JPS6235279A - Loran-c receiver - Google Patents

Abstract

PURPOSE:To continue accurate position measuring operation without causing any large position measurement error due to a cycle slip by detecting the oscillation error of tracking pulses from the tracking error of pulses tracking a received signal and correcting the oscillation frequency of the tracking pulses according to the detected error. CONSTITUTION:Received loran radio waves are coded by the quantizing circuit 18 of a receiver into binary signals, and a phase comparing circuit 20 compares the phase of the binary-coded data with the phase of tracking pulses 100 from a presettable counter 22 and supplies the comparison result to a loop filter 24. An increase or decrease in the preset value of the counter 22 is indicated to an MPU 26 with the output of the filter 24 and the counted value of the counter 22 is increased or decreased under the control of the MPU 26. Further, the counter 22 counts oscillating pulses of a crystal oscillator 28 and outputs the tracking pulses 100 synchronized with the loran pulses. Then, the tracking error of the tracking pulses 10 is detected by the circuit 20 and filter 24 and the frequency of the tracking pulses 100 is corrected according to the tracking error.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radio navigation receiver, and particularly to a Loran C receiver.

(Background of the Invention) In this type of receiver, the arrival time difference between Loran pulses transmitted from the master station and the slave station is determined, and position measurement is performed using the arrival time difference.

The arrival time difference is determined based on the phase tracking point of a pulse generated internally in synchronization with the Loran pulse in a predetermined cycle of the Loran pulse carrier wave.

Furthermore, in the past, the above-mentioned phase tracking has been performed using the PLL shown in FIG. is compared in phase with the carrier wave of the Loran pulse by the phase comparator 12.

And the comparison signal is LPF (loop filter) 14
The oscillation signal of the VCO 16 whose frequency corresponds to the comparison signal is supplied to the VCO 16 via the frequency divider 1.
0 to form a loop.

Here, if the level of the received radio wave drops significantly, the phase comparison operation of the phase comparator 12 becomes impossible and the PLL enters a so-called free run state, so the oscillation error of VC016 is accumulated, and as a result, the phase comparator 12 The comparison signal gradually moves away from the tracking carrier. If the comparison signal of the phase comparator 12 is separated from the tracking carrier wave of the Loran pulse by more than 1/2 recycle, a so-called cycle slip occurs, resulting in a large position measurement error.

Therefore, the VCO 16 uses a crystal oscillator whose oscillation frequency is compensated by temperature.

However, the oscillation error of the crystal oscillator is up to 11)
l) The carrier wave frequency of the Loran pulse is 1.
Considering that it is a QQKIIz, a cycle slip occurs after 5 seconds of free running.

Therefore, when the received radio waves are often weak, such as when a Loran C receiver is used to measure the running position of a vehicle, nickel slips are likely to occur, resulting in large position measurement errors.

As described above, in the prior art, there has been a problem in that when the level of the received signal drops sharply, a cycle slip occurs due to an oscillation error in the pulse that tracks the received signal, resulting in a large position measurement error.

(Object of the invention) The present invention has been made in view of the above-mentioned conventional problems, and
The purpose is to provide a Loran C receiver that generates tracking pulses at a highly accurate oscillation frequency and can avoid large position measurement errors due to cycle slips.

(Configuration of the Invention) In order to achieve the above object, an apparatus according to the present invention is configured as shown in FIG.

That is, in the figure, a tracking pulse that tracks the received signal is generated by the oscillation means a.

The oscillation error of the oscillation means a is detected from the tracking error of the tracking pulse by the oscillation error detection means.

Roughly based on the error, the period for correcting the oscillation frequency of the oscillation means a is determined by the correction period calculation means C.

Further, the oscillation frequency of the generating means a is corrected by the oscillation frequency correcting means d according to the oscillation error at that period.

(Description of Embodiments) Hereinafter, preferred embodiments of the apparatus according to the present invention will be described based on the drawings.

The quantization circuit 18 in FIG. 3 is supplied with the received signal of the Loran radio wave shown in FIG. 4(a), and in FIG. 4(a), the main station signal PM of the Loran radio wave.

The first slave signal S+r and the second slave signal S2 are sequentially transmitted at predetermined intervals from the Loran master station, the first slave station, and the second slave station.

These main station signal M, slave station signals S+, S2 are each 1 m
Consisting of multiple Loran pulse LPs spaced at 5ec intervals,
The Loran pulse LP is shown in FIG. 4(C).

The quantization circuit 18 shown in FIG.
The phase is compared with 0.

Roughly, the comparison signal of the phase comparison circuit 20 is passed through the loop filter 2.
4, and is averaged by this loop filter 24.

As shown in Japanese Patent Application No. 59-94330, it is also possible to control the control constant of the loop filter 24 to an optimum value according to the S/N ratio of the received signal.

The output pulse of the loop filter 24 instructs the MPU 26 to increase or decrease the preset j value of the preset counter 22, and the count value of the preset counter 22 is controlled to increase or decrease by 1 in accordance with the instructions.

The preset counter 22 counts the oscillation pulses of the crystal oscillator 28, thereby obtaining the tracking pulse 100.

With the above configuration, the tracking pulse 100 is the Loran pulse LP.
As a result, in this embodiment,
), the tracking pulse 100 is phase-tracked to the zero-crossing point in the third carrier cycle of the Loran pulse LP.

Furthermore, as understood from FIG. 4(b), the tracking pulse 10
0 is obtained for each Loran pulse LP.

When the tracking pulse 100 is obtained in this way, the main station signal M, the first slave station signal S5 . Arrival time difference of second slave signal S2 T M S I ITs+ −
92 and TS2-M are determined, and are used to measure the current traveling position of the vehicle.

Here, the carrier frequency of the Loran pulse LP is considered to have extremely high accuracy, and therefore in this embodiment, the oscillation frequency of the tracking pulse 100 is corrected as follows using this as a reference.

Due to the oscillation error of the crystal oscillator 28, the tracking pulse 100 moves from the normal tracking point P in FIG. 5(a) to the front as shown in FIG. is moved to the same figure (
As shown in C), the vehicle is controlled to advance and retreat l and 11 to the regular tracking point P.

Therefore, precera 1 ~ loop filter 2 that commands to increase/decrease the value
It becomes possible to detect the oscillation error of the tracking pulse 100 from the output pulse No. 4.

In this embodiment, detection of this oscillation error and correction of the oscillation frequency of the tracking pulse 100 are performed by the MPU 26, and in order to perform this processing, the S
A detection signal from the N ratio measuring circuit 30 is supplied to this MPU 26.

Note that the SN ratio measuring circuit 30 is
As shown in 5540, it is possible to sample the binarized data of the quantization circuit 18 and stochastically obtain the SN ratio.

In FIG. 6, the processing procedure of the MPU 26 for detecting the oscillation error of the crystal oscillator 28 and correcting the oscillation frequency is shown in flowcharts 1 to 1. The station with the highest ratio is selected (step 200).

Then, it is determined whether it is possible to use the received signal of the selected station as a reference for detecting the oscillation error of the tracking pulse 100 (step 202).

In this embodiment, when the S/N ratio of the selected station is good, it is determined that the received signal of the selected station can be used as the oscillation error detection reference for the tracking pulse 100.
When this determination is made, counting of output pulses of the loop filter 24 is started (step 204).

The counting continues for 5 seconds (step 206), and when 5 seconds have passed since the start of counting,
The count value at the time of elapsed time is 1 for the previous 5 seconds.
. . . , and the count value is successively integrated for 5 seconds (step 208).

Further, the integrated value is stored (step 210),
The preset value of the preset counter 22 is controlled by the integrated value, and the oscillation frequency of the tracking pulse 100 is corrected (step 212).

7 and 8 show the oscillation frequency correction process (step 212) in FIG. 6, and in the process of FIG. 7, the oscillation error detection operation (steps 204 to 210 in FIG. 6) is completed. If confirmed (affirmative determination in step 214), the correction period calculation process (step 2) of FIG.
16) is started.

In the process (step 216), the count time T (5SeC) is first divided by the count value N accumulated over 5 seconds of the loop filter 24 (step 21
8).

As a result, the oscillation error of the tracking pulse 100 is 0°1 μs.
The time t to reach ec is calculated, and the time t=0
．． 1 μsec is the amount by which the tracking pulse 100 is moved forward or backward when the preset value of the preset counter 22 is increased or decreased by the value 1, that is, the minimum unit correction amount for the oscillation frequency of the tracking pulse 100.

For example, if the output pulse of the preset counter 22 is counted +20 during the output pulse of the loop filter 24 for 5 seconds, the time t at which the oscillation error of the tracking pulse 100 becomes the minimum unit correction amount of 0.1 μsec is 0. 25 (
5/20) sec.

Next, the time t is the repetition period of the Loran radio wave (GRI
=0.0997 sec), the integer part n of the number of repetition periods of the Loran radio waves within that time is obtained (step 220).

In the above example, the time is 0.25 seconds, so
The integer part n of the period number is 2.

Furthermore, it is determined whether the remaining portion is more than half of the Roland radio wave repetition period (step 222), and in this example, the remaining portion is 0.0506 sec, which is more than half of the repetition period of 0.09973 eC. The value 1 is added to the integer part n of the number to round it up (step 224).

Note that if the remainder is less than half of the Loran radio wave repetition period, it is truncated, and the integer part of the repetition period number is left as is.

As described above, when the number of repetition periods n of the Loran radio waves within the time when the oscillation error of the tracking pulse 100 reaches the minimum unit correction ff10.1 μsec is determined (step 216>, the first GRI (first GRI) in FIG. The main station signal M and the first slave signal S1 in the 10-run radio wave repetition period)
A value P1 corresponding to the arrival time difference TM-s is set in the preset counter 22 (step 226).

Then, the countdown is performed (step 228
), when the count value becomes O and it is confirmed that the arrival time of the first slave signal S, has arrived, a value corresponding to the arrival time difference Ts1-s2 between the first slave signal @S1 and the second slave signal S2 is determined. P2 is set (step 232).

The countdown is performed roughly (step 234).
> When it is confirmed that the count value becomes O and the arrival time of the second slave signal S2 has arrived (step 236)
, the current repetition period (first GRr) corresponds to the number of periods n (assumed that n=3 as in the previous example) found in the process of FIG.
GRI) (step 238)
.

In this case, since the number of cycles is n=3, a negative determination is made, and the second slave signal S2 in the first GRI (20th run radio wave repetition period) and the second GRI (30th run radio wave repetition period) in FIG. ) is set in the preset counter 22 (step 240).

Then, the countdown is performed and the count value is O.
Then (steps 242 and 244), the same processing as above (steps 226 to 244) is performed in the second GRI (steps 242 and 244) in FIG.
It is repeated for the Loran radio wave repetition period).

After that, when the above processing is performed for the third GRI (30th run radio wave repetition period) in FIG. 9, since the period ln=3 here, the oscillation error is corrected and it is determined that it is the δ period. (affirmative determination in step 238).

In this case, since the output pulse count value of the loop filter 24 is positive (+20>), as can be understood from FIG. 9, the second slave signal S2 and the fourth GRI ( Arrival time difference TS2- with the main station signal M in the Loran radio wave repetition period)
The value P3 corresponding to M is increased by the value 1 (step 2
46).

As a result, the tracking pulse 100 is controlled by 0.1 μsec.

As described above, in this embodiment, the oscillation error of the tracking pulse 100 is the minimum unit correction of the oscillation error! (=0.1μ
sec ), the oscillation frequency of the tracking pulse 100 is corrected by a minimum unit correction amount of 0.1 μsec.

Therefore, according to this embodiment, the tracking pulse 100 can be accurately oscillated, and therefore, it is possible to continue to accurately measure the traveling position without causing a large position measurement error due to cycle slips.

Note that it is also preferable to change the processes in FIGS. 7 and 8 to the processes in FIGS. 10 and 11, respectively.

In that case, the number n1 of arrival time differences TM-8, at time t, the number n2 of arrival time differences TS+-92, and the arrival time difference T
'52-N's number n3 is successively determined (step 220-
1.220-2.220-3>, and their remainder values are greater than or equal to 1/2 of their Loran radio wave repetition period (in steps 222-1.222-2.222-3, each negative judgment), and these numbers n4, n2, and n3 are increased by 1 (step 224-1.224-2.224).
-3>, it is left as is in the following cases.

In addition, in the process of FIG. 10, the values P+, P2, P3
It is determined in advance whether or not the error correction period has come when presetting is performed (step 238-1.
238-2.238-3), when it is confirmed that the correction period has come, the above values P1, P2, and P3 are each increased or decreased by 1 and preset, and the oscillation frequency of the tracking pulse 100 for each arrival time difference is set. are each corrected.

Therefore, it is possible to more precisely modify the oscillation frequency of the tracking pulse 100.

(Effects of the Invention) As explained above, according to the present invention, the oscillation error of the tracking pulse is detected from the tracking error of the pulse tracking the received signal, and the oscillation frequency of the tracking pulse is corrected according to the detection error. Therefore, it is possible to continuously perform accurate position measurements without causing large-scale position measurements due to cycle slips.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to claims, Fig. 2 is an explanatory diagram of the configuration of a conventional device, Fig. 3 is an explanatory diagram of the configuration of a preferred embodiment of the device according to the present invention, and Fig. 4 is a phase tracking operation and arrival time difference calculation operation. FIG. 5 is a graph diagram explaining the oscillation error detection function of the tracking pulse, and FIGS. Figure 9 is an explanatory diagram of the oscillation error correction effect, Figure 10,
FIG. 11 is a flowchart showing another processing procedure of the MPU 26 in FIG. a...Oscillation means b...Oscillation error detection means C...Correction period calculation means d...Oscillation frequency correction means 18...Quantization circuit 20 ...Phase comparator circuit 22...Pricera 1 to counter 24...Loop filter 26...MPU 28...Crystal oscillator 30...S/N ratio measurement circuit Figure 4 Figure 5 Figure 8

Claims (1)

[Claims] (1) An oscillation means that generates a pulse to track a received signal, an oscillation error detection means that detects an oscillation error of the oscillation means from a tracking error of the tracking pulse, and a period for correcting the oscillation frequency of the oscillation means based on the oscillation error. 1. A Loran C receiver comprising: a corrected cycle calculation means for calculating the oscillation frequency according to the oscillation error; and an oscillation frequency correction means for correcting the oscillation frequency of the oscillation means by the cycle according to the oscillation error.