JPH0466316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a satellite navigation device that calculates and displays the current position, speed, and direction of a moving object such as a car, ship, or airplane.

[Conventional technology]

Traditionally, GPS (Global Positioning
System) There is a navigation device.

To determine the user's position three-dimensionally using satellite navigation, it is sufficient to determine three unknowns: three components in the earth-centered and earth-fixed coordinate system, latitude, longitude, and height (X, Y, Z). The principle of GPS navigation is to simultaneously receive and measure the distance from multiple satellites in medium-altitude orbits whose positions are known to the user. The moment-by-moment position of a satellite can be determined from orbital elements and expressed three-dimensionally. In order to find the user's three-dimensional position, if the distances from three satellites can be measured, the points of intersection of three spherical surfaces (X, Y,
Z) can be used to find the user's position.

In this way, in GPS navigation, calculations are performed using signals obtained by unidirectional propagation of radio waves from the satellite to the user. In addition, it is necessary to use a method in which clocks that match each other are placed and the propagation time of the radio waves is directly measured using the two clocks. However, it is not practical to equip each user with such a highly accurate clock. Therefore, the user receives radio waves from multiple satellites simultaneously, and detects the user's position based on pseudorange data including the time offset between each satellite and the user, and the position data of each satellite. In other words, the time T that matches the satellite clock is added as another unknown, and in addition to the three unknowns related to the position, four unknowns (X,
Y, Z, T) must be solved. for that purpose,
It must receive radio signals from four satellites scattered in the sky. When the moving object is a car or a ship, there is little change in height, so even if there is a slight error in height, the two-dimensional position of latitude and longitude is unlikely to be significantly deviated. Therefore, two-dimensional positioning is performed by entering a known value in the height (Z) and solving the three unknowns (X, Y, T) from the three satellites.

As one of the devices for implementing the above-mentioned GPS navigation, a one-channel sequential reception type device has been used. This type of equipment has one receiving channel, but uses a time-division method, receives signals from the multiple satellites mentioned above, and sequentially measures the pseudo distance from each satellite to the user. It calculates the position. This makes it a small, lightweight, and low-cost GPS navigation device.

[Problem that the invention seeks to solve]

In order to demodulate satellite signal data from received data, the GPS navigation device is equipped with a reference oscillator that serves as a source for synthesizing all local signals such as a frequency conversion frequency, a code generation clock, and a reference signal for phase comparison. The reference oscillator is, for example, a crystal oscillator, and since the oscillation frequency is not stable for a while after the power is turned on, the absolute frequency, that is, the frequency offset Δf with respect to the oscillation frequency by the high-precision oscillator in the satellite, fluctuates greatly.

Frequency offsets for GPS satellite navigation are described in "Ship Electronic Navigation Notes (35)" August 1979 issue of "Ship Science" published by the Japan Shipping Association, page 84, lines 13 to 20 in the left column.
This is a known phenomenon as described in the line.

However, in the one-channel sequential reception method described above, radio waves from multiple satellites are sequentially switched and received over time, so if the oscillation frequency of the reference oscillator changes while receiving signals from each satellite, the pseudo Since the distance was measured under a different frequency offset, it contains an error. A position calculated using a pseudorange that includes errors in this way has poor accuracy. In the past, the drawback was that less accurate data was output as is, leading to erroneous decisions.

The present invention has been made to eliminate these drawbacks, and provides a satellite navigation device that can output data on accuracy as well as measured position and velocity data.

[Means for solving problems]

A satellite navigation device to which the present invention is applied in order to solve the above problems has a one-channel sequential receiver that sequentially receives radio waves from a plurality of GPS satellites in a time-division manner. In a satellite navigation device that calculates the position of a moving object by measuring pseudo-distances between multiple satellites and a receiver using the signal received from the satellite and the signal received from the satellite, the frequency between the oscillation frequency of the satellite and the frequency from the reference oscillator is used. means for calculating the offset; means for calculating the offset fluctuation from the difference between the frequency offset calculated during the previous pseudorange measurement by the frequency offset calculation means and the frequency offset calculated this time; a plurality of threshold values set in advance and each Means for comparing the magnitude of the offset fluctuation with a threshold value and dividing the magnitude of the offset fluctuation into a plurality of regions, and means for outputting a value representing the region as data representing the accuracy of the measured position of the moving object. It is characterized by having the following.

[Effect]

As shown in FIG. 3a, the frequency offset Δf of the frequency oscillated by the reference oscillator 10 converges with the passage of time. As shown in FIG. 3b, as the frequency offset Δf converges, the reliability of the measured position and velocity of the moving body improves. Therefore, data representing accuracy based on the frequency offset Δf is output, allowing the observer to make an error-free judgment.

〔Example〕

A first embodiment of a satellite navigation device to which the present invention is applied is described below.
This will be explained using the block circuit diagram shown in the figure.

The circuit in the figure is a one-channel sequential reception circuit, in which 1 is a satellite signal receiving antenna, 2 is a radio frequency (RF) amplifier, 3 is a first frequency converter,
4 is the first intermediate frequency (IF) amplifier, 5 is the correlation second
a frequency converter, 6 a second intermediate frequency (IF) amplifier;
7 is a phase comparator, 8 is a central processing unit (CPU), 9 is a frequency synthesizer, 10 is a reference oscillator,
11 is a pseudo-noise code modulator, 12 is a numerically controlled oscillator for carrier phase synchronization (carrier NCO Numerical
13 is a pseudo-noise code generator, and 14 is a numerically controlled oscillator (code NCO) for pseudo-noise code phase synchronization.

When the power (not shown) is turned on in this circuit, satellite radio waves are received by the antenna 1, amplified by the high frequency amplifier 2, and then the reference frequency oscillated by the reference oscillator 10 is multiplied by the frequency synthesizer 9 to synthesize the local radio waves. The frequency is converted into a first intermediate frequency by a first frequency converter 3. This first intermediate frequency is amplified by a first intermediate frequency amplifier 4 and correlated by a second frequency converter 5.
to go into. On the other hand, the pseudo-noise code generated by the pseudo-noise code generator 13 and the output of the numerically controlled oscillator for carrier phase synchronization 12 are input to the pseudo-noise code modulator 11, and the modulated output is input to the correlation second frequency converter 5. do. The correlation second frequency converter 5 correlates the input first intermediate frequency with the modulation output of the pseudo-noise code modulator 11, and simultaneously
The intermediate frequency is converted to a second intermediate frequency. Second
The intermediate frequency is amplified by a second intermediate frequency amplifier 6,
The local frequency synthesized by the frequency synthesizer 9 is phase-compared with the phase comparator 7, and then input to the central processing unit 8.

That is, the carrier wave (carrier) is tracked in a closed loop of CPU 8 → carrier NCO 12 → pseudo noise code modulator 11 → correlation second frequency converter 5 → second IF amplifier 6 → phase comparator 7 → CPU 8. The phase of the pseudo noise code (code) is CPU8 → code NCO
14 → code generator 13 → pseudo noise code modulator 1
1 → correlation second frequency converter 5 → second IF amplifier 6 →
It is tracked in a closed loop of phase comparator 7 → CPU 8.

In this way, data demodulation of each satellite signal and pseudorange measurement are performed sequentially in a time-sharing manner.
The central processing unit 8 calculates the position, speed, and direction of the moving body and the frequency offset Δf of the reference oscillator 10, and outputs the results.

If the frequency offset Δf of the reference oscillator 10 varies greatly, the reliability of the calculated position, velocity, and orientation decreases. As shown in FIG. 3a, the frequency offset Δf converges as time passes. Therefore, reliability can be determined while measuring fluctuations in frequency offset Δf.

The flowchart in FIG. 2 shows a control procedure in which the central processing unit 8 determines the reliability of the calculated position, speed, and direction based on the fluctuation of the frequency offset Δf of the reference oscillator 10 and outputs it to the display means. This is explained by:

As shown in the figure, the power is turned on and the initial frequency offset Δf ₀ =A of the bridge quasi-oscillator 10 is set (step 21). In this case, A is the maximum expected frequency offset. In the next step 22, the frequency offset (frequency drift) thresholds are set as a=F ₀ , b=F ₁ , c=F ₂
and set. However, F ₀ >F ₁ <F ₂ . In step 23, the signals of four optimum satellites (or three satellites) are captured and tracked. Next, in step 24, trajectory data is collected, Doppler frequencies are measured, and pseudoranges are measured. In step 25, the above step 2
The frequency oscillated by the oscillator inside the satellite is calculated from the data of 4, along with the position, speed, and direction of the moving object, and the frequency offset is calculated from that frequency and the local frequency oscillated by the reference oscillator 10 and synthesized by the frequency synthesizer 9. Calculate and memorize △f _i . In step 26, the difference ΔF=|Δf _i −Δf _i-1 | between the frequency offset Δf _i and the previously calculated and stored frequency offset Δf _i-1 is determined. Step 27
If this ΔF is larger than the threshold a, the position,
Since the reliability of speed and direction is too low to be suitable for observation, we wait for time Δt to pass (step 2).
8), return to step 24. If ΔF is smaller than threshold a, it is determined in step 29 whether ΔF is larger than threshold b. If it is larger (a>ΔF>
b) Since the reliability is low, data indicating that the reliability is low is output together with the position, speed, and direction data (step 30). If ΔF is smaller than threshold b, it is further determined in step 31 whether ΔF is larger than threshold c. If it is larger (b>ΔF>c)
The reliability is medium, and data indicating the medium reliability is output together with position, speed, and direction data (step 32). If ΔF is smaller than the threshold c, then
The reliability is high, and data indicating that the reliability is high is output together with data on position, speed, and direction (step 33). After each data is output in steps 30, 32, and 33, the loop from step 24 is repeated again after waiting for time Δt to elapse.

As shown in FIG. 3a, the frequency offset Δf converges with the passage of time, so as shown in FIG. 3b, each time the above loop is repeated, the reliability, that is, the accuracy improves.

〔Effect of the invention〕

As explained above, in the satellite navigation device to which the present invention is applied, the oscillation frequency of the reference oscillator is not stable for a while after the power is turned on, so there is a large offset fluctuation in the frequency, which causes errors in the measured position, speed, and direction. If this occurs and the accuracy is poor, data representing reliability is output. Therefore, whether or not to use the measured position, speed, and direction can be determined based on the accuracy data as necessary. Furthermore, it is possible to prevent the observer from making incorrect judgments.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing an embodiment of a satellite navigation device to which the present invention is applied, Fig. 2 is a control flowchart of the central processing unit, and Fig. 3 is a diagram showing temporal changes in frequency offset and reliability. It is a figure explaining a relationship. 1...Antenna, 2...High frequency amplifier, 3...
first frequency converter, 4...first intermediate frequency amplifier,
5... Correlation second frequency converter, 6... Second intermediate frequency amplifier, 7... Phase comparator, 8... Central processing unit, 9... Frequency synthesizer, 10... Reference oscillator, 11... Pseudo-noise code modulator, 12... Numerically controlled oscillator for carrier phase synchronization, 13... Pseudo-noise code generator, 14... Pseudo-noise code synchronization numerically controlled oscillator.

Claims (1)

[Claims] 1. Has a 1-channel sequential receiver that sequentially receives radio waves from multiple GPS satellites in a time-division manner, and uses signals from a reference oscillator in the receiver and signals received from the satellites to communicate with multiple satellites and receivers. In a satellite navigation device that calculates the position of a moving object by measuring the pseudorange between the satellite and the reference oscillator, the satellite navigation device calculates the frequency offset between the oscillation frequency of the satellite and the frequency from the reference oscillator. This method calculates the offset fluctuation from the difference between the frequency offset calculated at the time and the frequency offset calculated this time. 1. A satellite navigation device comprising means for dividing the size into a plurality of regions, and means for outputting a value representing the region as data representing the accuracy of the measured position of a moving object.