JP3027076B2 - Multipoint voice communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of connecting terminals located at different points in a loop, transmitting a voice signal from each terminal in one direction on the loop transmission path, The present invention relates to a multipoint voice communication system in which voice communication between terminals is performed by receiving.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory diagram showing a connection example of a multipoint voice communication system according to the present invention, but is useful for generally explaining what a multipoint voice communication system is like. Since this is a diagram, a general description of the multipoint voice communication system will be given below with reference to the diagram.

[0005] In FIG. 1, each terminal is a terminal, and each terminal accommodates one line of an ISDN basic interface, and uses two channels provided by the one line (each of which is called a B channel). Connected to the device. In other words, if the terminal on the right is connected using one B channel, the terminal on the left is connected using the other B channel. In this way, four terminals or more are connected by a single B-channel loop, and a multipoint voice communication system is configured. On this loop, the audio signal is, for example, is being transmitted in the order of ￫￫￫￫.

FIG. 5 is a block diagram which will be described later as a configuration example of a terminal related to the present invention. Since FIG. 5 is a diagram useful for explaining a general configuration example of the terminal in FIG. A general configuration example of the terminal in FIG. 4 will be described with reference to FIG.

In FIG. 5, reference numeral 11 denotes an ISDN, 12 denotes a network interface unit, 13 denotes a transcoder (1), 14
Is a subtraction processing unit, 15 is an addition processing unit, 16 is a transcoder (2), 17 is an audio decoding unit, 18 is an audio output unit, 19
Is a voice input unit, 20 is a voice coding unit, 21 is a delay processing unit,
22 is an attenuation processing unit.

In FIG. 5, a voice signal flowing on a loop (transmission path) is transmitted from the ISDN 11 to the network interface unit 1.
2, a transcoder (1) 13, a subtraction processing unit 14, an addition processing unit 15, and a transcoder (2).
16, through the network interface unit 12 to the ISDN 11
To return to the loop (transmission path). At this time, the audio signal from the terminal input from the audio input unit 19 is
The audio signal is encoded by the audio encoding unit 20, added to the audio signal from the subtraction processing unit 14 by the addition processing unit 15, and exits on a loop (transmission path).

On the other hand, the subtraction processing section 14 converts the audio signal from the transcoder (1) 13 into an audio signal from its own terminal first (that is, before one round of the loop).
9. An audio signal transmitted on a loop (transmission path) via the audio signal encoding unit 20 is obtained by passing through the delay processing unit 21 (that is, the delay time in the delay processing unit 21 is equivalent to the delay time corresponding to one round of the loop). Since the subtraction is performed, it is possible to output only an audio signal that does not include an audio signal from the own terminal, that is, only an audio signal from another terminal, and this is decoded by the audio decoding unit 17 and is output from the audio output unit 18. Is output.

As a result, each terminal can listen to the audio signal from the other terminal and input the audio signal from the own terminal to the transmission line, thereby enabling voice communication with the other terminal. The attenuation processing unit 22 performs the subtraction by the subtraction processing unit 14 by matching the level of the audio signal output from the delay processing unit 21 with the level of the audio signal output from the transcoder (1) 13. It is inserted in order to make

As described above, the subtraction processing section 14 subtracts the audio signal that has passed through the delay processing section 21 and the attenuation processing section 22 from the audio signal output from the transcoder (1) 13. In this case, only the audio signal from the other terminal is output. That is, the audio signal from the own terminal before one round of the loop in the audio signal output from the transcoder (1) 13 is removed. Although it was erased, for various reasons, the withdrawal was not completely performed, and the withdrawal was insufficient, resulting in excess or withdrawal.

[0010] The result of the under-removal or over-removal is the result of noise, such as unremoved noise at the terminal, along with the noise mixed on the line due to a transmission error, etc., 11 → 12 → 13 →
The voice communication is interrupted by continuing on the loop (transmission path) via the route of 14 → 15 → 16 → 12 → 11.
In order to attenuate noise by inserting a signal attenuating element in the middle, conventionally, an attenuating element has been inserted into each terminal.

[0011]

As described above, when an attenuating element is inserted into each terminal, an attenuation process is performed on the digital signal. Therefore, errors due to quantization accumulate, and each terminal generates an error. However, there is a problem that a calculation error increases in the subtraction processing of the past input signal of the own terminal (before one round of the loop). In particular, when an audio signal is transmitted using a high-efficiency code, it is necessary to convert each terminal to linear data in order to perform a subtraction process, and there is a problem that errors become significant. In addition, when an attenuating element is inserted into each terminal, a voice signal, which is a main signal, is also attenuated at each terminal.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the problems of the prior art, reduce quantization errors, reduce noise, and realize and provide a multipoint voice communication system with good speech quality.

[0013]

In order to achieve the above object, according to the present invention, each terminal in a multipoint voice communication system comprises:
Subtracts the audio signal input from its own terminal when it leaves its terminal one round before the loop from the received audio signal received from the transmission line, and extracts only the audio signal input from the other terminal. Means, and an addition means for adding an audio signal newly input from the own terminal to the output audio signal from the subtraction means and sending the signal to a transmission path,

Any one of the terminals on the loop
In only one terminal, the input signal is attenuated by less than 1 in at least one of the routes from when the received voice signal is input from the transmission path, passes through the subtraction means and the addition means, and is output to the transmission path. Insert and connect the attenuating means that outputs the signal obtained by multiplying the constant as the output signal ,
Arithmetic error that can occur in the subtraction means and the transmission path
The transmission errors that may occur above were attenuated . At this time, the attenuating means is inserted and connected particularly in the route from the subtracting means to the adding means.

[0015]

Since quantization noise is generated by inserting an attenuating element in order to reduce calculation (subtraction) errors, the insertion of an attenuating element which causes the generation of such a quantization noise must be performed on a loop (transmission path). By limiting to any one terminal, noise of the entire system can be reduced. Further, the processing amount at the terminal where no attenuation element is inserted can be reduced, and the terminal configuration can be simplified.

Further, when the attenuating means is to be inserted and connected especially in the route from the subtracting means to the adding means, the voice communication is not performed in the mutual communication between the attenuating element insertion terminal and another terminal. Since the signal itself is not attenuated, for example, by designating the attenuating element insertion terminal as the host, there is an advantage that there is no deterioration in communication performance between the host and the member.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described by using an IS
A voice communication system using the DN basic interface will be described with reference to the drawings.

FIG. 4 is a block diagram showing a connection example of the multipoint voice communication system according to the present invention, as described above. In FIG. 1, each terminal accommodates one line of an ISDN basic interface and is connected to terminals at both ends by one B channel, respectively, so that a loop of one B channel is formed as a whole. FIG. 4 shows a case where the multipoint voice communication system according to the present invention is composed of four terminals. In this example,
It is assumed that the audio signal is transmitted in the order of →→→→ on this loop.

In the present invention, in the multipoint voice communication system shown in FIG. 4, any one specific terminal (eg, terminal)
Is characterized in that an attenuation element is inserted only in the other terminals and no attenuation element is inserted in other terminals ( terminals to ).

FIG. 1 is a block diagram showing a configuration example of an arbitrary specific terminal (for example, a terminal) into which an attenuation element is inserted as the terminal in FIG. In FIG. 1, the same components as those in FIG. 5 are denoted by the same reference numerals. In addition, reference numeral 50 denotes an attenuation processing unit as an attenuation element. This attenuation processing unit 50 represents an attenuation element inserted as an arbitrary specific terminal. The overall circuit operation remains the same as that described above with reference to FIG. Hereinafter, description related to the present invention will be provided.

Referring to FIG. The audio encoding unit 20 converts the audio signal input from the audio input unit 19 into a linear encoded signal. The audio decoding unit 17 converts the input linear encoded signal into an audio signal. The transcoder (1) 13 converts a high-efficiency code used for transmission into a linear encoded signal used for internal processing. For example,
When a code that is nonlinearly quantized by a μ-law method is used as a transmission code, the transcoder (1)
The μ-law coded signal is converted into a linear coded signal.

The transcoder (2) 16 converts a linear encoded signal used in internal processing into a high-efficiency code used for transmission. For example, when a code that is nonlinearly quantized by a μ-law method is used as a transmission code,
The transcoder (2) 16 converts the linear encoded signal into a μ-
Convert to a raw coded signal. Transcoder (1) 1
3 and the transcoder (2) 16 are inverse transforms of each other.

The subtraction processing section 14 includes a transcoder (1)
The audio signal from the delay processing unit 21 (corresponding to a signal input to the terminal in the past) is subtracted from the audio signal received from the terminal 13. The resulting audio signal is transmitted to the audio decoding unit 17 and the attenuation processing unit 50 as a result of the subtraction. Addition processing unit 1
5 adds the audio signal from the audio signal (current input signal of the terminal) and the attenuation processor 50 from the voice coding section 20. The signal resulting from the addition is transmitted to the transcoder (2) 16.

The attenuation processing section 50 is for attenuating quantization noise or the like circulating on a loop (transmission path). The input signal is multiplied by an attenuation constant α and output. α is a real number | α | <
It is one. The delay processing unit 21 sets a group delay time T required for the audio signal to make one round of the loop, and performs a subtraction process by delaying the input audio signal from the audio encoding unit 20 by the time T.
Transmit to the unit 14 . The measurement of the group delay time T can be obtained by performing the measurement by an appropriate known means.

The network interface unit 12 is an ISDN 11
Interface with In this example, since the flow of the audio signal is one-way, the network interface unit 12 uses the channel connected to the terminal (FIG. 4) as the reception channel and the channel connected to the terminal (FIG. 4) as the transmission channel. And The audio output unit 18 is a man-machine interface unit that outputs an audio signal received from the audio decoding unit 17. The voice input unit 19 is a man-machine interface for inputting a voice signal.

FIG. 5 is a block diagram showing a configuration example of a terminal (for example, terminal to) in which no attenuation element is inserted as the terminal in FIG. FIG. 5 has been briefly described above within the scope of a general terminal. here,
Hereinafter, description related to the present invention will be provided. As already apparent, FIG. 5 corresponds to a configuration obtained by removing the attenuation processing unit 50 from the configuration of FIG.

Now, assume that a certain terminal is a terminal n, and at a certain time t, this terminal n receives a voice signal Rin (n, t) from the transmission line and transmits a voice signal Sout (n, t). Suppose that it is transmitted to the transmission line. Those converted to linear coded signals are represented by Rin '(n, t), Sou
Assuming that t ′ (n, t), the received speech signal Rin ′ (n,
t) and the input signal Rout ′ (n, t) to the audio decoding unit
Rout ′ (n, t) = Rin ′ (n, t) −Sin ′
(N, t-T).

Further, the outgoing audio signal Sout '(n, t)
And Sout ′ (n, t) = Sin ′ (n, t) + α * (R
in ′ (n, t) −Sin ′ (n, t−T)).

Instead of the configuration shown in FIG. 1, it is also possible to insert and connect an attenuation processing unit 50 as an attenuation element at a stage subsequent to the addition processing unit as shown in FIG. In FIG. 4, each terminal configuration of the terminals to which no attenuation element is inserted is the same as that of FIG. 5 even in this case.

In this case, the received speech signal Rin 'after being converted into a linear encoded signal at the attenuating element insertion terminal (FIG. 2).
(N, t) and the input signal Rout ′ (n,
t) is Rout ′ (n, t) = Rin ′ (n, t) −α * Si
n ′ (n, t−T).

Also, the outgoing audio signal Sout '(n, t)
And the output signal Sin ′ (n, t) from the speech encoding unit is: Sout ′ (n, t) = α * ｛Sin ′ (n, t) + Rin ′ (n, t) −α
* Sin ′ (n, t−T)} .

Further, instead of the configuration shown in FIG.
As shown in (1), it is also possible to insert and connect an attenuation processing unit 50 as an attenuation element at a stage preceding the subtraction processing unit. In FIG. 4, each terminal configuration of the terminals to which no attenuation element is inserted is the same as that of FIG. 5 even in this case.

In this case, the received speech signal Rin 'after being converted to a linearly encoded signal at the attenuating element insertion terminal (FIG. 3).
(N, t) and the input signal Rout ′ (n,
t) is given by Rout ′ (n, t) = α * (Rin ′ (n, t) −S
in ′ (n, t−T)).

Also, the outgoing audio signal Sout '(n, t)
And Sout ′ (n, t) = Sin ′ (n, t) + α * (R
in ′ (n, t) −Sin ′ (n, t−T)).

In any of the terminals shown in FIGS. 1 to 3 and FIG. 5, the quantization noise generated in the transcoder, the subtraction processing unit and the attenuation processing unit, the noise generated in the transmission path, and the like of each terminal are:
Although it occurs in a speech path, it is attenuated each time it passes through a terminal having an attenuation element, so that it does not accumulate in a loop (transmission path).

In this embodiment, the case has been described where linear encoding / decoding is performed by the audio encoding unit and the audio decoding unit. However, in order to effectively use the existing module, the audio encoding unit / audio decoding unit includes μ. It is also possible to use a CODEC that performs high-efficiency encoding by a non-linear quantization method such as -law. In this case, insert the transcoder (2) between the subtraction unit and the audio decoding section, it may be inserted transcoder (1) in between the adder unit and delay processing unit voice code section.

[0037]

As described above, according to the present invention,
In addition to removing the noise in the loop (transmission path), the generation of the noise in the loop itself can be reduced in the first place, so that a good multipoint voice communication system can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an arbitrary specific terminal into which an attenuation element is inserted as a terminal in a multipoint voice communication system according to the present invention.

FIG. 2 is a block diagram showing another configuration example of an arbitrary specific terminal into which an attenuation element is inserted as a terminal in the multipoint voice communication system according to the present invention.

FIG. 3 is a block diagram showing still another configuration example of an arbitrary specific terminal into which an attenuation element is inserted as a terminal in the multipoint voice communication system according to the present invention.

FIG. 4 is an explanatory diagram showing a connection example of a multipoint voice communication system according to the present invention.

FIG. 5 is a block diagram showing a configuration example of a terminal to which no attenuation element is inserted as a terminal in the multipoint voice communication system according to the present invention.

[Explanation of symbols]

11 ISDN, 12 network interface unit, 13 transcoder (1), 14 subtraction processing unit, 15 addition processing unit, 16 transcoder (2), 17 audio decoding unit, 18 audio output unit 19 voice input unit, 20 voice code unit, 21 delay processing unit, 22 attenuation processing unit, 50
Attenuation processing unit (attenuation element)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-212162 (JP, A) JP-A-57-112167 (JP, A) JP-A-56-94895 (JP, A) 189005 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04M 3/56

Claims (2)

(57) [Claims] 1. A heat each terminal in each different point
Connected in a loop via a transmission path where transmission errors may occur ,
A multipoint audio communication system in which an audio signal from each terminal flows in one direction on the loop-shaped transmission path and is received by each terminal, thereby performing audio communication between the terminals. Is from the received audio signal received from the transmission path,
When it exits its own terminal one round before the loop, the audio signal input from its own terminal is subtracted by calculation, and only the audio signal input from another terminal is extracted and output.
Calculation means, and addition means for adding an audio signal newly input from the own terminal to the output audio signal from the subtraction means and transmitting the signal to the transmission path. In only one specific terminal, the input signal is provided in at least one of the routes from the time when the received voice signal is input from the transmission path, passes through the subtraction means and the addition means, and is output to the transmission path. Attenuating means for outputting as an output signal a signal obtained by multiplying the signal by an attenuation constant smaller than 1 and connecting the subtraction means
Calculation error that may occur in the
A multipoint voice communication system characterized by attenuating transmission errors . 2. The multipoint voice communication system according to claim 1, wherein said attenuation means is inserted and connected in a route from said subtraction means to said addition means. Communications system.