For cyclic codes some well-known lower bounds and some decoding methods up to the half of the bounds are suggested. Particularly, the shift bound is a good lower bound of the minimum distance for cyclic codes, Reed-Muller codes and geometric Goppa codes. In this paper we consider cyclic codes defined by their defining set, and new simple derivation of the shift bound using the discrete Fourier transform with unknown elements and the Blahut theorem is shown. Moreover two examples of binary cyclic codes are given.

The Schaub bound is one of well-known lower bounds of the minimum distance for given cyclic code C, and defined as the minimum value, which is a lower bound on rank of matrix corresponding a codeword, in defining sequence for all sub-cyclic codes of given code C. In this paper, we will try to show relationships between the Schaub bound, the Roos bound and the shift bound from numerical experiments. In order to reduce computational time for the Schaub bound, we claim one conjecture, from numerical examples in binary and ternary cases with short code length that the Schaub bound can be set the value from only defining sequence of given code C.

The authors proposed an algorithm for calculation of new lower bound (rank bounded distance) using the discrete Fourier transform in 2010. Afterward, we considered some algorithms to improve the original algorithm with moving the row or column. In this paper, we discuss the calculation method of the rank bounded distance by conjugate elements for cyclic codes.

We proposed a method for constructing constant-weight and multi-valued sequences from the cyclic difference sets by generalization of the method in binary case proposed by N. Li, X. Zeng and L. Hu in 2008. In this paper we give some properties about sets of such sequences and it is shown that a set of non-constant-weight sequences over Z4 with length 13 from the (13,4,1)-cyclic difference set, and a set of constant-weight sequences over Z5 with length 21 from the (21,5,1)-cyclic difference set have almost highest linear complexities and good profiles of all sequences' linear complexities. Moreover we investigate the value distribution, the linear complexity and correlation properties of a set of sequences with length 57 over GF(8) from the (57,8,1)-cyclic difference set. It is pointed out that this set also has good value distributions and almost highest linear complexities in similar to previous two sets over Z4 with length 13 and Z5 with length 21.

In this paper, we will show that some families of periodic sequences over Z4 and Z8 with period multiple of 2r-1 generated by r-th degree basic primitive polynomials assorted by the root of each polynomial, and give the exact distribution of sequences for each family. We also point out such an instability as an extreme increase of their linear complexities for the periodic sequences by one-symbol substitution, i.e., from the minimum value to the maximum value, for all the substitutions except one.

Firstly we show a usuful property of the fast algorithm for computing linear complexities of p-ary periodic sequences with period pn (p: a prime). Secondly the property is successfully applied to obtain the value distribution of the linear complexity for p-ary periodic sequences with period pn.

We discuss a typical profile of the k-error linear complexity for balanced binary exponent periodic sequences and the number of periodic distinct sequences by their profiles. A numerical example with period 16 is also shown.

For a cyclic code, the BCH Bound and the Hartmann-Tzeng bound are two of well-known lower bounds for its minimum distance. New bounds are proposed by N. Boston in 2001, that depend on defining set of cyclic code. In this paper, we consider the between the Boston bound and these two bounds for non-binary cyclic codes from numerical examples.

The shift bound is a good lower bound of the minimum distance for cyclic codes, Reed-Muller codes and geometric Goppa codes. It is necessary to construct the maximum value of the independent set. However, its computational complexity is very large. In this paper, we consider cyclic codes defined by their defining set, and a new method to calculate the lower bound of the minimum distance using the discrete Fourier transform (DFT) is shown. The computational complexity of this method is compared with the shift bound's one. Moreover construction of independent set is shown.