Optimal Binary (5, 3) Projective Space Codes from Maximal Partial Spreads

Recently a construction of optimal non-constant dimension subspace codes, also termed projective space codes, has been reported in a paper of Honold-Kiermaier-Kurz. Restricted to binary codes in a 5-dimensional ambient space with minimum subspace distance 3, these optimal codes may be interpreted in terms of maximal partial spreads of 2-dimensional subspaces. In a parallel development, an optimal binary (5, 3) code was obtained by a minimal change strategy on a nearly optimal example of Etzion and Vardy. In this paper, we report several examples of optimal binary (5, 3) codes obtained by the application of this strategy combined with changes to the spread structure of existing codes. We also establish that all our examples lie outside the framework of the construction of Honold et al.