FIBER OPTIC MICROCELLULAR RADIO

Procuring base station antenna sites for new cells of rapidly growing cellular mobile radio services can be difficult. In response to this difficulty, we envisage a distributed antenna system using optical fiber subcarrier transmission. The system consists of many small canisters which radiate and receive radio signals to and from mobile phones. An optical-fiber connected canister antenna can also serve as a supplement to cover dead spots of imperfect base station antenna coverage. Linear end-to-end transmission between the base station and canister antennas can be provided by direct modulation and direct detection of a 1.3-mu-m optical carrier with 850 MHz subcarriers. The system is designed to be retrofitted into the existing cellular radio system without modifying base station or mobile equipment. Both radio and optical link budgets together with the required dynamic range of widely varying mobile signals have been analyzed. Technical feasibility has been verified by signal-to-noise ratio and intermodulation distortion measurements using an analog version of the FT-G 1.7 Gb/s lightwave transmitter with a 25A ASTROTEC isolator, and a cost-effective receiver with an AT&T 116B detector. A prototype canister transceiver has been constructed and tested. Using the above components with existing base station and mobile equipment, a two-way audio link via 12 km of optical fiber and mobile radio path has been successfully demonstrated.