JP2000032507A - Equalization correction method for subscriber's line characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively set amplitude gain characteristic and frequency characteristic of a subscriber's line at high speed by a simple method by obtaining an attenuation constant and a phase constant of a subscriber's line and equalization correcting the amplitude attenuation characteristics and the frequency characteristics. SOLUTION: A digital phase synchronizing circuit 18 detects/phase compares an information pattern from an output of a low band pass filter 13, controls a frequency division ratio of a fixed frequency oscillator 180 output, receives a clock signal and maintains reproduction. An amplitude attenuation amount and a delay time value of a line are detected white increasing the clock signal inputted to an amplitude detection circuit 20 and a delay time detection circuit 21 from a transducer 10 as a reference, are inputted to an equalization correction amount calculation table 24, the kind of line is specified, an attenuation constant and a phase characteristics are obtained in a use frequency, and the amplitude attenuation characteristics and frequency characteristics of the line are comppehuded. Then, after a variable gain DC amplifier 20 is reset, a high band-pass frequency of a variable high band-pass filter 21 is made to change and is controlled, so that its output voltage value becomes equal to an input voltage of the variable gain DC amplifier 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for equalizing and correcting the characteristics of a subscriber line, and more particularly, to a system for transmitting digital information using the subscriber line. Equalization correction of subscriber line characteristics, which enables to understand the amplitude attenuation characteristics and frequency characteristics of the actual line by detecting the type, and to enable equalization correction of the line at low cost and high speed with a simple circuit configuration About the method.

[0002]

2. Description of the Related Art In recent years, with the spread of LANs and personal computer communication networks using digital communication networks of business operators, inexpensive two-way digital information transmission using existing analog subscriber lines for two-wire telephones has become possible. Is being done. This subscriber line has transmission characteristics that can secure sufficient quality for voice communication up to about 4 KHz, but when used for transmission of high frequency signals of 10 KHz or more, the longer the line, the higher the frequency. As the signal amplitude increases, the signal amplitude attenuates. Therefore, in order to perform high-speed signal transmission, it is necessary to understand the amplitude attenuation characteristics and frequency characteristics of an actual line and to equalize them.

FIG. 3A is a block diagram showing an example of a system for realizing a conventional method for correcting equalization of subscriber line characteristics. As shown in the figure, this system transmits digital information using an analog subscriber line laid between a general telephone subscriber and a station directly connected to the subscriber. , As subscriber line types, wire diameters of 0.4 mm, 0.5 mm, 0.65 mm and 0.9 m
m are used. The present system connects a station end of a subscriber line and a subscriber end to a home line terminal (hereinafter referred to as Did).
It is terminated by an ital Service Unit (DSU), and each DSU is connected to an in-station device and a subscriber terminal. Hereinafter, the operation of this system will be described.

[0004] The DSU converts the form of a signal between a subscriber line and a subscriber terminal or a central office, and adjusts the speed. Further, the DSU performs a trace between the built-in digital equalizer and the opposing DSU digital equalizer.
By transmitting and receiving signals by the ninging sequence, FIG.
As shown in (b), the function is provided for grasping the actual amplitude attenuation characteristics and frequency characteristics of the subscriber line and performing equalization correction to characteristics suitable for digital transmission.

FIG. 4A is a block diagram of a digital equalizer 1 incorporated in a conventional DSU. As shown in the figure,
The digital equalizer 1 includes a transformer 10 connected to a subscriber line, an analog AGC amplifier 11 and an A / D converter 12
And a low-pass filter (hereinafter, LPF) 13 and a digital phase-locked loop (hereinafter, DPLL) 18 for receiving and reproducing a clock necessary for the equalizer 1 from transmission information. ADF) 14 and interface
A face circuit (hereinafter referred to as INTF) 15 is connected in series, and an input terminal of the analog AGC amplifier 11 and the ADF 1
The transmission signal drive circuit 16 is inserted in parallel with the four output terminals, and the AGC control circuit 17 is inserted between the output of the LPF 13 and the input of the analog AGC amplifier 11. FIG. 4B shows an example of the block of the ADF 14. The delay unit 140 such as a large number of registers is connected in series, and an output extracted from the predetermined delay unit 140 is multiplied by a tap coefficient 141 (weighting). The output of the accumulator 142 for adding them is supplied as an ADF 14 output to the discrimination determination circuit 143, and the error signal between the obtained discrimination output and the ADF 14 output is fed back to the tap coefficient 141 to control the error amount. And minimize it.
FIG. 4C shows an example of the block of the DPLL 18, in which the fixed frequency oscillator output 180 is connected to the variable frequency divider 1
ADF14 output is connected to 81 inputs and pattern detector 182
, A phase comparator 183 and a loop filter 184, and the output of the loop filter 184 controls the output of the variable frequency divider 181 to receive and reproduce a predetermined clock signal. Hereinafter, the operation of the illustrated conventional digital equalizer 1 will be described in detail.

A digital information transmission system using a subscriber line includes a ping-pong transmission system in which transmission and reception signals are alternately transmitted in a time-division manner, and a two-wire transmission system in which transmission and reception signals are simultaneously transmitted.
Although there is an eco-canceller system or the like for canceling the wraparound of the transmission signal in the four-wire converter, the operation will be described here by taking a ping-pong transmission system using a two-wire subscriber line as an example. From the transmission signal drive circuit 16 of the digital equalizer 1 of the opposing DSU, signals 1 "and 0" are sent to the subscriber line.
Approximately 320 KBPS AMI (Alternate Mark) in which the number of bits in one frame is adjusted to be an even number in correspondence with the positive and negative bipolar pulses and the DC component fluctuation is removed.
Inversion) The encoded training sequence is transmitted, amplified by the analog AGC amplifier 11 through the transformer 10 of the digital equalizer 1 of the receiving side DSU, converted into a digital signal by the A / D converter 12, and subjected to waveform shaping by the LPF 13. Supply to ADF14. ADF14 is LPF
The AGC control circuit 17 inserted between the output of the LPF 13 and the input of the analog AGC amplifier 11 is controlled so that the peak value of the signal amplitude is detected in response to the output of the LPF 13 and the two sides have the same amplitude. Of the subscriber line is roughly adjusted with respect to the amplitude attenuation characteristic of the subscriber line so as to always maintain a predetermined value. The output of the LPF 13 is input to the delay unit 140 having a multi-stage configuration, and the output of the multi-stage delay unit 140 multiplied by a predetermined tap coefficient 141 is cumulatively added. The error signal generated between the 1 ", 0" discrimination output of the signal obtained by performing discrimination judgment on the characteristic and the output of the ADF 14 is fed back to the tap coefficient 141 to minimize the error amount. Control and fine adjustment of the gain and frequency characteristics as well as the output of the ADF 14 to the DPLL 1
8, a predetermined information pattern is detected, the phases are compared, and the phase difference is supplied from a loop filter 184 to a variable frequency divider 181 to which the output of a high-precision fixed oscillator 180 is input. By controlling, a predetermined clock signal having a constant period is always maintained. In this way, by sequentially changing the tap coefficient 141 of the output of the delay unit 140 of the ADF 14 and repeating the above operation, it is possible to obtain a desired gain and frequency characteristic and adapt the digital equalizer 1 to it. As described above, when the equalization correction of the receiving DSU is completed, the transmission sequence driving circuit 16 of the digital equalizing section 1 of the receiving DSU AMI-encodes the training sequence in which the digital equalizing section 1 of the opposing DSU has been encoded. Is transmitted and the equalization correction is performed by the same procedure.

[0007]

However, in the conventional equalization correction method for the subscriber line as described above, digital equalization is required to accurately equalize the amplitude attenuation characteristic and the frequency characteristic of the subscriber line. All amplitude gain characteristics and frequency characteristics matching the characteristics of the subscriber line must be prepared in the section 1. As a result, it is necessary to realize the ADF 14 by combining a multi-stage delay unit 140 and a large number of tap coefficients 141. For this reason, the ADF 14 becomes a complicated and expensive circuit, and the transmission and reception of the training sequence are repeated until the subscriber line converges to the predetermined amplitude gain and frequency characteristics. There is a problem that the delay is about several hundred ms or more including the correction).
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems associated with the conventional subscriber line equalization correction method, and is inexpensive by a simple method without complicating the equipment and / or system configuration. An object of the present invention is to provide an equalization correction method for a subscriber line that enables the amplitude gain characteristic and frequency characteristic of the subscriber line to be set at high speed (about several tens of ms including equalization correction for the opposing part). And

[0008]

In order to achieve the above-mentioned object, according to the present invention, a digital equalization unit in a DSU disposed opposite to a station side end of a subscriber line and a subscriber end is provided. In a method of equalizing correction of a subscriber line in a system for transmitting digital information by equalizing and correcting amplitude attenuation characteristics and frequency characteristics, a subscriber line is detected by detecting an amplitude attenuation and a delay time value in the subscriber line. The line type is specified to determine the attenuation constant and the phase constant of the subscriber line, and based on these, the amplitude attenuation characteristic and the frequency characteristic are equalized and corrected. It is a means that can do.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIGS. 1A and 1B show a DS for realizing the subscriber line equalization correction method of the present invention.
FIG. 4 is a block diagram showing one embodiment of a simplified equalization unit 2 incorporated in U. However, the circuit shown in FIGS.
4 (a) to 4 (c) are denoted by the same reference numerals as in FIGS. 4 (a) to 4 (c). As shown in FIG. 1A, a transformer 10, a variable gain DC amplifier 20, a variable high-pass filter 21, an A / D converter 12, an LPF 13, an INTF for terminating a subscriber line to an appropriate impedance.
15 and a variable gain DC amplifier 20 connected in series.
Transmission signal driving circuit 1 between input terminal and LPF 13 output terminal
6 are connected in parallel, the input terminals of the amplitude detection circuit 22 and the delay time detection circuit 23 are connected in parallel to the output terminal of the transformer 10, and the respective outputs are input to the equalization correction amount calculation table 24, and the output signal is output. Connected to control the variable gain DC amplifier 20 and the variable high-pass filter 21 by the
13 is supplied to the DPLL 18 to reproduce a clock signal, and to supply the clock signal to the amplitude detection circuit 22 and the delay time detection circuit 23. FIG. 1B shows a variable gain DC amplifier 2
The circuit of one embodiment of 0 and the variable high-pass filter 21 is shown. By controlling R2 and R4 using an electronic control volume or the like, the gain of the DC amplifier 20 and the cut-off frequency of the high-pass filter 21 are controlled. Is changed to equalize and correct the actual line characteristics. When the used frequency is high, the simplified equalizer 2 of the present invention has an attenuation characteristic with respect to the frequency of the actual line as a Δf characteristic at about 10 kHz or more as shown in FIG. This is performed by utilizing the fact that the correction can be performed by setting the cutoff frequency of 21. Hereinafter, the operation of the illustrated embodiment will be described in detail.

From the transmission signal drive circuit 16 of the opposite DSU simple equalizer 2, the above-mentioned AMI-encoded training sequence of about 320 KBPS is transmitted, and
The signal passes through a variable gain DC amplifier 20 having an initially set amplitude gain value and a high-pass frequency and a variable high-pass filter 21 through a transformer 10 of the SU simple equalizing unit 2 and is digitalized by an A / D converter 12. The signal is converted into a signal, and is supplied to the DPLL 18 after waveform shaping by the LPF 13. DPLL18 is LPF1
3 and receives the digitized training sequence, detects a predetermined information pattern, compares the phases, and uses the phase difference to determine the frequency non-ratio of the output of the fixed oscillator 180 with high accuracy. It controls to constantly receive a clock signal of about 320 BPS and maintain reproduction. On the other hand, the training sequence is simultaneously input from the transformer 10 to the amplitude detection circuit 20 and the delay time detection circuit 21 to detect and equalize the amplitude attenuation and the delay time value of the line with reference to the rising edge of the clock signal of the DPLL 18. A correction amount calculation table 24 is input to a table for comparing the amplitude attenuation amount and the delay time value of the line for each line type of the line used as the subscriber line in advance. The amplitude attenuation characteristic and the frequency characteristic of the line to be used are grasped by specifying the type and obtaining the attenuation constant α (dB / Km) and the phase characteristic β (rad / Km) at the operating frequency from another table. After that, the initially set amplitude gain value is reset to the variable gain DC amplifier 20 according to the characteristics of the actual line, and then the high pass frequency of the variable high pass filter 21 is changed so that the output voltage value becomes If the control is performed so as to be equal to the input voltage value of the variable gain DC amplifier 20, the equalization correction of the subscriber line is completed. After the completion of the equalization correction, the received signal is supplied from the INTF 15 to the subscriber terminal or the intra-office device, and digital information can be transmitted between them. When the equalization correction of the DSU on the receiving side is completed as described above, the transmission signal driving unit 16 of the simple equalizing unit 2 on the receiving side transmits the AM to the simple equalizing unit 2 of the opposite DSU.
The I-coded training sequence is sent out, and equalization correction is performed in the same procedure. Next, the operation of the amplitude detection circuit 22 and the delay time detection circuit 23 of the simplified equalizer 2 according to the embodiment of the present invention, and setting of the gain and frequency characteristics for the variable gain DC amplifier 20 and the variable high-pass filter 21 The method will be described in detail with reference to FIGS. 2A to 2D for describing the detection of the attenuation and the delay time of the subscriber line according to the present invention.

The input signal of FIG. 2A is the input signal of the amplitude detection circuit 22 and the delay time detection circuit 23 of FIG. 1A, and the timing between the waveform and the clock output of the DPLL 18 of FIG. Is shown in FIG. The amplitude detection circuit 22 measures a peak voltage value Vrp from a digital value obtained by A / D conversion of an input received signal waveform, and outputs a peak of a training sequence transmitted from the opposite DSU to the subscriber line.
The amplitude attenuation of the line is calculated from the ratio Vsp / Vrp in comparison with the voltage Vsp, and using this digital value, the time Trp at which Vrp is generated and the point Vro at which the received signal waveform value becomes zero are obtained. Time Tro is measured and the difference Trp−
The delay time value of the line is calculated from Tro, and as shown in an example in FIG. 2 (c), a table of the amplitude attenuation amount and the delay time value with the diameter of the subscriber line prepared in advance as a parameter. 2, the wire diameter of the corresponding wire type is determined with reference to FIG.
From (d), when the subscriber line is a distributed constant circuit of a two-wire balanced cable, the attenuation constant α (dB / Km) and the phase characteristic β (ra), which are secondary constants specific to the line type at the operating frequency, are used.
d / Km), the gain characteristic of the variable gain DC amplifier 20 is set, the cutoff frequency characteristic of the variable high-pass filter 21 is changed, and the output voltage value is
Is adjusted so as to be equal to the input voltage value of Eq. For example, when the amplitude attenuation amount = Vsp / Vro = 100 (40 dB) and the delay time value = Trp−Tsp = 1.5 μs, the line type is specified as 0.5 mm in FIG. From (d), the attenuation constant α = 11.0 dB / Km and the phase constant β = 11.0 at the operating frequency of about 300 kHz.
rad / Km is obtained, and the line length = 40/11 = 3.6.
4 km is obtained. That is, this subscriber line has a wire diameter of 0.5
mm, and at a line length of 3.64 km,
It is necessary to equalize and correct the amplitude attenuation amount at the use frequency of about 300 KHz = 40 dB and the phase change amount = 40 rad.
The gain is set to 40 dB by R2 of the variable gain DC amplifier 20 shown in FIG.
Is changed and the output value becomes equal to Vrp, the equalization correction of this line is completed. It should be noted that a gain may increase or decrease in the frequency characteristic at the same use frequency due to the difference in line type.
If the increase / decrease cannot be covered by only 4, the above-mentioned equalization correction can be made by changing R4 after semi-fixing R5 and setting the gain increase / decrease for each line type.

[0012]

According to the present invention, the line diameter of an existing analog subscriber line is specified by using a training sequence to estimate the characteristics of the actual line and perform equalization correction. In addition, high-speed operation is possible, and the effect is large as compared with the conventional equalization correction method for the subscriber line characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram of a simplified equalizer for realizing a subscriber line equivalent correction method according to the present invention.

FIG. 2 is a diagram for explaining detection of an amplitude attenuation amount and a delay time value of a subscriber line according to the present invention.

FIG. 3 is a block diagram showing an example of a conventional digital information transmission system using a subscriber line.

FIG. 4 is a block diagram of a digital equalizer for realizing a conventional equalization correction method for subscriber line characteristics.

[Explanation of symbols]

1: Digital equalizer, 2: Simple equalizer, 3-9: missing number,
10 Transformer 11 Analog AGC amplifier 12
A / D converter, 13 ... Low-pass filter (LPF), 1
4: Adaptive digital filter (ADF), 15: Interface circuit (INTF), 16: Transmission signal drive circuit, 17: AGC control circuit, 18: Digital phase-locked loop (DPLL), 19: Missing number, 20: Variable Gain DC amplifier, 21: variable high-pass filter, 22: amplitude detection circuit, 23: delay time detection circuit, 24: equalization correction amount calculation table, 140: delay unit, 141: tap coefficient, 142
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Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04B 3/48 H04B 3/48 H04L 12/02 H04L 11/02 Z

Claims (1)

[Claims] 1. A digital equalizer in a home line terminal disposed opposite to a station end of a subscriber line and a subscriber end to equalize and correct an amplitude attenuation characteristic and a frequency characteristic of the subscriber line. In the method for equalizing and correcting the subscriber line characteristic for a system for transmitting digital information, the method includes detecting an amplitude attenuation and a delay time value in the subscriber line and specifying a line type of the subscriber line. A method for equalizing and correcting subscriber line characteristics, wherein an attenuation constant and a phase constant of a subscriber line are obtained, and the amplitude attenuation characteristic and the frequency characteristic are equalized and corrected based on the attenuation constant and the phase constant.