JPH03226027A - Leading-in system for modem - Google Patents

Abstract

PURPOSE:To attain stable leading-in even when the reception signal with the periodicity is in use because of a few scramble stage number of a transmission section by generating a reference signal while keeping synchronization with a reception signal when the correlation with the reference signal stored in advance having periodicity and eliminating a component depending on the periodicity included in a decision error. CONSTITUTION:The reception signal from a demodulation and roll-off filter section 28 is given to a line deterioration factor elimination section 10 composed of an automatic equalizer AEQ and an automatic carrier frequency control circuit CAPC via a synchronization detection section 18 and outputs the reception signal cancelling a line deterioration factor according to an operating parameter set by leading-in the data. An output signal from the line deterioration factor elimination section 10 is given to a decision section 12 to decide a correct signal point with respect to the reception signal point. The decision by the decision section 12 uses the hard decision using a table or the soft decision using a Viterbi code corresponding to a treilis coding at a transmission side or both combination.

Description

[Detailed Description of the Invention] [Summary] Regarding a modem pull-in method in which the receiver is pulled in by a line reception signal without using a special training signal, the number of scrambling stages is small, so even if periodicity is added to the received signal, the line The aim is to enable stable data mode acquisition that is compatible with deterioration factors, by storing one cycle of the transmitted signal with periodicity depending on the number of scrambling stages of the transmitting modem as a reference signal, and by synchronizing this reference signal with the received signal. When detected, reference signals are generated sequentially while maintaining the synchronized state, and the previous judgment results are switched to the reference signals to create a judgment error and pull in that depends only on line characteristics, that is, eliminate line fluctuation factors. configured to draw in the operating parameters to be used.

[Industrial Application Field] The present invention relates to a modem pull-in method in which a receiving section is pulled in only by a line reception signal without using a training signal.

When data is pulled into the receiving section using a received signal from the line without using a special training signal, it is necessary that the received signals have no correlation, so pseudo-scrambling is performed on the transmitting side.

However, the line reception signal from a modem with a small number of scrambling stages has periodicity, and there is a problem that the automatic equalizer is drawn into equalization characteristics that are different from the original line characteristics. It is desirable to have an equalization characteristic that depends only on the line deterioration factor without any problems.

[Prior Art] Conventionally, in the data mode pull-in method of a multi-point connection modem as shown in FIG. After scrambling to eliminate
For example, the multiplier 64 performs amplitude orthogonal modulation and transmits the signal to the line 70. The reception section of the slave station modem 82 does not use a special training signal, but uses the line reception signal to control the automatic equalizer (A E Q) and automatic carrier frequency control circuit (CAP).
Data acquisition is performed to incorporate the operating parameters in C) into operating parameters that eliminate line deterioration factors.

Such data mode pull-in is based on the premise that the line reception signals input to the receiving section are uncorrelated, and therefore the transmitting modem 60 performs pseudo-scrambling.

FIG. 5 shows a scrambler 6 provided in the master station modem 60.
2 shows an example of shift register 6 with a predetermined number of stages.
6 and two adders 68, and a shift register 66
Shift stage be, b3. Output scrambled data as the sum of b7.

[Problem to be Solved by the Invention] However, in such a conventional data mode pull-in method, when the number of stages of the scrambler 62, that is, the number of stages of the shift register 66 used in the scrambler 62 is small, For example, in a modem that complies with CCIT Recommendation V, 27, periodicity appears in the input signal of the receiver, and due to the periodicity of the received signal that depends on the number of scrambling stages, the automatic equalizer can be adjusted to the original line characteristics shown in Figure 6. There is a problem in that the equalization characteristic is drawn into 100 which is different from 90.

In order to improve this problem, it is possible to reduce the periodicity of the signal by increasing the number of scrambling stages in the transmitter, but the scrambling method is specified by the CCIT recommendations, and in reality it is not possible to change the number of scrambling stages. It was impossible.

The present invention was made in view of these conventional problems, and provides a modem pull-in method that allows stable pull-in even when using a received signal with added periodicity due to a small number of scrambling stages in the transmitter. The purpose is to provide.

"Means to solve problems" FIG. 1 is a diagram explaining the principle of the present invention.

First, the present invention uses a subtracter 14 to determine the operating parameters of the line deterioration factor removing unit 10 provided in the receiving unit based on the line received signal from the transmitting modem with a small number of scrambling stages, without using a training signal. The present invention is directed to a modem pull-in method in which the modem pulls in operating parameters that match line deterioration factors based on the judgment error given by the difference between the input of the judgment unit 12 and the judgment result calculated by the method.

Regarding such a modem pull-in method, the present invention includes a reference signal storage unit 16 that stores in advance, as a reference signal, one cycle of a transmission signal having a periodicity depending on the number of scrambling steps of the transmitting modem, and a reference signal a synchronization detection unit 18 that compares a reference signal read from the storage unit 16 and set as a fixed value with a received signal and detects synchronization between the two; and a synchronization detection unit 18
When the synchronization detection output of the reference signal generation section 20 and the synchronization detection section 18 are obtained, the reference signal generation section 20 sequentially and repeatedly outputs the reference signal from the reference signal storage section 16 while maintaining the synchronization state. , a switching unit 22 that switches the determination result from the determination unit 12 for the subtracter 14 to the reference signal from the reference signal generation unit 20 to calculate a determination error;
It has been established that

Furthermore, the synchronization detection section 18 is configured to calculate the cross-correlation between the received signal sequence and the reference signal sequence, and generate a synchronization detection output when the cross-correlation value becomes a predetermined value or more.

[Operation] According to the pull-in method according to the present invention having such a configuration, when a received signal with periodicity added due to a small number of scrambling stages on the transmitting side is obtained, the reception signal having periodicity stored in advance is obtained. When the correlation with the reference signal is established, that is, when synchronization detection is performed, a reference signal is generated while maintaining synchronization with the received signal, and the reference signal is used in place of the determination result to determine the determination error, As a result, it is possible to remove the periodicity-dependent component included in the determination error, and to perform data acquisition for determining the operating parameters of the automatic equalizer and CAPC based on the determination error component that depends only on the line characteristics.

[Embodiment] FIG. 2 is a block diagram showing an embodiment of the present invention.

In FIG. 2, the line received signal is first sampled and converted into a digital signal by an A/D converter 24,
After the level is corrected by AGC control in the AGC circuit 26, the demodulation and roll-off filter section 28 demodulates the real component and the imaginary component indicating the signal point.

The received signal from the demodulation and roll-off filter section 28 is passed through the synchronization detection section 18 of the present invention, which will be explained later, to the automatic equalizer AEQ and the automatic carrier frequency control circuit CA.
is given to the line deterioration factor removal unit 10 composed of a PC,
A received signal with line deterioration factors canceled is output according to the operating parameters set by data acquisition.

The output signal from the line deterioration factor removing section 10 is given to the determining section 12, which determines the correct signal point for the received signal point. The determination by the determination unit 12 uses either a hard decision using a table or a soft decision using a Viterbi code corresponding to trellis encoding on the transmitting side, or a combination of both. The signal indicating the signal point determined by the determination unit 12 is demodulated into digital data using a mapping circuit, and then the scramble component is removed by a descrambler 42 and output as original data.

The operating parameters of the automatic equalizer AEQ and the automatic carrier frequency control circuit CAPC that constitute the line deterioration factor removal section 10 are controlled so as to minimize the determination error output from the subtracter 14. The subtracter 14 calculates the determination error as the difference between the input signal to the determination unit 12 and the output signal obtained from the determination result.

In addition to the configuration of the modem reception section, the present invention includes a synchronization detection section 18, a table ROM 16 as a reference signal storage section, and a table ROM 16 between the demodulation and roll-off filter section 28 and the line deterioration factor removal section 10. A switch 20 as a signal generating section and a selector 22 as a switching section are provided.

In the table ROM 16, one cycle of a transmission signal having periodicity depending on the number of scrambling stages of the transmitting modem is stored in advance as a reference signal sequence.

The synchronization detection unit 18 includes a shift register 30 that divides the received signal sequence from the demodulation and roll-off filter unit 28 into n stages and transmits it, and a shift register 30 that latches and shifts a reference signal sequence that has the same number of stages as the shift register 30. register 3
2.

In the table ROM 16, the readout operation of the reference signal series is performed in synchronization with the received signal series, and in the initial state, the switch 2
0 is turned on to set a reference signal sequence for one period in the shift register 32, and then the switch 20 is turned off to hold one sequence (one period) of reference signals in a fixed manner.

The outputs of each shift stage of the shift register 30 for the received signal sequence and the register 32 for the reference signal sequence are sent to a multiplier 34-1.
．． 34-2. . . 34-n, and the two are multiplied. The outputs of the multipliers 34-1 to 34-n are given to an adder 36, and the sum of the multiplication outputs is calculated.

That is, shift registers 30, 32, multipliers 34-1 to 34-3.
4-n and the adder 36, the synchronization detection unit 18 calculates the cross-correlation of the received signal sequence with respect to a fixedly set reference signal sequence.

Here, the received signal sequence for the shift register 30 is F
r(t), and the reference signal sequence fixedly set in the shift register 32 is Gr(t), the cross-correlation calculation of the next correlation value R is performed every time the received signal sequence is shifted by one bit.

The cross-correlation value R obtained by the adder 36 is subtracted by a predetermined constant in a subtracter 38 and then provided to the determination circuit 40 . When the value from the subtracter 38 exceeds a certain value, the determination circuit 40 determines that the received signal sequence is synchronized with the reference signal sequence and outputs a synchronization detection signal to the switch 20 and the selector 22.

Switch 2 receives a synchronization detection signal from synchronization detection section 18
0 switches from the previous OFF state to the ON state,
The reference signal sequence read from the table ROM 16 in synchronization with the received signal sequence is output to the shift register 32, and as a result, the reference signal sequence is sent to the selector 22 while maintaining the synchronization state of the received signal sequence and the reference signal sequence. A reference signal generation operation is performed to output the reference signal.

On the other hand, the selector 22 that receives the synchronization detection signal from the synchronization detection section 18 switches the output of the determination result from the determination section 12 to the subtracter 14 to the reference signal output obtained from the shift register 32, and the subtracter 14 A determination error signal sequence obtained by subtracting the received signal sequence for the determination unit 12 from the reference signal sequence is fed back to the line deterioration factor removal unit 10.

Therefore, in the automatic isometric cover AEQ and the automatic carrier frequency control unit CAPC that constitute the line deterioration factor removal unit 10, only the determination error component dependent on the line deterioration factor from which the periodicity of the received signal has been removed is fed back. , it is possible to perform data acquisition in which operating parameters are set so as to remove only determination error components that depend on line deterioration factors.

Therefore, even if periodicity appears in the received signal during data transmission,
Due to periodicity-dependent judgment errors, automatic equalizers and CAP
This eliminates the problem that the operating parameters of C are controlled, and because the number of scrambling stages is small, stable data acquisition can be performed even if periodicity appears in the received signal.

FIG. 3 shows the calculation state of the cross-correlation between the received signal sequence Fr(t) and the reference signal sequence Gr (t) in the synchronization detection section 18 of FIG. ) has periodicity with a peak value at the output shift stage, and this reference signal Gr
Assume that a received signal sequence Fr (t) having the same periodicity is input to the shift register 30 in a fixed setting state of (t), for example, in a state having a peak value at the first shift stage.

With respect to the temporal movement of the received signal sequence with respect to such a reference signal sequence, the cross-correlation value R output from the adder 36
is below a certain value until the peak part of the received signal sequence is shifted to the final shift stage, but at the timing when the peak part is shifted to the final shift stage, the cross-correlation value R increases extremely and exceeds the certain value. , whereby the synchronization of the received signal sequence with respect to the fixedly set reference signal sequence can be detected.

When one-end synchronization is detected in this way, as shown in FIG. 2, by turning on the switch 20, the received signal sequence and the reference signal sequence are sequentially shifted while maintaining the synchronized state, and as a result, they do not exhibit periodicity. It is possible to create a data pull-in state using received signals.

[Effects of the Invention] As described above, according to the present invention, it is possible to stabilize the equalization characteristics for eliminating line deterioration factors in a modem with a small number of scrambling stages without increasing the number of scrambling stages, and the receiving It greatly contributes to maintaining quality.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention; Fig. 2 is a diagram illustrating the configuration of an embodiment of the invention; Figure 3 is a detailed diagram illustrating the invention; Figure 4 is a diagram illustrating the configuration of a modem system; Figure 5 is a scrambler diagram; FIG. 6, a block diagram, is a line characteristic diagram based on automatic equalization. In the figure, 0 Line deterioration factor removal unit (AEQ, CAPC) 12 Judgment unit 14.38: Subtractor 16/Reference signal storage unit (table ROM) 18: Synchronization detection unit 20: Reference signal generation unit (switch) 22/Switching Section (selector) 24: A/D converter 26/AGC circuit 28 Demodulation and roll-off filter section 30.32: Shift registers 34-1 to 34-n: Multiplier 36, adder 40: Judgment circuit 42: Descrambler

Claims (3)

[Claims] (1) Receive a periodically scrambled data signal from the line, and operate according to the amount of difference between the waveform of the received data signal and the waveform of the data signal that should be received normally, as determined from the waveform. In a modem that equalizes signal degradation on the line according to parameters, reference signal generating means (20') generates a reference signal with a period corresponding to the scrambling period; the reference signal and the data signal are synchronization means (18) for detecting synchronization by comparison and repeatedly generating a reference signal while maintaining synchronization; when the synchronization means (18) detects synchronization, the output of the reference signal generation means (20'); A method for pulling in a modem, comprising: a correction means (22) for correcting the operating parameter according to the amount of difference between the reference signal and the waveform of the received data signal. (2) Regarding the line received signal from the transmitting modem with a small number of scramble steps, the line deterioration factor removal unit (1
0) is determined as the difference between the input of the determining unit (12) and the determination result. In the modem pull-in method, the modem pulls in the operating parameters to match the line deterioration factors based on the judgment error from the subtraction unit (14), which calculates the operating parameters as the difference between the input of the judgment unit (12) and the judgment result. a reference signal storage unit (16) in which one cycle of a transmission signal having periodicity dependent on the number of scrambling stages of the transmitting modem is stored in advance as a reference signal;
); and a synchronization detection section (18) that compares the received signal with a reference signal that is read out and fixed and set and detects synchronization between the two; when the synchronization detection output of the synchronization detection section (18) is obtained,
The reference signal storage unit (16) while maintaining the synchronization state.
A reference signal generator (which sequentially and repeatedly outputs reference signals from
20); When the synchronization detection output of the synchronization detection unit (18) is obtained, the determination unit (
A switching unit (22) that switches the determination result from the reference signal generating unit (20) to a reference signal from the reference signal generating unit (20) to calculate the determination error; (3) The synchronization detection unit (18) calculates the cross-correlation between the received signal sequence and the reference signal sequence, and generates a synchronization detection output when the cross-correlation value becomes a predetermined value or more. The modem pull-in method according to claim 1.