OFDM MATLAB Code

This section of MATLAB source code covers OFDM transmitter and OFDM receiver basic chain coded in matlab.

This page covers basic OFDM transmitter chain viz. binary data source,data mapping,IFFT,CP insertion. This time domain data is passed to the channel and AWGN. The OFDM receiver consists of CP removal,FFT, data demapping and decoding of the same data.

OFDM Transmitter part

clc;  

clear all;

close all;

%..............................................................

% Initiation

%..............................................................

no_of_data_bits = 64%Number of bits per channel extended to 128

M =4 %Number of subcarrier channel

n=256;%Total number of bits to be transmitted at the transmitter

block_size = 16; %Size of each OFDM block to add cyclic prefix

cp_len = floor(0.1 * block_size); %Length of the cyclic prefix

%............................................................

% Transmitter

%.........................................................

%.........................................................

% Source generation and modulation

%........................................................

% Generate random data source to be transmitted of length 64

data = randsrc(1, no_of_data_bits, 0:M-1);

figure(1),stem(data); grid on; xlabel('Data Points'); ylabel('Amplitude')

title('Original Data ')

% Perform QPSK modulation on the input source data

qpsk_modulated_data = pskmod(data, M);

figure(2),stem(qpsk_modulated_data);title('QPSK Modulation ')

%............................................................

%.............................................................

% Converting the series data stream into  four parallel data stream to form

% four sub carriers

S2P = reshape(qpsk_modulated_data, no_of_data_bits/M,M)

Sub_carrier1 = S2P(:,1)

Sub_carrier2 = S2P(:,2)

Sub_carrier3 = S2P(:,3)

Sub_carrier4 = S2P(:,4)

figure(3), subplot(4,1,1),stem(Sub_carrier1),title('Subcarrier1'),grid on;

subplot(4,1,2),stem(Sub_carrier2),title('Subcarrier2'),grid on;

subplot(4,1,3),stem(Sub_carrier3),title('Subcarrier3'),grid on;

subplot(4,1,4),stem(Sub_carrier4),title('Subcarrier4'),grid on;

%..................................................................

%..................................................................

%   IFFT OF FOUR SUB_CARRIERS

%.................................................................

%..............................................................

number_of_subcarriers=4;

cp_start=block_size-cp_len;

ifft_Subcarrier1 = ifft(Sub_carrier1)

ifft_Subcarrier2 = ifft(Sub_carrier2)

ifft_Subcarrier3 = ifft(Sub_carrier3)

ifft_Subcarrier4 = ifft(Sub_carrier4)

figure(4), subplot(4,1,1),plot(real(ifft_Subcarrier1),'r'),
title('IFFT on all the sub-carriers')

subplot(4,1,2),plot(real(ifft_Subcarrier2),'c')

subplot(4,1,3),plot(real(ifft_Subcarrier3),'b')

subplot(4,1,4),plot(real(ifft_Subcarrier4),'g')

%...........................................................

%...........................................................

%   ADD-CYCLIC PREFIX
%..........................................................

%............................................................

for i=1:number_of_subcarriers,

ifft_Subcarrier(:,i) = ifft((S2P(:,i)),16)% 16 is the ifft point

for j=1:cp_len,

cyclic_prefix(j,i) = ifft_Subcarrier(j+cp_start,i)

end

Append_prefix(:,i) = vertcat( cyclic_prefix(:,i), ifft_Subcarrier(:,i))
% Appends prefix to each subcarriers

end

A1=Append_prefix(:,1);

A2=Append_prefix(:,2);

A3=Append_prefix(:,3);

A4=Append_prefix(:,4);

figure(5), subplot(4,1,1),plot(real(A1),'r'),title('Cyclic prefix added to all the sub-carriers')

subplot(4,1,2),plot(real(A2),'c')

subplot(4,1,3),plot(real(A3),'b')

subplot(4,1,4),plot(real(A4),'g')

figure(11),plot((real(A1)),'r'),title('Orthogonality'),hold on ,plot((real(A2)),'c'),hold on ,
plot((real(A3)),'b'),hold on ,plot((real(A4)),'g'),hold on ,grid on


%Convert to serial stream for transmission

[rows_Append_prefix cols_Append_prefix]=size(Append_prefix)

len_ofdm_data = rows_Append_prefix*cols_Append_prefix

% OFDM signal to be transmitted

ofdm_signal = reshape(Append_prefix, 1, len_ofdm_data);

figure(6),plot(real(ofdm_signal)); xlabel('Time'); ylabel('Amplitude');

title('OFDM Signal');grid on;

%...............................................................

Passing time domain data through channel and AWGN

%.............................................................

channel = randn(1,2) + sqrt(-1)*randn(1,2);

after_channel = filter(channel, 1, ofdm_signal);

awgn_noise = awgn(zeros(1,length(after_channel)),0);

recvd_signal = awgn_noise+after_channel;   %   With AWGN noise

figure(7),plot(real(recvd_signal)),xlabel('Time'); ylabel('Amplitude');

title('OFDM Signal after passing through channel');grid on;

%...........................................................

OFDM receiver part

%..........................................................

recvd_signal_paralleled = reshape(recvd_signal,rows_Append_prefix, cols_Append_prefix);

%........................................................

%........................................................

%   Remove cyclic Prefix

%.......................................................

%......................................................

recvd_signal_paralleled(1:cp_len,:)=[];

R1=recvd_signal_paralleled(:,1);

R2=recvd_signal_paralleled(:,2);

R3=recvd_signal_paralleled(:,3);

R4=recvd_signal_paralleled(:,4);

figure(8),plot((imag(R1)),'r'),subplot(4,1,1),plot(real(R1),'r'),
title('Cyclic prefix removed from the four sub-carriers')

subplot(4,1,2),plot(real(R2),'c')

subplot(4,1,3),plot(real(R3),'b')

subplot(4,1,4),plot(real(R4),'g')

%...................................................

%...................................................

%   FFT Of recievied signal

for i=1:number_of_subcarriers,

%   FFT

fft_data(:,i) = fft(recvd_signal_paralleled(:,i),16);

end

F1=fft_data(:,1);

F2=fft_data(:,2);

F3=fft_data(:,3);

F4=fft_data(:,4);

figure(9), subplot(4,1,1),plot(real(F1),'r'),title('FFT of all the four sub-carriers')

subplot(4,1,2),plot(real(F2),'c')

subplot(4,1,3),plot(real(F3),'b')

subplot(4,1,4),plot(real(F4),'g')

%................................

%..............................

%   Signal Reconstructed

%..................................

%..................................

%   Conversion to serial and demodulationa

recvd_serial_data = reshape(fft_data, 1,(16*4));

qpsk_demodulated_data = pskdemod(recvd_serial_data,4);

figure(10)

stem(data)

hold on

stem(qpsk_demodulated_data,'rx');

grid on;xlabel('Data Points');ylabel('Amplitude');

title('Recieved Signal with error')

OFDM basic Tx-Rx Chain

The ofdm matlab code for the above block schematic is provided below for download. OFDM transmitter in this example consists of FEC encoder, BPSK modulator and 256 point IFFT. OFDM receiver part consists of FFT, BPSK demodulator and viterbi decoder.

BER curve for this OFDM matlab model is mentioned below taken after passing the transmitter data from AWGN channel.

BER Curve

DOWNLOAD Source Code

Download OFDM MATLAB source code files as per above block diagram.

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