JPS5832812B2 - Automatic equalizer control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling an automatic equalizer when a modem with a backward channel is used in a two-wire line.

Recently, as the amount of information has increased, even conversion lines have become 480
Transmissions of 0 bps and 9600 bps have come to be performed.

These high-speed transmission modems are naturally equipped with automatic equalizers.

Also, a backsword channel may be used to perform error control or the like.

When performing continuous ARQ on a 2-wire line using a backward channel, by outputting a backward carrier only when there is a backward request, the forward channel and backfood The ease of channel separation filters has already been demonstrated in our patent application 1984-143315 r error control system.
mentioned in.

The present invention improves upon the problems associated with automatic equalizers.

Now, in such a modem, the forward
Bandwidth is used separately for channel and backward channel.

When used in a two-wire system, the arrangement is as shown in Figure 2.

10 is a telephone line, and 11 is a hybrid coil.

The received signal is 10. The signal passes through a circuit called 1L12 and is supplied to a forward channel separation filter 13 and a backward separation filter 14.

15 is a forward signal demodulator, 16 is a backward signal demodulator, and 21 and 22 are signal lines that guide signals to the receiving terminal.

The transmitting side receives forward signals and backward signals from the transmitting terminal at 23.24.

19 is a forward signal modulator, 20 is a backward signal modulator, and both are combined at 18 and output through 17, 11°10.

Now, if Fig. 2 is the receiving side of the forward signal, the forward signal is 10° 11.12, 1 from the transmitting terminal.
Pass through 3, 15, 21.

The backsword signal does not come from the transmitting side.

Backward signal is 24, 20, 18, 17, 11, 1
0 and is sent to the sender.

However, the attenuation of the forward signal sent from the transmitting side can be up to 32 dB, and the attenuation of the forward signal sent from the transmitting side can be up to 32 dB. lL
There are cases where about 10 dB leaks, such as 12.

Therefore, when looking at point 12, the leaked backward signal may be larger than the received forward signal.

Although there are separation filters, there are 13 separation filters,
To completely remove leaked backward signals, large amounts of attenuation are required, which is expensive.

Accordingly, a method was previously filed as Japanese Patent Application No. 143315-1982 in which a backward carrier is output only when a backward signal must be sent during error control or the like.

In the invention according to this application, there is no problem even if the forward signal is erroneous due to leakage of the backward signal.

However, in such a case, other troubles may occur.

In other words, high-speed modems have an adaptive automatic equalizer on the receiving side, and large leakage signals can cause the tap gain of the automatic equalizer to go out of order.

The present invention is intended to prevent this.

The tap gain of the automatic equalizer is controlled as follows.

Cjk is the value of the jth tap gain at the time of the first sample, ek is the error signal at the time of the first sample, and X
k-j is the input amplitude value at the (k-j)th sample,
α is the control gain.

The above tap algorithm M S E (Mean
This is a general method called the 5quareError) method.

In the adaptive automatic equalizer, the equalization amount output The closest transmission level value is set as the transmission signal Ak. Find the error signal.

Therefore, if a large amount of miscellaneous input is applied to the input amplitude value over a long period of time, an accurate error signal will not be obtained, and Xk-j-ek will be random, so there is a risk that the tap gain will be an inappropriate value. There is.

This is true not only for the MSE method but also for other methods.

Therefore, if the backward signal leaks into the receiving side of the forward signal, it will adversely affect the automatic equalizer.

The present invention is characterized in that changes in coefficients such as tap gain of the adaptive automatic equalizer are prohibited during transmission of backward signals.

Furthermore, if the backward signal is carried by a carrier, it is preferable to detect the carrier of the backward signal.

There are several possible means for determining the period during which the carrier of the backsword signal is present.

The backsode signal modulator 20 naturally includes a circuit that generates a carrier, and should be able to control turning on and off the carrier, and a signal may be extracted from there.

Furthermore, since the interface signal "backward channel transmission request" from the terminal almost coincides with the carrier-on time of the backward signal, that signal can also be used.

Also, in this case, since leakage through 17 and lL12 becomes a problem, a large leakage signal also enters the backward signal demodulator 16, causing the backward channel reception carrier detection circuit included in 16 to operate. Conceivable.

It is therefore also possible to use a "bankword channel received carrier detection" signal.

Now, in order to prohibit the tap gain of the automatic equalizer from changing using these signals, the following procedure can be performed.

In the case of the MSE method, if ek is set to O in equation (1), Therefore, the tap gain does not change.

Of course, the tap gain does not change even if Xk-. is set to O, but since Xk-. is also used in the equation for calculating the output of equation (2), it cannot be set to O easily.

Making this possible depends on how the hardware is assembled.

In other words, Xk-. which performs the calculation of equation (1) and Xk-. which performs the calculation of equation (2) may be set to different routes, and a prohibition gate may be added to the former so that it can be set to 0.

FIG. 3 shows an embodiment of the present invention, in which ek is prohibited.

The input amplitude value comes into 30a.

Assuming that there are (2N-1) taps, the input amplitude at this time is Xk+N.

31a. 31b・・・・・・・・・31 p t 31
q is a one-sample delay element, and 30b has Xk
10N-1, 30c has Xk+N-2, 30h has Xk,
30 (l is Xk −N +1,30 r K&maXk
-N cars are output (°C).

32 a, 32 b...32h...
...32q. 32r is the tap gain, and the gain of each tap is CN, CN +1...
......, Co, ......"°CN-1,
It is CN.

33 a, 33 b ””33h・・・・・・・・・
- 33q and 33r are tap gain outputs.

Reference numeral 34 denotes an adder, which adds 2N+1 tap gain outputs and performs the calculation of equation (2).

35 is the equalizer output and its value Yk.

36 is an error calculation circuit which predicts Ak from Yk and performs the calculation (3).

37 is an error signal ek.

38 is an error output inhibit gate which is an important circuit of the present invention, and a backsword channel carrier-on signal 39
This circuit closes the gate when is on and prevents error output from being output.

In other words, the gate control function according to 39 is expressed by uk, ff Ot+ if the carrier is on, ff if the carrier is off.
, P+, 40 becomes ek"uk.

41at41b,...41h...
. . . 41 q and 41 r are tap gain control circuits that increase and decrease the respective tap gains.

For example, the output 42a of 41a has Xk + N "ek"
k.α is output and this value is subtracted from the tap gain C-8.

By doing the above, when the carrier of the buckler signal is on, ek-uk becomes 0, so there is no change in the tap gain.

In other words becomes.

For example, MZ F (modifiedF ore in
g) Legal hacker.

And it is sufficient.

As explained above, in the present invention, when a high-speed modem with a backward channel is used in two-wire mode, the tap of the automatic equalizer is
Gain errors can be prevented.

Further, in the above embodiment, a transversal type automatic equalizer that performs equalization in the time domain is used, but the present invention is not limited to this.

For example, even if it is an equalizer with a decision feedback path or a type that equalizes in the frequency domain, if it is an adaptive automatic equalizer, the characteristics (coefficients) will change depending on the received signal. .

At this time, the characteristics of the adaptive automatic equalizer may be disturbed by leakage from the backward channel, and it is clear that the present invention is effective.

[Brief explanation of drawings]

FIG. 1 is a spectrum diagram of a modem with a backward channel, FIG. 2 is an explanatory diagram of the configuration of a two-wire backward modem, and FIG. 3 is an embodiment of the present invention. 31a, 31b to 31q...Delay element, 32a
. 32b~32r...Tap-gain, 34...
... Adder, 36 ... Error calculation circuit, 38
...Error output prohibition gate, 41a, 41b~4
1r...Tap gain control circuit.

Claims (1)

[Claims] A modem that divides a 12-wire line into bands and transmits a first channel signal in the forward direction and a second channel signal in the reverse direction, the modem having an adaptive automatic equalizer, a demodulator that sends a signal of one channel to a receiving terminal; a modulator that supplies a signal from a transmitting terminal to the two-wire line; and a demodulator that sends a signal from the modulator to a second channel of the two-wire line. a detection means for detecting transmission of the second channel signal; A control method for an automatic equalizer, characterized in that if a signal transmission of the second channel is detected by a detection means, a change in coefficients of the adaptive automatic equalizer is prohibited.