%==========================================================================
% The mfile investigates the generation, transmission and reception of
% the OFDM signal without channel noise or HPA effect
% Written By : Baher Mohamed
%==========================================================================
clear all
clc
close
% ---------------
% A: Setting Parameters
% ---------------
M = 4; % QPSK signal constellation
no_of_data_points = 64; % have 64 data points
block_size = 8; % size of each ofdm block
cp_len = ceil(0.1*block_size); % length of cyclic prefix
no_of_ifft_points = block_size; % 8 points for the FFT/IFFT
no_of_fft_points = block_size;
% ---------------------------------------------
% B: % +++++ TRANSMITTER +++++
% ---------------------------------------------
% 1. Generate 1 x 64 vector of data points phase representations
data_source = randsrc(1, no_of_data_points, 0:M-1);
figure(1)
stem(data_source); grid on; xlabel('data points'); ylabel('transmitted data phase representation')
title('Transmitted Data "O"')
% 2. Perform QPSK modulation
qpsk_modulated_data = pskmod(data_source, M);
scatterplot(qpsk_modulated_data);title('qpsk modulated transmitted data')
% 3. Do IFFT on each block
% Make the serial stream a matrix where each column represents a pre-OFDM
% block (w/o cyclic prefixing)
% First: Find out the number of colums that will exist after reshaping
num_cols=length(qpsk_modulated_data)/block_size;
data_matrix = reshape(qpsk_modulated_data, block_size, num_cols);
% Second: Create empty matix to put the IFFT'd data
cp_start = block_size-cp_len;
cp_end = block_size;
% Third: Operate columnwise & do CP
for i=1:num_cols,
ifft_data_matrix(:,i) = ifft((data_matrix(:,i)),no_of_ifft_points);
% Compute and append Cyclic Prefix
for j=1:cp_len,
actual_cp(j,i) = ifft_data_matrix(j+cp_start,i);
end
% Append the CP to the existing block to create the actual OFDM block
ifft_data(:,i) = vertcat(actual_cp(:,i),ifft_data_matrix(:,i));
end
% 4. Convert to serial stream for transmission
[rows_ifft_data cols_ifft_data]=size(ifft_data);
len_ofdm_data = rows_ifft_data*cols_ifft_data;
% Actual OFDM signal to be transmitted
ofdm_signal = reshape(ifft_data, 1, len_ofdm_data);
figure(3)
plot(real(ofdm_signal)); xlabel('Time'); ylabel('Amplitude');
title('OFDM Signal');grid on;
% ------------------------------------------
% E: % +++++ RECEIVER +++++
% ------------------------------------------
% 1. Pass the ofdm signal through the channel
recvd_signal = ofdm_signal;
% 4. Convert Data back to "parallel" form to perform FFT
recvd_signal_matrix = reshape(recvd_signal,rows_ifft_data, cols_ifft_data);
% 5. Remove CP
recvd_signal_matrix(1:cp_len,:)=[];
% 6. Perform FFT
for i=1:cols_ifft_data,
% FFT
fft_data_matrix(:,i) = fft(recvd_signal_matrix(:,i),no_of_fft_points);
end
% 7. Convert to serial stream
recvd_serial_data = reshape(fft_data_matrix, 1,(block_size*num_cols));
% 8. Demodulate the data
qpsk_demodulated_data = pskdemod(recvd_serial_data,M);
scatterplot(qpsk_modulated_data);title('qpsk modulated received data')
figure(5)
stem(qpsk_demodulated_data,'rx');
grid on;xlabel('data points');ylabel('received data phase representation');title('Received Data "X"')
