Orthogonal Frequency Division Orthogonal Frequency Division MultiplexingMultiplexing

CMPE 530 – Mathematical CMPE 530 – Mathematical Foundations of Artificial IntelligenceFoundations of Artificial Intelligence

Project PresentationProject Presentation

BOĞAZİÇİ UNIVERSITYDepartment of Computer Engineering

Prepared by:Prepared by: Buluç Çelik - 2003700543Buluç Çelik - 2003700543

OutlineOutline

IntroductionIntroduction

Multiplexing BackgroundMultiplexing Background

Orthogonal Frequency Division MultiplexingOrthogonal Frequency Division Multiplexing

ConclusionConclusion

IntroductionIntroduction

Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing (OFDM) is a multiplexing technique where (OFDM) is a multiplexing technique where the data is distributed over a large number the data is distributed over a large number of sub-carriers spaced apart orthogonally.of sub-carriers spaced apart orthogonally.

Benefits:Benefits: High spectral efficiencyHigh spectral efficiency Resiliency to interferenceResiliency to interference

Introduction Introduction (Cont...)(Cont...)

Application areas include:Application areas include:

Digital Audio Broadcasting (DAB)Digital Audio Broadcasting (DAB)

Digital Terrestrial Television Broadcasting Digital Terrestrial Television Broadcasting (DTTB)(DTTB)

Wireless Local Area Networks Wireless Local Area Networks

Asymmetric Digital Subscriber Line (ADSL) Asymmetric Digital Subscriber Line (ADSL) standardstandard

IEEE 802.11a IEEE 802.11a

Multiplexing BackgroundMultiplexing Background

MultiplexingMultiplexing

The technique of having a transmission capacity The technique of having a transmission capacity to be shared by many transmission sources to be shared by many transmission sources

MUX DEMUX1 data link, n data channels

n inputs n outputs

Multiplexing Background Multiplexing Background (Cont...)(Cont...)

Time Division MultiplexingTime Division Multiplexing

Time

Frequency

Multiplexing Background Multiplexing Background (Cont...)(Cont...)

Frequency Division MultiplexingFrequency Division Multiplexing

Time

Frequency

Multiplexing Background Multiplexing Background (Cont...)(Cont...)

Frequency Division Multiplexing (cont...)Frequency Division Multiplexing (cont...)

ccc fffftf 2cos2

ccc fffffXtftx *2cos2.

fcfXfcfXfffffX cc *

Orthogonal Frequency Division Orthogonal Frequency Division MultiplexingMultiplexing

Orthogonal sub carriersOrthogonal sub carriers satisfying the following satisfying the following conditions are usedconditions are used

The modulation formula of an OFDM signal:The modulation formula of an OFDM signal:

nm

nmTtnftmf

T

oo ,0

,2/2cos2cos

0

nm

nmTtnftmf

T

oo ,0

,2/2sin2sin

0

02sin2cos0

T

oo tnftmf

1

0

2sin2cosN

ocnocn tnffbtnffats

Orthogonal Frequency Division Orthogonal Frequency Division Multiplexing Multiplexing (Cont...)(Cont...)

The Fourier transform of each sub-carrier signal is a The Fourier transform of each sub-carrier signal is a sincsinc function in frequency domain function in frequency domain

The zeroes of this The zeroes of this sincsinc function occur at intervals function occur at intervals ff00. .

Since the sub-carrier spacing is exactly Since the sub-carrier spacing is exactly ff00, there is no , there is no

inter sub-carrier interference.inter sub-carrier interference. Having Having

overlapping sub-overlapping sub-carrier carrier spectrums, spectrums, OFDM OFDM technique uses technique uses the spectrum the spectrum very efficiently.very efficiently.

ConclusionConclusion

OFDM has high spectral efficiencyOFDM has high spectral efficiency OFDM is resilient to RF interference OFDM is resilient to RF interference The implementation relies on very high The implementation relies on very high

speed DSP, which has only recently speed DSP, which has only recently become available at a price that makes become available at a price that makes OFDM a competitive technology in the OFDM a competitive technology in the marketplace.marketplace.

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