How can I use erasure information to do Reed Solomon decoding with the Communications Toolbox 4.1 (R2008a)?

I am performing Reed-Solomon encoding and decoding. I have erasure information; that is, I know the location of the errors in the encoded signal. I know that the Reed Solomon decoding algorithm can correct more errors if it has the erasure information. How can I use erasure information with the RSDEC function?

Answer 1

[MathWorks Support Team]

This change has been incorporated into the documentation in Release 2009a (R2009a). For previous releases, read below for any additional information.

The ability to use erasure information with the RSDEC function is not available in Communications Toolbox.

To work around this limitation, you can use the FEC.RSDEC decoder object from the Communications Toolbox, instead of the RSDEC function. The following example demonstrates how this object can be used with erasure information, with m = 3, k = 5, n = 7:

          %%Code parameters

          n = 7; k = 5;

          %%Construct encoder

          coder = fec.rsenc(n,k);

          %%Message to encode

          msg = [0 1 2 3 4]'

          %%Perform Coding

          code = encode(coder,msg)

          %%Construct decoder from encoder

          decoder = fec.rsdec(coder);

          %%Introduce 2 errors in the codeword

          code(end) = 1;

          code(end-1) = 0;

          %%Generate a vector of erasures-- 0 marks a good symbol, 1 marks an error location

          erasures = [0 0 0 0 0 1 1]';

          %%Decode the code without supplying the erasures

          %  Note that the decoded message is incorrect, because the number

          %  of errors (2) exceeds the correction capability (n-k)/2 = 1

          [decoded,cnumerr,ccode] = decode(decoder,code);

          decoded

          %%Decode the code without supplying the erasures

          %  Note that the decoded message is correct now

          [decoded_with_erasures,cnumerr,ccode] = decode(decoder,code,erasures);

          decoded_with_erasures

More details on the FEC.RSDEC object are available at the following link:

 <http://www.mathworks.com/access/helpdesk/help/toolbox/comm/ref/fec.rsdec.html>

Furthermore, if you have the Communications Blockset (a Simulink block library), you can also perform Reed Solomon decoding with erasure information in the Simulink environment. Examples are provided at the following documentation link:

 <http://www.mathworks.com/access/helpdesk/help/toolbox/commblks/ug/fp74297.html#brb6prx>