Sharif Digital Repository

In this thesis, a novel OFDMA-based cognitive cooperative relaying scheme is proposed in which cognitive users not only try not to interfere with primary users but also assist them by relaying their information. Both primary users (PU) and cognitive users (CR) communicate to a common base station (BS). Bit error probability (BEP) of primary users and outage probability of primary users are investigated to evaluate performance of the primary users. In all parts of this thesis, we assume that data of users is not jointly encoded across subcarriers. So, the outage probability and BEP are investigated for each subcarrier independently. In the last part of the thesis, it is assumed that data is... 

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,... 

Against the computational security, which guarantees the confidentiality via computational complexity, information theoretic secrecy considers the full information secrecy. The full information secrecy is the case when the mutual information rate between received signal of eavesdropper and the confidential message converges to zero. In this thesis we consider the fundamental limits of transmission security. For this, we first consider basic models with one transmitter, one receiver and one eavesdropper and after investigating previous works, models and performance criteria, we state our owns models and criterion. Since the full knowledge of CSI is an optimistic assumption, we consider the... 

In recent years, coded cooperation has been considered as one of the best methods to cope with fading and at the same time to achieve channel coding gain. On the other hand, the idea of network coding has been introduced for increasing the efficiency of cooperative networks. In addition, it has been shown that only by jointly designing of network coding and channel coding, the capacity will be achievable. Also, to adjust the rate to the channel capacity without requiring the channel state information at the transmitter, Rateless coding has been proposed. In this thesis above techniques are combined to gain their advantages and to improve system performance. To this end, first we consider a... 

In recent years, coded cooperation has been considered as one of the best methods to cope with fading and at the same time to achieve channel coding gain. There is a special case of cooperative networks that provide different level of user priority. Among all methods for creating user priority our motivation is to use of UEP codes for this propose. UEP codes are a special case of channel codes that provide different level of protection for message. It means that some part of message that has more protection it has less error. First we review all type of UEP codes and compare them in term of probability of bit error on the AWGN channel. And best code will be choosing for applying to this... 

In this thesis we consider the effect of random locations of users in the capacity analysis of SIR-based power control systems and comparison to the strength-based systems, for the first time. Unlike previous works we do not consider a simple deterministic uniform model for the analysis. We provide simulations and analytical solutions for calculating the interference statistics, based on which, we not only calculate the interference statistics, but also study the effect of locating a user in every location in the network coverage area and its share in the interference. We also calculate each cell’s share in every statistics of the interference. In this thesis, based on the common assumption... 

Solid-State Drives (SSDs) provide high performance, low power consumption, and hence are widely used in the I/O cache of enterprise storage systems and high performance servers. Although employing high performance SSDs in the I/O cache of storage systems significantly improves system performance, it comes with significant reliability threats for write operations upon power failures. In order to provide high level of reliability, storage architectures employ SSDs in I/O cache with RAID-1 configuration, however, such configuration only partially mitigates the reliability issues of the SSDs. In this thesis, we analyze the reliability of SSD-based I/O caches against power outage and high... 

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... 

In recent years, there has been an increased interest on employing low-cost, high-speed, low-latency wireless links for short range communications (< 10m). Ultra-wideband (UWB) radio is a promising technology to meet this interest. However, due to the limitation on its transmitted power level, UWB system faces major challenges to achieve an adequate system performance. Therefore, it is greatly necessary to find some efficient methods to enhance the system performance. Recently, cooperative diversity has emerged as an effective scheme to overcome multipath fading and thus to improve the quality of service in the physical layer of wireless networks without increasing the transmission power of... 

The purpose of this thesis is the presentation of an outage management scheme in a multi-microgrids system with a decentralized structure. The proposed method is designed in a two-step method to prevent damage to all microgrids and network components due to blackouts. In the first stage of this scheme, each microgrid alone provides its required power or curtails load due to the power deficiency. In the second stage, microgrids exchange power in a transactive energy environment, which is one of the new changes in active distribution systems with participation in market and price bidding, and all players of this market earn profit from their exchanges. In this case, the curtailed load will be... 

Wireless Body Area Network (WBAN) is one of the emerging technological trends that paves the way for the next generation medical systems by offering proactive wellness management and early detection of diseases. WBAN, as standardized by IEEE 802.15.6, is a network composed of intelligent, miniaturized, low power sensors that are strategically implanted in, placed on, or in close proximity to the human body. The sensors have responsibility for recording vital physiological signals and wirelessly transmitting them to a central hub for further processing. In this study, we have first investigated the applicable channel models for a typical WBAN. Considering various scenarios with different... 

Due to the widespread use of satellite communications including live TV broadcast, DVB-S and satellite Internet, it is necessary to accurately assess the level of signal received and the EIRP of the satellite. Nilesat21(7°W), Eutelsat3B(3°E), Badr(26°E), Express AM6(53°E) and Intelsat20(68.5°E) have been chosen to be meticulously assessed and analyzed.The chosen satellites contain the westernmost for Tehran to the easternmost, which has been listed above from west to east, respectively.In addition, the signal attenuation is closely monitored in the city of Tehran during rainfall for the above-mentioned satellites. In the meantime, the rain rate is also recorded.Another major factor that... 

The compute-and-forward (CMF) method has shown a great promise as an innovative approach to exploit interference towards achieving higher network throughput. Here, instead of recovering single messages, the relays attempt to reliably decode (compute) and pass an integer linear combination of the transmitted messages, referred to as an equation, to the destination. By receiving sufficient equations,the destination can solve the linear equation system to recover the desired messages.Two main challenges of the CMF methods are the computational complexity and the rank failure problem at the destination. In this thesis, to decrease the implementation as well as the computational complexity of the... 

Non-Orthogonal multiple access (NOMA) has been considered as a promising multiple access technique for the 5th generation (5G) of wireless networks. In contrast to orthogonal multiple access, NOMA supports more than one user in each subchannel and thus, improve spectral efficiency. On the other hand, energy efficiency which is another key consideration in future 5G networks, can be improved by energy harvesting (EH) methods. In the NOMA scheme, the user with the better channel condition performs successive interference cancellation (SIC) to detect the data of the user with the worse channel condition and then subtract it from the received signal to decode its own data. Since the data of the...