slide1
Download
Skip this Video
Download Presentation
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Loading in 2 Seconds...

play fullscreen
1 / 22

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


  • 54 Views
  • Uploaded on

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Explanation and Revision of Previous Time Synchronization Proposal to IEEE 802.15.4b ] Date Submitted: [ August 23, 2004 ]

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)' - sadie


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

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

Submission Title: [Explanation and Revision of Previous Time Synchronization Proposal to IEEE 802.15.4b]

Date Submitted: [August 23, 2004]

Source: [Huai-Rong Shao, Hui Dai and Jinyun Zhang] Company [Mitsubishi Electric Research Labs]

Address [8th Floor, 201 Broadway, Cambridge, MA 02139 ]

Voice:[617-621-7517], FAX: [617-621-7550], EMail:[[email protected]]

Re: [Response to call for proposal of IEEE 802.15.4b, Doc Number: 15-04-0239-00-004b.]

Abstract: [Further explanation and revision of shared time-base distribution methods proposed in 15-04-0313-01-004b]

Purpose: [Proposal to IEEE 802.15.4b Task Group]

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.

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

slide2

Time Synchronization Proposal-Explanation and Revision for Shared Time-Base Distribution Methods Proposed in Document 15-04-0313-01

Huai-Rong Shao, Hui Dai and Jinyun Zhang

Mitsubishi Electric Research Laboratories

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

outline
Outline
  • Proposal Summary
  • Motivation and Objectives
  • Method
    • Basic Scheme
    • High Accuracy Options
  • Cases
    • Use beacon for synchronization
    • Use general packets for synchronization
  • Discussions
  • Message Sequence Charts

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

proposal summary
Proposal Summary
  • Minimum changes to 802.15.4-2003
    • Add macSyncSymbolOffset attribute to MIB
  • Shared time-base distribution method
  • Basic scheme for both beacon-enabled and non-beacon network
  • Allow High Accuracy Options

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

motivation and objectives
Motivation and Objectives
  • Time synchronization is important
    • Maintain superframe/slot synchronization among devices
    • Fine-tuned coordination of wake/sleep duty cycles to reduce power consumption
    • Preserve the event orders
    • Time synchronization is also important to security protocols since the clock reading is often used for encryption key generation
    • Loop free routing (Robert Poor said)
  • Objective
    • A shared time-base distribution method with minimum modifications to 802.15.4-2003
    • Simple, Efficient and Flexible
  • Performance Consideration
    • Accuracy
    • Overhead

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

basic scheme
Basic Scheme
  • Step 1 : At T0 , sender obtains a timestamp
  • Step 2 : At T1 , a synchronization packet containing timestamp is sent on wireless channel
  • Step 3 : At T2 , receivers receive the synchronization packet. They then adjust local clocks according to the timestamp carried in synchronization packet

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

basic scheme cont d
Basic Scheme (cont’d)

Sender

Receiver

Step1: Get timestamp at T0

T0

T1

T2

time

Step3: Receive packet

at T2. Receiver adjusts

local clock according to

the timestamp

carried in the packet

Step2: Send Synchronization

frame at T1

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

high accuracy option
High Accuracy Option
  • Step 1 : Basic Scheme
  • Step 2 : Sender sends a second frame to receiver
    • The second frame contains the actual transmitting time of synchronization packet
  • Step 3 : Receiver adjusts the local clock again for higher accuracy

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

high accuracy option cont d
High Accuracy Option (cont’d)

Sender

Receiver

Step1 a: Get timestamp at T0

T0

T1

T2

T3

Step1 b: Send Synchronization

frame at T1

Step 1 c: Receive

Synchronization packet at T2 .Receiver adjusts local clock

Step 2: Send real

Timestamp, i.e. T1, at T3

Step 3: Receiver adjusts local clock

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

implementation choices
Implementation Choices

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

case i use beacon as synchronization packet
Case I : Use Beacon As Synchronization Packet
  • Beacon provides natural synchronization embodiment in beacon-enabled network.
  • Use of beacon can minimize modification to 802.15.4-2003
  • Beacon-enabled WPAN
    • Beacons are transmitted periodically
  • Nonbeacon-enabled WPAN
    • Ad hoc Beacons can be used
      • Association requires Beacon anyway
    • Synchronization frequency is implementation specific

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

case i interfaces and parameters
Case I : Interfaces and Parameters
  • Add symbol offset captured position attribute to MIB because this could be vendor specific
    • macSyncSymbolOffset
  • No other modification
    • Timestamp can be carried in the beacon payload.
    • macBeaconTxTime (page 136, Table 71) stores the actual beacon transmitted time
    • MLME-BEACON-NOTIFY.indicationis already specified in 802.15.4-2003, Page 75§7.1.5.1

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

case ii use general packet as synchronization packet
Case II : Use General Packet As Synchronization Packet
  • Beacon-enabled and Nonbeacon-enabled WPAN
    • Require higher layer to schedule synchronization packet transmission
    • More primitives are needed
  • Up to higher level to select configurations
    • Synchronization Frequency
    • Accuracy

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

case ii interface and parameters
Case II : Interface and Parameters
  • Add symbol offset captured position attribute to MIB because this could be vendor specific
    • macSyncSymbolOffset
  • Receiver reports timestamp to next higher layer
    • Add timestamp argument to MCPS-DATA.indication, page 60 §7.1.1.3
  • Sender reports the actual Tx time to next high layer
    • Add timestamp argument to MCPS-DATA.confirm, page 59 §7.1.1.2
    • OR Add macSyncTxTime to MIB to record the synchronization packet transmission time

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

discussion timestamp in basic scheme
Discussion: Timestamp in Basic Scheme
  • Timestamp carried in synchronization packet
    • A synchronization packet’s actual transmitting time can’t be carried in itself. Because actual transmitting time is captured during packet transmission according to 802.15.4-2003.
    • A timestamp different from actual transmitting time is put into synchronization packet at MAC layer or above.
    • The error can be possibly reduced by estimation.
      • Detailed error analysis and estimation are presented at the previous proposal
        • 15-04-0313-01-004b-enhancements-to-ieee-802-15-4

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

discussion other high accuracy options
Discussion: Other High Accuracy Options
  • SNTP-like Method
    • Step 1 : Basic Scheme
    • Step 2 : Receivers send response frame to the sender
      • Response frame contains received timestamp and the previous sync frame sequence number
    • Step 3 : Sender sends back calculation to reduce the propagation error
  • Problem
    • Too much overhead for WPAN
    • It mainly focus on reducing propagation error, which is NOT the major error source in 802.15.4

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

slide17

Discussion: SNTP-Like High Accuracy Option

Sender

Receiver

Step1 a: Get timestamp at T0

T0

T1

T2

T3

T4

Step 1 c: Receive

Synchronization packet at T2 .

Step1 b: Send Synchronization

frame at T1

Step 3: Sender sends feedback to reduce the propagation error at T4

Step 2: Receiver send response to sender at T3

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

conclusion
Conclusion
  • Works with both absolute clock and relative clock
  • Totally compatible with existing mechanisms
  • Minimum changes to 802.15.4-2003
  • Can be easily extended to multi-hops cases

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

msc basic scheme use beacon
MSC : Basic Scheme (Use beacon)

SENDER

RECEIVER

RECEIVER

MLME

Next Higher

Layer

SENDER

MLME

Next

Higher Layer

Beacon

( with Synchronize timestamp)

MLME-BEACON-NOTIFY.indication

(with time stamp)

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

msc high accuracy option use beacon
MSC : High Accuracy Option (Use beacon)

SENDER

RECEIVER

RECEIVER

MLME

Next Higher

Layer

SENDER

MLME

Next

Higher Layer

Beacon

( with Synchronize timestamp)

MLME-BEACON-NOTIFY.indication

(with time stamp)

Synchronization Follow Up

(with macSyncTxTime)

MCPS-DATA.indication

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

msc basic scheme use general packet
MSC : Basic Scheme (Use General Packet)

SENDER

RECEIVER

MAC

Layer

Next

High Layer

MAC

Layer

Next

High Layer

MCPS-DATA.request

Synchronization Packet

MCPS-DATA.indication

With timestamp

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

msc high accuracy option use general packet
MSC : High Accuracy Option (Use General Packet)

SENDER

RECEIVER

RECEIVER

MLME

Next Higher

Layer

SENDER

MLME

Next

Higher

Layer

MCPS-DATA.request

Synchronization Packet

MCPS-DATA.confirm

(with time stamp)

MCPS-DATA.indication

(with time stamp)

MCPS-DATA.request

Synchronization Follow Up

MCPS-DATA.indication

(with time stamp)

H. Shao, H. Dai, J. Zhang, Mitsubishi Electric

ad