JPH0748685B2 - Diversity reception method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a diversity receiving method in the case of receiving a signal which is data-transmitted by a propagation path such as a short-wave line with a lot of fading.

(Prior art and its problems) Diversity is known as a technique for ensuring good reception quality in a short-wave line or the like, which is often affected by fading in the propagation path. Specific methods of realizing diversity include frequency diversity and space diversity.

Frequency diversity has little fading correlation 2
Two receivers with different reception frequencies are installed in one antenna using waves to perform diversity reception. For example, in the short wave band, the propagation loss, the degree of fading, the interference interference situation from other stations, etc. Since they are different, there is a drawback that it is difficult to obtain an ideal diversity operation.

On the other hand, space diversity receives radio waves of the same frequency with two antennas that are spatially separated and performs diversity, but when the reception state of the reception frequency deteriorates, there is no effect of improving reception quality due to space diversity, There is a drawback that the operator must judge and change the reception frequency.

(Object of the Invention) An object of the present invention is to solve the drawbacks of the above-mentioned two types of diversity, detect a change in the reception status, and automatically switch the mode of diversity, and take advantage of the advantages of both diversity systems to reduce the influence of fading. It is to provide a reduced diversity reception method.

(Structure and Operation of the Invention) There are several methods for determining the reception status. However, the present invention utilizes that the magnitude of the phase fluctuation of the carrier changes corresponding to the S / N of the signal. Determine the reception status.

That is, the diversity receiving method of the present invention uses two independent radio waves in the case of receiving radio waves in which first and second two frequencies of different short-wave bands, which are different from each other, are constantly transmitted as a data transmission signal by being modulated with the same data. And two antennas connected to the two antennas and capable of independently changing the reception frequencies, the reception frequencies of the two receivers are set to the first frequency. Always compares the phase fluctuation amount of the received carrier wave, and switches the output of the receiver having the smaller phase fluctuation amount to output the space diversity reception at the first frequency. When both the amount of phase fluctuation of the received carrier due to the frequency becomes larger than a predetermined value, the receiving frequency of either one of the receivers is changed to the second frequency and the amount of phase fluctuation is compared, The output of the receiver with the smaller fluctuation amount is switched and output to perform frequency diversity reception with the first and second frequencies, and the phase fluctuation amount of the received carrier wave with the second frequency of the one receiver is predetermined. When the value is smaller than the value of, the receiving frequency of the other receiver is switched to the second frequency to compare the phase fluctuation amounts, and the output of the receiver with the smaller phase fluctuation amount is switched and output according to the second frequency. It is characterized in that it is configured to perform space diversity reception.

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

FIG. 1 is a block diagram of an embodiment of the present invention. 1 and 2
Is two antennas for space diversity, and 3 and 4 are two receivers whose reception frequencies can be set independently of each other. 5 to 16 are typical configuration examples of the internal circuit of each receiver, and 5 and 6 are high frequency amplifiers (RFA), 7 and 8
Is a frequency converter (MIX), 9 and 10 are local oscillators (OS
C), 11 and 12 are intermediate frequency amplifiers (IFA), 13 and 14 are demodulation circuits (DEM), and 15 and 16 are phase fluctuation detection circuits (PD). The configuration of the receivers 3 and 4 is that the output frequency (that is, the reception frequency) of the local oscillators (OSC) 9 and 10 can be switched from the outside and that the phase fluctuation detection circuits 15 and 16 are added. , It is no different from a receiver for normal data transmission. Reference numerals 17 to 20 denote circuits added for implementing the present invention. Reference numeral 17 denotes a switching circuit (which selects one of the outputs of both receivers 3 and 4 with less phase fluctuation (that is, a better reception condition) ( SW), 18 is the phase fluctuation detection circuit 15 of both receivers 3 and 4
And a comparator circuit (COMP) that compares the phase fluctuation amounts of the received signals from 16 and gives a switching signal to the switching circuit (SW) 17, 19 is the one with the smaller phase fluctuation amount of the received signals of both receivers 3 and 4. Judgment circuit (LEV) that compares the level with a preset threshold value to judge the magnitude of phase fluctuation, 20 is COMP18 and L
The output of EV19 is used to judge whether the frequency of the receiver should be changed, and the OS
It is a control circuit (CONT) that controls the frequency of the receiver by giving a control signal c ₁ or c ₂ to C 9 and 10.

First, the operation principle of determining the reception status based on the amount of phase fluctuation will be described. Figure 3 shows the relationship between the signal-to-noise ratio (S / N) and the probability density function of phase. The 0 on the horizontal axis is the position of the phase when the S / N is infinite. As the S / N becomes smaller, the phase will be distributed over a wider range. Therefore, if the phase when the S / N is infinity is used as a reference, the synchronous detection of the reception input is performed, and the absolute value thereof is taken and smoothed to detect the phase fluctuation corresponding to the S / N. In addition, if the reference phase cannot be obtained, the phase difference between symbols (so-called differential detection is performed) is obtained, or in the case of frequency shift modulation, even if the deviation from the correct shift frequency is obtained, synchronous detection is performed. The phase fluctuation detection can be performed in the same manner as.

FIG. 2 is a waveform example diagram for explaining the operation of the circuit of FIG. ₁ , and is a receiver based on the frequencies f ₁ and f _{2 of} two waves and the amount of phase fluctuation.
An example of automatic selection of 3 and 4 is shown below. Two waves f ₁ and f ₂
And Waveforms a ₁ and a 2 in FIG. ₂ show changes in the amount of phase fluctuation of the receivers 3 and 4 when f ₁ is received by the antennas 1 and 2, respectively, and b ₁ and b ₂ are the antennas 1 and 2, respectively. The change of the phase fluctuation amount when f ₂ is received is shown, and the vertical axis indicates that the fluctuation amount is small as it goes up and the fluctuation amount is big as it goes down. c ₁ and c ₂ are reception frequency switching signals of the receivers 3 and 4, which are given to the OSCs 9 and 10, respectively, and when level 1 is f ₁ ,
When it is 0, f ₂ is selected. d is the output of COMP18, both receivers
It is a comparison output of the phase fluctuation amounts of 3 and 4, and is given to SW17 to switch and select the output of the receiver 3 when the level is 1, and the output of the receiver 4 when the level is 0.

Based on the data of maximum usable frequency (MUF), which is one of the important parameters of short-wave band communication using the reflection of the ionosphere, two waves with little fading correlation according to the season, daytime, nighttime, and other conditions, such as f ₁ and f ₂ is selected.

In the initial state, it is assumed that the reception frequencies of both receivers 3 and 4 are set to f ₁ . In this state, the phase fluctuations of the reception signals of the receivers 3 and 4 are a ₁ and a ₂ . Until time t _1, the phase fluctuation amount above the threshold level (below the broken line) does not occur at the same time, so reception of f ₁ is continued, and as shown in d, _one of a ₁ and a ₂ with the smaller phase fluctuation amount (that is, S / Select the one with the larger N) and output. That is, spatial diversity is performed by receiving f ₁ . At time t ₁ , when the situation of f ₁ worsens and both phase fluctuations are above the threshold level (below the broken line), the frequency of the receiver a ₁ with the larger phase fluctuation a ₁ becomes f _{2 due} to the output c _{1 of} CONT ₂₀ . Be changed.
Therefore, the phase fluctuation of the received signal of the receiver 3 becomes b ₁ . Here, the phase variation b ₁ of phase fluctuation a ₂ and f ₂ of f ₁ are compared, b ₁
Is smaller and is below the threshold level (above the broken line), the frequency of the receiver 4 is also changed to f ₂ by the output c _{2 of} the CONT ₂₀ (time t ₂ ), and thereafter the space using f ₂ is used. Diversity reception (comparison between b ₁ and b ₂ ) is performed.

As described above, it is possible to realize diversity by making the best use of the advantages of frequency diversity and space diversity, that is, selecting the reception frequency with the smaller amount of phase fluctuation and performing space diversity at that frequency.

Further, at the start of reception, both receivers 3 and 4 are set to frequencies different from each other and the phase fluctuation amounts are compared, which is the same process as when the phase fluctuations deteriorate.

Further, when the frequency is three waves or more instead of two waves, the phase fluctuation amounts may be compared with each other and the frequency with the smallest phase fluctuation may be selected.

The method of determining the reception status by comparing the magnitudes of the phase fluctuations of the present invention makes it possible to prevent the reception level and the line quality from corresponding to each other when there is interference from other stations or when the noise level differs depending on the frequency. Even in such cases, there is a feature that there are few errors in the situation determination.

(Effects of the Invention) As described in detail above, the present invention can realize effective diversity and has a great effect in improving the reception error rate when receiving a data transmission signal in a propagation path with severe fading. In particular, the effect is extremely great in a line such as a short-wave line in which the reception status varies greatly with time.

[Brief description of drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a waveform example diagram for explaining the operation of the circuit of FIG. 1, and FIG. 3 is a phase distribution diagram of a carrier wave in the presence of noise. 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 ・ ・ ・ Phase fluctuation detection circuit, 17 ・ ・ ・ SW, 18 ・ ・ ・ Comparator, 19 ・ ・ ・ Judgment circuit, 20 ・ ・ ・ Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-166627 (JP, A) JP-A-52-79817 (JP, A) JP-A-2-70131 (JP, A)

Claims (1)

[Claims] 1. A first and a second 2 having different short-wave bands from each other.
When receiving a radio wave whose frequency is modulated with the same data and is always transmitted as a data transmission signal, two independent antennas and two antennas connected to the two antennas and capable of independently changing the reception frequency are used. In the first and second receivers, the reception frequency of the two receivers is set to the first frequency, and the phase fluctuation amount of the reception carrier is constantly compared to determine which of the receivers having the smaller phase fluctuation amount. When the output is switched and output to perform spatial diversity reception at the first frequency, and the phase fluctuation amount of the received carrier at the first frequency of the two receivers is both larger than a predetermined value, either one of them Changing the reception frequency of the receiver to the second frequency and comparing the phase fluctuation amounts, and switching the output of the receiver with the smaller phase fluctuation amount to output the frequency according to the first and second frequencies. Diversity reception is performed, and when the phase fluctuation amount of the reception carrier wave at the second frequency of the one receiver is smaller than a predetermined value, the reception frequency of the other receiver is switched to the second frequency and the phase fluctuation is performed. A diversity receiving method, characterized in that the amounts are compared and the output of the receiver with the smaller amount of phase fluctuation is switched and output to perform spatial diversity reception at the second frequency.