JP3124615B2 - Cross polarization interference compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-polarization interference compensator provided in a system for performing co-channel transmission using orthogonal polarization for compensating for inter-polarization interference.

[0002]

2. Description of the Related Art FIG. 4 shows a demodulator provided in a system for performing co-channel transmission using conventional orthogonal polarization (vertical (V) polarization and horizontal (H) polarization) and interference between cross polarizations. It is a block diagram showing a compensating device. In FIG. 4, 2
Reference numeral 1 denotes a V-polarization demodulator, and the V-polarization demodulator 21 is connected to a cross-polarization interference compensator 22 '.
The cross polarization interference canceller 22 'is connected to the H polarization demodulator 21'.

[0003] Further, an H polarization demodulator 21 'is connected to a cross polarization interference canceller 22 ", and
The cross polarization interference compensator 22 ″ is connected to the V polarization demodulator 21. Here, the V-polarization demodulation device 21 performs demodulation on the V-polarization (main polarization).
As shown in FIG. 2, a quadrature detector 5 that obtains two orthogonal detection outputs using a local oscillator 6, a low-pass filter 7, 7, an A / D (analog / digital) converter 8,
8. A distortion equalizer 9 is provided. With such a configuration, each detection output of the quadrature detector 5 is supplied to the low-pass filter 7.
, Is converted into a digital signal by the A / D converter 8, and the output from each A / D converter 8 is subjected to waveform equalization processing by the distortion equalizer 9, and the I-channel data signal And a Q-channel data signal.

A cross-polarization interference compensator 22 'in FIG. 4 compensates for inter-polarization interference, and is used to reduce interference between polarizations in a system for performing co-channel transmission using orthogonal polarization. Device. That is, the cross-polarization interference compensator 22 ′ adds the compensation signal to the output from the V-polarization demodulator 21 to compensate for the interference from the H-polarization of the V-polarization. Therefore, as shown in FIG. 5, the cross-polarization interference compensator 22 'includes a pair of A / D converters 1, 1 and a quadrature polarization compensation circuit (X
PIC) 4,4.

Here, the A / D converter 1 performs analog / digital conversion on the H-polarized signal, and
It outputs a digital signal of bits, and
The orthogonal polarization compensation circuit 4 outputs a compensation signal based on the digitally converted 8-bit signal, and includes a transversal filter and the like. Therefore, when a signal from the H-polarization demodulation device 21 'is input to each A / D converter 1, this signal is converted into a digital signal, and the 8-bit digital output is converted to a corresponding orthogonal polarization compensation signal. The signals are sent to the circuits 4 and each orthogonal polarization compensation circuit 4 outputs a compensation signal based on the input 8-bit signal.

The configuration of the H-polarization demodulator 21 'is substantially the same as that of the V-polarization demodulator 21, and the configuration of the cross-polarization interference compensator 22 "is similar to that of the cross-polarization interference compensator 2".
It is almost the same as that of 2 '. Therefore, the procedure of compensating for the interference wave from the V polarization of the H polarization is almost the same as the procedure of compensating for the interference wave from the H polarization of the V polarization.

[0007]

In the above-described cross-polarization interference compensating apparatus, there is a possibility that a DC component may be superimposed on the compensation signal, so that correct compensation cannot be performed. Therefore, for example, in the case of multi-level QAM, if it is desired to perform DC compensation on the input signal side of the cross-polarization interference compensator, a voltage fluctuation suppression circuit 23 as shown in FIG. It is conceivable to interpose between the output side.

That is, in the case of 16QAM, FIG.
As shown in the figure, 8 at the output side of the A / D converter 1
The third bit line of the two bit lines is connected to the input side of the voltage fluctuation suppression circuit 23. The output side of the voltage fluctuation suppression circuit 23 is connected to the input side of the A / D converter 1. That is, the third bit output is connected so as to be input to the voltage fluctuation suppression circuit 23, and the output of the voltage fluctuation suppression circuit 23 is connected so as to be added to the input signal to the A / D converter 1. Because

Here, the voltage fluctuation suppressing circuit 23 is provided to enable the orthogonal polarization compensating circuit 4 to perform correct compensation even if a direct current is superimposed on the input signal. Therefore, the voltage fluctuation suppression circuit 23
It comprises an integrator 2 connected to the bit output and a voltage comparator 3 connected to the integrator 2. First, the integrator 2 integrates the output of the A / D converter 1 in order to compensate for the superposition of the DC component on the polarization signal. The voltage comparator 3 compares the output of the integrator 2 with the desired output. This is to compare with a reference value and feed back the comparison result to the input side of the A / D converter 1.

The voltage fluctuation suppressing circuit 23 having the above-described configuration is connected to the A /
By providing the D converter 1, the following operation is performed. That is, the third of the A / D converter 1
When the bit output is output to the voltage fluctuation suppression circuit 23, the voltage fluctuation suppression circuit 23 monitors the fluctuation of the voltage of the input signal of the A / D converter 1 based on the transmitted signal from the third bit. That is, it monitors whether the signal point shown in FIG. 7 is above or below the threshold.

As a result, when it is detected that the DC voltage is superimposed and the voltage of the input signal fluctuates in the plus direction, that is, when the signal point enters the H (1) level region in FIG. The fluctuation suppressing circuit 23 sends the DC voltage returned in the negative direction to the input side of the A / D converter 1. Then, the input signal to the A / D converter 1 and the above-described negative DC voltage are added, and as a result, A / D
A signal from which a DC component has been removed is input to the D converter 1.

However, in such a cross-polarization interference compensator, since the compensation signal is obtained from the other polarization signal, the clock does not always punch out the center of the eye pattern. There is a possibility that a DC component may be superimposed on the data, so that correct compensation may not be performed. The present invention has been made in view of such a problem, and in a case where a DC is superimposed on an input signal, a clock does not always punch out the center of an eye pattern.
It is an object of the present invention to provide a cross-polarization interference compensator capable of performing correct compensation.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, reference numeral 1 denotes an A / D converter, and the output side of the A / D converter 1 is a quadrature polarization compensation circuit. (XPIC), but A / D
The first bit line on the output side of the converter 1 is also connected to the integrator 2. The integrator 2 is connected to a voltage comparator 3, and furthermore, the voltage comparator 3
Is connected to the input side of the A / D converter 1.

Here, the A / D converter 1 performs analog / digital conversion on an input signal.
The integrator 2 integrates the first bit output of the A / D converter 1. The voltage comparator 3 compares the output of the integrator 2 with a desired reference value and feeds back the comparison result to the input side of the A / D converter 1.

[0015]

In the above-described cross polarization interference canceling apparatus of the present invention,
As shown in FIG. 1, in an inter-polarization compensator provided in a system for performing co-channel transmission using orthogonal polarization and compensating for inter-polarization interference, an input signal is converted by an A / D converter 1 into an analog signal. / Digital conversion.

After that, as an input to the integrator 3, A /
The first bit output of the D converter 1 is used, and the first bit output of the A / D converter 1 is integrated by the integrator 2 that has received the output. The output of the integrator 2 is
The desired reference value is compared by the voltage comparator 3, and the comparison result is fed back to the input side of the A / D converter 1.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention. In FIG. 2, reference numeral 21 denotes a configuration similar to that of the V polarization demodulation device 21 in FIG. The cross polarization interference compensator 22 is used in place of the H polarization interference compensator 22 'in FIG.

Further, although not shown in FIG. 2, instead of the H polarization demodulator 21 'and the cross polarization interference compensator 22''shown in FIG. With the same configuration as the inter-wave interference compensator 22, a demodulator and a cross-polarization interference compensator that only reverse the polarization to be handled are provided. By the way, the cross-polarization interference compensator 22
Is an apparatus for compensating for interference between polarizations, and is an apparatus for reducing interference between polarizations in a system for performing co-channel transmission using orthogonal polarization. That is, the cross-polarization interference compensator 22 can output a compensation signal for compensating for an interference wave from the H polarization of the V polarization without the clock constantly punching the center of the eye pattern. It was done.

For this purpose, the H-polarization interference compensator 22
Has an A / D converter (A / D converter) 1 as shown in FIG. 2, and this A / D converter 1 is tentatively connected to an orthogonal polarization compensation circuit 4 by eight bit lines. ing. Further, a first bit line, which is a polarity bit of eight bit lines on the output side of the A / D converter 1, is connected to the input side of the voltage fluctuation suppression circuit 23.
The output side of the voltage fluctuation suppression circuit 23 is connected to the input side of the A / D converter 1.

That is, the first bit output of the A / D converter 1 is connected so as to be input to the voltage fluctuation suppressing circuit 23, and the output of the voltage fluctuation suppressing circuit 23 is used as the input of the A / D converter 1. , Are added so as to be added to the input signal. And the thing of such composition is 2
Each pair is provided in parallel so as to receive the same H-polarized signal.

That is, in each of the devices provided with the voltage fluctuation suppressing circuit 23, the conventional device takes the input of the voltage fluctuation suppressing circuit 23 from the output of the third bit.
The input is taken from the first bit output, and other configurations are the same. Here, the voltage fluctuation suppressing circuit 23 has the same configuration as the conventional one, and is configured by the integrator 2 and the voltage comparator (comparator) 3 described in the above conventional example.

FIG. 3 shows a detailed configuration of the integrator 2 and the voltage comparator 3 constituting the voltage fluctuation suppressing circuit 23. That is, the integrator 2 and the voltage comparator 3 include a latch circuit 12, a reference voltage calculation circuit 11, resistors 13, 15, 17, a capacitor 14, and an OP amplifier 16. The reference voltage calculation circuit 11
Is a resistor 11- connected to the non-inverted output of the latch circuit 12.
1, a resistor 11- connected to the inverted output of the latch circuit 12
2, an integrating circuit composed of a resistor 11-3, a resistor 11-4, and a capacitor 11-5 which are connected to the resistors 11-1 and 11-2 to take a wired OR.

With such a configuration, the input signal is A / D
Identified by converter 1 and by each output line,
The output to the orthogonal polarization compensation circuit 4 and the third bit output of the A / D converter 1 are also output to the voltage fluctuation suppression circuit 23. Then, the voltage fluctuation suppressing circuit 23 receives the transmitted signal by the latch circuit 12, outputs the output as it is to the resistor 13, and outputs the non-inverted output to the reference voltage calculating circuit 11. And inverted output.

Then, the reference voltage calculation circuit 11 takes the wired OR and uses it as a reference voltage of the OP amplifier, and outputs this to the OP amplifier 16 as a reference voltage. The detection signal passed through the resistor 13 is transmitted to the OP amplifier 16 and the resistor 15.
And output to the capacitor 14. In this way,
Each circuit receiving each of these signals monitors whether the signal point is above or below the threshold.

This monitoring is performed as shown in FIG.
This is performed by comparing the eye patterns shown in FIG. That is, when the DC voltage is superimposed on the input signal to the A / D converter 1, the voltage fluctuates in the plus direction, and in conjunction with this, the signal point on the eye pattern shown in FIG. Also moves in the plus direction and approaches the H (1) level. Then, it detects whether the signal point is at the H level or the L (0) level of the first bit output. At this time, ideally, the clock should always pass through the center of the eye pattern.
Is slightly shifted from the center because the clock obtained from the V polarization and the clock obtained from the H polarization interference compensator 22 by the H polarization interference compensator 22 are shifted.

However, as shown in FIG. 7, even if the clock slightly deviates from the eye pattern, the H level mark rate of the first bit when the DC component comes is lower than that of the third bit. In addition, it hardly changes to the H level due to the influence of the clock error. And now, A / D
When a DC voltage is superimposed on the input signal to the converter 1 and the voltage fluctuates in the plus direction, the signal point on the eye pattern also moves in the plus direction and becomes H level. Thus H
When the level is detected, the output side of the operational amplifier 16
The DC voltage that has moved in the negative direction is output and sent to the input side of the A / D converter 1 via the resistor 17.

The DC voltage moving in the negative direction is added to the input signal sent to the A / D converter 1, and as a result, the DC component is removed from the input of the A / D converter 1. The input signal is input. Thereafter, a compensation signal is generated by the orthogonal polarization compensation circuit (XPIC) 4 based on the signal subjected to the DC correction in this manner, and this is added to the output from the V-polarization demodulation device 21, and the The interference is compensated.

The H-polarization demodulator and the V-polarization interference compensator also operate in the same manner as the V-polarization demodulator 21 and the cross-polarization interference compensator 22 in the same manner. Is compensated. Thus, an A / D converter 1 that is provided in a system for performing co-channel transmission using orthogonal polarization and that performs analog / digital conversion on an input signal in a cross polarization compensation circuit that compensates for interference between polarizations. And an integrator 2 for integrating the output of the A / D converter 1 in order to compensate for the superposition of the DC component on the input signal.
And a comparator 3 which compares the output of the integrator 2 with a desired reference value and feeds back the comparison result to the input side of the A / D converter 1. /
Since the first bit output of the D converter 1 is used, even if DC is superimposed on the input signal, the DC component can be omitted, and correct compensation can be performed. Furthermore, even if the clock does not always punch the center of the eye pattern, the entire device can be correctly compensated without being affected.

As a result, a long-term voltage fluctuation can be compensated, and a circuit configuration can be made by adding only a small and simple improvement to the conventional cross polarization interference compensator. Can be easily changed.

[0030]

As described in detail above, according to the cross-polarization interference compensating apparatus of the present invention, the cross-polarization interference compensating system is provided in a system for performing co-channel transmission using orthogonal polarizations. An integrator that includes an A / D converter that performs analog-to-digital conversion on the compensation signal, and integrates an output of the A / D converter to compensate for superposition of a DC component on the compensation signal; The output of the integrator is compared with a desired reference value, and the comparison result is A / D
A comparator for feedback is provided on the input side of the converter, and a first bit output of the A / D converter is used as an input to the integrator, so that a compensation signal in the cross-polarization interference compensator is provided. Side DC compensation, and long-term voltage fluctuations can be compensated. Needless to say, since the circuit configuration can be made by adding only a small and simple improvement to the conventional cross-polarization interference compensator, there is an advantage that the circuit can be easily changed from the conventional circuit.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a block diagram showing one embodiment of the present invention.

FIG. 3 is a block diagram illustrating details of an A / D converter and a voltage fluctuation suppression circuit according to an embodiment of the present invention.

FIG. 4 is a block diagram showing an arrangement of a cross polarization demodulator and a cross polarization interference compensator in a conventional example.

FIG. 5 is a block diagram showing a V polarization demodulator and an H polarization interference compensator in a conventional example.

FIG. 6 is a block diagram showing a voltage fluctuation suppression circuit provided in an A / D converter in a conventional example.

FIG. 7 is a diagram illustrating signal points, identification points, and a first example of an A / D converter.
FIG. 4 is a diagram for explaining the relationship between up to three bits output.

[Explanation of symbols]

 Reference Signs List 1 A / D converter 2 Integrator 3 Voltage comparator 4 Quadrature polarization compensation circuit 5 Quadrature detector 6 Local oscillator 7 Low-pass filter 8 A / D converter 9 Distortion equalizer 11 Reference voltage calculation circuits 11-1 to 11-5 Resistor 12 Latch circuit 13, 15, 17 Resistor 14 Capacitor 16 OP amplifier 21 V polarization demodulator 22, 22 ', 22' 'Cross polarization interference compensator 21' H polarization demodulator 23 Voltage fluctuation suppression circuit

Continuing from the front page (72) Inventor Yoshiminami Aono 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Co., Ltd. 72) Inventor Satoshi Aikawa 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 1/10 H04B 1/12 H04J 11 / 00

Claims (1)

(57) [Claims] 1. A cross-polarization interference compensator provided in a system for performing co-channel transmission using orthogonal polarization and compensating for inter-polarization interference.
A D converter (1) is provided to compensate for the superposition of a DC component on the input signal.
An integrator (2) for integrating the output of the A / D converter (1)
And a comparator (3) that compares the output of the integrator (2) with a desired reference value and feeds back the comparison result to the input side of the A / D converter (1). As an input to the integrator (2), the A / D converter (1)
Wherein the first bit output of is used.
Cross polarization interference compensator.