dortmunduniversity

Faculty of Electrical Engineering & Information TechnologyComNets DortmundProf. Dr.-Ing. Christian Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Adaptive Random Frequency Hopping

Markus Putzke

15.03.2013

dortmunduniversity

Slide 2

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Overview Interference Issues of User Deployed Femtocells

Self-Organizing Interference Mitigation by Random Frequency Hopping

Introduction of System Model

Analytical Models for SINR and BER of Femtocell Users

Results and Performance Analysis (Analytical Models & Simulations)

Refinement: Fractional Frequency Reuse with Random Frequency Hopping

Conclusion and Outlook

dortmunduniversity

Slide 3

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Motivation User Deployed Femtocells

High spatial reuse to offload traffic Fixed backhaul to core network via broadband connection Random positions and random activity

Critical to performance improvement Self-Organization needed

MacrocellBase station

Macrocell MS

MacrocellBase station

Macrocell MS

Femtocell MS

FemtocellAccess Point

MacrocellBase station

Macrocell MS

Femtocell MS

FemtocellAccess Point

MacrocellBase station

Macrocell MS

Femtocell MS

FemtocellAccess Point

dortmunduniversity

Slide 4

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Limitations of centralized network planning Resource planning of OFDMA macrocells

No interference due to orthogonal centralizedplanning (time-frequency pattern)

Inefficient for Femtocells (unplanned deployment) Inter-Cell Interference between Femto- & Macrocell

Inter-Cell-Interference in the downlink

Freq

uenc

y

Base Station

Ad HocFemtocell

OFDMA Macrocell

ru

Mac

roce

ll Use

rs

ri ruFemtocell

Users

Interference

Range Expansion

dortmunduniversity

Slide 5

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Limitations of centralized network planning Resource planning of OFDMA macrocells

No interference due to orthogonal centralizedplanning (time-frequency pattern)

Inefficient for Femtocells (unplanned deployment) Inter-Cell Interference between Femto- & Macrocell

Inter-Cell-Interference in the uplink

Freq

uenc

y

Access Point

Base Station

Ad HocFemtocell

OFDMA Macrocell

ru

Mac

roce

ll Use

rs

ru

ri

Femtocell Users

Interference

dortmunduniversity

Slide 6

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

No exclusive resource allocation to target high spectral efficiency and spatial reuse

Frequency ICIC

Femtocell Scheduling Carrier Aggregation

Protected component carrier Time ICIC

Almost blank subframes

High Management Overhead and Capacity Issues

Existing Inter-Cell Interference Coordination (ICIC)

Base Station

Ad HocFemtocell

OFDMA Macrocell

Macroce

ll Use

rs

Femtocell Users

Victim User

Interference

Access Point

Base Station

Ad HocFemtocell

OFDMA Macrocell

Macroce

ll Use

rs

Femtocell Users

Victim UserFdb.

Interference

Access PointMacroce

ll Use

rs

Victim user determinedby measurements reports

dortmunduniversity

Slide 7

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Limitation of Interference with Random Frequency Hopping No sensing or monitoring of radio environment No exchange of information between cells Choose random hopping pattern

f

S(f)

Channel Bandwidth

fc f

S(f)

Channel Bandwidth

fc f

S(f)

Channel Bandwidth

fcf

S(f)fn(k)fn(k)

Channel Bandwidth

fc

... ...

Different Probability Density Functions (PDFs) possible Femtocell able to integrate itself (Self-Organization)

How much interference is introduced by Random Frequency Hopping (RFH)?

dortmunduniversity

Slide 8

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

System Model for Performance Evaluation Block diagram of analytical model and simulation

Interference signal is can be determined in an analytical way

DataOrigin

DigitalModulation

BPSKIFFT Analogous

Modulation

FadingChannel

DataSink

DigitalDemod FFT Analogous

Demod

RandomFrequency Hopping

DataOrigin

DigitalModulation

BPSKIFFT Analogous

Modulation

AWGN

CylicPrefix

CylicPrefix

CylicPrefix

OFDM Receiver

OFDM Transmitter

M Interferer RandomFrequency Hopping

zs

xs

xs+Mis

dortmunduniversity

Slide 9

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Analytical Model for the SINR (1) SINR of femtocell users

Transmitted OFDM signal of macrocell interferer

x(t) received by the femtocell and demodulated

tfjCtQdjN

d

d neeDztx 2)(2

1

0)(

T

C

CtQsjtfjMs dte

DetxAi m )(2

signal RF received

2 1)(Re

22

2

EE

ESINR

ni

y

y: signal from femtocelli: interference signaln: noise signal

fn: random carrier frequencyof macrocell user

N: number of subcarriersQ: subcarrier spacingT: symbol durationC: guard time

is: interference symbolszd: BPSK symbolsfm: random carrier frequency

of femtocell userA : Rayleigh/Rice amplitude

dortmunduniversity

Slide 10

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Analytical Model for the SINR (2) SINR of femtocell users for Rayleigh fading

with

where the expectation has to be evaluated according to

1

0

1

0

2ds,2

2

2 SNR1ReE

1N

s

N

dF

M

NDM

SINR

M: parameter Rayleigh distribution (macrocell)F: parameter Rayleigh distribution (femtocell)M: number of macrocell interferesfx = fn-fm: difference of random carrier frequenciespfx: PDF of fx

dz)(ReReE 2ds,

2ds,

zpzfxfx

x

CfjTfj

fsdQjee xx

2

22

ds,

dortmunduniversity

Slide 11

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Analytical Model for the BER: Frequency Non-Selective Channels BPSK: BER equals SER (Symbol Error Rate)

Can be solved with Laplace Transform

Numerical approximation with Gauss-Chebyshev

where

M

msss

A

rs nirxxpF

s1

withd)(BER

deeE

21BER

Fs

Ar

jc

jcs j

)(Im)(Re1BER2/

1kskks

ks crcr

xM

r

N

xds

x

s zpfDzxex

n

F

2

A-

0

1

0d,

2 eEdz)(RecoshE)(

c : Chernoff boundpr: Rayleigh/Rice distributionrk, k: numerical parameters

dortmunduniversity

Slide 12

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Parameter of Performance Analysis Scenario:

Random but coordinated approachNo Intra-Cell Interference

Worst case analysis Femtocell users located at cell edge

Comparison with FH-OFDMA systems (best case): Centralized and orthogonal planning

(no interference) Systems without resource planning (worst case): Macrocell interferers

transmit in same frequency bands as femtocell users Simulations of all systems

dortmunduniversity

Slide 13

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Performance Analysis: BER of Femtocell Users (1) BER versus distance to macrocell interferer ri

Access Point

Base Station

ruri

Femtocell User

Macrocell User

Scenario

Results

Access Point

Base Station

ruri

Femtocell User

Macrocell User

dortmunduniversity

Slide 14

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Performance Analysis: BER of Femtocell Users (2) BER versus distance to femtocell user ru

Scenario

Results

Access Point

Base Station

ruri

Femtocell User

Access Point

Base Station

ruri

Femtocell User

dortmunduniversity

Slide 15

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Performance Analysis: BER in Non-Frequency Selective Channels BER as a function of Rice factor K (PLOS/PNLOS)

The higher the Rice factor, the stronger the LOS power, the lower the BER K=0: Rayleigh fading

dortmunduniversity

Slide 16

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Fractional Frequency Reuse with Random Frequency Hopping

Classification of users: Femtocell edge (FE) and femtocell center users (FC) Macrocell center (MC) and macrocell users near the femtocell (ME)

Idea: Quasi orthogonal hopping PDFs of users nearby (at cell edge)

LTE Macrocell

Ad HocFemtocell

fFC

fFE

fME

fMC

Femtocell Frequency Change

Cell EdgeCell Center

Macrocell PDFs for the Femtocell

PDFs for the Macrocell

CellCenter

CellEdge

CellCenter

CellEdge

Details about this work can be found in WCNC 2013: Self-Organizing Fractional Frequency Reuse for Femtocells UsingAdaptive Random Frequency Hopping

dortmunduniversity

Slide 17

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Analytical Model for different PDFs

LTE Macrocell

Ad HocFemtocell

fFC

fFE

fME

fMC

Femtocell Frequency Change

Cell EdgeCell Center

Macrocell

The PDF pfx(z) can be derived from the scenario

pfx(z) Moving Macrocell user Moving femtocell userCenter fMC-fFE fME-fFC

Edge fME-fFE fME-fFE

dortmunduniversity

Slide 18

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Performance Analysis: BER of Femtocell Users (3) BER versus distance to macrocell interferer ri

Region 1: Macrocelluser near femtocell Region 2: Macrocell

user in cell center

dortmunduniversity

Slide 19

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Performance Analysis: BER of Femtocell Users (4) BER versus distance to femtocell user ru

Region 1: Femtocelluser in cell center Region 2: Femtocell

user at cell edge

dortmunduniversity

Slide 20

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Conclusion and Outlook Impact of Random frequency hopping as a self-organizing spectrum allocation

policy Inter-Cell Interference reduced by scrambling Quantification of impact by analytical models for the SINR/BER of femtocell

users All analytical models have been verified by simulations

Performance analysis shows that RFH is a low complexity solution to mitigate Inter-Cell-Interference Combination of Random Frequency Hopping with Fractional Frequency

Reuse further improves performance

Outlook Analysis of Random Frequency Hopping in multicellular environments Derivation of analytical models for the throughput and outage probability

dortmunduniversity

Slide 21

ComNets DortmundProf. Dr.-Ing. C. Wietfeld

Self-Organizing Interference Mitigation for Femtocells Using Frequency HoppingMarkus Putzke

Thank you for your attention!

Contact Information:

Address:TU Dortmund UniversityCommunication Networks InstituteOtto-Hahn-Str. 644227 Dortmund

Germany

Head of InstituteProf. Dr.-Ing. Christian Wietfeld

Point of Contact (POC):Markus Putzkefon.: +49 231 755 7963fax: +49 231 755 6136e-mail: Markus.Putzke@tu-dortmund.deinternet: http://www.cni.tu-dortmund.de