Robust ultrasonic indoor positioning system with high accuracy

A system for determining the location of a portable tag in a distinct zone comprising:

• at least a first array based ultrasound transmitter, wherein said array based ultrasound transmitter is configured to transmit ultrasound signals to two or more distinct sectors within said zone;
• a portable tag comprising a radio frequency transmitter that transmits a radio frequency signal and an ultrasound receiver configured to communicate with said first array based ultrasound transmitter;
• a radio frequency receiver configured to communicate with the radio frequency transmitter via said radio frequency signal;
• and
• a processor in communication with the first array based ultrasound transmitter and the radio frequency receiver, wherein the processor is configured to determine the location of the portable tag within said two or more distinct sectors based on information transmitted from the radio frequency transmitter on the portable tag via said radio frequency signal to the radio frequency receiver.