5G光载无线通信前传系统数字预失真线性化研究

第五代移动通信系统新空口(5G NR)的信号带宽、调制度和峰均比相比4G信号高很多。用于小蜂窝或微蜂窝基站组网的光载无线通信(Radio-over-Fiber, RoF)前传系统的非线性失真也更加严重。为了使5G NR信号线性传输，采用记忆多项式(Memory Polynomial, MP)和广义记忆多项式(Generalized Memory Polynomial, GMP)模型构建数字预失真器，矫正5G RoF前传系统的非线性。在实验中搭建了2 km光纤的RoF前传系统，并采用100 MHz带宽5G NR信号作为测试信号对其进行线性化测试。实验结果表明，采用MP和GMP数字预失真器进行线性化时，5G RoF前传系统的邻信道功率比(Adjacent Channel Power Ratio, ACPR)可分别改善13 dB和17 dB以上。这说明MP和GMP数字预失真器对5G RoF前传系统的非线性具有显著的抑制作用。因此基于MP和GMP两个模型的数字预失真器均可用于5G RoF前传系统的线性化，而且GMP预失真器比MP预失真器对该系统线性化的能力更强。

Investigation on Digital Predistortion Linearization of 5G Radio-over-Fiber Fronthaul System

The signal bandwidth, modulation and peak to average power ratio (PAPR) of the fifth generation mobile communication system new radio (5G NR) are much higher than those of 4G signal. The nonlinear distortion of the radio-over-fiber (RoF) fronthaul system used in small cell or micro cell base stations is more serious. In order to make 5G NR signal transmit linearly, this paper uses the memory polynomial (MP) and generalized memory polynomial (GMP) models to construct digital predistorters to correct the nonlinearity of 5G RoF fronthaul system. In this paper, a RoF fronthaul system with 2km fiber is built, and the linearization test is carried out with a 100 MHz bandwidth 5G NR signal. The experimental results show that using the MP and GMP digital predistorters for linearization, the adjacent channel power ratio (ACPR) of the 5G RoF fronthaul system can be improved by more than 13 dB and 17 dB respectively, which indicates that the MP and GMP digital predistorters can significantly suppress the nonlinearity of 5G RoF fronthaul system. Therefore, the digital predistorter based on MP and GMP models can be used for the linearization of the 5G RoF fronthaul system, and the GMP predistorter has stronger linearization ability for the system than the MP.