OFDM

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OFDM

• (Orthogonal Frequency Division Multiplexing )

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Objectives

• What is OFDM
• How OFDM works
• Types of OFDM
• Differences from other multiplexing techniques
• Applications

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What is OFDM

• Definition
• The first OFDM schemes presented in 1966
• Development of OFDM over years

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A
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How OFDM works

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

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Types of OFDM

• C-OFDM
• MIMO-OFDM
• V-OFDM
• W-OFDM
• Flash-OFDM

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C-OFDM

• Coded OFDM
• Digital Audio Broadcasting (DAB)
• Digital Video Broadcasting (DVB-T)
• COFDM offers real benefit in the presence of
  isolated narrow-band interfering signals

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Multiple Input, Multiple Output OFDM (MIMO-OFDM)

• Developed by Iospan Wireless
• Uses multiple antennas to transmit and receive
  radio signals
• Spatial multiplexing

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V-OFDM

• Vector OFDM
• Developed by CISCO
• Increases subscriber coverage
• Lowers the cost of provisioning and deploying
  infrastructure
• Employs both frequency and spatial diversity
• Creates a robust processing technique for
  multi-path fading and narrow band interference

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W-OFDM

• Wideband OFDM
• Invented by Wi-LAN
• Large spacing between carriers
• Advantages
• - Optimal performance against Multi-path
• - Less sensitive to carrier offset
• -Optimal power efficiency of the transmitter
  amplifier
• - More immune against fading

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Flash-OFDM

• Fast-hopped OFDM
• Wide-band spread-spectrum technology
• Avoids the compromises inherent in other mobile
  data systems
• Capability to work around interfering signals

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Differences from other multiplexing techniques

• OFDM versus WDM
• -more flexible
• -higher bandwidth efficiency

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Differences from other multiplexing techniques

• OFDM versus TDM
• -number of carriers
• -synchronization
• -sensitivity
• -capacity/efficiency advantages
• -complexity and cost issues

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Applications

• Digital Audio and Video Broadcasting
• Asymmetric Digital Subscriber Line (ADSL)
• Wireless Networking
• Power-line Technology