S.G. Tanyer

Voice activity detection in nonstationary noise

A new fusion method for voice activity detection in additive nonstationary noise is suggested. A performance study of the methods: fusion, the geometrically adaptive energy level, periodicity measure, and zero crossings rates, is presented. The new method is shown to operate reliably down to -5 dB SNR.

Broadcast analysis and prediction in the HF band

A comparative study of the commonly used methods for the prediction of the coverage area due to a transmitter operating in the HF band is presented. Those statistical model based tools are: ITU Rec. 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of Americas VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England, operating around 7.9-19.1 MHz (HF band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height, the calculated results are compared with the experimental data and the discrepancies are examined.

Voice activity detection in nonstationary Gaussian noise

The problem of voice activity detection in additive nonstationary Gaussian noise is considered. A new algorithm for the problem is presented. The algorithm utilizes the differences of the probability distribution properties of noise and speech signals. The magnitude density (mdf) and the magnitude distribution functions (MDF) are used to monitor the noise level for automatic threshold estimation. The estimate is shown to be accurate even when the analysis window does not fully contain non-speech signals and even in the presence of nonstationary noise. The voice activity detection algorithm is shown to operate reliably in SNR down to -5 dB. The method is compared with the periodicity measure method and zero-crossings method. Finally, a fusion algorithm utilizing those methods is suggested.

Comparison of the current methods for coverage area prediction for communication in the HF band

A comparative study of the commonly used methods for the prediction of the coverage area due to a transmitter operating at the HF hand is presented. Those statistical model-based tools are Ionospheric Communication analysis and Prediction Program; IONCAP, Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC, Voice of Americas VOACAP and ITUs REC 533, and those are illustrated by computing the coverage area of a typical transmitter located at Oxford, England operating at 13.399 MHz (HF band I). Those results are compared with the experimental data measured at Istanbul, Turkey for a transmitter located at Oxford, England. Finally, the same problem is analyzed by the ray-tracing technique using the experimental data. The advantages and the disadvantages of the methods are discussed.

High-frequency scattering by a conducting circular cylinder coated with a lossy dielectric of nonuniform thickness

A closed-form expression for the field produced by a plane wave incident on an infinitely long conducting cylinder, coated with a lossy dielectric of nonuniform thickness, is obtained using perturbation theory. This approximate series solution is later evaluated asymptotically for electrically large cylinder sizes. The scattered fields are interpreted using geometric optics and creeping waves. The fields are calculated using the exact series, the approximate perturbation series, and the high-frequency asymptotic solutions, and compared for different angles of incidence.

Randomness tests for the method of uniform sampling quasi-random number generator (MUS-QRNG)

Random number generation is still an important research field in many scientific applications today. Cryptography, Monte Carlo simulations and commertial applications all rely on reference random data. Randomness tests and basic statistics share the same history. Randomness can be summarized as the unpredictability of future samples of a random number generator even in the presence of known all past values. Various randomness tests are developed and due to their individual contributions, usually a battery of tests are applied to verify a random number generator. In signal processing however, the error of a specific observed sample set to a given distribution could be much more important when it is used as the input for a system model. Recently, this distance of finite samples set to a given distribution is studied and a quantitative measure for quality is proposed. Multi run computations like Monte Carlo simulations, often rely on accurate statistical data for high repetibility. Otherwise when the data is not accurate, the results could often rely on the source of random data generator. Many runs are often required to gain a confidence in the presence of those variances. In this work, recently proposed quasi-random number generator utilizing method of uniform sampling (MUS) is tested using standard goodness-of-fitness tests. MUS-QRNG numbers are shown to have exact statistics and also their randomness test results are observed to be similar to well known reference generator of Matlab. MUS-QRNG is proposed for high quality random data generation.

Analysis of wave propagation in inhomogeneous media using FDTD method and its applications

A new simulator to predict the wave propagation in inhomogeneous media is developed. The wave equation is approximated by the approximate difference equations using the finite difference time domain (FDTD) method. The effects of an aberrating layer on radar imaging are examined for various step and graded velocity profile aberrating layers. The method is illustrated for the case where the whole media is inhomogeneous. The permittivity of the medium is assumed to vary in a low-pass Gaussian manner above a constant value. This analysis of radar imaging becomes very important when the medium itself acts as many scatterers. The received echoes are calculated for various values of surface roughness and permittivity difference for both the aberrating layer and the inhomogeneous media. The effects of inhomogeneity on the point spread function (PSF) are analyzed. Later, the cross correlation between the echo signals received at different elements of the radar array are examined as a function of the distance between the elements. The effects of inhomogeneity of the medium on the cross correlation coefficients are also studied.

High frequency scattering by a conducting circular cylinder coated with a lossy dielectric of non uniform thickness

Parrikar et al. (1991) obtained a series solution for the scattering by an impedance cylinder embedded in a nonconcentric dielectric cylinder. Later, Raghep et al. (1988, 1991) studied the elliptic cylinder coated by a nonconfocal dielectric coating. These solutions are rapidly converging only for cylinder sizes comparable to or smaller than the wavelength. For electrically larger cylinders asymptotic solutions are required. The present paper gives an analytical solution to high frequency scattering by a conducting circular cylinder coated with a lossy dielectric of nonuniform thickness. It is assumed that the coating is thin.

An examination of the effect of polarization on the radiation losses of bent optical fibres

It has long been recognized that the bending losses in weakly guiding optical fibres are independent of the polarization for large bend radius. Here, we show this fact using the volume equivalent current method. The procedure is then applied to a helically bent fibre and it is shown that the radiation from the helical fibre is also independent of the polarization as long as the fibre is weakly guiding.

True Random Number Generation of very High Goodness-of-Fit and Randomness Qualities

The statistical nature of numerous problems in mathematics, physics and engineering have led to the development of methods for generating random data for a given distribution. Ancient methods include, dice, coin flipping and shuffling of cards. Today, various pseudo, quasi and true random generators (RNGs) are being proposed for their improved properties. In this work, test metrics for goodness-of-fit and randomness are reviewed. The method of uniform sampling (MUS) is modified for improving the randomness without harming the goodness-of-fit qualities. The test results illustrate that very high goodness-of-fit can be obtained even when the number of observed samples is as small as 10.