JPH0514246A - 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 normal adaptive type, the 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 wrapping around at 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]

In the echo canceller type preset type, there are provided a communication control circuit for detecting the absence of a communication signal and a hybrid circuit for performing a two-wire to four-wire conversion for executing an optimizing operation. A white noise generator applied from the 4-wire side input end, a changeover switch for changing over the white noise and the communication signal at the 4-wire side input end, and one of the white noise and the communication signal through the changeover switch. An adaptive filter for applying a signal obtained from the 4-wire side input end, attenuated and delayed based on the adaptation permission signal, to the 4-wire side output end of the hybrid circuit as a pseudo sneak signal, and a communication signal from the communication control circuit. When a non-existence signal indicating that the noise does not exist is obtained, the selector switch is switched to the white noise generator side to perform the optimization operation for the adaptive filter. Then, when it is completed, it is instructed to hold the attenuation amount and delay amount which are the optimum values obtained by the optimization operation, and when the absence signal is not applied during the optimization operation, the changeover switch is turned on. A success / failure determiner is provided for switching to the communication signal side, stopping the optimization operation this time, and instructing the adaptive filter to keep the optimum value obtained by the previous optimization operation as it is.

[0016]

[Operation] The training is performed by the white noise as the training signal immediately after the connection of the communication line is completed, and after the elapse of a certain time, the level of the training signal (white noise) at the output end of the hybrid circuit on the 4-wire side is sufficiently a predetermined level. It is possible to secure the training time immediately after the connection of the communication line is completed by determining whether it is below the level, and if it is below the level, end the training at that point, and if it is below the level, continue the training operation. If it is communication, the training is completed before the communication signal is output. Even if the training time cannot be secured immediately after the connection of the communication line and the communication signal is superimposed, the optimization operation is performed when the communication signal becomes silent. The possibility of operation failure is significantly reduced, and communication reliability 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 office line L0 is not completely achieved, the reception signal y ₀ (n)
Includes the wrap-around component d ₀ (n) of the transmission signal u ₀ (n) from the hybrid circuit 11a. Adaptive filter 12a to generate a pseudo echo signal d _0p (n) is a pseudo echo component inputs the transmission signal u ₀ (n), wraparound component d ₀ contained in the received signal y ₀ (n) (n) _Is input, and the estimated value is output as a pseudo echo signal d _0p (n), the adaptive permission signal INH ₀ , the transmission signal u ₀ (n), and the residual signal e ₀ (n) are input. An adaptive operation (hereinafter referred to as training) is performed to optimize the filter coefficient so that the pseudo echo signal d _0p (n) approaches the wraparound component d ₀ (n). Subtracter 18a subtracts the pseudo echo signal d _0p (n) from the received signal y ₀ (n), and outputs the residual signal e ₀ (n). Therefore, the residual signal e
_{At 0} (n), the received signal y ₀ from the office line L0
The component of (n) is preserved, and the wraparound component d ₀ (n) is suppressed. The multiplier 19a is an amplifier, and the residual signal e ₀
(N) is multiplied by the gain constant α ₀ to obtain the amplified received signal x
Output as ₁ (n). White noise generator 14
a is an uncorrelated signal with variance σ _N ² (for example, Gaussian noise)
To white noise N ₀ (n). white·
The 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. Changeover switch 17a is adapted permission signal switched by INH _0, adaptive permission signal INH ₀ is transmission signal u white noise N ₀ a (n) when showing the adaptive authorization
Output as ₀ (n). When the adaptation is prohibited, the selector switch 17a is switched to output the amplified reception signal x ₀ (n) which is the output of the circuit on the side of the office line L1 to the transmission signal u ₀ (n). The success / failure determiner 13a receives the call state signal S ₀ and the residual signal e ₀ (n) and outputs a signal for controlling whether the adaptive operation is permitted or prohibited to the adaptive permission signal IN.
Output as H ₀ . The call control circuit 30a uses the office line L0.
The call state signal S is determined by receiving a signal from the central line interface 20a to determine whether the call is in a call state or a call end state.
_{The value} is output as ₀ 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 "prohibition of adaptation".
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. When the adaptation permission signal INH ₀ indicates “adaption permission”, the adaptation operation is performed, and the tap coefficient correction circuit 110 outputs h _k (n + 1) = h _k (n) + μAe ₀ (n) (3) To do. However, A = u ₀ (n−k) (Nσ _N ² ) ⁻¹ , k = 0 to N−1, 0 <μ <2, μ is a correction coefficient, and σ _N ² is white noise N _It represents the variance (power) of 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, which includes a timer 131, a power detector 132, and a comparator 13.
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 station line L0 enters the call state, the call control circuit 30a outputs a "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 of a modem or the like on the station line L0, there is no noise in the adaptive operation, so that the received signal y
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 "adaption 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 also performed in parallel 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.

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 is connected to 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 is a PC that digitizes an analog signal from the station line L0 by a digital signal (for example, 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 in accordance with the transmission provisions stipulated in the main unit, and inputs the digital signal from the downward highway HW _D. 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 structure 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 transmits / receives a voice signal and control information to / from a telephone controlled by the microcomputer 90 via the control bus 99 and connected via a 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 state detector 40a receives the PCM reception signal c ₀ (n) and outputs a call state signal S ₀ as a signal indicating the call state. Adaptive filter 12a, subtractor 18a, success / failure determiner 13a, changeover switch 17a,
The white noise generator 14a and the multiplier 19a are shown in FIG.
The configuration is the same as that described in. Therefore, FIG.
Output y ₀ of the A / D converter 15a (n) is transmitted via the highway bus HW ₀ 1 in, or input of the D / A converter 16a in FIG. 1 u ₀ (n) is the highway bus HW _U 1 The circuit operates in exactly the same way as the circuit of FIG. However, the function of the call control circuit of FIG. 1 is that the call state detector 40a,
It is realized by a combination of the switching device 80, the microcomputer 90, and the call-end status code sending unit 70 shown in FIG. When the call-ending state is brought about by the combination of these, the switching device 80 is arranged so that the microcomputer 90 exchange-connects the call-ending state code sending unit 70 and the bidirectional amplification trunk 10.
Instruct. Thus, PCM received signal c ₀ bidirectional amplification trunk 10 received from the downward highway HW _D 1
By observing (n) in the call state detector 40a, the call termination state can be known. Similarly, in the case of 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. Therefore, the bidirectional amplification trunk 10 can know the call state from the fact that the call state detector 40a can no longer detect the end state code of the PCM reception signal c ₀ (n) received from the downlink highway HW _D 1.

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, and a determination circuit 43. The end-of-speech state code generation circuit 41 is a circuit for outputting a signal MUC indicating the end-of-speech state, and has a fixed code defined in the main device (the end-of-speech state code generation circuit of the end-of-speech state code transmission unit 70 of FIG. 8). The same code as the end-of-speech state code 79 output by 71) is output. The collation circuit 42 collates the PCM received signal c ₀ (n) with the end-of-speech state code MUC every time n, as shown in the operation flow of FIG. 10B (S1). (S1Y) Collation signal PC (n) = "1" (S1Y)
2) If they do not match, the collation signal PC (n) = “0” is set (S
3) Output. The determination circuit 43 includes a counter UC, counts the collation signal PC (n), and PC (n) =
If the number of occurrences of "1" is increased, "end call state" is output to the call state signal S ₀ .

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, "end state" is represented by S ₀ = "0"
Is represented by S ₀ = “1”. A reset counting method is used for the counting method of the counter UC (not shown) included in the determination circuit 43, and when S ₀ = “1” (S11N),
When the call signal is detected and the collation signal PC (n) = 0 (S12
Y), reset the counter UC to the initial value 0 (S1
3), the call state S ₀ = “1” is continuously output (S1
4). When the collation signal PC (n) = "1" (S12N),
Since no call signal is 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) (S16).
N), the value of the counter UC is held as it is (S17),
The determination circuit 43 keeps outputting the call state signal S ₀ = “1” (S18). If the call signal is not detected even in the next cycle, S
11N is selected, the operations of S12 to S18 are repeated, and when the value M (for example, 47) of the counter UC is detected (S16Y), the value of the counter UC is reset (S16Y).
19), set the call status signal S ₀ to "0" (S20),
Display the call termination status.

When the call state signal S ₀ is "0" and the call-end state is displayed (S11Y), when the call signal is not detected, PC (n) = "1" (S21Y), and the counter UC indicates The value is held as UC = 0 (S22), the call status signal S ₀ is also held as S ₀ = "0", and the call-end state is displayed (S23).

Next, from this state, the call state (PC (n)
= “0”) (S21N), the outputs of the A / D converters 53 and 63 of the station trunk 50 or the 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 call-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, the code that is not the call termination code is the collation circuit 4
2 is detected twice in succession (two consecutive P
C (n) = “0”), the determination circuit 43 determines that the “call state” (S24Y), resets to UC = 0 (S25),
S ₀ = 1 is output (S26). The counter value UC is N
When it has not reached (S24N), the value of the counter is advanced by 1 (S27), the set count value N is reached, and the call status signal S ₀ is kept at "0" (S28).
When a call signal is detected there (S21N), the count value UC = N has been reached (S24Y), the counter is reset (S25), the call status signal S ₀ becomes "1" (S26), and the call status is reached. Is displayed.

Since the operation is as described above, the call end state (S ₀
When a call signal is detected when "= 0", the call state is immediately changed to S ₀ = "1" and the call state is displayed. Once the call state is reached, the call signal is continuously detected, for example, 47 times. If so, S ₀ = “0” and the call-end state is displayed. The error rate of the highway HW is 10 ⁻¹¹ , S ₀
= 1 / the occurrence probability of the verification signal PC (n) at "1"
When 2, N = 1 and M = 47, the average time during which the determination circuit 43 continues to output the correct call status signal S ₀ is several hundred years or more, so that the correct call status signal S ₀ is virtually always output. You can think of continuing.

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 and the judging circuit 43 are the same as those described with reference to FIG. The matching circuit 42 uses the PCM of the current cycle of the input code string.
The received signal c ₀ (n) is collated with the PCM received signal c ₀ (n−1) from the delay circuit 44 one cycle before, and if they match, the collation signal PC (n) = “1” is output and they do not match. In this case, 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. "1" is continuously output to the output PC (n) when the bidirectional amplifying trunk 10 is connected to the call-end code sending unit 70, that is, when the call is completely put in the call-end state. Limited.

In this call state detection circuit 40B, the received signal c ₀ (n) which is a coded 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.
In the description of the main device of FIG.
I ignored the time required to control 0, but in reality it was 10
The switching device 80, the office line trunks 50-1 and 50-2, and the extension trunks 60-1 and 60-2 shown in FIG.
Etc. are controlled. Therefore, the actual trunk line trunk 50
-1, 50-2 are connected to the office lines L0, L1 and the microcomputer 90 instructs the switching device 80 to carry out the exchange connection between the bidirectional amplification trunk 10 and the office line trunks 50-1, 50-2. There is a time difference of several hundred ms between and. If the call state detectors 40 and 40B of the present invention (see FIGS.
If the bidirectional amplification trunk 10 is instructed to the bidirectional amplification trunk 10 by the instruction from the microcomputer 90 via the control bus 99 without using 2), several hundred ms is further added to the time difference. If the instructions of the microcomputer 90 are given in a random order, the bidirectional amplification trunk 10 may start the adaptive operation according to the instruction of the microcomputer 90 before the switching device 80 makes a switching connection.
Microcomputer 90 to bidirectional amplification trunk 10
There is a case where the instruction from is delayed. If the adaptive operation is started before the exchange connection is completed, the adaptive operation is performed without the hybrid circuit being connected, so that it is a malfunction completely and the microcomputer 9
If the instruction from 0 is delayed, the adaptive operation is not performed at the ideal time point, which hinders communication. However, since the call state detectors 40 and 40B are used in the present invention, it is possible to complete the adaptive operation immediately after the station line connection, which is less likely to interfere with communication. By using the method of providing the call state detectors 40 and 40B according to the present invention to know the call state, the call state can be known directly from the PCM received signal input to the bidirectional amplification trunk 10. Therefore, the microcomputer 90 Can almost ignore the effect of control time.

[0059]

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. In addition, in the main device of the existing exchanger,
Since the printed circuit board on which the bidirectional amplifier of the present invention is mounted can be replaced with the conventional bidirectional amplifier, the present invention can be applied to the conventional main device.

Further, the training can be performed without being restricted by the control time of the microcomputer. 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 trunks 11a, 11b Hybrid circuits 12a, 12b Adaptive filters 13a, 13b Success / failure determiners 14a, 14b White noise generators 15a, 15b A / D converters 16a, 16b D / A converters 17a, 17b Switching Switches 18a, 18b Subtractors 19a, 19b Multipliers 20a, 20b Station line interfaces 21a, 21b Highway receiving circuits 22a, 22b PCM-linear converters 23a, 23b Linear-PCM converters 24a, 24b Highway transmitting circuits 30a, 30b Communication control Circuits 40a, 40b Communication state detector 41 End-call state code generation circuit 42 Collation circuit 43 Judgment circuit 50 Station line trunk 51 Station line interface circuit 52 Hybrid circuit 53 A / D converter 54 Highway transmission circuit 55 Highway reception circuit 6 D / A converter 60 Extension trunk 61 Extension interface circuit 62 Hybrid circuit 63 A / D converter 64 Highway transmission circuit 65 Highway reception circuit 66 D / A converter 70 Termination state code transmission section 71 Termination state code generation circuit 72 highway transmission circuit 79 end 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 signals c ₀ (n), c ₁ (n) PCM reception signals 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) h _N-1 (n) the tap count p (n) residual signal power τ period _{u 0 (n), u 1} (n) transmission signal _{x 0 (n), x 1} (n) amplified received signal y ₀ ( n), y ₁ (n) Received signal CP (n) Comparison value HW Highway HW _D Downstream highway HW _U Upward highway INH ₀ , INH ₁ Adaptation permission signals L 0, L 1 Station lines N ₀ (n), N ₁ (n) White noise PC (n) Collation signal PSH Residual signal power threshold S ₀ , S ₁ Call state signal TM Judgment timing signal

Claims (3)

[Claims] 1. White noise generating means (14) for generating white noise in a silent period of a communication signal in order to measure in advance the amount of a part of the transmitted signal that appears as a sneak signal in the received signal. , Attenuating and delaying the white noise in the silent period to obtain a pseudo echo signal (d _op (n)) and superimposing it on the received signal so that the received signal has a minimum value. An adaptive filter means (12) for performing an operation for optimizing, and when the operation for optimizing is completed within the silent period, it is judged as successful and the state of the adaptive filter means is held, If the operation for optimizing is not completed within the above, it is judged as a failure, and the operation for optimizing is repeated to the adaptive filter in the next silent period. A bidirectional amplifier including a success / failure determination means (13) for executing the above-mentioned operation. 2. The transmission signal and the reception signal are encoded, and when the code value of the current cycle and the code value of the preceding cycle are high in frequency, it is determined that the call is in an end state, and the frequency of matching is low. The bidirectional amplifier according to claim 1, further comprising a call state detecting means (40, 40B) for determining that the call state is set, and for setting the period determined to be the call state to be the silent period. 3. The minimum value is set when the adaptive filter means performs an operation of superimposing the pseudo echo signal on the received signal so as to be a difference and optimizing the received signal to show the minimum value. , The voltage value of the superimposed received signal,
The bidirectional amplifier according to claim 1, wherein the bidirectional amplifier is obtained by one of a peak value and an autocorrelation value.