Classification of pseudo-cyclic MDS codes

Linear codes are considered. A code is characterized by the length n, the dimension k, and the minimum distance d. An (n,k,d) code over the finite field GF(q) is said to be maximum distance separable (MDS) if d=n-k+1. A. Krishna and D.V. Sarwate (1990) investigated the existence of pseudo-cyclic MDS codes over GF(q) of length n, where n divides q-1 or q+1. It is shown that the pseudo-cyclic MDS codes constructed by Krishna and Sarwate are generalised Reed-Solomon codes. Pseudo-cyclic codes are studied over GF(q), where n and q=p/sup h/ are not relatively prime. It is proven that pseudo-cyclic (n,k) MDS codes modulo (x/sup n/-a) over GF(q) exist, if and only if n= p. Furthermore, any pseudo-cyclic (p,k) code modulo (x/sup p/-a) over GF(q) turns out to be MDS and generalized Reed-Solomon. It is explicitly proven that some classes of pseudo-cyclic (n,k) MDS codes over GF(q) are generalized Reed-Solomon codes. Furthermore, pseudo-cyclic (q+1,4) MDS codes over GF(q), q even, are completely classified.<
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