JPH08149061A - Optimum receiving frequency selecting circuit - Google Patents

Abstract

PURPOSE: To accurately select and switch the optimum frequency of a demodulator in a short time when the frequency diversity is received through an HF circuit. CONSTITUTION: The S/N detecting circuits 3 and 6 detect the S/N levels of every bit and output them when these levels are demodulated by a demodulator circuit 2. A diversity circuit 7 outputs the data on the receiving system of a hither level as the demodulation data out of those data received from both demodulator circuits 2 and 5 based on the information given from the circuits 3 and 6. An S/N deciding circuit 8 instructs a distance calculating circuit 9 to switch the frequency when the S/N becomes less than its allowable level. The circuit 9 stores the positions of plural transmitting points, the angle of a transmitting antenna and the transmitting frequency and calculates the distance between the receiving and transmitting, points based on the input receiving position information. Then the circuit 9 decides an optimum frequency selecting order and gives a switching instruction decided by the calculated order to a frequency switching circuit 1 or 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for selecting an optimum reception frequency based on reception position information, and in particular, a reception signal state at the time of frequency diversity reception in a system for transmitting the same information by using different frequencies from a plurality of points in an HF line. The present invention relates to a circuit for automatically selecting an optimum frequency in a demodulator in the case where the power becomes worse.

[0002]

2. Description of the Related Art In frequency diversity reception using an HF line, the conventional optimum frequency automatic selection circuit for a demodulator when the state of the ionosphere deteriorates the received signal state is shown in FIG. There is.

The frequency switching circuits 1 and 4 switch frequencies according to an instruction from the S / N determination circuit 8. The demodulation circuits 2 and 5 demodulate the received modulated signal and output the demodulated data to the diversity circuit 7. The S / N detection circuits 3 and 6 detect the S / N level for each bit when demodulating by the demodulation circuits 2 and 5, and output it to the diversity circuit 7. The diversity circuit 7 receives the data of the receiving system having the larger S / N level according to the S / N level information for each bit from the S / N detection circuits 3 and 6 of the data output from the demodulation circuits 2 and 5. Is output as demodulation data. Also S
When the S / N level is lower than the system-acceptable S / N level (the level at which data errors are too large to recognize the received message), the / N determination circuit 8 outputs a frequency for each frequency to the frequency switching circuit 1 or 4. Switch to S /
When the N level exceeds the permissible value, an instruction is issued to maintain the current frequency.

[0004]

When the optimum frequency is automatically selected by the conventional selection circuit, there are the following problems.

(1) When there are many used frequencies, it takes time to search for the optimum frequency.

(2) When performing optimum frequency selection, it is necessary to always output demodulated data, so that one of the two reception systems is used.
If the system is performing optimum frequency selection, only the signal of the other system can be used as demodulated data. As a result, even if the signal condition deteriorates, diversity cannot be taken during the search. Therefore, it is necessary to minimize the optimum frequency switching time (the time to determine whether or not the signal is the optimum signal and determine it). Required. Therefore, it is possible to select a frequency that is not very good (the reception level is momentarily good, but there are many errors as a whole).

FIG. 4 illustrates an example of adverse effects due to (1) and (2). Since the S / N level of the receiving 2 system is less than the allowable value, the optimum frequency selection is started, the frequency selection number is switched from "2" in order, and when it becomes "9", S
Since the / N level exceeds the allowable value, the reception frequency is fixed to this, but this is the case where an error occurs in the reception 1 system during the switching time (single reception time).

In order to improve such a problem, an object of the present invention is to select and switch the optimum frequency in the demodulator when the received signal condition deteriorates when frequency diversity reception is performed on the HF line. It is to be able to do it accurately in a short time.

[0009]

The above object is to provide a circuit for selectively switching the optimum reception frequency in the demodulator according to the reception signal state at the time of frequency diversity reception, in which the positions of a plurality of transmission points and the angles of the transmission antennas are set. , And the transmission frequency are stored, the optimum frequency selection order is determined based on the reception position information, and a distance calculation circuit for instructing a switching instruction to the frequency switching circuit is provided.

[0010]

According to the above means, when the received signal state at the time of frequency diversity reception becomes lower than the allowable S / N level, the frequency switching circuit is instructed to switch the frequency and the optimum frequency is selectively switched. At this time, the distance calculation circuit stores the position of each of the plurality of transmission points, the angle of the transmission antenna, and the transmission frequency. When the reception position information is input, the distance from the reception point to the transmission point is calculated and the distance is calculated. The order of selection is determined so that the frequencies at the respective transmission points are set as the optimum frequencies in the order of the close to each other. In determining the optimum frequency selection order, the frequency of the transmission point in the dead zone has the lowest selection order. In this way, when the frequency is selected according to the received signal state at the time of frequency diversity reception, the frequency switching circuit is instructed to switch according to the optimum frequency selection order determined by the distance calculation circuit. By switching the frequency according to this selection order, the optimum frequency can be selected and set in a short time.

[0011]

EXAMPLES The present invention will be described below with reference to examples. In the application system of the present invention, there are a plurality of transmission points communicating in the HF band, the transmission power is the same, and the transmission points are fixed. The receiving point applies to a system that is moving and performing automatic optimal frequency selection performing frequency diversity reception.

In FIG. 1, the same symbols as those in FIG. 3 indicate the same or corresponding portions. The frequency switching circuits 1 and 4 switch frequencies according to an instruction from the distance calculation circuit 9. S
When the demodulation circuit 2 demodulates the / N detection circuits 3 and 6,
The S / N level for each bit is detected and output to the diversity circuit 7, which in turn outputs the demodulation circuits 2 and 5.
Based on the S / N level information for each bit from the S / N detection circuits 3 and 6 of the output data, the data of the receiving system with the higher level is output as demodulation data.

When the S / N judgment circuit 8 becomes lower than the S / N level which is systemally allowable (a level in which many data errors make it impossible to recognize a received message), the signal state to the distance calculation circuit 9 is changed. When an instruction is issued to switch the frequency of the bad reception system and the S / N level exceeds the allowable value,
Instruct to maintain the current frequency.

When the distance calculation circuit 9 receives an instruction to switch the frequency from the S / N determination circuit 8, the distance calculation circuit 9 calculates the distance from the transmission point to the reception point by using the reception position information input from the GPS or the like. Further, this distance calculation circuit 9 has a second
As in the example of the figure, the position of the dead zone is stored from the position of each transmission point A, B, C, the angle of the transmission antenna, and the transmission frequency, and the frequency is switched in the optimum frequency order according to the reception position information. As described above, the frequency switching circuit 1 or 4 is instructed. Communication using the frequency in the HF band utilizes the radio wave propagation characteristics due to reflection in the ionosphere. However, in the case of an HF line, as shown in FIG. There is a zone where communication is not possible due to a breakthrough. For example, in the case of the reception point (1), the frequency from the transmission point-A: f
₁ is a dead zone, which is the lowest in the frequency selection order. Then transmission point -B from reception point (1), when comparing the distance to the C, instructs the frequency switching circuit 1 or 4 to switch the frequency to f ₃ for who C is closer. According to this instruction, the frequency switching circuit 1 or 4 causes the frequency f
_{When the} S / N judgment circuit 8 recognizes the S / N level above the allowable value by switching to ₃ , the distance calculation circuit 9 is instructed to stop the frequency switching, and the distance calculation circuit 9 indicates the frequency. Remains at f ₃ . Further, when the S / N size circuit 8 does not recognize the S / N level above the allowable value, and the instruction to switch the frequency is issued continuously, the distance calculation circuit 9 sets the frequency to the next shortest distance f _2. The frequency switching circuit 1 or 4 is instructed to switch. Similarly, the frequency switching is performed in accordance with the selection order until the S / N determination circuit 8 gives an instruction to stop the frequency switching (in the case of the present embodiment, f ₁ is selected next).

Further, in the case of the receiving point (2), since it is not in the dead zone from each transmitting point, the distance comparison c <
From a <b, the order of selection is f ₃ → f ₁ → f ₂ .

As described above, when the user is not in the dead zone, the optimum frequency can be selected in a short time by determining the frequency selection order according to the distance and switching the selection in the order of the optimum frequency.

[0017]

As described above, according to the present invention, when frequency diversity reception is performed on the HF line, automatic selection and switching of the optimum frequency in the demodulator when the reception condition deteriorates are accurately performed in a short time. be able to.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a coverage area in an HF line.

FIG. 3 is a circuit configuration diagram of a conventional example.

FIG. 4 is a diagram illustrating an example of selecting a conventional optimum frequency.

[Explanation of symbols]

1, 4 ... Frequency switching circuit, 2, 5 ... Demodulation circuit, 3, 6 ...
S / N detection circuit, 7 ... Diversity circuit, 8 ... S / N determination circuit, 9 ... Distance calculation circuit.

Claims (1)

[Claims] 1. A circuit for selectively switching the optimum reception frequency in a demodulator according to a reception signal state at the time of frequency diversity reception in a system for transmitting information of different frequencies from a plurality of points on an HF line. Location of point,
An optimum reception frequency selection circuit, which is provided with a distance calculation circuit which stores an angle of a transmission antenna and a transmission frequency, determines an optimum frequency selection order based on reception position information, and gives a switching instruction to a frequency switching circuit.