A Further Investigation on Complete Complementary Codes from $q$-ary Functions

This research focuses on constructing $q$-ary functions for complete complementary codes (CCCs) with flexible parameters. Most existing work has primarily identified sufficient conditions for $q$-ary functions related to $q$-ary CCCs. To the best of the authors' knowledge, this study is the first to establish both the necessary and sufficient conditions for $q$-ary functions, encompassing most existing CCCs constructions as special cases. For $q$-ary CCCs with a length of $q^m$ and a set size of $q^{n+1}$, we begin by analyzing the necessary and sufficient conditions for $q$-ary functions defined over the domain $\mathbb{Z}_q^m$. Additionally, we construct CCCs with lengths given by $L = \prod_{i=1}^k p_i^{m_i}$, set sizes given by $K = \prod_{i=1}^k p_i^{n_i+1}$, and an alphabet size of $ν= \prod_{i=1}^k p_i$, where $p_1 < p_2 < \cdots < p_k$. To achieve these specific parameters, we examine the necessary and sufficient conditions for $ν$-ary functions over the domain $\mathbf{Z}_{p_1}^{m_1} \times \cdots \times \mathbf{Z}_{p_k}^{m_k}$, which is a subset of $\mathbb{Z}_ν^m$ and contains $\prod_{i=1}^k p_i^{m_i}$ vectors. In this context, $\mathbf{Z}_{p_i}^{m_i} = \{0, 1, \ldots, p_i - 1\}^{m_i}$, and $m$ is the sum of $m_1, m_2, \ldots, m_k$. The $q$-ary and $ν$-ary functions allow us to cover all possible length sequences. However, we find that the proposed $ν$-ary functions are more suitable for generating CCCs with a length of $L = \prod_{i=1}^k p_i^{m_i}$, particularly when $m_i$ is coprime to $m_j$ for some $1 \leq i \neq j \leq k$. While the proposed $q$-ary functions can also produce CCCs of the same length $L$, the set size and alphabet size become as large as $L$, since in this case, the only choice for $q$ is $L$. In contrast, the proposed $ν$-ary functions yield CCCs with a more flexible set size $K\leq L$ and an alphabet size of $ν<L$.