JP3458140B2 - Optimal reception frequency selection circuit - Google Patents

Description

Description: 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 more particularly, to transmitting the same information using different frequencies from a plurality of points on an HF line. The present invention relates to a circuit for automatically selecting an optimum frequency in a demodulator when a received signal condition during frequency diversity reception deteriorates in a system. 2. Description of the Related Art In frequency diversity reception using an HF line, the configuration of a conventional automatic selection circuit for an optimum frequency of a demodulator when a received signal condition is deteriorated due to an ionospheric condition is shown in FIG. It has become. The frequency switching circuits 1 and 4 switch the frequency in accordance with an instruction from the S / N determination circuit 8. Demodulation circuits 2 and 5 demodulate the received modulated signal and output demodulated data to 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 the same to the diversity circuit 7. Diversity circuit 7 uses the S / N level information of each bit from S / N detection circuits 3 and 6 among the data output from demodulation circuits 2 and 5 to receive the data of the reception system having the larger S / N level. Is output as demodulated data. Also S
When the S / N determination circuit 8 falls below the S / N level that is systematically acceptable (a level at which received data cannot be recognized due to an increase in data errors), the frequency switching circuit 1 or 4 controls the frequency switching circuit 1 or 4 for each frequency. To switch, and S /
When the N level becomes equal to or more than the allowable value, an instruction is issued to maintain the current frequency. [0004] When the optimum frequency is automatically selected by the above-mentioned conventional selection circuit, there are the following problems. (1) When a large number of frequencies are used, it takes time to search for the optimum frequency. (2) When the optimum frequency is selected, it is necessary to always output demodulated data.
If the system selects the optimum frequency, only the signal of the other system can be used as demodulated data. As a result, diversity cannot be obtained during a search even if the signal condition deteriorates. Therefore, it is necessary to minimize the optimal frequency switching time (time to determine whether the signal is an optimal signal and determine the signal) as much as possible. Required. For this reason, there is a possibility that a frequency that is not very good (the reception level is good instantaneously but there are many errors as a whole) may be selected. FIG. 4 illustrates an example in which the above (1) and (2) have an adverse effect. Since the S / N level of the reception 2 system is equal to or less than the allowable value, the optimum frequency selection is started, and the frequency selection number is sequentially switched from “2”.
Since the / N level becomes equal to or higher than the allowable value, the reception frequency is fixed to this value. However, this is a case where an error occurs in the reception 1 system during the switching time (independent reception time) is long. [0008] An object of the present invention is to improve the above problem by selecting and switching the optimum frequency in the demodulator when the received signal condition becomes poor when performing frequency diversity reception on an HF line. The aim is to be able to do it accurately in a short time. SUMMARY OF THE INVENTION The object of the present invention is to provide an optimum reception frequency according to a reception signal state at the time of frequency diversity reception.
In the optimal reception frequency selection circuit that performs selection switching of
Storing the position and the transmission frequency of the plurality of transmitting points, reception point
A distance calculation circuit that determines an optimum frequency selection order based on the position information of the location and instructs the frequency switching circuit to perform switching is provided.
Is in the dead zone of radio waves transmitted from the plurality of transmission points
If it exists, the distance calculation circuit
This is achieved by having the frequency of the point selected at the lowest order . According to the above means, when the received signal state at the time of frequency diversity reception becomes equal to or lower than an allowable S / N level, the frequency switching circuit is instructed to perform frequency switching, 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 calculation circuit calculates the distance from the reception point to the transmission point and calculates the distance. Are determined in order of decreasing the frequency of each transmission point as the optimum frequency. In determining the optimum frequency selection order, the frequency of the transmission point in the blind zone is set to the lowest selection order. When the frequency is selected according to the reception signal state at the time of the frequency diversity reception in this manner, a switching instruction is issued to the frequency switching circuit in accordance with the optimum frequency selection order determined from the distance calculation circuit. By switching the frequency in accordance with the selection order, the optimum frequency can be selected and set in a short time. An embodiment of the present invention will be described below. The application system of the present invention has a plurality of transmission points communicating in the HF band, has the same transmission power, and has fixed transmission points. The receiving point applies to systems that are moving, implementing automatic optimal frequency selection implementing frequency diversity reception. In FIG. 1, the same reference numerals as those in FIG. 3 denote the same or corresponding parts. The frequency switching circuits 1 and 4 perform frequency switching according to an instruction from the distance calculation circuit 9. S
/ N detection circuits 3 and 6 perform demodulation by demodulation circuit 2
The S / N level of each bit is detected and output to the diversity circuit 7, which 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 in the data output from the above, the data of the receiving system having the higher level is output as demodulated data. When the S / N determination circuit 8 falls below the S / N level that is permissible in the system (a level at which data errors increase and a received message cannot be recognized), the signal state is sent to the distance calculation circuit 9. An instruction is issued to switch the frequency of the bad receiving system, and when the S / N level becomes higher than the allowable value,
Instructs to maintain the current frequency. When receiving 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 using the reception position information input from the GPS or the like. Further, this distance calculation circuit 9
As shown in the example in the figure, the location of the dead zone is stored based on the positions of the transmission points A, B, and C, the angle of the transmission antenna, and the transmission frequency, and the frequency is switched in the order of the optimum frequency according to the reception position information. Thus, an instruction is issued to the frequency switching circuit 1 or 4. Communication using the HF band frequency utilizes radio wave propagation characteristics due to reflection at the ionosphere, but in the case of the HF line, as shown in FIG. There is a zone where communication is impossible due to penetration. 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 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 sets the frequency f
_{When the} S / N determination circuit 8 recognizes the S / N level exceeding the allowable value by switching to ₃ , the distance calculation circuit 9 is instructed to stop the frequency switching. As f ₃ . When the S / N level circuit 8 does not recognize the S / N level exceeding the allowable value and instructs to switch the frequency continuously, the distance calculation circuit 9 sets the frequency to f ₂ having the next closest distance. An instruction is issued to the frequency switching circuit 1 or 4 to switch. Until subsequent Similarly instructed to stop the frequency switching from S / N judgment circuit 8 is issued, performing frequency switching in accordance with the selection order (in this example, then selects the f _1). In the case of the receiving point (2), since the user is not in a dead zone from each transmitting point, the comparison of distances c <
Since a <b, the selection order is f ₃ → f ₁ → f ₂ . As described above, when the vehicle is not in the dead zone, the frequency selection order is determined according to the distance, and the selection is switched in the order of the optimum frequency, whereby the optimum frequency can be selected in a short time. According to the present invention described above, when frequency diversity reception is performed on an HF line, automatic selection and switching of the optimum frequency in the demodulator when the reception state deteriorates can be performed in a short time. It can be done accurately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a coverage area in an HF line; FIG. 3 is a circuit configuration diagram of a conventional example. FIG. 4 is an explanatory diagram of an example of a conventional optimal frequency selection. [Explanation of Reference Codes] 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)

(57) [Claims] 1. A frequency different from a plurality of points in an HF line
Frequency diversity reception in a system that transmits information
According to the received signal status ofSelection switching of the optimal reception frequency
Optimum receiving frequency selection circuitAtThe location and transmission frequency of multiple transmission points Remember,Receiving point
ofDetermine the optimal frequency selection order based on the location information and turn off the frequency.
A distance calculation circuit that instructs the replacement circuit to switchPrepared, The reception point is not able to receive radio waves transmitted from the plurality of transmission points.
When it exists in the sensitive zone, by the distance calculation circuit,
Make the frequency selection order of the transmission point the lowest That
Characteristic optimal receiving frequency selection circuit.