Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [TG5 Teleconference #3 21/02/2006] Date Submitted: [ 07 March, 2006] Source: [Michael Sim] Company [Panasonic Singapore Laboratories] Address [Blk 1022 Tai Seng Avenue #06-3530, Singapore, Singapore 534415, Singapore] Voice:[+65-6550-5323], FAX: [+65-6550-5201], E-Mail:[michael.simhc@sg.panasonic.com] Re: [TG5 Teleconference session #3] Abstract: [Clarification on time synchronization required and power consumption by non-BP and BP method] Purpose: [To aid discussion in the IEEE 802.15.5 Task Group] Notice: This document has been prepared to assist the IEEE P802.15. 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 P802.15. 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 802.11 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 05-0469-01 slide 15, that for distributed beaconing to work optimally, how to do MS or time synchronization need to be tackled Michael Sim, Panasonic Singapore Laboratories

3. Time Synchronization (How?) • Suggestions: • Use similar TSF as 802.11 • 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 Michael Sim, Panasonic Singapore Laboratories

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 8.4.3.6 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 RX-TX turnaround time Late start Guard time Michael Sim, Panasonic Singapore Laboratories

5. 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) Michael Sim, Panasonic Singapore Laboratories

6. 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 … … Michael Sim, Panasonic Singapore Laboratories

7. 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 … … Michael Sim, Panasonic Singapore Laboratories

8. 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 Michael Sim, Panasonic Singapore Laboratories

9. 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 Michael Sim, Panasonic Singapore Laboratories

10. 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 Michael Sim, Panasonic Singapore Laboratories