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MWAX comprises 24 new servers (+ 2 spares) and repurposes 10 of the existing servers on site at the MRO, occupying three racks. It makes use of the existing 100 Gbps fibre-optic link from site to the ten existing storage servers located in B206 on Curtin Campus. These ten servers will buffer MWA data pending transfer via a 100 Gbps fibre-optic link from B206 to the Pawsey Supercomputing Centre Output visibilities are transferred to Curtin, and ultimately Pawsey, via existing fibre-optic links.
This configuration is capable of simultaneous fine channelisation, cross-correlation, frequency/time averaging, and buffer storage for up to 256 tiles and up to 24 coarse channels of 1.28 MHz each. This represents twice the number of inputs and four times the number of output visibilities compared wuth the legacy system. At the time of writing, the MWA has 16 receivers, which process 128 tiles in total. This limits the input inputs to MWAX , such that it presently currently correlates only 128 tiles.
The MWAX correlator design employs a multicast architecture, allowing all receivers to each send their streams of high time resolution data to any number of multicast consumers with no additional load on the sender. Initially there will be 24 multicast receivers (one for each coarse channel for correlation and voltage capture), however, the multicast architecture allows for additional multicast receivers to utilize the same high time resolution data for other purposes. For example: RFI monitoring, transient detection and external instruments such as Breakthrough: Listen could commensally consume some or all of the high time resolution data without impacting the operation of the telescope.
The MWAX correlator employs the “FX” architecture where the input time samples for each signal path (antenna and polarization) are fine-channelized prior to cross-correlation, reducing the correlation process to complex multiplications in the frequency domain. Whereas the legacy correlator utilizes a polyphase filterbank for the F-engine, the MWAX correlator employs the FFT. For the X-engine, development time/cost has been was minimized by utilizing the existing open-source GPU correlator library “xGPU” (the same library at the heart of the legacy correlator). The standard xGPU library is used essentially unchanged for MWAX, with the exception of a small but crucial change to improve speed and reduce bus/memory traffic, found to be essential to making the design scalable to 256T and beyond (see MWAX xGPU on github).
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The output visibility modes of MWAX using for 128 tiles that run real-time on the as-built MWAX hardware configuration are available listed at this page: MWAX Correlator Modes (128T)
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