Ideal Filter Research Articles

Ideal time-frequency masking algorithms lead to different speech intelligibility and quality in normal-hearing and cochlear implant listeners.

Hearing impaired listeners using cochlear implants (CIs) suffer from a decrease in speech intelligibility (SI) in adverse listening conditions. Time-frequency masks are often applied to perform noise suppression in an attempt to increase SI. Two important masks are the so-called ideal binary mask (IBM) with its binary weights and the ideal Wiener filter (IWF) with its continuous weights. It is unclear which of the masks has the highest potential for SI and speech quality enhancement in CI users. In this study, both approaches for SI and quality enhancement were compared. The investigations were conducted in normal-hearing (NH) subjects listening to noise vocoder CI simulations and in CI users. The potential for SI improvement was assessed in a sentence recognition task with ideal mask estimates in multitalker babble and with an interfering talker. The robustness of the approaches was evaluated with simulated estimation errors. CI users assessed the speech quality in a preference rating. The IWF outperformed the IBM in NH listeners. In contrast, no significant difference was obtained in CI users. Estimation errors degraded SI in CI users for both approaches. In terms of quality, the IWF outperformed, slightly, the IBM processed signals. The outcomes of this study suggest that the mask pattern is not that crucial for CIs. Results of speech enhancement algorithms obtained with NH subjects listening to vocoded or normally processed stimuli do not translate to CI users. This outcome means that the effect of new strategies has to be quantified with the user group considered.

Extraordinary transverse magneto-optical Kerr effect in a superlens

It has been shown that a slab of a negative index material can behave as a superlens enhancing the imaging resolution beyond the wavelength limit. We show here that if such a slab possesses in addition some magneto-optical activity, it could act as an ideal optical filter and exhibit an extraordinary transverse magneto-optical Kerr effect. Moreover, we show that losses, which spoil the imaging resolution of these lenses, are a necessary ingredient to observe this effect.

Flexible Nyquist Pulse Sequence Generation With Variable Bandwidth and Repetition Rate

The rectangular spectrum of sinc-shaped Nyquist pulses enables the encoding of data in a minimum spectral width. Sinc pulses can improve optical sampling devices, could enable the implementation of ideal rectangular microwave photonics filters, and can be used for all-optical signal processing, spectroscopy, and light storage. Recently, the generation of sinc-pulse sequences with extraordinary quality was shown by the utilization of cascaded modulators. However, the line width and repetition rate of the pulses is limited by the modulator bandwidth. Here, we present the nonrestricted generation of flexible Nyquist pulse sequences. Therefore, multiple single lines of a comb generator are extracted with optical filters and subsequently processed by cascaded modulators. In a first proof-of-concept experiment, we achieved almost ideally sinc-shaped Nyquist pulses with a bandwidth of 286 GHz, a pulse width of 3.5 ps, and a duty cycle of 2.2%. However, sinc-shaped Nyquist pulse sequences in the femtosecond range with terahertz bandwidths would be possible with the method.

Design and performance of closed form method for cosine modulated filter bank using different windows functions

This paper presents an improved method for designing multichannel cosine modulated filter bank (CMFB) with reduced computational complexity and low design parameters. In this method, design problem of multi-channel CMFB is constructed as design of a prototype filter whose magnitude response at quadrature frequency is 0.707 which is utilized for finding the optimum passband edge frequency through empirical formula instead of using single or multivariable optimization technique. Performance of different adjustable window functions such as Saramaki, Ultraspherical, Cosh, Exponential and Roark's Transitional has been also examined with exploiting spline function in transition band of ideal filter response for designing CMFB. The simulation results presented in this paper clearly show the key advantageous features of this algorithm as compared to other known methods.

Realization of Root Raised Cosine Roll-Off Filters Using a Recursive FIR Filter Structure

Root raised cosine roll-off (RRC) filter is one of the most fundamental elements in modern digital communications. This paper proposes a new method to efficiently realize the RRC filter. The method employs cubic Hermite interpolation to obtain a piecewise-polynomial approximation for the impulse response of the RRC filter. Then, the approximated impulse response is efficiently realized by using a transversal filter with a very small number of taps followed by integrators with a simple recursive structure, named cascaded recursive finite impulse response (CR-FIR) filter. As an example, an RRC filter with roll-off factor 0.5 is constructed by using the CR-FIR filter with only nine multipliers. Performance of the RRC filter in matched filtering is examined by computer simulations. Then, it is shown that the constructed RRC matched filter has nearly the same performance as the ideal filter.

Analysis on Adjusting Effect and Spectral Characteristics of Digital Image Sampling

When it comes to the digitized image, it is a process of converting analog image of continuous tone which has been sampled and quantized into digital image. The application of digital technology in modern art has become one of the hot spot in this field. First of all, this paper undertakes the digital image process of image. According to the filtering properties of the Dirac function, this paper analyzes the two-dimensional sampling principle of digital image. Based on this, the relationship between image spectrum before sampling and after sampling is compared and analyzed according to the related properties of Fourier transform. And then it is obtained that it is concluded that the ideal low-pass filter can make the sample undistorted. By further analyzing the error of the sampling value quantification processing, the rebuilt best quantitative values of image can be obtained. Thats to say, the reconstruction of digital image is the inverse process of image sampling. To a certain extent, it provides scientific theoretical basis for the integration of digital image in modern art design.

TFT-LCD Spot-Type Defect Detection in Module Process

In this paper we present a global approach for the automatic inspection of spot-type defects in TFT-LCD module process. The proposed method is based on a global image reconstruction scheme using the Fourier transform. Since TFT-LCD surface has the statistical and periodic texture, the isotropic spread of frequency components in the power spectrum space forms the shape approximate to a circle. By computing the convolution between the Fourier transform result and a ideal low pass filter (ILPF) , we can remove the TFT-LCD periodic and repetitive patterns using the inverse Fourier transform. In the restored image, the global structurally textured background is eliminated and the spot-type defects are preserved. This converts the difficult defect detection in TFT-LCD images into a simple segmentation problem. The spot-type defects are classified into general point defects and spot Mura defects .The experimental results from point defects and spot Mura defects have shown the efficacy of the proposed method.

SU-E-J-223: A Method to Remove the Streaking Artifacts Caused by Calypso Couch Table Add-On in the MV Portal Images

Purpose: Calypso EM tracking is widely used to setup the prostate patient and to track prostate motion while daily MV portal images are used as the secondary method to verify patient setup. The severe streaking artifacts, caused by the Calypso couch table add-on, make the MV portal images almost impossible to review. The purpose of this work is to develop a novel method to reduce the streaking artifacts so that the portal images are usable to verify patient setup. Methods: We analyzed the corrupted portal images and identified that most streaking artifacts are stable horizontally but has more dramatic change vertically. Based on signal processing theory, we developed an artifact reduction algorithm 1) to filter out the low frequency signal along the horizontal direction using a ideal low-pass filter in the Fourier domain, and 2) to smooth the intensity variation in the vertical direction and to reduce the remaining high frequency noises by using 2D Gaussian low-pass filter with a small window size. Results: We have successfully applied the proposed algorithm on the corrupted MV portal images in both PA and lateral directions from multiple Calypso prostate patients. The results show that the algorithm is very effective to reduce the artifacts introduced by the Calypso couch table add-on. Patient anatomical structures are much more clearly after processing to support reviews of patient setup. Conclusion: In this work an effective method is proposed to reduce artifacts caused by the Calypso table in MV portal images while preserving the key components of original image. The method could assist the verification of Calypso guided patient setup using portal images.

40 Gbps 100-km SSMF VSB-IMDD OFDM transmission experiment based on FBG filter

This work studies the transmission performance of vestigial-sideband (VSB)–IMDD OFDM system by theoretical analysis and numerical simulation. The analysis shows that the detrimental effect of dispersion-induced power fading can be effectively suppressed. The presence of positive and negative chirp of modulator will increase the dispersion-, chirp- and VSB optical filter-induced subcarrier to subcarrier intermixing interference (SSII), which significantly restricts transmission performance. Relatively lower order Gaussian optical filter has almost the same performance with ideal rectangular filter over 100-km SMF transmission and have better performance in less than 60-km transmission. Furthermore, we successfully transmit a 40Gbps, 16QAM, MZM-based VSB-IMDD OFDM signal through 100-km of uncompensated standard single mode fiber (SSMF) by using an economical FBG optical filter. The experimental results show that available bandwidth has been extended up to 10GHz after 100-km SSMF transmission.

Fast digital envelope detector based on generalized harmonic wavelet transform for BOTDR performance improvement

We propose a fast digital envelope detector (DED) based on the generalized harmonic wavelet transform to improve the performance of coherent heterodyne Brillouin optical time domain reflectometry. The proposed DED can obtain undistorted envelopes due to the zero phase-shift ideal bandpass filter (BPF) characteristics of the generalized harmonic wavelet (GHW). Its envelope average ability benefits from the passband designing flexibility of the GHW, and its demodulation speed can be accelerated by using a fast algorithm that only analyses signals of interest within the passband of the GHW with reduced computational complexity. The feasibility and advantage of the proposed DED are verified by simulations and experiments. With an optimized bandwidth, Brillouin frequency shift accuracy improvements of 19.4% and 11.14%, as well as envelope demodulation speed increases of 39.1% and 24.9%, are experimentally attained by the proposed DED over Hilbert transform (HT) and Morlet wavelet transform (MWT) based DEDs, respectively. Spatial resolution by the proposed DED is undegraded, which is identical to the undegraded value by HT-DED with an allpass filter characteristic and better than the degraded value by MWT-DED with a Gaussian BPF characteristic.

Systems of Quotients of Lie Triple Systems

In this article, we introduce the notion of system of quotients of Lie triple systems and investigate some properties which can be lifted from a Lie triple system to its systems of quotients. We relate the notion of Lie triple system of Martindale-like quotients with respect to a filter of ideals and the notion of system of quotients, and prove that the system of quotients of a Lie triple system is equivalent to the algebra of quotients of a Lie algebra in some sense, and these allow us to construct the maximal system of quotients for nondegenerate Lie triple systems.

Efficacy of fixed filtration for rapid kVp‐switching dual energy x‐ray systems

Dose efficiency of dual kVp imaging can be improved if the two beams are filtered to remove photons in the common part of their spectra, thereby increasing spectral separation. While there are a number of advantages to rapid kVp-switching for dual energy, it may not be feasible to have two different filters for the two spectra. Therefore, the authors are interested in whether a fixed added filter can improve the dose efficiency of kVp-switching dual energy x-ray systems. The authors hypothesized that a K-edge filter would provide the energy selectivity needed to remove overlap of the spectra and hence increase the precision of material separation at constant dose. Preliminary simulations were done using calcium and water basis materials and 80 and 140 kVp x-ray spectra. Precision of the decomposition was evaluated based on the propagation of the Poisson noise through the decomposition function. Considering availability and cost, the authors chose a commercial Gd2O2S screen as the filter for their experimental validation. Experiments were conducted on a table-top system using a phantom with various thicknesses of acrylic and copper and 70 and 125 kVp x-ray spectra. The authors kept the phantom exposure roughly constant with and without filtration by adjusting the tube current. The filtered and unfiltered raw data of both low and high energy were decomposed into basis material and the variance of the decomposition for each thickness pair was calculated. To evaluate the filtration performance, the authors measured the ratio of material decomposition variance with and without filtration. Simulation results show that the ideal filter material depends on the object composition and thickness, and ranges across the lanthanide series, with higher atomic number filters being preferred for more attenuating objects. Variance reduction increases with filter thickness, and substantial reductions (40%) can be achieved with a 2× loss in intensity. The authors' experimental results validate the simulations, yet were overall slightly worse than expectation. For large objects, conventional (non-K-edge) beam hardening filters perform well. This study demonstrates the potential of fixed K-edge filtration to improve the dose efficiency and material decomposition precision for rapid kVp-switching dual energy systems.

Adaptive design of ideal low-pass filter based on Fourier-transform spectrum distribution of digital speckle interference fringe patterns by using edge-detection, morphological-operation, and Radon-transform algorithms

An adaptive method is proposed in this paper for design of an ideal low-pass filter based on the Fourier-transform spectrum distribution of digital speckle interference fringe patterns. The size and shape of the ideal low-pass filter can be determined automatically by using an adaptive method based on the edge detection and morphological operation. The cutoff frequency of the ideal low-pass filter along arbitrary direction can also be determined automatically by using an adaptive method based on the Radon transform. The ideal low-pass filter designed in the paper can be used effectively for denoising of digital speckle interference fringe patterns in phase-shifting digital speckle pattern interferometry.

A new approach for designing orthogonal wavelets for multicarrier applications

The Daubechies, coiflet and symlet wavelets, with properties of orthogonal wavelets are suitable for multicarrier transmission over band-limited channels. It has been shown that similar wavelets can be constructed by Lagrange approximation interpolation. In this work and using established wavelet design algorithms, it is shown that ideal filters can be approximated to construct new orthogonal wavelets. These new wavelets, in terms of BER, behave slightly better than the wavelets mentioned above, and much better than biorthogonal wavelets, in multipath channels with additive white Gaussian noise (AWGN). It is shown that the construction, which uses a simple simultaneous solution to obtain the wavelet filters from the ideal filters based on established wavelet design algorithms, is simple and can easily be reproduced. The Cramer–Rao lower bound is applied to access the BER performance of the proposed wavelet.

The Hodrick-Prescott Filter with a Time-Varying Penalization Parameter. An Application for the Trend Estimation of Global Temperature.

In this paper we use the Hodrick-Prescott filter for analysing global temperature data. We are especially concerned with a reliable estimation of the trend component at the end of the data sample. To this end we employ time-varying values for the penalization parameter. The optimal values are derived by a comparison with an ideal filter. The method is applied to temperature data for the northern hemisphere from 1850 to 2012. The main result is that for the optimal specification of the flexible penalization the trend component of temperature is still increasing, possibly with a somewhat lower pace.

Efficient Nonuniform Fourier Reconstruction for Spaceborne/Airborne Bistatic SAR

In this letter, an efficient imaging algorithm is proposed for reconstructing the spaceborne/airborne bistatic synthetic aperture radar (SA-BSAR) data acquired with a high squint angle. By utilizing the Taylor expansion and the chain rule for derivatives of composite function, the expression of the SA-BSAR ideal matching filter is converted to a 2-D nonuniform discrete Fourier transform (NUDFT). Due to neither input nor output data of the NUDFT being equispaced, nonuniform fast Fourier transform of type 3 (NUFFT-3) is implemented to speed up the SA-BSAR image reconstruction. The computation complexity of the proposed imaging algorithm is O(MNlogMN), where MN is the number of the image pixels. Simulation results demonstrate the validity of the proposed algorithm.

Optimal Least-Squares FIR Digital Filters for Compensation of Chromatic Dispersion in Digital Coherent Optical Receivers

This paper proposes optimal finite-length impulse response (FIR) digital filters, in the least-squares (LS) sense, for compensation of chromatic dispersion (CD) in digital coherent optical receivers. The proposed filters are based on the convex minimization of the energy of the complex error between the frequency responses of the actual CD compensation filter and the ideal CD compensation filter. The paper utilizes the fact that pulse shaping filters limit the effective bandwidth of the signal. Then, the filter design for CD compensation needs to be performed over a smaller frequency range, as compared to the whole frequency band in the existing CD compensation methods. By means of design examples, we show that our proposed optimal LS FIR CD compensation filters outperform the existing filters in terms of performance, implementation complexity, and delay.

Design of multi-carrier transceivers based on modified discrete fourier transform filter bank

In order to improve the poor frequency selectivity and spectral leakage of traditional Orthogonal Frequency Division Multiplexing(OFDM) multi-carrier transceiver,multi-carrier transceiver based on modified Discrete Fourier Transform(DFT) filter bank was introduced. The design problem of it was formulated as nonconstrained minimized optimization of perfect reconstruction error of modulated filter banks,and the modified window method was taken to design the prototype filter in the modulated filter banks and linear optimization was used to optimize the objective function. Compared to the traditional window method,a spline function was exploited in the transition band of ideal filter of the modified window to eliminate the Gibbs effect. The simulation results show that the designed filter bank with the proposed method gives a better performance in terms of stopband attenuation,and reconstruction error,and the resulted multicarrier transceiver a better Symbol Error Rate(SER) performance in Quadrature Phase Shift Keying(QPSK) modulation and the 3GPP TS 25. 104vehicular multipath and one-tap frequency-domain equalization.

Reduction of quantization noise via periodic code for oversampled input signals and the corresponding optimal code design

This paper proposes to reduce the quantization noise using a periodic code, derives a condition for achieving an improvement on the signal to noise ratio (SNR) performance, and proposes an optimal design for the periodic code. To reduce the quantization noise, oversampled input signals are first multiplied by the periodic code and then quantized via a quantizer. The signals are reconstructed via multiplying the quantized signals by the same periodic code and then passing through an ideal lowpass filter. To derive the condition for achieving an improvement on the SNR performance, first the quantization operator is modeled by a deterministic polynomial function. The coefficients in the polynomial function are defined in such a way that the total energy difference between the quantization function and the polynomial function is minimized subject to a specification on the upper bound of the absolute difference. This problem is actually a semi-infinite programming problem and our recently proposed dual parameterization method is employed for finding the globally optimal solution. Second, the condition for improving the SNR performance is derived via a frequency domain formulation. To optimally design the periodic code such that the SNR performance is maximized, a modified gradient descent method that can avoid the obtained solution to be trapped in a locally optimal point and guarantee its convergence is proposed. Computer numerical simulation results show that the proposed system could achieve a significant improvement compared to existing systems such as the conventional system without multiplying to the periodic code, the system with an additive dithering and a first order sigma delta modulator.

Quantum control with spectral constraints

Various constraints concerning control fields can be imposed in the realistic implementations of quantum control systems. One of the most important is the restriction on the frequency spectrum of acceptable control parameters. It is important to consider the limitations of experimental equipment when trying to find appropriate control parameters. Therefore, in this paper, we present a general method of obtaining a piecewise-constant controls, which are robust with respect to spectral constraints. We consider here a Heisenberg spin chain; however, the method can be applied to a system with more general interactions. To model experimental restrictions, we apply an ideal low-pass filter to numerically obtained control pulses. The usage of the proposed method has negligible impact on the control quality as opposed to the standard approach, which does not take into account spectral limitations.