GORA: Goodput Optimal Rate Adaptation for 802 GORA: Goodput Optimal Rate Adaptation for 802.11 using Medium Status Estimation Nicola Baldo, Federico Maguolo, Simone Merlin, Andrea Zanella, Michele Zorzi Diego Melpignano, David Siorpaes 802.11 Rate Adaptation However… Aim Choosing the 802.11 PHY rate R that maximizes saturation throughput Most well-known Rate-Adaptation schemes (ARF, AARF, RBAR, MBLAS) are designed for single user scenarios MPDU-Based Link Adaptation Scheme (MBLAS) choose the PHY rate that achieves the best througput RBAR & MBLAS are often considered optimal In realistic scenarios we have Throughput and MBLAS SNR thresholds, 1 user Throughput and MBLAS SNR thresholds, 6 users Multiple users Collisions and prolonged backoff time MBLAS and RBAR are not optimal any longer! Other schemes have been proposed (e.g. CARA) State of the art and hence Goodput Optimal Rate Adaptation Goal Features Method No overhead RTS/CTS not required Standard compliancy Terminal-centric No cooperation among STAs Dynamically estimate medium status Estimate expected gooudput for different R Choose R that max. expected goodput Adapt PHY rate to actual channel conditions: quality of the radio signal Level of contention for the medium access medium access delay Goodput Model Medium Status Estimation Definition Medium Status  =< Pcoll,  ,SNR> where: Pcoll : Collision probability  : Average tick period SNR : Signal to Noise Ratio Estimate From MAC counters and measures we get Estimated Pcoll and Perr, SNR=20 dB Scenario Performance Evaluation Reference “Ideal” schemes GORA with real SNR (instead of estimated SNR) MBLAS (MPDU-Based Link Adaptation Scheme) Schemes suitable for implementation: GORA with estimated SNR MBLAS with RTS-CTS Still suffer from SNR measurement issues Non-standard protocol Auto Rate Fallback (ARF) Single user 3 interferes 9 interferes SNR=10dB Results Single user scenario MBLAS with no RTS-CTS and GORA achive optimum performance Multi user scenarios: MBLAS is suboptimal because it does not take into account losses due to collisions GORA achieves the best throughput, especially whether the SNR is known