JPH0462513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an energy diffusion method implemented in satellite television broadcasting.

In satellite broadcasting, the frequency band used for downlink (e.g. 12 GHz band) is shared by terrestrial fixed services, broadcasting services, etc., but it is easier to protect terrestrial fixed services from satellite broadcasting services. In order to achieve this, we applied energy diffusion to make the spectral distribution of FM television radio waves uniform. According to current technical standards, the spectral power flux density measured in any 4kHz bandwidth is 22 dB compared to the power measured in the entire frequency band. This is expected to be decreasing.

The present invention aims to improve the diffusion effect compared to conventional methods in energy diffusion during such satellite television broadcasting.

[Prior art]

Traditionally, energy dispersion is based on the vertical scanning frequency of the television image signal (60Hz in the NTSC standard system;
A triangular wave with a period related to 50Hz for the PAL system and 60Hz for the 1125-line high-definition television (HDTV) system, specifically 30Hz or 15Hz for the NTSC system.
The Hz triangular wave was used as a spread signal and was superimposed on the television image signal. The frequency deviation at that time is about 600kHz, which is the same as the power flux density mentioned above.
Satisfies 22dB reduction. Furthermore, the effect of energy diffusion becomes greater as the amplitude of the superimposed triangular wave is increased, but if the amplitude is increased too much, interference will be caused to adjacent channels.

On the other hand, as in satellite broadcasting, television
Interference in FM transmission appears as beat interference on the screen. When energy is diffused using a 30Hz or 15Hz triangular wave as in the past, this beat frequency also changes at a cycle of 30Hz or 15Hz, respectively.
This change is recognized as flicker on the television screen. This is because the change is slow, so if you evaluate the beat frequency that visually causes the most interference, this becomes a guide to the interference on the screen.
The above can be expressed as a disturbance state as shown in FIG. In this case, as can be seen from the figure, the disturbance changes slowly, and when conventional energy diffusion was used, the movement of the beat stripes caused by the disturbance was clearly visible.

〔the purpose〕

The object of the present invention is to eliminate the above-mentioned conventional drawbacks, to make the beat disturbance appearing on the television screen as inconspicuous as possible, and to
The object of the present invention is to provide an energy diffusion method that can be applied to various scrambling methods as described later.

An object of the present invention is to provide an energy diffusion method particularly suitable for FM transmission such as 1125-line HDTV using the time axis compression multiplex subsampling method.

[Key points of the invention]

In order to make beat disturbances that appear on television screens less noticeable, the present invention uses a triangular wave associated with an extremely short horizontal scanning period as a spreading signal compared to conventional methods, and also time-division multiplexes a luminance signal and a chrominance signal. In order to be suitable for various types of television signals, the duty of the triangular wave (the time division ratio between the rising and falling parts) is not necessarily 50% as in the past.

That is, the present invention responds to the timing based on a television image signal in which a color signal and a luminance signal are time-base compression multiplexed and made independent of each other, and the period is the horizontal scanning period of the image signal or an integral multiple thereof, and the change is made. The present invention is characterized in that a spread signal consisting of a triangular wave whose curved point is located at the boundary between a luminance signal and a chrominance signal in units constituting the image signal is formed, and the spread signal is superimposed on the image signal in synchronization with the image signal.

Here, it is defined that the triangular wave includes one having a flat part corresponding to the horizontal synchronization period and clamp period of the television image signal.

[Embodiment] FIG. 2b shows the waveform of the spread signal used in the present invention together with the time-domain compression multiplexing (TCI) signal to be transmitted shown in FIG. 2a.

That is, in this embodiment, the horizontal synchronization period and clamp period of the transmission signal are set at a constant level,
It is a triangular wave that rises in the color signal portions C1 and C2 and falls in the luminance signal portion Y.

It will be explained below that the diffusion effect is improved by setting the period of the diffusion signal to be the horizontal scanning period or an integral multiple thereof. In other words, when the frequency of the spread signal is increased, for example, when the repetition frequency is increased to a frequency corresponding to the horizontal scanning period, as shown in Figure 3, the fluctuation period of the beat disturbance that appears on the screen becomes shorter, which is the problem that appears in the conventional method. The flicker-like interference will no longer be visible, and the interference will no longer be visually noticeable. More precisely, at this time, a crepe-like beat disturbance pattern will appear on the screen, but since its fluctuation period is short, it is necessary to look at the average level instead of looking at the peak of the disturbance as in the conventional method. Therefore, the appearance of the beat stripes is much improved compared to the conventional method shown in FIG.

Figure 4 shows an example of the configuration of the transmitting side when performing FM transmission by satellite by superimposing the spread signal (triangular wave) with the horizontal scanning period shown in Figure 2b on the TCI signal shown in Figure 2a. show.

The TCI signal encoder 1 supplies the counter 2 with a control signal and a clock signal for controlling the duty of the triangular wave and the timings of the flat part, rising part, and falling part. The counter 2 counts the clock signals based on the control signal, performs counting up to a predetermined timing with a counting slope according to the duty, and converts the triangular wave in the form of a digital signal into an analog signal using the D/A converter 3. After converting the signal into a triangular wave, its amplitude is adjusted by a variable attenuator 4, added to the TCI signal by an adder 5, and taken out from an output terminal 6.

FIG. 5 shows an example of a configuration for removing the above-mentioned spread signal from a signal received on the receiving side to obtain a transmission signal (TCI signal). The received signal is input terminal 1
1 to synchronization signal and clock signal regeneration circuit 12
is added to create a clock signal and a control signal,
These two signals are supplied to the counter 13 to generate a triangular wave in the form of a digital signal with the same waveform as the triangular wave generated on the transmitting side. After converting this into a triangular wave of an analog signal by the D/A converter 14, adjusting the amplitude of the triangular wave by the variable attenuator 15, and subtracting it from the received signal in the subtracter 16, the spread signal can be removed. I can do it. The signal obtained in the above manner is supplied to the TCI signal decoder 17 to restore a high-definition television signal.

In the above, the spread signal is applied to counters 2 and 13.
It is formed through digital circuits such as
Of course, this can also be created directly in an analog way.

Next, a case will be described in which the energy diffusion method according to the present invention is applied to scrambled TCI signals. The scrambling method is a method in which the positions of the color signals C1, C2 and the luminance signal Y are swapped within one horizontal scanning period, and the horizontal scanning periods in which the swapping occurs and the horizontal scanning periods in which the swapping is not performed are determined by a pseudo-random signal. It shall be. FIG. 6a shows the transmitted signal when the positions are simply swapped, and FIG. 6b shows the spread signal in that case.

In this embodiment, due to a simple position change, discontinuity occurs in the superimposed spread signal (see FIG. 6b), which may cause damage to the horizontal synchronization period or clamp period.

Note that when the spread signal in FIG. 2b is used for the transmission signal in FIG. 6a, the triangular wave changes from a rising portion to a falling portion in the middle of the luminance signal during the horizontal scanning period when the position is swapped. Therefore, if the removal of the spread signal on the receiving side is insufficient, it tends to interfere with the viewing of television programs.

In order to avoid this, as shown in Fig. 7a and b, during the horizontal scanning period in which the positions are exchanged, the time arrangement of the luminance signal Y and color signals C1 and C2 is reversed. Make it. In this case, as can be seen from FIG. 7b, no discontinuity occurs in the spread signal, so that the above-mentioned drawbacks such as damage to the horizontal synchronization period or clamp period do not occur.

In addition, in the above explanation, as a transmission signal
We assumed TCI signals, which is the current standard method.
Of course, even with NTSC signals, a triangular wave with a horizontal scanning period in which the horizontal synchronization period is flat, the horizontal blanking period corresponds to the rising part, and the signal period corresponds to the falling part may be used as the spreading signal. It is.

Furthermore, the spread signal of the horizontal scanning period is
In the case of signals, the horizontal synchronization period and clamp period are flattened, and in the case of NTSC signals, the horizontal synchronization period is flattened. This is because the flat portion may become unstable and the clamp level may become unstable, making it difficult to reproduce high-quality television images. However, if there is no such fear, this flat portion may not necessarily be provided.

Furthermore, it goes without saying that the various triangular waves described above may have their polarities reversed.

Note that in the method of the present invention, the FM of the television signal
Even in transmission, if beat interference has already occurred, the purpose is to make the change in beat interference less noticeable due to energy diffusion.
The period of the triangular wave, which is a spread signal, is one horizontal scanning period.
Of course, it does not have to be a period, but may be a time length corresponding to a plurality of periods (even in this case, a spread signal that changes sufficiently quickly can be obtained).

〔effect〕

By carrying out the present invention, the period of fluctuation of the beat disturbance appearing on the television screen is shortened, and it is possible to perform energy diffusion with a much greater diffusion effect than in conventional systems. In addition, when the period of the spread signal explained in the example is set to the time length of one horizontal scanning period, the duty of the triangular wave that is the spread signal is not 50%, and the boundary (inflection point) between the rising part and the falling part is Since it is located between the luminance signal Y and the color signals C1 and C2, even if the removal of the diffused signal is insufficient on the receiving side, it is unlikely to cause visual interference.

Further, when the transmitted signal is scrambled, even if the scrambling is performed by simply exchanging the positions, a sufficient spreading effect can be obtained without causing much interference to the transmitted signal. (See Figure 6) Furthermore, as in the embodiment shown in Figure 7, if the time sequence of the signals in the horizontal scanning period where the positions are swapped is reversed, discontinuities will not occur in the spread signal. Therefore, completely good characteristics can be obtained including the horizontal synchronization period and clamp period.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the state of beat disturbance by the conventional spreading method, Fig. 2 a and b are signal waveform diagrams showing the waveform of the TCI signal and the waveform of the spread signal transmitted by the present invention, and Fig. 3 is FIG. 4 is an explanatory diagram of the state of beat disturbance by the spreading method of the present invention.
A block diagram showing an example of a circuit for superimposing a spread signal on a TCI signal; FIG. 5 is a block diagram showing an example of a circuit on the receiving side for removing a spread signal from a superimposed and transmitted signal according to the present invention; 6th
Figures a and b are diagrams showing an example of scrambling by simple position swapping, and Figures 7a and b are diagrams showing an example of scrambling in which the time arrangement of signals is reversed in the horizontal scanning period with position swapping. be. 1...TCI signal encoder, 2...counter, 3...
D/A converter, 4... variable attenuator, 5... adder, 6... output terminal, 11... input terminal, 12... synchronization signal and clock signal regeneration circuit, 13... counter, 14... D/A converter, 15... Variable attenuator, 16...subtractor, 17...TCI signal decoder.

Claims (1)

[Scope of Claims] 1. In response to timing based on a television image signal in which a color signal and a luminance signal are time-base compression multiplexed and made independent of each other, the period is the horizontal scanning period of the image signal or an integral multiple thereof; The method is characterized in that a spread signal consisting of a triangular wave whose inflection point is located at the boundary between a luminance signal and a chrominance signal of units constituting the image signal is formed, and the spread signal is synchronously superimposed on the image signal. Energy diffusion method. 2. The energy diffusion method according to claim 1, wherein the triangular wave has a flat portion corresponding to a horizontal synchronization period and a clamp period of the image signal.