International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP)

Blind Reconciliation with Protograph LDPC Code Extension for FSO-Based Satellite QKD Systems

Cuong T. Nguyen, Hoang D. Le, Vuong V. Mai, Phuc V. Trinh, Anh T. Pham

Published Jul 17, 2024• 3 citations

Abstract

A significant breakthrough in space-based quantum key distribution (QKD) inaugurated by the Micius satellite has brought us closer to the era of global QKD networks. An essential step in the post-processing QKD is key reconciliation (KR), which eliminates the mismatch in the raw keys between two legitimate users. However, the fluctuation in the quantum bit-error rate (QBER) caused by the free-space optical (FSO) turbulence channels poses various challenges for the KR design. This paper addresses the design of blind KR schemes for FSO-based low Earth orbit (LEO) satellite QKD systems, which allow operating without a prior QBER estimation. Specifically, we present a novel blind KR scheme with a protograph low-density parity check (LDPC) code extension. The proposed LDPC structure is constructed by gradually extending and exhaustively searching among all possible solutions. The proposed design is evaluated in terms of the final key rate performance over the QKD systems using a dual-threshold/direct detection (DT/DD) scheme. Simulation results confirm the effectiveness of our proposed design compared to the state-of-the-art design in different turbulence channel conditions.

DOI: 10.1109/csndsp60683.2024.10636513

Related papers

Key Reconciliation with RC-LDPC/Error Estimation for Satellite-based FSO/QKD Systems

Cuong T. Nguyen, Hoang D. Le, Anshul Jaiswal +2 more

Satellite-based free-space optics (FSO) quantum key distribution (QKD) systems have recently attracted significant research interest due to their potential to enable globally secured applications. However, the inherent uncertainty of FSO channels, caused by weather conditions and satellite mobility, induces severe fluctuations in quantum bit-error rate (QBER) between legitimate users. This makes designing an efficient key reconciliation, an essential step in the QKD post-processing, particularly challenging. In this work, we propose a key reconciliation scheme that combines protograph rate-compatible (RC) low-density parity-check (LDPC) codes with a syndrome-based error estimation method. The proposed error estimation method reduces the number of communication rounds without requiring additional information disclosure. Furthermore, to our best knowledge, an analytical framework is first developed to evaluate end-to-end secret-key throughput (SKT), accounting for the impact of imperfect error estimation and dynamic FSO channel conditions. Numerical results demonstrate that the proposed scheme consistently outperforms conventional blind reconciliation under diverse FSO channel conditions and provide practical guidelines for system parameter selection. Finally, we validate the proposed framework through a case study that incorporates data from a Starlink low-Earth orbit (LEO) satellite and moving ground vehicles.

arXiv:2609.25646IEEE Transactions on Vehicular TechnologyJan 1, 20260 citations

Rateless Protograph LDPC Codes for Quantum Key Distribution

Alberto Tarable, Rudi Paolo Paganelli, Marco Ferrari

Information Reconciliation (IR) is a key step in Quantum key distribution (QKD). In recent years, blind reconciliation based on low-density parity-check (LDPC) codes has replaced Cascade as a standardde facto, since it guarantees efficient information reconciliation without a priori quantum bit error rate estimation and with limited interactivity between the parties, which is essential in high key-rate and long distance QKD links. In this paper, a novel blind reconciliation scheme based on rateless protograph LDPC codes is proposed. The rate adaptivity, essential for blind reconciliation, is obtained by progressively splitting LDPC check nodes, which ensures a number of degrees of freedom larger than puncturing in code design. The protograph nature of the LDPC codes allows to use the same designed codes with a large variety of sifted-key lengths, enabling a blocklength flexibility, which is important in largely varying key-rate link conditions. The code design is based on a new protograph Discretized Density Evolution tool.

IEEE Transactions on Quantum EngineeringJan 1, 202413 citations

Network Coding Aided Hybrid EB/PM Satellite-based FSO/QKD Systems

Minh Q. Vu, Hoang D. Le, Ngoc The Dang +1 more

This paper addresses the design of global-scale free-space optics/quantum key distribution (FSO/QKD) networks comprising geostationary (GEO) and low Earth orbit (LEO) satellites. In particular, we present a novel implementation of network coding aided hybrid entanglement-based/prepare-and-measure (EB/PM) for satellite continuous-variable QKD (CV-QKD) using a dual-threshold/direct-detection (DT/DD) scheme. The system performance is analyzed in terms of final key-creation rates by considering the effects of atmospheric turbulence, receiver noise, and unauthorized receiver attack (URA) from eavesdroppers. Also, we investigate the feasibility of a case study for the existing GEO and LEO satellites from Japan QKD network.

International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC)Jun 25, 20230 citations

Flexible Blind Information Reconciliation for QKD based on Rateless Protograph LDPC codes

Marco Ferrari, Alberto Tarable, Rudi Paolo Paganelli

Information Reconciliation (IR) is a crucial step in the process of distillation of unconditionally secure keys in Quantum key distribution (QKD). Novel IR rateless codes based on protograph low-density parity-check (LDPC) codes have been recently designed to replace Cascade. In this paper, a blind IR protocol is described that exploits all the features of rateless protograph LDPC codes.

International Conference on Transparent Optical NetworksJul 14, 20241 citation

Free-space continuous-variable quantum key distribution in atmospheric channels based on low-density parity-check codes

Ying Guo, Xiaoxue Wang, Cailang Xie +1 more

Abstract Free-space continuous-variable quantum key distribution (CV-QKD) links provide greater information capability and broader geographical coverage. A major challenge for the practical use of free-space quantum systems is that the signal-to-noise ratios of the channels are relatively low and are sensitive to atmospheric disturbance. The atmospheric channel has several negative characteristics that diminish the secret key rate, such as beam extinction and various turbulence effects. The effect of beam wandering on the quantum properties is mainly considered, and the probability distribution of the transmission coefficient is derived to establish the channel model. Low-density parity-check (LDPC) codes operated in the reconciliation procedure are utilized to deal with information interactivity. However, the LDPC codes need to be chosen from a range of codes, where the code rate is considered in low signal-to-noise ratio free-space links. The accumulate–repeat–accumulate code is adopted to improve the decoding threshold of a code. It is found that the multi-edge feature of extended codes is beneficial to the performance of short- and medium-length codes. And numerical results show the proposed scheme provides enhancement in the reconciliation efficiency. LDPC codes containing an additional structure that facilitates decoding could be suitable for free-space CV-QKD protocols when weak atmospheric turbulence is considered.

Laser Physics LettersMar 13, 20207 citations

Communication System Performance Analysis of Satellite-to-Ground BB84 Quantum Key Distribution over Gamma–Gamma Turbulence Channels with Pointing Errors.

Sahil Bhardwaj¹, Vikas Sidhu

Abstract Quantum Key Distribution (QKD) provides information-theoretic security for future communication networks by exploiting the fundamental principles of quantum mechanics. However, satellite-to-ground QKD links suffer significant performance degradation due to atmospheric turbulence, absorption, scattering, and satellite-induced pointing errors. This paper investigates the BB84 QKD protocol over a Free-Space Optical (FSO) channel modeled using the Gamma–Gamma distribution, which accurately captures both small-scale and large-scale atmospheric irradiance fluctuations. Closed-form and numerical results for outage probability and Quantum Bit Error Rate (QBER) are presented under weak, moderate, and strong turbulence regimes. The Secure Key Rate (SKR) is analyzed as a function of link distance under clear and foggy weather conditions. Additionally, the impact of satellite vibration is evaluated using a jitter-dependent pointing error model, demonstrating that misalignment significantly reduces link reliability. Simulation results show that strong turbulence conditions introduce more than 15 dB SNR penalty compared to clear-sky operation, while haze conditions limit QKD range to under 8–10 km. These findings provide practical performance benchmarks for Low-Earth Orbit (LEO) quantum downlinks in realistic atmospheric environments. The results provide practical insights for electronic receiver design and system implementation of satellite quantum communication links.

Mar 5, 20260 citations