End-to-end constellation shaping for fiber-terahertz integrated communications

In 6G areas such as wireless fronthaul and access networks, the coexistence of multiple linear and nonlinear distortions in fiber-terahertz links poses significant challenges for achieving high spectral efficiency. In this paper, we propose an end-to-end four-dimensional joint geometric and probabilistic shaping (E2E-4D-JGPS) for a fiber-terahertz integrated communication system. Firstly, a constellation-level equalized channel modeling method based on the mixture density network (MDN) is developed. Then, we use it to connect the constellation shaper in the transmitter and the de-mapper in the receiver, and implement generalized mutual information (GMI) as the optimization metric to adaptively design a constellation diagram close to the global optimum according to the damage mechanism of the hybrid links. Finally, we demonstrate it in a 300 GHz independent-sideband (ISB) modulated 2×2 MIMO fiber-terahertz communication system. Compared with the traditional 2D-32QAM format, the 4D-OS1024-PS learned by the E2E-4D-JGPS framework can improve the sensitivity gain of more than 1.68 dB at the GMI threshold of 8.5 bit/4D-sym and increase the data rate to 16 Gbps, which has better nonlinear distortion and noise tolerance.