光载无线通信系统射频信号相移特性研究

Phase-Shift Characteristics of Radio Frequency Signals for Radio over Fiber Transmission Systems

测试研制的28GHz光载无线通信系统时发现,经光纤传输后接收端恢复的基带信号眼图会随时间出现张开与闭合的现象,使通信系统的可靠性遭到破坏。通过实验研究和理论分析发现,射频信号的传输时延会随着光纤周围温度的变化而改变,尤其对载波频率较高、传输距离较长的光载无线通信系统的可靠性影响更为严重。为了克服上述相位漂移问题,提出并实验论证了一种基于载波恢复技术的改进型光载无线通信系统,采用二次下变频结构,从中频信号中提取同步时钟,恢复出幅度稳定的原始基带数据。实验系统实现了28GHz载频、1Gb/s数据速率、25km的光纤传输,系统的误码率小于10^(-9)。

In the developed 28 GHz radio over fiber（RoF）transmission system,an eye diagram of the recovered baseband data changes between opening and closing with time after transmission through an optical fiber,which results in a destruction of the communication reliability.After a detailed experimental investigation and theoretical analysis on this phenomenon,we find the propagation delay of radio frequency（RF）signals changes with the temperature variation of the optical fiber,which can extremely destroy the communication reliability,especially for the RoF system with a high-frequency carrier and a long-distance transmission.In this paper,we propose and experimentally demonstrate an improved RoF system to overcome the phase-shift variation based on the carrier recovery technique.We employ a dual down-conversion structure and extract synchronous clock from the intermediate frequency signal to acquire a stable recovered original baseband data.A low bit error rate（less than 10^-9）is achieved after transmission over a 25 km single mode fiber in this improved 28 GHz RoF system with a data signal of 1 Gb/s.