JPH0426239A - Signal converter - Google Patents

Abstract

PURPOSE:To transmit a sound or a data service signal having the completely same capacity as a satellite broadcasting by a CATV or the like by limiting the band of a video signal and converting a sound signal to a signal caused by a carrier away from the main carrier frequency of the video signal. CONSTITUTION:Satellite broadcasting receivers 301 and 302 output an inputted satellite broadcasting signal 300 after converting it to digital signals 303 and 305 and on the other hand, video signals 304 and 306 having about 4.5MHz band width are demodulated and outputted. Digital signal conversion circuits 307 and 308 convert the digital signals 303 and 305 to 16 QAM signals 312 and 314 in the respective channels of the CATV and output them. Picture processing parts 309 and 310 output the video signals 304 and 306 after limiting the band to 4.18MHz for the normal ground system video signal. VSBAM modulators 316 and 317 execute VSBAM modulation to the band-limited video signals outputted from the picture processing parts 309 and 310 with the respective channels of the CATV as the carriers and output those signals. Thus, without enlarging the band width, the video signal and the digital signal similar to the same channel satellite broadcasting signal can be transmitted in the transmission system of the CATV or the like.

Description

[Detailed description of the invention] [Industrial application field 1 The present invention relates to a signal conversion device.

[Summary of the Invention] The present invention provides a broadcast signal having the same content as a satellite broadcast signal, for example, at a channel arrangement interval of 6 MHz in CATV, etc.
A signal conversion device that converts video signals and audio signals so that they fit within the band without causing any interference, the video signal is band-limited, and the audio signal is limited to the DQPSK used in satellite broadcasting. For example, 1 due to a carrier that is about 4.5 MHz away from the main carrier frequency of the video signal.
By converting to a signal such as 6QAM, the conventional 6M
This makes it possible to transmit voice or future data service signals with the same capacity of 2,048 Mbps as satellite broadcasting on CATV, etc., without changing the channel arrangement for each Hz.

Note that this summary is provided solely for the purpose of quickly accessing the technical content of the present invention, and does not have any influence on the technical scope of the present invention or the interpretation of rights.

[Conventional technology] Conventionally, in order to receive a satellite broadcasting signal and transmit the digital signal (bit rate: 2048M2O48) to a line such as CATV, (a) the current method is to transmit a digital signal of 3 or 4 waves with a 6MHz bandwidth. A method of multiplexing with FDM using DQPSK, which is exactly the same as the digital signal of satellite broadcasting, (b
) A method of transmitting digital signals using TDM at a bit rate of about 8 Mbps with a bandwidth of 6 MHz; (c) A method of decoding the digital signal of the satellite broadcasting signal and modulating the audio signal with the same analog signal as the conventional terrestrial system and transmitting it. The method has been put into practical use.

[Problem to be Solved by the Invention 1] However, in (a) and (b) above, the audio signal is sent to a 6Hz band separate from the video signal, so when used in the same way as a conventional TV, In terms of channel selection, the signal processing on the receiving side is thorough.

In addition, since (c) above is an analog system, which is the same as the conventional method, it is not possible to transmit audio signals of quality equivalent to B mode, and A
Even if it corresponds to the mode, it is not possible to transmit audio signals of 3 or 4 channels, and it is not possible to transmit new information using data channels specified by satellite broadcasting.

An object of the present invention is to provide a signal conversion device that solves the above problems.

[Means for Solving the Problems J] In order to achieve the above object, the present invention provides separation means for separating a video signal, an audio signal, and a digital signal modulated by a data signal from a satellite broadcasting signal, and a video signal from the separation means. Band-limiting means for band-limiting a signal; converting means for converting the digitally modulated signal from the separating means into another digital modulation method; and a video signal from the band-limiting means and a digital modulation signal from the converting means. The invention is characterized by comprising means for synthesizing and outputting.

[Function 1] According to the present invention, with the above configuration, information exactly the same as a satellite broadcasting signal can be transmitted by CATV or the like.

[Embodiment] FIG. 2 shows an example of arrangement of TV signals in CATV. The spacing between each channel is 6 MHz. Adjacent video carrier f
vo, fVI and the audio carriers fAQ, FAI are each maintained at an interval of 6 MHz. The upper sideband of the video signal is flat up to 4.18MHz, and above that it is 4.5M)
It is designed to be attenuated by 25 or 30 dB at z.
An FM converted audio signal is placed at 4.5 MHz. - On the other hand, the lower sideband of the video signal is flat from the carrier frequency to -0.75 MHz, and -1.25 MHz.
It is decreasing towards.

In the TV signal of normal terrestrial broadcasting, the audio carrier is 16 dB lower than the video carrier, but in CATV, the audio carrier is -9 dB lower than the video carrier. ~-14
dB.

FIG. 3 shows a system diagram of a CATV receiver.

The frequency of the CATV signal is normally increased to around 700 MH2 by a double superhetero gain type converter 21, and then the frequency is converted to match the frequency of an empty channel of the TV receiver 22. At this time, a trap may be placed in the receiver at -1.5 MHz (audio carrier) so that the lower audio beat does not interfere.

FIG. 1 shows the configuration of a transmitter for satellite broadcast Z channel according to the present invention.

300 is a satellite broadcasting signal (IGHz) obtained through an antenna (and converter); 301 and 302 are satellite broadcasting receivers which receive digital signals of the input satellite broadcasting signals at 1", '0"' digital signal (2,048 is also □) 303 , 305 is converted and output, and a video signal 304°3 with a bandwidth of about 4.5 MHz is output.
06 is demodulated and output.

307 and 308 are digital signal conversion circuits,
Digital signals 303 from receivers 301 and 302
, 305 for each channel (e.g., Fig. 2 fA
16 (IAM signal 312,
314 and output. 309 and 310 are video processing units, which limit the band of the video signals 304 and 306 from the receivers 301 and 302 to a normal terrestrial video signal of 4.18 MHz as shown in FIG. 2, and output the same. 316
, 317 is a normal VSBAM modulator, which converts the band-limited video signals 313 and 315 output from the video processing units 309 and 310 to each CATV channel (e.g.
Fig. 2 fvo, fv+) is used as a carrier wave to perform VSRAM modulation and output.

330 and 331 are adders, and digital signal conversion circuits 307 and 3 (160AM signal 312 from It
, 314 and video modulation signals 318 and 319 from modulators 316 and 317, respectively, are added and output. The summed output signals 320 and 321 are added together by an adder 332 and outputted as a CATV signal for each channel.

It should be noted that the video processing units 304 and 306 are equipped with four
．． The video signal may be band-limited to about 0 MHz. By doing this, it is possible to secure a sufficient band for the digital audio signal, and conversely, it is possible to lower the level of the digital audio signal, thereby reducing interference to upper channels. Further, in the receivers 301 and 302, the input signal is once subjected to the original error correction decoding and then again to the error correction code to generate the digital signals 303 and 305.
may be output.

The bandwidth of the 16QAM signal is 2.048M bit rate.
Since it is bps, it is 2.048MHz/ with a roll-off rate of 0%.
4 = 0, 512 MHz is required. In reality, it is difficult to transmit signals with a roll-off rate of 0%, so if the roll-off rate is 30%, the bandwidth is 1.3 Xo, 512 =
The frequency becomes 0.6656MHz. Therefore, 4.5MHz
A band of ±0.3328 MHz is required, centered on .

The spectrum near the digital signal in this case is shown in FIG. 4 (numeral 41 indicates the audio signal, and numeral 42 indicates the video signal), assuming that the roll-off is applied half to the transmitting and receiving signals, and the transmitting signal has 30% of the route. Even with the signal configuration shown in FIG. 4, the high frequency components of the video signal are not high in level, so sufficient transmission is possible, but in order to reduce interference from the video signal 42, the bandwidth of the video signal 42 can be set to about 4 MHz. It is also possible to limit it.

Furthermore, as shown in FIG. 5, if the roll-off rate of the audio signal 43 is further reduced to about 20%, the bandwidth of the audio signal 43 becomes 0.6144 MHz, and the adjacent video signal 44°45
The amount of interference will be reduced.

Furthermore, as shown in FIG. 6, the bandwidth of the video signal 46 is slightly narrowed to such an extent that the deterioration is not noticeable (dotted line in the diagram), thereby reducing the amount of interference to the digital signal 47, and at the same time reducing the amount of interference to the video signal 48 of the upper channel. It is also effective to reduce the lower sideband (dotted line in the figure).In particular, for the carrier frequency of the lower sideband of the video signal, the part from 10.7 to -1.25MHz is actually not used. Therefore, it is best to delete this part as much as possible.

Although the above example shows the case where the carrier frequency of the digital signal is separated from the carrier frequency of the video signal by 4.5 MHz, it is also effective to shift the carrier frequency of the digital signal 49 as shown in FIG. here 12
The carrier frequency of the digital signal 49 is moved up by 5 KHz, and the carrier frequency of the digital signal 49 is placed at fa + 4.625 MHz.

In this way, the carrier of the digital signal 49 is positioned in a well-balanced manner between two adjacent channels. Note that even in this case, there is no problem even if the band of the video signal 50.51 is limited as shown in FIG. In addition, in this case, in order to improve the quality of the trap inserted into the adjacent 4.5 MHz in the converter 21 shown in FIG. 3, a trap is added to the converter 21 shown in FIG. It is better to reduce 625 MHz. That is, for example, in the intermediate frequency processing circuit of the converter 21, +1.5M)1z or +
1.375 MI (Insert a trap at z to minimize interference with the video signal.

Also, as shown by the dotted line in FIG. 6, the curve of the lower sideband of the video signal 48 of the upper channel is shaved so that it becomes the same attenuation curve as that of the upper sideband of the same signal 48 of 4.18 to 4.5 MHz. , fv, (carrier frequency of the video signal 48) -1,07 becomes the limit frequency of the video and audio signal 48 of the upper channel, and from fo+4.5MHz to fo+4.
The space between 93 MHz is empty < (0,43 MHz). Therefore, as shown in FIG. 8, 0.43 points in the digital signal are fo+ 4.5 + -= fa+4.715M1
(If z is used, the balance will be better. Note that the roll-off rate of the digital signal in this case is 30%, but it is 20%.
% is also possible.

Although the example explained above was about a 16QAM digital signal, other digital modulation methods such as 640AM may be used for the digital signal. Case 9
As shown in the figure.

Note that when using a multilevel modulation method such as 64QAM, it is also possible to simultaneously transmit conventional analog audio signals. Also, even if the signal is not so multilevel,
It goes without saying that a similar effect can be obtained by removing the lower sideband video signal of the upper adjacent ah.

[Effect of the invention 1] As explained above, according to the present invention, it is possible to transmit the same video signal and digital signal as a satellite broadcasting signal on the same channel in a transmission system such as CATV without expanding the bandwidth. .

[Brief explanation of the drawing]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a CA
FIG. 3 is a diagram showing a TV signal arrangement on a TV, FIG. 3 is a diagram of a CATV receiving system receiving port, and FIGS. 4 to 9 are diagrams showing various examples of spectra of digital modulation signals. 301, 302...Receiver, 307, 308...Digital signal conversion circuit, 30
9, 310... Video signal band limiting circuit. 316, 317... Video signal modulation circuit.

Claims (1)

[Claims] 1) Separation means for separating a video signal, an audio signal, and a digital signal modulated by a data signal from a satellite broadcasting signal; Bandwidth limiting means for band-limiting the video signal from the separation means; A conversion means for converting the digitally modulated signal from the separation means into another digital modulation method, and a means for combining and outputting the video signal from the band limiting means and the digital modulation signal from the conversion means. A signal conversion device characterized by: