OFDM and MCCDMA: An Implementation using MATLAB

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OFDM and MC-CDMA An Implementation using MATLAB

• Arjun R. Kurpad 1PI99EC 014
• Ashish Uthama 1PI99EC 017
• Saptarshi Sen 1PI99EC 089
• Shounak Mondal 1PI99EC 096

Internal Guide Ms. Geetha Prakash, Lecturer,
PESIT External Guide Dr. Girish Chandra,
Scientist, NAL
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Motivation

• High transmission rates over wireline and
  wireless channels with protection from multipath
  fading
• Predicted technique in fourth Generation (4G)
  mobile phones
• Ideal for bandwidth hogging applications like
  Video Conferencing, DAB, DVB, etc
• Multiuser capacity possible using MC-CDMA

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Objectives

• Simulation of a baseband communication system
  using OFDM
• Using this system to transfer files between
  computers using the sound card
• Simulation of wireless environment using fading
  channels
• Multi-User Capability using MC-CDMA
• Plotting of BER curves and constellations

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Advantages of OFDM

• Allows carriers to overlap (no guard band),
  resulting in lesser wasted bandwidth without any
  Inter Carrier Interference (ICI)
• High data rate distributed over multiple carriers
  resulting in lower symbol rate (more immune to
  ISI)
• Permits higher data rate as compared to FDM
• Increased security and bandwidth efficiency
  possible using CDMA OFDM (MC-CDMA)
• Simple guard intervals make the system more
  robust to multipath effects.

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What is OFDM ??Orthogonality in time domain
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What is OFDM ??Orthogonality in frequency domain

• Each carrier is modulated using BPSK / QPSK /
  M-ary QAM
• Frequency response for each carrier is a Sinc(X)
  
• Overlap of frequency response is possible as
  against FDM where inter-carrier spacing is a must
• Frequency responses of the carriers overlap at
  zero crossings avoiding Inter Carrier
  Interference

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OFDM Methodology
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Understanding Multipath
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Why we need the Guard Period
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Equalization

• Performed in frequency domain
• FFT compulsorily performed in Receiver
• Time domain convolution replaced with frequency
  domain multiplication computationally simpler
  code
• Adaptive filters used

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Multicarrier Code Division Multiple Access
(MC-CDMA)

• Combination of CDMA-OFDM to provide multi user
  capability
• Frequency Diversity avoids deep fades
• Simple receiver structure

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MC-CDMA Transmitter
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MC-CDMA Receiver
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Design and Implementation

• The Environment
• Windows OS
• MATLAB (R12) Toolboxes
• The design approach
• Modular
• Tandem development of Tx and Rx

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The Modules

• Modulator module
• BPSK, QPSK, 8QAM
• Channel module
• AWGN, Fading, Physical
• Equalizer module
• MC-CDMA module

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The Physical Channel

• Separate channel module
• Uses DAC/ADC capacity of the sound card
• Unique synchronization scheme
• Time synchronization
• Gain correction

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The Physical Channel
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Results

• Constellation diagrams
• Performance of Physical channel
• BER curves for various combinations

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Constellation diagram
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BER Curve
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Screen Shots

• SS1.bmp

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Applications

• PC to PC file transfer using the ubiquitous sound
  card
• Digital audio broadcasting (DAB), wireless
  CD-quality sound transmission
• Digital video broadcasting (DVB), specifically,
  digital terrestrial television broadcasting
  (DTTB)
• Wireless LAN 802.11a
• ADSL (asymmetric digital subscriber line), also
  called DMT (Digital Multi Tone)

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Demonstration of the OFDM system