fpga-based dedispersion for fast transient search
DESCRIPTION
FPGA-based Dedispersion for Fast Transient Search. John Dickey 23 Nov 2005 Orange, NSW. ALTIUM, Ltd. corporate donation: FPGA application development software, nanoboard platform, design tools, and training, retail purchase price of everything ~$150,000. - PowerPoint PPT PresentationTRANSCRIPT
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FPGA-based Dedispersionfor Fast Transient Search
John Dickey
23 Nov 2005
Orange, NSW
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ALTIUM, Ltd. corporate donation: FPGA applicationdevelopment software, nanoboard platform, design tools, and training, retail purchase price of everything ~$150,000.Partial funding by an ARC Discovery grant.
UTas Staff: JD,Simon Ellingsen (senior lecturer)Eric Baynes (sr. electronics tech)Aidan Hotan (postdoc)Jamie Stevens (postdoc)three grad students (associated)
David Warren (Altium and UTas)Brett Muir (design engineer)John Russell (digital engineer)
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FPGA applications in Radio Astronomy
• Pulsar and transient searches (dedispersion)• Autocorrelators (spectrometers)• Cross-correlators (interferometry, VLBI)• Data editing, calibration, mapping• Real-time adjustment of receivers, delays…• Multi-beaming, focal plane array processing
• Studying the e-field at the Nyquist rate
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UTas - Altium Board
• design nearly finished (Brett Muir, John Russell)
chips purchased, board fabrication in ~1.5 month
• Xilinx virtex 4 - SX55 workhorse FPGA
• Xilinx spartan 3 (for jtag chain) and
virtex 2-pro (for control)
• memory, ethernet, config devices
• high speed scsi-2 input plus up/down links
The goal: a general purpose boardto replace all observatory backends!
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Xilinx Virtex-4 SX55
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
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QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
512 times:
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
55,296 times:
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Correlator Implementation
Using Altium Virtex 4 SX35 daughterboard with nanoboard
Device performs autocorrelation and cross correlationof RF input signals plus noise at speeds up to 80 M s/s.
FPGA substrate provides latch in, shift register, multiply and accumulate, readout, and VGA graphics display.
Embedded (simulated) processors provide program control.
August 2005 -- Aidan Hotan:
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digitised signal in
shift withadjustabletime step
present data
x
x
x
x
x
x
x
x
x
x
x
x
multiply andaccumulate
Correlator Architecture
FourierTransformusingsynthesizedTSK3000processoron-boardFPGA
autocorrelationfunction
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Example of SX55 application:
Fourier Transform Dedispersion
February? 2006:
digitised signal in
shift atadjustabletime step
latch
FFT, bit-reverse, magnitude Dynamic Spectra
Floating-pointProcessors
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frequency
time
Dedispersion from Dynamic Spectra
timeseries
Sum along dispersion lines• fast algorithm• addition (can use gates only)
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The Observing Frequency and the DM Determine the Storage and Computation
Load
t
N
t
Nyquist Cells: t = 1/2
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The Observing Frequency and the DM Determine the Storage and Computation
Load
t
for DM=100, = 100 MHzt = 30ms = 6000 t where
N
t
t
for N=1000 frequency channels, t = 5 s
example: observing at 1.4 GHz
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Xilinx Virtex 4 SX55
This FPGA chip is effectively a
512 processor supercomputer,with
a substrate of 55,296 logic cells
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Speed is No Problem…For a 64 channel spectrum,the SX55 could use a DSPfor every block. Thus it cancompute a new spectrum every 4 clock cycles = 10 ns,for a sample rate of 0.16 ns,bandwidth of 3.2 GHz.
For a 512 channel spectrum,the SX55 could use a DSPfor every row. Thus it cancompute a new spectrum every 36 clock cycles = 90 ns,for a sample rate of 0.18 ns,bandwidth of 2.8 GHz.
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… so the DSP’s can do several jobs.
timeseries
thresholding, RFI suppression…
For a 100 MHz bandwidth, the FPGA could take the Fouriertransform 30 times in the N t time it takes to collect the data.
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Want Correlators?
The EVLA correlator will handle 40 antennas (780 baselines)with 8 bands of 2 GHz each. This would require about 400FPGA’s similar to the SX55, cost ~$500K (vs. $12M budget).
The LN-SD SKA (~4000 antennas ?), say 107 baselines, BW ~ 1GHz(?) could be done with a few 104 Virtex 4’s.Today’s cost, a few 107 $. In 2015, by Moore’s Law, ~105 $.(This is without any grouping of the antennas into “stations”,and assuming direct FT rather than cross correlation.)
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Conclusions
• FPGA technology offers the advantages of the “software correlator”, i.e. to upgrade to new platforms without reworking the design.
• Altium design tools make programming the FPGA as easy as … (as programming a computer?).
• We can finally do our signal processing at the Nyquist rate, in real time!!