Orthogonal Frequency Division Multiplexing (Ofdm)
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This document discusses Orthogonal Frequency Division Multiplexing (OFDM). It defines OFDM as a digital multi-carrier modulation technique that uses a large number of closely spaced orthogonal sub-carrier signals to carry data. The document outlines the advantages of OFDM, which include being robust against interference and fading, and its efficient implementation using FFT. Examples of applications that use OFDM are given as digital audio/video broadcasting, ADSL, wireless networking and power-line technology.
Orthogonal Frequency Division Multiplexing (Ofdm)
- 1. University Of Garden City For Science & Technology Topic :- Orthogonal Frequency Division Multiplexing (OFDM) Prepared by:- SHOAYB MOHAMED EMAIL:- Supercadde6@gmail.com
- 2. ORTHOGONALFREQUENCY DIVISION MULTIPLEXING(OFDM) CONTENTS DEFINATION OFOFDM OFDMVSFDM OFDMADVANTAGES OFDMDIS-ADVANTAGES TYPESOFOFDM OFDMSYSTEMMODEL APPLICATIONS
- 3. 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
- 4. 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.
- 5. 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
- 6. 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.
- 7. ADVANTAGES OF OFDM Can easily adapt to severe channel conditions without complex time-domain equalization Robust against narrow-band co-channel interference Robust against inter-symbol interference (ISI) and fading caused by multipath propagation Efficient implementation using fast Fourier transform (FFT) Low sensitivity to time synchronization errors Tuned sub-channel receiver filters are not required (unlike conventional-FDM) Facilitates single frequency networks (SFNs) (i.e. transmitter macro-diversity)
- 8. DIS-ADVANTAGES OF OFDM Sensitive to Doppler shift Sensitive to frequency synchronization problems High 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
- 9. OFDM SYSTEM MODEL (TRANSMITER) • Serial to parallel conversion • QPSK modulation • DAC • Inverse Fast Fourier –Transform
- 10. OFDM SYSTEM MODEL (RECEIVER) • Low pass filter • ADC • Fast Fourier-Transform
- 13. 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
- 14. 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-path Less sensitive to carrier offset Optimal power efficiency of the transmitter amplifier More immune against fading
- 15. 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
- 16. APPLICATIONS Digital Audio and Video Broadcasting Asymmetric Digital Subscriber Line (ADSL) Wireless Networking Power-line Technology