| 摘要 |
First and second radio communication units communicate using the frequency band of an existing microwave transmission system. A judgment whether the first communication unit is within communication range is performed based on information specifying the position of a base station of another radio communication system which is obtained therefrom. If found to be within communication range, the first communication unit shifts to a state and transmits a registration message to the second communication unit, which is then shifted to a transmission state. Interference in the existing microwave transmission system is prevented with a simple construction and without adding a circuit for confirming the present position of a communication unit.
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