1. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 1 Paging Power Saving Analysis Update 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 Date:2007-01-12 Authors:

2. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 2 Abstract This document provides a range of power saving analysis in support of Idle Mode and WLAN Paging proposal (doc 11-07-0060r0), based on different use cases and device power consumptions.

3. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 3 Agenda Motivation Idle Mode and Paging Concepts Power Consumption Models Power Saving Benefit

4. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 4 Extend battery standby hours for handhelds and Ultra Mobile PCs in support of applications such as: - VoIP over WLAN - Instant Messenger - Push Email Motivation

5. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 5 Power Consumption Issues When a standby mode STA is moving, the STA has to wake up to re-associate with the visited APs, which causes: –Scanning –BSS transition Needs to wake up OS Key Management and Derivations Exchange of Authentication and Reassociation messages

6. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 6 Introducing Idle Mode and Paging Idle Mode: save power and resources –STA enters “deep sleep” if there is no outgoing/incoming traffic –If STA roams out of the coverage area of the last known associated AP, STA doesn’t need to reassociate with a new AP when it is in “idle mode” Paging: wake STA to receive packet –Infrastructure will “page” the client if there is incoming traffic –STA wakes up at a longer “sleep” interval to check for incoming frame, and STA will associate with an AP when it receives the “paging” Protocol Overview (Beacon/Probe Response) –Idle Mode Request (STA  AP) and Response (AP  STA) frames –Enter Idle Mode/Exit Idle Mode –Paging Indication element –Included in the Beacon frame at Paging Interval –Included in the Probe Response frame as per STA requests

7. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 7 Power Saving Analysis Modes Considered and Assumptions Legacy Power Saving Mode (PSM) –The STA is on standby (i.e., it has no data to send/receive) –STAs wake up at Listen Interval (configurable, e.g. 2sec) to receive Beacon and check whether there is any incoming traffic –Roaming requires scanning and re-association Paging Mode (PM) –The STA is on standby (i.e., it has no data to send/receive) –STAs wake up at paging Interval (configurable, e.g. 2sec) to receive Beacon and check whether there is any incoming traffic –No required re-association while roaming within the Paging Group, but needs scanning to find an AP in the paging group Note that any layer 3 and above messages, e.g. Multicast/broadcast/keep- alive, are not considered for either mode.

8. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 8 Power Consumption Model Standby Hours (SH) –SH = Battery Capacity (WATTHOUR)/PC Power Consumption (PC), mW –Power Consumption while Receiving Beacons (PC_B) Total receiving beacon time over an hour (BT) = awake time receiving beacon(11.7ms or 11.8ms) *(3600s/2s between beacons) PC_B = BT/3600000ms * (Device_Idle_PC + RF_Rx_PC) –Power Consumption while Roaming (PC_R) Total Roaming Awake Time (RAT) P_R = RAT/3600000ms * (Device_Idle_Active_PC + RF_Tx_Rx_PC) –Power Consumption while Idle (do nothing) (PC_I) Idle time (IT) = 3600000ms – BT - RAT PC_I = IT/3600000ms * (Device_Idle_PC + RF_Idle_PC) –Total Power Consumption: PC = PC_B + PC_R + PC_I

9. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 9 Awake Time and PCPSM Mode STAPaging Mode STA Scanning time (ST)Active scanning per channel: 12ms to 20ms = 2 ms + 10ms/18ms Passive scanning per channel: 105ms = 100ms + 5 ms Active scanning with a perfect.11k support: 36 ms : 12ms x 3 (only.11g) Active scanning maximum with no 11k support: 480ms : 20ms x (11+13) (dual band, all channels) Active scanning (assumed): 240ms= 20ms x 12 (dual band) * Passive scanning : 1856ms = 20ms x 11 + 105ms x 8 (dual band) Passive scanning (assumed) : 500ms =~520ms=20ms x 5 + 105ms x 4 (dual band) Number of triggered scans/roams over an hourNN/2 ** System resume time (SRT)Phone: 50ms; UMPC: 500ms0 Transition time (TT)11r: 50ms;0 Waiting time after Assoc. (WT)Average 50ms0 *** Total Roam Power Consumption (PC-R): Note: RF_Rx_Tx_PC = 0.4 * RF_Tx_PC + 0.6 * RF_Rx_PC 1/3600000 x N (ST * (Device_Idle_PC +RF_Rx_Tx_PC) + SRT * 2 * (Device_Active_PC + RF_Rx_PC) + (TT+WT) * (Device_Active_PC + RF_Rx_Tx_PC)) 1/3600000 * N/2 * ST * (Device_Idle_PC + RF_Rx_Tx_PC) Roam Awake time (RAT) and Power Consumption *“An Empirical Analysis of the IEEE 802.11 MAC Layer Handoff Process” by Arunesh Mishra et al. **Paging scan is less frequent than a legacy device roaming scan, at the ratio of cell size and beacon coverage. Ratio could be: 1/1 ~ 1/4. The more optimized and highly dense the network, the larger difference. Ratio of ½ is assumed here. See backup slides. ***Paging Indication received in Probe Response during the active scanning

10. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 10 Use Cases and Estimated BSS Transition Rate Assume AP Cell Radius is ~40ft and Walking speed is ~ 4 ft/s. Our statistical data shows Average Time in Cell (ATC) is ~30s (conservatively) Carpeted Enterprise –Assume an engineer moves 1 time per hour for a meeting or break, 5 minutes walking per office hour. –Estimated total transitions over an office hour: 5*60s/30s = 10 Manufacturing (e.g. Semiconductor Fabrication) –Assume a Fab technician walks 30 minutes per hour wearing a WiFi phone, although sometimes those movements might be within the same cell (25%) –Estimated total transitions per working hour: 30*60/ 30s *75%= 45 Hospital –Best case: Assume a hospital nurse walks 30 minutes per working hour wearing a WiFi phone or carrying a UMPC. At times, though, those movements might be within the same cell (25%). –Estimated total transitions per working hour: 30*60/ 30s*0.75 = 45 –Note that a lot of interference in a hospital setting may cause more scans and roams. Based on the various BSS transition rates, the following power consumption comparison is given in a range of [0 roams, 60 roams]

11. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 11 Power Consumption Comparison based on various Data Sets We have calculated power consumption comparisons based on: –Roam rate in a range of [0 roams, 60 roams] –Scanning time at: 36ms, 240ms and 500ms –3 Phone devices and 3 UMPC devices with various Tx/Rx//Idle Power Consumption data –Phone - 400mW/200mW/3mW –Phone - 550mW/350mW/5.5mW –Phone - 800mW/500mW/5.5mW –UMPC - 500mW/300mW/5.5mW –UMPC - 800mW/500mW/5.5mW –UMPC - 1200mW/800mW/5.5mW

12. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 12 UMPC Standby Hours – Scanning Time @ 240ms Battery Capacity = 11840 mWH // 3200mA x 3.7 V RF_Tx_PC = 800mW RF_Rx_PC = 500mW RF_Idle_PC = 5.5mW Device_Active_PC = 1200mW Device_Idle_PC = 95mW 4.92% 22.10%

13. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 13 Phone Standby Hours - Scanning time @ 240ms Battery Capacity = 3240 mWH // 900mA x 3.6 V RF_Tx_PC = 550mW RF_Rx_PC = 350mW RF_Idle_PC = 5.5mW Device_Active_PC = 150mW Device_Idle_PC = 10mW 2.36% 10.65%

14. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 14 Power Saving Percentage - Scanning Time @36ms For a “less-mobile” user (10 roams per hour): 1.19% - 5.57% For a “more-mobile” user (45 roams per hour): 7.01% - 25.16%

15. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 15 Power Saving Percentage - Scanning Time @500ms For a “less-mobile” user (10 roams per hour): 2.73% - 6.12% For a “more-mobile” user (45 roams per hour): 12% - 27.08%

16. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 16 Summary With what we have done today, you can consider the power consumption of your devices and your use cases, and determine power saving benefits of WLAN Paging and Idle Mode proposal. Thank You!

17. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 17 802.11g AP Coverage Area* Coverage area Transmit power: 15dBm OFDM 90 95 100 140 180 210 250 300ft 54Mbps 48Mbps 36Mbps 24Mbps 18Mbps 12Mbps 9Mbps 6Mbps Sufficient to cover 20,000 sq. ft Sufficient to cover 60,000 sq. ft cover 306,000 sq. ft

18. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 18 Paging Mode Scanning at 2.4GHz

19. doc.: IEEE 802.11-07/0058r0 Submission January 2007 Emily Qi et alSlide 19 Battery Standby Hours Calculation Office/Working hours only shall be considered for standby hours calculation For a dual mode phone, if mobile user is not in the office and WiFi network is not available, device will connect to the cellular network. So battery life shall not be considered as part of WiFi standby hours. For a pure WiFi, if mobile user is not in the office, there are two possibilities: –Leave it at the office and power off – for energy efficiency concerns –Bring it home. WiFi network discovery on the way back home consumes a lot of power –In either case, battery life shall not be considered as part of WiFi standby hours.