JP2804689B2 - Loop type N-1 addition method - Google Patents

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 to a method of adding voice when a plurality of terminals are connected in a loop and a voice conference is performed by multipoint terminals. And 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,
2. Description of the Related Art A technology for connecting a telephone via a communication network to hold a voice conference is known. In particular, a technique is known in which each terminal uses two communication paths and connects each of the communication paths to a different ground, thereby forming a loop (loop) transmission path as a whole to conduct a voice conference. .

[0003] As a conventional technique of this kind, for example, techniques described in JP-A-56-65561 and JP-A-58-3361 are known.

In the prior art, a plurality of terminals for telephone conference are connected as a ring node in a network, and each node drops and inserts voice. Then, in this conventional technique, the voice received by the terminal in the past is subtracted from the voice received from the loop, and this is used as the received voice of the own terminal. That is, a so-called N-1 addition method is used.

[0005]

According to the prior art, as a transmission / reception signal with respect to a loop transmission line, a signal which has been encoded with high efficiency for band compression, for example, a PCM (pulse code modulation) μ-Law code or , ADPCM (Adaptive Differential Pulse Code Modulation) or the like. Since such codes cannot be directly added or subtracted,
After conversion to a linear code, an addition / subtraction operation (N-1 addition) must be performed. At this time, so-called quantization noise is generated and mixed into the communication path.

For this reason, in the prior art, the quantization noise generated at each node in the loop is circulated in the loop. However, the loop itself, which is a communication path, performs signal processing on the quantization noise. Because it is considered to constitute a perfect integrator, the noise power in the loop increases,
There is a problem that the original communication quality is deteriorated.

[0007] Further, in the above-mentioned conventional technology, in each terminal,
In some cases, a part of the received component may be mixed into the transmission input again to generate an echo, and this reverberation component circulates in a loop together with the main signal. However, when the number N of connected terminals increases, this effect should be ignored. This causes a problem that communication quality deteriorates.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, remove noise in a loop, and reduce reverberation components to maintain good conference call quality. To provide a suitable loop type N-1 addition method.

[0009]

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

[0010] Further, the above-mentioned object is, after making a round of the loop,
Since the returning voice signal of the own terminal is attenuated by α to the Nth power (N is the number of terminals), the subtraction for α of the Nth power is also considered in the subtraction for canceling the own voice. Is achieved by doing so.

That is, the object is to subtract a signal obtained by amplitude-adjusting a past input signal from the own terminal from a received input signal from the receiving channel to cancel the signal of the own terminal, and use this as a received output signal. This is achieved by adding the current input signal of the terminal itself to this signal and multiplying the signal by a loop attenuation constant to obtain a transmission path transmission signal.

In the above-described configuration, the input signal received from the transmission path is RIN (t), and the output signal transmitted to the transmission path is SOUT (t).
(T) When the transmission input signal of the terminal is SIN (t) and the reception output signal of the terminal is ROUT (t), the loop-type N-1 addition method according to the present invention is realized by the following equation. This is achieved by configuring

[0013]

Y (t) = RIN (t) −SIN (t−ΔT) · α ^N

[0014]

ROUT (t) = y (t) · β

[0015]

SOUT (t) = {y (t) + SIN (t)} · α

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

Further, the object is to subtract a signal obtained by amplitude-adjusting a past input signal from the own terminal from a received input signal from a receiving channel to cancel the signal of the own terminal, and use this as a received output signal, This is achieved by multiplying the received output signal by a loop attenuation constant and adding the current input signal of the terminal itself to the transmission output signal.

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

[0019]

Y (t) = RIN (t) −α ^N−1 · SIN (t−ΔT)

[0020]

ROUT (t) = β · y (t)

[0021]

SOUT (t) = α · y (t) + SIN (t)

Further, the object of the present invention is to reduce the SIN in the above-mentioned (Equation 1) to (Equation 6) in order to cancel as much as possible the reverberation component which is going to go through the loop.
(T) The polarity of the signal is set to, for example, an opposite-phase input [−SIN (t) input] at an even-numbered (odd-numbered) terminal and an SIN (t) input at an odd-numbered (even-numbered) terminal. Is 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 another as it passes through it. The Nth power of the attenuation constant α is also used to adjust its amplitude level for canceling its own voice after one loop. Note that the original voice signal other than noise is also calculated by the above-described attenuation constant α.
Alpha every passing nodes, α ^2, α ^3, subjected to damping and ...... but, alpha is the effect because it is set to a constant than 1 close to 1 can be practically negligible.

Next, the canceling action of the reverberation component will be described. Hereinafter, only the reverberation component will be described separately from the main signal component based on 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 split into two hands when it reaches the next terminal B. One of them goes through the main signal route and appears at its output with an attenuation of α. On the other hand, the reverberation component there passes through the reverberation 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.

[0026] The component achieves the terminal C, also a main signal route and at the output end divided into a reverberant route signals passing through the echo _{route, e (t) + r b} e
(T) + _{[e (t) + r b e} (t) ] is expressed as r _C.
This is a second-order reflection component in the formula r _b r _C e (t) can be ignored as a small. In fact, e
Since (t) itself is a reflection component, the signal represented by the above equation is a reflection signal for three times in convenience.

Then, the signal output is e (t) +
_{r b e (t) + r} C e and becomes (t), equal in each terminal reflection characteristics at each terminal, a r _b = r _C, and,
Since the polarities of the transmission input amplifiers are in an opposite phase relationship between adjacent terminals, they are canceled out, and as a result, only e (t) is output as an echo signal.

As described above, according to the present invention, the reverberation component is reduced by one every time the signal passes through the even-numbered and odd-numbered terminals.
The next component cancels out, and the reverberation component via the main signal route returns to terminal A, like the main signal, e (t
−ΔT), and the echo signal can be prevented from circulating in the loop.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the loop type N-1 addition system according to the present invention will be described below in detail 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 an N-1 adder circuit according to an embodiment of the present invention is connected in a loop to hold an N-party conference. FIG. 1 and 2, 1 to N are N-1 adder circuits, 11 and 21 are conversion circuits for mutually converting input / output signals into linear codes, and 31 and 41 are conversion circuits for mutually converting linear codes and high efficiency codes. Circuit (transcoder), 100, 400
Is an adder / subtractor, 200, 300, and 500 are multipliers, 600
Is a delay circuit, and 700 is a loop delay measuring device.

First, a conference using a loop transmission line to which the present invention is applied will be described with reference to FIG. FIG.
, N N-1 adders 1, 2,..., N
A ring via the communication channels CHi and CHj, respectively.
Connected. Each of the N-1 adding circuits is configured to receive an insertion signal SIN (t) from outside and drop out a reception signal from the loop to obtain ROUT (t). The system to which the present invention is applied
N terminal (N terminal) by the form of such terminal and transmission path
However, conversations (meetings) can be freely performed.

The N-1 addition circuit in each terminal is configured as shown in FIG.
(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 sending a signal SOUT (t) to the loop are provided.

The circuit 11 for converting the insertion signal SIN (t) into a linear code, for example, outputs the insertion signal SIN (t) in μ-L
In the case of the output signal of the aw encoder, it is a conversion circuit or the like for converting the μ-law coded signal into a linear signal, and the inverse conversion circuit 21 performs the reverse code conversion as described above. The conversion circuit (transcoder) 31 is an encoder for performing high-efficiency encoding of the linear code again, and may be, for example, a μ-law encoder, an ADPCM encoder, or the like. The conversion circuit 41 receives the signal RIN (t) from the loop transmission path.
Is converted to a linear code.
Law decoder, ADPCM decoder and the like.

The subtractor 100 is a subtractor for subtracting SIN (t-ΔT), which is a signal transmitted by the terminal 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 a value α according to the total ground number N arranged on the loop. . The adder 400 is an adder that superposes the voice insertion SIN (t) of the own terminal on the loop cyclic signal. The multiplier 500 is a multiplier provided to attenuate cyclical quantization noise and the like, and a numerical value smaller than 1 close to 1 is given as a multiplication coefficient α. The value of α exactly matches the α raised to the Nth power.

The multiplier 300 is a multiplier provided for slightly adjusting the amplitude when the ROUT (t) signal is extracted from the signal circulating on the loop. The multiplier coefficient value β is α And an appropriate value of β ≧ 1 depending on the values of N and N. The delay circuit 600 is set to a value equal to the delay time ΔT of the signal group that goes around the loop,
Is a delay circuit for delaying the insertion signal SIN (t) to be applied to the delay circuit by ΔT. The value of the delay time is determined by the delay amount measuring device 7.
The value measured by 00 is set in advance. The group delay time of a signal circulating on a loop can be measured by a suitable known means, but will not be described here because it departs from the gist of the present invention.

The configuration of the N-1 adder circuit shown in FIG. 1 as described above realizes the above-described equations (Equation 1), (Equation 2), and (Equation 3). In the illustrated N-1 adder 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 every time they pass through a node. Does not accumulate in a loop. In addition, the original voice signal component is also attenuated by 20 Log α (db) per node, but the amount is small and does not hinder communication. In the above description, if necessary, 20Logβ (db)
Can be corrected.

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

Although not shown, the embodiment of the present invention shown in FIG. 2 has a transmission input signal SIN applied 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 reverberation signal from circulating in the loop as described above, and it is possible to prevent the deterioration of the voice quality due to the reverberation signal. The aforementioned inverting amplifier is
Actually, it can be easily realized by the input code conversion unit performing the sign inversion processing.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention. The reference numerals in FIG. 3 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-described (Equation 4) to (Equation 6) are realized. Is something you can do.

According to another embodiment of the present invention, as compared with the above-described embodiment of the present invention, while maintaining the same noise reduction effect, the loop attenuation of the main signal is reduced by 20Logα.
(Db).

According to the above-described embodiment of the present invention, noise components introduced into the loop and circulating through the loop due to the introduction of the loop attenuation constant, for example, quantization noise by the high-efficiency coding apparatus, transmission path Equivalent noise caused by an error, overflow noise caused by intra-node addition, and the like can be removed, and a high-quality audio conference can be performed.

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 to oscillate. Since the inside tour can be eliminated, a good N-party conference can be realized.

[0044]

As described above, according to the present invention, the present invention is suitable for use in a voice conference in which noise in a loop can be removed, reverberation components can be reduced, and good conference call quality can be maintained. A simple loop-type N-1 addition method can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a situation in which N-1 adder circuits according to an embodiment of the present invention are connected in a loop and an N-party conference is held.

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

[Description of Codes] 1-N N-1 Addition Circuits 11, 21 Conversion Circuits for Converting Input / Output Signals to Linear Codes 31, 41 Conversion Circuits (Transcoders) for Converting Linear Codes to High Efficiency Codes 100, 400 Adder / subtractor 200, 300, 500 Multiplier 600 Delay circuit 700 Loop delay measuring device

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hisashi Ibaraki 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-57-93768 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H04M 3/56 H04L 12/42

Claims (5)

(57) [Claims] 1. A plurality (N) connected to a loop transmission path
In a loop-type N-1 addition scheme of a voice terminal that enables conversation between two terminals, a signal obtained by amplitude-adjusting a past input signal from the terminal itself is subtracted from a reception input signal from a reception channel to generate a signal. A loop type characterized by canceling a terminal signal, making this a reception output signal, adding the current input signal of the terminal itself to this signal, and multiplying this signal by a loop attenuation constant to obtain a transmission path transmission signal. N-1 addition method. 2. A plurality (N) connected to a loop type transmission line.
In a loop-type N-1 addition system of a voice-based terminal that enables conversation between two terminals, a reception input signal RIN (t) from a reception channel and a transmission output signal SO to a transmission channel
UT (t), transmission input signal SIN (t) from own terminal,
During the own terminal reception output signal ROUT (t), y (t) = RIN (t) −SIN (t−ΔT) · α ^N ROUT (t) = y (t) · β SOUT (t) = {y (t) + SIN (t)} · α (where α is an attenuation constant smaller than 1, β is an amplification constant satisfying β ≧ 1, and N is included in the loop transmission path. Number of terminals, ΔT
Is a signal transmission delay time of one round of the loop, and t is a time variable). 3. A plurality (N) connected to a loop transmission path
In a loop-type N-1 addition scheme of a voice terminal that enables conversation between two terminals, a signal obtained by amplitude-adjusting a past input signal from the terminal itself is subtracted from a reception input signal from a reception channel to generate a signal. A loop characterized by canceling a signal of a terminal, using the signal as a reception output signal, multiplying the reception output signal by a loop attenuation constant, and adding the current input signal of the terminal itself to a transmission line transmission signal. Type N-1 addition method. 4. A plurality (N) connected to a loop transmission path
In a loop-type N-1 addition system of a voice-based terminal that enables conversation between two terminals, a reception input signal RIN (t) from a reception channel and a transmission output signal SO to a transmission channel
UT (t), transmission input signal SIN (t) from own terminal,
During the own terminal reception output signal ROUT (t), y (t) = RIN (t) −α ^N−1 · SIN (t−ΔT) ROUT (t) = β · y (T) SOUT (t) = α · y (t) + SIN (t) (where α is an attenuation constant smaller than 1, β is an amplification constant satisfying β ≧ 1, and N is included in the loop transmission path. Number of terminals, 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 the own terminal, an even-numbered (odd-numbered) terminal out of a plurality (N) of the terminals inverts the input signal to form an odd-numbered (even-numbered) terminal. 5. The loop-type N-1 addition method according to claim 1, wherein the input unit receives the input signal as it is.