Search

Abstract: In this paper, we study the design and implementation of digital secure communication systems via synchronized Sprott chaotic circuits. First, using the variable structure control (VSC) technique, we propose a control law to cope with the synchronization problem of the master and slave Sprott circuits. Then, according to the concept of equivalence control, it can ensure that the message embedded in the transmitter (master Sprott circuit) can be recovered in the receiver (slave Sprott circuit). Then a digital secure communication system based on synchronized coupled chaotic systems is implemented using basic electronic components. Finally, both simulation results and the experimental results demonstrate the proposed VSC-based synchronization scheme''s success in the secure communication application. [Copyright &y& Elsevier]

Abstract: We consider the problem of tracking a “smart” target. That is, a target that is aware it is being tracked and modifies its behaviour accordingly. To track such targets effectively it is necessary to modify the behaviour of the tracking sensor in response to the target. We consider that the best framework for such a problem is that of a mathematical game. In this paper, we consider an idealised version of this problem that illustrates some of the issues that can occur when attempting to track a smart target and the utility of a game theoretic framework. [Copyright &y& Elsevier]

Abstract: Scattering centers model (SCM) is usually considered for modeling target backscattered signal in high-resolution radar. In this case the impulse response of each scattering center is represented by a time-delayed Dirac pulse. Some of most popular superresolution imagery techniques, such as MUSIC or ESPRIT, are well-matched to this model. Under this hypothesis, they outperform Fourier-based techniques in terms of both spatial and dynamic resolutions. However, the behavior of real-world targets is often very different from that of the SCM. Indeed, their reflectivity function is not confined just to several perfectly localized scattering centers, but it can be rather approximated by a set of scattering regions having different spatial extent. SCM becomes then inappropriate and the superresolution methods may provide unexpected results. Furthermore, the amplitude information is difficult to interpret in this case. In this paper we propose an extension of two superresolution methods, MUSIC and ESPRIT, to cope with extended scattering centers (ESC). According to this model, the impulse response of an ESC is not a Dirac pulse, but a window of finite support. Besides the position, the size (spatial extent) of this window is also recovered. This additional information about the target structure can be used for increasing ATR (automatic target recognition) accuracy and robustness. [Copyright &y& Elsevier]

Abstract: This paper presents the multiplierless CIC compensation filter based on the 2M-order filter and the sharpening technique. This technique proposed by Kaiser and Hamming attempts to improve the pass band and the stop band of a symmetric nonrecursive filter using the multiple copies of the same filter. We have considered the simplest sharpening polynomial that improves the frequency characteristic with minimum increase in computational complexity. The proposed filter provides wideband compensation over the specified CIC main lobe bandwidth. The design parameter is a single integer b which depends on K, the number of cascade CIC stages and is independent on the decimation factor M. The values of b tabulated here were obtained from MATLAB simulations. A number of demonstrated characteristics make the proposed structure a good candidate for software defined radio (SDR) applications. [Copyright &y& Elsevier]

Abstract: Finding the position of a radiative source based on time-difference-of-arrival (TDOA) measurements from spatially separated receivers has important applications in sonar, radar, mobile communications and sensor networks. Each TDOA defines a hyperbolic locus on which the source must lie and the position estimate can then be determined with the knowledge of the sensor array geometry. While extensive research works have been performed on algorithm development for TDOA estimation and TDOA-based localization, limited attention has been paid in sensor array geometry design. In this paper, an optimum two-dimensional sensor placement strategy is derived with the use of optimum TDOA measurements, assuming that each sensor receives a white signal source in the presence of additive white noise. The minimum achievable Cramér–Rao lower bound is also produced. [Copyright &y& Elsevier]

Abstract: Quality of service (QoS) is a measure of a communication network performance that reflects the transmission quality and service availability as perceived by the users. In the context of telecommunications, voice communication quality is the most visible and important aspects to QoS, and the ability to monitor and design for this quality should be a top priority. Voice quality refers to the clearness of a speaker''s voice as perceived by a listener. Its measurement offers a means of adding the human end-user''s perspective to traditional ways of performing network management evaluation of voice telephony services. Traditionally, measurement of users'' perception of voice quality has been performed by expensive and time-consuming subjective listening tests. Over the last decade, numerous attempts have been made to supplement subjective tests with objective measurements based on algorithms that can be computerised and automated. This paper examines some of the technicalities associated with voice quality measurement, and presents a review of current subjective and objective voice quality measurement methods and standards as applied to telecommunication systems and devices, with particular focus on recent and internationally standardised methods. [Copyright &y& Elsevier]

Abstract: Traditionally, inverse synthetic aperture radar (ISAR) image frames are classified individually in an automatic target recognition system. When information from different image frames is combined, it is usually in the context of time-averaging to remove statistically independent noise fluctuations between images. The sea state induced variability of the ship target projections between frames, however, also provides additional information about the target, which can be used to construct a 3D representation of the target scatterer positions. In this paper, a method for classifying a ship based on 3D scatterer information from a sequence of 2D ISAR images is described. A preliminary classification result for simulated ISAR images of nine types of ship is also provided. [Copyright &y& Elsevier]

Abstract: This paper examines the problem of adaptive beam scheduling to minimise target tracking error with a phased array radar. It is shown that this can be posed in a framework that is similar to a particular type of dynamic programming problem known as the restless bandit problem. We will show that when the problem is put in this framework it has an indexable solution under certain circumstances. [Copyright &y& Elsevier]

Abstract: Embedded software processing requirements will exceed 1 trillion operations per second in the 2005–2010 time frame. Consequently, efficient use of processors and memory, at all levels, is essential. In many defense environments, e.g., radar, as well as medical and other real-time embedded systems, operations are primarily array-based. Although languages support high level, monolithic, array based computation through classes, functions, templates (C++), and grammars (Fortran 95, ZPL), limited optimizations occur to eliminate array valued temporaries, which for embedded real time systems, is enormous. Without an underlying theory of arrays, e.g., an algebra and index calculus, it is difficult, if not impossible to provide such optimizations. This paper presents a Mathematics of Arrays and Psi Calculus. Together they are used to reason about array based computation in radar; the algorithm, decomposition, mapping to processors and memory, performance. [Copyright &y& Elsevier]

Abstract: This paper presents the comparative study of various wavelet filter based denoising methods according to different thresholding values applied to ultrasound images. An original image is transformed into a multi scale wavelet domain and the wavelet coefficients are processed by a soft thresholding method. The denoised image is the output image obtained from the inverse wavelet transform of the threshold coefficients using Donoho''s method. It has been observed that such denoising methods are effective in the sense that they preserve the edge details besides suppressing the noise. The comparative evaluation of the denoising performance is shown using statistical significance tests for different wavelet filters. Image quality parameters such as peak signal-to-noise ratio, normalized mean square error, and correlation coefficient have been used to evaluate the performance of wavelet filters. The performance has also been compared with the adaptive weighted median filtering method. [Copyright &y& Elsevier]

Abstract: A FIR csinc interpolative filter design for bandpass signals is presented in this paper. The filter coefficients are calculated from the covariance of basis functions for the bandpass function space. They are invariant with respect to the samples of the input signals. The csinc model also works for low-pass signals as one of the design parameters approaches zero. The performance of the csinc filter is analyzed from the perspectives of accuracy, stability, and adaptation to noise in the samples. Comparisons are made between the csinc model and the existing interpolation models in the literature. [Copyright &y& Elsevier]

Abstract: The Savitzky–Golay (SG) filters are generally used for smoothing and differentiation in many fields. The properties of the SG smoothing filters have been well studied. However, the properties of the SG differentiation filters or SG digital differentiators (SGDD, for the first order differentiation) are not developed well somehow, although they have been widely used. In the paper, the properties of the SGDD are discussed in detail. The effects of the SGDD on a noise-free single Gaussian line and a noise-free Gaussian doublet are studied via simulation. The results indicate that the contrast and resolution loss of the SGDD depends on the ratio of the width of signal derivative and filter length. The linear SGDD is not preferable for preserving small details of signal derivative from this study. The cubic and quintic SGDD with the choice of appropriate filter length are recommended in order to maintain the resolution of signal derivative. [Copyright &y& Elsevier]