Sharif Digital Repository

Cognitive Radio (CR), as a new concept to efficiently utilize a licensed spectrum, and this has received intensive attension in recent years. By applying the cognitive technique, an unlicensed user (the secondary user (SU)) is allowed to transmit at the Primary User’s (PU) spectrum band under some conditions. Different approaches have been introduced to be utilized by the SU in order to be able to efficiently transmit at the PR’s spectrum without any sustainsial destructive effects on PR transmission and reception, which one of them is using multiple antenna in the cognitive transmitter. Hereby, CR is able to increase its throughput without substansial harmfull effect on PR’ transmission by... 

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... 

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... 

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... 

In recent years with the increase of cellular phone subscribers, demand for high capacity networks is inevitable. For this reason, different methods have been proposed to increase the channel capacity. One method which has become popular in recent years is utilizing of Smart Antenna Systems. Smart antennas basically attempt to enhance the desired signal power and suppress the interferers by beamforming toward the DOA (direction-of-arrival) of the desired signal and nullsteering in the interferences’ DOAs. Smart Antennas first find the direction of signal sources, and then put the main gain toward the desired signal and put the nulls toward unwanted signals. As a result, we can obtain the... 

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... 

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... 

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... 

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,... 

Analysis of traditional spectrum allocation schemes shows underutilization of radio spectrum. This is main motivation behind deployment of cognitive radios and improving spectrum efficiency. One of the most important issues in cognitive radio networks is to guarantee quality of service (QoS) constraints for the primary users. Another problem which must be considered during network design is to design distributed algorithm with few amount of control messages. However, there is a tradeoff between to be distributed of algorithm and to be efficient. We have used game theory to analyze convergence, effectiveness and uniqueness of stable point of network.
This thesis is organized in two parts.... 

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... 

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... 

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... 

In this study we investigate the performance of amplify-and-forward (AF) and beamforming schemes in wireless networks. In our study we consider a general cooperative network consisting one transmit-receive pair and an arbitrary number of relays in which each relay has a separate power constraint. A two-step master-slave protocol is deployed in which at the first stage, relays listen to the transmitter and at the second stage, relays forward the recently received signal coherently. Main contributions of this dissertation are providing the exact closed-form of bit error rate analysis in the case of general AF networks, providing an integral-form upper bound of error probability of network... 

The significant growth in wireless data traffic over the past few years has necessitated the use of new frequency bands for wireless communications. With the advent of the fifth-generation mobile network (5G), millimeter wave band will be widely employed for the purpose of wireless data transmission, increasing in channel bandwidth and data rate. Due to high propagation loss, severe vulnerability to blockage and poor reflection in millimeter wave frequencies, beamforming for antenna arrays is being considered a key enabler for millimeter wave applications in 5G. Beamforming contributes significantly to maintaining channel stability and capacity through enhancing Signal-to-Noise-Ratio (SNR)... 

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... 

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... 

Medical ultrasound imaging is one of the common imaging methods in modern medicine, which is used to diagnose and even treat some diseases due to its cheapness and harmlessness. Medical ultrasound transducer arrays have a significant error rate. They are a major cause of failure in ultrasound imaging systems. This problem causes a noticeable decrease in the quality of the images and medical misdiagnoses. The topics of accurate detection of the location and severity of the error or failure, as well as the compensation for weak transducers by signal processing methods, have received less attention from predecessor researchers. In this thesis, an innovative method for accurate error detection... 

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 (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...