JPH0821883B2 - Echo canceller - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller used for a 2-wire-4 wire circuit, a teleconference system, and the like in telephone election.

2. Description of the Related Art FIG. 2 shows the configuration of a conventional echo canceller.

In FIG. 2, 3 is a shift register for holding the signal sequence Xj input from the reception input terminal 1, 4 is the input signal sequence Xj held by the shift register 3, and the output signal of the subtracter 9 described later. A correction amount calculator for calculating the correction amount ΔHj of the estimated impulse response Hj (coefficient) by means of 6 adds the estimated impulse response Hj held by the shift register 5 and the correction amount ΔHj calculated by the correction amount calculator 4. ,
An adder for outputting to the register 5, and 7 for the shift register 3
The convolution operation unit which performs a convolution operation by the input signal sequence Xj held by and the estimated impulse response Hj held by the register 5 to generate a pseudo echo, and 9 subtracts the pseudo echo from the signal input from the transmission input terminal 8. And a subtracter that outputs to the transmission output terminal 10.

In FIG. 2, the signal input from the reception input terminal 1 is output via the reception output terminal 2, and the echo signal is input from the transmission input terminal 8 via the echo path and is output to the transmission output terminal 10 without being suppressed. Will be a problem.

Therefore, in the conventional echo canceller, the correction amount calculator 4 uses the input signal sequence Xj held by the shift register 3.
And the output signal of the subtractor 9 calculate the correction amount ΔHj of the estimated impulse response Hj for each sample so that the power of the transmission output signal is minimized, and the estimated impulse response of the reception output terminal 2 and the transmission input terminal 8 is calculated. Echo is suppressed by approaching the impulse response of the echo path between them.

However, in the above-mentioned conventional echo canceller, when the estimated impulse response is calculated with a fixed point, the amplitude of the impulse response of the echo path is unknown, so the estimated impulse can be obtained with the optimum decimal point. Therefore, there is a problem that the echo cannot be efficiently suppressed.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide an echo canceller that can efficiently suppress echo.

Means for Solving the Problems In order to achieve the above object, the present invention provides a reception input terminal for inputting a reception input signal, a first register for storing a signal string of the reception input signal, and the reception input signal. A reception output terminal that outputs to the reception side, a reception input signal that this reception output terminal outputs passes through an echo path, a transmission input terminal that is input as a transmission input signal, and an estimated signal sequence of the impulse response of the echo path is stored. A second register,
The estimated signal sequence output from the second register and the signal sequence of the reception input signal output from the first register are subjected to a convolution operation to generate a pseudo echo, and a convolution operation is performed from the transmission input signal. A subtractor for subtracting the pseudo echo output by the arithmetic unit, a transmission output terminal for outputting a transmission output signal output by the subtractor, an impulse response estimated by the signal sequence of the reception input signal and the output signal of the subtractor Correction amount calculator for calculating the correction amount signal of the estimated signal sequence, a peak detector for detecting the peak value of the estimated signal sequence and outputting it as a shift signal, and the correction amount signal for determining the decimal point position by the shift signal. A first shifter for moving, an adder for adding an output signal of the first shifter to the estimated signal sequence to perform correction, and a correction for the estimated signal sequence, The second shifter for moving the decimal point position of the signal of the constant signal sequence by the shift signal and outputting it to the adder, and the first and second shifters for the subtraction input when calculating the transmission output signal A third shifter for moving the decimal point position of the pseudo echo in the opposite direction is provided.

Effect According to the present invention, even if the amplitude of the impulse response of the echo path is unknown, since the pseudo echo is generated by the optimum impulse of the decimal point, the echo can be efficiently suppressed.

EXAMPLES Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of an echo canceller according to the present invention, and the same components as those shown in FIG. 2 are designated by the same reference numerals.

In FIG. 1, 1 is a voice signal (digital signal X
j) is input to the receiving input terminal, 2 is a receiving output terminal from which the audio signal from the receiving input terminal 1 is output to the receiving side (not shown), and 8 is a transmitting input terminal to which the audio signal from the receiving side is input. , 10 are transmission output terminals to which the audio signal from the transmission input terminal 8 is output.

Reference numeral 3 is a shift register for holding the signal train Xj input from the reception input terminal 1, and 4 is an estimated impulse response Hj based on the input signal train Xj held by the shift register 3 and the output signal of the subtracter 9 described later. (Coefficient) correction amount ΔHj
Is a correction amount calculator for calculating

11 is a peak detector that detects the peak value of the estimated impulse response Hj held by the shift register 5 and calculates the optimum decimal point position of the estimated impulse response Hj, as will be described later, and 12 is held by the shift register 5. The shifter 13 for shifting the estimated impulse response Hj to the decimal point position calculated by the peak detector 11, the correction amount ΔHj calculated by the correction amount calculator 4 to the decimal point position calculated by the peak detector 11. Shifter, 6 is shifter
This is an adder that adds the estimated impulse responses Hj shifted by 12 and 13 and outputs them to the register 5.

7 is the input signal sequence held by the shift register 3
Estimated impulse response Hj held by Xj and register 5
The convolution operation unit that performs the convolution operation by means of the above to generate a pseudo echo, 14 is a shifter for returning the pseudo echo output from the convolution operation unit 7 to the original decimal point position, and 9 is a signal input from the transmission input terminal 8. This is a subtractor that subtracts the pseudo echo from the shifter 14 and outputs it to the transmission output terminal 10.

 Next, the operation of the above embodiment will be described.

In FIG. 1, the signal input from the reception input terminal 1 is output via the reception output terminal 2, and the echo signal is input from the transmission input terminal 8 via the echo path and is output to the transmission output terminal 10 without being suppressed. Will be a problem.

Therefore, the correction amount calculator 4 uses the input signal sequence Xj held by the shift register 3 and the output signal of the subtractor 9 for each sample so that the power of the transmission output signal is minimized. The correction amount ΔHj is calculated, the estimated impulse response is brought close to the impulse response of the echo path between the reception output terminal 2 and the transmission input terminal 8, and the echo is suppressed.

Further, the peak detector 11 detects the peak value of the estimated impulse response Hj held by the shift register 5 for each predetermined number of samples, and predicts, for example, a peak factor of 6 dB (for 1 bit), and calculates the digit of the estimated impulse response Hj. The number of bits for moving the decimal point position of the estimated impulse response Hj so that the drop is minimized, that is, the upper 2 bits are "00" (for positive) or "11" (for negative). k
Is calculated and the shifters 12 and 13 are controlled.

In this case, the peak detector 11 is the convolution calculator 7
So that the pseudo echo output by will return to the original decimal point position,
The number of bits (-k) is output to the shifter 14.

Therefore, according to the above-described embodiment, the peak detector 11 detects the peak value of the estimated impulse response Hj for each predetermined number of samples, and considers the peak factor of 6 dB (1 bit) to estimate the estimated impulse response Hj. Calculate the optimal decimal point,
Controls shifters 12, 13, and 14 so that estimated impulse response
Elimination of Hj is reduced, and echo can be suppressed effectively.

In the above embodiment, a wired circuit is used to control the decimal point position of the estimated impulse response Hj, but the present invention can be realized by software.

EFFECTS OF THE INVENTION As apparent from the above embodiments, the present invention provides a reception input terminal for receiving a reception input signal, a first register for storing a signal string of the reception input signal, and the reception input signal for the reception side. A reception output terminal for outputting, a reception input signal output from this reception output terminal passes through an echo path, and is input as a transmission input signal; and a second signal storing an estimated signal sequence of the impulse response of the echo path. A register, a convolution calculator that convolves the estimated signal sequence output from the second register and the signal sequence of the reception input signal output from the first register to generate a pseudo echo, and the transmission input signal. , A subtractor for subtracting the pseudo echo output from the convolution operator, a transmission output terminal for outputting a transmission output signal output by the subtractor, and the reception input A correction amount calculator that calculates a correction amount signal of the estimated signal sequence of the estimated impulse response by the signal sequence of the signal and the output signal of the subtractor, and peak detection that detects the peak value of the estimated signal sequence and outputs it as a shift signal A first shifter for moving the decimal point position of the correction amount signal by the shift signal, an adder for adding the output signal of the first shifter to the estimated signal sequence for correction, and the estimated signal The second shifter, which shifts the decimal point position of the signal of the estimated signal sequence by the shift signal and outputs it to the adder when correcting the sequence, and the first shifter for the subtraction input when the transmission output signal is calculated. , And a third shifter for moving the decimal point position of the pseudo echo in the opposite direction to the second shifter, even if the amplitude of the impulse response of the echo path is unknown, The echo replica generated at the estimated impulse of optimal point, thus, has the effect that it is possible to suppress the echo efficiently. Further, the present invention has an effect that it can be implemented with a simple circuit configuration as compared with the floating point method, and can be easily implemented as software.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of an echo canceller according to the present invention, and FIG. 2 is a functional block diagram showing a conventional echo canceller. 3, 5 ... Shift register, 4 ... Estimated impulse response correction amount calculator, 6 ... Adder, 7 ... Convolution calculator, 9
...... Subtractor, 11 …… Peak detector, 12,13,14 …… Shifter.

Claims (1)

[Claims] 1. A reception input terminal for receiving a reception input signal,
A first register that stores a signal string of the reception input signal, a reception output terminal that outputs the reception input signal to the reception side, and a reception input signal that is output from the reception output terminal passes through an echo path, and a transmission input signal. Input terminal, a second register for storing an estimated signal sequence of the impulse response of the echo path, the estimated signal sequence output by the second register, and the reception output by the first register. A convolutional operator that performs a convolutional operation on the signal sequence of the input signal to generate a pseudo echo, a subtractor that subtracts the pseudo echo output by the convolutional operator from the transmission input signal, and a transmission output output by the subtractor A transmission output terminal for outputting a signal, and a correction amount signal of the estimated signal sequence of the estimated impulse response by the signal sequence of the received input signal and the output signal of the subtractor. A correction amount calculator for calculating, a peak detector for detecting the peak value of the estimated signal sequence and outputting it as a shift signal, a first shifter for moving the correction amount signal by the shift signal to a decimal point position, An adder for adding the output signal of the first shifter to the estimated signal sequence to make a correction, and a signal for the estimated signal sequence being moved by the shift signal to move the decimal point position when the estimated signal sequence is corrected. And a third shifter for moving the decimal point position of the pseudo echo in the opposite direction to the first and second shifters due to the subtraction input when calculating the transmission output signal. Echo canceller with.