Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/vlbi/dokuwiki/lib/exe/fetch.php/difx/meetings/korea2013/difx2013-phillips.pdf Äàòà èçìåíåíèÿ: Fri Oct 18 04:23:57 2013 Äàòà èíäåêñèðîâàíèÿ: Tue Apr 12 12:43:42 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: eit

Xcube Linear2Circular
Chris Phillips 15 October 2013
CASS


Xcube Wideband VLBI Backend


X cube Data Logger
· 100% COTS hardware recorder
·Proprietary so
· 16 Gbps capability
·External replaceable storage modules ­Up to 32 TB packs

· Management of slow or broken disks · Standard file systems


Back View of Chassis

SAS Disk Cables
(16 x 300MB/s)

Ethernet (2 x 10Gb/s)
© 2010 XCube R&D

Self Contained Disk Pack Cooling and Power


Xcube Internals
· "Mix and Match" approach to plug in devices
·1 or 2 dual 10 Gbps Ethernet ­Intel SPP+ Op\cal module needed ·Can support up to 4 disk modules ·GPU for number crunching ·Other op\ons available ­However may run out of slots....

5 | DIFX KOREA 2013 Chris Phillips


Data access
· Data cannot be accessed directly
·Cannot directly use standard transfer so
· Supplied with easy to use library to read data from diskpack
·Can copy "raw" files and decode on a different system

· Easy to write code to copy off disk · Time filtering etc available not tested

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Xcube Access
· Xcube supply (closed source) libraries to access data files
·Distributed as part of DIFX ·utilities/trunk/xcube

· Has concept of "packet reader"
·Read each recorded packet in series ·Each packet is (system) \me stamped ·Time filtering available

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Xcube Terminology
· Recording split into "Projects"
·We would use one project per experiment ·Cannot name project!

· Projects split into "Streams"
·Usually one stream per start/stop ·E.g. Set of scans with no gap

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Xcube UFliFes
· x3projects · lf1list
List projects on disk ·List first few packets of project/stream ·Check VDIF recorded data is OK ·Extract VDIF recorded data to file (with filtering) ·Xcube HRFT sampler specific

· lf1vdifcheck · lf1extract

· hr<2vdif, hr
9 | DIFX KOREA 2013 Chris Phillips


Xcube sampler (HRFT)
· 4 Channel 1 Gsample/sec
·4x512 MHz IFs

· For each IF 16 channel polyphase filterbank
·32 MHz channels, complex "double sideband" sampling

· Re quan\za\on to 2 bit · 8 Gbps VLBI

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HRFT data
· HRFT data is not VLBI formaped
· · · · Mark5B bit encoding No explicit \me encoding Channel order not similar to any VLBI format Synchronized to 1PPS

· To convert to VDIF need to
·Flip bits ·Reorder channels ·Add VDIF header

· DIFX integra\on?
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Linear 2 Circular


Linear PolarizaFons
· While VLBI standard is to use circular polariza\ons, linear polariza\ons are "beper":
·Easier to make wideband receivers ·Beper separa\on between polariza\ons

· Need to convert linear to circular for compa\bility with other antennas and calibra\on and analysis so 13 | VLBI TECHNOLOGY KOREA Chris Phillips


Digital PolarizaFon Conversion
· Digital polariza\on conversion can overcome wideband problem · Conceptually easy:
·Has worked very well with ATCA for 20 years ·Align amplitude, phase and delay between two polariza\ons ·Rotate phase of one polariza\on by 90 degrees ·Simply add and subtract two linear polariza\ons

· Essen\ally same as hybrids · Ideally added to VLBI DAS firmware but never implemented
14 | VLBI TECHNOLOGY KOREA Chris Phillips


L2C in DiFX
· Can we do circular conversion within DIFX · Very "cheap" to do conversion a ·Biggest DIFX change is to get calibra\on values into correlator ·Side benefit is polariza\on dependent delay offset



15 | VLBI TECHNOLOGY KOREA Chris Phillips


FFT



Xmult



FFT

Amplitude & Phase Correc\on




Add and subtract

Xmult



16 | VLBI TECHNOLOGY KOREA Chris Phillips


Vex2difx Changes
· clockOffset, clockRate, deltaClock & deltaClockRate simple arithme\c parsing
clockOffset = -45.9-0.0043


· freqClockOffs encodes polariza\on specific delay and phase offsets
IFdelay:Polarisa\onDelay:Polarisa\onPhase
freqClockOff = 0:0.023:10, 0.003:0.045:-30.3

17 | DIFX KOREA 2013 Chris Phillips




Enabling Linear2Circular
· Available in branches/linear2circular · Set "PROCESSING METHOD=LINEAR2CIRCULAR" in .input file · Minor changes in mode.cpp to do conversion a ·Need slight further code change as does not support kurtosis mode

18 | DIFX KOREA 2013 Chris Phillips


Status
· Delay and phase offsets seem to work OK
·Not exhaus\vely tested ·Could be moved to trunk

· Tes\ng of L2C not promising ­ no apparent change in cross polarisa\on amplitudes
·Could be calibra\on of offsets is wrong ·Could be coding error

· More tes\ng needed

19 | DIFX KOREA 2013 Chris Phillips


Complex Sampling


Complex Sampling
· Polyphase filterbanks naturally produce complex sampled data
·Can do "direct" complex sampling also

· There are, at least, 2 types of complex sampling schemes: Single Sideband and Double Sideband · Single Sideband complex support in DIFX for awhile, Double sideband in complex_dsb branch
·Set encoding in .v2d file:
sampling = COMPLEX_DSB

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Double Sideband

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Thank you
Astronomy and Space Science Chris Phillips t +61 2 9123 4567 E chris.phillips@csiro.au w www.csiro.au/atnf

ASTRONOMY AND SPACE SCIENCE