Orthogonal Frequency Division Multiplexing

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Orthogonal Frequency Division Multiplexing
BOGAZIÇI UNIVERSITY Department of Computer
Engineering

• CMPE 530 Mathematical Foundations of Artificial
  Intelligence
• Project Presentation

Prepared by Buluç Çelik - 2003700543
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Outline

• Introduction
• Multiplexing Background
• Orthogonal Frequency Division Multiplexing
• Conclusion

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Introduction

• Orthogonal Frequency Division Multiplexing (OFDM)
  is a multiplexing technique where the data is
  distributed over a large number of sub-carriers
  spaced apart orthogonally.
• Benefits
• High spectral efficiency
• Resiliency to interference

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Introduction (Cont...)

• Application areas include
• Digital Audio Broadcasting (DAB)
• Digital Terrestrial Television Broadcasting
  (DTTB)
• Wireless Local Area Networks
• Asymmetric Digital Subscriber Line (ADSL)
  standard
• IEEE 802.11a

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Multiplexing Background

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

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Multiplexing Background (Cont...)

• Time Division Multiplexing

Time
Frequency
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Multiplexing Background (Cont...)

• Frequency Division Multiplexing

Time
Frequency
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Multiplexing Background (Cont...)

• Frequency Division Multiplexing (cont...)

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Orthogonal Frequency Division Multiplexing

• Orthogonal sub carriers satisfying the following
  conditions are used
• The modulation formula of an OFDM signal

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Orthogonal Frequency Division Multiplexing
(Cont...)

• The Fourier transform of each sub-carrier signal
  is a sinc function in frequency domain
• The zeroes of this sinc function occur at
  intervals f0. Since the sub-carrier spacing is
  exactly f0, there is no inter sub-carrier
  interference.

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

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Conclusion

• OFDM has high spectral efficiency
• OFDM is resilient to RF interference
• The implementation relies on very high speed DSP,
  which has only recently become available at a
  price that makes OFDM a competitive technology in
  the marketplace.

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