Low-Complexity Geometrical Shaping for 4D Modulation Formats via Amplitude Coding

Signal shaping is vital to approach Shannon's capacity, yet it challenging implement at very high speeds. For example, probabilistic often requires arithmetic coding realize the target distribution. Geometric look-up tables store constellation points. In this paper, we propose a four-dimensional amplitude (4D-AC) geometrical shaper architecture. The proposed architecture can generate in real time geometrically shaped 4D formats via simple logic circuit operations and two conventional quadrature modulation (QAM) modulators. This paper describes 4D-AC used generating approximated versions of recently orthant symmetric with spectral efficiencies 6 bit/4D-sym 7 bit/4D-sym, respectively. Numerical results show losses below 0.05 dB when compared against baseline formats.