Sharif Digital Repository

Recently, cooperative communications have gained much interest due to its ability to mitigate fading in wireless networks through achieving spatial diversity while resolving the difficulties of installing multiple antennas on small communication terminals. There have been considerable research efforts on the performance analysis of cooperative diversity. This is while most of the current works assume that perfect knowledge of the channel information is available at the destination and/or relay terminals. However, in many practical scenarios, due to the errors caused by Doppler shift or noise on the pilot signals the perfect estimation of channel coefficients is not possible. In this thesis,... 

In this thesis, we consider Compute and Forward schemes in relay assisted cooperative communication networks. The main problem associated with the compute and Forward scheme is the possible dependency of the relayed equations to the destination, which leads to the outage and thus the very low achievable rate. We propose several approaches to deal with this problem. In the first part of the thesis, we consider a cooperative network consisting of multi users, multi relays, and one common destination with no direct links between the users and the destination. We propose three strategies to lessen the aforementioned problem associated with the conventional compute and forward relaying scheme,... 

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 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...