OFDM and MCCDMA An Implementation using MATLAB Arjun
OFDM and MC-CDMA: An Implementation using MATLAB Arjun R. Kurpad Ashish Uthama Saptarshi Sen Shounak Mondal Internal Guide: External Guide: 1 PI 99 EC 014 017 089 096 Ms. Geetha Prakash, Lecturer, PESIT Dr. Girish Chandra, Scientist, NAL
Motivation… High transmission rates over wireline and wireless channels with protection from multipath fading Predicted technique in fourth Generation (4 G) 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 intercarrier 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: n n Windows OS MATLAB (R 12) + Toolboxes The design approach: n n Modular Tandem development of Tx and Rx
The Modules §Modulator module: Data Parameters FTX (The Transmitter) Channel Module BPSK, QPSK, 8 QAM Modulator Module §Channel module: AWGN, Fading, Physical Demodulator Module §Equalizer module §MC-CDMA module Equalizer Module FRX (The Receiver) Parameters Data
The Physical Channel Separate channel module Uses DAC/ADC capacity of the sound card Unique synchronization scheme: w Time synchronization w 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 SS 1. bmp
Applications 1. PC to PC file transfer using the ubiquitous sound card 2. Digital audio broadcasting (DAB), wireless CDquality sound transmission 3. Digital video broadcasting (DVB), specifically, digital terrestrial television broadcasting (DTTB) 4. Wireless LAN 802. 11 a 5. ADSL (asymmetric digital subscriber line), also called DMT (Digital Multi Tone)
Demonstration of the OFDM system…
- Slides: 23