OFDM is a digital modulation technique that divides the available bandwidth into multiple non-overlapping frequency sub-bands or carriers, with each sub-band being modulated with a low data rate. It provides benefits like high spectral efficiency, resilience to radio interference and multipath distortion. Some types of OFDM include COFDM, MIMO-OFDM, V-OFDM, W-OFDM and Flash-OFDM. It has advantages over other multiplexing techniques like WDM and TDM and is used in technologies like WiFi, DSL, digital TV and audio broadcasting.

1. Prepared By:
M. AFTAB ALAM 2097-FET/BSEE/F-13
Course Instructor:
DR.WASEEM KHAN

2.  Faculty of Engineering and Technology
Department of Electrical Engineering
International Islamic University,
Islamabad
 aftabalam2097@gmail.com

3. Introduction to OFDM
 A method of encoding digital data on multiple carrier
frequencies
o Wikipedia
 An FDM modulation technique for transmitting large amounts
of digital data over a radio wave
o Webopedia
 A method of digital modulation in which a signal is split into
several narrowband channels at different frequencies.
o Search Networking
 A digital transmission technique that uses a large number of
carriers spaced apart at slightly different frequencies
o PC Magazine Encyclope

4. Definition
 o Total bandwidth available within a communications system
is divided intosmaller non-overlapping frequency sub-bands
 Usually a separate data signal is associated to each
frequency sub-band
 Passband filter at receiver extracts requested frequency
sub-band / data signal

5. Types of OFDM
 C-OFDM
 MIMO-OFDM
 V-OFDM
 W-OFDM
 Flash-OFDM

6. 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

7. Multiple Input, Multiple Output OFDM
(MIMO-OFDM)
 Developed by Iospan Wireless
 Uses multiple antennas to transmit and receive radio signals
 Spatial multiplexing

8. 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

9. 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

10. 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

11. Differences from other multiplexing
techniques
 OFDM versus WDM
 -more flexible
 -higher bandwidth efficiency

12. Differences from other multiplexing
techniques
 OFDM versus TDM
 -number of carriers
 -synchronization
 -sensitivity
 -capacity/efficiency advantages
 -complexity and cost issues

13. OFDM ADVANTAGES
 OFDM is spectrally efficient
 IFFT/FFT operation ensures that sub-carriers do not interfere
with each other.
 OFDM has an inherent robustness against narrowband interference.
 Narrowband interference will affect at most a couple
of subchannels.
 Information from the affected subchannels can be
erased and recovered via the forward error
correction (FEC) codes.
 Equalization is very simple compared to Single-Carrier systems

14. OFDM ADVANTAGES
 OFDM has excellent robustness in multi-path environments.
 Cyclic prefix preserves orthogonality between sub-
carriers.
 Cyclic prefix allows the receiver to capture multi-
path energy more efficiently.
 Ability to comply with world-wide regulations:
 Bands and tones can be dynamically turned on/off
to comply with changing regulations.
 Coexistence with current and future systems:
 Bands and tones can be dynamically turned on/off
for enhanced coexistence with the other devices.

15. OFDM DRAWBACKS
 High sensitivity inter-channel interference, ICI
 OFDM is sensitive to frequency, clock and phase offset
 The OFDM time-domain signal has a relatively large peak-to-
average ratio
 tends to reduce the power efficiency of the RF amplifier
 non-linear amplification destroys the orthogonality of the OFDM
signal and introduced out-of-band radiation

16. Usage of OFDM
 Wired
 o Power Line Communications
 o Modern DSL
 Wireless
 o Modern WiFi access points – IEEE 802.11g
 o HD Radio broadcastmodems

17. Usage of OFDM
 Digital Audio and Video Broadcasting
 Asymmetric Digital Subscriber Line (ADSL)
 Wireless Networking
 Power-line Technology