JPS60219821A - Conference telephone system - Google Patents

Abstract

PURPOSE:To separate only a faulty channel by placing emphasis on a function fault of an echo canceller arranged to each channel and applying retraining to a fault detected at a level of each echo canceller. CONSTITUTION:An output of the echo cancellers 1-4-n-4 of each channel is subjected to time division multiplex and transmitted to a conference telephone set 2 via a transmission switch 4 as a transmission signal and also given to an echo canceller falut detecting circuit 3 at the same time. Supervisory control circuits 1-5-n-5 arranged at each channel extract an echo canceller fault detecting signal relating to the own channel, turn off the transmission switch 4 by using the signal as the start signal and a noise generator 5 is driven. The supervisory control circuits 1-5-n-5 stop a noise generating command to the noise generator 5 after a prescribed timing, an echo canceller fault detection signal is observed and when the said signal is at an L level, the transmission switch 4 is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conference telephone system using time-division multiplexed PCM No. 91 as input/output signals and a Yanceler during echo.

A conference call is realized by adding and synthesizing the audio signals of other channels excluding the audio signal of the own channel for one conference participant, and distributing the synthesized audio signal to the receiving section of each subscriber. .

Implementing such conference calls through their functional requirements is problematic. Generally, the subscriber line of a public telephone line consists of two lines, and the toll exchange system consists of four lines.

For this reason, a hybrid transformer that performs 2-wire to 4-wire conversion is always used in public telephone networks. A hybrid transformer exhibits ideal operation if its input and output terminals satisfy impedance matching conditions, but if it is connected to a circuit network that does not satisfy the ideal impedance conditions, such as a subscriber line leading to a telephone set, As is well known, a reverberation phenomenon occurs in which the receiving side signal is output to the transmitting side. 4 including two hybrid transformers with opposing reverberation amounts in the no-hybrid transformer.
An example of a situation in which the loop gain in the I#4 section is 1 or more, or in a situation close to IK, is 0g or more, which causes an oscillating situation called ringing, is a normal telephone line. The case of a one-to-one communication system is shown, which is a general operation example, but in the case of a multi-pair communication system such as realizing a conference call where the number of subscribers is n (n≧3), Due to the presence of multiple loops, the stability of this system is much worse than that of the one-to-one communication system described above. An example of loop loss estimation in such a case is shown in Proceedings of the 1985 National Conference of the Institute of Electronics and Communication Engineers (IEICE) under the title "One Type of Branch Amplifier for Conference Telephones". Conventionally, in such cases, for example, the voice signal of the subscriber with the highest speech energy is transmitted without loss on the sending side, and with loss on the receiving side.
By providing a loss to the transmitting side of the other plurality of subscribers and at the same time providing no loss to the receiving side, the loop loss of the multiplex loop is increased and ringing is prevented. Such a method is undesirable from the viewpoint of the naturalness of the conversation, since switching is performed using audio signals, and intermittent switching occurs due to collisions between audio signals that are difficult to quantitatively understand. In order to solve these shortcomings, a conference telephone device in which an echo canceller is installed at each subscriber has been proposed. A conference telephone device equipped with an echo canceller has a lower noise level due to electrical conditions than the previous switching method. To provide a comfortable conference call that exhibits better effects in terms of naturalness, etc. belonging to margin level 1 call quality. Even with echo-cancelling type 2 conference telephone equipment that exhibits such excellent effects, if for some reason the echo canceler itself malfunctions and no longer fulfills its function, the comfort that was expected from the echo canceller may be lost. conference calls will no longer be provided. As an example of an echo canceller failure, if a conference call consisting of one subscriber is interrupted by one subscriber's echo canceller, this is not the reason for invalidating the entire conference. is useless, and in such a case, the subscriber system corresponding to the failure echo cancellation 2 is separated from the conference, thereby preventing the effect on the entire conference and allowing the remaining n-1 subscribers to hold the conference. It is desirable to continue the telephone call.The purpose of the present invention is to provide a conference telephone system that minimizes shadowing over the entire conference telephone call due to individual echo canceller failures in a conference telephone device using echo canceling. Then it becomes 6.

In order to achieve the above object, a conference telephone system according to the present invention includes a conference telephone device composed of n channels and an echo canceller arranged in each of the conference telephone devices, and a signal indicating that there is no double talk state. and a first means for detecting a fault in the echo canceller by inputting a transmitting channel signal from which the echo signal is removed by the echo canceler 2 and inputted to the conference telephone device; a second means for blocking input of the transmission channel signal to the conference telephone device and at the same time transmitting a noise signal in place of the reception channel signal output from the conference telephone device;
Stopping the transmission of the noise signal after an arbitrary period of time, and at the same time, using the first means, determine whether the echo canceller 2 is good or bad, and if it is good, allow the input of the transmission channel signal to the conference telephone device; Further, in the case of no, it is constituted by means for keeping the input in a cut-off state.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, the conference system of the present invention includes one subscriber terminal IA, 2A of a plenary conference telephone device.

...nA (hereinafter, subscriber number is used synonymously with channel number), and hybrid transformers 1-1 to n-1
, encoders 1-2 to n-2, decoders 1-3 to n-3, echo cancelers 21-4 to n-4, and supervisory control circuit 1.
-5 to n-5, a conference telephone device 2 that operates in time division multiplexing corresponding to channels 1 to n, respectively, an echo canceller failure detection circuit 3, and a transmission switch 4.
and a noise generator 5. Also a, b,
Each line c, d, e, f represents a time division multiplexed signal. The operation of the present invention based on the above configuration is as follows. Echo cancellation for each channel 21-4~n
The output of -4 is time-division multiplexed and sent to the conference telephone device 2 via the transmission switch as a transmission signal a, and at the same time is sent to the echo canceller failure detection circuit 3. As shown in FIG. 2, the echo canceller failure detection circuit 3 includes a comparison circuit 3-2 that constantly measures the level of the transmitted signal a and sends out an IH level when the measured level exceeds a predetermined threshold α, It has a gate circuit 3-3 that receives the signal. In this gate circuit 3-3, the echo canceller 2 of each channel necessarily has it internally, and multiplexes the double talk detection signal which indicates l l (level) when there is no double talk, and which indicates the eLm level when there is double talk. The converted double talk signal and the above comparison signal and K
Thus, an echo canceller failure detection signal C is created. This signal C is sent to the monitoring control circuit n-5 of each channel.

The reason why signal C indicates the detection of 2 faults on echo can is as follows. In a non-double talk state where a signal exists only on the receiver side of each channel, echo canceler 2 suppresses the echo signal generated in hybrid circuit n-1, and its level at the echo canceler output is equal to that of a normal echo canceler. Considering the average amount of erasure that occurs, it can be expected that a certain average value Bt- will be shown. At this time, if the echo cancel 2 failure detection circuit detects a level that is, for example, 20 dB higher than the average value B, it is natural to assume that the echo cancel 2 of the corresponding channel is abnormal. Therefore, in this case, if a value 10 dB larger than the average value B is set as the threshold value α, the circuit 3-1 sends out an H level. This H level naturally occurs in a double talk state, and therefore, in order to use this 1H level to confirm the suppression function of the echo canceller itself, it is necessary to extract a time period in which there is no double talk. The two-person gate circuit 3-3 is provided for this purpose.

As is clear from the above, the echo canceller can be determined to be normal as long as the echo Jansage failure detection signal C is at the level aI.

Next, there is a monitoring control circuit 1 arranged for each channel.
-5 to n-5 extract the echo canceller failure detection signal C related to the own channel, and use this as a starting signal to turn off the transmission switch with the transmit control signal / and send out noise only to the receiving side of the own channel. Therefore, the noise generator 5 is driven by the noise generation command signal d. Monitoring control episode 1f! 11-5 to n-5 After the timing T, the noise generation command to the noise generator 5 is stopped, and the echo canceller failure detection signal C, which is δ in the input signal, is observed again. If this signal is at L level, When the transmission switch is turned ON again and the transmission switch is at H level, the transmission switch is kept at l0FF. Here, the purpose of the transmission on the receiver side during the noise time T is a training action in which the echo canceller 2 is caused to converge due to noise in order to confirm the operation of the echo canceller.

Each component of the present invention described above is concretely realized, for example, as described below. The conference telephone device 2 can be constituted by, for example, a digital conference telephone device disclosed in Japanese Patent Laid-Open No. 52-25508. The echo Yanceler failure detection circuit 3 is a level detection circuit 3 as shown in FIG.
-1. It is composed of a magnitude comparison circuit 3-2 and a two-person gate circuit 3-3. The circuit 3-1 can refer to, for example, a circuit that always exists inside the echo can 2 and calculates the power of an accurate input signal. Circuit 3-2.3-3 is commercially available. The transmission switch 4 is realized by a gate circuit shown in (a) K in FIG. 3 and a 2-1 selection circuit (multiplexing circuit) shown in (b) K in FIG. Both are commercially available. The noise generator 5 is realized with the circuit configuration shown in FIG. Circuit 4 in the same diagram
-1 indicates the same circuit as shown in FIG. 3(b), which uses the noise generation command signal d as a selection signal to output either the output signal of the conference telephone device or the output signal of the noise generation circuit 4-2.

The noise generation circuit 4-2 is a pseudo 2 random sequence generation circuit driven by a 7-frame clock, or a read-on memory that actually encodes noise! This can be realized by storing the data if and scanning it frame by frame.

FIG. 5 is a circuit diagram showing an example of a supervisory control circuit. In the figure, since timer 6 initially outputs L level, AND circuit 7 is supplied with a signal H level inverted by inverter 8. In this state, when the fault detection circuit C (for example, H level) is applied to the AND circuit 7 via the terminal 9, the AND circuit W87 gives 1 (level) to the 7th lip-flop (FF) 1O and 11, thereby causing the FF10 outputs a transmission control signal ft-.On the other hand, FF
11 operates to supply the H level to the AND circuit 13, thereby supplying the clock given from the clock generation circuit to the timer 6 via the AND circuit 13t-. Also, the output of FFII is the noise generator drive signal d from terminal 13.
is output as Timer 6 counts this clock and supplies a timer output signal H level to FF10 and IIK after a predetermined period of time. In response to this timer output, FF10 outputs the signal C applied from the terminal 9 to the terminal 12 as the signal I, so if the % terminal IK signal C is not applied, the signal f becomes L level and the fault is cleared. That is, the fault detection signal is rechecked after a predetermined time.

As explained above, the conference telephone axis system using the echo canceller according to the present invention places importance on the malfunction of the echo canceller arranged for each channel, and detects it by each echo canceller. If there is a true failure, Jin and K will be able to separate only the corresponding channel from the conference, preventing the impact from affecting the entire conference. You can get the effect that you can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
Figures 3, 4 and 5 are figures showing a portion of the invention in detail. In FIG. 1, 1-1 to n-1... hybrid transformer, 1-2 to n-2... encoder, 1
-3~n-3・old・・code L 1-4~n-4・・・・
...Yancera during echo, l-5 to n-5...Monitoring control circuit, 2...Conference telephone device, 3...
...fault detection circuit, 4...transmission switch, 5.
...Noise generator. Way l (2) b way ? (α) (b) way 3 flash

Claims (1)

[Claims] In a conference telephone system in which a conference telephone device consisting of n-channels and a knee-center Yanceler is placed in each of the conference telephone devices, a signal indicating that there is no double talk state and an echo signal are removed by the echo canceller and the means for detecting a fault in the echo canceler 2 by inputting a transmission channel signal manually input to the conference telephone device; and prohibiting input of the transmission channel signal to the conference telephone device by an output signal of the first means. and a second means for transmitting a noise signal in place of the received channel signal outputted from the conference telephone device; and a second means for stopping the transmission of the noise signal after an arbitrary period of time; and third means for determining whether the transmitting channel signal is acceptable or not, and if it is acceptable, allowing the input of the transmission channel signal to the conference telephone device, and if not, keeping the input in a blocked state until t. t
- Conference telephone system with e feature.