1. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 1 IEEE 1588 over 802.11b Afshaneh Pakdaman San Francisco State University John Eidson Agilent Laboratories, Palo Alto, CA Todor Cooklev San Francisco State University tcooklev@sfsu.edu

2. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 2 Outline Introduction EEE 1588 IEEE 802.11b IEEE 1588 Clock Synchronization over IEEE 802.11b Wireless Local Area Network Conclusions Future work

3. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 3 Clock synchronization is needed in various home, office, and industrial automation applications. Synchronization protocols are used to precisely synchronize independent clocks throughout a distributed system. Synchronization allows transactions between distributed systems to be controlled on time basis. Why do we need to synchronize the clock?

4. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 4 IEEE 1588 IEEE 1588 is a new standard for precise clock synchronization for networked measurement and control systems in the LAN environment. Sub-microsecond synchronization of real-time clocks Intended for relatively localized systems typical of industrial automation and test and measurement environments. Applicable to local areas networks supporting multicast communications (including but not limited to Ethernet)

5. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 5 IEEE 1588 (continued) Simple, administration free installation Support heterogeneous systems of clocks with varying precision, resolution and stability Minimal resource requirements on networks and host components. Develop a supplement to 1588 for operation over WLAN (future work).

6. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 6 1588 Timing Related Messages Four types of timing messages: Sync, Follow_Up, Delay_Req, Delay_Resp Issuing and response to these messages dependent on the ‘state’ of each clock The Sync and Delay_Req messages are time stamped when they sent and received

7. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 7 Detection of Sync messages Application layer Network protocol stack Sync and Delay_Req message detector Physical layer e.g. interface in Ethernet e.g. IEEE 802.11b in Ad Hoc mode

8. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 8 Timing Latency & Fluctuation msecs of delay and fluctuation Application layer Network protocol stack Physical layer < 100 nsecs of delay and fluctuation Application layer Network protocol stack Physical layer Repeater, Switch, or Router Repeaters & Switches: fluctuations ~100ns to usec Routers:fluctuations ~ms

9. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 9 802.11b PHY and MAC layer Data is exchanged between the MAC and the PHY by series of PHY-DATA requests issues by MAC and PHY-DATA. confirm primitives issued by PHY. The PHY layer indicated Last_Symbol_on_Air event to the MAC layer using PHY- TXEND.confirm.

10. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 10 At the other node: The PHY layer indicates the Last_Symbol_On_Air event to the MAC layer using the PHY_RXEND. indication primitive. PHY and MAC layer (continued)

11. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 11 PHY_TXEND.req PHY_TXEND.conf MAC PHY PLCP PHY_TXSTART. req PHY_TXSTART. confirm PHY_DATA.req Time PHY_DATA. confirm PMD_TXPWRLVL.req PMD_RATE.req PMD_ANTSEL.req PMD_TXSTART.req PMD_DATA.req PMD_RATE.req PMD_DATA.req PMD_RATE.req PMD_MODULATION.req PMD_DATA.req PMD_TXEND.req SYNC SFD LENGTH SIGNAL, SERVICE CRC PSDU PHY PMD TX Power RAMP on Scramble start CRC 16 start CRC 16 end TX Power RAMP off PLCP Transmit Procedure ---

12. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 12 Mapping 1588 over 802.11b Processing Delay Jitter between the Transmitter and Receiver devices Delay spread

13. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 13 Mapping 1588 over 802.11b (continued) Time stamp point Last_Symbol_on_Air This indication is observable by all the stations. It is readily available from the PHY layer in the form of either PHY_RXEND indication or PHY_TXEND indication.

14. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 14 LAST DATA BIT SAMPLED TX PORT TIMING TXCLK TX_PE TXD TX_RDY FIRST DATA BIT SAMPLED DATA RX PORT TIMING RXCLK RX_PE MD_RDY RXD Timing Diagram LSBDATA PACKETMSB LSBDATA PACKETMSB

15. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 15

16. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 16

17. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 17 Time interval between TX_RDY on Device A and MD_RDY on Device B falling edge

18. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 18 Time interval between TX_RDY on Device A and MD_RDY on Device B rising edge

19. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 19 Time interval between TX_PE on Device A and RX_PE on Device B falling edge

20. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 20 Time interval between TX_CLK, TX_RDY and MD_RDY falling edge

21. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 21 Time interval between TX_CLK, TX_RDY and MD_RDY falling edge

22. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 22

23. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 23

24. doc.: IEEE 802.11-04/1080r0 Submission September 2004 Todor Cooklev, SF State UniversitySlide 24 Conclusions State the meaning of the results in terms of synchronization, IEEE 1588 can be implemented over WLAN. TX_RDY and MD_RDY Falling edge looks best for implementing 1588. PHY jitter is 500 to 600 ns and the average offset is 7.35 us.