Bounds and Constructions of Locally Repairable Codes: Parity-check Matrix Approach
A $q$-ary $(n,k,r)$ locally repairable code (LRC) is an $[n,k,d]$ linear code over $\mathbb{F}_q$ such that every code symbol can be recovered by accessing at most $r$ other code symbols. The well-known Singleton-like bound says that $d \le n-k-\lceil k/r\rceil +2$ and an LRC is said to be optimal if it attains this bound. In this paper, we study the bounds and constructions of LRCs from the view of parity-check matrices. Firstly, a simple and unified framework based on parity-check matrix to analyze the bounds of LRCs is proposed. Several useful structural properties on $q$-ary optimal LRCs are obtained. We derive an upper bound on the minimum distance of $q$-ary optimal $(n,k,r)$-LRCs in terms of the field size $q$. Then, we focus on constructions of optimal LRCs over binary field. It is proved that there are only 5 classes of possible parameters with which optimal binary $(n,k,r)$-LRCs exist. Moreover, by employing the proposed parity-check matrix approach, we completely enumerate all these 5 classes of possible optimal binary LRCs attaining the Singleton-like bound in the sense of equivalence of linear codes.