JPH03220829A - Cross polarized wave interference elimination circuit - Google Patents

Abstract

PURPOSE:To suppress leakage of an excess level interference signal of a different polarized wave side onto a main polarized wave demodulation system and to prevent deterioration in the characteristic by providing a signal suppression circuit to an input or an output side of a transversal filter and suppressing an input signal or an output signal of the transversal filter at a fault of a different polarized wave signal. CONSTITUTION:One signal (main polarized wave signal) in orthogonal two polarized wave reception signals is subject to demodulation processing by a demodulator 3 via an input terminal 1 and the other signal (different polarized wave signal) is subject to demodulation processing by a demodulator 4 via an input terminal 2. A variable attenuator 7 being a signal suppression circuit is interposed between an output of a transversal filter 5 and an input of the demodulator 3 and the attenuation is controlled by a reset signal 9. When the demodulator 4 at the different polarized wave side gives an abnormal output due to extreme level reduction or noise increase resulting from fading and occurrence of an interference signal of a high level such as a radar signal, a different polarized wave signal abnormity detection circuit 8 generates a reset signal 9 to reset the transversal filter 5 and the variable attenuator 7 receives the reset signal 9 to maximize its attenuation.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a cross-polarization interference removal circuit used in an orthogonal polarization communication system that uses two mutually orthogonal polarizations, and particularly relates to a cross-polarization interference removal circuit for use in a transversal filter. Regarding interference prevention technology at the time of reset.

(Prior Art) As is well known, in a microwave digital radio communication system, a multilevel digital modulation method is adopted from the viewpoint of effective frequency utilization, and two mutually orthogonal polarized waves of the same frequency (for example, horizontal An orthogonal polarization communication method that uses polarized waves, vertically polarized waves, right-handed circularly polarized waves, left-handed circularly polarized waves, etc.) is adopted.

By the way, when adopting an orthogonal polarization communication method, cross-polarization interference may occur between both polarization signals due to the anisotropy of a medium such as raindrops during rain. Therefore, the demodulation side of this type of digital wireless communication system has conventionally included a cross-polarization interference cancellation circuit as shown in FIG. 3, for example. The cross-polarization interference removal operation is described in, for example, Japanese Patent Application Laid-Open No. 55-133156.
Publication No.

As proposed in Publication No. 59-77734, etc.
There are cases in which this is carried out in an intermediate frequency band and cases in which it is carried out in a baseband, and FIG. 3 shows a configuration example of the intermediate frequency type.

Among the received signals of two orthogonal polarizations, one signal (main polarization signal) is demodulated by demodulator 3 via input terminal 1, and the other signal (different polarization signal) is sent to input terminal 2. The input signal of the demodulator 3 is subjected to demodulation processing by the demodulator 4 through which a part of the different polarization signal, which is the input signal of the demodulator 4, is combined with the main polarization signal via the transversal filter 5. Ru.

That is, the transversal filter 5 sends a signal having the same amplitude and opposite phase to the different polarization signal leaked into the main polarization signal to the demodulator 4.
, and combines it with the main polarization signal at the input stage of the demodulator 3 to suppress interference components.

At this time, the degree of coupling is determined based on the tap control signal from the tap control signal generation circuit 6.

The tap control signal generation circuit 6 forms and outputs a tap control signal for controlling the tap coefficients of the transversal filter 5 based on the error signal obtained by the demodulator 3 and the reproduced signal obtained by the demodulator 4. For a specific control method, please refer to, for example, Japanese Patent Laid-Open No. 112739/1983.

By the way, if there is an extreme level drop or noise increase due to fading or the like on the different polarization side, the demodulator 4 will lose carrier synchronization and an abnormality will occur in the demodulated output. In this case, the cross-polarization interference removal circuit will not operate normally, and will instead end up injecting interference into the main polarization signal.

Therefore, a different polarization signal abnormality detection circuit 8 is provided to monitor the output state of the demodulator 4, and when an abnormality is detected, a reset signal 9 is generated, thereby setting each tap coefficient of the transversal filter 5 to zero. That is, the transversal filter 5 is operated to reduce the amount of coupling to zero,
This is done so that no disturbance is caused to the demodulator 3 on the main polarization side that is not out of synchronization. The content of the abnormality detection is, for example, that the demodulator 4 on the side of different polarization has lost carrier synchronization, or that the code error rate on the side of different polarization has deteriorated abnormally. (Refer to Publication No. 1977-77734).

<Problems to be Solved by the Invention> As mentioned above, in the conventional cross-polarization interference removal circuit, when the demodulator on the side of different polarization becomes abnormal, it is necessary to prevent disturbance from being caused to the demodulation system on the main polarization side. Therefore, each tap coefficient of the transversal filter is set to zero, and the output signal level is set to zero, but this is because the amount of isolation (attenuation) of each tap of the transversal filter is infinite. However, in reality, it may not be possible to obtain a predetermined amount of attenuation that can be considered infinite due to variations in hardware scale and characteristics.

Then, for example, if an excessively high level interference signal such as a radar signal occurs on the side of a different polarization in the propagation path, the attenuation of the transversal filter alone will not be able to sufficiently suppress the interference signal, and the main polarization side will be demodulated. There is a problem in that residual interference components that have escaped suppression enter the system, resulting in quality deterioration.

The present invention was made in view of such conventional problems, and its purpose is to prevent interference when an excessively high level of interference signal occurs on the side of different polarization and the demodulator on the side of different polarization goes into an abnormal state. It is an object of the present invention to provide a cross-polarization interference removal circuit that can avoid affecting the main polarization side demodulation system.

(Means for Solving the Problems) In order to achieve the above object, the cross-polarization interference removal circuit of the present invention has the following configuration.

That is, the cross-polarization interference cancellation circuit of the present invention includes a first demodulator that receives one signal (main polarization signal) as an input signal among the received signals of 21 orthogonal waves, and a first demodulator that receives the other signal (different polarization signal) as an input signal. a second demodulator which receives a signal> as an input signal; a tap control signal generation circuit which receives an error signal from the first demodulator and a reproduction signal from the second demodulator to generate a tap control signal; a different polarization signal abnormality detection circuit that monitors the output state of the second demodulator and outputs a reset signal when an abnormal state occurs; a signal to be combined with a signal, or
A signal for coupling the detection output signal of the second demodulator to the detection output signal of the first demodulator is formed by controlling the coupling amount based on the tap control signal, and the coupling is performed in response to the reset signal. a transversal filter that operates to reduce the amount of interference to zero; and a cross-polarization interference removal circuit that removes a different polarization signal leaking into a main polarization signal; A signal suppression circuit for suppressing an input signal or an output signal is provided.

(Function) Next, the function of the cross-polarization interference removal circuit of the present invention configured as described above will be explained.

When the demodulator on the different polarization side (second demodulator) goes into an abnormal state, the transversal filter is set to the reset state, but at the same time, the signal suppression circuit is activated and the input signal or output of the transversal filter is Suppress the signal.

As a result, if the cause of resetting the transversal filter is an excessive level interference signal on the side of a different polarization, even if the attenuation amount of each tap at the time of resetting the transversal filter is finite, the input signal or output signal will be suppressed. Therefore, leakage to the main polarization side demodulation system can be prevented, and characteristic deterioration due to interference can be prevented.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a cross-polarization interference cancellation circuit according to an embodiment of the present invention. The cross-polarization interference cancellation circuit according to the present embodiment is of an intermediate frequency type similar to the conventional example, and includes a transversal filter. A variable attenuator 7 serving as a signal suppression circuit is interposed between the output of the demodulator 5 and the input of the demodulator 3, and the amount of attenuation of this variable attenuator 7 is controlled by a reset signal 9.

In other words, as mentioned above, if an extreme level drop or noise increase due to fading or the like or a high level interference signal such as a radar signal occurs on the different polarization side and the demodulator 4 outputs abnormally, the different polarization signal becomes abnormal. The detection circuit 8 issues a reset signal 9 and resets the transversal filter 5.
At this time, the variable attenuator 7 receives this reset signal 9 and operates to maximize its attenuation amount.

Therefore, if the cause of resetting the transversal filter 5 is an excessive level interference signal on the side of different polarization, even if the amount of attenuation of each tap at the time of resetting the transversal filter 5 is finite, the interference leaked to the output side. The signal is sufficiently suppressed by the variable attenuator 7, and is prevented from being coupled to the main polarization signal, which is the input signal of the demodulator 3. This effect can be similarly obtained even if the variable attenuator 7 is provided on the input side of the transversal filter 5.

Note that if the different polarization signal is normal, the reset signal 9 will not be generated, so the variable attenuator 7 operates to minimize its attenuation amount. In other words, the cross-polarization interference removal circuit operates in the same manner as the conventional circuit, and removes the different polarization components that have leaked into the main polarization signal.

Here, the detection target of the different polarization signal abnormality detection circuit 8 is as described above, but it is generally composed of a frame synchronization circuit or a parity error detector used in a digital signal transmission system, and detects a frame synchronization out-of-frame signal. Alternatively, the output signal of the parity error counter is used as the reset signal 9.

Although FIG. 1 shows an intermediate frequency type device, it can be easily inferred that the present invention can be similarly applied to a baseband type device, so the illustration and explanation thereof will be omitted.

Next, FIG. 2 shows an example of the configuration of the variable attenuator 7.

In FIG. 2, the output signal of the transversal filter 5 is input to the input terminal IO. This is bypass capacitor 11. The signal is output from the output terminal 17 via the PIN diode 13 and the bypass capacitor I5, and is combined with the input signal of the demodulator 3. Incidentally, reference numerals 12 and 14 indicate choke coils, which exhibit sufficiently high impedance to transmission signals.

Here, on/off control of the PIN diode 13 is performed by the reset signal 9 applied to the input terminal 16. In other words, when the different polarization signal is normal, there is an abnormality detection port for the different polarization signal! Since @8 does not detect any abnormality, it outputs the reset signal 9 with a positive voltage value sufficient to turn on the PIN diode 13 (conducting state). As a result of the application to the anode, the PIN diode 13 becomes conductive, the amount of attenuation between the input terminal 10 and the output terminal 17 becomes minimum, and the output signal of the transversal filter 5 is output from the output terminal 17 almost unchanged.

On the other hand, when the different polarization signal is abnormal, the different polarization signal abnormality detection circuit 8 detects the abnormality and outputs a reset signal 9 of about Ov. As a result, the DC potential difference between the anode and cathode of the PIN diode 13 becomes zero, the PIN diode 13 is placed in a cut-off state, and the amount of attenuation between the input terminal 10 and the output terminal 17 becomes maximum. In other words, even if an interference signal exists in the output signal of the transversal filter 5, it is sufficiently attenuated by the variable attenuator 7 and is not coupled to the input signal (main polarization signal) of the demodulator 3.

In addition to the configuration shown in FIG. 2, the signal suppression circuit can also be configured with a switch circuit using a relay or the like, for example.

(Effects of the Invention) As explained above, according to the cross-polarization interference removal circuit of the present invention, a signal suppression circuit is provided on the input side or output side of the transversal filter, and when an abnormality of a different polarization signal occurs, the transversal filter Since the input signal or output signal of the transversal filter is suppressed, even if the attenuation amount of each tap at the time of resetting the transversal filter is a finite value rather than a value that can be considered infinite due to variations in characteristics, the reset When the cause is an excessive level interference signal on the side of different polarization, leakage of the interference signal to the demodulation system on the main polarization side can be sufficiently suppressed, and characteristic deterioration can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a cross-polarization interference cancellation circuit according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a variable attenuator serving as a signal suppression circuit, and FIG. 3 is a conventional cross-polarization interference cancellation circuit. FIG. 1.2...Input terminal for received signal, 3,4...
... Demodulator, 5 ... Transversal filter, 6 ... Tap control signal generation circuit, 7
...Variable attenuator, 8...Different polarization signal abnormality detection circuit.

Claims (1)

[Claims] A first demodulator that receives one of the received signals of two orthogonal polarizations (main polarization signal) as an input signal, and a second demodulator that uses the other signal (different polarization signal) as an input signal. and;
a tap control signal generation circuit that receives an error signal from the first demodulator and a reproduced signal from the second demodulator and generates a tap control signal; monitors an output state of the second demodulator to indicate an abnormal state; a different polarization signal abnormality detection circuit that outputs a reset signal when A signal for coupling the detection output signal to the detection output signal of the first demodulator is formed by controlling the coupling amount based on the tap control signal, and the coupling quantity is set to zero in response to the reset signal. A cross-polarization interference removal circuit for removing a cross-polarization signal leaked into a main polarization signal, comprising: an operating transversal filter; 1. A cross-polarization interference removal circuit, comprising: a signal suppression circuit for suppressing signals.