Notice that, at the point where you do the zero-padding, binaryMsg is an 8-by-M matrix, where M is the number of characters in the original message:
msg = 'message'; % 7 characters long
% Convert the message to ASCII codes
asciiMsg = uint8(msg);
% Convert the ASCII codes to binary and concatenate them into a single vector
binaryMsg = dec2bin(asciiMsg, 8) - '0';
binaryMsg = binaryMsg.' % 8-by-7 after transposing
Now, length returns the size of the largest dimension, so length(binaryMsg) is:
- the length of the message, if the message is 8 or more characters long, or
- 8, if the message is 8 or fewer characters long
What I think you meant, instead of length(binaryMsg), is size(binaryMsg,2) or numel(asciiMsg).
However, that's not going to work either because this
binaryMsg = [zeros(1, numPaddingZeros), binaryMsg(:).'].';
is only padding numPaddingZeros zeros, instead of 8*numPaddingZeros zeros (i.e., a column's worth of zeros for each "missing" column of binaryMsg), so you'll get an error using reshape on the next line any time the message length is more than 8 and not a multiple of 4.
Instead of padding binaryMsg with zeros, you could more easily pad asciiMsg with numPaddingZeros zeros, before binaryMsg is created.
However, I don't think you need any zero-padding at all because the purpose of zero-padding in this case is to make sure the number of elements in binaryMsg (not the number of columns) is a multple of 4 (so that you can encode each sequence of 4 bits by multiplying with G to get 7 encoded bits), and since you are expressing each character as 8 bits when you do
binaryMsg = dec2bin(asciiMsg, 8) - '0';
% ^ eight bits specified
you are guaranteeing that numel(binaryMsg) is a multiple of 8 (and therefore a multiple of 4); no zero-padding is necessary.
