Erik Lindskog Hemanth Sampath Ravi Narasimhan February 16 2004 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

Record & Playback PHY Abstraction Scheme February 16 2004 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 (and power control) as part of PHY [IEEE 802.11-04/01 72r0] Option to allow modeling of feedback delays in rate adaptation Easy interface to merge different PHY and MAC proposals ! E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

Simulation Diagram February 16 2004 E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

Channel Sequence T : Small enough to track channel, February 16 2004 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

PHY simulation with rate adaptation February 16 2004 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

Example Raw BER to PER mapping February 16 2004 Example Raw BER to PER mapping Two simulations: ¾ FEC, Marvell Indoor 3 (150ns DS), 1x1 SISO, 4QAM in red x ¾ FEC, Marvell Indoor 1 (50ns DS), 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

February 16 2004 Example PHY Record Records can be stored in *.txt files and exchanged between companies for merging different PHY and MAC proposals. For presentations, records can be abstracted into a histogram of rates and PER E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

Estimated Simulation Time for Generating Records February 16 2004 Estimated Simulation Time for Generating Records In Marvell MATLAB PHY simulator: Simulating a 1000 byte packet transmission on a 2 GHz processor in MATLAB takes 2.5 seconds on average. (0.5-4.5 sec depending on rate) Record with 1000 entries would take 1000 entries x 2.5 seconds/entry ~= 42 minutes. Example Usage Scenario: Usage Model with 5 users (stations), would require 10 records (uplink and downlink) Total simulation time = 10 records x 42 minutes / record = 7 hours Comparison: This time is similar to getting one PER vs SNR plot (assuming 1000 byte packet transmission and 10 SNR points). E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

February 16 2004 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. Advantage: MAC simulation can test different PHY proposals via their PHY records! E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

Example MAC simulation February 16 2004 Example MAC simulation 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

Modeling Feedback Delays February 16 2004 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

Conclusions Record-Playback methodology has several advantages: February 16 2004 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. Easy to merge different PHY and MAC proposals! 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