RU2101878C1 - Method of multiplexing of broadcast television radio channel - Google Patents

Abstract

FIELD: television engineering, applicable in broadcast television systems, mainly direct television via artificial earth satellites. SUBSTANCE: broadcast television radio channel is multiplexed by the polarization method, when two television signals U₁ and U₂ produced with the aid of synchronous and cophasal scanners with similar frequency bands and without a frequency intermittency of spectra, with special "polarization channel identification signals" separated in time introduced in their composition, are transmitted at similar carrier frequencies, but with different polarization of radio waves. EFFECT: enhanced information content transmitted via the broadcast television radio channel with preservation of compatibility with the existing television systems. 6 wdg

Description

 The invention relates to television technology and can be used in broadcast television systems, mainly direct television (NTV) via artificial Earth satellites (AES).

 Known methods of multiplexing a television channel: frequency, time and combined time-frequency, which solve the problem of increasing the amount of transmitted information, subject to compatibility with the black-and-white television system (BST). For color television systems (CT), additional information is color information, for stereo color systems (CCT) about the second frame of a stereo pair, for systems with increased image quality, information provides an additional increase in clarity, increase in frame format, etc. So, with the frequency compression method, the main luminance signal, which determines the overall sharpness of the image, is transmitted by a wide frequency band, and additional information signals are transmitted by narrow frequency bands on a subcarrier, the frequency of which is chosen close to the upper edge of the spectrum of the luminance signal. In DT systems, three luminance and two color-difference signals are transmitted, with a band ratio of 4: 1: 1 (or 4: 2: 2 in component systems) [1] For example, in the PAL DT system, with the frequency multiplexing of a television channel, quadrature modulation of the color subcarrier is applied color signals.

 In the time-frequency compression method (CT SECAM system), color difference signals are also transmitted on the color subcarrier, but alternately through the line, with further restoration of the simultaneity of signals in the receiver using the delay line for the time of the horizontal interval.

 A temporary compaction method (IAC system) was developed specifically for satellite television. With this method, luminance and chrominance signals undergo time compression operations and are transmitted in turn during the row time: part of the row interval is the compressed luminance signal, the other part is one of two compressed color-difference signals alternating through the line or both color-difference signals one after another in some versions of MAK systems . On the receiving side, the luminance and color signals are restored to their original form and fed to the video inputs of the receiver, or the television signal is encoded using one of the composite CT systems and fed to the antenna input of the receiver.

 In SCT systems where the image of two frames of a stereo pair is transmitted, the number of signals must be increased. So, in SCT systems compatible with the PAL CT system or the NIIR CT system, one stereo pair frame is transmitted in color by three signals in the usual 4: 1: 1 frequency band ratio, and the second monochromatic frame is transmitted by an additional narrow-band brightness signal with a total band ratio of 4 : 1: 1 + 1. In the SCT system compatible with the CEKAM CT system, three narrow-band signals of the second frame are additionally transmitted with a band ratio of 4: 1: 1 + 1: 1: 1.

 A common disadvantage of the above methods of compression is that no additional sealing signal should in principle have the same wide frequency band as the main brightness signal due to violation of the compatibility condition with the black-and-white television system.

 With frequency multiplexing, this would lead to unacceptable interference, and with a temporary unacceptable decrease in clarity or a decrease in frame rate.

Of the known technical solutions, the closest in technical essence to the claimed method is the combined frequency-polarization compaction method, in which two TV radio signals are transmitted over the air simultaneously at the same carrier frequency, but with orthogonal polarization of the radio waves. This method has been proposed for the DT system, an alternative to the known ones, and for stereo television systems, black and white or color. One radio signal transmitted the main luminance signal V _Y1 (in the SCT system, a narrowband luminance signal of the second frame of the stereo pair V _Y2 was added to it by frequency multiplexing), and the second radio signal transmitted two color-difference signals V _{(RY) 1} and V _{(BY) 1} , previously transferred to color subcarriers F _add1 and F _add2 , equal to the odd harmonics of the half-line frequency, to ensure the interleaving of the spectra ( _figure 1). On the receiving side, the luminance and color signals were obtained with mutual interference, since during the propagation of radio waves the polarization orthogonality can be violated. Therefore, an antenna designed to receive radio waves of a certain polarization also receives a weakened signal, which was transmitted with orthogonal polarization. The attenuation of interference from differently polarized radio waves in terrestrial broadcasting conditions is at least 18 dB ≈ (10 times) according to the CCIR data. The clarity of interference on the screens of black and white TVs is also reduced due to the frequency interleaving of the spectra of luminance and color difference signals. And in color and stereo televisions designed to receive such signals, it is possible to completely eliminate the interfering signal. If on the transmitting side the luminance signal V _Y V _Y1 + V _Y2 and the color signal V _C V _{(RY) 1} + V _{(BY) 1} , then on the receiving side, taking into account mutual interference, the luminance signal U _Y V _Y + aV _C and the signal chroma U _C V _C + aV _Y , where "a" and "b" are the coefficients of adding one signal to another. To completely decouple the luminance and color signals in each gain channel, the corresponding fraction of the other is subtracted from one signal
U _YCOR = U _Y aU _C V _Y + aV _C + a (V _C + bV _Y ) V _Y (1-ab);
U _CCOR = U _C bU _Y V _Y + bV _Y + b (V _Y + aV _C ) V _C (1-ab).

 A sign of determining the coefficients "a" and "b" in the formulas for "cleaning" is the signal level in those parts of the spectrum where it should not be (Fig. 2).

The frequency-polarization method of compaction also ensures full compatibility with any central heating system if the full color television signal (PCTS) of this system V _Y1 + V _C1 is transmitted with one polarization, and with orthogonal polarization in the same radio channel and on the same carrier frequency F _from the signal is transmitted additional information V _add , previously transferred to the subcarrier F _add , equal to the odd harmonic of the half-line frequency, so that the frequency interleaving of the spectra is obtained (figure 3). An additional signal can transmit an image of the second frame of a stereo pair or information of the edges of the main mono frame to increase the format, etc.

 The disadvantages of the prototype method of frequency-polarization compaction is that the frequency band of the compression signal of additional information should be less than that of the main brightness signal, because of the need to first transfer it to the subcarrier frequency, and the automation of determining the coefficients presents some technical difficulties "a" and "b", since it is necessary to select certain sections of the frequency spectrum (comb filter or other) and weigh the signal there, which depends on the transmitted image CONTROL.

 The aim of the invention is to double the amount of information transmitted via a broadcast television channel, while maintaining compatibility with existing television systems.

This goal is achieved by the fact that the broadcast channel of the broadcast television is compressed by the polarization method, in which two television signals U ₁ and U ₂ are generated at the same carrier frequencies, but with different polarization of the radio waves, generated using synchronous and common-mode scanning devices with the same frequency bands and without frequency interleaving of spectra, with special “polarization channel identification signals” (SIPC) introduced into their composition, which are separated in time.

Television signals U ₁ and U ₂ can be: PCTs of different programs encoded in different or identical CT systems, CCT [1-4] with different or the same scrambling laws or without it; television signals of one program, and then one of them is encoded by any DT system, and the other can be a television signal of a high-quality second color frame of a stereo pair; television signal of additional information for a system with a modified frame format or for a high-definition television system, etc.

 Thus, the proposed method for compressing a broadcast television radio channel is significantly universal in character and can be used to double the number of transmitted programs, without expanding the frequency range, to transmit mono-images of high quality and high definition, to transmit stereo programs while maintaining compatibility with existing television systems.

 The method can be used to seal radio channels of terrestrial television, but is primarily recommended for satellite radio channels for the following reasons.

 For direct broadcasting, satellites in geostationary orbit are used, the number of points on which is limited, as well as the number of frequency channels for broadcasting. Under these conditions, the double use of each frequency channel is very valuable.

 A satellite transmitter "illuminates" an area thousands of times larger than any VHF ground transmitter with tens of millions of subscribers. Therefore, even when transmitting one program with two radio signals (high-quality C DT, mono images of high quality and high definition), its cost increase due to the use of a second transmitter is not significant.

 A conventional TV cannot directly receive radio signals from a satellite, therefore, a two-channel signal processing path of different polarization is created in a satellite receiver, without affecting the circuit of a conventional TV.

 Receiving antennas of satellite television have a narrow radiation pattern and aim at satellites along the line of sight, which virtually eliminates the reception of radio signals reflected from any ground objects with a change in polarization. Decoupling due to different polarization is at least 28dB (25 times).

Each of the radio signals is received by its antenna with a corresponding polarizer (or one more complex antenna with two polarizers) and passes its own processing and amplification path in a satellite receiver. Due to crosstalk, each channel has its own TV signal with the addition of a weakened alien. In the first channel U _I U ₁ + aU ₂ , in the second channel U _II U ₂ + bU ₁ , where "a" and "b" are the coefficients of adding one television signal to another. In order to completely decouple the television signals U ₂ and U ₂ in each gain channel, the corresponding fraction of the other is subtracted from one signal in the same way as the prototype:
UI _COR U _I aU _II U ₁ (1-ab);
UII _COR = U _II bU _I U ₂ (1-ab).

To automate this operation and determining the coefficients "a" and "b" of the television signals U _1, U ₂ are special "signals identify the polarization channel" CASI-1 in the signal U ₁ and CASI-2 U ₂ signal. SIPK signals are transmitted in the intervals of the first or last lines of the field, the image of which practically goes beyond the picture tube frame. SIPK-1 and SIPK-2 are transmitted in one control line, but with a time spacing, or in two different control lines. In form, these can be video pulses ranging from white to black (Fig. 4, a), or a group of video pulses (Fig. 4, b), or radio pulses with different frequency filling (Fig. 4, c), etc.

 A sign of determining the coefficients "a" and "b" is the level of the corresponding SIPK at those times when it should not be (figure 5).

If the television signals U ₁ and U _{2 are} encoded according to one of the variants of the IAC system or according to the MUSE system, then, as is known, memory devices are included in the decoder circuit. Coefficient "a" is determined by the value of the signal in those cells of the memory of the signal U ₁ that correspond in time to the SIPK-2 signal, and where obviously there should not be a signal U ₁ . The coefficient "b" is determined by the magnitude of the signal in the cells of the memory of the signal U ₂ , which correspond to the time SIPK-1.

When signals are simultaneously output from the memory, U _I aU _II and U _II bU _{I are} subtracted digitally.

And if the television signals U ₁ and U _{2 are} encoded by some composite CT systems, then the “cleaning” can be carried out, for example, according to the following functional diagram (Fig. 6), we select the SIPC in the form of a video pulse (Fig. 4, a) .

The functional circuit contains 1 receiving channel of the signal U _I (which is a standard satellite television receiver, at the output of which the television signal is unipolar, i.e., without loss of DC component); 2 identical receiving channel of the signal U _II ; 3 delay line; 4 adder; 5 inverter; 6 adjustable signal divider U _II ; 7 - shaper control voltage; 8 block of comparators; 9 video amplifier; 10 diagram of the key AGC signal U ₁ ; 11 delay line; 12 adder; 13 inverter; 14 adjustable signal divider U _I , 15 driver voltage control; 16 block of comparators; 17 video amplifier; 18 schematic of the key AGC of the signal U ₂ ; 19 shaper strobe pulses.

A device for "cleaning" the signals from mutual interference contains a receiving channel of the signal U _I 1, the output of which is connected to the input of the adjustable signal divider U _I 14 and to the input of the delay line 3, the output of which is connected to the first input of the adder 4, the output of which is connected to the input of the unit comparators 8 and to an input of the video amplifier 9 the output of which is removed television signal U ₁ and which is connected with an input key circuit AGC signal U ₁ 10 whose output is connected to the control input of the video amplifier 9, the gate pulse generator 19, one output otorrhea connected to the control input of the comparator 16, and a second output connected to a control input of the comparator unit 8, the output of which is connected to the input of the control voltage 7, the output of which is connected to the control input of the adjustable divider signal U _II 6 whose output is connected to the input of the inverter 5 whose output is coupled to a second input of the adder 4, the receiving signal U _II channel 2, whose output is connected to the input of an adjustable signal divider 6 U _II and to the input of delay line 11, whose output is connected to a first input an adder 12 whose output is connected to the input of the comparator block 16 and to an input of a video amplifier 17, the output of which is removed television signal U ₂ and which is coupled to the input circuit key AGC signal U ₂ 18 whose output is connected to the control input of the video amplifier 17, the comparator unit 16 the output of which is connected to the input of the driver of the control voltage 15, the output of which is connected to the control input of an adjustable signal divider U _I 14, the output of which is connected to the input of the inverter 13, the output of which is connected to the second input of the adder 12.

The frequency pulses F _p and F _floor , necessary for the operation of the key AGC circuits of the signals U ₁ and U ₂ and the gate pulse shaper, are taken from the sweep circuits synchronized in the usual way.

 Adjustable signal dividers 6 and 14 can be performed, for example, in the form of a double differential circuit, which allows you to adjust the amplitude of the output signal by changing the potential at the control input.

 Shapers of control voltage 7 and 15 can be performed similarly to shapers of control voltage for adjusting brightness, contrast and saturation in remote control circuits of modern television receivers.

For the correct operation of the device for "cleaning" signals from mutual interference, it is necessary to first establish the same signal levels U _I and U _II using the AGC of satellite television receivers. Then, in the first channel of the device, SIPK-2 is extracted from the signal U _I by the method of temporary selection and its level is compared with the black level in the block of comparators. The signals “more” or “less” are fed to the driver of the control voltage, at the output of which the voltage increases or decreases until the signal U _II , which passed the adjustable divider and inverter, is summed with the signal U _I until the component aU _II completely disappears in the signal U _i . Similar operations with the corresponding signals are carried out on the second channel until the component in U _I completely disappears in the signal U _II . After that, the ranges of the corrected signals are finally set to nominal in the video amplifiers covered by AGC circuits.

 Thus, the polarization method of densifying a broadcast television’s radio channel with television signals generated using synchronous and common-mode scanning devices, with the same frequency bands and without frequency interleaving of the spectra, with special “polarization channel identification signals” introduced into their composition, allows achieving several advantages over with the prototype.

Existing receivers can receive two programs in the same frequency channel with the corresponding image quality color or black and white, as the method provides complete compatibility. At the same time, the versatility of the method in relation to the information transmitted by the signals U ₁ and U ₂ allows the release of new televisions that adapt to the quality of the transmitted program and reproduce images in black and white and color mono and stereo, with a 4/3 or 16/9 format, with increased clarity, etc., depending on what material is transmitted, the receiver is tuned automatically by an additional signal for recognizing the quality of the program or an additional feature embedded in the SIPC, which is not considered in this application.

Claims (1)

A method of sealing a broadcast television radio channel, based on the fact that the broadcast television channel is compressed by the polarization method, in which two television signals U ₁ and U ₂ are transmitted at the same carrier frequencies, but with different polarization of the radio waves, characterized in that the television signals U ₁ and U ₂ are formed by the in-phase synchronous and deploying devices with the same frequency bands with the introduction into their structure of special identification signals polarization channel that occupy about A certain place in the free lines of each of the television signals is separated by time between each other, and in the receiver the differently polarized signals received by the corresponding antennas are simultaneously amplified to nominal levels and detected in two parallel channels, and then the second signal is identified from the first signal by the method of temporary selection polarization channel, whose level equal to the level of crosstalk is compared in the comparator with the black level, as a result of which voltage, which determines an adjustable division ratio divider through which the first signal channel and a second signal is supplied is subtracted from the first signal to remove crosstalk, and the second channel signal is carried out similarly subtraction and elimination of crosstalk from the first signal.

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