1. Preferred Channel for Power Saving
January 2003
IEEE /100r1
Preferred Channel for Power Saving
2006-SEP-21
Authors:
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Joe Kwak, InterDigital
Submission

2. January 2003
IEEE /100r1
Introduction
Many new battery powered, phone-like devices for WLAN VoIP are entering the market.
Since WLAN geographic coverage is very limited (compared to cellular), these devices will use much power in channel scanning to locate an available network.
Standardized Channel Selection practices can save significant power (>80%) by limiting the number of channels scanned during initial network discovery.
New Preferred Channel defined here does this.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

3. OUTLINE Currently Specified Channel Space
New Preferred Channel Definition
Use of Preferred Channel
Power Savings using Preferred Channel
Other Considerations
Implementation Example
Straw Poll
Joe Kwak, InterDigital
Submission

4. Currently Specified Channel Space
Per Annex J in draft 6.0 of ma Specification and including TGk draft 4.1.
NEW CONCEPT: Define one channel in each Regulatory Class as the
"Preferred Channel" and insure there is always activity on that channel.
An Idle Preferred Channel means that all channels in that Regulatory Class
are idle. This greatly speeds Network Discovery.
Joe Kwak, InterDigital
Submission

5. Preferred Channel Definition for 2.4GHz
In USA or Europe need to scan only 1 channel.
In Japan need to scan only only 2 channels: 1& 14.
If Region is unknown, need to scan only 2 channels: 1 & 14.
Power is saved by scanning only 1 or 2 channels instead of 14, ===> 85% less scanning.
Joe Kwak, InterDigital
Submission

6. Preferred Channel Definition for 5 GHz
In USA need to scan only 8 of 41 channels (80% less).
In Europe need to scan only 3 of 19 channels (84% less).
In Japan need to scan only 6 of 32 channels (81% less).
If unknown, need to scan only 14 of 73 channels (81% less).
Joe Kwak, InterDigital
Submission

7. Power Savings for Network Discovery
Power savings is obtained by reducing number of scanned channels when searching for available BSS when STA is not connected to any network.
Power savings of 80-85% is guaranteed no matter what scanning mode or scanning period is used by the STA.
APs monitor Preferred Channel for the operating Regulatory Class and ensure that Preferred Channel is active.
STAs which passively scan a Preferred Channel and detect no activity need not scan any other channels in that Regulatory Class.
For mobile STAs out of radio range of any WLAN, network discovery is the only STA task and consumes 100% of the terminal's power.
For these STAs, power savings is very significant and can multiply standby time by a factor of 5 !!
Joe Kwak, InterDigital
Submission

8. Net Discovery in Dual Mode STAs
Cellular Metro Coverage area
WIFI Metro Coverage area
Metro Coverage area
WIFI covers 10% of cities, 1% of states
>90% of dual mode STAs doing net discovery
MAJOR Impact on dual mode product standby time.
Joe Kwak, InterDigital
Submission

9. Without Preferred Chan
Network Entry Process
Without Preferred Chan
With Preferred Chan
X n
Scan all channels
Find Beacon
Get AP Channel Report
Scan other channels
Select BSS/channel
Associate
Get Neighbor report
Scan preferred channels
Find Beacon or Get Beacon on NetAd channel
Get AP Channel Report
Scan other channels
Select BSS/channel
Associate
Get Neighbor report
(Network Discovery Phase)
X 1
For dual mode roaming STA, up to 90% of time spent in first step.
Use of Preferred Channel reduces power by >80% in first step. (.8 savings x .9 time: significant !)
Joe Kwak, InterDigital
Submission

10. Use of Preferred Channel
Preferred channel is favored when selecting channel for BSS operation.
NEW RULES:
1. AP will select Preferred Channel for operation unless: a. it is already in use b. it is unsuitable based on the AP's channel selection rules c. it has unacceptable interference, or is otherwise unsuitable.
2. AP operating on non-preferred channel shall: a. monitor Preferred Channel for continued activity b. if Preferred Channel is inactive, AP shall select STAs for Net Advice duty on Preferred Channel
3. STAs selected for Net Advice duty shall: a. share responsibility for transmitting Net Advice on preferred channel b. on-duty STA shall transmit Net Advice frame once each beacon period for an entire Net Advice Interval
Joe Kwak, InterDigital
Submission

11. NET ADVICE FRAME
If no BSS is operating on preferred Channel, Net advice frames are transmitted at the beacon rate and "point to" operating BSS channel.
Net Advice always transmitted at lowest rate and highest power.
Net Advice frame advertises the operating BSS of the on-duty STA:
Country, Regulatory Class, and BSS Channel values are for the BSS in which the on-duty STA is associated.
TXIDs and Timing provide information to coordinate the continued provision of Net Advice frames on the channel:
Current TXID: lowest byte of MAC address of transmitting STA
Next TXID: lowest byte of MAC address of next STA to transmit
Net Ad interval: period in which on-duty STA transmits Net Ad frames
Next Start: countdown to beginning of next Net Advice Interval
Joe Kwak, InterDigital
Submission

12. European Radar Regulations
Regulations prohibiting WLAN transmissions when radars are operating must always be followed.
Where regulations apply, an AP initiating Net Advice transmissions on an idle Preferred Channel shall ensure compliance with local regulations.
On-duty STAs transmitting Net Advice on the Preferred Channel shall be disabled by AP if regulations prohibit transmission on Preferred Channel.
STA doing network discovery which detects radar on Preferred Channel may scan all other channels for that Regulatory Class, i.e. fallback to current practice.
Joe Kwak, InterDigital
Submission

13. Shared Burden for Net Advice
Every STA has an enable bit for Net Advice functions which is set/reset by the AP.
The AP may configures the Net Advice Enabled bits for all BSS STAs to assign Net Advice duties on the Preferred Channel.
The AP may assume the duty and/or may select a number of STAs to share the duty to transmit the Net Advice frames.
The AP should not select battery limited STAs for Net Advice duty.
Selected STAs shall use a defined coordination technique to pass Net Advice duty from one STA to the next, each STA providing Net Advice frames for a single Net Advice Interval.
STA providing Net Advice shall have flexibility in scheduling its off-channel Net Advice duties along with its normal BSS operations.
If multiple BSSs are operating in the same regulatory class, selected STAs from all BSSs shall share duty to provide Net Advice frames.
Joe Kwak, InterDigital
Submission

14. NetAd Duty Example Operating Chan Net Ad Interval Beacon Interval
January 2003
IEEE /100r1
NetAd Duty Example
Operating Chan
Net Ad Interval
Beacon Interval
Preferred Chan
On-Duty Net Ad-
Next STA Net Ad+
On-Duty Net Ad+
Net Ad Duty Baton Pass
On-duty STA channel switch to preferred channel
All STAs in "pool" for NetAd duty randomly select time within next NetAd Interval for baton pass procedure.
Each STA in "pool" executes baton pass procedure at the selected time.
First STA to do baton pass gets duty assignment for next NetAd Interval.
This "shares" NetAd burden among all TGv STAs from ALL BSSs in local area, even without the need for a TGv AP.
Joe Kwak, InterDigital
Submission

15. January 2003
IEEE /100r1
NetAd Duty States
STA maintains state variable to implement Preferred Channel Procedure
Three Duty States are defined:
NO_DUTY: Entry state for NetAd duty and used to synchronize Interval Timing with other NetAd STAs. Can be steady state while BSS is operating on Preferred Channel.
ON_DUTY: STA has responsibility to transmit NetAd frames on Preferred Channel once each TBTT and to maintain Interval timing. Also has responsibility to handoff duty to another STA for next Interval.
OFF_DUTY: STA has responsibility to monitor Preferred Channel at the beginning of each Interval and to use random time draw to accept duty for next Interval.
Joe Kwak, InterDigital
Submission

16. Conclusions
This simple channel use convention can save significant power for STAs doing network discovery, multiplying standby time by a factor of 5.
New Net Advice function provides information on Preferred Channel to speed network discovery.
AP manages resources for Net Advice so that per-STA implementation burden is very low.
Net Advice on Preferred Channel is proposed in TGv for power savings
STRAW POLL FOR SUPPORT
Joe Kwak, InterDigital
Submission

17. STRAW POLL
Do you support use of Net Advice on designated Preferred Channels to improve STA power savings?
YES _______
NO _______
ABSTAIN _______
Joe Kwak, InterDigital
Submission