1. Submission Title: [Beacon design of BAN superframe]
January 2007
doc.: IEEE
September/2008
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Beacon design of BAN superframe]
Date Submitted: [September, 2008]
Source: [Bin Zhen, Huan-bang Li, Changle Li and Ryuji Kohno]
Company [National Institute of Information and Communications Technology (NICT)]
Contact: Bin Zhen
Voice: [ ,
Abstract: [This document describes the beacon design issue in TG6.]
Purpose: [To help discussion in IEEE ]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

2. Beacon design of BAN superframe
January 2007
doc.: IEEE
September/2008
Beacon design of BAN superframe
Bin Zhen, Huan-bang Li, Changle Li and Ryuji Kohno
National Institute of Information and Communications Technology (NICT)
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

3. January 2007
doc.: IEEE
September/2008
Review
When and how to wakeup an inactive device with the least power consumption?
Dynamic duty cycle of BAN devices
Both BAN coordinator and device have limited battery budget
Battery is more precious for device
Coordinator can also go to sleep
MAC layer clock
BAN superframe as time unit of the semi-synchronized piconet
Wakeup point in a “BAN day” and distributed listening to wakeup point to balance power consumption and packet latency
Slot scalability
BAN superframe is easy for QoS support
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

4. Clock maintenance Clock drift
January 2007
doc.: IEEE
September/2008
Clock maintenance
Clock drift
Typical clock accuracy is ±40ppm
Relative clock drift between coordinator and device doubles the value
Total clock offset is proportional with clock accuracy and sleep time
Sleep time
Clock accuracy: drift in unit time
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

5. Beacon in BAN superframe
January 2007
doc.: IEEE
September/2008
Beacon in BAN superframe
The device’s clock can be maintained by beacon listening at the wakeup points
An active BAN superframe is initialized by a beacon with more than one equally sized slot
The beacon consists of preamble and data
Preamble portion is used for bit-wise synchronization
Data part include header, payload and trailer
Active BAN superframe
Inactive BAN superframe
Preamble
Data
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

6. January 2007
doc.: IEEE
September/2008
Beacon listening
Except bit-wise synchronization, the beacon carries slot information of superframe
Where is the start or end of a slot?
How to cooperate beacon transmit/listen and maintain the slot information in an energy efficient way?
Beacon start at the Beginning of slot (B-B)
Beacon end at the End of slot (B-E)
Scheduled time
Listen time
Tx time
time
Relative clock offset
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

7. Beacon starts at the beginning of slot
January 2007
doc.: IEEE
September/2008
Beacon starts at the beginning of slot
It is the device’s duty to consider the clock offset
Beacons start at the beginning of slot, like and Bluetooth
Device must listen before the scheduled time
Slot is described by the start of beacon
Wakeup point
BAN superframe
beacon ……
Slot border
Device A:
Device B:
Start to listen
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

8. Beacon start at the beginning of slot (cont.)
January 2007
doc.: IEEE
September/2008
Beacon start at the beginning of slot (cont.)
Pros
Constant beacon preamble transmission and power saving of coordinator
Simple slot border detection
Cons
More power consumption of low duty cycle devices since device must listen before the beacon and assume the worst clock offset
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

9. Beacon end at the end of slot
January 2007
doc.: IEEE
September/2008
Beacon end at the end of slot
It is the coordinator’s duty to consider clock offset
Coordinator shall transmit before the scheduled time
But the beacon shall be end at the slot border
Device wakeup per its clock
Slot is described by the end of beacon
BAN superframe
Wakeup point
Start of beacon ……
Slot border
All devices
Start to listen
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

10. Beacon end at the end of slot (cont.)
January 2007
doc.: IEEE
September/2008
Beacon end at the end of slot (cont.)
Pros
Constant listening time and power saving of device
Cons
Coordinator must prepare the worst clock offset
Variable start time of beacon, which means variable preamble in beacon
More power consumption of coordinator
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

11. Dynamic beacon payload
January 2007
doc.: IEEE
September/2008
Dynamic beacon payload
Slot border can be determined by the end of preamble plus a constant of time delay
When real payload is less than the constant number, the left time to slot edge is known.
When real payload is more than the constant number, the beacon can cross to the next slot. The slot edge can be determined by the part of beacon payload.
Constant duration
Extra-preamble
Known duration
Normal preamble
portion
Slot border
Beacon frame
Slot border
Data portion
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

12. Where are the differences?
January 2007
doc.: IEEE
September/2008
Where are the differences?
Slot border in BAN superframe
Preamble
Data
To combat clock offset, extra Rv of beacon preamble must be 2Γ
B-B
Beacon listen
Extra transmission
Extra listening
Frame delimiter
To combat clock offset, extra Tx/Rv of beacon preamble must be Γ
B-E
Beacon listen
time
Slot border
Beacon frame
Slot border
Extra Tx/Rv
Normal preamble portion
Data portion
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

13. Where are the difference? (cont.)
January 2007
doc.: IEEE
September/2008
Where are the difference? (cont.)
B-B
B-E
Transmit of beacon preamble
Constant preamble
Additional preamble symbols
Listen of beacon preamble
Wakeup before the beacon preamble
Wakeup during the beacon preamble
Slot boundary
At the beginning of beacon
At the frame delimiter and a constant delay
Maximal sleeping time
No limitation
Limited by slot duration, frame delimiter and clock accuracy
Power
More power to listen at device
More power to transmit at coordinator
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

14. Clock offset estimation
January 2007
doc.: IEEE
September/2008
Clock offset estimation
Clock drift in a unit time can be measured and partially compensated to enable longer inactive period
Devices use its own clock to count the duration between two beacons, or
clock drift can be measured during synchronization
timestamp
Known duration per coordinator’s clock: Tc ……
Wakeup point
Wakeup point
Measured duration per device’s clock: Td
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

15. Clock drift compensation
January 2007
doc.: IEEE
September/2008
Clock drift compensation
Clock estimation accuracy can be ±10ppm
Clock drift compensation can be implemented by control the VCO of clock circuit
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips

16. Conclusions Two beacon designs in the BAN superframe
January 2007
doc.: IEEE
September/2008
Conclusions
Two beacon designs in the BAN superframe
Beacon starts at the beginning of a slot
Beacon ends at the end of a slot
B-E can save device’s power and maintain slot structure of BAN superframe
To enable TDMA based channel access
Zhen, Li, Li and Kohno
Carlos Cordeiro, Philips