1. GORA: Goodput Optimal Rate Adaptation for 802
GORA: Goodput Optimal Rate Adaptation for using Medium Status Estimation
Nicola Baldo, Federico Maguolo, Simone Merlin, Andrea Zanella, Michele Zorzi
Diego Melpignano, David Siorpaes
Rate Adaptation
However…
Aim
Choosing the 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