Thesis Defense - Amir Hossein Fahim Raouf (MSEE)

Amir Hossein Fahim Raouf – M.Sc. Electrical and Electronics Engineering

Prof. Murat Uysal – Advisor

Date: 27.07.2021

Time: 18:00

Location: This meeting will be held ONLINE. Please send an e-mail to gizem.bakir@ozyegin.edu.tr in order to participate in this defense.

Performance Analysis of Quantum Key Distribution in Underwater Channels

Thesis Committee:

Professor Murat Uysal, Özyeğin University

Assistant Professor Kadir Durak, Özyeğin University

Assistant Professor Bahattin Karakaya, Istanbul University

Abstract:

The current literature on quantum key distribution (QKD) is mainly limited to the transmissions over fiber optic, atmospheric or satellite links and are not directly applicable to underwater environments with different channel characteristics. Absorption, scattering, and turbulence experienced in underwater channels severely limit the range of quantum communication links.

In the first part of this thesis, we analyze the quantum bit error rate (QBER) and secret key rate (SKR) performance of the well-known BB84 protocol in underwater channels. As path loss model, we consider a modified version of Beer-Lambert formula which takes into account the effect of scattering. We derive a closed-form expression for the wave structure function to determine the average power transfer over turbulent underwater path and use this to obtain an upper bound on QBER as well as a lower bound on SKR. Based on the derived bounds, we present the performance of BB84 protocol in different water types including clear, coastal and turbid water and under different atmospheric conditions such as clear, hazy and overcast. We further investigate the effect of system parameters such as aperture size and detector field-of-view on QBER and SKR performance metrics.

In the second part of this thesis, as a potential solution to overcome range limitations, we investigate a multi-hop underwater QKD where intermediate nodes between the source and destination nodes help the key distribution. We consider the deployment of passive relays which simply redirect the qubits to the next relay node or the receiver without any measurement. Based on the near-field analysis, we present the performance of relay-assisted QKD scheme in terms of quantum bit error rate and secret key rate in different water types and turbulence conditions. We further investigate the effect of system parameters such as aperture size and detector field-of-view on the performance. Our results demonstrate under what conditions relay-assisted QKD can be beneficial and what end-to-end transmission distances can be supported with a multi-hop underwater QKD system.

In the last part of this thesis, we investigate the fundamental performance limits of decoy BB84 protocol over turbulent underwater channels and provide a comprehensive performance characterization. As path loss model, we consider a modified version of Beer-Lambert formula, which takes into account the effect of scattering. Based on near field analysis, we utilize the wave structure function to determine the average power transfer over turbulent underwater path and use this to obtain a lower bound on key generation rate. Based on this bound, we present the performance of decoy BB84 protocol in different water types (clear and coastal). We further investigate the effect of transmit aperture size and detector field of view.

Bio: 

Amir Hossein Fahim Raouf received his B.Sc. degree in Electrical and Communication Engineering from Isfahan University of Technology (IUT), Isfahan, Iran. In 2018, he joined the Communication Theory and Technologies (CT&T) Research Group, Ozyegin University, Istanbul, Turkey, as a research assistant working under the supervision of Professor Murat Uysal. His research interests are in general areas of communication theory, quantum communication, and optical wireless communication.