Selçuk Paker

Deterministic maximum likelihood approach for 3-D near field source localization

Summary In this paper, maximum likelihood estimator is proposed for passive localization of narrowband sources in the spherical coordinates (azimuth, elevation, and range). We adapt Expectation/Maximization iterative method to solve the complicated multi-parameter optimization problem appearing on the 3-D localization problem. The proposed algorithm is based on maximum likelihood criterion which employs the source signals recorded by 2-D array under near-field assumption. Expectation/Maximization algorithm decomposes the observed data into its components and then estimates the parameters of each signal component separately providing computationally efficient solution to the resulting optimization problem. Performance analysis of the proposed algorithm is then carried out through the evaluation of Cramer-Rao bounds. Finally, the applicability and effectiveness of the proposed algorithm is illustrated by some numerical simulations.

Maximum likelihood 3-D near-field source localization using the EM algorithm

In this paper, maximum likelihood estimator is proposed for passive localization of narrowband sources in the spherical coordinates (azimuth, elevation, range). We adapt expectation/maximization iterative method to solve the complicated multi-parameter optimization problem appearing on the 3-D localization problem. The proposed algorithm is based on maximum likelihood criterion, which employs the source signals recorded by 2-D array under near-field assumption. Expectation/maximization algorithm decomposes the observed data into its components and then estimates the parameters of each signal component separately providing computationally efficient solution to the resulting optimization problem. Finally, some numerical simulations illustrate the applicability and effectiveness of the proposed algorithm.

Image reconstruction with diffraction tomography using different inverse Radon transform algorithms

The penetration of microwaves in various materials gives active microwave imaging a large potential for some applications in medical imaging. This fairly recent imaging technique is aimed at obtaining some information about the physical properties of an object which is exposed to low power incident microwave radiation. Measured external scattered field data is used for the imaging purpose. In this computer simulation work, electromagnetic far field scattered data of a dielectric cylinder having infinite length are used for reconstruction under Born approximation. Using a series of integral transform, the three fold Radon transform integral is reduced into one fold. Having found the Radon transform of the object function, inverse Radon transform algorithms are used to reconstruct it. These three different inverse Radon transform methods are direct inverse Radon transform, convolution back projection and filter back projection. The result of the computer simulation algorithms of different methods are presented.<<ETX>>

SAR changes in a human head model for plane wave exposure (500 - 2500 MHz) and a comparison with IEEE 2005 safety limits.

In this paper, external electric field values that are derived from the largest peak average 10 g SAR (Specific Absorption Rate) results in a realistic human head model are compared with current IEEE and ICNIRP reference levels. The head is illuminated by a plane wave source at seven different frequencies ranging from 500 MHz to 2500 MHz, with five different incident directions and three polarizations. Results reveal that the presence of metallic wire spectacles reduces the external electric field levels in the region above 900 MHz. Comparison of derived electric field values shows that the current IEEE and ICNIRP safety limits provide a conservative estimate.

EM Based Stochastic Maximum Likelihood Approach for Localization of Near-field Sources in 3-D

Abstract The goal of this paper is to estimate the locations of unknown sources in 3-D space from the data collected by a 2-D rectangular array. Various studies employing different estimation methods under near-field and far-field assumptions were presented in the past. In most of the previous studies, location estimations of sources at the same plane with the antenna array were carried out by using algorithms having constraints for various situations indeed. In this study, location estimations of sources that are placed at a different plane from the antenna array is given. In other words, locations of sources in 3-D space is estimated by using a 2-D rectangular array. Maximum likelihood (ML) method is chosen as the estimator since it has a better resolution performance than the conventional methods in the presence of less number and highly correlated source signal samples and low signal to noise ratio. Besides these superiorities, stability, asymptotic unbiasedness, asymptotic minimum variance properties as well as no restrictions on the antenna array are motivated the application of ML approach. Despite these advantages, ML estimator has computational complexity. However, this problem is tackled by the application of Expectation/Maximization (EM) iterative algorithm which converts the multidimensional search problem to one dimensional parallel search problems in order to prevent computational complexity. EM iterative algorithm is therefore adapted to the localization problem by the data (complete data) assumed to arrive to the sensors separately instead of observed data (incomplete data). Furthermore, performance of the proposed algorithm is tested by deriving Cramer-Rao bounds based on the concentrated likelihood approach. Finally, the applicability and effectiveness of the proposed algorithm is illustrated by some numerical simulations

Ku - Band slotted rectangular patch array antenna design

In the recent years, microstrip antennas have quickly developed from a research novelty to a practical reality, with applications in a wide range of communication systems that must thank to their numerous appreciated features. The present work proposes a low nature slotted microstrip antenna with ground plane structure for Ku-band satellite communications. Firstly, a single Ku-band slotted patch antenna designed and then 2×2 array structure modelled and simulated by using Ansoft HFSS 3D electromagnetic simulation tool. High directivity of antenna has been realized by using full ground plane and via has fed array elements. Array feed circuit placed behind of antenna in the third layer. The gain of array antenna is about 12dBi and it is usable between 12.2 GHz and 13.1 GHz band frequency. The configuration of the proposed antenna shows the way to fabricate and make it appropriate for Ku-band applications in satellite communications.

Performance of a combined trellis coded quantization/modulation over wireless local-loop environment†

In this paper, a combined trellis coded quantization/modulation (TCQ/TCM) scheme is introduced for the wireless local-loop environment modelled with realizable and practical medium parameters. The performance analysis of the combined system is carried out through the evaluation of signal-to-quantization noise ratio (SQNR) versus signal-to-noise ratio (SNR) curves and bit error probability upper bounds. Simulation studies confirm the analytical results. Copyright

Jitter performance of neural network equivalent MPSK schemes over microwave channels

In this paper a new microwave channel model with realizable and practical parameters is defined for indoor mobile communication. The emphasis is on the jitter and error performance of trellis-coded MPSK and neural network equivalent systems over microwave channels with no channel state information (CSI) and no side information on the phase noise process. Analytical upper bounds are derived using the Chernoff bounding technique combined with a modified generating functional approach. It is shown that the neurocomputing results confirm the analytical results.

Effects of substrate thickness and dielectric to microstrip dipol antenna parameters for 2.4 GHz wireless communication devices

İt is aimed to design 2.4 GHz microstrip-dipole antennas for wireless communication systems by using different substrates with different physical properties in this paper. Designs were made according to general microstrip dipole structure. Ansoft HFSS programme was used for simulations of antennas and simulations were used to indicate effects of substrate thickness, tangent loss and dielectric to antenna.

Bi-static scattering width control of multiple coated PEC cylinder

In this study, we propose the method that determines the coated parameter values of the cylinder satisfying the desired bistatic scattering width (SW). We consider the infinitely long perfectly electric conductor (PEC) cylinder, which is illuminated by plane wave whose polarization is parallel to cylinder axis. Unknown scattered field coefficients are expressed by using boundary conditions in terms of coating parameters for fixed wavelength and radius of cylinder. Far field SW is obtained using the scattered coefficients and then steepest descent method is used to control the bi-static SW according to each coating complex wave number and thickness. Minimised bi-static SW was compared to those of PEC cylinder and good reduction values were observed over a wide frequency range and angle.