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Ongoing e-VLBI D evelopments with K5 VLBI System

Ongoing e-VLBI D evelopments with K5 VLBI System. Hiroshi Takeuchi, Tetsuro Kondo, Yasuhiro Koyama, and Moritaka Kimura Kashima Space Research Center/NICT. Outline. What is K5 VLBI system? VLBI@home (Internet-based distributed computing approach for VLBI correlator)

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Ongoing e-VLBI D evelopments with K5 VLBI System

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  1. Ongoing e-VLBI Developments with K5 VLBI System Hiroshi Takeuchi, Tetsuro Kondo, Yasuhiro Koyama, and Moritaka Kimura Kashima Space Research Center/NICT

  2. Outline • What is K5 VLBI system? • VLBI@home (Internet-based distributed computing approach for VLBI correlator) • Software baseband converter • Summary

  3. VLBI Systems developed at Kashima K4 Correlator K5 Data Acquisition Terminal K5 System K4 Terminal K4 (KSP) System K3 Correlator (Center) K3 Recorder (Right) 2000~ Real-time e-VLBI with IP PC based system Hard Disk Drives Software Correlator 1990~ Real-time e-VLBI with ATM Operational data rate: 256Mbps Max data rate: 2048Mbps Hardware Correlator K3 System 1983~ Longitudinal Recorder Open Reel Tapes Hardware Correlator

  4. K5 Family : Concept ADS1000 (1024Msample/sec 1ch 1bit or 2bits) PC-VSI Board (K5/VSI) (Supports VSI-H specifications) Correlator other DAS (Mark5) VSI VSI Internet IP-VLBI Board (K5 or K5/VSSP) (~16Msample/ch·sec, ~4ch, ~8bits) ADS2000 (64Msample/ch·sec ,16ch, 1bit or 2bits) PC : Data Acquisition & Software Correlator

  5. Specifications of K5/VSI VLBI system Single channel VSI Data Acquisition System Multi-channel VSI Data Acquisition System

  6. Specifications of K5/VSI VLBI system VSI Data Capture Board (PC-VSI board) VSI Data Recording System (PC-VSI board +RAID)

  7. Architecture of K5 data input module • In K5 system, captured data is not directly recorded to HDD, but transferred to PC’s shared memory. So, multiple software applications can access the data simultaneously in real-time. • Because of this function, various kinds of real-time operations are possible by writing PC software. Such as spectrometer, total power meter, oscilloscope, software correlator, p-cal detector, baseband converter, real-time data transfer, real-time recording, and so on.

  8. Software correlator by distributed computing Merit of software method: No limitations on correlator parameters (number of lags, number of stations, integration time, FX or XF …) VLBI@home:Screensaver-type distributed correlator program runs during the idle time.

  9. VLBI@home -Distributed correlator system over the Internet • Proceduresofdistributed correlation process • A client PC queries the control server about the location of K5 data file to be processed. • The control server determines the files to be processed based on the information in the database server and sends back the URL of the files. • The client PC downloads indicated K5 files from the VLBI stations by FTP. • Correlate the received data. • Correlator results, client conditions, and network status are sent to the control server. • Control server stores the results to the database server. Processing conditions are updated and published to the Internet. Return to 1. SQL ？

  10. Required network speed for VLBI@home • Distributed computing method is effective only in the environment, where Network bit rate ＞ Data processing rate • Current processing speed of software correlator(32 lags) : 15Mbps(Pentium4 3GHz) • 　・Network between Institutes (Dedicated network) • 1Gbps～100Mbps ＞ 15Mbps 　　→ Effective • 　・Network to the home (Public network) • 1 ～ 10Mbps　　　 ＜15Mbps 　　→ Not Effective! Empirical rule, Guilder’s law, says, “Network bandwidth grows at least three times faster than computer power”.

  11. Application：Rapid UT1-UTC estimation (June 29,2004) • After this session, Mark-5 data at Westford was transmitted to Kashima by FTP. • Received Mark-5 data was converted to K5 format, and correlated with VLBI@home. • Average processing speed:58.6Mbps (8 consumer PCs) • UT1 – UTC estimation was completed 4hours and 30 minutes after the last observation in the session.

  12. Development of software baseband converter • Conventional BBC(baseband converter) system Analog BBC Multi-channel A/D samplers after image rejection mixers.Demerit: Gain and phase fluctuations caused by the variations of ambient temperatures. Digital BBC(FPGA,ASIC) Digital baseband converters after a single-channel broadband A/D sampler. Demerit: Less flexibility for band selections.Highdevelopment and maintenance cost.

  13. Software BBC(SBBC) by K5/VSI system If sampling rate is lower than 2 Gbps, SBBC is realized by a current PC. Merit: High flexibility, low cost, integrated to network transmission system and recording system.

  14. SBBC - Specifications and algorithm • Lookup table method (Floating point) • Written in assembly language • Using vector operations(SSE2) and prefetch functions • Multi-thread(8 threads) Current speed: By using a current PC(Xeon 3GHz), 2 baseband channels can be extracted in real-time from 1Gbps of IF signals.

  15. Test experiment using the SBBC • April 18, 2004 • Parkes(PC-EVN) – Kashima(K5, SBBC) • At Kashima, 256-MHz of IF-signals were directly sampled and converted to 16-MHz of baseband signals by the software BBC system. • It is easy to perform the experiments between different VLBI systems, because of the flexibility of the software method.

  16. Summary • K5 VLBI system is a low-cost and high-performance pc-based VLBI system. • Because of the recent developments of consumer PCs, we can use software methods for the VLBI backend processes. For example, distributed software correlator and software BBCs.

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