Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2000-02-11
2001-07-17
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S214000, C342S357490
Reexamination Certificate
active
06263281
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a GPS positioning apparatus and method for measuring the position (three-dimensional coordinates (latitude, longitude and height) of an unknown point on the basis of signals transmitted from a plurality of GPS (Global Positioning System) satellites, and a computer readable recording medium on which a GPS positioning program is recorded.
BACKGROUND OF THE INVENTION
As the positioning methods, the hyperbolic navigation methods represented by the methods such as the Loran C navigation method or the omega navigation method were popularly used in ships or airplanes. However, the GPS positioning method is becoming popular and wide-spread because of its very high positioning accuracy. Positioning by the GPS is a technique in which radio waves output from a plurality of GPS satellites are received by a GPS receiver to measure the distance between the respective GPS satellite and the GPS receiver and to calculate the position of the GPS receiver (user). This technique is the core technique for satellite navigation methods for not only ships or airplanes but also automobiles.
However, in this positioning method there is a problem that the radio waves get delayed in the troposphere and the ionized layer. Further, there is an intentional degradation called SA (Selective Availability) generated by the Department of Defense of the U.S.A. in order to intentionally degrade the accuracy in view of the national defense strategies. Because of these problems, in a single positioning method which performs positioning utilizing only one GPS positioning apparatus, a positioning accuracy is about 100 m. At this 100-m-order positioning accuracy, in particular, some problems are posed when a ship enters a harbor or when the GPS is used as a car navigation system in urban areas.
In recent years, a relative positioning method (differential method or an interference positioning method) which uses the following technique has started attracting the attention. In this method, the observation error component generated by the single positioning method is canceled by using information sent from a reference station installed at a known point and observation information at a mobile station thereby improving the positioning accuracy.
The GPS is a positioning system constituted by 24 GPS satellites which fly in a circular orbit having a height of about 20,000 km. The GPS began to be developed by the Department of Defense in United States of America in 1970s to be used by the military and other alliance. This GPS is a system which can singularly perform positioning at a high accuracy on the sea and the land, i.e., in any area on the earth, and has replaced the conventional hyperbolic navigation methods such as the omega navigation method, the Loran C navigation method, and the Decca navigation method. A part of the signals from the GPS satellites have been made open to the public under certain conditions. Some signals from this part are used as positioning information in the car navigation or the like.
At present, the methods which use the GPS to perform positioning are roughly classified into two methods and both of them use GPS positioning apparatuses:
(1) Single positioning method
(2) Relative positioning method
The single positioning method mentioned above is the most basic positioning method. In this positioning method, at least four GPS satellites are simultaneously observed by a GPS positioning apparatus at an unknown point. On the basis of these four observation results, a total of four unknowns (latitude, longitude, height and clock error), i.e., unknown three-dimensional coordinates (latitude, longitude and height) and a clock error in the GPS positioning apparatus are obtained. More specifically, the GPS positioning apparatus calculates correlations between received signals (C/A codes) from the GPS satellites while the GPS positioning apparatus sequentially generates C/A codes (Clear and Acquisition) codes allocated to the GPS satellites to calculate propagation delay times. The C/A code is open to the public, and is a pseudo noise code having a code length of 1023 bits.
The GPS positioning apparatus then calculates pseudo distance up to the respective GPS satellite by multiplying the propagation delay times by the velocity of light. The pseudo distance is the sum of a true distance and an error distance between the GPS positioning apparatus and the satellite. Clock error, error of orbit information of the GPS satellite, fluctuation generated by the SA to the C/A code, propagation delay caused by the ionized layer, and propagation delay caused by the troposphere are generally the factors that generate an error in the measurement of the distance.
The GPS positioning apparatus obtains position information of each satellite from Ephemeris (satellite orbit information) included in a satellite message from each GPS satellite, and solves quaternary simultaneous equations (positioning equations) on the basis of the position information and the pseudo distance described above, thereby calculating the coordinates (X
u
, Y
u
, Z
u
) of an unknown point and a clock error (C
BU
). The quaternary simultaneous equations are expressed by the following equation (1):
(X
i
−X
u
)
2
+(Y
i
−Y
u
)
2
+(Z
i
−Z
u
)
2
=(R
i
−C
BU
)
2
(1)
wherein i (i=1, 2, 3, 4) represents a GPS satellite used in positioning, X
i
, Y
i
and Z
i
are coordinates (known) of the GPS satellite, X
u
, Y
u
and Z
u
are the positioning coordinates (unknown) of the GPS positioning apparatus, R
i
is the pseudo distance between the GPS positioning apparatus and the GPS satellite (known), and C
BU
is the clock error.
In this manner, in the single positioning method, the coordinates (X
u
, Y
u
, Z
u
) of an unknown point are calculated as positioning results. However, the positioning results include an error of orbit information of the GPS satellite described above, the error caused by a fluctuation generated intentionally by the SA to the C/A code, delay error caused by the ionized layer, and the error component based on a delay caused by the troposphere. Therefore, the positioning accuracy of the single positioning method is limited to about 100 m.
The relative positioning method of the item (
2
) is a method which performs positioning by using a plurality of GPS positioning apparatuses (a GPS positioning apparatus at a known point and a GPS positioning apparatus at an unknown point), and can perform positioning at an accuracy higher than that of the single positioning method of the item (
1
). The relative positioning methods are roughly classified into a differential method and an interference positioning method. The differential method is also called a DGPS (Differential GPS). According to the differential method, the GPS positioning apparatus at the known point and the GPS positioning apparatus at the unknown point perform single positioning using a pseudo distance to cancel a common error, thereby improving a positioning accuracy to several meters.
On the other hand, according to the interference positioning method, after the GPS positioning apparatus at the known point and the GPS positioning apparatus at the unknown point measure the phases (to be referred to as carrier wave phases hereinafter) of carrier waves from the GPS satellites, a base vector between the known point and the unknown point is calculated. Using this base vector, the relative three-dimensional coordinates of the known point with respect to the known point are calculated. Since this interference positioning method uses a carrier wave having a wavelength of about 20 cm, a resolution higher than that of the differential method using a C/A code having a wavelength of about 300 m is obtained. Thus, there is the advantage that the positioning accuracy is considerably improved.
A rough configuration of a GPS positioning system which uses the differential method and the interference positioning method will be described below with reference to FIG.
7
. The GPS satellites
Yamamoto Yousuke
Yambe Masaru
Camby Richard M.
Fujitsu Limited
Staas & Halsey , LLP
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