1. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 1 802.11s Power Saving Issues Date: 2008-10-17 Authors:

2. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 2 Mesh Active Scanning

3. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 3 Baseline BSS Active Scanning An active scanning STA uses the following steps to find BSSes: –Performs the Basic Access procedure as defined in 9.2.5.1; –Sends a probe request to the broadcast destination address; –Clears and starts a ProbeTimer; –IF PHY-CCA.indication (busy) has not been detected before the ProbeTimer reaches MinChannelTime, then scans the nest channel; –When scanning time reach MaxChannelTime, processes all received probe response. The following are true for an STA/AP to send a probe response –In each BSS, there is at least an active STA to receive and respond to probe request; –In an IBSS, the STA that generated the last Beacon frame shall be the active STA that responds to a probe request; –An AP shall be always active to respond to the received probe requests.

4. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 4 Mesh Active Scanning An active scanning MSTA (mesh STA) uses the following steps to find MBSSes (Mesh BSS): –Perform the Basic Access procedure as defined in 9.2.5.1; –Send a probe request to the broadcast destination address; –Clear and start a ProbeTimer; –IF PHY-CCA.indication (busy) has not been detected before the ProbeTimer reaches MinChannelTime, then scan the nest channel; –When scanning time reach MaxChannelTime, process all received probe response. After each power saving MSTA sending beacon interval and being active in its peer service interval (if there is any peer service interval), it will doze again. So the following assumption is not true –In each MBSS, there is at least an active MSTA to receive and respond to probe requests. An active scanning MSTA may not find an MBSS even if there is an MBSS.

5. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 5 Proposed solution Option 1: Assist active scanning with passive scanning –If a MSTA can not find a MBSS through an active scanning, it may do a passive scanning. Option 2: Disallow active scanning in a MBSS –This may make MBSS finding procedure longer. Option 3: There is at least an active MSTA in an MBSS at any time. –It is difficult to find an method in the current mesh beaconing mechanism.

6. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 6 Mesh Path Selection with Power Saving

7. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 7 HMWP PREQ Retransmission PREQ shall be repeatedly transmitted by a source MSTA using binary exponential backoff: –dot11MeshHWMPnetDiameterTraversalTime (10TUs) for the first transmission; –2*dot11MeshHWMPnetDiameterTraversalTime (20TUs) for the second transmission; –4*dot11MeshHWMPnetDiameterTraversalTime (40TUs) for the third transmission… The default PREQ retrying number is 3. The mean frame delay added because of power saving in a light sleep MSTA is 100TUs. The delay of PREQ is even longer since PREQ is broadcast frame. –Multiple PREQs with different source sequence number (SSN) between the same source/destination pair may exist in an MBSS at the same time.

8. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 8 PREQ with Power Saving MSTA When MSTA4 is in doze state, MSTA1 broadcasts PREQ with SSN=0 for MSTA6. MSTA1 MSTA2 MSTA3 MSTA4 MSTA5 MSTA6 MSTA4 is a power saving MP. PREQ for MSTA6 with source SN x S:x S:0

9. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 9 PREQ with Power Saving MSTA MSTA1 broadcasts sends PREQ with SSN=1 for MSTA6 since no PREP is received after dot11MeshHWMPnetDiameterTraversalTime. MSTA3 discards PREQ with SSN=0 since it receives a PREQ with SSN=1. MSTA1 MSTA2 MSTA3 MSTA4 MSTA5 MSTA6 MSTA4 is a power saving MP. PREQ for MSTA6 with source SN x S:x S:1

10. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 10 PREQ with Power Saving MSTA MSTA1 broadcasts PREQ with SSN=2 for MSTA6 since no PREP is received after 2* dot11MeshHWMPnetDiameterTraversalTime. MSTA3 discards PREQ with SSN=1 since it receives a PREQ with SSN=2. MSTA1 MSTA2 MSTA3 MSTA4 MSTA5 MSTA6 MSTA4 is a power saving MP. PREQ for MSTA6 with source SN x S:x S:2

11. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 11 PREQ with Power Saving MSTA MSTA1 broadcasts PREQ with SSN=3 for MSTA6 since no PREP is received after 4* dot11MeshHWMPnetDiameterTraversalTime. MSTA3 discards PREQ with SSN=2 since it receives a PREQ with SSN=3. MSTA1 MSTA2 MSTA3 MSTA4 MSTA5 MSTA6 MSTA4 is a power saving MP. PREQ for MSTA6 with source SN x S:x S:3

12. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 12 PREQ with Power Saving MSTA MSTA4 changes to active state. MSTA1 MSTA2 MSTA3 MSTA4 MSTA5 MSTA6 MSTA4 is a power saving MP. PREQ for MSTA6 with source SN x S:x MSTA3 broadcasts PREQ with SSN=3 for MSTA6. But MSTA4 can not receive it correctly. S:3

13. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 13 Proposed Solution 1 Make dot11MeshHWMPnetDiameterTraversalTime longer enough to compensate power saving delay. –It makes the path selection delay longer in an MBSS without power saving MSTA.

14. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 14 Proposed Solution 2 Each time a power saving MSTA sends a beacon, it sets the power saving remaining time in the beacon to dot11PsRemainTime. If an active MSTA receives a beacon and the power saving remaining time in a received beacon is larger than the time in its psRemainTimer (power saving remain timer), it set the psRemainTimer according to the received remaining time. If an active MSTA sends a beacon it will includes the power saving remaining time in the psRemainTimer in the beacon. If the psRemainTimer does not time out, a source STA may select the network diameter traversal time more than dot11MeshHWMPnetDiameterTraversalTime when using binary backoff to retransmit PREQ.

15. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 15 Scheduled Power Saving

16. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 16 Scheduled Power Saving The scheduled power saving is based on MDA. To implement the current scheduled power saving, two peer MSTAs need to be MDA capable MSTAs. To start to use the current scheduled power saving, a power saving MSTA needs to get its neighbor’s MDAOP information. A deep power saving MSTA can not use scheduled power saving.

17. doc.: IEEE 802.11-08/1234r0 Submission October 2008 L. Chu Etc.Slide 17 Proposed Scheduled Power Saving Decouple scheduled power saving with MDA. –This can make scheduled power saving more simple. –More MSTAs can implement scheduled power saving service. –A deep power saving MSTA can use scheduled power saving with its peer MSTAs. Two neighbor MSTAs negotiate with each other about awaking time for them to communicate with each other. The normal medium access procedure is used to contend the medium access right.