JPH04286234A - Cross polarization interference removal circuit - Google Patents

Abstract

PURPOSE:To execute reset before a bit error is caused by detecting the abnormality of a different polarization side demodulation system by providing a demodulation system abnormality detecting means in which the detection of the out-of-synchronism of a carrier wave and the detection of the disconnection of power supply of a demodulator are combined. CONSTITUTION:An AND gate 6, 6' monitors the abnormality signal 104, 104' of an out-of-synchronism detector 4, 4' and the abnormality signal 105, 105' of a power supply disconnection detector 5, 5; and when either of the abnormality signals is detected, it generates immediately the abnormality signal 106, 106'. In this case, a reset circuit 8, 8' generates the control signal 101, 101' of a variable coupler 2, 2' by integrating a correcting signal 103, 103 and when it receives the abnormality signal 106, 106' of the AND gate 6, 6', it sets the control signal 101, 101' to a predetermined initial value. Then, the correcting signal 103, 103' of the variable coupler 2, 2' is generated by obtaining correlation between the input signals of V and H and the error signals of reverse polarization H, V.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-polarization interference removal circuit applied to digital wireless communications.

0002

[Background Art] In recent years, in microwave radio communication, orthogonal polarization communication uses two orthogonal polarized waves of the same frequency (vertical and horizontal or left-handed circularly polarized wave and right-handed circularly polarized wave) to effectively utilize frequencies. The method is attracting attention. 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 two polarized waves. Therefore, various cross-polarization interference removal circuits have been proposed as circuits for removing this interference. However, in the above communication system, if an abnormality occurs in the demodulated output of one polarized wave (hereinafter referred to as different polarized wave), the cross-polarization interference cancellation circuit that is controlled using this demodulated information will not operate properly. The other polarized wave (hereinafter referred to as self-polarized wave)
This has the drawback of causing negative effects such as an increase in the amount of interference.

[0003] Conventionally, as a cross-polarization interference canceling circuit to eliminate this drawback, for example, Japanese Patent Publication No. 12136/1983 discloses an abnormality detection means for detecting carrier synchronization loss of a digital demodulator (hereinafter referred to as demodulator). A circuit has been proposed that has a reset means for setting the output of the cross-polarization interference cancellation circuit to a predetermined value using the output of the cross-polarization interference circuit, and has a function of suppressing an increase in the amount of interference to self-polarized waves. FIG. 4 shows a block diagram of this conventional example.

This conventional circuit includes digital demodulators 21 and 21' of a synchronous detection type that are connected to intermediate frequency IF outputs of V and H polarized waves and demodulate digital signals;
, H, and the variable couplers 22 and 22' are composed of IF band transversal filters that branch the IF outputs of IF outputs of oppositely polarized waves and couple them to the IF outputs of oppositely polarized waves, and whose coupling amount can be controlled, and demodulated baseband signals 120 and 120. a control signal generator 23 that generates control signals 121, 121' for the variable couplers 22, 22' based on
and an out-of-synchronization detector 24, 24' for detecting out-of-synchronization. The control signal generator 23 is composed of a control signal generator 27 and reset circuits 28 and 28'.
The control signal generator 27 receives a baseband input signal 120.
, 120', a reproduction function that estimates the transmitting side signal and reproduces the reproduction signal outputs 122, 122', and input signals 120, 120' and output signals 122,
122', and a function of generating correction signals 123 and 123' for sequentially correcting each control signal by determining the correlation between this error signal and the input signal. The reset circuits 28, 28' integrate the modified signals 123, 123' and output the variable couplers 22, 2.
2' control signals 121, 121', and abnormal signals 125, 125' of the out-of-synchronization detectors 24, 24'.
This circuit sets the control signal to a predetermined initial value when it receives the signal. The variable coupler correction signals 123 and 123' are generated by correlating the V and H input signals with the oppositely polarized H and V error signals, respectively. When the variable couplers 22, 22' are configured, for example, by a 3-tap transversal filter having three taps, leading, middle, and following, the control signals 121, 121' control the tap coefficients of the three taps, respectively. Each of the leading and trailing tap control signals is obtained by shifting the input signals 120 and 120', which are correlated with the error signal, forward or backward by one bit. Reset circuits 28, 28' are abnormal signal 1
25 and 125' set all tap coefficients to "0".

[0005] Now, different polarization (Here, it is assumed to be H polarization.)
If an abnormality occurs in the demodulation system, the demodulated signal becomes unstable and does not include baseband signal information transmitted with H polarization, even if bit synchronization is maintained by the demodulated output of the self-polarized wave. Therefore, the signal 120' and the self-polarized signal 1
A variable coupler 22 that minimizes the interference of different polarizations included in the self-polarized waves by determining the correlation with the error signal obtained from 20.
' control loop does not operate normally and control signal 121'
becomes indeterminate and fluctuates as meaningless disturbance information that happens to appear as a correction signal 123'.
There is a possibility that a signal that increases the interference rather than canceling the interference received by the self-polarized wave may be outputted to the output 127' of the variable coupler 23'. It causes it to get bigger. Similarly, the output 127 of the variable coupler 22, which is controlled by determining the correlation between the error signal obtained from the demodulated signal 120' of the different polarization and the signal 120 of the self-polarization, becomes unstable, and This increases the interference of the digital demodulator 21' and delays the recovery of carrier synchronization of the digital demodulator 21' and the return of the variable coupler 22 to normal operation. This relationship applies to the digital demodulator 2 on the V polarization side.
The same holds true when an abnormality occurs in the output 120 of 1. A conventional cross-polarization interference cancellation circuit with a reset function detects an abnormality in the demodulator output by monitoring an out-of-sync signal inside the demodulator using an out-of-sync detector, and then detects an abnormality in the output of the demodulator by monitoring an out-of-sync signal inside the demodulator. All tap coefficients of the transversal filter are set to "0", and the output of the variable coupler is set to "0".
We aim to eliminate these shortcomings by resetting it so that it becomes .

[0006]

[Problems to be Solved by the Invention] In such conventional circuits, when a sudden abnormality occurs, such as a power cut in the demodulation system of a different polarization, the output of the demodulation system immediately becomes unstable; Detection involves a time delay inherent to the detection circuit. That is, until the cross-polarization interference removal circuit is reset, there is a drawback that bit errors occur in the self-polarization demodulated signal due to disturbances in this circuit.

The present invention eliminates such drawbacks and detects demodulation system abnormalities on the side of different polarization using a demodulation system abnormality detection means that combines carrier wave synchronization detection of the demodulator and power failure detection, and detects abnormalities in the demodulation system on the side of different polarization. It is an object of the present invention to provide a cross-polarization interference cancellation circuit having means for performing a reset beforehand.

[0008]

[Means for Solving the Problems] The present invention provides a digital demodulator that demodulates each polarization signal that has been digitally modulated using an orthogonal polarization communication method that uses two polarization signals that are orthogonal to each other and have the same frequency; a variable coupler that is provided on the input side of the digital demodulator and couples one polarized wave signal to the other polarized wave and the amount of coupling is controlled by a control signal; a control signal generator provided on the output side of the coupler and generating a control signal given to the variable coupler based on the demodulated baseband signal; In the cross-polarization interference removal circuit, the cross-polarization interference removal circuit includes an abnormality detection means for setting the value of the control signal generated to the variable coupler to a predetermined value, wherein the abnormality detection means detects an abnormality in the demodulated output of the digital demodulator. The present invention is characterized in that it includes a first detection means for detecting, and a second detection means for detecting power-off of the power supply supplied to the demodulation system including the digital demodulator and the control signal generation circuit.

[0009] Here, the variable coupler may be provided on the output side of the digital demodulator, corresponding to the digital demodulator.

0010

[Operation] When the power to the demodulation system is cut off, the output of the demodulation system immediately becomes unstable. If this is detected as an out-of-synchronization, there will be a delay due to the time constant of the detector, and a bit error will occur in the normal composite signal, so the power-off is detected and the variable coupler is immediately reset.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention, which includes digital demodulators 1 and 1' using a synchronous detection method that are connected to intermediate frequency IF outputs of V and H polarizations and demodulate digital signals; Variable couplers 2, 2' each consisting of an IF band transversal filter that branches the H IF output and couples it to the oppositely polarized IF output, the amount of coupling being controllable.
and demodulated baseband signals 100, 100'
Control signals 101 and 10 for variable couplers 2 and 2' based on
a control signal generator 3 that generates a signal 1'; and desynchronization detectors 4, 4' that detect desynchronization of the digital demodulators 1, 1'.
, power-off detectors 5 and 5' for detecting a power-off of the demodulation system, and AND gates 6 and 6' that perform the logical product of the outputs of these two detectors.

That is, in this embodiment, FIGS. 1 and 2
As shown in FIG. 1, digital demodulators 1 and 1' demodulate each of the polarization signals that have been digitally modulated by an orthogonal polarization communication method that uses two polarization signals that are orthogonal to each other and have the same frequency. variable couplers 2 and 2', which are provided on the input side or the output side corresponding to 1 and 1', and couple the signal of one polarization to the other polarization, and the amount of coupling is controlled by a control signal; A control signal generator that is provided on the output side of the digital demodulators 1 and 1' and the variable couplers 2 and 2' and generates a control signal to be applied to the variable couplers 2 and 2' based on the demodulated baseband signal. 3 and digital demodulators 1 and 1
The present invention further comprises an abnormality detecting means for setting the value of the control signal generated by the control signal generator 3 to the variable couplers 2 and 2' to a predetermined value when an abnormal state of ' is detected. As a means for detecting abnormality, the abnormality detection means is
The signals are supplied to a demodulation system consisting of out-of-sync detectors 4 and 4', which are first detection means for detecting abnormal demodulated outputs of digital demodulators 1 and 1', digital demodulators 1 and 1', and control signal generation circuit 3. It includes power-off detectors 5 and 5' which are second detection means for detecting power-off of the power source.

Next, the operation of this embodiment will be explained. In this embodiment, the output of the above-mentioned detection circuit is set to negative logic in order to cope with the power-off. The control signal generator 3 includes a control signal generator 7 and reset circuits 8, 8', and the control signal generator 7 receives baseband input signals 100, 100.
A reproduction function that identifies and determines the signal on the transmitting side and reproduces the reproduced signal outputs 102 and 102', and input signal 1
00, 100' and output signals 102, 102', and correction signals 103, 103' that sequentially modify each control signal by finding the correlation between this error signal and the input signal. Equipped with a function to generate AND gates 6 and 6' are out-of-sync detectors 4 and 4
' and the abnormal signals 105, 105' of the power-off detectors 5, 5' are monitored, and when any one of the abnormal signals is detected, the abnormal signal 1 is immediately activated.
06, 106' are generated. Reset circuit 8, 8'
integrates the correction signals 103, 103' to generate control signals 101, 101' for the variable coupler, and upon receiving the abnormal signals 106, 106' from the AND gates 6, 6', determines the control signals 101, 101' in advance. This circuit sets the initial value. The correction signals 103 and 103' of the variable couplers 2 and 2' are generated by determining the correlation between the V and H input signals and the oppositely polarized H and V error signals, respectively. When the variable couplers 2 and 2' are configured, for example, by a 3-tap transversal filter having three taps, leading, middle, and trailing, the control signals 101 and 101' control the tap coefficients of the three taps, respectively. The leading and trailing tap control signals each have an input signal 100 or 100 that correlates with the error signal.
It is obtained by shifting 100' forward or backward by 1 bit. The reset circuits 8, 8' set all the leading, middle, and succeeding tap coefficients to "0" by the abnormal signals 106, 106'.

The reason for excluding the waveform equalizer in this case is that the presence of the waveform equalizer has no effect on the inherent performance improvement of the present invention. Even if a waveform equalizer is required due to line design, the performance improvement achieved by the present invention is not affected by adding it, and a corresponding effect can be obtained. In FIG. 1, both the V and H polarization inputs are signals obtained by converting radio signals of the same or substantially the same frequency modulated at the same bit rate to an intermediate frequency by the same local oscillator. By the way, there are two types of abnormalities in the demodulator output: one is when the bit error rate of the output gradually deteriorates due to the effects of fading, and the other is when the power to the demodulation system is cut off due to a sudden accident and the output becomes unstable instantaneously. be. In the former case, the line characteristics gradually deteriorate, and even just before carrier synchronization is lost, the demodulated output on the different polarization side contains sufficient information to control the variable coupler. That is, even if carrier synchronization is detected after it has been lost and the reset function is activated thereafter, the self-polarization side demodulated output is not adversely affected at all, and the conventional reset function is sufficiently effective. However, in the latter case, the output of the demodulator on the different polarization side becomes unstable immediately, but the out-of-sync signal has a propagation delay time due to the time constant of the large capacitance included inside the demodulator and out-of-sync detector. . As a result, during the delay time until the reset is performed, bit errors occur in the self-polarization side demodulated signal due to disturbance in the cross-polarization interference removal circuit.

However, when a power outage occurs, the power supply voltage immediately goes to "0" without any delay time, so only the power supply voltage is monitored, and when the voltage falls below the threshold, the variable coupling is immediately turned off. By resetting the device, abnormalities on the side of different polarization will not affect the side of self-polarization, and it is possible to prevent bit errors that occur in the conventional case.

As described above, the present invention has a demodulation system abnormality detection means that combines a demodulator output abnormality detection means such as a carrier synchronization detector on the side of different polarization and a demodulation system power failure detector, which can replace the conventional reset function. Use it more effectively.

FIG. 3 is a circuit diagram of an embodiment of the power failure detectors 4, 4' in FIG.
51 is set so that it exceeds the high/low level judgment threshold. When the power supply voltage is normal, the buffer output 152 is at a high level, but as soon as the power is turned off, the buffer output 152 is at a high level.
becomes a low level, and an abnormal signal is transmitted to the AND gates 6 and 6' in FIG.

FIG. 2 is a block diagram of a second embodiment of the present invention, which is an embodiment using a baseband transversal filter. Variable couplers 12 and 12' consisting of baseband transversal filters are connected after the digital demodulators 11 and 11' that demodulate the signals of each polarization, and generate a control signal having a reset function similar to that shown in FIG. control unit 13.

In the embodiments shown in FIGS. 1 and 3 described above, both variable couplers are reset by an abnormal signal from the out-of-synchronization detector of one polarization. A corresponding effect can be obtained even if emphasis is placed only on the influence of the other side on the normal polarized wave side and omitting the reset to promote recovery. In addition, in FIGS. 1 and 3, the demodulator output abnormality is detected by losing synchronization, but instead of the former, a code error detector is provided at the output of the digital demodulator, and the signal is sent periodically from the transmitting side. A detector may be used that detects an abnormality in the demodulated output by detecting an error in the known code received and generates an abnormal signal when this error deteriorates beyond a certain value.

[0020]

[Effects of the Invention] As explained above, when the power supply to the demodulation system on the different polarization side is cut off, the power supply interruption can be instantly detected, and an abnormality in the output on the different polarization side can be detected. At least this has the effect of not degrading the demodulated output on the self-polarized wave side or hastening the return to the normal state when the abnormality is recovered.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a block configuration diagram showing the configuration of a second embodiment of the present invention.

FIG. 3 is a circuit connection diagram showing the configuration of a power-off detector included in the embodiment of the present invention.

FIG. 4 is a block configuration diagram showing the configuration of a conventional example.

[Explanation of symbols]

1, 1', 11, 11', 21, 21' Digital demodulator 2, 2', 12, 12', 22, 22'
Variable coupler 3, 13, 23 Control signal generator 4, 4', 14, 14', 24, 24' Out-of-synchronization detector 5, 5', 15, 15' Power-off detector 6, 6', 16, 16' And gate 7, 27
Control signal generator 8, 8', 28, 28' Reset circuit 51, 5
2 Resistor 53 Buffer

Claims (2)

[Claims] Claim 1: A digital demodulator that demodulates each polarization signal digitally modulated by an orthogonal polarization communication method using two polarization signals that are orthogonal to each other and have the same frequency; A variable coupler is provided on the input side of the digital demodulator and the variable coupler is provided on the output side of the digital demodulator and the variable coupler, the coupling amount of which is controlled by a control signal. a control signal generator that generates a control signal to be applied to the variable coupler based on the demodulated baseband signal; and a control signal generator that generates a control signal to be applied to the variable coupler when an abnormal state of the digital demodulator is detected. In the cross-polarization interference removal circuit, the cross-polarization interference removal circuit includes an abnormality detection means for setting the value of the control signal to a predetermined value, the abnormality detection means comprising a first detection means for detecting an abnormality in the demodulated output of the digital demodulator; A cross-polarization interference removal circuit comprising: second detection means for detecting power-off of a power supply supplied to a demodulation system comprising the digital demodulator and the control signal generation circuit. 2. The cross-polarization interference removal circuit according to claim 1, wherein the variable coupler is provided on the output side of a digital demodulator in correspondence with the digital demodulator.