1. doc.: IEEE 802.11-12/0130r0 Submission January 2012 Seunghee Han, LG ElectronicsSlide 1 Beacon Reception of Long Sleeper Date: 2012-01-16 Authors:

2. doc.: IEEE 802.11-12/0130r0 Submission January 2012 Seunghee Han, LG ElectronicsSlide 2 Authors:

3. doc.: IEEE 802.11-12/0130r0 Submission Introduction TSF (Time Synchronization Function) timer accuracy –For STAs in a long sleep state (e.g., over 10 min.), problems of the TSF timer accuracy may arise Example: When the timer accuracy is ±0.01%, after 1000s, it becomes ±100ms –Due to the expanded possible TSF timer offset, such longer sleeper may not easily find periodic beacon frames January 2012 Seunghee Han, LG ElectronicsSlide 3

4. doc.: IEEE 802.11-12/0130r0 Submission Introduction Most sensor devices in 11ah are long sleepers [1,2] –Current spec. states that the accuracy of the TSF timer shall be no worse than ±0.01% Considering the worst case accuracy, after 1000s the time offset becomes ±100ms, almost like a beacon interval But, if the TSF timer accuracy of an AP is ± 0.001%, TSF timer error of the AP is ±10ms when the sleep period is 1000s –If TSF timer error becomes larger, anticipating Target Beacon Transmission Time (TBTT) becomes much harder To a STA listening to a Beacon frame, it should wake up at 100ms before for ±0.01% timer accuracy (the worst case) January 2012 Seunghee Han, LG ElectronicsSlide 4

5. doc.: IEEE 802.11-12/0130r0 Submission Beacon Reception of Long Sleeper TSF timer accuracy information from AP –If a STA knows TSF time accuracy information of an AP, it can calculate the TSF timer error occurred during its sleep period –Then, the STA can wake up at more exact time and it can reduce the unnecessary power consumption January 2012 Seunghee Han, LG ElectronicsSlide 5

6. doc.: IEEE 802.11-12/0130r0 Submission Beacon Reception of Long Sleeper Actual TSF timer accuracy –Power saving gain of the proposal depends on the actual TSF timer accuracy value of AP & STA Proposal: Announce the TSF timer accuracy information of AP to STAs If the accuracy isn’t much better than the worst case (±100 ppm), the effect of the TSF timer accuracy information is insignificant –Actual timer accuracy In general, oscillator accuracy value for WLAN is ±1ppm ~ ±50ppm –http://www.taitien.com.tw/en/applications_wimax.aspxhttp://www.taitien.com.tw/en/applications_wimax.aspx Various timer accuracy values for WLAN devices January 2012 Seunghee Han, LG ElectronicsSlide 6

7. doc.: IEEE 802.11-12/0130r0 Submission Beacon Reception of Long Sleeper Ex1) STA w/o TSF timer accuracy vs. STA w/ TSF timer accuracy –Beacon listening interval: 600s (10min) –AP timer accuracy: ±5ppm, STA timer accuracy : ±10ppm –STA knows its timer accuracy –STA w/ TSF timer accuracy can obtain power saving gain of (69-12)/69 = 82.6% January 2012 Seunghee Han, LG ElectronicsSlide 7

8. doc.: IEEE 802.11-12/0130r0 Submission Beacon Reception of Long Sleeper Ex2) STA w/o TSF timer accuracy vs. STA w/ TSF timer accuracy –Beacon listening interval: 600s (10min) –AP timer accuracy: ±20ppm, STA timer accuracy : ±10ppm –STA knows its timer accuracy –STA w/ TSF timer accuracy can obtain power saving gain of (78-30)/78 = 61.5% January 2012 Seunghee Han, LG ElectronicsSlide 8

9. doc.: IEEE 802.11-12/0130r0 Submission Beacon Reception of Long Sleeper Advantages of the TSF timer accuracy information –More flexible for various TSF timer accuracy values STA can predict TBTT more accurately for various TSF timer accuracy values E.g. 1) Wi-Fi Direct –A Group Owner (GO) stays awake and transmits beacon frames –This operation requires large power consumption –To reduce the power consumption, this GO can increase clock interval, even though it has an accurate oscillator –Then, the timer accuracy of this GO will become worse –But, overhead for TSF timer accuracy information is very small TSF timer accuracy information can be transmitted in Association Response This information requires only few bytes January 2012 Seunghee Han, LG ElectronicsSlide 9

10. doc.: IEEE 802.11-12/0130r0 Submission Conclusions Longer sleeper may not easily find periodic beacon frames For reducing the power consumption of listening to Beacon frame, an AP may provide its TSF timer accuracy information to a long sleeper –Long sleeper can wake up at more exact beacon reception time January 2012 Seunghee Han, LG ElectronicsSlide 10

11. doc.: IEEE 802.11-12/0130r0 Submission References [1] Rolf de Vegt, “Potential Compromise for 802.11ah Use Case Document,” 11-11/457r0. [2] Minho Cheong, “TGah Functional Requirements and Evaluation Methodology,” 11-11/905r4. January 2012 Seunghee Han, LG ElectronicsSlide 11

12. doc.: IEEE 802.11-12/0130r0 Submission Straw Poll 1 Do you support that an AP may provide its TSF timer accuracy information to non-AP STAs ? –Y: –N: –A: January 2012 Seunghee Han, LG ElectronicsSlide 12