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Existing hybrid ultrasound/RF positioning systems usually measure ultrasonic time-of-flight. This operation requires a wide bandwidth and this makes it rather noise sensitive, limiting the useful range. Therefore a new system is proposed where only the room-indicating capability of ultrasound is utilized and combined with RF. A portable tag obtains the room location by receiving a narrow bandwidth signal from a stationary ultrasound transmitter. The result is then relayed back over RF. This combines the high accuracy of ultrasound to pinpoint exactly the room location with the high communications capacity of RF that enables tracking of hundreds of simultaneously moving tags. Secondary parameters that may aid in refining the position such as ultrasound signal level and velocity may also be measured.
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