Sharif Digital Repository

Our ultimate goal in this thesis is to design a chaotic receiver for detecting small targets in sea clutter. Sea clutter at low grazing angle has a spiky behavior and in this thesis we desire to model this irregular behavior in the chaos theory frame work. Using a trend similar to statistical detection theory, we will obtain the suboptimal chaotic receiver and investigate the receiver noise effect on the optimality or sub optimality of the detector. Chaotic detector can be used in the coherent and non coherent mode. Although the coherent detector has a superior performance, the efficiency of the non coherent detector is acceptable as well. We will investigate the efficiency of the chaotic... 

Modern communication and space systems such as satellite communication devices, radars, SAR and radio astronomy interferometers are realized with large antenna arrays since this kind of radiating systems are able to generate radiation patterns with high directivity and resolution. In such a framework, conventional arrays with uniform inter-element spacing could be not satisfactory in terms of costs and dimensions. An interesting alternative is to reduce the array elements obtaining the so called ‘ thinned arrays’. Large thinned arrays have been exploited because of their advantages in terms of weight,consumption, hardware complexity, and cost over the... 

Today, SAR radars are one of the most practical tools for controlling and monitoring surface targets, and so far, several methods have been proposed to create a profile image of the reflection coefficient of surface targets in these Radars. The main problem in these methods is the ability to simultaneously create a reflection coefficient profile image for stationary and moving targets. To create a profile image of the reflection coefficient of moving targets, first it is necessary to detect and estimate its kinetic parameters.This thesis presents a method for detecting and estimating Ground moving targets parameters using Keystone transfer conversion and also presents a method for creating... 

Forward scatter radar is a special kind of bistatic radar. It is designed to detect targets near the transmitter-receiver line which is called baseline. It has a number of promising features such as larger target radar cross-section (RCS) than that of traditional radars, applicability of shadow inverse SAR (SISAR) algorithms, high performance in automatic target recognition and identification, and robustness to stealth technology. On the other hand, it also has some inherent limitations, including the absence of range resolution (potentially leading to a high Doppler clutter level) and operation within narrow angles relative to the transmitter-receiver baseline. Target detection in forward... 

The conventional bearing-only tracking solutions are based on Kalman filter. Whenever the problem equations are nonlinear, Extended Kalman Filter (EKF) or more complicated methods are used necessarily. However, EKF suffers of being biased and unstable. Here a new recursive method based on a linear modeling of the problem is proposed, the method does not need an initial guess and outperforms the Kalman filter in the terms of accuracy, complexity and stability. Furthermore, input information needed for the proposed tracking filter is just the observer position, time and value of each angle measurements and the computation load is less than even a simple EKF. mathematical analysis, as well as... 

In this dissertation, the application of frequency and space diversities in radar target parameter estimation are investigated. On this basis, multi-frequency signal is used to improve the range resolution, array structure is used to increase the angle estimation accuracy and the merger of the multi-frequency signal and array structure are used to increase the maximum number of targets that can be uniquely identified.Considering the desirable properties of multi-frequency signals such as high bandwidth efficiency, high range resolution achievement without chip length decrease and …, there has been increased interest in the vast area of research on the design of such signals that has... 

Target recognition techniques based on micro Doppler phenomenon are popular because they are applicable even on low resolution radars, in contrast to other techniques such as High Resolution Range Profile (HRRP) which need high resolution in range or angle. Usually, main purpose of such techniques is generating robust features against target initial state, velocity, aspect angle, etc. rather than features which exactly identify a target. Main approaches in the literature are based on time-frequency transforms (TFT) such as spectrogram in order to generate features to classify targets, but in this thesis, we propose a totally different method using Recurrence Plot for generating features... 

In this work, Hough detector has been compared with optimum detectors. We consider 2-D range-time data space, which is constructed by storing the radar returns from different range cells during several successive scans. In this space, target trajectory can be modeled as a straight line for short time intervals, and can be extracted by applying Hough transform transcendentally. In this work, a new detection method based on the likelihood ratio in the data space with Gaussian noise is introduced. ALR and GLR processors have been designed. Then formulas for probability of detection and false alarm rate is calculated, and verified via simulations. A new criterion for estimation quality is... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

The integration of radar and communication functionalities into a unified Joint Radar-Communication (JRC) system offers enhanced spectral efficiency and reduced hardware complexity. Recognized as a key enabler for next-generation wireless networks, JRC systems require a careful balance between radar and communication demands, where waveform design plays a pivotal role in achieving this equilibrium. Although waveform design has been extensively studied separately in radar and communication domains, the requirements of modern networks necessitate a unified approach that simultaneously addresses the needs of both systems. This thesis advances waveform design methodologies for JRC systems,... 

In this project a high spectral purity C-band (4.25-5GHz) frequency synthesizer has been analyzed and designed and implemented in CMOS 0.18μm technology. This synthesizer has been embedded in TX path of a transceiver module as a frequency translator for digital phased array system applications. The system includes Phase Locked Loops (PLLs) and Direct Digital Frequency Synthesizer (DDFS). Due to desired Low spur level (90 dBc) in C-band, system level design, frequency plan, choosing proper PLL topology and etc. have been considered in details. One of the important challenges in system design is the signal spectrum purity. In other words, the system should produce minimum phase noise. Output... 

By generalizing dictionary learning (DL) algorithms to Multidimensional (MD) mode and using them in applications where signals are inherently multidimensional, such as in three-dimensional (3D) Inverse Synthetic Aperture Radar (ISAR) imaging, it is possible to achieve much higher speed and less computational complexity. In this thesis, the formulation of the Multidimensional Dictionary Learning (MDDL) problem is expressed and six algorithms are proposed to solve it. The first one is based on the method of optimum directions (MOD) algorithm for 1D dictionary learning (1DDL), which uses alternating minimization and gradient projection approach. As the MDDL problem is non-convex, the second... 

Inspiring by recent developments of Multiple input multiple output (MIMO) communications, MIMO radar has been introduced and MIMO radar advantages such as higher degrees of freedom, improved resolution, and improved estimation accuracy are shown. These advantages have drawn attention of many researchers and engineers toward MIMO radar. On this basis, and during the recent years, in many researches, effect of increasing the number of antennas and pulses on the radar performance have been studied. Although MIMO radar has the aforementioned advantages, the hardware costs (due to multiple transmitters and multiple receivers), high energy consumption (multiple pulses), and computational... 

Multi-Input Multi-Output (MIMO) systems are a type of radar that utilizes multiple transmitters and multiple receivers along with various signaling techniques to optimize several aspects compared to conventional radars. The subject of this doctoral dissertation focuses on a specific type of MIMO radar known as Synthetic Impulse and Aperture Radar (SIAR). In this context, one of these MIMO radar models, recognized as SIAR, has unique characteristics that we will explore here. Initially, the sources will be examined, and the problem formulation of this type of radar will be analyzed. Subsequently, there will be an emphasis on target detection and separation in low-altitude scenarios. Various... 

There are a wide variety of radar systems that one of them is MIMO Radars. After a spark in communication in 1998 that developed MIMO communication, recently there has been a great attention towards MIMO radar systems. Researchers have studied this topic from several points of view. Generally, MIMO radar systems are divided into two categories: MIMO radars widely separated antennas and MIMO radars with collocated antennas. One of the important issues of widely separated MIMO radars, is the placement manner of receivers in the geometrical area. This radar’s performance is very dependent to placement of the antennas, because the performance is dependent to relative position of... 

In this thesis, we investigate the statistical performance of the array processing algorithms. Theoretical performance analysis leads to better methods that outperform the existing algorithms. Besides, analytical performance analysis, results in a more profound understanding of the nature of the considered problem. First of all, problem of covariance matrix estimation, in the non-Gaussian signal case will be investigated. We will focus on a nonparametric estimator which relies on the sign of the data to estimate the covariance matrix on an element-by-element basis. It was known that, sign estimator may give invalid covariance estimates in higher dimensions of the data. We prove this fact in... 

In this thesis, a new passive method suitable for Geolocating LPI radars is introduced. The method uses two Electronic Support (ES) 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 processing gain of the method 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 direction in radar location finding was analyzed. Furthurmore, the effect of the... 

Fog computing environment consists of several devices which distribute across an arbitrary topology. Each of these devices is capable of carrying out a designated computation simultaneously with other devices. One of the common ways of describing a computation is through the usage of workflows. Workflow is a flexible and formal way of modeling tasks and their requirements for execution. A workflow is essentially a DAG. Therefore, it can model the data dependency between tasks quite accurately. The complex structure of a workflow in conjunction with the homogenous nature of devices in a fog environment makes it difficult to find a resource management algorithm to minimize execution time, used... 

This project focuses on the design of fuel drop tanks for airplanes that add minimal drag and positive lift to the flying object. This will obviously effect the stability and dynamic performance of the airplane. To reduce adverse dynamic effects the tank was divided to several segment with a special emptying sequence. The add-on tank has to have no interference with the object existing systems and require minimum structural changes in the object. Several designs were proposed and the one gaining highest marks was selected. The flow field and the dynamic behavior of combined vehicle and drop tanks were studied using FE simulations. The result shows that adding a drop tank with optimized... 

Cancer can be defined as a stochastic phenomenon. Thus, the tumor growth can be defined as a stochastic process. A Cancer tumor can be analyzed by its geometric shape. Furthermore, computing fractal dimension of shapes is a useful technique to analyze chaosity and complexity of shapes. This approach can be used to compare results from laboratory with simulated results of a mathematical model. A stochastic model of tumor growth will be presented. And some geometrical properties will be analyzed through computer simulation of the model