1. Timing Measurement Date: 2008-11-10 Authors: November 2008
doc.: IEEE /2752r1
November 2008
Timing Measurement
Date:
Authors:
Ganesh Venkatesan, Intel Corporation
Peter Ecclesine, Cisco Systems

2. November 2007
doc.: IEEE /2752r1
November 2008
Abstract
This submission summarizes the Timing Measurement feature in v and described the Timing Synchronization Procedure.
Ganesh Venkatesan, Intel Corporation
Peter Ecclesine, Cisco Systems

3. Timing Measurement motivation
November 2007
doc.: IEEE /2752r1
November 2008
Timing Measurement motivation
Use the measurement data in a higher layer algorithm to:
Synchronize clocks between two STAs or synchronize systems to a common clock
Ganesh Venkatesan, Intel Corporation
Peter Ecclesine, Cisco Systems

4. Timing Measurement Support
November 2008
Timing Measurement Support
Exact value of t1 or t3 = Timestamp corresponding to start of Premable (Tx frame) + dot11MgmtOptionOffsetToPreamble + aTxRequestToAntennaConnectorDelay + aTxAntennaConnectorToMediumDelay
Exact value of t2 or t4 = Timestamp corresponding to the receipt of the start of Premable (Rx frame) - (aRxMediumToAntennaConnector Delay+ aRxAntennaConnectorToFirstIndicationDelay)
Ganesh Venkatesan, Intel Corporation

5. Timing Measurement Frame
November 2008
Timing Measurement Frame
Category
Action
Dialog Token
Follow Up Dialog Token
Timestamp Difference
(optional)
Timestamp
Timestamp Difference Accuracy
TimeStamp Accuracy (optional)
Timestamp Counter Units
Optional sub-elements
Octets 1
0 or 4
0 or 1
Variable
Ganesh Venkatesan, Intel Corporation

6. Frame Exchanges to Get the Required Data
November 2008
Ganesh Venkatesan, Intel Corporation

7. Timestamps Time of Departure Time of Arrival November 2008 * *
Timestamp corresponding to Tx of start of Preamble for the Tx frame
Delta to get the start of Preamble to the antenna connector
Delta to get the start of Preamble from the antenna connector to the medium t *
Reported in MLME.TIMINGMSMT.Confirm
Time of Arrival
Timestamp corresponding to Tx of start of Preamble for the Tx frame
Delta to get the start of Preamble to the antenna connector
Delta to get the start of Preamble from the antenna connector to the PMD t *
Reported in MLME.TIMINGMSMT.confirm
and MLME.TIMINGMSMT.indication
Ganesh Venkatesan, Intel Corporation

8. Transmit PLCP (example Clause 15 PHY)
November 2008
Transmit PLCP (example Clause 15 PHY)
Reported in PLME.TIMINGMSMT.confirm
Ganesh Venkatesan, Intel Corporation

9. What happens in the Tx PLCP?
November 2008
What happens in the Tx PLCP?
If the MIB variable dot11MgmtOptionTimingMsmt exists and is set to TRUE, the PLCP shall do the following:
Save the value of the Timestamp counter corresponding to the time when the PMD_TXSTART.request is received from the PHY PCLP, ta (described at the Time of Departure timestamp in TGv)
Add the offset to the start of Preamble for the outgoing frame is setup for transmission by the PMD to ta,
Forward t, timestamp to the PHY-PLCP
Ganesh Venkatesan, Intel Corporation

10. Receive PLCP (example Clause 15 PHY)
November 2008
Receive PLCP (example Clause 15 PHY)
Reported in MLME.TIMINGMSMT.indication and
in MLME.TIMINGMSMT.confirm
Ganesh Venkatesan, Intel Corporation

11. What happens in the Rx PLCP?
November 2008
What happens in the Rx PLCP?
If the MIB variable dot11MgmtOptionTimingMsmt exists and is set to TRUE, the PLCP shall do the following:
Save the value of the Timestamp counter corresponding to the time when the start of Preamble for the incoming frame is detected at the PMD, t,
Forward t, in RXVECTOR to the PHY-PLCP
Ganesh Venkatesan, Intel Corporation

12. November 2008
Measurement Accuracy
Accuracy requirements for timestamp depends on the application it is used for. Time Synchronization for 802.1AS applications is +/- 20nsec (40 nsec spread)
Accuracy reflects how close to the time at which the actual event occurred to the the reported timestamp.
Spread in the time it takes to schedule the transmission of a Tx frame in the PMD.
Spread in the point in time where timestamp corresponding to the start of preamble for the received Rx frame is recorded.
Note: Timestamp is always generated at a point in time where it is possible for the PMD. However, this is not the point in time we are interested. So, several constants are defined to adjust the timestamps.
Ganesh Venkatesan, Intel Corporation

13. November 2008
Backup
Ganesh Venkatesan, Intel Corporation

14. What is involved? Constants: PMD to Antenna connector delay
November 2008
What is involved?
Constants:
PMD to Antenna connector delay
Antenna Connector to Air Interface delay
Air Interface to Antenna Connector delay
Antenna Connector to PMD delay
How accurately can an implementation timestamp?
When did start of Preamble for a Tx frame get sent from the PMD?
When did the start of Preamble for a Rx frame get recognized at the PMD?
Ganesh Venkatesan, Intel Corporation