JP2524053B2 - Modem device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is based on CCITT (International Telegraph and Telephone Consultative Committee) Recommendation V.6. The present invention relates to a modem device standardized in 29, and more particularly to a modem transmitter for determining a sync signal with respect to a data rate used for controlling a carrier of a data transmitter.

[0002]

2. Description of the Related Art CCITT V. The sync signal for the data rate recommended in 29 is divided into four segments as shown in FIG. In the segment 2 of these synchronization signals, two signal elements A and B are alternately transmitted as shown in the signal space diagram of FIG. That is, the first transmitted signal element A is
It has a relative amplitude value of 3 and an absolute phase of 180 °. The second transmitted signal element B depends on the transmission rate, eg has a relative amplitude value of 3√2 and an absolute phase of 315 ° when the data rate is 9600 bits / s.

In the segment 3 of the synchronizing signal, two signal elements C and D as shown in FIG. 3 are transmitted according to the equalizer adjustment pattern. Sync signal segment 4
In the above, a continuous binary "1" is added to the input of the data scrambler and encoded and transmitted. Then, after these synchronization signals are transmitted, the transmitter carrier signal (CD, Data Carrier Detected) is turned on as shown in FIG. 4, and data transmission is started.

Conventionally, among these synchronizing signals, a timer is used for detecting in the segments 3 and 4, but in the segment 2, as shown in FIG. 5, a predetermined frequency (500 Hz, 1700 Hz, 2900Hz
) The energy level in the spectrum exceeds the preset reference level (Example: When the energy level of three spectrums is -15 (dB), the reference level is -9 (dB)). Was there.

[0005]

When detecting the energy of the spectrum of the predetermined frequency shown in FIG. 5, there is a confusing signal and this is shown in FIG. In FIG.
(A) includes white noise, (b) is affected by an EP tone (Talker Echo Protection Signal), and (c) is V.V. This is the case where a signal of 21 300 bit / s is received. Of these, in the cases of (b) and (c), the pattern of the spectrum of segment 2 is clearly different from the signal pattern, so it is possible to make a determination. .

[0006] Here, white noise means noise including components of all frequencies such as sunlight. In the case of this white noise, a predetermined frequency (500 Hz, 1700 Hz,
There is a problem that the energy level in the spectrum of 2900 Hz) may temporarily exceed the preset reference level, resulting in erroneous detection.

The present invention has been made in view of the above problems, and provides a modem device capable of reliably detecting the sync signal of the segment 2 without malfunction even when receiving white noise. With the goal.

[0008]

In order to achieve the above object, the present invention provides a predetermined frequency (500 Hz, 1700 Hz) of a synchronizing signal.
z, 2900 Hz) is the standard energy level
And an energy level detector that detects whether the energy level exceeds the reference level.
If it is determined that the sum of the Y coordinates of the A and B signals in the sync signal becomes negative a predetermined number of times or more,
And a coordinate determination unit that determines that the segment 2 of the number is detected .

Further, the coordinate determination unit is configured to determine that the sum of the Y coordinates is a predetermined number of times or more and a negative predetermined value or less.

[0010]

As shown in FIG. 3, the Y coordinate of the A signal is 0, the Y coordinate of the B signal is negative, and the sum of the Y coordinates of the A signal and the B signal is theoretically always negative. Therefore, the A signal and B received alternately
The sum of the Y coordinates of the signals becomes negative a predetermined number of times or more, and the frequencies 500 Hz, 1700 Hz, which have an energy level higher than the reference level shown in FIG.
The synchronization signal of the segment 2 can be determined under the condition that the two conditions that 2900 Hz are detected are satisfied.

Further, by setting the condition that the sum of the Y coordinates of the A signal and the B signal is equal to or less than a negative predetermined value a predetermined number of times, it becomes possible to more accurately determine the synchronization signal of the segment 2.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, received data is converted into digital data by an analog / digital converter 1 and divided into two, one is multiplied by cos ωt by a multiplier 2 and the other is multiplied by SIN ωt by a multiplier 2, and these values are rolled off.・ Pass through the filter 4.

V. The signal recommended in 29 uses quadrature amplitude modulation. In quadrature amplitude modulation or phase modulation, when the amplitude characteristic and the delay characteristic in the transmission band are not symmetrical with respect to the carrier frequency, intersymbol interference occurs and causes transmission error. Therefore, it is necessary to flatten the amplitude characteristic and the delay characteristic. The equalizer does this, and the automatic equalizer changes following the change in the line characteristics.
The data passed through the roll-off filter 4 is passed through the automatic equalizer 5, and the carrier wave phase correction unit 6 corrects the phase of the carrier wave (1700 Hz). When the transmission data is represented by a constellation pattern as shown in FIG. 3, the constellation starts to rotate counterclockwise when the phase increases in the + direction, and rotates clockwise when the phase becomes the − direction, so the correction is made to be stationary.

The coordinate determination unit 7 represents the input signal in a star pattern as shown in FIG. 3, checks the X and Y coordinates of each point,
When the position is not correct, the feedback is made to the automatic equalizer 5 and the carrier wave phase correction unit 6. The determination unit 8 determines whether the received data is proper data, and the descramble 9 restores the signal scrambled on the transmission side.

The output of the A / D converter 1 is also input to a low pass filter (BPF) 3 to pass five frequency bands. The training reception control unit 10 inputs this data, examines the synchronization signal, and controls each unit based on the result.

Next, the determination of the synchronization signal of segment 2 in this embodiment will be described. First, the predetermined frequency of the sync signal in segment 2 input from BPF3 (500
The training reception control unit 10 determines whether the energy level of the spectrum at (Hz, 1700 Hz, 2900 Hz) exceeds a preset reference level. By the way, when white noise is received, it may temporarily exceed a preset reference level, and erroneous detection may occur if only the training reception control unit 10 is detected.

Therefore, the coordinate determining section 7 also makes a determination.
FIG. 7 shows the relationship between the synchronization signals A and B in segment 2. The two signal elements A and B are transmitted alternately. The segment 2 is determined by detecting a predetermined number of times whether the sum of the Y coordinates of the signals A and B is below the X axis, that is, is negative. In the case of the present embodiment, it was found that the detection can be performed 18 times, and the determination can be made with an error of about 2%.

However, when the elements are concentrated near the origin of the signal space diagram as shown in FIG. 8, the probability of misjudgment increases only by using the X axis as a reference. Therefore the reference level -L _AB provided in the negative direction parallel to the X axis as shown in FIG. 7, the signal A, as the sum of the Y coordinate of B to determine a synchronization signal of the segment 2 when less than the predetermined number of times -L _AB To do. In this embodiment the -L _AB = -0.75,
By detecting 18 times, the synchronization signal of segment 2 can be discriminated almost certainly.

[0020]

As is apparent from the above description, in the present invention, when the synchronization signal of the segment 2 is discriminated, it is detected that the sum of the Y coordinates of the signal A and the signal B becomes negative a predetermined number of times, It can be accurately determined. Further, the determination accuracy is improved by detecting that the sum of the Y coordinates is less than or equal to a predetermined negative value.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 CCITT V. Figure 29 shows the sync signal for the recommended data rate

FIG. 3 is a diagram showing a constellation pattern of a synchronization signal.

FIG. 4 is a diagram showing a synchronization signal and a data signal.

FIG. 5 is a diagram showing a spectrum of a predetermined frequency of segment 2.

FIG. 6 is a diagram showing signal noise.

FIG. 7 is a diagram showing an operation of a coordinate determination unit.

FIG. 8 is a diagram showing a case where elements are concentrated near the origin of a signal space.

[Explanation of symbols]

 1 A / D converter 2 Multiplier 3 Bandpass filter 4 Roll-off filter 5 Automatic equalizer 6 Carrier wave phase correction unit 7 Coordinate judgment unit 8 Judgment unit 9 Descrambler 10 Training reception control unit

Claims (2)

(57) [Claims] 1. A predetermined frequency of a synchronizing signal (500 Hz, 1700
Hz, 2900 Hz) is the standard level
Energy level detector that detects whether the energy level exceeds the reference level, and if the energy level exceeds the reference level.
If it is determined that the sum of the Y coordinates of the A and B signals in the sync signal becomes negative a predetermined number of times or more,
Modem device being characterized in that a coordinate determination unit for determining that it has detected the No. of the segment 2. 2. The modem device according to claim 1, wherein the coordinate determination unit determines that the sum of the Y coordinates is a predetermined number of times or more and a negative predetermined value or less.