Dynamic range of analog fiber optic links used in microcellular mobile radio applications

Abstract

The use of analog fiber optic links for microcellular mobile radio communications has been the focus of considerable research recently. These systems have the advantages relative to coaxial cable of low noise and enormous bandwidth. Analog subcarrier multiplexing techniques are used for transmitting the mobile signals over the fiber. Use of this technology however presents some unique problems due to the nonlinearities of the fiber optics system and the noise introduced by it. In this thesis, we analyse the dynamic range of the fiber links used for these applications.

The dynamic range is limited by the noise and the nonlinear distortion introduced by the fiber link. The main sources of nonlinear distortion are threshold clipping, gain saturation of the laser, and the combination of laser chirp and fiber dispersion. We have analytically modeled these nonlinearities and used these models to understand the dependence of the nonlinear distortion on the physical parameters of the laser diode and the fiber and also on the modulation index per channel and the number of channels. The performance of the 1S- 19 AMPS signals and the IS-54IDMA signals in the presence of fiber link noise is also discussed. Finally, the dynamic range of the fiber link for both AMPS and IDMA signals has been analyzed. The dynamic range of the fiber link is limited by the threshold clipping nonlinearity. It is also highly dependent on the number of mobile signals that are being communicated over the fiber link.