The Square Kilometre Array (SKA) Central Signal Processor (CSP) is a real-time backend system that processes incoming astronomical signals to produce visibilities and detects and profiles pulsars. The CSP is composed of the Local Monitoring and Control (LMC), the Correlator and Beam-Former (CBF), and the Pulsar Search and Timing (PSS, PST) engines. Each subsystem is developed by a different team in the SKA control software domain following the Scaled Agile Framework (SAFe) to guarantee coherence in the development. The definition of an engineering User Interface (UI) for the CSP is challenging due to the variety of skills that are required to identify the most relevant design concepts and potential roadblocks to an effective representation and the fact that several teams are involved. For this reason, we chose to leverage a collaborative design approach that can easily fit SKA's biweekly sprint cadence while involving experts from different fields in a "think outside the box" process. Sketches and wireframes undergo multiple refinement sessions that lead to the realisation of an engineering dashboard representing the current state of CSP implementation. User testing sessions constitute the means by which the success of the proposed UI is measured. Additional positive effects are alignment across different teams on the current capabilities of the system and its future development, as well as a way for continuously adapting the UI to the system's evolution. In this paper, we describe the challenges we faced while coordinating the design across multiple teams, show how the process was implemented to fit the short agile iterations and overall SAFe framework and present the results of the work.

The Square Kilometre Array (SKA) Low telescope's correlator comprises a number of FPGA signal processing cards, 100 Gbps Ethernet (100GbE) network, and associated software [1].The correlator is required to support a range of different operating modes, with up to 4096 dual polarisation signals being correlated, multiple subarrays, and multiple different integration parameters.In this paper we describe an efficient, flexible and expandable implementation, using commercial off the shelf components.

The Square Kilometre Array Low is a next generation radio telescope, consisting of 512 antenna stations spread over 65 km, to be built in Western Australia. The correlator and beamformer (CBF) design is central to the telescope signal processing. CBF receives 6 Tera-bits-per-second (Tbps) of station data continuously and processes it in real time with a compute load of 2 Peta-operations-per-second (Pops). The correlator calculates up to 22 million cross products between all pairs of stations, whereas the beamformers (BFs) coherently sum station data to form more than 500 beams. The output of the correlator is up to 7 Tbps, and the BF 2 Tbps. The design philosophy, called "Atomic COTS," is based on commercial off-the-shelf (COTS) hardware. Data routing is implemented in network switches programmed using the Programming Protocol-Independent Packet Processors (P4) language and the signal processing occurs in COTS field-programmable gate array (FPGA) cards. The P4 language allows routing to be determined from the metadata in the Ethernet packets from the stations. That is, metadata describing the contents of the packet determines the routing. Each FPGA card inputs a fraction of the overall bandwidth for all stations and then implements the processing needed to generate complete science data products. Generation of complete science products in a single FPGA is named here as Atomic processing. A Tango distributed control system configures the multitude of processing modes as well as maintaining the overall health of the CBF system hardware. The resulting 6 Tbps in and 9 Tbps out, 2 Pops Atomic COTS network attached accelerator occupies five racks and consumes 60 kW. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.

Abstract In this paper, we describe the system design and capabilities of the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the conclusion of its construction project and commencement of science operations. ASKAP is one of the first radio telescopes to deploy phased array feed (PAF) technology on a large scale, giving it an instantaneous field of view that covers $31\,\textrm{deg}^{2}$ at $800\,\textrm{MHz}$. As a two-dimensional array of 36$\times$12 m antennas, with baselines ranging from 22 m to 6 km, ASKAP also has excellent snapshot imaging capability and 10 arcsec resolution. This, combined with 288 MHz of instantaneous bandwidth and a unique third axis of rotation on each antenna, gives ASKAP the capability to create high dynamic range images of large sky areas very quickly. It is an excellent telescope for surveys between 700 and $1800\,\textrm{MHz}$ and is expected to facilitate great advances in our understanding of galaxy formation, cosmology, and radio transients while opening new parameter space for discovery of the unknown.

In the last few years, Input/Output (I/O) bandwidth limitation of legacy computer architectures forced us to reconsider where and how to store and compute data across a large range of applications. This shift has been made possible with the concurrent development of both smartNICs and programmable switches with a common programming language (P4), and the advent of attached High Bandwidth Memory within smartNICs/FPGAs. Recently, proposals to use this kind of technology have emerged to tackle computer science related issues such as fast consensus algorithm in the network, network accelerated key-value stores, machine learning, or data-center data aggregation. In this paper, we introduce a novel architecture that leverages these advancements to potentially accelerate and improve the processing of radio-astronomy Digital Signal Processing (DSP), such as correlators or beamformers, at unprecedented continuous rates in what we have called the "Atomic COTS" design. We give an overview of this new type of architecture to accelerate digital signal processing, leveraging programmable switches and HBM capable FPGAs. We also discuss how to handle radio astronomy data streams to pre-process this stream of data for astronomy science products such as pulsar timing and search. Finally, we illustrate, using a proof of concept, how we can process emulated data from the Square Kilometer Array (SKA) project to time pulsars.

“Bluering” is the name given to a phased array receiver system that has considerable flexibility. This flexibility is in both the RF frequency range as well as the digital signal processing and communications. Bluering integrates a large number of very different technologies into one system package. In this paper a description of the major parts of Bluering are provided as well as some initial testing results.

Radio astronomy receiver development is focusing on increasing the field of view and bandwidth in tandem with the exponential increase in data volumes permitted by signal processing. We present recent receiver and signal processing developments from CSIRO and FAST.

The recent introduction by Xilinx of its range of RF System-on-Chip (RFSoC) devices is resulting in a fundamental shift in the way digital back-ends for radio astronomy instruments are being architected. The bringing together of 8 or 16 multi-Giga-sample per second Analogue to Digital Converters (ADCs) with large and feature rich Field Programmable Gate Array (FPGA) fabric and quad-core ARM processors all on a single chip has opened up new possibilities in high-performance, power-efficient RF sampling digital systems for radio astronomy.

In recent years, thermal management of FPGAs has attracted extensive scientific attention. However, the majority of proposed cooling solutions remain in research phase with prototypes not addressing the dynamic thermal needs of the full hardware configuration. In this work we present the design and fabrication of a full-board, direct liquid cooling, heat sink for densely packed FPGA-based processing boards. The liquid cooling heat sink design forms part of the high power consuming Gemini Line Replaceable Unit (LRU) processing board, developed for the Square Kilometre Array (SKA) low-frequency aperture array correlator and beam former (CBF). To test the cooling capabilities, in-house developed “heater-firmware” is used to generate 121 watt inside the FPGA and another 85 watt in peripheral heat sources. The presented results show that this direct liquid cooling solution is an efficient thermal design, not only suitable for large quantity production, but also for integration into a dense implementation of 12 Xilinx Ultrascale+ FPGA LRU boards in a standard sub-rack of 178x483x415mm. This configuration enables a processing capacity of 3.4 TMAC/s, while maintaining the die temperature of all FPGAs at a $60.6^{\circ}\mathrm{C}$ level with a water supply temperature of $33^{\circ}\mathrm{C}$.

Arrays for radio astronomy are challenging to build and operate due to their sheer size and data volume, but also due to the high expectations on signal fidelity and performance in challenging environments. This paper explores some of the next generation technology applicable to large antenna arrays, using the Square Kilometre Array (SKA) as an example. Fundamental components of these arrays are receivers for each signal path and the signal processing performed on these signals.

We report the detection of an ultra-bright fast radio burst (FRB) from a modest, 3.4-day pilot survey with the Australian Square Kilometre Array Pathfinder. The survey was conducted in a wide-field fly's-eye configuration using the phased-array-feed technology deployed on the array to instantaneously observe an effective area of 160 deg(2), and achieve an exposure totaling 13200 deg2 hr. We constrain the position of FRB. 170107 to a region 8' x 8' in size (90% containment) and its fluence to be 58 +/- 6 Jy ms. The spectrum of the burst shows a sharp cutoff above 1400 MHz, which could be due to either scintillation or an intrinsic feature of the burst. This confirms the existence of an ultra-bright (> 20 Jy ms) population of FRBs.

The Australian Square Kilometre Pathfinder ASKAP Design Enhancement (ADE) is the second generation architecture based on a distributed antenna system (DAS) with radio over fiber transmission (RFoF) from planar phased array feed (PAF) to the central site digital signal processing (DSP). With 36 × 12m reflector antennas and 188 elements per PAF, there are 6840 ports with signal and conversion (SAC) paths. Low cost implementation is key for phased array systems comprising thousands of elements. The implementation and component choices are critical to provide a viable project delivery; balancing component availability, RF performance, power consumption, maintenance and whole of life aspects. In this paper we mention discrete components used, basic subassembly performance and fiducial end to end compliance measurements.

In this paper the hardware designed for the SKA Low (Square Kilometre Array) correlator and beamformer (CBF) is discussed. SKA-Low is a low frequency aperture array (LFAA) to be located in remote Western Australia. The array is collecting radio signals in the frequency range from 50 to 350 MHz. The large number of dual polarization antennas (131072) are distributed over a total of 512 stations with a maximum spacing of 65 km. Each station forms a single dual polarization beam with a bandwidth of 300 MHz. The bandwidth is split into 384 coarse channels of 781250 Hz in width by LFAA station beamformers. The CBF hardware receives these station beam signals and splits them into finer channels using a polyphase filterbank. Thereafter the fine channels from all stations are aligned in time, correlated and simultaneously beamformed. There are two independent beamformers, one for pulsar search (PSS), that creates 500 array beams, and another for pulsar timing (PST), that creates 16 array beams. A variety of additional functionality and modes is required in the correlator and beamformers to meet the requirements. The core of the CBF hardware is a board with a Field Programmable Gate Array (FPGA), called Gemini, that can implement all functions of the CBF. The amount of input data and processing for CBF is that large, that it requires several hundreds of these FPGA boards. The current estimate is that the SKA Low CBF will need 288 FPGAs. The same board can be used for all functions, because it is the interconnect between boards and the FPGA firmware that determine the function. This versatile hardware design could therefore potentially be used for other radio telescopes or data processing systems as well.

This is an overview of the system level RF design for the second generation architecture used in the Australian Square Kilometre Array Pathfinder (ASKAP) [1] design enhancement (ADE). ADE is a distributed antenna system (DAS) of 36 reflector antennas each 12m in diameter. Each antenna has a planar Phased Array Feed (PAF) at the prime focus. The PAF contains 188 broadband 700-1800MHz receptors. Inside a PAF the radioastronomy (RA) signals are amplified, band selected and converted to 188 individual broadband RF over (singlemode optical) fiber (RFoF) lightwaves [2]. The entire ADE array has 6840 RFoF links, this includes transmission line delay metrology for each reflector. The longest RFoF span is 6km. Optical to RF demodulation of the RF sky signal at the central site Digital Signal Processing (DSP) shielded building is direct sampled in 12bit analog to digital convertors (ADCs). Digital beamforming provides 36 pencil beams, each of 384MHz bandwidth. The scale of ADE represents a leap forward in applied RF and photonic techniques to enable a simpler, lower cost, more modular, EMC compliant, phased array receiver architecture. ADE will provide unprecedented high speed sky surveys with an instantaneous widefield of view (30deg 2 at 1420MHz) capability for a new generation of radio astronomers.

The Square Kilometre Array (SKA) organisation is building a low frequency (50-350 MHz) aperture array to be located in remote Western Australia. The array consists of 512-stations, each consisting of 256-dual polarisation log-periodic antennas. The stations are distributed over a distance of 80km, with the greatest density of stations located in the central core. The input bandwidth is processed in a two stage polyphase filterbank, with the first stage channeliser producing 384 x 781 kHz narrow-band channels. Each station beamforms the antennas together to form a single dual polarisation beam with a bandwidth of 300 MHz (additional beams can also be traded for bandwidth). The second stage polyphase filterbank is located in a system called the Correlator and BeamFormer (CBF) which is the topic of this paper. In the CBF the station signals are first aligned in time. Thereafter the signals are simultaneously correlated and beamformed.