Problem to recover data from bit stream

I have a txt file that has data:

123456789 abcef

Now I want to read it and recover it from bit stream. How to do it by matlab. I try to do it but to recovery that data from bit stream, it does not work This is my code

fid=fopen('test.txt','r');
sStream=fread(fid,'*char')' % to stream

%%convert to bit stream 0-1
sPacket=dec2bin(sStream,8);

%%store in vector Example s=[10000 1000 11101110 ...]
sPacket =  str2num(reshape(sPacket',[],8))';

%%Let recovery it to 123456789 abcef
%%Problem in here
dPacket = {}
for idxsPacket = 1:size(sPacket,2)
  dPacket{idxsPacket} = char(bin2dec(num2str(sPacket(idxsPacket)))) ;
end

It does has error but the result is not correct. Could you help me fix it? This is result

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Answer 1

[Geoff Hayes]

The use of reshape is causing the problem. Is there a reason why this is being used?

After you have read in the data (from file), the characters are all converted to their equivalent binary representation in sPacket as

 sPacket =

 00110001
 00110010
 00110011
 00110100
 00110101
 00110110
 00110111
 00111000
 00111001
 00100000
 01100001
 01100010
 01100011
 01100101
 01100110

The transpose of sPacket is

 sPacket' =

 000000000000000
 000000000011111
 111111111111111
 111111111000000
 000000011000000
 000111100000011
 011001100001101
 101010101010110

which is an 8x15 matrix, and so has 8*15=120 elements. Invoking reshape produces

 reshape(sPacket',[],8)

 00011011
 00010001
 10000000
 11000000
 01100011
 00110000
 00011101
 11101110
 01011011
 00110001
 10010000
 11001000
 01100111
 00110011
 11011100

a 15x8 matrix where 15 is chosen because of the use of [] (and since there are 120 elements in sPacket, 120/8 = 15). But note how these 15 binary strings are very different from the 15 strings in sPacket.

sPacket2 is then the string to number conversion of the above, and the code then works backwards, inverting all previous operations to get the original characters

 for idxsPacket = 1:length(sPacket2)
     dPacket{idxsPacket} = char(bin2dec(num2str(sPacket2(idxsPacket)))) ;
 end

In the above, there is no attempt to invert the reshape operation, and so the characters that are produced are not the correct ones.

The easy fix is to just remove the reshape operation, replacing

 sPacket2 =  str2num(reshape(sPacket',[],8))';

with

 sPacket2 = str2num(sPacket)';

Try the above and see what happens!

[Toan]

Thank you sir, I edit by my code. It run successfully

fid=fopen('test.txt','r');
sStream=fread(fid,'*char')' % to stream

sPacket=dec2bin(sStream,8)-'0';
dPacket = {};
size(sPacket)
fwid=fopen('decoded_file.txt','w');
for idxsPacket = 1:size(sPacket);
  dPacket{idxsPacket} = char(bin2dec(num2str(sPacket(idxsPacket,:)))) ;
  fwrite(fwid, dPacket{idxsPacket});
end
dPacket
fclose(fid);
fclose(fwid);