JPH04185034A - Modem signal control system - Google Patents

Abstract

PURPOSE:To prevent a reception image from deteriorating by controlling an A/D converter, the equalizer of a demodulation circuit, and a phase circuit by the output of a control signal decision circuit which decides the output signal of a signal processing circuit. CONSTITUTION:In a demodulation side modem including a transmission system, the demodulation circuit is comprised of a QAM(quadrature amplitude modulation) demodulator 2, the equalizer 4, the phase circuit (rotating apparatuses 11, 13, decision apparatus 12, phase estimation part 10), and a timing estimation part 5. Timing estimation is performed by estimating a sampling rate, and phase estimation by estimating a carrier, and the equalizer 4 corrects frequency characteristic received by a transmission signal on a transmission line. An output facsimile signal can be obtained by controlling the A/D converter 1, the equalizer 4 of the demodulation circuit, and the phase circuit by the output of a control signal decision circuit 16 which decides the output signals of those signal processing circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modem signal control method, and more specifically,
This paper relates to a modem control signal generation circuit and its control method in facsimile transmission.

For example, it is particularly applicable to portable and vehicle-mounted facsimiles.

[Theft] qll Publicly known documents describing the prior art related to the present invention include the following.

For example, Japanese Unexamined Patent Publication No. 110420/1984 has been proposed as an automatic waveform equalizer using a transversal filter that is equipped with a protection circuit against divergence. The one in this publication includes a conduction detection circuit including means for detecting distortion of the equalizer input signal, means for branching the input signal of the equalizer, and one of the branch signals as an input signal, and a switching circuit including a switching means that uses the output signal of the equalizer as another input signal, the switching circuit is controlled by the output signal of the conduction detection circuit, and one of the two input signals is controlled. is the output signal.

In addition, even if the level of the received signal frequently drops due to changes in line characteristics, correction operations in the equalization and phase control sections are performed continuously, resulting in deterioration of the modem's characteristics. For example, Japanese Patent Application Laid-Open No. 2-57039 has been proposed to provide a modem device that avoids such problems. The device in this publication includes an amplitude determination unit that outputs a low-speed amplified signal when the average value of the received signal is smaller than a specified value, and outputs a high-speed amplified signal when the peak value is continuously smaller than the specified value for a certain period of time, and For the variable gain amplification section that amplifies the signal, gradual gain modification is performed using the low-speed amplification signal, rapid gain modification is performed using the high-speed amplification signal, and equalization and phase control are performed when a momentary line interruption is detected. The correction value for corrective operation in the section is held during that time, and the instantaneous line interruption is detected based on the output timing of the high-speed amplified signal.

Figure 3 is a system configuration diagram of a facsimile for a car phone. In Figure 1, 40.45 is a facsimile.

41 is the telephone channel and 42 is the transmitter.

43 is a radio channel and 44 is a mobile phone.

Wireless fax compatible with MCA (Multi-channel access)
However, facsimile signals are sent and received between a base station and a mobile station, whereas facsimiles for car phones are transmitted between offices and mobile stations.
Public line between fixed stations, 800 M between fixed station and car
By connecting with a Hz car telephone line, communication from offices other than the base station is possible. The difference in system configuration from wireless FAX is that a public line is included in the transmission route.

FIG. 4 is a model of the system configuration of a facsimile for a car phone, focusing on the equalizer on the receiving side. The transmission signal sent from the sending side FAX to the transmission path is 5(k),
Impulse response that indicates the frequency characteristics of the public line
(k). On the other hand, a car phone uses F in the 800MHz band.
Since it is M modulation, the detected signal that has undergone fading can be considered to be the sum of the detected output of the transmitted signal and the detected output of the interference wave. Therefore, the disturbance caused by fading added in the wireless transmission path Let v(k) be the interference signal component after detection by the wireless receiver.

When the input signal x(k) to the equalizer is determined, the following equation is obtained.

x (k) = s (k) books h (k) + v (k)
(1) Here, let w (k) be the characteristic of the equalizer, q (k) be its output, and let e (k) be the error between the outputs j (k) and q (k) of the determiner (QUA). , now, if the transmission system is only a public line, the disturbance v (k) is 0, and the equalizer characteristic w (k) is the input x (k) and the error e (k)
The inverse characteristic h-1(k
) will be updated sequentially.

By the way, it is known that v (k) is a burst-like deterioration caused by fading experienced in the radio wave band. Therefore, when a burst-like degraded signal is added to the previous system as v (k), the 1 equalizer performs an equalization operation that also includes this disturbance. There is no guarantee that a modem equalization system designed using this method will operate normally, and malfunctions may occur.

FIG. 5 is a block diagram of a conventional modem.

21 is an A/D converter, 22 is an automatic gain control circuit (AGC), and 22 is an automatic gain control circuit (AGC).
) and QAM demodulator (QuadratureAmpli
(orthogonal amplitude modulation), 23
is a low-pass filter (LPF), and 24 is an equalizer (EQ).
, 25 is a timing estimator, 26.29 is a rotator, 27
28 is a phase estimator, 30 is a decoder, 31 is a demodulator, and 32 is a phase circuit.

P S K (Phase 5hift Keying
: Phase modulation method), D P S K (Differe
ntial Phase 5hift Keying
In order to restore transmitted data from a received signal, modulation methods such as differential phase modulation (differential phase modulation) correct the frequency characteristics that the received signal receives on the transmission path, and correct the difference in carrier frequency between the transmitting and receiving sides (frequency offset). It is also necessary to correct phase jitter, extract a synchronization signal from the received signal, and then reproduce the transmitted data in synchronization with this synchronization signal.

In order to correct the frequency characteristics, an adaptive equalizer (A
A adaptive equalizer (adaptive equalizer) is used, and its equalizer coefficients are updated at the symbol rate so as to have the inverse characteristics of the transmission channel characteristics. Further, one frequency offset and phase jitter are performed by estimating the receiving point on the signal constituency and rotating it on the signal constellation by the estimated phase shift. Furthermore, as a method for extracting the synchronization signal from the received signal, PS
Taking the K modulation method as an example, first the passband signal (received signal) is multiplied by a carrier wave, passed through a waveform shaping filter to become a complex baseband signal, squared, and this frequency component is extracted by a bandpass filter. , by using a method to detect this as a synchronization signal and various coefficients obtained in the process of normally processing the received signal when reproducing the synchronization signal from the received signal, information for timing estimation is extracted from this, and based on this. There is also a synchronous reproduction method in which synchronous reproduction is performed by accelerating or delaying the sampling frequency of A/D conversion of a received signal.

However, in these systems, the equalizer coefficients may diverge in transmission systems where instantaneous interruptions and phase hits occur frequently.
The error in estimating the amount of rotation may increase.

Furthermore, there are problems in that the modem hangs up due to errors in the synchronization timing being reproduced or failure to detect the synchronization signal itself.

In addition to the usual means of detecting the synchronization signal from the received signal, methods for ensuring the operation of the synchronization signal include:

A voltage-controlled local oscillator that freely oscillates at the symbol rate, a phase comparator that detects the phase difference between the synchronization signal and the local oscillator, and a loop that removes unnecessary harmonics and noise from the output of this phase comparator. PLL consisting of a filter
A forced synchronization method consisting of a circuit and its control circuit or a received signal with an abnormal amplitude, etc. is detected, and timing estimation for synchronized playback is automatically stopped when it is determined that an error will occur in synchronized signal playback. , perform demodulation processing by fixing the synchronization signal as it was before the occurrence of the abnormal amplitude, and once the abnormal amplitude is no longer detected, timing estimation can be performed reliably, and control the synchronization signal extraction to restore the previous timing estimation operation. There was a method to achieve forced synchronization by adding an additional action.

However, with these methods, although it was possible to guarantee the synchronization signal, it was not possible to guarantee the operation of one phase rotation of other equalizers.

-15 The present invention was made in view of the above-mentioned circumstances,
A modem signal control method that controls the modem so that it operates normally (so that it does not diverge) even if the signal degrades due to disturbance, and that this control operates adaptively depending on the signal condition. It was made with the purpose of providing.

In order to achieve the above object, the present invention provides (1) a modem device for facsimile communication that transmits an image signal to a remote location via a communication line, which obtains a signal in the voice signal band as a facsimile signal; an A/D converter for converting the facsimile signal into a digital signal;
an automatic gain control circuit that obtains the amplitude of the output signal of the converter as a signal of a predetermined level; a demodulation circuit that uses the output signal of the automatic gain control circuit as an input signal; and an equalizer and a phase circuit of the coarse demodulation circuit. It consists of a signal processing circuit that obtains a signal and outputs a control signal, and a control signal judgment circuit that judges the output signal of the signal processing circuit. (2) the signal processing circuit is configured to control an equalizer and a phase circuit of the circuit to obtain an output facsimile signal; and (2) the signal processing circuit is configured to control equalizer coefficients obtained from the equalizer. Processing the signal to produce a control signal, comparing the control signal with a predetermined level, and using the result as an input signal to a control signal determination circuit; and (3) in (2) above.

The signal processing circuit has a function of operating to adaptively change a predetermined level according to a state of a signal represented by a parameter value related to an equalizer coefficient;
(4) In (1) above, the signal processing circuit obtains the output signal from the phase circuit, processes the output signal as a control signal, compares the signal value with a predetermined level, and obtains the result. (5) In (1), (2), or (4), the control signal determining circuit counts the input signal of the determining circuit for a predetermined period of time. (6) above-mentioned (1);
), (2) or (4), the control signal determination circuit monitors the input signal of the determination circuit at predetermined time intervals;
outputting a signal for returning the modem to the state before the control when the same state is detected consecutively at least a predetermined number of times or more; and (7) in (1) above, the automatic gain control A feature of the circuit is that the circuit is configured with an A/D converter provided after the circuit. An explanation will be given below based on one embodiment of the present invention.

In wireless fax and general digital mobile communications.

Research has focused on improving the degradation of received signals due to fading by diversity technology, high-speed equalizer technology, etc., improving the S/N ratio of the radio modulated signal itself, improving the detector performance, and coding technology.

In contrast, the automotive facsimile described here focuses on the telephone band signal after detection, which has deteriorated due to fading in the radio wave band, and guarantees the performance of the wired modem through signal processing in this telephone band. This is an attempt to improve the deterioration of received images.

When a burst disturbance is input to a wired facsimile modem, the modem malfunctions, resulting in image loss. Therefore, in a car telephone facsimile, instead of making the equalizer of the receiving modem follow the burst disturbance, it is simply the inverse continuity kl''(k) (=w(k) of the public line characteristic h(k).
)) It is better to operate the modem only so that. This results in the equalizer not being able to follow dynamic disturbances caused by fading (hereinafter simply referred to as disturbances).

This is because it is considered that the deterioration (image loss) of the received image can be reduced after all. That is, the proposed method detects a disturbance section from a detected signal in the telephone band, controls the operation of the modem in this section, and guarantees the operation of the modem during and after the disturbance section.

FIG. 1 is a block diagram of a demodulation side modem including a transmission system for explaining one embodiment of the modem signal control method according to the present invention. In the figure, 1 is an A/D converter, 2 is an automatic gain control circuit(
AGC) and QAM (Quadrature Amplifier)
itude Modulation: Quadrature amplitude modulation)
Demodulator, 3 is a low pass filter (LPF).

4 is an equalizer (EQ), 5 is a timing estimation section, 6 is a parameter (evaluation scale calculation section), 7 is a control section (CPU),
8 is a timing buffer (TimingBuffer
), 9 is a phase estimation buffer, 10 is a phase estimation unit, 1
1 is a rotator, and 12 is a discriminator (QUA).

13 is a rotator, 14 is an equalizer (EQ) buffer, 15 is a decoder, and 16 is a control signal determination circuit.

Note that the demodulation circuit includes a QAM demodulator 2, an equalizer 4, and a phase circuit (rotators 11, 13, determiner 12, phase estimation unit 10).
and a timing estimator 5, which uses a phase modulation method (PSK).
) or differential phase modulation (DPSK). This configuration uses timing estimation (Ti++ing
estimate), phase estimation (Phaseesti)
mate) and an equalizer are the basic functional units of the modem.

Timing estimation estimates the sampling rate, phase estimation estimates the carrier wave, and equalizer corrects the frequency characteristics that the transmission signal receives on the transmission path. The equalizer is a transversal type FIR (acyclic type: Finite
The coefficient convergence calculation is performed using the following equation.

c1=ci-r-e-al (2)
e = q - si (3) where ci is the coefficient of the equalizer filter tap, ai is the input time series to the equalizer, e is the error, r is the convergence coefficient, q is the equalizer output, and S is Equation (2), which is a decision point, means that the filter tap coefficients are converged so as to reduce the error e between the receiving point q and the decision point S, and as the error e increases, the convergence deteriorates. Note that timing estimation 1 dependent phase estimation is operated using information obtained from the equalizer.

Now consider the case where a burst disturbance is input to this equalizer. - As an example, assume that a signal with successive amplitude hits is input to the input sequence ai to the equalizer.

At this time, the reception point q increases according to equation (4), and as a result, the error e increases according to equation (3). Furthermore, according to equation (2), the equalizer coefficients begin to converge in the wrong direction by the amount that the error e increases, and since the disturbance is bursty, the coefficient calculations tend to diverge in this section. Furthermore, this influence spreads to timing estimation and phase estimation, making it impossible for the receiving modem to accurately demodulate the transmitted signal. As a result,
The system itself will hang up and images will be missing.

In order to prevent the occurrence of the chain-like divergent behavior described above, 1.
The vehicle-powered type has the configuration shown in Figure 1. Here, the evaluation scale (Parameters) is a part that detects the divergence state, each buffer holds the state of the modem function in a good reception state, and a part that guarantees the operation of the modem after the disturbance period and the end of the disturbance period. The control unit (CPU) is a part that controls the operation of the entire modem guarantee function by referring to the results of the evaluation scale.

In order to control the modem, an evaluation measure is required to detect the disturbance section from the received signal after detection.

As the evaluation scale, there are two methods: one that focuses on the received signal itself and uses its amplitude level, and the other that uses various parameters when demodulating the received signal.

However, the received signal handled here is an eight-phase DPSK (differential phase keying system) modulated wave, and furthermore, this signal is distorted by the frequency characteristics of the transmission system. Therefore, we believe that it is difficult to directly handle the received signal itself,
We focused on and utilized parameters related to the amplitude, phase, and synchronization of the input and output signals of the equalizer, which indirectly represent the signal state. These are two evaluation scales shown in the following equations.

■Te(k)=Te r(k)-Te r(k-1)(
6) Te r(k)=Re a 1(Ci-Co”)
(7) Here, k is the time, P is the average time length, and C
O indicates the coefficient of the center tap of the equalizer, and Ci indicates the coefficient of the tap next to the center tap (with a delay of one symbol).

(2) is the short-time average value of the error e in equation (2) for changing the coefficients of the equalizer, and can be considered to detect an abnormality that occurs in the amplitude of the received signal.

Also, ■ is the control amount Tar(k') for adjusting the timing.
It can be considered that the occurrence of disturbance is detected from the change in the timing adjustment amount. In addition, Ter(
k) using the coefficient ratio of the center tap and the next tap,
It is derived from the following equation.

(C, o is the conjugate complex number of CO) Here, equation (7) can be obtained from IC01 valve 1.

Next, the detection of the start end of the disturbance section and the control procedure will be explained. The determination of starting edge detection is made by comparing the above evaluation scale with a threshold value. Furthermore, in order to maintain the normal state of the modem, data is stored in the buffer until the beginning of the disturbance section is detected, and thereafter it is stopped until the end of the disturbance is inspected. The general steps are shown below.

(1) After starting the reception operation, start detecting the start end of the disturbance section.

(2) Perform normal demodulation processing.

(3) Carrier wave recovery, timing recovery, equalizer-like MC coefficients related to modem operation are held in a buffer.

(4) Calculate the evaluation scales ■E(k) and ■Te(k).

(5) Compare with threshold values THI and TH2, respectively.

(6) If a disturbance occurs when E(k)>THI or Te(k)>TH2, storage in the buffer is stopped and processing is shifted to detecting the end of the disturbance section. If not (
Return to 2) and repeat the subsequent processing.

In addition, here, the value of the evaluation scale is equalized by FIR (acyclic type:
Finite Impulse Re5ponse)
Since it is determined from the coefficients of the filter, there is a time delay corresponding to the number of filter taps between when the disturbance actually occurs and when it is detected. So the buffer is t=o (at time Ii)
The value from t=-P (a time point before P samples) is held.

Next, a procedure for detecting the end of the disturbance section and controlling it will be described.

The determination of whether to detect the end of the disturbance section is based on the state lI! stored in the buffer during the start end detection process. The values are replaced with the coefficients of each basic operation of the modem at fixed intervals (this is called coefficient refresh), and when the evaluation scale is below the threshold shown in Figure 2 for a fixed period of time (for example, level 1) , it is assumed that the termination has been detected. Therefore, the determination is made by introducing two factors: the time (L) for which the modem is operated after the coefficients are refreshed, and the time (R) for which the modem continues to operate after the modem enters the convergence state. The general steps above are as follows.

(1) Self-service that refreshes coefficients (2) Perform normal demodulation processing.

(3) Calculate the evaluation scale.

(4) Compare the evaluation scale with a threshold value, and count the duration i during which the evaluation value takes a value smaller than the threshold value.

If this value is R or more, the termination detection process is stopped and the start edge detection process is shifted.

(5) If it is larger than the threshold, count the duration j after refreshing the coefficient. If this value is greater than or equal to L, the process moves to (1); otherwise, the process moves to (2) and continues.

As shown in Figure 2, when determining at level 1, the starting point is the point of, the ending point is the @ point, the modem is not operating at the O point, so there is no divergence, and the ■ point is the initial point. (before ■)
Return to state.

In this way modem divergence can be prevented.

Further, in the TI1 interval and the T y × 4 interval in FIG. 2, an adaptive control function is realized in which no control is performed at all or only moderate control is performed.

In this way, even if the signal condition continues to be extremely poor, modem control is adaptively controlled, so line dropouts do not occur frequently.

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

Even if the signal deteriorates due to disturbance, modem divergence can be prevented, and even if the signal condition continues to be extremely poor, modem control is adaptively controlled, so line dropouts do not occur frequently. In other words, in facsimiles for car phones, we focus on the telephone band signal after detection that has deteriorated due to fading in the radio wave band, and guarantee the performance of the wired modem by signal processing in this telephone band. Detects the disturbance section from the telephone band detection signal and controls the modem operation in this section.
The operation of the modem during and after the disturbance period can be guaranteed.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the modem signal control method according to the present invention, FIG. 2 is a diagram for explaining the functions of the signal processing circuit output and the control signal determination circuit, and FIG. is a system configuration diagram of a car phone facsimile, Part 4
The figure shows a model of the system configuration of a facsimile for a car phone, focusing on an equalizer on the receiving side, and FIG. 5 is a diagram showing the configuration of a conventional modem. 1...A/D converter, 2...Automatic gain control circuit (AG
C) and QAM (Quadrature A*pli
demodulator, 3...low-pass filter (LPF), 4...
Equalizer (EQ), 5... timing estimator, 6... parameter (evaluation scale calculation unit), 7... control unit (CP
U), 8...Timing buffer y (Tfming
Buffer), 9-phase estimation buffer, 10.
... Phase estimation section, 11 ... Rotator, 12 ... Determiner (QUA), 13 ... Rotator, 14 ... Equalizer (EQ
) buffer, 15... decoder (Decoder),
16...Control signal determination circuit. (1 other person) - Figure 2 Figure 3 MS + Mobile 5tation Figure 4 QUA + QuantiZer

Claims (1)

[Claims] 1. A modem device for facsimile communication that transmits image signals to a remote location via a communication line, which obtains a signal in the audio signal band as a facsimile signal and converts the facsimile signal into a digital signal. /D converter, an automatic gain control circuit that obtains the amplitude of the output signal of the A/D converter as a signal of a predetermined level, a demodulation circuit that uses the output signal of the automatic gain control circuit as an input signal, and the demodulation circuit. It consists of a signal processing circuit that obtains signals from the equalizer and phase circuit of the circuit and outputs a control signal, and a control signal determination circuit that determines the output signal of the signal processing circuit. . A modem signal control method, characterized in that the A/D converter and the equalizer and phase circuit of the demodulation circuit are controlled to obtain an output facsimile signal. 2. The signal processing circuit processes a signal related to the equalizer coefficients obtained from the equalizer to generate a control signal, compares the control signal with a predetermined level, and sends the result to the control signal determination circuit. 2. The modem signal control method according to claim 1, wherein the modem signal control method is an input signal to the modem signal control method. 3. The signal processing circuit has a function of operating to adaptively change a predetermined level according to a state of a signal represented by a parameter value related to an equalizer coefficient. Modem signal control method described. 4. The signal processing circuit obtains the output signal from the phase circuit, processes the output signal as a control signal, compares the signal value with a predetermined level, and sends the result to the control signal determination circuit. 2. The modem signal control method according to claim 1, wherein the modem signal control method is an input signal. 5. The control signal determination circuit has a counting function that counts input signals of the determination circuit for a predetermined period of time, and operates to stop modem control and return the modem to the state before control when the input signal is equal to or greater than a predetermined value. 5. The modem signal control method according to claim 1, wherein the modem signal control method outputs a signal that causes the modem signal to be controlled. 6. The control signal determination circuit monitors the input signal of the determination circuit at predetermined time intervals, and returns the modem to a pre-control state if the same state is detected consecutively at least a predetermined number of times or more. 5. The modem signal control method according to claim 1, wherein a signal for restoring is output. 7. The modem signal control method according to claim 1, characterized in that a circuit configuration includes an A/D converter after the automatic gain control circuit.