JPH06189005A - Loop type n-1 adding system - Google Patents

Abstract

PURPOSE:To suppress a noise component and an echo component circulated inside a loop concerning a conference telephone for holding a conference among N persons by constituting a loop-shaped transmission line by connecting N voice system terminals while using two channels. CONSTITUTION:A received signal from a transmission line is decoded 41, an input signal in the past from the present terminal is amplitude adjusted 200, the signal of the present terminal is canceled and defined as a received output signal, further, the current input signal of the present terminal is added 400 to this signal, a loop attenuation constant is multiplied 500, and this signal is encoded 31 again and defined as a transmission line sending signal. In that case, the present terminal input signal is inputted after the polarity is inverted at an even (or odd) numbered terminal. Therefore, the various noice components injected into the loop-shaped transmission line can be attenuated and prevented from being accumulated, and the N-person conference can be satisfactorily held with high speaking quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop-type N-1 addition method, and more particularly, for adding voices when a plurality of terminals are connected in a loop and a voice conference is conducted by terminals at multiple points. The present invention relates to a loop type N-1 addition method suitable for use in

[0002]

2. Description of the Related Art Generally, a plurality of voice terminals, for example,
A technique is known in which a telephone is connected via a communication network to hold a voice conference. In particular, a technique is known in which each terminal uses two communication paths and connects each communication path to a different ground to form a loop-shaped transmission path as a whole to conduct a voice conference. .

As this type of conventional technique, for example, the techniques described in JP-A-56-65561 and JP-A-58-3361 are known.

[0004] In the above-mentioned prior art, a plurality of terminals that hold a telephone conference are connected as a ring node in the network, and each node drops and inserts voice. Then, in this conventional technique, the voice inserted by the own terminal in the past is subtracted from the received voice from the loop to make this the received voice of the own terminal, and further the new voice of the own terminal is added to the signal sent to the loop. The so-called N-1 addition method is used.

[0005]

In the above-mentioned prior art, as a transmission / reception signal to / from a loop transmission line, a high-efficiency coded signal for band compression, for example, PCM (pulse code modulation) μ-Law code, or , ADPCM (adaptive differential pulse code modulation) and the like. Such codes cannot be directly added or subtracted, so
The addition / subtraction operation (N-1 addition) must be performed after converting to a linear code. At this time, so-called quantization noise is generated and mixed into the speech path.

Therefore, in the above-mentioned conventional technique, this quantization noise generated at each node in the loop is circulated in the loop, but the loop itself, which is a communication path, performs signal processing for the quantization noise. Since it is considered that the complete integrator is configured, the noise power in the loop increases,
There is a problem that the original call quality is deteriorated.

Further, according to the above-mentioned prior art, in each terminal,
There is a case where a part of the reception component is mixed into the transmission input again to generate an echo, and this reverberation component circulates in the loop together with the main signal, but when the number N of connected terminals becomes large, this effect should be ignored. However, there is a problem that call quality is deteriorated.

The object of the present invention is to solve the above-mentioned problems of the prior art, to eliminate noise in a loop, and also to reduce echo components to maintain good conference call quality. And to provide a suitable loop type N-1 addition method.

[0009]

According to the present invention, the above object is to avoid that the loop type transmission line having the above-mentioned conventional terminal as a node is itself a perfect integrator of noise. This is achieved by introducing an attenuation constant α (α <1) into the loop so as to attenuate the noise component.

Further, the above-mentioned purpose is to
Since the voice signal confidence of the returning own terminal has been attenuated by α to the Nth power (N is the number of terminals), this attenuation of α to the Nth power is also considered for subtraction for canceling the own voice. It is achieved by doing so.

That is, the object is to cancel a signal of the own terminal by subtracting a signal obtained by amplitude-adjusting a past input signal from the own terminal from a received input signal from a reception channel, and making this a reception output signal, This is achieved by adding the current input signal of the terminal itself to this signal and then multiplying this signal by the loop attenuation constant to obtain the transmission line output signal.

In the above-mentioned configuration, the reception input signal from the transmission line is RIN (t) and the transmission output signal to the transmission line is SOUT.
(T), when the transmission input signal of the own terminal is SIN (t) and the reception output signal of the own terminal is ROUT (t), the loop type N-1 addition method according to the present invention is realized by the following equation. It is achieved by configuring

[0013]

[Equation 1]

[0014]

[Equation 2]

[0015]

[Equation 3]

However, in (Equation 1) to (Equation 3), t is a time variable, ΔT is a loop loop transmission line delay time in an operating state, N is the total number to ground, α is an attenuation constant, and β is an amplification constant.

Further, the above object is to cancel a signal of the own terminal by subtracting a signal obtained by amplitude-adjusting a past input signal from the own terminal from a received input signal from a receiving channel, and using this as a reception output signal, This is achieved by multiplying this received output signal by the loop attenuation constant and then adding this to the current input signal of the terminal itself to make it the transmission line output signal.

The above-mentioned configuration is achieved by modifying the loop-type N-1 addition method so as to realize the following equation.

[0019]

[Equation 4]

[0020]

[Equation 5]

[0021]

[Equation 6]

Further, the object of the present invention is to make the SINs in the above (Equation 1) to (Equation 6) in order to cancel as much as possible the reverberant components trying to circulate in the loop.
The polarity of the (t) signal is set to, for example, an opposite-phase input [-SIN (t) input] in the even-numbered (odd) terminal and SIN (t) input in the odd-numbered (even) terminal. Achieved by

[0023]

The damping constant α introduced for the present invention as described above
Acts to attenuate the noise injected into the loop one after the other as it passes through. Further, the Nth power of the attenuation constant α is also used to adjust the amplitude level of the own voice after the loop has been canceled. The original voice signal other than noise is also
Each time it passes through the node, it is attenuated by α, α ² , α ³ , ..., But since α is set to a constant close to 1 and smaller than 1, its influence can be practically ignored.

Next, the canceling action of the echo component will be described. In the following description, only the echo component is considered separately from the main signal component according to the principle of superposition.

Now, it is assumed that a part of the reception component of a certain terminal A is injected into the transmission input as an echo e (t).
This signal component is divided into two when reaching the next terminal B. One of them passes through the main signal route and appears at its output end after being attenuated by α. On the other hand, the reverberant component there passes through the reverberant route and is output. Signals passing through the echo route is expressed as _{e (t) + r b e} (t). Here, r _b is the reflection coefficient at the terminal B.

When this component reaches terminal C, it is divided into a main signal route and an echo route, appears at the output end, and the signal passing through the echo route is e (t) + r _b e.
It is represented by (t) + [e (t) + r _b e (t)] r _C.
The second-order reflection component r _b r _C e (t) in this equation can be ignored because it is small. In fact, e
Since (t) itself is a reflection component, the signal represented by the above equation is a reflection signal three times in total.

Then, the signal output is e (t) +
r _b e (t) + r _C e (t), but if the reflection characteristics at each terminal are the same, then r _b = r _C , and
Since the polarities of the transmission input amplifiers are set to be in a phase opposite to each other between adjacent terminals, these are canceled out, and as a result, only e (t) is output as an echo signal.

In this way, according to the present invention, the reverberant component is one of the reverberant components every time it passes through even-numbered and odd-numbered terminals.
When the next component is canceled and the reverberant component that has passed through the main signal route returns to the terminal A, e (t
It is possible to prevent the echo signal from being circulated in the loop by being canceled by −ΔT).

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a loop type N-1 addition system according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 illustrates a situation in which N-1 summing circuits according to an embodiment of the present invention are connected in a loop to hold an N-party conference. It is a figure. In FIGS. 1 and 2, 1 to N are N-1 addition circuits, 11 and 21 are conversion circuits that mutually convert input / output signals into linear codes, and 31 and 41 are conversions that mutually convert linear codes and high efficiency codes. Circuit (transcoder), 100, 400
Is an adder / subtractor, 200, 300, 500 are multipliers, 600
Is a delay circuit, and 700 is a loop delay measuring device.

First, referring to FIG. 2, a conference using a loop-shaped transmission line to which the present invention is applied will be described. Figure 2
, N N−1 adder circuits 1, 2, ..., N are
Rings via the channels CHi and CHj, respectively
Connected to each other. Each of the N-1 addition circuits is configured to obtain ROUT (t) by adding an insertion signal SIN (t) from the outside and dropping out a reception signal from the loop. The system to which the present invention is applied is
Depending on the form of such terminals and transmission lines, N persons (N terminals)
However, they can have a conversation (meeting) freely.

The N-1 addition circuit in each terminal is constructed as shown in FIG. 1, and the signal SIN from each terminal is
(T) Insertion terminal 10, signal ROUT from loop
An output terminal 20 for dropping out (t), a terminal 40 for receiving a signal RIN (t) from the loop, and a terminal 30 for transmitting a signal SOUT (t) to the loop are provided.

In the circuit 11 for converting the insertion signal SIN (t) into a linear code, for example, the insertion signal SIN (t) is μ-L.
When it is the output signal of the aw encoder, it is a conversion circuit or the like that converts the μ-Law encoded signal into a linear signal, and the inverse conversion circuit 21 performs the code conversion opposite to the above. The conversion circuit (transcoder) 31 is an encoder for highly efficient encoding of a linear code, and may be, for example, a μ-Law encoder or an ADPCM encoder. The conversion circuit 41 receives the received signal RIN (t) from the loop transmission line.
Is a circuit for converting to a linear code, and specifically, μ−
It is a Law decoder, an ADPCM decoder, or the like.

The subtractor 100 is a subtractor for subtracting SIN (t-ΔT), which is a signal transmitted by the terminal itself in the past, from the loop reception signal. The multiplier 200 is a multiplier for adjusting the amplitude of the signal SIN (t-ΔT), and the multiplication coefficient is set to the Nth power of the value α according to the total number N of grounds arranged on the loop. . The adder 400 is an adder that superimposes the voice insertion SIN (t) of its own terminal on the loop cyclic signal. The multiplier 500 is a multiplier provided for attenuating cyclic quantization noise and the like, and is given a value smaller than 1 which is close to 1 as the multiplication coefficient α. The value of α exactly matches the α of the Nth power of α.

The multiplier 300 is a multiplier provided for adjusting the amplitude to some extent when the ROUT (t) signal is extracted from the signal circulating on the loop. The multiplication coefficient value β is α And an appropriate value of β ≧ 1 depending on the values of N. In the delay circuit 600, a value equal to the delay time ΔT of the signal group that goes through the loop is set, and the multiplier 200
Is a delay circuit for delaying the insertion signal SIN (t) given to the signal ΔT. The value of this delay time is calculated by the delay amount measuring device 7
The value measured by 00 is preset. The group delay time of the signal circulating on the loop can be measured by an appropriate publicly known means, but it is outside the scope of the present invention and will not be described here.

The configuration of the N-1 adder circuit shown in FIG. 1 as described above realizes the equations (Equation 1), (Equation 2) and (Equation 3). Then, in the illustrated N-1 addition circuit, quantization noise and the like generated at the time of mutual conversion between the linear code and the transmission path code are added to the communication path every moment, but are attenuated each time when passing through the node. It does not accumulate in the loop. Further, the original voice signal component is also attenuated by 20 Log α (db) per node, but the amount thereof is small and it does not cause any trouble in the call. In the above, if necessary, 20Logβ (db)
Can be corrected.

According to the above-described embodiment of the present invention, good call quality can be ensured in the conference call using the loop type transmission line in this way.

Although not shown, the embodiment of the present invention shown in FIG. 2 is a transmission input signal SIN added from each terminal.
_i (t) (i = 1 to N) is an even-numbered terminal,
It is configured to be input via an inverting amplifier. As a result, it is possible to prevent the echo signal from circulating in the loop as described above, and it is possible to prevent deterioration of the voice quality due to the echo signal. The inverting amplifier described above
Actually, it can be easily realized by the input code conversion unit performing the code inversion process.

FIG. 3 is a block diagram showing the structure of another embodiment of the present invention, and the reference numerals in the drawing are the same as those in FIG.

In another embodiment of the present invention, the position of the multiplier 500 for attenuating the quantization noise and the like in FIG. 1 is changed, and the above-mentioned (Equation 4) to (Equation 6) are realized. It is something that can be done.

According to this other embodiment of the present invention, the loop attenuation amount of the main signal is reduced to 20 Log.alpha. While maintaining the same noise reduction effect as compared with the one embodiment of the present invention which has already been described.
It can be reduced by (db).

According to the above-described embodiment of the present invention, the noise component introduced into the loop by introducing the loop attenuation constant and circulating in the loop, for example, the quantization noise by the high-efficiency encoder, the transmission line Equivalent noise caused by an error or overflow noise caused by addition within a node can be removed, and a high quality audio conference can be held.

Further, according to the embodiment of the present invention, it is possible to suppress the noise circulating in the loop from destabilizing the loop and causing the loop oscillation, and the loop of the echo component based on the external spatial echo is suppressed. Since it is possible to remove the internal tour, it is possible to make a good N-party conference.

[0044]

As described above, according to the present invention, it is suitable for use in a voice conference in which noise in a loop is removed and an echo component is also reduced to maintain good conference call quality. It is possible to provide a simple loop type N-1 addition method.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a situation in which N-1 addition circuits according to an embodiment of the present invention are connected in a loop to hold an N-party conference.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention.

[Explanation of symbols]

1-NN-1 addition circuit 11,21 Conversion circuit which inter-converts an input / output signal into a linear code 31,41 Conversion circuit (transcoder) which mutually converts a linear code and a high efficiency code 100,400 Adder / subtractor 200,300 , 500 Multiplier 600 Delay circuit 700 Loop delay measuring device

Front page continuation (72) Inventor Hisashi Ibaraki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. A plurality (N) connected to a loop type transmission line.
In a loop-type N-1 addition method of a voice terminal that enables conversation between individual terminals, a signal obtained by amplitude-adjusting a past input signal from the own terminal is subtracted from a received input signal from a receiving channel, A loop type characterized by canceling the signal of the terminal, using this as the reception output signal, adding the current input signal of its own terminal to this, and then multiplying this signal by the loop attenuation constant to form the transmission line transmission signal. N-1 addition method. 2. A plurality (N) connected to a loop type transmission line.
In a loop-type N-1 addition method of voice terminals that enables conversation between individual terminals, a reception input signal RIN (t) from a reception channel and a transmission output signal SO to a transmission channel
UT (t), a transmission input signal SIN (t) from its own terminal,
Between the own terminal reception output signal ROUT (t), [Equation 2] [Equation 3] (However, α is an attenuation constant smaller than 1, β is an amplification constant such that β ≧ 1, N is the number of terminals included in the loop type transmission line, ΔT
Is a signal transmission delay time of one round of the loop, and t is a time variable). 3. A plurality of (N) connected to a loop type transmission line
In a loop-type N-1 addition method of a voice terminal that enables conversation between individual terminals, a signal obtained by amplitude-adjusting a past input signal from the own terminal is subtracted from a received input signal from a receiving channel, A loop characterized in that the terminal signal is canceled, this is used as the reception output signal, this reception output signal is multiplied by the loop attenuation constant, and then the current input signal of the own terminal is added to this as the transmission line transmission signal. Type N-1 addition method. 4. A plurality (N) connected to a loop type transmission line
In a loop-type N-1 addition method of voice terminals that enables conversation between individual terminals, a reception input signal RIN (t) from a reception channel and a transmission output signal SO to a transmission channel
UT (t), a transmission input signal SIN (t) from its own terminal,
Between the own terminal reception output signal ROUT (t), [Equation 5] [Equation 6] (However, α is an attenuation constant smaller than 1, β is an amplification constant such that β ≧ 1, N is the number of terminals included in the loop type transmission line, ΔT
Is a signal transmission delay time of one round of the loop, and t is a time variable). 5. When inputting a transmission input signal from its own terminal, an even-numbered terminal among a plurality of (N) terminals inverts the input signal and outputs an odd-numbered terminal. 5. The loop type N-1 addition method according to claim 1, wherein the input signal is input as it is.