JPH05175788A - Training signal detection system - Google Patents

Abstract

PURPOSE:To prevent the deteriorated efficiency of data transmission without mis-detection of a training signal by providing a limit range to an identification circuit and judging the reception of the training signal only when a received signal point enters a limit range and it is detected a final pattern is received. CONSTITUTION:When a signal is interrupted by a momentary interruption of a transmission line and the line is again connected, a biphase identification circuit 13 implements biphase identification and a reception signal is an octal phase modulation wave. Only when a received signal point is in existence within a limited range by an identification circuit 13, since an identification output is obtained, the coincidence with a final pattern of a phase 2 of a training signal is not taken by a comparator circuit 8 even when the coincidence has been takes for an octal phase modulation wave in a conventional system. Since an output of an identification circuit 4 having no limit function of the identification range has been outputted to a shift register 9 in the conventional system, the coincidence is taken even for the octal phase modulation wave and it has been decided in error as the training signal, but this system does not make mis-detection of the training signal through the reception of data modulation wave and surely detects the training signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator / demodulator (modem) in which a transmitting side sends a training signal before data transmission, and the receiving side receives the training signal to adjust an automatic equalizer or the like.

[0002]

2. Description of the Related Art A modem equipped with an automatic equalizer sends a special preconfigured signal called a training signal before starting data transmission. The receiving section of the modem of the partner station receives the training signal, detects that the training signal is received, and performs the initial setting of the automatic equalizer. Then, the transmission data is correctly restored from the subsequent modulated waves and is output to the terminal device as reception data. In other words, the automatic equalizer is initialized so that it has exactly the frequency characteristic of the transmission line, and the signal distorted through the transmission line is passed through the automatic equalizer to reduce the distortion as much as possible. The waveform is equalized to reduce bit errors.

This training signal is, for example, CCITT.
V. The long training signal recommended by 27bis has a configuration as shown in FIGS. 4 and 5. It is composed of three kinds of signals. Phase 1 modulates alternating signals of 0 ° and 180 ° phases, and phase 2 also modulates signals of 0 ° and 180 ° phases by PN (pseudo random) signals. The signal according to the sequence generated in 1 is modulated and transmitted, and in phase 3, 0 °, 45 °, 90 °, ...
A signal having eight phases of 270 ° and 315 ° is modulated according to the signal output from the scrambler output when the input of the scrambler is fixed to 1, and the signal is transmitted.

Whether or not the training signal has been received is detected by using a special signal which is usually phase inversion of phase 1. This signal has a certain length (CC
ITT V. It is 31 ms in 27 bis), which is an alternating inverted signal of 0 ° and 180 °, and is relatively easy to detect. In addition, by making this detection time as long as possible, it is possible to ensure distinction from signals other than the training signal.

However, for example, CCITT V. 27b
In the short training recommended by is, the phase 1 signal is very short (9 ms) as shown in FIG. Also, CC
If you try to use a shorter training signal without complying with the ITT recommendations, shorten phase 1
In some cases, only Phase 2 is used without even Phase 1. It is very difficult to detect that such a training signal has been received.

Therefore, when the training signal is received in the phase 1 as shown in FIG. 4 without detecting the training signal in the related art, the carrier is once disconnected due to the fact that there is no signal immediately before. Then, when some signal is received next time, whether it is a training signal (2-phase signal) or a modulated wave of data transmission (8-phase phase modulated signal) without detecting the training signal, 2
If the phases are discriminated and the pattern of the training signal immediately before the end of the phase 2, for example, the pattern of 7 symbols is detected, it is determined that the training is received. Then, when the training signal is received, the training is correctly performed, and it is understood that the training signal is received at the end of the phase 2 of the training signal. Further, when the received signal is not the training signal and the modulated wave of the data is cut off once due to a momentary interruption of the transmission path and is received again, it cannot be distinguished whether the received signal is the modulated wave or the training signal. Therefore, the two phases are similarly identified.

However, the modulated wave is a phase-modulated signal of 8 phases, and even if it is discriminated in 2 phases, the automatic equalizer itself does not diverge, and the updating speed is slow, but equalization is performed. Is possible and there is no big problem. While discriminating between the two phases, an attempt is made to detect the pattern of the training signal immediately before the end of phase 2 during a predetermined time. However, since it is not originally a training signal, the pattern immediately before the end cannot be detected. In that case, it is judged that the modulated wave is received, the mode is changed to the identification of 8 phases in the data mode, and the normal data mode operation is performed.

[0008]

However, the above-mentioned prior art has the following drawbacks. Immediately before the end of phase 2 of the training signal with a phase difference of 180 °, as shown in FIG. 6, in order to identify a wide range of two phases even when the received signal is momentarily cut off and a modulated wave of data is received. Pattern is not exactly the same, ie,
In some cases, even if the pattern of eight phases as shown in (4), it is erroneously detected as the detection pattern of the training signal immediately before the end of phase 2, and the modulated wave is regarded as the training signal. In other words, with the original training signal, the final pattern of phase 2 is ...
If 0, π, 0, π, π, 0, π, for example, in FIG. 7, even if signals of eight phases such as ..., A, C, H, F, C, B, E are received. Since the discrimination is performed at the discrimination boundary shown by the dotted line, ..., 0, π, 0, π,
It is determined that the signals π, 0, π have been received. If a training signal is received, the procedure such as sending the training signal to the modem of the partner station is determined, so if a false detection is made, such a wrong operation will be performed, or the training signal will be sent by doing so. Since data transmission is not possible inside, the efficiency of data transmission will be reduced. It is an object of the present invention to solve the above problem and prevent a modulated wave of data after a line interruption from being erroneously detected as a training signal.

[0009]

In order to achieve the above-mentioned object, the present invention provides a limit range in the discrimination circuit at the same time when the pattern immediately before the end of the phase 2 of the training signal is detected, and the received signal point is It is determined that the training signal is received only when it is detected that the final pattern is received within the limited range.

[0010]

As a result, what is regarded as the pattern immediately before the last of the phase 2 of the training signal when the phase-modulated signal of 8 phases, which is the modulated wave of the data, is discriminated by 2 phases,
By limiting the discrimination range, what is regarded as a training signal is not regarded as a training signal because the signal points spread in eight phases.

[0011]

1 is a block diagram showing the structure of the present invention. The received and demodulated baseband signal is input to the automatic equalization transversal filter 2. The frequency characteristic of the automatic equalization transversal filter 2 is determined by the tap coefficient forming the filter. And
The output signal is input to the switch circuit 3, and the switch circuit 3
The contact of is switched to the T side when receiving training and to the D side when receiving a modulated wave of data. The contact output on the T side is input to the 2-phase identification circuit 4, and the contact output on the D side is input to the 8-phase identification circuit 5. Here, the error between the received point and the ideal signal point to be originally received is calculated, and this error is used to change the tap coefficient of the transversal filter of the automatic equalizer by the following algorithm, for example. Distortion is reduced by equalizing the received signal.

That is, by repeating the following calculation many times, the frequency characteristic opposite to the frequency characteristic of the transmission line is realized by the transversal filter 2 of the automatic equalizer, and the frequency characteristic of the transmission line is reduced. The distorted signal is passed through the transversal filter 2 of the automatic equalizer to be input as the undistorted signal to the discrimination circuits 4 and 5 so that the reception point approaches the ideal point to be originally received, thereby eliminating the discrimination error. Try to reduce it.

[0013]

[Equation 1]

In this embodiment, switching of the switch circuit 3 is performed as follows. When the signal from the transmission line is cut off once, the cutoff period is more than a predetermined fixed time,
For example, when 20 ms or more elapses and the next time a signal is received, the switch circuit 3 is set to the T side and the two-phase identification circuit 4 performs the two-phase identification from the beginning, and the frequency characteristic of the automatic equalization transversal filter is transmitted. 8 is adjusted to the inverse characteristic of the frequency characteristic, and the discrimination is performed also in the discrimination circuit 13 having a limited discrimination range as shown in FIG.
In No. 3, the identification result is output when the received signal point is included in the limited area, and the identification result is not output when the received signal point is outside the limited range. The output of the identification circuit 13 is input to the shift register 9. The shift register 9 sequentially shifts for each identification. The REF circuit 7 stores the final pattern of phase 2 of the training signal (detection pattern, for 7 SI in this embodiment), and the comparison is performed for each shift. The comparison circuit 8 outputs the coincidence output only when the outputs of the REF circuit 7 and the shift register 9 coincide with each other. Therefore, when the coincidence output of the comparison circuit 8 is output when the final pattern of the phase 2 of the training signal is output, it is determined that the final pattern of the phase 2 of the training signal is received, and the training signal detection signal is trained. Output to the signal detection output terminal 14. When the training signal is received, since the signal itself has a two-phase phase, the final pattern of the two-phase phase 2 is naturally detected.

However, the signal is cut off due to a momentary interruption of the transmission line,
When they are connected again, the two-phase discrimination circuit 13 discriminates two phases, but the received signal is an eight-phase modulated wave. The reception points at the two-phase identification circuits 4 and 13 are as shown in FIGS. When the present invention is used, the discrimination output can be obtained only when the received signal point is within the limited range of the discrimination circuit 13. Therefore, in the present embodiment, even if the conventional 8-phase phase-modulated wave is matched. The comparison circuit 8 cannot match the final pattern of the training signal in phase 2. Conventionally, since the output of the discrimination circuit 4 having no limitation on the discrimination range is output to the shift register 9, there is a case where a phase-modulated wave of 8 phases can be matched, and it is erroneously determined as a training signal. In this way, the training signal can be reliably detected without receiving the modulated wave of data and erroneously detecting it as the training signal.

Further, in another embodiment, as shown in FIG. 2, the output of the discrimination circuit is input to the shift register 9 as in the conventional system, but the discrimination circuit 13 is different from the conventional system. As in the embodiment, the discrimination range is limited as shown in FIG. 8, and the discrimination circuit 13 outputs the signal only when the reception signal point is within the limited range as in the discrimination circuit 13. Similarly, the training signal can be reliably detected without receiving the 8-phase modulated wave of the data and erroneously detecting the training signal. However, also in the present invention, when the data itself is a signal having a phase of 0 ° and 180 ° and is completely the same as the pattern immediately before the last of the training signal, the training signal is received even if it is a modulated wave of the data. However, this probability is so small that it can be ignored, and there is no problem in practical use. In the embodiment of the present invention, the 8-phase phase modulation system is taken as an example, but of course other phase modulation systems such as 4-phase and the quadrature amplitude modulation system to which the elements of amplitude modulation are added can be similarly applied.

[0017]

As described above, according to the present invention, it is possible to prevent the training signal from being erroneously detected and prevent the data transmission efficiency from being lowered.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a block diagram showing a configuration of the present invention.

FIG. 3 is a block diagram of a conventional method.

FIG. 4 is a configuration diagram of a training signal.

FIG. 5 is a configuration diagram of a training signal.

FIG. 6 is an explanatory diagram of an identification operation when a training signal and a modulated wave of data are received.

FIG. 7 is an explanatory diagram of an identification operation when a training signal and a modulated wave of data are received.

FIG. 8 is an explanatory diagram of a limit range of the identification circuit.

[Explanation of symbols]

 1 Input Terminal 2 Automatic Equalization Transversal Filter 3, 6 Switch Circuit 4 2 Phase Discrimination Circuit 5 8 Phase Discrimination Circuit 7 REF Circuit 8 Comparison Circuit 9 Shift Register 10 Discrimination Error Calculation Circuit 11 Tap Update Circuit 13 Discrimination with Restriction Range Circuit 17 Training signal detection output terminal

Claims (2)

[Claims] 1. A training signal detection system of a modulator / demodulator in which an automatic equalizer for equalizing the distortion of a transmission line is built-in, and the automatic equalizer is initialized by a training signal. After that, the discrimination circuit for training is switched to the discrimination circuit for automatic equalization and the discrimination output of the discrimination circuit whose area is limited and the final part of the initial setting pattern of the automatic equalizer that constitutes a part of the training signal The training signal detection method is characterized in that the pattern stored in advance as a plurality of symbols is compared with each other, and if the patterns are matched, it is determined that the training signal is received. 2. A training signal detection system of a modulator / demodulator in which an automatic equalizer for equalizing distortion of a transmission line is built-in, and the automatic equalizer is initialized by a training signal. After that, the discrimination circuit for training is switched to, the discrimination area of the discrimination circuit for automatic equalization is limited, and the discrimination output and the final part of the initial setting pattern of the automatic equalizer that constitutes a part of the training signal are set. A training signal detection method characterized in that a pattern stored in advance as a plurality of symbols is compared with each other, and if the patterns are matched, it is determined that a training signal has been received.