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In this letter, we propose a novel and straightforward scheme for Q-band (33–50 GHz) millimeter-wave signal generation enabled by a Mach-Zehnder modulator (MZM)-based joint algorithm, which combines probabilistic shaping (PS) and precoding technology, to enhance the anti-interference ability of the transmission system. Based on the proposed scheme, we experimentally demonstrate the generation and transmission of 1.4-Gbaud 46-GHz PS-16-quadrature-amplitude-modulation (PS-16QAM) vector signals, showcasing improved bit-error-ratio (BER) in both standard single-mode fiber (SSMF) and wireless transmission cases. The proposed scheme exhibits a clear advantage in terms of nonlinear interference suppression and satisfies the hard-decision forward-error-correction (HD-FEC) threshold with a BER of 3.8 × 10−3 in radio-over-fiber (RoF) systems.

We present a probabilistically shaped (PS) time-frequency-packing (TFP) wavelength-division multiplexing superchannel system employing higher order modulation (HoM) formats, with an objective to improve the spectral efficiency (SE). However, TFP systems suffer from inter-symbol interference (ISI) and/or inter-carrier interference (ICI). Additionally, the bandwidth limitations of the wavelength selective switches in the fiber link may cause severe ISI for the edge sub-channels (SCs) in a superchannel. Mitigation of such interferences is particularly challenging for HoM systems, since the implementation of the well-known turbo equalization schemes, such as the Bahl-Cocke-Jelinek-Raviv equalizer, is computationally challenging for larger constellations. In this paper, we investigate an expectation propagation based, computationally efficient, turbo decision feedback equalizer for ISI cancellation, in tandem with a parallel interference cancellation based ICI mitigation. By optimizing the parameters in the shaping and the packing dimensions, we show through our numerical results that the proposed PS-TFP superchannels enabling 1.8 Tbps data rates offer up to 1.05 dB packing gain over an unpacked system using the same modulation format, and a 1.15 dB shaping gain over an unshaped system that uses a lower modulation order to achieve the same SE.

We experimentally demonstrate the transmission performance of the bit-loading discrete multi-tone (DMT) signal in intensity modulation and direct detection (IM-DD) system with a transmission distance of 2km and a net data rate of 108-Gb/s by two different shaping methods. A detailed comparison between the application of geometric shaping (GS) and probabilistic shaping (PS) in bit-loading DMT is presented. With continuous entropy loading for better channel fitting, probabilistically shaped bit-loading DMT achieves 1-dB receiver sensitivity gain compared to the conventional bit-loading DMT and outperforms geometrically shaped bit-loading DMT in the transmission experiment.

We investigate and compare the performance of star-shaped 16-ary quadrature amplitude modulation (Star-16QAM) and square-shaped 16QAM (Square-16QAM) in the probabilistic shaping (PS) and uniform schemes with coherent detection. With the help of PS technology, the bit error ratio (BER) improvement achieved in the PS-Star-16QAM scheme is greater than that of the PS-Square-16QAM when compared with the uniform schemes in our numerical simulation and experiment. Therefore, the PS-Star-16QAM shows superiority over the PS-Square-16QAM in terms of the BER improvement.