1. doc.: IEEE 802.11-10/0788r3 Submission Aggregate Block-ACK definition Date: 2010-07-15 July 2010 Jochen MirollSlide 1 Authors:

2. doc.: IEEE 802.11-10/0788r3 Submission Abstract This presentation explains how a Leader-Based Protocol (LBP) that aggregates feedback within the same time slot should be incorporated into TGaa Normative text will follow based on discussions Revisions of this document –Rev. 1 provides additional examples for frame exchange sequences –Rev. 2 has errors on slide 15: Frame Exchange Sequences (5) fixed –Rev. 3 finalizes this proposal by elaborating in detail a possible way of incorporating this into 11aa/D1.0 July 2010 Jochen MirollSlide 2

3. doc.: IEEE 802.11-10/0788r3 Submission Feedback aggregation in the same time slot How to get rid of the dependency on n? All receivers provide feedback, but this feedback from k≤n STAs is aggregated in a single time slot overhead(k) = overhead(1) Introduction of NACK –AP transmits a data frame –Then, AP asks for ACK/NACK If STA i has received the data frame: it responds with an ACK If STA j did not receive the data frame: it responds with NACK at the same time July 2010 Jochen Miroll3 AP1 STA 1 STA 2 STA 3 ACK NACK STA 4 NACK ?

4. doc.: IEEE 802.11-10/0788r3 Submission Leader-based feedback cancellation Groupcast becomes unicast to leader –non-leaders transmit a negative ACK if a frame is lost after being asked to do so – introduce the question “did you receive the frame?” Target: Larger groups (than 11aa MRG-BA should practically handle) –Overhead for asking about frame reception – same thing for 11aa MRG block-ACK request –In this presentation: Show how this overhead is reduced by data frame aggregation similar to 11aa MRG-BA Leader selection: choose the „weakest“ receiver (as seen by the AP) –So this STA’s ACKs can be cancelled with very high probability –But: No error correction guarantees in this scheme –“More reliable”, as compared to Multicast July 2010 Jochen Miroll4

5. doc.: IEEE 802.11-10/0788r3 Submission Recap: Results in the LBP-worst-case Worst case results where leader-selection would not be able to reliably determine SNR difference between receivers Ns2 – scenario: Rayleigh fading channel, equal AP- STAs distance feedback cancellation rate is about 76% for 2, more than 90% for more than 2, and already 99% for 5 receivers Measured: 3 rcvrs, 1 leader ~89% feedback cancellation success July 2010 Jochen Miroll5 Measurement parameterRate Software ACK loss avg.0.894134 Software NACK loss avg.0.753818 Hardware ACK-6 loss avg.0.893892 Hardware ACK-12 loss avg.0.854081

6. doc.: IEEE 802.11-10/0788r3 Submission Recap: Hybrid LBP (HLBP)* cf. doc.: IEEE 802.11-09/0290r1 July 2010 Jochen MirollSlide 6 * Assume e.g. DVB-IPDC or Raptor code on upper layer, MAC somehow knows which packets are systematic (DATA) or parity Phase ITransmit a block of frames, as in MRG BA. Here: systematic FEC part Phase IIParity phase. Instead of BAR/BA, do AggregateAckRequest/AggregateAck

7. doc.: IEEE 802.11-10/0788r3 Submission Motivation for (H)LBP with aggregation through cancellation Due to aggregation: Scales with the number of receivers –Only the number of retransmissions may increase with increasing group size, but not the protocol overhead Due to additional FEC: Degraded channel at one STA does less harm to overall performance –both in terms of errors and delay Hybrid LBP FEC –Enable cross-layer error correction through systematic packet level FEC controlled by upper layers (e.g. the application or a transport protocol other than TCP/UDP) –The remaining MAC mechanism is simple and easily implementable Predictable delay in error correction –due to aggregation of feedback in the same time slot –application layer is able to control the error correction delay July 2010 Jochen Miroll7

8. doc.: IEEE 802.11-10/0788r3 Submission Motivation for (H)LBP with aggregation through cancellation cont‘d About the error floor of feedback cancellation: –If leader is the weakest receiver, it probably looses packets at higher probability than the rest –If the weakest receiver is significantly weaker: cancellation success increases and the error floor becomes negligible (now also due to the capture effect!) –With increasing block length, independent errors at all stations within block become more likely How to choose the leader? –Incorporate aggregate Block-ACK in a way that AP can switch from ABA to BA without overhead. MRG BA feedback used to measure signal strength (or any other traffic from resp. STAs) Leader selection has further benefits –Rate adaptation: for the leader (since it’s the weakest STA in the group) –If AP detects that the stream rate is higher than what is served to the current leader, it can just select another STA in the group as the leader for the next block July 2010 Jochen Miroll8

9. doc.: IEEE 802.11-10/0788r3 Submission Aggregate Block-Ack Request Define an aggregate-BAR: “ABAR” MRG BAR information field: (Figure 7-13aa) Use reserved bit to indicate the request for aggregate feedback to MRG group members Bitmap Offset becomes ABAR leader indicator Bitmap preceded by ABAR minimum July 2010 Jochen MirollSlide 9 Bits: 8 1 7Variable MRG BAR Information Length reserved MRG BAR Bitmap Offset MRG BAR Partial Bitmap Bits: 8 1 78 Variable MRG BAR Information Length ABAR Flag (set to 1) MRG BAR Bitmap Offset (ABAR leader) ABAR minimum MRG BAR Partial Bitmap

10. doc.: IEEE 802.11-10/0788r3 Submission Aggregate Block-Ack Request Minimum Define an aggregate-BAR minimum (m): “m is the minimum number of frames a station has to have received within the last k frames, such that the upper layers can decode the current FEC block” The AP may, after transmitting k frames, ask the group members to (Negatively-)AggregateBlockACK m < k frames July 2010 Jochen MirollSlide 10

11. doc.: IEEE 802.11-10/0788r3 Submission Frame exchange sequences (1) July 2010 Jochen MirollSlide 11 AP1 Leader STA 2 STA 3 STA 4 DP ABARABAN-ABA DDDPPPPPPDDDDDDDDDDDDDDDDDD „Did you get 5 since BAR start seq#?“ Aggregate BA is cancelledBAR start seq# P frame exc. end DPP Packets avaliable in AP buffer for currently serviced MRG group: DDDDDD …

12. doc.: IEEE 802.11-10/0788r3 Submission Frame exchange sequences (2) July 2010 Jochen MirollSlide 12 AP1 Leader STA 2 STA 3 STA 4 DP ABARN-ABA N-AB DDDPPPPPPDDDDDDDDDDDDDDDDD „Did you get 5 since BAR start seq#?“ (note that 6 have been sent) N-ABA is receivedBAR start seq# ABARABA frame exc. end P „Did you get 5 since BAR start seq#?“ AP can decide whether to add redundancy/parity a-priori Reception of N-ABA and lack of ABA are treated as the same case

13. doc.: IEEE 802.11-10/0788r3 Submission Frame exchange sequences (3) July 2010 Jochen MirollSlide 13 AP1 Leader STA 2 STA 3 STA 4 DP ABARABAN-ABA beaconDDDPPPPPPDDDDDDDDDDDDDDDDDD „Did you get 5 since BAR start seq#?“ Aggregate BA is cancelled BAR start seq# Would ask „got 5 now?“ sent: 6 = 5 data + 1 parity interrupted by beacon ABARABA frame exc. end P „Did you get 6 since BAR start seq#?“ sent: 7 Assume everyone received the beacon Increases our seq# counter by one

14. doc.: IEEE 802.11-10/0788r3 Submission Frame exchange sequences (4) July 2010 Jochen MirollSlide 14 AP1 Leader STA 2 STA 3 STA 4 D ABARN-ABA N-AB DDDDDDDDDDDDDDD „Did you get 5 since BAR start seq#?“ BAR start seq# frame exc. end AP is limited in parity delivery as provided by the application layer Application layer can implicitly control MAC error correction delay N-ABA PPPP ABARN-ABA N-AB N-ABA PPP ABARN-ABA N-AB N-ABA

15. doc.: IEEE 802.11-10/0788r3 Submission Frame exchange sequences (5) July 2010 Jochen MirollSlide 15 AP1 Leader STA 2 STA 3 STA 4 D ABARN-ABA N-AB DDDPPPPDDDDDDDDDDDDDDDDD „Did you get 6 since BAR start seq#?“ BAR start seq# ABARABA frame exc. end P „Did you get 6 since BAR start seq#?“ Application layer can enforce a-priori packet FEC PPP „data“ packet carries parity N-ABA

16. doc.: IEEE 802.11-10/0788r3 Submission Conclusion Reception of N-ABA and lack of ABA are treated as the same case –It is not always necessary that feedback from the leader is cancelled If packets are (somehow) marked or the AP (somehow) determines that IP packets carry systematic FEC data or respectivly parity and it has some of them buffered –Application layer block coding and MAC Block-ACK can work more effectively together –AP can decide whether to add redundancy/parity a-priori –How this is implemented can be left to the manufacturer –Marking packets needs additional mechanisms, but this is out of scope of 11aa If application layer is not satisfied by MAC layer performance –it can conceal parity as data (purposely false marking) to enforce packet FEC July 2010 Jochen MirollSlide 16

17. doc.: IEEE 802.11-10/0788r3 Submission Revised Terminology Avoid the term „aggregate“ to avoid confusion with e.g. A-MSDU, i.e. frame aggregation Instead, since feedback from non-AP stations shall be transmitted at the same time, denote „simultaneous“ MRG Simultaneous-Block-ACK mode (SBA mode) MRG Simulaneous-Block-ACK Request (SBAR) –The request for a simultaneously transmitted Block ACKs MRG Simultaneous-Block-ACK (SBA) DEI is the Drop Eligibility Indicator present in 11aa Slide 17Jochen Miroll, Saarland University July 2010

18. doc.: IEEE 802.11-10/0788r3 Submission SBAR definition MRG BAR information field: (Figure 7-13aa) Use reserved bit to indicate the request for simultaneous feedback to MRG group members SBAR leader is encoded in MRG BAR Partial Bitmap Bitmap optionally preceded by SBAR Minimum* if MRG SBAR Mode is set to 1 –*Note: when MRG SBAR Mode is set to 1: 2 Bytes, 0: 1 Byte July 2010 Jochen MirollSlide 18 MRG BAR Information Length Reserved MRG BAR Bitmap Offset MRG BAR Partial Bitmap Bits: 8 1 7Variable MRG BAR Information Length MRG SBAR Mode SBAR Minimum MRG BAR Bitmap Offset MRG BAR Partial Bitmap Bits: 8 1 87 Variable

19. doc.: IEEE 802.11-10/0788r3 Submission SBAR leader AID and SBAR Minimum Encoding of SBAR leader AID –The AID of the leader is encoded in the Bitmap Offset field / Partial Bitmap as is the first STA in MRG Block-ACK, except that the Partial Bitmap is exactly one Byte and in it, exactly one bit is set, thus identifying the leader. Definition of SBAR Minimum field: –If the SBAR mode bit is set to 1, the SBAR Minimum field is defined as follows, otherwise it is omitted. –The SBAR Minimum field contains the value SBARmin “SBARmin is the minimum number of frames a station has to have received within the last k frames, such that the upper layers can decode the current FEC block whereas k is the number of previously transmitted group addressed frames without counting DEI frames” July 2010 Jochen MirollSlide 19

20. doc.: IEEE 802.11-10/0788r3 Submission SBA definition BA Control field with MRG bit (P802.11aa/D1.0) Proposed BA Control field with MRG bit and SBA bit July 2010 Jochen Miroll, Saarland UniversitySlide 20 BA Ack Policy Multi- TID Compressed Bitmap MRG Reserved TID_INFO B0B1B2B3 Bits: 1111 4 B4B11B12B15 6 Figure 7-16—BA Control field BA Ack Policy Multi- TID Compressed Bitmap MRG Reserved TID_INFO B0B1B2B3 Bits:1111 4 B4 B11B12B15 6 B5 SBA 1

21. doc.: IEEE 802.11-10/0788r3 Submission SBA bit definition STAs receiving an MRG BAR with SBAR bit set to 1 shall immediately compare their own AID to the one that is found in the BAR Then, they shall either a)set the SBA bit in the corresponding MRG BA to 0 if own AID is not equal to the single BAR AID b)set the SBA bit in the corresponding MRG BA to 1 if own AID is equal to the single BAR AID If the SBA bit is set to 1, the BA Information field in the Block Ack frame shall be a single octet equal to 0 –Note that this ensures the BA with SBA bit equal to 1 to be shorter than the otherwise unmodified BA with SBA bit equal to 0 July 2010 Jochen Miroll, Saarland UniversitySlide 21

22. doc.: IEEE 802.11-10/0788r3 Submission MRG SBA mode frame exchange 1.Preconditions: a)In MRG SBA mode, the AP may not transmit group addressed DEI frames together with non- DEI frames in the same block b)In MRG SBA mode, the AP may not transmit frames with different DA within the same block 2.In MRG SBA mode, the AP shall transmit (subject to the TXOP limit) a)all k non-DEI group addressed frames it has consecutively buffered, immediately followed by an SBAR with SBARmin=k b)an arbitrary subset p of DEI group addressed frames it has consecutively buffered, immediately followed by an SBAR with SBARmin=k (i.e. the previous k) c)any group addressed frame but shall then leave MRG SBA mode 3.The AP shall then flush all k or p consecutive, just transmitted frames from its buffers (all receiving STAs may do the same) 4.If interrupted before the SBAR, and management frames are transmitted during the interruption, the AP shall increase k by the number of management frames 5.If the AP, after having transmitted the SBAR, receives a)an SBA with SBA (negation) bit set to 0, goto 2.a) or 2.c) b)no SBA or an SBA with SBA (negation) bit set to 1, goto 2.b) or 2.c) Slide 22Jochen Miroll, Saarland University July 2010

23. doc.: IEEE 802.11-10/0788r3 Submission MRG SBA mode frame exchange sequence July 2010 Jochen MirollSlide 23 AP1 Leader STA 2 STA 3 STA 4 nDEI DEI SBARN-SBA beacon nDEI DEI nDEI „Did you get 5 since BAR start seq#?“ BAR start seq# Would ask „got 5 now?“ sent: 6 = 5 nDEI+ 1 DEI interrupted by beacon SBARSBA frame exc. end „Did you get 6 since BAR start seq#?“ Assume everyone received the beacon Increases our seq# counter by one DEI

24. doc.: IEEE 802.11-10/0788r3 Submission Motion Move to incorporate the text changes in doc.: IEEE 802.11-10/0904r0 into the TGaa draft 1.0 Moved: Seconded: Result: Slide 24Jochen Miroll, Saarland University July 2010