Spectrum Sharing for Unlicensed Bands

Spectrum Sharing for Unlicensed Bands

Raul Etkin, Abhay Parekh, and David TseDept of EECSU.C. Berkeley

Project supported by NSF ITR ANI-0326503 grant

DySPAN 2005, Nov. 10, 2005

2Spectrum Sharing for Unlicensed Bands

Problem: Spectrum SharingCan multiple heterogeneous wireless systems coexist and

share spectrum in a fair and efficient manner?

•Unlicensed setting

•Equal rights

•Different goals

Introduction

3Spectrum Sharing for Unlicensed Bands

Main Goals

• Find spectrum sharing rules that are:– Efficient– Fair– Robust against selfish behavior

• Study how to obtain good performance without

cooperation.

Introduction

4Spectrum Sharing for Unlicensed Bands

The Model• Flat Fading• Systems use Gaussian signals with

PSD {pi(f)}.

• Power constraint for each system.

• Total bandwidth W.

• Interference treated as noise.

• Design choice: power allocations over frequency.

Introduction

C1,1

C2,2

C1,2

C2,1

N0

N0

noise interference

5Spectrum Sharing for Unlicensed Bands

Static Gaussian Interference Game• M Players: the M systems

• Strategy of system: power allocation satisfying power constraint

• Utility of system i non-decreasing, concave on Ri.

• All parameters ({ci,j},{Pi},N0) are common knowledge.

• Players select their actions simultaneously.

Non-cooperative Scenarios

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Static Game AnalysisNon-cooperative Scenarios

full spread Nash equilibrium

Achievable ratesproportional fair

orthogonal

Unique if

XXinterference

limited

noise limited

price of anarchy

7Spectrum Sharing for Unlicensed Bands

Dynamic Game• What rate vectors are achievable as a N.E. in the dynamic game ?

Non-cooperative Scenarios

achievable with self enforcing strategies

Punishment strategies: encourage cooperation by threatening to spread

good behavior

punishment

8Spectrum Sharing for Unlicensed Bands

Example ANon-cooperative Scenarios

asymmetry in power and gains

802.11 bluetooth

full spread N.E.

proportional fair

9Spectrum Sharing for Unlicensed Bands

Example BNon-cooperative Scenarios

asymmetry in power

802.11

bluetooth

full spread N.E.

proportional fairQ: Can be achieved with other self enforcing strategies ?

No !best PF self enforcing point

10Spectrum Sharing for Unlicensed Bands

Asymmetry and FairnessNon-cooperative Scenarios

No Loss

No Loss

11Spectrum Sharing for Unlicensed Bands

Conclusions• With complete information and moderate asymmetry it is

possible to find policies that are fair, efficient and robust against selfish behavior.

• Results can be extended to:– Non-Gaussian signals– Any achievable rate region (with interference cancellation, etc.)

• Future research: – Find distributed algorithms that do not require complete

information and approximate the performance predicted here.– Investigate how to deal with cases of extreme asymmetry.

Conclusions

12Spectrum Sharing for Unlicensed Bands

Related Work• Distributed optimization of power spectral allocations for DSL using

iterative waterfilling [Cioffi, et al. 2001]

• Use of Game Theory to analyze outcomes of iterative waterfilling

algorithm [Cioffi, et al., 2002]

• Iterative waterfilling may lead to poor performance. Signal space

partitioning often leads to better results. [Popescu, Rose &

Popescu, 2004]

• Use of genetic algorithms to find good strategies in repeated games

with small strategy space. [Clemens & Rose, DySPAN 05]

Introduction