Sharif Digital Repository

Vertical plane launching ray tracing method has been applied for a real urban scenario and the delay characteristics of received signals in the overall coverage area have been extracted. Using these parameters, an equivalent channel power delay profile (ECPDP) has been introduced for the overall coverage area. For a millimeter wave wireless OFDM system, the optimum guard interval length which maximizes the mean of signal to interference and noise ratio has been simulated. Also, using the proposed ECPDP, the optimum guard interval length has been analytically extracted and compared with the simulated one  

One non-cooperative illuminator recently considered for passive radar applications is the DVB-T (Digital Video Broadcasting-Terrestrial) signal. The thumbtack ambiguity function of the DVB-T signal, in addition to being stationary over time, makes such a signal a good candidate for such applications. However, certain ambiguities in its ambiguity function necessitates certain issues to be carefully considered when the DVB-T signal is to be utilized in these scenarios. Methods have been already proposed to resolve them. In this paper, after studying the origins of these ambiguities, we propose special processing schemes to reduce the complexity of the parts associated with resolving these... 

In this research we have proposed a new definition for three-dimensional (3-D) integral imaging resolution. The general concept of two-dimensional (2-D) resolution used also for 3-D is failed to describe the 3-D resolvability completely. Thus, the researches focused on resolution improvement in 3-D integral imaging systems, didn't investigate thoroughly the effect of their method on the 3-D quality. The effect has only been shown on the 2-D resolution of each lateral reconstructed image. The newly introduced 3-D resolution concept has been demonstrated based on ray patterns, the cross-section between them and the sampling points. Consequently the effect of resulting sampling points in 3-D... 

The performance of the adaptive spatial resolution technique is improved by making the resolution function of the coordinate transformation as smooth as possible. To this end, the smoothness of the resolution function is probed and a quantitative criterion is proposed to make the jump points; which were conventionally equidistant from each other, regularized. The here-proposed regularization is applied to two different recent formulations and its effects on the overall convergence rate and on the presence of numerical artifacts in analysis of highly conducting gratings are studied. Dielectric and metallic gratings at optical and microwave frequencies are considered and the helpfulness of the... 

The vertical plane launching ray tracing method has been applied for a real urban scenario and the delay characteristics of received signals in the overall coverage area have been extracted. Using these parameters, an equivalent channel impulse response (ECIR) has been introduced for the overall coverage area. For an orthogonal frequency division multiplexing system, the optimum guard interval, which maximises the number of points with symbol error rate less than a threshold, has been simulated. Using the defined ECIR, the optimum guard interval could be analytically extracted  

Governing equations of a Raman fiber distributed temperature sensor supported by a counter propagating pumped Raman amplifier are written in the form of integral equations. Forward pump and backward going probe are in the pulsed and continuous wave modes of operation respectively. It is shown that powers of the forward and backward Raman signals (stokes and anti stokes) approximately are the convolution of the input forward pump pulse and corresponding optical fiber impulse responses. The Fourier Wavelet Regularized Deconvolution (ForWaRD) method is employed to improve the spatial resolution in fiber Raman distributed temperature sensor without reducing the pulse width of the laser source  

A significant challenge in spectrum sensing is to lessen the signal to noise ratio needed to detect the presence of primary users while the noise level may also be unknown. To meet this challenge, multi-antenna based techniques possess a greater efficiency compared to other algorithms. In a typical compact multi-antenna system, due to small interelement spacing, mutual coupling between thermal noises of adjacent receivers is significant. In this paper, unlike most of the spectrum sensing algorithms which assume spatially uncorrelated noise, the noises on the adjacent antennas can have arbitrary correlations. Also, in contrast to some other algorithms, no prior assumption is made on the... 

Electrical impedance tomography (EIT) is a simple, economic and healthy technique to capture images from the internal area of the body. Although EIT is cheaper and smaller than other imaging systems and requires no ionizing radiation, the resolution associated with this technique is intrinsically limited and the image reconstruction algorithms proposed up to now are not efficient enough. In addition to low resolution EIT is an ill-posed inverse problem. Block method in EIT is based on electrical properties of materials and used to enhance image resolution and also to improve the reconstruction algorithm. Recently an inverse solution for EIT based on block method has been developed, however,... 

Although there is an increasing interest in employing the depth data in computer vision applications, the spatial resolution of depth maps is still limited compared with typical visible-light images. A novel method is proposed to synthetically improve the spatial resolution of a single depth image. It integrates the higher-order terms into the Markov random field (MRF) formulation of example-based methods in order to improve the representational power of those methods. The inference is performed by approximately minimising the higher-order multi-label MRF energies. In addition, to improve the efficiency of the inference algorithm, a hierarchical scheme on the number of MRF states is... 

A resolution-improved active millimeter-wave (MMW) imaging structure, based on the theory of structured illumination, is proposed in this paper. The structured illumination is a well-defined concept for surpassing the diffraction limit in optical microscopy, where imposing grating patterns on the targeted object could help in moving the object frequency spectrum along the desired direction in the spatial frequency domain. This frequency shift helps in passing different parts of the object's frequency spectrum through the diffraction filter. The combination of resultant images provides a framework to pass a wider frequency band of the object, thereby achieving super-resolution. This idea has... 

Optical coherence tomography (OCT) is a noninvasive imaging modality that provides cross-sectional images from microstructures of tissues. This optical imaging system works based on Michelson interferometry principle and has intermediate resolution and penetration depth which makes it appropriate for imaging thin tissues such as skin and eye. OCT images suffer from three main artifacts that make images difficult to be analyzed. The first one is small grainy structures called speckle which degrade image quality and decreases axial and lateral resolution. The second one is light intensity attenuation which is a function of depth. It happens because of absorbing and scattering nature of tissue... 

In recent days imaging systems have seen considerable extended usage due to their ease of use and reasonable price. However, they have weaknesses lies in image resolution. In order to increase the quality of the images, due to the technical limitations and costs of hardware parts, software techniques like the super-resolution is used, which means increasing the density of pixels in the image. The super-resolution is broken down into two categories; super-resolution using a single image and super-resolution using multiple images. In this paper, a method for increasing image quality, based on the Dong method has been proposed. In the proposed method, which is based on only one image, tries to... 

Partial discharge (PD) measurement and identification have great importance to condition monitoring of power transformers. In this paper a new method for recognition of single and multi-source of PD based on extraction of high level image features have been introduced. A database, involving 365 samples of phase-resolved PD (PRPD) data, is developed by measurement carried out on transformer artificial defect models (having different sizes of defect) under a specific applied voltage, to be used for proposed algorithm validation. In the first step, each set of PRPD data is converted into grayscale images to represent different PD defects. Two “image feature extraction” methods, the Local Binary... 

The present study provides an inverse solution and analysis on a new approach for Electrical Impedance Tomography (EIT) process as block method in EIT. In this method, it is assumed that all of the panicles of each block have the same electrical properties (electrical conductivities). This technique is used to enhance image resolution and also to improve reconstruction algorithm. Although this method has been developed for 3D objects, in this study it is assumed that the subject has a (two-dimensional) rectangular shape and is made of fixed size blocks. By considering the previous conditions and computing relationship among currents, voltages and electrical impedances of blocks, the required... 

The technique of adaptive spatial resolution is for the first time applied in fast and efficient Fourier-based analysis of metallic lamellar gratings at microwave frequencies. Inasmuch as the ultrahigh-contrast permittivity profile of these structures is likely to incur numerical instabilities, the continuity condition is heedfully imposed on the transverse electromagnetic fields and an elegant, unconditionally stable matrix-based strategy is proposed to rigorously analyze the microwave transmission of these structures. © 2009 IEEE  

In this study, a new passive method suitable for geolocating low probability of intercept (LPI) radars is introduced. The method uses two electronic support receivers placed on a fast moving platform (e.g., an airplane or a satellite). The proposed method has a high processing gain, which makes it highly suitable for very weak LPI signals. The method processing gain was analytically derived and illustrated with simulation to determine if the proposed method can detect LPI radars in much lower SNRs compared to regular time-frequency LPI detection methods. Also, the resolution of the proposed method in both range and cross-range directions in radar location finding was analyzed. The results... 

Electroencephalogram (EEG) is a noninvasive, low-cost brain recording tool with high temporal but poor spatial resolution. In contrast, functional magnetic resonance imaging (fMRI) is a rather expensive brain recording tool with high spatial and poor temporal resolution. In this study, we aim at recovering the brain activity (source localization and activity-intensity) with high spatial resolution using only EEG recordings. Each EEG electrode records a linear combination of the activities of various parts of the brain. As a result, a multi-electrode EEG recording represents the brain activities via a linear mixing matrix. Due to distance attenuation, this matrix is almost sparse. Using...