To enhance the utility of portable telephone sets, a novel approach is proposed whereby an indoor radio PBX (private branch exchange) reuses frequency channels of an urban cellular radio without using additional frequency resources. The relation between microcell radius and antenna power of the indoor system in the presence of cochannel mutual interferences is shown. Calculations demonstrate that the proposed approach can decrease the total frequency channels to 85-60% of those of systems where the frequency channels of both systems are arranged independently in adjacent bands. A simple spectrum management system using autonomous distributed control to maintain cochannel interference sharing is shown.
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