Ultra-Low Power Time Synchronization Using Passive Radio Receivers Yin Chen † Qiang Wang * Marcus Chang † Andreas Terzis † † Computer Science Department Johns Hopkins University * Dept. of Control Science and Engineering Harbin Institute of Technology
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Ultra-Low Power Time Synchronization Using Passive Radio Receivers Yin Chen † Qiang Wang * Marcus Chang † Andreas Terzis † † Computer Science Department.
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Ultra-Low Power Time Synchronization Using Passive Radio Receivers
Yin Chen† Qiang Wang* Marcus Chang† Andreas Terzis†
†Computer Science DepartmentJohns Hopkins University
*Dept. of Control Science and EngineeringHarbin Institute of Technology
Motivation
• Message passing time synchronization– Requires the network be connected– Requires external time source for global
synchronization• Is there a low-power and low cost solution?
How did we disseminate time information in history?
Time Ball
Since half a century ago, we started to use RF time signals.
Current Day Time Sources
Station Country Frequency Launch Time
MSF Britain 60 kHz 1966
BPC China 68.5 kHz 2007
TDF France 162 kHz 1986
DCF77 Germany 77.5 kHz 1959
JJY Japan 40, 60 kHz 1999
RBU Russia 66.66 kHz 1965
WWVB USA 60 kHz 1963
LF Time Signal Radio Stations
Radio Controlled Clocks & Watches
This work will test DCF77 and WWVB
Contributions
• Ultra-low power universal time signal receiver• Evaluations on time signals availability and
accuracy in sensor network applications• Applications using this platform
The antenna is 10 cm in length
Smaller ones are available but we have not tested on our receiver
WWVB Radio Station• Located near Colorado, operated by NIST• Covers most of North America
WWVB Time Signal
• 60 kHz carrier wave• Pulse width modulation with amplitude-shift
keying• NIST claims– Frequency uncertainty of 1 part in 1012
– Provide UTC with an uncertainty of 100 micro seconds
WWVB Signal Propagation
• Part of the signal travels along the ground– Groundwave : more stable
• Another part is reflected from the ionosphere– Skywave : less stable
• At distance < 1000 km, groundwave dominates
• Longer path, a mix of both• Very long path, skywave only
WWVB Code Format
60 seconds
Bit value = 0 Bit value = 1 Marker bit
• Each frame lasts 60 seconds• Each bit lasts 1 second
2010-5-2406:11:00 UTC
Time Signal Receiver Design
• Requirements– Low power consumption– High accuracy– Low cost– Small form factor
Core Components• CME6005
• 40-120 kHz, can receive WWVB, DCF77, JJY, MSF and HBG• less than 90 uA in active mode and 0.03 uA when standby
• PIC16LF1827• 600 nA in sleep mode with a 32 KHz timer active• 800 uA when running at 4 MHz