This document discusses the implementation of OFDM and MC-CDMA modulation techniques using MATLAB. It motivates their use for high data rate applications and in 4G networks. The objectives are to simulate an OFDM baseband system to transfer files between PCs, model wireless fading channels, and demonstrate multi-user capability with MC-CDMA. Key sections explain OFDM methodology, guard periods, equalization in the frequency domain, and the MC-CDMA transmitter and receiver structure. The implementation in MATLAB is modular with components for modulation, channel modeling, equalization and MC-CDMA processing. Results show constellation diagrams and BER performance curves.

1. 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

2. 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

3. 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

4. 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.

5. What is OFDM ??
Orthogonality in time domain…

6. 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

7. OFDM Methodology

8. Understanding Multipath

9. Why we need the Guard Period…

10. Equalization Performed in frequency
domain
FFT compulsorily
performed in Receiver
Time domain
convolution replaced
with frequency domain
multiplication –
computationally simpler
code
Adaptive filters used

11. Multicarrier Code Division Multiple
Access (MC-CDMA)
Combination of CDMA-OFDM to provide
multi user capability
Frequency Diversity avoids deep fades
Simple receiver structure

12. MC-CDMA Transmitter

13. MC-CDMA Receiver

14. Design and Implementation
The Environment:
 Windows OS
 MATLAB (R12) + Toolboxes
The design approach:
 Modular
 Tandem development of Tx and Rx

15. The Modules
Modulator module:
BPSK, QPSK, 8QAM
Channel module:
AWGN, Fading, Physical
Equalizer module
MC-CDMA module
FTX (The Transmitter)
Data Parameters
Modulator Module
Channel Module
Equalizer Module FRX (The Receiver)
Demodulator Module
Data
Parameters

16. The Physical Channel
Separate channel module
Uses DAC/ADC capacity of the sound card
Unique synchronization scheme:
 Time synchronization
 Gain correction

17. The Physical Channel
Receiver Triggers here OFDM wave

18. Results
Constellation diagrams
Performance of Physical channel
BER curves for various combinations

19. Constellation diagram

20. BER Curve

21. Screen Shots
SS1.bmp

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

23. Demonstration of the
OFDM system…