doc.: IEEE /0788r0 Submission Aggregate Block-ACK definition Date: July 2010 Jochen MirollSlide 1 Authors:

doc.: IEEE /0788r0 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 July 2010 Jochen MirollSlide 2

doc.: IEEE /0788r0 Submission Recap and Background 11aa is standardizing Multicast ARQ: MRG –Gathering per-receiver feedback, the overhead due to the positive ACKs grows linearly with the number n of receivers How does 11aa MRG compensate for this increased overhead? –Aggregation of multiple frames: single-TID, uncompressed Block- ACK (802.11n) for MRG –Per-frame ACK becomes multi-frame Block-ACK bitmap for the last k frames –Still: overhead increases linearly with receivers n How to get rid of the dependency on n? –We have previously proposed a leader-based Multicast retransmission scheme to 11aa July 2010 Jochen Miroll3

doc.: IEEE /0788r0 Submission Feedback aggregation in the same time slot All receivers provide feedback, but it is aggregated in the one time slot - then (n = number of receivers) –overhead(n) = overhead(1) Idea: Introduce NACK –Transmit a data frame –Then, ask for ACK/NACK If STA i has received the frame: it responds with an ACK If STA j did not: it responds with NACK at the same time July 2010 Jochen Miroll4 AP1 STA 1 STA 2 STA 3 ACK NACK STA 4 NACK ?

doc.: IEEE /0788r0 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 Miroll5

doc.: IEEE /0788r0 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 Miroll6 Measurement parameterRate Software ACK loss avg Software NACK loss avg Hardware ACK-6 loss avg Hardware ACK-12 loss avg

doc.: IEEE /0788r0 Submission Recap: Hybrid LBP (HLBP)* cf. doc.: IEEE /0290r1 July 2010 Jochen MirollSlide 7 * 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

doc.: IEEE /0788r0 Submission Motivation for (H)LBP with aggregation through cancellation Scales with the number of receivers –Only the number of retransmissions may increase with increasing group size, but not the protocol overhead Degraded channel at one STA does not harm the other stations’ reception –both in terms of errors and delay Predictable delay in error correction –with limited # of retransmission rounds –due to aggregation of feedback in the same time slot Hybrid LBP –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, backwards compatible and easily implementable July 2010 Jochen Miroll8

doc.: IEEE /0788r0 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 itself becomes 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: MRG BAR Information Length ABAR Flag (set to 1) MRG BAR Bitmap Offset (ABAR leader) MRG BAR Partial Bitmap (ABAR minimum)

doc.: IEEE /0788r0 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

doc.: IEEE /0788r0 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# frame exc. end P

doc.: IEEE /0788r0 Submission Frame exchange sequences (2) July 2010 Jochen MirollSlide 12 AP1 Leader STA 2 STA 3 STA 4 DP ABARABAN-ABA beaconDDDPPPPPPDDDDDDDDDDDDDDDDDD „Did you get 5 since BAR start seq#?“ Aggregate BA is cancelledBAR start seq# Would ask „got 5 now?“ interrupted by beacon ABARABA frame exc. end P „Did you get 6 since BAR start seq#?“ Assume everyone received the beacon Increases our seq# counter by one

doc.: IEEE /0788r0 Submission Frame exchange sequences (3) July 2010 Jochen MirollSlide 13 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

doc.: IEEE /0788r0 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 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

doc.: IEEE /0788r0 Submission Questions and discussion July 2010 Jochen MirollSlide 15