1. Dynamic Data Rate and Transmit Power Adjustment in IEEE 802.11 Wireless LANs Pierre Chevillat, Jens Jelitto, and Hong Linh Truong IBM Zurich Research Laboratory International Journal of Wireless Information Networks Vol. 12, No. 3, July 2005

2. 2 Outline Introduction Joint power and data rate adaptation Rate selection Dynamic threshold High-Performance (HP) mode Low-Power (LP) mode Performance evaluation Conclusion

3. 3 Introduction To maximize the throughput or minimize the transmission delay High data rate is a right choice in many cases But high data rate may lead to an excessive number of retransmissions Low SNR S R High Low

4. 4 Introduction (cont.) Dynamically data rate selection could achieve a better throughput Better medium utilization Adapt to the channel condition

5. 5 Introduction (cont.) For battery-powered devices Transmission power awareness is crucial to save energy and prolong battery life When the distance to receiver is small Transmission power adjustment also helps reduce interference with neighbors

6. 6 Goal Adjusting jointly the transmit power level and the data rate to the radio channel conditions This method is fully compatible with the 802.11 wireless LAN standard Do not rely on the RTS/CTS protocol

7. 7 Goal (cont.) Optimize the throughput and transmit power for a given channel condition To transmit as many bits with as little energy as possible

8. 8 Rate selection There are four parameters in this algorithm s, f, S max and F max Concatenate successful transmissions count Concatenate failure transmissions count Successful threshold Failure threshold

9. 9 Rate selection (cont.) While the transmitter receiving an ACK frame s is increased by one f resets to zero Similarly, while the transmission is failed s resets to zero f is increased by one If s / f reaches S max / F max the data rate is increased/decreased the power level is decreased/increased

10. 10 Dynamic threshold adaptation The values of S max and F max are critical for the performance of the link adaptation scheme F max is set to 1 Immediate adaptation for the worse channel Decrease the data rate or increase the transmission power The optimum choice for S max depends on the channel dynamics

11. 11 Dynamic threshold adaptation (cont.) 1 1 2a2b Rapidly Slowly Rate increased

12. 12 High-Performance mode The primary goal for this mode is to support the highest possible data rate S max : rate increased Reduce the transmit power level F max : power level increased Reduce the transmission rate

13. 13 High-Performance mode (cont.) Failure Success

14. 14 High-Performance mode (cont.)

15. 15 Low-Power mode Use the lowest possible transmit power level Only adjust the transmit rate if we can’t decrease the power level Parameters dualities rate→ pow ++→ - - min→ max rate crit → pow crit pcnt→ rcnt P Max → R Max

16. 16 Rate Only mode Transmit power level is fixed Data rate is adjusted using the dynamic threshold adaptation scheme

17. 17 Performance Evaluations SimulatorC++ Packet length1000 Bytes Power levelMax: +10dBm, Min: -10dBm Power StepUp: +5dB, Down: -2dB ThresholdsS 1 =3, S 2 =10, F Max =1

18. 18 Throughput – distance between two nodes

19. 19 Average transmit power – distance between two nodes

20. 20 Power efficiency – distance between two nodes

21. 21 Mean Transfer Time (20M)

22. 22 Avg. Power and Power Efficiency

23. 23 Conclusion This paper have introduced new and simple but powerful dynamic link adaptation schemes These schemes utilize ACK frame for adjusting the link parameters No feedback is required from the receiver side All the schemes are fully compatible with the 802.11 wireless LAN standard

24. 24 Conclusion (cont.) These schemes should be applied to different services or requirements Ex: Power, performance

25. 25 Thank You !