1 / 24

Aggregate Block-ACK definition

Aggregate Block-ACK definition. Date: 2010-07-15. 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 Revisions of this document

brinly
Download Presentation

Aggregate Block-ACK definition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Aggregate Block-ACK definition Date: 2010-07-15 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 • 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 Jochen Miroll

  3. NACK NACK ACK 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≤nSTAs 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 dataframe: it responds with an ACK • If STA j did not receive the dataframe: it responds with NACKat the same time ? AP1 STA 1 STA 2 STA 3 STA 4 Jochen Miroll

  4. 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

  5. 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 Jochen Miroll

  6. 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

  7. 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 Jochen Miroll

  8. 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 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 preceded by 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 D D D D D D D P P P P P P P P P P ABA N-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 Packets avaliable in AP buffer for currently serviced MRG group: Jochen Miroll

  12. Frame exchange sequences (2) „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

  13. Frame exchange sequences (3) „Did you get 6 since BAR start seq#?“ sent: 7 „Did you get 5 since BAR start seq#?“ BAR start seq# Aggregate BA is cancelled frame exc. end Would ask „got 5 now?“ sent: 6 = 5 data + 1 parity 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

  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 as provided by the application layer Application layer can implicitly control MAC error correction delay Jochen Miroll

  15. Frame exchange sequences (5) „Did you get 6 since BAR start seq#?“ BAR start seq# frame exc. end „Did you get 6 since BAR start seq#?“ „data“ packet carries parity P D D D D D P P P P P ABA N-ABA N-ABA N-ABA ABAR ABAR AP1 D D D D D D D D D D D D D D D P P D Leader STA 2 STA 3 N-AB STA 4 Application layer can enforce a-priori packet FEC Jochen Miroll

  16. 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 Jochen Miroll

  17. 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 Jochen Miroll, Saarland University

  18. 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 Jochen Miroll

  19. 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” Jochen Miroll

  20. B0 B1 B2 B3 B4 B11 B12 B15 Compressed Bitmap BA Ack Policy Multi-TID Reserved TID_INFO MRG Bits: 1 1 1 1 6 4 Figure 7-16—BA Control field SBA definition • BA Control field with MRG bit (P802.11aa/D1.0) • Proposed BA Control field with MRG bit and SBA bit B11 B12 B15 B0 B1 B2 B3 B4 B5 Multi-TID Compressed Bitmap BA Ack Policy Reserved MRG SBA TID_INFO Bits: 1 1 1 1 1 6 4 Jochen Miroll, Saarland University

  21. 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 • set the SBA bit in the corresponding MRG BA to 0 if own AID is not equal to the single BAR AID • 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 Jochen Miroll, Saarland University

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

  23. MRG SBA mode frame exchange sequence „Did you get 6 since BAR start seq#?“ „Did you get 5 since BAR start seq#?“ BAR start seq# frame exc. end Would ask „got 5 now?“ sent: 6 = 5 nDEI+ 1 DEI interrupted by beacon nDEI nDEI nDEI nDEI nDEI DEI DEI DEI DEI beacon N-SBA SBA N-SBA SBAR SBAR AP1 nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI nDEI Leader STA 2 Assume everyone received the beacon Increases our seq# counter by one STA 3 STA 4 Jochen Miroll

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

More Related