Feedback-jamming ARQ mechanisms Mar 09 doc.: IEEE 802.11-09/0290r1 Mar 09 Feedback-jamming ARQ mechanisms Date: 2009-03-09 Authors: Jochen Miroll et al., Saarland University Jochen Miroll et al., Saarland University

Abstract NACK-jamming leader based Multicast Mar 09 doc.: IEEE 802.11-09/0290r1 Mar 09 Abstract NACK-jamming leader based Multicast Comparison with ACK polling Pros and Cons HLBP: Hybrid leader based Multicast protocol Evaluation criteria (cf. 08/1093r0) Summary Jochen Miroll et al., Saarland University Jochen Miroll et al., Saarland University

Glossary ACK-polling AP collects indivudial ACK from each STA Mar 09 Glossary ACK-polling AP collects indivudial ACK from each STA LBP Leader-Based Protocol NACK-jamming enforced collision of leader-ACK with non-leader NACK Synchronisation of Multicast STAs, event-driven or clocked HLBP Hybrid (w.r.t. coding) LBP Jochen Miroll et al., Saarland University

NACK jamming Leader Based Protocol Mar 09 doc.: IEEE 802.11-09/0290r1 Mar 09 NACK jamming Leader Based Protocol optional SEQ# indicator and NAV updater to synchronize jamming Jochen Miroll et al., Saarland University Jochen Miroll et al., Saarland University

NACK-jamming vs. Block-ACK polling Mar 09 NACK-jamming vs. Block-ACK polling NACK-jamming and ACK-polling Jochen Miroll et al., Saarland University

NACK jamming LBP summary (1) Pros Scalability: Depending on SEQ# signalling overhead Our simulation shows an example for 10-Block-ACK vs. 25 STAs From a latency PoV: Maximum delay is constant Determined by (pre-configured) number of retransmission rounds, independent of number of STAs Event driven, distributed, optimal feedback NACK+ACK at the same time Requires less strict synchronisation as compared to ACK-polling Purposely jamming the ACK is enforcing a collision – synchronisation need not be as strict as for TDMA, see next slide Jochen Miroll et al., Saarland University

Synchronisation: jamming vs. ACK Mar 09 Synchronisation: jamming vs. ACK Jamming Collision, Fail! SIFS SIFS Block ACK Req AP1 ACK Block ACK STA 1 (leader) NACK Block ACK STA r-1 NACK Block ACK STA r NACK Jamming Block Polling Jochen Miroll et al., Saarland University

NACK jamming LBP summary (2) doc.: IEEE 802.11-09/0290r1 Mar 09 NACK jamming LBP summary (2) Cons NACK-jamming still requires synchronisation of individual STAs But: If a STA is e.g. “too slow” to jam, it does not affect the others Scalability may not be an issue at home But: Other use-cases exist: large audience video broadcast, e.g. at public places like airports, etc. LBP: How to select the leader? But: ACK polling also requires knowledge at STAs about ACK sequence => Either mechanism requires some additional signalling Not applicable for blocks of frames But: This may be compensated by increased scalability Residual packet error rate (PER) (loss at each STA) unknown ACK-polling could count #ACKs from each STA Jochen Miroll et al., Saarland University Jochen Miroll et al., Saarland University

Increasing NACK-jamming efficiency: HLBP Mar 09 doc.: IEEE 802.11-09/0290r1 Mar 09 Increasing NACK-jamming efficiency: HLBP NACK-jamming destroys „positive information“ Block-NACK (similar to Block-ACK) is thus not possible Solution: Apply FEC to a block and Transmit block of frames Assume at least one STA did not receive at least one frame in block => ACK gets jammed Transmit FEC parity frames STAs try to recover the data from the frames + parity they received Repeat 2. until ACK does not get jammed anymore (or some retry limit reached) Problem solved, Block-NACK-jamming possible: The use of parity for retransmission eliminates the need for positive info Jochen Miroll et al., Saarland University Jochen Miroll et al., Saarland University

HLBP* Mar 09 Phase I Transmit a block of frames, similar to block-ACK Phase II Replace actual block-ACK phase with parity-NACK phase * A rateless FEC code is assumed in the figure, for e.g. for RS, parity would be parity OR data Jochen Miroll et al., Saarland University

HLBP vs. Block-ACK polling Mar 09 HLBP vs. Block-ACK polling Jochen Miroll et al., Saarland University

Evaluation criteria (cf. 08/1093r0) Mar 09 Evaluation criteria (cf. 08/1093r0) Flexibility of number of STAs in a group ACK-polling may be highly reliable (even the exact residual PER can be determined) and efficient for small audiences (including 5-10 STAs) NACK-jamming scales better (no limit on the size of the audience) but is less reliable (residual PER unknown, may even be perfectly unreliable for some STAs) Flexibility in the number of simultaneously active multicast streams We propose to have both ACK and NACK scheme, choose one for each MC group individually depending on the requirements Each STA receives a QoS comparable to a single stream unicast with limited retries Delay: w.r.t audience size: Const. for NACK-jamming Jitter: We believe it is not a major issue of the retransmission scheme (power-saving / time-slot management and the OS largely affect jitter) Jochen Miroll et al., Saarland University

Evaluation criteria (cf. 08/1093r0) Mar 09 Evaluation criteria (cf. 08/1093r0) Should make efficient use of the wireless medium, as video bandwidths can be high Probably good: to use a NACK scheme for „video“, ACK for „voice“ Flexible support for traffic shaping of video transmissions and power saving Again, flexibility by switching/selection between ACK/NACK scheme Compatible with legacy non-11aa STAs HLBP not backwards-compatible, but assume plain NACK-jamming is Provide support for duplicate detection Proposed NACK schemes require SEQ# to work Provide a mechanism to support rate adaptation NACK-jamming could even use unicast rate adaptation mechanism Provides a mode of operation that minimises the potential for requiring hardware modifications Provides a mode of operation that supports collision avoidance Jochen Miroll et al., Saarland University

Summary LBP with NACK jamming LBP with NACK jamming and power-saving For low jitter, low latency applications For error tolerant applications Improved scalability as compared to ACK-polling Represents the Broadcast paradigm (delay-constrained, quasi-reliable: QoS at a STA within a MC group could depend on distance from sender) LBP with NACK jamming and power-saving Block-ACK polling may be more efficient for small audiences => No Block-NACK possible, Block-ACK may have lower CHT HLBP It is a Block-NACK scheme, comparable to Block-ACK Most efficient in any scenario Most complex due to required FEC (could be done on application layer) Jochen Miroll et al., Saarland University

Mar 09 Questions? Jochen Miroll et al., Saarland University

Mar 09 References Multicast MAC Extensions for high rate real-time traffic in Wireless LANs http://www.nt.uni-saarland.de Jochen Miroll et al., Saarland University