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

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

2. Record & Playback PHY Abstraction Scheme • Includes: • Modified Black Box Methodology [IEEE 802.11-04/01 72r0] • Binary PER estimates from PHY package 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 (& 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 ! H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

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

4. Channel Sequences N: Large enough to capture the richness of the channel (example: 50) T: Small enough not to effect latency of traffic due to ‘black-outs’ and ‘all-pass’ periods due to the binary PER modeling (example: 1-10 ms) M Large enough to make effect of switching sequences negligible. (example: M = 100) P : P = M * t/T H. Sampath, E. Lindskog and 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 packet pass or fail in PHY simulation. • ‘Record’ recommended rates and packet pass or fail in a sequence. • Option to model effect of delays in rate adaptation • Compute and record packet pass or fail for a few (1-2?) previous rate, using current channel realization. H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

6. Example PHY Record Channel sequence n out of N: • 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 H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

7. Estimated Simulation Time for Generating Records • In Marvell MATLAB PHY simulator: • Simulating a 1000 byte packet transmission on a 2 GHz processor takes 2.5 seconds on average. • Record with 1000 entries (N = 50, P = 20) 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). H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

8. MAC Simulations • For each user, playback sequence of recommended rates and associated packet pass or fail events. • As an option, if packet pass or fail events for previous recommended rates are stored, then those events can be used to model delays in the rate adaptation algorithm. Advantage: MAC simulation can test different PHY proposals via their PHY records! H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

9. Example MAC simulation with Binary PER Channel sequence n out of N: H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

10. Modeling Feedback Delays Channel sequence n out of N: 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! H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor

11. Conclusions • Record-Playback methodology has several advantages: • Includes full 802.11n channel models. • Complete modeling of PHY with impairments. • Includes rate adaptation (with delays!). • Easy to merge different PHY and MAC proposals! • Compromises for Record-Playback method • Does not allow other than binary effects of interference – May be OK approximation for CSMA/CA multiple access scheme. • Limited Rate adaptation modeling: • Does not model PHY-MAC partitioning of rate adaptation. • Proposals likely to assume “best-case” rate adaptation algorithm H. Sampath, E. Lindskog and R. Narasimhan, Marvell Semiconductor