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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Time Synchronization for IEEE802.15.4e MAC] Date Submitted: [July, 2008] Source: [ChangSub Shin, Wun-Cheol Jeong, Soyoung Hwang, Anseok Lee, Seong-Soon Joo] Company [ETRI]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Time Synchronization for IEEE802.15.4e MAC] Date Submitted: [July, 2008] Source: [ChangSub Shin, Wun-Cheol Jeong, Soyoung Hwang, Anseok Lee, Seong-Soon Joo] Company [ETRI] Address [161 Gajeong-dong Yuseong-gu, Daejeon, Korea] Voice:[+82-42-860-1668], FAX: [+82-42-869-1712], E-Mail:[shincs@etri.re.kr] Re: [IEEE P802.15.4e Call For proposal] Abstract: [This document proposes time synchronization solution for IEEE802.15.4e MAC] Purpose: [This document is a response to call for preliminary proposals] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. ChangSub Shin et al

  2. Time Synchronization for IEEE802.15.4e MAC ChangSub Shin, Wun-Cheol Jeong, Soyoung Hwang, Anseok Lee, Seong-Soon Joo ETRI This work has been supported by the Ministry of Knowledge Economy (MKE) of the Republic of Korea under Grants 2008-F-052. ChangSub Shin et al

  3. Time Synchronization with IEEE802.15.4-2006 MAC • Beacon enabled mode • Only for tree topology using StartTime value • can’t support mesh topology • Beacon scheduling algorithm is required • in case of collision, beacon frame is lost • Traffic overhead with periodic beacon frames • Non beacon mode • Can’t support TDMA • Require long idle listening • high power consumption ChangSub Shin et al

  4. Time Synchronization for IEEE802.15.4e MAC • Considerations • Network-Wide Time Synchronization • with beacon • without beacon • operate in multi-hop mesh topology • peer-to-peer communication • Simple and Reliable • guarantee time accuracy within error boundary • Robust in change of topology ChangSub Shin et al

  5. July 2008 Network-Wide Time Synchronization with Beacon (1/1) back-off Active Duration Inactive Duration sync offset Beacon Sync Offset • Contention based Beacon with Adjusting Sync Offset (CB-ASO) • CSMA/CA before sending a beacon frame • Inform the beacon sync offset with beacon frame • Receiver adjusts the next start time of beacon using sync offset Slide 5 ChangSub Shin et al

  6. Sync-source A 1-hop C B 2-hop F D E 3-hop G J H I July 2008 Network-Wide Time Sync without Beacon (1/6) • Directional Time Diffused Synchronization (DTDS) • Sending timestamp in one direction with Sync frame • Relaying Sync frame with implicit ACK • Refrain backward flooding with the depth of hopping • offer the information of superframe structure Sync Frame Slide 6 ChangSub Shin et al

  7. July 2008 Network-Wide Time Sync without Beacon (2/6) • Time Stamp and Clock Adjusting • Estimated sending time • MAC-PHY interface delay time + PHY delay time • use timestamp defined in IEEE802.15.4-2006 • Clock compensation • Using simple liner-regression Insert Timestamp value (interface delay + PHY modulation delay) Backoff CCA Modulation and TX Sender MAC PHY Modulation and TX Receiver Get Timestamp value PHY ChangSub Shin et al

  8. July 2008 Network-Wide Time Sync without Beacon (3/6) • Merits • Simple • Robust in failure of device • Independent on network topology • Flexible and adaptable • Low traffic overhead • Low synchronization error • Support of global time information ChangSub Shin et al

  9. July 2008 Network-Wide Time Sync without Beacon (4/6) • Simple time sync test • Hardware platform • MCU : MSP430 • RF : CC2420 • Oscillator max skew : 20 ppm • Synch packet interval : every 4 minute test • test packet interval : every 1.1 second test ChangSub Shin et al

  10. July 2008 Network-Wide Time Sync without Beacon (5/6) • Design issues • Clock error value • Time duration of basic time slot • Error boundary • Guard time of basic time slot • Re-synchronization interval ChangSub Shin et al

  11. July 2008 Network-Wide Time Sync without Beacon (6/6) • Design time slot unit • 2400–2483.5 MHz O-QPSK PHY : max 133 bytes • Preamble : 4 bytes • SFD : 1 bytes • PHR : 1 bytes • Max PSDU size : 127 bytes • Pure max Tx time => 4.256 ms (133 bytes) • We have to consider proper value in implementation • => 1 tx + turn around time + 1 ack + 2 guard time • Example value of slot unit • => 625 symbols (10ms in 2.4) ChangSub Shin et al

  12. Thank you very much for your attention Any Questions? ChangSub Shin et al

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