Documentation

Integer-Output RS Decoder

Decode Reed-Solomon code to recover integer vector data

Library

Block sublibrary of Error Detection and Correction

Description

The Integer-Output RS Decoder block recovers a message vector from a Reed-Solomon codeword vector. For proper decoding, the parameter values in this block must match those in the corresponding Integer-Input RS Encoder block.

The Reed-Solomon code has message length K, and codeword length Nnumber of punctures. You specify N and K directly in the block dialog. The symbols for the code are integers between 0 and 2M-1, which represent elements of the finite field GF(2M). Restrictions on M and N are described in Restrictions on M and the Codeword Length N below.

The block can output shortened codewords when the Shortened message length S is specified. In this case, the codeword length N and message length K should specify the full-length (N, K) code that is shortened to an (NK+S, S) code.

The input and output are integer-valued signals that represent codewords and messages, respectively. The input and output signal lengths are listed in the Input and Output Signal Length in BCH and RS Blocks table on the BCH Decoder reference page. The block inherits the output data type from the input data type. For information about the data types each block port supports, see the Supported Data Types table.

For more information on representing data for Reed-Solomon codes, see the section Integer Format (Reed-Solomon Only).

If the decoder is processing multiple codewords per frame, then the same puncture pattern holds for all codewords.

The default value of M is ceil(log2(N+1)), that is, the smallest integer greater than or equal to log2(N+1). You can change the value of M from the default by specifying the primitive polynomial for GF(2M), as described in Specify the Primitive Polynomial below.

You can also specify the generator polynomial for the Reed-Solomon code, as described in Specify the Generator Polynomial.

An (N, K) Reed-Solomon code can correct up to floor((N-K)/2) symbol errors (not bit errors) in each codeword.

The second output is the number of errors detected during decoding of the codeword. A -1 indicates that the block detected more errors than it could correct using the coding scheme. An (N,K) Reed-Solomon code can correct up to floor((N-K)/2) symbol errors (not bit errors) in each codeword. The data type of this output is also inherited from the input signal.

You can disable the second output by deselecting Output number of corrected errors. This removes the block's second output port.

If decoding fails, the message portion of the decoder input is returned unchanged as the decoder output.

The sample times of the input and output signals are equal.

Punctured Codes

This block supports puncturing when you select the Punctured code parameter. This selection enables the Puncture vector parameter, which takes in a binary vector to specify the puncturing pattern. For a puncture vector, 1 represents that the data symbol passes unaltered, and 0 represents that the data symbol gets punctured, or removed, from the data stream. This convention is carried for both the encoder and the decoder. For more information, see Shortening, Puncturing, and Erasures.

    Note:   1s and 0s have precisely opposite meanings for the puncture and erasure vectors. For an erasure vector, 1 means that the data symbol is to be replaced with an erasure symbol, and 0 means that the data symbol is passed unaltered. This convention is carried for both the encoder and the decoder.

Dialog Box

Codeword length N

The codeword length.

Message length K

The message length.

Specify shortened message length

Selecting this check box enables the Shortened message length S text box.

Shortened message length S

The shortened message length. When you specify this parameter, provide full-length N and K values to specify the (N, K) code that is shortened to an (NK+S, S) code.

Specify generator polynomial

Selecting this check box enables the Generator polynomial text box.

Generator polynomial

Integer row vector whose entries are in the range from 0 to 2M-1, representing the generator polynomial in descending order of powers. Each coefficient is an element of the Galois field defined by the primitive polynomial.

This parameter applies only when you select Specify generator polynomial.

Specify primitive polynomial

Selecting this check box enables the Primitive polynomial text box.

Primitive polynomial

This parameter applies only when you select Specify primitive polynomial.

Binary row vector representing the primitive polynomial in descending order of powers.

Puncture code

Selecting this check box enables the Puncture vector text box.

Puncture vector

A column vector of length NK. In the Puncture vector, a value of 1 represents that the data symbol passes unaltered, and 0 represents that the data symbol gets punctured, or removed, from the data stream.

The default value is [ones(2,1); zeros(2,1)].

This parameter applies only when you select Puncture code.

Enable erasures input port

Selecting this check box will open the port, Era. This port accepts a binary column vector input signal with the same size as the codeword.

Erasure values of 1 represents symbols in the same position in the codeword that get erased, and values of 0 represent symbols that do not get erased.

Output number of corrected errors

When you select this check box, the block outputs the number of corrected errors in each word through a second output port. A decoding failure occurs when a certain word in the input contains more than (NK)/2 errors. A value of -1 indicates a decoding failure in the corresponding position in the second output vector.

Algorithm

This block uses the Berlekamp-Massey decoding algorithm. For information about this algorithm, see Algorithms for BCH and RS Errors-only Decoding.

Supported Data Types

PortSupported Data Types
In
  • Double-precision floating point

  • Single-precision floating point

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

Out
  • Double-precision floating point

  • Single-precision floating point

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

Era
  • Double-precision floating point

  • Boolean

Err
  • Double-precision floating point

  • Single-precision floating point

  • 8-, 16-, and 32-bit signed integers

  • If the input is uint8, uint16, or uint32, then the number of errors output datatype is int8, int16, or int32, respectively.

References

[1] Wicker, Stephen B., Error Control Systems for Digital Communication and Storage, Upper Saddle River, N.J., Prentice Hall, 1995.

[2] Berlekamp, Elwyn R., Algebraic Coding Theory, New York, McGraw-Hill, 1968.

[3] Clark, George C., Jr., and J. Bibb Cain, Error-Correction Coding for Digital Communications, New York, Plenum Press, 1981.

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