JPH0457420A - Video signal multiplex transmission system - Google Patents

Abstract

PURPOSE:To increase a video signal channel number available of transmission per one satellite repeater without deterioration in a video signal by synthesizing both two-channels of video base band signals while one is subject to frequency shift so as to avoid the overlap of the signal onto the other video base band signal in terms of frequency. CONSTITUTION:A 1st video base band signal in received 1st and 2nd video base band signal is frequency-shifted at a frequency shift addition means 3 so that the band of the 1st video base band signal is not overlapped onto the band of the 2nd video base band signal, the shifted 1st video base band signal is added to the 2nd video base band signal to generate a multiplexed video signal. The multiplexed video signal is fed to a filter inverse frequency shift means 4 via an FM modulation transmission means and a reception FM demodulation means. The filter inverse frequency shift means 4 filters the 2nd video base band signal from the multiplexed signal to reproduce the 2nd video base band signal and applies inverse frequency shift to the frequency shift implemented on the sender side to reproduce the 1st base band signal.

Description

[Detailed Description of the Invention] [Summary] Regarding a video signal multiplex transmission system used in wireless communication, particularly when transmitting video signals using a repeater mounted on a satellite, the present invention relates to a video signal multiplex transmission method that is used for transmitting video signals using a repeater mounted on a satellite. In order to increase the number of video signal channels that can be transmitted per unit, a frequency shifting/adding means is provided on the transmitting side, and a frequency shifting/adding means is provided on the receiving side.
Filtering and inverse frequency shifting means are respectively provided, and the input first . After frequency-shifting the first video baseband signal of the second video baseband signal by the frequency shifting/adding means so as not to overlap the band of the second video baseband signal, the second video baseband signal is A multiplexed video signal is generated in addition to the video baseband signal of A second video baseband signal is regenerated from the converted video signal using the filtering and inverse frequency shifting means, and a frequency shift opposite to that performed on the transmitting side is performed to produce a first video baseband signal. Configure it to play.

[Industrial application field]

In recent years, satellite communications that use geostationary satellites as relay stations have been rapidly developing, and video signal transmission is one of the communication media that uses satellites.

Here, the signal transmission bandwidth of the repeater is 27 MHz.

Alternatively, there are those with a frequency of about 36 MHz, and about 24 or 36 such repeaters are mounted on one geostationary satellite. The standard method is to transmit a video signal in one channel using one repeater.

Now, the main functions of a repeater are frequency conversion and power amplification. For example, a signal that reaches a satellite at a frequency in the 14 GHz band is frequency converted to 12 GHz by the repeater, and then the power is transferred to an amplifier using a traveling wave tube. It is amplified by an amplifier and sent back to Earth.

There is distortion in the input/output characteristics of this power amplifier.

The greater the output power, the greater the distortion of the signal. Therefore, an FM modulation method is used to transmit video signals, which causes less deterioration even when there is distortion in the transmission path.

However, with such a modulation method, the transmission bandwidth is, for example, 27
When using a MHz repeater, transmission of one channel of video signals is the limit.

On the other hand, since repeaters mounted on satellites are very expensive, it is strongly desired to increase the number of video signal channels that can be transmitted per repeater without deteriorating the video signals.

[Conventional technology] FIG. 13 shows a block diagram of a conventional example.

Hereinafter, a case will be described in which the transmission bandwidth of the repeater 75 is 36 MHz and two channels of video baseband signals are transmitted.

First, on the transmitting side, there is one FM modulator for one channel of video baseband signal, and the center frequency of the FM modulator is shifted so that the outputs of the two FM modulators do not overlap. However, this shift amount is 18 MHz between the center frequencies of the FM modulated waves.

Now, the FM modulator 71 generates an FM modulated wave using the #2 video baseband signal and sends it to the adder 73, and the FM modulator 72 generates an FM modulated wave using the #1 video baseband signal. It is also sent to the adder 73.

Therefore, the two FM modulated waves are arranged on the frequency axis by the adder, but the bandwidth of each Fl'l modulated wave is 18M.
The modulation degree is adjusted so as not to exceed Hz.

Then, the output of the adder 73 is transmitted to a transmitter 74 at a predetermined frequency of 1.
Since the signal is sent to the repeater 75 on the satellite at a predetermined power level, the repeater converts the signal to another predetermined frequency and power and sends it to the receiving side.

On the receiving side, a receiving section 76 frequency-converts and amplifies the radio waves from the repeater 75, and then demodulates them using FM demodulators 77 and 78 corresponding to the respective video carrier waves to generate a #2 video baseband signal and a #1 video baseband signal. Play the signal.

That is, one radio carrier wave is allocated to one video signal channel, and one repeater is configured to transmit a plurality of radio frequency signals.

[Problem to be solved by the invention]

Here, as mentioned above, two radio carrier waves pass through one repeater.
It becomes a wave. On the other hand, since the power amplifier of the repeater has nonlinearity in its input/output characteristics, common amplification of two waves generates unnecessary wave noise due to intermodulation products.

Therefore, in order to avoid such problems, the back-off of the power amplifier of the repeater is increased to, for example, 6 dB to lower the output power and reduce the noise caused by the intermodulation product.

As a result, the C/N of the signal received by the earth station is significantly degraded, and the quality of the reproduced video signal is degraded.

That is, when a video signal is transmitted through at least two channels, the C/N ratio of the received signal is significantly degraded, and the quality of the reproduced video signal is also degraded accordingly.

In order to improve the quality of the video signal, the diameter of the receiving antenna of the earth station (a parabolic antenna is used for boat fishing) must be increased, resulting in a significant increase in cost. Furthermore, the range of use of such large-diameter antennas is limited to international satellite communications.

Further, as a conventional example of transmitting multiple video signals using a single carrier wave, there is a method of time division multiplexing and transmitting, but this method has drawbacks such as increased hardware size and poor compatibility with NTSC video equipment.

An object of the present invention is to increase the number of video signal channels that can be transmitted per repeater without deteriorating the video signal.

[Means to solve problems] FIG. 1 shows a block diagram of the principle of the first invention.

In the figure, 1 is an FM modulation/transmission means, and 2 is a reception/jM demodulation means. 3 is a frequency shift/addition means; 4
is a filtering/inverse frequency shifting means on the receiving side.

Then, enter the first . After frequency-shifting the first video baseband signal of the second video baseband signal by the frequency shifting/adding means so as not to overlap the band of the second video baseband signal, the second video baseband signal is In addition to the video baseband signal, a multiplexed video signal is generated.

This multiplexed video signal is transmitted through FM modulation/transmission means, reception/FM
It is applied to the filtering and inverse frequency shifting means via demodulation means. This filtering/inverse frequency shifting means filters the multiplexed signal to reproduce the second video baseband signal, and also performs a frequency shift opposite to the frequency shift performed on the transmitting side to reproduce the first video baseband signal. Play.

Figures 2 and 3 are 2. The principle block diagram of the third invention is shown.

In the figure, 32 and 34 are transmission side balanced modulation parts, and 33 is a subcarrier generation part, both of which are components of the frequency shift part 31 in the frequency shift/addition means 3.

The transmission side balanced modulation section 32 uses subcarriers to send out a first video baseband signal whose frequency is shifted by a predetermined frequency, but another transmission side balanced modulation section 34
transmits a first video baseband signal whose frequency is shifted by a predetermined frequency and a subcarrier within a predetermined level range.

FIG. 4 shows a block diagram of the principle of the fourth invention.

In the figure, 43 is a subcarrier extraction section, and 44 is a receiving side balanced modulation section, both of which are components of the inverse frequency shift section 42 in the filtering/inverse frequency shift means 4.

Then, the reception side balanced modulation section 44 uses the subcarriers extracted from the multiplexed video signal in the subcarrier extraction section 43 to reverse frequency shift the frequency of the multiplexed video signal and reproduce the first video baseband signal. do.

FIG. 5 shows a block diagram of the principle of the fifth invention.

In the figure, 5 is a baseband processing means, and 6 is a baseband inverse processing means.

Then, the baseband processing means on the transmitting side receives the first . Horizontal in the second composite signal.

The vertical synchronization signal is converted into a small amplitude horizontal and vertical synchronization signal having a predetermined amplitude smaller than the amplitude of the horizontal and vertical synchronization signals, and a pseudo first. A composite signal of the two is generated.

This pseudo-first. The two composite signals are converted into a multiplexed video signal according to the first aspect of the present invention and sent to the receiving side. On the receiving side, pseudo first . A second composite signal is extracted and applied to baseband inverse processing means.

The baseband inverse processing means converts the small amplitude horizontal and vertical synchronization signals into the horizontal and vertical synchronization signals to reproduce the first and second composition signals.

That is, by multiplexing and transmitting video signals, cross-modulation is eliminated, so the power amplifier does not need to perform hack-off. Therefore, the number of video signal channels that can be transmitted per satellite repeater can be increased without deterioration of the video signal.

[Operation] The present invention frequency-shifts one of the video baseband signals of the two channels, and synthesizes the two signals so that they do not overlap in frequency with the one-spant signal to the other video. Then, the carrier wave is frequency modulated using this multiplexed baseband signal and transmitted.

On the receiving side, in order to demodulate and reproduce one of the video baseband signals, a frequency shift opposite to that on the transmitting side is performed to obtain a video baseband signal. The other video baseband signal is obtained by removing the frequency-shifted video baseband signal using a filter.

〔Example〕

6 is a block diagram of the first embodiment of the present invention, FIG. 7 is a block diagram of the second embodiment of the present invention, FIG. 8 is an explanatory diagram of the operation of FIG. 7, and FIG. 9 is a block diagram of the third embodiment of the present invention. ．． A block diagram of the embodiment of the fourth invention, FIG. 10 is an explanatory diagram of the operation of FIG. 9, FIG. 11 is a block diagram of the embodiment of the fifth invention (transmission side),
5 shows a block diagram (receiving side) of the fifth embodiment of the present invention.

Note that the symbols on the left side of FIGS. 8 and 10 indicate the waveforms of the portions with the same symbols in FIGS. 7 and 9. Also, the same reference numerals indicate the same objects throughout the figures.

Here, the frequency shift portion 31. The adder 32 is a component of the frequency shifting/adding means 3, the filtering section 41.degree., the inverse frequency shifting section 42 is a component of the filtering/inverse frequency shifting means 4, and the transmitting side balanced modulator 321. Bandpass filter 32
2 is a component of the transmitting side balanced modulation section 32, the transmitting side balanced modulator 341 . The bandpass filter 342 and the DC voltage application section 343 are components of the transmission side balanced modulator 34.

In addition, the receiving side balanced modulator 421. Bandpass filter 4
22. Subcarrier generator 423. Alternatively, the bandpass filter 424 is a component of the inverse frequency shift section 42, and the synchronization signal separator 5L 52. Switches 52, 56, high efficiency synchronous signal generators 53, 57. Adders 54 and 58 are components of the baseband processing means 5, and a synchronization signal separator 6164
．． NTSC synchronization signal generator 62.65. switch 63
．． 66 is a component of the baseband inverse processing means 6.

First, the operations in FIGS. 6, 7, and 9 will be explained with reference to FIGS. 8 and 10.

As shown in FIG. 6, the input first video baseband signal (hereinafter abbreviated as #1 video BB signal) is transmitted to the frequency shift portion 31 as a second video baseband signal (hereinafter abbreviated as #1 video BB signal).
2 video BB signal) is added to the adder 32.

In the frequency shift part, as shown in Figure 7, #1 video B
The B signal is applied to the internal balanced modulator 321 on the transmitting side, but since the subcarrier (for example, 9 MHz) from the subcarrier generator 331 is also added here, it is possible to obtain a double-side band signal with suppressed subcarriers. signal (hereinafter referred to as DSB
(abbreviated as "signal") is obtained (see Fig. 8--■, ■).

The upper sideband of this SB signal is removed by the roll-off filter 322 and added to the adder 32, but since the #1 video BB signal is added here as described above, it is synthesized (see Fig. 8). ~■, ■see).

As a result, #1 video BB signal and #2 video BB signal are changed from DC (50Hz in the figure) to 9M) as shown in Figure 8-■.
This results in frequency multiplexing within the baseband band up to 1z. Hereinafter, the multiplexed signal will be referred to as a multiplexed video signal.

This multiplexed video signal is subjected to FM modulation on a carrier by the FM modulator 11 shown in FIG. 6, and by appropriately selecting the degree of modulation, an FM modulated wave with a bandwidth of 27 MHz or 36 MHz can be obtained. The transmitter 12 transmits this FM modulated wave to a repeater on the satellite, and the receiver 21 receives the FM modulated wave returned from the repeater.

The receiving section 21 frequency-converts and amplifies the received signal and sends it to the FM demodulator 22, so this demodulator obtains a multiplexed video signal as shown in Figure 8 (■), but this multiplexed video signal is filtered. portion 41 and frequency shift portion 42.

Here, the filter section 41 is composed of a band-pass filter 411 as shown on the right side of FIG. 7, and the #2 video BB signal is reproduced by this filter.

In addition, in the receiving side balanced modulator 421 in the frequency shift part, the product of the multiplexed video signal and the subcarrier from the subcarrier generator 423 is taken, and after performing a frequency shift opposite to that on the transmitting side, the band pass #l video BB with shaped filter 422
The signal is played.

In FIG. 9, the balance degree of the transmitting side balanced modulator is changed so that subcarriers are output.

For this reason, a DC voltage is applied to the transmitting side balanced modulator 341 via the DC voltage application part 343 to disturb the balance of this modulator, so that the #1 image is DSB signal and subcarrier generator 33 by BB signal
1 appears at the output side of the transmitting side balanced modulator 341, while at the input side of the FM modulator 11, the subcarriers from FIG.
A multiplexed video signal as shown in (2) is obtained.

Now, this multiplexed video signal (including subcarriers) is F
It is sent to the receiving side via the M demodulator 11.

On the receiving side, the FM demodulator 22 extracts the multiplexed video signal and applies it to bandpass filters 411 and 424 and a balanced modulator 421 on the receiving side. Therefore, the narrowband bandpass filter 424 extracts subcarriers from the multiplexed video signal and applies them to the receiving side balanced modulator.

As a result, after the product of the multiplexed video signal and the subcarrier is calculated in the same way as described above, the #1 video BB signal is reproduced using the bandpass filter 422.

Further, the #2 video BB signal is reproduced through the bandpass filter 411.

In this case, since the subcarrier for one frequency shift is shared between the transmitting side and the receiving side, it is possible to avoid video waveform distortion due to the frequency difference.

Next, FIGS. 11 and 12 show a system in which the inefficiency of an NTSC composite signal (a signal generated by combining a blanked image signal and a synchronization signal) is improved and transmitted.

That is, of the amplitude of the NTSC video 8B signal, an amplitude of about 30x is allocated to the horizontal and vertical synchronizing signal parts. Therefore, this synchronization signal is replaced with a synchronization signal of small amplitude (only the amplitude of the synchronization signal is reduced) using a switch to multiplex the video BB signal.

By limiting signals unrelated to video quality to the necessary minimum in this way, it is possible to narrow the occupied bandwidth when performing FM modulation.

Now, the IIL #2 N5TC video signal is input to the synchronization signal separators 55 and 51 and switches 56 and 52. When the synchronization signal separators 55 and 51 detect a synchronization signal in the corresponding NTSC video signal, they send the detection signal to the switch 56.
52 and the high-efficiency synchronization signal generators 57 and 53.

Switches 56, 52 are then switched from an on to an off state, blocking passage of the corresponding NTSC video signal. Further, the high-efficiency synchronization signal generators 57.53 generate synchronization signals having an amplitude of about 5, for example, 30.chi.

Hereinafter, the NTSC video signal replaced with the small amplitude synchronization signal from the high efficiency synchronization signal generator will be referred to as a pseudo NTSC video signal.

The pseudo #I NTSC video signal from adder 58 is sent to transmitter balanced modulator 321 . Subcarrier generator 3
31. After frequency shifting with bandpass filter 322,
The adder 32 multiplexes the signal with the output from the adder 54 to obtain a multiplexed video signal.

In addition, since the switches 56 and 52 are in the on state for parts other than the synchronization signal, the #L#2 NTSC video signal passes through the adder 58 and 54 as it is and is multiplexed by the adder 32, so the adder 32 A multiplexed video signal with a small amplitude synchronization signal is applied to the mouth modulator 11 from .

On the other hand, on the receiving side in FIG.
, 411 to pseudo #I NTSC video signal, pseudo #2
An NTSC video signal is sent out.

When the synchronization signal separator 64.61 detects a small amplitude synchronization signal from the corresponding pseudo NTSC video signal, it drives the N5TC synchronization signal generator with the synchronization signal detection signal and simultaneously switches the switches 66 and 63 to the N5TC synchronization signal generator side. knock down.

Therefore, the #I N5TC video signal and #2 N5TC video signal in which the small amplitude synchronization signal is replaced with the regular N5TC synchronization signal are sent out.

This makes it possible to narrow the band of wireless transmission, and also allows NTS
This enables a highly compatible interface with C video equipment.

That is, since cross-modulation is eliminated by multiplexing and transmitting video signals, the power amplifier does not need to take backoff. Therefore, the number of video signal channels that can be transmitted per satellite repeater can be increased without deteriorating the video signal.

[Effects of the Invention] As described in detail above, according to the present invention, the number of video signal channels that can be transmitted per satellite repeater can be increased without deteriorating the video signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the first invention, and FIG. 2 is a block diagram of the principle of the second invention.
FIG. 3 is a block diagram of the principle of the third invention, FIG. 4 is a block diagram of the principle of the fourth invention, FIG. 5 is a block diagram of the principle of the fifth invention, 6 is a block diagram of the first embodiment of the present invention, FIG. 7 is a block diagram of the second embodiment of the present invention, FIG. 8 is an explanatory diagram of the operation of FIG. 7, and FIG. 9 is a block diagram of the third embodiment of the present invention. ．． A block diagram of the embodiment of the fourth invention, FIG. 10 is an explanatory diagram of the operation of FIG. 9, FIG. 11 is a block diagram of the embodiment of the fifth invention (transmission side), and FIG. FIG. 13 shows a block diagram of an embodiment of the present invention (receiving side), and FIG. 13 shows a block diagram of a conventional example. In the figure, ■ indicates FM modulation/transmission means, 2 indicates reception/FM demodulation means, 3 indicates frequency shift/addition means, 4 indicates filtering/inverse frequency shift means, 31 indicates frequency shift section, and 42 indicates inverse frequency shift section. . Figure 3 Envy Figure 10

Claims (1)

[Claims] 1. On the transmitting side, after the FM modulation/transmission means (1) generates an FM modulated wave using the input signal,
It is converted into electric power and sent to the wireless line, and on the receiving side, the receiving/FM demodulating means (2) receives the FM modulated wave, and when demodulating and extracting the input signal, the transmitting side performs frequency shifting and addition. The means (3) is provided on the receiving side, and the filtering/inverse frequency shifting means (4) is provided on the receiving side, and the first video baseband signal of the input first and second video baseband signals is provided on the transmitting side. After frequency shifting the band signal by the frequency shifting/adding means so as not to overlap the band of the second video baseband signal,
In addition to the video baseband signal, a multiplexed video signal is generated, and the multiplexed video signal is used as the input signal to perform the FM modulation.
In addition to the transmitting means, on the receiving side, the multiplexed video signal taken out from the receiving/FM demodulating means is regenerated into a second video baseband signal using the filtering/inverse frequency shifting means, and the transmitting side A video signal multiplex transmission system characterized in that a first video baseband signal is reproduced by performing a frequency shift opposite to the frequency shift performed in . 2. The frequency shift section (31) in the frequency shift/addition means (3) uses the subcarrier generation section (33) and the subcarriers from the subcarrier generation section to generate the first video baseband signal. 2. The video signal multiplex transmission system according to claim 1, further comprising a transmission side balanced modulation section (32) for shifting the frequency of the video signal by a predetermined frequency. 3. The frequency shift section in the frequency shift/addition means uses a subcarrier generation section (33) and subcarriers from the subcarrier generation section to change the frequency of the first video baseband signal by a predetermined frequency. 2. The video signal multiplex transmission system according to claim 1, further comprising a transmitting side balanced modulation section (34) which outputs subcarriers in a predetermined level range while shifting the subcarriers. 4. The inverse frequency shift section 42 in the filtering/inverse frequency shift means (4) uses a subcarrier extraction section (43) for extracting input subcarriers and subcarriers from the subcarrier extraction section. Receiving side balanced modulation part (4
4). The video signal multiplex transmission system according to claim 1, comprising: 5. The first and second composite signals including horizontal and vertical synchronization signals are converted into first and second video baseband signals, and a baseband processing means (5) is provided on the transmitting side and a baseband processing means on the receiving side. Inverse processing means (6) are respectively provided, and on the transmitting side, the baseband processing means converts the horizontal and vertical synchronization signals in the input first and second composite signals to a value smaller than the amplitude of the horizontal and vertical synchronization signals. The first and second pseudo composite signals generated by replacing them with small amplitude horizontal and vertical synchronization signals having a small predetermined amplitude are subjected to the frequency shift and
It is sent to the wireless line via the addition means (3) and the FM modulation/transmission means (1), and on the receiving side, it is sent via the reception/FM demodulation means (2) and the filtering/inverse frequency shifting means (4). The obtained pseudo first and second composite signals are processed by replacing the small amplitude horizontal and vertical synchronization signals with the horizontal and vertical synchronization signals by the baseband inverse processing means (6), and A video signal multiplex transmission system characterized by reproducing composition signals.