| 摘要 |
A network of receiving stations receives encoded signals from portable radio transmitters that are either hand held or implantable into the body. Each of the radio transmitters has a unique identification number associated with it that is transmitted as part of the signal. It is possible to estimate the location of any single transmitter by figuring out the bearing and range of the transmitters from one or more receiving stations based on signal strength as received by the stations. Because each transmitter has a unique identification number, it is possible to track the location of, for example, kidnapped children, by listening for a signal containing a specific identification number.
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