Abstract: A method and system is disclosed for determining the location of a member of a class of individual transmitter-receiver units distributed throughout a defined facility. A central station establishes a two-way communication channel with one or more relay stations and sends a coded message identifying a particular individual unit over the communication channel. The relay stations respond to the message by sending out wake-up signals and radiant energy inquiry signals. The individual unit identified in the inquiry signal responds with a radiant energy acknowledgment signal. Embodiments of the invention disclose the use of infrared energy or ultrasonic energy for the radiant energy. Ultrasonic signals are sent on a plurality of frequencies. The relay stations send identification signals to the central station which identify the sending relay station and indicate whether an acknowledgment signal was received.
Type:
Grant
Filed:
July 26, 1983
Date of Patent:
March 10, 1987
Assignee:
Teloc R & D Ltd.
Inventors:
Ramon H. Aires, Charles A. Clark, Jr., Roy A. Ito, Kenneth R. Hackett