Systems and methods for space-time determinations with reduced network traffic

• US 7,983,185 B2
• Filed: 02/12/2009
• Issued: 07/19/2011
• Est. Priority Date: 02/12/2009
• Status: Expired due to Fees

• Current Assignee: Digimarc Corporation
• Original Assignee: ZuluTime LLC
• Inventors: Freer, Harrison, Brunk, Hugh L., Rhoads, Geoffrey
• Primary Examiner(s): Kizou; Hassan
• Assistant Examiner(s): Jiang; Charles C
• Application Number:
  US12/370,466
• Publication Number:
  US 20100202300A1
• Time in Patent Office: 887 Days
• Field of Search: 701 1-302, 342104-146, 342350-465, 340988-996
• US Class Current: 370/252
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0676 Mutual

Abstract

Space-time solutions are determined by exchanging pings among nodes in a network. Each ping includes a current space-time state of the transmitting node, which includes the transmitting node'"'"'s currently estimated location and corrected time (as a count stamp). A particular node in the network receives pings from the other nodes in the network and uses the data in the received pings to estimate its own current position and to correct its own free-running clock relative to a common system time. As a service to the network, the particular node then transmits its corrected time (as a count stamp) and estimated position to the other nodes. In some embodiments, the space-time solutions discussed herein are used as backup to other navigation systems, such as the Automatic Dependent Surveillance-Broadcast (ADS-B) system.

Claims

1. A method of determining location and timing information of a local node in a network, the method comprising:

receiving, at the local node, pings from a plurality of remote nodes in the network, each ping comprising;

a transmit count stamp corresponding to a remote time when a respective remote node transmits the ping, the remote time based on an independent remote clock operating in the respective remote node; and

a remote location of the respective remote node at the remote time when the respective remote node transmits the ping;

defining respective rates, with respect to an independent local clock within the local node, for periodically calculating location solutions and clock solutions based on the received pings, the location solutions calculated at a first rate and the clock solutions calculated at a second rate, the second rate being less than the first rate;

for each ping received within a predetermined time interval;

associating a receive count stamp with the received ping, the receive count stamp corresponding to a local time when the ping is received, the local time based on the independent local clock; and

calculating relationships between the receive count stamp and the defined respective rates for periodically calculating the location solutions and the clock solutions; and

processing the transmit count stamps, the remote locations, the receive count stamps, the calculated relationships between the receive count stamps and the defined respective rates, and the local locations-corresponding to the respective pings received within the predetermined time interval to determine a plurality of clock solutions within the predetermined time interval for correlating the independent local clock with a network time, and to determine a plurality of location solutions within the predetermined time interval for estimating a new local location of the local node.

2. The method of claim 1, further comprising:

processing the plurality of clock solutions and the plurality of location solutions to determine a local space-time state comprising;

a local count stamp corresponding to a local time when the local space-time state is transmitted, the local time based on the independent local clock as correlated with the network time by the plurality of clock solutions; and

a local location corresponding to when the local space-time state is transmitted, the transmitted local location estimated using the plurality of location solutions and the local count stamp.

3. The method of claim 2, further comprising:

transmitting the local space-time state from the local node to the plurality of remote nodes in the network.

4. The method of claim 1, further comprising:

providing an initial local space-time state based on data received at the local node from a timing and/or location system.

5. The method of claim 4, further comprising:

transmitting the initial local space-time state from the local node to the plurality of remote nodes in the network.

6. The method of claim 4, further comprising:

determining the receive count stamps associated with each ping received during an initial solution period based on the initial local space-time state.

7. The method of claim 4, further comprising:

determining the local location associated with each ping received during an initial solution period based on the initial local space-time state.

8. The method of claim 4, further comprising:

determining an initial direction vector between the particular remote node and the local node based on the data received from the timing and/or location system.

9. The method of claim 4, wherein the timing and/or location system comprises a satellite based global positioning system (GPS).

10. The method of claim 4, wherein the timing and/or location system comprises an Automatic Dependent Surveillance—

Broadcast (ADS-B) system, and wherein at least one of the plurality of nodes is located within an aircraft, the method further comprising;

determining that satellite based navigation used by the ADS-B system is unavailable; and

in response to the unavailability of the satellite based navigation, determining the plurality of clock solutions and the plurality of location solutions.

11. The method of claim 1, wherein the second rate is half the first rate.

12. The system of claim 1, wherein calculating the relationships between the receive count stamp and the defined time intervals for periodically calculating the location solutions comprises:

calculating a first relationship determined by a plurality of location solution clock counts with respect to the receive count stamp; and

calculating a second relationship determined by the plurality of location solution clock counts and the receive count stamp,

wherein a sum of the first relationship and the second relationship equals 1.

13. The system of claim 12, wherein calculating the relationships between the receive count stamp and the defined time intervals for periodically calculating the clock solutions comprises:

calculating a third relationship determined by a plurality of clock solution clock counts with respect to the receive count stamp; and

calculating a fourth relationship determined by the plurality of clock solution clock counts and the receive count stamp,

wherein a sum of the third relationship and the fourth relationship equals 1.

14. A system for determining location and timing information, the system comprising:

a plurality of nodes in communication with one another, each node comprising;

an independent clock for generating count stamps;

a communication device for receiving remote pings from the other nodes, each remote ping including a transmit count stamp and a remote location of a transmitting node; and

a processor for;

defining respective rates, with respect to the independent clock within the respective node, for periodically calculating location solutions and clock solutions based on the received remote pings, the location solutions calculated at a first rate and the clock solutions calculated at a second rate, the second rate being less than the first rate;

associating each remote ping with a receive count stamp based on the independent clock;

calculating relationships between the receive count stamp and the defined respective rates for calculating the location solutions and the clock solutions; and

processing the transmit count stamps, the remote locations, the receive count stamps, the calculated relationships between the receive count stamps and the defined respective rates, and the local locations to determine a plurality of clock solutions for correlating the independent clock with a network time, and to determine a plurality of location solutions for estimating a new local location.

15. The system of claim 14, wherein the processor of each node is further configured to process the plurality of clock solutions and the plurality of location solutions to determine a local space-time state, and wherein the communication device of each node is further configured to transmit its local space-time state to the other nodes in the network.

16. The system of claim 14, wherein the communication device of each node is further configured to receive an initial local space-time state based on data received from a timing and/or location system and to transmit the initial local space-time state to the other nodes, and wherein the processor of each node is further configured to determine the receive count stamps and the local locations associated with each received remote ping based on the initial local space-time state.

17. The system of claim 16, wherein the timing and/or location system comprises an Automatic Dependent Surveillance—

Broadcast (ADS-B) system, wherein at least one of the plurality of nodes is located within an aircraft, and wherein the processor of each node is further configured to;

determine that satellite based navigation used by the ADS-B system is unavailable; and

in response to the unavailability of the satellite based navigation, determine the plurality of clock solutions and the plurality of location solutions.

18. The system of claim 16, wherein the timing and/or location system comprises a satellite based global positioning system (GPS).