Analysis of RoF-echo effect on OFDM signal transmission with EPWM format

Radio over Fiber (RoF) technology integrates wireless access into optical networks. It contributes much for spreading broadband wireless access services to in-building areas and outdoor dead-spots. However, OFDM signals which are widely employed in current broadband wireless access systems suffer from nonlinearity and echoes in RoF channels. The echoes are caused by multiple reflections of light and have long delay compared to the OFDM symbol duration. In this paper, a RoF-echo channel model is proposed and employed in the analysis of the echo effect on the RoF transmission. The validity of the model is confirmed by experimental results. The combined effects of nonlinear distortion and echoes in the RoF channel on normal OFDM and EPWM (Envelop Pulse-Width Modulation) formatted OFDM signals are analyzed and evaluated by measuring their EVM (Error Vector Magnitude) performances.