JPS5834977B2 - 2 Sen-4 Senhenkan Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 2-wire to 4-wire conversion circuit in which a hybrid coil is replaced with an electronic circuit.

In the public telephone network, in order to maintain the quality of a single call above a certain level, transmission loss, which is a controlling factor, is specified for the worst case of the transmission path from one subscriber to another subscriber.

On the other hand, the conventional transmission line is a two-wire system, and long-distance long-distance transmission lines are generally four-wire systems designed to reduce loss, and a two-wire to four-wire conversion circuit is inevitably required.

The conventional 2-wire to 4-wire conversion circuit uses a so-called hybrid coil (or hybrid coil) as shown in Figure 1.
transformers) are commonly used.

The hybrid coil HYB shown in FIG. 1 is an example in which the two-wire portion uses a balanced transmission type and the four-wire portion uses an unbalanced transmission type.

ZN is a balanced network and performs impedance matching with the network ZL connected to the two-wire terminal.

This mismatch attenuation RL is expressed by the following equation.

Equation (1) above has a large influence on transmission design conditions.For example, the 1-reverberation attenuation EL is known to cause received signals to interfere with transmission, so it is necessary to increase the attenuation. It is.

It is known that in a normal hybrid coil, the general formula for one reverberation loss is as follows.

EL yo RL +6 (ab) ・・・・・・・・・
(2) Therefore, the greatest goal is to set ZL=ZN.

However, although ZL has relatively small variations in general long-distance transmission lines, when considering a 4-wire subscriber line exchange, it becomes the composite impedance of the subscriber line and telephone, and it varies greatly. In this case, RL I can't make it big enough.

The present invention is intended to eliminate the above-mentioned conventional drawbacks, and its purpose is to provide a system that can increase the amount of reverberation attenuation regardless of variations in cable impedance, and eliminates the need for a hybrid coil. An object of the present invention is to provide a 2-wire to 4-wire conversion circuit.

FIG. 2 is a block diagram of a 2-wire to 4-wire conversion circuit showing one embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of FIG. 2.

In the figure, EC is an echo canceller, Bi2, BA
R is a PCM encoder and decoder in the case of a PCM time-division line, and is a booster in the case of an analog line.

T is a transformer, PS is an impulse sending circuit, X is a received signal storage circuit, H is an impulse response storage circuit, M is a product circuit,
S is a signal generation circuit that creates a pseudo echo signal, and ADD is an addition circuit that subtracts the pseudo echo signal from the echo signal.

Assume now that the 4-wire line portion (4WR, 4WS) is digitized using pulse code modulation.

When there is no received signal Response signals received thereafter are stored in the impulse response storage circuit H.

That is, when an impulse is sent out at the time shown in FIG. 3a, a response signal having the waveform shown in FIG. 4 appears, so h1 to hN are stored in register H for each sample point.

In this way, the signal to be received is N samples of the PCM m-bit quantized signal, and N originally requires an infinite time, but is set to a finite value within the allowable error range.

On the other hand, on the 4-wire line (4WR) side, there is a received signal storage circuit that stores N sample values of the signal X, that is, a register X.
At sample point xj, signal Xj -1.

xj-2,...xj-N (Fig. 4C)
reference).

The contents of these two registers H and
By multiplying up to N, the pseudo echo X' at time J is
echo, get j.

i.e. - whereas the actual echo signal is Xecho,j
Therefore, in the adder path ADD of the 4-wire line (4WS).

△=Xecho, j −X' echo, j
By performing the calculation in (4), it is possible to reduce the echo signal.

The above operations are performed for each sample time as shown in FIG. 3 d-1 to d-5.

In this way, in FIG. 2, the echo canceller E
Since the electronic circuit constituting C can suppress the echo signal of the 2-wire to 4-wire conversion circuit, a hybrid coil is not required.

FIG. 4a is a block diagram showing an example of a digital subscriber line exchange using the 2-wire to 4-wire circuit of the present invention, and FIG. 4 is a detailed block diagram of the intra-office trunk in FIG. 4a.

In the figure, 5UBI~n is the subscriber, T is the transformer-PC
M-10, DEC is PCM encoder, decoder - TD-8W
is a time division switch, ECI and EC2 are echo cancellers.

IOT is an intra-office trunk.

Figure 4a shows how only the echo canceller EC of the 2-wire to 4-wire conversion circuit in Figure 2 is connected to the internal trunk IOT.
, leaving only the encoder and decoder at the conversion point.

Each intra-office trunk IOT includes a pair of echo cancellers EC1 and E for one direction, as shown in FIG.
C2 is provided, and the echo of the 2-wire to 4-wire conversion circuit is
Economicalization is being achieved by using canceller EC as a common device.

Conventional 2-wire to 4-wire circuits using hybrid coils use the principle of forcibly returning the echo signal, but according to the present invention, the echo signal is passed through as is and canceled out by a pseudo signal. Since this principle is used, a hybrid coil is not required, and it is possible to increase the amount of reverberation attenuation regardless of variations in subscriber line impedance.

Note that the present invention can be applied to both digital circuit networks and analog circuit networks.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a conventional 2-wire to 4-wire conversion circuit, FIG. 2 is a block diagram of a 2-wire to 4-wire conversion circuit showing an embodiment of the present invention, and FIG. FIG. 4 is a block diagram showing an example of the case where the present invention is applied to a digital subscriber line exchange. EC: echo canceller, BAS, BAB,: encoder, decoder (or analog amplifier), T: transformer, P
S: impulse sending circuit, X: received signal storage circuit, H:
Impulse response storage circuit, M: product circuit, S: pseudo echo signal generation circuit, ADD: addition circuit for subtracting the echo signal and pseudo echo signal, TD-8W: time division switch, IOT: trunk within own station.

Claims (1)

[Claims] 1 In a 6-terminal network consisting of a 4-wire input terminal for receiving and transmitting signals in one direction only, and 1 branched 2-wire input/output and 4-wire output terminals, the 4-wire input terminal is used to receive the received signal. A circuit for storing the impulse for a certain period of time and a circuit for transmitting the impulse are provided, and the four-wire output terminal is provided with a circuit for receiving and storing a response, which is an echo signal of the impulse, and a circuit for receiving and storing a response, which is an echo signal of the impulse, from the received signal storage circuit and the impulse response storage circuit. A 2-wire to 4-wire conversion circuit comprising a circuit that cancels out a true echo signal of a received signal by a created pseudo-reverberation signal.