Necessary and sufficient conditions for tight equi-difference conflict-avoiding codes of weight three

  • Authors:
  • Koji Momihara

  • Affiliations:
  • Graduate School of Information Science, Nagoya University, Furo-cho, Chikusa-ku, Japan 464-8601

  • Venue:
  • Designs, Codes and Cryptography
  • Year:
  • 2007

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Abstract

A conflict-avoiding code (CAC) C of length n and weight k is a collection of k-subsets of $${\mathbb{Z}}_n$$ such that $$\Delta(x) \cap \Delta(y) = \emptyset$$ holds for any $$x,y\in C$$ , $$x\not= y$$ , where $$\Delta(x)=\{j-i\,|\, i,j\in x, i\not= j\}$$ . A CAC with maximum code size for given n and k is called optimal. Furthermore, an optimal CAC C is said to be tight equi-difference if $$\bigcup_{x\in C}\Delta(x)={\mathbb{Z}}_n\setminus \{0\}$$ holds and any codeword $$x\in C$$ has the form $$\{0,i,2i,\ldots,(k-1)i\}$$ . The concept of a CAC is motivated from applications in multiple-access communication systems. In this paper, we give a necessary and sufficient condition to construct tight equi-difference CACs of weight k = 3 and characterize the code length n's admitting the condition through a number theoretical approach.