JPS59139739A - Cross polarization interference deleting circuit - Google Patents

Abstract

PURPOSE:To stabilize the control regardless of the relation between the input frequency and the modulating speed by controlling the relation in phase between the taps of a transversal filter so as to obtain the same phase. CONSTITUTION:An input signal S0 is reduced to a delay signal S1 by a delay circuit 1, further to a delay signal S2 by a delay circuit 2. The signal S0 is branched and passes through phase compensating delay circuits 12 and 12' to be multiplied by a control signal by variable weighting circuits 3 and 6 respectively. In the same way, signals S1 and S2 are branched and pass through phase compensating delay circuits 13 13' as well as 14 and 14' to be multiplied by the control signals by variable weighting circuits 4 and 7, and 5 and 8 respectively. The output signals of circuits 3-5 and 6-8 are synthesized by signal synthesizing circuits 9-10 to be reduced to signals RS and IS, and outputted after synthesizing through a 90 deg. directional coupler 11 so as to obtain the 90 deg. phase relation between both signals. In such a way, the circuits 12-14' are provided at the tap input side to select the signals S0 and S2 in phase within a -90 deg.- +90 deg. range to the signal S1. In such a way, the correct control regardless of the relation between the input carrier frequency and the modulating speed is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interference compensation technique for cross-polarized waves that occurs due to the shared use of orthogonally polarized waves in wireless transmission, and in particular, to a technique for eliminating cross-polarized waves interference in a cross-polarized communication power system. The present invention relates to a cross-polarization interference removal circuit provided in an intermediate frequency band.

Microwave band wireless communications are rapidly developing, centering on terrestrial communications and satellite communications. The demand for wireless communication is expected to further increase in the future due to the expansion of mobile communication services, etc., and along with the development of frequency bands above quasi-miljon waves, so-called frequency reuse of current frequency bands with high practical value is required. There is a growing belief that The CCI (International Radiocommunication Consultative Commission) recommendations regarding FM radio frequency allocation between 4 and 5 GHz clearly specify the use of orthogonal polarization. In addition, in satellite communications, IN-based SAT (International Telecommunication Satellite Organization) is likely to put into practical use technology for sharing orthogonal polarization in the 4-6 GHz band, which has been used with single polarization on V time series satellites. It is.

In order to achieve this shared use of orthogonal polarization, it is important to improve the polarization characteristics of antennas and power supply equipment, as well as develop cross-polarization compensation circuits that compensate for deterioration of polarization characteristics during radio wave propagation due to rain, etc. It's on the agenda.

Originally, free space is a transmission line that is independent of two orthogonal polarized waves and can transmit both waves simultaneously, but in actual propagation paths, there is anisotropy in the medium such as rain, and it is difficult to use orthogonal polarized waves. If this method is adopted, the coupling between polarized waves due to the generation of cross-polarized waves will cause interference between channels of different polarizations.

Cross polarization compensation technology automatically compensates for such coupling between polarized waves by providing a compensation circuit within an antenna feeder or wireless device.

Conventionally, microwave band communication has centered on analog transmission centered on FM, so the cross-polarization compensating force method described above also uses a variable phase shifter and an attenuator around the antenna feeder to restore orthogonality. Methods that perform this, and methods that eliminate interference between different polarized waves by installing an interference wave compensation circuit in the intermediate frequency band, have been well studied and put into practical use.

In recent years, as digital transmission has come into use in the microwave band, there is a need to propose a more efficient cross-polarization compensation system that takes advantage of the characteristics of digital transmission.

In response to the above requirements, a cross-polarization compensation circuit that performs the cross-polarization compensation power formula in the baseband band based on demodulated baseband signal information in digital transmission was proposed, and it Through this, it has become possible to perform digital transmission that uses orthogonal polarization at the same carrier frequency. Regarding such a cross-polarization compensation circuit, there is a patent application filed in 1983-2 filed by the same applicant as the present application.
It is described in detail in the specification of No. 4764.

Now, it is known that if this type of cross-polarization compensation circuit is provided in the intermediate frequency band, the circuit configuration will be much easier than if it is provided in the baseband band.

However, when using a transversal filter as a variable coupling circuit for interference wave removal in the intermediate frequency band of the crisscross polarization communication power type, the input carrier frequency is selected to be equal to a positive integer multiple of the modulation rate. If the phase rotation with respect to the carrier wave in the delay circuit is an integer multiple of 2π, and the phase difference between each tag is not equal, this is a problem. Under conditions that are not equal to double, a phase difference occurs between each tap, and the ZF method has the drawback that it cannot be used as it is.

The present invention has been made to eliminate the above-mentioned drawbacks inherent in the prior art, and it is therefore an object of the present invention to provide a stable and stable signal even under conditions where the input carrier frequency is not equal to a positive integer multiple of the modulation rate. An object of the present invention is to provide a novel cross-polarization interference cancellation circuit that can perform control.

In order to achieve the above object, the present invention provides a transformer, (-Sal filter type variable In the cross-polarization interference canceling circuit in which the coupling circuit is biased, instead of using the known method of selecting the delay time of the signal delay circuit of the transnosal filter to be the reciprocal of the modulation speed of the digital orthogonal amplitude modulated wave that is the input signal, Even if a frequency offset occurs in the carrier frequency, the phase relationship between the taps is a specific phase relationship, and by choosing a value that is close to the reciprocal of the modulation rate,
That is, the structure includes a phase correction delay circuit that adjusts the phase relationship between the tags of the transversal filter so that they are substantially in phase with each other, and the input carrier frequency is equal to a positive integer multiple of the modulation speed. This makes control using the ZF method possible even under conditions where there is no such condition.

Hereinafter, a preferred embodiment of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, the input quadrature amplitude modulated wave is a 16-value quadrature amplitude modulated wave, and the variable coupling circuit is a 3-tap transversal filter provided in a medium frequency band.

In the figure, reference number 1.2 is a delay circuit constituting a transversal filter selected to be the reciprocal of the modulation rate of the input modulation signal, 3.4.5.6.7.8 is a variable weighting circuit, and 9. 10 is a signal synthesis circuit, 11 is a 90° force-directed coupler, and 12.12', 13.13', and 14.14' are carrier waves between taps of transversal filters so that the phase relationship is almost in phase with each other. The phase correction delay circuits that adjust (correct) are shown respectively.

The following explanation applies to a general L value (L=l'', l is an integer of 2 or more), and can be similarly applied to an N-tap (N is a positive integer) intermediate frequency band transversal filter. The explanation does not lose its generality.

The input signal So is a signal Sl delayed by the delay circuit 1.
The signal is further delayed by the delay circuit 2 and becomes the signal S2. The signal So is branched and sent to the phase correction delay circuit 12.
12', each variable weight signal is combined with a control signal in circuits 3 and 6. Further, the signal 8z is branched and multiplied by the phase correction delay circuits 13 and 13', respectively, and the variable weighting circuits 4 and 7 combine the signals with the control signals. Similarly, the signal S2 is also branched and passed through the phase correction delay circuit 14, and variable weighting is performed by circuits 5 and 8.
At , the control signal and the multiplication are combined. In the case of variable weighting, the output signals of the circuits 3 to 5 are combined in a signal combining circuit 9 to become a signal R8. - For power and variable weighting, the output signals of circuits 6 to 8 are synthesized by a signal synthesis circuit 10 to become a signal Is. The signals R8 and Is are combined in a 90° force-directional coupler 11 so that their phases are in a 90° relationship with each other,
An output signal is obtained.

Conventionally, in a cross-polarization interference removal circuit using an intermediate frequency band transverse filter, for the demodulated baseband signal and the error signal generated more frequently,
The ZF algorithm was not generally applicable. It is applicable only when the carrier frequency (fC) of the input modulation signal is equal to a positive integer multiple of the modulation rate (fS) of the input modulation signal.

In this case, the phase rotation of the carrier wave due to the delay times τl and τ2 in the delay circuit shown in FIG.

S has the same phase, so if there are no phase correction delay circuits 12.12', 13.13' and 14.14' in FIG.
14.14' delay time is all 0 seconds) method can be applied.

However, when fc=Nfm (N is a positive integer), the signals So, 8z, and 8g do not necessarily have the same phase, so the control system does not operate correctly. In other words, the conditions for correct operation are , the signal 81 is set to the reference phase (σ
), the signal of another tap (So
, 8 may be within the phase range of 190° to +90°.

Therefore, as shown in FIG. 1, phase correction delay circuits 12 to 14' are prepared on the input side of the taps, and the phases of the signals SO and Ss after passing through each tap are as follows. -90° when signal 8z is the reference phase (θ°)
By selecting it within the range of +900, it is possible to perform correct control even when the carrier frequency (fc) of the input modulation signal is not equal to a positive integer multiple of the modulation speed (f8) of the input modulation signal. It is.

Moreover, regarding the amount of delay, the phase correction delay circuit 12.
12', 13.13', and 14.14' are generally negligible amounts compared to the delay circuit 1.2, and do not impair the interference removal ability of the variable coupler.

In the above embodiment, a case has been described in which the input quadrature amplitude modulated wave is a 16-level quadrature amplitude modulated wave and the transversal filter provided in the intermediate frequency band is 3 taps, but the present invention is limited to this embodiment. It goes without saying that the scope of the present invention is not limited to this, and includes various modifications and changes within its scope.

As described above, according to the present invention, a simple ZF type algorithm is applied to the intermediate frequency band variable coupler under the condition that the input carrier frequency is not equal to a positive integer multiple of the modulation rate. Since the circuit can also be controlled stably, the circuit scale can be reduced and digitalization is easy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment according to the present invention. 1.2・Φ・Delay circuit, 3 to 8...Variable weighting circuit, 9.10...Signal synthesis circuit, 11...and 90° force directional coupler, 12.12', 13. 13', 14.14'
...Delay circuit for phase correction patent applicant NEC Corporation Representative Patent attorney Yutabe Kumagai

Claims (1)

[Claims] In order to remove the mixed polarization that has leaked into an orthogonal polarization communication system that uses two polarized waves that are orthogonal to each other, the signals of different polarization are combined into the main polarized wave in the intermediate frequency band, and the amount of coupling is calculated. In a cross-polarization interference removal circuit equipped with a transversal filter type variable coupler that can be controlled by a control signal, a phase correction delay is adjusted so that the phase relationship of carrier waves between taps of the transversal filter is almost in phase with each other. 1. A cross-polarization interference removal circuit, comprising: a circuit for correctly controlling the carrier wave frequency of an input modulation signal and the modulation speed of the input modulation signal, regardless of the relationship between the carrier wave frequency of the input modulation signal and the modulation speed of the input modulation signal.