KR100650889B1 - Method for removing reception echo of wireless communication terminal - Google Patents

Abstract

A received echo elimination method in a wireless communication terminal is provided to be capable of confirming whether an echo occurs by calculating cross correlation values for stored transmission and reception voice signals, and of obtaining time delay when the echo occurs to set the time delay as echo delay time, thus the received echo can be eliminated by using the echo delay time. During phone conversation, the level of a transmission voice signal is measured, and if the measured level is more than a predetermined threshold value, a received voice signal is stored for a predetermined time(201-203). A candidate of delay time which is likely to be returned to an echo is selected by using strength of the stored receiving voice signal(204). Cross correlation values of the transmission and reception voice signals for the delay time candidate are obtained, respectively, to confirm whether an echo occurs, and if so, the delay time candidate is set to echo delay time(205-207). The received echo is eliminated by using the echo delay time(208,209).

Description

Method for removing reception echo of wireless communication terminal

1A is an exemplary diagram in which a reception echo cancellation circuit is provided between a transmission / reception line of a voice signal of a wireless communication terminal according to the prior art;

Figure 1b is a block diagram of the reception echo cancellation circuit of Figure 1 according to the prior art,

2 is a flowchart illustrating a method for canceling reception echo of a wireless communication terminal according to the present invention.

* Explanation of symbols for the main parts of the drawings

101: transmission sound level detector 102: delay signal generator

103: echo cancellation unit 104: codec

105: transmit amplifier 106: receive amplifier

The present invention relates to a method for canceling a reception echo in a wireless communication terminal, and more particularly, after storing a transmitted voice signal, a cross correlation value is calculated for the stored transmission voice signal and the received voice signal. A wireless communication terminal that can check whether or not an occurrence occurs, obtain a time delay for an echo, set a time delay as an echo delay time, and eliminate reception echo using the delay. It relates to a reception echo cancellation method in.

In the present invention, a wireless communication terminal is a mobile communication terminal, a personal mobile communication terminal (PCS), a personal digital terminal (PDA), a smart phone, a next generation mobile communication terminal (IMT-2000), such as a wireless terminal while carrying a person A terminal capable of wireless communication.

In general, in the use of a wireless communication terminal, there are two main ways to reduce echo. One is to prevent the received voice signal from being transmitted again, and the other is to remove echoes from the received voice signal.

In short, the former is called "receiving echo cancellation" and the latter is called "receiving echo cancellation".

For the 'transmission echo cancellation', a method of removing transmission echo using digital signal processing (DSP) or using a separate chip is widely used.

On the other hand, as an example of the prior art for the 'receiving echo cancellation', "Eco suppression circuit of the wireless terminal (Korean Patent Publication No. 264442, May 31, 2000) (hereinafter referred to as" prior art ")" However, the prior art implements a fixed circuit that reduces (represses) the received volume for a certain time when the transmit volume (transmission level) is above a predetermined reference value.

In other words, as shown in FIG. 1A, a reception echo cancellation circuit is provided between a transmission / reception line of a voice signal of a wireless communication terminal, and the codec 104 is connected from the handset 11 to the transmission amplifier 105. Connected to the receive amplifier 106 from the codec 104 and to the handset 11 via the receive amplifier 106. The reception echo cancellation circuit 12 is provided between the codec 104 and the transmission / reception amplifiers 105 and 106.

As shown in FIG. 1B, the reception echo cancellation circuit 12 detects the peak value using the amplifier AMP1 and the diode D1 from the handset 11 using the output of the transmission amplifier 105. Transmission sound level detection unit 101 for detecting the level of the transmission sound by the charge / discharge circuit of capacitor C1 and resistor R1, and transmission detected from transmission sound level detection unit 101 using comparator AMP2. A delay for generating a delayed control signal in response to the operation of the resistor R5 and the diode D2 by outputting only a value above a predetermined level by comparing the output signal of the negative level with the reference value determined by the resistors R2 and R3. A signal generator 102 and an echo canceler 103 for driving the transistor Q1 according to a control signal output from the delayed signal generator 102 to cancel echoes of the tone.

The echo canceller 103 drives the transistor Q1 according to the delayed control signal to control the receiver amplifier 106 to cancel (more strictly suppresses) the echo, which will be described in more detail. When the chord is input to the song level detector 102 through the transmission amplifier 105, the control signal Vcon generated by the delay signal generator 102 turns the transistor Q1 on / off. And the switching operation is performed. For example, when the control signal Vcon is 5 V, the signal output from the audio output terminal A / O of the codec 104 is turned on and the level is separated by the resistors R6 and R7 so that the receiving amplifier 106 (In this case, the input impedance of the receiver amplifier is infinitely large, so it can be regarded as a separate value of R6 and R7 values). However, when the control signal Vcon is 0V, since the transistor Q1 is turned off, the signal output from the audio output terminal A / O of the codec 104 flows into the reception amplifier 106.

In this case, when a sounding tone occurs, the control signal Vcon has a value of 5V level delayed by td, and the transistor Q1 is turned on to divide the signal on the reception path and suppress it. At this time, the time of td is determined according to the discharge time according to the capacitor C1 and the resistor R1 and the reference value Vr of the comparator Amp2, and the suppression ratio for the received signal is determined by the resistors R6 and R7. do.

Therefore, in the prior art, when there is a call tone, the sender suppresses an echo signal due to a feedback loss by suppressing the received signal for a time delayed by a time delay from the point where there is no call tone.

However, in the prior art, a time delay is fixedly used, and it operates strictly as echo suppression to reduce the received volume for a fixed time in hardware rather than echo cancellation. Thus, while the implementation has the advantage of low cost, the echo cancellation operation is not very good.

Therefore, strictly speaking, the prior art is merely a 'receive echo suppression', and is not a 'receive echo removal' technique.

Therefore, the current terminal only uses the 'transmission echo cancellation' technology, but does not use the true 'receive echo cancellation' technology. However, when an echo occurs during a call, the terminal user may recognize it as a problem of his terminal without recognizing it as a problem of a counterpart terminal or a network problem. Therefore, the quality of experience can be further improved by inserting 'receive echo cancellation' into the terminal. However, when applying 'receiving echo cancellation', it is very important to know the echo delay time accurately in operation of the echo canceling unit. This is because 'Echo De-Echo' is usually used with a fixed echo delay time, whereas 'Echo Receive Echo' is a significant performance deterioration when the Echo Delay time is fixed. Can be used to improve performance.

Therefore, when a reception echo occurs, there is an urgent need for a method for quickly and accurately obtaining an echo delay time and eliminating echo using the echo delay time to solve a problem in which the terminal user hears his echo again.

The present invention has been proposed to meet the above-mentioned requirements. After storing the transmitted voice signal, the cross-correlation value of the stored transmit voice signal and the received voice signal is calculated to check whether or not an echo is generated, To obtain a time delay for the time delay, set the time delay to the echo delay time, and use this to remove the reception echo, to provide a reception echo cancellation method in the wireless communication terminal Its purpose is to.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a method for canceling a reception echo in a wireless communication terminal, wherein during a call, measuring a level of a transmission voice signal and storing the received voice signal for a predetermined time when a threshold value is exceeded. step; Selecting a candidate for a delay time that may have been returned to an echo using the signal strength in the stored received voice signal; Obtaining cross-correlation values of the transmission voice signal and the reception voice signal for the delay time candidate and checking whether an echo occurs, and setting the delay time candidate to an echo delay time as an echo occurs. step; And removing the received echo using the echo delay time.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart illustrating a method for canceling reception echo of a wireless communication terminal according to the present invention.

The reception echo cancellation method according to the present invention is an algorithm for operating an echo cancellation unit (103 in FIG. 1B) using the echo delay obtained from the reception echo, and the implementation itself is a digital signal processing (DSP). It can be implemented by algorithm or external chip.

First, the call is started 201, and the level of the transmission voice signal is measured in the call state, and then it is determined whether the magnitude S (n) of the transmission voice signal is greater than or equal to the threshold value St of the arbitrarily defined voice signal ( 202). At this time, for more accurate measurement, it would be more preferable that only the transmission voice signal exists without the reception voice signal. In other words, the other person did not speak, but only spoken to me.

As a result of the determination 202, if the magnitude S (n) of the transmission audio signal is not larger than the threshold value St of the arbitrarily defined voice signal, the determination process 202 is repeated.

However, if the determination result 202 indicates that the magnitude S (n) of the transmission audio signal is larger than the threshold value St of the arbitrarily defined voice signal, the received voice signal is stored for an arbitrarily designated time T1 to T2 ( 203).

In this way, the level of the transmitted audio signal is measured, and the level is equal to or more than a predetermined threshold St (experimentally determined, for example, 50% of the Max input voice), and only the transmitted audio signal is received without the received audio signal. If the condition is found, it starts to store the received voice signal for T1 ~ T2 time. At this time, T1, T2 is a time that can be arbitrarily set, and can be set as needed after confirming the Min / Max Delay time that occurs during actual use. For example, T1 is 20ms and T2 is about 1000ms.

Here, the reason for determining the state that there is only a transmission voice signal without a reception voice signal is that the present invention attempts to measure the delay when an echo occurs. The method of determining this is to measure the volume of the transmission audio signal and to determine the volume of the reception audio signal.

Thereafter, a time delay candidate Td [i], which is likely to be a time delay Td, may be returned to the echo using the signal strength of the received voice signal stored for T1 to T2 times (204).

For example, when I say "ah", I check the intervals where there are sounds of some magnitude in the received voice for 20ms to 1000ms, during which time this sound is likely to return to echo, If there is no sound for a while, there is no echo, and if there is any sound, it is registered as an echo candidate and the echo is checked. That is, the time from the time of transmitting "A" to the received voice with a certain magnitude or more is selected as a candidate for the delay time.

Next, a cross correlation between the transmission audio signal S (n) and the reception audio signal R (n) is obtained for each time delay candidate Td [i] (205). For example, if there is an echo "ah" among the voices I receive when I say "Ah", the cross-correlation value will be large, but if I say "Ah", the other person said "you" In this case, the cross correlation value is small. Using this, it is checked whether it is an echo or a sound spoken by the other party.

Thereafter, it is checked whether the cross correlation value C (i) of the transmitted / received speech signal obtained for each of the time delay candidates Td [i] is larger than a predetermined threshold value Ct (206). ).

It becomes equal to or more than the threshold value Ct which is arbitrarily determined from the cross correlation values C (i) of the transmission / reception voice signals obtained for each of the test result 206 and the time delay candidate Td [i]. If there is no value, the time delay Td is set to 0 (210) and the determination process 202 is repeated.

However, a threshold value Ct or more arbitrarily determined among the cross correlation values C (i) of the transmission / reception voice signals obtained for each of the test result 206 and the time delay candidate Td [i]. If there is a value, the time delay candidate Td [i] is set as an echo delay time (207). For example, if the level of "ah" I said is slightly different, but the same "ah" returns to the echo, the cross correlation value is large, and if I say "ah" but the other person also "ah" The cross correlation value is smaller than this, and thus it is possible to check whether the cross correlation value is an echo or not, and if it is an echo, if it is an echo, The time difference of the received audio signal becomes the echo delay time.

Finally, it is determined whether the time delay Td is 0 (208). If the time delay Td is not 0, the echo canceling unit 103 is operated using the echo delay time to remove the echo (209). . For example, if a predetermined echo signal is added to an antiphase from a signal including an echo, a signal missing as much as an echo is obtained.

However, if the determination result 208, time delay Td is 0 (not likely to return to the echo), the determination process 202 is repeated.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

According to the present invention as described above, when an echo occurs, the echo delay time is obtained quickly and accurately, and the echo is removed by using the echo delay time, thereby improving echo cancellation performance.

Claims (5)

In the reception echo cancellation method in a wireless communication terminal, Measuring a level of a transmission voice signal during a call and storing the received voice signal for a predetermined time when the threshold value is exceeded; Selecting a candidate for a delay time that may have been returned to an echo using the signal strength in the stored received voice signal; Obtaining cross-correlation values of the transmission voice signal and the reception voice signal for the delay time candidate and checking whether an echo occurs, and setting the delay time candidate to an echo delay time as an echo occurs. step; And Canceling the received echo using the echo delay time Receiving echo cancellation method in a wireless communication terminal comprising a. The method of claim 1, The echo delay time is, And a time difference between a sent voice signal and a received voice signal. The method of claim 1, At the time of selecting the delay time candidate, A method for canceling reception echo in a wireless communication terminal, characterized in that the time from the point at which the spoken voice is transmitted to the voice received at a predetermined size or more is selected as a candidate for the delay time. The method of claim 1, Based on the cross-correlation value, Receiving echo in a wireless communication terminal, characterized in that it is possible to determine whether the echo by the voice spoken by oneself or the voice spoken by the other party. The method according to any one of claims 1 to 4, The process of removing the reception echo, A method of canceling reception echo in a wireless communication terminal, characterized in that the echo signal is removed from an input signal including an echo by adding in a reverse phase to remove the echo.

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