JPH01188128A - Interference compensation circuit between cross polarized waves - Google Patents

Abstract

PURPOSE:To make a system applicable even when a main signal and an interference signal differ by using a 3rd frequency conversion circuit so as to apply frequency shift in a way of maintaining the relation between the leaked frequency of an interference signal component onto a main signal and the frequency of the main signal before and after frequency conversion and detecting the interference signal by the same carrier as that of the main signal. CONSTITUTION:Let the oscillated frequencies of 1st and 2nd local oscillators be respectively fVL, fHL and the oscillated frequency of a 3rd local oscillator be (fVL-fHL), then the frequency of the interference signal outputted from the 3rd frequency conversion circuit 43 is higher than the intermediate frequency of the main signal by (fVL-fHL). The frequency (fVL-fHL) is coincident with a difference (fV-fH) between the frequency of the main signal and the frequency of the interference signal. Thus, the difference between the intermediate frequency of the main signal obtained from the 1st frequency conversion circuit 4 and the frequency of the interference signal obtained from the 3rd frequency conversion circuit 43 is the difference from the frequencies of the main signal and the interference signal. Thus, sufficient interference compensation is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a cross-width interwave interference compensation circuit in a digital communication system.

``Prior art'' In wireless transmission systems, signals are transmitted independently using polarization planes that are orthogonal to each other in the same frequency band, that is, vertical (V) polarization and horizontal (I4) polarization. It is possible to obtain twice the transmission capacity of the transmission method. However, in order to realize this transmission system using orthogonal polarization, it is necessary to eliminate interference between both width waves and maintain their degree of separation above a certain value. The technique for this purpose is called cross-polarization interference compensation.

An example of the configuration of a conventional cross-polarization interference compensation circuit is shown in FIG. Below, FIG. 8 will be explained.

The main signal received from the main antenna l for main signal reception ° (in this case ■polarized wave and a digital signal) is subject to interference from signals of other systems (in this case ■ interference from polarized wave). There is. This main signal passes through a horizontal/vertical (H/V) polarization splitter 2, passes through a channel filter 3 inserted as necessary, and is converted into an intermediate frequency band by a frequency conversion circuit 4.

On the other hand, the signal that is the source of interference is obtained from the horizontal and vertical polarization splitter, and after passing through the channel filter 5 inserted as necessary to improve the S/N, the signal is sent to the main signal receiver. Using a local oscillation signal from a common local oscillator 7, the frequency conversion circuit 6 converts the signal into an intermediate frequency band.

This interference signal is passed through a variable combiner VC comprising a delay circuit 8.9 with a delay time T (T is the data period), a complex weighting circuit +0.11°12, and an adder 13. In the variable coupler VC, the complex weighting circuit +0.11.12 is adjusted to create a compensation signal having an opposite phase and equal amplitude to the interference component leaked into the main signal. This compensation signal is supplied from the adder 13 to the adder 14, where it is added to the main signal output from the frequency conversion circuit 4 to cancel interference components in the main signal.

Note that the delay adjustment line τ1 inserted on the output side of the frequency conversion circuit 4 is used to adjust the times of the main signal system and the interference signal system.

The weighting circuits to, 11 and 12 are controlled as follows. The output signal of the adder 14 is fed to a demodulator DM in order to detect the in-phase and quadrature components of the interference components remaining therein. This demodulator DM uses a reference carrier wave 23 reproduced from the main signal.

That is, the reference carrier wave 23 is supplied to the quadrature phase coherent detection circuit 15 via the 90 degree phase shifter 24, and is also directly supplied to the quadrature phase coherent detection circuit 16.
The output of the in-phase component is obtained from the detector circuit 6, and the output of the orthogonal component is obtained from the detection circuit 15.

After passing through harmonic removal filters 18 and 17, these signals are passed through an error signal generation circuit 102 that detects residual interference components.
．． 101 to obtain an in-phase component error signal e+ and a quadrature component error signal eQ.

The error signal generation circuits 102 and 101 include the identification circuit 20
．． 19 and subtractors 22 and 21, outputs the difference between the input and output of the discrimination circuit 20 as an in-phase component error signal e□, and outputs the difference between the input and output of the discrimination circuit 19 as a quadrature component error signal eQ. It is something.

On the other hand, the interference signal output from the frequency conversion circuit 6 is transmitted through a delay adjustment line τ that adjusts the time between the interference signal system and the main signal system.
After passing through 2, it is detected in the same way as above.

That is, using a fundamental carrier wave 31 and a 90 degree phase shifter 32,
The signal is detected by quadrature phase synchronous detection circuits 25 and 26, an in-phase output is obtained from the detection circuit 26, and an orthogonal output is obtained from the detection circuit 25. After passing through harmonic removal filters 28.27, these signals are binarized through identification circuits 30.29 and output as polar signals a+, ac).

As described above, the error signals (subtraction 322.21 output) ex, eQs obtained from the main signal component and the polarity signals al, aQ obtained from the interference wave component are input to the variable coupler control circuit 33, and the variable coupler Complex weighted control signals Ci-3 and Ct output from the control circuit 33.

CI□ is utilized to control the multiple search weighting circuits 10, 11, 12, typically by a zero-forcing algorithm.

FIG. 9 shows a specific circuit example of the complex weighting circuit IO. Note that the complex weighting circuits II and 12 are similarly configured.

An interference signal from the frequency conversion circuit 6 shown in FIG. 8 is input to the hybrid board 37. This long sword signal is distributed by the hybrid 37 and input to multipliers 35 and 36. These multipliers 35 and 36 include a variable combiner control circuit 33.
, the weighted control signal CI-1 (= Xt-+ +
jYt-+) is supplied.

That is, the multiplier 35 receives the weighting control signal Yt-
+ is supplied, and the multiplier 36 is supplied with a weighting control signal X+-
+ is supplied. After arbitrary weighting, the signals are combined by a 90-degree combiner 34, and the output thereof is supplied to the adder 13 (FIG. 8).

The variable coupler control circuit 33 is shown in FIG. Demodulator DM
The error signals eq, e+ and polarity signal aQ obtained from
. Exclusive OR39. The outputs of the exclusive and OR 39a are summed through a resistor 40 and input to an integrator 41, which outputs complex weighted control signals Ct-, , C□, C□, 1, thereby producing the above-mentioned results. weighting control is performed.

``Problems to be Solved by the Invention'' The conventional cross-polarization interference compensation circuit described above works when the main signal and the interference signal have the same frequency, but when the frequency difference between the main signal and the interference signal is large, Couldn't use it.

This is due to the following reason.

As shown in FIG. 11(a), consider a case where the main signal (V polarization; frequency rv) and the interference signal (H polarization; frequency fu) have different frequencies. Here, it is assumed that interference occurs in a certain frequency band of the main signal from the interference signal (the shaded area in the figure).

When the main signal and interference signal are frequency-converted to an intermediate frequency band, the result is as shown in FIG. 11(b). In other words, since the frequency is converted so that the intermediate frequency of the main signal and the intermediate frequency of the interference signal match, the interference component (
(the shaded area in the figure) and the frequency of the interference signal that caused this interference will be shifted.

Therefore, when the conventional cross-polarization interference compensation circuit shown in FIG. The result was random, and no interference compensation effect could be achieved.

The present invention was made against this background, and an object of the present invention is to provide a cross-polarization interference compensation circuit that operates normally even when the main signal and the interference signal do not have the same frequency.

"Means for Solving the Problems" In order to solve the above problems, the present invention provides a main antenna for receiving a main signal, an interference signal receiving means for receiving an interference signal, and a main antenna for receiving an interference signal. first and second local oscillators that generate first and second local oscillation signals having a frequency difference equal to the frequency difference of the interference signals; and a first local oscillator that converts the frequency of the main signal by the first local oscillation signal. a frequency conversion circuit that converts the interference signal into the second frequency conversion circuit;
a second frequency conversion circuit that performs frequency conversion using a local oscillation signal; and a third frequency conversion circuit that generates a third local oscillation signal having a frequency equal to the frequency difference between the eleventh and second local oscillation signals.
a third frequency conversion circuit that converts the frequency of the output signal of the second frequency conversion circuit using the third local oscillation signal; a variable coupler that outputs a Mi-compensated signal that cancels interference components included in the main signal; an addition circuit that adds the output signal of the variable coupler and the output signal of the first frequency conversion circuit; and the variable coupler and a variable coupler control circuit that supplies a weighting control signal to the variable coupler control circuit.

To summarize the above, the points are that the third frequency conversion circuit shifts the frequency so that the relationship between the frequency of the interference signal component leaking into the main signal and the frequency of the main signal is maintained before and after frequency conversion. The most important feature is that the interference signal is detected using the same carrier wave as the main signal. In the conventional technology, the main signal and the interference signal have the same frequency, but the present invention is different in that it can be applied when these frequencies are different.

"Operation" According to the above configuration, the frequency is converted to the intermediate frequency band while maintaining the mutual relationship between the frequency of the interference component in the main signal and the frequency of the interference signal that caused this interference. Therefore, by using the main signal and interference signal obtained from these intermediate frequency bands, it becomes possible to obtain a correct compensation signal and perform sufficient interference compensation.

FIG. 11(c) shows this situation.

Here, the frequency of the main signal is fv, and the frequency of the interference signal is f
o, these intermediate frequencies as ``.,'' and ``, respectively.

+, (rov=r.,,), let the oscillation frequencies of the first and second local oscillators be f VL, !, respectively. '＋□,
If the oscillation frequency of the third local oscillator is (fvLrHL) (see Figure 1 for this), the frequency of the interference signal output from the third frequency conversion circuit is lower than the intermediate frequency of the main signal (rvt fHL). only becomes higher. This frequency (fvL-fHL) matches the difference (fv-f□) between the frequency of the main signal and the frequency of the interference signal. Therefore, the difference between the intermediate frequency of the main signal obtained from the first frequency conversion circuit and the frequency of the interference signal obtained from the third frequency conversion circuit is the difference in frequency between the main signal and the interference signal. That is, the relationship between the frequencies of the main signal and the interference signal is maintained before and after frequency conversion, making it possible to obtain a correct compensation signal. As a result, sufficient interference compensation is achieved.

"Example" Hereinafter, the present invention will be described in detail with reference to the drawings.

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

The main signal received from the main antenna l passes through the horizontal and vertical polarization splitter 2, and then passes through the channel filter 3 inserted as necessary, and is then connected to the main signal local oscillator 7 and the first frequency conversion circuit 4. is converted to an intermediate frequency.

On the other hand, the signal that is the source of interference is obtained through the main antenna 11 and horizontal/vertical polarization splitter 2, and its S/N is adjusted as necessary.
The signal is sent to a channel filter 5 inserted to improve the signal. The output of the channel filter 5 passes through the channel filter 3 having the same characteristics as the main signal, and after filtering out the main interference component that has entered the main signal, the output is converted into a second signal using the interference signal local oscillator 42. The frequency conversion circuit 6 converts the signal into an intermediate frequency. Note that the main antenna 1 and the horizontal/vertical polarization splitter 2 constitute interference signal receiving means.

The output of the frequency conversion circuit 6 is transmitted to the third frequency conversion circuit 43.
is supplied to The frequency conversion circuit 43 includes a local oscillator "5".
A third local oscillation signal is supplied from 45, mixed with the output signal of the frequency conversion circuit 6, and a difference signal thereof is output. In this case, the intermediate frequencies of the main signal and the interference signal are frequency-converted so that they match.

Here, the frequency of the main signal is fv, and the frequency of the interference signal is f
II, these intermediate frequencies are respectively r. V and fo++(fov=fa)I), the oscillation frequencies of the first and second local oscillators 7.42 are respectively f VL,
f HL% The oscillation frequency of the LaO2 part oscillator 45 is (f
vL-rllL), the third frequency conversion circuit 43
The intermediate frequency of the interference signal output from is higher than the intermediate frequency of the main signal by (rv, , -r, L).

This frequency (fv+-rot,) corresponds to the difference between the frequency of the main signal and the frequency of the interfering signal (rv-ro). Because, fvt I'uL” (fYfov) Qu fo
H)=fv f.

This is because the following formula holds true.

As a result, the intermediate frequency r of the main signal obtained from the first frequency conversion circuit 4. The difference between ν and the intermediate frequency of the interference signal obtained from the third frequency conversion circuit 43 is shown in FIG.
), this is the difference in frequency between the main signal and the interference signal. That is, the relationship between the frequencies of the main signal and the interference signal is maintained, making it possible to obtain a correct compensation signal. As a result,
Sufficient interference compensation can be obtained.

The output of the frequency conversion circuit 43 is the hybrid 37,
The multipliers 35 and 36 are inputted to the variable coupler VC composed of the multipliers 35 and 36 and the 90-degree combining 4B4, and the multipliers 35 and 36 are controlled so as to cancel the interference wave component included in the main signal.
The adder 14 adds it to the main signal.

Control of multipliers 35 and 36 is performed as follows. The interference signal is split into an in-phase component and a 90-degree component by a 90-degree splitter 44, and the main signal is split into in-phase components by a hybrid 37, and their correlations are taken by multipliers 35a and 36a to produce respective correlation signals. are input to the integrator 2341 for averaging, and the output signals of these integrators 41 control the multipliers 35 and 36.

As a result, an interference compensation signal is output from the 90-degree combination 4a4 of the variable coupler VC, and this compensation signal is added to the main signal by the adder 14 to perform interference compensation. In addition,
The above components 35a and 36a.

37, 41, and 44 constitute the variable coupler control circuit CT.

Although the above-mentioned first embodiment shows variable coupler l-tap control, multi-tap control can be considered in the same way.

FIG. 2 shows a configuration in which the variable coupler is under 3-tap control, and constitutes a second embodiment of the present invention.

This second embodiment has three variable couplers VCI to VC3 and three control circuits CT1 to CT3, each of which is similar to that of the first embodiment. That is, each variable coupler VCI-VC3 includes a hybrid 37, a multiplier 35 .
36 and a 90-degree composite 4a4, and each input terminal of variable couplers VCI, VC2, and VC3, that is, the input terminal of each hybrid 37, is connected to each tap of a 3-tap delay circuit 8.9. . Note that the operation of this embodiment is
Same as tap control, but generally more than l-tap.
Better interference compensation characteristics can be obtained.

FIG. 3 is a diagram illustrating a third embodiment of the present invention.

In the first embodiment, the multiplier 35 of the complex weighting circuit
．． 36 was controlled using a correlation signal in an intermediate frequency band, whereas in this third embodiment, a correlation signal in a baseband band is used.

The connection from the main antenna l to the demodulator DM is the same as in the first embodiment described above.

Control of multipliers 35 and 36 is performed as follows.

Adder! The main signal output from 4 is supplied to the demodulator DM. This is to detect the in-phase and quadrature components of the remaining interference components. The demodulator DM uses the reference carrier wave 23 reproduced from the main signal. That is, the reference carrier wave 23 is supplied to the quadrature phase coherent detection circuit 15 via the 90 degree phase shifter 24, and is also directly supplied to the quadrature phase coherent detection circuit 16. As a result, the in-phase component of the main signal is obtained from the detection circuit 16, and the orthogonal component of the main signal is obtained from the detection circuit 15. After passing through harmonic removal filters 18.17, these signals are passed through two error signal generation circuits 102.101 for detecting residual interference components to generate an in-phase error signal and a quadrature error signal. A signal "eQ" is obtained.

The interfering signal is also demodulated using the same reference carrier 23 as above. That is, the reference carrier wave 23 is supplied to the quadrature phase coherent detection circuit 25 via the 90 degree phase shifter 32, and is also directly supplied to the quadrature phase coherent detection circuit 26.
The in-phase component of the interference signal is obtained from the detection circuit 26, and the orthogonal component of the interference signal is obtained from the detection circuit 25. After passing through harmonic removal filters 28.27, these signals are binarized through identification circuits 30.29 and output as polarity signals al.

It is output as aQ.

In this way, the error signal obtained from the main signal component, that is, the output signal eo, es of the subtractor 21.22, and the polarity signal 2L□, aQ obtained from the interference wave component are input to the variable coupler control circuit 33a, Multiplier 3 by its output signal C4
Control 5.36. Note that the variable coupler control circuit 33a
is composed of a part of the variable coupler control circuit 33 shown in FIG. 10 (the part that forms the weighting control signal cl).

Note that the functions and effects of this embodiment are similar to those of the first embodiment.

In this third embodiment, the case where the variable coupler vc is controlled with one tap has been described, but the same applies to multi-tap control.

Figure 4 shows the three variable couplers VCI-VC3.
This figure shows the configuration of tap control and constitutes a fourth embodiment of the present invention. The configuration of this 3-tap control part is as follows:
This is similar to the case of the second embodiment shown in FIG. Further, the variable coupler control circuit 33 is similar to that shown in FIG. 1O. The operation of this embodiment also conforms to one-tap control.

FIG. 5 shows the configuration of a fifth embodiment of the present invention, which is a configuration in which the orthogonal component of the interference signal baseband is removed from the fourth embodiment.

That is, the variable coupler control circuit 46 has a configuration lacking the orthogonal component ao of FIG. 3, and its configuration is as shown in FIG. 6.

FIG. 7 shows the configuration of a sixth embodiment of the present invention, in which the configuration of the variable coupler (transversal filter section) of the fifth embodiment is changed.

That is, the weighting signal X l-1+ X t+ X
One adder 14a adds the outputs of the three multipliers 36 each having r*+ as its input, and performs three multiplications using the weighting signal y□-1+ y sr Y +, + as each input. Each output of the adder 35 is added by another adder 14a, and then these two adders +4
The outputs of a are combined by a 90 degree combination 4a4, and this combination result is output as the output signal of the variable coupler VC, and this output is added to the intermediate frequency signal of the main signal in the adder 14. It is now possible to do so.

In addition, in the fifth and sixth embodiments described above, a delay circuit with multiple taps was used for the variable coupler, but the first delay circuit in FIG.
It is also possible to use a variable coupler l-tap without a delay circuit similar to the embodiment.

Further, in each of the embodiments described above, the main signal and the interference signal are passed through the channel filter 3, but this is not essential. However, by using a channel filter, the compensation effect can be further increased. This is because, as shown in Figure 1+ (a), the broken line part of the interference signal is removed by the channel filter, and only the part that actually caused interference (the solid line part of the interference signal in the figure) is extracted. .

Furthermore, it is possible to use an A/D converter as one method for realizing the identification circuit and the error signal generation circuit. For example, if the main signal is 16QAM, the demodulated signal will be a 4-value signal, so if you sample it with an A/D converter that has an output of 3 bits or more, the most significant bit will be a polar signal, as shown in Figure 12. The third most significant bit becomes a binary signal representing an error signal.

Furthermore, in the variable coupler control circuits 33, 33a, 46, the polarity signals aQ, a-- are shown as binarized digital signals, but a binarizing circuit is not necessarily required. In this case, an analog multiplier may be used instead of the digital multiplier (exclusive OR) in the variable coupler control circuit.

"Effects of the Invention" As explained above, the present invention is capable of compensating cross-polarization interference when the main signal and interference signal do not have the same frequency using a frequency shift configuration, similar to the cross-polarization interference compensation circuit having the same frequency. It has the advantage of being able to handle

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the first embodiment that best represents the features of the present invention, FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of the fourth embodiment of the present invention, FIG. 5 is a block diagram of the fifth embodiment of the present invention, and FIG. 6 is the block diagram of the fifth embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a variable coupler control circuit according to an embodiment. FIG. 7 is a block diagram showing the configuration of a sixth embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of a conventional interference compensation circuit. Figure 9 is a diagram showing the configuration of the complex weighting circuit in the interference compensation circuit, Figure 10 is a circuit diagram showing the configuration of the variable coupler control circuit in the interference compensation circuit, and Figure 11 is a diagram showing the configuration of the variable coupler control circuit in the interference compensation circuit. FIG. 12 is a diagram for explaining these relationships and the relationship between intermediate frequency signals in different cases, and FIG. 9 is a diagram for explaining a level diagram of a four-level A/D converter. l...Main antenna, 2...Horizontal/vertical polarization splitter, 3.5...Channel filter, 4.6...
... Frequency conversion circuit, 7 ... Local oscillator, 8.9 ... Delay circuit, 10.11.12 ... Complex weighting circuit, +
3.14, l4a-adder, 15.16. ．． 2
5.26...Quadrature phase synchronous detection circuit, 17.1
B, 27.28...Harmonic removal filter, 1
9.20, 29.30...Identification circuit, 21.2
2...Subtractor, 23.31...Reference carrier wave, 24.32...90 degree phase shifter, 33...
...Variable coupler control circuit, 34...90 degree synthesis 4.35.36...Multiplier, 37...
Hybrid, 38...Delay circuit, 39...
...Exclusive OR, 40...Resistor, 41.
...Integrator, 42...Local oscillator for interference wave signal, 43...
...Frequency conversion circuit, 44...90 degree divider,
45... Local oscillator, 46... Variable coupler control circuit, 101.102
...Error signal generation circuit. VC...variable coupler, CT...variable coupler control circuit. Applicant: Nippon Telegraph and Telephone Corporation Figure 9 11 circuits with double weights Figure 12 Special Elephant Channel Fo+ (C) & f0V (fvt-f HL)

Claims (1)

[Claims] A main antenna for receiving a main signal, an interference signal receiving means for receiving an interference signal, and first and second antennas having a frequency difference equal to the frequency difference between the main signal and the interference signal. first and second local oscillators that generate local oscillation signals; a first frequency conversion circuit that converts the frequency of the main signal using the first local oscillation signal; and a first frequency conversion circuit that converts the frequency of the main signal using the first local oscillation signal; a second frequency conversion circuit that performs frequency conversion based on a signal; a third local oscillator that generates a third local oscillation signal having a frequency equal to the frequency difference between the first and second local oscillation signals; a third frequency conversion circuit that frequency converts the output signal of the frequency conversion circuit using the third local oscillation signal; a variable coupler that outputs a canceling compensation signal; an adder circuit that adds the output signal of the variable coupler and the output signal of the first frequency conversion circuit; and a variable coupler that supplies a weighting control signal to the variable coupler. 1. A cross-polarization interference compensation circuit comprising: a controller control circuit;