1. TWSTFT using DPN signals
Yi-Jiun Huang and Wen-Hung Tseng
National Time and Frequency Standard Lab.,
Chunghwa Telecommunication Laboratories (TL), Taiwan
APMP 2012
November 26, 2012
Wellington, New Zealand
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2. Outline Introduce DPN TWSTFT signal and system
DPN TWSTFT 2010 and 2012
Time link result and TDEV comparison
Summary and discussion
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3. Dual Pseudorandom Noise (DPN) Signal
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4. Communication Channel
DPN TWSTFT System
Conventional Modem does not support TX/RX function for DPN
Hardware:
Arbitrary waveform generator
A/D sampler
Software: (especially at RX)
Signal acquisition  tracking
Group delay estimation, i.e. τ = - dφ/dω
(Use GPU for accelerating correlation and convolution)
A/D
Sampler, 64Msps
Arbitrary
Waveform Generator
Communication Channel
Sample Stream
Software
PC with GPU
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5. DPN TWSTFT System (Receiver)
A/D
FFT
LNB I F T
Phase
Detector
Group
Delay
Band Pass Filter
LO, 11.3 GHz
Down Converter
NCO, higher tone
NCO, lower tone
UTC (TL)
Pseudorandom Code
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6. DPN TWSTFT System @ 2010 UTC(TL) UTC(NICT) IS-8 AWG A/D AWG A/D
66.4 MHz
86.4MHz
66.4 MHz
86.4MHz
Wideband BPF 20MHz
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7. Time Link 2010
17 days
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8. Time Link 2010
2 days
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9. TDEV Comparison @ 2010 PPP: 15ps@300s DPN: 9.9ps@300s
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10. Modification of DPN system @ 2012
To improve short term resolution:
Increase band separation (not occupied bandwidth)
Use narrow BPF to avoid in-band noise thus get high signal-to-noise ratio
Unfortunately, observations: 300 (real time) 
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11. DPN TWSTFT System @ 2012 UTC(TL) UTC(NICT) GE-23 54.175MHz AWG A/D AWG
Wideband BPF 32MHz
Narrowband BPF 4MHz
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12. TDEV Comparison @ 2012 DPN: 14.9ps@300s PPP: 12.3ps@300s
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13. Comparison DPN TWSTFT Experiment @2010 @2012 future Observation
300 5min 15
300
Real-time observation?
Yes No
Separation
20 MHz
31.2 MHz
Single bandwidth / code rate
200 kHz /
kcps
Band Pass Filter TL
4MHz x
2MHz x TL
300 s
9.9 ps
14.9 ps
< 10 ps(expected)
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14. Summary and Discussion
We appreciate NICT colleagues for their great deals of system development and equipment
DPN saves more bandwidth (200kHz x 2) than conventional TWSTFT (2.5 MHz)
DPN provides the same resolution (10 ps level) as GPS PPP and DPN can be perform in real-time
DPN TWSTFT has been conducted between NICT and TL (baseline more than 2000km) for 9 months, and it agreed with Cirt. T. Only a fixed offset existed due to no calibration
Software-based receiver can be more flexible than the conventional one, e.g. decoding algorithm can be modified
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15. Summary and Discussion
We appreciate NICT colleagues for their great deals of system development and equipment
DPN saves more bandwidth (200kHz x 2) than conventional TWSTFT (2.5 MHz)
DPN provides the same resolution (10 ps level) as GPS PPP and DPN can be perform in real-time
DPN TWSTFT has been conducted between NICT and TL (baseline more than 2000km) for 9 months, and it agreed with Cirt. T. Only a fixed offset existed due to no calibration
Software-based receiver can be more flexible than the conventional one, e.g. decoding algorithm can be modified
Thank you for your listening!!
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