Doc.: IEEE 15-08-0617-01-004e SubmissionSlide 1 Project: IEEE P802.15 Working Group for Wireless...
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doc.: IEEE 15-08-0617-01- 004e Submiss ion Slide 1 Project: Project: IEEE P802.15 Working Group for Wireless Personal Area IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Networks (WPANs) Submission Title: [Network-wide Time Synchronization for TDMA MAC] Date Submitted: [September, 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: [[email protected]] 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 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 ChangSub Shin et al September 2008
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Transcript of Doc.: IEEE 15-08-0617-01-004e SubmissionSlide 1 Project: IEEE P802.15 Working Group for Wireless...
doc.: IEEE 15-08-0617-01-004e
Submission
Slide 1
Project: Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Network-wide Time Synchronization for TDMA MAC]Date Submitted: [September, 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:[[email protected]]
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 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
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
ChangSub Shin et alSlide 2
Network-wide Time Synchronization for TDMA MAC
ChangSub Shin, Wun-Cheol Jeong, Soyoung Hwang,
Anseok Lee, Seong-Soon Joo
ETRI
September 2008
This work has been supported by the Ministry of Knowledge Economy (MKE) of the Republic of Korea under Grants 2008-F-052.
doc.: IEEE 15-08-0617-01-004e
Submission
• TG4e MAC requirements for industrial applications• Low latency• Robustness• Low energy consumption
• IEEE802.15.4-2006 MAC cannot support TG4e requirements• TDMA based frequency hopping MAC
=> need time synchronization mechanism
Motivation
ChangSub Shin et alSlide 3
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Network-wide multi-hop time synchronization• Support mesh topology• Simple and reliable• Guarantee time accuracy within error boundary• Robust in change of topology• Error recovery from a fail node• Low control traffic for synchronization
Time synchronization requirements for TDMA
ChangSub Shin et alSlide 4
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Clock Drift Problem• Frequency change with time
• Message-Delivery Uncertainty Problem• send, access, transmission, propagation, reception and
receive time
• Multi-hop Time-Synchronization Problem• Error Increases with hop distance
• Dynamic topology change
• Overhead of control packet for sync
• Unreliable & unstable
WSN Time Synchronization Problems
ChangSub Shin et alSlide 5
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Decomposition of the message delivery uncertainties(1) Send Time—time used to assemble the message and issue the send request to the MAC layer
on the transmitter side. Nondeterministic, hundreds of milliseconds error.
(2) Access Time—waiting time to access channel for transmitting frame. Nondeterministic, varying from milliseconds up to seconds.
(3) Transmission Time—the time it takes for the sender to transmit the message. Deterministic, tens of milliseconds.
(4) Propagation Time—the time it takes for the message to transmit from sender to receiver once it has left the sender. highly deterministic, less than one microsecond (for ranges under 300 meters).
(5) Reception Time—the time it takes for the receiver to receive the message. It is the same as the transmission time. The transmission and reception times overlapping.
(6) Receive Time—time to process the incoming message and to notify the receiver application. Its characteristics are similar to that of send time.
Directional Time Diffused Synchronization (DTDS) (1/10)
ChangSub Shin et al
September 2008
Slide 6
Source: The Flooding Time Synchronization Protocol [Miklos Maroti et al / SenSys’04]
doc.: IEEE 15-08-0617-01-004e
Submission
• Pair-wise synchronization• Sender
• Insert timestamp value after backoff+CCA • Send timestamp value in the sync frame
• Receiver• Get timestamp value(defined 15.4 MAC) at receiving sync frame
• Synchronize with sender’s time
Directional Time Diffused Synchronization (DTDS) (2/10)
Backoff
MAC
Insert TimestampCCA Transmitting
PHY
Receiving
PHY
Sender
Receiver
Get Timestamp
ChangSub Shin et alSlide 7
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Network-Wide Time Synchronization• PAN Coordinator (sync source)
• Start synchronization by broadcasting sync frame• Diffusion count value of Synchronization frame should be
increased by one for each hop• May offer additional information such as superframe structure
• Coordinator and end device• Synchronization frame including the lowest diffusion depth or
the latest timestamp value is accepted for time synchronization• Keep its own diffusion depth counter for sync frame• Reliable broadcasting sync frame using broadcast-ack address• Refrain backward flooding with the diffusion count value
Directional Time Diffused Synchronization (DTDS) (3/10)
ChangSub Shin et alSlide 8
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Network-Wide Time Synchronization
Directional Time Diffused Synchronization (DTDS) (4/10)
ChangSub Shin et alSlide 9
A
CB
DF
G
IH
J
E
Depth-1
Depth-2
Depth 3
Sync-source
September 2008
(1)
(2)(3)
(4)
(5) (6)
doc.: IEEE 15-08-0617-01-004e
Submission
• Select sync reference node from neighbor nodes • Wait [X]time from first received sync packet
• Select time (2)
• Method 1 : Select the only the earliest time
• Method 2 : Average time value of all received sync time
Directional Time Diffused Synchronization (DTDS) (5/10)
ChangSub Shin et alSlide 10
70
65
75
65
70
65
75
70
Method 1Method 2
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Compensate clock method• Get a time value from neighbor nodes at n times
• Average the consecutive time values
• Compensate own time value without re-sync frame
Directional Time Diffused Synchronization (DTDS) (6/10)
ChangSub Shin et al
Re-sync interval
Get a time value at n times and average
September 2008
Slide 11
Re-sync interval
Compensate time value without re-sync frame
Te = n : the number of sampled valueTk : current timeTe : estimated time
doc.: IEEE 15-08-0617-01-004e
Submission
• advantage• Simple• Robust in failure of device • Independent on network topology• Flexible and adaptable• Low traffic overhead• Low synchronization error using MAC-layer
timestamp• Can support of global time information
Directional Time Diffused Synchronization (DTDS) (7/10)
ChangSub Shin et alSlide 12
September 2008
doc.: IEEE 15-08-0617-01-004e
Submission
• Design issues• Clock accuracy• Time duration of basic time slot• Error boundary• Guard time of basic time slot• Re-synchronization interval
Directional Time Diffused Synchronization (DTDS) (8/10)
ChangSub Shin et al
September 2008
Slide 13
doc.: IEEE 15-08-0617-01-004e
Submission
• 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)
Directional Time Diffused Synchronization (DTDS) (9/10)
ChangSub Shin et al
September 2008
Slide 14
doc.: IEEE 15-08-0617-01-004e
Submission
• Error boundary and re-sync interval• For example,
• error boundary : +/-1ms • synchronization error : 50us • Clock accuracy : +/-10ppm• Per hop accumulated error : 0.8 us (average
backoff delay(40ms))• 1 hop Re-sync interval < ( 1ms - 0.05ms) / (20ppm) =
48s• 5 hop Re-sync interval < ( 1ms - 0.05ms – 0.004 ms) /
(20ppm) = 47.3s
Directional Time Diffused Synchronization (DTDS) (10/10)
ChangSub Shin et al
September 2008
Slide 15
doc.: IEEE 15-08-0617-01-004e
Submission
Procedure of Synchronization
ChangSub Shin et al
September 2008
Slide 16
A
B C
D E
doc.: IEEE 15-08-0617-01-004e
Submission
• PIB
Define PIB, Primitives
ChangSub Shin et al
September 2008
Slide 17
attribute Type description
macSyncInterval 3 bytes The number of interval times for re-synchronization.
macReceivedTimestamp 3 bytes Time of receiving the first bit of the SFD field. A symbol unit
macReceivedTimestampList List A consecutive timestamp value of receiving sync frame. For S/W time conpensation
• PrimitivesName Request Indication Response Confirm description
MLME-START-SYNC O O Start synchronization by PAN Coordinator
MLME-SYNC-FAIL O Notify sync fail to the next higher layer
doc.: IEEE 15-08-0617-01-004e
Submission
• Sync frame : propagate timestamp for synchronization• Timestamp : time value for synchronization
• Sync interval : the number of interval times for re-synchronization
• Diffusion depth : hop count from PAN Coordinator for preventing backward time update
Define Frame Format (1/2)
ChangSub Shin et al
September 2008
Slide 18
4 bytes 3 bytes 3 bytes 1 bytes 2 bytes
Timestamp_second
Timestamp_us Sync interval Diffusion depth Ack address
doc.: IEEE 15-08-0617-01-004e
Submission
• Sync request frame : request synchronization to neighbor nodes in case of loss synchronization• Diffusion depth : sync requesting node’s hop count from
PAN Coordinator
Define Frame Format (2/2)
ChangSub Shin et al
September 2008
Slide 19
1 bytes
Diffusion depth
doc.: IEEE 15-08-0617-01-004e
Submission
Thank you very much for your attention
Any Questions?
ChangSub Shin et alSlide 20
September 2008
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