Ofdm

OFDMOFDM((Orthogonal Frequency Division MultiplexingOrthogonal Frequency Division Multiplexing) )

ObjectivesObjectives

What is OFDMWhat is OFDM How OFDM worksHow OFDM works Types of OFDMTypes of OFDM Differences from other multiplexing Differences from other multiplexing

techniquestechniques ApplicationsApplications

What is OFDMWhat is OFDM

DefinitionDefinition

The first OFDM schemes presented in The first OFDM schemes presented in 19661966

Development of OFDM over yearsDevelopment of OFDM over years

A

F

How OFDM worksHow OFDM works

It distributes the data over a large number It distributes the data over a large number of carriers that are spaced apart at precise of carriers that are spaced apart at precise frequencies. This spacing provides the frequencies. This spacing provides the "orthogonality" in this technique which "orthogonality" in this technique which prevents the demodulators from seeing prevents the demodulators from seeing frequencies other than their own.frequencies other than their own.

Types of OFDMTypes of OFDM

C-OFDMC-OFDM

MIMO-OFDMMIMO-OFDM

V-OFDMV-OFDM

W-OFDMW-OFDM

Flash-OFDMFlash-OFDM

C-OFDMC-OFDM

Coded OFDMCoded OFDM Digital Audio Digital Audio

Broadcasting (DAB)Broadcasting (DAB) Digital Video Digital Video

Broadcasting (DVB-T)Broadcasting (DVB-T)

COFDM offers real COFDM offers real benefit in the benefit in the presence of isolated presence of isolated narrow-band narrow-band interfering signals interfering signals

Multiple Input, Multiple Output Multiple Input, Multiple Output OFDM )MIMO-OFDM(OFDM )MIMO-OFDM(

Developed by Iospan WirelessDeveloped by Iospan Wireless UUses multiple antennas to transmit ses multiple antennas to transmit

and receive radio signalsand receive radio signals SSpatial multiplexingpatial multiplexing

V-OFDMV-OFDM

Vector OFDM Vector OFDM Developed by CISCODeveloped by CISCO Increases subscriber coverageIncreases subscriber coverage Lowers the cost of provisioning and Lowers the cost of provisioning and

deploying infrastructure deploying infrastructure Employs both frequency and spatial Employs both frequency and spatial

diversity diversity Creates a robust processing technique for Creates a robust processing technique for

multi-path fading and narrow band multi-path fading and narrow band interference interference

…

Subscriber

Base Station

Paths

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W-OFDMW-OFDM Wideband OFDM Wideband OFDM Invented by Wi-LAN Invented by Wi-LAN Large spacing between carriers Large spacing between carriers Advantages:Advantages:- Optimal performance against Multi-path- Optimal performance against Multi-path

- Less sensitive to carrier offset- Less sensitive to carrier offset

-Optimal power efficiency of the transmitter -Optimal power efficiency of the transmitter amplifieramplifier

- More immune against fading - More immune against fading

Flash-OFDMFlash-OFDM

Fast-hopped OFDM Fast-hopped OFDM Wide-band spread-spectrum Wide-band spread-spectrum

technology technology Avoids the compromises inherent in Avoids the compromises inherent in

other mobile data systems other mobile data systems Capability to work around interfering Capability to work around interfering

signals signals

Differences from other multiplexing Differences from other multiplexing techniquestechniques

OFDM versus WDMOFDM versus WDM

-more flexible -more flexible

-higher bandwidth efficiency -higher bandwidth efficiency

Differences from other multiplexing Differences from other multiplexing techniquestechniques

OFDM versus OFDM versus TDMTDM

-number of carriers -number of carriers

-synchronization -synchronization

-sensitivity-sensitivity

-capacity/efficiency advantages-capacity/efficiency advantages

--complexity and cost issues complexity and cost issues

ApplicationsApplications

Digital Audio and Video Digital Audio and Video BroadcastingBroadcasting

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

Wireless NetworkingWireless Networking Power-line TechnologyPower-line Technology