چكيده به لاتين
This thesis presents a robust secure scheme which is implemented in physical layer, by means of which message signals are confidentially transmitted in dual-hop MIMO one-way relay-based communication systems. This scheme is based on four techniques, namely Relay Windowing (RW), Double Transmit Antenna Selection (DTAS), Secret Sharing (SS), and Physical Layer-Based Encryption (PLBE), respectively. According to RW technique, the source transmitter selects two relays which can result in the maximum amount of SNR level amongst all the relays. Then, during two orthogonal time slots, the transmitter sends a k-bit original data block, having previously been split into two sub blocks by means of SS technique, to the selected relays. The selected relays, after that they separately encrypt their data through Vernam cipher, send the ciphered data to the destination during two other orthogonal time slots. Thus, in the first hop and during the first two time slots, the message signal is sent to the relays and in the second hop and during the second two time slots, the message data is sent to the destination.
The transmission scheme in each hop is conducted based on TAS/MRC scheme in general. However, in particular, in replace of using one antenna to send the carrier wave, two antennas are applied to send the single RF chain. Consequently, the MRC receiver having been used in this thesis, is designed based on double transmit antennas. As a result, the transmission scheme which is conducted in this thesis, is named “DTAS/DRAS-MRC” which is completely described in the following chapters. Additionally, based on the worst case scenario, it is assumed that the passive eavesdropper is also equipped to this transmission scheme.
To analyze the secrecy performance of the system, each of the above-mentioned techniques are thoroughly evaluated from a data confidentiality viewpoint. Furthermore, to effectively demonstrate the confidentiality performance of the system, the secrecy performance is evaluated both at the destination and the relays nodes. As a result, the secrecy evaluations are presented through the secrecy outage probability metric (SOP), which is shown in mathematical closed form expressions, as well as conceptual analyses. Moreover, since in practical applications, channel state information (CSI) tends to be outdated due to the channel feedback delay, all the simulations of the following article are conducted with outdated CSIs. Theoretical analyses and simulation results demonstrate that RW technique leads to a SOP reduction at the relays node. As a result, the data confidentiality in the channels between the source transmitter and the selected relays is preserved. These analyses prove that the more the relays number increases, the better the data confidentiality is preserved. On the other hand, if the eavesdropper does not know about using DTAS technique, the results prove that the secrecy performance of the legitimate system improves. This is because the SNR value of the eavesdropper receiver as compared to that of the legitimate receiver, decreases, since the passive eavesdropper applies the MRC receiver working with one transmit antenna. Furthermore, security analyses demonstrate that SS technique due to data transmission separation, results in the system robustness in front of such attacks as brute force at both the relays and the destination nodes. Finally, by Vernam cipher, PLBE technique leads to data confidentiality preserving in the channels between the selected relays and the destination.
Keywords – Encryption, Outdated Channel State Information, Physical Layer Security, Secrecy Outage Probability, MRC Receiver, Transmit Antenna Selection