Ultra-Low Power Time Synchronization Using Passive Radio Receivers

Yin Cheny, Qiang Wangz, Marcus Changy, Andreas TerzisyJohns Hopkins University, Harbin Institute of Technology

IPSN 2011

Presenter: SY

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

universal time signal re

ceiver

Their accuracy is in ms

GPS, RBS, FTSP, PulseSync

Power line

Outline

• Time Signal Radio Stations• Universal Time Signal Receiver• Evaluation• Applications And Conclusion

Time Signal Radio Stations

• Broadcast time signal periodically• Some of the time signal radio stations

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

DCF77

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

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

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

Outline

• Time Signal Radio Stations• Universal Time Signal Receiver• Evaluation• Applications And Conclusion

Universal Time Signal ReceiverAntenna

CME6005 radio chipMicrocontroller PIC16LF1827

25 m

m

33 mm

analog time signals digital outputs

Interrupt:Record timer value

Interrupt:Record timer valueCalculate interval

Power Consumption: 90uA

one-pulse-per-second (1PPS)

UART output

output

Power Consumption: 0.6uA (sleep)800uA (Active)

Power Consumption

Compare Power Consumption

• FTSP

• Universal Time Signal Receiver

• Compare

Synchronization Error

Signal Availability

• Hourly decoded ratio

Signal Availability

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

Synchronous MAC Protocols

• Implemented a time-scheduled version of LPL• running CTP on top• Duty cycles

Other Applications

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

Conclusion

• Implemented universal time signal receiver– Very low power– Millisecond accuracy– Wide availability