Li Haibo, Hu Rong, Yang Qi, Luo Ming, He Zhixue, Jiang Peng, Liu Yongpiao, Li Xiang, Yu Shaohua
Opt Express. 2017 Jan 9;25(1):1-9. doi: 10.1364/OE.25.000001.
An improved high-order delta-sigma modulator with multi-level quantizer is proposed to enable carrier aggregation of 4G-LTE signals in mobile fronthaul. Different from conventional delta-sigma modulation-based digital mobile fronthaul, a 2-bit quantizer is employed to reduce the quantization noise, which enabling the transmission via PAM-4 based IM-DD channel. Moreover, we employ the 4th-order high-pass filter (HPF) to replace the 1st-order HPF in the conventional delta-sigma modulator, resulting in a much better noise shaping performance. In the experiment, a PAM-4 based mobile fronthaul transmission of 32 aggregated 4G-LTE signals with a CPRI equivalent data rate of 39.32-Gb/s is demonstrated in a single-λ 10-Gb/s IM-DD channel. Significant improvement of 68% is achieved in the average EVM performance compared to the previous delta-sigma modulation-based digital mobile fronthaul.
提出了一种改进的带多级量化器的高阶Delta-Sigma调制器，以实现移动前传中4G-LTE信号的载波聚合。与传统的基于Delta-Sigma调制的数字移动前传不同，采用2位量化器来降低量化噪声，从而能够通过基于PAM-4的强度调制直接检测（IM-DD）信道进行传输。此外，我们采用四阶高通滤波器（HPF）取代传统Delta-Sigma调制器中的一阶HPF，从而获得更好的噪声整形性能。在实验中，在单波长10 Gb/s的IM-DD信道中展示了基于PAM-4的移动前传传输，该传输聚合了32个4G-LTE信号，CPRI等效数据速率为39.32 Gb/s。与之前基于Delta-Sigma调制的数字移动前传相比，平均误差向量幅度（EVM）性能显著提高了68%。
