IEEE Consumer Communications & Networking Conference (CCNC) 2008, Las Vegas, USA

Transcription

1 RARA: Rate Adaptation Using Rate-adaptive adaptive Acknowledgment for IEEE WLANs IEEE Consumer Communications & Networking Conference (CCNC) 2008, Las Vegas, USA 정하경 Hakyung Jung School of Computer Science and Engineering Seoul National University, Korea

2 IEEE Rate Adaptation The a/b/g/n standards allow the use of multiple transmission rates b, 4 rate options (1,2,5.5,11Mbps) a, 8 rate options (6,9,12,18,24,36,48,54 Mbps) g, 12 rate options (11a set + 11b set) The method to select the transmission rate in real time is called Rate Adaptation Rate adaptation is important yet unspecified by the standards 2/14

3 Rate Adaptation Example 54Mbps Signal is good Sender Receiver 12Mbps Signal becomes weaker Sender Receiver Ideally, the transmission rate should be adjusted according to the channel condition 3/14

4 Importance of Rate Adaptation Rate adaptation plays a critical role to the throughput performance Rate too high loss ratio increases throughput decreases Rate too low under-utilize the capacity throughput decreases 4/14

5 Outline Related work Motivation Proposed algorithm Simulation Results Conclusion 5/14

6 Related Work Open-loop approach (ARF, AARF, CARA, RRAA,...) pros cons simple to implement standard compliant in general may misinterpret the causes of frame losses Closed-loop approach (RBAR, OAR, ) pros cons accurate channel estimation by receivers RTS/CTS exchange overhead not conform to the standard 6/14

7 Motivation requires ACK frames be transmitted at a rate, constrained by: Tx rate of ACK frame Tx rate of preceding DATA frame ACK frame should be selected within basic rate set What happens if we use the next lower(or higher) rate than the legacy ACK rate? Still interoperable and possible to be used to inform the transmitter of the channel condition information for the next data frame 7/14

8 Proposed rate adaptation When to increase the Tx rate scheme: RARA When to decrease the Tx rate Not the scope of this work Any schemes can be combined (ARF, CARA,.) 8/14

9 Operation Example Data Transmission at 11Mbps Data Transmission at 5.5Mbps ACK Transmission at 2Mbps ACK Transmission at 1Mbps ARF operation AP MS RARA operation AP MS rsnr of MS 11Mbps 5.5Mbps 2Mbps 1Mbps 9/14

10 Simulation Setup ns-2 simulator b PHY & indoor environment Empirical BER vs. SNR curves (by Intersil) Transmission power: 15 dbm Background noise level: -94 dbm Large scale model: Shadowing model (path-loss exponent of 4) Small scale model: Ricean fading model (RiceanK 3 dbm) Basic rate set: 1 and 2 Mbps LLC/IP/UDP, MSDU length: 1500bytes, Saturated traffic Testing schemes ARF, Adaptive-ARF(AARF), CARA RARA, RARA+CARA 10/14

11 Simulation Results (1/3) One-to-one topology with various distance From 5 to 60 meters Throughput curve of RA schemes follows the outer envelope of those of single-rate schemes RARA achieves better throughput over the entire range 11/14

12 Simulation Results (2/3) Star topology with varying number of contending stations ARF and AARF shows poor performance Not able to differentiate collisions from channel errors RARA performs better than CARA CARA acts the same with ARF to decide when to increase Tx rate 12/14

13 Simulation Results (3/3) One-to-one topology with varying Ricean parameter K Every scheme performs better as K increases RARA achieves better than others for the entire range of K 13/14

14 Conclusion We proposed a novel rate adaptation scheme, Receiver controls the ACK transmission rate as a means to dictate the sender to adjust data transmission rate Responsive to time-varying wireless channel owing to the accurate and instant feedback Compared with previous closed-loop schemes, adjusting ACK transmission rate is not costly Future Works Analytical study Comparison with closed-loop scheme e.g. RBAR 14/14

15 Any Questions? Thank you!! 15/16

16 Modified NAV operation 16/16