Method of and apparatus for obtaining vehicle heading information
First Claim
1. A method of obtaining vehicle heading information from a global positioning system (GPS), characterized in that the heading information is determined from
where k is equal to the speed of light c divided by the GPS center frequency, Δ
f=kΔ
d+V.sub.1X ·
cosθ
.sub.1X +V.sub.1Y ·
cosθ
.sub.1Y +V.sub.1Z ·
cosθ
.sub.1Z -m·
cosφ
·
cosθ
.sub.1N -m·
sinφ
cosθ
.sub.1E
f is the total frequency offset perceived at the vehicle by a GPS receiver, Δ
d is the amount by which the frequency of any local oscillator(s) in the GPS receiver have drifted from a nominal frequency, V1X is the velocity of a satellite in the direction X, V1Y is the velocity of the satellite in the direction Y, V1Z is the velocity of the satellite in the direction Z, where X,Y,Z are the axes of an Earth centered, Earth fixed (ECEF) coordinate system, θ
1X is the angle between the line joining the vehicle and the satellite to the axis X, θ
1Y is the angle between the line joining the vehicle and the satellite to the axis Y, θ
1Z is the angle between the line joining the vehicle and the satellite to the axis Z, m is the speed of the vehicle, φ
is the vehicle'"'"'s heading from its local North axis, θ
1N is the angle between the line joining the vehicle and the satellite to the vehicle'"'"'s local North axis, θ
1E is the angle between the line joining the vehicle and the satellite to the vehicle'"'"'s local East axis.
2 Assignments
0 Petitions
Accused Products
Abstract
When fewer than three of the satellites of a satellite global positioning system (GPS) such as NAVSTAR are visible to a user (15), the user cannot obtain independent positional information from the system. Since a satellite (11) in such a system is moving with respect to a user (15), its signals are received with a Doppler offset from their normal centre frequency and the frequency offset due to the satellite motion alone is calculable for a user at an approximate location from a given satellite. An additional Doppler frequency offset will result from any movement of the user. The magnitude of the additional frequency shift, in conjunction with the known speed (m) of the user, can be used to calculate the angle between the satellite motion (V1) and the user'"'"'s motion and since the direction of the former is known, the user'"'"'s heading from local North (N) can be calculated in instances where only one or two GPS satellites (11,12) are visible to a user.
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Citations
13 Claims
- 1. A method of obtaining vehicle heading information from a global positioning system (GPS), characterized in that the heading information is determined from
- space="preserve" listing-type="equation">kΔ
f=kΔ
d+V.sub.1X ·
cosθ
.sub.1X +V.sub.1Y ·
cosθ
.sub.1Y +V.sub.1Z ·
cosθ
.sub.1Z -m·
cosφ
·
cosθ
.sub.1N -m·
sinφ
cosθ
.sub.1E
where k is equal to the speed of light c divided by the GPS center frequency, Δ
f is the total frequency offset perceived at the vehicle by a GPS receiver, Δ
d is the amount by which the frequency of any local oscillator(s) in the GPS receiver have drifted from a nominal frequency, V1X is the velocity of a satellite in the direction X, V1Y is the velocity of the satellite in the direction Y, V1Z is the velocity of the satellite in the direction Z, where X,Y,Z are the axes of an Earth centered, Earth fixed (ECEF) coordinate system, θ
1X is the angle between the line joining the vehicle and the satellite to the axis X, θ
1Y is the angle between the line joining the vehicle and the satellite to the axis Y, θ
1Z is the angle between the line joining the vehicle and the satellite to the axis Z, m is the speed of the vehicle, φ
is the vehicle'"'"'s heading from its local North axis, θ
1N is the angle between the line joining the vehicle and the satellite to the vehicle'"'"'s local North axis, θ
1E is the angle between the line joining the vehicle and the satellite to the vehicle'"'"'s local East axis.- View Dependent Claims (2, 3, 4, 5, 11, 12)
- space="preserve" listing-type="equation">kΔ
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6. A method of obtaining vehicle heading information from a Global Positioning System (GPS), comprising the steps of:
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a) determining the Doppler frequency offset present on a signal received at the approximate location of the vehicle from at least one GPS satellite due to the motion of the satellite alone, b) measuring the Doppler frequency offset present on a signal received at the vehicle from the satellite and the motion of the vehicle combined, c) measuring the speed of the vehicle, and d) deriving the heading of the vehicle from a difference between the Doppler frequency offset due to the motion of the satellite alone, the measured Doppler frequency offset present on a signal received at the vehicle and the speed of the vehicle. - View Dependent Claims (7, 8, 9, 10)
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13. A GPS receiver capable of receiving signals from a plurality of GPS satellites, wherein the receiver has means for determining its present heading by determining the Doppler frequency offset present on a signals received at the approximate location of the vehicle from at least one GPS satellite due to the motion of the satellite alone, measuring the Doppler frequency offset present on a signal received at the vehicle from the satellite and the motion of the vehicle combined, measuring the speed of the vehicle, and deriving the heading of the vehicle from a difference between the Doppler frequency offset due to the motion of the satellite alone, the measured Doppler frequency offset present on a signal received at the vehicle and the speed of the vehicle.
Specification