JP2003515749A - Method and receiver for GPS navigation - Google Patents

Abstract

A method for determining the position of a GPS receiver and a GPS receiver using the method are disclosed, comprising: (a) determining a pseudorange from at least four orbiting GPS satellites; (B) providing a pseudorange from a virtual satellite centered on the earth to the previously known position of the GPS receiver, and (c) from the pseudoranges of (a) and (b), Determining the position of

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for determining the position of a GPS receiver and a GPS receiver for this method.

[0002]

[Prior art]

Currently, GPS is particularly relevant to the NAVSTSR GPS, an all-weather space-based navigation system developed and operated by the US Department of Defense. However, the general law underlying GPS is general,
It is not limited to Navsta. Therefore, in the following, GPS refers to any global positioning system having multiple radio transmitters at different locations and a receiver that uses information about the time of arrival of the radio transmitter's transmissions to determine its location.

The general law underlying GPS and the methods and devices for implementing it are known. For example, one can see the principle and application of GPS (editor, Kaplan), which has an International Standard Book Number of 0-89006-793-7 of Artech House. Hereinafter referred to as "Kaplan".

As is well known, pseudorange measurements are required on at least four orbiting satellites to determine the position of the GPS receiver and the time offset between this receiver clock and the time of the GPS system. In situations where only signals from three orbiting satellites can be collected, it is usually not possible to determine the position of the GPS receiver. However, from Japanese Patent Application 63-134975 (A), "GPS navigation arithmetic processing method and GPS navigation arithmetic processing apparatus using the method", a virtual satellite placed at the center of the earth is assumed, It is known to provide a fourth pseudorange up to the known position fix of The virtual satellite pseudorange augments the three measured pseudoranges and allows the position of the GPS receiver to be estimated.

[0005]

[Problems to be Solved by the Invention]

It is an object of the present invention to provide an improved GPS navigation method and apparatus.

[0006]

[Means for Solving the Problems]

Therefore, the method for determining the position of the GPS receiver is (a) at least four orbits G
Determining a pseudorange from a PS satellite, (b) providing a pseudorange from a virtual satellite located at the center of the earth to a previously known position of the GPS receiver, and (c) (a) And (b) determining the position of the GPS receiver from the pseudo range.

A GPS receiver using the method according to the invention also has at least four orbits GP
It has a receiving means for collecting S satellite signals and a processing means for giving the pseudo ranges of (a) and (b) and obtaining the position of the GPS receiver from these pseudo ranges.

While it is not necessary to determine the current position of the GPS receiver when signals from at least four GPS satellites are collected, the inventor has found that pseudoranges from virtual satellites centered on the earth It has been recognized that the use of can actually improve the accuracy of the desired position.

The method of the invention is particularly suitable for terrestrial use of GPS receivers, especially for vehicle navigation. It is reasonably correct that the assumption that the altitude since the last known position fix is constant during such use is reasonably correct, and users on the ground are at least indirect to the surface of the earth for at least most of the time. , The altitude changes occur relatively slowly.

Further, with respect to a GPS receiver that determines its position from a Navsta GPS signal that has the effect of selective availability, the improved accuracy obtained from the present invention is further due to the selective availability error exceeding the rate of change of altitude of the user. Caused by the rate of change.

The method and GPS receiver according to the invention are described only by way of example with reference to FIGS.

[0012]

DETAILED DESCRIPTION OF THE INVENTION

Three-dimensional position (x _u , _yu , z _u ) of GPS receiver, receiver clock and GP
To determine the time offset t _u with the S system time, a pseudorange measurement ρ is performed on four orbiting satellites according to known methods.

[0013]   The measured pseudorange can be expressed as:

Ρ _j = ‖s _j −u‖ + ct _u [Formula 1] However, in the Cartesian coordinate system, s represents the position of the satellite, u represents the position of the GPS receiver, and c is the speed of light. j ranges from 1 to 4 and refers to satellites. Equation 1 can be extended to the following set of equations.

[Equation 1] Here, x _j , y _j, and z _j indicate the three-dimensional position of the j-th satellite.

Another pseudorange is provided from a previously known location of the GPS receiver from a virtual satellite centered on the earth. Since the virtual satellite position vector is (0,0,0), the virtual satellite pseudorange ρ _ce can be expressed as:

[Equation 2] Here, u'denotes a previously known position. The virtual satellite velocity vector is (0, 0, 0
), Its Doppler shift is zero.

Since equations 2 to 6 are overdetermined (there are more than unknowns), the error in the value of the pseudorange makes the above equations correct for any combination of position and time offset. The above formula is inconsistent in that it is prevented from being solved. Instead, linearization is used to obtain the best estimate of the three-dimensional position (x _u , _yu , z _u ) of the GPS receiver and the time offset t _u between the receiver clock and the GPS system time. Conventional iterative methods based on can be used. Such methods are well known. See, for example, Kaplan section 2.4.2.

The position produced using the method for determining the position of a GPS receiver according to the invention when 3 to 7 signals from orbit satellites are collected using both real and simulated data. The error was compared with the traditional method.

Real data was obtained by collecting the Navsta GPS signals acted upon by selective availability, and thus when the GPS receiver was stationary, by analyzing a conventional GPS device using the present invention. The simulated data was obtained using conventional simulation equipment, which was based on a moving vehicle scenario with accurate satellite ephemeris data and associated pseudoranges.

FIG. 1 relates to actual data, and shows the position error E (meter) on the vertical axis with respect to the number j of orbit satellites collected on the horizontal axis. Curve 1 shows the position error for a conventional method of generating a position fix based solely on signals collected from orbit satellites.
Thus, at least four orbit satellite signals are needed. Curve 2 shows the position error for the method according to the invention.

FIG. 2 is the same as FIG. 1 except that it is based on simulated data. Curves 3 and 4 show the position error for the conventional method for determining the position of the GPS receiver and the method according to the invention, respectively.

From FIGS. 1 and 2, if pseudoranges are obtained from four orbiting satellites, the accuracy of the position fix is about 8% by providing an additional pseudorange from a virtual satellite centered on the earth. It can be seen that the results are improved (actual data) and 50% (simulated data). When the pseudo range is obtained from 5 orbit satellites, the accuracy of the position fix is improved by about 14% (actual data) and 63% (simulated data). The difference in improvement between the real and simulated data is especially due to the absence of selective availability errors in the simulation.

Equations 1-5 describe the pseudorange of the simplified model for purposes of illustration only. In fact, many factors, including atmospheric delays, receiver noise and resolution offsets, multipath offsets, receiver hardware offsets, and selective availability degradation cause measurement pseudorange errors. These errors are compensated accordingly and are described in Kaplan section 7.1.2.

FIG. 3 schematically shows a GPS receiver implementing the method according to the invention. The GPS receiver is a generally known architecture with receiving means in the form of an antenna 5 and a signal preprocessor 6. In use, a radio frequency (RF) signal is received by the antenna and pre-processed by the pre-processor. This pre-processing is typically passive passband filtering, pre-amplification, intermediate frequency (IF) down-conversion, and AD conversion to minimize out-of-band RF interference. The GPS receiver further comprises a number of receiver channels 7, a receiver processor 8 and processing means 7, 8, 9 such as a navigation processor 9. The digitized IF signal is processed on each of the digital receiver channels, and the satellite signal is collected and tracked on each digital receiver channel in cooperation with the receiver processor. Methods of such acquisition and tracking are well known, for example see Kaplan chapters 4 (GPS satellite signal characteristics) and 5 (GPS satellite signal acquisition and tracking) of the same book.

Using the collected navigation information, including the time of arrival of the transmission, the navigation processor 9 is in accordance with the method of the present invention, ie from a virtual satellite centered on the earth to a known position beyond the GPS receiver. By giving a pseudo range up to
Calculate the receiver position. The calculated position is then communicated to the user, typically through a user interface 10 such as a display device.

The processing means 7, 8 and 9 are general-purpose microprocessors or GPS special purpose ICs.
Conveniently provided in any of the following forms, the method according to the present invention can be realized by using suitable programming and configuration of such processing means. Of course, such programming and configuration is well known and will be performed by one of ordinary skill in the art without undue burden.

[Brief description of drawings]

FIG. 1 shows the G according to the invention in the case where 3 to 7 signals are collected from an orbiting satellite.
6 is a graph showing a positional error caused by using the method of obtaining the position of the PS receiver in comparison with the conventional method.

FIG. 2 shows a G according to the present invention in the case where 3 to 7 signals are collected from an orbiting satellite.
7 is another graph showing the positional error caused by using the method for determining the position of the PS receiver, compared with the conventional method.

[Figure 3]   1 schematically shows a GPS receiver implementing the method according to the invention.

[Explanation of symbols]

  5 antennas   6 Signal preprocessor   7 receiver channels   8 receiver processor   9 Navigation processor   10 User interface

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuru Andrew             Netherlands 5656 aer ind             Fenprof Holstraan 6 F term (reference) 2F029 AA02 AB07 AC03                 5J062 AA05 AA13 BB01 CC07

Claims (3)

[Claims] 1. A method for determining the position of a GPS receiver, the method comprising: (a) determining a pseudorange from at least four orbiting GPS satellites; and (b) determining the pseudorange from a virtual satellite located at the center of the earth. A method comprising the steps of providing a pseudorange to a previously known position of a GPS receiver, and (c) determining the position of the GPS receiver from the pseudoranges of (a) and (b) above. 2. Receiving means for receiving signals from at least four orbital GPS satellites; (a) obtaining a pseudo range from at least four orbital GPS satellites; and (b).
A process of giving a pseudo range from a virtual satellite placed at the center of the earth to a previously known position of the GPS receiver, and obtaining the position of the GPS receiver from the pseudo ranges of (a) and (b). A GPS receiver having means. 3. A GPS receiver as described with reference to the accompanying drawings.