Short Response Frame for NDP PS-Poll

1. Short Response Frame for NDP PS-Poll Authors: Date: 2013-01-13 Shoukang Zheng, I2R

2. Shoukang Zheng, I2R

3. Shoukang Zheng, I2R

4. Shoukang Zheng, I2R

5. Motivation • Both Short ACK [1] and NDP type PS-Poll [2] have been accepted into IEEE 802.11ah SFD • Problem Review • Current Short ACK can not acknowledge NDP PS-Poll • Short ACK requires Scrambling Seed and Partial FCS to compute ACK ID • NDP PS-Poll does NOT have scrambling seed and partial FCS (only 4-bit CRC) • We propose to modify Short ACK for consideration Shoukang Zheng, I2R

6. Recap: Current Short ACK [1] Shoukang Zheng, I2R

7. Recap: NDP type PS-Poll [2] Shoukang Zheng, I2R

8. Modified Short ACK for NDP PS-Poll Shoukang Zheng, I2R

9. Frame Exchange Procedure • If received NDP PS-Poll (indicated by NDP type) • AP shall send modified short ACK with Long ACK ID (slide 8 w/o duration field) which is computed based on • Received frame PBSSID, PAID, CRC bits • If received Non-NDP PS-Poll (indicated by NDP type) • AP may send original short ACK as in [1] • ACK ID is computed based on Partial FCS and Scrambling Seed Shoukang Zheng, I2R

10. Discussions • Both PAID and PBSSID are included to avoid false cases (see backup for more details) • 18-21 bit ACK ID with sufficient protection Shoukang Zheng, I2R

11. Straw Poll 1 • Do you support a modified short ACK to acknowledge NDP type PS-Poll with the ACK ID field computed as in Slide 8? • Yes • No • Abstain Shoukang Zheng, I2R

12. Motion 1 • Move to include in the SFD a modified short ACK to acknowledge NDP type PS-Poll with the ACK ID field computed as in Slide 8? • Yes • No • Abstain Shoukang Zheng, I2R

13. Reference • [1] 12/324r2 Short Ack • [2] 12/848r0 NDP Type PS-Poll frame Shoukang Zheng, I2R

14. Backup Shoukang Zheng, I2R

15. False Short Ack for NDP Type PS-Poll (1) NDP type PS-Poll NDP type PS-Poll A AP B • Two concurrent transmissions of NDP type PS-Poll: A->AP and B->AP • Both A and B expect short Ack from AP • Suppose that AP can only receive a strong signal from A and respond to A’s NDP PS-Poll with short Ack that can reach B • B receives AP’s short Ack, which should carry identification of STA e.g. AID info in short response frame SIG so that the possibility of this false short Ack case should be zero ShortAck ShortAck ? NDP PS-Poll A NDP PS-Poll B AP Short Ack Shoukang Zheng, I2R

16. False Short Ack for NDP Type PS-Poll (2) NDP type PS-Poll NDP type PS-Poll NDP type PS-Poll ? A AP1 AP2 • Two concurrent transmissions of NDP type PS-Poll: A->AP1 and B->AP2 • A expects a short Ack from AP1 and B expects a short Ack from AP2 • Suppose that AP1 responds to A’s NDP PS-Poll with short Ack that can reach B, but AP2 can’t receive B’s NDP PS-Poll • B receive AP1’s short Ack, If B have a shorter transmission range when it sends NDP PS-Poll that can reach AP1, and AP1 have a longer transmission range when it sends NDP short Ack that can reach B, false short Ack occurs if scrambled PBSSID and PAID bits in NDP PS-Poll frame are same for A and B • The possibility of this false short Ack case could be very low because • it carries both AP and STA’s identification and duplicate prob. of same NDP PS-Poll’s TA (e.g. scrambled PBSSID) bits is low • B’s transmission will likely corrupt A’s transmission at AP1, if B’s transmission range is long • B may be able to detect if it can hear AP1’s beacon frame B ShortAck ShortAck ShortAck NDP PS-Poll A AP1 Short Ack NDP PS-Poll B AP2 Short Ack Shoukang Zheng, I2R