JP2708768B2 - Training signal detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A training signal detection device for detecting a training signal, which detects a training signal such as an AA signal, an AC signal, or an S signal by a simple configuration from a baseband signal obtained by demodulating a received signal. , And information on whether the received signal has been carrier-shifted with respect to the demodulated baseband signal, and the baseband signal or the carrier-shifted signal and the delay. The AA signal, AC signal, S
It is configured to detect a training signal such as a signal. In addition, for a baseband signal obtained by demodulating a received signal or a signal that is carrier-shifted as necessary, phase inversion is detected and a CC signal from an AA signal, a CA signal from an AC signal, and a CA signal from an AC signal.
It is configured to detect a change from a signal to an AC signal and a change from an S signal to a signal.

[Industrial applications]

The present invention relates to a training signal detection method for detecting a training signal.

[Problems to be solved by conventional technology and invention]

According to the CCITT rules, when using a line connected between the calling mode modem and the answering mode modem and performing mutual communication, as shown in FIG. 6, various training signals such as AA signal, AC signal, It is necessary to transmit or receive and detect the S signal. For example, calling mode modem
After sending the AA signal to the answer mode modem, it is necessary to detect the AC signal that is to be returned from the answer mode modem. Further, the calling mode modem needs to detect a state in which the AC alternating signal sent from the answer mode modem has changed to a CA alternating signal, and then send a CC signal to the answer mode modem.

An object of the present invention is to detect a training signal such as an AA signal, an AC signal, and an S signal by a simple configuration from a baseband signal obtained by demodulating a received signal, and to detect a change from an AA signal to a CA signal. I have.

[Means for solving the problem]

Means for solving the problem will be described with reference to FIG.

In FIG. 1, a demodulator 1 is for demodulating a received signal to generate a baseband signal.

The multiplier 4 shifts the carrier of the baseband signal as needed.

The delay element 6 delays the baseband signal or the carrier-shifted signal _ai .

The multiplier 7 multiplies a baseband signal or a carrier-shifted signal _ai by a complex conjugate signal of the delayed signal _ai-1 .

The determining unit 9 determines which of the training signals, such as the AA signal, the AC signal, and the S signal, based on the result multiplied by the multiplier 7 and the like.

The phase inversion detecting section 10 detects that the phase has been inverted.

[Action]

As shown in FIG. 1, according to the present invention, a baseband signal obtained by demodulating a received signal by a demodulator 1 or a signal _ai carrier-shifted by a multiplier 4 if necessary, and a signal _ai delayed by a delay element 6 _If the value obtained by multiplying the complex conjugate signal of _i-1 exists in a predetermined determination plane (in the determination plane in FIG. 3), when the value is detected by the determination unit 9, the corresponding AA signal, AC signal, S It is determined that the signal is a training signal such as a signal.

Also, the baseband signal demodulated from the received signal by the demodulator 1 or the signal a _i carrier-shifted by the multiplier 4 as necessary is input to the phase inversion detection unit 10 to detect that the phase has been inverted. It is detected that the corresponding AA signal has changed to a CC signal, the AC signal has changed to a CA signal, the CA signal has changed to an AC signal, or the like.

Therefore, it is possible to detect a training signal such as an AA signal, an AC signal, and an S signal, and to detect a change from an AC signal to a CA signal with a simple configuration from the baseband signal obtained by demodulating the received signal.

〔Example〕

Next, the configuration and operation of one embodiment of the present invention will be sequentially described in detail with reference to FIGS.

In Figure 1, the demodulator 1 is for demodulating a received signal, for example, a carrier signal (cos2πf _c, -sin2π
f _c ). f _c is a carrier frequency, for example, 1800 Hz.

The roll-off filter (ROF) 2 is for extracting a baseband signal by blocking harmonic components.

The AGC (automatic gain control circuit) 3 controls the gain so that the amplitude of the baseband signal extracted by the roll-off filter 2 becomes constant. As a result, a baseband signal as shown in FIG. 2 is obtained.

The multiplier 4, the baseband signal, for example an AC signal, multiplied by _{CAR.X = COS2πf c2 t, CAR.Y =} -SIN2πf c2 t, performs a carrier shift corresponding to f _c2 = 1200 Hz. For other baseband signals such as AA signals and S signals, there is no need to carry out carrier shift.
= 1, CAR.Y = 0. The signal multiplied by the multiplier 4 is as shown in FIG.

The LPF (1) 5 cuts off the high frequency component of the signal multiplied by the multiplier 4 and extracts a desired DC component. The signal output from the LPF (1) 5 has only a DC component as shown in FIG.

Delay element 6 is intended to generate a signal a _i-1 obtained by delaying the signal a _i.

The multiplier 7 multiplies the signal a _i by the complex conjugate of the delayed signal a _i−1 .

The LPF (2) 8 is for extracting a low-frequency component by cutting off a high-frequency component of the multiplication result.

The determining unit 9 determines which training signal is used. For example, it is to determine which of the A signal, the AC signal in FIG. 2A, the AC signal in FIG. 2B, and the S signal in FIG. 2C. This judgment is LPF
(2) When the signal output from 8 exists in the shaded area in FIG. 3, it is determined that the signal is the corresponding AA signal, AC signal, or S signal. AC signal is carrier shifted and LPF
(2) The determination is made when the signal output from 8 exists within the hatched area in FIG. The AA signal and the S signal are in a state without carrier shift, and as described from the training signal example in FIG. 6, the AA signal is detected by the answer mode modem, and the S signal is detected by the calling mode modem. Therefore, these can be distinguished.

The phase inversion detecting section 10 detects that the phase has been inverted with respect to the baseband signal or the carrier-shifted signal output from the LPF (1) 5 as shown in FIG. , An AC signal to a CA signal, a CA signal to an AC signal, an S signal to a signal, and the like. This means that the multipliers 11-1, 11-2, 11
-3, integrator 12, phase error corrector 13, and phase inverting unit
Combine 14 as shown to make PLL (phase locked loop)
To detect that the phase of the baseband signal or the carrier-shifted signal is inverted (described later with reference to FIG. 5).

Next, an operation for detecting a training signal such as an AA signal, an AC signal, and an S signal will be described.

In FIG. 2, when a signal on a line is received and demodulated to extract a baseband signal, the result is as shown in FIG. The AC signal in which the baseband signal in FIG. 2 does not include a DC component (FIG. 2B) is multiplied by a subcarrier and carrier-shifted as shown in FIG. The high-frequency component is cut off and only the DC component is extracted as shown in FIG. In the other FIG. 2 (a) AA signal and FIG. 2 (c) S signal, since a DC component exists in the baseband signal, the carrier signal is not shifted without carrier shift.
Only the DC component is extracted as shown in the figure. The signal _ai of these DC components is multiplied by the complex conjugate of the delayed signal _ai-1 . For example, if the signal a _i = exp (jθ),
The complex conjugate of the signal a _i-1 = exp (jθ) delayed by one is e
xp (−jθ). Therefore, the product of them is exp (jθ) × exp (−jθ) = 1. If the product of the two exists in the shaded area in FIG. 3, it is determined that the corresponding AA signal, AC signal, or S signal is present. The shaded area in FIG. 3 indicates a range in which the conditions shown in the figure are satisfied.

Next, referring to FIG. 5, from the AA signal to the CC signal and from the AC signal
The operation of detecting a change from a CA signal, a CA signal to an AC signal, and a change from an S signal to a signal will be described.

In FIG. 5, a PLL operation for detecting the AA signal, the AC signal, and the S signal is performed. This is the AA signal, AC
The operation of the phase inversion detection unit 10 in FIG. 1 is performed so that the original signal of which the change is to be detected among the signal and the S signal is, for example, as shown in FIG. Means.

In the figure, inversion is detected from + to-of REAL. This is because the phase of the signal input to the phase inversion detection unit 10 is inverted by 180 degrees from the state where the positive of the REAL component is detected as shown in FIG. R
This means detecting a state in which the EAL component changes from positive to negative.

In the figure, the output is returned to (A, 0). This means that the output of the REAL component of the phase inversion detecting section 10 in FIG. In order to return to the positive value, the phase inverting unit 14 in FIG. 1 switches the value input to the multiplier 11-2 from “1” to “−1” or from “−1” to “1”. Done.

With the above procedure, a change in the training signal from the AA signal to the CC signal or the like is detected.

〔The invention's effect〕

As described above, according to the present invention, a baseband signal obtained by demodulating a received signal or a signal obtained by carrier-shifting a baseband signal is multiplied by a complex conjugate signal obtained by delaying this signal to obtain any training signal. Is adopted, and the switching of the training signal is detected by detecting the phase inversion, so the training signal such as AA signal, AC signal, S signal, etc. can be obtained by a simple configuration and simple processing. Can be detected, and a change in the training signal from the AC signal to the CA signal can be detected. Further, since the training signal and its change are detected using the baseband signal, the detection accuracy is high.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the present invention, FIG. 3 is an example of a determination plane, FIG. 4 is an example of a vector plane, and FIG. FIG. 6 shows an example of a training signal between modems. In the figure, 1 is a demodulator, 4 and 7 are multipliers, 6 is a delay element, 9
Denotes a determination unit, and 10 denotes a phase inversion detection unit.

Claims (3)

(57) [Claims] An apparatus for detecting a training signal, comprising: a demodulator for demodulating a received signal to generate a baseband signal; and a frequency shift (hereinafter referred to as a carrier shift) for the generated baseband signal or the baseband signal. A multiplier that multiplies one of the baseband signals or a complex conjugate of a signal obtained by delaying a carrier-shifted signal, information on whether the baseband signal is carrier-shifted, and a result of the multiplication. Based on at least AA
A training signal detection device, comprising: a circuit for detecting a training signal of a signal or an AC signal and an S signal. 2. The method according to claim 2, wherein the signal is a CC signal or the AA signal.
The training signal detecting apparatus according to claim 1, wherein a training signal of a CA signal and an S (bar) signal is detected in addition to the AC signal and the S signal. 3. A training signal detecting apparatus for detecting a training signal, comprising: a demodulator for generating a baseband signal obtained by demodulating a received signal; and AA detecting that the phase of the generated baseband signal is inverted. Detects that the phase of the CC signal or the carrier-shifted signal of the generated baseband signal is inverted from the signal, and detects the AC signal from the CA signal and the CA signal from the CA signal.
A training signal detection device, comprising: a signal; and a circuit that detects that the phase of the generated baseband signal is inverted and detects a change from an S signal to an S (bar) signal.