WP12: Networking and reference time and frequency

February 12, 2010
At each antenna array of the EISCAT_3D system, high quality timing and frequency reference signals must be generated and distributed to all elements to achieve the stringent synchronisation (to better than 50 ps) required for the overall system to function as intended. Also, command data must be passed to each array element and the data streams from the receiving elements must be collected, concentrated, and routed onto a performance network. This
Work Package was tasked with examining possible methods for guaranteeing time synchronisation, and developing a technical solution to ensure that the required accuracy could be maintained.

Some of the conclusions from this Work Package were:

• The standard deviation of the sampling time of the ADC of each antenna throughout the array, which
  has to be better than 160 ps, with 50 ps allotted to the timing distribution system.
• Two different approaches has been evaluated for the timing distribution:
  • The cable-based system has been evaluated in simulation and have an approximate standard deviation of 30-45 ps depending mostly on the reflection between front-end and antenna.
  • The GNSS-based system has been evaluated in hardware tests, but with a limited baselength and using post-processing. The results show that a standard deviation of 20 ps is readily achievable with simple calculations.
• The main difference between the two systems is that the cable-based system uses more hardware than the GNSS-based system. On the other hand, the cable-based system is capable of not only calibrating the timing, but also the gain of each channel compared to the others.
• A survey of the hardware that is available from different manufacturers wer made.

The work in this Work Package was performed by EISCAT Scientific Association.