Expanded Capability of the Breakthrough Listen Parkes Data Recorder for Observations with the UWL Receiver

The CSIRO Parkes radio telescope, known as Murriyang in Wiradjuri, is a primary observing facility within the Breakthrough Listen (BL) search for intelligent life beyond Earth (Worden et al. 2017). The new Parkes ultra-wideband low (UWL) receiver covers 704–4032 MHz continuously in one package (Hobbs et al. 2020), replacing four receiver packages (10/50, OH, Galileo and AT -S band receiver) previously used to cover the 704–4032 MHz band. Notably, the UWL replaces the 10 cm component of the 10/50 receiver, which was used in previous Breakthrough Listen observations across 2600–3450 MHz (Price et al. 2020). Here, we report on the hardware upgrade and expanded software capability for the Breakthrough Listen Parkes Data Recorder (BLPDR) (Price et al. 2018) to support continued SETI observations with Parkes.

Technical details of the UWL system are provided by Hobbs et al. (2020). Briefly, the dual-polarization receiver consists of a cryogenically cooled feed and low-noise amplifiers, connected to a room-temperature analog signal chain of filters and amplifiers that prepares the signal for digitization. A pair of triplexers (one for each polarization) splits the signal into three bands: 704–1344, 1344–2368, and 2368–4032 MHz.

Each band is digitized using 12-bit analog to digital converters, which are located within the focus cabin. Digitized data are sent via single-mode optical fiber to custom digital signal processing boards that implement a polyphase filterbank to split the signal into 26 subbands, each of 128 MHz width. The subbands are output over high-speed Ethernet at 16-bit depth as a stream of UDP ⁹ packets of size 8272 B.

The aggregate data rate from the 52 UDP streams is 215.072 Gb s⁻¹, and data are sent as multicast traffic. Data are ingested into a 64-port Cisco 3164PQ network switch  co-located with and connected to the primary GPU-based data processing cluster known as "MEDUSA." A block diagram for the UWL–BLPDR system is shown in Figure 1.

Zoom In Zoom Out Reset image size

The use of IPv4 multicast allows multiple devices to "subscribe" to the UWL multicast streams; crucially, this allows simultaneous operation of BLPDR and Medusa. In order to access the data streams, we provisioned a set of eight 40 GbE links between the Medusa Cisco 3164Q switch, and the BLPDR Arista 7050QX switch. These links use 40 GbE LR4L-type transceivers, which output at 1310 nm wavelength along single-mode fiber; although the BL and Medusa racks are only several meters apart, fibers must be fed through RF-tight waveguides that mitigate any potential radio interference generated within the racks (precluding the use of cheaper multi-mode optics).

The 8 × 40 GbE links are aggregated into a port channel (group), using standard Ethernet Link Aggregation Control Protocol (LACP). A hashing scheme on the Cisco switch is used to balance load across the links, manually dividing the 52 streams across the eight links based on multicast IP ¹⁰ address. To enable BL compute nodes to join multicast groups, an IGMP ¹¹ querier was configured on the Arista switch.

To contain UWL traffic, the port channel is assigned as an access port to an Ethernet VLAN. ¹² Switch ports corresponding to BL compute nodes are assigned to the VLAN as trunk ports, and each compute node is assigned a VLAN virtual interface.

As detailed by Price et al. (2018), the BLPDR consists of 26 compute nodes (+1 spare), which fortuitously maps one-to-one with the 26 UWL subbands. Each compute node subscribes to a dual-polarization pair of UDP multicast streams, totaling 8.272 Gb s⁻¹ of data ingest. During the link upgrades, we also installed two extra storage nodes, each of which provides 219 TB of storage capacity.

In early UWL observations (2019 January–June), data were recorded reusing the Medusa packet capture code, which is implemented in PSRDADA, ¹³ connected via a ring buffer to a Bifrost pipeline (Cranmer et al. 2017) to produce narrowband spectra. After 2019 June, a custom code rawspec ¹⁴ was implemented on top of the HASHPIPE ¹⁵ pipeline framework (MacMahon et al. 2018). Rawspec computes full-Stokes polarimetry products, and uses less GPU memory, allowing for finer resolution spectra to be generated.

The incoming UDP packets from the UWL conform to the VDIF specification; ¹⁶ this required implementing codes to extract VDIF metadata and reinterpret the packet data payload. To decrease CPU usage and improve reliability, we implemented a packet capture frontend called Hpguppi_daq for the Rawspec code using Infiniband verbs, to perform a zero-copy from the network interface card to user space, without using CPU cycles (see MacArthur et al. 2017); this approach was also used in the Medusa packet capture code.

A broad overview of BL data products and file formats is given by Lebofsky et al. (2019); however, UWL data differ in resolution. For the UWL, data output from the Bifrost pipeline has resolution ∼3.81 Hz (2²⁵ channels across a 128 MHz subband), with ∼16.78 s integration time. Stokes-I data are output in Sigproc ¹⁷ filterbank format, but are converted into HDF5 ¹⁸ when archived. A separate filterbank file is created on each compute node, for a total of 26 files per observation.

Rawspec outputs three data products, with time and frequency resolutions of (2 Hz, 15.0 s), (0.5 MHz, 100 μs), and (2 kHz, 1 s). The 2 Hz resolution data product is Stokes-I only, while the other data products are full Stokes.

The UWL–BLPDR system is being used for technosignature searches on nearby stars and galaxies (Isaacson et al. 2017), the Galactic center (Gajjar et al. 2019), the BL "exotica" catalog (Lacki et al. 2020), and targets of interest from TESS (Traas et al. 2021), as well as for follow-up of BL MeerKAT observations (Isaacson 2018). BLPDR is also available for shared-risk ancillary science observations. ¹⁹

Breakthrough Listen is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation. ²⁰ The Parkes radio telescope is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. The authors thank the tireless Parkes engineering staff.