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

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

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

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.

What is OFDM ?? Orthogonality in time domain…

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

OFDM Methodology

Understanding Multipath

Why we need the Guard Period…

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

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

MC-CDMA Transmitter

MC-CDMA Receiver

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

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

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

The Physical Channel Receiver Triggers here OFDM wave

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

Constellation diagram

BER Curve

Screen Shots SS1.bmp

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 a 5. A DSL (asymmetric digital subscriber line), also called DMT (Digital Multi Tone)

Demonstration of the OFDM system…