Dynamic Data Rate and Transmit Power Adjustment in IEEE 802.11 Wireless LANs

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

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 R High Low S

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

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. 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. 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. Failure threshold Successful threshold Concatenate failure transmissions count Concatenate successful transmissions count Rate selection • There are four parameters in this algorithm • s, f, Smax and Fmax

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 Smax / Fmax • the data rate is increased/decreased • the power level is decreased/increased

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

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

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

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

14. High-Performance mode (cont.)

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 • ratecrit → powcrit • pcnt → rcnt • PMax → RMax

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

17. Performance Evaluations

18. Throughput – distance between two nodes

19. Average transmit power – distance between two nodes

20. Power efficiency – distance between two nodes

21. Mean Transfer Time (20M)

22. Avg. Power and Power Efficiency

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

25. Thank You !