Ronald Y. Chang†, Zhifeng Tao ◊, Jinyun Zhang ◊ and C.-C. Jay Kuo† †Ming Hsieh Department...

A Graph Approach to Dynamic Fractional Frequency Reuse (FFR) in Multi-Cell OFDMA Networks

Ronald Y. Chang†, Zhifeng Tao◊, Jinyun Zhang ◊ and C.-C. Jay Kuo††Ming Hsieh Department of Electrical Engineering and Signal and Image Processing Institute University of Southern California◊ Mitsubishi Electric Research Labs (MERL)

ICC 2009

Outline

Introduction System description Previous interference management schemes Proposed dynamic FFR scheme using the

graph approach Simulation results Conclusion

Introduction

Inter-cell interference(ICI)

MS

MS

MS

MS MS

MS

MS

MS

frequency

Introduction

Inter-cell interference

MS

MS

MS

MS MS

MS

MS

MS

frequency

Introduction

Inter-cell interference

MS

MS

MS

MS MS

MS

MS

MS

frequency

Introduction

Modification all these schemes are of fixed configuration

Goal Enhance overall cell throughput and service rate

System description

downlink cellular system with L BSs, each serving M(l) MSs, l = 1, 2, ... ,L

The downlink signal for MS m is sent with power Pm

System description

A set of N subchannels is available for resource allocation

slow fading (i.e., path loss)fast fading(i.e., Rayleigh fading)

anchor (or serving) BS for MS m

set of interfering MSs thermal noise density subchannel bandwidth

System description

The theoretical cell throughput(bits/sec) for cell l

set of MSs that are being served in cell l

System description

The service rate in cell l

cardinality of the set S(l)

Previous interference management schemes

Reuse-3

1

2

3Cell 1

Cell 2

Cell 3,44

Previous interference management schemes

Reuse-3

1

2

3

Cell 1 Cell 2 Cell 3,4

4

Previous interference management schemes

FFR-A

1

2

3

Cell 1 Cell 2 Cell 3

Previous interference management schemes

FFR-B

1

2

3

Cell 1 Cell 2 Cell 3

Proposed dynamic FFR scheme using the graph approach

Example scenario

BS1

BS2

BS3

MS2MS4

MS3MS5

MS1

Proposed dynamic FFR scheme using the graph approach

The graph construction rule for FFR-A MS a and MS b are users of the same cell MS a is a cell-edge user of cell i and MS b is a cell-

edge user of cell j, where cell i and cell j are neighbors

MS a is a cell-center user of cell i and MS b is a cell-edge user of cell j, where cell i and cell j are neighbors

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

Proposed dynamic FFR scheme using the graph approach

The graph construction rule for FFR-A Interference graph

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

MS1

MS2MS3

MS4

MS5

Cell 1 Cell 2 Cell 3

Proposed dynamic FFR scheme using the graph approach

The graph construction rule for FFR-B MS a and MS b are users of the same cell MS a is a cell-edge user of cell i and MS b is a cell-

edge user of cell j, where cell i and cell j are neighbors

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

Proposed dynamic FFR scheme using the graph approach

The graph construction rule for FFR-B Interference graph

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

MS1

MS2MS3

MS4

MS5

Cell 1 Cell 2 Cell 3

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS1

MS2MS3

MS4

MS5

MS1

MS2MS3

MS4

MS5FFR-A FFR-B

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS1

MS2MS3

MS4

MS5FFR-B

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

Cell 1 Cell 2 Cell 3MS1

MS1={1,2,3}MS2={1,2,3}MS3={1,2,3}

MS4={1,2,3}MS5={1,2,3}

123

MS4={1,2}MS5={1,2}

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS2MS3

MS4

MS5FFR-B

BS1

BS2

BS3MS2MS4

MS5MS3

MS1

Cell 1 Cell 2 Cell 3

MS5

123MS2={1,2,3}

MS3={1,2,3}

MS4={1,2}MS5={1,2}

MS3={1,3}MS4={1}

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS2MS3

MS4

FFR-BBS1

BS2

BS3MS2MS4

MS5MS3

MS1

Cell 1 Cell 2 Cell 3MS4 1

23MS2={1,2,3}

MS3={1,3}

MS4={1}

MS2={2,3}

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS2MS3

FFR-BBS1

BS2

BS3MS2MS4

MS5MS3

MS1

Cell 1 Cell 2 Cell 3

MS2

123MS2={2,3}

MS3={1,3}

Proposed dynamic FFR scheme using the graph approach

a(x) is defined as the set of colors that may be used to color node x

MS3

FFR-BBS1

BS2

BS3MS2MS4

MS5MS3

MS1

Cell 1 Cell 2 Cell 3

MS3

123

MS3={1,3}

Simulation results

Simulation results

The cell throughput in symmetric cell load scenarios

Simulation results

The service rate in symmetric cell load scenarios

Simulation results

The cell throughput in asymmetric cell load scenarios

Simulation results

The service rate in asymmetric cell load scenarios

Conclusion

A dynamic fractional frequency reuse (FFR) framework for multi-cell OFDMA networks was proposed in this work.

The dynamic feature is characterized by the capability of adjusting the spectral resource to varying cell load conditions.

The proposed dynamic scheme is shown to deliver higher cell throughput and service rate, especially in asymmetric cell load scenarios.