JPH06196951A - Bidirectional amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] A bidirectional amplifier that amplifies an attenuated signal in a 2-wire transmission line. [Structure] Hybrid circuit 11a for 2-wire and 4-wire exchange
The white noise 14a is applied to the input end of the filter in a silent period, the adaptive filter 12a is provided between the input end and the output end, the pseudo echo signal d _0p (n) is created, and the optimization operation of the adaptive filter 11a is performed. Communicate by obtaining a value and setting it. If the optimization operation is completed during the silent period, it is determined to be successful, and if it is not completed, it is determined to be unsuccessful, and the success / failure determiner 13a determines the optimization operation. [Effect] When the optimizing operation is not completed within a slight silent period at the start of communication, the silent period during communication is detected and the optimizing operation is performed, resulting in a large change in the attenuation amount of the communication line. You can surely deal with it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional amplifier for amplifying a signal attenuated in a two-line transmission line such as a telephone, a facsimile and a data.

[0002]

2. Description of the Related Art When bidirectional amplification is performed for the purpose of amplifying an attenuated signal in bidirectional communication using a two-wire line for transmitting telephone, facsimile, data, etc., two-wire to four-wire conversion is performed by a hybrid circuit. After that, the unidirectional amplifier performs amplification in each direction. However, the general subscriber line has different line types and line lengths for each line, so that the impedance is not constant, and a hybrid circuit having a fixed constant cannot achieve perfect impedance matching. When impedance matching cannot be achieved, that is, when the hybrid balance is lost, the signal at the 4-wire side input end of the hybrid circuit wraps around to the 4-wire side output end. If amplification is performed without removing this loop-in signal, in an extreme case, a 4-wire loop formed by the hybrid circuit causes oscillation, and a large echo is generated even when oscillation does not occur. For this reason, in the case where the 2-wire / 4-wire conversion is performed only by the hybrid circuit having the fixed constant, if the line condition is changed, the amplification is almost impossible.

As a technique for solving this problem, echo.
There is a bidirectional amplifier using a suppressor system or an echo canceller system.

Bidirectional amplifiers using the echo suppressor system take advantage of the fact that normal voice communication is conversational or nonsimultaneous bidirectional communication. For example, when the signal level of the speaker A is higher than the signal level of the speaker B, it is considered that there is no signal of the speaker B, and only the signal of the speaker A is amplified and the signal of the speaker B is suppressed and attenuated. Let By controlling the call direction in this way, it becomes possible to amplify the signal while suppressing the gain of the 4-wire loop. The echo suppressor system has the advantages that it is easy to control and can be constructed at low cost. On the other hand, since the control cannot be performed unless the signal level of the speaker A or the speaker B is detected and which signal is to be suppressed, the head disconnection is inevitably present and is essentially Since it does not allow simultaneous calls, it has the drawback that it tends to interfere with natural calls.

A bidirectional amplifier using the echo canceller system has a pseudo sneak-loop signal generating section inside, and a 2-wire 4-wire amplifier.
To cancel a signal in which a signal on the transmission side wraps around a line on the receiving side in a hybrid circuit that performs line conversion with a pseudo wraparound signal output from a pseudo wraparound signal generation unit, and to attenuate a signal that makes a loop in a 4-wire loop. Enables amplification. The pseudo wraparound signal generator is composed of a variable tap coefficient transversal filter that can change the attenuation amount and delay time, and while observing the wraparound signal generated in the hybrid circuit, corrects the tap coefficient to minimize it. To do. Therefore, even if the condition of the telephone line changes, it is possible to adapt to the change and reduce the sneak signal. Since the echo canceller system does not need to control the call direction, there is no head disconnection that occurs in the echo suppressor system, and simultaneous two-way communication can be performed without any trouble.

Bidirectional amplifiers using the echo canceller system are roughly classified into preset type and always adaptive type in terms of their control systems. In the echo canceller type preset type, it is necessary to determine the tap coefficient of the transversal filter in order to set the attenuation amount and delay time of the pseudo wraparound signal, and in order to obtain the tap coefficient, the training signal of the hybrid circuit is used. The optimum value of the tap coefficient of the transversal filter is determined (optimization) by sending out from the 4-wire side input end (transmission side) and monitoring the wraparound amount of the training signal appearing at the 4-wire side input end (reception side). ) Do. This optimizing operation is completed within a fixed time when there is no communication signal, and thereafter, communication is performed with the optimized tap coefficient value held.

In the constant adaptation type, a signal at the 4-wire side input end of the hybrid circuit that appears during communication is used without using a special training signal, and the amount of the signal sneaking into the 4-wire side output end of the hybrid circuit is monitored. This optimizes the tap coefficients of the transversal filter.

The advantage of the preset type is that the training signal can be arbitrarily selected because the training is performed during the period when the communication signal does not exist. In the tap coefficient optimizing operation, how fast it can converge to the optimum value (obtain the optimum value) is a problem, and the input to the pseudo wraparound signal generation unit (the signal at the 4-wire side input end of the hybrid circuit is a problem). ), A signal with less autocorrelation is required. If a signal with a small autocorrelation is selected as the training signal, it is possible to quickly converge to an optimum value. The disadvantages of the preset type are that the optimizing operation must be completed within a certain period, and that it cannot be dealt with if the line conditions change during communication. However, since the condition of the once connected telephone line rarely changes during communication, it cannot be a fatal defect.

The advantage of the always-adaptive type is that the optimization can be executed at any time during communication, and that it can cope with a change in line conditions during communication.
However, since the optimizing operation is performed using a signal such as a voice signal or a modem signal, there is a drawback that a signal having a relatively high autocorrelation must be premised. If such a signal is used as a premise, the convergence to the optimum value becomes rather gradual, and the tap coefficient may not be optimized in the initial stage after the start of communication. Therefore, it is necessary to set the amplification factor of the amplifier to a small value in the initial stage after the start of communication and then to gradually increase it, which may impair a natural call or normal communication.

In the comparison of the advantages and disadvantages of the echo canceller type preset type and the always adaptive type described above, if the assumption is that the condition of the once connected telephone line rarely changes during communication, , The preset type is excellent. In the case of the preset type using the echo canceller method, if the initial training fails, the tap coefficient is not optimized thereafter, so that the communication cannot be continued and the connection of the communication line must be abandoned. Therefore, it is very important at what point in the communication to carry out training. There are three conditions necessary for successful training. The first is that the line to be trained has been connected (the line is terminated at the local exchange side), the second is that the communication is silent, and the third is that the line is silent. A certain period can be predicted.

The first condition is, of course, because training is possible only after the communication line is connected.

The second condition is important because the training is possible only in the silent state, and is related to the success / failure of the training. The pseudo sneak signal generation unit outputs the signal at the 4-wire side input terminal of the hybrid circuit to 4
It monitors how much it leaks to the line side output terminal and generates a pseudo wraparound signal. If a signal other than the sneak signal, for example, an audio signal is superimposed on the 4-wire side output terminal from the 2-wire side terminal, the monitored content is different from the true sneak signal. As a result, the tap coefficient does not converge to the optimum value, and the training ends in failure. Since it is difficult to know during transmission of the training signal whether or not an undesired signal is superimposed on the 2-wire side terminal, the training needs to be performed in a silent state.

The third condition is a condition required for training control, and it is necessary to ensure that the silent state continues for a required period after the start of training. In communication, there are many silent periods that can satisfy the training period, but most of these depend on the communication content, so it is difficult to schedule them in advance as a training period.

[0014]

In the echo canceller type preset type, as a silent period in which there is a high possibility that the above three conditions are satisfied, the period from the completion of the line connection to the actual output of the communication signal. Conceivable. This period is the time it takes for a human to pick up the handset and start a conversation or the communication machine to respond with a timer, and is present in most communications. That is,
If the training period is set immediately after the line connection is completed, the training will be successful in most communications. However, with a small probability, the communication signal may be output immediately after the line connection is completed, and even if it is not output immediately, the communication signal may be mixed before the training ends. There was an unsolved problem of failure.

[0015]

[MEANS FOR SOLVING THE PROBLEMS] In a preset type of echo canceller system, a communication control circuit for detecting the absence of a communication signal (silence) in a call state, and a 2-wire 4-wire for executing an optimizing operation. A white noise generator applied from the 4-wire side input end of the hybrid circuit for conversion, a changeover switch for switching between white noise and communication signal at the 4-wire side input end, and communication with white noise via the changeover switch Communication with an adaptive filter for obtaining one of the signals from the 4-wire side input terminal, attenuating based on the adaptation permission signal, and applying the delayed signal to the 4-wire side output terminal of the hybrid circuit as a pseudo sneak signal When a non-existence signal indicating that there is no communication signal from the control circuit is obtained, the changeover switch is changed to the white noise generator side and adapted. The filter is instructed to carry out an optimizing operation, and when it is completed, it is instructed to hold the attenuation amount and delay amount which are the optimum values obtained by the optimizing operation, and the absence signal is applied during the optimizing operation. When it disappears (sound condition), switch the selector switch to the communication signal side, stop the optimization operation this time, and instruct the adaptive filter to keep the optimum value obtained by the previous optimization operation. And a success / failure deciding device for doing so.

[0016]

In the communication control circuit, the call state and the call end state are periodically monitored to determine the call state and the received signal exists or the received signal is amplified. There is no received signal and the received signal is not amplified. These states are judged from the presence or absence of the received signal and the connection status of the communication line. Training is performed with white noise, which is a training signal, during a silent period in a call state immediately after the connection of the communication line is completed, and after a certain period of time, the level of the training signal (white noise) at the 4-wire side output end of the hybrid circuit is a predetermined level. If it is below the level, if it is below the level, the training is ended at that point, and if it is not below the level, the training operation is continued and there is a silent period immediately after the connection of the communication line is completed. If the communication allows the training time to be secured, the training is completed before the communication signal is output. Even if the communication signal becomes audible immediately after the connection of the communication line is completed and the training signal cannot be secured and the communication signal is superimposed, the optimization operation is performed when the communication signal becomes silent. From
The probability of failure of the optimization operation is significantly reduced, and the reliability of communication is improved.

Since the bidirectional amplifier according to the present invention does not require any special control from the outside, it can be replaced with the conventional bidirectional amplifier incorporated in the conventional telephone device.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows an office line L0 and an office line L1 (hereinafter,
The communication line is called a station line) and is connected by a bidirectional amplifier. In the figure, the circuit configuration on the left and right of the dashed line in the center is exactly the same, so the circuit on the left side of the office line L0 will be described.

In FIG. 1, the office line L0 is connected to the hybrid circuit 11a and the call control circuit 30a via the office line interface 20a. Reference numeral 15a is an A / D converter, which converts an analog signal from the hybrid circuit 11a into a reception signal y ₀ (n) which is a digital signal. 1
6a is a D / A converter, which converts the transmission signal u ₀ (n) into an analog signal and applies it to the hybrid circuit 11a,
Two-line to four-line conversion is performed, and the line is transmitted to the office line L0 via the office line interface 20a.

When the impedance matching with the station line L0 is not perfectly achieved, the reception signal y ₀ (n) has a wraparound component d ₀ (n) of the transmission signal u ₀ (n) from the hybrid circuit 11a. Is included. Adaptive filter 12a that generates a pseudo echo signal d _0p (n) that is a pseudo wraparound component
Receives the transmitted signal u ₀ (n) and receives the received signal y ₀
The wraparound component d ₀ (n) included in (n) is estimated, the delay filter operation for outputting the estimated value as the pseudo echo signal d _0p (n), the adaptive permission signal INH ₀ , and the transmission signal u
An adaptive operation (hereinafter referred to as training) that optimizes the filter coefficient so that the pseudo echo signal d _0p (n) approaches the wraparound component d ₀ (n) by inputting ₀ (n) and the residual signal e ₀ (n). )I do.

The subtractor 18a subtracts the pseudo echo signal d _0p (n) from the received signal y ₀ (n) to _obtain the residual signal e.
₀ (n) is output. Therefore, the residual signal e ₀ (n)
In, the component of the received signal y ₀ (n) from the station line L0 is preserved and the wraparound component d ₀ (n) is suppressed. The multiplier 19a is an amplifier, which multiplies the residual signal e ₀ (n) by the gain constant α ₀ and outputs the amplified received signal x ₁ (n). The white noise generator 14a outputs an uncorrelated signal (for example, Gaussian noise) having a variance σ _N ² to the white noise N ₀ (n). White noise generator 14a
Is realized, for example, by preliminarily storing a non-correlated signal of variance σ _N ^{2 in} a ROM (read only memory) and sequentially reading this. The changeover switch 17a is
It is switched by the adaptive permission signal INH _0, white when the adaptive permission signal INH ₀ indicates an adaptive authorization
The noise N ₀ (n) is output as the transmission signal u ₀ (n). When the adaptation is prohibited, the changeover switch 17a is changed over so that the amplified reception signal x which is the output of the circuit on the side of the office line L1.
₀ (n) is output as the transmission signal u ₀ (n).

The success / failure determiner 13a has a communication state signal S.
₀ , the residual signal e ₀ (n) is input, and a signal for controlling whether the adaptive operation is permitted or prohibited is used as the adaptive permission signal INH.
Output as ₀ . The call control circuit 30a receives a signal from the station line interface 20a to determine whether the station line L0 is in the call state or the call termination state, and the call state signal S ₀ is received.
Is output to the success / failure determiner 13a.

FIG. 2 shows an example of the configuration of the adaptive filter 12. In FIG. 2, the adaptive filter 12 includes an adaptive filter group 101 that performs a filter operation, a tap coefficient correction circuit 110 that performs an adaptive operation, and a tap coefficient unit 111. The adaptive filter group 101 includes adaptive filter elements 102-1 to 102- (N-1) for obtaining a unit delay time T,
Multipliers 103-1 to 103-N, adders 104-1 to 1
04- (N-1), and the pseudo echo signal d
_0p (n) is represented by d _0p (n) = Σh _k (n) u ₀ (n−k) (1). However, Σ represents the sum from k = 0 to N−1, k also represents the time kT, and h _k (n)
Is a coefficient to be multiplied by a signal delayed by kT at time nT, and represents a tap coefficient from each of the tap coefficient units 111-1 to 111-N applied to the adaptive filter group 101, where N is the number of taps of the adaptive filter group 101. Represents

The tap coefficient correction circuit 110 is composed of an arithmetic circuit, and the adaptation permission signal INH ₀ is "adaptation prohibited".
Is instructed, the tap coefficient is not corrected in order to stop the adaptive operation, and h _k (n + 1) = h _k (n) (2) where k = 0 to N−1 is output. Adaptation permission signal IN
When H ₀ indicates “adaptive permission”, the adaptive operation is performed, and the tap coefficient correction circuit 110 outputs h _k (n + 1) = h _k (n) + μAe ₀ (n) (3). However, A = u ₀ (n−k) (Nσ _N ² ) ⁻¹
Where k = 0 to N−1, 0 <μ <2, μ is a correction coefficient, and σ _N ² is the variance (power) of the white noise N ₀ (n). The second term on the right side of the equation (3) represents the correction amount of the tap coefficient, which normalizes the transmission signal u ₀ (n−k) by N · σ _N ² and makes it proportional to the residual signal e ₀ (n).

FIG. 3 shows the configuration of the success / failure determiner 13. The timer 131, the power detector 132, and the comparator 13 are shown in FIG.
3, the determination circuit 134.

The timer 131 outputs a decision timing signal TM used in the decision circuit 134. When the call state signal S ₀ (n) indicates the "end call state", the timer 131 is cleared and the determination timing signal TM is not output. When the call state signal S ₀ (n) indicates the “call state”, the adaptive filter 12a when the transmission signal u ₀ (n), which is the input signal of the adaptive filter 12a, is white noise for a certain period of time τ. The value is selected to be larger than the convergence time of (in this embodiment, τ = 75 ms).
The determination timing signal TM is output every time. For example, the residual signal power p (n) can be obtained as a moving average value of the squared amplitude value e ₀ (n) ² of the residual signal e ₀ (n) using the following equation (4).

P (n) = λp (n−1) + (1−λ) e ₀ (n) ² (4) However, λ is a forgetting coefficient with a smaller weight for the past data, and 0 <λ <Choose to 1. The comparator 133 has a residual signal power p (n) and a predetermined residual signal power threshold PSH.
Is compared and the comparison result is output as a comparison value CP (n). The determination circuit 134 receives the call status signal S ₀ , the determination timing signal TM, and the comparison value CP (n) as inputs, and outputs the adaptation permission signal INH ₀ .

FIG. 4 shows a timing chart for explaining the operation of the decision circuit 134. When the call state signal S ₀ of (a) is the “end-of-talk state”, the adaptive permission signal INH of (d) is set regardless of the determination timing signal TM of (b) and the comparison value CP (n) of (e). ₀ is set as “prohibition”. When the call state signal S ₀ of (a) changes from the “end state” to the “call state”, the adaptation permission signal I of (d)
NH ₀ is “adaptation permission”. After that, if the comparison value CP (n) of (e) at the determination timing of the determination timing signal TM of (b) indicates that p (n)> PSH, the adaptation permission signal INH of (d) ₀ is left as “adaptive permission”, and at the determination timing executed in each cycle τ of the determination timing signal TM in (b),
If the comparison value CP (n) of (e) indicates that p (n) ≦ PSH, the adaptation permission signal INH ₀ of (d) is set to “prohibition of adaptation”. After the “adaptation is prohibited”, until the call state signal S ₀ of (a) changes from the “end state” to the “talk state” again, the determination timing signals TM and (e) of (b) The adaptation permission signal INH _{0 is set} to “prohibition of adaptation” regardless of the state of the comparison value CP (n).

The operation of the bidirectional amplifier configured as described above will be described by taking the circuit on the station line L0 side as an example.

In FIG. 1, when the office line L0 is in the call-released state, the call control circuit 30a outputs a call-state signal S ₀ indicating that the call is in the "call-released state". At this time, the success / failure determiner 13a
Outputs "adaptation prohibited" to the adaptation permission signal INH ₀ . Further, the values of the tap coefficients h _k (n) of the adaptive filter 12a are all initialized to 0 (or the adaptive value in the last talking state may be used).

Next, when the office line L0 enters the call state, the call control circuit 30a outputs the "call state" to the call state signal S ₀ . The success / failure determiner 13a receives the adaptation permission signal INH _{0 when the} call state signal S ₀ becomes “call state”.
Is set as “adaptive permission”, and the changeover switch 17a is controlled.
White noise N ₀ (n) as the transmitted signal u ₀ (n)
Is output to cause the adaptive filter 12a to start the adaptive operation.

During the adaptive operation, if there is no voice or a signal such as a modem on the station line L0, it means that there is no noise in the adaptive operation.
The ₀ (n) only wraparound component d ₀ (n) of the hybrid circuit 11a is output. It faithfully reflects the wraparound characteristic of the hybrid circuit 11a. Therefore, in this case, the pseudo echo signal d _0p (n) approaches the wraparound component d ₀ (n) with time, and the residual signal e
₀ (n) approaches 0, and the residual signal power p (n) also approaches 0. On the other hand, if there is a voice signal or a signal from a modem or the like on the station line L0 during the adaptive operation, it acts as noise with respect to the adaptive operation, so that the received signal y ₀ (n) faithfully reflects the wraparound characteristic of the hybrid circuit 11a. However, the transfer function (adaptive filter) obtained by the adaptive operation is far from the transfer function that causes the wraparound component d ₀ (n) in the hybrid circuit 11a.
Therefore, the wrap-around component d ₀ (n) cannot be canceled by using the pseudo echo signal d _0p (n), and further, the residual signal e _0.
Since the signal of voice or modem is also stored in (n), the residual signal power p (n) has a large value.

Therefore, the success / failure determiner 13a outputs the residual signal power p at regular intervals τ from the start of "adaptive permission".
Observe (n) and monitor whether the adaptation succeeded or failed. That is, the residual signal power p (n) is compared with a predetermined residual signal power threshold PSH, and the residual signal power p
When (n) is larger than the residual signal power threshold PSH, it is determined that some noise is mixed (failed). When it is determined that the error has occurred, the adaptive filter 12a is made to perform the adaptive operation again, so that the adaptive permission signal INH ₀ is left as “adaptive permission” and the residual signal power p (n) is maintained after a certain time τ has passed.
, And determine whether the adaptive action succeeded or failed. These operations are repeated until the success is determined. When it is determined to be successful, thereafter, the adaptive permission signal INH _{0 is set} to “inhibit adaptation”, the adaptive operation of the adaptive filter 12a is stopped (the tap coefficient is held), the switch is controlled, and the transmission signal u ₀ (n) is obtained. The amplified reception signal x ₀ (n) is output. After that, the transmission signal u ₀ superimposed on the reception signal y ₀ (n)
The wrap-around component d ₀ (n) of (n) is converted into the pseudo echo signal d _0p which is the output of the adaptive filter 12a in which the adaptive operation is stopped.
(N) is used to cancel in the subtractor 18a.

The adaptive operation described above is performed in parallel also in the circuit on the side of the office line L1. When the adaptive operation is completed on both the station line L0 and the station line L1, the received signal y ₀ (n) on the station line L0 side is amplified by α ₀ times by the multiplier 19a, and the transmitted signal u on the station line L1 side. ₁ (n), and the reception signal y ₁ (n) on the station line L1 side is amplified by α ₁ times by the multiplier 19b and output as the transmission signal u ₀ (n) on the station line L0 side. . It should be noted that the gain constants α ₀ and α ₁ are set to values smaller than the wraparound attenuation amount obtained by the hybrid circuit 11a and the adaptive filter 12a in order to prevent oscillation.

Although the success / failure determiner 13a uses the power of the residual signal e ₀ (n) for comparison,
The comparison may be performed using the voltage or the peak value of the residual signal e ₀ (n). This is because there is a relationship that when the power is large, the voltage is small, and when the power is small, the amplitude value is small. Further, when there is a signal with strong autocorrelation such as voice on the station line L0 during the adaptive operation, the residual signal e
_{Since 0} (n) also has a strong autocorrelation, the residual signal e
_The comparison may be performed using the autocorrelation value of the residual signal e ₀ (n) instead of the power of ₀ (n).

Next, an embodiment in which the bidirectional amplifier according to this embodiment is applied to the main unit of a telephone exchange will be described with reference to FIG.

FIG. 5 shows an example composed of a main unit and a plurality of telephones connected to the main unit. The main unit includes a local line L0,
L1 is connected. Main devices are station trunks 50-1 and 50-2 as station line interfaces, extension trunks 60-1 and 60-2 as extension interfaces, bidirectional amplification trunk 10 according to the present invention, and a switching device for connecting the trunks. 80, a call-end status code sending unit 70, a highway bus HW, a microcomputer 90 for controlling the operation of the main unit, and a control bus 99.

The highway bus HW is a trunk line trunk 5
0-1, 50-2, extension trunks 60-1, 60-2,
Bidirectional amplification trunk 10, a plurality of upstream highways HW _U from the clearing state code transmission section 70 to the switching device 80, the switching device 80 to the office line trunks 50-1 and 50-2, and the extension trunks 60-1 and 60-2. , Bidirectional amplification trunk 10
Consisting of a plurality of downward highway HW _D towards. The office line trunks 50-1 and 50-2 perform A / D conversion on the voices and signals from the office lines L0 and L1, and send the voices and signals to the ascending highway HW _U, and _D and the voices and signals from the descending highway HWD.
/ A conversion is performed and the data is sent to the office lines L1 and L0.

The extension trunks 60-1 and 60-2 perform A / D conversion of voices and signals from the telephone and send them to the up highway HW _U , and D / A voices and signals from the down highway HW _D. Convert and send to phone. The end-of-speech state code sending unit 70 outputs a signal indicating the end-of-speech state (for example, silence) to the ascending highway HW _U. The switching device 80 follows the instruction of the microcomputer 90 and goes up the highway H.
By W _U and switched connection the speech signal of the downward highway HW _D, the connection between the central office line L0, L1 and the phone connection between the telephones to each other, the connection of the station line L0, L1 and bidirectional amplification trunk 10, The telephone and the bidirectional amplification trunk 10 are connected to form a speech path. For the trunk in the call-ending state (bidirectional amplification trunk 10, office line trunk 50, extension trunk 60), the up highway HW _U of the call-ending state code sending unit 70 is the down highway HW of the trunk in the call-ending state. _Switch to _D. Microcomputer 90
Controls the operation of the main unit via the control bus 99.

FIG. 6 shows the configuration of the office line trunk 50. The office line interface circuit 51, the hybrid circuit 52, the A / D conversion circuit 53, the D / A conversion circuit 56, the highway transmission circuit 54, and the highway reception. It is composed of a circuit 55.

The office line interface circuit 51 uses the office line L0.
And a direct current closing circuit, a dial sending circuit, an incoming call detecting circuit and a reverse detecting circuit which are not shown. Each of these detection circuits informs the microcomputer 90 of the detection result via the control bus 99, and a DC closing circuit and a dial sending circuit (not shown) are controlled by the microcomputer 90 via the control bus 99. . The hybrid circuit 52 is 2
Line-to-line conversion is performed.

The A / D conversion circuit 53 digitizes an analog signal from the office line L0 into a digital signal (for example, a PC digitized by a code rule called μ-1aw or A-1aw).
M signal). The highway transmission circuit 54 is
The output of the D conversion circuit 53 is output to the ascending highway HW _U according to the transmission regulation defined in the main device. Further, the highway transmission circuit 54 outputs a silent signal during a period in which the station line interface circuit 51 is not DC-closed.

The highway receiving circuit 55 inputs a digital signal from the downstream highway HW _{D in} accordance with the transmission regulation defined in the main device. D / A conversion circuit 56 converts the digital signal input from the downward highway HW _D into an analog signal. The hybrid circuit 52, the A / D conversion circuit 53, and the D / A conversion circuit 56 included in the office line trunk 50 of FIG. 6 are the hybrid circuit 11a, the A / D converter 15a, and the D / A converter 16a of FIG. Equivalent to.

FIG. 7 shows the configuration of the extension trunk 60. The extension interface circuit 61, the hybrid circuit 62, the A / D conversion circuit 63, the D / A conversion circuit 66, the highway transmission circuit 64, and the highway reception circuit 65. Composed of.

The extension interface circuit 61 sends and receives voice signals and control information to and from the telephone set which is controlled by the microcomputer 90 via the control bus 99 and connected via the transmission path. The hybrid circuit 62 performs 2-line to 4-line conversion. The A / D converter 63 converts an analog signal from the telephone into a digital signal. Highway transmission circuit 6
4 outputs the output of the A / D converter 63 to the ascending highway HW _U according to the transmission regulation defined in the main device. Further, the highway transmission circuit 64 outputs a silent signal during the period when the extension interface circuit 61 is not transmitting / receiving a voice signal to / from the telephone. The highway receiving circuit 65 follows the transmission regulations defined in the main device,
Input a digital signal from W _D. D / A conversion circuit 66
Converts the digital signal input from the downward highway HW _D into an analog signal. The hybrid circuit 62, the A / D converter 63, and the D / A converter 66 of this circuit are
The hybrid circuit 11a and the A / D converter 15a of FIG.
It corresponds to the D / A converter 16a.

FIG. 8A shows the structure of the call-end status code transmission section 70, which is composed of a call-end status code generation circuit 71 and a highway transmission circuit 72. End-state code sending unit 7
Reference numeral 0 is a circuit that outputs a signal indicating the call termination state, and outputs a constant code defined in the main device. An example of this code is a silence code, which is 16 in the case of the μ-1aw coding rule.
It is "00" in radix and "2A" or "AA" in hexadecimal in the case of A-1aw coding rule. Highway bus H
When the signal polarity of W is a negative logic, it becomes "FF" in the case of the code μ-1aw coding rule and "D5" or "55" in the case of the code A-1aw coding rule. These codes represent silence, and are generally used in the main device as an end-of-speech state code for preventing a click sound from being generated at the time of shifting to the call state.

FIG. 8B shows an end-of-speech state code generation circuit 71.
3 shows the state of the call-end-state code generating circuit 71 when the call-end state code 79 for which is generated is "00". The highway transmission circuit 72 outputs the call-end state code 79 to the ascending highway HW _U in accordance with the regulations set in the main device.

FIG. 9 shows the structure of the bidirectional amplification trunk 10. The bidirectional amplification trunk 10 connects the downstream highway HW _D 1 and the upstream highway HW _U 2, and connects the downstream highway HW _D 2 and the upstream highway HW _U 1 while amplifying them. In the figure, the circuits on the left and right of the dashed line in the center have exactly the same circuit configuration, so only the circuit on the left will be described. The same symbols are attached to the same components as those shown in FIG.

In FIG. 9, the highway receiving circuit 21a
(Abbreviated as R _{0 in the} figure) is the PCM received signal c from the downlink highway HW _D 1 in accordance with the transmission regulation defined in the main device.
Enter ₀ (n). The PCM-linear converter 22a (abbreviated as P / L in the figure) converts the PCM reception signal c ₀ (n) into a linear signal and outputs it as a reception signal y ₀ (n). The linear-PCM converter 23a (abbreviated as L / P in the figure) encodes the transmission signal u ₀ (n) which is a linear signal and outputs it as a PCM transmission signal b ₀ (n). The highway transmission circuit 24a (abbreviated as T _{0 in the} figure) is a PCM.
The transmission signal b ₀ (n) is output to the upstream highway HW _U 1 in accordance with the transmission regulation defined in the main device.

The call status detector 40a receives a control command from the microcomputer 90 via the control bus 99 and performs the same function as the call control circuit 30a of FIG.
The M reception signal c ₀ (n) is input, and the call state signal S ₀ is output as a signal indicating the call state. Adaptive filter 12
a, subtractor 18a, success / failure determiner 13a, changeover switch 17a, white noise generator 14a, multiplier 19
a has the same configuration as that described in FIG.

Therefore, the A / D converter 1 in FIG.
5a of the output y ₀ (n) is transmitted via the highway bus HW _D 1, or, D / A converter 16 in FIG. 1
It operates in exactly the same way as the circuit of FIG. 1 except that the input u ₀ (n) of a is transmitted via the highway bus HW _U 1.
However, the function of the call control circuit of FIG. 1 is that in the embodiment of FIG. 9, the call state detector 40a, the switching device 80 of FIG.
It is realized by the microcomputer 90 judging from the function obtained by the combination of the above and issuing a control command to the control bus 99.

When the call is released by the combination of these, the microcomputer 90 instructs the switching device 80 to exchange-connect the call termination state code sending unit 70 and the bidirectional amplification trunk 10, and the bidirectional amplification trunk 10 is connected. To instruct the bidirectional amplification to end. Similarly, when making a call, the microcomputer 90 instructs the switching device 80 to switch and connect the office line trunk 50 or the extension trunk 60 and the bidirectional amplification trunk 10,
The bidirectional amplification trunk 10 is instructed to start bidirectional amplification.

However, the microcomputer 90 normally controls the station trunk 50, the extension trunk 60, the switching device 80, etc. at a cycle of about 100 ms.
There is a time difference between the two instructions, the switched connection instruction for 0 and the bidirectional amplification instruction for the bidirectional amplification trunk 10. Further, since the microcomputer 90 controls all the constituent elements in the main device, there is a time lag in the instruction for processing control. Therefore, two instructions may be given, such as instructing the switching device 80 in advance and then instructing the bidirectional amplification trunk 10 or instructing the bidirectional amplification trunk 10 first and then the switching device 80. There may be a time difference of about several 100 ms before and after.

In this way, an instruction to start amplification is obtained from the microcomputer 90 through the control bus 99, and
When the highway HW of the office line trunk 50 or the extension trunk 60 and the bidirectional amplification trunk 10 is connected by the switching device 80, the call state detector 40a must detect the call state. Call state detector 40a is PCM reception signal c received from the downward highway HW _D 1
The switching state of the switching device 80 can be known by periodically monitoring ₀ (n) and detecting whether or not it is the call termination code.

FIG. 10A shows the configuration of the call state detector 40a in FIG. 9, which is composed of a call termination state code generation circuit 41, a collation circuit 42, a determination circuit 43, and a call state determination circuit 44. It The termination state code generation circuit 41 is a circuit that outputs a signal MUC indicating the termination state, and has a fixed code defined in the main device (the termination state code transmission unit 7 in FIG. 8).
The same code as the end-of-speech state code 79 output from the end-of-speech state code generation circuit 71 of 0) is output. The matching circuit 42 is shown in FIG.
As shown in the operation flow in FIG.
The M received signal c ₀ (n) is collated with the end-of-speech state code MUC (S1), and if they match (S1Y), the collation signal PC
(N) = "1" (S2), if they do not match, collation signal PC
(N) = "0" is output (S3). The determination circuit 43 is
If the number of occurrences of PC (n) = "1" increases, the exchange state signal S ₀ ′ indicating the exchange state of the exchange 80 indicates "end call" Output "state".

When the microcomputer 90 instructs the control bus 99 to start amplification and the exchange status signal S ₀ ′ is “communication status”, the communication status determination circuit 44 indicates “communication status” as the communication status signal S _0. When the instruction to end the amplification is given from the microcomputer 90 and when the exchange status signal S ₀ ′ is in the “end-of-talk state”, the talking state signal S ₀ is output as the “end-of-talk state”.

In this way, the call-end state code generation circuit 41, the collation circuit 42, and the determination circuit 43 detect the call state of the switching device 80, and the call state determination circuit 44 detects the state detected by this determination circuit 43 and the micro state. The output of the call status signal S ₀ is determined by the amplification start instruction from the computer 90.

In the call end state, the PCM received signal c ₀
Since the end state code is received in (n), the probability of occurrence of the collation signal PC (n) = “1” is 1 (corresponding to each sample) unless there is interference due to noise or the like. In the call state, the A / D converter 53 (FIG. 6) of the office line trunk 50 or the extension trunk 60 is used for the PCM reception signal c ₀ (n).
The output of 63 (FIG. 7) is connected. When there is a voice or signal from the office line L0, the PCM reception signal c ₀
Since (n) takes various values, the collation signal PC (n) =
The probability of occurrence of "1" is much less than 1. When there is no voice or signal from the office line L0, the A / D converters 53 and 63 should output a code representing silence, but in reality, the A / D converters 53 and 63 perform quantization. Due to the presence of noise, the LSB of the PCM reception signal c ₀ (n)
Since the (least significant) bit changes, the collation signal PC (n)
The probability of occurrence of "1" is considerably smaller than 1.

As described above, the probability of occurrence of the collation signal PC (n) = “1” is considerably smaller than 1 in the call state regardless of the presence or absence of voice or signal from the station line L0. Using the above-mentioned empirically known statistical properties, when the probability of occurrence of the collation signal PC (n) = “1” is close to 1, it is set as the “end of call state” and the collation signal PC (n) = “1” When the probability of occurrence is close to 0, it is set to "call state".

FIG. 11 shows an operation flow of the decision circuit 43 of FIG. 10A, in which the protection counter U is provided at each time n.
The counting operation of C and the determination of the call state are performed. In the following, the “end state” is represented by S ₀ ′ = “0”, and the “talk state” is S ₀ ′. = Represented by "1". A reset counting method is used for the counting method of the counter UC (not shown) included in the determination circuit 43, and S ₀ ′ is used. = "1" (S1
1N), when the call signal is detected and the collation signal PC (n) = 0 (S12Y), the counter UC is reset to the initial value 0 (S13), and the "call state" S ₀ ′ = “1” is continuously output (S14). If the collation signal PC (n) = “1” (S1
2N), since the call signal is not detected, the value of the counter UC is increased (S15). If the value of the counter UC has not reached the predetermined value M (for example, 47) (S
16N), the value of the counter UC is held as it is (S1
7), the decision circuit 43 indicates that the exchange status signal is "Speaking"
₀ ′ The state where "1" is output is kept (S18).
If no call signal is detected also in the next cycle, S11N is selected in steps S11 and S12 to S18.
When the value M (for example, 47) of the counter UC is detected (S16Y), the counter UC is repeated.
Is reset (S19), and the exchange status signal S ₀ ′ Is set to "0" (S20), and the "end call state" is displayed.

Exchange status signal S ₀ ′ Is "0" and the "end call state" is displayed (S11Y), PC (n) = "1" when no call signal is detected (S21).
Y), the value of the counter UC is held as UC = 0 (S22), and the exchange status signal S ₀ ′ Also S ₀ ′ = “0” is held as it is and the “end-of-call state” is displayed (S23).

Next, from this state, "call state" (PC
When (n) = “0”) is transitioned (S21N), the outputs of the A / D converters 53 and 63 of the office line trunk 50 or extension trunk 60 are connected to the PCM received signal c ₀ (n), and c ₀ A code (for example, a voice code) that is not the call termination code is output to (n). In this embodiment, the "end state"
S ₀ ′ The upper limit value N of the counter UC at = “0” is selected as 1. This is because the noise mixed in the highway HW or the like can be practically ignored, and when the call-end state code is not detected about twice consecutively, that is, when the voice code is detected twice consecutively, it is regarded as a call state. Because you can. Therefore, when the collation circuit 42 detects a code that is not the end-of-speech state twice in succession (PC (n) = “0” twice in succession), the determination circuit 43 determines that it is in the “communication state” ( S24Y), reset to UC = 0 (S
25), S ₀ ′ = 1 is output (S26). When the counter value UC has not reached N (S24N), the counter value is advanced by 1 (S27), the set count value N is reached, and the exchange status signal S ₀ ′ is held at “0”. (S28). When a call signal is detected there (S21
N), because the count value UC = N has been reached (S24)
Y) The counter is reset (S25) and the exchange status signal S ₀ ′ Becomes "1" (S26) and the "call state" is displayed.

Since it operates in this way, "end call state"
(S ₀ ′ If a call signal is detected while the signal is "0"), S ₀ ′ is immediately detected. = "1" changed to "call state"
Is displayed, and once the call signal is detected, if the call signal is continuously detected, for example, 47 times, S ₀ ′ = “0” and the “end-of-call state” is displayed. Highway HW
Error rate of 10 ^-11 and S ₀ ′ = “1”
When the probability of occurrence of C (n) is 1/2, N = 1, and M = 47, the average time during which the decision circuit 43 continues to output the correct exchange status signal S ₀ ′ is several hundred years or more. Above all, the correct exchange status signal S ₀ ′ Can be considered to continue to be output.

In the call state judging circuit 44, since the call state of the exchange 80 can be known from the exchange state signal S ₀ ′ thus obtained, the microcomputer 90 gives an instruction to start amplification through the control bus 99. Yes, and when the exchange status signal S ₀ ′ is “talking”, the talk status signal S _{0 is set} to “talking” so that the bidirectional amplification trunk 10 and the office line trunk 50 are always connected to each other. The signal S ₀ can be "talking".

In the description of the call status detector 40 of FIG. 10, the call termination status code is set to one type in the main unit, and it is assumed that the call status detector 40 is aware of it. , It is not always necessary to specify the call termination status code. That is, the call state detector 40 can operate without knowing what kind of code is selected as the call-end state code in the main device. FIG. 12 shows the configuration of such a call state detector 40B. Show.

In FIG. 12, the collating circuit 42, the judging circuit 43, and the call state judging circuit 44 are the same as those described in FIG. 10 (a). The matching circuit 42 receives the PCM reception signal c ₀ (n) of the current cycle and the PCM reception signal c ₀ (n−1) of one cycle before from the delay circuit 44 in the input code string.
And collate, and if they match, collation signal PC (n) = "1"
Is output, and if there is no match, the collation signal PC (n) = "0"
Is output. As described above, the A / D converters 53 and 63 of the office line trunk 50 or the extension trunk 60 never output one type of continuous code. Output PC
The continuous output of "1" to (n) is limited to the case where the bidirectional amplification trunk 10 is connected to the call termination state code transmission unit 70, that is, when the call termination state is completely terminated. It

In this call state detection circuit 40B, the received signal c ₀ (n) which is an encoded signal is input, but this is received signal y which is the output of the PCM-linear converter 22a (FIG. 9). Even if it is replaced by ₀ (n), the same purpose as described above can be achieved. However, in that case, the number of bits of the reception signal y ₀ (n) is larger than that of the PCM reception signal c ₀ (n) (for example, the μ-law PCM signal has 8 bits, and it is converted into a linear signal. If 1
4 bits), the scale of the matching circuit 42 increases.

The instruction to start amplification of the microcomputer 90 to the bidirectional amplifier 10 and the instruction to connect the highway HW of the station trunk 50 or the extension trunk 60 and the bidirectional trunk 10 to the switching device 80 are issued at the same time. I don't know. If the call state detectors 40, 4 of the present invention
0B (FIGS. 10 and 12) is not used, and if the communication state is known only by the instruction to start amplification from the microcomputer 90, the switching device 80 starts the adaptive operation before the switching connection and the hybrid circuit. The adaptive operation performed in the state where is not connected is a malfunction. However, in the present invention, since the call state detectors 40 and 40B are used, the connection state of the exchange 80 is monitored by the determination circuit 43, the microcomputer 90 gives an instruction to start amplification, and the hybrid circuit 11 is connected. When the communication state is determined, the communication state determination circuit 44 determines that it is in the "communication state" and starts the adaptive operation, so that the correct adaptive operation can be surely performed.

[0070]

As is apparent from the above description, according to the present invention, the training time is secured immediately after the line connection is completed by providing the success / failure determiner in the bidirectional amplifier of the preset type echo canceller system. In addition, even in the communication in which the communication signal is superimposed immediately after the line connection is completed, the correct adaptive operation can be performed by utilizing the silent period of the communication existing thereafter. In addition, a signal with little autocorrelation such as white noise can be used as a training signal, the convergence time is extremely short, and training is successful if a slight silent period exists during communication. In the initial stage of communication, whether it is human conversation or machine-to-machine communication, there is no case where full-duplex communication is sent by both the sender and the receiver, and half-duplex communication is sent by only one. In most cases, there is always a silence. Therefore, the adaptive operation can be completed in the initial stage of communication, and the amplification can be performed in both directions from that point, so that no discomfort or communication delay occurs. Further, the training can be performed without being restricted by the control time of the microcomputer and the control procedure. Therefore, the effect of the present invention is extremely large.

[Brief description of drawings]

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

FIG. 2 is a circuit configuration diagram of an embodiment of an adaptive filter which is a component included in the circuit shown in FIG.

FIG. 3 is a circuit configuration diagram of an embodiment of a success / failure determiner that is a component included in the circuit shown in FIG.

FIG. 4 is a timing chart showing the operation of a determination circuit which is a component of the success / failure determiner shown in FIG.

FIG. 5 is a circuit configuration diagram when the bidirectional amplifier according to the present invention is incorporated in a main unit of a telephone exchange.

FIG. 6 is a circuit configuration diagram of a station line trunk which is a component of the main device shown in FIG.

FIG. 7 is a circuit configuration diagram of an extension trunk that is a component of the main device shown in FIG.

8A and 8B are a circuit configuration diagram of a call termination state sending unit which is a component of the main device shown in FIG. 5 and a code diagram showing a call termination state code generated from the circuit.

9 is a circuit configuration diagram of an embodiment of a bidirectional amplification trunk according to the present invention, which is a component of the main unit shown in FIG.

10 is a circuit configuration diagram of a call state detector which is a component of the bidirectional amplification trunk shown in FIG. 9 and a flowchart showing an operation flow of a matching circuit included therein.

11 is a flowchart showing an operation flow of a determination circuit which is a component of the call state detector shown in FIG.

FIG. 12 is a circuit configuration diagram of another embodiment of the call state detector.

[Explanation of symbols]

10 Bidirectional amplification trunk 11a, 11b Hybrid circuit 12a, 12b Adaptive filter 13a, 13b Success / failure determiner 14a, 14b White noise generator 15a, 15b A / D converter 16a, 16b D / A converter 17a, 17b Switching Switch 18a, 18b Subtractor 19a, 19b Multiplier 20a, 20b Station line interface 21a, 21b Highway receiving circuit 22a, 22b PCM-linear converter 23a, 23b Linear-PCM converter 24a, 24b Highway transmitting circuit 30a, 30b Communication control Circuits 40a, 40b Communication state detector 41 End-call state code generation circuit 42 Collation circuit 43 Judgment circuit 44 Call state judgment circuit 50 Station line trunk 51 Station line interface circuit 52 Hybrid circuit 53 A / D converter 54 High Way transmitting circuit 55 Highway receiving circuit 56 D / A converter 60 Extension trunk 61 Extension interface circuit 62 Hybrid circuit 63 A / D converter 64 Highway transmitting circuit 65 Highway receiving circuit 66 D / A converter 70 End-state code transmission Part 71 Call state code generation circuit 72 Highway transmission circuit 79 Call state code 80 Switching device 90 Microcomputer 99 Control bus 101 Adaptive filter group 102 Adaptive filter element 103 Multiplier 104 Adder 110 Tap coefficient correction circuit 111 Tap coefficient unit 131 Timer 132 Power detector 133 Comparator 134 Judgment circuit α ₀ , α ₁ Gain constants b ₀ (n), b ₁ (n) PCM transmission signal c ₀ (n), c ₁ (n) PCM reception signal d ₀ ( n), d ₁ (n) wraparound component d _0p (n), d _1p (n ) Pseudo echo signal e ₀ (n), e ₁ (n) residual signal h ₀ (n) to h _N-1 (n) tap count p (n) residual signal power τ period u ₀ (n), u ₁ (n) Transmission signal x ₀ (n), x ₁ (n) Amplified reception signal y ₀ (n), y ₁ (n) Reception signal CP (n) Comparison value HW Highway HWD _D Downward Highway HW _U Upward Highway INH ₀ , INH ₁ Adaptive permission signal L0, L1 Station line N ₀ (n), N ₁ (n) White noise PC (n) Collation signal PSH Residual signal power threshold S ₀ , S ₁ Talk state signal S ₀ ′ Exchange status signal TM judgment timing signal

Claims (1)

[Claims] 1. A white noise generating means for generating white noise in a silent period of a communication signal in order to measure an amount of a part of a transmission signal that wraps around into a reception signal and appears as a signal in a call state. ), And the white noise is attenuated and delayed in the silent period to obtain a pseudo echo signal (d _op (n)) and superimposed so as to be a difference with the received signal, and the received signal shows a minimum value. Adaptive filter means (12) that performs an operation for optimizing as described above, and periodically (τ) is monitored in the call state, and it is determined that the operation for optimizing is completed within the silent period. And hold the state of the adaptive filter means,
If the optimizing operation is not completed within the silent period, it is determined that the operation is unsuccessful, and the optimizing operation is repeatedly executed by the adaptive filter in the silent period that occurs next. Judgment means (13)
The transmission signal and the reception signal are encoded, and the code value at the current encoding time (n) and the previous encoding time (n-
When the frequency with which the code value in 1) matches is high and when the received signal is not amplified, it is determined that the call is in an end state,
When the frequency of coincidence is not high and the received signal is amplified, it is determined that the communication state is the communication state, and the communication state detecting means (30, 40) for detecting the silent period in the period determined to be the communication state. , 40B, 99).