Effect of nonlinearities on outage performance of fiber-fed microcellular networks for GMSK systems

Application of fiber for remoting the complex RF signal processing and control procedures in a microcellular system has attracted much attention. This paper investigates the effect of the laser diode nonlinearities on the outage performance of a Gaussian minimum shift keying (GMSK)-based system in a Rician channel. The analysis presented assumes that in contrast to the rapid (or short-term) fluctuations modeled by the Rician distribution, the slow (or long-term) fluctuations due to shadowing or near-far effects are compensated (in an exact sense) by power control schemes. The nonlinearity of the laser diode is shown to create a tradeoff between the outage and system parameters such as radio capacity and threshold bit-error rate (BER). The optical noises, such as shot noise, thermal noise, and relative intensity noise, are shown to degrade the outage of the system. Also, in addition to the usual improvement of outage with a strong specular component, it is observed that the specularity of the channel in a small measure mitigates the effective nonlinearity of the system and thus increases the dynamic range of the system. Design equations are provided for optimal performance.