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Signal Transport and Networks

Signal transport and networks will be the backbone of the SKA telescope; they will interface with almost every aspect of the system and will ultimately represent the largest and most challenging network system in science.

An average of 8 Terabits per second of data will be transmitted both from the dishes and from the low-frequency aperture array to central processors at the sites in South Africa and Australia. This is a rate 100,000 times faster than the projected global average broadband speed in 2022 (source: CISCO; November 2018).

The physical network infrastructure will primarily use optical fibre cable. Optical fibres are strands of silica based glass as thin as a human hair. Light can be transmitted along the fibre over great distances at very high data rates providing an ideal medium for the transmission of the large volumes of data required for high-sensitivity radio astronomy.

Optical fibres will be essential to transport huge amounts of data to the central SKA processor node (credit: Wikimedia Commons).

The ability of optical fibres to carry large amounts of data over long distances at high speed can increase the sensitivity of the radio telescope because it maximises the volume of data transmitted from the receptors to the correlators located at each site.

This means that distant galaxies, only glimpsed by extended observations today, will routinely be observed in a fraction of the time, giving astronomers using the SKA more data than has ever been available in the history of radio astronomy.

The huge distances that the spiral SKA configuration will span means that the SKA will need enormous quantities of optical fibre, enough in fact, to wrap twice around the Earth!

Signal transport and networks are also essential for the operation of the SKA as it works as an interferometer. The functions of these transport networks will include timing and synchronisation, monitoring and control, the transmission of data from the receptors to the correlator as well as data connectivity externally for users across the world. Timing and the arrival of signals will form the backbone of how these vast interferometric networks will function.

Time distribution network:

The SKA telescope will make synchronous observations with antennas at diverse locations. This requires very precise timing. The local clocks used in these systems have to be very stable in order to minimise signal loss and mis timing of data during integration in the local correlators, as well as for calibration purposes.

The stability requirements are dependent on the observing frequencies, but at the highest frequencies foreseen for the SKA, clock stabilities of the order of Pico (10-12) seconds in 1 second will be required.

Monitoring and control:

The SKA will also include a monitoring and control network. It will be diverse and connect every antenna in the array with an operations centre. The precise architecture of this array is being developed alongside the SKA system design. Every one of the radio telescopes in the network will be continually monitored.

Digital system processing and computing connectivity:

The SKA will include very large digital signal processing and high performance computing facilities. The interconnection between these two functions of the telescope will be a significant network in its own right and will carry many thousands of Gigabits of data per second.

Connections to the outside world:

The processed data from the SKA telescope will be used by an international community of astronomers who will require connections to the high performance computing facility and enormous archive capability to store the data.

This connectivity will be limited by that available on international connection systems, but there is a desire to reach hundreds of Gigabits per second. This will require network infrastructure will surpass the global internet by a huge factor in terms of the amounts of data being sent globally. Signal processing has never witnessed anything on this scale.