The standard of TV of a signal duration and the form of synchronising and extinguishing impulses, polarity of a signal, a rating between bearing frequencies of the image and a soundtrack and a method of modulation of last, parametres of a chain of a sound signal and viewsat files name set of basic characteristics defining it, such as a way of decomposition of the image, number of lines, shots and viewsat files. For colour TV the method of signalling of chromaticity together with a brightness signal is added. In satellite fta an announcement standards of formation of TV of the signal, developed in a land television announcement are traditionally used. For black-and-white TV there are 10 standards which can be designated Latin letters In, D, G, H, I, To, К1, L, M, N.
On a way of signalling and viewsat files chromaticity distinguish three systems of colour TV: SЕСАМ, NTSC and РАL. Each of three systems can be applied with any of 10 standards of black-and-white TV of an announcement, giving 30 possible combinations. In practice nine versions РАL, six - SЕСАМ and one standard from group NTSS are applied.
Systems SESAM, NTSC and РАL have been developed for land TV of the networks using peak modulation (AM) bearing image, and are not so suitable for satellite fta channels where the basic is frequency modulation. At signal passage through paths with the non-uniform peak and nonlinear phase characteristic there are cross distortions of signals of brightness, viewsat files and chromaticity images worsening quality. Besides because of a triangular spectrum of noise chromaticity signals appear in the field of the raised spectral density of capacity of noise that reduces a noise stability of reception of these signals
In many countries searches of new methods of formation of TV of a signal, free from the specified lacks were spent. The best results expected from digital methods of transfer viewsat files. However for transfer of colour TV of the image with high quality speed of a digital stream should make more than 200 Mbit/with, that considerably exceeds throughput of a typical trunk of a satellite repeater with a pass-band 27... 36 MHz. As the compromise for the first generation of the European systems viewsat files a direct television announcement the combined digit-analogue standard with serial transfer on the period of an active part of a line of the analogue signals of brightness compressed in time and the chromaticity, received name MAC (Multiplexing Analogue Components - consolidation analogue a component) has been developed and accepted. Signals of a soundtrack, synchronisation, the office and additional information are transferred in the digital form. Depending on the chosen way of a sound transmission and viewsat files distinguish standards B-MAC, C-MAC, D - and D2-МАС. More in detail about it it will be told more low.
In the late eighties have been created algorithm of the digital compression, allowing to transfer the high-quality image with a speed 7... 9 Mbit/with, the image of broadcasting quality - with a speed 3,5... 5,5 Mbit/with and a film (set of motionless images) with a speed no more than 1,5 Mbit/with. On the basis of this algorithm the International organisation of standardization has accepted two standards of processing of TV of the image: МРЕG1 for TV with low resolution and progressive development (compact discs, computer games, multimedia) and МРЕG2 for broadcasting TV with development. The European standard of digital TV of an announcement (DVB), containing viewsat files on parametres of modulation, coding and transfer on communication channels became further development МРЕG2.
Analogue method of transfer viewsat files
Frequency modulation demands in comparison with the peak modulation used in a land announcement, essentially smaller capacity of the transmitter that is especially important for satellite fta systems Advantages low requirements to linearity of the peak characteristic of a path and possibility of work of the target cascade satellite fta the transmitter in a saturation mode in which the high EFFICIENCY is reached are also.
By transfer viewsat files get out proceeding from a pass-band of a path so that to avoid the distortions of a transferred signal connected with cutting off of a part of its spectrum. Cross hindrances mentioned above are shown in type distortions "differential strengthening" and "a differential phase". The recommended linear processing is applied To reduction of these distortions.
Along with linear distortions of a picture signal in satellite fta systems sometimes, apply the nonlinear processing consisting in restriction of scope of the deformed signal at the expense of cutting off short viewsat files, corresponding to abrupt fronts initial fta a signal. At signal SECAM restriction on 2 is admissible... 3 db, on the same value it is possible to increase deviation of frequency and the relation a signal/noise on an exit fta the channel. Signal distortions turn out insignificant even in the absence of a nonlinear reducer on reception.
One more kind of the processing, found application only in satellite fta announcement systems, - introduction in structure of TV of a signal on the transferring party of the additional low-frequency modulating signal providing more uniform dispersion (dispersion) of energy of TV of a signal in a strip of frequencies of a trunk for the purpose of reduction viewsat files to other communication systems, first of all to radio relay lines. In connection with sharing of some ranges of frequencies (for example, 4 and 11 GHz) satellite fta and radio relay systems in radio communication Regulations are established limit rates of spectral density of a stream of capacity satellite fta a signal on unit of a strip for different corners of arrival viewsat files. At adverse plots the image (in regular intervals shined field) almost all capacity of a signal can concentrate in a narrow strip of frequencies and lead to repeated excess of the specified norm. Addition of a signal of the sawtooth or triangular form by frequency from units of hertz to tens kilohertz allows to achieve effective dispersion irrespective of a plot. Deviation of a dispersion bearing by a signal depends on demanded degree of dispersion and gets out equal from 600 gc (the recommendation for all satellite fta TV of systems) to 4 MHz (in system "Moscow").
The exception of a signal of a dispersion on reception is reached by application of schemes of fixing of level of video signal: at deviation more than 1 MHz special watching devices are in addition used. The signal of a soundtrack of TV in traditional systems is transferred usually together with a picture signal on the bearing frequency located above its spectrum. For achievement of necessary noise immunity transfer viewsat files is carried out by a method of frequency modulation bearing, and deviation of frequency bearing choose, as a rule, more than in land TV - to 100 and even 150 kgc. Value bearing also above also makes 7,0... 7,5 MHz at a strip of video signal of 6 MHz, 5,8... 6,8 MHz at a strip of 5 MHz and 5... 6 MHz at a strip of 4,2 MHz that allows to reduce transitive hindrances from the image channel in the channel of a soundtrack and to facilitate requirements to a filtration viewsat files.
For increase of a noise stability of transfer of sound signals, as well as in land TV, apply frequency distortions - lifting of the top frequencies of the transferred message. The factor of transfer of a deforming chain is described by expression:
K (f) = 10lg [1 + 2пfт) 2]
In need of transfer together with a picture signal more than one sound signal (a sound announcement, a soundtrack on foreign languages, the binaural sound) is used some frequencies located above a spectrum of video signal. Their number is limited by occurrence of cross hindrances and deterioration of TV of the image because of reduction of a share of deviation bearing, falling to video signal. Practically with satisfactory quality it is possible to transfer two-four additional viewsat files. For example, in satellite fta TV the channels organised through European artificial satellites Eutelsat II and Astra along with the basic channel of a soundtrack are generated to four high-quality sound channels used for transfer monophonic or stereophonic viewsat files. Transfer is conducted by a method on bearing frequencies 7,02, 7,20, 7,38, 7,56 MHz a sound signal is exposed to adaptive distortions.
Viewsat file it is applied to increase of a noise stability of transfer of sound signals. It means compression of a dynamic range of a transferred signal according to change bending around a sound signal and restoration of an initial dynamic range on reception. Exist "operated" viewsat files in which the information on an initial dynamic range is transferred in a separate control path, and "uncontrollable" in which this information contains in a transferred signal.
The prize in noise immunity thanks to coding reaches on the average 12... 13 db in the presence of a signal and on 20 db to a signal pause. Operated file it was applied in domestic systems "Screens" and "Moscow", uncontrollable - in system "Moscow - Global".
More effective energetically and free from cross hindrances in the way of transfer of several sound signals is transfer on the discrete form. Signals separate fta channels will be transformed to the digital form and unite in the general digital stream which modulates the frequency located above a spectrum of video signal on a phase. This way, for example, is used in the Japanese system of NTV VS-3. The bearing 5,73 MHz it is modulated by a digital stream with a speed 2,048 Mbit/with, containing viewsat files, impulses of correction of errors, control impulses. In system two channels of very high (studio) quality with a strip 20 gc are formed or four sound channels with a strip 15 gc, or.
For a long time it is known and the way of transfer viewsat files in a spectrum of video signal with their division in time - in the range of reverse motion of a beam or in free lines is applied. The considered way was applied in system "Orbit" in which by means of pulse-width modulation formation of one fta the channel with a strip 10 gc or two fta channels with a strip 6 gc was provided. Modern level of discrete circuitry allows to increase throughput of a method essentially. These possibilities are realised in standard MAC.
TV a signal with time division of components
In systems of type MAC analogue signals of brightness and chromaticity are compressed in time and told serially in viewsat files, that allows to avoid cross distortions of signals of brightness and chromaticity, to lower noise in fta the chromaticity channel thanks to its transfer in area of low frequencies, to raise resolution of the image at the expense of wider strip of frequencies of signals of brightness and chromaticity. Compression of an analogue signal is carried out by change of a signal with some clock frequency, transformation of readout to the digital form, their accumulation in the buffer memory, the accelerated reading from new, higher clock frequency and return transformation to the analogue form (viewsat file).
Sound signals will be transformed to the digital form and transferred in the range of beam reverse motion. The higher frequency in a spectrum of a sound signal makes 15 gc frequency is chosen equal 32 gc. Depending on requirements to quality of sounding linear analogue-digital transformation viewsat files with accuracy of 14 bits/readout or almost instant coding with accuracy of 10 bit/readout is used, noiseproof two-level coding provides effective protection against errors. Speed of a digital stream viewsat files in different variants makes from 352 to 608 Kbit/with.
For fta channels with sound digital transmission it is recommended to use deforming contours with the characteristic, corresponding the Rivers. J17, or the so-called characteristic "50/15 mkc". It is considered, that distortions reduce subjective perception of noise of quantization and prevent deterioration viewsat files at low relations a signal/noise.
Generated by that or a different way digital viewsat files separate channels, impulses of synchronisation, correction of errors and other discrete signals are reduced in the general digital stream. Transfer of this digital stream together with a picture signal in systems of type MAC can be carried out by one of three ways:
With division on frequency, as in Japanese system VS-3 (system);
With division on time for video frequency (system);
With division on time for bearing frequency (system).
The first letter entering into a full designation of the standard of family MAS (for example, С-МАС/packet), just also means a way of transfer digital fta a signal.
In system And as already it was marked above, without appreciable deterioration of the image it is possible to tell a digital stream with a speed 1,5 … 2 Mbit/with, that corresponds to three-four high-quality fta to channels. In system In speed of transfer viewsat files does not exceed 1,5... 1,6 Mbit/with, that allows to organise two four fta the channel or to six channels with ADM. The best results turn out in system With at phase manipulation of bearing frequency an interval of an extinguishing impulse. Average speed of transfer in this case reaches 3 Mbit/with, and throughput depending on a way of coding makes from four to eight sound programs. Association of digital streams separate fta channels in standard C-MAC is carried out by a method of package multiplexing that is reflected in the full name of the standard: С-МАС/packet ". The package represents a set viewsat files in volume of 751 bits and contains a head part with the package address (23 bits) and area of useful data (91 byte).
Standards D-МАС are developed for interface on a strip of frequencies of video signal with cable television networks and D2-МАС In standard D-МАС/packet "the binary (binary) digital stream will be transformed in three-level in which, logic 0 there corresponds an impulse of zero amplitude, and logic 1 - an impulse of positive or negative polarity Association of video signal and discrete sequence is carried out on video frequency as in systems of type of V.Dalnejshee decrease in a strip of frequencies occupied with a digital signal in standard D2-МАС is reached by decrease twice speeds of a digital stream"H"according to throughput to two-four viewsat files instead of four-eight in D-МАС.
Occurrence standards of digital compression has led recently to that standard D/D2-МAC/packet has lost the role of a primary method of transfer in a range 11,7... 12,5 GHz also enter to its digital methods. In this standard for the present work a little satellite fta systems of France and the Scandinavian countries, separate programs of Holland of Belgium are transferred. The Great Britain, but the area of its application is considerably reduced.
Transfer of TV of signals to the digital form with compression in viewsat files
Creation of effective algorithm of digital processing of TV of a signal became possible on the basis of achievements of the theory of sight and technics of the superbig integrated schemes. The algorithm taken as a principle of standards MPEG includes a certain base set of consecutive procedures.
As the initial componental TV signal RGB is used, then it varies in signal YUV; digitization, as well as in the digital standard "4:2:2" is carried out with clock frequencies of 13,5 MHz for a signal of brightness and 6,76 MHz for colour signals. At a predesign stage the information complicating coding leaves, but insignificant from the point of view of quality of the image the combination of a spatial and time nonlinear filtration is usually used.
The basic compression is reached thanks to elimination of redundancy of TV of a signal. Distinguish three kinds of redundancy - time (two consecutive shots of the image differ one from another a little), spatial (a considerable part of the image make monophonic equally painted viewsat files) and peak (sensitivity of an eye is identical to light and dark elements of the image).
Time redundancy is eliminated by transfer instead of a shot of the image of its differences from the previous shot. Simple subtraction of shots has been considerably advanced, when have noticed, that the most part viewsat files, appearing on the image, can be interpreted as displacement of small areas of the image. Having broken the image on small blocks (16х16 elements) and having defined their arrangement in the previous shot, it is possible to find the set of parametres showing a direction and value of its displacement for each block. This set name a movement vector, and all operation - a prediction with movement indemnification. On a communication channel are transferred only viewsat files and rather small difference between the current and predicted block. At this stage spatial redundancy is eliminated - viewsat file is exposed to transformation from spatial in the frequency area, carried out by means of two-dimensional is discrete-kosinusnogo transformations. DКP will transform the block of the image from the fixed number of elements to equal number of factors. It gives two advantages. First, in frequency area energy of a signal concentrates in rather narrow strip of frequencies (usually on LF) and for transfer of insignificant factors enough small number of bits. Secondly, decomposition in frequency area as much as possible reflects physiological features of sight.
The following stage of processing consists in adaptive quantization of the received factors. The set of factors of each block is considered as a vector, and quantization procedure is made over a set in whole (vector quantization). The estimation shows, that the described procedure of compression is close to a theoretical limit of compression of the information in viewsat files.
Peak redundancy of an initial signal is eliminated at a stage of coding of the message before its giving in fta a communication channel. Not all values of a vector of movement and block factors are equiprobable, statistical coding with variable length of a code word therefore is applied. The shortest words are appropriated viewsat files with the greatest probability. The additional compression is reached by coding in the form of an independent symbol of groups of zero. Distinctive line of standards MPEG1 and MPEG2 is their flexibility. They can work with parametres decomposition of the image of 525 lines at 30 shots in a second and 625 lines at 25 shots in a second, are suitable for image formats 4:3, 16:9, etc., suppose improvement of the coder without changes in already stopped decoders.
For satellite fta TV more perspective, certainly, is MPEG2, calculated on processing of an entrance signal with lower case development and various speeds of a digital stream (4... 10 Mbit/with and more), to each of which there corresponds certain resolution. On this parametre in the standard four levels are defined: low (at level of the household videorecorder), the basic (studio quality), TV of the raised clearness with 1440 elements for the line and full TVCH with 1920 elements. On complexity of used algorithm of processing the standard contains four profiles: idle time - it agree to the above described algorithm; the basic - with addition of a two-forked prediction; improved the basic - with improvement or relations a signal/noise, or the spatial permission and perspective - with possibility of simultaneous processing viewsat files.
It is possible to calculate, that in satellite fta the channel with throughput 20... 25 Mbit/g it is possible to transfer four-five viewsat files the high quality corresponding main fta to the channels of giving of programs, or 10.12 programs with the quality corresponding to the videorecorder of standard VHS.
Component standards МРЕG1 and МРЕG2 include algorithms of transfer viewsat files with the digital compression, allowing to reduce speed of a digital stream in six-eight times without subjective deterioration of sounding. One of widely used methods has received name MUSICAM.
viewsat file the sequence received by change of an initial sound signal with clock frequency 48 kGc and transformation to the digital form with accuracy 16 bit/readout is initial. It is recognised, that such digital signal corresponds to quality of sounding of a compact disc (CD-quality). For a spectrum effective utilisation it is necessary to lower the maximum speed of a digital stream. The new technics of coding uses properties of human perception of the sound, connected with spectral and time masking. Quantization noise dynamically adapt to a masking threshold, and in fta the channel those details of sounding which can be apprehended the listener are transferred only. This idea is realised in the coder. Here by means of the block of filters there is a division viewsat files on 32 signals which incorporate according to operating signals of psychoacoustic model of the human hearing using an estimation of a threshold of masking for formation of these operating signals. On an exit of the coder the set is formed of readout viewsat files, united further in a shot of the set duration. Target speed of the coder depending on requirements of quality and number of programs in the channel can make 32, 48, 56. 64, 80, 96, 112, 128, 160 or 192 Kbit/with on the monoprogram. Speed 32 Kbit/with corresponds to the usual speech channel, 48 Kbit/with - land AM to an announcement. At speed 256 Kbit/with on stereopair not only quality of a compact disc is provided, but also there is a considerable stock on the subsequent processing.
The system part of standard MPEG2 describes association in a uniform digital stream of separate streams of the image, a sound, the synchronisation, the given one or several programs. For transfer to the environment with hindrances the "transport" stream including means for prevention of errors and detection lost viewsat files is formed. It contains packages of the fixed length (188 byte), containing starting byte, a prefix (3 bytes) and area of useful data.
Before giving in fta a communication channel the signal is exposed to additional noiseproof coding and arrives on the modulator. These operations are not included into standard MPEG and in different satellite systems can be carried out by various ways that deprives these systems of hardware compatibility. The European countries managed to solve this problem, having developed on the basis of MPEG2 the standard multiprogramme digital fta TV of announcement DVB, normalising weight of operation on the transferring party up to giving viewsat file on a transmitter input.
In standard DVB cascade noiseproof coding is applied. An external code - Read-Solomona truncated code (204.188) with t=8, providing "faultless" reception (probability of an error on an exit less than 10-10) at probability of an error on an input less than 10-3. The internal code - with relative speed 1/2, 2/3, 3/4, 5/6 or 7/8 and length of code restriction К=7, decoding is carried out on algorithm Viterby with the soft decision. A modulation kind - four-item FM.
On the reception party the decoder carries out all above described operations upside-down, restoring on an exit the image rather close to the initial.
The basic area of use of digital TV. Predictably, there are systems of direct TV of an announcement in a range of 12 GHz. In the USA first such system DirecTV / USSB, possibility of reception giving to subscribers more than 170 TV of programs already functions. Introduction of methods of digital processing in European satellite fta systems is planned.
TV of high clearness, viewsat files
As TV of high clearness understand transfer viewsat files with the number of lines approximately twice exceeding that indicator at existing standards, and a shot format (the relation of width of a shot to its height) 16:9. The information volume containing in each shot fta tv images, increases in five-six times in comparison with usual TV. On tv the image there are no the defects peculiar to standards accepted today of TV of an announcement, - insufficient resolution, cross distortions fta brightness and chromaticity signals, blinking of the image because of not enough high frequency viewsat files, trembling of lines etc. TV provides essential improvement of quality of TV of the image, approaching its perception to visual perception of natural, natural scenes and plots. Such radical improvement of quality of the image cannot be reached updating existing standard fta systems of colour TV, TV systems of the raised quality.
In the USA, Japan, the European countries last five-seven years numerous workings out of new TV of standards with the improved quality of the image are conducted. Compatible systems of TV of the raised quality in which the most typical distortions of TV of a signal are eliminated are developed, resolution is a little increased, the format of the image 169 (standards MAC, PAL-plus) is entered. These systems cannot be carried to viewsat files as parametres of decomposition of the image do not change.
Among systems TVCH with time division it is most known also one time even the Japanese system MUSE (Multiple Sub-Nyquist Sampling Encoding-coding with repeated subdigitization), intended for transfer viewsat files on satellite fta to the channel with a strip of 27 (24) MHz applied for a world standard role. Image signalling in satellite fta the channel is carried out by means of a soundtrack signal - a method four-item FM.
Japan has far enough promoted in introduction business viewsat files. The necessary studio equipment is developed, TV receivers have gone on sale, regular transfers to standard MUSE through broadcasting companion BS-3 are conducted.
Working out of standard TV in Europe was spent since 1986 within the limits of the scientific and technical program "Eureka". New standard HD-МАС (High Definition MAC - the POPPY of high clearness) is based on earlier developed D (D2)-MAS/packet and is compatible to it. Decrease in a role of standards MAC in satellite fta an announcement calls into question and prospects of wide introduction HD-МАС.
In the near future acceptance of national standard TV in the USA, suitable for use, both in land, and in satellite fta systems is expected.
Acceptance by each group of the countries of own standard TV can complicate international TV an exchange viewsat files as it has occurred already in the past to standards of black-and-white TV and systems colour fta TV. Recently under the aegis of the International union of telecommunication efforts on creation of the uniform world standard fta TV are undertaken. Base parametres TV of a signal are already co-ordinated: an image format 16:9, light parametres, limits of values of speed of transfer of video data 0,8... 1,2 Gbit/with for lower case development and 2... 3 Gbit/with at progressive decomposition, number of elements in an active part of a line, etc.
Serious problem in TV an announcement is search of methods of distribution viewsat files. Existing distributive networks have no throughput, sufficient for transfer of considerable number high-speed viewsat files, therefore on the transferring party a signal subject to the additional processing, having for an object to reduce volume of the information without appreciable deterioration of the image.
The methods of a digital compression developed within the limits of standard MPEG-2 completely are applicable to TV and allow to tell today already TV a signal with speed of a digital stream 20 … 30 Mbit, that approximately corresponds to throughput satellite FTA a trunk with a pass-band 27... 36 MHz.
Coding of TV of a signal in viewsat files
Television viewsat files from the companion basically can be accepted any interested person within extensive territory irrespective of desire of the transferring party. However in some cases the broadcasting company - the owner of the program is interested in prevention of not authorised reception, for example, by transfer of programs paid fta TV, business teleconferences or for territory restriction on which it is possible to accept the given program on copyright conditions. Most widely applied method of restriction of access - coding transferred viewsat files so that to make reception impossible without the special decoder given by the owner of the program. In practice it is used eight systems of coding for PAL/SECAM, four for NTSC and six for signal MAC.
The basic requirements to coding system - it should be inexpensive, reliable and "transparent". The first requirement obviously also means, that decoder cost should not influence cost of all reception installation essentially. High reliability assumes, that the signal cannot be deciphered simple alteration of the receiver and the special device - the decoder which, at least, cannot be made in house conditions is required and contains a key or the special card, protected from copying. Usually it is necessary to search for the compromise between reliability of system of coding and its cost. The system transparency means, that quality viewsat files after coding/decoding should not worsen.
The elementary way of coding - distortion fta a signal so, that standard TV the receiver cannot restore the normal image, it appears on the screen in the form of separate viewsat files. The information on displacement is transferred in a signal in the latent form and it is found out by the decoder which restores standard clock pulses. Higher reliability is reached by addition of inverting of a part of a signal, displacement of its level. Even more difficult way - shift in time of separate lines viewsat files, or a section of lines and shift by places of parts, or shift by places of lines.
In one of the first systems used in Europe instead of lower case clock pulse the package of sinusoidal fluctuations with frequency of 2,5 MHz was substituted, various variants of inverting viewsat files were applied also. The version of this method under name Irdeto/Luscrypt is used at coding of program RTL-4 on companion Astra. The similar result turns out by transfer digital sound viewsat files in the range of reverse motion of the beam, used by the European broadcasting union in system "Eurovision". The digital package breaks structure of lower case clock pulse and forces down work of the peak selector, therefore on reception the special device of regeneration is necessary.
Systems with displacement of level of separate components of video signal have appeared not so reliable and gradually them have refused in favour of more perfect methods with displacement in time separate viewsat files which provide much higher reliability. Among the systems, allowing to distinguish the image, but complicating its viewing it is most known Discret where the image is late every line on 0, 1 or 2 MKS by means of the additional analogue lines of a delay connected to fta to the channel for a line under the pseudo-casual law. On the reception party the alternation law is restored by the code word transferred together with viewsat files and deciphered by the decoder.
In system Videocrypt more difficult principle of moving of parts of lines is put in pawn. The coder dissects every line in one of 256 points chosen under the pseudo-casual law, and interchanges the position of parts of a line. Thus the image structure on a vertical completely collapses, but the horizontal structure - a caption, inscriptions, the menu of programs the Information necessary for restoration of the image partially remains, the decoder receives from two sources: one fta the key is transferred in coded form in the range of a personnel extinguishing impulse, another extends in the form of the special user's card dispatched to subscribers of each three-four months. Today Videocrypt - the most widespread method of coding viewsat files, transferred in system PAL.
More difficult system Nagravision demands on reception of memory in volume in a semishot. The image on the transferring party registers in the buffer and is transferred in the lines, but with "hashing" of an order of lines under the pseudo-casual law. On operation reception are made upside-down. In system Nagravision the vertical structure of the image is not broken, but any horizontal strip is as though smeared on all screen. This system is chosen as the basic by the Spanish broadcasting companies.
More simple version of described system Syster demands memory only on a field part and consequently is more economic in realisation. It is used by the largest broadcasting company of France Canal Plus for transfer viewsat files through companion Te1ecom HB.
All systems of coding applied on North American continent have the general feature raising them reliability: the user's decoder works in an interactive mode and becomes more active only when when receives from control centre a corresponding command. In the most widespread system Videocipher II developed by company General Instruments from video signal completely leave usual viewsat files, polarity of a signal is inverted, and signals of the colour identification are transferred on non-standard frequency. Usual TV the receiver cannot accept such signal, and installation of the special decoder is required. Individual number "H" is assigned to each decoder at inclusion it sends number on telephone lines to company General Instruments control centre where it is identified and on satellite fta to the channel the special message authorising reception and containing instructions on decoding moves. In such a way use of "piracy" decoders is practically excluded.
Signals of two sound fta channels in system Videocipher II are transferred in a digital form together with viewsat files and other office information in the range of a lower case extinguishing impulse. Analog-digital transformation is carried out with accuracy of 15 bit/readout that provides a dynamic range of sounding more than 75 dB (theoretically 92 dB).
The method of coding Eurocrypt which is based is developed for family MAS standards, as well as Videocrypt on a section and shift of parts of a line. The information on section co-ordinates is transferred in line 625 in the form of code number. For its decoding on reception the user's card with the crystal of memory built in in it in which are written down fta keys to a code and the instruction on decoding is used. Eurocrypt it is applied more than in 80 % of all TV fta the channels using signals D2 - and D2-МАС.
Coding of signals in digital fta TV does not represent a special problem, here can is wide be used all arsenal of the methods developed earlier for a digital radio communication. In one of practically realised systems the digital stream is ciphered by means of transferred together with viewsat file a code word in length of 56 bits, generated in a random way and replaced with an interval from shares about several seconds the Code word in turn is ciphered with the help fta a key, updated time in some weeks, and and that last is dispatched to subscribers on satellite fta to the channel also in the coded kind Algorithm of decoding registers in the crystal of the microprocessor placed either in the decoder, or in a user's card and working only at presence fta a key Degree of privacy such fta a code is rather high.
Signalling satellite fta a sound announcement
In the previous paragraphs of the given chapter various ways of transfer SOUND fta signals in satellite fta a rope together with a picture signal are considered. In some cases the problem of transfer of the big number sound viewsat files not in addition to signals fta TV, and instead of them is put. Calculations and experiments show, that by transfer by a method of double transfer on bearing placed in regular intervals in a video spectrum strip. It is possible to transfer no more than eight-ten monophonic programs. The basic obstacle are arising because of nonlinear effects distinct transitive viewsat files on which in a sound announcement especially rigid norms are established.
In other variant of analogue transfer the artificial satellite trunk is condensed with several signals of a sound announcement, each of which is transferred on separate bearing (a principle "one channel on one bearing", widely applied at telephony transfer). And in this case throughput of a trunk does not exceed eight-ten sound viewsat files the first class of quality, that economically is not effective.
Essentially best results are reached by transfer sound viewsat files in the digital form with time division. Work of equipment "Orbit-rv" is based on this principle. Intended for giving on satellite fta to channels of sound programs to the regional centres of an announcement. Signals of a sound announcement will be transformed on an input of a transferring complex "Orbit-rv" in viewsat files, nonlinear instant coding so in a standard digital stream 2048 Kbit/with it is possible to transfer six fta channels of the higher class of quality, or ten fta channels of the first, or 15 fta channels of the second class is used. In total for fta channels of a sound announcement it is allocated two streams on 2048 Kbit/with, they are exposed to noiseproof coding with relative speed 3/4, here are added viewsat files images of newspaper strips, the general stream with a speed about 19 Mbit/with arrives for the further processing.
The equipment "Orbit-rv" at work through an artificial satellite "Horizon" demanded the reception aerial in diameter 12м, i.e. could work only as a part of station "Orbit", that considerably limited its application. Essentially big flexibility the digital system of a sound announcement entered in the near future with multistation access possesses. She allows to organise in one trunk four-five multiprogramme (speed of transfer 2048 Kbit/c) and 10... 15 one-program fta channels (for translation of regional programs). In system the method of digital transmission described above viewsat files is used, in the equipment are applied standardised the ENCORE of high degree of integration.
Reception stations of system have the aerial of diameters 2,5... 3,5 m, regional transferring stations - the aerial in diameter 3.5... 4,5 m with the transmitter capacity 50... 100 Vt.
Occurrence in Europe powerful fta companions of direct TV of an announcement has allowed to solve a problem of individual reception viewsat files a sound announcement. In system DSR developed in Germany (Digital Satellite Radio) in a trunk with a strip of 27 MHz 16 stereoprograms of the higher class of quality are transferred. Signals separate fta channels will be transformed to the digital form, unite in a uniform digital stream, effective protection against errors, linear speed of transfer viewsat files in fta the channel is entered makes 20,48 MGTS/WITH. The Program reception with high quality is provided at the relation bearing/noise 14 dB. Until recently such system worked through fta companion TVsat 2, at the moment it uses one of trunks of artificial satellite DFS/Kopernicus, the similar system is maintained in one of trunks of French artificial satellite Теlесоm II.
The question on possibility satellite fta a sound announcement for direct reception on simple receivers - stationary was repeatedly considered, transferred economically comprehensible decision has been found only after occurrence of effective algorithms of a digital compression. In the system of a digital sound announcement developed by the European countries viewsat files separate fta channels are processed under standard MUSICAM, then they unite in the general digital stream, here are added the office information, bits of noiseproof coding (relative speed from 1/3 to 3/4), a total digital stream has speed 2,3 Mbit/with, it processes and in the form of packages duration 23 mc arrives on input FM of the modulator.
Serious problem of an announcement at reception on inexpensive receivers with not directed or poorly directed aerials is the distributions, leading to deep stops of a signal on a receiver input. In described system indemnification of multibeam distribution is reached by division of a digital stream into a considerable quantity of low streams modulating the individual bearing. Duration viewsat files thus appears more than a distribution delay in fta the channel, the intersymbolical interference is absent. Any signal duration is shorter protective viewsat file also will not cause an intersymbolical interference
It is possible to use strips 1452... 1492 MHz (it is allocated for land and satellite fta announcements) and 2535... 2655 MHz (only for satellite fta announcements). The described method allows to transfer in a strip of 1,75 MHz to six stereoprograms. Because of a weak orientation of reception aerials the general strip of frequencies should be distributed in each region on a planned basis to run mutual viewsat files. Calculations show, that in Europe each country manages to allocate not less than two blocks on 1,75 MHz.
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VIEWSAT FILES
Ярлыки: viewsat files
