Ultra-Low Power Time
Synchronization Using Passive
Radio Receivers
Yin Cheny, Qiang Wangz, Marcus Changy, Andreas Terzisy
Johns 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 GPS, RBS, FTSP, PulseSync
– 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 Power line
Their accuracy is in ms
Outline
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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
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Time Signal Radio Stations
Universal Time Signal Receiver
Evaluation
Applications And Conclusion
Universal Time Signal Receiver
Antenna
output
25 mm
one-pulse-persecond (1PPS)
CME6005 radio chip
33 mm
analog time signals
digital outputs
Interrupt:
Record
timer value
Power Consumption: 90uA
Microcontroller
PIC16LF1827
Interrupt:
Record timer value
Calculate interval
Power Consumption:
0.6uA (sleep)
800uA (Active)
UART output
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
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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