1. OFDM and MC-CDMA: An Implementation using MATLAB Arjun R. Kurpad1PI99EC 014 Ashish Uthama1PI99EC 017 Saptarshi Sen1PI99EC 089 Shounak Mondal1PI99EC 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. A DSL (asymmetric digital subscriber line), also called DMT (Digital Multi Tone)

23. Demonstration of the OFDM system…