University Of Garden City For Science & Technology

Topic :- Orthogonal Frequency Division Multiplexing (OFDM)

Prepared by:- SHOAYB MOHAMEDEMAIL:- Supercadde6@gmail.com

ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM)CONTENTS DEFINATION OF OFDM OFDM VS FDM OFDM ADVANTAGES OFDM DIS-ADVANTAGES TYPES OF OFDM OFDM SYSTEM MODEL APPLICATIONS

DEFINATIONS OF OFDM

Orthogonal Frequency Division Multiplexing:-

Is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data

DEFINATIONS OF (OFDM)OFDM is a method of encoding digital data on multiple

carrier frequencies OFDM has developed into a popular scheme for

wideband digital communication, used in applications such as digital television and audio broadcasting, DSL Internet access, wireless networks, power line networks, and 4G mobile communications.

OFDM is also modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

OFDM VS FDM

As shown in the figure in FDM systems carriers are far apart with respect to each other and in OFDM systems carriers are densely packed and are orthogonal to the other carriers. Orthogonal means peak of one carrier occurs at null of the other. Hence OFDM system is bandwidth efficient compare to FDM system. In FDM system carriers are not orthogonal

OFDM system usually will have more Peak-to Average Power ration i.e. PAPR compare to FDM system. PAPR can be reduced by use of scrambler module and other techniques in OFDM systems

OFDM system provides higher data rate compare to FDM system in the same bandwidth usage.

 FDM systems are used in radio, satellite communications requiring good amount of guard bands between adjacent frequency bands. while OFDM systems are used in wimax-16d/16e, wlan-11g/11n and LTE technologies requiring higher

data rate and mainly used for broadband internet service.

ADVANTAGES OF OFDMCan easily adapt to severe channel conditions without

complex time-domain equalizationRobust against narrow-band co-channel interferenceRobust against inter-symbol interference (ISI) and

fading caused by multipath propagationEfficient implementation using fast Fourier

transform (FFT)Low sensitivity to time synchronization errorsTuned sub-channel receiver filters are not required

(unlike conventional-FDM)Facilitates single frequency networks (SFNs) (i.e.

transmitter macro-diversity)

DIS-ADVANTAGES OF OFDM

Sensitive to Doppler shiftSensitive to frequency synchronization problemsHigh peak-to-average-power ratio (PAPR),

requiring linear transmitter circuitry, which suffers from poor power efficiency

Loss of efficiency caused by cyclic prefix/guard interval

OFDM SYSTEM MODEL (TRANSMITER)

• Serial to parallel conversion• QPSK modulation• DAC• Inverse Fast Fourier –Transform 

OFDM SYSTEM MODEL (RECEIVER)

• Low pass filter• ADC• Fast Fourier-Transform

GENERAL BLOCK DIAGRAM

TYPES OF OFDMC-OFDM

MIMO-OFDM

V-OFDM

W-OFDM

Flash-OFDM

Coded (C-OFDM )Digital Audio Broadcasting (DAB)Digital Video Broadcasting (DVB-T)

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

Multiple Input, Multiple Output OFDM (MIMO-OFDM)

Developed by Iospan Wireless Uses multiple antennas to transmit and receive

radio signals Spatial multiplexing

VICTOR (V-OFDM)Developed by CISCO Increases subscriber coverage Employs both frequency and spatial diversity

Wideband (W-OFDM )Invented by Wi-LAN Large spacing between carriers ADVANTAGES:-Optimal performance against Multi-pathLess sensitive to carrier offsetOptimal power efficiency of the transmitter

amplifierMore immune against fading

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

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