LAUSR

Radio over Fiber (RoF) is a promising technology for extending broadband wireless access to indoor and outdoor dead spots. However, commonly applied intensity-modulation / direct-detection RoF transmission presents some nonlinearity and produces echo distortion. Since multiple carrier modulation signals such as Orthogonal Frequency Division Multiplexing (OFDM) are widely employed in broadband wireless systems, the above issues become more serious. The OFDM signals have high Peak-to-Average Power Ratio, which makes them more sensitive to nonlinearity. Moreover, the large delay of optical echoes that are caused by the discontinuity of refractive index at both ends of Electrical/Optical (E/O) and Optical/Electrical converters exceeds the guard time of current OFDM symbols when the length of optical fiber is long. Since the nonlinearity and echo exist simultaneously in RoF channels, their composite effect is mathematically analyzed in this paper. A RoF-echo model is proposed for the modeling of the multiple light reflections and its validity is confirmed by experiments. Then, Envelop-Pulse-Width-Modulation- (EPWM-) RoF transmission is proposed for dealing with the nonlinearity and echo in RoF channel. The performance of the EPWM-RoF scheme for OFDM signal transmission is evaluated by simulations, which reveals that the scheme improves the transmission quality in Error Vector Magnitude under the composite environment of E/O nonlinearity and optical echo.