Mobile terminals, methods, and program products for generating a magnetic ...

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(12) United States Patent

Jendbro et al.

(io) Patent No.: (45) Date of Patent:

US 7,069,145 B2 Jun. 27, 2006

(54) MOBILE TERMINALS, METHODS, AND

PROGRAM PRODUCTS FOR GENERATING
A MAGNETIC HEADING BASED ON
POSITION

(75) Inventors: Magnus Jendbro, Lund (SE); Gunnar Klinghult, Lund (SE)

(73) Assignee: Sony Ericsson Mobile

Communications AB (SE)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 90 days.

(21) Appl. No.: 10/837,837

(22) Filed: May 3, 2004

(65) Prior Publication Data

US 2005/0246099 Al Nov. 3, 2005

(51) Int. CI.

G01C17/38 (2006.01)
G01C 21/00 (2006.01)

(52) U.S. CI 701/207

Field of Classification Search None

See application file for complete search history.

(58) (56)

References Cited

U.S. PATENT DOCUMENTS 4,212,443 A * 7/1980 Duncan et al

244/177

Mobile terminals, methods, and program products for generating a magnetic heading. A geographic position of the mobile terminal is determined. A magnetic field at the mobile terminal is sensed. A magnetic inclination and/or a magnetic declination of the magnetic field is determined based on the determined geographic position. A magnetic heading is determined for the mobile terminal based on the sensed magnetic field and based on the determined magnetic inclination and/or magnetic declination.

22 Claims, 2 Drawing Sheets

1

MOBILE TERMINALS, METHODS, AND
PROGRAM PRODUCTS FOR GENERATING
A MAGNETIC HEADING BASED ON
POSITION

BACKGROUND OF THE INVENTION

The present invention relates to the field of global positioning in general and more particularly, to determining the orientation of a mobile terminal.

Some mobile devices include an electronic magnetic compass, which may be used to generate a magnetic heading that is displayed to a user. Example mobile devices that include a magnetic compass include some global position system (GPS) units and some mobile telephones. The magnetic compass may include a two or three axis magnetic field sensor. When using a two axis magnetic field sensor, the mobile device should be aligned with the earth's horizontal surface while the magnetic field strength is measured, otherwise the accuracy of the resulting magnetic heading can be reduced. Aligning the mobile device with the earth's horizontal surface may not be a convenient requirement to place on a user and/or may limit how the mobile device can be mounted on a vehicle or worn by a user.

The mobile device may include two tilt sensors (e.g., each tilt sensor with one axis) that sense the orientation of the mobile device relative to the earth's surface. Information from the tilt sensors can then be combined with information from the magnetic sensor to provide heading information that may be less sensitive to the orientation of the mobile device.

SUMMARY OF THE INVENTION

Mobile terminals, methods, and program products for generating a magnetic heading are provided according to various embodiments of the present invention. A geographic position of the mobile terminal is determined. A magnetic field at the mobile terminal is sensed. A magnetic inclination and/or a magnetic declination of the magnetic field is determined based on the determined geographic position. A magnetic heading is determined for the mobile terminal based on the sensed magnetic field and based on the determined magnetic inclination and/or magnetic declination. Accordingly, the mobile terminal may compensate for its orientation based on the determined magnetic inclination and/or the determined magnetic declination, and may perform such orientation compensation without use of tilt sensors or in combination with one or more tilt sensors. Reducing or eliminating the need for tilt sensors may reduce the complexity and/or cost of the mobile terminal.

In some further embodiments of the present invention, the magnetic inclination and the magnetic declination of the magnetic field may both be determined based on the determined geographic position. The magnetic heading may then be determined based on the sensed magnetic field and both of the determined magnetic inclination and declination. The geographic position may be determined by: receiving satellite signals at the mobile terminal, and by determining the geographic position based on the received satellite signals; by receiving cellular signals at the mobile terminal, and by determining the geographic position based on the received cellular signals; by triangulating the position of the mobile terminal based on wireless communication signals from a plurality of terrestrial wireless communication signal transmitters; by receiving it from a wireless network; and/or by receiving at the mobile terminal country code information

2

and/or cell identification information from a wireless network, and by determining the geographic position based on the received country code information and/or the cell identification information.

5 In some other embodiments of the present invention, a database is provided in the mobile terminal that contains information on the magnetic inclinations and/or magnetic declinations associated with geographic positions, and the information in the database is used to determine the mag

10 netic inclination and/or the magnetic declination of the magnetic field for a determined geographic position. The magnetic inclination and/or the magnetic declination of the magnetic field may be requesting from a wireless network based on the determined geographic position.

15 In yet some other embodiments of the present invention, the magnetic heading for the mobile terminal may be determined based on the following equation:

25 where C is the Direction Cosine Matrix, Hx, Hy and Hz represent the sensed magnetic field, 8 represents the determined magnetic inclination, y represents the determined magnetic declination (based on the current position), and Ho represents an absolute strength of the sensed magnetic field,

30 which is determined based on the following equation:

Ho^H^+Hf+Hz2.

In some other embodiments of the present invention, a mobile terminal includes a position determination unit, a

35 magnetic field sensor, and a processor. The position determination unit is configured to determine a geographic position of the mobile terminal. The magnetic field sensor is configured to sense a magnetic field at the mobile terminal. The processor unit is configured to determine a magnetic

40 inclination and/or a magnetic declination of the magnetic field based on the determined geographic position, and is configured to determine a magnetic heading for the mobile terminal based on the sensed magnetic field and based on the determined magnetic inclination and/or magnetic declina

45 tion.

In some further embodiments of the present invention, the processor unit may be configured to determine both the magnetic inclination and the magnetic declination of the magnetic field based on the determined geographic position,

50 and is configured to determine the magnetic heading for the mobile terminal based on the sensed magnetic field and based on both of the determined magnetic inclination and declination. The processor unit may include a memory in which a plurality of geographic locations are associated with

55 a plurality of pairs of magnetic inclinations and a magnetic declinations. The processor unit may be configured to request from a wireless network the magnetic inclination and/or the magnetic declination of the magnetic field based on the determined geographic position. The position deter

60 mination unit may be configured to determine the geographic position of the mobile terminal by: receiving satellite signals and determining the geographic position terminal based on the received satellite signals; receiving wireless communication signals from a plurality of terrestrial wire

65 less communication signal transmitters, and triangulating the position of the mobile terminal based on the received wireless communication signals; receiving the geographic