JPH1168633A - Method and system for frequency diversity reception - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain an effective diversity with less error by not using analog informant that might be less reliable depending on a modulation system and a state of space as diversity discrimination information but by using digital information after demodulation with higher accuracy as the diversity discrimination information. SOLUTION: A modulation signal that is modulated with the same data with an error check code added to them and transmitted is received by receivers 1, 2, and given to demodulation circuits 11, 12 as reception waves A, B, where they are demodulated. The demodulated data are given to an error code check circuit 20, which detects the number of errors of the demodulation data. A diversity circuit 30 counts the number of detected errors by each byte, compares the numbers and selects a receiver which provides less number of errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency diversity receiving method and apparatus for receiving a plurality of modulated signals having different frequencies transmitted through a fading channel such as a short-wave (HF) line.

[0002]

2. Description of the Related Art HF which is often affected by fading of a propagation path
2. Description of the Related Art Frequency diversity is known as one of techniques for securing good reception quality in a line or the like. In this frequency diversity, a plurality of receivers having different reception frequencies are provided in one antenna by using a plurality of waves having little correlation of fading, and diversity reception is performed.

FIG. 4 shows a conventional frequency diversity receiver. This shows an example of a receiving circuit that receives two modulated reception waves A and B having different frequencies and performs diversity.

The demodulation circuits 11 and 12 receive the received waves A,
B bit synchronization processing and demodulation are performed. The level value for each sampling is output to the level detection circuits 21 and 22, and the demodulated data is output to the diversity circuit 3. The level detection circuits 21 and 22 integrate the level value for each sampling in bit units, and output the integration result in bit units to the diversity circuit 3. Diversity circuit 30 compares the level information corresponding to the bit synchronization from level detection circuits 21 and 22, and outputs demodulated data of the higher-level received wave as a demodulated signal for each bit.

[0005]

However, the above-mentioned conventional frequency diversity receiving apparatus uses frequency diversity based on analog information (reception level information for each bit) which may be unreliable depending on the modulation method and spatial condition. Therefore, there is a case where there is not much difference in the reception level information for each bit, and effective diversity cannot be realized.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem of the prior art by using highly accurate demodulated digital information as diversity judgment information instead of using analog information. It is an object of the present invention to provide a frequency diversity receiving method and apparatus capable of realizing effective diversity with less frequency.

[0007]

According to the first aspect of the present invention, a plurality of modulated signals transmitted by modulating different frequencies in a short-wave band with the same data to which an error detection code or an error correction code is added are transmitted. Are received by a plurality of receivers each having the different frequency set as a reception frequency, the received waves are demodulated, the number of errors in the demodulated data is detected, and the number of errors is compared. This is a frequency diversity reception method characterized by outputting demodulated data having a smaller number as a demodulated signal.

According to a second aspect of the present invention, a plurality of modulated signals transmitted by modulating different frequencies in a short wave band with the same data to which an error detection code or an error correction code is added are transmitted to the different frequency bands. In a frequency diversity receiver that receives a plurality of receivers each set as a reception frequency, a plurality of demodulation circuits that demodulate each of the received waves and output demodulated data, and output from the plurality of demodulation circuits An error code detection circuit that detects the number of errors in each demodulated data and outputs the number of errors;
Compare the number of errors output from the error code detection circuit,
And a diversity circuit that outputs demodulated data of the demodulation circuit having the smaller number of errors as a demodulated signal.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a frequency diversity receiving method and apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a receiving circuit of a frequency diversity receiving apparatus using an error detection code according to the present embodiment. Here, a modulated signal transmitted by modulating the same data to which an error detection code is added at two different frequencies in the HF band is transmitted to two receivers each having two different frequencies set as reception frequencies. The case of demodulation by receiving at 1 and 2 will be described. The receiving device is receiver 1,
In addition to the two, there are two demodulation circuits 11 and 12, an error code detection circuit 20, and a diversity circuit 30.

The demodulation circuits 11 and 12 perform bit synchronization processing and demodulation of received waves A and B, which are received modulated signals,
The demodulated data is output to the error code detection circuit 20.

The error code detection circuit 20 performs frame synchronization detection on the demodulated data for each byte, detects the number of errors for the received waves A and B, and outputs the demodulated data for each byte together with the detection signal to the diversity circuit 30. Output.

The diversity circuit 30 compares the number of errors per byte from the error code detection circuit 20 with respect to the received wave A and the received wave B, and demodulates the demodulated data of the smaller number of received waves into one byte. Output as a demodulated signal in units.

FIG. 2 shows a schematic configuration of the error code detection circuit 20 and the diversity circuit 30 of FIG. 1. The modulated signal of each receiving system output from the error detection circuits 23 and 24 of the transmission code detection circuit 20 is shown. The error numbers of the counters 31 and 3
2 is counted and compared by the comparator 33 in byte units, and the selector 34 is controlled according to the comparison result.
The demodulated data of the receiving system with the smaller number of errors is selected and output as a demodulated signal.

Now, based on the data of the maximum usable frequency which is one of the important parameters of the HF band communication utilizing the reflection of the ionosphere, two waves having a low correlation of fading are selected according to the season, daytime, nighttime and other conditions. You. These two waves are modulated by the same data to which the error detection code is added, and the modulated signals transmitted are received by the receivers 1 and 2 and enter the demodulation circuits 11 and 12 as received waves A and B, When the demodulated data is input to the error code detection circuit 20, the number of errors is detected for each demodulated data. Since the error that occurs in the HF channel is a burst error that occurs under fading, as shown in FIG. 3, when the reception level of the receiver decreases, the number of errors increases in accordance with the degree of the decrease. Therefore, when the number of detected errors is counted for each byte by the diversity circuit 30 and the number is compared with each other, and a receiver having a smaller number of errors is selected, good reception quality can always be ensured.

As described above, in the present embodiment, not the analog information but the digital information of the number of errors is used as the diversity judgment information to select the receiving system with the smaller number of errors. It is possible to realize highly accurate and effective diversity without being affected. In addition, since the number of errors is compared not for each bit but for each byte, the difference in digital information becomes remarkable, and more accurate and effective diversity can be realized.

In the above-described embodiment, a case has been described where an error detection code is added to transmission data.
The case where an error correction code is added may be used. In this case, errors are detected by the error correction code, and most of them are corrected,
Since the number of errors after error correction, that is, the number of errors in the output code of the apparatus, is greatly improved, only the comparison between the improved ones is performed, and basically the error detection code is added. As in the case of the above, a good reception output can always be obtained.

Further, in the above-described embodiment, a case has been described where two transmission signals having different frequencies are received. However, the present invention is not limited to two transmission signals, and three or more transmission signals having different frequencies are received. It can be applied to the case.

[0019]

According to the method of the present invention, frequency diversity is performed by using the number of errors, which is digital information after demodulation. Therefore, compared with the conventional example utilizing analog information with low reliability, the method is not affected by the modulation method. Therefore, effective diversity with few errors can be realized. Further, according to the device of the present invention, the above effects can be appropriately obtained with a simple structure.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a frequency diversity receiver according to the present invention.

FIG. 2 is a configuration diagram schematically illustrating an error code detection circuit and a diversity circuit of FIG. 1;

FIG. 3 is an explanatory diagram showing an example of a transmission line burst error.

FIG. 4 is a circuit configuration diagram of a conventional frequency diversity receiver.

[Explanation of symbols]

 A, B Received wave 1, 2 Receiver 11, 12 Demodulation circuit 20 Error code detection circuit 30 Diversity circuit

Claims (2)

[Claims] 1. A plurality of modulated signals transmitted by modulating different frequencies in a short-wave band with the same data to which an error detection code or an error correction code is added, and the different frequencies are set as reception frequencies. Received by multiple receivers, demodulates the received waves, detects the number of errors in the demodulated data, compares the number of errors, and outputs the demodulated data with the smaller number of errors as a demodulated signal. A frequency diversity receiving method characterized by the above-mentioned. 2. A plurality of modulated signals transmitted by modulating different frequencies in a short-wave band with the same data to which an error detection code or an error correction code is added, and the different frequencies are set as reception frequencies. In a frequency diversity receiver for receiving by a plurality of receivers, a plurality of demodulation circuits for demodulating each received wave and outputting demodulated data, and an error number of each demodulated data output from the plurality of demodulation circuits are provided. The error code detection circuit that detects each of them and outputs the number of errors is compared with the number of errors output from the error code detection circuit.
A diversity circuit that outputs demodulated data of a demodulation circuit having the smaller number of errors as a demodulated signal.