A class of narrow-sense BCH codes over F_q of length q^m-1/2
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BCH codes with efficient encoding and decoding algorithms have many applications in communications, cryptography and combinatorics design. This paper studies a class of linear codes of length q^m-1/2 over F_q with special trace representation, where q is an odd prime power. With the help of the inner distributions of some subsets of association schemes from bilinear forms associated with quadratic forms, we determine the weight enumerators of these codes. From determining some cyclotomic coset leaders δ_i of cyclotomic cosets modulo q^m-1/2, we prove that narrow-sense BCH codes of length q^m-1/2 with designed distance δ_i=q^m-q^m-1/2-1-q^m-3/2+i-1/2 have the corresponding trace representation, and have the minimal distance d=δ_i and the Bose distance d_B=δ_i, where 1≤ i≤m+3/4.
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