doc.: ieee 802.15-11-0598-00-004k submission etri sep 2011 slide 1 project: ieee p802.15 working...
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doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 1
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: [Global Time Synchronization for Low-Energy Wide Area Monitoring]Date Submitted: [Sep 15, 2011]Source: [Seong-Soon Joo, Bong-Soo Kim, Jong-Arm Jun]Company: [ETRI]Address: [161 Gajeong-dong, Yuseong-gu, Daejeon, KOREA]Voice: [+82-42-860-6333], FAX: [+82-42-860-4197], E-Mail: [[email protected]]
Re: [IEEE 802 TG4k issues a call for proposal]
Abstract: [Global time synchronization for low-energy wide area monitoring is proposed.]
Purpose: [To contribute the initial process of preparing draft for TG4k]
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.
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 2
Global Time Synchronization for Low-Energy Wide Area Monitoring
Seong-Soon Joo*, Bong-Soo Kim, Jong-Arm Jun
ETRI
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 3
Time and Low Energy Wide Area Monitoring (I)
• synchronized measuring – the times of occurrence of physical events
• often crucial for the observer • to associate event reports with the originating physical events
• need accurate time-stamping of measured quantities– acoustic leak detection mechanisms
• that can pinpoint the location of a leak given a known speed-of-sound through a pipe.– synchro-phasor measurements
• relative phase relationship between current and voltage at various locations can be measured
• if an absolute time basis is communicated to multiple end-points.– determining location of sensor nodes
• based on the measurement of time of flight or difference of arrival time of certain signals also require finely synchronized time.
– distributed observations into a coherent estimate of the original phenomenon • requires accurate time-stamping.
source: Mark Wilbur, IEEE 15-11-0397-00-004k,“Time Synchronization in Wireless Sensor Networks”
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 4
Time and Low Energy Wide Area Monitoring (II)
• global time synchronization for time-stamping– need global master time clock
• for synchronizing distributed devices’ local time clock• periodical time synchronization for compensating local clock drift
• over-the-air time synchronization– coordinator is power-free
• may have high precision clock • afford to transmit clock information periodically in any time scale
– adjust clock drift of a local device based upon coordinator master clock
• beacon frame as a global clock tick – need a message to broadcast global clock time– beacon interval can be clock leap second
– use sequence number of beacon frame for clock sampling
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 5
• time expression in LECIM network– multi-superframe of TG4e DSME MAC
• sequence # of master beacon• superframe ID• slot ID
– precision of clock tick• length of slot• BPSK, data rate 20kbps (BO = 14, SO = 5, MO = 9)
– 96ms
Time and Low Energy Wide Area Monitoring (III)
B B B B B B B B
512 superframes, 8,192 slots
2,343 beacons in 24 hours
assigned to device
i
assigned to device
i
assigned to device
i
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 6
• time synchronization– initiate time synchronization– in phase with the global time clock– recover from the loss of time synchronization
• how to achieve low energy time synchronization?– advantage of power-free coordinator– balancing the energy consumption with precision of clock– virtue of multi-superframe structure
Time and Low Energy Wide Area Monitoring (IV)
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 7
Level 0 Time Synchronization• initiate time synchronization
– two options• find beacon • request global time
– dependent on PHY • power consumption on RX and TX• symbol rate
• request global time– device requests synchronized global time
• use grade 0 link• LECIM MAC management command frame: SyncReq
– coordinator responds with current global time• ACK frame (seq. # of master beacon, superframe ID, slot ID)
device
coordinator
SyncReq ACKwake up
sleep
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 8
Level 1 Time Synchronization (I)• clock drift compensation
– two options• periodical wake up• request global time
– dependent on usage of links• need operation and maintenance command and control for LECIM• frequency of measuring events
device
coordinator
SyncReq ACKwake up
sleep
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 9
Level 1 Time Synchronization (II)
BI BI*2Wo
coordinator
device
adjust clock
adjust clock
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 10
Level 1 Time Synchronization (III)
device
device
adjust clock
adjust clock adjust clock
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 11
Level 2 Time Synchronization• implicit exchange of time information
– frame from the coordinator• receive management frame transmitted on management slot• compensate clock drift with estimated time of management slot
– device : (estimated current seq. # of master beacon, superframe ID, slot ID)– received: (seq. # of master beacon, superframe ID, slot ID)
– frame from a device• receive data frame, command frame transmitted on device slot• save the time of slot at which frame is received
device
coordinator
datamanagement
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 12
Amendment to TG4e
• MAC PIB– extend macBSN– add macWakeupOrder
• MAC management primitive & command– add MLME-TIME-SYNC– add Time synchronization request command
• MAC frame format– short frame header– beacon format
doc.: IEEE 802.15-11-0598-00-004k
Submission
ETRI
Sep 2011
Slide 13
Thanks for your Attention!