A simple bidirectional radio over fiber (RoF) design based on orthogonal frequency division multiplexing (OFDM)-based millimeter wave (mm-wave) signal generation and transmission with compensation of linear and non-linear impairment with the aid of sparse second-order Volterra non-linear equalizer (S2-VNLE) is proposed. At the central station (CS), an optical 60 GHz OFDM-based mm-wave downlink signal is generated by a 16-QAM downlink radio frequency (RF) signal. The generated OFDM-based downlink mm-wave signal is transmitted to the base station (BS) via bidirectional single-mode fiber (SMF) of length 75 km. At BS, the downlink signal is photo detected and transmitted via an antenna to the user end. The 16-QAM uplink RF signal, obtained via a receiving antenna from the user end, is modulated on the unused carrier of the downlink mm-wave signal. The modulated uplink signal is transmitted to the CS through the same bidirectional fiber. The carrier reuse and fiber reuse reduce the system complexity. However, the simultaneous signal co-propagation may induce linear and non-linear impairment, further degrading the system performance and has to be compensated. The compensation of linear and non-linear impairment is done by full Volterra non-linear equalization (FVNLE). However, pruning the insignificant Volterra filter coefficient enables a reduction in computational complexity. The sparse second-order Volterra non-linear equalization (S2-VNLE) is obtained by l1-regularization to cut off the kernels with a moderate contribution. The weights of the tap coefficient are updated by the RLS algorithm. The transmission performance of compensated bidirectional RoF system is investigated. The performance analysis of the bidirectional RoF system shows improved efficiency, having performance closer to FVNLE with reduced system and computational complexity.

中文翻译：

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采用基于 l1 正则化的稀疏二阶 volterra 非线性均衡器的双向光纤无线电系统的增强性能

一种简单的双向光纤无线电 (RoF) 设计基于正交频分复用 (OFDM) 毫米波 (mm-wave) 信号生成和传输，并借助稀疏二阶 Volterra 补偿线性和非线性损伤提出了非线性均衡器（S2-VNLE）。在中心站 (CS)，基于 60 GHz OFDM 的毫米波光学下行链路信号由 16-QAM 下行链路射频 (RF) 信号生成。生成的基于 OFDM 的下行毫米波信号通过长度为 75 公里的双向单模光纤 (SMF) 传输到基站 (BS)。在基站，下行信号被光检测并通过天线传输到用户端。用户端通过接收天线获得的16-QAM上行射频信号调制在下行毫米波信号的未使用载波上。调制后的上行信号通过同一条双向光纤传输到CS。载波复用和光纤复用降低了系统复杂度。然而，同时信号共同传播可能会引起线性和非线性损伤，进一步降低系统性能并且必须进行补偿。线性和非线性损伤的补偿是通过完全 Volterra 非线性均衡 (FVNLE) 完成的。然而，修剪无关紧要的 Volterra 滤波器系数可以降低计算复杂度。稀疏二阶Volterra非线性均衡（S2-VNLE）是通过l1-regularization得到的，以截断具有中等贡献的核。抽头系数的权重由 RLS 算法更新。研究了补偿双向 RoF 系统的传输性能。