Non-orthogonal multiple access scheme based on color-coded four-dimensional constellation pairing mapping

This paper proposes a short-range optical access method based on four-dimensional non-orthogonal multiple access (4D-NOMA), utilizing 4D constellation pairing mapping and two-dimensional inverse discrete Fresnel transform (2D-IDFnT) technology, achieving high compatibility with OFDM systems. An innovative color-coded 4D constellation pair mapping scheme was designed, introducing two types of four-dimensional spatial structures with 32 constellation points. By extending the three-dimensional constellation to four dimensions through color coding, the constellation figure of merit (CFM) increased by 22.2%. A 43.29 Gb/s 4D-NOMA transmission over a seven-core optical fiber was successfully demonstrated, verifying the feasibility and superiority of the proposed solution. Compared to conventional low-dimensional constellations, 4D-NOMA exhibits significant improvements in bit error rate and signal transmission sensitivity. Under the HD-FEC threshold, it provides approximately 0.9 dB and 1.3 dB sensitivity gains over traditional three-dimensional and two-dimensional constellations, respectively. This study indicates that the four-dimensional constellation structure and the 4D-NOMA scheme hold great potential for future short-range optical access systems.