Object location monitoring within buildings

• US 6,529,164 B1
• Filed: 03/30/2001
• Issued: 03/04/2003
• Est. Priority Date: 03/31/2000
• Status: Expired due to Term

• Current Assignee: GE Medical Systems Information Technologies Incorporated (General Electric Company)
• Original Assignee: GE Medical Systems Information Technologies Incorporated (General Electric Company)
• Inventors: Carter, Scott J.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/822,122
• Time in Patent Office: 704 Days
• Field of Search: 342/463, 342/464, 342/465, 342/385, 342/386
• US Class Current: 342/463
• CPC Class Codes: G01S 2205/002 for traffic control, mobile tracking, guidance, surveillance or anti-collision
• CPC Class Codes: G01S 2205/02 Indoor
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: G01S 5/0269 Inferred or constrained positioning, e.g. employing knowledge of the physical or electromagnetic environment, state of motion or other contextual information to infer or constrain a position

Abstract

An object location monitoring system tracks the locations of portable transceivers that attach to movable objects, such as patients within a hospital. The system preferably tracks the locations of the transceivers by combining a signal strength based locating process with a topological tracking process. Beacons that intermittently transmit unique ID codes are mounted to walls or other structures throughout a building, and are maintained in synchronization using the 60 Hz cycle of a standard 120V AC power signal, either directly or by monitoring flicker of fluorescent lighting. The transceivers receive the transmissions of nearby beacons, determine the signal strengths of such transmissions, and forward associated data to a server. The server uses this data to determine the location of each transceiver, and uses expected travel times between specific locations to resolve ambiguities. In a preferred embodiment, the transceivers are ambulatory transceivers that also sense and transmit physiologic data of patients.

Claims

1. An object location tracking system, comprising:

a plurality of beacons spatially distributed within a building, each beacon transmitting a respective ID signal, the plurality of beacons being generally synchronized with each other based on a phase of an AC power signal within the building, and being programmed to transmit their respective ID signals during assigned timeslots such that transmissions of ID signals for different beacons do not substantially interfere with each other;

at least one transceiver device which receives the transmissions of ID signals from nearby beacons and determines received signal strengths of such transmissions, the transceiver device adapted to be attached to a movable object, and

a processing module which uses information reflective of the received signal strengths of the beacon transmissions as received by the transceiver device to determine a current location of the transceiver device.

2. The object location tracking system as in claim 1, wherein the processing module uses a topological tracking method to resolve ambiguities in object location determinations resulting from the information reflective of the received signal strengths.

3. The object location tracking system as in claim 2, wherein the processing module implements the topological tracking method using a table that stores data indicating minimum times for an object to travel between selected locations.

4. The object location tracking system as in claim 3, wherein the processing module determines a current location of the transceiver device by at least:

identifying a set of beacons that currently produce highest received signal strengths;

mapping the set of beacons to one or more corresponding locations using data reflective of expected received signal strengths in selected areas of the building; and

when the set of beacons maps to multiple locations, using minimum travel times read from the table to evaluate the multiple locations as candidates.

5. The object location tracking system as in claim 2, wherein the topologic tracking method uses a set of rules specifying valid transitions between locations.

6. The object location tracking system as in claim 1, wherein at least some of the beacons determine the phase of the AC power signal by monitoring a flicker of lighting within the building.

7. The object location tracking system as in claim 1, wherein the processing module comprises a program executed by a server connected to a local area network.

8. The object location tracking system as in claim 1, wherein the processing module comprises a program executed by a network access point with which the transceiver device communicates by wireless communications.

9. The object location tracking system as in claim 1, wherein the processing module comprises a program executed by the transceiver device.

10. The object location tracking system as in claim 1, wherein the transceiver device receives the transmissions of ID signals from the beacons without becoming synchronized with the beacons.

11. The object location tracking system as in claim 1, wherein the transceiver device is an ambulatory transceiver device adapted to be worn by a patient and to sense and transmit physiologic data of the patient.

12. An object location tracking system, comprising:

a plurality of beacons spatially distributed within a building, each beacon transmitting a respective ID signal;

at least one transceiver device which receives the transmissions of ID signals from nearby beacons and determines received signal strengths of such transmissions, the transceiver device adapted to be attached to a movable object, and

a processing module which uses information reflective of the received signal strengths of the transmissions received by the transceiver device, in combination with a topological tracking method using rules regarding plausible state transitions, to determine a current location of the transceiver device.

13. The object location tracking system as in claim 12, wherein the processing module implements the topological tracking method using table that stores data indicating minimum travel times for an object to travel between selected locations.

14. The object location tracking system as in claim 13, wherein the processing module determines a current location of the transceiver device by at least:

identifying a set of beacons that produce highest received signal strengths;

mapping the set of beacons to one or more corresponding locations; and

when the set of beacons maps to multiple locations, using minimum travel times read from the table to evaluate the multiple locations as candidates.

15. The object location tracking system as in claim 12, wherein the plurality of beacons are generally synchronized with each other based on a phase of an AC power signal within the building.

16. The object location tracking system as in claim 15, wherein at least some of the beacons are configured to determine the phase of the AC power signal by monitoring a flicker of lighting within the building.

17. The object location tracking system as in claim 12, wherein the processing module comprises a program executed by a server connected to a local area network.

18. The object location tracking system as in claim 12, wherein the processing module comprises a program executed by a network access point with which the transceiver communicates by wireless communications.

19. The object location tracking system as in claim 12, wherein the processing module comprises a program executed by the transceiver device.

20. The object location tracking system as in claim 12, wherein the transceiver device receives the transmissions from the beacons without becoming synchronized with the beacons.

21. The object location tracking system as in claim 12, wherein the transceiver device is an ambulatory transceiver device adapted to be worn by a patient and to sense and transmit physiologic data of the patient.

22. A method of detecting a location of a transceiver device that attaches to a movable object, comprising:

with the transceiver device, receiving RF transmissions from beacons that are spatially distributed within a building structure, and measuring received signal strengths of the transmissions;

mapping a set of beacons that currently produce highest received signal strengths;

as measured by the transceiver device, to at least one possible transceiver location using data reflective of expected received signal strengths in selected areas of the building structure; and

when the set of beacons maps to multiple possible transceiver locations, evaluate the multiple transceiver locations as candidates using minimum travel times for the object to travel between selected locations.

23. The method as in claim 22, wherein receiving the RF transmission from the beacons comprises monitoring a beacon transmission frequency during TDMA timeslots not used by the transceiver device, said TDMA timeslots being timeslots of a TDMA frame used by the transceiver device to communicate with an access point.

24. The method as in claim 22, further comprising substantially synchronization the beacons to a phase of an AC power signal within the building.

25. A beacon, comprising:

a photodetector that converts light received from an external light source into a corresponding voltage signal;

a phase detection circuit that monitors the voltage signal to detect a phase of an AC power source of the external light source; and

a transmitter that intermittently transmits an RF signal during a time period which is dependent upon the phase of the AC power source as detected by the phase detection circuit.

26. The beacon as in claim 25, further comprising a power supply circuit that converts the voltage signal into a DC power signal used to power at least the transmitter.

27. The beacon as in claim 25, wherein the phase detection circuit comprises an analog-to-digital converter that converts the signal into a digital representation, and a microcontroller that processes the digital signal to detect the phase of the AC power source.

28. The beacon as in claim 25, wherein the beacon is adapted to be externally programmed with a value that specifies the time period.