Quantum key distribution (QKD) has been identified as a viable solution for secure underwater communication. This study aims to characterize the impact of natural turbulent waters on systems. The performance of QKD systems is analyzed in terms of the quantum bit error rate and the secret key rate. We expand upon previous studies which only considered large separations by including large and small separations by comparing the turbulence length scale with the distance between two observation points. To that end, we obtain the analytical expression of the wave structure function (WSF) for small separation for propagating Gaussian beams. Since the WSF describes how the amplitude and phase of an optical wave change as it travels through the varying refractive index of the turbulent medium over a given distance, the accurate characterization remains essential in terms of revealing the beam wavefront distortion. Leveraging the practical parameters of underwater environment and communication systems, we demonstrate that the average temperature, average salinity concentration, temperature-salinity gradient, temperature and energy dissipation rates of turbulent water impact the performance and security of the QKD systems to a nonnegligible extent. It is also observed that the waters having high chlorophyll concentrations, e.g., coastal waters, drastically decrease the performance of the QKD systems due to strong absorption and scattering effects. The findings and insights gained from this study may help advance secure underwater communication, which in turn will aid in establishing future QKD networks. Potential applications of this research include secure underwater communication for defense, data gathering for marine environmental monitoring, remote data transmission, and deep-sea exploration.
Quantum key distribution (QKD) has been identified as a viable solution for secure underwater communication. This study aims to characterize the impact of natural turbulent waters on systems. The performance of QKD systems is analyzed in terms of the quantum bit error rate and the secret key rate. We expand upon previous studies which only considered large separations by including large and small separations by comparing the turbulence length scale with the distance between two observation points. To that end, we obtain the analytical expression of the wave structure function (WSF) for small separation for propagating Gaussian beams. Since the WSF describes how the amplitude and phase of an optical wave change as it travels through the varying refractive index of the turbulent medium over a given distance, the accurate characterization remains essential in terms of revealing the beam wavefront distortion. Leveraging the practical parameters of underwater environment and communication systems, we demonstrate that the average temperature, average salinity concentration, temperature-salinity gradient, temperature and energy dissipation rates of turbulent water impact the performance and security of the QKD systems to a nonnegligible extent. It is also observed that the waters having high chlorophyll concentrations, e.g., coastal waters, drastically decrease the performance of the QKD systems due to strong absorption and scattering effects. The findings and insights gained from this study may help advance secure underwater communication, which in turn will aid in establishing future QKD networks. Potential applications of this research include secure underwater communication for defense, data gathering for marine environmental monitoring, remote data transmission, and deep-sea exploration.
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. 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 QBER and SKR in different water types and turbulence conditions. 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. 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 type.
Absorption, scattering, and turbulence experienced in underwater channels severely limit the range of quantum communication links. In this paper, as a potential solution to overcome range limitations, we investigate a multi-hop underwater quantum key distribution (QKD) where intermediate nodes between the source and destination nodes help the key distribution. We consider the deployment of passive relays that 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 a 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.
The current literature on quantum key distribution is limited mainly to transmissions over fiber optic, atmospheric, or satellite links and is not directly applicable to underwater environments with different channel characteristics. In this paper, we analyze the quantum bit error rate (QBER) and secret key rate (SKR) performance of the well-known BB84 protocol in underwater channels. As a path loss model, we consider a modified version of the 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 a 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 the BB84 protocol in different water types including clear, coastal, and turbid 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 this work we study the underwater optical channel, making a feasibility analysis on the development of a high-speed communication system with security guaranteed by Quantum Key Distribution (QKD) protocol. In particular, we introduce a new model for the attenuation of the underwater medium which includes the effect of turbulence within the marine environment.We report the performance of the system focusing on the most important figures of merit, such as the secret key rate of the quantum channel and the bit rate of the classical channel at the physical layer as a function of the total link range. We carried out these analyses depending on various environmental conditions, such as the geographical area, depth, path-loss and turbulence models. The communication protocols considered are the BB84 with time-bin encoding for QKD and baseband On-Off Keying (OOK) modulation for classical data communication for a maximum link range of 100 meters.
Underwater wireless communication is rapidly advancing, finding applications in diverse fields such as oceanography, defense, and commercial ventures. However, ensuring security in such transmissions is crucial due to the sensitive nature of the data involved and the challenges posed by the underwater environment. While classical encryption techniques provide some level of security, the emergence of quantum computing presents opportunities and challenges. Quantum key distribution (QKD) offers theoretically unbreakable encryption, making it an attractive solution. Extending QKD capabilities to underwater environments is a significant endeavor in this context. This paper explores the feasibility of applying an entanglement-based non-coherent QKD protocol inspired by the BBM92 protocol to underwater visible light communication (VLC)/QKD systems. We investigate the system’s design criteria and analyze its secret key performance, addressing challenges such as water absorption and turbulence-induced fading, focusing on addressing unauthorized receiver attacks. Through analysis and the considered case study, the feasibility and efficacy of this approach are explored, contributing to the advancement of secure underwater communications.
We devoted to analyzing information transfer in quantum channels in terms of the performance of quantum key distribution (QKD) free-space optical (FSO) communication systems through Bennett and Brassard 84 (BB84) protocol by taking into account the combined effect of attenuation, turbulence, pointing error, and angle of arrival (AOA) fluctuations. Path loss is modeled by Beer-Lambert law, and the turbulent channel is assumed to be Fisher-Snedecor F distributed. The pointing error and AOA fluctuations are modeled by Hoyt and Rayleigh distributions, respectively. The error and sift probabilities, quantum bit error rate, and secret key rate of a QKD FSO system are obtained in analytical form, and results are presented depending on various parameters. It is shown that increased beam waist, beam deviation, AOA fluctuations, and propagation distance cause performance degradation and less secure information transmission. However, an increase in the ratio of horizontal and vertical beam misalignments, field of view, average photon number per pulse, visibility of the atmospheric environment, and optical beam wavelength impact the performance of QKD FSO systems positively. The effect of the turbulence structure constant is observed to be modest on the performance of the QKD FSO system.