JP2533145B2 - CAPC method - Google Patents

Description

Detailed Description of the Invention [Table of Contents] Outline Industrial field of application Conventional technology Problems to be solved by the invention Means for solving problems Action Example I. Correspondence between example and FIG. II. Assumptions in the Embodiment III. Configuration of the Embodiment IV. Operation of the Embodiment V. Summary of the Embodiment VI. Modified Embodiment of the Invention [Summary] Regarding the CAPC system applied to the receiving unit of the modem, reception The data point distance of the equalized digital demodulated signal is calculated for the purpose of preventing the phase jitter correction from being affected even if the signal has noise, and the data point distance is set to a predetermined threshold value. If it is larger than the above, a signal obtained by normalizing the digital demodulated signal with a normalized data signal is used for the correction of the conventional CAPC method, and if not, it is configured not to be used, and the phase jitter correction is correctly performed by noise. Prevent it from disappearing To reduce the error in the data judgment due to noise.

[Industrial applications]

The present invention relates to a CAPC system, and more particularly, to a CAPC system adapted to be applied to a receiving section of a modem.

[Conventional technology]

Conventionally, the receiving section of a modem to which the CAPC (Carrier Automatic Phase Control) method is applied is shown by function as shown in FIG. That is, roughly classified by function, an automatic gain control circuit (AGC) 411, a demodulator (DEM) 413, a roll-off filter (ROF) 415, an automatic equalizer (AEQ) 417, and a determination circuit 425.
Consists of

Here, the received signal (analog signal) introduced into this modem via the analog line is first gain-compensated by the automatic gain control circuit 411. This automatic gain control circuit 4
The output signal (analog signal) gain-compensated by 11 is sampled and demodulated by the demodulator 413, and at the time of its analog-digital conversion, the roll-off filter 415 removes the influence of folding in the demodulator 413. The digital signal obtained by demodulation by the demodulator 413 and the roll-off filter 415 is a signal on the baseband, and is then supplied to the automatic equalizer 417.
Here, distortions due to various line characteristics are compensated.

That is, the automatic gain control circuit 411 compensates for the signal amplitude, the roll-off filter 415 compensates for intersymbol interference, and the automatic equalizer 417 compensates static characteristics (frequency characteristics, delay characteristics, etc.).

However, the line characteristics change dynamically. For example, carrier jitter will be present in the demodulated received signal 418. Such a dynamically fluctuating one cannot be compensated by the above circuits, and therefore, even if the demodulated received signal 418 is supplied to the judging circuit 425 as it is, an error occurs in the data judgment. Therefore, a compensation circuit based on CAPC is interposed between the automatic equalizer 417 and the determination circuit 425.

There, the demodulated received signal 4 obtained from the automatic equalizer 417
18 is supplied to one end of the multiplier 421.

The received signal for judgment 423 from the multiplier 421 is the judgment circuit 425.
And a determination data output signal 427 from the determination circuit 425 is supplied to a data terminal (DTE) (not shown). Also,
The normalized data signal 429 is output from the determination circuit 425 to the multiplier 41.
Supplied to the other end of 9. The CAPC correction data signal 431 from the multiplier 419 is input to the CAPC correction circuit 433, and the phase error correction amount output signal 435 is supplied to the other end of the multiplier 421.

In this way, based on the normalized data signal 429 from the judgment circuit 425, the CAPC correction circuit 433 can correct the phase change caused by the fluctuation of the dynamic characteristic.

In the operation of the CAPC system configured as described above, the demodulated received signal 418 from the automatic equalizer 417 is transmitted on the complex plane by the fifth
It is assumed that it is the R point as shown in FIG.

That is, the vector that points to this point Is.

At this time, the point D indicated by the decision data output signal 427 and the normalized data N point indicated by the normalized data signal 429 are output from the decision circuit 425.

Now the vector of point D It is represented by. Also, the vector of normalized data N points It is represented by.

by the way, Complex conjugate of The relationship is established.

Therefore, By taking ((b) of FIG. 4), the phase error correction amount of the demodulated received signal 418 can be created as follows.

If A / A _D ≈1, then the result of equation (5) is
−sin θ ₀ ≈−θ ₀ , and this θ ₀ is extremely small.

Where the normalized data as the normalized data signal 429 Is the demodulated received signal 418 This is done not only to find the magnitude of the amplitude A of P.

[Problems to be solved by the invention]

By the way, in the conventional CAPC correction method described above,
Demodulated received signal 418 If there is noise on the When applied, the noise may be enlarged, which greatly hinders the phase jitter correction. An example of the phase error correction amount output (phase error correction amount output signal 435) when such noise and phase jitter are included is shown in FIG.

The problem caused by the inclusion of such noise and phase jitter becomes remarkable in the case of a high data transmission rate such as 19.2 kbit / s.

For example, the noise expansion in the case of being determined as the innermost point in the data point arrangement is about 6 times, and the noise expansion is about 2 at the second point.
It was double.

The present invention was created in view of such a point, and an object thereof is to provide a CAPC method that does not affect the phase jitter correction even if the received signal has noise. .

[Means for solving problems]

FIG. 1 is a block diagram of the principle of the CAPC system of the present invention.

In the figure, an equalizing means 115 receives a digital demodulated signal obtained by demodulating an analog signal received via an analog line, equalizes the digital demodulated signal, and outputs the result as an equalized output signal.

The CAPC correction means 121 corrects the equalized output signal with a correction instruction signal and outputs the corrected signal as a signal to be judged.

The judging means 127 receives the judgment signal, judges data, outputs a judgment data output signal showing the data judgment result supplied to the digital device in the next stage, and normalizes the judgment signal. The normalized data signal of is output.

The calculating means 116 calculates the data point distance based on the equalized output signal.

Comparing means 131 compares the data point distance with a predetermined threshold value and outputs a comparison signal according to the comparison result, and the comparison signal, the signal to be judged, and the normalized data signal. The correction instruction signal is output based on

The present invention is configured to correct the equalized output signal by the correction instruction signal based on the comparison signal, the determined signal, and the normalized data signal.

[Action]

After the analog signal received via the analog line is demodulated, the digital demodulated signal is provided in the equalizing means 115 with compensation for static characteristic changes of the analog line.

The data point distance output from the calculation means 116 is supplied to the comparison means 131. To the comparing means 131, the signal to be judged and the normalized data signal are supplied from the CAPC correcting means 121 and the judging means 127. The comparing means 131 outputs the correction instruction signal based on the comparison signal of the comparison result of the data point distance and the predetermined threshold value, the judged signal, and the normalized data signal.

The CAPC correction means 121 gives a correction according to the correction instruction signal supplied from the comparison means 131 to the equalization output signal output from the equalization means 115.

The determination means 127 performs data determination on the determination target signal output from the CAPC correction means 121 and outputs a determination data output signal.

Thus, the comparison signal indicating the comparison result of the data point distance of the equalized output signal and the predetermined threshold value, the signal to be determined, the correction instruction signal based on the normalized data signal is output, Since the equalization output signal is corrected by the correction instruction signal, the correction instruction signal that has been conventionally output regardless of the magnitude of noise is not output when the influence due to noise becomes large. Therefore, the error in data determination due to noise is reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows the configuration of the CAPC system in one embodiment of the present invention.

I. Correspondence between Embodiment and FIG. 1 Here, the correspondence between the embodiment of the present invention and FIG. 1 will be described.

 The equalizing means 115 corresponds to the automatic equalizer 417.

 The calculating means 116 corresponds to the square distance calculating circuit 251.

The CAPC correction means 121 corresponds to the CAPC correction circuit 433 and the multiplier 421.

 The determination means 127 corresponds to the determination circuit 425.

The comparison means 131 corresponds to the comparator 257 and the multipliers 119 and 261.

An embodiment of the present invention will be described below on the basis of the above correspondence.

II. Premise in the embodiment The data transmission rate handled by the modem is, for example, 19.2kb
If it's very fast, like it / s, the data point array is 16
The score is 0, which is extremely high. In that case, inside the eye pattern, the vector of normalized data The amplitude (distance) of the If there is noise on the background, the noise will be magnified.

From this point of view, in this embodiment, the normalized data is not used for the data inside the eye pattern. That is, the normal data is used for CAPC correction only with respect to the received signal of a certain fixed magnitude.

III. Structure of Embodiment The overall structure of the CAPC system in the embodiment of the present invention is the same as that shown in FIG. A characteristic part of the embodiment of the present invention is that a square distance calculation circuit 251, a comparator 257, and a multiplier 261 are provided in the conventional CAPC system shown in FIG. Therefore, the same reference numerals as those in FIG. 3 indicate corresponding circuit portions, and detailed description thereof will be omitted.

In FIG. 2, the digital demodulated signal demodulated by the demodulator 413 of FIG. 3 and passed through the roll-off filter 415 is equalized by the automatic equalizer 417. The demodulated received signal 418 (equalized output signal described in the claims) output from the automatic equalizer 417 is supplied to one end of the multiplier 421.

The received signal for determination 223 from the multiplier 421 is the determination circuit 425.
And the determination data output signal 227 from the determination circuit 425 is supplied to a data terminal (DTE) (not shown). The received signal for judgment 223 corresponds to the signal to be judged described in the scope of claims, and is the same as the conventional signal described in the section [Prior Art].
It is the same signal as the received signal for determination 423 in the CAPC method, and is the signal that is the target of signal point determination. Further, the normalization data signal 229 is supplied from the determination circuit 425 to the multiplier 419.

The normalized data signal 229 is used to normalize the demodulated received signal 418 to generate the phase error correction amount signal in the CAPC system, as described in the eighth negative sixth row to the last row of the ninth page. It is a signal.

The demodulated received signal 418 is introduced into the square distance calculation circuit 251, and the square distance signal 253 representing the square distance calculated by the square distance calculation circuit 251 is supplied to the non-inverting input terminal of the comparator 257. The square distance signal corresponds to the data point distance described in the claims and represents, for example, the distance from the origin on the phase plane. A threshold signal 255 representing the distance threshold r is supplied to the inverting input terminal of the comparator 257.

The comparison output signal 259 representing the comparison result in the comparator 257 is supplied to one end of the newly provided multiplier 261 and the demodulation / normalization multiplication signal from the multiplier 419 is supplied to the other end of the multiplier 261. 231 is introduced. Further, the CAPC correction data signal 232 from the multiplier 261 is supplied to the CAPC correction circuit 433.

The data transmission speed handled by this modem is 19.2 kbit / s.
, The data point array is 160 points. In that case, since the square distances of, for example, four points arranged inside are known, the distance based on them is set as the threshold r. According to whether the square distance is larger than the threshold value r, it is determined whether the data is inside or outside the four points.

The phase error correction amount output signal 235 from the CAPC correction circuit 433 is supplied to the other end of the multiplier 421.

The phase error correction amount signal 235 corresponds to the correction instruction signal described in the claims.

In this way, the CAPC correction circuit 433 can be corrected based on the normalized data signal 229 from the determination circuit 425.

IV. Operation of Example Next, an example of the above-described configuration will be described.

In the figure, a received signal (analog signal) introduced into the modem via an analog line is demodulated, digitally converted, and then equalized by an automatic equalizer 417.

The demodulated received signal 418 thus output is supplied to the multiplier 421. The demodulated received signal 418 is also supplied to the square distance calculation circuit 251. This squared distance calculation circuit 251
The squared distance between the data points is obtained based on the demodulated received signal 418 introduced.

The comparator 257 compares the squared distance represented by the squared distance signal 253 with the threshold value r. If the calculated square distance is larger than the threshold value r, the comparison output signal 259 takes "1", and if the square distance is smaller than the threshold value r, the comparison output signal 259 takes "0".

Now, in the demodulated received signal 418, the square distance calculation circuit 2
If the squared distance obtained at 51 is smaller than the threshold value r, the comparison output signal 259 taking "0" is supplied to the multiplier 261. Therefore, even if the demodulation / normalization multiplication signal 231 obtained from the multiplier 419 based on the normalized data signal 229 and the received signal for determination 223 is introduced into the multiplier 261, the CAPC correction data signal 232 is “0”. Is. Accordingly, the CAPC correction circuit 4
33 does not receive new feedback and the phase error correction amount output signal 235 holds the correction signal pulled up to the previous symbol. In this case, for the data points inside, the CAPC
Since the noise is not expanded with the correction, there is no error in data determination due to the noise.

On the other hand, in the demodulated received signal 418, if the squared distance obtained by the squared distance calculation circuit 251 is larger than the threshold value r, the comparison output signal 259 that takes “1” is the multiplier 261.
Is supplied to. As a result, the demodulation / normalization multiplication signal 231 obtained from the multiplier 419 based on the normalized data signal 229 and the received signal for determination 223 is introduced into the multiplier 261, and the CAPC correction circuit 232 is directly used as the CAPC correction circuit. Supplied to the 433. In this case, the CAPC correction circuit 433 supplies the jitter-corrected phase error correction amount output signal 235 to the multiplier 421. Therefore, the demodulated received signal 418 is output from the multiplier 421.
The received signal for judgment 223 whose jitter has been corrected by the product of the output signal 235 and the phase error correction amount output signal 235 is supplied to the judgment circuit 425. As a result, the data points on the outer side are subjected to CAPC correction in the same manner as in the conventional example, and then data determination is performed.

V. Summary of Embodiments As described above, in order to obtain the CAPC correction data signal 232 to be supplied to the CAPC correction circuit 433, the demodulation / reception is performed depending on whether the square distance indicated by the demodulation signal 418 is larger than the threshold value r. It determines whether to use the normalized multiplication signal 231. That is, when the noise is likely to be enlarged, the phase jitter correction amount is not used to avoid the enlargement due to the noise.

VI. Modified Embodiment of the Invention In the above-described embodiment of the present invention, after the demodulation / normalization multiplication signal 231 is obtained, the comparison output signal 259 is multiplied, but the order of this multiplication is It is not limited to this.
For example, the comparison output signal 259 may be multiplied by the normalized data signal 229, and then the result may be multiplied by the demodulated signal 418. By doing so, it is possible to determine whether to use the signal 229 obtained by normalizing the demodulated signal 418 with the normalized data signal 229 depending on whether or not the squared distance indicated by the demodulated signal 418 is larger than the threshold value r. .

Further, although the threshold value r is based on the distances at the four inner points in the eye pattern, the threshold value r is not limited to this, and a plurality of data points may be taken as necessary. It may be determined in consideration of the data transmission rate handled by the modem.

Furthermore, in “I. Correspondence between Example and FIG. 1”,
Although the correspondence between the present invention and the embodiments has been described, the present invention is not limited to this, and it will be easily understood by those skilled in the art that there are various modifications.

〔The invention's effect〕

As described above, according to the present invention, depending on whether the data point distance of the equalized output signal is larger than a predetermined threshold value,
Since it is determined whether to use the signal obtained by correcting the signal to be judged with the normalized data signal for CAPC correction, it is possible to reduce the error in data judgment due to noise.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the CAPC system of the present invention, FIG. 2 is a block diagram of the structure of the CAPC system according to an embodiment of the present invention, FIG. 3 is a block diagram of a conventional example, and FIG. FIG. 5 and FIG. 5 are explanatory diagrams of the state of the amount of phase jitter in the conventional example. In the figure, 115 is equalization means, 116 is calculation means, 121 is CAPC correction means, 1
27 is a judging means, 131 is a comparing means, 223 and 423 are received signals for judgment, 227 and 427 are judgment data output signals, 229 and 429 are normalized data signals, 231 is a demodulation / normalized multiplication signal, 232 is a CAPC correction data signal, and 235 and 435 are 235 and 435. Phase error correction amount output signal, 251
Is a square distance calculation circuit, 253 is a square distance signal, 255 is a threshold signal, 257 is a comparator, 257 is a comparison output signal, 411 is an automatic gain control circuit, 413 is a demodulator, 415 is a roll-off filter, and 417 is An automatic equalizer, 418 is a demodulated reception signal, 425 is a determination circuit, 431 is a CAPC correction data signal, and 433 is a CAPC correction circuit.

Claims (3)

(57) [Claims] 1. An equalizing means for receiving a digital demodulated signal obtained by demodulating an analog signal received via an analog line, equalizing the digital demodulated signal, and outputting the result as an equalized output signal, The digitalized output signal is corrected by the correction instruction signal and the corrected signal is output as the judgment target signal; and the data to be supplied to the digital device at the next stage for receiving the judgment target signal for data judgment. Judgment means for outputting a judgment data output signal indicating a judgment result and outputting a normalized data signal for normalizing the signal to be judged, and calculating means for calculating a data point distance based on the equalized output signal. And comparing the data point distance with a predetermined threshold value, outputting a comparison signal according to the comparison result, and comparing the comparison signal, the determined signal, and the normalized data. CAPC method characterized by comprising a comparison means for outputting said correction instruction signal based on the signal. 2. The comparing means, if the data point distance represented by the equalized output signal is larger than the threshold value, the signal to be judged is normalized with the normalized data signal. As the correction instruction signal, if the data point distance represented by the equalized output signal is smaller than the threshold value, do not output a signal obtained by normalizing the signal to be judged with the normalized data signal. Claim 1 characterized by being configured to control
The CAPC method described in the section. 3. The CAPC correction means, when the correction instruction signal is output, outputs a determination signal based on the correction instruction signal and the equalization output signal, and does not output the correction instruction signal. The CAPC according to claim 1 or 2, wherein the equalized output signal is output as a signal to be determined.
method.