1. Panasonic Singapore Laboratories
TG5 Teleconference #3 21/02/2006
Michael Sim
Panasonic Singapore Laboratories

2. Time Synchronization (Overview)
In 15.3, a PNC provides time synchronization to all DEVs and child/neighbor piconets. (section 8.6 Synchronization)
In IBSS mode (ad hoc mode where EVERY device beacons) time synchronization, every station maintains a TSF (Time Synchronization Function) timer. Each device adopt the timing received from beacon or any probe response that has a TSF value later than its own TSF timer. (section 11.1 Synchronization)
In time synchronization, we synchronized to a reference device rather than a “Slot Boundary” or a “BP start time” because those are relative and may be different from each device’s perspective due to clock inaccuracy.
Mentioned in doc slide 15, that for distributed beaconing to work optimally, how to do MS or time synchronization need to be tackled
2019/6/16
Panasonic Singapore Lab

3. Time Synchronization (How?)
Suggestions:
Use similar TSF as
Every beacon includes TSF timer
Every device follows the fastest/slowest TSF and its adopt slot boundary
Philips proposed following the fastest device in guard interval
Clarifications:
Non-BP approach have the option to synchronize slot boundary using standard methods stated above
For distributed beaconing to work optimally, non-BP approach only need to synchronize slot-boundary
For BP approach, not just slot boundary need to be synchronized, the start of superframe need to synchronized such that all start at the same slot
2019/6/16
Panasonic Singapore Lab

4. Time Synchronization (Details)
Using guard time for synchronization:
Note:
For Non-BP approach, do not need “late start guard time” as CAP is contention based
RX-TX turnaround time is 10µs for 15.3 PHY
Reference for 15.3 guard time calculation in section Guard Time
Non-BP approach
BP approach B
CAP B
Early start
Guard time
Early start
Guard time
Early start
Guard time
Beacon
CAP
Beacon
Beacon
RX-TX
turnaround time
RX-TX
turnaround time
RX-TX
turnaround time
Late start
Guard time
RX-TX
turnaround
time
2019/6/16
Panasonic Singapore Lab

5. Panasonic Singapore Lab
Power Saving Issue
How much power does it require to switch a PHY from RX to TX (and vice-versa)?
Does switching PHY to RX/TX mode for beacon frame TX or RX constitutes significant power issue?
Let:
PS be power consumed to switch to PHY RX/TX mode
TS = RX-TX turnaround time
PSRX be the power consumed to be in RX mode for duration of TS
PBTX and PBRX be the power required to receive and transmit beacon frame respectively
Question 1: Is PS >> PRX ?
Question 2: How much power does it take for a particular device for beaconing? (Assume N beaconing devices)
2019/6/16
Panasonic Singapore Lab

6. Panasonic Singapore Lab
Power Calculation (1)
Case 1: Non-BP Approach:
Assumption:
Do not include power consumed while listening in guard time
Power used:
= 2PS + PBTX + (PS + PBRX)(N-1)
= [PBTX + (N-1)PBRX] + (N+1)PS
x (N-1) PS
PBTX PS PS
PBRX … …
2019/6/16
Panasonic Singapore Lab

7. Panasonic Singapore Lab
Power Calculation (2)
Case 2: BP Approach:
Assumption:
Do not include power consumed while listening in guard time
Do not include power consumed while listening to additional 3 announcement slots
Power Used:
= PS + PBRX + (PRX + PBRX)M + PS + PBTX + PS + PBRX + (N-M-3)(PRX + PBRX) + PS
= [PBTX + (N-1)PBRX] + 4PS + (N-3)PRX
1 Beacons
x M
x 2
x (N–M–3) PS
PBRX
PRX
PBRX PS
PBTX PS
PBRX
PRX
PBRX PS … …
2019/6/16
Panasonic Singapore Lab

8. Panasonic Singapore Lab
Power Calculation (3)
Verdict: On top of power required to RX and TX beacon frames,
Non BP method needs additional: (N+1)PS
BP method needs additional: 4PS + (N-3)PRX
If PS ≈ PRX, Power required for both is about the same
Note that:
BP method have additional guard time and RX time during guard time and is not considered in calculation
BP method requires additional 3 announcement slots which is also not considered
2019/6/16
Panasonic Singapore Lab

9. Already provide backward
Power Saving Issue (2)
What if PS >> PRX ?
If so, to provide backward compatibility to 15.3, in using beaconing using beacon period + additional PN beaconing, isn’t it a power issue?
BP approach
Non-BP approach
< +
Already provide backward
compatibility to 15.3
2019/6/16
Panasonic Singapore Lab

10. Panasonic Singapore Lab
In Summary…
Time synchronization is important for distributed beaconing
Provide slot boundary synchronization
Optimal use of medium access time
Details need to be worked out. (Good news: There are existing methods we can use )
Panasonic proposal provides for time synchronization
Same time synchronization method can be used for beaconing or non-beaconing approach
Non-beaconing approach does not need to synchronize superframe start time
Power consumption in switching from RX to TX (and vice versa) for beacon TX and RX is lesser in non-beaconing approach since inherently it is already fully compatible with 15.3 superframe structure and does not need to perform additional PN beaconing
2019/6/16
Panasonic Singapore Lab