doc.: ieee 802.11-04/1080r0 submission september 2004 todor cooklev, sf state universityslide 1 ieee...
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September 2004
Todor Cooklev, SF State University
Slide 1
doc.: IEEE 802.11-04/1080r0
Submission
IEEE 1588 over 802.11b
Afshaneh PakdamanSan Francisco State University
John Eidson Agilent Laboratories, Palo Alto, CA
Todor CooklevSan Francisco State University
tcooklev@sfsu.edu
September 2004
Todor Cooklev, SF State University
Slide 2
doc.: IEEE 802.11-04/1080r0
Submission
Outline
• Introduction• EEE 1588• IEEE 802.11b• IEEE 1588 Clock Synchronization over
IEEE 802.11b Wireless Local Area Network
• Conclusions• Future work
September 2004
Todor Cooklev, SF State University
Slide 3
doc.: IEEE 802.11-04/1080r0
Submission
• 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?Why do we need to synchronize the clock?
September 2004
Todor Cooklev, SF State University
Slide 4
doc.: IEEE 802.11-04/1080r0
Submission
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)
September 2004
Todor Cooklev, SF State University
Slide 5
doc.: IEEE 802.11-04/1080r0
Submission
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).
September 2004
Todor Cooklev, SF State University
Slide 6
doc.: IEEE 802.11-04/1080r0
Submission
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
September 2004
Todor Cooklev, SF State University
Slide 7
doc.: IEEE 802.11-04/1080r0
Submission
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
September 2004
Todor Cooklev, SF State University
Slide 8
doc.: IEEE 802.11-04/1080r0
Submission
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
RouterRepeaters & Switches:fluctuations ~100ns to usecRouters:fluctuations ~ms
September 2004
Todor Cooklev, SF State University
Slide 9
doc.: IEEE 802.11-04/1080r0
Submission
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.
September 2004
Todor Cooklev, SF State University
Slide 10
doc.: IEEE 802.11-04/1080r0
Submission
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)
September 2004
Todor Cooklev, SF State University
Slide 11
doc.: IEEE 802.11-04/1080r0
Submission
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
SY
NC
SF
DLE
NG
TH
SIG
NA
L, SE
RV
ICE
CR
CP
SD
U
PHY
PMD
TX Power RAMP on Scramble start
CRC 16 start
CRC 16 end
TX Power RAMP
off
PLCP Transmit Procedure
------
---
September 2004
Todor Cooklev, SF State University
Slide 12
doc.: IEEE 802.11-04/1080r0
Submission
Mapping 1588 over 802.11b
• Processing Delay
• Jitter between the Transmitter and Receiver devices
• Delay spread
September 2004
Todor Cooklev, SF State University
Slide 13
doc.: IEEE 802.11-04/1080r0
Submission
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.
September 2004
Todor Cooklev, SF State University
Slide 14
doc.: IEEE 802.11-04/1080r0
Submission
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
September 2004
Todor Cooklev, SF State University
Slide 15
doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 16
doc.: IEEE 802.11-04/1080r0
Submission
September 2004
Todor Cooklev, SF State University
Slide 17
doc.: IEEE 802.11-04/1080r0
Submission
Time interval between TX_RDY on Device A and MD_RDY on Device B falling edge
September 2004
Todor Cooklev, SF State University
Slide 18
doc.: IEEE 802.11-04/1080r0
Submission
Time interval between TX_RDY on Device A and MD_RDY on Device B rising edge
September 2004
Todor Cooklev, SF State University
Slide 19
doc.: IEEE 802.11-04/1080r0
Submission
Time interval between TX_PE on Device A and RX_PE on Device B falling edge
September 2004
Todor Cooklev, SF State University
Slide 20
doc.: IEEE 802.11-04/1080r0
Submission
Time interval between TX_CLK, TX_RDY and MD_RDY falling edge
September 2004
Todor Cooklev, SF State University
Slide 21
doc.: IEEE 802.11-04/1080r0
Submission
Time interval between TX_CLK, TX_RDY and MD_RDY falling edge
September 2004
Todor Cooklev, SF State University
Slide 22
doc.: IEEE 802.11-04/1080r0
Submission
Time interval TX_RDY and MD_RDYfalling edge
0
20
40
60
80
100
120
Time Microsecond
Da
ta s
am
pli
ng
10
00
.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
Frequency
Cumulative %
September 2004
Todor Cooklev, SF State University
Slide 23
doc.: IEEE 802.11-04/1080r0
Submission
Time interval TX_RDY and MD_RDYfalling edge
050
100150200250300350400450500
Time Microsecond
Da
ta s
am
pli
ng
10
00
.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
Frequency
Cumulative%
September 2004
Todor Cooklev, SF State University
Slide 24
doc.: IEEE 802.11-04/1080r0
Submission
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.
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