1. Erik Lindskog Hemanth Sampath Ravi Narasimhan
February
Record and Playback PHY Abstraction for n MAC Simulations - Using Soft PER Estimates
Erik Lindskog Hemanth Sampath
Ravi Narasimhan
E. Lindskog, H. Sampath, R. Narasimhan, Marvell Semiconductor

2. Record & Playback PHY Abstraction Scheme
February
Record & Playback PHY Abstraction Scheme
Includes:
Modified Black Box Methodology [IEEE /01 72r0]
PER estimation from raw BER simulations, related to [IEEE / r0] 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 /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

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

4. Channel Sequence T : Small enough to track channel,
February
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
February
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
February
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

7. February
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

8. Estimated Simulation Time for Generating Records
February
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. ( 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

9. February
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

10. Example MAC simulation
February
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

11. Modeling Feedback Delays
February
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

12. Conclusions Record-Playback methodology has several advantages:
February
Conclusions
Record-Playback methodology has several advantages:
Includes full n 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