Real-Time Location Systems and Methods
First Claim
1. A method of determining location of a transponder in a locating system, the system including a plurality of spaced-apart stationary readers having known locations, one of the readers being designated as a master reader with respect to the transponder and at least three of the readers being designated as slave readers with respect to the transponder, the method comprising:
- broadcasting a transponder locate signal from the transponder;
broadcasting a master locate signal from the master reader;
detecting the master locate signal and the transponder locate signal at each of the slave readers and measuring a delay time between time of receipt of the two signals;
calculating a first differential distance between a first one of the slave readers and a second one of the slave readers and the transponder based on the measured delay times at the first and second slave readers, wherein the first differential distance defines a first hyperbola;
calculating a second differential distance between the first one of the slave readers and a third one of the slave readers and the transponder based on the measured delay times at the first and third slave readers, wherein the second differential distance defines a second hyperbola; and
determining a likely location of the transponder based on a point of intersection between the first and second hyperbolas.
7 Assignments
0 Petitions
Accused Products
Abstract
A real-time location system for identifying and locating tagged items. The system may include an identification protocol that tracks in-network transponders and assigns dynamic in-network identification numbers to in-network transponders. The system includes a locator function that employs time-of-arrival analysis. Rather than attempt to synchronize the time base at each reader, the system and process eliminate the need to sync the readers and also eliminate the impact of differential receive delays in the respective readers. Both the transponder and a master reader transmit locate signals, which are measured at slave readers. The system relies on differences in time-of-arrival of the two signals at the respective slave readers to determine the likely location of the transponder.
172 Citations
20 Claims
-
1. A method of determining location of a transponder in a locating system, the system including a plurality of spaced-apart stationary readers having known locations, one of the readers being designated as a master reader with respect to the transponder and at least three of the readers being designated as slave readers with respect to the transponder, the method comprising:
-
broadcasting a transponder locate signal from the transponder; broadcasting a master locate signal from the master reader; detecting the master locate signal and the transponder locate signal at each of the slave readers and measuring a delay time between time of receipt of the two signals; calculating a first differential distance between a first one of the slave readers and a second one of the slave readers and the transponder based on the measured delay times at the first and second slave readers, wherein the first differential distance defines a first hyperbola; calculating a second differential distance between the first one of the slave readers and a third one of the slave readers and the transponder based on the measured delay times at the first and third slave readers, wherein the second differential distance defines a second hyperbola; and determining a likely location of the transponder based on a point of intersection between the first and second hyperbolas. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. A real-time location system, comprising:
-
at least one transponder, the transponder including an antenna, a transceiver, a controller, a power source and memory; a plurality of spaced-apart stationary readers having known locations, one of the readers being designated as a master reader with respect to the transponder and at least three of the readers being designated as slave readers with respect to the transponder; and a locator processor and locator memory in communication with the plurality of spaced-apart stationary readers, the memory storing a locator module configuring the processor to determine a likely location of the transponder, wherein the transponder is configured to broadcast a transponder locate signal, wherein the master reader is configured to broadcast a master locate signal, wherein each of the slave readers is configured to receive the master locate signal and the transponder locate signal and measure a delay time between time of receipt of the two signals, and to report the delay time to the locator module, and wherein the locator module is configured to calculate a first differential distance between a first one of the slave readers and a second one of the slave readers and the transponder based on the measured delay times at the first and second slave readers, wherein the first differential distance defines a first hyperbola, calculate a second differential distance between the first one of the slave readers and a third one of the slave readers and the transponder based on the measured delay times at the first and third slave readers, wherein the second differential distance defines a second hyperbola, and determine the likely location of the transponder based on a point of intersection between the first and second hyperbolas. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
-
-
19. A real-time location system, comprising:
-
a plurality of stationary readers; and at least one transponder, the transponder including an antenna, a transceiver, a controller, a power source and memory, the memory containing a unique transponder identification number; wherein the transponder includes a broadcast module configured to broadcast an RF transponder signal containing the transponder identification number when the transponder is in an out-of-network state, wherein the transponder includes a program module configured to receive RF commands from one of the readers, and wherein the program module is configured to transition the transponder to an in-network state on reception of a command signal assigning a node identification number to the transponder, and wherein the broadcast module is configured to broadcast the RF transponder signal containing the node identification number instead of the transponder identification number when the transponder is in the in-network state, and wherein the node identification number is shorter in length than the transponder identification number.
-
-
20. A method for compensating for an oscillator error in a transponder, the transponder being adapted for use in a real-time location system including at least one reader, the method comprising:
-
providing transponder with predetermined time interval between transmissions; receiving a first transmission from the transponder; receiving a second transmission from the transponder after a time measured by the at least one reader; determining a difference between the measured time and the predetermined time interval; determining the oscillator error based on the difference and calculating a deviation factor for correcting the oscillator error; and applying the deviation factor at the transponder to correct the oscillator error.
-
Specification