Abstract
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift scan radio telescope operating across the 400–800 MHz band. CHIME is located at the Dominion Radio Astrophysical ...Observatory near Penticton, BC, Canada. The instrument is designed to map neutral hydrogen over the redshift range 0.8–2.5 to constrain the expansion history of the universe. This goal drives the design features of the instrument. CHIME consists of four parallel cylindrical reflectors, oriented north–south, each 100 m × 20 m and outfitted with a 256-element dual-polarization linear feed array. CHIME observes a two-degree-wide stripe covering the entire meridian at any given moment, observing three-quarters of the sky every day owing to Earth’s rotation. An FX correlator utilizes field-programmable gate arrays and graphics processing units to digitize and correlate the signals, with different correlation products generated for cosmological, fast radio burst, pulsar, very long baseline interferometry, and 21 cm absorber back ends. For the cosmology back end, the
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correlation matrix is formed for 1024 frequency channels across the band every 31 ms. A data receiver system applies calibration and flagging and, for our primary cosmological data product, stacks redundant baselines and integrates for 10 s. We present an overview of the instrument, its performance metrics based on the first 3 yr of science data, and we describe the current progress in characterizing CHIME’s primary beam response. We also present maps of the sky derived from CHIME data; we are using versions of these maps for a cosmological stacking analysis, as well as for investigation of Galactic foregrounds.
We present the implementation of a spectral kurtosis-based Radio-Frequency Interference detection system on the CHIME instrument and its reduced-scale pathfinder. Our implementation extends ...single-receiver formulations to the case of a compact array, combining samples from multiple receivers to improve the confidence with which RFI is detected. Through comparison between on-sky data and simulations, we show that the statistical properties of the canonical spectral kurtosis estimator are functionally unchanged by cross-array integration. Moreover, by comparison of simultaneous data from CHIME and the Pathfinder, we evaluate our implementation’s capacity for interference discrimination for compact arrays of various sizes. We conclude that a spectral kurtosis-based implementation provides a scalable, high cadence RFI discriminator for compact multi-receiver arrays.
This thesis presents the design, development, operation, and performance of digital signal processing systems for the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and its Pathfinder. CHIME ...is designed to investigate the behaviour of Dark Energy in order to constrain its physical mechanism; it will do so by examining the geometry of the recent universe using as a `standard ruler' the imprint of the Baryon Acoustic Oscillation (BAO) feature in the 21 cm emission of neutral Hydrogen.In order to construct the complete set of visibilities for CHIME's 2048 inputs and 400\,MHz of bandwidth, the FX correlator's X-Engine must be capable of ingesting 6 Tib/s of data and completing 8.4×1014 complex multiply-and-accumulate operations per second; these requirements make CHIME's X-Engine by far the largest currently in operation. Using mass-produced Graphics Processing Units (GPUs), commercial off-the-shelf computer hardware, and a sealed-loop liquid-cooling system, the CHIME correlator X-Engine achieves high performance and exceptional efficiency. This thesis presents a detailed description of the X-Engine hardware design and a thorough evaluation of its performance, with additional commentary on aspects of the design and deployment which may warrant additional consideration by those planning similar systems.The substantial computational power available in the correlator system provided an opportunity for pre-integration excision of transient Radio-Frequency Interference (RFI). A number of RFI mitigation techniques were examined, including Median Absolute Deviation and Spectral Kurtosis measures; the latter was implemented on CHIME and the Pathfinder, and results from tests of the RFI detection system are presented.The CHIME Pathfinder, in addition to acting as a test-bed for hardware and analysis techniques, produced an archive of visibility data spanning three years; from this, maps were produced covering the entire northern sky for 609 sidereal days. This thesis details the data processing pipeline which was employed to generate these maps as well as analysis of the resulting data products with regards to their overall variability and the properties of known point-like sources.
The Case for SoC in Future Radio Astronomy Ojeda, Omar A. Yeste; Denman, Nolan; Wunduke, Stephen
2022 IEEE 35th International System-on-Chip Conference (SOCC),
2022-Sept.-5
Conference Proceeding
Summary form only. Radio-astronomical interferometers are superb instruments key to understanding our Universe and the physical laws that govern it. At the core of such machines, a Central Signal ...Processor (CSP) combines the information received from multiple antennas in real time by means of cross-correlation and beamforming. The CSP reduces the input data rate by several orders of magnitude, so that astronomical data can be stored for offline processing. This paper makes a case for the use of SoC in future radio astronomy as a more environmentally sustainable alternative, in comparison with modern CSP designs based on FPGA technology, as well as a more economical one in the long term.
The Next-Generation Very Large Array (ngVLA) is a future radio astronomy facility, building on the existing Very Large Array in New Mexico, which promises an order of magnitude improvement over ...current capabilities in terms of sensitivity, angular and spectral resolutions. With 263 antennas up to thousands of miles away, each one generating almost a terabit-per-second of data to be processed in real time, the design of a Central Signal Processor for the ngVLA project appears as a formidable technical challenge. We propose the SCalable, REconfigurable And Modular (SCREAM) design concept based on highly optimized building blocks that connect to each other to form the system, thus enabling economies of scale while minimizing hardware cost, size, and power. Functional flexibility is obtained through block reconfigurability. Its scalable architecture makes the SCREAM design a suitable candidate not only for the ngVLA, but also for any potential future interferometer facilities.
We present an overview of the Graphics Processing Unit (GPU) based spatial processing system created for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The design employs AMD S9300x2 ...GPUs and readily-available commercial hardware in its processing nodes to provide a cost- and power-efficient processing substrate. These nodes are supported by a liquid-cooling system which allows continuous operation with modest power consumption and in all but the most adverse conditions. Capable of continuously correlating 2048 receiver-polarizations across 400\,MHz of bandwidth, the CHIME X-engine constitutes the most powerful radio correlator currently in existence. It receives \(6.6\)\,Tb/s of channelized data from CHIME's FPGA-based F-engine, and the primary correlation task requires \(8.39\times10^{14}\) complex multiply-and-accumulate operations per second. The same system also provides formed-beam data products to commensal FRB and Pulsar experiments; it constitutes a general spatial-processing system of unprecedented scale and capability, with correspondingly great challenges in computation, data transport, heat dissipation, and interference shielding.
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