1. Speculative Power Save concept
September 2006
doc.: IEEE /1461r0
September 2006
Speculative Power Save concept
Date:
Authors:
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Peter Ecclesine, Cisco Systems
Peter Ecclesine, Cisco Systems

2. September 2006
doc.: IEEE /1461r0
September 2006
Abstract
Speculative Power Save enhances standby time by letting stations get back to sleep sooner
The enhancements are related to TGv Objective: Power Saving (Req. #2010).
The text is aligned with P REVma/D8.0 and P802.11v-D0.04.
Peter Ecclesine, Cisco Systems
Peter Ecclesine, Cisco Systems

3. September 2006
Req 2010: Power Saving
“TGv shall support one or more power saving schemes to optimize the STA’s power consumption during prolonged time periods of no transmission or reception activity in the order of several hundred’s of ms’s or above.”
In every 24/7 week, probably 60 hours are not busy ;-) and when a STA is not transmitting much, it still needs to receive beacon frames from the Access Point
Receiving and processing beacon frames is a substantial component of standby time power consumption
Peter Ecclesine, Cisco Systems

4. September 2006
Overview
[11.2] Power Management uses the Traffic Indication Map (TIM) in every AP beacon frame to indicate that buffered MSDUs are available to STAs that are in Power Save mode.
[ ] A ‘zero TIM’ is a six octet Information Element indicating no buffered MSDUs for any STA.
Observation – there is a Reserved bit in every PLCP header, and it is protected by the PLCP header checksum
Induction – if a Reserved bit in PLCP headers of beacon frames was defined ‘Zero Traffic Beacon Indication’, then STAs could Power Save until the next beacon time
Peter Ecclesine, Cisco Systems

5. Estimating Power Savings
September 2006
Estimating Power Savings
Must process PLCP header in any case
Should process 22 octets of general frame
Frame Control (2) , Duration/ID (2), three address fields (18)
Beacon frames have many additional elements – Table 26 plus an FCS (4)
Timestamp (8), SSID (2-34), Supported rates (3), TIM (6-256), Country (8-256), Power Constraint (3), Supported Channels (4-256), Extended Rates (3-257), Extended Capabilities (3-257)
Minimum ratio of power to process beacon frame could be ~22: (22+44) or ~ one half less power consumption
Peter Ecclesine, Cisco Systems

6. PLCP headers and checksums
September 2006
PLCP headers and checksums
Service octet - Reserved octet (b0-b7)
Signal octet - 1 Reserved bit (b4)
Service octet - 5 Reserved bits (b0, b1, b4, b5, b6)
Service octet - 3 Reserved bits (b0, b1, b4)
CRC-16
bit parity of Signal bits 0-16
, CRC-16
19 – same as clause 17 OFDM or clause 18
Peter Ecclesine, Cisco Systems

7. Why is this ‘Speculative?’
September 2006
Why is this ‘Speculative?’
The receiving STA could process just beacon frame PLCP header, Frame Control field and address fields, and decide to doze, without receiving and processing the entire frame
The decision is based on the nominal values of reception quality indicators actually measured during the reception of those fields, and the assumed correctness of the PLCP header and fields processed
If reception quality is low, remain awake and process the entire frame
Peter Ecclesine, Cisco Systems

8. What if ‘doze’ is chosen in error?
September 2006
What if ‘doze’ is chosen in error?
[ ] ‘ListenInterval’ controls AP aging, and AP may discard any buffered traffic.
‘The exact specification of the aging function is beyond the scope of this standard.’
TGv can specify that the aging function be after double the ‘ListenInterval’ when Speculative Power Save is in use, which is only for ‘Zero Traffic Beacon Indication’ beacon frames.
This gives Power Save STAs some grace in low traffic times
Peter Ecclesine, Cisco Systems

9. Zero Traffic Beacon Indication
September 2006
Zero Traffic Beacon Indication
The ZTBI bit in beacon frame PLCP headers indicates:
Zero TIM: a TIM where the DTIM count is zero, and there are no buffered broadcast, multi-cast or unicast frames.
No frame elements requiring action in the regulatory domain (e.g. no DFS Channel Switch Announcement)
Helps with the wireless VLAN problem
Sets of beacon frames for each VLAN means there are lots more beacon frames per second.
Helps in home networks
Multiple WLAN devices in use, many 24/7
Peter Ecclesine, Cisco Systems

10. September 2006
Operational behavior
Speculative Power Save should be used by all TGv compliant STAs in Infrastructure mode (A PC12)
Peter Ecclesine, Cisco Systems

11. September 2006
Questions/Answers
Peter Ecclesine, Cisco Systems

12. September 2006
Strawpoll
Move to create normative text describing Speculative Power Save for inclusion into the TGv draft.
In favor:
Not in favor:
Abstain:
Peter Ecclesine, Cisco Systems