JPS6235278A - Loran-c receiver - Google Patents

Abstract

PURPOSE:To evade the generation of a periodic slip regardless of a drop in reception level by detecting the oscillation error of a tracking pulse of the basis of a received signal, correcting an oscillation frequency with the accumulat ed value of the error, and inhibiting the oscillation frequency from being over corrected. CONSTITUTION:Radio waves received from a master and a slave station are quantized by the quantizing circuit 18 of a receiver and supplied to a phase comparing circuit 20 and an SN ratio measuring circuit 30. This circuit 20 compares the phase of the binary-coded data with the phase of the tracking pulse 100 of a presettable counter 22 and its comparison signal is supplied to and averaged by a loop counter 24. Output pulses of this filter 24 command an MPU 26 to increase or decrease the preset value of the counter 22 and the MPU 26 increases or decrease the counter value of the counter 22 one by one. Then, the oscillation error of the tracking pulses is detected on the basis of the received signal and the detection signal is accumulated to corrected the oscillation frequency of a crystal oscillator 28 with the accumulated value while inhibiting the oscillation frequency from being overcorrected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to radio navigation receivers, and more particularly to Loran C receivers.

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

The above-mentioned arrival time difference is determined based on the phase tracking point of a pulse generated internally in rotation with the Loran pulse and phase-tracked to a predetermined length cycle of the Loran pulse carrier wave.

Generally speaking, in the past, the above phase tracking has been performed using the PLL shown in FIG. A phase comparator 12 compares the phase with the carrier wave of the Loran pulse.

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 the VCO 16 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 deviates from the tracking carrier wave of the Loran pulse by more than 1/2 cycle, 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 lpp
m, and the carrier wave frequency of Loran pulse is 1QQK
Taking into account that the speed is 1100 Hz, 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, cycle slips are likely to occur, resulting in large position measurement errors.

As described above, conventional methods have had the problem that when the level of the received signal drops significantly, 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 pulse that tracks the received signal is generated by the oscillation means a, and the tracking error of this tracking pulse with respect to the received signal is detected by the tracking pulse error detection means.

The oscillation error of the oscillation means a is detected by the oscillation error detection means C from the tracking error of the tracking pulse, and the error is roughly accumulated by the oscillation error accumulation means d.

Further, when the tracking error of the tracking pulse is within the permissible range, the oscillation frequency of the oscillation means a is corrected by the oscillation frequency correction means e using the oscillation error accumulated by the oscillation error accumulation means d.

(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).
), the main station signal M and the first slave signal S of Loran radio waves
+, the second slave station signal S2 is sequentially transmitted at predetermined intervals from the Loran master station, the first slave station, and the second slave station.

These main station signal M, secondary frequency signal +, S2 are each 1m5Q
A plurality of Loran pulses LP arranged at C intervals are shown in FIG. 4(C).

The quantization circuit 18 shown in FIG.
The phase is compared with 00.

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 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, and the tracking pulse 100 is obtained by the count.

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

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

When 100 tracking pulses are obtained in this way, the main station signal M, the first slave signal S7. Arrival time difference TM sl of the second slave signal S2.

Ts+-62*TS2-M are determined and 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 movement toward and from the regular tracking point P is controlled.

Therefore, the loop filter 24 commands to increase or decrease the preset value.
It becomes possible to detect the oscillation error of the tracking pulse 100 due to the oscillation error of the crystal oscillator 28 from the output pulse of the .

In this embodiment, the detection of the oscillation error of Poko and the correction of the oscillation frequency of the tracking pulse 100 are performed by MPIJ26,
In order to perform this processing, the MPU 26 is supplied with a detection signal from an SN ratio measuring circuit 30 that measures the SN ratio of the received signal.

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.

FIG. 6 shows a flowchart of the processing procedure of the MPU 26 for detecting an oscillation error in the tracking pulse 100 and correcting the oscillation frequency. A station is selected (step 200).

Then, it is determined whether the received signal of the selected station can be used 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 standard of the tracking pulse 100.
When this determination is made, it is determined whether the oscillation error (tracking error) of the tracking pulse 100 exceeds the allowable range (step 203).

At this time, if the tracking error is outside the allowable range, the above process is simply repeated, but if it is determined that the tracking error is within the allowable range, counting of the output pulses of the loop filter 24 is started (step 204). ).

The counting continues for 5 seconds (step 206), and when 5 seconds have elapsed since the start of counting, the count value at that time is added to the previous 5 second count value, and thus the 5 second count value is successively integrated (step 208), and when the integrated value is stored (step 210), the preset value of the preset counter 22 is controlled by the integrated brightness value, and the tracking pulse 10 is
The oscillation frequency of 0 is modified (step 212).

Next, the operation performed by the above processing will be explained in detail.

N1[N pulses are output from the loop filter 24 for 5 seconds, and the tracking pulses 100 become 0.2
When the oscillation error E of the crystal oscillator 28 is υ1wJ by μsec, the oscillation error E of the crystal oscillator 28 is as follows.The preset counter 22 is controlled by the MPU 26 to cancel the oscillation error. However, this control is controlled by the preset value control for phase tracking. It is done separately.

In FIG. 7, the process in FIG. 6 is started from time 1=0, and the tracking error increases from the start according to the characteristic 102 in FIG.

During that time, the output pulses of the loop filter 24 are counted, and when the output pulse count 1 of the loop counter 24 reaches +20 after 5 seconds, the oscillation error E becomes 0.
．． 8 (=20X0.2÷5) ppm, and the presetting of the loop counter 22 is controlled by the MPU 26 so that this error E=0.8 ppm is canceled out.

Therefore, time t=time t when 5 seconds have passed since Q.

After that, the oscillation error is 0.2 (=1-o
, a>ppm, and the oscillation error of the crystal oscillator 28 is 1 p
It is very small compared to Dm.

Here, if preset value control to cancel out a slight oscillation error of 2 ppm is performed in addition to the original preset value control for phase tracking, the The output pulse count value of the loop filter 24 is about +10, and the oscillation error E is 1.
．． 2=(20+1O>Xo, 2÷5 (ppm).

In other words, if the oscillation error is accumulated during the 5 seconds from time t1 to time t2, from the time 10 seconds have passed (time i2), the slight oscillation error E = 0.21)I) is excessive compared to m. A correction will be made, and the oscillation error E will increase on the contrary.

Therefore, if this overcorrection is predicted (Fig. 6 Step 2)
If the determination is positive at 03), the detection of the error is prohibited for 5 seconds from time t1.

During that time, Briseler 1-value control is performed using the oscillation error accumulated up to the time t, thereby reducing the tracking error according to characteristic 104 in FIG.

Then, when 10 seconds have elapsed (at time t2), the oscillation error starts to accumulate, and when 15 seconds have elapsed (time t3), the output pulse count value of the loop filter 24 becomes about +4.

Therefore, the oscillation error E caused by C at that time is 0.96=(20
+4) xo, 2÷5 (ppm), and the error E
= 0.96 ppm is canceled by the MPU 26 so that the precera 1 value of the counter 22 is controlled.

Further, after time t, oscillation errors are accumulated in the same way, and the output pulse count value of the loop filter 24, which is opened after 20 seconds has passed, becomes approximately +1, and the oscillation error opening at that time is 1 (20+4+1)Xo, 2 ÷5
(1)l)m).

As explained above, according to this embodiment, the tracking pulse 100 is generated based on the received signal (the error is detected, and the accumulated oscillation error controls the precerta 1 value of the precera 1 to counter 22). Since the oscillation error of the crystal oscillator 28 is absorbed, it is possible to effectively avoid the occurrence of cycle slips due to a drop in the level of the received signal, making it possible to continue accurate position measurements without causing large position measurement errors. becomes.

As a result, an oscillator with low oscillation accuracy can be used to obtain the tracking pulse 100, and therefore it is possible to reduce the cost of the receiver.

Furthermore, according to this embodiment, the oscillation error detection value is invalidated when overcorrection of the oscillation frequency is predicted, so it is possible to always obtain an accurate measurement position.

(Effects of the Invention) As explained above, according to the present invention, the oscillation error of the tracking pulse is detected based on the received signal, the oscillation frequency is corrected by the accumulated detection error, and over-correction of the oscillation error is roughly avoided. Since this is prohibited, cycle slips can be effectively avoided and accurate position measurements can be continuously performed regardless of a drop in reception level or the like.

[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. 5 is a graph explaining the tracking pulse oscillation error detection function, and FIG.
Flowchart 1 showing the processing procedure of PtJ26 and FIG. 7 are characteristic diagrams illustrating the tracking error correction effect. Oscillation means b...Tracking pulse error detection means C...Oscillation error calculation means d...Oscillation error accumulation means d...Oscillation frequency correction means 18...Quantization circuit 20...Phase Comparison circuit 22...Preset counter 24...Loop filter 26...MPU 28...Crystal oscillator 30...SN ratio measurement circuit Patent applicant Nissan Motor Co., Ltd. Figure 1 Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] (1) An oscillation means that generates a pulse to track the received signal, a tracking pulse error detection means that detects a tracking error of the tracking pulse by comparing the received signal and the tracking pulse, and an oscillation means that detects a tracking error of the tracking pulse by comparing the received signal and the tracking pulse. oscillation error detection means for detecting oscillation errors; oscillation error accumulation means for accumulating oscillation errors; and oscillation means for correcting the oscillation frequency of the oscillation means by the accumulated oscillation errors when the tracking error of the tracking pulse is within an allowable range. A Loran C receiver comprising: frequency modification means;