基于隐含导频的长距离IM/DD DFT-S-OFDM无源光网络的实验系统研究
Experimental Demonstration of a Long Reach IM/DD DFT-S-OFDM PON Using Superimposed Training

基于隐含导频、超奈奎斯特镜像混叠和直接检测，首次在IM/DD光通信系统中使用基于隐含导频（ST）的信道估计和均衡方式，通过实验实现了速率为20 Gb/s的正交相移键控（QPSK）离散傅里叶变换扩展正交频分复用（DFT-S-OFDM）信号传输832 km的光通信系统.使用隐含导频信道估计（ST-CE）方法来均衡信道的线性损伤，关键是把隐含导频（ST）算术叠加在数据信号上，而不占用单独的时隙. 通过对接收到的信号进行1阶统计分析估计出精确的信道. 为了增加传输距离，根据超奈奎斯特镜像混叠的方法增加接收机带宽来补偿色散引起的功率衰落. 结果显示，在长距离强度调制/直接检测（IM/DD）DFT-S-OFDM无源光网络（PON）系统中，采用ST-CE能得到更高的频谱效率，且其信道估计性能与TA-CE相当. 该方法节省了带宽，提高了频谱利用率.
： An 83.2- km, 20-Gb/s QPSK DFT-S-OFDM PON based on superimposed training (ST), super-Nyquist image induced aliasing, and direct detection (DD) is first experimentally demonstrated using superimposed training-aided channel estimation (ST-CE) and equalization. Instead of training-aided channel estimation (TA-CE), the linear impairments of the channel using superimposed training without any bandwidth loss is equalized. The idea of ST-CE is that the training sequences (TS) are arithmetically added to the information symbols instead of being placed in separate exclusive time slots. Accurate CE is obtained by using the first-order statistics of the received signals. To further increase the reachable distance, the receiver bandwidth is slightly increased and super-Nyquist image induced aliasing to compensate the dispersion induced power fading is used. Results show that the superimposed training channel estimation (ST-CE) achieve similar estimation performance as that of the TA-CE method in a long reach IM/DD DFT-S-OFDM passive optical network (PON) system, without compromising its spectral efficiency. This method can save bandwidth, and improve the utilization of the spectrum