1. On the (In)feasibility of Fine Grained Power Control
Vivek Vishal Shrivastava Dheeraj Agrawal
Arunesh Mishra Suman Banerjee
Tamer Nadeem (Siemens Research)
Department Of Computer Sciences
University of Wisconsin-Madison
I am going to talk about some natural incentives to enable cooperation in p2p streaming scenarios. This is joint work with ….
Sep 27, 2006
MobiCom SRC ‘06

2. Transmission Power Control
Energy Efficiency
Spectral Efficiency
High Power
Low Power
Sep 27, 2006
MobiCom SRC ‘06

3. Transmission Power Control
A wide variety of power control algorithms have been proposed in literature
Few have made it to practice
This gap has been attributed to lack of sophisticated hardware
Absence of fine grained power levels in current state of the art wireless cards
Sep 27, 2006
MobiCom SRC ‘06

4. Transmission Power Control
A wide variety of power control algorithms have been proposed in literature
Few have made it to practice
This gap has been attributed to lack of sophisticated hardware
Absence of fine grained power levels in current state of the art wireless cards
Our claim: Even if fine-grained power control was
available in wireless cards, no algorithm will be able
to take advantage of it in any practical setting due to significant RSS variations
Sep 27, 2006
MobiCom SRC ‘06

5. The Essence
Q. What granularity of power control is practically usable and how do we determine these discrete power levels ?
Sep 27, 2006
MobiCom SRC ‘06

6. The Essence
Q. What granularity of power control is practically usable and how do we determine these discrete power levels ?
A1. In practical settings, significant overlap between RSS for different power levels makes fine grained power control infeasible
Sep 27, 2006
MobiCom SRC ‘06

7. The Essence
Q. What granularity of power control is practically usable and how do we determine these discrete power levels ?
A1. In practical settings, significant overlap between RSS for different power levels makes fine grained power control infeasible
A2. Few carefully chosen, environment dependent, discrete power levels are practically usable
Sep 27, 2006
MobiCom SRC ‘06

8. In this talk, we substantiate these claims and build an empirical power control model on the basis of these guidelines
Sep 27, 2006
MobiCom SRC ‘06

9. Some Existing Power Control Approaches
PCMA [Infocom ‘01]
An interesting work that proposed use of power control for throughput enhancement
Designed power controlled medium access
Receiver finds optimum power and sends a feedback to the transmitter
Use of out-of-band busy tones to silence neighbors
Other approaches: SHUSH[WICON ‘05], IPMA[SCC 2003]
Sep 27, 2006
MobiCom SRC ‘06

10. Some Existing Power Control Approaches
PCMA [Infocom ‘01]
One of the first works to use power control for throughput enhancement
Designed power controlled medium access
Receiver finds optimum power and sends a feedback to the transmitter
Use of out-of-band busy tones to silence neighbors
Other approaches: SHUSH[WICON ‘05], IPMA[SCC 2003]
Works well with fine grained power control
What happens if RSS variations are present?
Sep 27, 2006
MobiCom SRC ‘06

11. Limitations
Use of fine grained power levels works well in the absence of RSS variations
Sep 27, 2006
MobiCom SRC ‘06

12. However, RSS variations are significant in typical wireless scenarios
Limitations
Use of fine grained power levels works well in the absence of RSS variations
However, RSS variations are significant in typical wireless scenarios
Sep 27, 2006
MobiCom SRC ‘06

13. RSS Variations Multipath, fading, shadowing External Interference
Sep 27, 2006
MobiCom SRC ‘06

14. RSS Variations Multipath, fading, shadowing External Interference
20% packets are received at RSS of 22dBm
overlap
Sep 27, 2006
MobiCom SRC ‘06

15. RSS Variations Multipath, fading, shadowing External Interference
40,50,60 mw have significant overlap
Sep 27, 2006
MobiCom SRC ‘06

16. RSS Variations Multipath, fading, shadowing External Interference with
without
Sep 27, 2006
MobiCom SRC ‘06

17. Implications of RSS variations
Receiver cannot distinguish two transmit power levels with significant overlap
Only transmit power levels with minimum overlap be used together
Needs some number of packets (>1) to characterize RSS distribution
Sep 27, 2006
MobiCom SRC ‘06

18. The Essence - Part I
Q. What granularity of power control is practically usable and how do we determine these discrete power levels ?
A1. In practical settings, significant overlap between RSS for different power levels makes fine grained power control infeasible
Sep 27, 2006
MobiCom SRC ‘06

19. RSS variations are environment dependent
Line of Sight
Non Line of Sight
Non Line of Sight with Hotspot Interference
Non Line of Sight with controlled interference
Sep 27, 2006
MobiCom SRC ‘06

20. Practical Transmit Power Control
Sample sufficient number of packets at each power level
Sep 27, 2006
MobiCom SRC ‘06

21. Practical Transmit Power Control
Sample sufficient number of packets at each power level
Characterize RSS distribution
Sep 27, 2006
MobiCom SRC ‘06

22. Practical Transmit Power Control
Operate on power levels with non-overlapping RSS distributions
Sample sufficient number of packets at each power level
Characterize RSS distribution
Sep 27, 2006
MobiCom SRC ‘06

23. Characterizing RSS distribution
What is the minimum sample size to accurately capture RSS distribution?
Sep 27, 2006
MobiCom SRC ‘06

24. Characterizing RSS distribution
What is the minimum sample size to accurately capture RSS distribution?
RSS variations are typical of a particular indoor environment
Different number of packets may be required to accurately capture RSS distribution
Brute Force : Capture very large number of packets for determining RSS distribution
Sep 27, 2006
MobiCom SRC ‘06

25. Characterizing RSS distribution
What is the minimum sample size to accurately capture RSS distribution?
RSS variations are typical of a particular indoor environment
Different number of packets may be required to accurately capture RSS distribution
Brute Force : Capture very large number of packets for determining RSS distribution
Can we do better ?
Sep 27, 2006
MobiCom SRC ‘06

26. Online Mechanism Normalized Kullback-Leibler Divergence (NKLD)
Quantifies the distance or relative entropy between two distributions
Operating point
Sep 27, 2006
MobiCom SRC ‘06

27. Online Mechanism
Sep 27, 2006
MobiCom SRC ‘06

28. Evaluation accuracy of RSS distributions obtained with Online Mechanism
Sep 27, 2006
MobiCom SRC ‘06

29. Online Mechanism
Sample sufficient number of packets, to capture RSS distribution with some accuracy
Profile different available power levels
Find the power levels with non overlapping RSS distribution
Repeat this procedure periodically to cope up with large scale variations in channel conditions
Sep 27, 2006
MobiCom SRC ‘06

30. Experimental Testbed 12 8 10 11
Sep 27, 2006
MobiCom SRC ‘06

31. The final outcome
Number of power levels 3 1 2 3
Feasible Power Levels at four receivers in the testbed
Sep 27, 2006
MobiCom SRC ‘06

32. The Essence – Part II
Q. What granularity of power control is practically usable and how do we determine these discrete power levels ?
A1. In practical settings, significant overlap between RSS for different power levels makes fine grained power control infeasible
A2. Few carefully chosen, environment dependent, discrete power levels are practically usable
Sep 27, 2006
MobiCom SRC ‘06

33. Future Work
Use our model as a module in previously proposed Transmit Power Control mechanisms
Sep 27, 2006
MobiCom SRC ‘06

34. Future Work
Use our model as a module in previously proposed Transmit Power Control mechanisms
Study the interdependence between power and data rates, in view of few discrete power levels
Sep 27, 2006
MobiCom SRC ‘06

35. Future Work
Use our model as a module Transmit Power Control mechanisms
Study interdependence between power and data rates, in view of few discrete power levels
Build a practical transmit power control mechanism using the guidelines discussed here
Sep 27, 2006
MobiCom SRC ‘06

36. Questions ?
Sep 27, 2006
MobiCom SRC ‘06