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 frequency

Introduction  Inter-cell interference MS frequency

Introduction  Inter-cell interference 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 P m

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 densitysubchannel 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 Cell 1 Cell 2 Cell 3,4 4

Previous interference management schemes  Reuse Cell 1Cell 2Cell 3,4 4

Previous interference management schemes  FFR-A Cell 1Cell 2Cell 3

Previous interference management schemes  FFR-B Cell 1Cell 2Cell 3

Proposed dynamic FFR scheme using the graph approach  Example scenario BS1 BS2 BS3 MS2 MS4 MS3 MS5 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 BS3 MS2 MS4 MS5 MS3 MS1

Proposed dynamic FFR scheme using the graph approach  The graph construction rule for FFR-A  Interference graph BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 MS2MS3MS4MS5 Cell 1Cell 2Cell 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 BS3 MS2 MS4 MS5 MS3 MS1

Proposed dynamic FFR scheme using the graph approach  The graph construction rule for FFR-B  Interference graph BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 MS2MS3MS4MS5 Cell 1Cell 2Cell 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 MS1MS2MS3MS4MS5MS1MS2MS3MS4MS5 FFR-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 MS1MS2MS3MS4MS5 FFR-B BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 Cell 1Cell 2Cell 3 MS1 MS1={1,2,3} MS2={1,2,3} MS3={1,2,3} MS4={1,2,3} MS5={1,2,3} 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 MS2MS3MS4MS5 FFR-B BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 Cell 1Cell 2Cell 3 MS MS2={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 MS2MS3MS4 FFR-B BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 Cell 1Cell 2Cell 3 MS MS2={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-B BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 Cell 1Cell 2Cell 3 MS MS2={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-B BS1 BS2 BS3 MS2 MS4 MS5 MS3 MS1 Cell 1Cell 2Cell 3 MS MS3={1,3}

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.