The Murchison Widefield Array Correlator

The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day^(−1) of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces

Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs

The Murchison Widefield Array (MWA) is a next-generation radio telescope currently under construction in the remote Western Australia Outback. Raw data will be generated continuously at 5GiB/s, grouped into 8s cadences. This high throughput motivates the development of on-site, real time processing and reduction in preference to archiving, transport and off-line processing. Each batch of 8s data must be completely reduced before the next batch arrives. Maintaining real time operation will require a sustained performance of around 2.5TFLOP/s (including convolutions, FFTs, interpolations and matrix multiplications). We describe a scalable heterogeneous computing pipeline implementation, exploiting both the high computing density and FLOP-per-Watt ratio of modern GPUs. The architecture is highly parallel within and across nodes, with all major processing elements performed by GPUs. Necessary scatter-gather operations along the pipeline are loosely synchronized between the nodes hosting the GPUs. The MWA will be a frontier scientific instrument and a pathfinder for planned peta- and exascale facilities.Comment: Version accepted by Comp. Phys. Com

The Murchison Widefield Array

It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky.Comment: Accepted for publication in Proceedings of Science [PoS(RFI2010)016]. 6 pages and 3 figures. Presented at RFI2010, the Third Workshop on RFI Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland

A GPU based real-time software correlation system for the Murchison Widefield Array prototype

Modern graphics processing units (GPUs) are inexpensive commodity hardware that offer Tflop/s theoretical computing capacity. GPUs are well suited to many compute-intensive tasks including digital signal processing. We describe the implementation and performance of a GPU-based digital correlator for radio astronomy. The correlator is implemented using the NVIDIA CUDA development environment. We evaluate three design options on two generations of NVIDIA hardware. The different designs utilize the internal registers, shared memory and multiprocessors in different ways. We find that optimal performance is achieved with the design that minimizes global memory reads on recent generations of hardware. The GPU-based correlator outperforms a single-threaded CPU equivalent by a factor of 60 for a 32 antenna array, and runs on commodity PC hardware. The extra compute capability provided by the GPU maximises the correlation capability of a PC while retaining the fast development time associated with using standard hardware, networking and programming languages. In this way, a GPU-based correlation system represents a middle ground in design space between high performance, custom built hardware and pure CPU-based software correlation. The correlator was deployed at the Murchison Widefield Array 32 antenna prototype system where it ran in real-time for extended periods. We briefly describe the data capture, streaming and correlation system for the prototype array.Comment: 11 pages, to appear in PAS

The Murchison Widefield Array: Design Overview

The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities.Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings of the IEE

Realisation of a low frequency SKA Precursor: The Murchison Widefield Array

The Murchison Widefield Array is a low frequency (80-300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given

Realisation of a low frequency SKA Precursor: The Murchison Widefield Array

The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given