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

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. Outline. Why do we focus on

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

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  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 douros@aueb.gr

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

  9. Power Control Taxonomy (2)

  10. VOICE NETWORKS DATA NETWORKS NOISELESS NOISY NO COST FUNCTION COST FUNCTION SIR BASED SINR BASED UTILITY BASED NET UTILITY BASED Power Control Taxonomy (3) • Why don’t 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/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 douros@aueb.gr http://mm.aueb.gr/~douros

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