1. WWRF26 Meeting WG8 Spectrum Issues 11-13 April 2011, Doha, Qatar
Utility-based power control for interference mitigation in a mixed femtocell-macrocell environment
Vaggelis G. Douros
George C. Polyzos
WWRF26 Meeting WG8 Spectrum Issues April 2011, Doha, Qatar
19/2/2019

2. Outline Why do we focus on
interference (mitigation)?
(utility-based) power control?
femtocell networks?
Interference mitigation through power control in a mixed femtocell-macrocell environment
A model with different objective functions for femtocells and macrocells
What if there are still unsatisfied nodes?
Conclusions

3. Some couples may not communicate efficiently 
Motivation (1)
Deadline is today!
This is urgent!
The food is delicious
Fantastic shirt!
Some couples may not communicate efficiently 

4. Motivation (2) N couples of friends discuss in the same cafeteria
Each couple aims at achieving a (different) “minimum quality of discussion”
Discussions of other couples may prevent an efficient communication
N pairs of wireless nodes (e.g., BSs-MNs, APs-Clients) transmit their data sharing the same wireless medium
Each pair aims at achieving a (different) (SINR) target
Interference among wireless devices may prevent an efficient communication
Competition for resources among multiple players, where the influence from each player is different

5. Why Femtocells? (1) Femtocell access points (FAPs)
low-power access points
provide voice and broadband services
allow a small number of simultaneous calls and data sessions
connect to the service provider’s network via broadband

6. Why Femtocells? (2) (+) dense deployment increase spectrum reuse
(+) better indoor coverage superior indoor reception
(+) low(er) cost (than macrocell deployment)
(+) plug and play installation …
(-) interference: This is the challenge!

7. Fundamentals of Power Control
Power control is a standard radio resource management method for interference mitigation
Analogy: A person that increases/ reduces his level of voice
Interference

8. Power Control Taxonomy (1)
[Douros & Polyzos, Elsevier COMCOM, 2011]
VOICE NETWORKS
NOISELESS
NOISY
SIR BASED
SINR BASED
DATA NETWORKS
NO COST FUNCTION
COST FUNCTION
UTILITY BASED
NET UTILITY BASED

9. Power Control Taxonomy (2)
Power Control: Voice Networks vs. Data Networks
Voice Networks
Data Networks
SI(N)R Based
(Net) Utility Based
Hard SINR targets
Soft SINR targets
Simplicity
Complexity
One metric
Many metrics
Engineering perspective
Economic perspective

10. Power Control Taxonomy (3)
Why don’t we combine these approaches?
VOICE NETWORKS
NOISELESS
NOISY
SIR BASED
SINR BASED
DATA NETWORKS
NO COST FUNCTION
COST FUNCTION
UTILITY BASED
NET UTILITY BASED

11. Power Control in a mixed femtocell-macrocell environment (1)
N transmitters share the same portion of the spectrum
N1 macrocell transmitters
high(er) priority to be served by the operators
low(er) QoS demands (than femtocells)
N2 femtocell transmitters
are deployed by indoor users for their self interest
should not create high interference to macrocell users
high(er) QoS demands
Conclusion: Difficult to describe their needs and restrictions with the same model

12. Power Control in a mixed femtocell-macrocell environment (2)
We can use different objective functions!
Macrocell Transmitter Objective Function:
subject to and
Femtocell Transmitter Objective Function:
subject to and

13. Power Control in a mixed femtocell-macrocell environment (3)
N1 macrocell transmitters
high(er) priority to be served by the operators
use any transmission power up to Pmax without pricing
low(er) QoS demands (than femtocells)
SINRmax
N2 femtocell transmitters
FAPs should not create high interference to macrocell users
pricing is used to discourage them from creating high interference to the macrocell users
high(er) QoS demands
No SINRmax

14. Power Control in a mixed femtocell-macrocell environment (4)
Each macrocell transmitter updates its power using
Each femtocell transmitter updates its power using

15. Power Control in a mixed femtocell-macrocell environment (5)
(+) simple scheme!
(+) fully distributed algorithm
(+) incentive compatible
at steady state, each transmitter cannot improve its utility unilaterally
(?) right selection of the system parameters
e.g. to reduce the outage probability, to increase the (total) throughput etc…

16. A supplementary approach (1)
And if there are still unsatisfied wireless nodes?
This is not only applicable to macrocells/femtocells
One solution: One/ many nodes need to “power off”
E.g. Trunc(ated) Power Control [Zander, TVT ’92]
“N-1” links apply a power control algorithm
the one that is furthest from its SINR target powers off
(-) Unfair for this node – no opportunity to achieve its target
More importantly, how to oblige an autonomous entity to power off?

17. A supplementary approach (2)
They should start negotiations! [Douros, Polyzos, Toumpis, VTC2011-Spring]
Links that have achieved their targets do not participate in the negotiations
Unsatisfied links negotiate in pairs. Each one uses part of its budget to make an offer to the other
“I offer you X credits if you reduce your power Y %”
These virtual credits may be used for future networking functions [Blazevic et al., IEEE Comm. Mag. ’01]

18. A supplementary approach (3)
How to choose who makes an offer?
How to choose to whom it offers?
Choose randomly one among the set of unsatisfied nodes
(-) This demands an external entity
A distributed approach: Each unsatisfied link decides independently whether it is a “Seller” or a “Buyer” and broadcasts its status to the network
Which is the desired percentage reduction Pred?
The minimum needed to achieve its target in the next round (but if, e.g., the node is distant this may be impossible)

19. A supplementary approach (4)
If there is an agreement, the Seller reduces its transmission power to the agreeing level
Otherwise, the Buyer voluntarily reduces a bit its current transmission power

20. A Toy Example

21. SINR Evolution

22. Zander’s Scheme: SINR Evolution

23. Zander’s Scheme: Power Evolution

24. Our Scheme: SINR Evolution

25. Our Scheme: Power Evolution

26. “The Meat” Modern/ Future wireless networks
heterogeneous needs
heterogeneous targets
interference remains a big challenge
Conditio sine qua non for interference mitigation: There is no “one-size fits-all” solution!
We need many algorithms that (may) vary with the time
We just show an example using power control in a mixed femtocell-macrocell environment
(+) simple, distributed, incentive compatible…deserves a try!

27.  Shukran!  Vaggelis G. Douros Mobile Multimedia Laboratory
Department of Informatics
Athens University of Economics and Business