1. National Astronomical Observatory of Japan Yusuke Kono
VSOP-2 Link System
National Astronomical Observatory of Japan
Yusuke Kono

2. Outline Onboard Link system update Frequency selection
General over view
Ka-band OBS frequency changed
Frequency selection
Downlink 37.5GHz or 26GHz?
The common design of Tracking station

3. Observation System × × × × × × Observation Frequency
Q-band: GHz
K-band: GHz
X-band: GHz
Intermediate
GHz
Base Band
1.3 GHz
Q-band (R) LNA × LO
(36/34GHz) ～
Q-band (L) LNA ×
K-band (R) LNA × ×
ADC DF
MOD
IF-SWITCH (6 to 2 ) LO
(29.2GHz) ～
Synthesizer
Ka-TX
K-band (L) LNA × ×
ADC DF
1024Mbps
Synthesizer
VLBI DATA
Rate: 512/256 Msps
Bit: 1/2 bit
Channel: 2 ch
X-band (R) LNA
X-band (L) LNA
GRT: 512Msps(2bit) or 256Msps(2bit) expected

4. Ka Antenna Diameter 80cm Efficiency 70 % WaveGuide&Rotary Joint
TWTA(20W) inside
60W power consumption
radiated through a heat pipe to space

5. Link frequency selection : Frequency Allocation
Uplink
Three Space Research bands in 13~17GHz are hopeless (JAXA Frequency room)
GHz , GHz , GHz
Uplink is 40 GHz
Downlink
26GHz and 37.5 GHz possible
26 GHz band will be heavily used by the time that VSOP-2 is launched. Many missions are being planned for this band including NASA's Lunar Exploration Missions, some L1 and L2 missions like JWST, and some wideband low Earth orbiters like NOAA's NPOESS.  Most of these missions will receive higher priority than VSOP-2 if there is a need for coordination.
37.5 GHz is wide open and there won't be any need for coordination or worries about interference to VSOP-2 or from VSOP-2 to other missions.

6. Link frequency selection : Ionoshphere
VSOP-2 OBS/link simulation (by Dr.Asaki)
Software: ARIS
MS-TID (Medium Scale Traveling Ionospheric Disturbance) ~0.2TECU
Zenith TEC bias error~6 or 60 TECU
Conclusion
Ionosheric effect of 37.5GHz is smaller than 26GHz
Tropospheric error in fringe phase of VLBI observation is outstanding.
40/26 and 40/37.5 GHz system possible

7. Onboard Lo-Phase (Zenith TEC Bias : 6 TECU)
40GHz/26GHz
40GHz/37GHz
43GHz: 15.0 deg
22GHz: 7.9 deg
43GHz: 1.9 deg
22GHz: 1.0 deg
Black: 43GHz Red: 22GHz

8. Space-VLBI Fringe Phase (MS-TID , Zenith TEC Bias : 60 TECU)
60 min (Tropospheric and Ionospheric Errors)
40GHz/26GHz
40GHz/37GHz
Black: 43GHz Red: 22GHz

9. 43GHz Coherence
No difference
22GHz Coherence
No difference

10. Link frequency selection : Link margin
Link design 26GHz 37.5GHz d( )
TX Gain dB
Feed Loss dB
Space LossdB
Rain Loss dB
Atm Loss dB
RX Gain dB (AE 34, 42%)
Tsys dB
Total dB

11. Rain condition of UDSC
One-hour rainfall data at Usuda deep space center
Nov.9,2005- Nov.9,2006
Time (2mm/h) is 2% of time!

12. Interference of 26GHz to K-band LNA
Less than -60 dBm
(Tx 20W, Off-beam interference, space loss)
< LNA saturation level +9dBm

13. Technical easiness 26 / 40GHz
Wider frequency range than waveguide and waveguide Rotary joint frequency specification ( GHz)
More complicated Ka-ant system
Setting TX-HPA at the top of the boom is not good for thermal control

14. Link frequency selection: summary
The downlink of 26GHz has several attractive merits comparing with 37.5 GHz. But,
It is too severe to get the 26 GHz band allocation
40/26GHz link will increase complexity of the onboard system
Construction cost of the s/c same
40/37GHz link is also feasible
The downlink of 37.5 GHz proposed

15. AE of UDSC

16. The common design of Tracking station
Based on Halca method
NRAO GB project book

17. Functional requirement 1
Radio links to s/c
Astronomical data downlink
Time transfer uplink
Time transfer downlink
Realtime signal Processing
Astronomical data
Time transfer

18. Functional requirement 2
Interface
From mission operation
From orbit determination center
To correlation center
To orbit determination center
To mission operation

19. Functional requirement 3
Automation
Normal operation
Recovery from link dropout
Recovery after station power failure

20. System design 1 Main antenna Feed and Optics RF subsystem
Wideband data subsystem
Two way timing
Reference distribution
Control and monitoring

21. System design 2 Design principles Compact design
Careful choice of reference signals
Wideband design
Avoidance of ALC loops
Use of exiting design whenever possible
Built-in test facilities and monitoring

22. System design 3 Link budget Downlink

23. System design 4 Link budget two way timing

24. System design 5
Required Dynamic range
Packaging and cabling

25. Required basic function of Onboard link system
Data transmission
1024 Mbps QPSK, Diff.Enc
37.5 GHz, 20 Watt (-2dB Backoff)
EIRP 83.9 dBm
80cm HGA, RHCP
TLM (bitrate TBD) data merged
Coherent transponder
Uplink carrier receiver

26. Required basic function for tracking station 1
Standard clock transfer
Uplink transmission
Carrier of 40GHz, EIRP 93.5 dBm, RHCP
Downlink carrier recovery
Carrier of 37.5GHz, RHCP
Measurement of phase difference between up and downlink
DeltaT correction file output
Doppler compensation by prediction

27. Required basic function for tracking station 2
Data downlink demodulation
37.5 GHz QPSK, RHCP
Required BER 1E-2
Data and carrier recovery
Data storage
Data Storage
1024Mbps, 11 T Byte / 24h
VSI-H&S compatibility (for correlators)
Realtime/quasi-realtime TLM QL

28. Principles of BER
The cross-correlation SNR or sensitivity of the spacecraft data (with transmission errors) against ground telescope data (no quantization bit errors) is degraded by the BER loss factor
VSOP is designed for BER = 5E-4, so its factor is negligible.
The calibrated sensitivity loss for the best ground radio telescope is taken to be 2% (0.980).
Correspondingly, BER = 1E-2.
Designing for BER = 1E-2 is a strictly worst-case condition. Most of the time the BER will be much lower.
Springett 2002

29. ~ VSOP-2 Ground System Antenna Room Operation Center Feed U/C O/E E/O
TX GEN ~
LOGEN
O/E
E/O
Doppler Cntr / meas.
Feed
D/C
O/E
E/O
Demodulator
Antenna Room
Operation Center

30. ~ ~ Operation Center TX GEN D/A DIFF ENC DATA GEN D/A Demodulator A/D
1.54GHz+fud
1.5GHz
1.5GHz
REF
GEN
LPF
D/A
100MHz
E/O SW
BPF ~
NCO Fo
(nominal)
DIFF ENC
DATA GEN
5MHz
5MHz
STD
CLK
LPF
D/A
GPS
1.5GHz
Doppler
Control
Meas.
DOP
CONT UP
Fup (PREDICT)
1pps
TIME DEC
E/O
100MHz
Time
DOP
CONT DW
Fdw (PREDICT)
Doppler
Control PC
Copper
Count
Dop.Cnt
Demodulator
Control PC
1.5GHz
NCO
Remote
station
LPF
A/D TI
COUNT
1.54GHz+fdd
O/E
BPF ~
NCO PD
BIT SYNC
DIFF ENC
FRAME
SYNC
VSI
I/F
Storage
BER
MEAS
LPF
A/D
1.5GHz

31. Antenna Room HPA Translator LNA Antenna Room ATT BPF BPF O/E O/E Feed
POWER
METER
4.388+fud GHz
1.54+fud GHz
ATT
BPF
BPF
O/E
fud GHz
HPA
2.848GHz
35.9 GHz
100MHz
2.848GHz
X 2828
/1000
O/E
Feed
DIP
BPF
HYB
X 359
Translator
fdd GHz
35.9 GHz
LNA
1.54+fdd GHz
BPF
BPF
O/E
Antenna Room

33. ASTRO-G Ka-Band Link Simulations
Uplink / Downlink
40GHz / 26GHz
40GHz / 37GHz
Effects of the onboard local phase due to the ionosphere
ARIS simulations
MS-TID (Medium Scale Traveling Ionospheric Disturbance)
Zenith TEC bias error

34. Discussion TLM Header Mobile TX simulator Phase Detection method
Realtime/Quasi-realtime
Mobile TX simulator
Phase Detection method
VLBI Data storage
VSI I/F
MarkVB
RVDB of Japan
Data transportation
PM TEST and schedule

35. 2-way Link: the effect of the ionosphere Δφion
N : TEC [el./m2]
fobs : Observing frequency [GHz]
fup : Uplink frequency [GHz]
fdown:Downlink frequency [GHz]
c : Velocity of light [m/s]

36. Ka Tracking Simulations
Black : Usuda
Red : Goldstone
Blue : Tidbinbilla
Pink : Hart
Yellow: Malind

37. Onboard Lo-Phase (Zenith TEC Bias : 60 TECU)
40GHz/26GHz
40GHz/37GHz
43GHz: 62.5 deg
22GHz: 45.8 deg
43GHz: 17.9 deg
22GHz: 9.3 deg
Black: 43GHz Red: 22GHz

38. Onboard Lo-Phase (Zenith TEC Bias : 6 TECU)
40GHz/26GHz
40GHz/37GHz
43GHz: 15.0 deg
22GHz: 7.9 deg
43GHz: 1.9 deg
22GHz: 1.0 deg
Black: 43GHz Red: 22GHz

39. Space-VLBI Fringe Phase (MS-TID , Zenith TEC Bias : 60 TECU)
60 min (Tropospheric and Ionospheric Errors)
40GHz/26GHz
40GHz/37GHz
Black: 43GHz Red: 22GHz

40. 43GHz Coherence
No difference
22GHz Coherence
No difference

42. Principles of Link Design
But extremes for these conditions are very rarely concurrent, so most of the time there will be a substantial excess of performance (a positive link margin of many dB). This is excessive design, a waste of link resources.
A statistical link design methodology reflects the fact that temporal variation of the parameters rarely results in simultaneous worst-case extremes.
Springett 2002