JPH03280748A - Loop type digital transmission line - Google Patents

Abstract

PURPOSE:To attain communication with plural terminal equipments without echo by selecting a delay circuit providing a delay time of normal state and a delay time in response to the distance at fault state and sending delay time information to an echo cancel circuit to cancel echo. CONSTITUTION:Delay circuits 1-N are provided, which provide a delay time of normal state and a delay time in response to the distance on the occurrence of a fault in a loop transmission line. On the other hand, fault production alarm information S9 giving a fault location is inputted to a control circuit 3 selecting the circuits 1-N to control a selector circuit 4. Then the information of the delay time of the selected circuit among the circuits 1-N is fed to an echo cancel circuit 11A, in which echo is cancelled. Thus, even when a fault takes place at any location on the transmission line, the echo cancellation corresponding to the delay time is implemented and a communication line without echo is formed with N-sets of terminal equipments.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a loop-type digital transmission line, and in particular to a loop-type digital transmission line that realizes N-to-N voice communication between N terminal devices when a failure occurs. The present invention relates to a loop-type digital transmission line that cancels echoes of loopback signals in cases where the loopback signals are echoed.

[Conventional technology]

Conventionally, in this type of Poob type digital transmission line, as shown in the block diagram of Fig. 3, the digital audio output signal S1 generated at the local station existing in the digitized loop type transmission line is delayed in the transmission line. 1, the output signal S3 from the echo canceling circuit 11, and the transmission data S8 from the own station are digitally added together. The circuit 12 and the echo canceling circuit 13 which cancels the inverse e-signal S7 which is converted into an analog signal S4 by the A converting circuit 14 and is passed around from the hybrid circuit 15 after i. An N-to-N voice communication system was used that enabled simultaneous calls between multiple stations with the same configuration. As shown in Figure 2(a), usually
Voice echo cancellation is being performed on the transmission line 1 which constitutes a normal loop, but for example, if a failure occurs between points E and t=-, as shown in Figure 2(b), In this case, the audio signal on the path C-D from the terminal equipment C is reflected at D and becomes a reverberation bus at D-C, and the audio signal on the path C-B-A-F-E is reflected at E and becomes E-F. -The echo delay times of the A-B-C echo buses are different, so the echo cancellation pitches do not match. Also, as shown in Figure 2 ((''), the failure point E
If the distances between -F and terminal equipment C are approximately the same 12 distances, then the delay time of both is the same, and operation is possible by readjusting the echo cancellation circuit 11.1. :.

[Problems to be Solved by the Invention 7] In the conventional loop-type digital transmission line mentioned above, the echo cancellation circuit works as if the transmission line were one! C) The following mechanism responds based on the delay time when the transmission line is disconnected. It has the disadvantage that it cannot be used.

[Means for Solving the Problems:] The loop-type digital transmission line of the present invention is capable of transmitting echoed audio signals transmitted from the own station and arriving at the own station after being delayed on the loop transmission line. an echo cancellation circuit that cancels the signal; an addition circuit that digitally adds the output signal of the echo cancellation circuit and the audio digital signal transmitted by the local station; and a D/A-A/D conversion circuit that converts the output signal into an analog signal. A loop-type digital transmission line having a plurality of terminal devices including an echo canceling circuit for canceling echoes caused by wrap-around from a hybrid circuit distributing the converted audio signal and transmitting/receiving the audio signal, The first 14174 circuit provides the delay time when the audio digital signal is normally transmitted through the loop transmission path, and the loopback signal when a transmission path failure occurs in the loop, and the distance of the transmission path changes depending on the location of the failure A- t:me I) 717 for selecting one of the outputs of the plurality of delay circuits, and the outputs of the first and second delay circuits, each giving a delay time of - The plurality of terminal devices include a lid circuit and a control circuit that controls switching of the selector circuit based on information on the location of failure inputted from the outside. 6 [Embodiment] Next, the present invention will be explained with reference to the drawings. do.

Figure 1 is a block diagram showing an embodiment of the present invention. The echo cancellation circuit of the echo cancellation signal S2 does not take into account the normal delay amount of 17/17), and cancels the echoes corresponding to the respective delay times when failures occur at various locations. Can not do it. In the embodiment shown in FIG. 1, delay circuits 1 and 2 are connected to delay circuits 1 and 2 which can vary delay times corresponding to the normal delay time and the transmission distance when a failure occurs in the loop transmission line.

On the other hand, failure alarm information S9 indicating the location of the failure
is input to the control circuit 3, and the day 1. The control circuit 3 which selects one of the setter circuits 1-...-N controls the setter circuit 'd@4.
1 Send to A to erase echo. By adopting this J: configuration, complete echo cancellation is performed no matter where a fault occurs on the transmission path, and N terminal devices and NNN
Voice communication is possible.

[Effects of the Invention] As explained above, the present invention provides a conventional loop-type digital transmission line with day 1. By adding a circuit, a selector circuit of N 14174 circuits, and a control circuit based on fault information, echo cancellation corresponding to each delay time is possible no matter where a fault occurs on the transmission path. This has the effect of making it possible to configure an echo-free communication line with N terminal devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
Figures a), (b), and (c) are state diagrams of a general loop type digital transmission line during normal operation and failure, and the third section is a block diagram of a conventional loop type digital transmission line. 1.2~N...Delay circuit, 3...Control circuit, 4
...Selector circuit, 11. IIA... Echo cancellation circuit, 12... Addition circuit, 13... Echo cancellation circuit, 14
...A/D, D/A conversion circuit, 15...hybrid circuit.

Claims (1)

[Scope of Claims] An echo canceling circuit for canceling a reverberated audio signal returned to the local station while an audio digital signal sent from the local station is delayed in a loop transmission path, and an output of the echo canceling circuit. A hybrid system that distributes audio signals, including an adder circuit that performs digital addition of the signal and the audio digital signal transmitted by the local station, and an audio signal that is converted from the output signal into an analog signal by a D/A/A/D conversion circuit. In a loop-type digital transmission line having a plurality of terminal devices including an echo canceling circuit that cancels echoes caused by looping around from the circuit, a loop-type digital transmission line that provides a delay time when the audio digital signal is normally transmitted through the loop transmission line is provided. 1 delay circuit,
a plurality of second delay circuits that provide respective delay times when the distance of the transmission path changes depending on the location of the failure in the loopback signal when a transmission path failure occurs in the loop; and the first and second delay circuits. A loop type digital device characterized in that the plurality of terminal devices include a selector circuit for selecting one of the outputs, and a control circuit for controlling switching of the selector circuit based on information on the location of failure inputted from the outside. transmission line.