JPH05211460A - Automatic equalizer system for qam modem - Google Patents

Abstract

PURPOSE:To select an automatic equalizer with less data transmission delay in the transmission through a line with small distortion and to select an automatic equalizer with a large equalization capability in the transmission through a line with large distortion. CONSTITUTION:A reception signal is demodulated by a demodulator 1 and distortion of a telephone line or the like is equalized by a 1st automatic equalizer 2 and a 2nd automatic equalizer 5. A reception signal equalized by the 1st automatic equalizer 2 is given to a 1st coordinate discrimination means 3 to discriminate a coordinate on a complex plane and a 1st reference coordinate is outputted. A reception signal equalized by the 2nd automatic equalizer 5 is given to a 2nd coordinate discrimination means 6 to discriminate a coordinate on a complex plane and a 2nd reference coordinate is outputted. A 1st error extract means 4 calculates an error between an output of the 1st automatic equalizer 2 with the 1st reference coordinate on the complex plane and a 2nd error extract means 7 calculates an error between an output of the 2nd automatic equalizer 5 with the 2nd reference coordinate on the complex plane. The 1st automatic equalizer 2 and the 2nd automatic equalizer 5 are sequentially corrected based on the error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a QAM data receiver which receives a QAM (quadrature amplitude modulation) signal as a reception signal and obtains a reception code, and more particularly to an automatic equalizer system.

[0002]

2. Description of the Related Art In digital data transmission using a QAM data modem, amplitude distortion, delay distortion, etc. on the line are
This causes a transmission error and is a factor that deteriorates the quality of information transmission. For this reason, conventionally, this type of modem has generally used a system using an automatic equalizer that equalizes line distortion by a successive adaptive FIR filter. However, the FIR type filter has a feature that when the number of filter stages increases, the equalization capability increases, but the data transmission delay increases.

[0003]

In this conventional automatic equalizer system, the worst expected value of the line distortion is generally designed to be equalized. However, in order to equalize a large distortion, there is a problem that the number of stages of the FIR filter becomes large and the data transmission delay becomes large.

Further, in order to reduce the data transmission delay,
When the number of filter stages is reduced, there is a problem that the data transmission quality deteriorates in a line with large distortion.

An object of the present invention is to select an automatic equalizer with a small data transmission delay for transmission over a line with a small distortion, and to select an automatic equalizer with a large equalization capability for a transmission over a line with a large distortion. It's about choosing.

[0006]

In order to achieve the above-mentioned object, the present invention is a QAM data modem receiver in which a demodulator for demodulating a received signal and the line distortion of the output of the demodulator are equalized. A first automatic equalizer with a large equalizing capacity
First coordinate determining means for outputting a first reference coordinate value on the complex plane of the output of the first automatic equalizer, and an error from the output of the first coordinate determining means and the output of the first automatic equalizer. First error extracting means for obtaining the corrected signal of the first automatic equalizer, a second automatic equalizer having a small equalizing ability to equalize the line distortion of the output of the demodulator, and the second automatic equalizer. Second coordinate equalization means for outputting a second reference coordinate value on the complex plane of the output of the converter, and second automatic equalization by obtaining an error from the output of the second coordinate determination means and the output of the second automatic equalizer. Second error extracting means used as a correction signal of the detector, the output of the first error extracting means, and the second
Level difference determining means for determining the magnitude of the output of the error extracting means, and a switcher for selecting either the output of the first coordinate determining means or the output of the second coordinate determining means based on the output of the level difference determining means. A decoder for decoding the received data from the output of the switch is provided.

[0007]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. In FIG. 1, 1 is a demodulator for demodulating a received signal, 2
Is a first automatic equalizer having a large equalization ability to equalize the line distortion of the received signal, 3 is a coordinate point on the complex plane of the output signal of the first automatic equalizer 2, and the first reference coordinate value The first coordinate determining means 4 for outputting the first error determining means 4 obtains a first error signal from the first reference coordinate value and the output of the first automatic equalizer, and uses it as a correction signal of the first automatic equalizer. Reference numeral 5 is a second automatic equalizer having a small equalizing ability to equalize the line distortion of the received signal, and 6 is a coordinate point on the complex plane of the output signal of the second automatic equalizer.
Second coordinate determining means for outputting the reference coordinate value and the received code, 7
Is a second error extracting means for obtaining a second error signal from the second reference coordinate value and the output of the second automatic equalizer, and is a correction signal of the second automatic equalizer, and 8 is a first error signal and a second error signal. The level difference determining means for determining the level difference of the above, the switch 9 for selecting either the first coordinate determining means 3 or the second coordinate determining means 6 according to the determination result of the level difference determining means 8, and 10 the switch 9
It is a decoder that decodes the received data from the reference coordinate values selected in.

Next, the operation of the automatic equalizer having the above configuration will be described.

The received signal is demodulated by the demodulator 1, and the distortion of the telephone line or the like is equalized by the first automatic equalizer 2 and the second automatic equalizer 5. The received signal equalized by the first automatic equalizer 2 determines the coordinate point on the complex plane by the first coordinate determining means 3 and outputs the first reference coordinate value. The received signal equalized by the second automatic equalizer 5 determines the coordinate point on the complex plane by the second coordinate determining means 6 and outputs the second reference coordinate value. The first error extracting means 4 calculates an error value on the complex plane between the output of the first automatic equalizer 2 and the first reference coordinate value, and the second error extracting means 7 calculates the second automatic equalizer 5. Calculate the error value on the complex plane between the output of and the second reference coordinate value. The first automatic equalizer 2 and the second automatic equalizer 5 are sequentially corrected by the error value.

Since the first automatic equalizer has a large number of taps in the FIR type filter, it can equalize even large line distortion, but has a large data transmission delay. The second automatic equalizer is F
Since the number of taps of the IR type filter is small, only a small line distortion can be equalized, but the data transmission delay is small.

A feature of the QAM data transmission system is that a synchronization signal is generated at the time of initial pull-in to pull in the automatic equalizer. Then, data transmission becomes possible only after the synchronization signal ends.

If the automatic equalizer is sufficiently equalized, the error signal has a small error, and if the equalization is insufficient,
There is a large error.

Here, at the end of the synchronization signal, the level difference judging means 8 judges the levels of the first error signal and the second error signal and determines whether the second error signal is sufficiently small or the first error signal.
When there is almost no difference between the error signal and the second error signal,
When it is determined that the second automatic equalizer 5 can perform sufficient equalization, the switch 9 is controlled to select the output of the second coordinate determination means 6. When the second error signal is large and the first error signal is small, it is determined that the second automatic equalizer 5 cannot sufficiently equalize, and the switch 9 is controlled so as to select the output of the first coordinate determining means 3. To do.

[0015]

As described above, according to the present invention, two types of automatic equalizers having different equalizing capabilities are configured in parallel, and either one is selected at the time of initial pull-in, and a line with small distortion is used. In the case of transmission, since an automatic equalizer with a small data transmission delay is selected, the transmission throughput is improved, and in a transmission with a large distortion line, an automatic equalizer with a large equalization capability is selected. The effect of eliminating the deterioration of quality is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Demodulator 2 1st automatic equalizer 3 1st coordinate determination means 4 1st error extraction means 5 2nd automatic equalizer 6 2nd coordinate determination means 7 2nd error extraction means 8 Level difference determination means 9 Switching device 10 Decoder

Claims (2)

[Claims] 1. A QAM data modem receiver comprising: a demodulator for demodulating a received signal; a first automatic equalizer having a large equalization capability for equalizing line distortion of an output of the demodulator; A first coordinate determining means for outputting a first reference coordinate value on the complex plane of the output of the first automatic equalizer; and an error obtained from the output of the first coordinate determining means and the output of the first automatic equalizer. 1
A first error extracting means for making a correction signal of the automatic equalizer and a second small equalizing ability for equalizing the line distortion of the output of the demodulator.
An automatic equalizer, a second coordinate judging means for outputting a second reference coordinate value on the complex plane of the output of the second automatic equalizer, an output of the second coordinate judging means and the second automatic equalizer Second error extracting means for obtaining an error from the output of the second automatic equalizer and a correction signal for the second automatic equalizer, and a level difference for determining the magnitude of the output of the first error extracting means and the output of the second error extracting means. Determining means, a switcher for selecting either the output of the first coordinate determining means or the output of the second coordinate determining means based on the output of the level difference determining means, and the decoder for decoding the received data from the output of the switcher. An automatic equalizer system in a QAM modem, characterized by being provided with. 2. The level difference judging means judges the level of the output of the first error extracting means and the output of the second error extracting means, and whether the output of the second error extracting means is sufficiently small,
Alternatively, when there is almost no difference between the output of the first error extraction means and the output of the second error extraction means, the second error
The switch is controlled so as to select the output of the coordinate determining means, and when the output of the second error extracting means is large and the output of the first error extracting means is small, the output of the first coordinate determining means is selected. The automatic equalizer system in a QAM modem according to claim 1, wherein the switching unit is controlled so as to perform the above-mentioned operation.