Sharif Digital Repository

In this thesis we consider transmitting an analog Gaussian source over an AWGN channel in the presence of an interference completely known at the transmitter intwo cases: 1) Compression bandwidth with interference uncorrelated with the sourceand 2) Matched bandwidth channel in the presence of interference correlated withthe source to be transmitted. We study joint source-channel coding schemes basedon hybrid digital-analog (HDA) codes. After providng a brief review, we will proposetwo new schemes for the ?rst case and one novel scheme for the second case. Aswe will see both schemes for the ?rst case achieve the optimal mean-squared error(MSE) distortion. The proposed HDA schemes can... 

In this thesis after the study of the reported works on butterfly network, we improve the rate region of full duplex butterfly network. We use a simple specification of lattice codes to break code book into two code books. By selection of the coded message of the two transmitters in symetric butterfly channel from these two code books, we can decode the sum of the two messages and recover each messages by simple mod operation. The simulation shows that the rate region is improved  

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 of the achievable secrecy rate in channels has always been of significant importance.The importance further increased probably due to development of new generations of communication networks in recent years. The secrecy rate refers to the maximum transmission rate for which transmitted data during the transmission process is guaranteed to be error-free and not sniffable. In this thesis, we will investigate the two-hop channel with untrusted relay using lattice coding. In other words, the purpose of this study is to provide a decoder-encoder architecture based on lattice codes, in order to obtain a secrecy rate in a channel where two pairs of transmitter-receivers attempt to exchange... 

IoT security is an important step in the rapid development of its applications and ser-vices. Many security protocols have been defined to maintain security at higher communication layers, such as the transport layer and the application layer, but with the advent of quantum computers due to high-speed parallel computing, the previous methods are no longer secure and we have to establish security at lower layers such as the physical layer. The efficiency of IoT devices depends on the reliability of their message transmission. Cyber-attacks such as data injection, eavesdropping and man-in-the-middle can lead to security challenges. In this study, we propose a new deep learning based component... 

Random codes can achieve the capacity region of so many channels like AWGN channel, multiple access channel (MAC), etc. Recently, it is shown that these codes cannot achieve any positive rate for some channels such as doubly dirty MAC.Because of this fact and also practical consideration, structured codes have been introduced recently. It is shown that one of the structured codes, referred to as lattice codes, can achieve positive rates for doubly dirty MAC. These codes can also achieve the capacity of AWGN channel, MAC and Broadcast channel. For these reasons, in this work we analyze the performance of lattice codes over relay channels as well as interference channels. Here, we implement... 

In this thesis, we investigate a passive forward scattering radar system based on satellite signal. In this thesis we have used the GPS satellite signal as a non-cooperative transmitter.In order to analyze the passive forward scattering radar system as a subset of the bistatic radars, first the features and equations of the bistatic radar will be presented, and then we will discuss the important advantages and disadvantages of the passive forward scattering radar.In order to investigate the features of passive forward scattering radar based on satellite signal, an appropriate geometry will be presented with the characteristics of this radar and parameters such as time delay between direct... 

Although in the network information theory most of results are based on applying random codes, one of the important challenges is to design linear structured codes that achieves the performance close to the performance of random codes. Recently, it is shown that lattice codes can be designed as good codes for quantization and also capacity-achieving in additive white Gaussian noise (AWGN) channel. Due to such a good performance, lattice codes can be designed properly and applied in various problems in network information theory.In this work, we study the performance of lattice codes for the following problems:1. Gaussian multiple access channel (MAC) with state: A joint source channel coding... 

Polar codes were introduced by Arikan in 2009. These codes are the first family of codes that with low encoding complexity and successive cancellation decoder, can achieve the channel capacity. Polar codes, at first were implemented for channel coding, but in 2010 performance of these codes in binary and q-ary alphabet source was studied. It is shown that these codes can perform efficiently in channel coding and source coding. On the other hand, one of the most important continuous sources are Gaussian sources. Due to the importance of Gaussian sources and good performance of polar codes, we try to evaluate the performance of these codes in Gaussian sources. Note that, these codes have... 

Due to serious challenges of SRAM based caches in sub-micron region, researchers seek for new alternatives. Among the proposed options, STT-RAM seems to be a promising candidate. STT-RAMs with high density, low static power consumption and proper scalability open a new door to respond to future demands. But, unfortunately adopting these type of memories coupled with the limited number of write operation and consequently short lifetime issue. Hence, for practical usage of these type of memories, we must address the short lifetime problem efficiently. This way, using a decoupled caches structure which provide better opportunity of relocation, we propose Caribou to extend the lifetime of... 

Passive bistatic radars (PBR) using transmitters of opportunity have attracted a lot of attention recently. Advantages of these radars include the covert operation as well as the low cost of their building and maintenance. Such radars are intended to use signals in the environment as transmitters. These transmitters can be terrestrial transmitters such as TV broadcasts or even satellite transmitters such as global positioning system (GPS) satellites.Satellite transmitters have global coverage and their signal is available at all times, but the design of these transmitters for non-radar applications causes the reduction of the reception power at receivers. So BR systems have attempted to use... 

In recent years, with the continuous growth and development of wireless communication systems, the demand for the use of radio spectrum has increased significantly, which has led to problems such as a shortage of spectrum. An effective solution to the spectrum shortage problem is to use cognitive radio. One of the main functions of cognitive radio networks is spectrum sensing and our focus in this study is to examine machine learning and deep learning methods to improve cooperative spectrum sensing. Since channel and noise parameters are not accurate in telecommunication systems, we need to use a method to estimate these parameters. In this regard, the structure of Bayesian with neural... 

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)... 

The fifth generation of mobile communication has a significant development in comparison to the last generations. However, the available frequency bands in sub-6 GHz frequencies are insufficient to fulfill this development. So the mm-waves bands play an essential role in 5G. The 5G applications demand antennas with low dimensions, wide beam, high gain, and wide bandwidth. In this thesis, a mm-wave antenna is designed and optimized by machine learning to meet 5G requirements. In addition, two arrays of this antenna are proposed with 4 and 8 elements. The analog beamforming is achieved by means of these arrays. The 4-element array is simulated in an IPhone package model. Finally, an antenna... 

With the increasing use of wireless communications, the need for optimal utilization of bandwidth and energy has become undeniable. Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising technology for the efficient use of telecommunications resources. One proposed model of these surfaces is the Simultaneously Transmitting and Reflecting RIS (STAR-RIS), which, unlike conventional reflective surfaces, can simultaneously reflect part of the incoming waves and transmit part of them. This study examines the potential use of these surfaces in simultaneous wireless information and power transfer networks. In the defined problem, energy receivers are not reliable, and there is a... 

Intercellular coordination is a technique to mitigate intercell interference. In this technique, base stations of different cells coordinate with each other to send data for all users, so each user is serviced by several base stations. Nowadays, with the increasing use of wireless networks, the design of these networks is very important. Most problems in the design of wireless networks are due to limitations such as: interference, the lack of bandwidth and changes of channel. Using all channels in each cell is a suggested method to use the bandwidths efficiently; however it increases intercell interferences hence a method to control interference is needed. Coping with interference can be... 

Surveillance systems play an important role in the modern world. Nowadays, CCTV cameras are installed in many places to monitor various events. These cameras produce video data in a very large volume and size. One of the main challenges in this field is analyzing the content of these videos and summarizing and storing them in compressed formats such as text to save storage space. With the advancement of computing tools and the success of deep learning algorithms in solving many problems such as object detection, human action recognition and machine translation, many efforts have been made to describe video content. Most of these methods have described open domain videos and a limited number... 

Satisfying the growing demands for mobile services and radio communications makes the future wireless networks to fully reuse resources such as available frequency bands, which in turn leads to profound increase in inter-cell interferences (ICI). Forcing higher interference may degrade the performance of systems in serving the users especially in cell-edges. Necessity of mitigating ICI along with higher data rate requirements push the communication engineers to advanced technologies utilization. As a result of higher complexity based on promising technologies, resource management would play even a major role in next generation mobile networks. Analyzing these technical challenges that have... 

This thesis considers the problem of communicating correlated Gaussian sources through a Gaussian multiple-access channel (MAC). A well known application of these problems is a sensor network. In a distributed sensor network, sensors measure the required parameters from the environment, encode and transmit them to a fusion center through a multiple-access channel. Then, the fusion center makes a decision about the environmental measured parameters by data processing on the received data from sensors. In these networks, one of the main concerns is the power limitation at sensors. As a result, we usually look for an encoding method that is not only simple but also has a nearly optimal... 

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...