JPH0779179A - Echo canceller and communication equipment - Google Patents

Abstract

PURPOSE:To provide an echo canceller and the communication equipment in which echo cancellation processing is executed efficiently without deteriorating echo eliminating quantity and the processing time is reduced. CONSTITUTION:Tap registers of 40 sets of a tap register 61 of a sub canceller SQa are divided into four groups and switches S2, S3 are switched for each sampling frequency and a tap coefficient of the tap register for each group is updated by tap coefficient correction circuits Tl-T4 with respect to the tap registers of the four groups. An integration circuit 62 convolutes the updated tap coefficient and the transmission data of a transmission data register 63 to generate a pseudo echo signal y*a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller, a communication device, etc., and relates to updating (correction) of tap coefficients.

[0002]

2. Description of the Related Art In recent years, an echo canceller has been variously developed as an important device as a constituent element of a communication system.

As a technique of such an echo canceller,
Reference: Published by Japan Industrial Technology Center Co., Ltd., 1986
December 20, 2012, first edition issued, "Echo Canceller Technology"
Etc.

Therefore, a basic configuration of an example of this echo canceller is shown in FIG. In FIG. 2, the transmission data is output to the telephone line through the hybrid transformer 51. Here, the hybrid transformer 5 of the transmission data
Along with the supply to 1, the near-end echo is generated, and this near-end echo component is given to the subtraction circuit 52. At the same time, the received data from the telephone line is given to the subtraction circuit 52 through the hybrid transformer 51. Further, a far-end echo on the telephone line side is also generated by the output of the transmission data to the telephone line, and it is given to the subtraction circuit 52 through the hybrid transformer 51 together with the reception data.

That is, the input 52a of the subtraction circuit 52 is supplied with other near-end echo components and far-end echo components of the received data. The received data cannot be used correctly unless these echo components are removed from the received data.

Therefore, generally, a configuration is adopted in which these near-end echo components and far-end echo components are removed. That is, as shown in FIG. 2, a near-end echo canceller 53, a far-end echo canceller 54, and the like are provided. With these configurations, for example, the near-end echo canceller 5
Reference numeral 3 predicts the transfer characteristic of the near-end echo path from the transmission data by using a transversal filter or the like to generate a pseudo near-end echo signal, and the subtractor circuit 52 through the adder circuit 55.
Give to.

Further, in order to remove the far-end echo component from the telephone line side, the transmission data is delayed by the bulk delay circuit 56 for a required time (the time until the far-end echo component arrives), and the far-end echo canceller. Give to 54. Then, the far-end echo canceller 54 predicts the transfer characteristic of the far-end echo path using a transversal filter or the like, generates a pseudo far-end echo signal, and supplies the pseudo far-end echo signal to the subtraction circuit 52 through the addition circuit 55.

Then, the subtraction circuit 52 removes the pseudo near-end echo signal and the pseudo far-end echo signal from the received signal from the hybrid transformer 51, and outputs the removed signal as received data.

By the way, the near-end echo canceller 53 and the far-end echo canceller 54 generally use a transversal filter (skew filter), and the number of taps of this transversal filter is set to an appropriate number of taps. By selecting and appropriately setting the tap coefficient of each tap, training is performed in a certain period so as to approach (converge) the actual echo signal.

For the method of this training, see CC
ITT Recommendation V. It is also shown in 32 bis and the like, and for example, the training time of the echo canceller during the handshake is set.

The above echo canceller is generally composed of a transversal filter circuit and
A tap correction circuit is also configured at the same time.

By the way, FIG. 3 is a block diagram of the sub-canceller. In FIG. 3, when a transmission symbol is used for tap input of an echo canceller (sub cancellers 1 to n), what is actually input to the tap is a baud rate b, which is 1 / n of the sampling frequency a. become. For example, V. For a 32 modem,
Since the baud rate b is 2400 baud, the tap input of each sub-canceller is once in four times, and zero is input in the subsequent three times.

Therefore, in practice, as shown in FIG. 3, the echo canceller is divided into four subcancellers 1 to 4, and one of the subcancellers is operated for each sampling frequency. Many.

[0014]

The tap number N of the echo canceller described above is determined, for example, from the following relationship. That is, assuming that the maximum impulse response time of the actual echo path is D and the tap time interval is T, the following relationship exists.

D = N × T The number N of taps is a parameter indicating the performance of the echo canceller. Therefore, if the number of taps N is made larger than necessary, there is a problem that the accumulation of calculation errors causes a reduction in the echo cancellation amount and a reduction in the convergence speed.

On the contrary, if the number of taps N is insufficient, the impulse response time obtained in the pseudo echo path becomes shorter than the impulse response time in the actual echo path, which causes a problem that the amount of echo cancellation decreases.

Since various problems as described above may occur, it is preferable that the number of taps N is necessary and minimized, but in actuality, the digital signal processing (D
Calculation by SP) is complicated and enormous. Therefore, the digital signal processing required for modem modulation / demodulation processing is
There is also a problem that both processes must be performed in parallel by using a digital signal process (DSP) different from the above-described processing circuit with the number of taps N.

For example, when a modem system with an echo canceller is realized by using MSM699210 manufactured by Oki Electric Industry Co., Ltd. as a conventional DSP LSI, FIG.
FIG. 1 is a diagram showing an example of the configuration of a conventional modem system. In FIG. 4, the echo canceller 61 is an L of the DSP 1.
It consisted of SI. Further, the demodulation circuit 57 that demodulates the error signal e from the subtraction circuit 52 and the modulation circuit that modulates the encoded data can be configured by the DSP 2 of the above-described LSI. Further, a trellis encoding circuit 60 for encoding data
And the Viterbi decoding circuit 58 for decoding from the demodulated signal can be configured by the DSP 3 of the above LSI.

The operation timing of FIG. 4 is shown in FIG.
Is shown in. In FIG. 5, assuming that the clock frequency (sanunpling frequency) is 7.2 kHz,
During this time, DSP1 processes the modem program. Then, in parallel with this processing, the DSP 2 performs the processing of the echo canceller program at a time of 7.2 kHz. Furthermore, during this 7.2 kHz period, the above-mentioned 2
During data transmission in parallel with one processing, program processing for trellis coding and Viterbi decoding is performed.

As can be seen from FIG. 5, the processing time of the echo canceller shown in FIG. 5C is the longest. If the processing time can be shortened, it may be possible to make the system of the modem system by the DSPs 1 to 3 more efficient. Such improvements are desired.

Due to the above problems, in the arithmetic processing of the echo canceller, a mechanism for reducing the enormous amount of tap number calculation without reducing the echo cancellation amount is required. ing. Moreover, the modulation / demodulation arithmetic processing required for the modem is incorporated in the same digital signal processing (DSP), and a mechanism for downsizing the processing circuit is also required.

The present invention has been made in view of the above problems, and an object of the present invention is to efficiently perform echo cancellation processing without reducing the echo removal amount,
An object of the present invention is to provide an echo canceller and a communication device that reduce processing time.

[0023]

In order to achieve the above object, the first invention comprises a pseudo echo signal generating means for generating a pseudo echo signal by using a plurality of tap coefficients, and the pseudo echo generating means. In an echo canceller that generates a pseudo echo signal while updating the tap coefficient of, and removes the echo from this pseudo echo signal and the received signal,
It was realized with the following characteristic configuration.

That is, the tap coefficient update grouping means for grouping the update of the tap coefficients of the plurality of taps of the pseudo echo signal generating means and performing the update for each group is provided.

The second invention further comprises a pseudo echo signal generating means for generating a pseudo echo signal using a plurality of tap coefficients, and the pseudo echo signal is generated while updating the tap coefficient of the pseudo echo generating means. However, the communication device that removes the echo from the pseudo echo signal and the received signal has the following characteristic configuration.

That is, the tap coefficient updating grouping means for grouping the updating of the tap coefficients of the plurality of taps of the pseudo echo signal generating means and changing the grouping of the tap coefficient updating according to the communication state is provided. Is characterized by.

The communication state means, for example, a training state, a data transmission state, a non-transmission state, or the like.

The communication device can be applied to various communication devices that require an echo canceling function, such as a modem, a data terminal device, and a voice device.

[0029]

According to the echo canceller of the first aspect of the invention, by updating the tap coefficients of a plurality of taps into groups, the tap coefficients are not updated at once for all the taps but are grouped as needed. By doing this for each time, an appropriate pseudo echo can be generated without significantly deteriorating the echo removal amount.
It can be generated while reducing the processing amount of updating the tap coefficient.

Thus, by removing the appropriate pseudo echo signal from the received signal, the received signal can be shaped into an optimum received signal.

According to the communication device of the second invention, the update of the tap coefficient of a plurality of taps is grouped, and further, according to the communication state, for example, training or data transmission, the group is updated. By changing the conversion state, the coefficient can be updated in the tap coefficient group corresponding to this state. Therefore, it is possible to generate an appropriate pseudo echo while reducing the processing amount for updating the tap coefficient without significantly deteriorating the echo removal amount according to the communication state.

For example, when the communication state is training, the number of groups for updating the coefficient is changed to a small number,
During data transmission, the number of coefficient update groups can be changed many. This allows the coefficient update during training to be relatively coarse (eg, 4 groups).
Even if the tap coefficient is updated, there is no problem if the minimum level of erasure amount necessary for data transmission is obtained, and the update processing amount can be reduced, so that the processing time can be shortened.

Further, during data transmission, by changing the number of groups for coefficient update more (for example, from 4 to 2), even if the tap coefficient is updated more coarsely, a pseudo echo signal is generated with high accuracy. , Can be shaped into the optimum received signal.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention applied to a modem system having an echo canceling function will be described with reference to the drawings.

(Structure of Modem System): FIG.
It is a functional block diagram of the modem system of one Example. 6 is different from the conventional configuration of FIG. 4 in that the DSP 4 has sub-cancellers SQa to SQc.
And the modulation / demodulation circuits 2 and 4, the trellis coding circuit 5, the Viterbi coding circuit 3, and the like.

Then, the error signal e of the subtraction circuit 1 is sampled by the switch S3 at a sampling frequency (for example, 7.2 kHz).
Are sequentially switched by and are given to the sub cancellers SQa to SQc.

Then, the control circuit 8 gives communication state information to the tap coefficient correction units 7 of the sub-cancellers SQa to SQc in accordance with the communication state, and controls the grouping of tap coefficient correction.

(Structure of Sub Canceller): FIG.
It is a functional block diagram of one example. In this FIG.
The specific structural example of subcancellers SQa-SQc is shown. Incidentally, in FIG. 1, the configuration of the sub-canceller SQa is shown in detail as a representative. The other sub-cancellers SQb and SQc have the same configuration as the sub-canceller SQa.

Therefore, the sub-canceller SQa is composed of a pseudo echo generating section 6 and a tap correcting section 7. Then, the pseudo echo generating unit 6 uses the tap register 6
1, an integrating circuit 62, and a transmission data register 63. The tap coefficient correction unit 7 is composed of tap coefficient correction circuits T1 to T4 and switches S4 to S5.

Then, the error signal e is given to the switch S4 through the switch S3, where it is switched at the sampling frequency of 7.2 kHz and given to the tap coefficient correction circuits T1 to T4.

Then, the tap coefficient correction circuits T1 to T4 sequentially operate at every sampling frequency of 7.2 kHz,
The tap coefficient correction circuits T1 to T4 correct the tap coefficients of the assigned registers TR1 to TR40 of the tap register 61.

Then, the tap coefficient corrected for taps and the data of the transmission data register 63 are integrated by the integrating circuit 62 to generate pseudo echo signals y ^{* a to} y ^* c, which are given to the subtracting circuit 1. . Then, the subtraction circuit 1 subtracts the pseudo echo signals y ^{* a to} y ^* c from the reception signal y and gives the error signal e to the demodulation circuit 2.

Then, according to the communication status information from the control circuit 8, the tap coefficient correction unit 7 changes the grouping of tap coefficient correction. That is, the tap correction group of the tap coefficient correction unit 7 is changed according to training (handshake) information, data transmission information, and the like.

(Structure of Pseudo Echo Generator 6): FIG.
FIG. 3 is a functional block diagram of a pseudo echo generation unit 6 according to an embodiment. In FIG. 7, the pseudo echo generating unit 6 includes a tap register 61, an integrating circuit 62, and a data register 6
3 and 3. Then, the tap register 61
Is composed of, for example, 40-tap registers TR1 to TR40. The integration circuit 62 is composed of 40 multiplication circuits J1 to J40 and an adder 62a. The data register 63 is composed of shift registers DR1 to DR40.

The 40 tap coefficients TK1 to TK40 from the tap coefficient correction unit 7 are stored and set in the registers TR1 to TR40 of the corresponding tap register 61. Then, the tap coefficients set in the registers TR1 to TR40 of the tap register 61 are respectively
It is given to the multipliers J1 to J40 of the integrating circuit 62.

On the other hand, the data for transmission in FIG. 7 is sequentially given to the shift registers DR1 to DR40 of the data register 63 and set. Then, the data set in the shift registers DR1 to DR40 of the data register 63 are given to the multipliers J1 to J40 of the integrating circuit 62. The multipliers J1 to J40 are connected to the tap register 6
Tap coefficients TK1 to TK40 from 1 and data Xi
(I = 1 to n) is multiplied, and each multiplication result is given to the adder 62a.

Then, the adder 62 of the integrating circuit 62 of FIG.
a adds all the multiplication results of the multipliers J1 to J40, and adds the addition result to the pseudo echo signal y of the sub canceller SQa.
^It is given to the subtraction circuit 1 as ^* a.

The above-described tap coefficient of the tap register 61 is configured to be set to 40 taps. What is characteristic of this embodiment is that 40 taps are not corrected at one time. By the tap coefficient correction circuits T1 to T4,
Divide 40 pieces into 4 groups, 10 pieces per group,
The tap coefficient is corrected every 10 samplings in one sampling cycle. For example, this 4 group structure is
Performed during data transmission. During data transmission, modem processing, trellis coding processing and Viterbi decoding processing other than echo cancellation processing must be performed, so the number of divisions is increased and the amount of tap coefficient modification is reduced. .

Also, during training, only echo cancellation processing and modem processing need be performed.
It is also possible to adopt a configuration in which the number of groups is set to, for example, two, the correction amount of the tap coefficient is increased, and the echo cancellation processing is performed with high accuracy.

(Operation of Sub Canceller): FIG.
7 is an operation timing chart of the sub-canceller of one embodiment. In FIG. 8, when the switches S4 and S5 of the tap coefficient correction unit 7 of the sub canceller SQa are switched at, for example, a clock of 7.2 kHz (FIG. 8).
(A)). Then, when the control circuit 8 of FIG. 6 gives, for example, training mode information as the communication state information, as shown in FIG. 8B, the modem program processing and the echo cancellation program are performed during the period of 7.2 kHz. And processing. In this case, for example, the number of tap correction groups is set to 2 and 40 taps are set to 2
Divided into 20 groups, sampling frequency 7.2kH
Perform tap correction for each z.

On the other hand, when the data transmission is started, the control circuit 8 in FIG. 6 gives the data in the data transmission to the tap coefficient correcting section 7 as the communication state information, as shown in FIG. 8C. In addition, the modem program processing, the echo cancellation program processing, the trellis coding program processing, and the Viterbi decoding program processing are performed during the period of 7.2 kHz. Since these processes are performed, the number of tap coefficient correction groups is corrected every 4 groups in order to reduce the processing amount of the echo cancellation processing.

(Structure of tap coefficient correction group):
FIG. 9 is an explanatory diagram of the order of tap coefficient correction according to the embodiment. In FIG. 9, the registers TR1 to TR40 of the tap register 61 are divided into four groups G1 to G4,
The tap coefficient correction sequence is shown.

That is, first, the group G1 is, for example, a group performed by the tap coefficient correction circuit T1, and here, the registers TR1, 5, 9, 13, 17, 21, 2 are used.
Correct the tap coefficients of 5, 29, 33, and 37.

In the next sampling period (clock),
In the group G2, the registers TR2, 6, 10, 14, 18, 22, 26, 3 are set by the tap coefficient correction circuit T2.
Modify the tap factors of 0, 34, 38.

In the next sampling period (clock),
In the group G3, the tap coefficient correction circuit T3 allows the registers TR3, 7, 11, 15, 19, 23, 27, 3 to be registered.
Correct the tap coefficient of 1, 35, 39.

In the next sampling period (clock),
In the group G4, the tap coefficient correction circuit T3 allows the registers TR4, 8, 12, 16, 20, 24, 28, 3 to be registered.
Modify the tap factors of 2, 36, 40.

In FIG. 9 described above, the order of coefficient correction in the case of four groups has been described, but when dividing into two groups this time, for example, in the first group, for example, registers TR (2n + 1), n = 0 to 19 are corrected, and in the second group, for example, register TR (2n + 2), n =
It may be to modify 0 to 19.

(Echo cancellation processing): FIG.
6 is a processing flowchart of echo cancellation. In FIG. 10, first, an initial tap coefficient (for example, 0
Or 1) is set in the tap register 61 (S1
1). Next, a tap coefficient calculation coefficient β (for example, 0 ≦ β ≦ 1) is set in the tap coefficient correction circuits T1 to T4 (S).
12). Next, the previous error signal e output from the subtraction circuit 1 is multiplied by this coefficient β (S13).

In FIG. 10, the tap coefficient correction circuits T1 to T4 determine the previous tap coefficient and S13 (e.multidot.e).
β) and the difference is set as A (S14), and this tap coefficient A is set as a new tap coefficient in the register of the corresponding group of the tap register 61 (S1).
5). The pseudo echo signal y ^* is generated using the newly set tap coefficient (S16). Subtraction is performed by the subtraction circuit 1 using this pseudo echo signal y ^* to obtain a new error signal e (S17).

In the same manner, the above-described processes of S13 to S17 are performed, a pseudo echo signal is generated with the optimum tap coefficient, and echo cancellation is performed.

(Effect of One Embodiment): According to the above one embodiment, since the coefficient correction (update) is performed for each group, the processing amount of echo cancellation processing can be reduced as compared with the conventional case. . Moreover, the number of groups is increased during training, the number of coefficient updates is reduced, the number of groups is increased during data transmission, the number of coefficient updates is further reduced, and the tap coefficient processing amount is efficiently increased as necessary. Since it can be adjusted, the processing amount can be reduced more and more.

Since the processing amount of the echo cancellation processing can be reduced as described above, by using one DSP LSI, the program processing such as the echo cancellation processing, the modem processing, the Viterbi decoding processing and the trellis coding processing can be performed. You can do it.

(Other Embodiments) (1) In the above embodiment, the configuration of the echo canceller and the modem is not limited to the configurations shown in FIGS. 1, 6 and 7.
Other functional units may be added.

(2) Further, in the above embodiment, an example in which the echo canceller is applied to the modem is shown, but the invention is not limited to this. For example, it can be applied to a voice recognition device, a data terminal device, a telephone device, and the like.

(3) Furthermore, FIG. 7 and FIG. 9 of the above-mentioned embodiment.
In the above, the number of taps is 40, but the number is not limited to this.
Also, the number of groups is not limited to 4 or 2.

(4) Furthermore, the operation timing is not limited to the operation order shown in FIG. A processing flow chart for coefficient correction is also shown in FIG. 10, but the flow of processing is not limited to this.

As described above, various configurations can be realized without changing the gist of the present invention.

[0068]

As described above, according to the echo canceller of the first invention, the update of the tap coefficients of the plurality of taps of the pseudo echo signal generating means is grouped, and the tap coefficient for making the update for each group. By providing the update grouping means, without reducing the echo removal amount,
It is possible to efficiently perform the echo cancellation processing and reduce the processing time.

Also, in the communication device of the second invention,
Echo removal amount is provided by grouping the tap coefficient updates of the plurality of taps of the pseudo echo signal generating means, and further by providing the tap coefficient update grouping means for changing the grouping of the tap coefficient updates according to the communication state. Echo cancellation processing efficiently without reducing
The processing time can be reduced, and the optimum received signal can be obtained.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a sub-canceller according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a conventional echo canceller.

FIG. 3 is a functional block diagram of a conventional sub canceller.

FIG. 4 is a functional block diagram of a conventional modem system.

FIG. 5 is an operation timing chart of a conventional modem system.

FIG. 6 is a functional block diagram of a modem system according to an embodiment.

FIG. 7 is a functional block diagram of a pseudo echo generating unit according to an embodiment.

FIG. 8 is an operation timing chart of the modem system according to the embodiment.

FIG. 9 is an explanatory diagram of a tap coefficient correction sequence according to an embodiment.

FIG. 10 is a processing flowchart of echo cancellation according to an embodiment.

[Explanation of symbols]

1 ... Subtraction circuit, 2 ... Demodulation circuit, 3 ... Viterbi decoding circuit,
4 ... Modulation circuit, 5 ... Trellis coding circuit, 6 ... Pseudo echo generation unit, 7 ... Tap coefficient correction unit, 51 ... Hybrid transformer (HYB), 61 ... Tap register, 62 ... Integration circuit, 63 ... Transmission data register, SQa-SQc ...
Sub cancellers, S1 to S3 ... Switches, T1 to T4 ...
Tap coefficient correction circuit, y ^* a to y ^* c ... Pseudo echo signal.

Claims (2)

[Claims] 1. A pseudo echo signal generating means for generating a pseudo echo signal by using a plurality of tap coefficients, wherein the pseudo echo signal is generated while updating the tap coefficient of the pseudo echo generating means. In the echo canceller for removing echo from the received signal and the received signal, the tap coefficient update grouping means for grouping the update of the tap coefficient of the plurality of taps of the pseudo echo signal generating means and performing the update for each group is provided. Echo canceller featuring. 2. A pseudo echo signal generating means for generating a pseudo echo signal by using a plurality of tap coefficients, the pseudo echo signal being generated while updating the tap coefficient of the pseudo echo generating means. In the communication device for removing echo from the received signal and the received signal, tap coefficients for updating the tap coefficients of the plurality of taps of the pseudo echo signal generating means are grouped, and the tap coefficient for changing the grouping of tap coefficient updates is changed according to the communication state. A communication device comprising update grouping means.