Rate Optimal Binary Linear Locally Repairable Codes with Small Availability

TL;DR

This paper derives tight bounds and structural insights for rate-optimal binary linear locally repairable codes with small availability, and introduces geometric constructions based on polyhedra.

Contribution

It establishes new upper bounds, proves uniqueness of certain codes, and introduces geometric code constructions related to Platonic solids.

Findings

Tight upper bounds on code rate for (r,2) and (2,3) availability.

Uniqueness results showing codes are direct sums of shorter codes.

Construction of codes from convex polyhedra, including Platonic solids.

Abstract

A locally repairable code with availability has the property that every code symbol can be recovered from multiple, disjoint subsets of other symbols of small size. In particular, a code symbol is said to have $(r,t)$-availability if it can be recovered from $t$ disjoint subsets, each of size at most $r$. A code with availability is said to be 'rate-optimal', if its rate is maximum among the class of codes with given locality, availability, and alphabet size. This paper focuses on rate-optimal binary, linear codes with small availability, and makes four contributions. First, it establishes tight upper bounds on the rate of binary linear codes with $(r,2)$ and $(2,3)$ availability. Second, it establishes a uniqueness result for binary rate-optimal codes, showing that for certain classes of binary linear codes with $(r,2)$ and $(2,3)$-availability, any rate optimal code must be a direct sum of shorter rate optimal codes. Third, it presents novel upper bounds on the rates of binary linear codes with $(2,t)$ and $(r,3)$-availability. In particular, the main contribution here is a new method for bounding the number of cosets of the dual of a code with availability, using its covering properties. Finally, it presents a class of locally repairable linear codes associated with convex polyhedra, focusing on the codes associated with the Platonic solids. It demonstrates that these codes are locally repairable with $t = 2$, and that the codes associated with (geometric) dual polyhedra are (coding theoretic) duals of each other.