[Paper Review] Feasibility of Quantum Key Distribution from High Altitude Platforms

Yi Chu, Ross Donaldson+2 more|arXiv (Cornell University)|Dec 14, 2020

Quantum Information and Cryptography46 references4 citations

TL;DR

This paper investigates the feasibility of deploying Quantum Key Distribution (QKD) from High Altitude Platforms (HAPs) at 20 km altitude, demonstrating through detailed link budget analysis that sufficient signal strength is achievable under most conditions. The generous link budget enables the use of diverged beams, significantly simplifying Pointing, Acquisition, and Tracking (PAT) systems and expanding potential deployment scenarios for QKD.

ABSTRACT

This paper presents the feasibility study of deploying Quantum Key Distribution (QKD) from High Altitude Platforms (HAPs), as a way of securing future communications applications and services. The paper provides a thorough review of the state of the art HAP technologies and summarises the benefits that HAPs can bring to the QKD services. A detailed link budget analysis is presented in the paper to evaluate the feasibility of delivering QKD from stratospheric HAPs flying at 20 km altitude. The results show a generous link budget under most operating conditions which brings the possibility of using diverged beams, thereby simplifying the Pointing, Acquisition and Tracking (PAT) of the optical system on the HAPs and ground, potentially widening the range of future use cases where QKD could be a viable solution.

Motivation & Objective

• To assess the technical feasibility of using High Altitude Platforms (HAPs) for Quantum Key Distribution (QKD) in future secure communication networks.
• To evaluate the performance of QKD links from stratospheric HAPs at 20 km altitude under realistic atmospheric and environmental conditions.
• To determine whether the link budget supports practical QKD deployment with simplified Pointing, Acquisition, and Tracking (PAT) mechanisms.
• To identify operational conditions and system parameters that enable robust, long-range QKD transmission from HAPs.
• To explore the potential of using diverged beams in HAP-based QKD to reduce PAT complexity and broaden application scope.

Proposed method

• Conducting a comprehensive link budget analysis for QKD links from HAPs at 20 km altitude, accounting for atmospheric attenuation, beam divergence, and background noise.
• Modeling the optical channel using standard atmospheric models to estimate signal power at the ground receiver for various weather and visibility conditions.
• Evaluating the impact of beam divergence on signal power and Bit Error Rate (BER) performance, particularly under low signal-to-noise conditions.
• Assessing the feasibility of using non-telecentric, diverged beams to reduce the stringent PAT requirements typically imposed by narrow-beam systems.
• Simulating system performance across different transmission distances and environmental parameters, including aerosol and molecular scattering.
• Comparing the results against established QKD performance thresholds to determine viability for real-world deployment.

Experimental results

Research questions

• RQ1 Can QKD be practically deployed from High Altitude Platforms at 20 km altitude with acceptable signal-to-noise ratios?
• RQ2 What is the required link budget for secure QKD operation from a HAP, and is it achievable under typical stratospheric conditions?
• RQ3 To what extent can beam divergence be increased without degrading QKD performance, thereby reducing PAT system complexity?
• RQ4 How do atmospheric conditions such as aerosol concentration and visibility affect the feasibility of HAP-based QKD?
• RQ5 What are the operational trade-offs between beam divergence, link margin, and system robustness in HAP-to-ground QKD links?

Key findings

• The link budget analysis shows a generous margin under most operating conditions, indicating strong feasibility for QKD from HAPs at 20 km altitude.
• The system achieves sufficient signal power even with moderate beam divergence, enabling the use of less complex PAT mechanisms.
• Background noise and atmospheric attenuation are manageable within the model, especially under clear-sky conditions with good visibility.
• The results support the use of diverged beams, which significantly reduces the need for high-precision tracking systems on both HAP and ground stations.
• The system remains viable across a wide range of environmental conditions, including moderate aerosol loading and variable weather patterns.
• The study confirms that HAP-based QKD can support secure key exchange over distances relevant to regional or national quantum communication networks.