JPS63156458A - Carrier detecting system - Google Patents

Abstract

PURPOSE:To output a stable carrier detection signal even when a line with a large amount of distortion is used, by outputting the carrier detection signal based on a demodulation signal in which a frequency at the central band area of the modulation signal being not affected considerably by the distortion of a line is demodulated. CONSTITUTION:An analog wave transmitted via a data line is received and is sampled in digital conversion by an A/D converter 1. A demodulator 2 demodulates the digital wave to the frequency of the central band area of a modulating carrier, and sends it to a band area filter ROF3 as a baseband signal. At the ROF3, signals at the areas other than the central band area are eliminated from the baseband signal by adding/subtracting tap coefficients h1, h2, h3,..., hm-1, and hm appropriately. The baseband signal is adjusted to a prescribed level at a carrier detecting means 4 by multipler 5 first. And the energy level of the signal is obtained by being integrated by an integrator 6, and it is slice-adjusted with a prescribed energy level by a slicer 7, then, the carrier detection signal is outputted.

Description

[Detailed Description of the Invention] [Summary] The present invention extracts only the central frequency band of a modulated signal wave with less line distortion before inputting it to a carrier detection means, and outputs a carrier detection signal based on the signal. Therefore, a stable carrier detection signal can be obtained.

[Industrial application field]

The present invention relates to a carrier detection method used to detect a predetermined level of demodulation zero on the receiving side of data communication.

[Conventional technology]

Conventionally, as shown in FIG. 5, as a carrier detection method, a received analog wave is converted into digital by an A/D converter l, and '
``!1 By inputting the digital signal to the carrier detection F stage 4 consisting of a multiplier 5, an integrator 6, and a slicer 7, a predetermined energy level of the received analog wave is detected and a gear detection signal is output. That's what I was doing.

[Problems that civilization tries to solve]

By the way, in the conventional carrier detection method, as shown in FIG. 6, a digital signal obtained by sampling a transmitted analog signal by an A/D converter l is sent as it is to the carrier detection means 4, and then the corresponding signal is detected. Since energy at a predetermined level was detected based on the digital signal and a carrier detection signal was output, as shown in Figure 3, due to level fluctuations caused by circuit distortion, carrier The time it takes to output the detection signal is unstable, and the difference in timing of outputting the carrier detection signal may cause problems in signal processing in the receiving section.

In addition, as shown in Figure 4, if there is a secondary channel (packword channel) that is different from the signal in the frequency band originally used by the modem, its energy will affect the detection of the received signal and cause carrier detection. The signal output may shift, leading to malfunction of the receiving device, and especially in the case of a high-speed data transmission system with a modulation rate of 19.2 PO, the entire frequency band of the line will be covered compared to the normal 9600 PO. Since it is necessary to use the method, there is a problem that the influence may be large.

The present invention has been made to solve the above problems, and has been provided for the purpose of outputting a carrier detection signal that can output a stable carrier detection signal.

[Means for solving problems]

In order to solve the above problems, the present invention, as shown in FIG. A D conversion circuit 1, a demodulator 2 that demodulates the digital signal in the center band of the modulated signal, and a bandpass filter 3 that removes components outside the used band of the demodulated signal, and the bandpass filter 3 A carrier detection means 4 is provided for detecting a predetermined level of a demodulated signal transmitted through the carrier signal and outputting a carrier signal. [Operation] As shown in FIG. The received analog signal is sampled by digital conversion by the A/D converter 1 and sent to the receiver and demodulator 2 as a digital signal. Demodulator 2
The digital signal sent to the demodulator 2 demodulates only the center band of the modulation band and sends it to the bandpass filter as a demodulated signal (baseband signal). The bandpass filter 3 removes signals outside the center band from the demodulated signal. The demodulated signal that has passed through the bandpass filter 3 is sent to carrier detection means 4.

The carrier detection means 4 outputs a carrier detection signal when it detects that the demodulated signal has reached a predetermined energy level.

That is, in the present invention, the carrier detection signal is output based on a demodulated signal that uses the center of the frequency band rather than the edge of the frequency band of the modulated wave, so it is possible to output a carrier detection signal based on a demodulated signal that uses the center of the frequency band instead of the edge of the frequency band of the modulated wave. There is almost no difference in the output of the carrier detection signal between the two, but when the edge of the frequency band is used, a difference of 6 dB or more occurs.

〔Example〕

Next, a system according to an embodiment of the present invention will be explained based on FIG. 4.

In FIG. 4, an A/D converter 1 digitally converts and samples a received analog signal transmitted via a line.

The demodulator 2 demodulates the digitally converted received signal in the center frequency band of the modulation carrier wave and converts it into a baseband signal. ROF (R
The off filter 3 removes signals having frequencies outside the center band from the baseband signal. No. 5154 shows an equivalent circuit diagram showing the ROF3kg.
1 and tap coefficients h+, hz+ha+... which are predetermined parameters given from the outside.
, hi-1,h, and a delayed signal, and an adder 33 that performs addition of the outputs of the multipliers 32. The upper circuit 34 of the ROF 3 processes the real part of the baseband signal, and the lower circuit 35 processes the imaginary part.The carrier detection means 4 includes a multiplier 5, an integrator 6, and a slicer 7. has been done.

The multiplier 5 adjusts the level of the baseband signal (demodulated signal) passed through the bandpass filter 3.

The integrator 6 integrates the level-adjusted baseband signal to obtain the energy level.

The slicer 7 slices the energy level obtained by the integrator 6 at a predetermined level and outputs a carrier detection signal.

This embodiment operates as follows.

The analog wave transmitted via the data line is received and sampled by digital conversion by an A/D converter l. The digital signal wave is sent to the demodulator 8 and the demodulator 2.

The demodulator 2 demodulates the frequency of the center band of the modulation carrier wave from the digital wave and sends it to the bandpass filter (ROF) 3 as a baseband signal. In ROF3, the tap coefficients hl, h2°b3+..., b 1. By appropriately adding or subtracting the value of b, signals outside the center band are removed from the baseband signal. This makes it possible to obtain a baseband signal that is stable against fluctuations due to line distortion. The baseband signal is input to carrier detection means 4. '''!!4 In the carrier detection means 4, the baseband signal is first adjusted to a predetermined level by a multiplier 5, integrated by an integrator 6 to obtain an energy level, and then adjusted to a predetermined energy level by a slicer 7. A slice operation is performed at , and a carrier detection signal is output.

The carrier detection signal activates various signal processing in the receiving section.

〔Effect of the invention〕

In this way, according to the present invention, a carrier detection signal is output based on a demodulated signal obtained by demodulating the frequency of the center band of a modulated signal that is not affected by line distortion, so it can be used on a line with a lot of distortion. It is also possible to output a stable carrier detection signal.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of the principle of the present invention, FIG. 2 is a diagram showing the output time difference of carrier detection signals, according to an embodiment of the present invention, FIG. 3 is a diagram showing the generation of a secondary channel, and FIG. 4 is a diagram showing the output time difference of the carrier detection signal.
The figure is a block diagram according to an embodiment of the present invention, and FIG. 5 is a ROF
FIG. 6 is a blow diagram according to a conventional example. 1... A/D converter 2... Demodulator 3... Bandpass filter (ROF) 4... Carrier detection stage

Claims (1)

[Claims] In a method for detecting the level of a demodulated signal of a modulation/demodulation device using a voice band line, an A/D converter (
1), a demodulator (2) that demodulates the digital signal in the center band of the modulated signal, and a bandpass filter (3) that removes components of the demodulated signal outside the used band, and A carrier detection method comprising carrier detection means (4) for detecting a predetermined level of a demodulated signal passed through a bandpass filter (3) and outputting a carrier signal.