Enabling & Support

Secure Clock Synchronization

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ESA / Enabling & Support / Space Engineering & Technology
715 - Abstract:

The present technology refers to a method to enable the secure synchronization of time clocks of multiple receivers. The method allows to transfer time accurately, securely and ubiquitously. The technology has a broad portfolio of applications like emerging fixed and mobile services. For instance, autonomous vehicles, terrestrial positioning, 5G mobile bread, etc. can benefit from the invention.

ESA is looking for partners who would be interested in licensing and implementing this patent.


The European Space Agency proposes an invention for transferring time accurately, securely and ubiquitously. The technique is based on a Common View Satellite Time Transfer (CVSTT) method. CVSTT makes use of the exchange of information about the reception time of a reference signals for any two receivers observing a common transmitter, i.e. a LEO satellite or terrestrial transmitters. With this knowledge, the offset between the receiver clocks can be identified and the clocks can be synchronized. 

To allow a secure time transfer, the observation parameters, such as observation time window, tracked carrier frequency, signal bandwidth, type of observed signal, are exchanged through a secured channel prior to the observation of a common transmitter. This allows to avoid spoofing and other mechanisms to disturb the transmitted signal. The parameter exchange during configuration should be repeated on a regularly basis. 

Making use of the known CVSTT method, the signals received by the receivers are passed to a cross correlation function. The cross correlation function gives correlation values as an output, as shown in the Figure 1. Using the peak correlation value and the second biggest peak value, a correlation ratio is computed. The use of the correlation value allows to reject ambiguous measurements, due to missing confidence, if the peaks are similar in their absolute value. If the correlation ratio delivers reasonable values, the method gives an accurate estimation of the true clock delay and supports the time correction algorithm. 

Due to the inventions advantages - security, traceability, indoor availability, precision and accuracy - the invention has a broad portfolio of applications.

Example of a cross correlation function
Example of a cross correlation function

Innovations and advantages:

The innovative concept of time transfer introduced in this patent has the following advantages, compared to other methods:

  • Solution can be built with low cost equipment and minimal investment on the basis of the current infrastructure
  • Jamming, spoofing and meaconing can be avoided or significantly mitigated
  • Secure and traceable time transfer through standardized protocols
  • Can be used in indoor environments without degraded performance
  • Precise and accurate time synchronization

Domain of application:

The invention offers a broad portfolio of applications, i.e.:

  • Emerging fixed and mobile services (e.g. autonomous transportation, Internet of Things, terrestrial positioning, 5G mobile broadband, 5G enhanced machine to machine communication, 5G vehicle to everything (V2X), etc.)
  • Big data and cloud processing
  • Terrestrial telecommunication and mission critical communications
  • Power grid distribution and maintenance sector
  • Financial sector (e.g. for timestamping transactions in trading systems)

Industries in these sectors might be interested in the patent and are welcome to get in touch with the European Space Agency for further information.