Reconstruction Codes for Deletions and Insertions: Connection, Distinction, and Construction

TL;DR

This paper explores the bounds and constructions of reconstruction codes for deletions and insertions, revealing fundamental connections, distinctions, and new bounds for minimum redundancy in various scenarios.

Contribution

It establishes a key connection between deletion and insertion reconstruction codes, disproves a conjecture, and constructs codes with tight bounds for small N values.

Findings

Reconstruction codes for insertions are less redundant than for deletions when N=O(n^{t-1}).

Disproved a previous conjecture about deletion reconstruction code redundancy.

Constructed codes with explicit bounds for N up to 5, extending prior results.

Abstract

Let $\mathcal{B}(\cdot)$ be an error ball function. A set of $q$-ary sequences of length $n$ is referred to as an \emph{$(n,q,N;\mathcal{B})$-reconstruction code} if each sequence $\boldsymbol{x}$ within this set can be uniquely reconstructed from any $N$ distinct elements within its error ball $\mathcal{B}(\boldsymbol{x})$. The main objective in this area is to determine or establish bounds for the minimum redundancy of $(n,q,N;\mathcal{B})$-reconstruction codes, denoted by $\rho(n,q,N;\mathcal{B})$. In this paper, we investigate reconstruction codes where the error ball is either the \emph{$t$-deletion ball} $\mathcal{D}_t(\cdot)$ or the \emph{$t$-insertion ball} $\mathcal{I}_t(\cdot)$. Firstly, we establish a fundamental connection between reconstruction codes for deletions and insertions. For any positive integers $n,t,q,N$, any $(n,q,N;\mathcal{I}_t)$-reconstruction code is also an $(n,q,N;\mathcal{D}_t)$-reconstruction code. This leads to the inequality $\rho(n,q,N;\mathcal{D}_t)\leq \rho(n,q,N;\mathcal{I}_t)$. Then, we identify a significant distinction between reconstruction codes for deletions and insertions when $N=O(n^{t-1})$ and $t\geq 2$. For deletions, we prove that $\rho(n,q,\tfrac{2(q-1)^{t-1}}{q^{t-1}(t-1)!}n^{t-1}+O(n^{t-2});\mathcal{D}_t)=O(1)$, which disproves a conjecture posed in \cite{Chrisnata-22-IT}. For insertions, we show that $\rho(n,q,\tfrac{(q-1)^{t-1}}{(t-1)!}n^{t-1}+O(n^{t-2});\mathcal{I}_t)=\log\log n + O(1)$, which extends a key result from \cite{Ye-23-IT}. Finally, we construct $(n,q,N;\mathcal{B})$-reconstruction codes, where $\mathcal{B}\in \{\mathcal{D}_2,\mathcal{I}_2\}$, for $N \in \{2,3, 4, 5\}$ and establish respective upper bounds of $3\log n+O(\log\log n)$, $3\log n+O(1)$, $2\log n+O(\log\log n)$ and $\log n+O(\log\log n)$ on the minimum redundancy $\rho(n,q,N;\mathcal{B})$. This generalizes results previously established in \cite{Sun-23-IT}.