Ultra-Low Power Time Synchronization Using Passive Radio Receivers

1. Ultra-Low Power Time Synchronization Using Passive Radio Receivers Yin Cheny, QiangWangz, Marcus Changy, Andreas Terzisy Johns Hopkins University, Harbin Institute of Technology IPSN 2011 Presenter: SY

2. Time Synchronization Protocols • GPS, RBS, FTSP, PulseSync, Power line, etc. • Desired properties • Low-power consumption • Support for large scale networks • Accuracy that is independent of network size • Access to UTC time • Support for disconnected operation • Low latency • Operate in both indoors and outdoors GPS, RBS, FTSP, PulseSync universal time signal receiver Power line Their accuracy is in ms

3. Outline • Time Signal Radio Stations • Universal Time Signal Receiver • Evaluation • Applications And Conclusion

4. Time Signal Radio Stations • Broadcast time signal periodically • Some of the time signal radio stations

5. WWVB Radio Station • Location: Fort Collins, Colorado • National Institute of Standards and Technology (NIST) • Coverage Area • http://www.nist.gov/pml/div688/grp40/vb-coverage.cfm

6. DCF77 • Location: Mainflingen, Germany • German national meteorology institute (PTB) • Coverage area

7. LF Radio Waves • Two components • Ground wave • follows the Earth’s curvature • Sky wave • Earth’s ionosphere • For 50 kW DCF77 transmitter • within 600 km  ground wave dominates • 600-1100 km  ground wave and sky wave equal magnitude • beyond 1100 km  only the refracted sky wave

8. WWVB Data Frame • One-bit-per-second time code • Each frame contains 60 bits • Data frames transmitted back-to-back • 60 frames per hour • Start-of-a-second time stamps 06:11 UTC on the 144th day (May 24) of 2010 DST bits indicate that the daylight saving time is active

9. Outline • Time Signal Radio Stations • Universal Time Signal Receiver • Evaluation • Applications And Conclusion

10. Universal Time Signal Receiver Antenna output one-pulse-per-second (1PPS) 25 mm CME6005 radio chip Microcontroller PIC16LF1827 33 mm analog time signals digital outputs UART output Interrupt: Record timer value Calculate interval Interrupt: Record timer value Power Consumption: 90uA Power Consumption: 0.6uA (sleep) 800uA (Active)

11. Power Consumption

12. Compare Power Consumption • FTSP • Universal Time Signal Receiver • Compare

13. Synchronization Error

14. Signal Availability • Hourly decoded ratio

15. Signal Availability

16. Some Notes • Interference • Steel frame buildings completely shield • Brick buildings allow signal reception • CRT screens can interfere from 5-10 meters • Laptops can interfere within one meter • Local Time Signal Generators • Up to 50 meters radius

17. Synchronous MAC Protocols • Implemented a time-scheduled version of LPL • running CTP on top • Duty cycles

18. Other Applications • Latency Reduction • Sparse Networks • Drop-in Replacement for GPS • Network-Wide Wakeup • Failure-Prone Sensor Networks

19. Conclusion • Implemented universal time signal receiver • Very low power • Millisecond accuracy • Wide availability