Global satellite infrastructure has transformed maritime data links, allowing ships to share real-time details—such as location, speed, and environmental readings—with orbiting platforms. Yet conventional encryption methods can be compromised, threatening the confidentiality of these exchanges. Quantum Key Distribution (QKD) inherently detects any interception during key setup, offering a robust security layer. In our Satellite Vehicular Communication (SVC) framework, we integrate two entanglement-based QKD protocols: BBM92, which uses satellite-generated entangled photon pairs, and Measurement-Device-Independent QKD, which removes trust assumptions from the measurement hardware. We evaluate performance over free-space optical paths up to 25 km under realistic noise and weather scenarios. Findings show that MDIQKD achieves higher raw key generation rates but experiences rising quantum bit error rates at extended ranges, whereas BBM92 delivers lower error rates and steadier secure key throughput at moderate distances.
Global satellite infrastructure has transformed maritime data links, allowing ships to share real-time details—such as location, speed, and environmental readings—with orbiting platforms. Yet conventional encryption methods can be compromised, threatening the confidentiality of these exchanges. Quantum Key Distribution (QKD) inherently detects any interception during key setup, offering a robust security layer. In our Satellite Vehicular Communication (SVC) framework, we integrate two entanglement-based QKD protocols: BBM92, which uses satellite-generated entangled photon pairs, and Measurement-Device-Independent QKD, which removes trust assumptions from the measurement hardware. We evaluate performance over free-space optical paths up to 25 km under realistic noise and weather scenarios. Findings show that MDIQKD achieves higher raw key generation rates but experiences rising quantum bit error rates at extended ranges, whereas BBM92 delivers lower error rates and steadier secure key throughput at moderate distances.
Entanglement-based quantum key distribution (QKD) protocols, such as E91 and BBM92, offer strong information-theoretic security and are naturally suited for satellite-to-satellite QKD (SatQKD) links. However, implementing these protocols over long-distance inter-satellite free-space optical (FSO) channels poses critical physical-layer challenges that are not addressed in the existing literature. In particular, photon losses due to beam divergence, pointing errors, and background noise can severely degrade the key generation rate and quantum bit error rate (QBER), especially under narrow receiver field-of-view (FoV) constraints. This paper presents a comprehensive performance analysis of entanglement-based inter-satellite QKD, focusing on photon-level modeling and the impact of practical impairments. We develop analytical expressions for signal detection probabilities, background photon influence, multi-pair emissions, and QBER, incorporating key parameters such as link distance, transmitter tracking jitter, receiver misalignment, and photon pair generation rate. Simulation results reveal the nonlinear sensitivity of system performance to tracking error and FoV limitations, and highlight optimal parameter regimes that jointly maximize secret key rate while maintaining QBER below acceptable thresholds. The proposed model provides actionable design insights for reliable and efficient deployment of entanglement-based SatQKD systems.
Establishing information-theoretically secure communication between arbitrary locations on Earth is a central goal of quantum networking, for which space-based distribution of quantum entanglement is a leading approach. Modelling and analysis of the performance of satellite entanglement pair distribution is therefore important for the architecture and design of future constellations and space systems. However, entanglement-based quantum key distribution in the absence of quantum repeaters, is especially prone to finite-key effects due to low coincident count rates compared to trusted-node single-path links. Quantifying these effects under realistic orbital conditions is therefore essential for the design of practical satellite quantum communication systems. Here, we develop a high-fidelity model of pair distribution from a low-Earth-orbit satellite that captures orbital dynamics, elevation-dependent loss, background noise, and extraneous detector effects. Integrating this with a finite-key security framework for the BBM92 protocol, we optimise the secret key length across different overpass geometries, orbital altitudes, and optical ground station (OGS) separations. We show that secure key generation remains feasible in early clear daytime conditions using baseline parameters representative of current technologies, while showing that modest system improvements could further extend daytime operation. Finally, we evaluate the annual secret key performance for representative intercity-scale OGS pairings. Our results provide quantitative performance bounds and practical design guidelines for near-term entanglement-based satellite QKD, enabling informed trade-offs between satellite payload complexity, ground infrastructure, and achievable secure key throughput.
Quantum Key Distribution (QKD) has emerged as a fundamentally secure approach to communication in the era of quantum computing, offering protection against threats posed to classical cryptographic schemes such as RSA and Diffie-Hellman. This thesis presents a comprehensive performance analysis of satellite-based QKD protocols, focusing on both prepare-and-measure and entanglement-based schemes under realistic atmospheric and operational conditions. The study begins by introducing the theoretical foundations of quantum communication, including qubits, entanglement, and quantum entropy, and motivates the need for satellite-based QKD to overcome the distance limitations of fiber-based systems. Subsequently, the thesis evaluates four prominent QKD protocols-BB84, B92, BBM92, and E91-using a circular beam propagation model that incorporates atmospheric effects such as diffraction, turbulence, attenuation, and pointing errors, along with environmental noise contributions for uplink and downlink. Comparative numerical simulations reveal that protocol performance is strongly influenced by channel asymmetries, beam propagation characteristics, and noise, providing guidance on optimal protocol selection for low Earth orbit (LEO) satellite links. The research further investigates high-dimensional (HD) QKD protocols, specifically HD-BB84 and HD-Extended B92, using the elliptic-beam approximation to account for turbulence-induced distortions for both uplink and downlink. Simulations under vary ing system dimensions, weather conditions, and zenith angles demonstrate that HD-BB84 achieves higher key rates, superior noise tolerance, and more favorable probability distributions of the key rate compared to HD-Extended B92, highlighting the advantages of high-dimensional encoding for robust satellite-based QKD.
Satellite-based free-space quantum key distribution (QKD) provides a practical framework for achieving secure global communication beyond the limitations of optical fibers. In this work, the quantum bit error rate (QBER) and secure key rate of four representative protocols-BB84, B92, BBM92, and E91 are investigated over low earth orbit (LEO) links in both uplink and downlink configurations. The optical link is modeled using a Gaussian beam formalism, incorporating the effects of diffraction, pointing errors, atmospheric turbulence, and background noise contributions. The protocols are examined under day and night-time operating conditions, and their dependence on the zenith angle is analyzed. The findings show that downlink links generally exhibit lower QBER and higher secure key rates than uplinks, and among prepare-and-measure schemes, BB84 consistently outperforms B92, while in entanglement-based approaches, BBM92 achieves higher key rates than E91.
Experimental deployment of quantum communication over Earth-satellite channels opens the way to a secure global quantum Internet. In this work, we present results from a real-time prototype quantum key distribution (QKD) system, which entails the development of optical systems including the encoding of entangled photon pairs, the development of transmitters for quantum signaling through an emulated Earth-satellite channel, and the development of quantum-decoding receivers. A unique aspect of our system is the integration of QKD with existing cryptographic methods to ensure quantum-resistant security, even at low-key rates. In addition, we report the use of specially designed error-reconciliation codes that optimize the security versus key-rate trade-off. Our work demonstrates, for the first time, a deployment of the BBM92 protocol that offers both post-quantum security via the advanced encryption standard (AES) and quantum security via an entanglement-based QKD protocol. If either the AES or the QKD is compromised through some adversary attack, our system still delivers state-of-the-art communications secure against future quantum computers.
Satellite-based free-space optical links can act as time-varying optical wireless interconnects that distribute quantum resources across space-terrestrial infrastructures, complementing the 6G vision of integrated non-terrestrial networks. Among quantum communication services, Quantum Key Distribution (QKD) is the most mature and is therefore adopted as an illustrative use case. This paper develops an attenuation-centric framework for satellite QKD based on weak-coherentpulse BB84. The considered system model links orbital geometry and optical terminal parameters to an equivalent channel transmissivity, which governs detection statistics, quantum bit error rate (QBER), and secret key generation through secrecy bounds. We derive the secret-fraction cutoff behavior with respect to channel attenuation and show how it induces time-dependent secret key rates during satellite overpasses. Numerical results using orbital data and representative parameters from the 'Micius' mission show that the minimum slant range over the onemonth observation window spans approximately 400-2400 km; approximately 34% of passes have minimum slant ranges below 900 km, and favorable passes yield secret key rates on the order of a few kbps. The proposed modeling approach provides a link-level building block for future network-level studies, where scheduling and routing of quantum-secured services can be informed by predicted key generation windows over satellite optical interconnects.