JP2002101023A - Echo canceller - Google Patents

Abstract

(57) [Problem] To provide an echo canceller capable of minimizing a line echo generated at the start of a call. SOLUTION: A pseudo echo generation circuit which has a transmission characteristic equivalent to a transmission path of a signal whose echo wraps around from a fixed line network, and generates a pseudo echo signal by passing a transmission signal from a transmission side mobile station. 201 and a subtractor 20 for subtracting a pseudo echo signal from a received signal from a mobile station on the receiving side.
2, an echo level detection circuit 204 for detecting a residual echo from the output of the subtractor, a non-linear processor 206 for setting the output of the subtractor to a signal level based on the given input / output characteristic, and an operation threshold of the non-linear processor as an echo. An operation threshold value setting circuit 205 for setting according to the level of the detection output of the level detection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller, and more particularly, to an echo canceller provided on a base station side of a mobile communication system in which a mobile communication system such as a mobile phone system and a fixed communication network such as a public network are connected. The present invention relates to an echo canceller that cancels a line echo.

[0002]

2. Description of the Related Art The configuration of a conventional echo canceller is shown in FIG. In the figure, an echo canceller 300 is provided in a base station of a mobile communication system, and has a pseudo echo generation circuit 301, a subtractor 302, and a non-linear processor (NLP) 303. Input port 31
0 is a port to which the voice of the speaker from the mobile station on the transmitting side is input, and the output port 320 is a port to which the voice signal of the speaker from the mobile station on the receiving side or the fixed telephone is output. An output port 311 is an output port for inputting a voice signal of a speaker on the transmission side, which is output to a mobile station on the reception side or a fixed telephone, connected to a line on the fixed line network side, and an input port 321. Is a port to which the voice signal of the speaker from the receiving mobile station or the fixed telephone including the line echo from the fixed line network is input.

In the above configuration, the pseudo echo generation circuit 3
01 is set at the beginning of a call so as to have transmission characteristics equivalent to the transmission path of the line echo from the receiving side input from the input port 321, and the transmission signal from the mobile station on the transmission side is transmitted from the input port 310. (Speaker voice signal) is input to the pseudo echo generation circuit 301. The pseudo echo generation circuit 301 outputs a pseudo echo signal to the subtractor 302 by passing a transmission signal from the mobile station on the transmission side.

The subtractor 302 subtracts the pseudo echo signal from the voice signal of the speaker from the receiving mobile station or the fixed telephone including the line echo from the fixed line network input from the input port 321 and outputs the result. The output signal is output to the nonlinear processor 303. Non-linear processor 3
03 is generated at the start of a call by processing the output of the subtracter 302 to a signal level based on a predetermined input / output characteristic, for example, the input / output characteristic as shown in FIG. 3 or FIG. The residual echo is removed, and output to the mobile station on the transmission side from the output port 320.

FIGS. 3 and 4 show a non-linear processor 303 which outputs zero when the input signal level is equal to or lower than a predetermined operation threshold value | X0 |, and outputs a signal proportional to the input signal when the input signal level is equal to or higher than | X0 |. 5 shows the input / output characteristics. That is, the pseudo echo generation circuit 301
Until the coefficient of each tap in the adaptive filter constituting the pseudo echo generation circuit is set so that the transmission characteristic of the adaptive filter constituting the pseudo echo generation circuit is equivalent to the transmission characteristic of the line echo transmission path from the receiving side. The output includes an echo that cannot be completely removed, that is, a residual echo. The nonlinear processor 303 is provided to remove a residual echo based on the above characteristics.

The nonlinear processor of the echo canceller is described in ITU-T (International Telecommunications).
communication Union− Telecommunication Standardiz
ationSector) International Recommendation G. The description can be seen at 165. The outline of the input / output characteristics of the non-linear processor,
Only an example of its use is shown. When the echo canceller is actually used, the operation threshold of the non-linear processor is fixed, and the control of the non-linear processor only selects whether to activate or non-operate, and the Nothing changes the operating threshold value of the nonlinear processor according to the level of the generated echo.

[0007]

A learning period (non-convergence period) from when a line is set in a call sequence until the echo canceller finishes learning the echo characteristics of the line,
That is, during the period until the coefficient of each tap in the adaptive filter of the echo canceller is initially set, most of the voice emitted by the user of the mobile phone as the mobile station in the mobile phone system as the mobile communication system is folded back, A harsh echo is generated and the call is disturbed. In this case, operating the non-linear processor in the echo canceller as described above is an effective solution for suppressing the echo, but if the non-linear processor is used without any limitation, a part of the necessary voice is also canceled. There was a problem that the call was rather unnatural.

The present invention has been made in view of such circumstances, and provides an echo canceller capable of minimizing a line echo generated at the start of a call by effectively controlling a nonlinear processor. With the goal.

[0009]

According to one aspect of the present invention, there is provided a mobile communication system comprising: a mobile station; and a base station for performing line connection control on a plurality of mobile stations in a jurisdiction area. An echo canceller in which a network is connected to a fixed line network and cancels line echo provided in the base station, wherein the echo canceller is equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network. Pseudo-echo generation circuit for generating a pseudo-echo signal by passing a transmission signal from a transmission-side mobile station, and subtraction for subtracting the pseudo-echo signal from a reception signal from a reception-side mobile station A subtractor, an echo level detection circuit for detecting a residual echo from the output of the subtractor, and a signal level based on a given input / output characteristic. And having a non-linear processor, the operation threshold value setting circuit for setting in response to operating threshold of the non-linear processor to the level of the detection output of said echo level detection circuit.

[0010] According to the first aspect of the present invention, by having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and transmitting a transmission signal from a transmission-side mobile station, A pseudo echo generation circuit that generates a pseudo echo signal, a subtractor that subtracts the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an echo level detection circuit that detects a residual echo from an output of the subtractor, A non-linear processor that sets an output of the subtractor to a signal level based on a given input / output characteristic, and an operation threshold setting circuit that sets an operation threshold of the non-linear processor according to a level of a detection output of the echo level detection circuit. , It is possible to dynamically control the non-linear processor operation threshold value according to the level of the residual echo, and to receive audio with less auditory discomfort Possible to become.

The invention described in claim 2 is the first invention.
The echo canceller according to claim 1, further comprising a transmission level detection circuit that detects a level of a transmission signal from the mobile station on the transmission side, wherein the operation threshold setting circuit includes an output level and a transmission level of the echo level detection circuit. A ratio between the output level of the detection circuit and an operation threshold value of the nonlinear processor is dynamically set such that the ratio is proportional to the operation threshold value of the nonlinear processor.

According to the second aspect of the present invention, the operation threshold value setting circuit calculates a ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and calculates the ratio and the operation threshold value of the nonlinear processor. Is dynamically set so that the non-linear processor has a proportional relation, so that it is possible to receive a sound with less auditory discomfort.

According to a third aspect of the present invention, a mobile communication network having a mobile station and a base station that performs line connection control on a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling a line echo provided in the base station, wherein the echo canceller has transmission characteristics equivalent to a transmission path of a signal from which the echo wraps around from the fixed line network, and A pseudo echo generation circuit for generating a pseudo echo signal by passing a transmission signal from a station, a subtractor for subtracting the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an output of the subtractor. A non-linear processor that sets a signal level based on the input / output characteristics, a timer circuit that measures the time from the start of the call until a certain time elapses, Based on the output signal of the timer circuit, the operation threshold of the non-linear processor is set to a relatively large value until a certain period of time has elapsed since the start of the call after the start of the call, and the operation threshold has been set after the elapse of the certain period of time. An operation threshold value setting circuit for setting a smaller threshold value.

According to the third aspect of the present invention, transmission characteristics are equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and a transmission signal from a mobile station on the transmission side is passed. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, a timer circuit that measures the time until a certain time elapses from the start of the call, and an operation threshold of the non-linear processor based on an output signal of the timer circuit. Until the elapse, set the operation threshold of the nonlinear processor to a relatively large value,
And, after the lapse of the certain time, the operation threshold setting circuit for setting the operation threshold to a small value, so that the operation threshold of the nonlinear processor is increased during the non-convergence time of the adaptive filter constituting the echo canceller. After that, by setting the operation threshold small,
Voice reception with less discomfort is enabled. Claim 3
In the invention described in (1), since the operation threshold value of the non-linear processor is set according to the lapse of time after the start of a call, an echo level detection circuit for detecting a residual echo and a level of a transmission signal from a mobile station on the transmission side are detected. This eliminates the need for a transmission level detection circuit and simplifies the circuit configuration.

According to a fourth aspect of the present invention, a mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling a line echo provided in the base station, wherein the echo canceller has transmission characteristics equivalent to a transmission path of a signal from which the echo wraps around from the fixed line network, and A pseudo echo generation circuit for generating a pseudo echo signal by passing a transmission signal from a station, a subtractor for subtracting the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an output of the subtractor. A non-linear processor that sets the signal level based on the input / output characteristics, and a timer circuit that measures the time from the start of the call until a certain time elapses, Based on the output signal of the timer circuit, the operation threshold of the non-linear processor is set to be relatively large until a certain period of time elapses after the start of the call, and the non-linear processor is set to the non-linear state after the elapse of the certain period. An operation threshold setting circuit for setting the processor to a non-operation state.

According to the fourth aspect of the present invention, by having a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and transmitting a transmission signal from a transmission-side mobile station, A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, a timer circuit that measures the time until a certain time elapses from the start of the call, and an operation threshold of the non-linear processor based on an output signal of the timer circuit. Until the elapse, set the operation threshold of the nonlinear processor to a relatively large value,
And, after the lapse of the predetermined time, since it has an operation threshold value setting circuit that makes the non-linear processor in an inactive state,
Residual echo at the start of a call can be efficiently removed, so that audio reception with less auditory discomfort is possible.

According to a fifth aspect of the present invention, a mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network, An echo canceller for canceling a line echo provided in the base station, wherein the echo canceller has transmission characteristics equivalent to a transmission path of a signal from which the echo wraps around from the fixed line network, and A pseudo echo generation circuit for generating a pseudo echo signal by passing a transmission signal from a station, a subtractor for subtracting the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an output of the subtractor. A non-linear processor for setting a signal level based on input / output characteristics, an echo level detection circuit for detecting a residual echo from an output of the subtractor, A transmission level detection circuit for detecting a level of a transmission signal from a mobile station, a timer circuit for measuring a time period from when the call starts until a certain time elapses, and after a call starts based on an output signal of the timer circuit. Until a certain time elapses, the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit is calculated, and the ratio between this ratio and the operation threshold value of the non-linear processor becomes a small value. Thus, the operation threshold of the nonlinear processor is set, and after the lapse of the predetermined time, the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit and the ratio of the operation threshold of the nonlinear processor is An operation threshold value setting circuit for setting the value to a large value.

According to the fifth aspect of the present invention, the mobile station has transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and transmits a transmission signal from a mobile station on the transmission side. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
A timer circuit that measures the time until a certain time elapses from the start of the call, and until a certain time elapses after the start of the call based on the output signal of the timer circuit,
Taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and setting the operation threshold value of the nonlinear processor so that the ratio between the ratio and the operation threshold value of the nonlinear processor becomes a small value. And after the elapse of the predetermined time, an operation of setting the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit and the operation threshold value of the non-linear processor to be a large value. A threshold setting circuit, so that the operation threshold of the non-linear processor is increased with respect to the amount of change in the level of the residual echo in the non-convergence time zone (within a predetermined time) of the adaptive filter constituting the echo canceller at the start of a call. After that, the residual echo level was reduced with respect to the amount of change, so that the residual echo at the start of the call was efficiently removed. It can, hearing on, it is possible to little voice reception discomfort.

According to a sixth aspect of the present invention, there is provided a mobile communication network having a mobile station and a base station for performing a line connection control for a plurality of mobile stations in a jurisdiction area, wherein the mobile communication network is connected to a fixed network. An echo canceller for canceling a line echo provided in the base station, wherein the echo canceller has transmission characteristics equivalent to a transmission path of a signal from which the echo wraps around from the fixed line network, and A pseudo echo generation circuit for generating a pseudo echo signal by passing a transmission signal from a station, a subtractor for subtracting the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an output of the subtractor. A non-linear processor for setting a signal level based on input / output characteristics, an echo level detection circuit for detecting a residual echo from an output of the subtractor, A transmission level detection circuit for detecting a level of a transmission signal from a mobile station, a timer circuit for measuring a time period from when the call starts until a certain time elapses, and after a call starts based on an output signal of the timer circuit. Until a certain time elapses, the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit is calculated, and the ratio between this ratio and the operation threshold value of the non-linear processor becomes a small value. And an operation threshold value setting circuit for setting the operation threshold value of the non-linear processor and setting the non-linear processor to the non-operation state after the lapse of the predetermined time.

According to the sixth aspect of the present invention, by having a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and transmitting a transmission signal from a mobile station on the transmission side, A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
A timer circuit that measures the time until a certain time elapses from the start of the call, and until a certain time elapses after the start of the call based on the output signal of the timer circuit,
Taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and setting the operation threshold value of the nonlinear processor so that the ratio between the ratio and the operation threshold value of the nonlinear processor becomes a small value. And an operation threshold setting circuit for setting the non-linear processor to be in the non-operation state after the lapse of the predetermined time, so that the operation threshold of the non-linear processor is set to a non-convergence time zone (a predetermined time) at the start of a call. ) Is increased with respect to the amount of change in the level of the residual echo, and then the non-linear processor is deactivated, so that the residual echo at the start of a call can be efficiently removed,
Voice reception with less discomfort is enabled.

According to a seventh aspect of the present invention, a mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network, An echo canceller for canceling a line echo provided in the base station, wherein the echo canceller has transmission characteristics equivalent to a transmission path of a signal from which the echo wraps around from the fixed line network, and A pseudo echo generation circuit for generating a pseudo echo signal by passing a transmission signal from a station, a subtractor for subtracting the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an output of the subtractor. A non-linear processor for setting a signal level based on input / output characteristics, an echo level detection circuit for detecting a residual echo from an output of the subtractor, A transmission level detection circuit for detecting a level of a transmission signal from a mobile station, and an operation threshold setting for initially setting the operation threshold of the non-linear processor larger at the start of a call, and thereafter setting the operation threshold smaller. And an operation threshold setting circuit,
The operation of switching from the larger operation threshold to the smaller operation threshold is determined by taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and the ratio between this ratio and the operation threshold of the nonlinear processor is calculated. It is characterized in that it is executed when it becomes smaller than a predetermined value.

According to the seventh aspect of the present invention, the transmission signal from the mobile station on the transmission side has a transmission characteristic equivalent to the transmission path of the signal from which the echo wraps around from the fixed line network. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
An operation threshold setting circuit for initially setting the operation threshold of the non-linear processor at the start of a call, and thereafter setting the operation threshold to a small value, wherein the operation threshold setting circuit comprises the large operation threshold The operation of switching from the operation threshold value to a smaller operation threshold value is determined by taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and the ratio between this ratio and the operation threshold value of the nonlinear processor becomes smaller than a predetermined value. At the time of execution, by appropriately selecting the predetermined value,
The operation threshold value of the nonlinear processor can be set so that the non-convergence time zone at the start of a call (within a predetermined time) is increased with respect to the amount of change in the level of the residual echo, and is reduced after the elapse of the non-convergence time zone. In addition, it is possible to efficiently remove the residual echo at the start of a call, and it is possible to receive a sound with less auditory discomfort.

The invention described in claim 8 is the first invention.
In the echo canceller according to any one of to 7,
Further, a transmission path determining means for detecting whether or not the transmission path between the calling terminals is a complete digital path,
The operation threshold setting circuit sets the non-linear processor to a non-operational state when the transmission path determination unit determines that the transmission path between the terminals that are talking is a complete digital path.

According to the eighth aspect of the present invention, the transmission path determination means detects whether or not the transmission path between the calling terminals is a complete digital path, and the operation threshold setting circuit sets the transmission path. When the determination unit determines that the transmission path between the terminals that talk is a complete digital path, the control for setting the threshold value of the non-linear processor is stopped, and the non-linear processor is set to a non-operation state. Therefore, unnecessary control operation of the echo canceller can be eliminated.

Further, the invention according to claim 9 has a portable telephone as a mobile station and a base station which performs line connection control for a plurality of mobile stations in a jurisdiction area, and is connected to a fixed line network. In the mobile phone system, the base station is provided with an echo canceller for canceling a line echo from a fixed line network, and the echo canceller is equivalent to a transmission path of a signal whose echo wraps around from the fixed line network. Pseudo-echo generation circuit for generating a pseudo-echo signal by passing a transmission signal from a transmission-side mobile station, and subtraction for subtracting the pseudo-echo signal from a reception signal from a reception-side mobile station A non-linear processor that sets the output of the subtractor to a signal level based on a given input / output characteristic, and an operation threshold of the non-linear processor. And a operation threshold setting circuit for,
The mobile station has operation means for setting an operation threshold of the non-linear processor, and communication means for transmitting setting information set by the operation means to the base station. An operation threshold of the nonlinear processor is set based on the received setting information.

According to a ninth aspect of the present invention, in the portable telephone system, the base station is provided with an echo canceller for canceling a line echo from a fixed line network, and the echo canceller is provided with the fixed line. A pseudo echo generation circuit having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from a network and generating a pseudo echo signal by passing a transmission signal from a mobile station on the transmission side;
A subtractor for subtracting the pseudo echo signal from a received signal from a mobile station on the receiving side; a non-linear processor for setting an output of the subtractor to a signal level based on a given input / output characteristic; and an operation threshold of the non-linear processor Operating threshold value setting circuit for setting the operating threshold of the non-linear processor, and a communication unit for transmitting setting information set by the operating unit to the base station. Has, the operation threshold setting circuit, since the operation threshold of the nonlinear processor is set based on the setting information received from the mobile station, by setting the operation threshold of the nonlinear processor in the echo canceller from the mobile station side, Efficiently eliminates residual echo at the start of a call, enabling audio reception with less auditory discomfort That.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration of a communication network to which the present invention is applied. In FIG. 1, a mobile communication network A is connected to another mobile communication network B via a fixed line network 1 such as a public line network. The fixed network 1 is an analog network. Mobile communication network A,
B is, for example, a mobile phone system, and the mobile station 10-
Reference numerals 1 and 10-2 denote mobile phones. The mobile communication network A includes a mobile station 10-1, a base station (BS) 20-1 installed in an area under the jurisdiction of the mobile station 10-1, and performing line connection control between the mobile stations, and a base station 20-1. And a control station (CS) 30-1 connected to the fixed line network 1 for controlling the plurality of base stations in general. Although a plurality of mobile stations and a plurality of base stations exist in the mobile communication network A, only one is shown for convenience of explanation.

On the other hand, the mobile communication network B comprises a mobile station 10-2 and a base station (B
S) 20-2, 20-3,..., 20-N and the base station (B
S) It has a control station 30-2 connected to a fixed line network that controls the whole of 20-2, 20-3,..., 20-N. Base stations 20-1, 20-2, 20-3, ..., 20
Each of −N is provided with an echo canceller 200. In the above configuration, the mobile station 10-1 of the mobile communication network A and the mobile station 10 of the mobile communication network B
-2, a line is connected and a call is made.

Mobile station 10-1 of mobile communication network A
Is transmitted to the fixed line network 1 via the base station 20-1 and the control station 30-1, and further transmitted from the fixed line network 1 to the control station 30-2 and the mobile station 1 of the mobile communication network B.
It is transmitted to the mobile station 10-2 via the base station 20-3 installed in the area under the jurisdiction of O-2. Here, mobile station 1
The voice signal transmitted from 0-1 to the mobile station 10-02 is
A line echo 50 is generated due to impedance mismatch in a hybrid circuit (4-wire to 2-wire conversion circuit) arranged at the terminal point of the fixed line network 1.

The line echo 50 is transmitted to the control station 30-1,
An attempt is made to return to the mobile station 10-1, which is the transmitting side, via the base station 20-1, but is canceled by the echo canceller 200 provided in the base station 20-1. At the start of the call, the adaptive filter of the echo canceller does not converge at the start of the call among the line echoes caused by the impedance mismatch in the hybrid circuit of the fixed line network (analog line) 1 during a call by the mobile phone as the mobile station. The echo generated under the state has a great influence on the voice of the call, but according to the present invention, the echo at the start of the call is minimized by effectively controlling the non-linear processor constituting the echo canceller 200 described later. can do.

Next, the echo canceller 20 shown in FIG.
FIG. 2 shows a specific configuration of 0. In the figure, an echo canceller 200 includes a pseudo echo generation circuit 201, a subtractor 202, a transmission level detection circuit 203, an echo level detection circuit 204, an operation threshold setting circuit 205, a non-linear processor (NLP) 206, And a transmission path determination unit 207. Also, the input port 210 (Ri
n) is a port to which the voice signal of the speaker from the transmitting mobile station is input, and the output port 220 (Sout) is to output the voice signal of the speaker from the receiving mobile station or the fixed telephone. Port.

The output port 211 (Rout) is a voice of a speaker from a mobile station on the receiving side connected to the line on the fixed network 1 side or a mobile station on the transmitting side output to the fixed telephone. An output port to which a signal is output and an input port 221 (Sin) are ports to which a voice signal of a speaker from a receiving mobile station or a fixed telephone including a line echo from the fixed line network 1 is input.

The pseudo echo generation circuit 201 includes an adaptive filter, and has a coefficient of each tap of the adaptive filter so as to have a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network 1. And a function of generating a pseudo echo signal for canceling a line echo by passing a transmission signal (voice signal) from a mobile station on the transmission side. Further, the subtractor 202 has a function of subtracting a pseudo echo signal from a received signal from a mobile station on the receiving side to eliminate an echo included in the received signal.

The transmission level detection circuit 203 has a function of detecting the level of the transmission signal from the mobile station on the transmission side, and the echo level detection circuit 204 has a function of detecting the level of the residual echo from the output of the subtracter 202. have. In the operating state, the non-linear processor 206 has, for example, input / output characteristics having operation thresholds as shown in FIGS. 3 and 4, and outputs when the input signal (audio input signal) is lower than a predetermined level. When the level is set to zero and the level is equal to or higher than a predetermined level, a signal having a level proportional to the input is output.

That is, it has a function of setting the output of the subtracter 202 to a signal level based on the given input / output characteristic. However, in the above-described input / output characteristics of the non-linear processor 206, in the conventional echo canceller, the operation threshold value of the non-linear processor was used in a fixed state. The operation threshold in the characteristic is set to be changeable by the operation threshold setting circuit 205. In addition, the nonlinear processor 20
6 is a through state in which the input signal is output as it is in the non-operation state.

The operation threshold setting circuit 205 sets the operation threshold of the nonlinear processor 206 to the echo level detection circuit 20.
4 has a function of dynamically setting according to the level of the detection output, that is, the level of the residual echo. The transmission path determination unit 207 has a function of detecting whether or not the transmission path between the calling terminals is a complete digital path. Specifically, the exchange in the fixed line network 1 has a function of notifying the information as to whether or not the transmission path between the above-mentioned calling terminals is entirely a digital path. The unit 207 has a function of detecting whether or not the transmission path is a complete digital path based on the received path information.

In the above configuration, a voice signal from a speaker of the mobile station 10-1 of the mobile communication network A is output from the input port 210 of the echo canceller 200 to the output port 211 connected to the control station 30-1. At the same time, it is input to the transmission level detection circuit 203 and the pseudo echo generation circuit 201. In the pseudo echo generation circuit 201,
The coefficient of each tap of the adaptive filter is set so as to have a transmission characteristic equivalent to a transmission path of a signal whose echo wraps around from the fixed line network 1, and a transmission signal (voice signal) from the mobile station 10-1 on the transmission side is set. Signal) to generate a pseudo echo signal for canceling the line echo,
Output to

A reception signal from the mobile station 10-2 on the receiving side is input from the input port 221,
At 2, the echo contained in the received signal is canceled by subtracting the pseudo echo signal from the received signal from the mobile station 10-2 on the receiving side. However, since a certain amount of time is required from the start of the call to the convergence of the coefficients of the taps of the adaptive filters constituting the pseudo echo generation circuit 201, immediately after the start of the call, the non-convergence time period of the adaptive filter , The residual echo is included in the audio signal output from the subtractor 202.

The received signal including the residual echo from the mobile station 10-2 on the receiving side is output to the echo level detection circuit 204 and the non-linear processor 206. On the other hand, a voice signal (transmission signal) from the speaker of the mobile station 10-1 is input to the transmission level detection circuit 203, and the transmission level detection circuit 203 detects the level of the transmission signal and outputs the detection signal. Output to the operation threshold setting circuit 205. The echo level detection circuit 204 detects the level of the residual echo included in the output signal of the subtracter 202, and outputs this detection signal to the operation threshold setting circuit 205.

The transmission route judgment unit 207 receives path information indicating whether or not it is from an exchange (not shown) of the fixed line network 1. In the present embodiment, since the fixed line network 1 is an analog line network, path information indicating that it is not a complete digital path is received from the switch of the fixed line network 1,
Information indicating that the transmission path between the mobile station 10-1 and the mobile station 10-2 is not a complete digital path is output to the operation threshold setting circuit 205.

Here, when the transmission path between the mobile station 10-1 and the mobile station 10-2 is a complete digital path, for example, if the fixed line network is an IS
In the case of a digital network such as a DN, since the mobile communication networks A and B are digital networks, the transmission path between the mobile station 10-1 and the mobile station 10-2 is a complete digital path, and No echo occurs. Therefore, in this case, the control for setting the threshold value of the non-linear processor 206 is stopped, and the non-linear processor 206 is set to the non-operation state. This can eliminate unnecessary control operations of the echo canceller.

Now, the mobile station 1
The operation threshold value setting circuit 205, which receives the information indicating that the transmission path between 0-1 and the mobile station 10-2 is not a complete digital path, determines the detection output of the echo level detection circuit 204, that is, the level of the residual echo. The operation threshold value in the input / output characteristics of the nonlinear processor 206 is set accordingly. Specifically, the operation threshold setting circuit 205 calculates the ratio between the output level of the echo level detection circuit 204 and the output level of the transmission level detection circuit 203, and the ratio and the operation threshold of the non-linear processor 206 have a proportional relationship. Thus, the operation threshold of the nonlinear processor 206 is dynamically set.

Thus, the operation threshold value in the input / output characteristics is set so as to be large when the level of the residual echo is high and to be small when the level of the residual echo is low, according to the level of the detected residual echo. The nonlinear processor 206 is controlled as described above, and an audio signal in which the residual echo is minimized is output from the output port 220 to the mobile station 10-1 on the transmission side.

As described above, according to the present embodiment, the operation threshold value setting circuit 205 calculates the ratio between the output level of the echo level detection circuit 204 and the output level of the transmission level detection circuit 203, and calculates this ratio and the nonlinear processor Since the operation threshold of the non-linear processor 206 is dynamically set so that the operation threshold of the non-linear processor 206 is proportional to the operation threshold of the non-linear processor 206, it is possible to efficiently remove a residual echo at the start of a call, and to receive audio with less auditory discomfort. Becomes possible.

As another embodiment of the echo canceller 200, as shown in FIG. 5, a timer circuit 300 for measuring the time from the start of a call until a predetermined time elapses is provided. Timer circuit 30
A function of setting an operation threshold value in the input / output characteristics of the nonlinear processor 206 based on an output signal of 0 may be provided. That is, the operation threshold setting circuit 205
However, based on the output signal of the timer circuit 300, the operation threshold of the nonlinear processor 206 is set to a large value (Vth1) until a certain time Δt elapses after the start of the call (after time t0) as shown in FIG. After the elapse of the predetermined time (after time tn), the operation threshold value is reduced (Vth2 <Vth
It may be set to 1). The configuration of the waist of the echo canceller shown in FIG. 5 is the same as the configuration shown in FIG. 2 except that a timer circuit 300 is added.

As described above, according to the present embodiment, the operation threshold of the nonlinear processor 206 is increased during the non-convergence time of the adaptive filter constituting the echo canceller 200, and thereafter, the operation threshold is decreased. By setting, it is possible to receive audio with less sense of incompatibility. Further, since the operation threshold value of the non-linear processor 206 is set based on the lapse of time after the start of a call, an echo level detection circuit 204 for detecting a residual echo, and a transmission level for detecting the level of a transmission signal from a mobile station on the transmission side. There is also an effect that the detection circuit 203 can be omitted, and the circuit configuration is simplified.

The operation threshold value setting circuit 205 sets the operation threshold value of the non-linear processor 206 based on the output signal of the timer circuit 300 to a larger value (Vth1) until a certain time Δt has elapsed since the start of the call (after time t0). ) And after the lapse of the predetermined time (after the time tn), a function of disabling the nonlinear processor 206 may be provided. In this case, the operation threshold of the nonlinear processor 206 needs to be set to one.

As described above, the nonlinear processor 206
The operation threshold value is set to a relatively large value after the start of a call until a certain time elapses, and after the elapse of the certain time, the non-linear processor 206 is set to a non-operating state. Efficient removal is possible, and audio reception with less auditory discomfort is possible.

Also, as shown in FIG. 5, the operation threshold setting circuit 205 determines the output level of the echo level detection circuit 204 based on the output signal of the timer circuit 300 until a certain period of time elapses after the start of the call. The ratio between the output level of the transmission level detection circuit 203 and the operation threshold of the non-linear processor 206 is set so that the ratio between the ratio and the operation threshold of the non-linear processor 206 becomes a small value. Has a function of setting the ratio between the output level of the echo level detection circuit 204 and the output level of the transmission level detection circuit 203 and the operation threshold value of the non-linear processor 206 to be a relatively large value. Is also good.

That is, the operation threshold of the non-linear processor is set to be larger in the non-convergence time zone (within a predetermined time) of the adaptive filter constituting the echo canceller at the start of a call with respect to the level change of the residual echo. May be reduced with respect to the amount of change in the level. By doing so, it is possible to efficiently remove the residual echo at the start of the call, and it is possible to receive audio with a sense of hearing that is uncomfortable.

The operation threshold value setting circuit 205 controls the echo level detection circuit 204 based on the output signal of the timer circuit 300 until a certain period of time elapses after the start of the call.
Of the output level of the nonlinear processor 206 and the output level of the transmission level detection circuit 203, and the operation threshold value of the nonlinear processor 206 is set so that the ratio of the output level to the operation threshold value of the nonlinear processor 206 becomes a small value. After the lapse of time, a function of setting the non-linear processor 206 to be in an inactive state may be provided.

That is, the operation threshold value of the non-linear processor 206 is set to a non-convergence time zone at the start of a call (within a predetermined time).
May be increased with respect to the amount of change in the level of the residual echo, and then the non-linear processor 206 may be brought into a non-operation state. By doing so, it is possible to efficiently remove the residual echo at the start of a call,
Voice reception with less discomfort is enabled.

When the operation threshold of the non-linear processor 206 is initially set to be relatively large at the start of a call in the operation threshold setting circuit 205, and thereafter the operation threshold is set to be small, the operation threshold is set to be smaller than the larger operation threshold. The operation for switching to the operation threshold value of the echo level detection circuit 2
04 and the output level of the transmission level detection circuit 203.
A function may be provided that is executed when the ratio of the operation threshold value to the operation threshold value becomes smaller than a predetermined value.

By appropriately selecting the above predetermined value,
The operation threshold value of the non-linear processor 206 can be set so that the non-convergence time zone at the start of a call (within a predetermined time) is larger than the change amount of the level of the residual echo, and becomes smaller after the elapse of the non-convergence time zone. Therefore, it is possible to efficiently remove the residual echo at the start of the call, and it is possible to receive a sound with less discomfort in hearing.

In the portable telephone system, the base station is provided with an echo canceller for canceling the line echo from the fixed line network. A pseudo-echo generation circuit having transmission characteristics equivalent to a transmission path and generating a pseudo-echo signal by passing a transmission signal from a transmission-side mobile station; and a pseudo-echo signal from a reception signal from a reception-side mobile station. A subtractor, a non-linear processor that sets an output of the subtractor to a signal level based on a given input / output characteristic, and an operation threshold setting circuit that sets an operation threshold of the non-linear processor, Operating means for setting an operation threshold value of the non-linear processor in the mobile station; and setting information set by the operating means. The provided communication means for transmitting to said base station, said operating threshold setting circuit may be configured to set the operating threshold of the non-linear processor in accordance with the setting information received from the mobile station.

With this configuration, by setting the operation threshold value of the non-linear processor in the echo canceller from the mobile station side, it is possible to efficiently remove the residual echo at the start of a call, and to provide a sense of incongruity in hearing. It is possible to receive less voice.

[0057]

As described above, according to the first aspect of the present invention, the transmission side has a transmission characteristic equivalent to a transmission path of a signal from which an echo wraps around a fixed line network, and A pseudo echo generation circuit that generates a pseudo echo signal by passing a transmission signal from a station, and a subtracter that subtracts the pseudo echo signal from a reception signal from a mobile station on the receiving side,
An echo level detection circuit for detecting a residual echo from the output of the subtracter, a non-linear processor for setting the output of the subtractor to a signal level based on a given input / output characteristic, and setting the operation threshold of the non-linear processor to the echo level An operation threshold setting circuit that sets the operation threshold according to the level of the detection output of the detection circuit, so that the operation threshold of the non-linear processor can be dynamically controlled in accordance with the level of the residual echo. Becomes possible.

According to the second aspect of the present invention, the operation threshold setting circuit obtains a ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and calculates the ratio and the operation of the non-linear processor. Since the operation threshold value of the non-linear processor is dynamically set so that the threshold value is proportional to the threshold value, it is possible to receive a sound with less auditory discomfort.

According to the third aspect of the present invention, the transmission signal has a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from a fixed line network, and transmits a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and an output of the subtracter based on input / output characteristics given. A non-linear processor for setting a signal level, a timer circuit for measuring a time until a certain time elapses from the start of the call, and an operation threshold value of the non-linear processor based on an output signal of the timer circuit for a certain time after the start of the call An operation of setting the operation threshold of the nonlinear processor to a relatively large value until time elapses, and setting the operation threshold to a small value after the elapse of the predetermined time Since the threshold value of the non-linear processor is increased during the non-convergence time period of the adaptive filter constituting the echo canceller, the operation threshold value is increased, and thereafter, the operation threshold value is set smaller, so that the auditory sense of discomfort is increased. It is possible to receive less voice.

According to the third aspect of the present invention, since the operation threshold of the non-linear processor is set based on the lapse of time after the start of a call, an echo level detection circuit for detecting a residual echo and a mobile station on the transmission side are provided. This eliminates the need for a transmission level detection circuit for detecting the level of the transmission signal, thereby simplifying the circuit configuration.

According to the fourth aspect of the present invention, the transmission signal from the mobile station on the transmission side has a transmission characteristic equivalent to the transmission path of the signal from which the echo wraps around from the fixed line network. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, a timer circuit that measures the time until a certain time elapses from the start of the call, and an operation threshold of the non-linear processor based on an output signal of the timer circuit. Until the elapse, set the operation threshold of the nonlinear processor to a relatively large value,
And, after the lapse of the predetermined time, since it has an operation threshold value setting circuit that makes the non-linear processor in an inactive state,
Residual echo at the start of a call can be efficiently removed, so that audio reception with less auditory discomfort is possible.

According to the fifth aspect of the present invention, the transmission signal from the mobile station on the transmitting side has a transmission characteristic equivalent to a transmission path of a signal whose echo wraps around from the fixed line network. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
A timer circuit that measures the time until a certain time elapses from the start of the call, and until a certain time elapses after the start of the call based on the output signal of the timer circuit,
Taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and setting the operation threshold value of the nonlinear processor so that the ratio between the ratio and the operation threshold value of the nonlinear processor becomes a small value. And after the elapse of the predetermined time, an operation of setting the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit and the operation threshold value of the non-linear processor to be a large value. A threshold setting circuit, so that the operation threshold of the non-linear processor is increased with respect to the amount of change in the level of the residual echo in the non-convergence time zone (within a predetermined time) of the adaptive filter constituting the echo canceller at the start of a call. After that, the residual echo level was reduced with respect to the amount of change, so that the residual echo at the start of the call was efficiently removed. It can, hearing on, it is possible to little voice reception discomfort.

According to the sixth aspect of the present invention, the transmission signal from the mobile station on the transmitting side has a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
A timer circuit that measures the time until a certain time elapses from the start of the call, and until a certain time elapses after the start of the call based on the output signal of the timer circuit,
Taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and setting the operation threshold value of the nonlinear processor so that the ratio between the ratio and the operation threshold value of the nonlinear processor becomes a small value. And an operation threshold setting circuit for setting the non-linear processor to be in the non-operation state after the lapse of the predetermined time, so that the operation threshold of the non-linear processor is set to a non-convergence time zone (a predetermined time) at the start of a call. ) Is increased with respect to the amount of change in the level of the residual echo, and then the non-linear processor is deactivated, so that the residual echo at the start of a call can be efficiently removed,
Voice reception with less discomfort is enabled.

According to the seventh aspect of the present invention, the transmission signal from the mobile station on the transmitting side has a transmission characteristic equivalent to a transmission path of a signal whose echo wraps around from the fixed line network. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit that detects a residual echo from the output of the subtractor, a transmission level detection circuit that detects the level of a transmission signal from the transmitting side mobile station,
An operation threshold setting circuit for initially setting the operation threshold of the non-linear processor at the start of a call, and thereafter setting the operation threshold to a small value, wherein the operation threshold setting circuit comprises the large operation threshold The operation of switching from the operation threshold value to a smaller operation threshold value is determined by taking the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and the ratio between this ratio and the operation threshold value of the nonlinear processor becomes smaller than a predetermined value. At the time of execution, by appropriately selecting the predetermined value,
The operation threshold value of the nonlinear processor can be set so that the non-convergence time zone at the start of a call (within a predetermined time) is increased with respect to the amount of change in the level of the residual echo, and is reduced after the elapse of the non-convergence time zone. In addition, it is possible to efficiently remove the residual echo at the start of a call, and it is possible to receive a sound with less auditory discomfort.

According to the eighth aspect of the present invention, the transmission path determination means detects whether or not the transmission path between the communicating terminals is a complete digital path, and the operation threshold setting circuit sets the transmission path When the determination unit determines that the transmission path between the terminals that talk is a complete digital path, the control for setting the threshold value of the non-linear processor is stopped, and the non-linear processor is set to a non-operation state. Therefore, unnecessary control operation of the echo canceller can be eliminated.

According to the ninth aspect of the present invention, in the portable telephone system, the base station is provided with an echo canceller for canceling a line echo from a fixed line network, and the echo canceller is provided with the fixed line. A pseudo echo generation circuit having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from a network and generating a pseudo echo signal by passing a transmission signal from a mobile station on the transmission side;
A subtractor for subtracting the pseudo echo signal from a received signal from a mobile station on the receiving side; a non-linear processor for setting an output of the subtractor to a signal level based on a given input / output characteristic; and an operation threshold of the non-linear processor Operating threshold value setting circuit for setting the operating threshold of the non-linear processor, and a communication unit for transmitting setting information set by the operating unit to the base station. Has, the operation threshold setting circuit, since the operation threshold of the nonlinear processor is set based on the setting information received from the mobile station, by setting the operation threshold of the nonlinear processor in the echo canceller from the mobile station side, Efficiently eliminates residual echo at the start of a call, enabling audio reception with less auditory discomfort That.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a communication network to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of an echo canceller according to the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing an example of input / output characteristics of a non-linear processor in an echo canceller.

FIG. 4 is a characteristic diagram showing another example of the input / output characteristics of the non-linear processor in the echo canceller.

FIG. 5 is a block diagram showing a configuration of a main part of an echo canceller according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of control characteristics of an operation threshold value setting circuit in the echo canceller according to the embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a conventional echo canceller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed line network 10-1, 10-2 Mobile station 20-1 to 20-N Base station 30-1, 30-2 Control station 200 Echo canceller 201 Pseudo echo generation circuit 202 Subtractor 203 Transmission level detection circuit 204 Echo level Detection circuit 205 Operation threshold value setting circuit 206 Nonlinear processor (NLP) 207 Transmission path determination unit

Claims (9)

[Claims] 1. A mobile communication network having a mobile station and a base station that controls line connection to a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo echo generation circuit that generates a pseudo echo signal, a subtractor that subtracts the pseudo echo signal from a reception signal from a mobile station on the receiving side, and an echo level detection circuit that detects a residual echo from an output of the subtractor, A non-linear processor that sets the output of the subtractor to a signal level based on a given input / output characteristic; An operation threshold value setting circuit that sets an operation threshold value according to the level of the detection output of the echo level detection circuit. 2. A transmission level detection circuit for detecting a level of a transmission signal from the mobile station on the transmission side, wherein the operation threshold setting circuit includes an output level of the echo level detection circuit and a transmission level detection circuit. 2. The echo according to claim 1, wherein a ratio between the output level of the non-linear processor and the operation threshold of the non-linear processor is dynamically set so that the ratio is proportional to the operation threshold of the non-linear processor. Canceller. 3. A mobile communication network having a mobile station and a base station that controls line connection to a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, a timer circuit for measuring the time from the start of the call until a certain time elapses, and a timer circuit based on an output signal of the timer circuit. The operation threshold value of the non-linear processor is set to a relatively large value after the start of the call until a certain time elapses, and the operation threshold value is set to a small value after the elapse of the certain time. An echo canceller, comprising: a setting circuit. 4. A mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, a timer circuit for measuring the time from the start of the call until a certain time elapses, and a timer circuit based on an output signal of the timer circuit. Setting the operation threshold value of the non-linear processor to a relatively large value until a certain period of time elapses after the start of a call, and setting the non-linear processor to a non-operation state after the elapse of the certain time period. And a threshold setting circuit. 5. A mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit for detecting a residual echo from the output of the subtractor, and a level of a transmission signal from the mobile station on the transmission side. A transmission level detection circuit for detecting a call, a timer circuit for measuring a time until a certain time elapses from the start of the call, and a timer circuit for measuring a time until a certain time elapses after the start of the call based on an output signal of the timer circuit. Takes the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and sets the operation threshold of the non-linear processor so that the ratio between the ratio and the operation threshold of the non-linear processor becomes a small value. And after the lapse of the predetermined time, the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit and the ratio of the operation threshold value of the non-linear processor are set to a relatively large value. An operation threshold setting circuit that performs the operation. 6. A mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit for detecting a residual echo from the output of the subtractor, and a level of a transmission signal from the mobile station on the transmission side. A transmission level detection circuit for detecting a call, a timer circuit for measuring a time until a certain time elapses from the start of the call, and a timer circuit for measuring a time until a certain time elapses after the start of the call based on an output signal of the timer circuit. Takes the ratio between the output level of the echo level detection circuit and the output level of the transmission level detection circuit, and sets the operation threshold of the non-linear processor so that the ratio between the ratio and the operation threshold of the non-linear processor becomes a small value. And an operation threshold setting circuit for setting the non-linear processor to be in an inactive state after the predetermined time has elapsed. 7. A mobile communication network having a mobile station and a base station that performs line connection control for a plurality of mobile stations in a jurisdiction area is connected to a fixed line network. An echo canceller for canceling, the echo canceller having transmission characteristics equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and passing a transmission signal from a transmission-side mobile station. A pseudo-echo generating circuit for generating a pseudo-echo signal, a subtractor for subtracting the pseudo-echo signal from a received signal from a mobile station on the receiving side, and a signal level based on input / output characteristics given an output of the subtractor A non-linear processor, an echo level detection circuit for detecting a residual echo from the output of the subtractor, and a level of a transmission signal from the mobile station on the transmission side. A transmission level detection circuit that detects a threshold value, and an operation threshold value setting circuit that first sets the operation threshold value of the nonlinear processor at the start of a call, and then sets the operation threshold value smaller.
The operation threshold setting circuit takes an operation of switching from the larger operation threshold to a smaller operation threshold by taking a ratio between an output level of the echo level detection circuit and an output level of the transmission level detection circuit, and this ratio and the nonlinear processor An echo canceller that is executed when a ratio of the echo canceller to an operation threshold value becomes smaller than a predetermined value. 8. A transmission path determining means for detecting whether or not a transmission path between communication terminals is a complete digital path. The echo canceller according to any one of claims 1 to 7, wherein when it is determined that the transmission path between the terminals to be executed is a complete digital path, the non-linear processor is set to a non-operation state. 9. A mobile phone system having a mobile phone as a mobile station and a base station for performing line connection control for a plurality of mobile stations in a jurisdiction area, wherein the base station is connected to a fixed line network. Has an echo canceller that cancels the line echo from the fixed line network,
The echo canceller has a transmission characteristic equivalent to a transmission path of a signal in which an echo wraps around from the fixed line network, and generates a pseudo echo signal by passing a transmission signal from a transmission-side mobile station. A generating circuit, a subtractor for subtracting the pseudo echo signal from a received signal from a mobile station on the receiving side, a non-linear processor for setting an output of the subtractor to a signal level based on a given input / output characteristic, and An operation threshold setting circuit for setting an operation threshold of a processor, wherein the mobile station transmits to the base station operation means for setting an operation threshold of the non-linear processor, and setting information set by the operation means. Communication means, the operation threshold setting circuit, the operation threshold of the nonlinear processor based on the setting information received from the mobile station Mobile telephone system which is characterized by a constant.