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Aggregate Block-ACK definition

Aggregate Block-ACK definition. Date: 2010-07-10. Authors:. 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. Recap and Background.

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Aggregate Block-ACK definition

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  1. Aggregate Block-ACK definition Date: 2010-07-10 Authors: Jochen Miroll

  2. 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 Jochen Miroll

  3. 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 Jochen Miroll

  4. NACK NACK ACK Feedback aggregation in the same time slot • All receiversprovidefeedback, butitisaggregated in theone time slot - then(n = numberofreceivers) • overhead(n) = overhead(1) • Idea: Introduce NACK • Transmit a dataframe • Then, askfor ACK/NACK • If STA i hasreceivedtheframe:itrespondswith an ACK • If STA j did not:itrespondswith NACKatthe same time ? AP1 STA 1 STA 2 STA 3 STA 4 Jochen Miroll

  5. 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 Jochen Miroll

  6. Recap: Results in the LBP-worst-case • Worstcaseresults whereleader-selectionwould not beabletoreliablydetermine SNR differencebetweenreceivers • 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% feedbackcancellationsuccess Jochen Miroll

  7. Recap: Hybrid LBP (HLBP)*cf. doc.: IEEE 802.11-09/0290r1 Phase I Transmit a block of frames, as in MRG BA. Here: systematic FEC part Phase II Parity phase. Instead of BAR/BA, do AggregateAckRequest/AggregateAck * Assume e.g. DVB-IPDC or Raptor code on upper layer, MAC somehow knows which packets are systematic (DATA) or parity Jochen Miroll

  8. 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 Jochen Miroll

  9. 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 Jochen Miroll

  10. 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 Jochen Miroll

  11. Frame exchange sequences (1) „Did you get 5 since BAR start seq#?“ BAR start seq# frame exc. end Aggregate BA is cancelled D D D D D P P P P P P P P N-ABA ABA N-ABA ABAR AP1 D D D D D D D D D D D D D D D D D Leader STA 2 STA 3 STA 4 Jochen Miroll

  12. Frame exchange sequences (2) „Did you get 5 since BAR start seq#?“ „Did you get 6 since BAR start seq#?“ BAR start seq# frame exc. end Aggregate BA is cancelled Would ask „got 5 now?“ interrupted by beacon D D D D D P P P P P P P P beacon N-ABA ABA ABA N-ABA ABAR ABAR AP1 D D D D D D D D D D D D D D D D D Leader STA 2 Assume everyone received the beacon Increases our seq# counter by one STA 3 STA 4 Jochen Miroll

  13. Frame exchange sequences (3) „Did you get 5 since BAR start seq#?“ (note that 6 have been sent) „Did you get 5 since BAR start seq#?“ BAR start seq# frame exc. end N-ABA is received D D D D D P P P P P P P P N-ABA ABA ABAR ABAR AP1 D D D D D D D D D D D D D D D D Leader STA 2 STA 3 N-AB STA 4 AP can decide whether to add redundancy/parity a-priori Reception of N-ABA and lack of ABA are treated as the same case Jochen Miroll

  14. Frame exchange sequences (4) „Did you get 5 since BAR start seq#?“ BAR start seq# frame exc. end D D D D D P P P P P P P N-ABA N-ABA N-ABA N-ABA N-ABA N-ABA N-ABA N-ABA N-ABA ABAR ABAR ABAR AP1 D D D D D D D D D D D Leader STA 2 STA 3 N-AB N-AB N-AB STA 4 AP is limited in parity delivery by the application layer Application layer can implicitly control MAC error correction delay Jochen Miroll

  15. Questions and discussion Jochen Miroll

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