| 摘要 |
A communication system (10) includes a population of mobile units (24) which communicate with a control station. Communications take place between the control station and the mobile units (24) so that the system (10) may gain knowledge about the mobile units' locations. The mobile units (24) occasionally initiate such communications automatically. The control station sends data defining a target area (72, FIG. 5) to the mobile units. The mobile units (24) reside in the target areas (72) when the target areas (72) are first assigned, but the mobile units (24) are free to move. The control station transmits broadcast signals to geographically spaced apart cells (36, FIG. 2). The broadcast signals convey current data identifying the service areas covered by the cells (36). The mobile units (24) automatically initiate communications when their assigned target areas (72) do not coincide with the service areas for the broadcast signals they can receive.
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