Realtime VLBI experiences and
future plans of CRL
Y. Koyama, T. Kondo, J. Nakajima, M. Sekido,
M. Kimura, H. Kiuchi, J. Amagai, and T. Yoshino
Communications Research Laboratory
Realtime VLBI over ATM
Key Stone Project (1993-2001)
– 2.488 Gbps STM-16/OC-48 connection to 4 sites
– data recorder was transparently replaced by the network
(ID-1 format data stream is transmitted to the correlator)
ATM and IP
ATM : Asynchronous Transfer Mode
– low level protocol, good for high speed communications
– bandwidth can be guaranteed
– stable time delay and data sequence
– expensive, mainly used for backbone networks
IP : Internet Protocol
– network layer protocol which enables packet switching
– outstanding universality
– unstable time delay and data sequence
– data rate is not guaranteed
Realtime VLBI Correlator
ATM receiver
+
VLBI ATM interface
Correlator
Full automation with realtime VLBI
Conventional tape-based VLBI
01:15 UT
set tapes
23:45 UT
observations
tape
pickup
next
morning
tape
delivery
Realtime VLBI
01:15 UT
00:45 UT
observations and
data
data
correlation processing analysis release
correlation
processing
data
data
analysis release
Site motion monitoring with realtime VLBI
Geophysical Interpretation
Dyke and Strike Slip Model
EOP estimation with realtime VLBI
200
Wobble (δx)
mas
Solid Line : IERS Bulletin B
-200
500
Wobble (δy)
mas
200
100
200
300
DOY (1998)
EOP estimation with realtime VLBI
UT1-UTC
200
Solid Line : IERS Bulletin B
msec.
-200
UT1-UTC
500
micro
sec.
200
KSP - IERS Bulletin B
IERS Prediction - IERS Bulletin B
100
200
300 DOY (1998)
Radio source flux monitoring with realtime VLBI
Jy
the next step : IP
high speed continuous data stream by using IP
– high demand from many applications
– challenging research theme for network specialist
– possibilities to use existing infrastructure
possible strategies
– use existing protocol like FTP : ftp-VLBI
– transparent replacement of ATM system : Uose-san et al.
– develop a protocol which can identify the BBC channel,
observing station, and radio source information : Kondosan et al.
IP VLBI board
z
PCI PC board which includes
– 4 ch. A/D sampler
– programmable chip to generate formatted data stream
z
cheap realization of VLBI data acquisition system
– adequate for small groups to join the development project
– has possibilities to be used for other purposes
ex. spectrometer, spacecraft tracking, planetary radar
Reference signals
10MHz (+10dBm), 1PPS
Number of INPUT CH
1 : main board only
4 : with auxiliary board
A/D
1, 2, 4, 8 bits
Sampling Freq.
40kHz, 100kHz, 200kHz, 500kHz,
1MHz, 2MHz, 4MHz, 8MHz, 16MHz
PC correlator
z
each PC unit correlates 1 ch./baseline data
– freely expandable
– can process realtime VLBI, e-VLBI, and even tape-
based VLBI if VSI-DOM is available
MultiMulti-channel Internet VLBI system
A
K5 PC-based Terminal
PCPC-based VLBI
ch 1
ch 2
K-5
K5Data
DataAcquisition
AcquisitionTerminal
Terminal
Reference signal distributor
16 ch. video amps
A
ch 1
B
A
ch N
ch 2
B
Rack mount server with
IP-VLBI board (x 4)
B
Hard disk drive 120GB x 16
ch 2
ch 1
A
B
ch N
ch N
Band width
synthesis
Internet
Data Transmission
Data Reception
Correlation Processing
Improved connectivity with VSI
correlators
A/D samplers
data recorders
ADS1000
1024 Msps-1/2bit-1ch.
ADS2000
2~64Msps-1/2 bit-16ch.
DIR1000, DIR2000
(SONY) 64~1024Mbps
Gigabit Correlator
1024 Mbps
VSI
ADS4000
2048 Msps-1/2bit-1ch.
IP VLBI board
0.04~16Msps-1~8bit-4ch.
KSP Correlator
64~256 Mbps
GBR1000, GBR2000D
(Toshiba) 1024Mbps
PC
Internet
PC Correlator
Future Plans
z
realtime IP-VLBI and e-VLBI demonstration
between Haystack and Kashima
– investigations of the feasibility just began
z
2 Gbps ATM real-time VLBI
– Galaxy project : Kashima(34m)-Usuda(64m) baseline
z
hardware/software developments
– K-5 system (or Versatile Scientific Terminal?)
– PC correlator : data format
– VSI interfaces