This paper reports the influence of optical reflection induced noise and distortion for optical fiber feeder systems for microcellular mobile communication systems. Since the optical feeder requires very wide dynamic range, noise and distortion must be suppressed to an extremely low level. From optical transmission experiments and theoretical analysis, the basic characteristics of the reflection induced noise and distortion were investigated. By using these results, it was estimated that, for currently used analog mobile telephone systems, the number of connectors with 35 dB reflectance must be limited to less than 17, in order to suppress the noise caused by the connector reflections. Moreover, it was confirmed that the reflection induced distortion drastically decreases according to the increase of the length between reflectors. Therefore, the distortion can be suppressed by expanding the connector spacing to more than 7 meters.

This paper reports performance improvement in an optical fiber feeder for microcellular mobile radio systems. A low noise optical receiver using a transformer resonant circuit is described. With this receiver, CNR degradation due to receiver noise is suppressed to less than 0.9dB. Furthermore, two novel techniques, the use of a multiple-LD transmitter and automatic LD input level control, are proposed. The multiple-LD transmitter increases transmitter output power and reduces the transmitter noise. With a dual-LD transmitter, it is possible to increase the optical loss margin by 3.1dB, which corresponds to transmission length expansion of 6.2km, or to improve the received CNR by 2.8dB, which enables communication range expansion. Automatic LD input level control, which optimizes LD input level according to the received radio power, can expand the actual dynamic range of the up link.

This paper summarizes basic system design for an optical fiber feeder for microcellular mobile communication systems. The optical feeder enables compact and low cost base stations, easy radio channel control and flexible mobile communication systems. Basic transmission characteristics are investigated through optical transmission experiments. By using these results, feeder performance is estimated and optimal system parameters are designed.