Expandable, decentralized position tracking systems and methods

1. A position tracking system comprising:

at least three spatially separated radiofrequency (RF) sources of radio signals, each RF source being disposed in an area at a location known to that RF source, each RF source including an RF transmitter configured to transmit radio signals that carry a unique identifier and the known location of that RF source; and

at least one tag each coupled to a different mobile object, each tag including a radio module with an RF receiver for receiving the radio signals transmitted by the at least three spatially separated RF sources, memory storing executable code, and a processor that executes the executable code stored in the memory compute a range from that tag to each of the at least three spatially separated RF sources, a given tag of the at least one tag including a barometric sensor, the processor of the given tag computing a position of the given tag based on the at least three ranges computed by the processor of the given tag and on a pressure measurement made by the barometric sensor of the given tag.

2. The position tracking system of claim 1 , wherein one or more of the at least three spatially separated RF sources of radio signals is a stationary node.

3. The position tracking system of claim 1 , wherein one or more of the at least three spatially separated RF sources of radio signals is an uplink node having an uplink module that is in communication with an external network and configured to send the computed position of the at least one tag to a server system on the external network.

4. The position tracking system of claim 3 , wherein the uplink node is a configuration node, and the processor of the configuration node is configured to command a given RF source of the at least three RF sources to enter tag mode in which the given RF source computes its location.

5. The position tracking system of claim 1 , wherein one of the at least three spatially separated RF sources of radio signals is a second tag of the at least one tag.

6. The position tracking system of claim 1 , wherein each of the at least three RF sources includes a barometric sensor for making pressure measurements, and wherein the radio module of the given tag includes an RF transmitter, the processor of the given tag being configured to cause the RF transmitter to send a message addressed to a specific RF source of the at least three RF sources, the message requesting a pressure measurement made by the barometric sensor of that specific RF source.

7. The position tracking system of claim 6 , wherein the RF receiver of the given tag receives a reply message containing the pressure measurement made by the barometric sensor of the specific RF source, and the processor of the given tag is configured to adjust the pressure measurement made by the barometric sensor of the given tag in response to the pressure measurement received from the specific RF source before computing the position of the tag based on the at least three computed ranges and on the pressure measurement made by the barometric sensor of the given tag.

8. The position tracking system of claim 6 , wherein the processor of the given tag is configured to select the specific RF source from among the at least three RF sources in order to send the message requesting a pressure measurement based on proximity to the given tag.

9. The position tracking system of claim 1 , wherein the given tag of the at least one tag further includes an accelerometer that detects when the given tag moves and when the tag is stationary, and the processor of the given tag is configured to place the given tag in sleep mode to conserve power when the given tag ceases moving and becomes stationary.

10. The position tracking system of claim 9 , wherein the radio module of the given tag includes an RF transmitter, and the processor of the given tag is configured to cause the given tag to exit sleep mode and the RF transmitter to send a message addressed to a specific RF source of the at least three RF sources in response to the accelerometer detecting motion of the given tag, the message including the position computed by the given tag and requesting that the computed position of the given tag be sent to an RF source in communication with an external network.

11. The position tracking system of claim 1 , wherein the radio module of the given tag of the at least one tag includes an RF transmitter, and the processor of the given tag is configured to cause the RF transmitter to send a message addressed to a specific RF source of the at least three RF sources, the message containing the position computed by the given tag and requesting that the computed position of the given tag be sent to an RF source in communication with an external network.

12. The position tracking system of claim 11 , wherein the processor of the given tag is configured to place the given tag in sleep mode to conserve power after sending the message that requests the computed position of the given tag be sent to an RF source in communication with an external network.

13. A method of position tracking system comprising:

receiving, by a tag coupled to a mobile object, radio signals from at least three spatially separated radio-frequency (RF) sources;

acquiring, by the tag, a unique identifier for and known location of each of the at least three RF sources from the radio signals received from that RF source;

measuring, by the tag, pressure;

computing, by the tag, a range to each of the at least three RF sources from communications exchanged with that RF source; and

computing, by the tag, a three-dimensional position of the tag based on the computed ranges to the at least three RF sources and on the pressure measured by the tag.

14. The method of claim 13 , further comprising:

sending, by the tag, a message to a physically closest RF source of the at least three RF sources;

receiving, by the tag, a reply message containing pressure data from the physically closest RF source of the at least three RF sources in response to the sent message; and

adjusting the pressure measured by the tag in response to the pressure data received from the physically closest RF source of the at least three RF sources before computing the three-dimensional position of the tag based on the computed ranges to the at least three RF sources and on the pressure measured by the tag.

15. The method of claim 14 , further comprising:

detecting, by the tag, when the tag moves and when the tag is stationary; and

entering, by the tag, sleep mode to conserve power when the tag ceases moving and becomes stationary.

16. The method of claim 15 , further comprising:

exiting sleep mode and transmitting, by the tag, the computed position in a message addressed to a specific RF source of the at least three RF sources in response to detecting motion of the tag; and

requesting, by the message, that the specific RF source forward the computed position to an RF source that is in communication with an external network.

17. The method of claim 14 , further comprising:

transmitting, by the tag, the computed position in a message addressed to a specific RF source of the at least three RF sources; and

requesting, by the message, that the computed position of the given tag be sent to an RF source in communication with an external network.

18. The method of claim 17 , further comprising placing the tag in sleep mode to conserve power after transmitting the computed position in the message addressed to the specific RF source of the at least three RF sources.