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10 years of LOFAR highlights: RSP boards make sure beamforming is possible

By André Gunst

LOFAR is the first radio telescope of its size, wherein tens of thousands of small antenna elements are used instead of a few big dishes, as was more common in radio astronomy. All these antennas generate enormous amounts of data 24/7.

Published by the editorial team, 2 June 2020

The first stage of combining all that data and reducing it for subsequent stages is done by the Remote Station Processing (RSP) board. A complex board equipped with 5 high-end Field Programmable Gate Arrays (FPGA) at the time of installation. The processing load of each Dutch station was distributed over 12 of these boards. These boards were all serialized to each other, each board processing its partial sum. The last board in the chain calculated the final station output product. The RSP boards resulted in the first large scale beamformer systems applied in radio astronomy.

How does beamforming work? This video explains it.

The main cost driver of the RSP boards were the FPGAs, which were tendered after the prototype design was complete. We had to completely re-factor the RSP board because the competitor vendor was awarded for the tender. The consequence was a re-design of the board and porting the existing firmware to the FPGA type of the awarded vendor.

Prototype of RSP board with the Altera FPGA, which was later replaced by a Xilinx FPGA, credit ASTRON.

During the RSP board design, one of the ambitions was to be able to off-load all incoming data for later use. Unfortunately at that time, the cost impact did not justify the “nice to have” functionality.  As a consequence, LOFAR functionality added to LOFAR later, like AARTFAAC, costed extra design effort to realize. However, in LOFAR2.0 all of the incoming data can potentially be offloaded because the selected hardware (UniBoard^2) has much more IO capability.

On 12 June 2020, LOFAR celebrates its tenth anniversary. The radio telescope is the world’s largest low frequency instrument and is one of the pathfinders of the Square Kilometre Array (SKA), which is currently being developed. Throughout its ten years of operation, LOFAR has made some amazing discoveries. It has been a key part of groundbreaking research, both in astronomy and engineering. Here we feature some – but definitely not all – of these past highlights, with surely more to come in the future.



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