A Novel Shaping Distribution Identification Based on QPSK-Assisted FFT for Probabilistic Shaping QAM OWC Systems

A shaping distribution identification method using digital frequency offset loading is proposed for probabilistically shaped M-quadrature amplitude modulation (PS-MQAM) optical wireless communication systems. The shaping distribution is encoded as four-bit information of digital frequency offset, which can be estimated by QPSK-selection assisted fast-Fourier-transform. Numerical results validate the scheme on eight PS-MQAM signals under various signal-to-noise ratios and suggest that the proposed scheme has a good performance using only a small number of QAM symbols.