Satellite QKD Time Synchronization Using Correlated Laser Pulses
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Solution Overview
Problem
The challenge of achieving precise time synchronization between a satellite and a ground station in quantum key distribution systems is exacerbated by the loss of photons during terrestrial transmission and the constant movement of the satellite, leading to changing link distances and Doppler shifts, which complicates the correlation of photon events.
Innovation Solution
A method involving a separate synchronization laser emitting pulses with a pseudo-random pattern is used to align the timing between the satellite and ground station by correlating detected synchronization pulses with a known pattern, allowing for the conversion of reception times to emission times using polynomial fitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If satellite based QKD is used to overcome terrestrial loss limitations, then communication distance is improved, but time synchronization complexity increases due to Doppler shifts and changing link distances
Solution Approach 1:
The patent segments the time synchronization process into multiple components: separate synchronization laser pulses from quantum signal pulses, distinct processing for clock offset and Doppler shift compensation, and independent correlation analysis. This segmentation allows each component to be optimized independently, reducing overall system complexity while maintaining accurate time synchronization across varying distances and Doppler conditions
Solution Approach 2:
The patent introduces a dedicated synchronization laser pulse as an intermediary carrier that carries timing information separately from the quantum signal. This intermediary pulse enables the ground station to track satellite timing without being affected by quantum signal losses and Doppler shifts, simplifying the synchronization process while enabling long-distance communication
2Length of moving object
If photons are transmitted through atmosphere to achieve inter-continental QKD, then communication distance is improved, but photon loss increases
Solution Approach 1:
The patent extracts the timing synchronization function from the quantum signal transmission. By using separate synchronization laser pulses that are not subject to quantum signal losses, the system can maintain accurate time synchronization even when quantum photons are lost during atmospheric transmission, enabling reliable long-distance QKD
Solution Approach 2:
The patent employs periodic synchronization pulses transmitted at regular intervals to establish and maintain time alignment. These periodic pulses allow the ground station to continuously track satellite position and adjust for Doppler shifts, ensuring accurate timing throughout the communication session despite atmospheric losses
3Adaptability or versatility
If satellite moves continuously to provide coverage, then system versatility is improved, but time synchronization accuracy deteriorates due to changing link distances and Doppler shifts
Solution Approach 1:
The patent implements dynamic time synchronization that adapts to changing satellite conditions. The system continuously monitors and adjusts for Doppler shifts and link distance variations in real-time, allowing accurate time synchronization to be maintained despite the satellite's continuous movement and changing orbital position
Solution Approach 2:
The patent employs feedback mechanisms where the ground station receives synchronization pulses, processes timing information, and uses this feedback to adjust and refine time alignment. The system continuously monitors timing deviations caused by satellite motion and applies corrections, maintaining synchronization accuracy while allowing the satellite to move freely for coverage
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures robust time synchronization, enabling accurate correlation of photon events for secure key distribution by compensating for Doppler shifts and timing jitter, thereby maintaining the reliability of quantum key distribution protocols.
Implementation Method 1
A method involving a separate synchronization laser emitting pulses with a pseudo-random pattern is used to align the timing between the satellite and ground station
Implementation Method 2
compensating for Doppler shifts and timing jitter, thereby maintaining the reliability of quantum key distribution protocols
Data Source
Figure 1
Figure 2A~2B
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AI summary
A method and system for time synchronisation in a satellite based quantum key distribution (QKD) system, by: at a transmitter, emitting a first series of laser pulses, the first series of laser pulses being encoded to form a quantum beam; at the transmitter, emitting a second series of laser pulses, the second series of laser pulses having a predetermined repeating pattern; and at the transmitter, sending the first and second series of laser pulses to a receiver. At a receiver, receiving the first series of laser pulses and the second series of laser pulses at the receiver and determining reception times of pulses of the first series of laser pulses and pulses of the second series of laser pulses. Comparing the received second series of laser pulses to the predetermined pattern at different points in the predetermined pattern, and determining the point at which the received second series of laser pulses is most strongly correlated to the predetermined pattern; with the received second series of laser pulses aligned to the predetermined pattern at the determined point, determining a relationship fitting respective reception times of a plurality of the received pulses to respective emission times of corresponding ones of the second series of laser pulses; and using the determined relationship to convert between reception times of the first series of laser pulses and emission times of corresponding ones of the first series of laser pulses.