JPS6011859B2 - Mutual interference coefficient detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a coefficient of mutual interference from two angle modulated waves received while mutually interfering with each other in a wireless communication system.

In recent years, in microwave communication systems including the use of communication satellites, orthogonal polarization is used for effective frequency use, and two communication signals are transmitted at the same frequency, for example, one of them is a right-handed circularly polarized wave.
A method has been proposed in which the other wave is transmitted as a left-handed circularly polarized wave.

In this case, it is of course necessary that the antenna system has sufficient cross-polarization discrimination, but mutual interference due to deterioration of cross-polarization discrimination in the propagation path due to rain or other causes becomes a problem. The deterioration of the cross-polarization discrimination degree can be compensated for, and one method thereof is shown in Patent Iso No. 50-2 Gikka 4 "Cross-Polarization Compensation System." Since the deterioration of the cross-polarization harmonic U degree changes over time due to changes in rainfall intensity, etc., the compensation method described above reduces the amplitude phase of the interference wave mixed into the received wave due to the deterioration of the cross-polarization discrimination degree. It is necessary to detect this, adjust the amount of compensation accordingly, and control so that the degree of discrimination is always the best. In such a case, there is a method that detects the mutual interference coefficient of the two received waves and uses it for controlling the cross-polarization compensation method. Conventionally, two pilot signals of different frequencies have been used to detect mutual interference coefficients. In other words, that first wave (
F,) is transmitted with a certain orthogonal polarization (W,), and one other wave (F,
2) with another orthogonal polarization (W2), on the receiving side, the polarization W, including the frequency F and the interference wave F2
The frequency F2 and the interference wave F, component are received in the polarized wave W2. Since F, and F2 have different frequencies, they can be easily separated by a narrow band filter, and the ratio (including amplitude and phase) of the F2 component in W and the F2 component in W2 is calculated, and F in W2, component and W, F in
- Mutual interference coefficient can be easily detected by taking the ratio of the components. However, the conventional method using a pilot signal requires an extra frequency band and power for the pilot signal, which has the disadvantage of reducing the effect of effective frequency use by using cross-polarized waves. SUMMARY OF THE INVENTION An object of the present invention is to provide means for detecting mutual interference coefficients using communication signals themselves in order to eliminate this drawback. The present invention
When two or more communication signals are received while causing mutual interference, means for generating an estimated value signal of a received wave from each received signal, and means for subtracting the estimated value signal from each received signal. A mutual interference coefficient detection device is provided, which detects mutually interfering components.

The operating principle of the present invention is as follows. When detecting the mutual interference coefficient using communication signals, the spectrum of the desired wave and the spectrum of the interference wave are mixed within the same band, and it is impossible to separate the two using a simple wave device. . If one of the transmitted waves of the two communication signals is x and the other is equalized, and one of the two received waves is y and the other is y2, then y, = T, . x, 10T, 2 also, y2
=T2, x, +T22.

Here, T, . ,T,2,L, ,T2 are mutual interference coefficients that should be detected by this method. Note that the mutual interference coefficient includes both amplitude and phase boundaries (or both terms of an in-phase component and a quadrature component), and is expressed as a complex number. Received wave y,
mainly receives the transmitted wave x, and the slope is adjusted to receive x2, so generally ITul》IT,
2l and IT22l》IT2,l. Therefore, in order to detect the mutual interference coefficient, first, the received wave y is demodulated and remodulated using a phase-coherent loop circuit, etc.
The transmitted wave x, is estimated and an estimated wave x, is created. Then, a method can be considered in which correlation detection is performed on the received wave C2 using the estimated wave x as a reference wave to detect the coefficients T2 and /L2 of the x component in y2. However, this method has the disadvantage that large detection errors may occur. It is the reference wave x
, contains the component x2 as an error, and x,
This is because when performing correlation detection on and y2, the correlation between the x2 component in x and the underground homogeneous component is detected and appears. The size of this error is determined by the size of the coefficient you want to know (L,
/T22), while approximately (1/2)(T, 2/T
、． ), and (T2,/T22) and (T,2/T, .
) is about the same size, then a detection error of about 1/2 will be included. In order to eliminate this drawback, it is sufficient to remove as much of the cedar component as possible from the inside during the above-mentioned correlation detection. This can be done by creating a perfect estimated wave average and subtracting it from y2. Based on this principle, the present invention makes it possible to detect the mutual interference coefficient of two communication signals with little error. The present invention will be explained in detail below with reference to Examples.

FIG. 1 is a schematic diagram showing how mutual interference occurs due to deterioration of cross-polarization discrimination due to rain on a propagation path.

The first transmission wave x transmitted from the first and second satellite communication ground stations S, ES2, respectively via the communication satellite CS, and the second transmission wave polarization orthogonal thereto are as follows: At the third satellite communication ground station ES3, the first received wave y and the second received wave y receive mutual interference due to rain. FIG. 2 shows a block diagram of an embodiment of the most general configuration for various modulation schemes of the present invention.
Two input signals y, , are applied to input terminals 1 and 2, respectively.

y, includes the interference signal cedar in addition to the desired signal x, and y2
includes an interference signal x in addition to the desired signal. The average amplitude of each input signal is made constant by the automatic gain control circuits 10 and 20, and the respective outputs 51
, 61. Each of these signals is branched into two, one of which is applied to demodulators 11 and 21, where the input signal is demodulated and an estimated value of the original modulated signal of the transmitted signal is obtained. Depending on the modulation method used, the bandwidth and statistical properties of the modulated signal, and taking into account the presence of interference signals, this demodulator is designed to perform demodulation that is as close as possible to the original modulated signal. It is desirable to use one that can provide a signal. For example, if the modulation method is AM or PM, a synchronous detection method is preferable, and if the modulation method is FM, a phase-locked loop method is preferable. The outputs of demodulators 11, 21 are then applied to respective modulators 12, 22 and re-modulated to provide estimates 52, 62 of the transmitted signal.

However, 52 and 62 must be coherent with the desired signal x, in each y, y2, and this can be achieved by using phase synchronization techniques in the demodulator and modulator. It is possible. Next, the other branch signals 51 and 61 are sent to subtracters 13 and 23, respectively.
2 to obtain the difference output 54,64.

54 is the value obtained by subtracting the estimated value 52 of the desired wave x, from 51, which is obtained by removing the component included in 52 among the interference waves in 51, and other estimation errors of the desired wave x, It will include.

The same applies to 64.

Next, 64 rotates the phase of 52 and 52 by n/2 (14
) is detected (15, 16), and the magnitude of the in-phase value of 52, which is the estimated value of x, of the x component in 64 is taken out to the output terminal 3. The size is taken out to the output terminal 4. Similarly, the magnitude of the equal component in 54 that is in phase with 62, which is the estimated value of cedar, is output to the output terminal 5, and the magnitude of the right angle component is output to 6. As explained above, it is clear that the output terminals 3 to 6 output an output proportional to the mutual interference coefficient. Now, as is clear from the above description, in order for the device of the present invention to function effectively, it is necessary to perform some interference suppression during demodulation and remodulation.

Otherwise, when the subtracter subtracts the estimated value of the desired wave from the input signal, the interference wave will also be subtracted at the same time, leaving only noise. Therefore, although the present invention cannot be applied to the SSB-AM system, it is effective for most other modulation systems. Modulation methods to which the present invention can be applied include AA, FM, PM, FSK, PSK, a combination thereof, and a mixed modulation method that simultaneously modulates both amplitude and phase, which are widely used in wireless communications. The present invention is applicable to most modulation schemes. FIG. 3 is a block diagram of an embodiment in which the present invention is applied to an FM system.

In the circuit of this figure, the demodulator 11 and modulator 1 of the circuit of FIG.
2 is replaced with a phase locked loop consisting of a phase detector 35, a loop filter 17 and a variable frequency oscillator 36. The same applies to the circuit on the second input signal side. Considering that there is a phase difference of input spike/2, the output of the variable frequency oscillator in the phase-locked loop is the third
The output of variable frequency oscillator 36 in the figure corresponds to 53 in FIG. 2, and the output of scale/2 phase shifter 14 in FIG. 3 corresponds to 52 in FIG. The same applies to the circuit on the second input signal side. Further, in the circuit shown in FIG. 3, the automatic gain control circuit 10 is controlled by the output of the Hata product detector 18 of 52 and 51, but it is obvious that the automatic gain control circuit 10 may be controlled by other methods. It is.
The same applies to the circuit on the second input signal side. The apparatus shown in FIG. 3 uses a broadband subtractor and a wave/2 shifter, but it is difficult to realize these with good characteristics.

Therefore, although the other circuits become complicated, a block diagram of another embodiment of the present invention is shown in FIG. 4, which is improved so that the subtracter and phase shifter can be used for a single frequency. . For convenience of explanation, the frequency of the first transmission signal is assumed to be f, and the frequency of the second transmission signal is also assumed to be f. The received signal at Isogo 1 contains a mixture of the desired wave component f and the interference wave component. After this input signal is made constant by the automatic gain control circuit 1, the average amplitude is applied to the frequency converter 19, and mixed with the output 58 of the variable frequency oscillator 36.
The frequency component 55 of the difference is extracted from the bandpass filter 30'. The phase difference between 55 and the output 70 of the reference frequency oscillator 39 is detected by the phase detector 35, and the output is passed through the loop filter 7 to control the frequency of 36.

That is, 19, 30, 35, 17, 36, and 39 form a frequency conversion type phase-locked loop, and the frequency of the output 55 is equal to fr, where the frequency of the output 70 of 39 is fr.

The output 58 of 36 is considered to be the result of frequency conversion of the estimated value of the desired wave, and its frequency is f, 10 fr, and even if , changes, it changes accordingly, so the frequency component of the difference is In some 55, the frequency change of f is suppressed and becomes a constant frequency fr, which includes a residual phase shift corresponding to the tracking error of 36 and a frequency-converted interference wave component. On the other hand, the phase of the reference signal is rotated by /2 (14
) and 55 are subjected to Hata product detection (18). Since the output is proportional to the amplitude of the later component in 55, it is used as a control signal for the automatic gain control circuit 10.

Now, if we subtract 71 from 55 using the subtractor 13, we get
The desired wave component in 55 and 71 both have a frequency fr and are in phase, so it is possible to eliminate them, and in the output 56 of 13 there is a residual phase shift and a frequency-converted component. Only interference wave components are included. When this difference signal 56 and the output 58 of the variable frequency oscillator 36 are added to the frequency converter 31 and the sum frequency component of both is extracted by the band filter 32, the frequency f2 of the interference wave is restored to the output 59. be done. However, the component of f, contains only a small amount related to the amount of residual phase shift contained in 56.
On the other hand, the input signal at terminal 2 is processed in the same way, and the frequency of the output 68 of variable frequency oscillator 46 is 10 fr.

Therefore, the outputs 59 and 68 obtained earlier are transferred to the frequency converter 3.
In addition to 3, when the difference frequency component is extracted by the band filter 34, the frequency change of f2 is suppressed in the output 57, and the frequency of 57 becomes fr. In addition, in 68, the component of f, which is included as an interference wave in the input signal of terminal 2, is included as a frequency of 10 fr even after frequency conversion. Since it is suppressed to a small amount, the amount related to the f· component included in the difference frequency signal 57 between the two is small. Therefore, the amplitude and phase of the mother force 57 are approximately equal to the terminal 1
It is related to the amplitude and phase of the interference wave component at terminal 2.
There is only a slight amount of false distortion caused by the presence of interference wave components. Therefore, the output 57 is the reference wave 70 and its bamboo/2
By performing Hata product detection with the phase rotation wave 71, the amplitude and phase of the interference wave included in the input signal of the terminal 1 can be detected. The same applies to the detection of interference waves included in the input signal of terminal 2.

In this embodiment, the same effect can be obtained by using narrow-band filters in place of the subtracters 13 and 23. Although the above embodiments include an automatic gain control circuit, this is unnecessary if there is no or only slight gain variation in the transmission path.

Furthermore, any circuit such as a combination of a demodulator and a modulator or a phase-locked loop may be used as long as it can obtain an estimated value of the desired wave from the input signal. Further, the Hata product detection circuit for obtaining the detection output may be any circuit as long as it can detect the amplitude, phase, etc. when one signal component contains a signal component that is correlated with another signal. Further, in the above description, the mutual interference coefficient detection apparatus was described in the case of mutual interference of two waves, but the mutual interference coefficient can be detected in exactly the same manner even in the case of three or more waves mutually interfering.

In order to explain the effects of the present invention, the mutual interference coefficient detection device of the present invention and, for example, the above-mentioned patent No. 50-25844 "
Figure 5 shows the cross-polarization compensator shown in "Cross-Polarization Compensation Method" when combined.

In the figure, a radio wave received by an antenna 101 is separated by a polarization separator 102 into mutually orthogonal polarization components 201 and 202. However, the polarization components 201 and 202 include interference wave components due to deterioration of the cross-polarization discrimination degree due to rain or the like. 103 is a crossed polarization compensator;
If this is well controlled, it is possible to compensate for the deterioration in the degree of cross-polarization discrimination and reduce the interference wave components contained in the outputs I and 2.

Therefore, the output 2 of communication receiving demodulators 105 and 106
03 and 204, good signals with reduced interference due to interference are obtained. Here, the crossed polarization compensator 103
A mutual interference coefficient detection device 104 of the present invention is connected to outputs 1 and 2 of the
and 6 are used to control the crossed polarization compensator 103.

That is, the interference wave components included in 1 and 2 are
By the negative feedback loop consisting of 3 and 104, in an ideal case where there is no detection error ≦ or control error, the number can be reduced to zero in principle.

As described in detail above, the present invention is a means for detecting the mutual interference coefficient directly from the communication signal with less error when two or more waves interfere with each other and are received. By using this detected mutual interference coefficient as a control signal for an interference compensation method, it is possible to minimize the influence of interference and provide an efficient communication method. .

[Brief explanation of drawings]

Figure 1 is a Hamishiki diagram of the situation where mutual interference occurs in a communication system.
Fig. 2 is a block diagram of the first embodiment of the present invention, Fig. 3 is a block diagram of the second embodiment of the invention, Fig. 4 is a block diagram of the third embodiment of the invention, and Fig. 5 is a block diagram of the present invention. FIG. 2 is an explanatory block diagram when the mutual interference coefficient detection device of the invention is combined with a crossed polarization compensation device. In the figure, 1, 2...input terminals, 3, 4, 5, 6...
...Output terminal, 10,20...Automatic gain control circuit, 11,21...Demodulator, 12,22...
...Modulator, 13.23 ...Subtractor, 14,24
...Medium/2 phase shifter, 15, IS, 18, 25, 26
, 28... Hatamoto detector, 17, 27... Loop filter, 30, 40, 32, 42, 34, 44... Obishiro filter, 19, 29, 31, 41, 33 ,43...
・Frequency converter, 35.45...phase detector,
36, 46... variable frequency oscillator, 39...
... Reference signal oscillator, 51, 61 ... Signal with constant average amplitude, 52, 62 ... Estimated output signal, 53, 63
...52, 62 scale/2 rotation signal, 54, 64...
...Signal obtained by subtracting the estimated signal from the input signal, 55, 65
...Frequency change suppression signal, 56, 66...
Frequency-converted interference signal, 57, 67... Frequency change suppressed interference signal, 58, 68...
Signal obtained by converting the frequency of the estimated signal, 59, 69...
・Restored interference signal, 70...Reference wave, 71
．． ．． ．． ．． ．． ．． Shore/2 rotation reference wave signal, 101...
・Antenna, 102...Polarization separator, 103...
... Cross polarization compensation device, 104 ... Mutual interference coefficient detection device of the present invention, 105, 106 ... Communication reception demodulation device, 201, 202 ... Orthogonal polarization Components 203, 204... are demodulated output signals. Cum 1
2 drawings S drawing Zum drawing groove J box

Claims (1)

[Claims] 1. In a receiving device used in a communication system in which two or more communication signals are received by mutual interference, each received wave distributed to each receiving system is demodulated in response to the two or more communication signals. means for forming an estimated wave of each received wave by re-modulating the received wave, means for subtracting the estimated wave from each received wave, and output of the subtracting means from the estimated wave of another receiving system. and means for performing product detection using waves whose phases are shifted by π/2.