JP3116982B2 - Automatic equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic equalizer, and more particularly to an automatic equalizer for use on a receiving side of a digital radio communication system using a multilevel quadrature amplitude modulation system or a polyphase modulation system in which orthogonal polarizations are arranged in a co-channel arrangement. Automatic equalizer to be used.

[0002]

2. Description of the Related Art In recent years, in digital radio communication systems,
It is necessary to overcome the degradation of channel quality due to frequency selective fading that occurs in the propagation path. For this purpose, a transversal equalizer using a linear transversal filter is used on the receiving side. Further, there is a decision feedback equalizer having a strong equalization characteristic.

[0003] In a transmission line in which orthogonal polarizations are arranged in a co-channel arrangement, a cross polarization interference compensator is used on the receiving side to compensate for cross polarization interference.

FIG. 2 shows a configuration of a conventional automatic equalizer. This automatic equalizer is a combination of a decision feedback equalizer and a cross polarization interference compensator.

[0005] An automatic equalizer receives an analog burst band signal on the self-polarization side and an analog burst band signal on the different polarization side from a demodulator (not shown) as first and second input signals, respectively. 2 input terminals 11 and 12. The automatic equalizer outputs an output signal from an output terminal 13.

The automatic equalizer has first and second analog / digital (A / D) converters 16 and 17, a decision feedback equalizer 20 ', and a cross polarization interference compensator 30. . The cross polarization interference compensator 30 includes a transversal filter 31 and a subtractor 32.

The first A / D converter 16 samples and quantizes the first input signal and outputs a first digital signal sequence. The decision feedback equalizer 20 'equalizes intersymbol interference caused by frequency selective fading occurring on the propagation path in the first digital signal sequence, and outputs an equalized digital signal.

The second A / D converter 17 samples and quantizes the second input signal and outputs a second digital signal sequence. The transversal filter 31 weights the second digital signal sequence for cross-polarization interference compensation, and outputs a cross-polarization interference compensation digital signal. The subtractor 32 subtracts the digital signal for cross polarization interference compensation from the equalized digital signal, and outputs the signal after cross polarization interference compensation from the output terminal 13 as an output signal.

FIG. 3 shows a conventional decision feedback equalizer 20 'having a 5-tap configuration. The decision feedback equalizer 20 'has a front equalizer 21 and a rear equalizer 22.

The forward equalizer 21 includes first and second delay circuits 41 and 42 and first to third multipliers 51,
52 and 53, and a first adder 61. In the forward equalizer 21, the first digital signal sequence is supplied to a first delay circuit 41 and a first multiplier 51. The first delay circuit 41 delays the first digital signal sequence to generate a first digital signal sequence.
And outputs the delayed signal. The first delayed signal is supplied to a second delay circuit 42 and a second multiplier 52. The second delay circuit 42 delays the first delayed signal and outputs a second delayed signal. The second delayed signal is supplied to a third multiplier 53.

The first to third multipliers 51 to 53 respectively apply a control signal generation circuit (not shown) to the first digital signal sequence, the first delayed signal and the second delayed signal. ) Supplied from the first to third tap coefficients C
_-2 , C _-1 and C ₀ are multiplied to output first to third multiplied signals m _-2 , m _-1 and m ₀ . These first to third multiplied signals m _-2 , m _-1 and m ₀ are added to a first adder 6.
1 and the first adder 61 adds these signals and outputs a first added signal.

The backward equalizer 22 includes third and fourth delay circuits 43 and 44, fourth and fifth multipliers 54 and 55, and second and third adders 62 and 63.
And a determination circuit 71. In the backward equalizer 22, the determination circuit 71 determines the output signal (equalized digital signal) of the decision feedback equalizer 20 'and outputs the determined signal. The determined signal is supplied to the third delay circuit 43. The third delay circuit 43 delays the determined signal and outputs a third delayed signal. The third delayed signal is supplied to a fourth delay circuit 44 and a fourth multiplier 54. The fourth delay circuit 44 delays the third delayed signal and outputs a fourth delayed signal. The fourth delayed signal is supplied to a fifth multiplier 55.

Fourth and fifth multipliers 54 and 55
Multiplies the third delayed signal and the fourth delayed signal by fourth and fifth tap coefficients C ₁ and C ₂ supplied from a control signal generation circuit (not shown), respectively. , The fourth and fifth multiplied signals m ₁ and m ₂
Is output. The fourth and fifth multiplied signals m ₁ and m ₂ are supplied to a second adder 62 and a second adder 6
2 adds these signals and outputs a second added signal. The second added signal is supplied to a third adder 63. The third adder 63 is also supplied with the first added signal from the first adder 61. Third
Adder 63 adds the first added signal and the second added signal, and outputs the third added signal as an equalized digital signal.

The first to fourth delay circuits 41 to 44
Is composed of a flip-flop or the like, and generally gives a one-bit delay to a signal input thereto.

For details of the decision feedback equalizer,
See, for example, Japanese Patent Application No. 2-30827. For details of the cross-polarization interference compensator, see, for example, Japanese Patent Application No. 2-124141.

[0016]

As described above, in the conventional automatic equalizer, the intersymbol interference is equalized by the decision feedback equalizer before the cross polarization interference compensation. Therefore, when cross polarization interference occurs in the propagation path, a signal including a cross polarization interference component is fed back to the rear equalizer of the decision feedback equalizer. As a result, the conventional automatic equalizer has a drawback that the equalization capability of intersymbol interference is deteriorated.

Accordingly, an object of the present invention is to provide an automatic equalizer capable of obtaining sufficient equalization characteristics of intersymbol interference even when cross polarization interference exists.

[0018]

According to a first aspect of the present invention, there is provided an automatic equalizer for generating an intersymbol interference or the like for a first signal corresponding to a signal supplied from a demodulator on the self-polarization side. And a cross-polarization interference compensator for compensating for cross-polarization interference from a second signal obtained by detecting a modulated wave on the different polarization side, The cross polarization interference compensator includes an automatic equalizer including a transversal filter that outputs a cross polarization interference compensation signal, and a subtractor that compensates for cross polarization interference using the cross polarization interference compensation signal. , The subtractor is disposed at a stage prior to the decision feedback equalizer, subtracts the cross polarization interference compensation signal from the first signal, and outputs the signal after cross polarization interference compensation to the decision feedback type equalizer. It is characterized in that it is supplied to an equalizer.

An automatic equalizer according to a second aspect of the present invention comprises:
A first analog / digital converter that receives a first analog baseband signal supplied from a demodulator on its own polarization side, samples and quantizes the first analog baseband signal, and outputs a first digital signal sequence A converter and a second analog baseband signal obtained by detecting a modulated wave on a different polarization side are received, the second analog baseband signal is sampled and quantized, and a second digital signal sequence is output. A second analog / digital converter, a transversal filter for outputting a cross polarization interference compensation signal in response to the second digital signal sequence, and the cross polarization interference signal from the first digital signal sequence. A subtractor for subtracting the compensation signal and outputting a signal after cross polarization interference compensation, and an equalization signal for equalizing the intersymbol interference of the signal after cross polarization interference compensation and equalizing the signal after intersymbol interference equalization When And having a decision feedback equalizer that output Te.

[0020]

[0021]

[0022]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, an automatic equalizer according to an embodiment of the present invention is different from that shown in FIG. 2 except that the arrangement of the decision feedback equalizer is different. It has a similar configuration. Therefore, reference numeral 20 is assigned to the decision feedback equalizer. The same components as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.

[0024]

[0025]

[0026]

[0027]

In this embodiment, the subtractor 32 is disposed between the A / D converter 16 and the decision feedback equalizer 20, and the subtractor 32 has the first signal from the A / D converter 16. And the digital signal for cross polarization interference compensation output from the transversal filter 31 are given. The subtracter 32 subtracts the digital signal sequence for cross polarization interference compensation from the first digital signal sequence, The digital signal sequence after the polarization interference compensation is output. Will be. The digital signal sequence after the cross polarization interference compensation is applied to the decision feedback equalizer 20.
Compensates for the intersymbol interference and is output.

In this embodiment, after the cross polarization interference is compensated, the decision feedback equalizer 20 compensates for the intersymbol interference of the digital signal sequence. Intersymbol interference can be compensated without being affected by wave interference. As a result, cross polarization interference and intersymbol interference can be completely eliminated.

[0030]

As described above, in the automatic equalizer of the present invention, the signal after the cross polarization interference compensation is equalized by the decision feedback equalizer to compensate for the intersymbol interference. As a result, there is an effect that it is possible to compensate for the cross-polarization interference and to obtain a sufficient equalization characteristic of the inter-symbol interference.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic equalizer according to the present invention.

FIG. 2 is a block diagram showing a conventional automatic equalizer.

FIG. 3 is a block diagram showing a decision feedback equalizer used in an automatic equalizer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11, 12 Input terminal 13 Output terminal 16, 17 A / D converter 20 Decision feedback equalizer 21 Forward equalizer 22 Back equalizer 30 Cross polarization interference compensator 31 Transversal filter 32 Subtractor

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H04L 25/03 H04L 25/03 C (58) Field surveyed (Int.Cl. ⁷ , DB name) H03H 15/00-21/00 H04B 1 / 76-3/44 H04B 3/50-3/60 H04B 7/005-7/015 H04J 1/00-1/20 H04J 4/00-15/00 H04L 5/00-5/12 H04L 25/00 -25/66

Claims (2)

(57) [Claims] 1. A decision feedback equalizer that equalizes intersymbol interference to a first signal corresponding to a signal supplied from a demodulator on a self-polarization side, and a modulated wave on a different polarization side. And a cross-polarization interference compensator for compensating for cross-polarization interference from the second signal obtained by detecting the cross-polarization interference, and the cross-polarization interference compensator outputs a cross-polarization interference compensation signal. In an automatic equalizer including a transversal filter and a subtracter that compensates for cross-polarization interference using the cross-polarization interference compensation signal, the subtractor is disposed at a stage preceding the decision feedback equalizer. Wherein the signal for compensating for cross-polarization interference is supplied to the decision feedback equalizer by subtracting the cross-polarization interference compensation signal from the first signal. . 2. A method for receiving a first analog baseband signal supplied from a demodulator on the self-polarization side, sample-quantizing the first analog baseband signal, and outputting a first digital signal sequence. And a second analog / digital converter and a second analog baseband signal obtained by detecting a modulated wave on a different polarization side, sample-quantize the second analog baseband signal, and perform second quantization. A second analog / digital converter for outputting a digital signal sequence;
And a transversal filter for outputting a cross-polarization interference compensation signal in response to the digital signal sequence of (i), and a signal after cross-polarization interference compensation by subtracting the cross-polarization interference compensation signal from the first digital signal sequence And a decision feedback equalizer that equalizes the intersymbol interference of the signal after the cross polarization interference compensation and outputs the signal after the intersymbol interference equalization as an equalized signal. Features automatic equalizer.