Concetti Chiave
This paper establishes necessary and sufficient conditions for a k-dimensional linear code over the ring $\mathbb{Z}_{p^l}$ to achieve minimality. It also provides upper and lower bounds for the existence of minimal linear codes of a given dimension.
Sintesi
The paper explores the structure of modules over the ring $\mathbb{Z}_{p^l}$ and uses this understanding to derive necessary and sufficient conditions for the minimality of linear codes over this ring.
Key highlights:
- Defines the concepts of support, cover, Hamming distance, weight, and minimal codewords for linear codes over $\mathbb{Z}_{p^l}$.
- Proves that the orthogonal complement of a root word (a vector with at least one unit component) is a free module of dimension k-1, while the orthogonal complement of a non-root word is a finitely generated module.
- Establishes that the double orthogonal of a vector is the submodule generated by that vector.
- Provides a necessary and sufficient condition for a codeword to be minimal: the submodule generated by the vectors orthogonal to the codeword must equal the full orthogonal complement.
- Extends the concept of the parameter n(k;q) from finite fields to the ring $\mathbb{Z}_{p^l}$, proving that minimal linear codes of dimension k exist if and only if the length n is at least n(k;$p^l$).
- Derives upper and lower bounds for n(k;$p^l$), showing that $(k-1)p^l + p^{l-k} < n(k;p^l) \leq \frac{k(k-1)}{2}(p^l + p^{l-1} - 2) + k$ for $k \geq 3$, and $p^l + p^{l-2} + 1 < n(k;p^l) \leq \frac{k(k-1)}{2}(p^l + p^{l-1} - 2) + k$ for $k = 2$.