Signal Processing

Signal Processing – The Key to the SKA telescopes’ power

Signal processing is an integral part of the radio astronomy process. It is used for pre-processing data for specific science requirements in preparation for making the stunning high-resolution radio images that the SKA will eventually produce.

Signal processing also handles the complex operation of beam-forming, which enables the radio signals to initially be received from across the sky from any direction, and with the SKA, in multiple directions at the same time.

Optical cross connects, similar to the technology shown in the first image on this page, channel data from the receivers to the correlator and are one of a variety of possible solutions for the SKA currently being tested.

The cross-connect allows high speed switching of optical fibre signals. This is a cost and power efficient way of providing what is commonly referred to as a “corner-turn” on the data which will be needed for processes such as beam-forming and correlation.

Pre-processing

Data from each SKA telescope will be sent to the central correlator, which will house high-speed computers designed to combined the signals from multiple telescopes. These correlators will be situated near the core of the array, where the data will be combined and synchronised.

Filters will then be used to separate the radio frequency signals required for astronomy from any interfering radio frequency signal that would contaminate the data. This is one reason why the SKA locations have to be as radio quiet as possible.

Beam forming

Beam forming is a signal processing technique that is used in radio astronomy to observe radio signals from specific regions of the sky. Whereas radio dishes mechanically turn to observe an area of sky, the aperture array antennas that will be used in the SKA have no moving parts and so the beams are electronically steered to observe specific regions.

Autodetection

The SKA will use signal processing to automatically detect the repetitive pulsed signal of objects such as pulsars (the collapsed spinning core of a dead star first discovered by Jocelyn Bell and Anthony Hewish) in the data. In addition to pulsars, the SKA will automatically detect transient events. These unexpected and unpredictable astronomical events include supernovae, gamma‐ray bursts and micro‐lensing events, which can temporarily brighten objects in the far reaches of the Universe, due to the gravity of a foreground object acting as a lens.

Both methods of auto-detection are time‐frequency based observations and require high time resolution data.

Algorithm development

The SKA will stretch signal processing algorithm development in two vital areas. Faster and better ways will be developed to make the high dynamic range (A ratio of 106:1) images required for SKA science. Effective radio interference (RFI) mitigation algorithms will also be needed to enable observations across wide segments of the radio spectrum. The algorithms used will need to be as efficient as possible, to process the huge amounts of data coming through the system.

Processing

SKA signal processing has considerable processing and signal transport requirements due to its sheer scale of the array. Thousands of telescopes providing data simultaneously across two continents.

The signal processing will require exceptionally high-speed computer systems, that must meet budget, processing and thermal requirements.

Four signal processing technologies are currently being developed and tested by the astronomy engineering community, as potential solutions:

General Purpose Processors
Graphics Processing Unit (GPU)
Field Programmable Gate Arrays (FPGA)
Application Specific Integrated Circuit (ASIC)