This paper proposes to design a satellite-based free-space quantum key distribution (QKD) systems using quadrature phase-shift-keying (QPSK) signaling. Our proposed QKD system based on continuous variable encoding to provide the secret-key transmission, where the key information is encoded on four coherent states corresponding to QPSK modulation scheme. In addition, we use heterodyne detection receiver to improve the receiver sensitivity thus decode the signal with high fidelity. The performance of the proposed free-space QKD system is analytically investigated. More especially, the mathematical expression for quantum bit error rate (QBER) is derived taking into account the effect of physical layer impairments and parameters. The numerical results help to determine the appropriate values of system's parameters such as the threshold coefficients and the required transmitted power.
This paper proposes to design a satellite-based free-space quantum key distribution (QKD) systems using quadrature phase-shift-keying (QPSK) signaling. Our proposed QKD system based on continuous variable encoding to provide the secret-key transmission, where the key information is encoded on four coherent states corresponding to QPSK modulation scheme. In addition, we use heterodyne detection receiver to improve the receiver sensitivity thus decode the signal with high fidelity. The performance of the proposed free-space QKD system is analytically investigated. More especially, the mathematical expression for quantum bit error rate (QBER) is derived taking into account the effect of physical layer impairments and parameters. The numerical results help to determine the appropriate values of system's parameters such as the threshold coefficients and the required transmitted power.
Satellite QKD/FSO systems, which facilitate quantum key distribution (QKD) over free-space optical (FSO) links between satellites and ground stations, present a promising pathway toward achieving global security in upcoming sixth-generation (6G) wireless communications. Our study focuses on a superior type of these systems, the satellite EB/CV-QKD/FSO, which utilizes the continuous-variable (CV) method for quantum state representation and the entanglement-based (EB) scheme for QKD implementation. We propose the use of optical phase-shift keying (QPSK) signaling and dual-threshold/heterodyne detection (DT/HD) receivers to bolster the reliability and feasibility of satellite EB/CV-QKD/FSO systems. Closed-form expressions for key system performance metrics are derived using improved channel modeling. Numerical results are presented to showcase the effects of channel impairments on the system performance. We also provide recommendations for optimal system setup parameters, aiming to enhance performance.
This paper proposes a novel design and analyzes security performance of quantum key distribution (QKD) protocol over free-space optics (FSO). Unlike conventional QKD protocols based on physical characteristics of quantum mechanics, the proposed QKD protocol can be implemented on standard FSO systems using subcarrier intensity modulation binary phase shift keying and direct detection with a dual-threshold receiver. Under security constraints, the design criteria for FSO transmitter and receiver, in particular, the modulation depth and the selection of dual-threshold detection, respectively, is analytically investigated. For the security analysis, quantum bit error rate, ergodic secret-key rate, and final key-creation rate are concisely derived in novel closed-form expressions in terms of finite power series, taking into account the channel loss, atmospheric turbulence-induced fading, and receiver noises. Furthermore, Monte-Carlo simulations are performed to verify analytical results and the feasibility of the proposed QKD protocol.
This paper proposes a novel two-way free-space quantum key distribution (QKD) protocol, which can be implemented using standard free-space optical (FSO) systems with subcarrier intensity-modulation (SIM) binary phase-shift-keying (BPSK) and direct-detection (DD) receiver. Different eavesdropping threats, including unauthorized receiver, beam-splitting, and intercept-resend attacks, are considered in the security analysis of the proposed protocol. Under the constraints on security requirements, we analytically investigate the design criteria for transmitter and receiver, in particular, the intensity modulation depth at the transmitter and the dual-threshold setting of the receiver in two-way free-space QKD systems. Quantum bit error rate (QBER), the ergodic secret-key rate, and the probability of detecting eavesdropper of the proposed system are analytically derived in closed-form expressions, considering the atmospheric loss, turbulence, and receiver noises.
Abstract Distributing cryptographic keys over public channels in a way that can provide information-theoretic security is the holy grail for secure communication. This can be achieved by exploiting quantum mechanical principles in so-called quantum key distribution (QKD). Continuous-variable (CV) QKD based on coherent states, in particular, is an attractive scheme for secure communication since it requires only standard telecommunication technology that can operate at room temperature. However, a recently discovered side-channel created in the process of state preparation leads to a leakage of information about the transmitted quantum state, opening a security loophole for eavesdroppers to compromise the security of the CVQKD system. Here, we present a CVQKD system without this modulation leakage vulnerability. Our implementation is based on a baseband modulation approach and uses an in-phase and quadrature (IQ) modulator for state preparation and radio frequency heterodyne detection together with carefully designed digital signal processing for state measurement. We consider practical aspects in the implementation and demonstrate the generation of a composable secret key secure against collective attacks. This work is a step towards protecting CVQKD systems against practical imperfections of physical devices and operational limitations without performance degradation.
This paper significantly advances the application of Quantum Key Distribution (QKD) in Free- Space Optics (FSO) satellite-based quantum communication. We propose an innovative satellite quantum channel model and derive the secret quantum key distribution rate achievable through this channel. Unlike existing models that approximate the noise in quantum channels as merely Gaussian distributed, our model incorporates a hybrid noise analysis, accounting for both quantum Poissonian noise and classical Additive-White-Gaussian Noise (AWGN). This hybrid approach acknowledges the dual vulnerability of continuous variables (CV) Gaussian quantum channels to both quantum and classical noise, thereby offering a more realistic assessment of the quantum Secret Key Rate (SKR). This paper delves into the variation of SKR with the Signal-to-Noise Ratio (SNR) under various influencing parameters. We identify and analyze critical factors such as reconciliation efficiency, transmission coefficient, transmission efficiency, the quantum Poissonian noise parameter, and the satellite altitude. These parameters are pivotal in determining the SKR in FSO satellite quantum channels, highlighting the challenges of satellitebased quantum communication. Our work provides a comprehensive framework for understanding and optimizing SKR in satellite-based QKD systems, paving the way for more efficient and secure quantum communication networks.
This paper aims at proposing a novel satellite quantum key distribution (QKD) system for vehicular networks. Quantum key from a satellite (i.e., a trusted node) is transmitted through a free-space optical (FSO) channel to a high-attitude platform (HAP) using radio-over-FSO (RoFSO) technique. HAP playing a role as a relaying node forwards the key to moving vehicles via millimeter-wave (MMW) channel. Key information generated is encoded on MMW subcarrier using binary phase shift keying (BPSK) signaling and then recovered at the receiver thanks to a dual-threshold detector. We derive the mathematical expressions for security analysis of the proposed QKD system in terms of quantum bit error rate and ergodic secret-key rate taking into account the channel loss and receiver noise. The numerical results confirm the feasibility of the proposed QKD system.