JPS6295478A - GPS reception system - Google Patents

Abstract

PURPOSE:To determine the position of a satellite accurately and to perform high-precision position measurement by synchronizing a user clock with the clock of a GPS system. CONSTITUTION:A spread spectrum signal of 1.5GHz transmitted by the satellite is synchronized with a C/A code determined according to the satellite, and then an epoch signal with a 1msec period is obtained. Further, a synchronizing signal is detected and a demodulated signal of 1bit/20msec is obtained through a COSTAS circuit. For the purpose, a user timer is synchronized with the variation timing of the demodulated signal shown by a downward arrow. The user clock is reset at the variation timing of the demodulated signal and dummy distances R1-R4 are measured at this resetting point of time or at intervals of 20msec (user timer) from the resetting point of time. Consequently, satellite positions U1-W1 are found accurately and high-precision position measurement is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a GPS receiving system, particularly a UPS receiving system suitable for measuring the position of land mobile objects such as automobiles.

[Background of the invention]

In recent years, the so-called GPS (Global
The positioning system) has started to receive a lot of attention.

Figure 5 shows the GPS positioning yA principle. The distance ρi between the satellite position and the user position is found by measuring the propagation time of the signal transmitted from the satellite, and the satellite position is estimated by solving Kepler's equation from the transmission time.
1 and (U+, V+.

The user position (X, Y, Z) is calculated from W+).

This is known, for example, from Japanese Patent Application Laid-open No. 55-117977 and Japanese Patent Application Laid-Open No. 59-88666, and as shown below, ρ=[ρ
l, ρ2. ρ3. By measuring ρ4]7 and solving the simultaneous equations given by equation (1), the user position W(X, Y,
Z+ is required.

・・・・・・・・・(1) (Longitude-Latitude-Height) Coordinate transformation ρI= ≠Tπ■Tmu4. h112+[Vl-Y(tl, 4.h
l12+[Wl-Z(A,4.h))2+c-b
・・・・・・・・・(2
) Here, tt; latitude (1attitude) tl;
Longitude (Iongi tude 1h; Altitude (alti)
tude 1 e2=1-(1-f)"=1-(1-1/298.2
612= 6.69431774X10-3 a; Semi-major axis of WGS-72 (=6,378,135 m
lf; Flatness C of Wos-72; 299792458 m/5 When formula (2) is linearized, δρ=[G]δU or δU=l:G)''・δρ...
......(5) Here, δU=[tt r , δt1. δh, δB)”.

δρ=[δρ, 15ρ2. δρ3. δρ4〕0...
・・・・・・(6) ・・・・・・・・・(7) ・・・・・・・・・(8) ・・・・・・・・・(9) ・・・・・・・・・...αO Here, ......0υ Also, regarding aρ1/&b in equation (7), it becomes.

FIG. 6 shows the calculation procedure of the positioning algorithm given by equations (1) to (14). As the user's initial position, latitude,
The longitude and height may be given within an error range of approximately 300 [m], and the initial ffi of the user's clock bias b may be set to zero.

In the GPS positioning algorithm shown above, even if there is a time difference between the user clock and the GPS system clock, it does not seem to affect the positioning results because the clock bias b is unknown, but in reality, this magnitude is This becomes a problem, and this point will be explained below.

Both the user position Fft (U + , VI, W + ) and the user position (X, Y, Z) change from moment to moment, but in order to solve the simultaneous equations in equation (1), the pseudo distance ρ1 is measured. Everything must be synchronized by time.

In this case, clock bias b, that is, user clock and G
The deviation of the PS system clock is an unknown quantity, but since the pseudorange measurement range is within the period (1 msec1) of the epoch signal transmitted from the satellite, the clock bias b obtained by equation (1) also depends on this epoch signal. It is within the period. Figure 7 shows the user bias b that exceeds the epoch period.
The relationship between the user bias b and the user bias b considered in equation (1) is shown below. As can be seen from FIG. 7, b is the bias of the user clock that is not included in the pseudorange ρ1, and FIG. 8 shows the results of a simulation of the relationship between the user bias b that exceeds this epoch period and the positioning error.

Therefore, for example, if b is 5m5eC, a positioning error of 10 to 25m will appear.

[Purpose of the invention]

The present invention was made against the above-mentioned background, and its purpose is to solve the problems of the prior art described above, and to provide high-speed radio communication even in poor radio wave environments such as in land mobile vehicles. The purpose of the present invention is to provide a GPS receiving system that can perform accurate positioning.

[Summary of the invention]

The key point of the present invention is to focus on the fact that the data signal transmitted from the satellite, that is, the demodulated signal of the receiving system, is synchronized with the GPS system clock, and to synchronize the pseudo distance measurement with the timing of the change in the demodulated signal. The point is that
Furthermore, a microcomputer with high processing performance is used to select a satellite with a good S/N ratio as the satellite that determines the measurement timing.

[Embodiments of the invention]

Hereinafter, the GPS receiving system according to the present invention will be explained in detail with reference to illustrated embodiments.

As shown in Figure 1, 1°5()R transmitted from the satellite
By synchronizing the spread spectrum signals of 2 with the C/A code determined for each satellite, an epoch signal with a period of 1 m (8) is obtained. Furthermore, the synchronization signal is detected, and a demodulated signal of 1.720 mm is obtained via the C08TAS circuit.

Therefore, in one embodiment of the present invention, the user clock is synchronized with the change timing of the demodulated signal shown by the ↓ mark in the example of the demodulated signal in FIG.

Figure 2 shows the synchronization method in this embodiment.
The user clock is reset at the timing of the change in the demodulated signal, and the pseudo distance (I, R2, Rs,
R4).

Therefore, according to this embodiment, the satellite position (Ul.

VI, W+) can be determined accurately, and as a result, highly accurate positioning can be obtained.

Next, in the embodiment, the GP8 receiving system is equipped with a microcomputer capable of high-speed processing, and the accuracy of the user's clock can be further improved as described below.

That is, the antenna used in the GPS receiving system is omnidirectional, and its performance deteriorates in the horizontal direction as shown in FIG. As a result, the S/N of the received signal varies depending on the satellite elevation angle, as shown in FIG.

On the other hand, when the S/N decreases, fluctuations occur in the demodulated signal, which tends to cause errors in the timing of time adjustment.

By the way, three or four satellites are required for positioning calculations, but only one of them is required for creating a timing signal for time adjustment.

Therefore, in this embodiment, the above-mentioned microcomputer selects the one with the largest angle of elevation among the plurality of satellites in a receivable state at that time as the satellite for time adjustment.

Therefore, according to this embodiment, the demodulated signal used to generate the timing signal for resetting the user clock is always a signal with a good S/N ratio, so that variations in synchronization can be kept to a minimum.

〔Effect of the invention〕

As explained above, according to the present invention, the user clock can be synchronized with the GPS system clock, thereby eliminating the drawbacks of the prior art and making it possible to accurately determine the satellite position. Positioning can be performed.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is an explanatory diagram of synchronization timing in a GPS reception system according to the present invention, FIG.
Characteristic diagram of the receiving antenna, Fig. 4 is an explanatory diagram showing the relationship between the S/N of the satellite signal and the elevation angle, Fig. 5 is an explanatory diagram of the GPS system, and Fig. 6 is an explanatory diagram showing the positioning algorithm by the GPS system. , FIG. 7 is an explanatory diagram showing the problems of the prior art, and FIG. 8 is an explanatory diagram showing the relationship between user clock bias and positioning error. (U + , V + , W Il”・Satellite position, (
X, Y, Z) - user position, b...clock bias, b...user pie

Claims (1)

[Claims] 1. A method of generating an epoch signal for pseudorange measurement in synchronization with a signal transmitted from a GPS satellite, and generating a demodulated signal for obtaining data for positioning calculation based on this epoch signal. 1. A GPS receiving system according to claim 1, wherein a user clock necessary for generating the epoch signal is synchronized with the timing at which the demodulated signal changes. 2. In claim 1, the demodulated signal for timing adjustment is based on a signal received from a satellite whose elevation angle is the largest among a plurality of satellites that can be received at that time. A GPS receiving system comprising: