Showing papers on "Quadrature mirror filter published in 2001"

Wavelet based OFDM for wireless channels

Abstract: The main objective of this paper is to replace the conventional Fourier based complex exponential carriers of the OFDM system with some orthonormal wavelets in order to reduce the level of interference. The wavelets are derived from multistage tree-structured Haar and Daubechies orthonormal quadrature mirror filter (QMF) bank. Compared with the conventional OFDM, it is found that the Haar and Daubechies-based orthonormal wavelets are capable of reducing the power of intersymbol interference (ISI) and intercarrier interference (ICI), which are caused by the loss in orthogonality between the carriers as a result of the multipath wireless channel.

Wavelets in Signal and Image Analysis

Abstract: The intention of this paper is to pro vide an elementary introduction to the subject of discret e-time wavelets. It defines the discret e-t ime wavelet s and reviews t heir properties in a syste mat ic and consiste nt way. Different kinds of ort hogona lity between the wavelets are addressed and the corres pond ing sufficient and necessary condit ions ar e derived . It is shown when discret e-t ime wavelets can be samples of continuous-t ime wavelet s. The condit ions for shift-invari an ce of discrete-time wavelet representations are given in det ail. The appearance of two biorthogonal representation sets of discrete-ti me wavelet s from t he binary subband decomposition /reconstruction of signals is pointed out . When t he numher of different representation scales is finit e, it is shown that in order to obtain the orthogonality betwe en wavelet s, the known requircm cnt for wavelet generating filter can be relaxed .

Adaptive array processing for multipath fading mitigation via exploitation of filter banks

Abstract: We propose subband adaptive array processing for mitigation of both intersymbol interference (ISI) and cochannel interference (CCI) in digital mobile communications. Subband adaptive array processing employs filter banks in a front end to an adaptive array receiver. By decomposing the signals into a set of subband signals, the analysis filters enhance the correlation of multipath rays in each subband. This enhancement is blind in the sense that no a priori knowledge of the temporal characteristics or spatial signatures of arriving signals is required. With the increased coherence, the desired signal can be effectively equalized by subsequent spatial processing. Further, the CCI signals and their multipaths can be suppressed with fewer degrees of freedom. The effects of quadrature mirror filter and discrete Fourier transform filter banks on multipath correlation are delineated.

Radio fm receiver

Abstract: A radio FM receiver is provided with a receiver portion with quadrature channels for converting received radio frequency signals into center frequency quadrature signals, a center frequency filter circuit connected to the former for suppressing undesirable image frequencies, and a first quadrature PLL demodulator for demodulating the obtained center frequency quadrature signals, said PLL being tuned to the carrier frequency within the selected frequency band. An error detector is furthermore present for detecting amplitude and phase errors in the quadrature channels, which error detector in response to the quadrature components of the center frequency signals, the quadrature signals of a VCO in the quadrature PLL demodulator, and the filtered difference said quadrature components of the center frequency signal, supplies amplitude and phase correction signals to a quadrature channel correction network which is provided between the filter circuit and the quadrature PLL demodulator.

Multirate signal processing on finite fields

Abstract: The paper addresses the problem of multirate signal processing over arbitrary fields. Studies of multirate systems and filter banks have proceeded in parallel, and a wealth of results are available in literature. The authors concentrate their attention on cyclic systems. These structures are ideally suited to generalising the concepts to finite fields. The perfect reconstruction property for quadrature mirror filter banks is obtained. It is shown how the cyclic wavelet transform (CWT) can be derived from such systems; the relationships between cyclic filter banks and CWTs are explored in detail. The results obtained are potentially very well suited for speech and image encoding, as well as for fast algorithms in signal processing.

New natural selection process and chromosome encoding for the design of multiplierless lattice QMF using genetic algorithm

Abstract: A new natural selection process and chromosome encoding for the design of signed power-of-two (SPT) coefficient lattice structure quadrature mirror filter (QMF) bank using a genetic algorithm (GA) is presented. In the design of filters using genetic algorithms, in general, genetic operations may render the SPT representation of a value noncanonical. In this paper, a new encoding scheme is introduced to encode the SPT values. In this new scheme, the canonical property of the SPT values is preserved under genetic operations. Additionally, a new feature which drastically improves the performance of the GA is introduced. The new feature is: the probability of mutation for each codon of a chromosome is weighted by the reciprocal of its effect. Owing to the new feature, the performance of our new GA outperforms conventional GA.

Wavelet multi-resolution waveforms

Abstract: A method for designing Wavelets for communications and radar which combines requirements for Wavelets and finite impulse response FIR filters including no excess bandwidth, linear performance metrics for passband, stopband, quadrature mirror filter QMF properties, intersymbol interference, and adjacent channel interference, polystatic filter design requirements, and non-linear metrics for bandwidth efficient modulation BEM and synthetic aperture radar SAR. Demonstrated linear design methodology finds the best design coordinates to minimize the weighted sum of the contributing least-squares LS error metrics for the respective performance requirements. Design coordinates are mapped into the optimum FIR symbol time response. Harmonic design coordinates provide multi-resolution properties and enable a single design to generate Wavelets for arbitrary parameters which include dilation, down-sampling, up-sampling, time translation, frequency translation, sample rate, symbol rate, symbol length, and set of design harmonics. Non-linear applications introduce additional constraints. Performance examples are linear communications, BEM, and SAR.

Efficient design of a class of multiplier-less perfect reconstruction two-channel filter banks and wavelets with prescribed output accuracy

Abstract: This paper proposes a novel algorithm for the design and hardware reduction of a class of multiplier-less two-channel perfect reconstruction (PR) filter banks (FB) using sum-of-powers-of-two (SOPOT) coefficients. It minimizes a more realistic hardware cost, such as adder cells, subject to a prescribed output accuracy taking account of rounding and overflow effects, instead of using just the SOPOT terms as in conventional methods. Furthermore, by using multiplier blocks (MB) to implement the filters in the FBs, significant overall saving in hardware resources can be achieved. An effective random search algorithm is also proposed to solve the design problem, which is also applicable to PR IIR FBs with highly nonlinear objective functions. Perfect reconstruction multirate filter have important applications in signal analysis, signal coding and the design of wavelet bases.

Demodulator having automatic quadrature control function

Abstract: A demodulator for automatically performing quadrature control in which there is no necessity for the modulator side to perform precision adjustment and deterioration in characteristics e.g., error rate is suppressed for long. The demodulator includes a quadrature controller fed with an in-phase component and a quadrature component output from the quadrature detecting unit to correct quadrature error between phases of in-phase and quadrature signals based on a quadrature error signal, an automatic gain controller AGC outputting in-phase and quadrature components of a demodulated signal corrected for amplitude errors by an amplitude error signal, an error detection unit fed with in-phase and quadrature components of the demodulated signal to output in-phase and quadrature components and polarity signals, an amplitude error detector outputting in-phase and quadrature components of the amplitude error to the AGC based on the in-phase and quadrature components and the respective polarity signals, and a quadrature error detection unit generating a quadrature error signal Qd based on the in-phase and quadrature components and the polarity signals to output the generated quadrature error signal to the quadrature controller.

On the design of near-perfect-reconstruction IIR QMF banks using FIR phase-compensation filters

Abstract: We describe a novel approach for the design of near-perfect-reconstruction mixed FIR-/allpass-based quadrature mirror filter banks. The design is carried out in the polyphase domain, where FIR filters, obtained via simple closed-form expressions, are employed for compensating the nonlinear phase introduced by the allpass filters. Starting from a generalized two-band structure, we introduce three different types of analysis-synthesis banks based on the same design principle. In all systems the remaining linear and phase distortions can be made arbitrarily small at the expense of additional system delay. Simultaneously, aliasing can be minimized, or completely canceled if further delay can be tolerated.

Quadrature Receiver with Orthogonality Correction

Abstract: A receive method in a communication system is provided. The method includes the steps of: generating a quadrature signal from the receive signal; compensating orthogonality error and gain imbalance for the receive signal and the quadrature signal; and converting the receive signal and the quadrature signal into first complex frequency band signal by first analytic sine wave.

VLSI architecture of QMF for DWT integrated system

Abstract: Wavelet transform has become a suitable tool for DSP signal manipulation especially in image compression. A VLSI implementation of a CMOS circuit realizing a Discrete Wave Transform ( DWT) for Daubecchie's 6 using a novel realization of Quadrature Mirror Filter [QMF] is presented. The new design of the DWT system which is based on a new Finite Impulse Response filter FIR requires less Si area to be implemented, since the FIR filter is implemented using mixed parallel / sequential architecture resulting in reducing the number of binary multipliers used which are the major bottle neck governing the performance of the DSP processing. Consequently, it results in a much faster system. Moreover, the use of parallel multipliers results in less power dissipation.

Analysis of mammographic microcalcifications using a computationally efficient filter bank

Abstract: We present a new method for classification of malignant and benign clusters of microcalcifications in digital mammograms. A computationally efficient infinite impulse response (IIR) quadrature mirror filter (QMF) bank is used as a tool for extracting texture and shape features. The filter bank splits the input image into four subbands: low-low band, low-high band, high-low band and high-high band. Texture and shape features based on cooccurrence matrices are computed from the subsampled subbands. The low-low band extracts the information of spatial dependence and the higher frequency bands extract the shape information. The results of an experimental study demonstrate that our approach drastically improves the overall performance compared to a manual system.

On filter banks with rational oversampling

Abstract: Despite the great popularity of critically-decimated filter banks, oversampled filter banks are useful in applications where data expansion is not a problem. We studied oversampled filter banks and showed that for some popular classes of filter banks it is not possible to obtain perfect reconstruction with rational (non-integer) oversampling ratios. Nevertheless, it is always possible to oversample the analysis filter bank by an integer factor, ie, there will be a similar synthesis bank which would provide perfect reconstruction. The analysis is carried within a time-aliasing framework development to analyze non-critically decimated filter banks.

Realization of quadrature coherent detection by direct sampling of IF signal

Abstract: Presents the development of modern signal processing techniques, a new implementation method which realizes quadrature coherent detection by direct sampling of IF signal generated during the implementation of traditional quadrature coherent detection with analog elements in the form of two parallel baseband channels where in phase (I) and quadrature (Q) components of ceived IF singnal where, the imperfect matching of the separate channels due to the analog elements results in high phase and amplitude which meets the needs for high performance radar signal processing, the elementary principles and the implementation process for each method and concludes from simulation results to compare their features and application conditions that the new approach can satisfy of the requirements of high performance SP.

Digital Image Coding with Hybrid Wavelet Packet Transform

Abstract: The hybrid wavelet packet improves the performance of wavelet packet transform by choosing appropriate quadrature mirror filters. Therfore it is proposed for digital image compression in this paper. We use a top-down scheme to optimize the hybrid wavelet packet and the wavelet coefficients are quantized with a successive approximation algorithm and then coded with context-based arithmetic coding. Experimental result shows that the proposed algorithm has better performance than SPIHT and EZW for images with complex texture.

Quadrature frequency multiplier

Abstract: Quadrature frequency multiplier comprising a frequency doubler included in a quadrature signal path, said frequency doubler receiving a quadrature input signal and providing a quadrature output signal of a frequency, which is double that of said input signal. An array of such frequency doublers allow to derive from an input quadrature signal of a frequency fin, quadrature signals at frequencies mutually differing by a multiplication factor of 2 n . To derive quadrature signals at a frequency in between, the invention makes use of a quadrature image frequency cancelling mixer stage having first and second quadrature inputs coupled to said quadrature signal path across said frequency doubler and providing a quadrature signal at a quadrature output having a frequency corresponding to the sum or difference of the frequencies of the signals at said first and second quadrature inputs and differing from the frequencies of the signals occurring in said quadrature signal path.

High-fidelity adaptive medical image reconstruction using real-time wavelet filter design for fast Internet transmission and display

Abstract: Most high resolution medical images such as X-ray radiographic images require enormous storage space and considerable time for transmission and viewing. We propose a wavelet design that creates the optimal filter taps for any class of images adaptively for high fidelity image reconstruction using an energy compacted section of the wavelet decomposed original image with considerable reduction in memory requirement as well as in execution, transmission, and viewing time. This optimal filter tap design is based on two-channel perfect reconstruction quadrature mirror filter (PR-QMF) banks using an interior-point-based optimization algorithm. The algorithm finds wavelet filter taps that allows the smallest amount of energy in the detail sections of the wavelet decomposition of an image in real time. Once the filter taps have been created and a one level wavelet transform has been performed, the energy compacted component of the image containing one fourth of the number of elements in the original image, is retained without any significant loss in the information content. This energy compacted section of the image is then used for any chosen advanced compression algorithm. This technique provides a significant reduction in execution time without an appreciable increase in distortion for advanced lossy image compression algorithms.

A real-valued block filter bank with perfect-reconstruction property

Abstract: This paper discusses the perfect reconstruction (PR) condition of a maximally decimated block filter bank, which uses cyclic convolutions instead of linear convolutions used in the usual filter banks. This type of filter bank is particularly useful for subband coding for image data. It is observed that the PR condition of the block filter bank is less restrictive than that of the usual FIR filter banks. The PR condition is expressed in terms of DFT of the analysis filters for convenience of the filter design.

Improvement of factorization for two-channel perfect reconstruction FIR filter banks

Abstract: There is an increasing interest in designing structurally perfect reconstruction (PR) filter banks because the system can be implemented by using sum of powers-of-two (SOPOT) coefficients. The structurally PR filter banks can be designed by factorization based on the lifting scheme. But there exist some problems that are addressed in this paper. Improvement of the factorization to solve the problems is proposed. The procedures of proof for the improvement are given. Finally, the given examples show that the proposed method is effective.

A sequential reoptimization approach for the design of signed power-of-two coefficient lattice QMF bank

Abstract: This paper presents a sequential optimization approach for the design of lattice structure quadrature mirror filter (QMF) banks subject to the sum of signed power-of-two (SPT) coefficient constraints. The lattice structure QMF bank structurally guarantees the perfect reconstruction (PR) property. Nevertheless, its frequency response is still adversely affected by coefficient quantization. In this paper, a frequency response deterioration measure is developed from the lattice coefficient analysis. Based on this frequency response deterioration measure, the coefficient which will cause the largest deterioration in the frequency response of the filter is selected for quantization first. After the coefficient is quantized, the remaining unquantized coefficients are reoptimized. The process of quantizing the coefficient and reoptimizing the remaining unquantized coefficient is repeated until all the coefficients are quantized. The frequency responses of the filters obtained using our algorithm are significantly superior to those obtained by simple rounding of the coefficient values.