JPH0481746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spatial wave tracking method for a device that uses Loran C radio waves to measure the position of a ship, aircraft, vehicle, etc.

(Prior art) Conventionally, in this type of Loran C receiver, the spatial wave tracking method when terrestrial wave tracking becomes impossible is to correct with a fixed value using a published spatial wave correction value. was going there.

(Problems to be Solved) Therefore, the accuracy of the correction is insufficient, and furthermore, it is difficult to perform the correction automatically.

The purpose of the present invention is to eliminate the drawbacks of the conventional method, and to make it possible to use spatial waves with high precision, the purpose of the present invention is to utilize the Loran C signal, which can expand the range of use of Loran navigation. An object of the present invention is to provide a spatial wave tracking method.

(Means for Solving the Problems) The present invention continuously samples the amplitude of a signal during a period including the third cycle of terrestrial waves and a spatial wave behind the terrestrial waves, and based on the obtained sample values. When the third cycle of the terrestrial wave can be detected, the zero crossing point of the third cycle of the terrestrial wave is detected and tracked, and when the level of the terrestrial wave drops to near the level where the third cycle can be detected. , detecting the zero-crossing point of the cycle where the amplitude of the spatial wave is maximum during the sampling period, and from the zero-crossing point of the third cycle of the terrestrial wave to the zero-crossing point of the cycle where the amplitude of the spatial wave is maximum. When the third cycle of the terrestrial wave becomes difficult to detect, the tracking point is moved to the zero crossing point of the cycle where the amplitude of the spatial wave is maximum, and the time difference is stored. The time difference between the two stations is set as a spatial wave correction value, and the time difference between the main station signal and the slave signal of Loran C measured with the tracking point of the spatial wave as a reference is corrected with the space wave correction value. .

(Example) An example of an apparatus for carrying out the method of the present invention will be described below with reference to FIG.

In FIG. 1, 1 is a reception antenna, 2 is a signal sample section of the Loran signal, 3 is a terrestrial wave/space wave detection section, 4 is a correction value measurement section for a spatial wave correction value, and 5 is a terrestrial 3-cycle determination section. , 6 is a phase control unit for signal tracking points, and 7 is a time difference correction unit for measuring time differences.

Next, the operation of this device will be explained. To explain the signal from one transmitting station (station A) of Ronn C, Figure 2 shows the received waveform when both terrestrial waves and spatial waves can be detected, and the terrestrial wave tracking point (zero crossing point of the third cycle). T ₁ and the spatial wave tracking point (zero crossing point of the cycle where the amplitude is maximum) T ₂ are shown. 1st
The signal sampling unit 2 shown in the figure continuously samples the amplitude of the signal over a sufficiently wide range including T ₁ and T ₂ . Here, even if the sampling range of the signal is narrow and the maximum of the spatial wave signal cannot be detected and the spatial wave detection point T ₂ is in front of the maximum of the spatial wave close to T ₁ , when the terrestrial wave is attenuated. , the signal-to-noise ratio at T ₂ is
The method of the present invention is effective as long as the point is better than that of _T1 . Next, when the terrestrial wave/space wave detection unit 3 detects that terrestrial wave tracking is possible based on the sample value obtained by the signal sample unit 2, the 3-cycle determination unit 5 detects the zero of the 3rd cycle of the terrestrial wave. The intersection point is detected, and the phase difference control unit 6 detects the terrestrial signal.
Let the zero crossing point of the cycle be the terrestrial tracking point _T1 .
Next, when the level of the terrestrial wave drops to near the third cycle detectable level, the terrestrial/spatial wave detector 3 detects the zero crossing point T ₂ of the cycle in which the amplitude of the spatial wave is maximum during the sampling period. is detected and used as a spatial wave tracking point, and the time difference between the terrestrial wave tracking point T ₁ and the spatial wave tracking point T ₂ is measured and stored in the correction value measurement unit 4, and is used as a spatial wave correction value. Furthermore, when the terrestrial tracking point _T1 cannot be detected and tracking becomes difficult as shown in FIG. 3, the phase control unit 6 moves the signal tracking point to a position _T2 backward by T.
The time difference corrector 7 corrects the time difference between the main station signal and the slave signal of Loran C measured at the spatial wave tracking point _T2 using the spatial wave correction value.

Since the phase of the spatial wave does not necessarily match the phase of the terrestrial wave, the value of T is n × 10 μs + Δt (n is a positive integer, 10 μs is one period of the Loran C frequency of 100 kHz,
Δt is the time deviation). Therefore, the time interval of the sampling signal generated by the signal sampling section 2 affects the accuracy when tracking the spatial wave. on the other hand,
According to the sampling theorem, a sampling interval of 2.5 μs is sufficient. As shown in Figure 4, the sample interval is 2.5μs
(lower case) and large, as an example,
T immediately after phase control using the characteristics of zero point phase tracking
By calculating the difference between the tracking point and the tracking point after a certain period of time, it is possible to obtain an extremely accurate correction value.
In addition, as a second example, the position B of the zero crossing point can be determined from the ratio of the levels of two points A and C that sandwich the zero crossing point.
It is possible to calculate the corrected time difference with high accuracy. Furthermore, as shown in FIG. 5, it is clear that when sufficiently fine sampling can be achieved, a highly accurate correction value can be obtained immediately after phase control.

Next, as shown in Figure 3, after the terrestrial wave has attenuated and the tracking has shifted from the terrestrial wave to the spatial wave, if the terrestrial wave cannot be detected and only the spatial wave is detected, the tracking of the spatial wave While tracking the signal at point _T2 , the system always monitors a time point T ahead, and when a signal is detected at time _T1 , the tracking point is returned to _T1 , which is the terrestrial wave.

However, the delay time T of the spatial wave signal from the terrestrial wave may vary over time due to changes in the state of the ionosphere, so the phase control unit 6 returns the tracking point to the terrestrial signal, and Once again, the 3 cycle determination unit 5 in FIG.
The zero crossing point of the cycle is detected and moved to the regular terrestrial tracking point.

On the other hand, when only a spatial wave is detected in the first signal tracking as shown in FIG. 3, the method of the present invention can be operated as is by temporarily setting T to about 30 μs.

(Effects of the Invention) As explained above, the present invention detects the tracking point of the spatial wave by using the terrestrial wave of the Loran C signal and the sample value of the amplitude of the spatial wave. The time difference between the main station signal and the slave station signal of Loran C can be obtained with the same accuracy as when tracking terrestrial waves. Furthermore, in order to track terrestrial waves and spatial waves, it is not necessary to have two tracking systems, but only one system, so the circuit and control can be simplified and costs can be kept low.
Furthermore, the tracking limit of the Loran C signal does not depend on the signal level of the third cycle of terrestrial waves, and spatial waves with higher signal levels can now be used, reaching areas that were previously difficult to use. Conventionally, there is an advantage that it is possible to expand the highly accurate positioning capability of the Loran C signal even under adverse conditions where the Loran C radio waves cannot be used.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of a device implementing the method of the present invention, and FIG. 2 is a signal waveform diagram at a receiving point when terrestrial waves and spatial waves arrive.
Figure 3 is a signal waveform diagram when no terrestrial waves can be observed and only spatial waves can be observed, and Figure 4 is a signal waveform diagram when moving from terrestrial wave tracking to spatial wave tracking when a 2.5 μs interval is used for signal sampling. FIG. 5 is a diagram showing the correspondence between sample points and waveforms of a signal in the spatial wave portion, and is a diagram showing a case where fine intervals of 0.5 μs are used for signal sampling. 1...Antenna, 2...Signal sample section, 3...
Terrestrial wave/space wave detection section, 4... Correction value measurement section, 5
...3 cycle determination section, 6...phase control section, 7...
...Time difference correction section.

Claims (1)

[Claims] 1 When the third cycle of terrestrial waves can be detected based on the sampled values obtained by continuously sampling the amplitude of the signal during the period including the third cycle of terrestrial waves and the spatial waves behind the terrestrial waves. detects and tracks the zero crossing point of the third cycle of the terrestrial wave, and when the level of the terrestrial wave drops to near the third cycle detectable level, the amplitude of the spatial wave reaches its maximum during the sampling period. detect the zero-crossing point of the cycle in which the amplitude of the spatial wave becomes maximum, measure the time difference from the zero-crossing point of the third cycle of the terrestrial wave to the zero-crossing point of the cycle in which the amplitude of the spatial wave is maximum, and store the time difference; When the third cycle of the terrestrial wave becomes difficult to detect, the tracking point is moved to the zero-crossing point of the cycle where the amplitude of the spatial wave is maximum, and the stored time difference is used as the spatial wave correction value, and the spatial wave is A spatial wave tracking method for a Loran C signal, characterized in that a time difference between a main station signal and a slave signal of Loran C measured with the tracking point of the wave as a reference is corrected using the spatial wave correction value.