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    Optimal Scheduling in Wirelessly-powered Communication Networks

    , Ph.D. Dissertation Sharif University of Technology Movahednasab, Mohammad (Author) ; Pakravan, Mohammad Reza (Supervisor)
    In this thesis, we study optimal scheduling in a multi-hop wirelessly-powered network. We propose an online control policy for energy transfer from the energy access point to the wireless nodes and for data transfer among the nodes. With our proposed control policy, all data queues of the nodes are stable, while the average energy consumption of the network is shown to be within a bounded gap of the minimum energy required for stabilizing the network. Our proposed policy is designed using a quadratic Lyapunov function to capture the limitations on the energy consumption of the nodes imposed by their bachery levels. We show that under the proposed control policy, the bachlog level in the data... 

    Non-coherent DOA Estimation Via Majorization-Minimization Using Sign Information

    , M.Sc. Thesis Sharif University of Technology Delbari, Mohamad Reza (Author) ; Marvasti, Farrokh (Supervisor)
    Direction of arrival (DOA) estimation has various applications in different areas such as wireless communication and signal processing in medical applications. Most of the previous methods were not based on digitalization, but the advantages of digitalized methods have been proved in recent decades. Furthermore, because of existing the phase error, we need to use the algorithms to find the solution with amplitude measurements. A solution method to this problem was introduced in 2015 for the first time, and then newer algorithms were proposed. However, most of them need reference signals to resolve the inherent ambiguity of the problem. By contrast, this dissertation not only does not use... 

    Increasing Operating Range of Wideband Reconnaissance Receivers, by Using Antenna Arrays

    , Ph.D. Dissertation Sharif University of Technology Sobhani, Ghasem (Author) ; Behnia, Fereidoon (Supervisor)
    Passive wideband reconnaissance receivers, listen to the radio and radar signals in the environment and estimate their important parameters such as direction of arrival (DOA). The wideband attribute for these receivers is to refer to their ability to receive wideband signals.Due to the use of processing gain, LPI radars reduce their transmitted signal power to see and not to be seen. On the other hand reconnaissance receivers can not have much processing gain, because they do not know the nature of the transmitted signal; Therefore, to increase the operational range of these systems, it is necessary to increase the signal to noise power ratio (SNR). This thesis examines the use of antenna... 

    Design of a Phased Array Receiver for 5G Applications

    , M.Sc. Thesis Sharif University of Technology Tahbaz Alli, Parsa (Author) ; Sharif Bakhtiar, Mehrdad (Supervisor)
    Next-generation wireless communication requires phased-array systems to ensure Gb/s data communication. This work demonstrates a four-element phased array receiver based on N-path filters for the 5G-FR1 frequency band. The behaviour of the circuit including non-idealities and effects due to mismatch in the paths is modeled and verified via simulations. As the time-variant nature of the N-path filter introduces multiple frequency translations, third harmonic selection of the switching frequency rather than the fundamental helps to reduce the input frequency of the multiphase clock generator by a factor of three. Therefore, the proposed structure is capable of third harmonic reception as well... 

    Phase Shifter Response Compensation in Microwave Band

    , M.Sc. Thesis Sharif University of Technology Aghaei Saem, Ali (Author) ; Khavasi, Amin (Supervisor) ; Fakharzadeh, Mohammad (Co-Supervisor)
    A phase shifter is a microwave element that changes the phase of the input signal at a specific center frequency and bandwidth and, ideally, produces a signal with the same amplitude and a modified phase at the output. In practice, this phase change in the passive phase shifter is accompanied by a decrease in amplitude due to different factors. Various use cases can be described for phase shifters in telecommunication circuits, but its most important application is in regulating the relative phase of each antenna in a phased array system, which is the most common method of beam steering and forming. A phased array system is one of the leading solutions to achieve beamforming and high... 

    A Deep Learning MIMO Communication System Based on Auto-encoder Design

    , M.Sc. Thesis Sharif University of Technology Mirzaee, Ali (Author) ; Hossein Khalaj, Babak (Supervisor)
    Today, the use of deep learning algorithms in the design of communication systems has received much attention. One of these areas is the partial or total design of these systems using deep networks. The overall design of a communication system using deep networks allows for global optimization and can provide better performance in cases where classical methods have suboptimal performance without significantly increasing the computational load. In this research, a comprehensive architecture for designing communication systems based on Auto-encoder neural networks is presented. This architecture has the same functionality as classical systems, considering all parts of these systems including... 

    A Novel Simultaneous Frequency and Spatial Filtering Methodology for Beam-forming and Null-steering in Integrated Phased-Array Systems Using N-path technique

    , Ph.D. Dissertation Sharif University of Technology Karami, Poorya (Author) ; Atarodi, Mojtaba (Supervisor)
    In the communication systems, there are two types of blockers: in-band and out-of-band. High frequency pre-filters and band-pass filters can be used to suppress the out-of band blockers. However, using these methods does not affect the in-band interferers. Spatial filtering by means of phased array antennas and using frequency filtering can suppress both types of interferers. In a typical phased array receiver, all of the received signals pass through active blocks (such as LNAs, active phase shifters, driver amplifiers, etc.) that amplify the interferers before canceling them. Therefore, because of the high strength of the interferers, the dynamic range of the front-end blocks preceding... 

    Improving the Performance of Time Modulated Array by Designing Proper Switching Sequence

    , Ph.D. Dissertation Sharif University of Technology Mazaheri Kalahrody, Mohammad Hossein (Author) ; Akbari, Mahmood (Supervisor) ; Fakharzadeh, Mohammad (Supervisor)
    Time-Modulated Array is known as an electrical beamforming technique that has lower cost and complexity compared to the conventional beamforming techniques. In a Time-Modulated Array, the antennas are turned on and off periodically, so the harmonics of the switching appear in the spectrum of the signal. The radiation characteristics of the array such as Side Lobe Level and beam orientation can be controlled at these harmonics, also known as sidebands. The capability of the array in creating multiple simultaneous radiation patterns has paved the way toward employing this technique in wireless communication applications. In this thesis we explore the basic fundamentals and the characteristics... 

    Beamforming in SAR Satellites for Nadir Echo Suppression

    , Ph.D. Dissertation Sharif University of Technology Khosravi, Mahdi (Author) ; Bastani, Mohammad Hassan (Supervisor) ; Fakharzadeh, Mohammad (Supervisor)
    In synthetic aperture radar (SAR) satellites, the nadir echo is defined as the backscattered signal from the point directly below the satellite on the earth surface. If the timing of the radar is such that the nadir echo arrives at the receiver while the receiver is turned on for receiving the desired signal, it could damage the receiver or disrupt the resulting SAR image, unless it is suppressed enough by proper design of antenna radiation pattern. In current SAR satellites, ”avoiding” this phenomenon is associated with two problems: 1) limiting the swath width, 2) imposing stringent restrictions on the selection of pulse repeatition frequency (PRF). Therefore, ”suppressing” the nadir echo,... 

    Fusion of Audio and Visual Occurrences using Fuzzy Logic for Improving Perception Quality of Events

    , Ph.D. Dissertation Sharif University of Technology Faraji, Mohammad Mahdi (Author) ; Bagheri Shouraki, Saeed (Supervisor)
    The ability of human to analyze the environment around them has been an inspiring source for event analysis research. Since human perception of the environment is formed in a multi-modal space, many efforts have been made to fuse information to create an intelligent fusion. In this study, we want to better understand the environment using information fusion. For this purpose, fuzzy fusion of audio and video signals based on ink drop spread operator is performed for recognizing and tracking of the targets using several scenarios of the AV16.3 dataset. We then focused on the fusion of audio data for sound source localization, one of the most important applications in evaluating fusion... 

    Design and Simulation of mmWave Antenna Arrays with Novel 3D Geometries for 5G Wireless Applications

    , M.Sc. Thesis Sharif University of Technology Ahmadi, Nima (Author) ; Farzaneh, Forouhar (Supervisor)
    In the new generations of mobile communication systems, smart antennas are used to achieve higher capacities. Since these systems have the ability to form a radiation pattern where the desired signal is received with minimum distortion and inteferers are received with a significant attenuation therefore their application makes it possible to have a large signal to inteference ratio. In addition by setting the main beam direction towards the desired signal, it is conceivable to realize the the communication with a lower power. The optimal methods for angle-of-arrival estimation and beamforming in one and two dimensional structures has been studied in the literature, but the three dimensional... 

    Secure Communication via Cooperation and Cooperative Jamming

    , M.Sc. Thesis Sharif University of Technology Hatami, Mohammad (Author) ; Behroozi, Hamid (Supervisor)
    The broadcast nature of wireless communications makes the propagation medium vulnerable to security attacks such as eavesdropping and jamming from adversarial or unauthorized users. Applying physical layer secrecy approaches will enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without using any secret keys. However, physical layer security approaches are typically feasible only when the source-eavesdropper channel is weaker than the source-destination channel. Cooperative jamming can be used to overcome this challenge and increase the secrecy rate. In this thesis, the security of two-phase relaying system with multiple... 

    Analysis and Design of a Multi-Beam Millimeter-Wave Antenna

    , M.Sc. Thesis Sharif University of Technology Kazemi, Hamid Reza (Author) ; Borji, Amir (Supervisor)
    So far, Investigations have shown that microstrip antennas (MSA) offer a lot of advantages at microwave and millimeter wave frequencies. These advantages include small size, large impedance bandwidth, high radiation efficiency, ease of fabrication, low price, and simple and easy excitation (such as probe coupling,aperture coupling or proximity coupling).Microstrip antennas are fabricated in many different shapes such as square,rectangle, circle, etc. The proposed antenna in this dissertation is a multi-beam millimeter wave antenna with annular ring strip. This antenna is a multi-beam antenna with the ability to switch between different beams. Beam direction switches by changing the position... 

    Design and Simulation of Smart Patch Antenna Array in 2.4 GHz band

    , M.Sc. Thesis Sharif University of Technology Hosseini, Mahdi (Author) ; Farzaneh, Forouhar (Supervisor)
    Over the past few years , demand for wireless communication services have grown at a formidable rate. As such we need to find new ways to support more and more wireless users in a confined space. this means that the capacity of networks should be significantly increased to overcome formidable rate of subscribers growth. That is why the smart antennas have become very popular in communication systems. Smart antennas are a kind of adaptive antenna arrays with smart signal processing algorithms used to find direction of arrival(DOA) of the signal, and use it to calculate suitable weights to direct the antenna beam on the desired user and nulling interferences. In this thesis, DOA estimation... 

    Beamforming Through Array Thinning

    , M.Sc. Thesis Sharif University of Technology Tohidi, Ehsan (Author) ; Nayebi, Mohammad Mahdi (Supervisor)
    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... 

    Interference Avoidance Algorithms in Cognitive Radio Networks and Performance Analysis

    , M.Sc. Thesis Sharif University of Technology Mohammadbeiki, Akram (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Cognitive radio faces specific challenges due to its special spectrum access scheme. Providing required QoS and preventing irrecoverable interference on the primary users is among the crucial requirements. Beam forming is one of the interference avoidance schemes utilized in MIMO networks. Most of the studies on this scheme assume that each symbol is transmitted via vectors in order to grant desired beam forming and specific combinations in the receiver. Since transmitting multiple symbols at every transmission can provide higher data rates, it seems necessary to exploit beam forming through matrixes instead of vectors. In this thesis, by neglecting the interference of the secondary user,... 

    Designi an Adaptive Beamforming Algorithm, Robust Against Direction-of-Arrival Mismatch

    , M.Sc. Thesis Sharif University of Technology Rahmani, Mostafa (Author) ; Bastani, Mohammad Hasan (Supervisor)
    Adaptive beamforming performance is very sensitive to any mismatch between actual and presumed steering vectors of desired signal. In addition to this sensitivity, presence of desired signal in training snapshots dramatically reduces the convergence rate, as compared to the case that signal-free training snapshots are available.
    The present work is aimed at proposing a new adaptive beamformer that is robust against direction-of-arrival (DOA) mismatch and has high convergence rate. This method is based on desired signal elimination from training snapshots and sub-array beamforming technique. To this end, a Blocking matrix that converts primary data to desired signal free data is... 

    Direction of Arrival Estimation and Digital Beamforming in the Presence of Mutual Coupling Effects and Implementation

    , Ph.D. Dissertation Sharif University of Technology Emadi, Mohammad (Author) ; Haj Sadeghi, Khosrow (Supervisor)
    Different beamforming methods are prevalent in wireless and mobile communication systems. However, a lot of practical issues, such as the quality of these methods in compact arrays and the huge computational burden are the major defects of the proposed methods. These problems restrict most of the algorithms to the theoretical domain and render them anappropriate for commercial applications. Therefore, the major focus of this thesis is on the practical issues in the implementation of the digital beam steering and direction of arrival estimation systems for linear, circular and random array configurations. To do so, compact arrays with super directivity are presented and considered. Different... 

    Distributed Transmission in Relay Coordinated Multi-point (COMP) Networks

    , M.Sc. Thesis Sharif University of Technology Pilaram, Hossein (Author) ; Hossein Khalaj, Babak (Supervisor) ; Behroozi, Hamid (Supervisor)
    Time offset (TO) at an orthogonal frequency division multiplexing (OFDM) system destroys orthogonality of subcarriers and causes interchannel interference (ICI) and inter symbol interference (ISI). This problem is more challenging in multi-user multi-input multi-output (MU-MIMO) OFDM systems such as coordinated multi-point (CoMP) uplink transmission where joint processing is performed at base stations (BSs) and different delays form users to BSs cannot be compensated by timing strategies. In this thesis, we use delay-amplify and forward relays and post processing at receivers to decrease signal to interference plus noise ratio (SINR) degradation due to large TOs at insufficient cyclic prefix... 

    MIMO Radars Waveform Design

    , M.Sc. Thesis Sharif University of Technology Shadi, Kamal (Author) ; Behnia, F (Supervisor)
    MIMO radar is a next generation radar which transmits arbitrary waveforms at each one of its apertures. It has been shown that design of waveforms for MIMO radars in order to synthesize a desired spatial beampattern, is mapped into a waveform correlation matrix (R) design in the narrowband case. Therefore, waveform design in MIMO radar for beamforming could be broken into two steps, namely correlation matrix design and waveform synthesis for achieving given R. As of now, given a desired beampattern or estimated location information of targets, calculating R has been modeled as an optimization problem like SDP. Also, in some special cases like rectangular beampattern, close form solutions for...