APSR: digital signal processing at Parkes

Willem van Straten, Andrew Jameson and Matthew Bailes

Centre for Astrophysics & SupercomputingThird ATNF Gravitational Wave Workshop 2009

ATNF Parkes Swinburne Recorder

Combination of FPGAs and CPUs PDFB3 implements polyphase filterbank 16 processing nodes receive sub-band as UDP stream

Real-time and/or offline data reduction record data to disk at 1.6 GB/s for 2.5 hours

Remote control and monitoring web-based interface

Parkes Digital Filterbank

Designed/developed at ATNF 2 x Compact Array Broad-band (CABB) board up to 2048 channel polyphase filterbank real-time RFI mitigation

CABB = 2GHz correlator modularity of FPGA design hardware re-use

APSR Features

Phase-coherent dispersion removal (up to 1024 MHz) Automatic impulsive interference excision

RFI, lightning, etc.

Single-pulse capability with real-time calibration and/or giant pulse selection

Fold multiple pulsars simultaneously globular clusters, binary pulsar

Computation of auxiliary statistics e.g. fourth-order moments

Phase-coherent dispersion removal

Observed voltage signal is deconvolved impulse response function of ISM plasma dispersion

Convolution performed in frequency domain more efficient, requires FFT

Nfft proportional to DM 2/3

Phase-coherent dispersion removal

flops = 5NlogN / tFFT

on each APSR node: (assuming DM=10)

centrefrequency

bandwidth per node

optimal Nfft required Gflops

3.1 GHz 64 MHz 128k 12

1.4 GHz 16 MHz 128k 2.9

700 MHz 4 MHz 64k 0.7

FFT benchmarks

700 MHz700 MHz

1.4 GHz1.4 GHz

3.1 GHz3.1 GHz

Multi-threaded dspsr

thread-safe revisions to underlying library thread-shared buffering of overlap regions

overlap-save method of discrete convolution

thread-coordinated output of results threads combine results every 10 seconds

near linear scaling of performance!

Coherent Dedispersion - History

1971 - 0.125 MHz @ Arecibo XDS Sigma 5 magnetic tape 20% duty cycle for 3 minutes

1987 - 1.5 MHz Reticon R5601 chip real-time!

1998 - 16 MHz @ Parkes S2, VHS tape

1999 - 20 MHz @ Parkes CPSR, DLT tape

2002 - 128 MHz CPSR2, high-speed disk

2007 - 1024 MHz APSR, real-time

XDS Sigma 5: picture

XDS Sigma 5 vs iPod

APSR web-based interfaceAPSR web-based interface

1824-2452: DFB3

1824-2452: APSR

CAL lightning: DFB3

CAL lightning: APSR

Single pulse

Average pulse

Testing & Commissioning

Polarimetric Calibration High-precision timing Frequency response tests User and TCS interface improvements

GOAL: National Facility Instrument