Determining the location of a mobile computing device

Patent metadata

Field	Value
Publication number	US-10866303-B2
Application number	US-201916691752-A
Country	US
Kind code	B2
Filing date	Nov 22, 2019
Priority date	Jun 13, 2014
Publication date	Dec 15, 2020
Grant date	Dec 15, 2020

Abstract

A method of determining the location of a mobile computing device includes measuring a first time of flight (ToF) value and a first value of received energy of direct path (EDP) (P R ) of a number of acknowledgement (ACK) packets received in response to a number of first probe packets sent to a first mobile device. The method calculates a preliminary distance value (d 0 ) using a ToF-based distance equation, selects an ACK packet with a distance closest to d 0 from the number of ACK packets, calculates an initial path loss exponent (γ 0 ) of the selected ACK packet sample using d 0 and P R . With the access point, the method also includes measuring a second P R for a second number of ACK packets received in response to a number of second probe packets sent to the first mobile device, calculates a supplemental distance value using an EDP-based distance equation and the γ 0 , and determines the location of the mobile device using multilateration and the supplemental distance value.

First claim

What is claimed is:

1. A method of determining the location of a mobile computing device comprising:
measuring a first time of flight (ToF) value and a first value of received energy of direct path (EDP) (P R ) of acknowledgement (ACK) packets received in response to first probe packets sent to a first mobile device;
calculating a preliminary distance value (d 0 ) using a ToF-based distance equation;
selecting an ACK packet with a distance closest to d 0 from the ACK packets;
calculating an initial path loss exponent (γ 0 ) of the selected ACK packet sample using d 0 and P R ;
with the access point, measuring a second P R for second ACK packets received in response to second probe packets sent to the first mobile device;
calculating a supplemental distance value using an EDP-based distance equation and the γ 0 ; and
determining the location of the mobile device using multilateration and the supplemental distance value.

2. The method of claim 1 , in which ToF-based distance equation comprises:
ToF=(ToA−ToD−SIFS)/2

where ToA (time-of-arrival) is a time when the access point begins receiving the ACK packets, ToD (time-of-departure) is a time when the probe packets are transmitted, and SIFS is the short interframe space.

3. The method of claim 1 , in which the EDP-based distance equation comprises:
P R =P 0 −10γ log( d )

where P R is the value of received energy of direct path (EDP) at the access point, P 0 is an initial value of energy of direct path (EDP), γ is a path loss exponent and d is the distance between the first mobile device and the access point.

4. The method of claim 1 , in which the number of first probe packets comprises one hundred packets.

5. The method of claim 1 , in which the number of second probe packets comprises one packet.

6. The method of claim 1 , further comprising storing the time of flight (ToF) and an energy of direct path (EDP) measurements.

7. The method of claim 1 , in which the area in which the method operates is an indoor area.

8. The method of claim 1 , further comprising:
measuring a second time of flight (ToF) value and a third P R of third acknowledgement (ACK) packets received in response to third probe packets being sent to the first mobile device;
removing outlying ToF values using a propagation delay estimated from the EDP-based distance equation;
calculating the supplemental distance using a median of valid ToF measurements;
updating the initial path loss exponent (γ 0 ) using the EDP-based distance equation; and
using the updated path loss exponent (γ 0 ) in a subsequent calculation using the EDP-based distance equation.

9. The method of claim 8 , in which the number of third probe packets is less than the number of first probe packets.

10. The method of claim 8 , in which the number of third probe packets is ten.

11. The method of claim 1 , in which the method is performed for additional mobile devices in a round robin scheduling process, the number of mobile devices included with a given round being based on an overhead, the overhead representing a time fraction that probe packets can be transmitted per second.

12. The method of claim 1 , in which determining the location of the mobile device using multilateration and the supplemental distance value comprises performing the method of claim 1 with respect to a plurality of access points and the first mobile device.

13. A computer program product for determining the location of a mobile device, the computer program product comprising:
a non-transitory computer readable storage medium comprising computer usable program code embodied therewith, the computer usable program code comprising:
computer usable program code to, when executed by a processor, calculate a preliminary distance value (d_o) based on a measured first time of flight (ToF) value and a first value or received energy of direct path (EDP) (PR) derived from first acknowledgement (ACK) packets;
computer usable program code to, when executed by the processor, select an ACK packet with a distance closest to d_o;
computer usable program code to, when executed by processor, calculate an initial path loss exponent (y_o) of the selected ACK packet sample using d_o and P R ;
computer usable program code to, when executed by the processor, measure a second P R for a second ACK packets;
computer usable program code to, when executed by the processor, calculate a supplemental distance value using an EDP-based distance equation and the y_o;
computer usable program code to, when executed by the processor, measure a second ToF value and a third P R of third ACK packets;
computer usable program code to, when executed by the processor, remove outlying ToF Values using a propagation delay estimated from an EDP-based distance estimation;
computer usable program code to, when executed by the processor, update the y_o based on the ToF values from which outliers were removed; and
computer usable program code to, when executed by the processor, determine the location of the mobile device using multilateration and the supplemental distance value and updated y_o.

14. The computer program product of claim 13 , further comprising:
computer usable program code to, when executed by the processor, determine an overhead of probe packets; and
perform a plurality of iterations of a round robin scheduling process.

15. An access point, comprising:
a processor; and
a memory, the memory comprising executable code that, when executed by the processor:
calculates a preliminary distance value (d_o) based on a measured first time of flight (ToF) value and a first value of received energy of direct path (EDP) (P R ) derived from first acknowledgement (ACK) packets;
selects an ACK packet with a distance closest to d_o;
calculates an initial path loss exponent (y_o) of the selected ACK packet sample using do and P R ;
measures a second Pa for second ACK packets;
calculates a supplemental distance value using an EDP-based distance equation and the y_o;
measures a second ToF value and a third P R of third ACK packets;
removes outlying ToF values using a propagation delay estimated from an EDP-based distance estimation;
updates the y_o based on the ToF values from which outliers were removed; and
determine the location of the mobile device using multilateration and the supplemental distance value and updated y_o.

Assignees

• Hewlett Packard Entpr Dev Lp

Inventors

• Kim Dongho
• Sen Souvik

Classifications

• G01S5/14 Primary

  Determining absolute distances from a plurality of spaced points of known location · CPC title

• H04W64/00

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

• G01S5/04

  Position of source determined by a plurality of spaced direction-finders · CPC title

• G01S5/0215

  Interference · CPC title