JPH01314033A - Modem - Google Patents

Abstract

PURPOSE:To reduce the bit accuracy of an A/D converter by varying the amplification factor of an amplification means so that the reception signal reaches a signal level proper to an input of the A/D conversion means. CONSTITUTION:An amplification means 107 amplifies a reception signal and an analog-digital(A/D) conversion means 115 converts an analog signal outputted by the amplifier means 107 into a digital signal. An elimination means 109 uses a digital signal to eliminate an echo by a transmission signal and a level detection means 111 measures the reception signal level by using the output of the elimination means 109. A setting means 113 uses a level detection means 111 to set the amplification factor of the amplification means 107 so as to bring a proper signal level inputted to the A/D conversion means 115 based on the result of measurement. Thus, the required processing bit accuracy of the digital processing section is reduced.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems Action Examples ■, Correspondence between the Examples and FIG. 1 ■ 5 Configuration and operation of the embodiment (i) First embodiment (ii) Level detection circuit (in) setting section (iv) Second embodiment (v) Third embodiment ■ Summary of embodiments ■ 0 Modifications of the invention Effects of the Aspect Invention [Summary] Relating to a modem in which the received signal level input to the built-in analog-to-digital conversion means is appropriately set, the bit accuracy of the analog-to-digital conversion means possessed by the modem is reduced. an amplifying means for amplifying a received signal, an analog-to-digital converting means for converting an analog signal outputted by the amplifying means into a digital signal, and a removing means for removing an echo caused by a transmitted signal using the digital signal; Level detection means measures the received signal level using the output from the removal means, and the amplification factor of the amplification means is adjusted so that an appropriate signal level is input to the analog-to-digital conversion means based on the measurement result by the level detection means. and a setting means for setting.

[Industrial application field]

The present invention relates to a modem, and more particularly to a modem in which the level of a received signal input to an analog-to-digital conversion means is appropriately set.

[Conventional technology]

In a modem that performs full-duplex communication using a two-wire line, reflections of transmitted signals occur at the connection between the subscriber's line and the trunk line. Therefore, at the connection between the subscriber's line and the trunk line,
Impedance matching is performed to prevent reflected signals from the transmission line from entering the reception line.

However, it is extremely difficult to perfectly match this impedance, and in reality, reflected signals corresponding to the transmitted signal enter the receiving line (this is called an echo).

Furthermore, while propagating within the line, the transmitted and received signals are influenced by the characteristics of the line and arrive at a level that is attenuated from the level at which it was transmitted.

Generally, switched line modems require line connection means by dialing before data transmission. below,
The modem that performs the dialing is called the calling modem, and the modem that receives the dialing call is called the answering modem.

The modem includes a transmitting section and a receiving section inside. The signal is transmitted as a digital signal from the transmitter and is converted to an analog signal before entering the trunk line. Echoes occur where this signal is supplied to the trunk line. When a signal is sent from the modem's transmitting line to the trunk line, the echo that wraps around to the modem's receiving line is called a "near-end echo." Further, the signal entering the trunk line propagates within the trunk transmission line and is received by the response modem reception line. Echoes also occur here, and echoes that loop around to the trunk receiving line at the modem connection are called "far-end echoes."

The reception section of the modem not only receives the transmission signal from the other party, but also receives the near-end echo and far-end echo caused by the transmission signal that has looped around to the reception line.

Therefore, the received signal is an echo of the transmitted signal to the other station,
It consists of the transmitted signal from the other station.

The signal received from this trunk line is an analog signal,
The signal is converted into a digital signal for digital signal processing in the receiving section. Furthermore, in order to receive only the signal from the other station, it is necessary to cancel the near-end echo and far-end echo.

This echo cancellation is performed by converting the received signal into a digital signal and then using an echo canceller to remove the echo component estimated from the transmitted signal from the received signal. Therefore, the receiving section receives a signal from which echo components have been removed as a transmission signal from the other station. In this way,
Modem transmission and reception takes place.

[Problem to be solved by the invention]

By the way, in the above-mentioned conventional system, since the signal is attenuated while propagating within the line, the level of the received signal differs depending on the relationship between the modem used and the relay line. On the other hand, since an analog-to-digital (A/D) converter also has an appropriate signal level as an input, an A/D converter corresponding to the received signal is required.

For example, if the transmitted signal level is OdB and the received signal level from the other station is 143 dB, this signal is
To receive at a ratio of 30 dB, a dynamic range of approximately 73 dB is required. In reality, since it is necessary to take into account the peak value of the analog signal, an even larger dynamic range is required as the dynamic range of the A/D converter.

Therefore, in order for the modem to handle input signals with a wide range of levels, it is necessary to have an A/D converter with a large number of bits and a digital signal processor.

The present invention has been created in view of these points, and allows the received signal to be A/D-processed at an appropriate signal level without increasing the number of bits in the A/D converter and digital signal processing section. The object is to provide a modem capable of inputting a converter and a digital signal processing section.

[Means to solve the problem]

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

In the figure, amplification means 107 amplifies the received signal. Analog-digital conversion means 115 converts the analog signal output by amplification means 107 into a digital signal. The removing means 109 uses a digital signal to remove the echo caused by the transmitted signal. The level detection means 111 measures the received signal level based on the output from the removal means 109. The setting means 113 sets the amplification factor of the amplification means 107 based on the measurement result by the level detection means 111 so that the signal level input to the analog-digital conversion means 115 is appropriate.

Therefore, as a whole, the amplification factor of the amplification means 107 is configured to be varied so that the received signal has a signal level suitable for input to the analog-to-digital conversion means 115.

[For production]

In the reception signal processing of the modem, the signal transmitted to the reception line within the modem is amplified by the amplifying means 107 and then digitized by the analog-to-digital converter 115. From the digitized signal, the removing means 10
9 removes the echo caused by the response signal from the transmitter in the modem and extracts only the signal from the partner station. The extracted signal is input to level detection means 111, and its level is measured.

The setting means 113 estimates, for example, the worst value of the near-end echo from the response signal level output by the modem itself, and uses this estimated near-end echo level and the level of the received signal measured by the level detection means 111. , the received signal is converted into an analog-to-digital conversion means 11 possessed by the modem.
Set the amplification factor to obtain an appropriate signal level input to 5.

Based on this result, the amplification factor of the amplification means 107 is set.

Setting of this amplification factor is performed using, for example, a control signal sent at the beginning of the handshake.

Therefore, the signal to be actually received that is sent following the control signal is transmitted to the amplifying means 107 whose amplification factor is variably set.
After being amplified by the analog-to-digital converter 115 and digitized by the analog-to-digital converter 115, the signal is received by the receiver.

In the present invention, in order to amplify the signal according to the magnitude of the received signal, the signal is inputted at an appropriate signal level to the analog-to-digital conversion means 115 possessed by the modem.
The required processing bit accuracy in the digital processing part can be reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIGS. 2 to 4 show three examples of configurations of modems according to embodiments of the present invention.

Further, FIG. 5 shows two examples of the configuration of the level detection circuit used in the embodiment of the present invention.

(2) Correspondence with Actual Example FIG. 1 Here, the correspondence between the embodiment of the present invention and FIG. 1 will be shown.

Amplifying means 107 corresponds to amplifier 207.

The removal means 109 corresponds to a band-elimination filter (BEF) 209.

The level detection means 111 corresponds to the level detection circuit 211.

The setting means 113 corresponds to the setting section 213.

Analog-digital conversion means 115 is A/D converter 2
It corresponds to 15.

Examples of the present invention will be described below assuming that the correspondence relationship as described above exists.

2. Configuration and operation of the embodiment (i) First embodiment In FIG. an amplifier 207 that amplifies the received signal from the other station, and an A/D converter 215 that converts the received analog signal into a digital signal.
, a far-end echo canceller (FEEC) 219 and a near-end echo canceller (NEE) for canceling echoes.
C) 221, a BEF 209, a level detection circuit 211, a setting section 213, and a receiving section 205 that receives the signal, which constitutes a circuit for setting the amplification factor of the signal using the signal sent at the beginning of the handshake. It is configured.

The modem (9600bps) with the above configuration is CCIT
It has been recommended by V32 of T (International Telegraph and Telephone Advisory Committee), and its handshake is shown in Figure 6.

In Figures 2 and 6, when the modem operates as an answering modem, when the answering modem receives a signal to start transmitting from the calling modem, it returns a 2100Hz answer back tone, and the calling modem that receives this signal 18001(
Returns AA times signal of z. When the response modem receives the AA double signal, it transmits AC and CA double signals of 300011z and 600 Hz. In this case, the receiving line of the answering modem receives a near-end echo caused by the AA double signal and the AC and CA double signals issued by the modem itself. After the received signal is converted into a digital signal by the A/D converter 215, the BEF 209 blocks only the near-end echo of the AC and CA double signals and extracts the AA double signal from the calling modem.

This signal level is measured by the level detection circuit 211, and the measurement result is sent to the setting section 213.

The setting unit 213 further estimates the worst value of the near-end echo by inputting the transmission level 231 of the signal transmitted by the response modem. Then, in order to input the signal at an appropriate signal level for the A/D converter 215, an amplification factor for amplifying the received signal is set based on the measured received signal level and the estimated near-end echo level. This result is sent to amplifier 207, and the amplification factor is set.

This amplification factor setting is based on AA from the calling modem.

After receiving the CC signal, everything is finished before the answering modem sends a training signal for its echo canceller. When the training of the answering modem is completed, a training signal for the echo canceller of the calling modem is transmitted, followed by a signal to be actually received. The sent signal is amplified by the amplification factor set in the amplifier 207 and input to the A/D converter 215. After the signal is converted into a digital signal by the A/D converter 215, echoes are canceled by the FEEC 219 and NEEC 221, and the signal is received by the receiving unit 205 in a form in which the signal component from the calling modem remains. In this embodiment, a signal containing an echo is amplified, and then the echo is removed.

Similar operations are performed to process received signals when operating as a calling modem. The difference from operating as an answering modem is that the answering modem uses the AA double signal to measure the level of the received signal from the other station, whereas the calling modem uses the answering modem's echo canceller training signal. That's true. AC, CA double signal,
Since the attenuation is significant in the frequency band, it is not suitable for measuring received signal levels. When measuring a damage signal in the calling modem, echo blocking by the BEF 209 is not performed because no transmission signal is output from the calling modem while the training signal is being received.

The amplification factor setting in the calling modem is performed at the end of transmission of the echo canceller training signal from the answering modem.

(ii) Level detection circuit In FIG. 5(a), the level detection circuit includes three multipliers 511, 513 and 517, and two adders 515.
and 519, and an integrator 505.

This level detection circuit receives an input signal 50 supplied via BEF 209 or directly from A/D converter 215.
The power of 1 is calculated by multipliers 511 and 513, the adder 515 subtracts the signal from a preset reference signal 503, the multiplier 517 multiplies it by a coefficient, and the integrator 505 subtracts the signal. Integrate. This detection circuit outputs the result as a level signal 507 and supplies it to the setting section 213.

Another level detection circuit shown in FIG. 5(b) includes a multiplier 513. Low-pass filter 603 and determiner 605
Consisted of.

In this level detection circuit, the power of an input signal 501 is calculated by a multiplier 513, and the signal is converted to a DC signal via a low-pass filter 603. After that, discriminator 6
05, the signal level is measured and the result is output as a level signal 507.

(iii) Setting section The relational expressions used for setting will be explained with reference to FIG. Here, the transmission section 701 transmits a signal, and the D/A converter 70 transmits a signal.
3, the near-end echo 713 of the transmitted signal 711, and the received signal 715 from the other station have signal levels that can be input to the A/D converter 707, so the following relationship exists: satisfy.

and RnyGeLO=201og(10+10) where,
The left side is the maximum value of the signal that can be input to the A/D converter, 0 (d
B), and the right side shows that the maximum received signal is the A/D converter 707.
It represents the relationship when input into . S (dB) is the transmitted signal 711 L (dB) is the amount of loss when the transmitted signal becomes an echo, Pe (dB) is the peak-to-average level amplitude ratio of the near-end echo analog signal, and Pr (dB) is the received signal The peak-to-average level amplitude ratio of the analog signal, RO
(dB) is the maximum value of the received signal that can be input to the A/D converter 707. (S-L) (dB) is near-end echo 1
Represents 13.

When the above relationship is satisfied, if the received signal R (dB) is measured, the signal -X (d
B) is given by the following formula.

Therefore, when the received signal level R is measured using the handshake control signal, the signal amplification is calculated from the measured received signal level and the estimated near-end echo level. X in the above relationship can be found as a ratio.

(iv) Second Embodiment FIG. 3 shows a second embodiment of the present invention. In the figure, in addition to the first embodiment described above, a D/A converter 223 that converts an echo canceller signal into an analog signal, and a receiving section 2
05 as a digital signal, an amplifier 227 that amplifies the signal that controls the echo canceller, and an automatic gain controller (AGC) 229 that controls the signal to the receiver 205. be done.

The modem having the above-described configuration differs from the first embodiment in that echo cancellation of the received signal is performed using an analog signal.

The echoes of the received signal are converted into FEEC219, NEE
It is canceled by C221.

Therefore, only the signal component from the other station is amplified by the amplifier 207 and input to the A/D converter 215, where it is converted into a digital signal. The process of measuring the received signal level from the digitized signal and setting the amplification factor is the same as in the first embodiment.

In the second embodiment, in order to perform echo cancellation before signal amplification, the echo canceller is controlled so that the amplification factors are set to FEEC219 and NEEC22 by the amplifier 227.
I am giving feedback to 1.

Further, the received signal is sent to the receiving section 20 without passing through the amplifier 207.
5 is man-powered. In other words, the received signal is directly transmitted to the amplifier 207.
Instead of being amplified by the AGC 229, the received signal is amplified after the echo component is removed from the received signal. The echo-cancelled signal is sent to the AGC
229 and is digitized via the A/D converter 225 and received by the receiving section 205.

(v) Third Embodiment FIG. 4 shows a third embodiment of the present invention. In addition to the first embodiment, this embodiment includes a D/A converter 223 that converts the echo canceller signal into an analog signal, and an A/D converter 225 that sends the signal to the receiving section 205 as a digital signal. Ru.

In the operation of the modem configured as described above, echo cancellation is performed at the analog signal stage, similar to the second embodiment. Second
The difference with the embodiment is that when a signal is received, the amplifier 20
In order to perform echo cancellation after being amplified by 7, the signal is amplified including the echo.

■Summary of Examples As described above, when the modem of the present invention receives a signal, it measures the received signal level using the control signal sent at the beginning of the handshake, and also measures its own transmitted signal level. The echo levels are then predicted and used to predict the received signal level. Based on the prediction, determine the signal amplification factor for inputting the received signal to the A/D converter,
Set the amplification factor on the amplifier and receive.

Therefore, even if the signal is attenuated due to the influence of the line,
It is possible to find the amplification factor at the handshake control signal stage, and adjust the signal level sent after the control signal to an appropriate signal level for the A/D converter possessed by the modem. can.

■1 Invention: Form P. In addition, in ``correspondence between the embodiment example and FIG. 1'',
Although the correspondence between the present invention and the embodiments has been described, those skilled in the art can easily imagine that the present invention is not limited to this and that there are various modifications.

[Effects of the Invention] As described above, according to the present invention, the level of the input signal to the A/D converter can be adjusted to a desired level according to the level of the received signal. The bit precision of the converter can be reduced, which is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of a modem according to the present invention, FIG. 2 is a block diagram of the configuration of a modem according to a first embodiment of the present invention, FIG. 3 is a block diagram of the configuration of a modem according to a second embodiment of the present invention, 4 is a configuration block diagram of a modem according to a third embodiment of the present invention, FIG. 5 is a configuration block diagram of a level detection circuit of the present invention, FIG. 6 is an explanatory diagram of handshake used in the modem of the present invention, FIG. 7 is a signal flow diagram within the modem of the present invention. In the figure, 107 is an amplification means, 109 is a removal means, 111 is a level detection means, 113 is a setting means, 115 is an analog-digital conversion means, 201.70
1 is a transmission section, 205.705 is a reception section, 207.227., 709 is an amplifier, 209 is a band-elimination filter (BEF), 211 is a level detection circuit, 213 is a setting section, 231 is a transmission level signal, 501 is an input signal, 503 is a reference signal, 505 is an integrator, 507 is a level signal, 603 is a low-pass filter, 605 is a discriminator, 711 is a transmitted signal, 713 is a near-end echo, and 715 is a received signal. (A 7th exit of the mountain road, I/7 Figure 5)

Claims (1)

[Claims] (1) an amplifying means (107) for amplifying a received signal; an analog-to-digital converting means (115) for converting an analog signal outputted by the amplifying means (107) into a digital signal; and using the digital signal, a removing means (109) for removing an echo caused by a transmitted signal; and the removing means (109).
) for measuring the received signal level based on the output from the level detecting means (111), and determining an appropriate signal level to be input to the analog-to-digital converting means (115) based on the measurement result by the level detecting means (111). The amplification means (
107) Setting means (113) for setting the amplification factor;