Error Using horzcat in MATLAB

Question

James Manns 2024-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/2112306-error-using-horzcat-in-matlab

评论： James Manns 2024-4-27

How to correct the following error in MATLAB? The received image is just a block of static.

clc;
clear all;
% Load the lenna image
lenna = imread('lenna.png');
% Convert image to grayscale
lenna_gray = rgb2gray(lenna);
% Convert pixel values to bits
lenna_bits = reshape(de2bi(lenna_gray), [], 1);
% BPSK modulation
Eb_No_low = 0; % Low SNR
Eb_No_high = 4; % High SNR
SNR_low = 10^(Eb_No_low/10);
SNR_high = 10^(Eb_No_high/10);
% Transmit and receive at low SNR
received_low = awgn(double(lenna_bits), SNR_low, 'measured'); 
% Demodulation
decoded_low = received_low < 0;
% Reshape decoded bits to original image size
decoded_image_low  = reshape(decoded_low, size(lenna_gray, 1), []);
% Plot original and received image at low SNR
figure;
subplot(1,2,1); imshow(lenna_gray); title('Original Image');
subplot(1,2,2); imshow(decoded_image_low); title('Received Image (0 dB SNR)');
% Transmit and receive at high SNR
received_high = awgn(double(lenna_bits), SNR_high, 'measured');
% Demodulation
decoded_high = received_high < 0;
% Reshape decoded bits to original image size
decoded_image_high  = reshape(decoded_high, size(lenna_gray, 1), []);
% Plot original and received image at high SNR
figure;
subplot(1,2,1); imshow(lenna_gray); title('Original Image');
subplot(1,2,2); imshow(decoded_image_high); title('Received Image (4 dB SNR)');
% Linear error detection code
% Example: Hamming (7,4) code
parityMatrix = [1 1 1 0 1 0 0; 1 1 0 1 0 1 0; 1 0 1 1 0 0 1];
generatorMatrix = [eye(4) parityMatrix'];
% Encode the data
encoded_data = mod(lenna_bits * generatorMatrix, 2);
% Add noise for linear error detection code
received_data = awgn(double(encoded_data), Eb_No_low, 'measured');
% Syndrome lookup table for error detection
syndrome_table = syndtable(parityMatrix);
% Decoding with error detection
decoded_data = zeros(size(encoded_data));
errors = zeros(size(encoded_data, 1), 1);
for i = 1:size(encoded_data, 1)
    syndrome = mod(received_data(i, :) * parityMatrix', 2);
    if sum(syndrome) ~= 0 % Error detected
        errors(i) = 1;
    else
        decoded_data(i, :) = received_data(i, :);
    end
end
% Count number of retransmission requests at different SNRs
SNRs = [0, 2, 4, 6, 8, 10];
retransmissions = zeros(size(SNRs));
for i = 1:length(SNRs)
    SNR = 10^(SNRs(i)/10);
    received_data = awgn(encoded_data, SNR, 'measured');
    errors = zeros(size(encoded_data, 1), 1);
    for j = 1:size(encoded_data, 1)
        syndrome = mod(received_data(j, :) * parityMatrix', 2);
        if sum(syndrome) ~= 0 % Error detected
            errors(j) = 1;
            retransmissions(i) = retransmissions(i) + 1;
        end
    end
end
% Plot number of retransmissions against SNR values
figure;
plot(SNRs, retransmissions, '-o');
xlabel('SNR (dB)');
ylabel('Number of Retransmissions');
title('Number of Retransmissions vs SNR');
% Error correction code
% Example: Reed-Solomon code
n = 255;
k = 223;
t = 16;
rs_encoder = comm.RSEncoder(n, k);
rs_decoder = comm.RSDecoder(n, k);
% Encode data
encoded_rs = step(rs_encoder, double(lenna_bits));
% Add noise for Reed-Solomon code
received_rs_low = awgn(double(encoded_rs), Eb_No_low, 'measured'); 
received_rs_high = awgn(double(encoded_rs), Eb_No_high, 'measured'); 
% Decode received data
decoded_rs_low = step(rs_decoder, received_rs_low);
decoded_rs_high = step(rs_decoder, received_rs_high);
% Reshape decoded bits to original image size
decoded_image_rs_low = reshape(decoded_rs_low, size(lenna_gray));
decoded_image_rs_high = reshape(decoded_rs_high, size(lenna_gray));
% Plot original and received images with error correction
figure;
subplot(1,2,1); imshow(decoded_image_low); title('Received Image (0 dB SNR, No Error Correction)');
subplot(1,2,2); imshow(decoded_image_rs_low); title('Received Image (0 dB SNR, Error Correction)');
figure;
subplot(1,2,1); imshow(decoded_image_high); title('Received Image (4 dB SNR, No Error Correction)');
subplot(1,2,2); imshow(decoded_image_rs_high); title('Received Image (4 dB SNR, Error Correction)');