On the minimum distance of array-based spatially-coupled low-density parity-check codes

An array low-density parity-check (LDPC) code is a quasi-cyclic LDPC code specified by two integers q and m, where q is an odd prime and m ≤ q. The exact minimum distance, for small q and m, has been calculated, and tight upper bounds on it for m ≤ 7 have been derived. In this work, we study the minimum distance of the spatially-coupled version of these codes. In particular, several tight upper bounds on the optimal minimum distance for coupling length at least two and m = 3; 4; 5, that are independent of q and that are valid for all values of q ≥ q₀ where q₀ depends on m, are presented. Furthermore, we show by exhaustive search that by carefully selecting the edge spreading or unwrapping procedure, the minimum distance (when q is not very large) can be significantly increased, especially for m = 5.