Your SlideShare is downloading. ×
0
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Syncob
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Syncob

194

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
194
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
1
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Syncob Collaborative Time Synchronization in Wireless Sensor NetworksAlbert Krohn1, Michael Beigl2, Christian Decker3, Till Riedel3 Particle GmbH, Germany 1 2 DUS/Universität Braunschweig, Germany 3 TecO/Universität Karlsruhe, Germany
  • 2. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 2 Motivation: Collaborative Sensing  Wireless Sensor Networks  Collaborative monitoring  Duty cycle − 100ms every 2sec − Short time to communicate  Important: synchronization
  • 3. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 3 Motivation: Ultrasound location ∆t  Distance: time of flight  Nodes only measure time  Approx. 10µs per 3mm  Accurate synchronization  Global timestamps for
  • 4. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 4 Sync times at different layers
  • 5. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 5 Physical Layer Synchronization  On PHY: Only radio propagation delays  Very deterministic  Accurate synchronization  Simple for single source of synchronization  More complicated for distributed operation − All nodes re-synchronize their neighbors − Need for coordination
  • 6. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 6 Conflicting sync  Random access  Especially problematic in dense scenarios  Can be resolved via CSMA  Hidden or Exposed Terminal Problems  Can make synchronization unstable
  • 7. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 7 Conflict-free sync  Multiple access  Good for static topologies  Can use CDMA,FDMA for beacons  Difficult to choose non-overlapping codes/freq  Inefficient for mobile scenarios
  • 8. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 8 SynCob: Collaborative Sync  Collaborative time synchronization  Send simultaneously on same frequency band  Use principles of cooperate transmission  Receiver can still decode the synchronization  Support for ad-hoc, mobile scenarios  Implementation for low-cost hardware Collaborative synchronization
  • 9. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 9 Related Work  Link Layer: e.g. LTS, mini-sync  Physical layer: RBS, BITMac BitMAC − Collision-free synchronization − Proposes “or” on PHY “Identical transmissions by two senders with small synchronization errors. The receiver will see slightly stretched “1”bits and slightly compressed “0”bits ” Source: Ringwald,M. ,Römer K.: BitMac A Deterministic, Collision-Free and Robust MAC Protocol for Sensor Nodes. EWSN 2005
  • 10. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 10 Sync symbol sequence 10101010101011001 S1S0S1S0S1S0S1S0S1S0S1S0S1S1S0S0S1  No channel or source coding!  Superimpose two sync symbols  Special case of cooperative transmission: − Narrow band radio − Can be used with FSK,ASK or OOK − Here: Narrow band binary OOK/ASK  S = active S = inactive 1 0
  • 11. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 11 Excursion:superimposed radio 10101010101011001 OR 10101010101011001
  • 12. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 12 Superimposing sync sequences 10101010101011001 OR 10101010101011001 10101010100011001
  • 13. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 13 Superimposing sync sequences
  • 14. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 14 Destructive interference We do not have an “OR” behavior on the channel !!
  • 15. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 15 Using signatures to handle interference  Spread spectrum  Add noise to carrier  Simulation of 2 signals with power 1  Alternative: ML energy-detector  See also:Albert Krohn, et. al.:The implementation of non- coherent cooperativetransmission for WSNs. INSS 06.
  • 16. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 16 Distributed Synchronization  No predefined roles  Each node is responsible for: − Establishing sync − Keeping up the sync − Rate control  No additional communication channel necessary  No cooperate in ad-hoc manner
  • 17. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 17 Time shifts ∆t  not trivial for detector to make binary decision  Signal boarders get fuzzy  See again:Albert Krohn, et. al.:The implementation of non- coherent cooperativetransmission for WSNs. INSS 06.
  • 18. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 18 Resynchronization  Maximum initial offset t∆init after sync  Maximum tolerable offset ttol  Quartz accuracy k  Oscillating Period T0 1 1  Oscillating difference ∆ T = T 0( − ) 2k 2 1−k 1+ k 1−k   ttol=t∆init+tresync 2k  für k2<<1: ttol=tresync2k+t∆init = t∆ init + tresync ttol ( 1 − k2
  • 19. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 19 Implementation: Particle AwareCon Protocol
  • 20. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 20 Implementation: Particle AwareCon Protocol  Particle Computer Sensor Nodes −TR1001 Transceiver OOK/ASK − 8bit 5MHz PIC18F6720 MCU (t∆init=0.2µs) − 10 ppm Quarz (k=10 *10-6)  S1 and S0 24µs, data rate 125kbit/s (ttol=4µs) tresync=(ttol-t∆init)/2k=190ms  Framesize 13ms =>4% every 14 frames (Current Syncob/Awarecon synchronizes every slot and changes status to unsynchronized after 7 for stability)
  • 21. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 21 Implementation: Sync propagation time Sync to network Sync to single partner 1 cumulated probability functions 0 20 Delay [ms] 100
  • 22. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 22 Issues/ Future work  Over-sized loops − Synchronization returns over multiple hops − Limit maximum time-shift − Assumptions about physical and topological layout necessary  Concurrent island − Two synchronized networks join − Collision Detection/Resolution − Single channel approach − Preference based election
  • 23. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 23 Conclusion  High Accuracy < 10µs  Syncob suited for WSN fusion and coordination  Can be used for sound based location  No additional coordination necessary  Ideal for mobile ad-hoc scenarios − Averages sync collaboratively − Locally adapts to network density
  • 24. 08.06.07 - INSS 07 Syncob: Collaborative Time Synchronization in Wireless Sensor Networks 24 Question?

×