Fiber-optic microcellular system has been studied actively as an excellent system for solving the equipment cost problems in microcellular systems. However, the occurrence of intermodulation distortion (IMD) arising from the nonlinearity of the laser diode used for E/O conversion which degrades the transmission quality is a serious problem in this system. In this paper, we propose a new frequency switching/IM3 reduction method, which dynamically reassigns the carrier frequencies to minimize the carrier to IMD power ratio under the hostile environment with time-varying received carrier strength, and analyze the performance improvements by the proposed method. The improvements obtained both for the worst value of the overall CNR and for the overall CNR in a specific user are numerically made clear. It is also shown that if the interval between frequency reassignings is set less than one second, a sufficient improvement in the overall CNR is achievable.

Recently, making good use of the advantages of optical fibers such as wide bandwidth and low loss, it has been investigated to apply optical fiber link to microcellular mobile communication systems. This system allows complex equipment to be located at microcell control station, and can simplify the equipment of microcell base stations compared with the conventional systems. In this paper, we analyze the performance of optical fiber link for microcellular mobile communication systems, taking radio link fading and optical link nonlinear distortions into consideration. From the calculated results, it is disclosed that the effect of both items does not generate the significant excess CNR degradation, and the correct CNR can be approximately calculated by using CNR of non-faded case. And it is also disclosed that the degradation of CNR due to optical link nonlinearity is slightly improved by taking adjacent channel signal fade into consideration.