Utility-based power control for interference mitigation in a mixed femtocell-macrocell environment

1
Utility-based power control for interference
mitigation in a mixed femtocell-macrocell
environment
Vaggelis G. Douros George C. Polyzos
WWRF26 Meeting WG8
Spectrum Issues 11-13
April 2011, Doha, Qatar
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
Motivation (1)
This is urgent!
Deadline is today!
The food is delicious
Fantastic shirt!
Some couples may not communicate efficiently ?
4
Motivation (2)

• 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

• 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

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 providers network via
  broadband

http//www.femtoforum.org/
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

9
Power Control Taxonomy (2)
Power Control Voice Networks vs. Data Networks 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 dont we combine these approaches?

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/femtocel
  ls
• 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
Zanders Scheme SINR Evolution
23
Zanders 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
  compatibledeserves a try!

27
? Shukran! ?

• Vaggelis G. Douros
• Mobile Multimedia Laboratory
• Department of Informatics
• Athens University of Economics and Business
• douros_at_aueb.gr
• http//mm.aueb.gr/douros