Fast coding in digital steganography

Dynamical running coding was previously proposed as a method for construction of steganographic schemes in digital steganography. In this article, a new approach of fast coding is proposed to improve steganographic efficiency. Original embedding method is discussed in two cases of constructing different generating matrix; however, the proposed method generalizes the problem to only one case by changing the construction method from the original method. Therefore, the complexity of the proposed method is less than the original method. Meanwhile, both theoretical analysis and experiment results show better performance in terms of distortions and alterations of the cover objects when embedding the same amount of information data bits, which proves a better resistance against steganalysis.     

Fast digital frequency synthesiser

A new phase-locked-loop type frequency synthesiser is described and tested which employs a digital-analogue convertor to give very rapid coarse frequency switching and optimum lock in speed anywhere in a wide frequency range. The experimental results are in good agreement with theory.     

Fast digital locally monotonic regression

Locally monotonic regression is the optimal counterpart of iterated median filtering. In a previous paper, Restrepo and Bovik (see ibid., vol.41, no.9, p.2796-2810, 1993) developed an elegant mathematical framework in which they studied locally monotonic regressions in R^N. The drawback is that the complexity of their algorithms is exponential in N. We consider digital locally monotonic regressions, in which the output symbols are drawn from a finite alphabet and, by making a connection to Viterbi decoding, provide a fast O(|A|²αN) algorithm that computes any such regression, where |A| is the size of the digital output alphabet, a stands for lomo degree, and N is the sample size. This is linear in N, and it renders the technique applicable in practice     

Fast computation of radiation integral for reflector antennas

A FORTRAN IV program to compute the field scattered by parabolic reflector antennas in a prescribed plane cut is presented. This program was executed on the UNIVAC 1100/80 at the University of Naples. A flowchart of the main program is provided     

Fast number-theoretic transforms for digital filtering

A special number-theoretic transform that can be computed, using a high-radix fast Fourier transform, is defined on primes of the form (2n ? 1) 2n +1. Methods for finding these primes and the primitive dth roots of unity in a field modulo such primes are also included.     

Fast algorithm for digital logarithmic conversion

The use of homomorphic filtering in many problems involving nonlinear combination of signals requires complex logarithmic converters. A fast algorithm for digital logarithmic conversion is developed which uses simple computer manipulations. The algorithm trades accuracy for speed, but is found to be adequate in a number of applications tested so far.     

Fast digital convolution using p-adic transforms

A transform, with similar properties to number theoretic transforms, is defined in a finite segmented p-adic field. It is shown that such a transform has a larger dynamic range than the ordinary number-theoretic transform for a given prime p. In addition any rational number may be represented in this field exactly, leading to error-free arithmetic.     

Fast word synchronisation for digital pulse-position modulation

A new word synchronisation method for digital pulse-position modulation is proposed which allows faster frame acquisition. Application is intended in high-speed wireless optical communications     

Fast solution of electromagnetic integral equations using adaptivewavelet packet transform

The adaptive wavelet packet transform is applied to sparsify the moment matrices for the fast solution of electromagnetic integral equations. In the algorithm, a cost function is employed to adaptively select the optimal wavelet packet expansion/testing functions to achieve the maximum sparsity possible in the resulting transformed system. The search for the best wavelet packet basis and the moment matrix transformation are implemented by repeated two-channel filtering of the original moment matrix with a pair of quadrature filters. It is found that the sparsified matrix has above-threshold elements that grow only as O(N^1.4) for typical scatterers. Consequently the operations to solve the transformed moment equation using the conjugate gradient method scales as O(N^1.4). The additional computational cost for carrying out the adaptive wavelet packet transform is evaluated and discussed     

Fast solution of mixed-potential time-domain integral equations for half-space environments

A fast Fourier transform-accelerated integral-equation based algorithm to efficiently analyze transient scattering from planar perfect electrically conducting objects residing above or inside a potentially lossy dielectric half-space is presented. The algorithm requires O(N/sub t/N/sub s/(logN/sub s/+log/sup 2/N/sub t/)) CPU and O(N/sub t/N/sub s/) memory resources when analyzing electromagnetic wave interactions with uniformly meshed planar structures. Here, N/sub t/ and N/sub s/ are the numbers of simulation time steps and spatial unknowns, respectively. The proposed scheme is therefore far more efficient than classical time-marching solvers, the CPU and memory requirements of which scale as O(N/sub t//sup 2/N/sub s//sup 2/) and O(N/sub t/N/sub s//sup 2/). In the proposed scheme, all pertinent time-domain half-space Green functions are (pre) computed from their frequency-domain counterparts via inverse discrete Fourier transformation. In this process, in-band aliasing is avoided through the application of a smooth and interpolatory window. Numerical results demonstrate the accuracy and efficiency of the proposed algorithm.     

Fast digital processing of images of artificial Earth satellites

Experiments on the improvement of images of artificial Earth satellites are performed via the methods of digital postdetection filtering in the case when a telescope with an aperture diameter of approximately 1 m is employed to observe extended objects. The resolution obtained in white-light observations is three times higher than the atmosphere-limited resolution. The results of calibration of the processing method with the use of speckle images of a single star are presented. Photographs of recorded and recovered images of the International Space Station and Saturn are presented.     

On numerical evaluation of a convolution-type integral

A simple approach is developed for numerical evaluation of a convolution-type integral. This method involves deriving and solving numerically a differential equation instead of evaluating the original integral by the regular method. It shows great advantages in saving computer time. The most important use of the method occurs when the integral must be evaluated repeatedly.     

Fast adaptive digital equalization by recurrent neural networks

Neural networks (NNs) have been extensively applied to many signal processing problems. In particular, due to their capacity to form complex decision regions, NNs have been successfully used in adaptive equalization of digital communication channels. The mean square error (MSE) criterion, which is usually adopted in neural learning, is not directly related to the minimization of the classification error, i.e., bit error rate (BER), which is of interest in channel equalization. Moreover, common gradient-based learning techniques are often characterized by slow speed of convergence and numerical ill conditioning. In this paper, we introduce a novel approach to learning in recurrent neural networks (RNNs) that exploits the principle of discriminative learning, minimizing an error functional that is a direct measure of the classification error. The proposed method extends to RNNs a technique applied with success to fast learning of feedforward NNs and is based on the descent of the error functional in the space of the linear combinations of the neurons (the neuron space); its main features are higher speed of convergence and better numerical conditioning w.r.t. gradient-based approaches, whereas numerical stability is assured by the use of robust least squares solvers. Experiments regarding the equalization of PAM signals in different transmission channels are described, which demonstrate the effectiveness of the proposed approach     

一种基于正交检波的快速数字AGC系统方案

提出一种快速数字AGC系统方案,系统中采用Hilbert(希尔伯特)正交检波方法,由于Hilbert滤波器的幅度衰减作用会导致检波输出产生波动,从而影响AGC系统输出信号的稳定性,通过在原检波输出端求平均值使检波输出稳定;同时引入正交检波输出与输入信号幅值的比值参数δ,简化系统的理论分析过程,在设计中通过仿真分析δ,能准确地确定系统的各参数值.基于以上改进的AGC系统结合文中的理论方法,使得该系统具有设计简单、工作稳定、易控制等优点.     

Fast convergent integral equation solution of strip gratings on dielectric substrate

A fast convergent integral equation solution to the scattering problem of a transverse electric/transverse magnetic (TE/TM) plane wave by a one-dimensional periodic array of thin metal strips on a dielectric substrate is described. The formulation of the integral equation is similar to that derived by Montgomery for a two-dimensional periodic array of thin conductors on a dielectric substrate. However, the basis functions which satisfy the appropriate edge conditions are incorporated here for the unknown current expansion on the strips. Following the standard Galerkin's procedure, one may readily determine the induced currents on the strips and thus the reflected and transmitted fields. Sample numerical results are given and good agreement with previously published data is obtained. It is found that the convergence rate of this method is improved by an order of magnitude. Also it is shown that the dielectric substrate has a strong effect on the scattering from the large spacing strip grating.     

Fast fault-tolerant digital convolution using a polynomial residuenumber system

A fault-tolerant convolution algorithm that is an extension of residue-number-system fault-tolerance schemes applied to polynomial rings is described. The algorithm is suitable for implementation on multiprocessor systems and is able to concurrently mask processor failures. A fast algorithm based on long division for detecting and correcting multiple processor failures is presented. Moduli polynomials that yield an efficient and robust fast-Fourier transform (FFT)-based algorithm are selected. For this implementation, a single fault detection and correction is studied, and a generalized-likelihood-ratio test is applied to optimally detect system failures in the presence of computational noise. The coding scheme is capable of protecting over 90% of the computation involved in convolution. Parts not covered by the scheme are assumed to be protected via triple modular redundancy. This hybrid approach can detect and correct any single system failure with as little as 70% overhead, compared with 200% needed for a system fully protected via modular redundancy     

Fast evaluation of logarithms in fields of characteristic two

A method for determining logarithms in GF(2^{n})is presented. Its asymptotic running time isO(exp (cn^{1/3} log^{2/3} n))for a small constantc, while, by comparison, Adleman's scheme runs in timeO(exp (c^{'}n^{1/2} log^{1/2} n )). The ideas give a dramatic improvement even for moderate-sized fields such as GF(2^{127}), and make (barely) possible computations in fields of size around2^{400}. The method is not applicable to GF(q)for a large primeq.     

Fast realisation of 2-D digital filters using logarithmic number systems

Previous papers of mine have discussed the approximation of 2-D digital filter coefficients with algebraic sums of integer powers of the base in a logarithmic number system. The results already obtained suggest a sequential memory-oriented realisation which is faster than the standard implementation.