MATLAB: Generate a checksum compliant with ISO 13239 using the General CRC Generator block

checkCommunications Toolboxcyclicredundancy

How do I generate a checksum compliant with ISO 13239 using the 'General CRC Generator' block?

Best Answer

In order to generate a checksum compliant with ISO 13239 using the 'General CRC Generator' block, ensure the 'General CRC Generator' dialog parameters are set as follows:

- Initial states: 1

- Direct method: checked

- Reflect Input Bytes: checked

- Reflect checksums before final XOR: checked

- Final XOR: 1

- Checksums per frame: 1

Additionally, ensure the most significant bit of the input signal corresponds to the first element of the input binary column vector.

The output binary column vector consists of the the original word with the cyclic redundancy code bits appended to the end. The first element of the output binary vector corresponds to the most significant bit of the input signal.

Related Solutions

MATLAB: Though image is hidden in the cover image as by your code but when noise is added then we lost the watermark , what if we add checksum to the watermark image and we can construct the watermark.

Checksum would only help you to detect whether the watermark was still intact: it would not allow you to correct a watermark that has been altered. You need an Error Correcting Code (ECC) for that. One example is CRC, Cyclic Redundancy Check

MATLAB: How to configure crc.generator object from to implement X.25 Standard Cyclic Redundancy Check (CRC) coding with the Communications Toolbox 4.4 (R2009b)

The capability of directly generating X.25 Frame Checking Sequence using the GENERATE method of CRC.GENERATOR object is not available in Communications Toolbox 4.4 (R2009b).

However, the X.25 standard can be implemented using the crc.generator object. By default, crc.generator object is a CRC-CCITT generator, which is what X.25 implementation uses. However, X.25 does something extra, which is described in Section 2.2.7.4 of the X.25 documentation:

 The FCS field shall be a 16-bit sequence. It shall be the ones complement of the sum (modulo 2) of:
 1) the remainder of xk (x15 + x14 + x13 + x12 + x11 + x10 + x9 + x8 + x7 + x6 + x5 + x4 + x3 + x2 + x + 1) divided (modulo 2) by the generator polynomial x16 + x12 + x5 + 1, where k is the number of bits in the frame existing between, but not including, the final bit of the opening flag and the first bit of the FCS, excluding bits (synchronous transmission) or octets (start/stop transmission) inserted for transparency, and bits inserted for transmission timing (i.e. start or stop bits); and
 2) the remainder of the division (modulo 2) by the generator polynomial x16 + x12 + x5 + 1 of the product of x16 by the content of the frame, existing between but not including, the final bit of the opening flag and the first bit of the FCS, excluding bits (synchronous transmission) or octets (start/stop transmission) inserted for transparency and bits inserted for transmission timing (i.e. start or stop bits).

As a workaround, the following code implements X.25 standard using crc.generator object:

% Input
Address = [1 1 0 0 0 0 0 0];
UA = [1 1 0 0 1 1 1 0];
Input = [Address UA]';
% Expected FCS
FCS = [1 1 0 0 1 1 0 0 0 0 1 0 0 1 1 0];
k = length(Input);
h = crc.generator;
% Remainder of step 1)
cw1 = generate(h,[ones(16, 1); zeros(k-16,1)]);
% Remainder of step 2)
cw2 = generate(h,Input);
% Add the remainders and complement:
Workaround_FCS = not(mod(cw1(end-16+1:end) + cw2(end-16+1:end),2))';
% The result matches the FCS of X.25 standard test sequence
isequal(FCS,Workaround_FCS)

Best Answer

Related Solutions

MATLAB: Though image is hidden in the cover image as by your code but when noise is added then we lost the watermark , what if we add checksum to the watermark image and we can construct the watermark.

MATLAB: How to configure crc.generator object from to implement X.25 Standard Cyclic Redundancy Check (CRC) coding with the Communications Toolbox 4.4 (R2009b)

Related Question