Sharif Digital Repository

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... 

In this thesis, we investigate the achievable secrecy rate in a relay channel where the source and the destination wish to keep the information confidential from an untrusted relay (potential eavesdropper). The relay has no energy supply, and harvests its required energy for relaying from its received signals. For radio-frequency (RF) Energy Harvesting (EH) at the relay,we adopt power splitting (PS) and time switching (TS) approach. We study the problem of achieving positive secrecy rates between the transmitter and the receiver while making use of an untrusted relay. Energy limitation at the relay makes the problem more interesting. Because,the relay must choose either to eavesdrop the... 

The increasing expansion of wireless communications and the increase in information traffic and the number of communication users, and on the other hand, the frequency and energy frequency limitations have led to the emergence of new generation communications. In the fifth generation of communications, one of the solutions to ensure the optimal use of bandwidth is the use of the non-orthogonal multiple access (NOMA) schema, which of course, the use of such a scheme in the system naturally increases the complexity of the receivers. Unlike most access methods in previous generations of communications, the goal of NOMA is the simultaneous use of multiple users from a frequency band for data... 

Nowadays, number of the users in wireless networks are increasing due to the high speed data transmission. Increasing number of the users increases the required bandwidth and power resource. Using non-orthogonal multiple access (NOMA) is a promising approach to decrease the significant bandwidth and also the required power of the network. NOMA systems decrease the latency of the users and also improve the spectral efficiency by serving multiple users. As signals are transmitting in wireless networks, the internal and also external eavesdroppers have access to the message of the legitimate users in the networks. Therefore, some sort of secrecy of the messages of the users must be provided.... 

Thorough investigation of the Cloud-RAN (C-RAN) architecture has recently shown that CRAN can bring advanced cooperated and coordinated processing capabilities as well as the multiplexing gains toward future radio access networks. The baseband processing of each base station instance can now be flexibly split into smaller functional components, that can be placed either at remote radio units (RRUs) or baseband units (BBUs), depending on the available resources. In this project, we investigate recent implemented methods in C-RAN. also, we propose, develop and implement new architectural frameworks for C-RAN that can support both a flexible functional split and a new functional splitting known... 

Security for wireless communication networks has become a crucial issue because of the broadcast nature of wireless channels. On every cellular network Since it is possible for passive nodes to easily overhear the confidential information transmitted between transmitter and receiver, it is necessary to provide secure communication.When a cellular user wants to communicate with a node or base station on the cellular network, it expects that information will be transmitted and received without interference, with enough quality and without eavesdropping. On the other hand In practical scenarios, we know that cellular network nodes are not equipped with ideal equipment and some percent... 

The rapid development of wireless communications, e.g., the sixth generation (6G) networks, together with the emergence of various technologies for exchanging data has made the information security a big concern. In other words, today’s decentralized wireless networks face with major challenges in terms of key distribution and management of traditional cryptographic techniques. In contrast, the approach of PHY layer security, which wisely utilizes the inherent characteristics of wireless links, has been introduced to address provable and lightweight security mechanisms. In addition, learning-based techniques have shown to be able to provide well-established mechanisms in enhancing the... 

The ever-increasing demand for wireless communication has raised the need for better utilization of bandwidth and energy. Intelligent Reflecting Surface (IRS) is an emerging technology that has been proposed for the sixth generation of wireless communication. In this thesis, we study the essential role these surfaces can play in improving the physical layer security.First, we consider a relatively realistic scenario for the location of the eavesdroppers. In this scenario, we will assume that the transmitters, users, and eavesdroppers all use a single antenna configuration, and the eavesdroppers are placed randomly across the studied region. Two notable parameters in physical layer security,... 

In modern wireless communication networks,that we have heterogeneous, asynchronous and ultra low latency networks and Due to the high processing power required by conventional cryptographic systems based on computational security, information theoritc security can play important role in the future development of these systems. Security in this case does not depend on the eavesdropper's computing power, but on the statistical independence between the main message and the received message of the eavesdropper. In recent years, polar codes have created new arenas, as they were the provable channel codes that could achieve capacity and reliability simultaneously. In addition, the clear structure,... 

Considering the advantages of optical communications and code division multiple access technique, Optical Code Division Multiple Access Networks (OCDMANs) was introduced. Thence, many researchers have suggested methods for creating Quality of Service (QoS) differentiated classes in OCDMANs. In this thesis, we have comprehensive review on the QoS assignment methods and enhance them by offering new techniques. In physical layer, we concentrate on variable chip rate OCDMANs and in MAC sub-layer, a new algorithm named Adaptive Level Control (ALC) is introduced. Then, we focus on the physical design of OCDMANs. Firstly, we solve the problem of one-class OCDMAN and introduce few simple and... 

In wireless powered communication networks (WPCNs), wireless nodes are charged via an access point. In these networks, an access point transfers power to the nodes, and then, the nodes use the received power to transmit their information to the access point. Due to the wireless transmission of the information, eavesdropping of it is an important vulnerability in these networks. The conventional method to resolve this security problem is using cryptography algorithms. However, this method needs key management and complex encryption algorithms to be used by the nodes, which may not be applicable. Physical layer security (PLS), which uses the channel characteristics, is a more suitable way to... 

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...