Simulation Methodologies and Radio Impairment Modeling for Fair TGn Proposal Comparisons

1. Simulation Methodologies andRadio Impairment Modeling for Fair TGn Proposal Comparisons Jeff Gilbert Atheros Communications Jeff Gilbert, Atheros Communications

2. The Problem • Well specified: • Usage models • Also specifies some basic PHY characteristics • Channel models • Currently unspecified: • Radio impairment models • PHY abstraction used in MAC / system simulations • Both can dramatically affect comparison of proposals Jeff Gilbert, Atheros Communications

3. Radio Impairments • Several categories of impairments to consider: • Link margin components (Tx power, ant gain, Rx NF) • Synthesizer phase noise and frequency offset • Non-linearities (PA primarily) • Baseband impairments (I/Q mismatch etc.) • We need to decide as a group which to include and assure that all proposal simulations are consistent Jeff Gilbert, Atheros Communications

4. Radio Impairments I • This group affects link margin • Output power – some combination of: • Per chain PA limits – 17-20dBm? • EIRP (w/ any beamforming gains) limits • Beamformed EIRP increases w/ NumAnts2 allowing large gains • Individual antenna gain • Just use 0 dBi? 3 dBi? Omni directional, any polarization • Receiver noise floor • Specify as PSD or NF (as in usage models) – not noise floor • These could dramatically scale obtainable ranges – must be specified for fair comparisons Jeff Gilbert, Atheros Communications

5. Radio Impairments II • Phase noise (synthesizer) • Primary motivator for pilots and pilot tracking • Could also limit constellation size • Typically specified as shaped noise spectrum • Independent per-chain or common – affects pilot schemes • Frequency offset • Same as 11a or 11g is likely fine (specify one…) • Without phase noise and frequency offset, pilot and freq offset detection schemes cannot be fairly evaluated and we could select an inferior or unimplementable proposal Jeff Gilbert, Atheros Communications

6. Radio Impairments III • Non-linearities (PA, mixer) • This will limit the power usable for high-order constellations • If the PHY models are used to compute spectral mask for interference / capacity then this could be needed since it affects spectral regrowth • While nonlinearity is a critical implementation issue, it will likely not affect the implementability of proposals (beyond Tx power limit). If spectral mask is important then may be needed. Jeff Gilbert, Atheros Communications

7. Radio Impairments IV • Baseband impairments • I/Q mismatch • A/D converter resolution • Baseband noise floors • While these are critical implementation issues, likely they will not affect the implementability of proposals • Timing offset • Signal detection included in proposals? • At least require randomized sample timing Jeff Gilbert, Atheros Communications

8. PHY Modeling in System Sims • How TGn differs from other task groups • MAC & PHY w/throughput measured at MAC SAP • Time-varying channel creates time-varying PERs • Time-varying channel could affect systems w/feedback • PHY abstraction used in MAC / System simulations • Including full PHY model in system sims not feasible • However time-varying PER affects delay jitter and error rate application sees – thus modeling is critical • Limits specified in usage models subject to variations in methods used to measure them Jeff Gilbert, Atheros Communications

9. Possible Modeling Solutions • Modeling time-varying channels • PHY simulations per distance and get average PER • Use fixed time and number of packets • Could include fixed fading penalty instead • Could use full Markov model • Feedback systems need explicit modeling • PHY level simulations should incorporate interval between channel sounding and transmission incorporate the effect of channel variations TGn should specify how to generate consistent results but not own simulation or require specific packages Jeff Gilbert, Atheros Communications

10. Modeling Interference • Interference model impacts large enterprise usage model • Cellular reuse implies that co-channel and adjacent-channel interference will impact performance and system capacity • Several options for modeling interference • Simplified system-capacity reduction factor model given specified # channels (Cramer) • Per-connection PHY model using desired and interferer distance in 2-D table • Can be per-packet or per-symbol interference granularity • Solicit input from 802.19? Jeff Gilbert, Atheros Communications

11. Layer 3 and above Parameters • TCP stack parameters for TCP streams • TCP Window size will affect how much aggregation is possible • Aggregation is a key technique that most proposals will need to use to obtain the desired performance • Others? Jeff Gilbert, Atheros Communications

12. What to do? • Various implementation options: • Separate group / document referenced by FRCC? • Just add to Usage Models • Just add to Functional Requirements / Comparison Criteria • Just add to Channel Models • Some combination of the above Jeff Gilbert, Atheros Communications

13. Conclusions • 802.11n has taken great steps towards a smooth proposal comparison process • Still some ambiguity in radio impairments and PHY / MAC co-simulation • Key is balancing accuracy and effort • Simple (perfect) radio and PHY / MAC interface can be used – but it is critical that this is specified and uniform • Time spent now will be saved later! Jeff Gilbert, Atheros Communications