1. Transmit Power Requirements
May 2005
doc.: IEEE yy/xxxxr0
May 2005
Transmit Power Requirements
Date:
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Joe Epstein, Meru Networks
Joe Epstein, Meru Networks

2. May 2005
doc.: IEEE yy/xxxxr0
May 2005
Abstract
Reviews use of Transmit Power Control (TPC) to increase wireless network capacity. Suggests that we evaluate existing mechanisms
Joe Epstein, Meru Networks
Joe Epstein, Meru Networks

3. Contents Background The problem Common Uses
May 2005
Contents
Background
The problem
Common Uses
How This Affects What We Do
A Few More Considerations
Suggestions
Joe Epstein, Meru Networks

4. Background What is Transmit Power Control? Mechanisms
May 2005
Background
What is Transmit Power Control?
Ability to require that a STA constrain transmit power to within some bounds
Mechanisms
Defined in h, and extended by k
BSS-wide constraints provided by occasional advertisements, with STA having its own control within constraints
802.11h was motivated originally for regulatory compliance.
Of course, h does acknowledge other uses
Joe Epstein, Meru Networks

5. Background (2) Why do TPC?
May 2005
Background (2)
Why do TPC?
Smaller cells leads to greater capacity: spatial reuse.
Joe Epstein, Meru Networks

6. Background (3) Why control the stations’ power levels?
May 2005
Background (3)
Why control the stations’ power levels?
Asymmetric or non-uniform cell sizes do not work well with CSMA/CA AP
STA AP
Client thinks it can speak to AP;
AP can not successfully respond
STA 2
STA 1
Station 1 is hidden from Station 2
Creates more hidden stations, which is bad given the handshaking nature of the protocol
Thus, both sides need to agree
Joe Epstein, Meru Networks

7. Considerations Diminishing to negative returns on cell shrinkage
May 2005
Considerations
Diminishing to negative returns on cell shrinkage
Increased protocol overhead (handovers and such)
Lower transmit powers increases dominance of variable channel affects
Attenuation by the user’s body
The orientation of the station
Multipath
Higher power burst transmissions or interference
Different clients have different accuracies and precisions for power settings
This certainly varies over different antenna configurations
This may vary over different PHYs
Transitions from high-power to low-power coverage areas are difficult
Again, causes lack of uniform cell sizes, increasing collisions
Joe Epstein, Meru Networks

8. Recommendation We may already be far along
We should consider sensitivity mechanisms as well (other presentations)
May get us involved in discussion on what sensitivity truly means: carrier sense definitions
Let’s keep on thinking about the existing and in-progress mechanisms
Let’s ensure that it’s possible to make things work well in a heterogeneous client environment
This may involve making sure that accuracies are given correctly and that the behaviors are somewhat predictable
Let’s ask whether we should think about transitions in coverage across cells of different power levels
Joe Epstein, Meru Networks