WO2000050917A1 - Vehicle navigation system with correction for selective availability - Google Patents

Vehicle navigation system with correction for selective availability Download PDF

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Publication number
WO2000050917A1
WO2000050917A1 PCT/US2000/004417 US0004417W WO0050917A1 WO 2000050917 A1 WO2000050917 A1 WO 2000050917A1 US 0004417 W US0004417 W US 0004417W WO 0050917 A1 WO0050917 A1 WO 0050917A1
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WO
WIPO (PCT)
Prior art keywords
gps
vehicle
error
database
determining
Prior art date
Application number
PCT/US2000/004417
Other languages
French (fr)
Inventor
John D. Begin
Original Assignee
Magellan Dis Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Magellan Dis Inc. filed Critical Magellan Dis Inc.
Priority to AU37034/00A priority Critical patent/AU3703400A/en
Publication of WO2000050917A1 publication Critical patent/WO2000050917A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/40—Correcting position, velocity or attitude
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
    • G01C21/26—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 specially adapted for navigation in a road network
    • G01C21/28—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 specially adapted for navigation in a road network with correlation of data from several navigational instruments
    • G01C21/30—Map- or contour-matching

Definitions

  • the present invention relates generally to vehicle navigation systems and more particularly to a system and method for correcting for the effects of selective availability.
  • GPS global positioning system
  • dead reckoning systems Many known vehicle navigation systems utilize the global positioning system (GPS), alone or together with dead reckoning systems, to determine the position of the vehicle.
  • GPS global positioning system
  • the commercially available GPS signals include intentionally placed error which reduces the accuracy of the GPS position solution ("selective availability").
  • One technique utilized to correct for selective availability is differential GPS.
  • one GPS receiver is placed at a known, fixed location. The GPS receiver receives the GPS signals with the error and compares these signals with its known position to determine the error. Correction information is then transmitted from the fixed GPS receiver to other remote GPS receivers at unknown locations. These remote GPS receivers can use the correction information to reduce the effects of selective availability. The cost of this type of system is generally prohibitive in vehicle navigation systems.
  • the present invention provides a vehicle navigation system which provides correction for selective availability in a moving vehicle.
  • the system determines the error, or some of the error, in the GPS signal based upon information from other systems, such a map matching or dead reckoning. Since the error in the GPS signal changes slowly, the determined error can be used subsequently to propagate the position of the vehicle for a pe ⁇ od of time after the error is determined.
  • the navigation system can correct for the error in terms of correcting the net effect of all of the errors from each of the GPS satellite signals, i.e. provide a correction to the position solution
  • the navigation system may also deduce the error from each satellite individually. At times, the navigation system may only provide correction of the GPS solution m one dimension. The amount of correction provided and the amount of error which can be determined depends upon the type of information received from the other systems and the known uncertainty of that information.
  • Figure 1 is a schematic of the navigation system of the present invention installed in a vehicle
  • Figure 2 illustrates how the navigation system of Figure 1 provides correction while travelling along several road segments
  • FIG 3 illustrates an alternative method to that shown in Figure 2.
  • the navigation system 20 of the present invention is shown schematically in Figure 1.
  • the navigation system 20 includes a CPU 22 having RAM 23 and connected to a display 24, such as a high resolution LCD or flat panel display.
  • the CPU 22 is also connected to an input device 26 such as a mouse, keyboard, key pad, remote device or microphone Alternatively, the display 24 can be a touch screen display.
  • the navigation system 20 further includes a storage device 28, such as a hard d ⁇ ve 28 or CD ROM, connected to the CPU 22
  • the storage device 28 contains a database 29 including a map of all the roads in the area to be traveled by the vehicle 32 as well as the locations of potential destinations, such as addresses, hotels, restaurants, or previously stored locations.
  • the software for the CPU 22, including the graphical user interface, route guidance, operating system, position-determining software, etc may also be stored in storage device 28 or alternatively in ROM or flash memory.
  • the navigation system 20 preferably includes position and motion determining devices, such as a GPS receiver 34, a gyroscope 36, a compass 38, a wheel speed sensor 40 and a multi-axis accelerometer 42, all connected to the CPU 22 (connections not shown for simplicity).
  • position and motion determining devices are well known and are commercially available.
  • the position and motion determining devices determine the position of the vehicle 32 relative to the database of roads utilizing dead-reckoning, map- matching, etc.
  • the user can select a destination relative to the database of roads utilizing the input device 26 and the display 24.
  • the navigation system 20 calculates and displays a recommended route directing the driver of the vehicle 32 to the desired destination.
  • the navigation system 20 displays turn-by-turn instructions on display 24, guiding the driver to the desired destination.
  • the GPS receiver 34 receives signals from a plurality of satellites 46a-d. In a manner well known, the GPS receiver 34 determines a distance or "pseudorange" d a -d to each of the satellites 46a-d, respectively. Each pseudorange da-dd may include an intentionally introduced error ⁇ a-d (positive or negative). The position of each satellite 46a-d is also nominally known, but may also include an intentionally introduced error ⁇ a-d. As is well known, the resulting GPS position solution can include an error of 50 meters, or even 100 meters.
  • the errors, ⁇ a-d and ⁇ a-d, intentionally introduced into the data are known as "selective availability.”
  • the errors ⁇ a-d and ⁇ a-d may each vary independently, but usually are held constant (or varied only slightly) for several minutes at a time.
  • this determined error can be used for some period of time afterward to correct subsequent GPS position solutions and increase the accuracy of a determined position of the vehicle 32.
  • a vehicle traveling from node E to node A and then turning at node A in the direction toward node B will establish, through map matching, the map-matching position yi of the vehicle 32 at node A with great accuracy and certainty (within 15 meters).
  • the GPS position solution due to selective availability and other errors, may indicate a GPS position solution at xi. Since the GPS position solution xi is known to have error up to 100 meters and since the map matching solution yi at node A is known to be of high accuracy and certainty (less than 15 meters), the CPU 22 calculates a correction vector 50 (displacement and direction) from GPS position solution i to map matching position solution yi.
  • the position solution from the other sensors 36, 38, 40, 42 loses accuracy and certainty.
  • the vehicle 32 may be known to be on the road segment AB with high certainty, its exact location on road segment AB diminishes as the vehicle 32 travels from node A to node B.
  • the vehicle speed sensor 40 is not precisely calibrated, it may indicate that the vehicle 32 is in position y 2 on road segment AB, while GPS receiver 34 indicates a GPS position solution at point x 2 .
  • the CPU 22 assumes that the GPS position solution x 2 includes the same errors, or substantially the same errors, ⁇ a-d and ⁇ a-d that were present in GPS position solution xi.
  • the CPU 22 applies the correction vector 50 to the GPS position solution x 2 to obtain a corrected GPS solution z 2 . If the time between GPS position solution i and x 2 is only a few minutes (2-3 minutes or less), then the corrected GPS position solution z 2 has very high accuracy and certainty, approximately 10-20 meters.
  • the corrected GPS position solution such as z$, which is obtained by applying correction vector 52 to GPS position solution x 5 will not always give a corrected GPS position solution g 5 which is on the road segment BC, particularly since the certainty and accuracy of the correction vector is reduced over time.
  • the corrected GPS position solution z 5 has a reduced accuracy and certainty, as shown by the circle 54 centered on corrected GPS position solution z 5 .
  • the dead-reckoning/map matching solution y 5 has greatly reduced accuracy in the direction of road segment BC and higher certainty in the direction perpendicular to road segment BC.
  • the position of the vehicle 32 may again be known with great accuracy and certainty at node C by map matching.
  • Node C may simply comprise a "shape point" in the road, which is sufficient for a map matching algorithm to determine with great accuracy and certainty the position of the vehicle 32 relative to the road segment BC, CD.
  • the CPU 22 therefore determines a new correction vector 62 by comparing GPS position solution x 6 and map matching position solution y 6 at node C. This correction vector 62 would then be utilized to correct the GPS position solution as the vehicle 32 travels past the node C to propagate position.
  • the CPU 22 can calculate each of the pseudorange errors ⁇ a-d individually.
  • the accuracy with which this can be done depends upon the similarity of correction vectors 50, 52 and 62, as well as the magnitude of the ephemeris errors ⁇ a-d, respectively. For example, if correction vectors 50, 52 and 62 are identical or almost identical and ephemeris error ⁇ a is relatively small, then the pseudorange error ⁇ a can be calculated. The same is true for satellites 46b-d.
  • the CPU 22 (or GPS receiver 34) can more accurately correct GPS solutions from the GPS receiver 34. Further, knowing each of the pseudorange errors ⁇ a-d, the CPU 22 can more easily detect a change in the intentionally introduced pseudorange error in any one of the satellites 46a-d, and make an appropriate correction.
  • a correction vector 70 may be established between the GPS position solution x 7 which is simply perpendicular to road segment FG. This correction vector 70 would provide some correction for the selective availability and intentionally introduced errors which remain generally constant as the vehicle travels from point F to node G.

Abstract

A navigation system provides for correction for the selective availabitily GPS errors based upon information from other systems, such as map matching and dead reckoning. Based upon the information from the other systems, the navigation system can determine the error in GPS solution. These errors and corrections are utilized by the navigation system to propagate vehicle position for a limited time after they are determined.

Description

VEHICLE NAVIGATION SYSTEM WITH CORRECTION FOR SELECTIVE AVAILABILITY
BACKGROUND OF THE INVENTION
The present invention relates generally to vehicle navigation systems and more particularly to a system and method for correcting for the effects of selective availability.
Many known vehicle navigation systems utilize the global positioning system (GPS), alone or together with dead reckoning systems, to determine the position of the vehicle. As is well known, the commercially available GPS signals include intentionally placed error which reduces the accuracy of the GPS position solution ("selective availability"). One technique utilized to correct for selective availability is differential GPS. Generally, one GPS receiver is placed at a known, fixed location. The GPS receiver receives the GPS signals with the error and compares these signals with its known position to determine the error. Correction information is then transmitted from the fixed GPS receiver to other remote GPS receivers at unknown locations. These remote GPS receivers can use the correction information to reduce the effects of selective availability. The cost of this type of system is generally prohibitive in vehicle navigation systems.
Other systems filter the signals from the GPS system to provide some correction for selective availability. These techniques often use the Markovian principal. This only provides limited correction for selective availability.
SUMMARY OF THE INVENTION
The present invention provides a vehicle navigation system which provides correction for selective availability in a moving vehicle. In very general terms, the system determines the error, or some of the error, in the GPS signal based upon information from other systems, such a map matching or dead reckoning. Since the error in the GPS signal changes slowly, the determined error can be used subsequently to propagate the position of the vehicle for a peπod of time after the error is determined. Depending upon the information received from the other systems, the navigation system can correct for the error in terms of correcting the net effect of all of the errors from each of the GPS satellite signals, i.e. provide a correction to the position solution The navigation system may also deduce the error from each satellite individually. At times, the navigation system may only provide correction of the GPS solution m one dimension. The amount of correction provided and the amount of error which can be determined depends upon the type of information received from the other systems and the known uncertainty of that information.
BRIEF DESCRIPTION OF THE DRAWINGS Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed descπption when considered in connection with the accompanying drawings wherein: Figure 1 is a schematic of the navigation system of the present invention installed in a vehicle,
Figure 2 illustrates how the navigation system of Figure 1 provides correction while travelling along several road segments; and
Figure 3 illustrates an alternative method to that shown in Figure 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The navigation system 20 of the present invention is shown schematically in Figure 1. The navigation system 20 includes a CPU 22 having RAM 23 and connected to a display 24, such as a high resolution LCD or flat panel display. The CPU 22 is also connected to an input device 26 such as a mouse, keyboard, key pad, remote device or microphone Alternatively, the display 24 can be a touch screen display. The navigation system 20 further includes a storage device 28, such as a hard dπve 28 or CD ROM, connected to the CPU 22 The storage device 28 contains a database 29 including a map of all the roads in the area to be traveled by the vehicle 32 as well as the locations of potential destinations, such as addresses, hotels, restaurants, or previously stored locations. The software for the CPU 22, including the graphical user interface, route guidance, operating system, position-determining software, etc may also be stored in storage device 28 or alternatively in ROM or flash memory. The navigation system 20 preferably includes position and motion determining devices, such as a GPS receiver 34, a gyroscope 36, a compass 38, a wheel speed sensor 40 and a multi-axis accelerometer 42, all connected to the CPU 22 (connections not shown for simplicity). Such position and motion determining devices are well known and are commercially available. Generally, the position and motion determining devices determine the position of the vehicle 32 relative to the database of roads utilizing dead-reckoning, map- matching, etc. Further, as is known in navigation systems, the user can select a destination relative to the database of roads utilizing the input device 26 and the display 24. The navigation system 20 then calculates and displays a recommended route directing the driver of the vehicle 32 to the desired destination. Preferably, the navigation system 20 displays turn-by-turn instructions on display 24, guiding the driver to the desired destination.
As is well known, the GPS receiver 34 receives signals from a plurality of satellites 46a-d. In a manner well known, the GPS receiver 34 determines a distance or "pseudorange" da-d to each of the satellites 46a-d, respectively. Each pseudorange da-dd may include an intentionally introduced error δa-d (positive or negative). The position of each satellite 46a-d is also nominally known, but may also include an intentionally introduced error Δa-d. As is well known, the resulting GPS position solution can include an error of 50 meters, or even 100 meters. The errors, δa-d and Δa-d, intentionally introduced into the data are known as "selective availability." Generally, it is known that the errors δa-d and Δa-d may each vary independently, but usually are held constant (or varied only slightly) for several minutes at a time. Thus, in the present invention, if error or some of the error or the net effect of all of the errors can be determined, this determined error can be used for some period of time afterward to correct subsequent GPS position solutions and increase the accuracy of a determined position of the vehicle 32.
The inventive technique for correcting for selective availability will be described with respect to Figure 2. It should be understood that the steps described herein would be performed by the CPU 22 in determining a position solution and propagating the position of the vehicle 32 relative to the database 29 of roads. In Figure 2, several road segments AE, AB, BC from the database 29 of roads (Figure 1) are illustrated. Generally, utilizing information from other sensors 36, 38, 42 and 40 on the vehicle 32 in combination with map matching, the position of the vehicle 32 relative to the database 29 of roads is known with great certainty at certain times. At these times, the error and the GPS solution position can be determined and a correction vector can be applied to compensate for this error. This correction vector is then applied to subsequent GPS position solutions to provide a corrected GPS position solution which has a higher degree of certainty than that of the other sensors in the vehicle 32.
The more detailed example will be given with respect to Figure 2. A vehicle traveling from node E to node A and then turning at node A in the direction toward node B will establish, through map matching, the map-matching position yi of the vehicle 32 at node A with great accuracy and certainty (within 15 meters). While the vehicle 32 is at node A, the GPS position solution, due to selective availability and other errors, may indicate a GPS position solution at xi. Since the GPS position solution xi is known to have error up to 100 meters and since the map matching solution yi at node A is known to be of high accuracy and certainty (less than 15 meters), the CPU 22 calculates a correction vector 50 (displacement and direction) from GPS position solution i to map matching position solution yi.
Next, as the vehicle travels from node A toward node B, the position solution from the other sensors 36, 38, 40, 42 loses accuracy and certainty. Although the vehicle 32 may be known to be on the road segment AB with high certainty, its exact location on road segment AB diminishes as the vehicle 32 travels from node A to node B. For example, if the vehicle speed sensor 40 is not precisely calibrated, it may indicate that the vehicle 32 is in position y2 on road segment AB, while GPS receiver 34 indicates a GPS position solution at point x2. In the navigation system 20 of the present invention, the CPU 22 assumes that the GPS position solution x2 includes the same errors, or substantially the same errors, δa-d and Δa-d that were present in GPS position solution xi. Thus, the CPU 22 applies the correction vector 50 to the GPS position solution x2 to obtain a corrected GPS solution z2. If the time between GPS position solution i and x2 is only a few minutes (2-3 minutes or less), then the corrected GPS position solution z2 has very high accuracy and certainty, approximately 10-20 meters.
As the vehicle 32 proceeds further along road segment AB, the accuracy and certainty of the correction vector 50 diminishes over time, because the errors δa-d and Δa-d change very slowly over time.
When the vehicle 32 reaches (or passes) node B and proceeds in a direction toward node c, the accuracy and certainty of the matching solution y3 is again high and a new correction vector 52 is established based upon the map matching solution x3 and a GPS position solution x3. This correction vector 52 is utilized to correct the GPS position solutions obtained while the vehicle is traveling along segment be. For example, GPS position solution x is corrected by correction vector 52 to obtain a corrected GPS position solution z4 on or near segment BC.
Of course, the corrected GPS position solution, such as z$, which is obtained by applying correction vector 52 to GPS position solution x5 will not always give a corrected GPS position solution g5 which is on the road segment BC, particularly since the certainty and accuracy of the correction vector is reduced over time. In this case, the corrected GPS position solution z5 has a reduced accuracy and certainty, as shown by the circle 54 centered on corrected GPS position solution z5. At the same time, the dead-reckoning/map matching solution y5 has greatly reduced accuracy in the direction of road segment BC and higher certainty in the direction perpendicular to road segment BC. In other words, there is high certainty that the vehicle 32 is on road segment BC, but the accuracy and certainty of the position of the vehicle between node B and node C decreases as the vehicle travels from node B to node C. Thus, the certainty of dead-reckoning/map matching position solution y5 is shown with the oval 56, oriented along segment BC. Integrating the two position solutions y5 and z5 takes into account their different accuracies and certainties as they have changed over time or distance and the fact that position solution y5 has greater accuracy and certainty in one dimension (perpendicular to BC) than in another dimension (parallel to segment BC). Integrating these two position solutions y5 and z5 according to these considerations, the CPU 22 determines that the vehicle 32 is at point 60. As the vehicle 32 travels along road segment BC through node C, the position of the vehicle 32 may again be known with great accuracy and certainty at node C by map matching. Node C may simply comprise a "shape point" in the road, which is sufficient for a map matching algorithm to determine with great accuracy and certainty the position of the vehicle 32 relative to the road segment BC, CD. The CPU 22 therefore determines a new correction vector 62 by comparing GPS position solution x6 and map matching position solution y6 at node C. This correction vector 62 would then be utilized to correct the GPS position solution as the vehicle 32 travels past the node C to propagate position.
In the example given with respect to Figure 2 above, it is assumed that the distance between nodes A and B is sufficient such that the certainty and accuracy of the correction vector 50 would deteriorate somewhat during the time it takes the vehicle to travel from node A to node B. Also, in the example given above, the time required for the vehicle to travel from node B to node C (more than 10 minutes) would be sufficient that the accuracy and certainty of correction vector 52 may deteriorate significantly as would the exact dead reckoned position of the vehicle between node B and node C.
If, on the other hand, the length of road segments AB, BC and CD are short enough, or for whatever reason, correction vectors 50, 52 and 62 are determined to be substantially similar, then the CPU 22 can calculate each of the pseudorange errors δa-d individually. The accuracy with which this can be done (if at all) depends upon the similarity of correction vectors 50, 52 and 62, as well as the magnitude of the ephemeris errors Δa-d, respectively. For example, if correction vectors 50, 52 and 62 are identical or almost identical and ephemeris error Δa is relatively small, then the pseudorange error δa can be calculated. The same is true for satellites 46b-d. Knowing the pseudorange errors δa-d, the CPU 22 (or GPS receiver 34) can more accurately correct GPS solutions from the GPS receiver 34. Further, knowing each of the pseudorange errors δa-d, the CPU 22 can more easily detect a change in the intentionally introduced pseudorange error in any one of the satellites 46a-d, and make an appropriate correction.
In an alternative embodiment, referring to Figure 3, when a vehicle is on a long road segment FG without shape points, it is known with a high degree of accuracy and certainty that the vehicle lies on road segment FG. However, the position on FG is unknown or known without great accuracy or certainty. A correction vector 70 may be established between the GPS position solution x7 which is simply perpendicular to road segment FG. This correction vector 70 would provide some correction for the selective availability and intentionally introduced errors which remain generally constant as the vehicle travels from point F to node G.
In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.

Claims

WHAT IS CLAIMED IS:
1. A method for determining the position of a vehicle including the steps of: a. receiving a plurality of GPS signals from a plurality of GPS satellites, the
GPS signals each including an error; b. determining a position of the vehicle relative to a database; c. determining the error of the GPS signals based upon the position of the vehicle relative to the database as determined in said step b.; and d. determining the position of the vehicle relative to the database based upon the GPS signals and the error determined in said step c.
2. The method of claim 1 wherein said step b. includes the use of map- matching to determine the position of the vehicle relative to the database.
3. The method of claim 1 wherein said step b. includes the use of dead- reckoning to determine the position of the vehicle relative to the database.
4. The method of claim 1 wherein said step c. includes the step of determining the error of each GPS signal individually.
5. The method of claim 1 wherein said step c. includes the steps of: calculating ideal GPS signals based upon said position determined in said step b.; and comparing said ideal GPS signals with said GPS signals received in said step a..
6. The method of claim 1 wherein said step d. includes the step of modeling the error of each of said plurality of GPS satellites individually.
7. The method of claim 1 wherein said step d. includes the step of modeling a net effect of the error of the plurality of signals.
8. A system for determining the position of a vehicle including: a GPS receiver for receiving a plurality of GPS signals each including an error; a positioning system for determining a position of the vehicle relative to a database; means for determining the errors of the GPS signals based upon the position of the vehicle relative to the database as determined by the positioning system; and means for determining the position of the vehicle relative to the database based upon the GPS signals and the errors.
9. The system for determining the position of a vehicle according to claim 8 wherein said positioning system utilizes map-matching to determine the position of the vehicle relative to said database.
PCT/US2000/004417 1999-02-22 2000-02-21 Vehicle navigation system with correction for selective availability WO2000050917A1 (en)

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