JPH03255733A - Diversity reception method - Google Patents

Abstract

PURPOSE:To improve the rate of reception error by judging a reception condition according to a code error rate when the two mutually different frequencies of a short wave band are modulated by the same data including an error detection code or an error correction code and a data transmission signal to be transmitted is always received. CONSTITUTION:When two mutually different frequencies f1 and f2 of the short wave band are modulated by the same data including the error detection code or the error correction code and radio waves to be always transmitted as the data transmission signals are received, for two receivers 3 and 4 for which the two mutually different frequencies f1 and f2 are respectively set as reception frequencies, space diversity reception is executed while matching the reception frequency of the other receiver to the reception frequency of one receiver for which a code error rate (e) of a demodulation output is smaller. When the code error rate (e) of the demodulation outputs from the receivers 3 and 4 is made more than a prescribed error rate, the reception frequency of one of the receivers 3 and 4 is changed to the other reception frequency out of the two mutually different frequencies f1 and f2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field to which the Invention Pertains) The present invention relates to a frequency reception method for receiving a signal transmitted through a propagation path with a lot of fading, such as a shortwave line.

(Prior Art and Its Problems) Diversity is known as a technique for ensuring good reception quality in shortwave lines, etc., which are often affected by propagation path fading. Specific methods for achieving diversity include frequency diversity and spatial diversity.

Frequency diversity is less correlated with fading2
For example, in the shortwave band, propagation loss, degree of fading, interference from other stations, etc. vary depending on the frequency. Since they are different, there is a drawback that it is difficult to obtain ideal diversity operation.

On the other hand, spatial diversity is either performed by receiving radio waves of the same frequency using two spatially separated antennas, or if the reception condition of the received frequency deteriorates, the reception quality improvement effect of spatial diversity will not be achieved. The disadvantage is that the operator must make a judgment to change the receiving frequency.

(Objective of the Invention) The object of the present invention is to solve the drawbacks of the above two types of diversity, detect changes in reception conditions and automatically switch the diversity mode, and take advantage of the advantages of both diversity methods to reduce the effects of fading. An object of the present invention is to provide a reduced diversity reception method.

(Structure and operation of the invention) There are several methods for determining the reception status, but in the present invention, the reception status is modulated with two different frequencies in the shortwave band or with the same data containing an error detection code or an error correction code. The present invention is characterized by utilizing the fact that when receiving data transmission signals that are constantly sent out, it is possible to judge whether the reception status is good or bad based on the error detection output of these codes, that is, the code error rate.

That is, the diversity reception method of the present invention receives radio waves that are modulated with two different frequencies in a short wave band or with the same data containing an error detection code or an error correction code and are constantly transmitted as a data transmission signal. In this case, in the case of two independent antennas and two receivers each connected to the two antennas and capable of independently changing reception frequencies, Spatial diversity reception is performed by a frequency selection method in which the reception frequency of the other receiver is matched to the reception frequency of the receiver with the smaller error rate obtained by comparing the code error rates of the demodulated outputs of the receivers, and 2. When the code error rates of the demodulated outputs of the two receivers both exceed a predetermined error rate, the receiving frequency of one of the two receivers is changed to the other receiving frequency of the two mutually different frequencies. The present invention is characterized in that it is configured to adopt the frequency selection method by changing to the above.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the invention.

1 and 2 are two antennas for space diversity, and 3 and 4 are two receivers that can set reception frequencies independently of each other, and include demodulation circuits 13 and 14 and error correction circuits 15 and 16. 5 to 16 are typical configuration examples of the internal circuits of the receiver, 5 and 6 are radio frequency amplifiers (RFA), 7 and 8 are frequency converters (MIX), and 9 and 1O are local oscillators (O3
C), 11 and 12 are intermediate frequency amplifiers (IFA), 13
and 14 are demodulation circuits (DEM), and 15 and 16 are error correction circuits (FEC').

The configuration of this receiver is a local oscillator (O3C) 9 and an IO
The output frequency (i.e., the reception frequency) of
Other than the fact that the error detection output g can be taken out in addition to the corrected code output e from 6, there is no difference from a normal data transmission receiver having an error correction function. 1
7.18.19 are circuits added to implement the present invention, 17 is a switching circuit (SW) for selecting the output with the smaller bit error rate among the error correction outputs e of both receivers, 18
is a comparison circuit (C○MP), which calculates the respective code error rates from the error detection output g of both receivers, compares the results, and gives a switching signal to the switching circuit (SW) 17, and at the same time This error rate is compared with the lower threshold value to determine whether it is less than a predetermined error rate. 19 is CO
Based on the two comparison outputs of MP18, it is determined whether the receiver frequency needs to be changed and the control signal C1 is sent to 03C9 and 03CIO.
Alternatively, it is a control circuit (CONT) that controls the receiving frequency of the receiver by giving C2.

FIG. 2 is a waveform diagram for explaining the operation of the circuit shown in FIG. 1, and shows an example of automatic selection of the receiver 3.4 based on the frequencies of two waves and the code error rate. Let the two waves be 11 and T2. Waveforms a1 and C2 in FIG. 2 are changes in bit error rates of receivers 3 and 4 when fl is received by antennas 1 and 2, respectively, and bl and b2 are T by antennas 1 and 2, respectively.
2 shows the change in the bit error rate when receiving the data, and the vertical axis indicates that the higher the vertical axis is, the smaller the error rate is, and the lower the vertical axis is, the higher the error rate is. cl and C2 are frequency switching signals for the receivers 3 and 4, which are applied to ○SC9 and ○5C10, respectively, to select fl when the level is 1 and T2 when the level is 0. C0NT1
The output d of 9 is the comparison output of the error rate of both receivers 3゜4.
When the signal is applied to W17, the output of the receiver 3 is selected when the level is 1, and the output of the receiver 4 is selected when the signal is 0.

Based on data on the maximum usable frequency (MUF), which is an important parameter for shortwave communication that utilizes reflections from the ionosphere, two waves with low fading correlation, such as fl and T2, according to the season, daytime and nighttime, and other conditions. selected.

In the initial state, it is assumed that the receiving frequency of both receivers 3 and 4 is set to f. In this state, receivers 3 and 4
The error rate e of the output is al and C2. Time t
1) Since the error rate of both al and C2 does not exceed the threshold level (below the broken line) at the same time, continue receiving fl, and select the demodulation output with the smaller error rate of al and C2 as shown in d. Output. That is, spatial diversity is performed by receiving fl. At time t1, f
If the situation of l worsens and the error rate of both al and C2 levels is above the threshold level (below the broken line), the frequency of the receiver 3 of a1 with the larger error rate or the output C1 of C0NT19 changes to T2. . Therefore, receiver 3
The error rate of the received output is bl. Here, the error rate a2 of fl and the error rate b1 of T2 are compared, and since bl is smaller and is below the threshold level, the frequency of the receiver 4 is also changed to T2 by C2 (time t2).
, thereafter, spatial diversity reception using T2 (b.

and b2) will be performed.

With error correction codes, even if errors are detected, most of them are corrected, and the error rate after error correction, that is, the error rate of the pressure code of the device, is greatly improved. If the threshold level of the error rate is set to a value that is slightly smaller than the error rate before correction (the error rate seen by error detection) when the error rate after correction becomes the acceptable limit for use, the error rate will always be good. It is possible to obtain a receiving output.

As described above, it is possible to realize diversity that takes advantage of the advantages of frequency diversity and spatial diversity by selecting a frequency with a good error rate and performing spatial diversity on each of the frequencies f1 and T2.

Furthermore, at the start of reception, the same process as when the error rate worsens may be performed, in which both receivers are set to different frequencies f and T2, respectively, and the code error rates are compared.

Furthermore, if there are three or more waves instead of two frequencies, the error rates may be compared for all waves and the frequency with the lowest error rate may be selected.

Note that in cases where there is interference from other stations or where the noise level varies depending on the frequency, the reception level and line quality may no longer correspond, or the method of determining the reception status using the bit error rate of the present invention is as follows. This also has the advantage of reducing errors in situational judgment.

(Effects of the Invention) As described in detail above, the present invention can achieve effective diversity and has a great effect on improving the reception error rate when receiving data transmission signals on a propagation path with severe fading. This is particularly effective for shortwave lines where reception conditions vary greatly depending on time.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform side diagram illustrating the operation of the circuit of FIG. 1. 1.2... Antenna, 3, 4... Receiver, 5, 6.
...High frequency amplifier, 7.8...Frequency converter, 9゜10...Local oscillator, 11゜12...Intermediate frequency amplifier, 13゜14...Demodulation circuit, 15゜16...Error Correction circuit, 17...SW, 18...Comparator, 19...Picture production circuit. agent

Claims (1)

[Claims] When receiving radio waves that are modulated with the same data containing an error detection code or an error correction code on two different frequencies in the short wave band and are constantly transmitted as a data transmission signal, 2. in two independent antennas and two receivers connected to the two antennas and capable of independently changing reception frequencies, demodulation of the two receivers each having the two different frequencies set as reception frequencies. Space diversity reception is performed by a frequency selection method in which the reception frequency of the other receiver is matched to the reception frequency of the receiver with the smaller error rate obtained by comparing the bit error rates of the outputs, and the two receivers When the code error rates of the demodulated outputs of both become equal to or higher than a predetermined error rate, the reception frequency of one of the two receivers is changed to another reception frequency of the two mutually different frequencies. A diversity reception method, characterized in that it is configured to adopt the frequency selection method.