JP2828910B2 - Interference wave removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interfering wave removing circuit for removing an interfering wave incident from a side lobe region of a main antenna in a communication receiver or the like. In particular, the present invention relates to an interfering wave removing circuit for providing an auxiliary antenna separately from a main antenna and removing an interfering wave based on a signal input from the auxiliary antenna in a closed loop configuration.

[0002]

2. Description of the Related Art A method for removing unnecessary interference waves incident from a side lobe region of a main antenna by providing another auxiliary antenna in a receiving device of a communication device or the like generally uses a side lobe canceller (hereinafter referred to as SLC). Also known as

[0003] Inside the receiving device, a portion for removing an interfering wave may be any of RF, IF, and video bands. In addition, various algorithms are used for removing the interference wave. In general, I
A method of forming a closed loop circuit in the F band is used. FIG. 4 shows an example in which an SLC circuit is provided in the IF band of the receiving device. The received signal from the main antenna 1 is input to the RF amplifier 3a and amplified. Then, the amplified signal wave mixer 4a inputs the amplified signal wave mixer 4a and converts it into an IF signal. The converted IF signal is input to a band-pass filter (hereinafter, referred to as BPF) 6a, and an unnecessary signal outside the IF band is removed. The signal from which unnecessary signals have been removed is
The signal is input to the IF amplifier 7a and amplified. This amplified signal wave is input to the SLC circuit 8 as a main channel signal.

On the other hand, the reception signal of the auxiliary antenna 2 is transmitted to the RF amplifier 3b and the mixer 4 in the same manner as the main channel signal.
b, through the BPF 6b and the IF amplifier 7b, is input to the other terminal of the SLC circuit 8 as an auxiliary channel signal. Note that a common local signal is applied from the local oscillator 5 to the mixers 4a and 4b. The SLC circuit 8 receives the main channel signal and the auxiliary channel signal, and based on the auxiliary channel signal, an occurrence of interference is removed from the main channel signal. Then, a signal from which the interference is removed is output.

FIG. 5 shows a configuration example of a conventional SLC circuit. The main channel signal is subjected to a power divider (hereinafter, referred to as PD) after the interference is subtracted by the subtractor 20.
). One of the equally divided signals is taken out as an SLC output, and the other is further supplied to the PD 17. Then, the signal is further equally divided in the PD 17.

On the other hand, the auxiliary channel signal is divided into equal parts by the PD 10 and then to the limiter amplifiers 11 and 90.
° is supplied to the hybrid 12. This limiter amplifier 1
In 1, the so-called limiting-amplified auxiliary channel signal is converted into two signals having different phases from each other in the 90 ° hybrid 15. That is, this 9
In the 0 ° hybrid 15, the signal is divided into I and Q signals having different phases by 90 °. The I and Q signals are
The two signals output from the PD 17 are correlated with each other. This correlation is taken in the two correlators 16a and 16b as shown in FIG. Thus, two baseband signals are output from the correlators 16a and 16b. These two baseband signals are amplified in amplifiers 18a and 18b, respectively, and are integrated in integrators 19a and 19b. In this way, the correlation between the I and Q signals in the auxiliary channel and the signal in the main channel has been determined. The other signal equally divided in the PD 10 is 9
It is supplied to the 0 ° hybrid 12. The 90 ° hybrid 12 converts the auxiliary channel signal into I and Q signals having phases different from each other by 90 °, similarly to the above-described 90 ° hybrid 15. As shown in FIG.
These two I and Q signals are modulated by the two baseband signals in modulators 14a and 14b, respectively, and power-combined in a power combiner (hereinafter referred to as PC) 13. An IF signal is obtained by the power combining in the PC 13. Since the obtained IF signal has the same amplitude and the same phase as the main channel IF signal, the interference signal component of the main channel is removed by combining the two in the subtractor 20.

As described above, in principle, the amplitude ratio, the phase difference, and the information are obtained between the signals of the main channel and the auxiliary channel, and these differences are corrected by the modulator, and the signal of the main channel and the signal of the main channel are corrected. By creating the same signal, if the same signal is subtracted from the main channel, only the interference wave component can be obtained.

As described above, the closed loop SLC
The rejection ratio of the interfering wave in the circuit will be described below when only the interfering wave is input. The conventional S shown in FIG.
In the LC circuit, the subtractor 20, the PD 21, the correlator 16
a or 16b, amplifier 18a or 18b, integrator 19a
Or 19b, the modulator 14a or 14b, the PC 13, and the subtractor 20 by the two closed-loop operations of the I channel and the Q channel, so that only the interference wave is input. Integrator output signal of the thus when only disturbance is the loop operation is converged by being inputted, i.e. the modulator signal _{W J is, W J = W OPT Gh |} X | / (1 + Gh | X |) ... (1) G in this equation (1) is the gain in the loop, h
Is the output voltage of the limiter amplifier, and X is the input voltage from the auxiliary channel side of the modulator. W _OPT is an optimum value for completely removing interference, and is expressed by the following equation (2).

[0009] _{W OPT = J M / J A} ... (2) J A of the equation (2) is the input signal to the auxiliary channel of the SLC circuit. Also, the J _M is an input signal to the main channel, which is a complex number having an amplitude and phase information.

[0010] For jammer, the modulator generates a different I and Q signals 90 ° out of phase with each other, a complex operation is performed by the auxiliary channel input signal and the W _J, results main channel input signal of the operational And the interference wave is removed. Here, the rejection ratio CR of the interference wave is represented by the following equation (3).

CR = 1 / (1 + Gh | X |) (3) As described above, the operation of removing the interference wave by the SLC circuit configured by the closed loop is assisted by following the W _OPT as described above. The control is performed so that the correlation value between the channel and the main channel signal becomes zero. That is, the closed loop in this conventional example constitutes one servo system. The loop gain becomes Gh | X |, which depends on the circuit constant and the auxiliary channel input voltage, respectively.

[0012]

In the conventional interfering wave removing circuit shown in FIG. 4, when the signal input to the auxiliary channel of the SLC circuit is only the interfering wave, the above equation (3) is used. As shown in (1), an effect of removing an interfering wave depending on the loop gain is expected.

However, the input signal to the auxiliary channel of the SLC circuit is generally not only an interference wave. That is, it includes thermal noise generated or amplified in the input portion of the auxiliary channel system and the front end. If the disturbance power is not negligible compared to the power of this noise,
The actual rejection ratio of the interference wave is not only the loop gain,
/ N ratio (the ratio between the interference wave input to the auxiliary channel of the SLC circuit and the thermal noise power). Therefore, there is a problem that the effect of removing the interference wave by the set loop gain cannot be obtained as expected.

The cause of such a phenomenon will be described below with reference to FIG. FIG. 6 shows a state in which the modulation signal is shown on the X, Y complex plane. It should be noted that an I or Q error signal which is a source of a closed-loop following operation in the Z-axis direction is shown for convenience. Further, the amplitudes of the interference waves input to the main channel and the auxiliary channel of the SLC circuit are assumed to be equal.

When only the interference wave is input, the SLC
The circuit operates at any point (W) on the complex plane that depends on the voltage ratio and phase difference of the interfering waves received by the main antenna and the auxiliary antenna.
_OPT ) as a target value, and a modulated signal at a point (W _J ) determined according to the loop gain is generated. As a result, an interference wave is removed.

On the other hand, when no interference wave is input to the auxiliary channel and only thermal noise is added, there is no correlation between the thermal noise and the thermal noise input to the main channel. Therefore, the SLC circuit sets the origin on the complex plane to the target value (W
_A so-called following operation is performed as _OPTN ). As a result, a modulated signal at a point (W _N ) determined according to the loop gain is generated. In the above operation for thermal noise, the target value is always the origin on the complex plane. The operation of the SLC circuit for controlling the correlation value to 0 by not sending the subtraction signal from the modulator to the main channel side is the same as the case where only the interference wave is input.

Next, the case where the interference wave and the thermal noise are input simultaneously will be described. In this case, the two operations, that is, the case where only the interference wave is input and the case where only the thermal noise is input, are superimposed. SLC
The circuit attempts to follow two target values W _OPT and W _OPTN . However, since these two points are different, the follow-up forces of the closed loop attract each other and the error signal becomes zero.
At the point (W _JN ), and the following operation stops.
This is shown in FIG. In FIG.
_{The OPT} is a point at which the interference wave is completely removed. The error signal for the interference wave becomes 0, but an error signal proportional to the thermal noise power appears. On the other hand, an error signal proportional to the power of the interference wave appears in W _OPTN .

In the region where the J / N ratio is small as described above, the follow-up of the SLC circuit to the W _OPT due to the thermal noise input to the auxiliary channel is pulled toward the origin depending on the J / N ratio. There is a problem that a rejection ratio of an interference wave depending on a gain cannot be obtained. For example, when the loop gain is 40 db, under ideal conditions where no thermal noise is input, the rejection ratio of the interfering wave is approximately −40 dB.
b, but when the J / N ratio is 1, the removal ratio can only be obtained up to about -6 db. An object of the present invention is to improve such a drawback, eliminate the restriction on the rejection ratio of an interference wave caused by thermal noise in a region where the J / N ratio is small, and obtain a high interference wave rejection ratio.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to receive a signal from a main antenna and an auxiliary antenna for suppressing a disturbance wave, and to receive a disturbance wave incident from a side lobe region of the main antenna. Power measurement for measuring the sum of the power of the interference wave input via the auxiliary antenna and the power of the thermal noise generated or amplified by the interference wave removal circuit itself in the interference wave removal circuit that removes the noise in a closed loop configuration Means, based on the sum of the power of the disturbing wave and the thermal noise measured by the power measuring means, power ratio calculating means for calculating the ratio of the power of the disturbing wave and the power of the thermal noise,
A sample / hold circuit for sampling / holding the modulated signal generated by the closed loop operation; and a sample / hold circuit for amplification / amplitude according to the power ratio calculated by the power ratio calculation means.
A DC amplifier that amplifies the modulation signal held by the hold circuit, an output signal of the DC amplifier, and a changeover switch that selects one of the modulation signal and outputs the selected signal; An interference wave elimination circuit, comprising: correcting a modulation signal obtained by a closed loop operation, and removing an interference wave in a closed loop by using the corrected modulation signal.

[0020]

The changeover switch according to the present invention removes an interference wave caused by thermal noise by removing an interference wave with an open-loop modulation signal corrected based on the modulation signal obtained by the closed-loop operation. The deterioration of the ratio can be prevented.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment S of the present invention.
An LC circuit is shown. The SLC circuit shown in FIG. 1 is obtained by adding predetermined circuits or components to the conventional SLC circuit shown in FIG. SLC in this embodiment
A directional coupler (hereinafter, referred to as "J") and a thermal noise (N) for picking up a disturbance (J) and a thermal noise (N) are provided at an auxiliary channel input of the circuit.
DC) 30 is provided. The sum of the power of the interference wave (J) and the thermal noise (N) picked up by the DC 30 is measured by the power measurement circuit 31. The J / N ratio is calculated in the gain control circuit 32 based on the measurement value measured by the power measurement circuit 31. The gain control circuit 32 outputs a signal for correcting and controlling the modulation signal obtained by the closed loop operation based on the calculation result.

On the other hand, sample and hold circuits 33a and 33b are connected to the output terminals of the integrators 19a and 19b, respectively. The sample and hold circuits 33a, 33
3b is a circuit for holding the modulation signal obtained by the closed loop operation. These sample and hold circuits 33a and 33b
Are corrected by the variable gain amplifiers 34a and 34b. The correction in the variable gain amplifiers 34a and 34b is performed based on the control signal sent from the gain control circuit 32 described above.

As shown in FIG. 1, the modulator 14
a and 14b are supplied to an integrator 19 as in the prior art.
a, 19b or a signal from the variable gain amplifiers 34a, 34b.
a, 35b. That is, the switches 35a and 35b are switches for switching to a closed loop operation to obtain a modulation signal, and thereafter switching to an open loop operation using the corrected modulation signal from the variable gain amplifiers 34a and 34b.

A feature of the present embodiment is that the switching between the closed loop operation and the open loop operation can prevent the deterioration of the interference wave rejection ratio due to the thermal noise. The other configuration in FIG. 1 is the same as that of the conventional SLC circuit shown in FIG.

As described above, FIG. 4 shows an example in which a conventional SLC circuit is provided. In the example shown in FIG. 4, the SLC circuit 8 is replaced with the SL shown in FIG.
It can be replaced with a C circuit. Hereinafter, the operation of the SLC circuit when the SLC circuit 8 in FIG. 4 is replaced with the SLC circuit according to the present embodiment shown in FIG. 1 will be described.

First, the thermal noise power (N) input to the auxiliary channel of the SLC circuit is expressed by the following equation (4).

N = F · k · T · B · G (4) In the equation (4), F represents the noise figure of the front end. B represents the pass band width of the front end, and G represents its gain. K is Boltzmann's constant and T is the absolute temperature. As long as the operating temperature of the front end does not greatly change, the thermal noise power (N) has a constant value determined by the above parameters constituting the front end.

The power measurement circuit 31 receives both the disturbance power (J) and the thermal noise power (N). For example, if a logarithmic amplifier or the like is used, the sum (M) of the disturbance and the thermal noise is obtained. = J + N) is obtained by being converted into a voltage. on the other hand,
By removing the input from the auxiliary antenna and terminating the RF amplifier 3b, it is possible to measure only the thermal noise (N). This value can be measured in advance as M _N = N. As described above, this value takes a constant value determined by the parameters of the front end. Therefore, the J / N ratio can be obtained by performing an operation shown in the following equation (5) in the gain control circuit 32.

J / N = (M−M _N ) / M _N (5) However, when a logarithmic amplifier is used in the power measurement circuit 31, it is necessary to perform the above calculation by returning to the true number. is there.

If such a calculation is previously written in a ROM or the like as a table representing the relationship between the input and the output, the J / N ratio can be immediately obtained from the sum of the interference wave and the thermal noise.

Next, a method of setting the gains of the variable gain amplifiers 34a and 34b based on the J / N ratio thus obtained will be described with reference to FIG. In FIG. 6, two triangles formed by an error signal of thermal noise (proportional to N) and W _JN , and an error signal of disturbing wave (proportional to J) and W _JN are similar triangles to each other. Therefore, when W _OPT is obtained from W _JN , it is expressed by the following equation (6).

W _OPT = W _JN (1 + 1 / J / N) (6) In the equation (6), W _JN is a modulation signal obtained by a closed loop operation. Further, since the J / N ratio is a signal obtained by the interference wave canceling circuit of the present invention, from the above, for example, J / N
It can be understood that when the gain of the variable gain amplifiers 34a and 34b is adjusted to 2 when = 1, an optimal modulated signal W _OPT that does not cause deterioration of an interference wave due to thermal noise can be obtained.

The switching between the closed-loop operation and the open-loop operation of the modulation signal is preferably carried out every time the incident condition of the interference wave changes or periodically. Ideally, such switching should be performed every time the incident condition of the interference wave changes, but if it is difficult to detect that the incident condition has changed, the switching is performed at regular intervals. Is simple.

As described above, in the method of correcting the gain, the control characteristic of the modulator is linear, that is, the modulation signal is reduced by 1 /.
It is assumed that the amplitude of the subtraction signal output from the modulator when it is set to 2 becomes １ ／. In general, a mixer is used as a modulator. In this case, since the control characteristics of the modulator are not linear, the control signal output from the gain control circuit is a signal that takes into account the control characteristics of the modulator. It is preferred to do so. That is, the gain control circuit 32 according to the present embodiment includes a function of a so-called linearizer that makes the control characteristics of the modulator appear linear. The function of this linearizer is similar to that of the gain control circuit 32.
It is also preferable to include them in a variable gain amplifier instead of including them.

FIG. 2 shows an embodiment in which the function of such a linearizer is provided externally. As shown in FIG. 2, the linearizers 36a and 36b linearize the signal selected by the switches 35a and 35b, and then supply the linearized signals to the modulators 14a and 14b. The SLC circuit shown in FIG.
It is the same as the SLC circuit shown in FIG. 1 except for a and 36b.

FIG. 3 shows an actual circuit example of the gain control circuit and the linearizer. As shown in FIG. 3, the gain control circuit and the linearizer can be realized with the same configuration. As shown in FIG. 3, the power measurement value or the modulation signal is first supplied to the AD converter 41. The AD converter 41 converts an input analog signal into a digital signal. The converted digital data is supplied to the ROM table 42 as an address signal. The ROM table 42 is a table in which the calculation result shown in the above equation (6) is written in advance when used as a gain control circuit, while the output signal of the modulator is used when used in a linearizer. Is written in such a way that is proportional to the modulation signal. Such a correction value can be obtained by measuring the characteristics of the modulator in advance. The output signal of the ROM table 42 is D
The signal is converted into an analog signal in the A converter 43. Thus, the DA converter 43 outputs the gain correction value or the linearizer correction value to the outside.

As described above, according to the present embodiment, based on the modulated signal obtained by the closed loop operation, the interfering wave is removed by the corrected open loop modulated signal. Interference can prevent the rejection ratio from deteriorating.

[0039]

As described above, the interference wave elimination circuit according to the present invention can reduce the deterioration of the interference wave elimination ratio caused by the thermal noise input together with the interference wave to the auxiliary channel. As a result, even when the J / N ratio is small, a sufficient interference wave removing effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an SLC circuit according to a preferred embodiment of the present invention.

FIG. 2 is a configuration block diagram illustrating a configuration of a gain control circuit or a linearizer of a modulator.

FIG. 3 is a configuration block diagram of a gain correction circuit according to the present embodiment.

FIG. 4 is a block diagram illustrating a configuration of a receiving device including an interference wave removing circuit.

FIG. 5 is a circuit diagram of a conventional interference wave removing circuit.

FIG. 6 is an explanatory diagram showing a state in which a disturbance noise rejection ratio is deteriorated by thermal noise.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main antenna 2 Auxiliary antenna 3a, 3b RF amplifier 4a, 4b Mixer 5 Local oscillator 6a, 6b BPF 7a, 7b IF amplifier 8 SLC circuit 10, 17, 21 PD 11 Limiter amplifier 12, 15, 90 90 degree hybrid 13 PC 14a, 14b Modulator 16a, 16b Correlator 18a, 18b Amplifier 19a, 19b Integrator 20 Subtractor 30 DC 31 Power measurement circuit 32 Gain control circuit 33a, 33b Sample hold circuit 34a, 34b Variable gain amplifier 35a, 35b Switch 36a, 36b Linearizer 41 AD converter 42 ROM table 43 DA converter

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Seiichi Kanegae 325 Kamimachiya, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Kamakura Works (72) Inventor Jun Shimada 325 Kamimachiya, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Kamakura Works (58) Fields surveyed (Int. Cl. ⁶ , DB name) H04B 1/10

Claims (1)

(57) [Claims] 1. An interference wave removing circuit for receiving signals from a main antenna and an auxiliary antenna for suppressing interference waves and removing an interference wave incident from a side lobe region of the main antenna in a closed loop configuration, wherein the auxiliary antenna And the power of the interfering wave input through
Power measurement means for measuring the sum of the power of the thermal noise generated or amplified by the interference wave removal circuit itself, and the interference wave and the thermal noise measured by the power measurement means. Power ratio calculating means for calculating a ratio between power and the power of the thermal noise; a sample / hold circuit for sampling / holding a modulation signal generated in a closed loop operation; and a power ratio calculated by the power ratio calculating means. A DC amplifier that amplifies the modulated signal held by the sample / hold circuit with the amplification factor, and selects one of the output signal of the DC amplifier and the modulated signal, and outputs the selected signal. And a correction switch for correcting the modulated signal obtained by the closed-loop operation, and removing the interfering signal in the closed loop using the corrected modulated signal. Interference wave cancel circuit according to symptoms.