Sharif Digital Repository

Achieving various data rates over a wide range of applications and in a multiple-access scenario should be done under certain power and bandwidth constraints. Emerging UWB communications has opened a novel perspective against different wireless network challenges, especially overwhelming data rates. In the research field, we begin our thesis with exposition of UWB, narrowband interference and spread time codes. We elaborate on the properties of spread time codes through frequency domain analysis of a reusable multiple-access scheme. Evaluating the variance of ISI, MAI and RUI, we demonstrate the spread time codes behave in an optimum manner, i.e., the most RUI resistibility, along with all... 

In this thesis, we study and analyze the performance of matched and partially-matched re-ceivers for a typical Ultra Wide-band Spectrally-Encoded Spread-Time (SE/ST) CDMA in the presence of multiple tone jammers and a coexisting OFDM system. We investigate a scenario in which there is not any information about the jammer and OFDM subcarrier frequencies in the transmitter side and we try to cancel jammers and interferences at the receiver. For this case, we demonstrate that by using a partially-matched filter at the receiver in an environment with multiple tone jammers and some coexisting systems the performance of the SE/ST system can be improved. We also assume K asynchronous users and... 

Increasing need to high rates of transmission through radio channels is a challenging problem in wireless communications. Simple implementation and high spectral efficiency of OFDM system turned it into a suitable choice to meet this need. Accurate estimation of the communication channel has a significant impact on performance of Orthogonal Frequency Division Multiplexing (OFDM) systems. Conventional methods of channel estimation are not able to exploit the inherent sparsity of the channel that is due to sparse distribution of scaterrers. On the other hand, Compressed Sensing (CS) is getting attention in variety of aspects such as communications, recently.CS-based channel estimation exploits... 

Synthetic Aperture Radar (SAR) is a coherent imaging technique capable of generating fine resolution images from long term standoff ranges, either day or night. The use of multiple antennas for SAR is referred to as multichannel SAR or Multiple-Input Multiple-Output(MIMO) SAR and offers the additional abilities to perform height estimation of the ground, improve the resolution and suppress undesired interferences. Ground moving target indication (GMTI) is the one that we explored in this research. Since the pattern of moving target in imaging zone is sparse, we can use compressed sensing for reducing computational complexity caused by additional channels. In our thesis, after modelling the... 

By direct and alternating electric field applied to thin film of liquid suspended in the air we can spin out and control it. Rotation pattern depends on the geometry of the electrodes and the applied magnetic field. This is called a rotating liquid film (Liquid Film Motor). To determine the cause of rotation, different models have been proposed. In this project we have tried to check the accuracy of any of the models. Using particle velocimetry using the photo, we calculate the velocity pattern. Then, using the Navier-Stokes equation calculate the acceleration and viscosity from the velocity. Then, for a special arrangement using a finite diffrent method, electric potential and the electric... 

The present study was an endeavor to investigate the effectiveness of English full and keyword captions in comparison to Farsi full and keyword subtitles and no caption with regard to English language learners’ listening comprehension and incidental vocabulary acquisition. For this purpose, 76 English as a foreign language (EFL) learners at Sharif University of Technology from five intact classes were assigned to each condition. Preliminary English test was administered to measure learners’ listening performance before and after the treatment. Researcher-made vocabulary tests based on the difficult words that were captioned in the videos were included in vocabulary tests. The treatment... 

The present study, which is about practical methods of improving productivity in Mashhad ring factory, is presented in five chapters. In the foreword, the need for an attitude to improve productivity at the national level as well as in industry has been mentioned and has laid the groundwork for starting a discussion of productivity and practical solutions to improve it. In the first chapter, by defining productivity, considers the different perceptions of societies about productivity and finally deals with misconceptions about the concept of productivity. In the second chapter, based on committed articles from the American Society of Industrial Engineering, discusses the role of industrial... 

Nowadays, ultra-wideband (UWB) communication systems are in focus because of their attractive features such as high capacity, low power consumption and robustness against fading. On the other hand, spectrally-encoded spread-time (SE/ST) systems with superior ability on interference suppression provide proper multiuser efficiency over UWB channels. Coherent SE/ST code division multiple access (CDMA) systems are widely addressed in the literature requiring accurate channel estimation and high implementation complexity. In this paper we propose multi-level SE/ST CDMA system with non-coherent detection by considering two different scenarios: i) Known :only channel gain components of desired user... 

Today, with the expanding usage of wireless communication systems, the need for system which uses the spectrum efficiently is inevitable. Therefore, Cognitive Radio structures have be the center of attention, recently. In cognitive radio structures, the system tries to use the empty spectrum efficientlyin time, frequency, and space domain. Autonomous Vehicular Networks are interesting application, in which cognitive radio can be used. In such networks, due to high speed, the channel state changes drastically which negatively affects the system.Hence, in this thesis, an OFDM-based multiuser structure is designed which work properly in such condition. For designing the structure, a doubly...