JPH0389641A - Cross polarization interference eliminating device - Google Patents

Abstract

PURPOSE:To suppress the transient response of an automatic gain control circuit in the case of the restoration of the reception signal level to a prescribed value by increasing the loop time constant of the automatic gain control circuit when the reception signal level is reduced to a value smaller than the prescribed value. CONSTITUTION:When the reception signal on the different polarization side is interrupted, an AGC circuit 8 receives the detection signal and is switched to increase the loop time constant. Consequently, when the reception signal is restored to the regular level, its variance is smoothed, and an excessive signal is not applied to an input terminal 2 on the different polarization side. Level detectors 3 and 4 release 'interruption-detection' after the proper time lapses when the reception signal is restored to the regular level. Thus, AGC circuits 7 and 8 restore the loop time constant to the original value, and the gain control is switched to that in normalcy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a cross-polarization interference canceling device used in an orthogonal polarization communication system that uses two mutually orthogonal polarized waves, and particularly relates to This invention relates to interference prevention technology when resetting a cross-polarization interference removal circuit, which is a component.

(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, conventionally, on the demodulation side in this type of digital wireless communication system, for example, the second
A crossed single-line wave interference canceling device as shown in the figure is provided.

The cross-polarization interference removal operation is sometimes performed in the intermediate frequency band and sometimes in the baseband (for example,
5-133156, Japanese Patent Application Laid-Open No. 59-77734>, the cross-polarization interference cancellation circuit 25 shown in FIG. 6 shows an example of an intermediate frequency type configuration. Circuit (automatic gain control circuit) 22. Same 2
3 are respectively prefixed, and these input terminals (20, 21
) Even if there is a level fluctuation in the received signal applied to the receiver due to fluctuations in the received electric field, etc., the received signal at a constant level is supplied to the input terminal (1°2) of the cross-polarization interference removal circuit 25. ing.

Among the received signals of the two orthogonal leakage waves, one received signal is demodulated by the demodulator 11 via the input terminal 1, and the other received signal is demodulated by the demodulator 12 via the input terminal 2. The input signal of the demodulator 11 is one received signal combined with the output signal of the transversal filter 5, and the input signal of the demodulator 12 is the other received signal combined with the output signal of the transversal filter 6. It has been made possible. Here, the transversal filter 5 takes as an input signal the branch reception signal 19 which is a part of the other reception signal, and the transversal filter 6 takes the branch reception signal 18 which is a part of one reception signal as an input signal,
Both are under the control of the control circuit 13 and perform similar operations.

That is, if one received signal is called a main polarization signal and the other reception signal is called a different polarization signal, the transversal filter 5 is
A signal with the same amplitude and opposite phase as the different polarization component leaked into the main polarization signal is generated based on the branch reception signal 19 which is a different polarization signal, and is converted into the main polarization signal at the input stage of the demodulator 11. At this time, the degree of coupling is determined based on the control signal 9 from the control circuit 13.

The control circuit 13 outputs an error signal from the demodulator on the main polarization side (demodulator 11 in the above example) and a reproduced data signal obtained from the demodulator on the different polarization side (demodulator 12 in the example above). Based on this, a control signal (9, 10) is formed and output, and the corresponding transversal filter (5°6) is controlled. For a specific control method, please refer to, for example, Japanese Patent Laid-Open No. 112739/1983.

By the way, when the input signal level of a demodulator drops extremely (this occurs due to fading, etc.) or when noise increases, the demodulator loses carrier synchronization and an abnormality occurs in the demodulated output. The polarization interference removal circuit 25 will no longer operate normally, and will instead inject interference into the main polarization signal.
The control circuit 13 has a function of resetting the cross-polarization interference removal circuit 25 in such a case. That is, the control circuit 13 obtains an asynchronous detection signal from the demodulator (11, 12), and when one or both of the demodulators 11 and 12 is out of synchronization, the control circuit 13 detects the asynchronous detection signal from the corresponding transversal filter (5, 12).
Each tap coefficient in 6) is set to zero to prevent a delay in recovery to normal control operation due to divergence of the transversal filter. The original purpose of this reset is to prevent even if the demodulator on the different polarization side becomes out of synchronization, it will not disturb the demodulator on the main polarization side, which is not out of synchronization. Please refer to the above-mentioned Japanese Unexamined Patent Publication No. 59-77734, which shows an example of the above-mentioned reset method.

(Problem to be Solved by the Invention) In this way, in the cross leakage interference removal circuit, 1'! When the t"A unit is out of synchronization, each tap coefficient of the transversal filter is set to zero, but from the original purpose of reset, this means that the attenuation (isolation amount) of each tap of the transversal filter is zero. This means that the attenuation amount is set to infinity, and it is necessary to have a predetermined amount of attenuation that at least allows the output signal level to be considered to be zero.However, in reality, variations in the scale and characteristics of the hardware of the transversal filter, etc. Since it is difficult to obtain the specified amount of attenuation required for the system, if a sudden change occurs in the level of the received signal of a different polarization, it will cause interference to the main polarization side demodulation system, resulting in poor characteristics. There is the problem of inviting people.

For example, as described above, the AGC circuit (22, 23) is installed in front of the cross-polarization interference removal circuit 25, but for maintenance etc., the input terminal 21 of the AGC circuit 23 on the side of different polarization is connected. Consider the operation when the input terminal 21 is disconnected, the input terminal 21 is reconnected after maintenance work is completed, and a signal is applied.

FIG. 3 shows the transient response characteristics of the AGC circuit 23 in such a case by changing the envelope line.
3, when an input signal is applied at time To, the output signal level increases rapidly and quickly reaches the maximum level A, then gradually decreases to a steady level at time T1, and maintains that normal level thereafter. do.

Therefore, the demodulator 12 on the different polarization side operates at time T. Of course, if the previous input signal was cut off, it would be in an asynchronous state, but at time T, time T! Since the input signal level is high during the period up to T1, the demodulator 12 remains out of synchronization during this period, and synchronization is established only at time T1.

Therefore, the transversal filter 5 is set to the reset state before time T1, including when the input signal is cut off, and is set to the reset state before time T1.
After l, the control mode will be switched to self*flt control mode.

Here, the problem is time T. Gara time T! This is the operation between wi up to . That is, in this time domain, the transversal filter 5 is in a reset state because the demodulator 12 is asynchronous, but as mentioned above, the amount of tap attenuation is finite due to variations in hardware, so the maximum level A is input. The signal leaks to the output of the transversal filter 5 without being attenuated completely, and is coupled to the input of the demodulator 11 as an interference wave, causing a problem that the characteristics of the main polarization signal are temporarily degraded. It is.

The present invention has been made in view of these conventional problems, and the object thereof is to provide a cross-polarization interference canceling device in which an automatic gain control circuit is provided in front of a cross-dissipating interference canceling circuit. Automatic gain 114 that appears when a sudden change occurs
It is an object of the present invention to provide a cross-polarization interference canceling device that can suppress the transient response of a circuit and thereby prevent temporary deterioration of cross-polarization interference cancellation characteristics.

(Means for Solving the Problems) In order to achieve the above object, the cross-polarization interference removing device of the present invention has the following tank bottom.

That is, the cross-polarization interference canceling device of the present invention includes two systems of automatic gain control circuits that perform automatic gain control on each of the received signals of two orthogonal polarizations to maintain a constant output signal level; A cross-polarization system configured to receive the outputs of each control circuit and remove the other signal (different polarization side signal) that has leaked into one signal (main polarization side signal) using a transversal filter. wave removal circuit;
A cross-polarization interference canceling device comprising; two levels of level detectors that emit a detection signal when the input signal level of each of the two lines of automatic gain control circuits becomes equal to or less than a specified value; The automatic gain control circuit is configured to increase a loop time constant in response to detection signals from corresponding ones of the two series of level detectors.

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

When the received signal level on the different polarization side of the two series of automatic gain control circuits falls below the specified value, for example, when "input is cut off", the automatic gain control circuit on the different polarization side will change the loop time constant. works to increase the size.

Therefore, when the received signal level on the different polarization side recovers to the specified value, the transient characteristic shown in Figure 3 above will change due to the large loop time constant. is smoothed, and the different polarization side input of the cross polarization interference removal circuit does not reach an excessive level.

In this way, it is possible to prevent temporary deterioration of cross-polarization interference removal characteristics.

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

FIG. 1 shows an example of the configuration of a cross-polarization interference canceling device according to an embodiment of the present invention. Components that are the same as those of the conventional device are given the same reference numerals and their explanations will be omitted.

In the present invention, as shown in FIG.
22, 23>, an AGC circuit <7.8) with a variable or switchable loop time constant is provided, as well as a level detector (3, 4) for detecting a change in the level of the received signal. , the loop time constant of the AGC circuit (7, 8) can be changed by the detection signal of the level detector (3, 4).

Specifically, when the received signal on the side of the different polarization becomes "off", the AGC circuit 8 receives the detection signal and switches to increase the loop time constant. As a result, when the received signal recovers to its normal level, the transient characteristics shown in Figure 3 above would normally be exhibited by increasing the loop time constant, so the fluctuations will be smoothed out and the side of the different polarization will be An excessive signal will not be applied to the input terminal 2 of.

That is, it is possible to prevent temporary characteristic deterioration as in the prior art to the demodulation system on the main polarization side of the cross-polarization interference removal circuit 25.

Note that the level detectors (3, 4) release the "off detection" after an appropriate period of time when the received signal has recovered to the normal level. As a result, the AGC circuit (7, 8>) returns the loop time constant to its original value and shifts to normal gain control.

(Effects of the Invention) As explained above, according to the cross-polarization interference canceling device of the present invention, the loop time constant of the automatic gain control circuit is increased when the received signal level falls below a specified value. Therefore, when the received signal level recovers to the specified value, the transient response of the automatic gain control circuit can be suppressed.As a result, it is possible to prevent excessive signals from being input to the cross-polarization interference cancellation circuit.
This has the effect of preventing temporary deterioration of cross-polarization interference removal characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a cross-polarization interference removal device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional device, and FIG. 3 is a diagram of transient response characteristics of an AGC circuit on the side of different polarization. It is. 1.2, 20.21...Input terminal for received signal,
3.4...Level detector, 5,6...
・Transversal filter, 7, 8...A
GC circuit, 11.12... Demodulator, 13...
...Control circuit, 14.15...Output terminal,
25...Cross polarization interference removal circuit.

Claims (1)

[Claims] two systems of automatic gain control circuits that perform automatic gain control on each of the received signals of two orthogonal polarizations to keep the output signal level constant; a cross-polarization interference removal device comprising: a cross-polarization removal circuit configured to perform a removal operation centered on a transversal filter of the other signal (different polarization side signal) that has leaked into the other signal (polarization-side signal); and; In: Two series of level detectors are provided which emit a detection signal when the input signal level of each of the two series of automatic gain control circuits becomes equal to or less than a specified value; A cross-polarization interference canceling device characterized in that the loop time constant is increased in response to a detection signal of a corresponding level detector.