“…To further improve the signal distance and, accordingly, SER characteristics, in this article we will discuss 4D constructions of hybrid type constellations of size M, which will be built based on a combination of BFSK and MAPSK modulations (the so-called BFSK-MAPSK signals). The main novelty of this paper is the presentation of a general regular method of constructing such 4D constellations that uses an analysis line different from [7] and for particular cases leads to the optimal construction of [7]. In the new scheme, MAPSK modulation uses two-level circular signal constellations with energy levels-high (E H ) and low (E L ).…”