doc: ieee 802.11-06/0956r2november 2006 submission joe kwak, interdigital 1 preferred channel for...

Submission Joe Kwak, InterDigital1

doc: IEEE 802.11-06/0956r2November 2006

Preferred Channel for Power Saving

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2006-NOV-15Authors:

Name Company Address Phone emailJoe Kwak InterDigital Bolingbrook, IL 630-739-4159 [email protected]

MarianRudolf

InterDigital 1000 Sherbrooke W.Montreal, QC, CanadaH3A 3G4

+1 514 904 6258 [email protected]

JariJokela

Nokia +358 50 486 0445 [email protected]

Tim Olson Consultant 408-505-1742 [email protected]



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.



OUTLINE Currently Specified Channel Space Power Savings using Preferred

Channel New Preferred Channel Definition Use of Preferred Channel Other Considerations Implementation Example Straw Poll



Currently Specified Channel SpacePer Annex J in draft 9.0 of 802.11ma Specification and including TGk draft 6.0.

NEW CONCEPT: Define one channel in each defined Channel Set 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.

Band

Region

Count of Regulatory

Classes

Count of Unique Defined

Channel Sets

Count of Unique Defined

Channels 2.4 GHz USA 1 1 11 2.4 GHz Europe 1 +1 +2 2.4 GHz Japan 2 +1= 3 TOTAL +1 = 14 TOTAL 5 GHz Europe 3 3 19 5 GHz USA 11 +4 +22 5 GHz Japan 29 +6 = 13 TOTAL +32 = 73 TOTAL



Preferred Channel Power Savings for 2.4GHz

Band

Region

Defined Channel Set

2.4 GHz USA 1-11 2.4 GHz Europe

& Japan 1-13

2.4 GHz Japan 14

Only scan 1 channel per defined channel set. In USA or Europe need to scan only 1 channel. In Japan need to scan only only 2 channels. If Region is unknown, need to scan only 2 channels Power is saved by scanning only 1 or 2 channels instead of 14, ===> 85%

less scanning.



Preferred Channel Power Savings for 5 GHz

Only scan 1 channel per defined channel set. 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 7 of 32 channels (78% less). If unknown, need to scan only 15 of 73 channels (80% less).

Band Region Defined Channel Set 5 GHz USA & Europe 36,40,44,48 5 GHz USA & Europe 52,56,60,64 5 GHz USA & Europe 100,104,108,12,116,120,124,128,132,

136,140 5 GHz USA 149,153,157,161 5 GHz USA 165 5 GHz USA 1,2,3,4,5,6,7,8,9,10 5 GHz USA 11,13,15,17,19 5 GHz USA 21,25 5 GHz Japan 34,38,42,46 5 GHz Japan 8,12,16 5 GHz Japan 184,188,192,196 5 GHz Japan 7,8,9,11 5 GHz Japan 183,184,185,187,188,189 5 GHz Japan 6,7,8,9,10,11 5 GHz Japan 182,183,184,185,186,187,188,189



NEW Definition for Preferred Channel

Selecting one fixed Preferred Channel within each defined channel set will not meet European regulations for uniform spreading.

Uniform spreading requires aggregate equiprobable channel selection from the available channel set.

Preferred Channel is randomly reselected daily for each defined channel set.

This satisfies European regulations and is sufficient to provide 80% power savings in all regulatory domains.



Preferred Channel Definition Preferred Channel is randomly selected using the same

Pseudo Random Number Generator (PRNG) already used in 802.11 for WEP encryption.

Procedure RC4 is called to generate a random number which selects the Preferred Channel for each day:

DATE= YYYY*365 + MM*31 +DD where DDMMYYYY is the current date

SEED= DATE*10E12 +DATE*10E6 +DATE Preferred Channel Order = (call RC4(SEED,64))modQ

where a call to RC4() returns a random 64 bit number andwhere Q is the number of channels in a defined channel set

Preferred Channel Order indicates which channel (first, second, third, etc.) in the defined channel set to use as the Preferred Channel.



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 !!



Net Discovery in Dual Mode STAs

WIFI covers 10% of cities, 1% of states >90% of dual mode STAs doing net discovery MAJOR Impact on dual mode product standby time.

Cellular Metro Coverage areaWIFI Metro Coverage area

Metro Coverage area



Network Entry Process

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

X n

X 1

Without Preferred Chan With Preferred Chan

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 !)

(Network Discovery Phase)



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



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

Country RegulatoryClass

BSSChannel

CurrentTXID

NextTXID Timing

Octets: 3 1 1 1 1 2



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.



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.



NetAd Duty Example

All STAs in "pool" for NetAd duty randomly select time within the first TBTT in the 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.

Operating Chan

Net Ad IntervalBeacon 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

Net Ad IntervalBeacon 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

On-Duty Net Ad+



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.



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 transmissions on Preferred Channel provide pointer to active BSS channel decrease number of scanned channels and 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



STRAW POLL

Do you support use of Net Advice on designated Preferred Channels to improve STA power savings?

YES _______ NO _______ ABSTAIN _______

doc: ieee 802.11-06/0956r2november 2006 submission joe kwak, interdigital 1 preferred channel for...

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