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Timing Measurement

Timing Measurement

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Timing Measurement

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  1. Timing Measurement Authors: Date: 2008-11-10 Ganesh Venkatesan, Intel Corporation

  2. Abstract This submission summarizes the Timing Measurement feature in 802.11v and described the Timing Synchronization Procedure. Ganesh Venkatesan, Intel Corporation

  3. 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

  4. 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 Ganesh Venkatesan, Intel Corporation

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

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

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

  9. 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) Reported in MLME.TIMINGMSMT.indication and in MLME.TIMINGMSMT.confirm Ganesh Venkatesan, Intel Corporation

  11. 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. 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. Backup Ganesh Venkatesan, Intel Corporation

  14. 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