apsr: digital signal processing at parkes willem van straten, andrew jameson and matthew bailes...
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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