KR100443009B1 - Apparatus and method for time domain echo canceller of DMT - Google Patents

Abstract

The present invention is to provide a time domain echo canceller device of the DMT and a control method thereof, comprising: an DMT echo having an encoder, a first IFFT, a P / S converter, a transmit / receive hybrid filter, a first delay unit, and a third adder A canceller comprising: a second delayer for delaying an output signal of the transmission / reception hybrid filter, a first adder for adding an output of the second delayer and an output of a fourth adder, and delaying the output of the first adder. A third delay unit, an S / P converter that converts serial data of the third delay unit into parallel data, an FFT that FFTs the output of the S / P converter, and a second subtracting output of the echo canceller from the output of the FFT. An echo canceler for receiving an output from the adder, a second adder and receiving the output of the encoder to perform echo canceling, second and third IFFTs respectively performing IFFT on the output of the echo canceller; Third adder and the first 2, a signal compensator for receiving the output of the IFFT and performing signal compensation, and a fourth adder for adding the signal compensator and the output of the third IFFT to the first adder and outputting the signal to the first adder. The echo impulse response in the time domain can be obtained to improve the performance of the echo canceller.

Description

DMT's time domain echo canceller device and its control method {Apparatus and method for time domain echo canceller of DMT}

The present invention relates to a time domain echo canceller of Discrete Multitone Modulation (DMT). In particular, an echo impulse response of a time domain is obtained from a central office (CO) to obtain echo cancellation. The present invention relates to a time-domain echo canceller device of a DMT and a control method thereof, which are suitable for improving the performance of a circulator.

In general, DMT is an American National Standard Institute (ANSI) standard modulation technology used for Asynchronous Digital Subscriber Line (ADSL).

1 is a block diagram of a time domain echo canceller of a conventional DMT.

Here, reference numeral 11 is an encoder for encoding input parallel data, and 12 is a first IFFT for performing an inverse fast fourier transform (IFFT) on a signal encoded by the encoder 11 to send a reverb signal. 13 is a P / S (Parallel to Serial) converter for converting parallel data output from the first IFFT 12 into serial data, and 14 is an input of the P / S converter 13. It is a transmission / reception hybrid filter that transmits and receives data and receives downsamples a remote signal through a line.

Reference numeral 15 denotes a first adder which adds an output of the transmission / reception hybrid filter 14 and an output of the signal compensator 24, and 16 denotes parallel data of serial data output from the first adder 15. S / P (Serial to Parallel) transform unit to convert, 17 is an FFT performing a Fast Fourier Transform (FFT) to the output of the S / P conversion unit 16, 18 is an output of the FFT (17) Is a second adder subtracting the output of the echo canceller 20, and 19 is a receiver that receives the output of the second adder 18.

In addition, reference numeral 20 denotes an echo canceler that receives an output of the second adder 18 and an output of the encoder 11 to perform echo canceling, and 21 denotes an echo canceller ( A second IFFT performing an IFFT on the output of 20), 22 is a delay unit for delaying the output of the first IFFT 12, and 23 is a delay unit 22 at the output of the first IFFT 12 And a third adder subtracting the output of the reference signal, and 24 denotes an output of the third adder 23 and the second IFFT 21 by performing signal compensation to the second adder 15. It is a signal cancellation unit (Tail Cancellation and Cyclic Reconstruction).

Therefore, the echo canceller of the DMT includes the first to third adders 15, 18, 23, the S / P converter 16, the FFT 17, the echo canceller 20, and the second IFFT 21. ), A delay unit 22 and a signal compensator 24.

In the DMT, the signal sent by the transmitting end is incomplete by the transmitting / receiving hybrid filter 14 so that an unwanted signal enters the receiving end.

You want to receive only remote signals at the receiving end, but you will receive unwanted signals, ie echoes sent from the transmission.

In general, the echo path loss (Kep) is 17dB, the channel loss (Channel Loss, Kch) is 23dB, and the signal-to-noise ratio (SNR) margin is 44dB.

Therefore, ECHO (Kec) to be removed at the receiving end is as follows.

Kec = SNR + Kch-Kep = 50dB, ie 50dB or more should be removed.

However, since the DMT sends symbols in units of frames, there are discontinuous parts in time domain echoes.

In this part, there is a tail by the previous symbol and a transition by the current symbol.

In addition, in DMT, the received frame is matched to the remote signal, so there is a frame mismatch between the echo and the remote signal.

In the prior art, the echo impulse response obtained in the time domain is divided into three cases to compensate for such discontinuities, and even frame mismatch with the remote signal, and then FFT to perform echo cancellation in the frequency domain.

2 is a flowchart illustrating a time domain echo canceller control method of a conventional DMT.

As shown therein, a step of modeling an echo path through a reverb signal is performed and IFFT to obtain an echo impulse response (ST11); Determining a valid portion of the obtained echo impulse response, determining where the discontinuous portion of the echo signal is based on its position, and determining the degree of inconsistency of the remote signal of the echo (ST12) (ST13); Performing a convolution in the time domain after the determination to compensate for an inconsistency (ST14); After the compensation, an FFT is performed and an echo canceller is performed in the frequency domain (ST15).

Therefore, in the prior art, the echo path is modeled in the frequency domain through a reverb signal (PATTERN DATA) and then IFFT is obtained to obtain an echo impulse response.

From the obtained echo impulse response, a valid section is determined, where the discontinuous portion of the echo signal is determined according to its position, and the mismatch between the echo and the remote signal is determined.

Once the discrete portion and the degree of mismatch are determined, convolution is performed in the time domain with the selected portion of the time domain signal at the transmitting side to compensate for this portion.

This convolution compensates for (periodically) discontinuous parts (ie, TAIL of the previous symbol + TRANSITION of the current symbol), and also compensates for mismatched parts of the remote signal and echo. FFT is performed to perform echo cancellation in the frequency domain.

Referring to the operation of the prior art in more detail as follows.

The sender first sends a signal (periodic signal), which enters the receiver via an echo path.

This signal is called an echo, and the echo canceller 20 models a complex one tap for each bin to model the transmission / reception hybrid filter 14 that is an echo path. At this time, the update method uses LMS (Least Mean Squared).

After the echo path is modeled, a time domain echo impulse response is obtained after IFFT through the second IFFT 21.

Since the DMT sends data in units of frames, the transition of the tail of the previous symbol and the current symbol occurs. Also, because the frame is tuned to the remote signal, the echo signal is out of frame.

Thus, the signal compensator 24 and the first adder 15 are blocks that compensate for tails, transitions, and frame mismatches.

According to the shape of the time domain echo impulse response obtained as described above, the tail of the previous symbol, the transition of the current symbol, and the frame mismatch of the first IFFT 12 of the transmitting side in the signal compensation unit 24. The output is compensated with the value obtained from the convolution with the selected sample during the time-domain echo impulse response.

This is FFTed by the FFT 17 and finally eliminated by the second adder 18. At this time, of course, the section in which the most energy is collected among the 512 samples is taken.

3 is a waveform diagram showing a form of an echo impulse response when performing a time domain echo canceller of a conventional DMT.

Depending on the type of echo impulse response, there are three cases as shown in (a), (b) and (c) of FIG. 3.

The prior art has a problem that the configuration is very complicated because it has to be configured to satisfy the operation for the three cases as shown in FIG. That is, the values that need to be convolved in the signal compensator 24 are different according to the frame mismatch, thereby increasing the complexity of the signal compensator 24.

In addition, there is a problem in that the performance of echo canceling occurs in the process of compensating the transition and the non-transition part to match the frame synchronization of the echo and the remote signal received at the receiver. That is, the number of samples of the echo impulse response is actually 512 samples, of which about 256 samples are written, and there is a problem in that accuracy is reduced to compensate for frame mismatch with 256 samples.

In addition, since the FFT eliminates the compensated signal in the frequency domain, a truncation error that may occur in the FFT may be included.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to obtain a time-domain echo impulse response on the CO side, and to improve the performance of the echo canceller. It is to provide a canceller device and a control method thereof.

In order to achieve the above object, a DMT time domain echo canceller device according to an embodiment of the present invention includes an encoder, a first IFFT, a P / S converter, a transmit / receive hybrid filter, a first delay unit, and a third adder. A DMT echo canceller having a section, comprising: a second delay section for delaying an output signal of a transmission / reception hybrid filter, a first adding section for adding an output of the second delay section and an output of a fourth adding section, and the first addition section; A third delay unit for delaying the negative output, an S / P converter for converting serial data of the third delay unit into parallel data, an FFT for FFT the output of the S / P converter, and an echo at the output of the FFT A second adder which subtracts the output of the canceller, an echo canceler that receives the output of the second adder and receives the output of the encoder and performs echo cancellation, and an IFFT for the output of the echo canceller, respectively Undertake A first and second IFFTs, a signal compensator configured to perform signal compensation by receiving the outputs of the third adder and the second IFFT, and add the outputs of the signal compensator and the third IFFT to add the first and second IFFTs; The technical configuration is characterized by including the fourth adder outputted to the adder.

In order to achieve the above object, the DMT time domain echo canceller control method according to an embodiment of the present invention performs an FFT through a transmit / receive hybrid filter on a received echo by sending a reverb signal, A first step of modeling a frequency-domain echo path as a complex one tap; obtaining a time-domain echo impulse response by IFFTing the frequency-domain echo path at a second IFFT after the first step, and determining a valid interval among the time-domain echo impulse responses And a second step of delaying a second delay part in a reception path after the second step, having a back part of a previous symbol and a back part of a current symbol, and forming an echo signal; after the third step In the third IFFT, the 512 point IFFT after multiplying the frequency-domain echo path in the echo signal by the frequency symbol sent by the transmitter. A fourth step of eliminating the echoes in the time domain so as to eliminate the echo; and a fifth step of delaying the third delay part again so that the delay of the reception path is a symbol delay after the fourth step. Performance is characterized by its technical construction.

1 is a block diagram of a time domain echo canceller of a conventional DMT.

2 is a flowchart illustrating a time domain echo canceller control method of a conventional DMT.

3 is a waveform diagram showing a form of an echo impulse response when performing a time domain echo canceller of a conventional DMT.

4 is a block diagram of a DMT time domain echo canceller device according to the present invention.

5 is a flowchart illustrating a method of controlling a time domain echo canceller of a DMT according to the present invention.

FIG. 6 is a waveform diagram illustrating a shape of a time domain echo impulse response when a DMT performs time domain echo canceller according to the present invention.

FIG. 7 is a waveform diagram after giving a delay of a predetermined sample with respect to FIG. 6 when performing time-domain echo canceller of DMT according to the present invention.

Explanation of symbols on the main parts of the drawings

11: encoder 12, 21, 33, 34: IFFT

13: P / S converter 14: transmission and reception hybrid filter

15, 18, 23, 36: Adder 16: S / P Converter

17: FFT 19: Receiver

20: echo canceller 22, 31, 32: delay unit

35: signal compensation unit

Hereinafter, an embodiment according to the present invention configured as described above, a time domain echo canceller device of the DMT and a control method thereof will be described in detail with reference to the accompanying drawings. A block diagram of a time-domain echo canceller device is described below. The configuration of the DMT echo canceller of the present invention is as follows. [0032] An encoder 11 and a signal encoded by the encoder 11 for encoding input parallel data are described. Parallel to Serial (P / S) for converting parallel data output from the first IFFT 12 and the first IFFT 12 to perform an inverse fast fourier transform (IFFT) to send a reverb signal. Transmitting and receiving hybrid filter 14 which receives the output of the converter 13 and the P / S converter 13, transmits and receives data, and receives and downsamples a remote signal through a line. Send and receive hive A second delay unit 31 for delaying the signal of the filter 14, a first adder 15 for adding the output of the second delay unit 31 and the output of the fourth adder 36, and A third delay unit 32 for delaying the output of the first adder 15, an S / P converter 16 for converting serial data of the third delay unit 32 into parallel data, and an S / P ( Serial to Parallel) FFT (17) for outputting the Fourier Transform (FFT) of the conversion unit 16, and the second adder (18) for subtracting the output of the echo canceller 20 from the output of the FFT (17) , IFFT is performed on the outputs of the echo canceller 20 and the echo canceller 20 to perform echo cancellation by receiving the output of the second adder 18 and the output of the encoder 11. A signal compensation unit 35 and a signal compensation unit 35 which perform signal compensation by receiving the second and third IFFTs 33 and 34 and the output of the second IFFT 33. The output of the first and the output of the third IFFT 34 by adding the first And a fourth adder 36 for outputting to the adder 15. FIG. 5 is a flowchart showing a time domain echo canceller control method of the DMT according to the present invention. First step ST21 (ST23) ) Sends a reverb signal to FFT (17) via the transmit / receive hybrid filter (14), which is an echo path, from the echo canceller (20), and then model the frequency domain echo path as a complex one tap in the frequency domain. In a second step ST24 and a step ST25, the frequency domain echo path is IFFTed in the second IFFT 33 to obtain a time domain echo impulse response after the first step, and a valid section M is determined among the time domain echo impulse responses. In the third step ST26 and ST27, after the second delay part 31 is delayed in the reception path after the second step, the second delay part 31 compensates with the rear part of the previous symbol and the rear part of the current symbol and forms an echo signal. Step 4 (ST28) is the echo signal after the third step After multiplying the frequency-domain echo path by the frequency symbol sent from the transmitter, subtracting it by 512-point IFFT to eliminate the echo in the time domain. In the fifth step (ST29), the delay of the reception path after the fourth step is equal to the symbol delay. The operation of the time-domain echo canceller device of the DMT of the present invention and its control method will be described in detail with reference to the accompanying drawings as follows. A signal received through the encoder 11 is the first IFFT. The output signal is sent through the (12), and this enters the receiving end via the echo path. The echo signal is adapted to the complex one tap for each bin in the echo canceller 20, which is an echo path. The transmit / receive hybrid filter 14 is modeled. At this time, the update method uses LMS. When the echo path is modeled, the IFFT is obtained through the second IFFT 33, and then a time domain echo impulse response is obtained. In the obtained time domain echo impulse response, the effective interval M with the most power is obtained. In general, when a 512-point IFFT is performed, about 200 samples are taken as valid intervals, thus delaying the reception path so that the first start of interval M of about 200 samples comes first in the time-domain impulse response. After observing the time domain echo impulse response, the delay number of the second delay unit 31 is set to match the frame of the echo and the remote signal. In order to model the transition by the previous symbol and the transition by the current symbol, only a predetermined portion of the first IFFT 12 on the transmitting side is taken and the signal compensator 3 In 5), the time domain echo impulse response and convolution are performed and brought to the fourth adder 36. The third IFFT 34 compensates for the steady state portion excluding the tail of the previous symbol and the transition of the current symbol. To do this, multiply the frequency-domain symbol (complex value) and the frequency-domain echo response (complex value) of the transmitter, and IFFT it to 512 points. Performing IFFT can reduce the complexity much more than obtaining a value through convolution. If the third delay unit 32 delays and outputs the delayed signal to be delayed, the signal from which the echo is removed is input to the receiver 19. Instead of eliminating the echo, the echo is removed from the time domain. FIG. 6 is a waveform diagram illustrating the time-domain echo impulse response when the DMT performs the time-domain echo canceller. Figure 7 is a post gave a delay of a predetermined sample for FIG When multiple time-domain echo canceller of DMT according to the present invention performs waveform 6. FIG. 7 is a graph of the time-domain echo impulse response of FIG. 6, with a delay of x / 8 samples in the reception path. When the above-described 512-point IFFT is performed, the first start of the interval M of about 200 samples is obtained from the time-domain impulse response. It was to come first.

The portion to be compensated is the transition of the tail of the previous symbol and the current symbol, which is compensated with 199 samples after the previous symbol (but M = 200) and 199 samples after the current symbol. This results in an echo signal without tails and transitions.

If the tail and transition-free echo signals are multiplied by the frequency domain echo path and the frequency symbol sent by the transmitter, and subtracted with 512 POINTS IFFT, all echoes are lost in the time domain.

After eliminating all the echoes, if the third delay unit 32 gives a delay so that the delay of the reception path becomes a symbol delay, the time domain echo canceller is completed.

Thus, the received frame synchronization that is set to the remote signal does not deviate at all and becomes an echo canceller in the time domain.

Referring to the operation of the present invention in more detail as follows.

First, the echo canceller of the DMT of the present invention includes the first to fourth adders 15, 18, 23, 36, the S / P converter 16, the FFT 17, and the echo canceller 20. And second and third IFFTs 33 and 34, first to third delay units 22 and 31 and 32, and a signal compensator 24.

So the first IFFT 12 on the sending side sends a signal (periodic signal) and it enters the receiving end via the echo path.

The incoming signal is called an echo, and the echo canceler 20 models a complex one tap for each bin to model the transmission / reception hybrid filter 14 which is an echo path. At this time, the update method uses LMS.

If the echo path is modeled, a time domain echo impulse response is obtained after IFFT through the second IFFT 33.

After observing the time domain echo impulse response, the number of delays of the second delay unit 31 is determined. This is to virtually match the frame of the echo and remote signal.

Since the delay is delayed by the second delay unit 31, only a predetermined portion of the IFFT of the transmitting side is taken to model the tail of the previous symbol and the transition of the current symbol, and then the time compensator 35 performs a time domain echo impulse response and the like. The convolution is performed and brought to the fourth adder 36. This process can greatly reduce the complexity of the convolution calculation in the signal compensator 35. In the third IFFT 34, the steady state portion excluding the tail of the previous symbol and the transition of the current symbol. To compensate, multiply the frequency-domain symbol (complex value) and the frequency-domain echo response (complex value) on the transmitting side, and then IFFT it. In the third delay unit 32, the delay is further reduced so that the reception path becomes a symbol delay. The received signal is transmitted to the receiver 19 via the S / P converter 16 and the FFT 17, thereby completing the time domain echo canceller.

Unlike the prior art, the present invention compensates for the echo in the time domain and eliminates the echo in the time domain rather than eliminating it in the frequency domain.

In addition, instead of using convolution to compensate for the steady state, multiply in the frequency domain and then IFFT the third IFFT 34, thereby improving performance and reducing complexity in convolution.

In addition, the present invention eliminates all echoes in the time domain unlike the prior art, thereby preventing truncation errors.

As such, the present invention improves the performance of the echo canceller by obtaining the echo impulse response in the time domain on the CO side.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

As described above, the DMT time domain echo canceller apparatus and control method thereof have an effect of obtaining an echo impulse response in the time domain on the CO side to improve the performance of the echo canceller.

The present invention can significantly reduce the complexity of the convolution calculation in the signal compensator 35, so that the algorithm of the entire system can be simply implemented.

In addition, the present invention has the effect of reducing the complexity and improving the performance of the echo canceller using a 512 point IFFT to compensate for the steady state (steady state).

Furthermore, the present invention has an effect of preventing truncation errors since all of them are removed in the time domain without FFT to eliminate echoes in the frequency domain.

Claims (3)

In the DMT echo canceller having an encoder, a first IFFT, a P / S converter, a transmit / receive hybrid filter, a first delay unit, and a third adder, A second delay unit for delaying an output signal of the transmission / reception hybrid filter; A first adder which adds an output of the second delay unit and an output of a fourth adder; A third delay unit for delaying the output of the first adder; An S / P converter converting serial data of the third delay unit into parallel data; An FFT for FFTing the output of the S / P converter; A second adder which subtracts the output of the echo canceller from the output of the FFT; An echo canceller configured to receive an output of the second adder and to perform an echo canceling operation by receiving an output of the encoder; Second and third IFFTs respectively performing an IFFT on an output of the echo canceller; A signal compensator configured to receive the outputs of the third adder and the second IFFT and perform signal compensation; And a fourth adder configured to add the signal compensator and the outputs of the third IFFT to the first adder to output the signal to the first adder. Performing a FFT on a received echo by transmitting and receiving a reverb signal, and modeling a frequency domain echo path as a complex one tap in an echo canceller; A second step of IFFTing the frequency domain echo path after the first step to obtain a time domain echo impulse response and determining a valid interval among the time domain echo impulse responses; A third step of delaying the second delay part in the reception path after the second step and then compensating with the back part of the previous symbol and the back part of the current symbol and forming an echo signal; A fourth step of multiplying the frequency domain echo path from the echo signal in the third IFFT after the third step by the frequency symbol sent by the transmitter, and subtracting the result by 512 point IFFT to remove the echo in the time domain; And a fifth step of delaying again at the third delay unit such that a delay of the reception path is a symbol delay at the third delay unit after the fourth step. delete