ultra-low power time synchronization using passive radio receivers yin cheny, qiang wangz, marcus...
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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 sig
nal receiver
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