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 11-13 April 2011, Doha, Qatar 19/2/2019 douros@aueb.gr

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

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 

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

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/

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!

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

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

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

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

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

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

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

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

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…

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?

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]

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)

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

A Toy Example

SINR Evolution

Zander’s Scheme: SINR Evolution

Zander’s Scheme: Power Evolution

Our Scheme: SINR Evolution

Our Scheme: Power Evolution

“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!

 Shukran!  Vaggelis G. Douros Mobile Multimedia Laboratory Department of Informatics Athens University of Economics and Business douros@aueb.gr http://mm.aueb.gr/~douros