System for indoor and outdoor position measurement

A system for measuring the position of one or more object in an area of interest, the system comprising:

• a primary beacon located at a first fixed position in or near the area of interest, the primary beacon comprising:
• a primary signal generator which generates a time referenced primary signal;
• a primary transceiver for sending the primary signal to two or more secondary beacons and to one or more portable tag and for receiving an echo signal;
• and
• a primary circuit for measuring the time at which the primary signal is sent and echo signal are received by the primary beacon,
• two or more secondary beacons located at different fixed positions in or near the area of interest, the secondary beacon comprising:
• a secondary signal generator which generates a time referenced echo signal in response to the receipt of the primary signal;
• and
• a secondary transceiver for receiving the primary signal and transmitting the echo signal to one or more portable tag and to the primary beacon;
• and a secondary circuit for measuring the time at which the primary signal is received and echo signal sent;
• one or more portable tag, the portable tag being attachable to the object, the portable tag comprising:
• a tag receiver for receiving and measuring the time referenced signal from the primary beacon, the time referenced echo from the secondary beacon and receiving time delay information comprising primary signal time delay information and echo signal delay information;
• a portable tag circuit for calculating the distance of the portable tag to the primary and secondary beacons by means of a time of flight calculation which uses, the known position of the primary and secondary beacons, the time referenced signals and the delay information such that the portable tag calculates its own position.