What is OFDM?Orthogonal Frequency Division Multiplexing

What is orthogonal frequency division multiplexing?

In OFDM, a single data stream is divided into several parallel streams, and each of the data stream(also known as sub-set) is multiplied by either a specific carrier frequency or code, and then all the parallel data streams are combined together using IFFT to make OFDM symbols for transmission. If each individual parallel data is multiplied by frequency then it is called OFDM, when a sub-set of data is multiplied by a code then it is called CDM or code division multiplexing. In fact OFDM is a special type of frequency division multiplexing (FDM). Unlike FDM, signals are not multiplied by a single carrier in OFDM- each sub-set of carrier creates a sub-channel for communication which has the advantage of less prone to interference since each sub-carrier frequency is kept orthogonal to each other.

difference between ofdm, TDM and CDM
difference between ofdm, TDM and CDM

OFDM Receiver

OFDM Receiver
OFDM Receiver
OFDM spectrum
OFDM spectrum

Advantages of OFDM

  • Huge bandwidth efficiency due to reduced carrier spacing (orthogonal carriers overlap)
  • Simple Equalization simplified, or eliminated
  • OFDM signals are resistant to fading
  • Scalable data transfer rate in different channel conditions
  • Single Frequency Networks are possible (broadcast application)



Disadvantages of OFDM

  • Still higher Peak-to-average ratio of OFDM signals are major problems in receiver.
  • OFDM singles are very sensitive to phase noise, timing and frequency offsets
  • OFDM receivers are very complex.
  • Expensive transmitters and receivers.
  • Data transmission rate get reduced for the requirement of guard interval.

Application Areas of OFDM

  • For broadcasting (TV and Radio)
  • Wi-Fi LAN, Wireless local loop (WLL)
  • Fourth generation Cellular transmission.
  • WiMax

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