Noise robust geometric constellation design for 32QAM discrete spectrum nonlinear frequency division multiplexing...

Nonlinear frequency division multiplexing (NFDM) systems utilize the nonlinear Fourier transform to address Kerr nonlinearity in optical fiber communications. However, they are highly sensitive to signal impairments such as amplified spontaneous emission (ASE) noise and phase noise, which pose significant challenges for practical implementation in real-world systems. To address the key issue of NFDM systems, this paper first analyzes the modeling characteristics of ASE noise in the discrete spectrum NFDM system. Based on this analysis, it designs an olive-shaped 32-ary quadrature amplitude modulation (32QAM) geometric constellation to improve noise robustness. The simulation results show that the proposed Olive-32QAM constellation increases the transmission distance by 133 km compared to traditional 32-ary amplitude phase shift keying (32APSK) and by 157 km compared to traditional 32QAM. Meanwhile, its phase noise tolerance is increased to over 1.9 kHz, demonstrating a stronger ability to withstand phase noise. Furthermore, leveraging the geometric characteristics of the Olive-32QAM constellation, this paper optimizes the carrier phase recovery (CPR) algorithm using principal component analysis and maximum likelihood, reducing its computational complexity. Compared with the blind phase search (BPS) CPR algorithm, the proposed CPR algorithm achieves an optical signal-to-noise ratio gain of up to 3.2 dB while maintaining a computational complexity of only about 1.2% of that of the BPS algorithm.