Record and Playback PHY Abstraction for 802.11n MAC Simulations - Using Soft PER Estimates

1. Record and Playback PHY Abstraction for 802.11n MAC Simulations- Using Soft PER Estimates Erik Lindskog Hemanth Sampath Ravi Narasimhan erikl@marvell.com hsampath@marvell.com ravin@marvell.com E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

2. Record & Playback PHY Abstraction Scheme • Includes: • Modified Black Box Methodology [IEEE 802.11-04/01 72r0] • PER estimation from raw BER simulations, related to [IEEE 802.11-11/03 0863r0] but here based on simulations. • Advantages: • Limited set of PHY simulations required. • Good modeling of 11n channel characteristics & variations. • Accurate modeling of PHY proposals with all impairments. • Include rate adaptation as part of PHY [IEEE 802.11-04/01 72r0] • Option to allow modeling of feedback delays in rate adaptation E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

3. Simulation Diagram E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

4. Channel Sequence • T : Small enough to track channel, • say T=1/10th of the channel coherence time • P: Large enough to capture richness of channel • say P*T=100 coherence times E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

5. PHY simulation with rate adaptation • Step through the channel realizations in the channel sequence. • For each channel realization: • Compute a recommended rate with a rate-adaptation algorithm. • Compute PER estimator from a raw BER simulation. • ‘Record’ recommended rates and packet error estimators in a sequence • Option to model effect of delays in rate adaptation • Compute and record PER estimates for a few (1-2?) previous rates. E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

6. Example Raw BER to PER mapping Two simulations: • ¾ FEC, Marvell Indoor 3, 1x1 SISO, 4QAM in red x • ¾ FEC, Marvell Indoor 1, 3x4 MIMO, 64QAM in blue dots The two different cases have very similar Raw BER to PER mappings. PER=f(Raw BER,FEC,Pkt size) E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

7. Example PHY Record E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

8. MAC simulations • For each user, playback sequence of recommended rates and associated PER estimates • A random draw based on the PER estimate determines if a packet passes or fails. • If PER estimates for previous recommened rates are stored then those PER estimates can be used to model delays in the rate adaptation algorithm. E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

9. Example MAC simulation E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

10. Modeling Feedback Delays PHY simulation is performed for both current rate and “previous” rate (Due to feedback delay) using the current channel realization MAC simulation can either use current rate or “previous rate” due to Feedback delays! E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

11. Conclusions • Record-Playback methodology has several advantages: • Includes full 802.11n channel models. • Includes effect of time correlated channel variations. • Complete modeling of PHY with impairments. • Includes rate adaptation. • Can include effects of delays in rate adaptation. • Compromises for Record-Playback method • Approximate modeling of packet error events - As most methods • Does not allow other than binary effects of interference – May be OK approximation for CSMA/CA multiple access scheme. • Coarse rate adaptation performed only the MAC (using, for example, retransmission information) is not modeled. • Current proposal does not model effects of error in scramble state estimation but this can probably be included. E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor