Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2002-05-06
2002-11-19
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S214000, C342S357490
Reexamination Certificate
active
06484098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a GPS (Global Positioning System) method of and a GPS apparatus for measuring or positioning a current position of a movable body on the basis of radio waves received from GPS satellites and to a navigation system including the GPS apparatus. The present invention also relates to a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the GPS apparatus.
2. Description of the Related Art
In recent years, a GPS measurement has been broadly used in a navigation system of a movable body such as a vehicle, an airplane, a ship, or the like. Coordinates of the GPS satellites, which are the basis of the GPS measurement, are obtained by solving the Kepler's equation with the system time included in the transmitted data of the received radio waves i.e., in the down links, at a plurality of monitor stations on the earth. Then, an orbit constant (position) of the satellite as obtained in this manner is transmitted as one portion of the transmitted data of the transmitted radio wave i.e., the up link, to the corresponding GPS satellite. As a result, each GPS satellite transmits its own position information included in the down link data.
In the case of 3D (3-dimensional) positioning measurement based on the radio waves received from the GPS satellites in this kind, it measures a pseudo-range r, which is a distance from a GPS receiver to each GPS satellite, on the basis of (i) the position information of each GPS satellite included in the radio wave received from each GPS satellite and (ii) a time length required for the received radio wave coming from each GPS satellite to the GPS receiver, basically as to four GPS satellites. This pseudo-range r is represented as a four-variable function of a clock error t and the coordinates (x, y, z) of the GPS receiver. Therefore, if the four pseudo-ranges r are measured depending on the radio waves received from the four GPS satellites, the four functions are obtained, so that the clock error t and the coordinates (x, y, z) of the GPS receiver can be calculated by solving the four nonlinear simultaneous equations. Then, the above-calculated coordinates are regarded as the current position of a movable body on which the GPS receiver is mounted.
In fact, however, it often happens that the radio waves from five or more GPS satellites can be received at the same time, and thus, a positioning solution of five (or six or more) nonlinear simultaneous equations for four variables x, y, z and t are calculated by the least square method on the basis of the five or more pseudo-ranges r to increase a positioning accuracy.
By the way, one disadvantage of the GPS measurement is the generation of measurement error of the pseudo-range by a multi-path. More specifically, the radio wave from the GPS satellite may have other paths to go through to the GPS receiver after reflecting on the surface of a huge building or the like once or more times, in addition to the path to go direct to the GPS receiver, especially around the huge building such as a skyscraper, a high-rise building, or the like. This phenomenon, under which the radio waves are received at the same time through a plurality of radio wave paths from the one identical GPS satellite, is called as a “multi-path”. When the multi-path is generated, an error is generated in the time length required for the received radio waves coming to the GPS receiver, and on the basis of this error, an error is generated in the pseudo-range. Then, when the multi-path is generated, the pseudo-range based on a regular radio wave path and the pseudo-ranged based on an irregular radio wave path are irregularly and alternatively measured, so that the arrival time and the pseudo-range are changed or flickered at a short cycle. Thus, the accuracy of the GPS measurement deteriorates extremely.
Therefore, a device for detecting the generation of the multi-path is installed, and if the multi-path is generated, such a correction that the GPS satellite related to the generation of the multi-path is eliminated from an object of the GPS measurement is performed, for example. According to this detection and correction of the multi-path, when the generation of the multi-path is detected as for the one or more received radio waves, this or these are eliminated from the measurement object and it is performed the GPS measurement based on at least four received radio waves. Moreover, in the case that only three received radio waves are left as a result of eliminating the radio waves, in each of which the generation of the multi-path is detected ,from the measurement object because of a bad environment of receiving radio waves, such a technique that the GPS measurement is performed by switching the 3D positioning measurement to the 2D positioning measurement has been developed. More concretely, in the GPS 2D positioning measurement, the pseudo-range from each GPS satellite to the GPS receiver is measured by using (i) the time length required for the received radio wave to reach from each GPS satellite to the GPS receiver, and (ii) the position information of each GPS satellite, which is included in the radio wave received from each GPS satellite, basically about three GPS satellites under the assumption that their distances from the earth are rarely changed for a short time.
However, according to the present inventors' research, the above-mentioned technique, which detects the generation of the multi-path and eliminates the error of the pseudo-range, is not essentially accurate on its detection. Thus, there is a problem that the radio wave received through the normal radio wave path may be often erroneously eliminated from the measurement object of the GPS measurement by misdetection of the multi-path and the accuracy of the GPS measurement further deteriorates.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a GPS method and a GPS apparatus, which can detect the generation of the multi-path and correct an error of the pseudo-range caused by the effect of the multi-path, as well as reduce the deterioration of the positioning accuracy even when the generation of the multi-path is erroneously detected, a navigation system including the GPS apparatus, a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the GPS apparatus.
The above object of the present invention can be achieved by a GPS method provided with: a measurement process of measuring each pseudo-range ri (i=1, 2, . . . , n) from respective one of received radio waves from n GPS satellites (n is a natural number equal to or greater than 3) captured by a GPS receiver mounted on a movable body; a detection process of detecting a generation of a multi-path of the respective one of the received radio waves; a first calculation process of approximately calculating a clock error t and coordinates (x, y, z) of the GPS receiver as a solution of n simultaneous equations by performing a convergence calculation with respect to n functions fi (x, y, z, t) having such variables as the clock error t and the coordinates (x, y, z), each of the n functions fi (x, y, z, t) representing the pseudo-range ri; a second calculation process of approximately calculating the clock error t and the coordinates (x, y, z) as a solution of n+1 simultaneous equations by performing a convergence calculation with respect to total n+1 functions obtained by adding one &agr; fn+1 (x, y, z, t) to the n functions fi (x, y, z, t), where the one &agr; fn+1 (x, y, z, t) is obtained by applying a weighting &agr; (&agr; is a real number which is equal to or greater than 1) to one function fn+1 (x, y, z, t) having such variables as the clock error t and the coordinates (x, y, z), the one function fn+1 (x, y, z, t) representing a pseudo-range rn+1 obtained when the center of the earth is regarded as one GPS satellite; an ou
Camby Richard M.
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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