Space time calibration for networks using state model of node clock parameters

Patent metadata

Field	Value
Publication number	US-9414239-B2
Application number	US-201213523659-A
Country	US
Kind code	B2
Filing date	Jun 14, 2012
Priority date	Jun 14, 2012
Publication date	Aug 9, 2016
Grant date	Aug 9, 2016

Abstract

A space time calibration method determines location and timing for nodes in a network using a model of the state of clocks in the network nodes and observations of clock count stamps over an observation interval. At least one of the nodes in the network is moving, and the nodes have free running clocks, with corresponding clock error parameters. The method obtains observations of clock stamps for transmissions between nodes occurring over a time interval. It applies the observations to a model of network state, and generates from the model an update of network state. This update is a function of the observations and an estimate of the network state. The network state provides estimates of location parameters and clock parameters of the nodes in the network.

First claim

I claim:

1. A method for determining location and timing for wi-fi nodes in a wi-fi network, wherein at least one of the nodes is moving, and the nodes have free running clocks, with a corresponding clock error parameter, the method comprising:
obtaining observations of count stamps from the free running clocks for wi-fi packet transmissions between nodes in a group of the nodes occurring over a current time interval, the nodes in the group having a radio, and a processor for obtaining a count stamp from the free running clock in the node, the count stamp corresponding to receipt of a wi-fi packet transmission from another node in the group;
with a programmed processor, generating from the model an estimate of network state based on the observations and a previous estimate of the network state, the network state comprising:
a first difference between a previous clock parameter in a previous time interval and a corresponding clock parameter in the current time interval;
a second difference between location parameter estimates in the previous time interval and corresponding location parameters in the current time interval;
the model of network state characterizing statistical properties of errors between clock and location parameter estimates for a previous time interval and corresponding clock and location parameters in the current time interval;

with a programmed processor, adding the estimate of network state to clock parameter and location parameter estimates of a previous time interval to recursively calculate updated clock parameter and location parameter estimates for the current time interval; and
providing a solution of node position from the location parameter estimates for the current time interval via wireless transmission to at least one of the nodes.

2. The method of claim 1 where the model of network state models relationships between position of network nodes using coarse direction vectors representing coarse directions between corresponding pairs of nodes.

3. The method of claim 1 wherein the clock parameters comprise a rate offset and a clock error.

4. The method of claim 1 wherein the network state is based on statistical properties of clocks within the nodes.

5. The method of claim 1 wherein the model comprises a model of location error of nodes.

6. A system for determining location and timing for wi-fi nodes in a wi-fi network, the system comprising:
a router in communication with network nodes for receiving, via wi-fi packet transmission from radios in the nodes, ping data transmitted between the nodes, the ping data comprising observations of clock count stamps from clocks in the nodes for pings of wi-fi packets wirelessly transmitted between radios in pairs of the nodes;
clock count stamps being produced by a processor in a node by latching count values of a clock in a node upon receipt of a wi-fi packet;
a processing agent in communication with the router for receiving the ping data and organizing the ping data for a time interval; and
a solution agent for receiving the organized ping data from the processing agent and applying the organized ping data to a model of network state, and generating from the model an estimate of network state based on the observations and a previous estimate of the network state, the network state comprising:
a first difference between a previous clock parameter in a previous time interval and a corresponding clock parameter in the current time interval;
a second difference between location parameter estimates in the previous time interval and corresponding location parameters in the current time interval;
the model of network state characterizing statistical properties of errors between clock and location parameter estimates for a previous time interval and corresponding clock and location parameters in the current time interval;
the solution agent configured to add the estimate of network state to clock parameter and location parameter estimates of a previous time interval to recursively calculate updated clock parameter and location parameter estimates for the current time interval, the solution agent in communication with a wireless radio, the solution agent configured to provide a solution of node position from the location parameter estimates for the current time interval via wireless transmission from the wireless radio to at least one of the nodes.

7. The system of claim 6 further including a grouping agent, the grouping agent in communication with the router for establishing the network of nodes that participate in providing the ping data that is organized and applied to the model of network state.

8. The system of claim 7 wherein the grouping agent is in communication with the processing agent for identifying the nodes that form the network for determining position and timing solutions by the solution agent, the processing agent using identification of the network from the grouping agent to organize ping data into the organized ping data.

9. A method for determining position of a first node in a network of devices, the method comprising:
receiving timing for wi-fi transmission of signals between radios in pairs of nodes in the network, the timing providing time of flight of the signals based on internal, free running clocks in the nodes;
with a processor, initializing a model of state of position of the nodes in the network;
with a processor, generating from the model an estimate of state based on the observations of the timing over a current time interval and a previous estimate of state, the state comprising:
a first difference between a previous clock parameter in a previous time interval and a corresponding clock parameter in the current time interval;
a second difference between location parameter estimates in the previous time interval and corresponding location parameters in the current time interval;
the model of state characterizing statistical properties of errors between clock and location parameter estimates for a previous time interval and corresponding clock and location parameters in the current time interval;
with a processor, adding the estimate of state to clock parameter and location parameter estimates of a previous time interval to recursively calculate updated clock parameter and location parameter estimates for the current time interval; and
with a processor in communication with a wireless radio, providing a solution of node position of the first node from the location parameter estimates for the current time interval, the solution being provided to the first node via wireless transmission from the wireless radio to a radio in the first node.

10. The method of claim 9 further including collecting the timing from the nodes and, for pairs of nodes in the network, organizing the timing into relationships between error in relative position of the nodes of a pair and differences between estimated and observed distances between the nodes of a pair.

11. The method of claim 10 wherein the relationships are linearized such that the model of the state is based on linear relationships for error in relative position of pairs of nodes.

12. The method of claim 11 wherein the relationships are linearized based on a coarse direction vector estimating direction between nodes in a pair.

13. The method of claim 9 wherein the model of state is based in part on variance in clock rate and clock offset of the clocks in the nodes.

14. The method of claim 9 wherein updating the model includes updating an estimate of node clock parameters based on input clock estimates and observations of clock parameters over a time interval.

15.

Assignees

• Brunk Hugh L
• Digimarc Corp

Inventors

• Brunk Hugh L

Classifications

• G01S5/021

  Calibration, monitoring or correction (G01S5/0252 takes precedence) · CPC title

• H04W64/00 Primary

  Locating users or terminals {or network equipment} for network management purposes, e.g. mobility management · CPC title

• H04W24/00 Primary

  Supervisory, monitoring or testing arrangements · CPC title

• G01S5/0289

  of multiple transceivers, e.g. in ad hoc networks · CPC title