JPH04330839A - Modem device - Google Patents

Abstract

PURPOSE:To speedily recover a mode itself to a normal state by preventing the divergence of the like of an equalizer or the like, and preliminarily preventing a malfunction, even when a disturbance or the like is added. CONSTITUTION:A signal deterioration detecting means 109 detects the level change of a received signal LRS, and applies a deterioration detecting signal DS according as the level change is larger or not than a reference value RFS, to a control means 112. The control means 112 controls the transmission of a phase error signal PES from a phase error detecting means 200 to a loop filter 113 according to the deterioration detecting signal DS, and when the level change of the received signal LRS is large due to the disturbance or the like, the control means 112 stops the transmission of the phase error signal PES to the loop filter 113 by the deterioration detecting signal DS indicating the result, so that a phase error correction can be prevented from being operated based on the phase error signal PES having a possibility of error due to the disturbance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device used in data transmission systems, facsimiles, and the like.

0002

2. Description of the Related Art Generally, in a data transmission system, a modem device on the receiving side converts a received signal transmitted from the transmitting side into a complex baseband signal using a demodulated carrier of a known frequency, and Intersymbol interference is removed by an automatic equalizer, and the original code sequence is reproduced by a decoder from the output signal of the automatic equalizer.

By the way, if the amount of deterioration of waveform distortion due to group delay or the like in the transmission line is so large as to exceed the equalization ability of the automatic equalizer, the automatic equalizer becomes unable to perform equalization and diverges. As a result, the modem device malfunctions. Conventionally, in order to restore the modem device so that normal data transmission is possible again even if the automatic equalizer diverges, for example, Japanese Patent Laid-Open No.
A technique as disclosed in No. 239157 is known.

In this technology, the decoder is equipped with a function to reproduce the original code sequence, as well as a function to check code errors and generate an error detection pulse when an error occurs, and calculate the error rate by counting the error detection pulses. When deterioration of the carrier is detected, the phase of the demodulated carrier is controlled by applying it to a variable phase shifter. As a result, even if the automatic equalizer diverges due to transmission path switching, etc., it is possible to re-intract it by repeating phase control of the demodulated carrier, making it possible to continue normal data transmission.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, since the code error is detected when it occurs, it is necessary to detect malfunction of the modem device before the code error occurs. The disadvantage is that it cannot be prevented from occurring.

SUMMARY OF THE INVENTION An object of the present invention is to provide a modem device that can prevent the equalizer from dispersing even when a disturbance is applied, and can quickly return to a normal state after the disturbance ends. It is said that

[0007]

Means for Solving the Problems In order to achieve the above object, the present invention provides a demodulating means for demodulating a received signal using a demodulated carrier, and a phase error signal for detecting a phase error of the demodulated carrier to generate a phase error signal. an error detection means, a phase correction means for correcting a phase error based on a phase error signal, a signal deterioration detection means for detecting a level change of a received signal and generating a deterioration detection signal, and a phase error signal based on the deterioration detection signal. The present invention is characterized by comprising a control means for controlling transmission to the phase correction means.

[0008] The present invention also includes demodulating means for demodulating a received signal using a demodulated carrier, phase error detecting means for detecting a phase error of the demodulated carrier and generating a phase error signal, and correcting the phase error based on the phase error signal. a phase correction means for performing;
a determiner that compares the demodulated signal with the original value and generates an error signal indicating the deviation; a signal deterioration detection means that detects the level of the error signal and generates a deterioration detection signal;
The present invention is characterized by comprising a control means for controlling transmission of the phase error signal to the phase correction means based on the deterioration detection signal.

Further, the control means is configured to stop transmitting the phase error signal to the phase correction means in response to the deterioration detection signal, or attenuate the phase error signal and transmit it to the phase correction means. It is characterized by

0010

In the modem device configured as described above, the signal deterioration detection means detects a change in the level of the received signal, and when this is greater than, for example, a certain reference value, it generates a deterioration detection signal to that effect. The control means controls transmission of the phase error signal from the phase error detection means to the phase correction means when receiving the deterioration detection signal indicating that the level change of the received signal is larger than the reference value. For example, when the level change of the received signal is large due to the occurrence of a disturbance, the control means stops transmitting the phase error signal to the phase correction means using the deterioration detection signal, or attenuates the phase error signal and transmits the phase error signal to the phase correction means. to prevent phase error correction from being performed based on a phase error signal that may be erroneous due to disturbance.

Furthermore, the signal deterioration detecting means may detect the level of the error signal from the determining means instead of detecting the level change of the received signal.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a block diagram of a first embodiment of a modem device according to the present invention. Referring to FIG. 1, this modem device includes an automatic level adjustment means 101 that adjusts the level of a received signal RS, a demodulated carrier generation means 108 that generates a demodulated carrier signal, and a demodulated carrier signal that converts the level-adjusted received signal LRS into a demodulated carrier signal. demodulating means 102 that demodulates using
Complex baseband signal C output from demodulation means 102
A low-pass filter 105 that removes unnecessary high-frequency components from the BS, an equalizer 106 that corrects transmission path characteristics for the output signal from the low-pass filter 105, and an equalizer 1.
The output signal CBSF from 06 is set to a predetermined reference value C.
Determiner 107 that compares with RF and outputs decoded output CO
, the output signal CBSF from the equalizer 106 and the reference value CR
Phase error detection means 200 that performs subtraction with F to detect the phase error of the demodulated carrier and generate a phase error signal PES.
, a loop filter 113 that removes the high frequency component of the phase error signal PES and supplies it to the demodulation carrier generation means 108 as a control input CI, and a level-adjusted received signal LR.
The signal deterioration detection means 109 detects a level change of S and outputs a deterioration detection signal DS, and the control means 112 controls transmission of the phase error signal PES to the loop filter 113 based on the deterioration detection signal DS. There is.

Specifically, the demodulating means 102 includes a multiplier 1
03, 104, demodulated carrier generation means 10
The demodulated carrier signals CS and CC having a phase difference of 90° from each other are multiplied and demodulated by the received signal LRS in multipliers 103 and 104, respectively, and are output as a complex baseband signal CBS.

Further, the demodulated carrier generation means 108 is composed of, for example, an oscillator, and the demodulated carrier signals CS and CC, which have a phase difference of 90° from each other and are to be given to the demodulated means 102, have a frequency determined by the control input CI. It is output as .

In this first embodiment, the phase error is corrected by directly controlling the oscillation frequency of the demodulating carrier generating means 108, and therefore the demodulating carrier generating means 108 corrects the phase error. It is configured to also serve as a correction means. In such a configuration, the loop of the phase error detection means 200, the loop filter 113, and the demodulation carrier generation means 108 is a phase control loop (PLL).
It becomes.

Further, the signal deterioration detection means 109 specifically includes a level detection means 110 that detects the level of the received signal and outputs a level signal LS;
The comparison means 111 compares the detected level signal LS with a predetermined reference signal RFS and outputs a deterioration detection signal DS.

For example, when trying to detect an abnormality in which the signal level decreases, such as a momentary disconnection of a line, the comparison means 111 detects the presence of signal deterioration when the level signal LS becomes smaller than the reference signal RFS. For example, logical value “1”
”, and when the level signal LS becomes larger than the reference signal RFS, it may be configured to output a deterioration detection signal DS with a logic value of “0”, which does not indicate the presence of signal deterioration. can.

Alternatively, when attempting to detect an abnormality accompanied by an increase in the signal level, such as the mixing of billing pulses in a telephone line, signal deterioration can be detected when the level signal LS becomes larger than the reference signal RFS. For example, a deterioration detection signal DS of logical value "1" indicating the existence of the deterioration detection signal DS is output, and a level signal LS
It may be configured to output a deterioration detection signal DS, which does not indicate the presence of signal deterioration and has a logical value of "0", for example, when the signal becomes smaller than the reference signal RFS.

Alternatively, when attempting to detect both an abnormality accompanied by a decrease in the signal level and an abnormality accompanied by an increase in the signal level, the magnitude of the level signal LS is set within a predetermined range. A deterioration detection signal DS with a logical value of "1", for example, which indicates the presence of signal deterioration when the signal deviates from the range, is output, and a deterioration detection signal DS with a logical value of "0", which does not indicate the presence of signal deterioration when it is within a predetermined range, is output. It may be configured to output the detection signal DS. Note that the predetermined range can be set, for example, as a range from 0.5 times to twice the magnitude of the reference signal RFS.

Next, the processing operation of the modem device of the first embodiment having such a configuration will be explained. Assuming that a modem device is used on the receiving side, when a received signal RS is input from the transmitting side to this modem device via a transmission path, the received signal RS is adjusted to an appropriate level by automatic level adjusting means 101 and then demodulated by demodulating means 102. join. In the demodulating means 102, a multiplier 103 multiplies the demodulated carrier signals CS and CC, which have a phase difference of 90 degrees from each other, from the demodulated carrier generating means 108 and the received signal LRS from the automatic level adjusting means 101.
, 104. Thereby, the complex baseband signal CBS output from the demodulating means 102 has unnecessary high frequency components removed by the low pass filter 105, and then is applied to the equalizer 106, where the transmission path characteristics are corrected. After that, the output signal C from the equalizer 106
The BSF is compared with a predetermined reference value CRF in the determiner 107 and output as a decoded output CO.

At this time, the phase error detection means 200
The output signal CBSF from the equalizer 106 and the reference value CRF are subtracted, and the difference is passed to the control means 112 as a phase error signal PES. When no disturbance is applied to the transmission path and the deterioration detection signal DS from the signal deterioration detection means 109 does not indicate the presence of signal deterioration, the control means 11
2 is a phase error signal PE from the phase error detection means 200.
S is directly transmitted to the loop filter 113.

Thereby, the loop filter 113 removes the high frequency component from the phase error signal PES and supplies it as the control input CI to the demodulation carrier generation means 108. In the demodulated carrier generation means 108, control inputs CI,
That is, the oscillation frequency is directly controlled by the phase error signal PES, thereby correcting the phase error.

In this way, when no disturbance is applied, the phase error detection means 200 and the loop filter 11
3. Phase control loop (P
Phase error correction is performed by LL).

When operating under such conditions, if a disturbance is applied to the transmission path, the automatic level adjustment means 101 is generally configured not to follow rapid level changes in order to prevent signal distortion. However, if the above-mentioned disturbance is accompanied by a rapid level change, the level change remains in the output LRS of the automatic level adjustment means 101. The level detection means 110 of the signal deterioration detection means 109 detects this level change as a level signal LS, and the comparison means 11
1, this is compared with the reference value RFS. As a result,
When the disturbance is sudden, for example, accompanied by a rapid level change, the deterioration detection signal DS from the signal deterioration detection means 109 indicates the presence of signal deterioration, and in this case, the control means 112 detects the phase error. The transmission of the phase error signal PES from the detection means 200 to the loop filter 113 is stopped.

[0025] This makes it possible to prevent the demodulation carrier generation means 108 from correcting the phase error based on the phase error signal PES that may be incorrect due to disturbance, and effectively prevent malfunctions of the phase control loop. It becomes possible to do so. In other words, even if a disturbance etc. is added to the transmission path, the equalizer etc. performs phase control before it diverges.
It is possible to prevent incorrect phase control of the demodulated carrier signal PLL due to disturbances, etc., prevent divergence of the equalizer, etc., and quickly restore the device itself to a steady state after the disturbance, etc. ends. .

Note that the control means 112 can also be configured as shown in FIG. In the example of FIG. 2, the control means 1
12 is composed of an attenuator 300 having a predetermined amount of attenuation and a switch 301 that switches signals based on the deterioration detection signal DS. If the state indicates the existence of the signal, for example, the logical value is "1", the phase error signal PES is transmitted via the attenuator 300 to the loop filter 113 and the demodulation carrier generation means 108, and the deterioration detection signal DS indicates the deterioration of the signal. For example, when the logic value is "0", the phase error signal PES is transmitted directly to the loop filter 113 and the demodulated carrier generating means 108 without passing through the attenuator 300.

In such a configuration, the signal deterioration detection means 1
When the deterioration detection signal DS from 09 indicates the presence of signal deterioration, the switch 301 of the control means 112
The phase error signal PES from the phase error detection means 200 is switched to be transmitted to the loop filter 113 via the attenuator 300. That is, when the signal deterioration detection means 109 detects signal deterioration, the control means 112 outputs the phase error signal PES, which is the output of the phase error detection means 200, to the attenuator 30.
It is attenuated by 0 and transmitted to the loop filter 113. In this way, in the example of FIG. 2, when signal deterioration is detected, the possibly erroneous phase error signal PES is attenuated and then transmitted to the loop filter 113. Also, the situation in which the phase control loop malfunctions can be reduced.

FIG. 3 is a block diagram of a second embodiment of a modem device according to the present invention. In the modem device of FIG. 3, the determiner 107 compares the output signal CBSF from the equalizer 106 with a predetermined reference value CRF and outputs the decoded output CO, and at the same time outputs the decoded output CO. An error signal EO indicating the amount of deviation is output. Furthermore, the signal deterioration detecting means 109 in FIG.
It is designed to detect signal deterioration. That is, the comparison means 111 of the signal deterioration detection means 109 compares the error signal EO with a predetermined reference signal RFS, outputs a deterioration detection signal DS, and supplies this to the control means 112.

Next, the processing operation of the modem device of the second embodiment having such a configuration will be explained. When the output signal CBSF is output from the equalizer 106, the determiner 107
This output signal CBSF is compared with a predetermined reference value CRF, and at the same time a decoded output CO is output, and an error signal EO indicating the amount of deviation between the output signal CBSF and the reference value CRF is output.
Output. It should be noted that since CRF and CBSF are complex numbers, they are two-dimensional vector quantities, and therefore, the error signal EO is calculated and outputted by the determiner 107 as shown in the following equation.

[0030]

[Math 1]

Here, re indicates the real part and im indicates the imaginary part. The EO calculated by equation 1 represents the difference between the value that the received signal should have and the actually received value, so
When signal degradation in the transmission path increases, EO also increases. Therefore, by monitoring the magnitude of EO, signal deterioration in the transmission path can be detected.

That is, when the error signal EO of the determiner 107 is applied to the signal deterioration detecting means 109, the signal deterioration detecting means 109 converts the error signal EO into a predetermined reference signal RF.
If EO is larger than RFS, for example, the deterioration detection signal DS of logical value "1" is set, and EO is set to RFS.
If it is smaller, for example, a deterioration detection signal DS with a logical value of "0" is output to the control means 112.

The control means 112 controls the signal deterioration detection means 10.
When the deterioration detection signal DS from 9 indicates the presence of signal deterioration, for example, has a logical value of "1", the transmission of PES to CI is stopped, and the state in which DS does not indicate signal deterioration;
For example, if the logical value is “0”, PES is used as is.
Communicate to. Therefore, when the signal deterioration detection means 109 detects signal deterioration by inspecting the error signal, the control means 1
12 prevents the phase error signal PES, which is the output of the phase error detection means 200, from being transmitted to the loop filter 113, and prevents the phase control loop from malfunctioning due to the possibly erroneous phase error signal PES. be able to.

Note that the control means 112 can also be configured as shown in FIG. 4, as in the first embodiment. In this case, as in FIG. 2, the control means 112 is composed of an attenuator 300 having a predetermined amount of attenuation, and a switch 301 that switches signals according to the deterioration detection signal DS.
When the signal deterioration detection means 109 detects signal deterioration by detecting the error signal EO, the control means 112 attenuates the phase error signal PES, which is the output of the phase error detection means 200, with an attenuator 300 and transmits it to the loop filter 113. death,
It is possible to prevent malfunctions of the phase control loop due to a possibly erroneous phase error signal PES.

FIG. 5 is a block diagram of a third embodiment of a modem device according to the present invention. In the modem devices of the first and second embodiments described above, the demodulation carrier generation means 108 also served as the phase error correction means, but in the third embodiment, the demodulation carrier generation means 108 also functions as the phase error correction means, as shown in FIG. is an oscillator with a fixed frequency, and the phase error correction means is made up of an equalizer 106 and a determiner 10 separately from the demodulation carrier generation means 108.
7.

Referring to FIG. 5, the phase error correction means 40
0 is the phase error correction amount θ from the loop filter 113
an exponential function generator 402 that generates an exponential function exp{-jθ} according to the phase error correction amount θ; and a complex multiplier that multiplies the demodulated complex baseband signal by the exponential function exp{-jθ} that corresponds to the phase error correction amount θ. 401, and the phase error can be corrected by multiplying the demodulated complex baseband signal by an exponential function exp{-jθ} corresponding to the phase error correction amount θ.

Note that the control means 112 can also be constructed as shown in FIG. 6, as in the first and second embodiments. In this case, as in FIGS. 2 and 4, the control means 1
12 is composed of an attenuator 300 having a predetermined attenuation amount and a switch 301 that switches signals according to the deterioration detection signal DS. When the signal deterioration detection means 109 detects signal deterioration, the control means 112 Phase error detection means 20
The phase error signal PES, which is the output of 0, is attenuated by the attenuator 300 and transmitted to the loop filter 113, thereby making it possible to prevent the phase control loop from malfunctioning due to the possibly erroneous phase error signal PES.

In the third embodiment, although FIG. 5 corresponds to FIG. 1, in the modem device of FIG. By providing a correction means and inputting the phase error correction amount θ from the loop filter 113 to the correction means, phase error correction can be performed.

[0039]

[Effects of the Invention] As explained above, according to the present invention,
The control means controls the transmission of the phase error signal to the phase correction means based on a deterioration detection signal outputted from the signal deterioration detection means in accordance with a level change of the received signal or the level of the error signal, and the control means controls the transmission of the phase error signal to the phase correction means. When the level change of the received signal or the level of the error signal becomes larger than a certain reference value due to the addition of the above, the control means stops transmitting the phase error signal to the phase correction means based on the deterioration detection signal to that effect, or Since the phase error signal is attenuated and transmitted to the phase correction means, this prevents phase error correction from being performed based on the phase error signal that may be erroneous due to disturbance, and prevents malfunction of the modem device. This allows the modem device to quickly return to its normal state after the disturbance ends.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of a modem device according to the present invention.

FIG. 2 is a diagram showing a configuration example of a control means of the modem device in FIG. 1;

FIG. 3 is a block diagram of a second embodiment of a modem device according to the present invention.

FIG. 4 is a diagram showing a configuration example of a control means of the modem device of FIG. 3;

FIG. 5 is a block diagram of a third embodiment of a modem device according to the present invention.

FIG. 6 is a diagram showing an example of the configuration of a control means of the modem device in FIG. 5;

[Explanation of symbols]

101 Automatic level adjustment means 102 Demodulation means 105 Low pass filter 106 Equalizer 107 Judgment device 108 Demodulation carrier generation means 109 Signal deterioration detection means 112 Control means 113 Loop filter 200 Phase error detection means

Claims (4)

[Claims] 1. A demodulating means for demodulating a received signal using a demodulated carrier; a phase error detecting means for detecting a phase error of the demodulated carrier and generating a phase error signal; and a phase error detection means for correcting the phase error based on the phase error signal. a signal deterioration detection means for detecting a level change in a received signal and generating a deterioration detection signal; and a control means for controlling transmission of a phase error signal to the phase correction means based on the deterioration detection signal. A modem device characterized by: 2. Demodulating means for demodulating a received signal using a demodulated carrier, phase error detecting means for detecting a phase error of the demodulated carrier and generating a phase error signal, and correcting the phase error based on the phase error signal. a determiner that compares the demodulated signal with the original value and generates an error signal indicating the deviation; and a signal deterioration detection means that detects the level of the error signal and generates a deterioration detection signal. and control means for controlling transmission of the phase error signal to the phase correction means based on the deterioration detection signal. 3. The modem device according to claim 1, wherein the control means stops transmitting the phase error signal to the phase correction means in response to the deterioration detection signal. 4. The modem device according to claim 1, wherein the control means is configured to attenuate the phase error signal using the deterioration detection signal and transmit it to the phase correction means.