Cyclic linear \(q\)-ary code 

Description

A \(q\)-ary code of length \(n\) is cyclic if, for each codeword \(c_1 c_2 \cdots c_n\), the cyclically shifted string \(c_n c_1 \cdots c_{n-1}\) is also a codeword. A cyclic code is called primitive when \(n=q^r-1\) for some \(r\geq 2\). A shortened cyclic code is obtained from a cyclic code by taking only codewords with the first \(j\) zero entries, and deleting those zeroes.

Cyclic-to-polynomial correspondence

Cyclic-to-polynomial correspondence: Cyclic linear \(q\)-ary codes and their properties can be naturally formulated using the theory of polynomials. Codewords \(c_1 c_2 \cdots c_n\) of a cyclic \(q\)-ary code can be thought of as coefficients in a polynomial \(c_1+c_2 x+\cdots+c_n x^{n-1}\) in the set of polynomials with \(q\)-ary coefficients, \(\mathbb{F}_q[x]\) with \(\mathbb{F}_q=GF(q)\). Polynomials corresponding to codewords of a linear cyclic code form an ideal (i.e., are closed under multiplication and addition) in the ring \(\mathbb{F}_q[x]/(x^n-1)\) (i.e., the set of equivalence classes of polynomials congruent modulo \(x^n-1\)). Multiplication of a codeword polynomial \(c(x)\) by \(x\) in such a ring corresponds to a cyclic shift of the corresponding codeword string.

Codeword polynomials of a cyclic code can be generated, via multiplication, by a generator polynomial \(g(x)\). A particular generator polynomial \(e(x)\) has the additional property of being idempotent, i.e., \(e(x)^2=e(x)\). Given a generator polynomial, the corresponding check polynomial \(h(x)=(x^n-1)/g(x)\) yields zero when multiplying a codeword polynomial. Its coefficients correspond to the code's parity check matrix.

Since the generator polynomial \(g(x)\) is a polynomial over \(GF(q)\), it can be factorized over some potentially larger splitting field (just like \(x^2+1\) can be factorized over the complex numbers but not the reals). Whenever \(q\) and \(n\) are relatively prime, cyclic codes can also be defined in terms of roots of \(g(x)\). Such roots are called zeroes of the code, and they are all powers of a primitive \(n\)th root of unity because \(g(x)\) is a divisor of \(x^n-1\). Since the generator polynomial generates all codeword polynomials \(c(x)\) by multiplication by \(x\), its zeroes are also zeroes of those polynomials.

Protection

Shift bound [1] gives a lower bound on the distance of cyclic \(q\)-ary codes.

Decoding

Meggitt decoder [2].Information set decoding (ISD) [3], a probabilistic decoding strategy that essentially tries to guess \(k\) correct positions in the received word, where \(k\) is the size of the code. Then, an error vector is constructed to map the received word onto the nearest codeword, assuming the \(k\) positions are error free. When the Hamming weight of the error vector is low enough, that codeword is assumed to be the intended transmission.Permutation decoding [4].

Notes

See Ch. 7 of Ref. [5] for an exposition.

Parents

  • Group-algebra code — A length-\(n\) cyclic \(q\)-ary linear code is an Abelian group-algebra code for the cyclic group with \(n\) elements \( \mathbb{Z}_n \).
  • Cyclic code

Children

Cousins

References

[1]
J. van Lint and R. Wilson, “On the minimum distance of cyclic codes”, IEEE Transactions on Information Theory 32, 23 (1986) DOI
[2]
J. Meggitt, “Error correcting codes and their implementation for data transmission systems”, IEEE Transactions on Information Theory 7, 234 (1961) DOI
[3]
E. Prange, “The use of information sets in decoding cyclic codes”, IEEE Transactions on Information Theory 8, 5 (1962) DOI
[4]
J. Macwilliams, “Permutation Decoding of Systematic Codes”, Bell System Technical Journal 43, 485 (1964) DOI
[5]
F. J. MacWilliams and N. J. A. Sloane. The theory of error correcting codes. Elsevier, 1977.
[6]
L. Babai, A. Shpilka, and D. Stefankovic, “Locally Testable Cyclic Codes”, IEEE Transactions on Information Theory 51, 2849 (2005) DOI
[7]
M. Sudan, “Invariance in Property Testing”, Property Testing 211 (2010) DOI
[8]
Yan Jia, San Ling, and Chaoping Xing, “On Self-Dual Cyclic Codes Over Finite Fields”, IEEE Transactions on Information Theory 57, 2243 (2011) DOI
[9]
S. Jitman et al., “Abelian Codes in Principal Ideal Group Algebras”, IEEE Transactions on Information Theory 59, 3046 (2013) DOI
[10]
V. D. Tonchev, "Codes and designs." Concise Encyclopedia of Coding Theory (Chapman and Hall/CRC, 2021) DOI
[11]
M. A. Tsfasman and S. G. Vlăduţ, Algebraic-Geometric Codes (Springer Netherlands, 1991) DOI
[12]
W. Willems, "Codes in Group Algebras." Concise Encyclopedia of Coding Theory (Chapman and Hall/CRC, 2021) DOI
[13]
G. G. La Guardia, “New Quantum MDS Codes”, IEEE Transactions on Information Theory 57, 5551 (2011) DOI
[14]
Y. Tang et al., “New quantum codes from dual-containing cyclic codes over finite rings”, (2016) arXiv:1608.06674
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Zoo Code ID: q-ary_cyclic

Cite as:
“Cyclic linear \(q\)-ary code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022. https://errorcorrectionzoo.org/c/q-ary_cyclic
BibTeX:
@incollection{eczoo_q-ary_cyclic, title={Cyclic linear \(q\)-ary code}, booktitle={The Error Correction Zoo}, year={2022}, editor={Albert, Victor V. and Faist, Philippe}, url={https://errorcorrectionzoo.org/c/q-ary_cyclic} }
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“Cyclic linear \(q\)-ary code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022. https://errorcorrectionzoo.org/c/q-ary_cyclic

Github: https://github.com/errorcorrectionzoo/eczoo_data/edit/main/codes/classical/q-ary_digits/group/cyclic/q-ary_cyclic.yml.