System for tracking an object using pulsed frequency hopping

• US 9,933,509 B2
• Filed: 12/12/2014
• Issued: 04/03/2018
• Est. Priority Date: 11/10/2011
• Status: Active Grant

• Current Assignee: Position Imaging, Inc.
• Original Assignee: Position Imaging, Inc.
• Inventors: Hill, Edward L., Min, Guohua, Deffebach, III, Harry Lee
• Primary Examiner(s): Nguyen, Chuong P
• Application Number:
  US14/568,390
• Publication Number:
  US 20150097732A1
• Time in Patent Office: 1,208 Days
• Field of Search: 342465, 342450, 342451
• CPC Class Codes: G01S 5/0215 Interference
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence

Abstract

Tracking systems and methods for obtaining position coordinates of transmitters are provided. One or more transmitters send multiple carrier signals to multiple receivers, where the time difference of arrival of the multiple carrier signals are used to determine the location of each transmitter. Accuracy is obtained by using phase information of multiple carrier frequencies for time difference of arrival measurements. The accuracy obtained by a receiver depends on the quality of the received carrier signal; a received carrier signal may become distorted by the presence of multipath interference. By using multiple signals with different frequencies, the system can screen or compensate for multipath effects. This screening can be accomplished either through various signal-sampling techniques or by averaging the signals received at the receiver. Because signals with different frequencies have different multipath experiences, a computer can analyze and compensate for “good” and “bad” signals.

Claims

1. A system for tracking a position of a transmitter, the system comprising:

the transmitter configured to transmit pulsed frequency-hopping electromagnetic signals and a reference signal, each frequency-hopping electromagnetic signal including a plurality of carrier signals at different frequencies;

at least three receiver antennae configured to receive the frequency-hopping electromagnetic signals transmitted by the transmitter; and

a central controller in communication with the transmitter and the at least three receiver antennae, the central controller being configured to acquire the reference signal from the transmitter, to acquire the frequency-hopping electromagnetic signals from the least three receiver antennae, to detect the carrier signals in the frequency-hopping electromagnetic signals, and to compute phase differences between the detected carrier signals and the reference signal, the central controller being further configured to calculate the position of the transmitter based on these computed phase differences.

2. The system of claim 1, wherein the central controller computes a best fit track of transmitter movement based on the computed phase differences using a best-line-fit technique.

3. The system of claim 2, wherein the central controller calculates an error range for the best fit track of the transmitter based on an expected linear progression of the phase differences, and if a transmitter position is identified by the central controller to be outside of the error range of the best fit track, the central controller either ignores the identified transmitter position or determines a new best fit track based on continued position tracking of the transmitter.

4. The system of claim 3, wherein if the central controller ignores the identified transmitter position, the central controller represents a track of the transmitter movement with a best-fit curve or line between a transmitter position determined before the identified transmitter position and a transmitter position determined after the identified transmitter position.

5. The system of claim 2, wherein if the identified a transmitter position is identified by the central controller to be outside of the error range of the best fit track on a given frequency, the transmitter and the at least three receivers at least temporarily stop using that given frequency.

6. The system of claim 1 wherein the central processing unit includes an analog to digital converter configured to digitize the computed phase differences to produce digital data representing the computer phase differences.

7. The system of claim 6 further comprising a computer system coupled to the central processing unit and configured to receive and convert the digital data representing the computer phase differences into time difference of arrival of the plurality of carrier signals of each frequency-hopping electromagnetic signal.

8. A system for tracking a position of a transmitter, the system comprising:

a transmitter configured to transmit frequency-hopping electromagnetic signals, each frequency-hopping electromagnetic signal including a plurality of carrier signals at different frequencies;

at least three receiver antennae configured to receive the frequency-hopping electromagnetic signals transmitted by the transmitter; and

a central controller in communication with the at least three receiver antennae to acquire the frequency-hopping electromagnetic signals from the least three receiver antennae and to compute phase differences based on these frequency-hopping electromagnetic signals, the central controller further configured to i) calculate the position of the transmitter based on these computed phase differences, and to ii) perform a calibration routine that steps through frequencies with the transmitter whereby phase integrity of the electromagnetic signals is calibrated at a plurality of frequencies, and wherein the central controller and the transmitter use frequencies within a range determined by phase relationships of the plurality of frequencies, for position tracking calculations.

9. The system of claim 8, wherein the transmitter is positioned at a known location relative to the at least three receiver antennae, and the central controller compares an expected position of the transmitter based on the known location to the transmitter position calculated based on the computed phase differences.

10. The system of claim 8 wherein if one or more given frequencies in a frequency-hopping network fail to provide phase integrity to allow for tracking of the transmitter, the one or more given frequencies are eliminated from use by the transmitter and the at least three receiver antennae.

11. A method for setting up a system for tracking an RF transmitter, comprising:

placing the RF transmitter in a fixed location;

placing at least three receiver antennae in locations within RF signal range of the RF transmitter, the at least three receiver antennae being in communication with a CPU;

establishing communication on a first frequency between the RF transmitter and at least one of the at least three receiver antennae and calculating a position of the RF transmitter relative to the at least one receiver antenna using phase data of signals transmitted by the RF transmitter;

frequency hopping to at least one other frequency and calculating the position of the RF transmitter using the phase data of the signals transmitted by the RF transmitter relative to the at least one receiver antenna;

determining a range of error for a position of the RF transmitter based on the fixed location and positions of the RF transmitter as calculated using other frequencies, other antennae data, or a combination of both other frequencies and other antennae data;

determining if the calculated positions of the RF transmitter based on the multiple frequencies are within the range of error; and

determining a present position of the RF transmitter based on the calculated positions of the RF transmitter that are within the range of error.

12. The method of claim 11, further comprising:

establishing communication on the first frequency between the RF transmitter and a second of the at least three receiver antennae, and calculating a position of the RF transmitter relative to the second antenna using phase data of the signals transmitted by the RF transmitter;

frequency hopping to at least one other frequency and calculating the position of the RF transmitter using phase data of the signals transmitted from the RF transmitter relative to the second antenna of the at least three receiver antennae; and

determining if the calculated locations of the RF transmitter on the multiple frequencies are acceptable for determining the present position of the RF transmitter.

13. The method of claim 12, further comprising comparing the position of the fixed RF transmitter as calculated using time of arrival data determined from the phase differences from the multiple frequency phase data from the transmitter to a first antenna of the at least three receiver antennae to data calculated using data from the second antenna of the at least three receiver antennae.

14. The method of claim 12, further comprising excluding from frequency hopping by the RF transmitter a frequency that produces a location of the RF transmitter outside the range of error for the position of the RF transmitter.