JPH02295242A - Cross polalization interference eliminating circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of characteristic of a demodulation system of the main polarization side by providing a limiter before or after a transversal filter which produces a signal to eliminate the hetero polarization signal component leaked into a main polarization signal. CONSTITUTION:When the demodulators 9 and 10 are synchronous with each other and at the same time the signals of the input terminals 1 and 2 are kept at the normal levels, a transversal filter 5 is controlled by a control circuit 11 to eliminate the hetero polarization component leaked into the main polarization. A limiter 3 which is limited by the threshold amplitude is set before or after the filter 5 when a hetero polarization reception signal has an amplitude larger than the threshold amplitude before said reception signal is stabilized at a steady level. Thus the deterioration of characteristic can be prevented for a demodulation system of the main polarization side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cross-polarization interference cancellation circuit used in a digital wireless communication system using two orthogonal polarizations.

[Conventional technology]

In wireless communication systems, two orthogonal polarized waves (vertical polarized wave and horizontal polarized wave, or left-handed circularly polarized wave and right-handed circularly polarized wave) of the same frequency are sometimes used in order to utilize frequencies effectively. Orthogonal polarized waves generate cross-polarized waves due to anisotropy of the medium quality due to rain, etc., and cross-polarized waves interference occurs between the two polarized waves.

As a cross-polarization interference removal device suitable for digital wireless communications, it controls the transversal filter based on the information of the demodulated baseband signals of both the main polarization side receiving interference and the different polarization side providing cross-polarization. Devices for removing waves have been proposed (for example, JP-A-55-133156, JP-A-59-7-7-7-3-4, etc.).
. In such equipment, if the demodulator loses carrier synchronization due to an extreme level drop due to phasing or an increase in noise due to different polarization, and an abnormality occurs in the demodulated output, the cross-polarization interference removal circuit will not operate properly. , on the contrary, interference will be injected into the main polarized wave, so it is necessary to reset at this time. In Japanese Patent Application Laid-open No. 59-77734,
A method has been proposed in which the transversal filter installed in the cross-polarization interference removal circuit is reset when carrier synchronization loss of the demodulator on the side of different polarization is detected or when the bit error rate on the side of different polarization is abnormally degraded. has been done.

The conventional technique will be further explained with reference to FIG.

In FIG. 3, block 24 is a cross-polarization interference cancellation circuit according to the prior art, 1.2 is the main polarization and different polarization reception signal input terminals, and 5 and 6 are for removing interference signals that have leaked in. transversal filter for
and 10 are demodulators, 11 are transversal filters 5 and 6, and 1 indicates output terminals of demodulators 9 and 10, respectively.

In order to cancel the different polarization signal that has leaked into the main polarization signal in the propagation path, based on the branch reception signal 15 of the different polarization that is the interference wave,
The transversal filter 5 generates a signal with the same amplitude and opposite phase as the different polarization signal component mixed into the main polarization signal input to the human input terminal 1. Interference components are suppressed by combining with the received signal.

The transversal filter 5 is controlled by a control circuit 11 that generates a control signal based on the error signal obtained by the demodulator 9 and the reproduced signal obtained by the demodulator 10. For a specific control method, please refer to Japanese Unexamined Patent Application Publication No. 112739/1984, as an example thereof is shown. The control circuit 11 inputs the detection signals of the demodulators 9 and 10, and when either or both of the demodulators 9 and 10 are asynchronous,
In order to prevent the transversal filter 5 from diverging and delaying the recovery of I control, the transversal filter 5.
It has a function to set each of the 6 tap coefficients to zero.

An example of a reset method is JP-A-5-9-7 7-7-3
This is disclosed in Publication No. 4, so please refer to it.

[Problem that the invention seeks to solve]

A problem with the conventional cross-polarization interference removal circuit 24 described above is the amount of isolation (attenuation amount) of each tap of the transversal filter 5. Ideally, in accordance with the original purpose of resetting, the output signal level of the transversal filter 5 should be set to zero in order to avoid disturbing the demodulator key 9. In other words, each of the transversal filters 5 It is desirable that the tap has an infinite amount of attenuation, but it is difficult to obtain the required amount of attenuation due to variations in hardware scale and characteristics.

For this reason, as shown in FIG.
In a system where circuits (automatic gain control circuits) 22 and 23 are connected, when the manual signal 21 of the AGC circuit 23 on the different polarization side is disconnected for maintenance etc. and then reconnected, the following occurs. perform an action. That is, AGC circuit 2
3, the different polarization side demodulator 10 is in an asynchronous state, so the transversal filter 5 is placed in a reset state through the control circuit 11 as described above. After this, when a signal is suddenly connected to the input of the AGC circuit 23, the output level of the AGC circuit 23 first reaches an excessive level and then settles down to a required constant level, as shown in FIG. The reason for this is that the AGC circuit 23 exhibits certain finite transient response characteristics. Explaining FIG. 4, the AGC circuit input signal is cut off until time T0, and a signal is input at time T0. A is the AGC circuit for time T,
Synchronization is established. Therefore, before time T, the transversal filter 5 was placed in a reset state, and at time T,
After that, it switches to automatic control mode. The problem here is between time T0 and T1, and the following problems occur. That is, in this time domain, the transversal filter 5 is in a reset state because the demodulator 10 is asynchronous, but as described above, the amount of tap attenuation is finite due to hardware variations, etc., so an excessive level A is input. Then, the signal leaks to the output of the transversal filter 5 without being attenuated completely, and the demodulator:! This will be fed into the input of P9 as an interference wave, and the characteristics of the main polarized wave will be temporarily degraded.

An object of the present invention is to provide cross-polarization interference that can prevent characteristic deterioration in the demodulation system on the main polarization side even if an excessively high level signal is applied to the transversal filter from the different polarization side when resetting the transversal filter. The object of the present invention is to provide a removal circuit.

[Means to solve the problem]

The cross-polarization interference cancellation circuit of the present invention includes a two-series demodulator that demodulates two systems of digitally modulated received signals of an orthogonal polarization communication system that uses two mutually orthogonal polarizations, and A transversal device is installed in front of the first demodulator on the side of the demodulator that removes mixed polarization signals, and is capable of combining signals of different polarization into the main polarization and controlling the amount of coupling using a control signal. The transversal filter includes a filter, a limiter provided before or after the transversal filter, and a control circuit connected to the two systems of demodulators for controlling the transversal filter.

〔Example〕

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

customer An embodiment according to the invention is shown in FIG.

1 is a main polarization reception signal input terminal, 2 is a different polarization reception signal input terminal, 5 and 6 are transversal filters for suppressing cross-polarization interference, 3 and 4 are limiters, and 9 and 10 are each a main polarization reception signal input terminal. The demodulators 11 on the wave side and the different polarization side are control circuits for controlling the transversal filters 5 and 6, and also have a reset function as described above.

7 and Y8 are control signals for transversal filters 5 and 6, 14 and 15 are branch outputs of each received signal, and 1
2 and 13 indicate output terminals of demodulators 9 and 10.

To explain the operation of the embodiment shown in FIG. 1 in the case of removing cross-polarization interference that has entered the main polarization, the demodulator 9
and 10 are in a synchronous state and the signals at input terminals 1 and 2 are at normal levels, the transversal filter 5 is controlled by the control circuit 11 to remove the different polarization components that have leaked into the main polarization. .

As shown in FIG. 4, when the different polarization received signal has an amplitude that exceeds the threshold amplitude B before settling down to a steady level, as shown in FIG. Limiter 3 that is limited by amplitude B before
By providing this, it is possible to prevent characteristic deterioration of the demodulation system on the main polarization side.

The limiter 3 can be composed of two diodes, as shown in FIG. 2 as an example. In this case, the threshold amplitude B is determined by the forward voltage value of each diode.

Note that the same effect can be obtained even if the limiter 3 is placed after the transversal filter 5.

〔Effect of the invention〕

As explained above, the present invention provides a limiter before or after the transversal filter that creates a signal that cancels out the different polarization signal components mixed into the main polarization signal.
Even if the signal on the side of different polarization that is branched toward the transversal filter reaches an excessive level when the transversal filter is reset, it is possible to prevent characteristic deterioration in the demodulation system on the main polarization side.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
A circuit diagram of the limiter 3 in the figure, FIG. 3 is a block diagram of an example of a conventional cross-polarization interference removal circuit, and FIG. 4 is a circuit diagram of the AGC circuit 23 in FIG. AGC transmitter, 5.6... Transversal filter, 12.13... Demodulator 9
, 1l output terminal, 1 4, 5... Branch reception signal.

Claims (1)

[Claims] Demodulating two series of digitally modulated received signals of an orthogonal polarization communication system that uses two mutually orthogonal polarizations 2
A demodulator is installed in front of the first demodulator on the side that removes the mixed polarization signal that has leaked out of these two demodulators, and combines the mixed polarization signal with the main polarization signal. A transversal filter whose coupling amount can be controlled by a control signal, a limiter provided before or after the transversal filter, and a control circuit connected to the two systems of demodulators to control the transversal filter. A cross-polarization interference removal circuit characterized by: