JP4062050B2 - Data communication device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data communication apparatus such as a high-speed modem that performs full-duplex data communication using an echo canceller technique.
[0002]
[Prior art]
A user can connect a computer, a terminal, or the like to a packet switching network or ISDN data communication network, and communicate with a plurality of other parties via the data communication network. There are four types: telephone, telegraph, packet switching (for data), and circuit switching (for data). In a data connection through an exchange, a data communication device such as a modem is coupled to a telephone station of a general subscriber telephone network (PSTN) via a “subscribe line” such as a pair of telephone lines.
As a terminal interface in such data communication, there is a V series interface for analog data transmission called a modem interface (ITU-T recommendation (International Telecommunication Union-Telecommunication Standardization Sector)).
[0003]
FIG. 10 is a diagram illustrating a configuration example of a conventional data communication apparatus (modem).
The transmission signal is converted into a four-line / two-line conversion by a hybrid circuit (two-line / four-line conversion circuit) 13 via a transmission circuit modulator 11 and a digital / analog converter 12, and then transmitted to a subscription line 21. The received signal is input from the joining line 21 to the hybrid circuit 13 and is converted into two-wire four-wire, and then sent to the receiver via the analog / digital converter 14, the echo canceling unit 15, and the receiving circuit demodulator 16. Sent. The echo cancel unit 15 includes an adaptive filter 17 and an adder circuit 18.
[0004]
When full-duplex communication is performed using a two-wire general public line, as shown in FIG. 10, the transmission signal wraps around the reception path by the hybrid circuit 13 (broken line arrow) and is mixed into the reception signal as an echo ( Near-end echo). Note that there is also an echo (far end echo) generated in the subscriber line accommodated by the exchange station ahead of the subscriber line 21. These echoes are noise for the receiver and greatly affect the reception performance.
A data communication device with a low bit rate can perform full-duplex communication that is not affected by echo signals by separating the transmission and reception signal bands, but a high bit rate high-speed modem uses a wide band. Can not separate the bands. Therefore, as shown in FIG. 11, full-duplex communication is realized using an echo cancellation technique using an adaptive filter 17. ITU-V. 34 or V.V. 90 corresponds to this case.
[0005]
11 and 12 are conceptual diagrams of line connection of a conventional data communication system. In FIG. 11, both modems 10 and 40 are analog modems. In FIG. 12, the modem 60 on one side is a digital modem connected to a digital line.
In FIG. Connected with an analog modem standard such as 34, both near-end and far-end echoes exist. That is, V.I. 34 from the modem 10 via the subscriber line 21 to the switching center 20A, the general subscriber telephone network (PSTN) 30, and from the switching center 20B via the subscriber line 21 to the remote end modem (V.34) 40 on the other side. It is connected.
On the other hand, in the case of FIG. 90 connection, and only near-end echo exists. That is, V.I. 90 The modem 50 is connected via the subscriber line (analog) 21 to the switching center 20A and from the general subscriber telephone network (PSTN) 30 via the digital line 31 to the modem (digital) 60 at the other party's central site. Has been. In the connection with the digital line 31, no echo is generated, so that only an echo between the subscriber line 21, that is, a near-end echo exists.
[0006]
As is generally known, the echo canceller technique adaptively learns a pseudo echo signal from a transmission signal (reference signal) and a circulated echo signal, and uses the learned echo path response characteristics to include the received echo signal in the received signal. Only the echo component is removed.
Normally, the adaptive processing function of an echo canceller mainly consists of a transversal filter and a coefficient correction unit that sequentially updates the filter coefficients. Generally, as a filter coefficient estimation technique of the transversal filter, that is, a coefficient update technique, A comparatively simple learning identification method is used in terms of stability and convergence, and relatively computationally.
[0007]
In addition, ITU-V. 34 or V.V. In a communication protocol using an echo cancellation technique such as 90, a learning interval for echo cancellation is defined in the connection training sequence. In that section, it is recommended to perform half-duplex communication and learn filter coefficients, which is an adaptive process of the echo canceller. After learning, the echo of the transmission signal can be removed, so that full-duplex communication is possible.
However, if the echo cannot be completely eliminated by the echo canceller, it remains in the received signal as it is as a “residual echo component”, which degrades the reception performance as noise (here, any line noise is smaller than the residual echo) Assumed.)
In recent years, the performance of general public lines has increased, and attenuation, noise, and the like have decreased. On the other hand, with the increase in communication speed, this slight error becomes a bottleneck in performance. In particular, V.I. In a high-speed modem such as 90, the processing performance of the echo canceller greatly affects the reception performance.
[0008]
Reasons for the deterioration of the performance of the echo canceller include the following.
1) Limit value of the amount of echo suppression due to the calculation accuracy of the adaptive filter
2) Adaptation limit due to noise
3) Short learning limit in connection sequence
4) Limiting frequency resolution by limiting filter TAP length
5) Increased echo amount due to impedance mismatch in hybrid circuit / Color of echo spectrum
6) Problem of calculation accuracy at the band edge
Various methods have been proposed for the above problems.
[0009]
For example, in the technique described in Japanese Patent Application Laid-Open No. 2002-232329, the echo cancellation for the low frequency band is proposed for the problem 4), and the low frequency echo canceller is used in combination with the normal echo canceller. And performance improvement is realized.
That is, in addition to a normal FIR filter (Finite Impulse Response), LPF (Low Pass Filter) and FIR filters are used in combination. By configuring the LPF using IIR, a filter with a spectrum arranged in order from a large pulse to a small pulse is formed, and this is shaped by FIR, and the transfer function is added by matching the gain and phase. A better approximation.
[0010]
As for the above 5), a method of reducing the impedance mismatch and suppressing the echo amount is generally performed by designing the line impedance to be designed with 600Ω in accordance with the actual line impedance. .
As for the above 6), for example, an improvement technique is considered by the technique disclosed in Japanese Patent Laid-Open No. 8-237176. This is because a pre-emphasis filter is provided on both the transmission side and the reception side, and in particular, the receiver portion of the modem processes the reception signal with the pre-emphasis filter on the reception signal before performing echo cancellation.
According to this, since the high band is generally attenuated due to the frequency characteristic of the line, sufficient calculation accuracy cannot be obtained at the band end on the high band side. For this purpose, the same high-pass filter (HPF) as that on the transmission side is provided in the reception unit to improve the echo component removal performance at the band edge.
[0011]
However, the technique disclosed in the above publication is a solution for the far-end echo and does not mention the near-end echo. In fact, as described in 5) above, the impedance mismatch in the hybrid circuit causes problems such as near-end echo increase and echo spectrum coloration, and the near-end echo canceller also has problems with the calculation accuracy at the band end. Become.
The problem of calculation accuracy at the band edge does not only occur when the echo is attenuated, but also occurs when the difference between the echo level in the signal band and the echo level at the band edge is large, and echo cancellation is effectively performed. As a result, it is not removed.
[0012]
[Patent Document 1]
JP 2002-232329 A
[Patent Document 2]
JP-A-8-237176
[0013]
[Problems to be solved by the invention]
As described above, the conventional echo cancellation technique cannot effectively remove the echo.
FIG. 13 is a diagram illustrating frequency characteristics of a transmission signal in the related art, FIG. 14 is a frequency characteristics diagram of the echo signal,FIG.It is a frequency characteristic figure of a residual echo signal at the time of the end of echo cancellation learning.
The echo signal in FIG. 14 wraps around the transmission signal in FIG. 13 via the hybrid circuit and is mixed into the reception signal. Processing to remove only the echo component from the received signal using an adaptive filter is performed, but the frequency characteristics of the residual echo signal at the time when echo cancellation learning is completed isFIG.As shown.
Thus, the residual echo component at the band edge is V.V. Since it is present as noise in the used reception band at 90, reception performance is hindered.
[0014]
For example, V.I. When the transmission signal and reception signal of the 34 modem use the same signal band, the performance can be improved to some extent by providing the same band limiting filter for both. However, V. When the signal band of the transmission signal and the signal band of the reception signal are different as in the case of 90 modem, the method cannot be used. In particular, V.I. Since 90 modem uses almost the entire band from 0 to 4 kHz for the received signal, it is not possible to provide a band limiting filter for limiting echo (limited by the transmission signal band) in the receiving unit.
V. Since the bandwidth used at 90 is close to 4 kHz, processing may be performed with 16 kHz sampling for the purpose of improving performance, and the processing bandwidth may be widened. Due to the difference, degradation of echo cancellation performance at the band edge appears remarkably, which hinders reception performance.
[0015]
In order to suppress the near-end echo amount, it is conceivable to reduce the transmission level, but in this case, the transmission data rate on the transmission side is sacrificed. Although it is possible to increase the learning time to compensate for the calculation accuracy at the band edge, the echo cancellation learning time in the data modem connection sequence is short, and learning does not end within that time. Is not a solution.
[0016]
Therefore, an object of the present invention is to solve such a conventional problem and suppress the echo cancellation performance by suppressing the residual echo amount at the band edge of the echo signal in the echo cancellation for removing the wraparound echo signal of the transmission signal. An object of the present invention is to provide a data communication apparatus that can improve and improve the reception performance of a high-speed modem.
[0017]
[Means for Solving the Problems]
  The data communication apparatus according to the present invention uses a transmission signal as a reference signal, adaptively estimates a pseudo echo signal from the reference signal and an echo signal that wraps around the reception path, and inverts the pseudo echo signal to obtain a reception signal. In addition, in a full-duplex data communication apparatus having an adaptive filter that removes echoes, an FIR type band having a frequency characteristic that boosts the vicinity of the band end of the signal band with respect to a reference signal input to the adaptive filter. The edge boost filter has the same number of taps as the FIR type band edge boost filter that processes the reference signal, and has a band-pass filter characteristic in which a cutoff frequency is set at the band edge of the transmission signal band. AndConvert transmission signal to analog signalDigital analog conversion meansIn front ofAnd an FIR type bandpass filter provided (corresponding to claim 1).
  As a result, there is an effect of further suppressing the residual echo at the band edge that cannot be completely suppressed by the processing.
[0018]
Also, in order to match the band edge boost frequency band of the band edge boost filter to the used signal band corresponding to the symbol rate of the transmission data, the filter coefficient of the band edge boost filter corresponding to the band is retained. And a means for switching the coefficient of the FIR type band edge boost filter for each signal band to be used (corresponding to claim 2).
  As a result, the band edge boost frequency band of the band edge boost filter can be adjusted for each used signal band corresponding to the symbol rate of the transmission data, and the echo component at the band edge can be appropriately removed.
[0019]
  In addition, in order to match the band-pass filter coefficient applied to the transmission signal to the band edge frequency characteristics for each used signal band corresponding to the symbol rate of the transmission data, the filter coefficient of the band-pass filter corresponding to the band is retained. In addition, there is provided a means for switching the coefficient of the FIR type band pass filter for each signal band to be used (corresponding to claim 3).
Thereby, the coefficient of BPF (Bamd Pass Filter) can be switched for every used signal band according to the symbol rate of transmission data, and the echo component at the band edge can be appropriately removed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a block diagram (corresponding to claim 1) of a data communication apparatus showing Embodiment 1 of the present invention.
In FIG. 1, band edge boost processing is performed by providing a band edge boost filter 19 for the reference signal, in contrast to a normal echo canceller configuration. That is, in addition to the adaptive filter 17 that adaptively estimates the pseudo echo signal using the transmission signal of the normal configuration and the received echo signal, the band edge boost filter 19 is provided at the reference signal input of the adaptive filter 17.
Since no processing is performed on the transmission signal, there is no influence on the transmission data communication. In other words, no filtering process is inserted in either the transmission side signal or the reception side signal, so that the calculation accuracy of the echo canceller at the band edge can be improved without affecting the transmission data rate and reception data rate. Since the residual echo component at the band edge can be suppressed, the reception performance is improved.
[0021]
  FIG. 4 is a diagram illustrating frequency characteristics of an output signal obtained by performing band edge boost filter processing on the transmission signal (reference signal) of FIG. 13 described above.FIG.FIG. 4 is a diagram showing frequency characteristics of the band edge boost filter 19.
  The frequency characteristic of the band edge boost filter 19 is determined from the frequency characteristic of the transmission signal shown in FIG.FIG.As shown in FIG. 2, the frequency band has a characteristic of boosting the frequency band. The frequency characteristic of the reference signal after the band edge boost filter processing at this time becomes a characteristic as shown in FIG. 4, and it can be seen that the voltage is boosted at the band edge.
  Band edge boost·filterA residual echo characteristic as shown in FIG. 8 is obtained by learning echo cancellation from the reference signal after processing and the near-end echo signal shown in FIG.
[0022]
Next, a modification of the first embodiment will be described (corresponding to claim 2).
In the data communication apparatus shown in FIG. 1, the filter 19 inserted on the reference signal side of the adaptive filter 17 is composed of an FIR filter type filter.
FIR filters have no feedback and output is not returned to the input side, that is, non-recursive filters, which have a delay circuit on the input side and a delay circuit on the output side. It is done. The impulse response of this filter is called a finite impulse response type filter because its duration is finite.
By configuring the band edge boost filter 19 with an FIR filter, a linear phase filter is used, so that the performance of the echo canceller can be prevented from deteriorating.
[0023]
(Embodiment 2)
FIG. 2 is a block diagram of a data communication apparatus showing a second embodiment of the present invention (corresponding to claims 3 and 4).
In the second embodiment, a BPF or a delay circuit 20 is provided in the transmission signal circuit in addition to the configuration of FIG. That is, in the data communication apparatus of FIG. 1, the same delay time as that of a 1/2 tap of the FIR filter inserted on the reference signal side of the adaptive filter is generated on the transmission side. As a result, the same delay as that on the reference side occurs, so that the tap length of the adaptive filter 17 can be used effectively without causing a delay in the impulse response of the echo path learned by the adaptive filter 17.
[0024]
A data communication apparatus (modem) shown in FIG. 2 includes a transmission modulator (Tx) 11, a D / A converter (DAC) 12, a hybrid circuit 13, an A / D converter (ADC) 14, an echo cancellation unit 15, and a reception. A demodulator (Rx) 16 is provided, and a band edge boost filter 19 and a band limiting filter (BPF) or a delay term (Delay) 20 are further provided.
The modem is an ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) standard V.30. 34, V.R. Assuming a high-speed modem having 90 or the like, V.V. Consider the case of 90. In this embodiment, the far-end echo canceller and the near-end echo canceller can be handled in exactly the same way. Consider the case of only near-end echo assuming 90.
[0025]
Next, another example (corresponding to claim 4) of the second embodiment will be described. The invention of claim 4 is an FIR type band limit having the same number of taps as the FIR filter 19 inserted in the reference signal of the adaptive filter 17 as shown in FIG. 2 with respect to the configuration of FIG. 1 (corresponding to claim 2). The filter 20 is inserted on the transmission side.
This is used in place of the delay term in the invention of claim 3 and has the effect of further suppressing the residual echo at the band edge that cannot be suppressed in the invention of claim 2.
However, inserting the band limiting filter 20 on the transmission side may affect the transmission data rate. Therefore, it is necessary to design the characteristic of the band limiting filter 20 so as to secure the transmission band as much as possible and limit the band at the band edge so as not to affect the transmission rate.
[0026]
(Other examples of Embodiment 2)
Next, still another example (corresponding to claim 5) of the second embodiment will be described.
The invention of claim 5 switches the coefficients of the FIR type band edge boost filter 19 according to the symbol rate of the transmission data in the invention of claim 2 (FIG. 2).
V. 34, V.R. The connection sequence of 90 performs connection according to the procedure constituted by Phase1 to Phase4. At this time, there is a phase for mutually determining a transmission symbol rate before the phase for performing echo cancellation learning. According to this recommendation procedure, since the transmission symbol rate is determined at the time when learning of echo cancellation is started, switching to a coefficient that boosts the band edge of the signal band corresponding to the determined transmission symbol rate is performed. For example, a plurality of partial filters may be provided for each signal band corresponding to the symbol rate, and one of these may be selectively switched.
As a result, the band edge boost frequency band of the band edge boost filter 19 can be adjusted for each used signal band corresponding to the symbol rate of the transmission data, and the echo component at the band edge can be appropriately removed. Become.
FIG. 3 is a diagram illustrating signal frequencies in the case of two different transmission symbol rates. As can be seen, the two signals have different bands.
[0027]
(Other examples of Embodiment 2)
Next, another example (corresponding to claim 6) of the second embodiment will be described.
According to a sixth aspect of the present invention, in the fourth and fifth aspects of the present invention, the coefficient of the FIR band limiting filter 20 inserted into the transmission signal is switched according to the symbol rate of the transmission data. For example, a plurality of partial band limiting filters may be provided for each signal band corresponding to the symbol rate, and one of these may be selectively switched.
As described above, since the transmission symbol rate is determined in advance and the transmission signal band is determined before the start of the echo cancellation learning, switching the BPF 20 coefficient to the coefficient for that band makes it possible to appropriately echo at the band edge. It becomes possible to remove components.
[0028]
(Comparison with conventional)
In the prior art, as shown in FIG. 10, there is no band edge boost filter, band limiting filter (BPF) or delay term (Delay). Therefore, the signal transmitted from the transmission modulator 11 is converted into an analog signal through the D / A conversion circuit 12, converted by the hybrid circuit 13 into four-wire / two-wire, and then transmitted to the general public line 21. Then, the transmission signal is subjected to 2-wire 4-wire conversion in the hybrid circuit of the telephone office, A / D converted, and sent to the partner modem. In these two hybrid circuits, a signal sneak occurs from the transmission path to the reception path, and enters the A / D conversion circuit 14 as an echo. The received signal is processed by the echo cancellation unit 15 via the adder 18 and the echo signal is also removed by subtracting the pseudo echo signal from the received signal.
However, in practice, the echo cannot be removed due to various causes, and the residual echo has a bad influence on the reception performance as noise.
[0029]
The general echo cancellation unit 15 configures an echo canceller using FIR in order to adaptively estimate the transfer function of the echo path. The filter coefficient is updated so that the difference is reduced using an LMS (Least Mean Square) method or the like using the difference signal during half-duplex training as an error signal.
The modem establishes a connection with the other modem according to the connection sequence indicated in the recommendation. In the initial connection sequence, information exchange with the other modem and the characteristics of the line are grasped, and the respective transmission symbol rates are determined. Thereafter, the transfer function of the echo path is estimated by a half-duplex echo cancellation training sequence.
The characteristics when echo cancellation processing is performed with an actual signal are as follows. 13 shows the frequency characteristic of the transmission signal, FIG. 14 shows the frequency characteristic of the near-end echo, and FIG. 15 shows the characteristic of the residual echo after the echo cancellation learning by the conventional method. As shown in FIG. 15, it is apparent that the conventional method does not perform sufficient echo cancellation processing at the band edge.
[0030]
Therefore, in the present invention, as shown in FIG. 1, band edge boost processing is performed on the reference signal for a normal echo canceller configuration. In this case, since no processing is performed on the reference signal, there is no influence on the transmission data communication.
At this time, it is better to provide a delay term in the transmission signal as shown in FIG. The delay alone does not affect the transmission data communication. The reason for providing the delay is that a delay occurs in the transfer function (impulse response) estimated by the echo cancellation by the band edge boost filter processing, and the tap length of the estimated transfer function is a finite length. When the length cannot be increased, the tail portion of the transfer function is cut by the delay time. This adversely affects echo cancellation learning. In order to correct this, a delay term of 1/2 tap length of the band edge boost filter 19 may be provided in the transmission signal.
[0031]
A residual echo characteristic as shown in FIG. 8 is obtained from the reference signal after the band edge boost processing as shown in FIG. 4 and the near-end echo signal shown in FIG. 14 by learning of echo cancellation.FIG.It can be clearly seen that the residual echo characteristics in the conventional method shown in Fig. 8 are improved by the effective echo cancellation at the band edge as shown in FIG.
This is because the calculation accuracy in the vicinity of the band edge frequency is increased by boosting the band edge of the reference signal.
However, a residual echo component at the band edge is still slightly confirmed.
[0032]
Next, as shown in FIG. 2, the transmission signal is subjected to band limiting filter processing. When the transmission signal is subjected to filtering, transmission data communication is affected. Therefore, the BPF 20 to be used has a filter characteristic that ensures a sufficient transmission signal band and cuts the band outside the band edge. And it is necessary to confirm that there is no influence on transmission data communication.
FIG. 5 is a diagram showing the BPF characteristics when the transmission signal characteristics are as shown in FIG.
At this time, by making the number of taps of the band limiting filter 20 the same as the number of taps of the band edge boost filter 19, the delay term of the transmission signal becomes unnecessary.
[0033]
FIG. 9 is a diagram showing the residual echo characteristics after the echo canceller learning when the transmission signal is subjected to the above BPF processing.
Since the residual echo characteristics after the echo canceller learning when the BPF 20 is inserted into the transmission signal are as shown in FIG. 9, it can be seen that the echo cancellation performance is further improved.
This is because the minute signal at the band edge of the circulated transmission signal echo causes a calculation error in the echo cancellation learning. By suppressing the minute signal component at the band edge from the transmission signal by the BPF 20, echo cancellation is performed. This is because it becomes possible to improve the performance.
[0034]
The filter characteristics of the band edge boost filter 19 and the BPF 20 described above need to match the signal band (band end) of the transmission signal.
Since this transmission signal band varies depending on the transmission symbol rate, it is changed according to the transmission symbol rate.
V. 34 or V.V. In the 90 method, the transmission symbol rate is determined from the line status or the like during the initial connection sequence. Therefore, since the transmission symbol rate is determined at the start of learning of the echo canceller, if a filter coefficient corresponding to the symbol rate is held in advance, it is possible to cope with the selection of the coefficient.
[0035]
5 and 7 are diagrams illustrating the characteristics of transmission BPFs for different signal bands.
6 and 16 are diagrams showing band edge boost filter characteristics for different signal bands.
As described above, the characteristics of the band edge boost filter 19 and the BPF 20 need to be slightly different depending on the signal band (band end) of the transmission signal.
[0036]
【The invention's effect】
As described above, according to the present invention, in echo cancellation for removing the wraparound echo signal of the transmission signal, the echo cancellation performance is improved by suppressing the residual echo amount at the band edge of the echo signal. It is possible to improve reception performance.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of a data communication apparatus showing a first embodiment of the present invention.
FIG. 2 is a block configuration diagram of a data communication apparatus showing Embodiment 2 of the present invention.
FIG. 3 is a signal frequency characteristic diagram of two different transmission symbol rates in the present invention.
FIG. 4 is a frequency characteristic diagram of an output signal obtained by performing band edge boost filter processing on a transmission signal according to the present invention.
FIG. 5 is a frequency characteristic diagram of a transmission BPF for a signal band in the present invention.
[Fig. 6]What is Figure 4It is a frequency characteristic figure of the band edge boost filter for different signal bands.
[Fig. 7]What is Figure 5It is a frequency characteristic figure of transmission BPF for different signal bands.
FIG. 8 is a frequency characteristic diagram of residual echo by learning of echo cancellation in the present invention.
FIG. 9 is a frequency characteristic diagram of a residual echo after echo canceller learning when BPF processing is performed in the present invention.
FIG. 10 is a block diagram showing an example of a conventional data communication apparatus (modem).
FIG. 11 is a conceptual diagram of line connection when both conventional modems are analog modems.
FIG. 12 is a conceptual diagram of line connection in the case of a conventional digital modem on one side.
FIG. 13 is a frequency characteristic diagram of a conventional transmission signal.
FIG. 14 is a frequency characteristic diagram of an echo signal by a conventional transmission signal.
FIG. 15 is a frequency characteristic diagram of a residual echo signal after completion of conventional echo cancellation learning.
FIG. 16 is a frequency characteristic diagram of a conventional band edge boost filter.

Claims (3)

Adaptively estimating a pseudo echo signal from a reference signal and an echo signal circulated in a reception path, using the transmission signal as a reference signal, and inverting the phase of the pseudo echo signal to add the received signal to the received signal and removing the echo In a full-duplex data communication device having a filter,
An FIR type band edge boost filter having a frequency characteristic that boosts the vicinity of the band edge of the signal band with respect to the reference signal input to the adaptive filter;
It has the same number of taps as the FIR type band edge boost filter that processes the reference signal, has a band-pass filter characteristic in which a cutoff frequency is set at the band edge of the transmission signal band, and the transmission signal is analog. A data communication apparatus comprising: an FIR type band-pass filter provided in a preceding stage of a digital / analog converting means for converting into a signal . The data communication apparatus according to claim 1, wherein
In order to adjust the band edge boost frequency band of the band edge boost filter for each used signal band according to the symbol rate of transmission data, the filter coefficient of the band edge boost filter corresponding to the band is retained, A data communication apparatus comprising means for switching coefficients of an FIR type band edge boost filter for each signal band to be used. The data communication device according to claim 1 or 2,
In order to match the band-pass filter coefficient applied to the transmission signal to the band edge frequency characteristics for each used signal band corresponding to the symbol rate of the transmission data, the filter coefficient of the band-pass filter corresponding to the band is retained, A data communication apparatus comprising means for switching a coefficient of an FIR type band pass filter for each signal band to be used.

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