Patent ID: 8779895

Claim:
A zone location system arranged to determine in which zone of a predetermined set of zones a portable tag is present, the system comprising: a set of ultrasound transmitters located in respective zones of the predetermined set of zones, wherein the ultrasound transmitters are arranged to generate an ultrasound signal; a portable tag with an associated identification code, the portable tag comprising: an ultrasound receiver arranged to receive the ultrasound signal, a signal processing means arranged to: measure a strength of the received ultrasound signal and to generate a first data value accordingly, and measure a Doppler shift parameter based on the received ultrasound signal, and generate a second data value accordingly; and a Radio Frequency transmitter arranged to transmit a Radio Frequency signal with data representing the identification code, and the first and second data values; a Radio Frequency station arranged to receive the Radio Frequency signal from the portable tag; and a processor operationally connected to the Radio Frequency station, the processor being arranged to: identify the portable tag based on the identification code, determine in which zone the portable tag is present, based on detecting which of the set of ultrasound transmitters is/are capable of establishing ultrasound communication with the portable tag, use the second data value to determine a relative movement between the portable tag and one of the ultrasound transmitters, and determine a position within said zone, based on the first data value and the determined relative movement.