JPS5977734A - Circuit for eliminating interference of cross polarization - Google Patents

Abstract

PURPOSE:To quicken the restoration to a normal state, by detecting a failure in digital demodulation output and resetting a demodulated output value to a set value to prevent the deterioration in demodulated output of other polarized wave. CONSTITUTION:When the carrier wave synchronism of a digital demodulator 3 of polarized wave is out, a control loop of a variable coupler 2 is not operated normally and there exists a possibility that a signal increasing the interference is outputted to an output 107, and it is a cause to increase a code error of a regenerated output 103'. Further, it is a cause of delaying the restoration of carrier synchronism of the demodulator 3 and of the variable coupler 2' to normal operation. Thus, an out of synchronism detector 5 detects the out of synchronism and a failure signal 106 discharges integrators of reset circuits 8, 8' to make the all outputs 107, 107' of couplers 2, 2' zero, thus defects are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to a cross-polarization interference cancellation circuit, especially to digital wireless communication, and when an abnormality occurs in one polarization, it prevents the spread to the other polarization, and the abnormality is recovered. The present invention relates to a cross-polarization interference canceling circuit that includes means for promoting recovery when a cross-polarization interference occurs.

In recent years, orthogonal polarization communication methods, which utilize frequencies effectively by using two orthogonal polarized waves of the same frequency (vertical and horizontal or left-handed circularly polarized waves and right-handed circularly polarized waves), have attracted attention in microwave wireless communications. There is. Such two orthogonal polarized waves generate cross-polarized waves due to the anisotropy of the medium due to rainfall, etc., and cross-polarized waves interference occurs between the waves on both sides. Conventionally, as a cross-polarization interference removal circuit suitable for digital wireless communication, for example, Japanese Patent Application Laid-Open No. 55-1
No. 33156 proposes a circuit that controls a transversal filter based on demodulated baseband signal information to eliminate cross-polarization interference.

However, with such conventional circuits, the expected effect can be obtained when the reception input exceeds a certain value and the modulator is operating normally, but as will be explained later, when the received input is above a certain value, the expected effect can be obtained. (To) If an abnormality occurs in the demodulated output due to an extreme decrease in the level of the polarized wave due to fading or an increase in noise, which causes the demodulator to lose synchronization with the carrier wave and an abnormality occurs in the demodulated output, the interference wave removal circuit will not operate normally, and conversely, the horizontal n If interference i is injected into the polarized wave to increase the sign error of the H polarized wave, or from the H polarized wave.
Due to the inflow of interference into polarized waves, there are disadvantages such as (1) delay in convergence of control operations when polarized waves are recovered from abnormalities;

The object of the present invention is to provide a cross polarization system which eliminates the above-mentioned drawbacks, prevents an abnormality in at least one polarized wave from adversely degrading the other polarized wave, and which quickly returns to normal operation when the abnormality occurs. An object of the present invention is to provide a wave interference cancellation circuit.

The cross-polarization interference cancellation circuit of the present invention includes at least one digital demodulator that demodulates a digitally modulated received signal of an orthogonal polarization communication method using two mutually orthogonal polarizations having the same frequency; at least one variable coupler provided in front of or on the digital demodulator and capable of coupling the signal of one polarization to the other polarization and controlling the amount of coupling by a control signal; and after the digital demodulator and the variable coupler. and a control signal generator that generates the control signal of the variable coupler based on the demodulated baseband signal, the cross-polarization interference removal circuit detects an abnormality in the demodulated output of the digital demodulator. and a reset means for setting at least one output of the variable coupler to a predetermined value based on the output of the abnormality detection means.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of the first embodiment of the present invention, in which V, H
Adaptive waveform equalization 4a1, 1' consisting of IF band transversal filters connected to the intermediate frequency (IF) output of each polarized wave and performing waveform equalization, and IF ratio outputs of V and H are branched and inverted, respectively. A variable coupler 2.2' consisting of an IF band transversal filter that couples to the waveform equalization amount output of the polarized wave and whose coupling amount can be controlled, and a digital signal connected to the output of the waveform equalization amount 1,1'. Digital demodulators 3, 3' of a synchronous detection method demodulate the demodulated baseband signal Zoo, waveform equalizers l, 1' and variable coupling a 2, 2' (D control m code 101, 101'
a control signal generator 4 that generates signals 102, 102;
The digital demodulator 1 is composed of an out-of-synchronization detector 5 and 5' for detecting out-of-synchronization of the digital demodulators 1 and 1'. The control signal generator 4 includes a control signal generator 6 and four sets of reset circuits 7 and 7.
'.

8.8', the control signal generation unit 6 performs identification judgment on the baseband input signal 100,100''t, estimates the signal on the transmitting side, and outputs the reproduced signal 103.103.
' playback function and input signal 100°100
an error signal generation function that generates all error signals from the difference between the output signals 103 and 103', and a correction signal 104 that sequentially corrects each control signal by finding the correlation between this error signal and the input signal.
, 104', 105, 105'. The reset circuits 7, 7' and 8.8' integrate the correction signals 104, 104' and 105°105'e, respectively, to generate control signals for the waveform equalizer and variable coupler,
Abnormal signals 106, 106' of out-of-sync detectors 5, 5'
This circuit sets the control signal to a predetermined initial value upon receiving the signal. Waveform equalizer correction signals 104, 104'
are generated by calculating the correlation between the input signals of the same polarization of V and H and the error signal, respectively, and the correction signals 105. of the variable coupler are generated. i
05' is generated by calculating the correlation between the V and H input signals and the oppositely polarized H and V error signals. Waveform equalizer l, 1'
For example, when the variable coupler 2.2' is constituted by a 3-tap transaxial filter having three taps (leading, intermediate, and trailing), each control signal 101, 1
01' and 102t102' each include three control signals that control the tap coefficients of three taps, and each preceding and following tag control signal changes the input signal 100 or 10σ, which correlates with the error signal, by 1 bit. It can be found by The reset circuits 7 and 7' set the tag coefficient of the intermediate tap to 1 and the tap coefficients of the preceding and succeeding taps to O by the abnormal signals 106 and 106', respectively, and the reset circuits 8 and 8' set the tag coefficient of the intermediate tap to 0 by the abnormal signals 106 and 106', respectively. Set all tap coefficients to 0 by .

The circuit shown in FIG. 1 described above is a conventional cross-polarization interference canceling circuit except for the out-of-synchronization detectors 5, 5' and the reset function by the abnormal signals 106, 106' of each reset circuit. In other words, an IP band transversal filter is used for the waveform equalizer and variable coupler, but Japanese Patent Laid-Open No. 55-1
It is based on the same technical idea as the one described in Publication No. 33156, and the control method is exactly the same]. ), the actual control circuit is configured to perform all digital processing.

This control algorithm using a demodulated baseband signal can be applied to general microwave band communications where the intermediate frequency (fc) cannot necessarily be selected as an integer multiple of the modulation frequency (fs), using an IF band transversal filter. The method applied to the type waveform thickener was patented in 1984-21.
This method, which was proposed in No. 5217, can be similarly applied to a cross-polarization interference removal circuit using an IP band transversal filter. Since this method is not directly related to the present patent, it will be omitted here, but if necessary, please refer to the above-mentioned Japanese Patent Application No. 56-215271. In addition,
In FIG. 1, both the V and H polarized input signals are the same signal modulated at the same bit rate and are signals obtained by converting radio signals of the same frequency to an intermediate frequency by the same local oscillator.

Now, if the carrier synchronization of the digital demodulation D3 of the ■ polarization is lost, the demodulated output 100 no longer contains the base transmitted in the ■ polarization, even if the bit synchronization is maintained by the demodulator output of the H polarization. Does not include band signal information.

Therefore, the control loop of the variable coupler 2, which calculates the correlation between the signal 100 and the error signal obtained from the H-polarized signal 100' and minimizes the interference of the V-polarized wave included in the H-polarized wave, operates normally. As a result, the control signal 102 becomes unstable and fluctuates as meaningless disturbance information that happens to appear as the correction signal 105, and the output 107 of the variable coupler 2 has no signal that cancels out the interference of the H polarization. On the other hand, there is a possibility that a signal that increases interference will be output, which will increase the sign error of the V-polarized reproduced output 103'. Similarly,
■The output 107' of the variable coupler, which is controlled by determining the correlation between the error signal obtained from the demodulated polarized signal 100 and the H-polarized signal 100', also becomes unstable, causing ■ interference to the polarized wave. This causes a delay in recovery of carrier synchronization of the digital demodulator 3 and return of the variable coupler to normal operation. In the circuit according to the first embodiment of the present invention shown in FIG.
6 discharges the integrators of the reset circuits 8, 8', each tap coefficient of the transversal filter is set to 0, and the outputs 107, 107' of the variable coupler 2.2' are all set to 0. The disadvantages can be removed. Note that in the waveform equalizer 1, the tap coefficient of the intermediate tap is 1, as is already done in conventional waveform equalizers.
The preceding and succeeding tap coefficients are controlled to be O. The same holds true for the loss of carrier synchronization of H polarized waves.p,
The variable couplers 2, 2' are reset by the abnormal signal 106'.

FIG. 2 is a block diagram of an embodiment of an element circuit that controls each tap of the reset circuits 7.7' and 8.8' in FIG.
It is composed of AND/NAND gates 61 and 63, an AND gate 62, an OR gate 64, an integrating circuit 65, and a level shift circuit 66.
(synchronized state) correction signal 104.104', 10
5 and 105' are normally integrated by the integrating circuit 65, but when the abnormal signal is 101, the output of the integrating circuit 65 is discharged and fixed to the threshold value of the AND/NAND gate 63. The level shift circuit 66 outputs control signals 101, 101', 102, 10 different from this threshold value.
It is used to give the initial value of 2'. Details of this circuit are described in Japanese Patent Application No. 56-215271, so please refer to it. Further, as the out-of-synchronization detection circuit, various circuits described in Japanese Patent Application Laid-Open No. 17661/1982 can be used.

FIG. 3 is a block diagram of a second embodiment of the present invention, and is an embodiment using a transversal filter for the baseband band. Digital demodulator 1 that demodulates each polarized signal
3 and 13' are connected to a waveform equalizer 11.11' consisting of a baseband transversal filter and variable couplers 12 and 12', and a control having a reset function similar to that shown in FIG. It is controlled by a signal generator 14. The operating principle of the circuit shown in FIG. 3 is the same as that shown in FIG. 1, although the positions of the digital demodulator, variable coupler, and waveform equalizer are swapped, and the present invention allows the circuit shown in FIG.・Equivalent effects can be obtained.

FIG. 4 is a block diagram of a third embodiment of the present invention, which is aimed at a satellite communication system with less interference fading.
This is an example using control by perturbation method (Japanese Patent Application No. 56-055530). In FIG. 4, variable coupler 22.2
2' is composed of one variable weighting circuit, and the control signal 122' of the variable coupler 22' that removes the interference of the V polarization is unrelated to the demodulation output 120' of the H polarization; The control signal generator 26 generates the perturbation signal superimposed on the demodulated output 120 and the control signal 122'. Similarly, the control signal 12 of the variable coupler 22 that removes H-polarized interference
2 is a control signal generating section 26' that outputs V polarized wave 4 output 12.
Generated independently of 0. Therefore, ■ polarization demodulator 23
There is no fear that the out-of-synchronization will increase the interference of the H polarized wave, and the output 126 of the out-of-synchronization detector 25 is applied to the control signal generator 26 for the purpose of returning to the normal state when the synchronization is restored.
22' to an initial value. Similarly, the output 126' of the H polarization out-of-sync detector 23' is H
The control signal 12 is applied to the control signal generator 26' on the polarization side.
Reset 2. Note that 123 and 123' are reproduction output signals.

FIG. 5 is a block diagram of an embodiment of the control signal generators 26, 26' shown in FIG.
an oscillator 71 that generates a perturbation signal to be superimposed on the signal 22'; a correlator 72 that calculates the correlation between the error signal and the perturbation signal;
An integrator 73 having a reset function that divides the output of the correlator 72, an inverter 74 that inverts the output and creates a control signal, and an adder 75 that superimposes a perturbation signal on the control signal.
and an attenuator 76 that controls the magnitude of the superimposed perturbation signal.
and a low-pass filter 77 that calculates the average value of the error signal that controls the attenuator 76. According to this circuit, a perturbation is added to the output of the variable coupler 22, 22', and the error signal included in the attenuator 76 is perturbed. The direction of sequential control is determined by detecting the perturbation component caused by the correlator 72, and cross-polarization interference waves can be removed without using demodulated signal information of the opposite polarization. For details of the operating principle and circuit, please refer to the aforementioned Japanese Patent Application No. 56-055530. In the embodiments shown in FIGS. 1 and 3, the variable coupler is branched from before the waveform equalizer. However, the same effect can be obtained with waves. In addition, although it is configured so that an abnormal signal from the out-of-synchronization detector for one polarization causes both variable couplers to be reset, it is important to note that only the influence from the polarization side where the abnormality has occurred to the normal polarization side is affected. Even if you emphasize this and omit the reset to promote recovery, a corresponding effect can be obtained. Note that the control signal generation method is based on the ZF method algorithm, but the third
In the case of the baseband band shown in the figure, the well-known ME method is used together with the ZF method.
A similar effect can be expected by using the algorithm (root mean square equalization method). In addition, in the embodiment shown in FIG. 4, the variable coupler is made up of one variable weighting circuit, but the first
It is also possible to use the same transversal filter as shown in FIGS.

Historically, all of the above-mentioned embodiments detect and reset the digital demodulator when it is out of synchronization. It is configured to do
A code error detector is installed at the output of the digital demodulator to detect an error in the known code periodically sent from the transmitting side, thereby detecting an abnormality in the demodulated output, and detects an abnormality in the demodulated output when this error exceeds a certain value. Alternatively, the variable coupler may be reset when the output voltage deteriorates. In this case, a differential detection type digital demodulator can be used. Further, the reset method is not limited to the circuit of the embodiment shown in FIG. 2, but a more general circuit using an initial value setting power supply and a switching circuit can also be used, and the set value does not necessarily have to be 0 coupling. . In addition, although the explanation so far has been based on the case where the receiving station uses demodulated V and H double-side signals, it is also possible that a single station, such as a satellite communication ground station, does not necessarily use both-side signals. For example, in FIG. 4, when only V polarization is used, the variable coupler 22, the digital demodulator 23' and the out-of-synchronization detector 25 can be omitted. ' and the control signal generating section 26' can be omitted, and the effects of the present invention can still be achieved even if they are omitted altogether. Furthermore, the present invention is applicable even when each polarized wave is orthogonally modulated.

As explained in detail above, according to the cross-polarization interference cancellation circuit of the present invention, in an orthogonal polarization communication system that performs digital communication using two orthogonal polarizations, the demodulator for one polarization When an abnormality occurs in the output, there is an effect that at least the demodulated output of the other polarized wave is not degraded or the return to the normal state is accelerated when the abnormality is recovered.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of the reset circuit of FIG. 1, and FIG. 3 is a block diagram of a second embodiment of the present invention. FIG. 4 is a block diagram of a third embodiment of the present invention, and FIG. 5 is a block diagram of an embodiment of the control signal generating section of FIG. 4. 1, 1', 11, 11'... Waveform equalization amount, 2.2', 12°12', 22, 22'...
...Variable coupler, 3, 3', 13, 13',
. 23.23'...Digital demodulator, 4,14
...Control signal generator, 5.5', 15.15'
, 25.25'... Out-of-synchronization detector, 6, 26
．． 26'... Control signal generation section, 7, 7',
8, 8'... Reset circuit, 61, 63.
...AND/NAND gate, 62...
AND gate, 64...OR gate, 65...
...Integrator circuit, 66... Level 7 circuit, 70... Signal identification/1 difference detector, 71...
...Oscillator, 72...Correlator, 73...
...Integrator, 74...Inverter, 75...
... Adder, 76th l Figure Atsushi 2 mouths 5 Figure 3 1ri 5 High 4 Hard Z5 Figure η

Claims (1)

[Claims] at least one digital demodulator for demodulating a digitally modulated received signal of an orthogonal polarization communication system using two mutually orthogonal polarizations at the same frequency; at least one variable coupler capable of coupling the wave signal to the other polarized wave and controlling the amount of coupling by a control signal; and a variable coupler provided after the digital demodulator and the variable coupler and based on the demodulated baseband signal. a control signal generator for generating the control signal of the variable coupler; at least one abnormality detection means for detecting an abnormality in the demodulated output of the digital demodulator; At least one of the variable couplers is detected by the output of the detection means.
and a reset means for setting two outputs to predetermined values.