. This structure and its generalization to n-dimensions form a convenient setting for wavelet analysis and computations based on simplicial grids. keywords: wavelets, image encoding, image compression, image scanning, filtering, triangulation, binary trees.

More results on orthogonal wavelets with optimum time-frequency resolution

Abstract: Signal decomposition techniques are an important tool for analyzing nonstationary signals. The proper selection of time-frequency basis functions for the decomposition is essential to a variety of signal processing applications. The discrete wavelet transform (DWT) is increasingly being used for signal analysis, but not until recently has attention been paid to the time-frequency resolution property of wavelets. This paper describes additional results on our procedure to design wavelets with better time-frequency resolution. In particular, our optimal duration-bandwidth product wavelets (ODBW) have better duration-bandwidth product, as a function of wavelet-defining filter length N, than Daubechies' minimum phase and least- asymmetric wavelets, and Dorize and Villemoes' optimum wavelets over the range N equals 8 to 64. Some examples and comparisons with these traditional wavelets are presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Synthesis of extremal wavelet-generating filters using Gaussian quadrature

Abstract: Orthogonal wavelets can be generated from finite impulse response quadrature mirror filters; these filters are also used in perfect reconstruction filter banks. This paper addresses the problem of efficiently synthesizing such filters. A class of extremal filters is defined by the property that their magnitude spectrum maximizes an integral criterion. It is found that these filters are characterized by their zeros on the unit circle, which frequently can be obtained from a set of orthogonal polynomials. A family of filters is constructed that minimize the subband aliasing energy and can generate wavelets with an arbitrary number of vanishing moments. The algorithm for generating these filters makes use of the Levinson recursions, Gaussian quadrature and a fast version of Euclid's algorithm. Similar to other methods for constructing quadrature mirror filters, the spectral factorization of a polynomial is the computationally expensive part of this algorithm. >

PR-QMF based codes for multipath/multiuser communications

Abstract: One common type of interference in a mobile communications channel is multipath interference. Traditionally, the DSSS/CDMA systems utilize maximal length sequences (m-sequences) as the spreading codes. The m-sequences were chosen because they possess the desired randomness properties and are easily generated via shift registers. The perfect reconstruction quadrature mirror filter (PR-QMF) based spread spectrum codes were proposed as an alternative to the m-sequences. A class of spreading codes based on PR-QMF subband trees is examined. After developing the properties of these codes as they relate to the multipath and multiuser channels, objective and constraint functions are formulated which incorporate these properties. These functions are then used in a multivariable optimization problem to determine the PR-QMF coefficients for use in the subband tree structure. Once the subband tree is complete, the spreading codes can then be extracted for use. It is shown that in the limiting cases, the optimal solutions tend towards TDMA and FDMA like structures.

Design of perfect reconstruction QMF banks by a null-space projection method

Abstract: A new method is proposed for the design of two-channel linear-phase perfect reconstruction QMF banks. The analysis lowpass filter is first designed by a conventional method, and then the synthesis lowpass filter is obtained by using a null-space projection approach. This method is then extended to the design of two-channel perfect reconstruction QMF banks with low reconstruction delay, which are desirable in some applications. Two design examples are given to illustrate the proposed methods.

Projection minimization techniques for orthogonal QMF filters with vanishing moments

Abstract: In many applications, a cost function is available that determines how "good" the filters of a filter bank decomposition are at performing a particular job. For example, in signal compression, the filters of a quadrature mirror filter (QMF) bank could be rated on their accuracy in compression and reconstruction of a given input signal. Given a cost function and the constraint set, it would be useful to be able to use an iterative minimization algorithm, e.g., steepest descent, to minimize the cost function while satisfying all of the constraints. The resulting performance would exceed an implementation that was not application specific (i.e., fixed filters). A projection minimization approach is taken with the particulars of this application determining the projection space. A constrained conjugate gradient descent approach is taken in choosing a filter pair that minimizes a cost function, but the methodology could be easily modified and applied to a wide variety of iterative minimization techniques. >

Optimally smooth symmetric quadrature mirror filters for image coding

Abstract: Symmetric quadrature mirror filters (QMFs) offer several advantages for wavelet-based image coding. Symmetry and odd-length contribute to efficient boundary handling and preservation of edge detail. Symmetric QMFs can be obtained by mildly relaxing the filter bank orthogonality conditions. We describe a computational algorithm for these filter banks which is also symmetric in the sense that the analysis and synthesis operations have identical implementations, up to a delay. The essence of a wavelet transform is its multiresolution decomposition, obtained by iterating the lowpass filter. This allows one to introduce a new design criterion, smoothness (good behavior) of the lowpass filter under iteration. This design constraint can be expressed solely in terms of the lowpass filter tap values (via the eigenvalue decomposition of a certain finite-dimensional matrix). Our innovation is to design near- orthogonal QMFs with linear-phase symmetry which are optimized for smoothness under iteration, not for stopband rejection. The new class of optimally smooth QMF filter banks yields high performance in a practical image compression system.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A way of multi-channel A/D for UWB signal

Abstract: A method for ultra wide band (UWB) signal A/D conversion and reconstruction of signal waveform is introduced. Its basic idea is to decompose a signal into several contiguous frequency bands so that a specific subconverter can be assigned to each band signal. The converted subband signal is then reconstructed by a quadrature mirror filter (QMF) bank. Simulation results prove the good performance of this arrangement.

Design of QMF banks using allpass filters

Abstract: The authors consider the design of quadrature mirror filter (QMF) banks using digital allpass filters. The QMF banks consisting of an allpass filter and a pure delay section have an approximately linear phase response, and the phase distortion can be minimised by using another additional allpass filter as an equaliser.

Optimization and performance of broadband microphone arrays

Abstract: This paper considers various wideband signal model optimization techniques and associated performanceresults for adaptive and steerable but fixed beam microphone array processing for hearing aid applications in free-space and reverberant conditions. We first review and compare various conventional broadband and narrowbandarray optimization techniques. These include the minimization of the output array power subject to desired signaldistortion constraint; the maximization of the array gain subject to white noise gain and linear constraints; andmaximum energy criterion subject to norm, linear, and quadratic distortion constraints. Then new results onmaximum energy criterion broadband array optimization formulated for sub-band processing are presented. Theuniformly spaced sub-band and the non-uniformly spaced sub-band using quadrature mirror filter approaches aretreated. Finally, various simulation results under the maximum energy criterion for free-space and reverberantconditions are presented to demonstrate the usefulness of this class of microphone arrays.Keywords: Broadband array, linear and quadratic constraints, maximum energy array, sub-band filtering, hear-ing aid.

Digital quadrature modulator

Abstract: A digitized quadrature modulator for receiving of I-channel input digital signal and Q-channel input digital signal, and for quadrature modulating the I-channel and Q-channel input digital signals by a digital signal processing. The modulator has a digital filter (504) for shaping the spectrum of the I-channel and Q-channel input digital signals to provide I-channel and Q-channel output signals, the output signals having a predetermined phase shift between the I-channel and the Q-channel so as to compensate a phase difference based upon the quadrature modulation by the digital signal processing, complementers (505a, 505b) for taking the complement of the I-channel and Q-channel output signals to provide I-channel and Q-channel complement signals, and a multiplexer (505c) for multiplexing the I-channel and Q-channel output signals from the digital filter and the I-channel and Q-channel complement signals from the complementers to provide a quadrature modulated output signal.

Information-theoretic performance of quadrature mirror filters

Abstract: Most existing quadrature mirror filters (QMFs) closely match the derived closed-form expression for an efficient class of QMFs. We use the closed-form expressions to derive the relationship between information-theoretic loss and the frequency selectivity of the QMF, by calculating first-order entropy as well as rate-distortion theoretic performance of a two band QMF system. We find that practical QMFs do not suffer a significant information-theoretic loss with first-order autoregressive Gaussian sources. With second-order autoregressive sources we find that practical QMFs suffer a notable information-theoretic loss when the bandwidth of the source is extremely narrow, but incur a small loss when the bandwidth is wider. We suggest that our results broadly apply to higher order autoregressive sources as well.

Optimal orthogonal boundary filter banks

Abstract: The use of a paraunitary filter bank for image processing requires a special treatment at image boundaries to ensure perfect reconstruction and orthogonality of these regions. Using time-varying boundary filter banks, we will discuss a procedure that explores all degrees of freedom of the border filters in a method essentially independent of signal extensions, allowing us to design optimal boundary filter banks, while maintaining fast implementation algorithms.

An image discrete wavelet transform and the hardware implementation

Abstract: Both the Discrete Wavelet Transform (DWT) and inverse DWT are implemented by using a lossless Quadrature Mirror Filter (QMF) bank which approximates a Gaussian function. The image passing through the finite impulse response (FIR) QMF filtering becomes blurred and thus requires less number of pixels. Data compression comes from the permissible bits per pixel (bpp) dynamic range and the compression of those filtered images having lesser details. The image reconstruction at a telereceiving station is accomplished by means of the inverse DWT. A Mexican-hat like function is used as a filter in the DWT. The numerical simulation is given and verified. A hardware implementation of the Mexican hat function is included. The SPICE simulation of the CMOS circuit to implement the Mexican hat function is also demonstrated.

Fingerprint data acquisition, desmearing, wavelet feature extraction, and identification

Abstract: In this paper, we present (1) a design concept of a fingerprint scanning system that can reject severely blurred inputs for retakes and then de-smear those less blurred prints. The de-smear algorithm is new and is based on the digital filter theory of the lossless QMF (quadrature mirror filter) subband coding. Then, we present (2) a new fingerprint minutia feature extraction methodology which uses a 2D STAR mother wavelet that can efficiently locate the fork feature anywhere on the fingerprints in parallel and is independent of its scale, shift, and rotation. Such a combined system can achieve high data compression to send through a binary facsimile machine that when combined with a tabletop computer can achieve the automatic finger identification systems (AFIS) using today's technology in the office environment. An interim recommendation for the National Crime Information Center is given about how to reduce the crime rate by an upgrade of today's police office technology in the light of the military expertise in ATR.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Adaptive antenna techniques using QMF banks

Abstract: An adaptive beamforming array antenna using a quadrature mirror filter to split the signal into sub-bands is discussed. The minimum variance distortionless response (MVDR) method is used in conjunction with the QR decomposition (QRD) algorithm for the evaluation of the antenna beamformer. The simulated results show that the speed of convergence of weights increases rapidly as the sub-banding is used.

Classification of microcalcifications using a multichannel filtering approach

Abstract: Presents a method for classification of Mammographic Microcalcifications using Quadrature Mirror Filter (QMF) bank subband decomposition as a tool for extracting textural features The QMF bank splits the input image into four subbands: low-low band, low-high band, high-low band and high-high band, and textural features based on co-occurrence matrices are computed from the subsampled subbands The low-low band extracts the information of spatial dependence and the higher frequency bands extract the structural information The experiments demonstrate that our approach can provide significant discrimination for classification of benign and malignant microcalcifications

Optimized perfect reconstruction quadrature mirror filter (PR-QMF) based codes for multi-user communications

Abstract: In communications systems, the message signal is sometimes spread over a large bandwidth in order to realize performance gains in the presence of narrowband interference, multipath propagation, and multiuser interference. The extent to which performance is improved is highly dependent upon the spreading code implemented. Traditionally, the spreading codes have consisted of pseudo-noise (PN) sequences whose chip values are limited to bipolar values. Recently, however, alternatives to the PN sequences have been studied including wavelet based and PR-QMF based spreading codes. The spreading codes implemented are the basis functions of a particular wavelet transform or PR-QMF bank. Since the choice of available basis functions is much larger than that of PN sequences, it is hoped that better performance can be achieved by choosing a basis tailored to the system requirements mentioned above. In this paper, a design method is presented to construct a PR-QMF bank which will generate spreading codes optimized for operating in a multiuser interference environment. Objective functions are developed for the design criteria and a multivariable constrained optimization problem is employed to generate the coefficients used in the filter bank. Once the filter bank is complete, the spreading codes are extracted and implemented in the spread spectrum system. System bit error rate (BER) curves are generated from computer simulation for analysis. Curves are generated for both the single user and the CDMA environment and performance is compared to that attained using gold codes.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A Subband Adaptive Filter with the Optimum Analysis Filter Bank

Abstract: Conventional subband ADFs (adaptive digital filters) using filter banks have shown degradation in performance because of the non-ideal nature of filters. For this problem, we propose a new type of subband ADF incorporating two types of analysis filter bank. In this paper, we show that we can design the optimum filter bank which minimizes the LMSE (least mean squared error). In other words, we can design a subband ADF with less MSE than that of conventional subband ADFs.