JPH06276182A - Full duplex communication control system - Google Patents

Abstract

PURPOSE:To perform stable data transmission by reducing near-end echo components in a full duplex communication system by a two-wire line. CONSTITUTION:Terminal equipments 7-i and 7-j provided with a transmission part 1, a reception part 2, a control part 3, an echo canceller 4 and a hybrid circuit 6 provided with a differential amplifier 5, resistors R1-R5 and a capacitor C1, etc., are connected through the two-wire circuit and data are transmitted with each other. In this full duplex communication system, carrier signals are transmitted from the transmission part 1 so as not to timewisely overlap one and the other of the terminal equipments 7-i and 7-j after an automatic response sequence. A hybrid circuit adjustment sequence for adjusting the circuit constant of the capacitor C1, the resistor R4 of the differential amplifier 5, etc., so as to minimize the near-end echo components due to the sneak path of the hybrid circuit 6 while transmitting the carrier signals is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-duplex communication control system for mutually transmitting data between terminal devices via a two-wire line. As a method for transmitting data between terminal devices via a two-wire line, a time division direction control transmission method (ping-pong transmission method), a frequency division transmission method, and an echo canceller transmission method are known. The time-division direction control transmission method switches the transmission direction (transmission and reception) of data between the up direction and the down direction at a predetermined cycle. The frequency division transmission method is a method of performing full-duplex communication by making the transmission frequencies of the upstream direction and the downstream direction different. In the echo canceller transmission system, the transmission frequency is the same, and the two-line circuit is connected through the hybrid circuit to cancel the echo component due to the wraparound of the hybrid circuit. There is a demand for improvement of transmission characteristics in this echo canceller system.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory diagram of a data transmission system, showing a case where terminal devices 47a and 47b are connected via a switching network 49 by two-wire lines 48a and 48b, respectively, to perform full-duplex communication. , The terminal devices 47a and 47b have the same configuration, and for simplification, only the main part inside the terminal device 47a is shown, 41 is a transmission unit, 42 is a reception unit, 43 is a control unit, and 44 is An echo canceller, 45 is a differential amplifier, 46 is a hybrid circuit, 50 is a buffer amplifier, 51 is a transformer, 52 is a subtracter, and R1 to R5 are resistors.

The hybrid circuit 46 includes a buffer amplifier 50, a differential amplifier 45, and resistors R1 to R5,
The transmission signal from the transmission unit 41 is sent from the buffer amplifier 50 to the two-wire line via the resistor R5 and the transformer 51. A part of the transmission signal is divided by the resistors R1 and R2 into a non-inverted input signal (+) of the differential amplifier 45, and divided by the resistors R3 and R4 into an inverted input terminal of the differential amplifier 45 ( -), And circuit constants are set so that the transmission signal does not appear at the output terminal of the differential amplifier 45, that is, the near-end echo does not occur.

The received signal through the transformer 51 is divided by the resistors R1 and R2 to be a non-inverted input signal (+) of the differential amplifier 45, and also divided by the resistors R5, R3 and R4 to be differential. The signals are input to the inverting input terminals (−) of the amplifier 45, and the reception signal is added to the reception unit 42 from the output terminal of the differential amplifier 45 via the subtractor 52.

The echo component is a far-end echo component in which a part of the transmission signal is returned from the partner terminal device, and a near-end component due to incomplete setting of the circuit constant of the differential amplifier 45 of the hybrid circuit 46 of the own terminal device. The echo canceller 44 generates a pseudo echo component based on the transmission signal and the estimation of the echo path, and the subtractor 52 cancels the echo component superimposed on the reception signal to reduce an error in the reception data. To do. The control unit 43 controls the transmission unit 41, the reception unit 42, the echo canceller 43, and the like according to the data transmission procedure.

[0006] FIG. FIG. 32 is an explanatory diagram of a sequence 32, in a case where full-duplex communication is performed by applying to a general exchange telephone network according to CCITT (International Telegraph and Telephone Consultative Committee) recommendation; from a calling side terminal device to a called side terminal When the subscriber number of the device is dialed, a calling signal is sent from the switching network to the destination terminal device. The response signal ANS of 2100 Hz is transmitted from the response mode modem corresponding to the called terminal device in response to the calling signal by the automatic response sequence.

In the calling mode modem corresponding to the calling side terminal device, when the response signal of 2100 Hz is received and detected, the signal AA is transmitted after a predetermined time. Answer Mode Modem
When this signal AA is received and detected, the signal AC is transmitted for a predetermined time and then the signal CA is transmitted. The calling mode modem
When the signal AC is received and detected, it is switched to the signal CC and transmitted. When the response mode modem detects and receives the signal CC,
The signal AC is switched and transmitted. When the calling mode modem receives and detects the signal AC, it stops sending the signal CC.

The signals A, B, C and D are A = 00, B = 01, C for continuous 2 bits (die bit).
= 11, D = 10, the signal AA indicates the state of AAAA ... which is an even multiple of the symbol time T, and the signal AC is the ACACAC ... which is an even multiple of the symbol time T.
And the signal CA is C which is an even multiple of the symbol time T.
.., and the signal CC indicates the state of CCCCCC ..., which is an even multiple of the symbol time T.

The response mode modem transmits the signal S for a predetermined time 16T after stopping the transmission of the signal AC,
An inverted signal * S is sent for a predetermined time. This signal S is the state of ABABAB ..., Signal * S is CDCDC
The state of D ... is shown. Next, the training signal TRN is transmitted. Next, 16-bit repetition rate information R1 is transmitted.

When the calling mode modem receives the speed information R1 from the answer mode modem, it sends the signal S for a predetermined time, then sends the inverted signal * S, and then the training signal TRN, Next, repetition 16-bit speed information R2, one-time 16-bit signal E, scrambled and encoded binary "1" signal B1, data DAT
A is sequentially sent out.

When the response mode modem receives and detects the signal S from the calling mode modem, it stops sending the speed information R1. Thereafter, when the training signal TRN from the calling mode modem is received and detected, the signals S, * S, the training signal TRN, the repetition 16-bit speed information R3, the 16-bit signal E once, the scrambled and encoded 2
A progressive "1" signal B1 and data DATA are sequentially transmitted. With the sequence as described above, full-duplex communication is performed between the calling mode modem and the answering mode modem.

[0012]

Hybrid circuit 46
The impedance on the side of the two-wire line seen from the above differs depending on the terminal device, and also differs depending on the captured two-line line. Therefore, the condition in which the near-end echo component is attenuated by the differential amplifier 45 and the resistors R1 to R5 and the like is deviated, and the near-end echo component increases and cannot be sufficiently canceled by the echo canceller 44. Is occurring. The present invention aims to provide a hybrid circuit adjustment sequence to attenuate near-end echo components.

[0013]

A full-duplex communication control system of the present invention will be described with reference to FIG. 1. A transmission unit 1, a reception unit 2, a control unit 3, an echo canceller 4, The terminal devices 7-i and 7-j provided with the hybrid circuit 6 for performing the 2-wire to 4-wire conversion by using the dynamic amplifier 5 are connected by an automatic response sequence to mutually transmit data via the 2-wire line. In the full-duplex communication system, the carrier signal is transmitted from the transmitter 1 after the automatic response sequence so that one of the terminal devices 7-i and 7-j does not overlap with the other in time. However, a hybrid circuit adjustment sequence for adjusting and setting the circuit constant of the hybrid circuit 6 is provided so that the near-end echo component due to the wraparound of the hybrid circuit 6 during the transmission of the carrier signal is minimized. Subtractor 9 transformer, the 10-switched network, R1
~ R5 is a resistor, C1 is a capacitor, and BF is a buffer amplifier.

[0014]

Operation: The terminal device 7-i, 7 is operated by the automatic response sequence.
After connection between -j, for example, the carrier signal of 1800 Hz is transmitted from the transmission unit 1 of the terminal device 7-i. At this time, the other terminal device 7-j is in a state of not transmitting anything. Therefore, since the near-end echo component due to the wraparound of the hybrid circuit 6 can be detected in the receiving unit 2 and the echo canceller 4, the circuits such as the resistors R4 and C1 are designed to minimize the near-end echo component. Adjust the constant. This allows the hybrid circuit 6 to be automatically adjusted to the optimum state even when the impedance of the two-wire line differs for each call.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is an explanatory view of essential parts of an embodiment of the present invention.
Only one terminal device is shown, 11 is a transmitter, 12 is a receiver, 13 is a controller, 14 is an echo canceller, 15 is a differential amplifier, 16 is a hybrid circuit, 17 is a level detector, 18 is a subtractor, Reference numeral 19 is a selector, 20 is a buffer amplifier, 21 is a transformer, R1 to R3, R5 and R6 are resistors, and CK1 to CKn are circuits composed of resistors and capacitors.

The transmitting unit 11, the receiving unit 12, the control unit 13, the hybrid circuit 14 and the like have the same structure as the conventional example,
The hybrid circuit 16 shows a case in which the circuit constant of the feedback circuit of the differential amplifier 15 can be selected by the selector 19. That is, when the carrier signal in the hybrid circuit adjustment sequence is sent from the transmitting unit 11, the selector 19 is controlled so that the output signal of the differential amplifier 15 becomes the minimum, and the feedback circuit CK1 of the differential amplifier 15 is controlled.
~ CKn are selectively connected.

FIG. 3 is a sequence diagram for explaining the main part of the embodiment of the present invention. When the calling mode modem makes a call to the answer mode modem, the answer mode modem sends the answer signal ANS of 2100 Hz. When the calling mode modem receives and detects the response signal ANS, it receives the signal AA after a predetermined time.
Is sent. When the response mode modem receives and detects the signal AA, the response mode modem sends the signal AC for a predetermined time, and then the signal CA.
Is sent. When the calling mode modem detects and receives the signal AC, it switches to the signal CC and transmits it. When the response mode modem receives and detects the signal CC, it switches to the signal AC and transmits it. When the calling mode modem receives and detects the signal AC, it stops sending the signal CC. The signals AA and A
Regarding C, CA, CC, etc., signal states similar to those of the above-mentioned conventional example are shown.

The response mode modem transmits a carrier signal CR of, for example, 1800 Hz, after a predetermined time, for example, 16T (T = symbol time), after the transmission of the signal AC is stopped. Further, the calling mode modem stops the transmission while the carrier signal CR is being sent from the response mode modem.
That is, the control unit 13 on the response mode modem side activates only the level detection unit 17 of the echo canceller 14 and controls the transmission unit 11 to send the above-mentioned carrier signal CR.

The carrier signal CR from the transmitter 11 is applied to the transformer 21 via the buffer amplifier 20 and the resistor R5, and is sent to the two-wire line via this transformer 21, or part of the resistor R1. Differential amplifier 15 via R3
Added to. The output signal of the differential amplifier 15 is detected by the level detecting unit 17, the selector 19 is controlled based on the level detection result so that the output signal approaches zero, and the feedback circuits CK1 to CKn of the differential amplifier 15 are controlled. Select and connect. In this case, the level detector 17 is
It is also possible to connect a filter with a pass center frequency of 00 Hz. By such control, the hybrid circuit is automatically adjusted to reduce the near-end echo, and is continuously held until the end of data.

When the automatic adjustment of the hybrid circuit 16 on the response mode modem side is completed, the transmission of the carrier signal CR is stopped. On the calling mode modem side, after confirming the stop of the carrier signal CR from the response mode modem side, the calling mode modem side sends the 1800 Hz carrier signal CR, and in the same manner as the response mode modem side described above. , Calling mode The hybrid circuit 16 on the modem side is automatically adjusted. On the calling mode modem side as well, as in the response mode modem side, the automatically adjusted state is held until the end of data.

Upon completion of the above-described hybrid circuit adjustment sequence for automatically adjusting the hybrid circuit on the response mode modem side and the hybrid circuit on the calling mode modem side, the response mode modem outputs the signals S, * S,
The training signal TRN and speed information R1 are transmitted. The calling mode modem receives the speed information R from the answer mode modem.
When 1 is received, signals S, * S, training signal TR
N, speed information R2 is transmitted. When the response mode modem receives and detects the signal S from the calling mode modem, it stops the transmission of the speed information R1 and sequentially detects the reception of the training signal TRN and sequentially transmits the signals S, * S and the training signal TRN. After the training sequence, full-duplex data transmission is performed.

As described above, the hybrid circuit 16 is automatically adjusted so that the carrier signal is transmitted from one terminal device to the other terminal device and the near-end echo can be reduced during that period. The data transmission in the echo canceller transmission system can be stabilized.

Further, the adjusting means of the hybrid circuit 16 is not limited to the above-mentioned embodiment, but various constitutions such as switching of circuit constants of the peripheral circuit of the differential amplifier 15 can be adopted. Feedback circuits CK1 to C
Kn indicates the case of a parallel circuit of a resistor and a capacitor, but various configurations may be adopted corresponding to the impedance characteristic of a two-wire line such as a feedback circuit in which a resistor is connected in series with a capacitor. it can. The transmission of the carrier signal CR in the hybrid circuit adjustment sequence is
It is also possible to start from the calling mode modem side. Further, the transmission time of the carrier signal CR can be set to, for example, an integral multiple of the symbol time T at which the automatic adjustment of the circuit constant can be completed.

[0024]

As described above, according to the present invention, after the automatic response sequence, the transmitting unit 1 prevents the terminal devices 7-i and 7-j from overlapping with each other in time. The carrier signal CR is transmitted and the carrier signal C
A hybrid circuit adjustment sequence for adjusting and setting the circuit constant of the differential amplifier of the hybrid circuit 6 is provided so that the near-end echo component due to the wraparound of the hybrid circuit 6 during R transmission is minimized. Even if the captured two-wire line is different every time, the near-end echo component can be reduced by the automatic adjustment of the circuit constant of the hybrid circuit 6, so that stable data transmission can be easily performed. There is an advantage that can be.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory view of a main part of the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a main part sequence according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a data transmission system.

FIG. 5: It is a sequence explanatory view of 32.

[Explanation of symbols]

 1 transmitter 2 receiver 3 controller 4 echo canceller 5 differential amplifier 6 hybrid circuit 7-i, 7-j terminal device 8 subtractor 9 transformer 10 switching network

Claims (1)

[Claims] 1. A 2-wire 4-wire conversion is performed using a transmitter (1), a receiver (2), a controller (3), an echo canceller (4), and a differential amplifier (5). A full-duplex communication system in which terminal devices (7-i) and (7-j) provided with a hybrid circuit (6) are connected by an automatic response sequence and data is mutually transmitted via a two-wire line. At the end of the automatic response sequence, the terminal device (7-
i) and (7-j) so that one of the other and the other do not temporally overlap with each other, the carrier signal is transmitted from the transmitting section (1), and the hybrid circuit (6) during the carrier signal transmission. The full-duplex communication control method is characterized in that a hybrid circuit adjustment sequence for adjusting and setting the circuit constant of the hybrid circuit (6) is provided so that the near-end echo component due to the wraparound of (4) is minimized.