Ongoing eVLBI Developments with K5 VLBI System

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

• What is K5 VLBI system?
• VLBI_at_home (Internet-based distributed computing
  approach for VLBI correlator)
• Software baseband converter
• Summary

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VLBI Systems developed at Kashima
K4 Correlator
K5 Data Acquisition Terminal
K4 Terminal
K5 System
K4 (KSP) System
K3 Correlator (Center) K3 Recorder (Right)
2000 Real-time e-VLBI with IP PC based
system Hard Disk Drives Software Correlator
K3 System
1990 Real-time e-VLBI with ATM Operational data
rate 256Mbps Max data rate 2048Mbps Hardware
Correlator
1983 Longitudinal Recorder Open Reel
Tapes Hardware Correlator
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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/chsec,
4ch, 8bits)
ADS2000 (64Msample/chsec ,16ch, 1bit or 2bits)
PC Data Acquisition Software Correlator
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Specifications of K5/VSI VLBI system
Single channel VSI Data Acquisition System
Multi-channel VSI Data Acquisition System
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Specifications of K5/VSI VLBI system
VSI Data Capture Board (PC-VSI board)
VSI Data Recording System (PC-VSI board RAID)
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Architecture of K5 data input module

• In K5 system, captured data is not directly
  recorded to HDD, but transferred to PCs 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.

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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_at_homeScreensaver-type distributed correlator
program runs during the idle time.
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VLBI_at_home -Distributed correlator system over the
Internet

• Procedures of distributed 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
?
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Required network speed for VLBI_at_home

• Distributed computing method is effective only in
  the environment, where
• Network bit rate gt Data processing rate
• Current processing speed of software
  correlator(32 lags) 15Mbps(Pentium4 3GHz)
• Network between Institutes (Dedicated network)
• 1Gbps100Mbps gt 15Mbps ? Effective
• Network to the home (Public network)
• 1 10Mbps lt15Mbps ? Not Effective!

Empirical rule, Guilders law, says, Network
bandwidth grows at least three times faster than
computer power.
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ApplicationRapid 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_at_home.
• Average processing speed58.6Mbps (8 consumer
  PCs)
• UT1 UTC estimation was completed 4hours and 30
  minutes after the last observation in the session.

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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. High development
and maintenance cost.
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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.
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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.
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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.

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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.