Sharif Digital Repository

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... 

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... 

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,... 

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.... 

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...