Feedback-jamming Multicast ARQ results with capture effect Nov 09 doc.: IEEE 802.11-09/1150r0 Nov 09 Feedback-jamming Multicast ARQ results with capture effect Date: 2009-11-13 Authors: Jochen Miroll, Saarland University Jochen Miroll, Saarland University

Abstract [place presentation abstract text here] Nov 09 Nov 09 doc.: IEEE 802.11-09/1150r0 Nov 09 Abstract [place presentation abstract text here] Jochen Miroll, Saarland University Jochen Miroll, Saarland University

Glossary ACK-polling As MRG BA does in P802.11aa D0.01 Nov 09 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

NACK jamming Leader Based Protocols Nov 09 NACK jamming Leader Based Protocols We propose(d) a leader based feedback jamming Multicast retransmission protocol for 11aa Refer to document 09/0290r1 Recap on next two slides Jochen Miroll, Saarland University

NACK jamming Leader Based Protocol Nov 09 doc.: IEEE 802.11-09/1150r0 Mar 09 NACK jamming Leader Based Protocol optional SEQ# indicator and NAV updater to synchronize jamming Jochen Miroll et al., Saarland University Jochen Miroll, Saarland University

HLBP* Nov 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, receiver counts FEC packets Jochen Miroll, Saarland University

NACK jamming Leader Based Protocols Nov 09 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

Nov 09 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

The „Capture Effect“ Power level difference Figure: Nov 09 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

The „Capture Effect“ Transmitting at the same time Nov 09 The „Capture Effect“ Transmitting at the same time Receiver is not synchronised PLCP of TX1, TX2 and TX3 overlap Question is: Can the receiver obtain Coarse timing from short preambles AGC Clock sync Fine timing from long preambles Channel equalization Rcv Sender Interferer 1 Interferer 2 Frames transmitted at the same time TX 1 TX 3 SIFS TX 2 Jochen Miroll, Saarland University

Nov 09 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 ACK Sender similar Interferer 1 similar Interferer 2 Very simliar frames Transmitted at the same time Jochen Miroll, Saarland University

Nov 09 Matlab Simulation To simulate „capturing“ in matlab we have built a complex baseband 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 AP1 STA 1 (leader) STA r-1 STA r NACK jitter ACK NACK SIFS Jamming * 802.11a GI: 16 samples, 0.8 us, SIFS: 16 us Jochen Miroll, Saarland University

ACK packet error rate over power difference of ACK and NACK Nov 09 Matlab results (AWGN) ACK packet error rate over power difference of ACK and NACK Jochen Miroll, Saarland University

Ns-2 simulation environment Nov 09 Ns-2 simulation environment ns-allinone-2.34 802.11Ext model which supports capture effect (see ref) Jochen Miroll, Saarland University

Ns-2 results Ns-2 parameters Nov 09 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 Jochen Miroll, Saarland University

Straw Poll Is TGaa interested in further results on NACK jamming? Yes: Nov 09 Straw Poll Is TGaa interested in further results on NACK jamming? Yes: No: Abstain: Jochen Miroll, Saarland University

Nov 09 Questions? Jochen Miroll, Saarland University

Nov 09 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