JPH0666710B2 - Eco-Cancell method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an echo-cancell system, and more particularly to an improvement of the echo-cancell system used in a full-duplex wireless communication system.

[Conventional technology]

Generally, in a full-duplex wireless communication system, mutual communication is performed using a telephone called a speakerphone or a conference telephone, which is capable of making a call by a microphone and a speaker without using a handset. In this case, the voice of the talker or the reverberant sound in the room where the talker is present goes directly into the microphone from the speaker of the speakerphone of the talker and is output from the speaker of the talker with a certain time delay, so-called echo Reach the ear of the talker. Since this echo sound acts as a disturbing sound for a telephone call, an echo suppression circuit called an echo canceller for removing it is built in the telephone.

FIG. 2 shows an example of an echo canceling method conventionally used in a dual wireless communication system. In FIG. 2, the voice of the talker is input to the modulation circuit 24 via the microphone 28, the low frequency amplification circuit 27 and the amplitude limiting circuit 25. The amplitude limiting circuit 25 has a characteristic that the signal shown in FIG. 3 (b) is output with respect to the signal input shown in FIG. 3 (a). Figure 3 (a) and (b)
In 101, 103 and 103 respectively indicate upper and lower clip levels corresponding to the center level 102.

The output of the amplitude limiting circuit 25 means a modulation signal for the modulation circuit 24. The signal frequency-modulated by the modulation circuit 24 by this modulation signal is amplified by the transmission circuit 26 and is shared by the antenna sharing circuit 22 and the antenna 15. Sent to the other party via.

Corresponding to the transmission from us, the signal sent from the other side is received by the antenna 15 and input to the receiving circuit 16 via the antenna sharing circuit 22 and demodulated. In this demodulated signal, in addition to the voice sent from the other party, the voice sent from me is mixed as an echo. An adaptive echo canceller 17 including an adder 18 and a pseudo echo generating circuit 19 is used to cancel this echo. In the adaptive echo canceller 17, the audio signal output from the low frequency amplification circuit 27 of the transmission system is input to the adder 18 via the pseudo echo generation circuit 19 and is demodulated from the reception circuit 16 in the adder 18. It acts to cancel the echo contained in the signal. The output of the adder 18 is fed back to the pseudo echo generating circuit 19 and the function of the adaptive echo canceller 17 is realized. Adaptive echo canceller
The audio signal output from 17 is amplified by the low-frequency amplifier circuit 6 and output via the speaker 7.

[Problems to be solved by the invention]

In the above-described conventional echo canceling method, the echo canceling audio signal input from the transmission system to the adaptive echo canceller 17 enables the echo canceling effect of the pseudo echo canceller 17 from the output side of the low frequency amplification circuit 27. In order to do so, it is required that the signal waveform of the echo in the demodulated signal and the waveform of the voice signal input to the pseudo echo generation circuit 19 are similar. However, when the level of the voice input through the microphone 28 is high, the echo corresponding to the clipped voice signal shown in FIG. 3B is received from the receiving circuit 16 via the amplitude limiting circuit 25. The waveform of the audio signal input to the adder circuit 18 while being input to the pseudo echo generating circuit 19 has an unclipped signal waveform as shown in FIG. 3 (a). Therefore, since the waveforms of the above two signals lack similarities, there is a drawback that the echo cannot be sufficiently canceled by the adaptive echo canceller 17.

[Means for solving problems]

The echo canceling method of the present invention is provided in advance as a constituent element of the transmitting circuit of the wireless transceiver as means for canceling the echo included in the reception demodulated signal of the predetermined wireless transceiver, and the An amplitude limiting circuit that limits the amplitude level to a predetermined value and outputs the modulated input signal, and an amplitude limited modulated input signal that is output from the amplitude limiting circuit are input to generate and output an echo cancellation signal. A pseudo echo generation circuit, the echo cancellation signal, and a demodulation signal output from a reception circuit included in the wireless transceiver are added to perform subtraction processing,
And an adder circuit for outputting a demodulated signal in which an echo component is canceled, and the demodulated signal output from the adder circuit is fed back to the pseudo echo generating circuit.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a main part of a wireless transceiver according to an embodiment of the present invention. As shown in FIG.
The wireless transceiver according to this embodiment includes an antenna 1, a receiving circuit 2, an adaptive echo canceller 3 including an adding circuit 4 and a pseudo echo generating circuit 5, low frequency amplifying circuits 6 and 13, a speaker 7 and an antenna. The shared circuit 8, a high-frequency power amplifier circuit 9, a transmission circuit 12 including a modulation circuit 10 and an amplitude limiting circuit 11, and a microphone 14 are provided.

In FIG. 1, the second part of the wireless transceiver according to the present invention is shown.
The difference between the conventional echo canceling method and the radio transceiver shown in the figure is that the echo canceling signal input from the transmitting system to the pseudo echo generating circuit 5 in the adaptive echo canceller 3 has a low frequency. This is not the audio signal output from the amplifier circuit 13, but the audio signal for modulation which is the output of the amplitude limiting circuit 11 in the transmission circuit 12. Except for this difference, the operation of each circuit and the like is the same as in the case of the wireless transceiver of FIG. The output of the amplitude limiting circuit 11 in FIG. 1 exhibits a clipped signal waveform as shown in FIG. 3 (b) when the level of the voice input from the microphone 14 is high. In addition, the signal waveform is held in a state similar to the echo waveform. Therefore, the adaptive echo canceller 3 effectively cancels the echo in the reception demodulated signal output from the reception circuit 2, and the voice sent from the desired other party is transmitted to the low frequency amplification circuit 6 and the speaker 7. The output is output via the echo.

〔The invention's effect〕

As described above, according to the present invention, in order to cancel the echo included in the reception demodulated signal of the wireless transceiver, the modulation input signal in the transmission system of the wireless transceiver is sent to a predetermined echo canceller as an echo canceling signal. By inputting, there is an effect that the echo caused by the voice of the speaker can be effectively suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a wireless transceiver according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a main part of a wireless transceiver in a conventional echo cancellation system.
3A and 3B are signal waveform diagrams at the input and output of the amplitude limiting circuit. In the figure, 1,15 ... antenna, 2,16 ... reception circuit, 3,
17 …… Adaptive echo canceller, 4,18 …… Adder, 5,19
…… Pseudo echo generator, 6,13,20,27 …… Low frequency amplifier circuit, 7,21 …… Speaker, 8,22 …… Antenna shared circuit, 9,
23 …… High frequency power amplifier circuit, 10,24 …… Modulation circuit, 11,25
...... Amplitude limiting circuit, 12,26 …… Transmitting circuit, 14,28 …… Microphone.

Claims (1)

[Claims] 1. A means for canceling an echo included in a received demodulated signal of a predetermined wireless transceiver, which is provided in advance as a constituent element of a transmission circuit of the wireless transceiver, and which has an amplitude level of a signal to be transmitted. An amplitude limiting circuit that limits the output to a predetermined value and outputs as a modulation input signal, and a pseudo echo that generates and outputs an echo cancellation signal by inputting the amplitude limited modulation input signal output from the amplitude limiting circuit. A generation circuit; an addition circuit that adds the echo cancellation signal and a demodulation signal output from a reception circuit included in the wireless transceiver to perform subtraction processing, and outputs a demodulation signal in which an echo component is canceled, And an echo canceling method, wherein the demodulated signal output from the adding circuit is fed back to the pseudo echo generating circuit.