JP3100465B2 - Squelch judgment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-vehicle receiver for receiving a signal from a fixed transmitting station installed on a road, and a squelch caused by another vehicle entering the fixed transmitting station and interrupting reception. The present invention relates to a squelch determination circuit for preventing unstable operation of a squelch.

[0002]

2. Description of the Related Art Normally, a radio apparatus uses a squelch circuit to determine the presence or absence of a received radio wave. In a squelch circuit, a demodulator output of a receiver or an audio frequency amplifier is opened and closed to prevent an excessive noise output from appearing in a receiver output when a carrier signal input to the receiver falls below a certain value. . Hereinafter, the squelch determination circuit of the in-vehicle receiver will be described.

FIG. 6 is a diagram showing a conventional squelch decision circuit, FIG. 7 is a diagram showing the relationship between the output signals of the reception level detection means and the reception decision level means of FIG. 6, and FIG. It is a figure showing the relation of judgment. The squelch determination circuit shown in FIG. 6 includes a reception level detection unit 2 that detects a reception level of a reception signal received by a vehicle-mounted antenna 1 from a fixed transmission station on a road.

Further, the squelch determining circuit includes a receiving level determining means 3 for determining whether the signal level detected by the receiving level detecting means 2 is higher than a threshold value. The reception determination means 3 outputs an "L (low)" signal if the detected reception level is below the threshold, and outputs an "H (low)" if it is above the threshold.
As shown in FIG. 7, when the reception level fluctuates around a threshold value, the output of the reception determination means changes from "H" to "L" or vice versa. I do.

[0005] The squelch determination circuit also includes a low-pass filter 4 for averaging the output of the reception determination level means 3. The low-pass filter 4 stabilizes the operation of the reception determining means 3 near the threshold value by this averaging, that is, removes the flutter of the determination. The flutter as described above is caused by the effects of fading, multipath, and the like when the reception input level is close to the threshold value in mobile communication.

Further, the squelch determination circuit includes TTL (Transistor Transistor logic) conversion means 5 for forming “H” and “L” signals from the output of the low-pass filter 4. As shown in FIG. 8, when the output signal of the TTL conversion means 5 is "H", it is determined that the vehicle has entered the reception area from the fixed transmitter, and data processing is started. If the output signal is "L", it is determined that the vehicle has deviated from the range that can be received from the fixed transmitter, and the data received so far is cleared and reset.

FIG. 9 is a diagram showing a conventional reception judging means in which a hysteresis is taken into consideration in order to suppress the judgment flutter.
As shown in the figure, since the reception determining means 30 has a hysteresis characteristic, it is possible to prevent the determination from fluttering more than the determining means shown in FIG.

[0008]

However, in the conventional squelch determination circuit, when data communication is performed between a fixed transmitting station installed on a road and an on-vehicle receiver, other vehicles (such as trucks and buses) are used. ), The reception is interrupted, which causes the following problem. FIG. 10 is a diagram for explaining the occurrence of interruption in reception. As shown in this figure, even within the reception range from the fixed transmission station, it is shadowed by large vehicles, etc., and after a certain period of time, it is determined that it has left the reception range of the fixed transmission station, and it is determined that there is no received radio wave I do. Then, clear and reset the data obtained so far. However, in such a case, the level of the input signal is actually equal to or lower than the threshold value. If lowered, it causes the above-mentioned flutter, so that there is a problem that it cannot be lowered.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a squelch determination circuit in which data is not cleared even when a large vehicle or the like enters a shadow with a fixed transmitting station.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention determines the presence or absence of a received radio wave when performing data communication between a fixed transmitting station on a road and a receiver mounted on a vehicle. The squelch determination circuit is provided with a reception level detection unit, a traveling distance detection unit, a reception radio wave storage unit, and a reception break determination unit.

The reception level detecting means detects a level of a radio signal from the fixed transmitting station. The running distance timing forming means forms a timing signal for each predetermined distance based on the running distance of the vehicle. The reception radio wave storage means stores a detection reception level of the reception level detection means based on a timing signal for each predetermined distance from the travel distance timing formation means.

The reception interruption determining means determines the reception interruption based on the reception radio wave stored in the reception radio wave storage means.

[0013]

According to the squelch determination circuit of the present invention, the level of the radio signal from the fixed transmitting station is detected by the reception level detecting means, and the mileage timing forming means determines the level of the radio signal every predetermined distance based on the mileage of the vehicle. A timing signal is formed, the received radio wave storage means stores a detected reception level of the reception level detection means by a timing signal for each predetermined distance from the traveling distance timing forming means, and the received radio wave storage is stored by the reception break determination means. The interruption of reception is determined from the received radio wave stored by the means. Therefore, even if there is no received radio wave, it is not determined that there is no received radio wave unless the vehicle travels a predetermined distance, so that there is no flutter due to the interruption of reception by another running vehicle between the fixed transmitting station and the squelch determination is more stable. It can be performed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a squelch determination circuit according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a configuration of a squelch determination unit in FIG. 1 differs from the configuration of the prior art in FIG. 5 in a squelch determination means 40 provided in place of the low-pass filter 4. In FIG. 2, a traveling distance timing is formed by a traveling pulse divider that divides a period of a traveling pulse used for measuring a vehicle speed and the like of an automobile, and forms a timing signal for each predetermined distance based on the traveling distance of the vehicle. A forming means 41 is provided. Here, it is assumed that the traveling pulse has a wheel diameter of 30 cm and one pulse is generated when the wheel makes one rotation. The running pulse divider 41
Is set to 10, for example.

The squelch judging means 40 comprises an N-stage shift register which receives the signal from the receiving judging means 3 and shifts the timing signal of the frequency divider 41 as a clock signal. Storage means 4
2 is provided. In the shift register 42, if the signal from the reception judgment means 3 is "H", there is a received radio wave: 1,
If “L”, no received radio wave: 0 is input. As an example, if the shift register 42 has eight stages, by the time the data input to the shift register 42 is output,
The wheel will travel the following distance L.

L = running pulse (30 cm) × division number (1)
0) × the number of stages of the shift register (8) = 24 m Next, the squelch determination means 40 includes a reception break determination circuit 43 for determining the presence or absence of a received radio wave. FIG. 3 is a diagram showing the determination of interruption of reception. The reception interruption determining circuit 43 inputs the bit signal of each stage of the shift register 42,
If at least one bit of the shift register has 1 as shown in FIG.
An "H" signal is output as an output signal. If all the bits of the shift register are 0 as shown in FIG. 2B, it is determined that there is no received radio wave, and "L" is output as an output signal. Here, the number of divisions of the traveling frequency divider and the number of stages of the shift register are merely examples, and are not limited thereto.

In a receiver equipped with a microcomputer, the data of the presence / absence of the radio wave received from the reception determining means 3 and a running pulse may be given to the microcomputer to realize the software. FIG. 4 is a diagram for explaining the presence / absence of a received radio wave at a break in reception. As shown in the figure, even if the reception input level is lower than the threshold value, the vehicle equipped with the receiver remains at the transmitter position, for example, proceeds by a predetermined distance L = 24 m, Thereafter, when the reception input level recovers the threshold value, it is determined that there is a received radio wave. The predetermined distance L is equal to or less than the threshold value L =
If the vehicle travels 24 m or more, it is determined that there is no received radio wave.

FIG. 5 is a diagram showing a comparison between the effect of the present invention and the effect of the related art. As shown in the figure, if the reception input level is smaller than the predetermined time threshold value, it is conventionally determined that there is no received radio wave. However, according to the present invention, it is not determined that there is no received radio wave unless the vehicle further advances a predetermined distance. . Therefore, fluttering is eliminated due to the effect of interruption of reception by the running vehicle, and more stable squelch determination can be performed.

[0019]

As described above, according to the present invention, a timing signal is formed for each predetermined distance based on the traveling distance of the vehicle, a detected reception level is stored based on the timing signal, and reception is performed from the stored reception radio wave. Since it is determined that there is no received radio wave, it is not determined that there is no received radio wave unless it travels a predetermined distance even if there is no received radio wave, so that there is no flapping due to the effect of reception interruption by another running vehicle between the fixed transmitting station and Further, a more stable squelch determination can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a squelch determination circuit according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a squelch determination unit in FIG. 1;

FIG. 3 is a diagram illustrating determination of interruption of reception.

FIG. 4 is a diagram for explaining the presence / absence of a received radio wave at a break in reception;

FIG. 5 is a diagram showing a comparison between the effects of the present invention and the related art.

FIG. 6 is a diagram illustrating a conventional squelch determination circuit.

FIG. 7 is a diagram illustrating a relationship between output signals of a reception level detection unit and a reception determination level unit of FIG. 6;

FIG. 8 is a diagram illustrating a relationship between a reception level and a reception determination in FIG. 6;

FIG. 9 is a diagram illustrating a conventional reception determination unit that takes hysteresis into account in order to suppress flutter in determination.

FIG. 10 is a diagram for explaining occurrence of interruption of reception.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 1 2 ... Reception level detection means 3 ... Reception judgment means 40 ... Squelch judgment means 41 ... Traveling distance timing formation means 42 ... Reception radio wave storage means 43 ... Reception discontinuity judgment means

Claims (1)

(57) [Claims] 1. A squelch determination circuit for determining the presence or absence of a received radio wave when performing data communication between a fixed transmission station on a road and a receiver mounted on a vehicle, comprising: Receiving level detecting means (2) for detecting a level; running distance timing forming means (41) for forming a timing signal for each predetermined distance based on the running distance of the vehicle; Received radio wave storage means (42) for storing a detected reception level of the reception level detection means (2) based on a timing signal for each distance, and determining a break in reception from the received radio wave stored in the received radio wave storage means (42) A squelch determination circuit including a reception break determination unit (43).