1. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 1 Preferred Channel for Power Saving Notice: This document has been prepared to assist IEEE 802.11. 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org 2007-JAN-17 Authors :

2. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 2 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.

3. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 3 OUTLINE Currently Specified Channel Space Power Savings using Preferred Channel New Preferred Channel Definition Use of Preferred Channel Other Considerations Straw Poll

4. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 4 Currently Specified Channel Space Per 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.

5. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 5 Preferred Channel Power Savings for 2.4GHz 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.

6. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 6 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).

7. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 7 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.

8. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 8 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 and where 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.

9. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 9 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 !!

10. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 10 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 area WIFI Metro Coverage area Metro Coverage area

11. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 11 Network Entry Process Scan all channels 87 channels max Find Beacon Get AP Channel Report Scan other channels Select BSS/channel Associate Get Neighbor report Scan preferred channels 16 channels max Find Beacon or find Network Advice Frame 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, 90% of time spent in first step. Use of Preferred Channel reduces power by >80% in first step. (.8 savings x.9 time: significant !)

12. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 12 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 transmit or selects STA(s) to transmit Net Advice frames on Preferred Channel 3. Selected STAs shall transmit Net Advice on Preferred Channel: Once each beacon period (TBTT) At beacon data rate & at max transmit power Switches to Preferred Channel, transmits and switches back

13. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 13 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 transmitting STA is associated.

14. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 14 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.

15. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 15 Shared Burden for Net Advice The AP is responsible for initiating and controlling Network Advice function. Every STA has enable bit for Net Advice functions which is set/reset by the AP. The AP may set its own Net Advice Enabled bit and provide Net Advice transmission itself, with no STA action required. The AP may set Net Advice Enabled bit in one or more STAs, tasking idle STAs to provide Network Advice transmissions on the Preferred Channel. The AP should not select battery limited STAs for Net Advice duty. STA providing Net Advice shall have flexibility in scheduling its off-channel Net Advice transmission along with its normal BSS operations. If multiple BSSs are operating in the same regulatory class, selected STAs from all BSSs may share duty to provide Net Advice frames.

16. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 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 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. STAs need not be involved. Net Advice on Preferred Channel is proposed in TGv for power savings STRAW POLL & VOTE FOR SUPPORT

17. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 17 STRAW POLL Do you support use of Net Advice on designated Preferred Channels to improve STA power savings? YES _______ NO _______ ABSTAIN _______

18. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 18 Motion Move to include 07/0118r0 into next version of TGv draft Moved:_Kwak_____ Second:__________ YES _______ NO _______ ABSTAIN _______

19. doc: IEEE 802.11-07/0120r0January 2007 Submission Kwak, Rudolf, Jokela 19