m km

1. doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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
LSB DATA PACKET MSB
LSB DATA PACKET MSB

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

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

17. doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 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 University
Slide 22
Time interval TX_RDY and MD_RDY
falling edge
0
20
40
60
80
100
120
0.000007122
7.17465E-06
7.22729E-06
7.27994E-06
7.33258E-06
7.38523E-06
7.43787E-06
7.49052E-06
Time Microsecond
Data
sampling
1000
.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
Frequency
Cumulative %

23. doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 23
Time interval TX_RDY and MD_RDY
falling edge
0
50
100
150
200
250
300
350
400
450
500
5
.
4
9
8
8
E
-
0
6
5
.
6
9
5
3
7
E
-
0
6
5
.
8
9
1
9
4
E
-
0
6
6
.
0
8
8
5
E
-
0
6
6
.
2
8
5
0
7
E
-
0
6
6
.
4
8
1
6
4
E
-
0
6
6
.
6
7
8
2
1
E
-
0
6
6
.
8
7
4
7
7
E
-
0
6
7
.
0
7
1
3
4
E
-
0
6
7
.
2
6
7
9
1
E
-
0
6
7
.
4
6
4
4
8
E
-
0
6
Time Microsecond
Data
sampling
1000
.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
Frequency
Cumulative
%

24. doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 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.