Radio positioning of a mobile receiver using a virtual positioning reference

• US 9,261,579 B2
• Filed: 10/04/2010
• Issued: 02/16/2016
• Est. Priority Date: 10/05/2009
• Status: Active Grant

• Current Assignee: BAE Systems Plc
• Original Assignee: BAE Systems Plc
• Inventors: Faragher, Ramsey Michael
• Primary Examiner(s): McGue, Frank J
• Application Number:
  US13/500,016
• Publication Number:
  US 20120194389A1
• Time in Patent Office: 1,961 Days
• Field of Search: 342/387, 342/458, 342/464
• US Class Current: 1/1
• CPC Class Codes: G01S 5/0221 Receivers
• CPC Class Codes: G01S 5/08 Position of single direction-finder fixed by determining direction of a plurality of spaced sources of known location
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

Methods and systems are disclosed for radio positioning of a mobile receiver using a virtual positioning reference established by logging a known position of the mobile receiver together with a local time at which a first instance of a predictably repeated code word is received by the mobile receiver from a terrestrial radio signal transmitter. During movement of the mobile receiver from the first known position to a second unknown position, a local clock is used to determine the time difference between when the virtual positioning reference is predicted to receive a second instance of the code word and when the mobile receiver actually receives the second instance of the code word.

Claims

1. A mobile receiver arranged to determine radio positioning information, said mobile receiver comprising:

a primary positioning resource configured for determining a position of the mobile receiver as being at a first receiver position;

a local clock;

a terrestrial receiver configured to scan for signals transmitted by terrestrial transmitters of a plurality of different transmitter types, said plurality of different transmitter types including at least one type of transmitter that transmits signals of opportunity that are not intended for navigational use;

a processor configured for distinguishing and identifying from among said signals a first signal transmitted by a first terrestrial transmitter having a known location, and for analyzing said first signal to determine a distinguishable, predictably repeated first code word and a repeat rate thereof,

said processor being further configured for establishing a first virtual positioning reference by logging the first receiver position together with a local time measured relative to said local clock at which a first instance of the first code word is received by the mobile receiver; and

a differential positioning unit configured for using an output of the local clock to determine a time difference between when the first virtual positioning reference is predicted to receive a second instance of the first code word and when the mobile receiver actually receives the second instance of the first code word when at a second receiver position, thereby determining radio positioning information pertaining to the second receiver position of the mobile receiver and

a display device configured to display the radio positioning information to a user.

2. A mobile receiver according to claim 1, comprising an inertial measurement unit configured to provide to the processor inertial measurement information pertaining to movement of the mobile receiver, said processor being further configured to determine a location of the second receiver position according to said radio positioning information and said inertial measurement information.

3. A method for obtaining radio positioning information relevant to a position of a mobile receiver, said method comprising:

determining the position of the mobile receiver as being at a first known position;

when the mobile receiver is at said first known position;

scanning for signals from terrestrial transmitters of a plurality of different transmitter types, said plurality of different transmitter types including at least one type of transmitter that transmits signals of opportunity that are not intended for navigational use;

distinguishing from among said signals a first signal transmitted by a first terrestrial transmitter having a known first transmitter location;

analyzing said first signal to identify a distinguishable, predictably repeated first code word and a repeat rate thereof; and

establishing a virtual positioning reference by logging the first known position together with a local time at which a first instance of the predictably repeated first code word is received by the mobile receiver from the first terrestrial transmitter, the local time being measured relative to a clock that is local to the mobile receiver;

running the local clock during movement of the mobile receiver from the first known position to a second position, said second position being unknown; and

when the mobile receiver is at the second position, using the local clock to determine a first time difference between when the virtual positioning reference is predicted to receive a second instance of the first code word and when the mobile receiver actually receives the second instance of the first code word, and thereby determining radio positioning information relevant to the second position of the mobile receiver and

displaying the radio positioning information to a user.

4. A method according to claim 3, comprising deriving the position of the mobile receiver at the first known position via a primary positioning resource local to the mobile receiver, the second position being at a position at which the primary positioning resource of the mobile receiver is rendered ineffective.

5. A method according to claim 3, comprising calculating the time difference using a differential positioning module local to the mobile receiver.

6. A method according to claim 3, comprising establishing a plurality of virtual positioning references at known locations that are geographically spaced apart from one another.

7. A method according to claim 3, comprising:

identifying a distinguishable, predictably repeated second code word transmitted by a second terrestrial transmitter having a known second transmitter location that is geometrically spaced apart from the known first transmitter location, and a repeat rate thereof;

when the mobile receiver is at the first known position, logging a local time at which a first instance of the second code word is received by the mobile receiver;

when the mobile receiver is at the second position, using the local clock to determine a second time difference between when the virtual positioning reference is predicted to receive a second instance of the second code word and when the mobile receiver actually receives the second instance of the second code word; and

synergistically determining the location of the second position from the first time difference and the second time difference using a trigonometric relationship.

8. A method according to claim 7, comprising capturing radio signal data using a radio signal capture window a length of which is limited to substantially a period of time of a most slowly repeating code word.

9. A method according to claim 3, comprising opening a radio signal capture window at substantially the time when the virtual positioning reference is predicted to receive the second instance of the first code word for substantially a time period required to receive the second code word.

10. A method according to claim 3, comprising estimating the second position of the mobile receiver by applying a Bayesian estimation filter to the radio positioning information.

11. A method according to claim 10, wherein the Bayesian estimation filter comprises a Kalman filter or a particle filter.

12. A method according to claim 10, wherein the application of a Bayesian estimation filter comprises loading the filter with at least one of:

error models associated with the first terrestrial transmitter;

error models associated with the mobile receiver; and

information from an inertial measurement unit about the movement of the mobile receiver.

13. The method of claim 3, comprising determining a location of the second position by combining the radio positioning information with inertial measurement information obtained from an inertial measurement unit.

14. A method for obtaining radio positioning information relevant to a position of a mobile receiver, said method comprising:

determining the position of the mobile receiver as being at a first known position;

when the mobile receiver is at said first known position;

scanning for signals from terrestrial transmitters of a plurality of different transmitter types, said plurality of different transmitter types including at least one type of transmitter that transmits signals of opportunity that are not intended for navigational use;

distinguishing from among said signals a first signal transmitted by a first terrestrial transmitter having a known first transmitter location;

analyzing said first signal to identify a distinguishable, predictably repeated first code word and a repeat rate thereof; and

establishing a virtual positioning reference by logging the first known position together with a local time at which a first instance of the predictably repeated first code word is received by the mobile receiver from the first terrestrial transmitter, the local time being measured relative to a clock that is local to the mobile receiver;

running the local clock during movement of the mobile receiver from the first known position to a second position, said second position being unknown; and

when the mobile receiver is at the second position, using the local clock to determine a first time difference between when the virtual positioning reference is predicted to receive a second instance of the first code word and when the mobile receiver actually receives the second instance of the first code word, and thereby determining radio positioning information relevant to the second position of the mobile receiver, and

displaying the radio positioning information to a user;

the method further comprising applying the equation;

c(t_New−

t_ref)=|r_New−

b|−

|r_ref−

b|+(α

_New−

α

_ref)+(ε

_New−

ε

_ref)

where;

c is the known speed of the radio waves;

t_New represents the time, measured at the mobile receiver using the local clock, at which the second instance of the first code word is received by the mobile receiver at the second position;

t_ref represents the time, measured at the mobile receiver using the local clock, at which the virtual positioning reference is predicted to receive the second instance of the first code word;

r_New is the second position of the mobile receiver;

b is the known first transmitter location;

r_ref is the first position of the mobile receiver;

α

_New and α

_ref represent offsets of the transmitter clock at t_New and t_ref respectively;

ε

_ref represents an error of the local clock when the reference measurements (t_ref) was established; and

ε

_New represents an error of the local clock when the reference measurement (t_New) was established.

15. A method according to claim 14, comprising taking a difference between a plurality of calculations of c(t_New−

t_ref) made using the equation formulated from pairs of measurements pertaining to a plurality of different terrestrial transmitters having known locations.

16. A method according to claim 14, comprising removing local clock errors by receiving transmissions from two different terrestrial transmitters ‘

A’ and

‘

B’ and

by applying the equation;

c(t^A_new−

t^A_ref)−

c(t^B_new−

t^B_ref)=(|r_new−

b^A|−

|r_ref−

b^A|+(ε

_new−

ε

_ref))−

(|r_new−

b^B|−

|r_ref−

b^B|+(ε

_new−

ε

_ref)).