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OFDM based transmitter and receiver

38 vues (au cours des 30 derniers jours)
Jose Iglesias
Jose Iglesias le 18 Avr 2023
Commenté : Jose Iglesias le 20 Avr 2023
I am trying to correct an error in my Matlab code. I am debugging my OFDM based transmitter and receiver with BPSK modulation Matlab code shown below. I tried a suggestion to remove an error I was getting when I would run my code. The suggestion was to change the following code instruction:
cp_len=floor(0.1*block_size); %Length of cyclic prefix
into the following code in order to convert 'cp_len' to integer
cp_len=round(0.1*block_size); %Length of cyclic prefix
I am still getting the following error.
Index in position 1 is invalid. Array indices must be positive integers or logical values.
Error in ofdm_bpsk_ji_2 (line 74)
cyclic_prefix = ifft_Subcarrier(end-cp_len+1:end, :);
Any suggestions on how I can remove this issue in my Matlab code? I am perusing the Mathworks forum and other sources to find a solution.The complete code is shown below. Thank you in advance!
clc;
clear all;
close all;
% Initiation
no_of_data_bits = 64;
M = 64; %Number of subcarrier channel
n = 256; %Total number of bits to be transmitted at transmitter
block_size=64; %Size of each OFDM block to add cyclic prefix
cp_len=round(0.1*block_size); %Length of cyclic prefix
% Read the video file
video = VideoReader('pexels-pixabay-856027-960x540-25fps.mp4');
% Loop through each frame of the video and convert it to a binary data stream
binary_data = [];
while hasFrame(video)
frame = readFrame(video);
% Convert the image to grayscale
gray_frame = rgb2gray(frame);
% Threshold the grayscale image to create a binary image
binary_frame = imbinarize(gray_frame);
% Reshape the binary image into a 1D array and append it to the binary data
binary_data = [binary_data reshape(binary_frame, 1, [])];
end
% Calculate the total number of bits in the video
total_bits = numel(binary_data);
% Use the binary data as the input source data
data = binary_data(1:no_of_data_bits);
figure(1)
stem(data);
grid on;
xlabel('DataPoints');
ylabel('Amplitude');
title('Original Data')
% Perform BPSK modulation on the input source data
psk_modulated_data = pskmod(data,2);
figure(2)
stem(psk_modulated_data);
title('PSK Modulation')
% Converting the series data stream into parallel data stream to form
% subcarriers
S2P = reshape(psk_modulated_data,no_of_data_bits/M,M);
figure(3)
stem(S2P)
title('Subcarriers')
grid on;
% Generate channel
channel = (randn(1, 10) + 1i * randn(1, 10)) / sqrt(2)
figure(4)
stem(channel);
grid on;
% IFFT of subcarriers and add cyclic prefix
number_of_subcarriers = M;
ifft_Subcarrier = ifft(S2P, block_size);
figure(5)
plot(real(ifft_Subcarrier),'r'),
title('IFFT on all the subcarriers')
% Add cyclic prefix
cyclic_prefix = ifft_Subcarrier(end-cp_len+1:end, :);
Append_prefix = [cyclic_prefix; ifft_Subcarrier];
figure(6)
plot(real(Append_prefix),'r')
% Initiate SNR range and BER array
SNR_range = -10:1:10;
BER = zeros(size(SNR_range));
% Loop over SNR range
for i = 1:length(SNR_range)
% Calculate noise variance for current SNR
snr = SNR_range(i);
noise_var = 1 / (10^(snr/10));
% Generate noisy channel coefficients
noisy_channel = channel + sqrt(noise_var/2)*(randn(1,10)+1i*randn(1,10));
% Convert to serial stream for transmission
ofdm_signal = Append_prefix(:).';
figure(7)
plot(real(ofdm_signal));
xlabel('Time');
ylabel('Amplitude');
title('OFDM Signal')
grid on
% Apply the channel
rx_signal = conv(ofdm_signal, channel, 'same');
% Remove cyclic prefix at the receiver
rx_no_cp = reshape(rx_signal, block_size+cp_len, M);
rx_no_cp(1:cp_len, :) = [];
% Perform FFT on received data
rx_fft = fft(rx_no_cp, block_size);
% Equalize channel effect
rx_equalized = rx_fft ./ channel(1);
% Perform BPSK demodulation
rx_demod = pskdemod(rx_equalized(:), 2);
% Calculate bit error rate
ber = sum(rx_demod ~= data.') / numel(data);
end
% Plot BER vs SNR
figure;
semilogy(SNR_range, BER);
grid on;
xlabel('SNR (dB)');
ylabel('Bit Error Rate');
title('Probability of Error vs SNR');
  2 commentaires
Daniel
Daniel le 19 Avr 2023
It's a little tricky to give good information on what's going wrong, as I can't replicate the error for a few reasons. After pasting your provided code into a temporary script, my line numbers don't match yours; and also, I'm having difficulty replicating the video file parsing stuff without that video file. Would you be able to attach a script that produces the error when run in a clean MATLAB instance in an otherwise empty directory?
Jose Iglesias
Jose Iglesias le 20 Avr 2023
Daniel,
Thanbk you for your response. I was able to resolve the issue by using this code:
cyclic_prefix = ifft_Subcarrier(:,end-cp_len+1:end);
Append_prefix = [cyclic_prefix ifft_Subcarrier];
At the momemnt I am still doing some trouble shooting and am currenlty trying add a zero padding to the channel of length
channel = [channel zeros(1, 64)];
I am doing this to equalize the channel since the OFDM sysytem has 64 subcarriers but I am getting an eror within the for loop for the "Loop over SNR range" section . This error states:
Arrays have incompatible sizes for this operation.
Error in ofdm_bpsk_ji_3 (line 102)
noisy_channel = channel + sqrt(noise_var/2)*(randn(1,10)+1i*randn(1,10));
I am going to post this new error and hopefully someone can give me some guidande on how to resolve this issue.

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