Further results on multiple coverings of the farthest-off points

Multiple coverings of the farthest-off points ((R,μ)-MCF codes) and the corresponding (ρ, μ)-saturating sets in projective spaces PG(N, q) are considered. We propose some methods which allow us to obtain new small (1, μ)-saturating sets and short (2, μ)-MCF codes with μ-density either equal to 1 (optimal saturating sets and almost perfect MCF-codes) or close to 1 (roughly 1+1/cq, c ≥ 1). In particular, we provide some algebraic constructions and bounds. Also, we classify minimal and optimal (1, μ)-saturating sets in PG(2, q), q small.