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Feedback-jamming Multicast ARQ results with capture effect

Feedback-jamming Multicast ARQ results with capture effect. Date: 2009-11-13. Authors:. Abstract. This presentation is an update on the NACK jamming LBP proposal previously made to TGaa by the authors and aims at disclosing some synergies between D0.02 MRG and LBP

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Feedback-jamming Multicast ARQ results with capture effect

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  1. Feedback-jamming Multicast ARQresults with capture effect Date: 2009-11-13 Authors: Jochen Miroll, Saarland University

  2. Abstract This presentation is an update on the NACK jamming LBP proposal previously made to TGaa by the authors and aims at disclosing some synergies between D0.02 MRG and LBP The capture effect with reasonable ACK/NACK frame structures is tested and evaluated to give an idea about the feasibility of NACK jamming in 11aa. Jochen Miroll, Saarland University

  3. Glossary ACK-polling As MRG BA does in P802.11aa D0.01 LBP Leader-Based Protocol NACK-jamming Enforced collision of leader-ACK with non-leader NACK ‘‘ probability Probability that ACK is lost due to simultaneous NACK HLBP Hybrid (w.r.t. coding) LBP Jochen Miroll, Saarland University

  4. NACK jamming Leader Based Protocols • We propose(d) a leader based feedback jamming Multicast retransmission protocol for 11aa • Neither compulsory nor contrary but complementary to the already specified MRG-BA in D0.02 • Previously we have shown an increased scalability of such a scheme w.r.t group size • Refer to document 09/0290r1 • Recap on next two slides Jochen Miroll, Saarland University

  5. Recap LBP optional SEQ# indicator and NAV updater to synchronize jamming Jochen Miroll et al., Saarland University

  6. Recap HLBP* 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, receiver counts FEC packets Jochen Miroll, Saarland University

  7. NACK jamming leader-based protocols • Scalability • Independent of number of number of client STAs per group • Leader selection and rate/link adaptation become related For the AP and leader the behaviour is similar to unicast (use ARF?) • Error correction delay • Independent of number of client STAs per group • HLBP • Enable cross-layer error correction, e.g. RS on application layer • Then the remaining MAC mechanism is quite simple • Parity / NACK phase could be moved to concealed retransmission multicast group similar to MRG unsolicited retries Jochen Miroll, Saarland University

  8. NACK jamming leader-based protocols • From March 09 meetings two fundamental questions arose: • Does the „capture effect“ impede the ACK/NACK jamming? • How is the jamming probability related to leader selection? • Thus we have conducted ns-2 and Matlab simulations for deriving NACK jamming probabilities Jochen Miroll, Saarland University

  9. The „Capture Effect“ • Capture Effect is described in the literature as the effect that a signal can be correctly received in the presence of another transmission. • Naively thinking: „how could this affect 802.11 wireless networks?“ • If an OFDM data symbol is being received and some other OFDM data symbol is „on the air“ (same channel), we assume increased (white) noise at the receiver => correct reception depends on the power difference • If two 802.11 frames start at approximately the same time with different content => Correct reception depends on phase and power difference Jochen Miroll, Saarland University

  10. The „Capture Effect“ • Power level difference • Assume interfering signal has flat spectrum within 20MHz channel • „Capture effect“ depends on the resulting SNR • Figure: • Packet error rate (1500B) in Rician fading channel with Rician factor 1 (analytical results from text books) Jochen Miroll, Saarland University

  11. SIFS TX 1 TX 3 TX 2 Rcv Sender Interferer 1 Interferer 2 Frames transmitted at the same time The „Capture Effect“ • Transmitting at the same time • Receiver is not synchronised • PLCP of TX1, TX2 and TX3 overlap • Question is: Can the receiver still obtain • Coarse timing from short preambles • AGC • Clock sync • Fine timing from long preambles • Channel equalization Jochen Miroll, Saarland University

  12. similar similar ACK The „Capture Effect“ • Transmitting (nearly) the same content at the same time • Assume ACK and NACK differ in only one bit • Conv. coded, scrambled signal „on the air“ will differ starting from the differing bit position • Receiver will see an echo • Could be beneficial, sync will probably be obtained • But starting from the differing bit position, the „echo“ ceases to be an echo and becomes interference SIFS Rcv Sender Interferer 1 Interferer 2 Very simliar frames Transmitted at the same time Jochen Miroll, Saarland University

  13. NACK frame • Why „very similar“ ACK/NACK frames? • We assume it to be unlikely that 11aa will introduce a „jamming signal“ • Instead, a new frame type is more likely to be specified • In the worst case (w.r.t. jamming probability) a new frame (NACK) may only differ from a standard ACK in one bit, i.e. the frame type. Jochen Miroll, Saarland University

  14. Jamming NACK NACK ACK SIFS AP1 STA 1 (leader) STA r-1 STA r NACK jitter Matlab Simulation • To simulate „capturing“ in matlab we implemented a complex baseband from scratch: • PLCP and OFDM signal generator • 10x upsampling to simulate „analog“ • Interferer with 1 bit difference in the MAC frame (type bit NACK/ACK) • Interferer jitters by +- GI (5% SIFS)* • AWGN / multipath channels • Viterbi decoding 10,000 simultaneous ACK/NACK transmissions * 802.11a GI: 16 samples, 0.8 us, SIFS: 16 us Jochen Miroll, Saarland University

  15. Matlab results (AWGN) ACK packet error rate over power difference of ACK and NACK Jochen Miroll, Saarland University

  16. Matlab results (AWGN) ACK packet error rate over power difference of ACK and NACK Jochen Miroll, Saarland University

  17. Ns-2 simulation environment • ns-allinone-2.34 • 802.11Ext model which supports capture effect (see ref) Jochen Miroll, Saarland University

  18. Ns-2 results • Ns-2 parameters • PLE: 3 • Rayleigh fading (param. Nakagami) • Tx power: 20dBm • 1 Leader and 1 non-leader, same distance to AP • Periodic leader selection (mean SNR decision) Jochen Miroll, Saarland University

  19. Questions? Jochen Miroll, Saarland University

  20. Straw Poll (1) • Is TGaa interested in further results on leader based NACK jamming for more reliable video groupcast? • Yes: • No: • Abstain: Jochen Miroll, Saarland University

  21. References • Q. Chen, F. Schmidt-Eisenlohr, D. Jiang, M. Torrent-Moreno, L. Delgrossi, and H. Hartenstein, "Overhaul of IEEE 802.11 modeling and simulation in NS-2," in Proc. Of the 10th ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM), 2007 • Multicast MAC Extensions for high rate real-time traffic in Wireless LANs • http://www.nt.uni-saarland.de Jochen Miroll, Saarland University

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