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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

OFDM MATLAB simulation code

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

OFDM BER curve

DOWNLOAD Source Code

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

Useful Links to MATLAB codes

Refer following as well as links mentioned on left side panel for useful MATLAB codes.
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OFDM Preamble generation
Time off estimation corr
Freq off estimation corr
channel estimation
11a WLAN channel
11g WLAN channel
15.3 UWB channel
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16d SUI Channel
16e wimax channel
Rician channel

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