JPH01253379A - Television signal transmission system and its receiver - Google Patents

Abstract

PURPOSE:To minimize the modification of a currently used transmitting-receiving facility by separating wide band television signals into low band components lower than the already using transmitting band of the conventional system and wide-band components higher then the low-band components and forming transmitting signals in such a way that the high-band components are modulated in amplitude by carriers and only modulated lower side band components are extracted and added to the low-band components. CONSTITUTION:For example, NTSC signals which are wide-band signals are separated into low-band components lower than 4.2MHz which is the band of the NTSC transmission line and high-band components higher than the low-band components by means of a 4.2-MHz LPF 1 and (4.2-6.5)-MHz BPF 2. The high-band components which are the output of the BPF 2 are modulated in amplitude by carriers of 22/7 fSC in frequency at a modulator 3. Of the amplitude-modulated high-band components, only lower side band components are fetched by a 7.1-MHz LPF 4 and added to the output of the LPF 1 which are the low-band components at an adder 6 after the components are doubled by a multiplier 5. The output of the adder 6 becomes video transmitting signals at the base band. The output of the adder 6 is modulated similar to the NTSC signals by means of a VSB-AM modulator 7 by using signals of fv as video carriers. Since the modulator 7 only changes the high-frequency band from the conventional 6MHz to 9MHz, the conventional modulator can be used as it is as the modulator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention is directed to ADTV (Advanced Definition)
The present invention relates to a system for transmitting a wider band television signal while maintaining compatibility with, for example, a conventional NTSC system receiving apparatus, and a receiving apparatus therefor.

(Summary of the Invention) The present invention relates to an ADTV system. For example, in the conventional NTSC system, this high frequency component is separated from a television signal having a high frequency component of 4.2 MH2 or more, which is outside the transmission band. The component is modulated with a carrier wave such that the lower sideband after modulation is in a frequency band higher than the audio carrier wave, and only the lower sideband after modulation is added to the low frequency component below 4.2 MH2 to generate the transmission signal. It is said that

In this way, it is possible to transmit a wideband television signal over a continuous 9 MHz high frequency channel without changing the high frequency stage of the current NTSC system transmitting and receiving equipment, and while maintaining compatibility with the NTSC system receiving equipment. .

(Conventional technology) No prior art equivalent to this type of technology has been found.

(Problems to be Solved by the Invention) For example, in the conventional NTSC system, the audio carrier wave is at 4.5 MHz, just above the 4.2 MHz video signal band, so the channel in MII2 is simply 9 consecutive high frequency bands. Even if it were, it would not be possible to transmit a wider band television signal to a conventional NTSC receiver while maintaining compatibility in both video and audio. Furthermore, the conventional method of mixing a 6 MHz high frequency band signal with a 3 MHz additional band signal at a high frequency stage has the drawback of requiring major changes to the current transmitting and receiving equipment.

Therefore, it is an object of the present invention to solve the above-mentioned drawbacks, to minimize changes in transmission/reception equipment, and to transmit wider-band television signals while maintaining compatibility of video and audio with conventional NTSC receivers. The present invention aims to provide a method and a receiving device for the same.

(Means for solving the problem) In order to achieve this object, the television transmission system of the present invention divides a wideband television signal into a low-frequency component below the transmission band of the existing conventional system and a wide-band component above the transmission band. This high-frequency component is amplitude-modulated using a carrier wave such that the lower sideband after modulation is in a frequency band higher than the audio carrier, and only the lower sideband after modulation is extracted and added to the low-frequency component. It is characterized in that it forms a transmission signal.

Further, the receiving device of the present invention includes means for separating the transmitted signal into a low-frequency component below an audio carrier wave and a high-frequency component above the audio carrier wave, and a means for separating the high-frequency component into a transmitting side. The present invention is characterized by comprising means for demodulating using a synchronized carrier wave, and means for adding the demodulated signal to the low frequency component.

(Examples) The present invention will be described in detail below by way of examples with reference to the accompanying drawings.

FIG. 1 shows a configuration block diagram of an embodiment of the transmitting side according to the present invention.

In Figure 1, the input signals are a video signal and an audio signal,
The video signal is, for example, a wideband NTSC signal. This N
The TSC signal is filtered by a 4.2 MHz LPF (low pass filter) and a 4.2 to 6.5 MH2BPP (band pass filter) 2, which is the band of the NTSC transmission path.
It is separated into low frequency components below M82 and high frequency components above that. The high-frequency component output from the BPF 2 is amplitude-modulated in the modulator 3 using a carrier wave having a frequency of 22/7fsc (fsc is the color subcarrier of NTSC). This results in 4.2~
The high frequency component of 6.5 Mll□ has a lower sideband in the band of 4.8 to 7.1MH2 and an upper sideband in the band of 15.5 to 17.8MH2 since 22/7fsc is approximately 11.3MH2. Produces a band. Of these, only the lower sideband is 7.1MHz L
It is taken out by PF4, multiplied by 2 by multiplier 5 to match the level with the low frequency component, and then added by adder 6, which is the low frequency component.
It is added to the FI output. The output of this adder 6 becomes a baseband video transmission signal.

The output of the adder 6 is modulated by a VSB-AM modulator 7 using f as a video carrier wave in the same way as an NTSC signal. This modulator 7 increases the high frequency band of this device from the conventional 6 MHz to 9 MHz.
M) A conventional modulator can be used as is by simply changing to lz. The audio signal is FM-modulated in the FM modulator 9 using fa = fv + 4.5 MHz as an audio carrier wave, just like NTSC, and added to the modulated video signal in the adder 8. The output of the adder 8 becomes the transmission signal of the present invention.

FIG. 2 shows a block diagram of the configuration of an embodiment of the receiving side according to the present invention. In FIG. 2, the transmission signal that is the input signal is separated into video and audio by the audio notch filter 10 and the audio BPF 18, and the audio signal that is the output of the audio BPF 18 is
Just like in the TSC, the FM demodulator 19 demodulates the signal into a baseband audio signal and outputs the audio signal. The video signal output from the audio notch filter 10 is VSB-A.
The M demodulator 11 demodulates the signal to baseband. Demodulator 11
The conventional demodulator can be used as is by simply changing the high frequency band from 6 MHz to 9M112. The output of the demodulator 11 is 4.5 Mll□LPF12 and 4.5 to 7.5
The MHz BPF 13 separates the sound carrier wave fA into low-frequency components below and above 4.5 MH□, which is a frequency corresponding to the baseband. B
The high-frequency component output from the PF 13 is demodulated in the demodulator 14 using a 22/7 fsc carrier wave synchronized with the transmitting side.

The demodulated signal is removed by a 7 MHz LPF 15 to remove twice the frequency component generated by synchronous detection, and then doubled by a multiplier 16 to match the level with the low frequency component, and then added to the low frequency component by an adder 17. Ru.

The output of the adder 17 becomes the video signal output.

FIG. 3 shows the spectrum of the signal transmitted by the circuit shown in FIG. The frequency f on the horizontal axis is expressed as an offset with respect to the frequency of the video carrier wave fv, which is set to 0. First of all-
The video signal in the frequency band of 1.25 to 4.5 Mn2 and the 4.5 MHz audio carrier fA (and its sidebands) are exactly the same signals as the conventional NTSC signal. For this reason, even if a transmission signal with the spectrum shown in Figure 3 is input to a conventional NTSC receiver, the IF (intermediate frequency) stage of the normal receiver will limit the band to f, +4.5 MH2 or less. Images are reproduced in exactly the same way, and there are no problems with compatibility.

On the other hand, in the receiver according to the method of the present invention shown in the second figure, 4.5~
The signals (additional signals) in the additional signal band distributed over 7.75M1+□ are correctly processed to reproduce a wideband video signal. The high frequency band of this transmission signal is 9M as shown in the figure.
]1□.

The solid line in the spectrum diagram shown in Figure 4 is the conventional high frequency 6M
This is the spectrum of an NTSC signal that uses the 11□ band, but if you try to simply widen the video signal band without using the present invention, it will become like the dotted line area U in the figure and crosstalk with the audio carrier wave will occur, so it is not used. Can not. Furthermore, if the additional signal band is placed below the high frequency band as shown in the dashed-dotted line area V in the figure, the result shown in the figure cannot be obtained by simply extending the high frequency band of a normal VSB-AM modulator downward. The resulting modulation cannot be realized, and even in demodulation, crosstalk occurs between the additional signal and the main signal simply by widening the band of the conventional demodulator. Therefore, this method requires major changes in the high frequency stages on both the transmitting and receiving sides.

The fifth unillustrated vector is for explaining the processing of the signal spectrum according to the present invention. Figure (a) shows the 4.2 M) 12LPFI and 4.2 to 6.5 of the first illustrated configuration diagram.
An example of the characteristics of MH2BPF2 is shown. If these two filters are made to have complementary characteristics centering around 4.2 Mn2, the total transmitting and receiving transmission characteristics according to the method of the present invention will be 6.5 Mn2.
The characteristics can be flat up to n2. ℃) in the same figure shows the modulation situation on the transmitting side. The component d in the same figure whose spectrum of the original signal has a band up to 6.5 Mn2
and component e, 4.2M112
Only the above component e is amplitude modulated with a carrier wave of 22/7 fsc, and its lower sideband appears at 4.8 to 7.1 MHz. Although not shown in the figure, unnecessary 15.5 to 17.
To reduce the upper sideband that appears at 8MH By adding the obtained signals (components shown in FIG. 5(b)), a transmission signal according to the present invention is obtained.

On the receiving side, as shown in FIG. 5(C), the main signal, that is, the low-frequency component d, and the additional signal f in the transmission signal are transmitted, for example, to ,
5 Mllz LPF12 and 4.5-7.5 Mn28
22/7 separated by PF13 and synchronized to the transmitting side
The original high-frequency component g is obtained by demodulating with the fsc carrier wave. At this time, the component g is doubled in order to match the level with the low frequency component d, and in order to eliminate more than twice the frequency component generated by synchronous detection, for example, the second diagram superimposed on the same figure is used. 7M llz LPF15 in the configuration diagram
Bandwidth is limited. If you add component g and component d, you get 6.5MH which is equivalent to the input signal on the transmitting side.

Band video signals can be obtained.

The carrier wave for modulating the high-frequency component was selected as 22/7fsc because it has an appropriate frequency value and a simple integer ratio to fsc, making phase synchronization on the receiving side easier. It is. Further, in the present invention, the lower sideband after being modulated by the carrier wave is used because a method using the upper sideband has a practical disadvantage. For example, as shown in Figure 6, if 2/7 fsc is used as the carrier wave for the high frequency component, the upper sideband after modulation will be 5
．． 2-7.5M1. It appears in almost an appropriate frequency band, but the lower sideband k is 3.2 to 5.5 M! (Appears in 2 and causes crosstalk with the upper sideband.The original signal band is
If the frequency is limited to about MH2, the lower sideband and upper sideband can be separated, but the frequency interval is narrow, and separation requires a filter with fairly steep characteristics. This problem can be alleviated by slightly changing the carrier frequency, but the transmission band is 6 MH.
It tends to be narrower than z.

In other words, a method using the lower sideband like the method of the present invention is more advantageous in practice.

The present invention can be used with other television signals having different carrier frequencies, frequency standards, and scanning standards other than those shown here. For example, those skilled in the art will easily understand that it can also be used for PAL and SECAM signals. Furthermore, even if the present invention is a television signal that does not conform to conventional standards, it can also be used for signals of HDTV and enhanced television when the television signal is compatible with NTSC signals. It is.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to minimize changes in the transmission and reception equipment of the current television system, and to maintain compatibility of video and audio with conventional reception devices. It becomes possible to transmit a television signal having a wideband video signal.

[Brief explanation of the drawing]

FIGS. 1 and 2 show block diagrams of embodiment configurations of the transmitting side and receiving side according to the present invention, respectively, and FIGS. 3 and 4 show examples of transmission signal spectra of the present invention and the conventional example. FIG. 5 and FIG. 6 are diagrams each showing an example of a spectrum for explaining the operation of the method of the present invention and a method other than the present invention. 1, 4.12.15...LPF (low pass filter) 2, . 13.18... BPF (band pass filter) 3... 1 modulator 5, 16... multiplier 6, 8.17... adder 7 ・VSB-AM modulator 9... PM modulation Equipment 10... Audio notch filter 11... VSB-AM demodulator 14.
...1 demodulator 19...FM demodulator Fig. 3 Diagram of J transmission signal according to the present invention Fig. 4 Conventional transmission signal O Spare F route (MHz) Fig. 5 Present invention Detailed explanation of (a) (b) (C)

Claims (1)

[Claims] 1. A wideband television signal is separated into a low frequency component below the transmission band of the existing conventional method and a wide frequency component above that, and after modulating this high frequency component, the lower side band becomes the audio signal. A television signal transmission system characterized in that amplitude modulation is performed using a carrier wave that is in a frequency band higher than the carrier wave, and only the lower sideband after modulation is extracted and added to the low frequency component to form a transmission signal. . 2. A receiving device for receiving a transmission signal according to claim 1, further comprising means for separating the transmission signal into a low frequency component below the audio carrier wave and a high frequency component above the audio carrier, and synchronizing the high frequency component with the transmitting side. What is claimed is: 1. A television signal receiving apparatus comprising: means for demodulating using a carrier wave; and means for adding the demodulated signal to the low frequency component.