JP3071811B2 - Modem control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hang-up control method for a modem, and more particularly, to a modem used for various modulation / demodulation methods, a modulation / demodulation method of a facsimile apparatus, synchronization detection of a data transmission method, and a timing recovery method. (MODEM; modem). For example, the present invention is applied to a facsimile apparatus, a communication modulation / demodulation method, mobile communication, and the like.

Conventional technology PSK (Phase Shift Keying: phase modulation method), DPSK (Di
Modulation methods such as fferential phase shift keying (differential phase modulation method) correct the frequency characteristics that the received signal receives on the transmission line in order to restore the transmission side data from the received signal.
Difference between carrier frequency on transmitting side and receiving side (frequency offset)
In addition, it is necessary to correct the phase jitter, extract the synchronization signal from the reception signal, and reproduce the transmission data in synchronization with the synchronization signal.

In order to correct the frequency characteristic, an adaptive equalizer is usually used, and the equalizer coefficient is updated at a symbol rate so as to have an inverse characteristic of the transmission path characteristic. In addition, correction of frequency offset and phase jitter is performed using signal constellation (signal point arrangement: S
This operation is performed by rotating the reception point by the estimated phase shift on the “ignal Constellation”. Furthermore, as a method of extracting a synchronization signal from a received signal, taking a PSK modulation method as an example, first multiply a passband signal (received signal) by a carrier wave, and form a complex baseband signal through a waveform shaping filter. A square is used to take out the synchronous frequency component with a band-pass filter, and this is detected as a synchronous signal. Various types of coefficients (for example, Synchronizer coefficient), and the timing estimation information is extracted from this, and based on this information, the synchronous reproduction method of performing synchronous reproduction by increasing or delaying the sampling frequency of A / D conversion of the received signal, etc. is there.

However, in these systems, in transmission systems where sudden disturbances such as instantaneous interruptions and phase hits frequently occur, the equalizer coefficient of the modem diverges, the estimation error of the rotation amount increases, and further reproduction is performed. However, there is a problem that the modem hangs up due to an error in the synchronization timing or failure to detect the synchronization signal itself.

For this situation, equalizer coefficients, carrier recovery,
First buffer means for buffering various coefficients relating to timing recovery for a predetermined number of symbol rates;
Second buffer means for buffering the coefficient value at the end of the facsimile training sequence, calculating means for calculating an evaluation value (evaluation scale) using input / output values of the equalizer, and monitoring means for monitoring the evaluation value An equalizer abnormality is detected by comparing the evaluation scale with a predetermined threshold value for each symbol rate, and timing abnormality (synchronization signal reproduction), an equalizer coefficient update operation,
When it is determined that the carrier recovery (phase shift correction) function malfunctions, the modem is provided with a function to guarantee the operation of timing recovery, equalizer coefficient update operation, carrier recovery, and a function to guarantee these functions. A control method for preventing a malfunction of has been proposed. However, in this case, since the convergence coefficient for adjusting the update speed of the equalizer filter tap is fixed (constant), the convergence speed is low, and therefore, it takes time for modem convergence, and the threshold value of the convergence condition is inappropriate. Quasi-stationary state where the modem does not converge completely (local minimum)
There was a problem of falling into. In addition, since the threshold value for detecting the start and end of the disturbance is fixed, the control of the modem is always performed depending on the transmission line whose S / N is extremely deteriorated, and the operation is not stable.

Japanese Patent Laid-Open No. 1-279617 relates to an automatic equalizing circuit for shaping a pulse waveform used in digital magnetic recording of a PCM signal to reduce distortion, and relates to a transversal filter. , A level detection circuit that detects the level of the input signal, a coefficient setting circuit that sets the coefficient value of the transversal filter from the input and output of the waveform equalization circuit, and an output of the level detection circuit. And a control circuit for controlling the operation of the coefficient setting circuit.

In addition, "Automatic equalizer" disclosed in JP-A-2-26406, "Modem device" disclosed in JP-A-2-57039, "Auto-equalizer" disclosed in JP-A-2-16066, and the like are proposed. However, the content of each of them is to prevent a malfunction of a modem or an equalizer by monitoring a line signal, and does not include a concept of refreshing or a concept of fast convergence.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and relates to an equalizer coefficient calculation after refreshing, which speeds up the coefficient convergence when a stationary signal is input after a disturbance, and sets a state of a modem. To provide a modem control method that controls the modem to always transition from the divergent state and divergent process to the steady state from the quasi-steady state by introducing a state measure that monitors the time. The purpose of the present invention is to provide a modem control method for obtaining a threshold suitable for this transmission system by referring to an average value.

To achieve the above object, the present invention provides: (1) In a phase modulation method used for data transmission, various coefficients relating to equalizer coefficients, carrier recovery, and timing recovery are stored in a first buffer means by a predetermined symbol rate number. Buffering the various coefficient values at the end of the facsimile training sequence by a second buffer means, calculating an evaluation scale using input / output values of an equalizer by a calculating means, The evaluation scale is monitored by monitoring means, the evaluation scale is constantly monitored for each of the symbol rates, the evaluation scale is compared with a predetermined threshold, and when the evaluation scale exceeds a predetermined threshold, the equalizer is controlled. Abnormality is detected, and timing recovery (synchronous signal reproduction), equalizer coefficient update calculation,
When it is determined that the carrier recovery (phase shift correction) function is in the direction of malfunction, the storage of the coefficient value in the first buffer means is stopped, and the timing recovery, equalizer coefficient update calculation, and carrier recovery calculation are performed. As a coefficient relating to the above, a refresh processing is performed by loading and using a coefficient value equal to or more than a predetermined number of symbol rates from the time when the abnormality is detected in the evaluation scale from the first buffer means,
Further, demodulation processing of the subsequent data is performed for a predetermined number of samples. If the number of samples whose evaluation scale is lower than a predetermined threshold value reaches a predetermined number in this predetermined sample section, the demodulation processing is continued as it is. In such a case, the same value as the coefficient value loaded from the first buffer means is refreshed and used for the coefficients relating to the timing recovery, the equalizer system number update operation, and the carrier recovery operation, and the comparison operation with the evaluation scale calculation is repeated. Thus, when the number of times of refreshing the coefficient exceeds a preset number of times, a modem control method for loading the coefficient value from the second buffer means and performing processing is provided. For the equalizer coefficient update calculation after performing, the steady-state signal after disturbance is changed by changing the coefficient convergence speed. Increasing the coefficient convergence speed when the force is applied, and (2) changing the convergence coefficient value relating to the equalizer coefficient update operation after performing the refresh stepwise for each predetermined number of samples; Furthermore, (3)
The convergence coefficient value relating to the equalizer coefficient update operation after the refresh is adaptively changed according to the value of the state scale, or (4) in the phase modulation method used for data transmission, the equalizer coefficient and the carrier Various coefficients relating to recovery and timing recovery are buffered by a first buffer means for a predetermined number of symbol rates,
The various coefficient values at the end of the facsimile training sequence are buffered by the second buffer means, an evaluation scale using input / output values of the equalizer is calculated by the calculation means, and the evaluation scale by the calculation means is monitored. To monitor by, constantly monitor the evaluation scale for each symbol rate, compare the evaluation scale with a predetermined threshold, when the evaluation scale exceeds a predetermined threshold, to detect an abnormality of the equalizer, When it is determined that the timing recovery (synchronization signal reproduction), the equalizer coefficient update calculation, and the carrier recovery (phase shift correction) functions are in the malfunction direction due to this abnormality, the storage of the coefficient values in the first buffer means is performed. Stop, timing recovery, equalizer coefficient update operation,
As a coefficient relating to the carrier recovery calculation, a coefficient value equal to or more than a predetermined number of symbol rates from the time when the abnormality is detected in the evaluation scale is loaded from the first buffer means and used to perform refresh processing. Data demodulation is performed for a predetermined number of samples. If the number of samples whose evaluation scale is lower than a predetermined threshold reaches a predetermined number in this predetermined sample section, the demodulation processing is continued as it is. Is used by refreshing and using the same value as the coefficient value loaded from the first buffer means for the coefficients relating to the timing recovery, the equalizer system update operation, and the carrier recovery operation, and repeating the comparison operation with the evaluation scale calculation. The end of the disturbance is detected.
If the number of coefficient refreshes exceeds a preset number, the modem value is loaded from the second buffer means to perform processing, and a threshold value used for detecting the start and end of a disturbance section is transmitted. (5) calculating a time average of the evaluation scale during a predetermined time after the end of the training, and multiplying the time average by a predetermined value; And (6) calculating a time average of the evaluation scale, and multiplying the time average by a predetermined value to obtain the threshold with different multiple values. . Hereinafter, a description will be given based on examples of the present invention.

The phase modulation method has the following configuration. That is, a conversion means for converting an image signal read from a document into a binary signal, and the binary data converted by the conversion means are modulated (phase-modulated) in association with the phase information of the carrier wave, and converted into a passband signal. A signal transmitting means for transmitting to a transmission path, and a conversion for receiving a passband signal transmitted by the transmitting means, multiplying the passband signal by a carrier wave, and passing through a waveform shaping filter to convert the signal into a complex baseband signal Means, reproducing means for reproducing synchronization from the received signal, adaptive equalizing means for equalizing frequency distortion received in the transmission system, and determining transmission data from the complex baseband signal in synchronization with the previous synchronizing signal. Determining means; decoding means for decoding the transmission data; and a phase shift (frequency offset) received when the received signal is converted into a complex baseband signal on a transmission path. Composed of a correcting means for correcting the fine phase jitter).

FIG. 1 is a configuration diagram of a demodulation-side modem for explaining an embodiment of a modem control system according to the present invention, wherein 1 denotes a modem.
A / D converter 2 and QAM (Quadrature Amplitude Modulatio)
n: Quadrature amplitude modulation) demodulator, 3 is a low-pass filter (LP
F), 4 is an equalizer (EQ), 5 is a timing estimator, 6 is an evaluation and state scale calculator, 7 is a controller (CPU), 8 is a timing buffer, 9 is a phase estimation buffer. , 10 is a phase estimator, 11 is a rotator, 12 is a decision unit (QU
A) and 13 are rotators, 14 is an equalizer (EQ) buffer, and 15 is a decoder.

An equalizer (EQ) 4 is a transversal type FIR (a non-cyclic type: Finite Impulse Response) constituting an equalizer part.
This is a filter, and the filter tap Ci is updated by the following formula: Ci = Ci−r · e · xi ^* (K) (1) Xi ^* is a conjugate complex number of the input to the equalizer 4, e is an error, and r is a coefficient (convergence coefficient) for adjusting the convergence speed. The reason why the modem diverges in FIG.
In equation (1), when a large disturbance is applied to the input X,
This is because the update operation of the filter coefficient is directed to the direction of divergence. Therefore, the diverging operation of the modem can be prevented unless the operation of the equalizer of the receiving modem is made to follow the dynamic characteristics caused by the sudden disturbance.

Further, after the disturbance, by increasing the coefficient convergence speed when a normal signal is input, it is possible to reduce a malfunction section of the modem. For this reason, buffering of each coefficient of the modem and calculation of an evaluation scale (including a state scale), and their control units are added to the normal receiving-side modem processing.
As processing, the control unit changes the value of the equalizer convergence coefficient r in a stepwise or adaptive manner with reference to the state scale in order to increase the convergence speed and avoid a fall in the quasi-steady state. A part to be added is added.

As an evaluation scale for detecting a disturbance section, for example, there are the following.

Ter (k) = Te (k) −Te (k−1) (3) Ter (k) = Real (C ₁ · C ₀ *) (4) First, the above evaluation scale will be described. Is a short-time average value of the error e of the output of the equalizer, and detects an abnormality occurring in the amplitude of the received signal. Is a difference value of the coefficient ratio between the center tap and the next tap of the equalizer coefficient. This indicates the amount of phase change, and detects sudden phase rotation caused by disturbance.

Also, S (k) is defined as a state scale indicating the state of the modem. S (k) is a parameter indicating the convergence state, quasi-stationary state, divergence process, and divergence state of the modem system. The parameter r of the equalizer coefficient convergence speed of the modem is adjusted by this S (k). For example, S (k) includes the following.

The buffer stores first and second buffer means for storing equalizer coefficients and coefficients relating to timing recovery and carrier recovery for a predetermined number of samples for each symbol rate, and buffering the various coefficient values at the end of facsimile training sequence. 2 buffers.

The operation of each block described above will be described below together with the process of detecting the start and end of a disturbance section.

FIG. 2 is a flowchart showing one embodiment of detection of the start of a disturbance section. Hereinafter, the steps will be sequentially described.

step1; The receiving modem starts detecting the beginning of the disturbance section after the operation starts. Processing of the received signal proceeds at the symbol rate according to normal modem processing.

step2; Determine whether the training is completed. If training is in progress, the process returns to step 1.

step3; After the end of the training, the carrier buffer recovery, the timing recovery, and the coefficients of the equalizer relating to the normal modem operation are held in the first buffer to guarantee the modem operation after the occurrence of the disturbance.

step4; Further, the above coefficient value at the end of the facsimile training sequence is stored in the second buffer.

step5; Next, E (k), Ter (k)
Is calculated.

step6: The evaluation scales calculated in step5 are compared with threshold values TH1 and TH2, respectively.

step7; Using TH1 and TH2 as thresholds, respectively, E (k)> TH1 or
When Ter (k)> TH2, it is assumed that a disturbance has occurred, the storage in the first buffer is stopped, and the process proceeds to the detection of the end of the disturbance section.

Here, the first buffer holds values from t = 0 (current time) to t = -L (time before L samples). This is because calculating the value of the evaluation scale from the input / output coefficients of the equalizer FIR filter involves a time lag of the number of filter taps until the occurrence of disturbance is detected.

FIG. 3 is a flowchart showing an embodiment of determining a threshold value including detection of the beginning of a disturbance section. Hereinafter, the steps will be sequentially described.

step1; The receiving modem starts detecting the beginning of the disturbance section after the operation starts. Processing of the received signal proceeds at the symbol rate according to normal modem processing.

step2; Determine whether the training is completed. If training is in progress, the process returns to step 1.

step3; After the end of the training, the carrier buffer recovery, the timing recovery, and the coefficients of the equalizer relating to the normal modem operation are held in the first buffer to guarantee the modem operation after the occurrence of the disturbance.

step4; Further, the coefficient value at the end of the facsimile training sequence is stored in the second buffer, and the counter C is set to 0.

step5; Next, E (k), Ter (k)
Is calculated.

step6: The counter C of the evaluation scale calculated in step 5 is compared with a predetermined threshold TH_COUNT.

step7; In step 6, if C <TH_COUNT, that is, if C is equal to or less than TH_COUNT, a fixed threshold TH_fix set in advance to a higher value is used as the threshold for detecting the start and end of the disturbance, and the counter C is set to C + 1. I do.

step8; In step 6, if C <TH_COUNT,
That is, when C is larger than TH_COUNT, C = 0 to C
Based on the time average value of the evaluation scale calculated between = TH_COUNT, the threshold is multiplied by a predetermined value to set the threshold for detecting the start and end of the disturbance. As the calculation at this time, for example, the following can be considered. When a threshold THs for detecting the beginning of the disturbance and a threshold THe for detecting the end of the disturbance are set, THs = m.avr (| evaluation scale |) THe = n.avr (| evaluation scale |). Here, m and n are arbitrary integers, but m> n, and are set tolerant to detection of the start of disturbance. Here, the time average of the absolute value of the evaluation scale is used as the time average of the evaluation scale, but this value may be anything.

step9: The evaluation scale calculated in step7 or step8 is compared with threshold values TH1 and TH2, respectively.

step10; With TH1 and TH2 as thresholds, respectively, it is assumed that a disturbance has occurred when E (k)> TH1 or Ter (k)> TH2, storage in the first buffer is stopped, and processing is performed to detect the end of the disturbance section Moves.

Here, the method of determining the threshold value for the method of increasing the convergence speed has been described. However, since the threshold value determination process is not limited to the speedup, the present invention can also be applied to a modem configuration that does not increase the speed.

FIGS. 4 (a) and 4 (b) are flowcharts showing an embodiment of detection of the end of a disturbance section. Hereinafter, the steps will be sequentially described.

The determination of disturbance end detection is performed by forcibly giving the coefficient value stored in the first buffer in the start end detection processing to the modem (this is called refresh), observing the evaluation scale, and determining whether this value satisfies a certain condition. It is assumed that the end has been detected. Here, the determination is made by introducing three parameters: a predetermined time j during which the modem is operated after the coefficient is refreshed, a time i that continues after the modem enters the convergence state, and a refresh count k.

step1; The counter k for counting the number of refreshes is set to 0.

step2: The convergence counter and the refresh counter i, j are set to 0, and k = k + 1.

step3: The number k of refreshes is compared with a threshold value TH3.

step4; If k> TH3 is not satisfied in step 3, the first buffer is refreshed with the value L samples before.

step5: In step 3, when k> TH3, refresh is performed using the coefficient value of the second buffer.

Step 6: Normal modem processing is performed (coefficient value is changed without storing in the first buffer).

step7,8; Calculate the evaluation scale and compare with the threshold.

step9: In step 8, if the evaluation scale to be compared is smaller than the threshold, i = i + 1. That is, the duration time i in which the evaluation value takes a value smaller than the threshold value is counted. If the value i is equal to or larger than R, the end detection processing is stopped, the convergence coefficient is fixed to the one used in the steady state, and the processing shifts to the start detection processing.

step10: In step 8, if the evaluation scale to be compared is larger than the threshold value, i = 0, and the duration j after the coefficient is refreshed is counted.

step11; Duration is set to j = j + 1.

step12; If the duration j = G, return to step2, i
If <R and j <G, the convergence coefficient is changed (step 13), and the process returns to step 6 to continue.

step13; FIG. 4 (b) shows a flowchart of the change of the convergence coefficient. The section G in which the modem processing is continued by performing the refresh is defined by the section lengths G1, G2, and G3.
And convergence coefficient values in this section are r1, r2, r3
The calculation is performed as In this case, the description has been made by dividing into three parts, but it may be divided into several parts.

step14: In step 12, if i = R and j <G, the convergence coefficient is reset to r = r_fixed.

In the control method shown in FIG. 4, if convergence does not proceed even when the second buffer is used, the modem is hung up.

FIG. 5 is a flowchart showing another embodiment of detecting the end of a disturbance section. The difference from the flowchart shown in FIG. 4 is that, in step 7, a part for calculating the state scale is added in addition to the evaluation scale, and the convergence coefficient in the refresh interval is adaptively changed by this state value. is there. All other parts are the same. In the case of FIG.
The relationship between the convergence coefficient r (k) and the state coefficient S (k) can be expressed by a function F of r (k) = F (S (k)).

FIG. 6 shows an example of the relationship between r (k) and S (k) based on the function F. Set the minimum and maximum values of the state scale to S_mi
n and S_max, and the minimum and maximum values of the convergence coefficient are r_min and r, respectively.
_max, and the section between them is linearly associated. FIG. 7 is a development of the correspondence of FIG. 6, and stepwise, log-like, exp-like, etc. correspondence can be considered.

Effects As is clear from the above description, the present invention has the following effects.

(1) Effect according to the first aspect: By detecting a disturbance from an input signal, divergence of a modem operation can be easily prevented, and convergence can be realized more quickly after a disturbance occurs.

(2) An effect corresponding to claims 2 and 3; the recovery (convergence) of the modem operation can be speeded up by changing the equalizer convergence coefficient r stepwise or adaptively, and at the same time, the state is monitored. By doing so, it is possible to control the modem system so that it is always in a normal state.

(3) Effect corresponding to claims 4, 5, and 6; a threshold value for disturbance detection suitable for the transmission system can be set, and the control of the modem can be operated more efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram of a modem on the demodulation side including a transmission system for explaining an embodiment of a modem control system according to the present invention. FIG. 2 is a flowchart showing an embodiment of detection of the beginning of a disturbance section. FIG. 3 is a flowchart showing an embodiment of determining a threshold including detection of a start end of a disturbance section, FIG. 4 is a flowchart showing an embodiment of end detection of a disturbance section, and FIG.
FIGS. 6 and 7 are flowcharts showing another embodiment of detection of the end of a disturbance section, and FIG.
It is a figure showing the relation between (k) and state scale S (k). 1 ... A / D converter, 2 ... QAM (Quadrature Amplitude M)
odulation: quadrature amplitude modulation) demodulator, 3... low-pass filter (LPF), 4... equalizer (EQ), 5... timing estimator, 6... evaluation, state scale calculator, 7. Unit (CPU), 8 Timing buffer (Timing Buffe
r), 9 ... phase estimation buffer, 10 ... phase estimation unit, 11
… Rotator, 12… Judge (QUA), 13… Rotator, 14
…… Equalizer (EQ) buffer, 15 …… Decoder (Decode)
r).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 3/00-3/44 H04L 27/00-27/38

Claims (6)

(57) [Claims] In a phase modulation system used for data transmission, various coefficients relating to an equalizer coefficient, carrier recovery, and timing recovery are buffered by a first buffer means for a predetermined number of symbol rates, and when a facsimile training sequence ends. Buffering the various coefficient values of the above by a second buffer means, calculating an evaluation scale using input / output values of the equalizer by an arithmetic means,
The evaluation scale by the arithmetic means is monitored by monitoring means, the evaluation scale is constantly monitored for each symbol rate, the evaluation scale is compared with a predetermined threshold, and when the evaluation scale exceeds a predetermined threshold, When the abnormality of the equalizer is detected and the timing recovery, the equalizer coefficient update operation, and the carrier recovery function are determined to be malfunctioning due to the abnormality, the storage of the coefficient value in the first buffer means is stopped. Then, as coefficients relating to the timing recovery, the equalizer coefficient update operation, and the carrier recovery operation, coefficient values equal to or less than a predetermined number of symbol rates from the point in time when an abnormality is detected in the evaluation scale are sent from the first buffer means. A refresh process for loading and using is performed, and a demodulation process of subsequent data is performed for a predetermined number of samples. If the number of samples at which the evaluation scale becomes lower than the predetermined threshold reaches a predetermined number, the demodulation process is continued as it is, and if not, it is involved in the timing recovery, the equalizer system update calculation, and the carrier recovery calculation. The same value as the coefficient value loaded from the first buffer means is refreshed and used as the coefficient, and the end of the disturbance is detected by repeating the comparison operation with the calculation of the evaluation scale, but the number of times the coefficient is refreshed is set in advance. If the number of times exceeds the number of times, the modem value is loaded from the second buffer means and the processing is performed, and the equalizer coefficient updating operation after refreshing is performed.
A modem control method characterized by increasing the coefficient convergence speed when a post-disturbance steady signal is input by changing the coefficient convergence speed. 2. The modem control method according to claim 1, wherein a convergence coefficient value relating to an equalizer coefficient update operation after the refresh is changed stepwise every predetermined number of samples. 3. The modem control method according to claim 1, wherein a convergence coefficient value relating to an equalizer coefficient update operation after the refresh is adaptively changed according to a state scale value. 4. A phase modulation method used for data transmission, wherein various coefficients relating to an equalizer coefficient, carrier recovery, and timing recovery are buffered by a first buffer means for a predetermined number of symbol rates, and when a facsimile training sequence ends. Buffering the various coefficient values of the above by a second buffer means, calculating an evaluation scale using input / output values of the equalizer by an arithmetic means,
The evaluation scale by the arithmetic means is monitored by monitoring means, the evaluation scale is constantly monitored for each symbol rate, the evaluation scale is compared with a predetermined threshold, and when the evaluation scale exceeds a predetermined threshold, When the abnormality of the equalizer is detected and the timing recovery, the equalizer coefficient update operation, and the carrier recovery function are determined to be malfunctioning due to the abnormality, the storage of the coefficient value in the first buffer means is stopped. Then, as coefficients relating to the timing recovery, the equalizer coefficient update operation, and the carrier recovery operation, coefficient values equal to or less than a predetermined number of symbol rates from the point in time when an abnormality is detected in the evaluation scale are sent from the first buffer means. A refresh process is performed by loading and using the data, and a demodulation process of subsequent data is performed for a predetermined number of samples. If the number of samples at which the evaluation scale becomes lower than the predetermined threshold reaches a predetermined number, the demodulation process is continued as it is, and if not, it is involved in the timing recovery, the equalizer system update calculation, and the carrier recovery calculation. The same value as the coefficient value loaded from the first buffer means is refreshed and used as the coefficient, and the end of the disturbance is detected by repeating the comparison operation with the calculation of the evaluation scale, but the number of times the coefficient is refreshed is set in advance. If the number of times exceeds the number of times, a modem control method for loading coefficients from the second buffer means and performing processing is performed, and a threshold used for detecting the start and end of a disturbance section is set according to the state of the transmission line. Characteristic modem control method. 5. The method according to claim 1, wherein a time average value of the evaluation scale is calculated for a predetermined period of time after the end of the training, and a threshold value is set by multiplying the time average value by a predetermined value. Item 4. The modem control method according to Item 4. 6. A time average value of the evaluation scale is calculated, and a threshold value is set by multiplying the time average value by a predetermined value. 6. The modem control method according to claim 5, wherein the value is obtained by a numerical value.