The standards videos analogue


PAL PAL NTSC SECAM
Abu Dhabi Madeira Antigues old Allemagne (Est)
Afghanistan Malawi Antilles Arabie Saoudite
Afrique du Sud Maldives Aruba Bénin
Albanie Malaisie Bahamas Bulgarie
Algérie Malta Barbades Cameroune
old Allemagne (Ouest) Monaco Bermudes Congo
Argentine Mozambique Bolivie Côte d’Ivoire
Australie Namibie Birmanie Chypre
Autriche Népal Canada Djibouti
Azores Netherland Chili égypte
Bahrain Nigeria Colombie France
Bangladesh Norvège Corée du Sud Gabon
Belgique Nouvelle-Guinée Costa Rica Gambia
Botswana Nouvelle-Zélande Cuba Grèce
Bhoutan Oman Curacao Guadeloupe
Brésil Ouganda équateur Guiana
Brunel Pakistan El Salvador Gulana-Fr
Cambodge Paraguay états-Unis Hongrie
Chine Portugal Guam Iran
Corée du Nord Qatar Guatémala Iraq
Cyprus-Turk Sabah Haiti Jibuti
Danmark Sarawak Hawaï Jordanie
Dubal Sierra Leone Honduras Lebanon
Espagne Singapoure Iles Cayman Lybie
Finlande Sri Lanka Iles Galapagos Luxembourg-Fr
Ghana Somalie Iles Vierges Madagascar
Gibraltar Soudan Jamaïque Mali
Groënland Suède Japon Martinique
Hong Kong Suisse Mexique Mauritanie
Iles Canarie Swaziland Micronésie Monaco
Iles Chanel Tanzanie Midway Island Mongolie
Iles Falkland Tchad Nicaragua Morocco
Iles Seychelles Thaïllande Okinawa Niger
Iles Solomon Tibet Panama Nouvelle Calédonie
Indes Tonga Pérou Pologne
Indonésie Transkei Phillipines Polynésie-Fr
Irelande Turquie Ponape Rép. Guyana
Iceland Turkménistan Porto Rico Réunion
Israël Union des émirats Arabe République Dominicaine Roumanie
Italie Uruguay Saïpan Sénégal
Jordanie Vatican Samoa Syrie
Kénya Vietnam St Kitts Tahiti
Koweit Yémen St Thomas Tchécoslovaquie
Laös Yougoslavie Surinam Togo
Lesotho Zambie Taïwan Tunisie
Liberia Zanzibar Trinidad Union états Indépendants(ex-URSS)
Luxembourg-All Zimbabwe Vanuatu Uper Volta
Macau   Vénézuella Zaïre
Terrestrial analogical television or TAT is the whole of the network of ground diffusion made up of transmitters (pilot) and local relay transmitters. This network uses waves known as hertzian.
The analogue signals SECAM and PAL in Europe, NTSC in the United States of America or Japan of the transmitters are received on the antennas VHF and UHF individual or collective which allow, according to the site features, of variable qualities of image, having been the subject of a coding.
Composition of an image
The fundamental characteristics of all the systems of television were mainly defined compared to physiological considerations of the human eye, such as:
Retinal persistence: 1 ⁄ 20 of second.
Resolution of the eye: 1 ' of angle approximately.
The golden section: concept of normal distance from observation of an object according to its dimensions (5 to 7 times its diagonal for a rectangular object, according to the painters)
In order to avoid an effect of flutter, the principle of structuring the image in two interlaced frames (even and odd frame) was selected. The period of each frame being of 1 ⁄ 50 of second, is that of the electrical communication.
To solve the problem of the vertical shift of the two frames without requiring too much precision of the generators of sweeping, it was fixed an odd number of lines, the first frame starting in the centre of the edge higher of the screen and the second than the upper left corner.
This system of double frame interlaced is common to all the standards of analogical television. The frame consists of two movements, one horizontal, describing a line from left to right on the restored image, the other vertical one, placing the lines the one under the others, top to bottom, these lines constituting the frame.
Each one of its movements includes two phases, a useful phase during which the useful signal of translation of the image is formed, a phase of suppression at the time which the movement of the spot is reversed. During this time, the signal is put at a constant tension of reference: the level of suppression.
It is necessary to synchronise the movement line and frame:
by insertion of a signal of synchro line
by insertion of information of synchro weaves.
In the principal standards, the number of lines is of
625 for the standards PAL and SECAM
525 for standard NTSC of use in Japan, the United States and Canada.
The number of frames per second is respectively of 25 and 30.
The period of an image is fixed at 40 ms, and thus that of a frame at 20 ms (Europe) .1 ⁄ 64 the frequency of sweeping line is thus of 625 X25, that is to say 15.625 Hz, or a period of 64 µs. For a format 4 ⁄ 3 the number of points per line is of 625 X 4 ⁄ 3, that is to say 833 points.
The band-width is maximum when one alternates the black spots and white, crenel of which the frequency is half of the transmitted points:
833 ⁄ 2 items X 625 lines X25 images ⁄ second = 6,5 MHz
This crenel would require the transmission of ten harmonics to be restored, in practise we observe great uniform zones which induce weaker frequencies. Time between two points of a line is T = (1 ⁄ 625) X (3 ⁄ 4) X 64 µs; the band-width of a first order system whose time of assembled to 90% gives 2,3 X T is a band-width of 2,3 ⁄ (2 X p X T) = approximately 4,77 MHz which is a theoretical value nearer to reality.
The time reserved for the return of sweeping is used to transmit impulses ensuring the synchronisation of the cycles of sweeping between transmitter and receiver. These signals are composed of several phases called:
pre-equalisation
synchro weaves
post-equalisation
In order to control the quality of a transmission, quantifiable parameters were defined; they make it possible to measure linear distortions or not, as well as the noise introduced by the transmission.
To control and possibly correct the performances of a system of transmission, one held in the whole of the lines transmitting the video information, certain number of them to transmit signals of control, of which the test lines.
They make it possible to characterise the network and are inserted into the beginning of the transmission chain for the periods of removal of the frame. These signals thus undergo same degradations as the image.
The composite video signal
A video signal consists of several parts:
the information of Luminance of a dynamics of 700 mV,
synchronisation line, impulse of 300 mV
the information of chrominance
a burst of synchronisation for the under carrying one chrominance
information of synchronisation weaves in certain lines.
Under a standardised load 75 O, the amplitude peak with peak of a video signal is 1 V. the duration of a line is of 64 µs, that is to say 15.625 Hz. The useful signal lasts 52 µs, synchronisation thus uses 12 µs.

Synthesis of the colours
With the monochromatic composite video signal, the colour is managed while adding under carrying modulated by signals chrominance and this, in order to constitute a new composite signal CVBS. For television colour, the image is transmitted in the form of two additional details: the luminance which expresses the luminosity and contours of the visualised forms and the chrominance, carrying information colour.
For reasons of compatibility with the preceding systems, the addition of the colour was to be made in order not to disturb the operation of a black and white television set. This chromatic information thus had like obligation to be positioned in a channel of 8MHz, occupied already by 5 MHz or 6 of video luminance as well as under carrying audio.
The signal of luminance Y is a linear combination of the three primary colours red, green blue. Having this information which represents the black and white signal, two complementary signals are necessary in order to transmit the colour: signals of chrominance blue and signals of chrominance red.
Y = 0,587V + 0,299R + 0,114B
Cb = 0,564 (B - Y)
Cr = 0,713 (R - Y)
systems of coding of the signals of chrominance:
System NTSC
The system SECAM
The system PAL
Emission, amplitude modulation and MA-BLR
The composite video signal (CVS) occupies a bandwidth from approximately 5 MHz according to the standard used. This signal baseband could modulate in amplitude carrying a HF (Amplitude modulation to double tape) and would occupy then 10 MHz of band-width. In theory, one of the two tapes can be removed, owing to the fact that each one of it transmits same information.
It would be thus possible to emit information in AM-BLU. However, the video signal has information with the low frequencies to which the eye is very sensitive, moreover, the difficulty in producing filters at the severe cut-off frequencies, without distortion of time of group, obliges to use the side tape-based system reduced: MA-BLR. This modulation is thus used on the transmitters of hertzian television (TDF).
In the case of the MA-BLR, a whole edge line is emitted as well as part of the second called heel. For the reception (in the television set), it should be made sure that the reduced side zone does not appear with an amplitude doubles on the level of the demodulator. In order to free itself from this problem, one uses a side filter of standardised Nyquist, the principle consists in transmitting half of the signal under the carrying one and half beyond on a certain waveband. In the majority of the cases, the signal is treated with an intermediate frequency of 38.9 MHz (under carrying image).
In reception the signal is transposed to 38,9 MHz the spectrum can be reversed if the frequency of the oscillator is higher than that of the channel (transposition supradyne), this FI is filtered by a FOS which recovers only the video signal (for example K6257K of Siemens Matsushita S+M) the band-width is of approximately 5 MHz; the losses are from approximately 6 dB with 38,9 MHz and 33,9 MHz. An important rejection is present at 32,4 MHz for a FOS adapted to the standard L, that represents a frequency 6,5 MHz before the carrying image located at 38,9 MHz; this rejection is located on the under carrying one sound.
Modulator MABLR is relatively complicated to realise and does not exist in an integrated way. It is necessary to use in this case an integrated circuit into modulation double intermediate frequency band 38,9 MHz. This standardised frequency is then filtered by a FOS with the specific gauge whose side is identical but the lower band-width more important in order to let pass the various audio subcarriers which are 6,5 MHz for monophony and 5,85 MHz for subcarrier NICAM.
Signal FI-MABLR undergoes then a double transposition, a first with a higher FI of 900 MHz for example, in order to be able to use a FOS gsm, then one second reconcilable transposition in UHF. The line of transposition is then 900 MHz beyond the useful line and thus easier to filter than in a simple transposition or a residual line parasitises would remain 38,9 MHz on both sides of the useful signal.
Characteristics of the principal standards
Standard B ⁄ G D L ⁄ L’ M (the United States)
VHF bandages I 47-68 48,5-100   54-88
VHF bandages III 174-230 174-230   174-216
UHF bandages IV & V 470-853   471-855 470-890
Variation image ⁄ sound 5,5 MHz 6,5 MHz 6,5 MHz 4,5 MHz
Width of the channel 8 MHz (G) 8 MHz 8 MHz 6 MHz
Deviation Fm ⁄ sound FM, 50 Khz FM, 50 Khz AM FM, 25 Khz
Many lines 625 625 625 525
Frequency line 15.625 Hz 15.625 Hz 15.625 Hz 15.750 Hz
Video band-width 5 MHz 6 MHz 5 MHz 4,2 MHz
Duration of a line 64 µs 64 µs 64 µs 63,5 µs
Duration weaves 20 ms 20 ms 20 ms 16,667 ms
PAL: alternation of phase according to the lines is a historical standard video colours with 25 frames per second and 625 lines per image (576 only are displayed because 8% of the lines are used with synchronisation and transport of certain digital data). The definition with the standard PAL can reach 720 × 576 lines (DIGITAL VERSATILE DISC). It is different from the standard of remote transmission which is associated for him), which defines the modulation of the signals (L, B, G, K, I).
Developed in Germany by Walter Bruch (1908-1990), PAL is exploited since the years 1960 mainly in Europe, in certain countries of South America, in Australia and in certain countries of Africa. Since 1995, the totality of the television sets colours marketed in the countries exploiting the SECAM integrate obligatorily compatible circuits PAL.
Historically, the competitors of the PAL are NTSC, of American origin and SECAM, French origin.
Diffusion
The standard PAL was largely spread in Europe, in particular in the main part of Western Europe (except in France which imposed the SECAM), in Africa and in part of Asia and South America. In certain areas, the standard PAL is obligatorily associated with a specific standard for its remote transmission (in accordance with a modulation symbolised by a letter: B ⁄ G, I, D ⁄ K, M or NR).
PAL B ⁄ G
PAL I
PAL D ⁄ K
PAL M
PAL NR
Description
The standard PAL is an evolution of standard NTSC and takes again several patents from the standard SECAM which corrected the principal defects of them.
In order to eliminate the variations of colorimetry, frequent during the modulation in NTSC, it was selected to reverse the phase of the carrying colour a line on two: a defect appearing on a line is then reversed on the following line, which involves their mutual cancellation.
The colour being made up of two elementary information: U = B there (difference in blue) and V = R there (difference in red), one needs theoretically two carrying (signals conveying a modulation) to transmit the video information.
To exploit only one carrying (just like in NTSC), the signal is modulated in amplitude and phase with only one carrying, but by taking up the idea of the alternation of the signals U and V from one line to another (the missing component is copied preceding line thanks to a delay line of 64 µs memorising this signal, the delay line found another application at the end of the years 1970 in television for the analogue encryption where several programmable delays are combined pseudo-by chance on various parts of the signal following a command defined by the key of encryption). The frequency of this carrying is roughly of 4,43 MHz - 4.433 618,75 Hz, for the PAL M and the PAL NR, this value becomes respectively 3,575611 MHz and 3,582056 MHz) because of the video band-width limited 4,2 MHz from these standards (channels of 6 MHz as in NTSC).
This point represents the main difference between PAL and SECAM. Televised, the PAL uses a video single frequency modulated mainly in amplitude for its subcarrier video (and identified by its phase which alternates 180° from one line to another, frames being identified by a salvo of initial lines out of phase of approximately 45°), the SECAM modulates also a single subcarrier (but this modulation of chromatic subcarrier is in frequencies and not in amplitude as out of PAL and NTSC) but whose relative frequency (and the bandwidth of modulation) alternate according to the nature of the signal transported (U or V, make Dr. or dB of it because the colorimetric model is slightly different to be able to adapt with the changing band-width of the chromatic signal): the identification colours of each frame (replaced in 1980 by the identification of the lines) is done in SECAM while detecting which of the two frequencies of subcarriers is used on the first line, where out of PAL one must detect the alternation of phase (which is detectable only in end of line at the time of the synchro of return of sweeping).
Compatibility
Because of similarity of synchronisation, the PAL and the SECAM are easily compatible thanks to a transcoder. This apparatus preserves the values of resolution and display (625 lines and 25 images ⁄ second) by transcribing only the signals of chrominance.
In the absence of transcoder, the images will be displayed in black and white.
On the other hand, between the PAL and the NTSC, it is advisable to exploit a convertor, which will compensate for the number of frames per second (25 or 30) and the resolution image (525 or 625 lines). Apart from the very expensive professional equipment broadcast, a convertor PAL ⁄ NTSC gets a poor image of quality (effects of jerk, loss of definition, colours less faithful, background noise).
So the series were turned a long time strips of them 16 or 35 mm of 24 frames per second rather than in video, the hardware of telecinema and the processes of jumper-down being particularly at the point right from the start of television.
Alternatives in remote transmission and conversion
PAL-N
Alternative PAL-N (625 lines 50 Hz, Chroma with 3.58 MHz), used in Argentina and Uruguay, uses the same colorimetric model YDbDr as the SECAM instead of model YUV, but this change is enough miner and very easy to adapt.
PAL-M
Alternative PAL-M exists for compatibility with format NTSC. It is mainly used on the networks of diffusion cables and American and Asian analogue satellites. This alternative is used in analogue terrestrial hertzian diffusion only in Brazil.
The idea of the alternation of the two chromatic components from one line to another is preserved, but the format of the image is adapted to be compatible with the NTSC: 525 lines with 60 Hz instead of 625 lines with 50 Hz, and two subcarriers Y and U ⁄ V are placed at the same relative frequencies as two subcarriers I and Q of the NTSC.
(the signal Q of the NTSC transports simultaneously its two colorimetric components on the same subcarrier modulated in amplitude, without alternation nor delay line, but in quadrature of phase one compared to the other. It is its larger defect because the phase is technically difficult to detect and stabilise precisely, all the more difficult as the signal Q is modulated in amplitude, which is the source of the chromatic aberrations and constant tunings on the apparatuses of reception and demodulation NTSC).
PAL-More
This alternative is adapted to format 6 ⁄ 9. It makes it possible to reproduce a signal for screen televisions broad respecting the integrity of the 576 useful lines. This standard entirely compatible with the standard television sets can be received only with one specific decoder or a compatible television set. It moreover is today supplanted by diffusion numerically of anamorphosées emissions intended exclusively for the television sets 16 ⁄ 9.
PAL 60 Hz
Only present in video output of domestic video apparatuses (such as DVD drives, LaserDisc, video game consoles), this signal exploits sweeping (synchronisation) NTSC (525 lines and 30 frames per second) and the chrominance PAL. It allows a relative compatibility of the North-American and Asian apparatuses with certain European television sets. It makes it possible to stabilise the image but it remains in black and white. Certain video games make it possible to choose or not the display in 60 Hz.
Exploitation
In all Europe, the standard PAL is exploited by the television sets (at least via the Péritélévision socket) marketed since 1995, the European readers or DVD recorders, the video games and other DivX readers. The digital broadcast (satellite, digital cable, TNT, the ADSL) TV uses a source with the signal PAL (SD) exploited by the television channels. The numerical receivers can integrate circuits and an analogue demodulation PAL (entered and left) to make them compatible with the conventional television sets.
In its televised form, the competitor SECAM is more exploited only in terrestrial analogue diffusion and will disappear definitively in 2010 in Europe, with the complete digitalization of transmitters (TNT).
NTSC (Committee of the system of national television) is an analogue standard of coding of the video colours launched to the USA in 1953. It is adapted to the video formats 525 lines and 30 frames per second. It can be exploited for the DVD-videos with a resolution of 720 × 480 lines. Standard NTSC is exploited in North America, in part of South America (NTSC-M) as well as Asia, of which Japan (NTSC-J).
Technical principles
In its professional form (collecting, cameras, studios, controls) the video signal colour is composed of two elementary information combined with the black and white signal (Y): U = B there (difference in blue) and V=R there (difference in red). In theory, two carrying distinct is essential to convey the data of chrominance and luminance (Y). In order to employ some that only one, the signal vidéocomposite is modulated in amplitude and phase with only one carrying.
The standard of remote transmission Q associated with the NTSC thus transports simultaneously its two colorimetric components on the same carrying one modulated in amplitude with a system quadrature of phase between two information of chrominance.
The frequency of this carrying is roughly of 3,58 MHz (except in version NTSC-4.43, where it is of 4,43 MHz what corresponds to carrying the PAL). In order to limit the influence of the quality of the reception on the variations of colorimetry, they are not directly the signals U and V which are modulated, but a combination of those named I and Q:
I = - 0,2676 * U + 0,7361 * V
Q = + 0.3869 * U + 0.4596 * V
One can directly obtain Y, I and Q according to R, G and b:
Y = +0,299 +0,587 +0,114 = R
I = +0,596 -0,274 -0,322 = G
Q = +0,212 -0,523 -0,311 = B
Alternative of the NTSC: PAL 60 Hz
There exists a technology invented after the war by the Americans to be able to read their video cassettes NTSC on the German television stations using the standard PAL. This process modifies the demodulation at the carrier frequency colour for 4,43 MHz (PAL 60). On the other hand, the image remains in definition 525 lines, it can then be anamorphosée (compressed vertically) or represent black bars in top and bottom of the screen. The signal is then composed of 60 frames (half images) a second or 30 frames per second.
Defects at the time of the remote transmission
Standard NTSC was the subject of critical sharp because of the mediocrity of the fidelity of the colours at the time of its reception with a conventional television set (going back to before 1990). This phenomenon generated by the weaknesses of the analogue circuits of demodulation and recombining of the signal vidéocomposite. Because of a dephasing of the chrominance, the most awkward phenomenon relates to the hue of the human skin then (the faces vary the greenish one with orange sinks). A specific tuning thus exists on all television sets NTSC: the function hoots which makes it possible to readjust the phase of the signal colour. However, this phenomenon is practically non-existent with the digital devices (DVD drive, demodulator cable, satellite, terrestrial, ADSL TV, video game console). This phenomenon does not exist at the two European competitors PAL and SECAM.
Compatibility
Between the NTSC and the PAL ⁄ SECAM, it is advisable to exploit a digitizer, which will compensate for the number of frames per second (25 or 30) and the resolution image (525 or 625 lines). Apart from the very expensive professional equipment broadcast (diffusion), a convertor PAL ⁄ NTSC gets a poor image of quality (effects of jerk, loss of definition, colours less faithful, background noise)
The SECAM term means sequential colour with memory, indicates a standard of video coding analogue colours, invented by Henri de France and marketed as from 1967. Adapted to the video formats 625 lines and 25 frames per second, the SECAM was mainly established in France (metropolitan and DOM-TOM), in the Eastern European countries, in French-speaking Africa, the countries of the ex-USSR and with the Middle East. It is associated according to the countries, to a standard of specific remote transmission (indicated by letters L ⁄ L’, B ⁄ G and D ⁄ K or K'/K1).
SECAM L ⁄ L’: Metropolitan France, certain program in Luxembourg.
SECAM B ⁄ G: Iran, Egypt, Saudi Arabia, Libya, Morocco, Tunisia, etc
SECAM D ⁄ K: old Eastern bloc (in train of change for PAL), C.E.I., DOM TOM, etc
SECAM K’ ⁄ K1: West Africa, etc
Technical principles
The three systems of television historical colours (NTSC, SECAM and PAL) were conceived to be compatible with the former standards of remote transmission black and white for reasons for compatibility: an old television set black and white must be able to restore the emissions emitted colours and a television set colours must make it possible to restore emissions diffused black and white. The additional data specific to the colour is thus added with (or combined with) the signals black and white.
The signal black and white or luminance (Y) constitutes the first video information to be exploited (first component of the vector). There thus remains two information (two components) known as of chrominance, to transmit. One chose to transmit U= (R there) *cte and V= (B there) *cte, because the information of green colour G is that which is closest to luminance Y. the SECAM is distinguished from the other standards on this point.
In NTSC and PAL, two signals of chrominance (U=cte* (R there) and V=cte* (B there)) are transmitted simultaneously, in amplitude and Phase modulation. Thus, for each line, and thus for each point, one has information Y, U and V, which makes it possible to reconstitute the 3 primary components R, G and B.
For the SECAM, information U and V are alternatively transmitted a line on two. As follows:
for a given line, one has information Y (the signal black and white, transmitted for each line) and U= (R there) *cte
for the following line, one has information Y and V= (B there) *cte
In this formula, the system would not make it possible to restore the three components R, G and B. All the astuteness consists in taking, for a line given, missing information U or V on the preceding line. For this purpose, a delay line of 64 µs (duration of a line) memorises the information of colour of a line (U or V), and restores it at the time of the reception of the following line, where combined with the information of colour of the latter (resp. V or U), it finally makes it possible to reach the three components of the vector of colour.
Thus, in SECAM, the resolution in chrominance is half less than the resolution in luminance (that of the image black and white). In practise, that does not pose a particular problem, because the human eye shows about the same characteristics (better resolution in luminance than in chrominance). It should be noted that this practise of division by two of chroma was taken again in standard JPEG and thus by heritage in standard MPEG-1, MPEG-2 and MPEG-4.
Only one signal colour is transmitted by line. This alternation involves a periodicity of four frames, however the inversion of the subcarrier (all three lines, 1 frame out of two) made pass this periodicity to twelve frames: one thus needs a group of six images to demodulate the signal colour completely, which makes this format unusable and immontable in production audio-visual.
The data of colour are transmitted in frequency modulation, which guaranties (only during the transmission) a better stability of the colours and decreases the perception of the information of colour in the video image in black and white. In the explanation which precedes, one considered to simplify that SECAM, just like PAL and NTSC, uses the space of colour YUV. It is not completely exact, because in SECAM, the components U and V are put on the scale: the three components are thus expressed in the space of YDbDr colour.
Theoretically better than the PAL for the hertzian remote transmission only because of a consolidation of the chrominance. The colours with the naked eye are saturated besides there than with PAL. This saturation besides can dribble on red or blue large surface very saturated.
PAL: Stability of the hue. Instability of saturation. Resolution high (to 550 points/line) but attached by the carrying colours at 416 points/lines. The television sets equipped with filter out of advanced comb can emerge up to 550 points lines however without really reaching this quality.
SECAM: Stability of the hue. Stability of saturation. Resolution high (to 600 points/line) but attached by the carrying colours at 374 points/lines on almost the whole of the television sets.
Technical limits and gaps
Video recording SECAM in analogue video
In the case of the video general public (VHS), there exist two modes of processing (recording/reading) of the signal colour SECAM.
The SECAM mode in a video tape recorder. Information colours contained in diffusion on carrying moreover high frequency which the basic signal is recorded at a frequency lower than carrying the video, for reasons of quality and band-width. Because of modulation in frequency modulation, the idea was simply to make pass the carrying one in a divider frequency by 4 (and a multiplication by 4 with the restitution), that makes it possible to carry out the processing with a hardware much less expensive than the common method used in the video tape recorder PAL.
The second mode derived from the SECAM is the MESECAM which one finds in Eastern Europe, the Middle East, Tunisia, Morocco and Greece. Moreover, it was exploited in French-speaking Switzerland (between 1978 and 1995). This method uses quite simply hardware standard PAL and the method used for conversion of frequency for the recording standard PAL more expensive than the simplified method of the SECAM. System MESECAM not existing as such, it acts here of the use of a video tape recorder PAL with a signal SECAM.
With the final one, although process VHS SECAM is theoretically less expensive since simpler, in practise with the increase in the diffusion of the video tape recorders, another problem appeared: the hardware for the French territory being different, it profits less reduction due to the mass production. Moreover, the need for being able to read cassettes PAL on French video tape recorder appeared quickly, with the result that a great number supported the 2 standards and were thus equipped with the 2 systems of decoding
For little that the television set manages the PAL and the SECAM: A signal SECAM recorded on a video tape recorder PAL (it is thus MESECAM) then read again on a video tape recorder PAL will be colours. Whereas a signal PAL recorded on a video tape recorder SECAM is always out of NB. The reading of the cassettes SECAM with a video tape recorder PAL is restored in black and white and conversely. The analogue tuners of video tape recorders VHS PAL with MESECAM sold in French-speaking Switzerland were modified of origin CCIR B ⁄ G. A small artisanal circuit with integrated circuit was added, allowing the reception of analogue standards L ⁄ L’, a label was affixed on the apparatus: PAL+SECAM. The tuner became multichannel, but the apparatus recorded the French chains by terrestrial hertzian way in mode MESECAM. The standard SECAM was abandoned as from the beginning of the year 1980 with the profit of the PAL by the professionals (chains, producers, duplication...) in the fields of the exploitation (studios, controls), recording and filing. Mainly for practical reasons: the catalogue of hardware PAL was more important and less expensive.
Disadvantage: the identifier colours SECAM
The process SECAM shows another defect. It relates to the signal of identification having to allow the decoder SECAM of the television set colours, the restitution of an image in conformity with the emission. Between 1965 and 1988, this transmission was exploited in synchronisation with the lines of the video signal (salvo of identification known as IDENTIFICATION LINE). Since, this signal was integrated in the frames of the video (IDENTIFICATION WEAVES, or Bottles). The television sets going back to before 1980 did not have these circuits systematically.
In the middle of the years 1960, during the adoption of the SECAM by all the Member States of the OIRT, the chains of TV of these countries diffused simultaneously, the 2 modes of identification. As for France, it chooses, in 1967, to diffuse the colour, only in identification WEAVES. The circuits SECAM of the TV will function obligatorily with this mode of transmission, until 1 December 1979. 14 March 1978, the French chains of TV choose, from now on, for the identification LINE, which is the obligatory mode of transmission of the colour SECAM (with a view to remove the identification WEAVES, it to replace by numeric signals such as the teletext, the VPS, the PDC, subtitling and in the case of Canal+, of the data intended for the decoders (access rights), as for an analogue video signal PAL).
History
The SECAM corrected well all the large defects of the NTSC, and the PAL was created starting from the SECAM like an intermediate standard, reiterating the main part of the improvements of the SECAM, in particular:
the clever sequential separation of the components of chrominance thanks to the invention and the use by Henri de France of the delay line of 64 µs to allow the memorising of information of chrominance of one line the other
modulation of the single subcarrier of colour (two carrying in NTSC, one dribbling on the other according to the conditions of transmissions and distances!), in frequency for the SECAM (better stability and thus quality), in amplitude for the PAL and the NTSC. In fact, in the 3rd version of the SECAM, one uses successively two subcarriers with 4,40625 MHz and 4,25 MHz
the use of a tape widened for the signal of chrominance thanks to the single subcarrier in SECAM (idea preserved out of PAL) compared to the weak tapes of two subcarriers NTSC
colorimetric model (for the demodulated signal) YUV corrected according to the lower relative sensitivity of blue compared to the red and thus converted into <Y, Dr., Db> with a weaker bandwidth requirement for the signal of chrominance when it transports the blue delta (this colorimetric model was also included in the PAL)
distinction of the lines even and odd (to distinguish the lines emitted in <Y, Dr> of the lines emitted in <Y, Db> by distinct frequencies of subcarrier, that of blue being slightly weaker and having thus a frequency modulation over a lower bandwidth, which would have made it possible to code an improved tape its (stereophony for example) or digital data (teletext, subtitling, time signals, téléservices...) in the free lines: novel idea not preserved in the PAL which uses a single frequency of subcarrier for the lines even or odd, but announces the frames colour modulated in amplitude without quadrature by an initial salvo including ⁄ understanding a line out of phase of approximately 45° (according to the parity of the frame) compared to the position of dephasing alternated to 0 or 180° (what is a specific system PAL incompatible with its predecessors SECAM and before him NTSC, but does not make qualitative improvement).
However, the SECAM then evolved ⁄ moved by taking account of the remarks of the manufacturers of the system PAL: the alternation of the frequencies of subcarriers for the even and odd lines was made optional, allowing the use of a single frequency of subcarrier (by preserving however its amplitude and frequency modulation not as out of PAL): it is the object of the alternative SECAM compared to the initial alternative L. [The preceding sentence is completely false. There are always two frequencies of subcarriers of chrominance in SECAM, and that does not have any relationship with the standards L and which relate to the difference between the subcarrier its and the subcarrier image]. The identification of the frames becomes obligatory then (or else the lines <Y, Dr> and <Y, Db> would be permuted what would have caused to permute the red and blue). This identification being able to be done is at the beginning of frame on the salvos of the first lines, or at the beginning of each line to indicate nature of it. The identification was the object of incompatibilities, and this is why the two systems of identification were employed simultaneously, which ate the remaining band-width and prevented its use for its stereophony (appeared much more quickly out of PAL and NTSC, the two systems not having to coexist simultaneously).
One could say however that the PAL slightly improved quality of colour for the blue component, by not reducing its band-width, as in SECAM, and simplified the design by avoiding double syntonization on the two frequencies of subcarrier. However, by making this operation, if the colorimetric model were simplified in <Y, Pr, Pb> with an equal processing for the red delta and the blue delta, the little which was gained was lost by the return to the amplitude modulation as in NTSC, with thus a stronger sensitivity to the disturbances and parasites during the transmission, and thus more chromatic aberrations.
In short, the SECAM indeed was a technically better invention, only a little too advances some compared to the time, and sufficiently not supported by the industrialists, a political will (releasing of the TV programmings still too controlled by the government, and did not dope rather quickly the French market to accelerate the adoption of the colour which was relatively long in France (of 1967 to 1983) what slowed down considerably the purchase of the receivers colours in France, in spite of the very early colour application of Antenna 2 as a second national chain.
The SECAM has in fact more suffered from the French regulation framework who imposed on the chains emissions with two simultaneous systems of identification of the frames, and too a long time also of the lack from freedom from programming in France with a very late opening to competition (problem even more critical in Eastern Europe, Albania and Greece where the SECAM had also been adopted in countries still politically not democratized, just as in Africa due to absence of sufficient means of production). In fact, it is the PAL (and its alternatives) which gained the most like common output norm because of its greater proximity at the same time of the NTSC and the SECAM as an intermediate standard combining compatibility with the NTSC and partly higher colorimetric quality of the SECAM.
The SECAM was ultimate of television to be associated with a stereophonic sound. Whereas the NTSC and especially the PAL could integrate stereophony as of the years 1960 (then the Surround effects as from the middle of the years 1980), the SECAM had to await the introduction of the process digital audio NICAM as from 1994 (its extension to the whole of the French transmitters proceeded until 1999). That is not due to coding SECAM itself but to the standard of French modulation L ⁄ L’, last normalises in the world to use the amplitude modulation to transmit the sound, with positive modulation of the image.
The SECAM could have succeeded in supplanting the NTSC for example in China and in Japan, if France had not been also protectionist by strongly taxing the imported Asian television sets (one still remembers in Asia the affaire the television sets and Asian video tape recorders blocked in customs in Poitiers). Prevented from producing in great volume of the compatible apparatuses SECAM, Asia has without problem produced at low prices apparatuses PAL and NTSC, and the equipment of reception PAL even made their breakthrough in the United States and Japan (except for the hertzian diffusion, become rather marginal because of its poor quality which was driving opening of the wired networks in these countries, whose subscribers were equipped with hardware Bi-standards supporting the modulation PAL of the wired networks, in its alternative M with 525 lines with 60 Hz, for fully benefitting from the improved colour, but as of the much better stereophonic sound out of PAL as in NTSC, and of teletext codable also in the remaining band-width).
The attempt at replacement of the SECAM by standard D2MAC (modulation video per packages associated with a numerical sound already exploited by satellite and on the cable) was quickly abandoned with the emergence of the video digitalization (which will become the MPEG) since 1993.
The NTSC will be the first standard colour to disappear, so much its use was given up and criticised, with the profit of the wired networks. The total conversion of the hertzian television of NTSC into PAL is not today any more of topicality, because the three systems will be replaced by digital television. The SECAM must normally die at the same time as the PAL, however, it is probable that the PAL will survive longer because of its world compatibility with practically all the equipment videos. There will remain sometimes the local modulation for the other apparatuses, and it is probable that this one will be everywhere out of PAL (or PAL-M in the United States for its version 60 Hz), even also more and more in YUV into analogue without modulation, or direct (by a video connexion DVI with a port its numerical, or a port HDMI combining both) this last possibility allowing the exploitation of protections DRM.
Definition
The general public being accustomed more has to speak in definition about the type 720* 576 qu ' in terms about band-width about 3,6 MHz for 625 lines, or that in terms of standard quality 500 lines try to define an equivalence in definition of Y, dB and Dr.
The three systems start by transforming signal RVB or the R V and B is analysed in 576 lines (488 in NTSC and PAL 60) say of them YUV here to simplify the comparison.
In SECAM: Then Y remains on 576 lines. U and V are brought back to 288 lines or U comes from the even lines and the V of the odd lines (does that of it changes with each half images).
Y is flexible in amplitude on 6 MHz in a channel 7 MHz in France to remain compatible with the television set to the standard L (standard black and white 625 lines). U and V in frequency on this same channel in an alternative way with respectively 4,40625 MHz and 4,25 MHz
In SECAM the duration of a line is of 64 µs whose 52 µs Consequently the SECAM is attached with:
Y = 3600000 ⁄ 25 ⁄ 625 * (52 ⁄ 64) *2 ⇒ 374 discrete values Y by lines.
U and V are modulated in frequency a line on 2 thus respectively to 4,40625 ⁄ 2 MHz and 4,25 ⁄ 2 MHz one with thus.
U= (4406250 ⁄ 2) ⁄ 25 ⁄ 625 * (52 ⁄ 64) *2 ⇒ 229 discrete values U for two lines.
V= (4250000 ⁄ 2) ⁄ 25 ⁄ 625 * (52 ⁄ 64) *2 ⇒ 221 discrete values V for two lines.
Out of PAL:
Y = 4000000 ⁄ 25 ⁄ 625 * (52 ⁄ 64) *2 ⇒ 416 values Y lines.
U = V = (2570000 ⁄ 2) ⁄ 25 ⁄ 625 * (52 ⁄ 64) *2 133 value U by lines, 133 values V by lines.
In NTSC:
Y = (3200000) ⁄ 30 ⁄ 525* (52 ⁄ 64) *2 ⇒ 330
U = V = (1500000) ⁄ 30 ⁄ 525* (52/64) *2 ⇒ 206
Effective definitions of the composites
  SECAM PAL NTSC
Y 374*576 416*576 330*488
U 229*288 133*576 154*488
V 221*288 133*576 154*488
D2-mac
Whereas with the system PAL all information (black and white signal, colour and its stereophony) is transmitted simultaneously and requires several carrying and of the equipment of filtering to separate them with the reception. In D2-MAC all the components of the image are transmitted successively after temporal compression.
The D2-MAC or D2 Mac Paquets is an intermediate standard of television between analogue and numerical owing to the fact that it combines an analogue video signal and a digital processing with a signal digital audio close to the terrestrial format of remote transmission Nicam.
D2 Mac is compatible with the format 16 ⁄ 9 as with the TVHD (a specific standard was defined for this purpose: HD Mac).
This system integrates electronic circuits and integrated softwares. It consists in treating video analogue by compressing it according to a base of time, the components of luminance and chrominance to juxtapose these signals sequentially. The audio signal numerical and is coded with the format MIC.
The French laboratories of the CCETT (common Centre of studies of remote transmission and telecommunications) made evolve ⁄ move D2 Mac by a numerical multiplexing of data to the package mode. The official terminology of the standard is D2-MAC/Packet (standard ETSI: ETS 300.250). The D2 prefix means duobinaire half-flow bus coding on line of the data is carried out by a code known as duobinaire. The half-flow term is introduced because there were several alternatives:
D2-MAC contains data to 10,125 Mbit ⁄ s
However, the standard D2 Mac is abandoned the 1erjanvier 2000 with the profit of DVB MPEG-2.
Standard D2-MAC developped at the point as from 1985, stopped its diffusion since the 1erjuillet 2006
HD-mac
HD-mac is a standard of analogue transmission of the high definition television which was proposed by the European commission in 1986.
It is a family member of the standards mac (Multiplexing off Analogue Components). It made integral part of the project Eureka 95 and constituted a first attempt of the EEC to deploy high definition television (TVHD) in Europe. It was a complex mixture of analogue video signals, multiplexed with a digital part including ⁄ understanding the sound and of the data of assistance to decoding (DATV). It provided 25 images to the format 16 ⁄ 9 a second, each one including ⁄ understanding 1250 lines, including 1152 really visible with the screen. Sweeping was interlaced, succeed at a frequency of frame of 50 Hz, as for traditional emissions PAL ⁄ SECAM. The signal was built by means of modified a D2-mac coder.
Convention of notation
width X height [standard of sweeping: I or p]/many complete images a second
Thus, the format 1280x720p ⁄ 60 diffuses at each second 60 images of 1280 pixels broad on 720 top, in progressive sweeping: the lines are transmitted in the natural order: 1,2,3,4,....
The format of the European emissions in standard definition is 720x576i ⁄ 25, that is to say 25 frames per second of 720 pixels broad on 576 top, in interlaced sweeping: the odd lines 1,3,5... are gathered in the odd frame, transmitted in first, then this one is followed even frame with lines 2,4,6,... There are thus two frames per image is a frequency of frame of 25 X 2 = 50 Hz.
A HD-mac receiver produced a signal with the useful format 1440x1152i ⁄ 25, that is to say exactly the double of the horizontal and vertical resolutions of the standard definition, and containing four times theoretically more information on the whole.
HD-mac could be decoded by D2-mac receivers, but in SDTV: in this mode, the displayable resolution was reduced to the standard definition of 576 lines (sullied with certain artefacts). To extract the full resolution of the signal, a specific HD-mac decoder was necessary.
Transmission
In the case of HD-mac, the data communication channel must guaranty a band-width from at least 11.14 MHz in baseband. The standard evokes the possibility of making pass the signal in channels with 8 MHz, but in this case, the data of assistance cannot be decoded any more correctly and one can draw only one image in standard definition from it, by means of a D2-mac receiver. To preserve all its qualities at the signal, it is thus necessary to count on a standard spacing of the channels of 12 MHz on a wired network. For the transmission by satellite, because of widening of the spectrum caused by the frequency modulation, the capacity of a complete transpondor was to be used, that is to say 27 36 MHz from bandwidth. It should be noted that the situation is similar in standard definition: a transpondor can lodge only one analogue chain. The passage in HD thus does not constitute a particular handicap in this context.
Tribulations of the standard
In May 1986, work on the HD-mac standard was officially launched. It was a question of countering the Japanese proposal, constant by American and who would have resulted in making system conceived by the NHK a world standard. This initiative of course aimed preserving the competitiveness of European industry, but also at producing a standard compatible with the frequency of frame of 50 Hz used by the majority of the countries of the world. To tell the truth, the 60 Hz of the Japanese proposal was not without causing some concerns with American themselves, because their infrastructure in standard definition, based on the NTSC M, rested on a real frequency of 59.94Hz. This apparently minor difference was in fact likely to cause considerable difficulties.
In the month of September 1988, Japanese carried out the first retransmission of the Olympic Games in high-definition, by means of their process Hi-Vision (the NHK produced programs with this format since 1982). At the same time, lasting this same September, Europe presented for the first time an credible alternative, in the shape of a complete chain of HD-mac transmission, to the IBC 88 in Brighton.
At the time of the Winter Olympics of 1992 and Olympic Games of summer of 1992, public demonstrations of diffusion in HD-mac took place. 60 HD-mac receivers for the plays of Albertville and 700 for the plays of Barcelona were set up in the Eurosites in order to show the possibilities of the standard. Vidéoprojecteur tritube HD 1152 lines was employed to restore an image of a few metres broad. One also found some television sets cathodic HD 16 ⁄ 9 Thomson Space system. The project could also use Rétroprojecteur television sets. Moreover, some 80000 owners of D2-mac receivers were able to follow the retransmission (in standard definition, however). It is estimated that 350.000 people in Europe could see this demonstration of European TVHD. This project was financed by the EEC. The signal, after conversion into PAL, was exploited by official operators.
The spectrum available in UHF being rare, HD-mac was exploitable de facto only by the operators of the cable and the satellites, which were limited in band-width. However, the standard never became popular among the operators. So the analogue High-definition could never replace the conventional emissions with the formats SECAM, returning not very gravitational the HD-mac receivers with the eyes of the potential consumers.
It had been forced on all the operators of satellite of strong power to use the mac standard as from 1986. However, the launching of satellites of average power by ITS and the use of the PAL enabled them to circumvent HD-mac, thus reducing their cost of diffusion. HD-mac (the alternative high-definition of mac) remained in spite of very for the intercontinental links by satellite.
The HD-mac standard was abandoned in 1993, and, since then, all the efforts of the European Union and the UER were concentrated on the system DVB (Digital Video Broadcasting), which is able to transmit as well the standard definition as the high-definition.
Technical details
The reduction of band-width
The signal was captured at the rate of 50 complete images a second (progressive sweeping), each one of them profiting from a definition from 2048×1152 pixels (it could thus be described by the notation 2048x1152p ⁄ 50). The image was with the format 16 ⁄ 9, with square pixels. This quality, however, was available only in studio, for example for applications such as the electronic cinema, or as source of input for the HD-mac coder who could transmit only one reduced part of this video information flow.
One started with a rééchantillonage which brought back the horizontal resolution to 1440 pixels, that is to say the double of the 720 points of the SD.
To increase the horizontal resolution, in the D2-mac standard, it is enough to increase the band-width. It was easy to carry out insofar as, contrary to the PAL, the sound is not transmitted on a separated subcarrier, but multiplexed with the image. Unfortunately, it was more complex to increase the vertical definition, because the frequency of line was to be maintained to 15.625 Hz to remain compatible with D2-mac. This left three possibilities:
50 frames per second with 288 lines for the scenes moving fast (mode 20 ms)
25 frames per second with 576 lines for the scenes moving moderate (mode 40 ms)
12,5 images per second with the totality of the 1152 lines for the slow movements (mode 80 ms)
The choice with the encoding was done not for the full picture, but individually, on each small block of 16x16 pixels which composed it. One inserted then in numerical flow DATV integrated into the mac multiplexing information allowing to control the method of rebuilding which the decoder should use. To decode the image completely, the analogue part of the mac signal was to be digitised, then read again several times starting from a memory.
The mode 20 ms offers an improved temporal definition, but the mode 80 ms is the only one to offer a space high-definition, with the direction where it is usually heard. It benefits from its reduced rate of 12,5 i ⁄ s to distribute the contents of image HD on 2 images SD, are 4 frames of 20 ms = 80 ms, which justifies its name.
But that is insufficient, because an image HD contains the equivalent of 4 images SD. To go further, one preserves only one pixel out of two of each horizontal line. This under-sampling is carried out in quincunx: so on each line the pixels are numbered independently from 1 to 1440, on the first line one preserves pixels 1,3,5... On the following line, one takes pixels 2,4,6... Then with the following line again 1,3,5. In this manner, one stores information on all the columns of image HD. With the reception, each missing pixel is surrounded by 4 pixels transmitted except on the edges of the image and can be replaced by an interpolation from those.
The office plurality of these operations led to a compression of a factor 4:1 which made it possible the signal high-definition to pass through standard a D2-mac channel. The decoder was then able to rebuild starting from this information an image with the format 1440x1152i ⁄ 25, interlaced, with a frequency of frame of 50 Hz, and always at the format 16 ⁄ 9, but this time with rectangular pixels.
Note: The standard explicitly does not specify the format of the image which the receiver must deliver. Thus a system capable of a sweeping with 100 Hz, for example, could have benefitted a better from the information produced by the mode 20 ms...
Progressive sweeping
One generally refers to the European systems as with standards 50 Hz (frequency of frame). It should however be realised that no element of the image is refreshed at this frequency. A point forms part of an even or odd frame inevitably, and only one frame of a given type is transmitted to each image. Cooling is thus done at the rate of image, that is to say only 25 times a second. The mode 20 ms of HD-mac implies a true cooling with 50 Hz, from where advantage of the cameras 50P (the standard envisages also the possibility of a sweeping 100 interlaced Hz).
It should be noted that the coder could work in procedure Caméra, in which the three modes of coding were exploited, but also in procedure film, which did not resort to the mode of coding 20 ms. In this case, it was possible to be satisfied with a source 50 Hz interlaced at the entry of the decoder.
The images theoretically produced by these cameras (2048x1152p ⁄ 50) represented a flow of pixels almost twice higher than those of the sytème Hi-Vision (1920x1035i ⁄ 30), but the HD-mac format could in retransmettre only one fraction, system MUSE in Japanese, also based on techniques of under-sampling, imposed restrictions of comparable nature).

The standards digital video


Use of the principal formats of digital broadcast in the world
Advanced Television Systems Committee (ATSC) is the group which contributed to the development of the new standard of digital television in the United States, which bears the same name. This one was also adopted by Canada, Mexico and South Korea. It must replace analogue system NTSC current. It can produce images of the type Wide Screen 16:9 of resolution maximum 1920 × 1080 pixels, that is to say six times better than old system NTSC. Various sizes of image are supported. To six virtual channels SDTV can be included in a simple emission. ATSC is also praised to have an audio quality of the cinema type because it employs the format Dolby Digital (AC-3) which provides of the 5.1 surround. A big number of services of the type given can also be provided.
ATSC coexists with standards DVB and ISDB.
Diffusers ATSC must maintain an analogue signal on two separated channels, because system ATSC requires the use of a whole channel of 6 MHz. This one was criticised because he is regarded as complicated and expensive to implement and to employ. Many aspects of the ATSC are patented, like audio coding AC-3, and the modulation VSB.Les standards ATSC are often ambiguous, an example is standard EIA-708 for the subtitles.
OFDM
The OFDM is a process of coding of numeric signals per distribution in orthogonal frequencies in the form of multiple subcarriers. This technique is the best means to currently fight against the selective channels in frequency. These channels appear in the presence of multiple ways and out of high banc. This is why one finds very this technique largely adopted in the majority of the applications to high banc.
DMT and COFDM indicate the same principle with in more one coding of information for this last).
The OFDM is a process of digital coding of the signals which is used inter alia for the mobile systems of transmissions to high banc of data. The OFDM is particularly well adapted to the data communication channels radio on long distances without multiple transmissions of wave (echoes), it then makes it possible to reduce the intersymbol interferences appreciably. On the other hand it can become unusable if the echoes are strong, it is then necessary to use COFDM.
The OFDM (or a comparable technique) is used in:
Principle
The principle of the OFDM consists in distributing on a great number of subcarriers the numeric signal which one wants to transmit. As if one combined the signal to be transmitted on a great number of independent systems of transmission and with different frequencies.
So that the frequencies of the subcarriers are closest possible and thus to transmit the maximum of information on a given portion of frequencies, the OFDM uses orthogonal subcarriers between them. The signals of the various subcarriers overlap but thanks to orthogonality do not interfere between them.
In does orthogonal coding, spacing between each subcarrier have to be equal to F = K (YOU) hertz, where YOU seconds are the useful duration of a symbol (c.a.d. window size of capture of the receiver), and K is a positive entirety, generally equal to 1. Consequently, with NR subcarriers, the total width of the band-width will be of B ˜ NR·? F (Hz).
Orthogonality also allows a high spectral effectiveness, the total flow approaching the flow of Nyquist, the band-width being almost used in its entirety. The orthogonal multiplexing produces an almost flat frequency spectrum (typical of a white vibration), which involves a minimum of interferences with the adjacent channels. A separate filtering of each subcarrier is not necessary for decoding, a Transform of Fourier FFT being sufficient to separate the carrying ones between them.
The signal to be transmitted is generally repeated on various subcarriers. Thus in a data communication channel with multiple paths where certain frequencies will be destroyed because of the destructive combination of paths, the system will be all the same able to recover the information lost on other carrier frequencies which will not have been destroyed. Each subcarrier is modulated independently by using numerical modulations: QPSK, QAM-4, QAM-16, QAM-64,
This principle makes it possible to limit the interference between symbols. To eliminate it, one can add an interval of guard (that is to say one period during which there is no transmission) after each emitted symbol, very large in front of the time of transmission (the distance separating the transmitter from the receiver divided by speed of light).
Decoding OFDM requires a very precise synchronisation of the frequency of the receiver with that of the transmitter. Any deviation in frequency involves the loss of the orthogonality of the subcarriers and creates consequently interferences between those. This synchronisation becomes difficult to carry out since the receiver is moving, in particular in the event of variation speed, direction or so of many unwanted echos are present.
Mathematical description
The low-pass equivalent of a signal OFDM is expressed as follows:
v (t) = ΣN-1k = 0 Ikei2πkt ⁄ T, 0 ≤ t < T
where
{Ik} is the symbols of data
NR is the number of subcarriers
T duration of block OFDM.
Spacing between carrying 1 ⁄ T Hz makes the subcarriers orthogonal between them, this property is expressed as follows:
1 ⁄ T ∫0T (ei2πk1t ⁄ T) * (ei2πk2t ⁄ T) dt = 1 ⁄ T ∫0T ei2π(k2 - k1) t ⁄ T dt = {1, k1 = k2 0, k1 ≠ k2}
where (.)*
corresponds to the complex combined operator.
To avoid the interference intersymbol in an environment of propagation multipath
an interval of guard -Tg ≤ t < 0
where Tg is the period of guard, is inserted before block OFDM
During this interval, a cyclic prefix is transmitted
This cyclic prefix is equal to the Tg last of block OFDM
Signal OFDM with the cyclic prefix is thus
v (t) = N-1Σk=0 Ikei2πkt ⁄ T, -Tg ≤ t < 0
The low-pass signal above can is to be made up of actual value or complex.
For the signal with actual values this one is generally transmitted in baseband and thus expressed
s (t) = R {v (t) ei2πƒct}
The signal in baseband with complex values is on the other hand modulated at a higher frequency ƒc.
COFDM
COFDM is a process which associates a coding of channel OFDM and a numerical modulation of the individualised signals.
Principle
The principle of the OFDM consists in dividing the channel into secondary canals and carrying out a transmission on each one of them by numerical modulation. This method makes it possible to correct long multitrajets but is not enough if these multitrajets is strong, certain frequencies (thus certain secondary canals) can then be very strongly attenuated. So in more the receiver is fixed, as it is the case for example for terrestrial television, these interferences will be prolonged making impossible the use of the secondary canals concerned.
In order to solve this problem, COFDM uses a correct coding of error associated with an interlacing between frequencies. One thus manages to approach the performances of a channel without echo.
Applications
This method is employed in particular by standard DVB-T used in France for digital terrestrial television.
The systems of numerical broadcasting DAB and DMB also use the process of coding of channel COFDM.
T-DMB
The T-DMB is a terrestrial system of digital broadcast based on the DIGITAL Audio Broadcasting (DAB) created in South Korea and developed and standardised in this same country, like by the European project EUREKA 147, gathering diffusers, manufacturers, research centres and operators. This system is already completely used in South Korea and with Brazil and the standards on which it is built allow the reception optimised of the televisual signals on any type of mobile multi-media apparatus, having a compatible tuner. This single advantage caused to make of South Korea, the country of the World having the strongest penetration of the use of television.
Description
This mode of diffusion is very robust in mobile thanks to the modulation used (DQPSK). It was developed for the diffusion of television of mobility on low-size apparatuses such as mobile phones or PDA.
This mode is standardised with the ETSI since June 2005 under numbers TS 102.427 and TS 102.428. This standard was amended in 2009 to add a radio operator profile to it. The T-DMB makes integral part of the three profiles of receiver of digital radio defined within the framework of the project Eureka 147.
This standard is designed to transmit services of radio or television. The T-DMB uses an audio and video coding very powerful. The T-DMB also makes it possible to diffuse interactive applications BIFS. The audio, video components and BIFS are synchronised thanks to the MPEG4-SL and are transported in a flow MPEG-2 TS. The T-DMB makes it possible to diffuse 9 radio operator services or 3 television services by multiplexes.
ISDB
The ISDB is a Japanese standard of diffusion of television and digital radio. She comprises several under-standards, which are the ISDB-T (for the diffusion known as terrestrial), the ISDB-S (for the satellite broadcast) and the ISDB-C (for the diffusion by cable). The ISDB-T itself is cut out in two standards known as 1seg and 13seg, the first being planned for the reception on mobile device.
This standard is mainly used in Japan and Brazil. It was defined by the ARIB, an organisation of Japanese standardisation. The video diffused is encoded with format MPEG-2.
The Conditional Access, which makes it possible to authorise only certain terminals to display certain chains (for paid television for example), is defined in standard ARIB STD-B25. This Conditional Access calls upon the encryption algorithm per block MULTI2.
DVB
Digital Video Broadcasting (shortened in DVB, and that one could translate by diffusion digital video), is a whole of standards of digital television enacted by consortium European DVB, and used in a great number of countries. Its principal competitors are the standards ATSC and standard ISDB.
History
Project DVB began the first phase of its work in 1993 at the same period when in North America, Large forum the Alliance also organises the same type of developments, with in line of sight, digital television then the High-definition. It should be stressed that certain implied actors take part at the same time in the two competitor forums but whose objectives are similar, in particular Europeans Philips Consumer Electronics and Thomson Consumer Electronics. This double implication supports successively adoption of several standards among which, the MPEG-2, modulations QPSK and OFDM as well as a series of patents whose licences are practically shared. Project DVB also exploits the experience gained by the same actors for the development, the launching and the exploitation of the analogue standards of television improved in Europe: D2 Mac, the HD Mac
The philosophy of project DVB
The major task consists in developing a complete succession of technologies of diffusion of digital television per satellite, cable and radio antenna in the form of pre-standardisation
Rather than to associate a single program by channel (or carrier frequency) of remote transmission, system DVB must be connected with a container which transports a combination of video sources, audio and given multimedia. It must be open (compatible) and evolutionary towards the SDTV (standard resolution), the EDTV (improved resolution) and the future HD TV, the format 16 ⁄ 9, the multichannel sound surround and be able to convey any form of numerical media to come
The objective consists in defining a series of standards in standard ETSI for the physical layers (combination of the data of diffused contents), the correction of errors (compensation in reception) and transport (transmission) for each mode of diffusion
A report ⁄ ratio ETSI must describe the principal systems of baseband representing of the options for the transmission
As far as possible, in order to reduce the industrial costs, the DVB must integrate common points between the various platforms of diffusion and lead to solutions accessible to the market general public.
The purpose of the project of DVB is not to reinvent but consist to employ again, officialise and harmonise the existing open standards, since they are available.
Technique
Demystification
Although standards DVB define only part of the process of digital television, these standards represent a large part of these technologies.
With the arrival of the encoding of the video and audio, it became possible to transmit more services in a band-width become well too narrow for the content providers wishing to offer more chains, as well as more targeted chains.
MPEG2 allowing finally a quality broadcast, it was thus enough to define a standard allowing the interworking of the equipment since the encoding and to the final decoder (final) installed at the televiewer.
At output of studio, the numeric signal is not yet exploitable for the televisual transmission. These signals are treated by coders in order to separate it video, the audio tracks (S) as well as the teletext. The encoding includes ⁄ understands also a data compression part, and for this reason, the most used today is still the standard MPEG-2 which is seen slowly replaced by standard MPEG-4.
Then, all these encoded services are multiplexed in order to add to it other functionalities such as subtitles DVB, the interactive applications, the Conditional Access allowing content protection, the protection of the individual by content-type (child, adult) and his marketing.
During the process of multiplexing, the various services (chains, plays, radio) are assembled in flow of transport (TS, Transport Stream) by the addition of tables DVB. Each TS can thus transport to 20 television channels, even more, dependently of the means of transport and the desired quality of encoding.
Once this finished process, these flows is transmitted either in the shape of a numerical bouquet towards the final customers who must thus have a decoder (Set-signal box) compatible which will make the opposite process: demultiplexing, checking of the access rights, decoding and transmission towards television, either by a modulator PAL, or by an output Peritel (SCART) or in the shape of a signal composite for the video and analogue for the audio.
All in all, standard DVB between thus concerned since the setting in multiplexing to the output of the final decoder.
Diffusion of the programs
The DVB is especially a standard which relates to the indication diffused in flow (tables DVB), as well as the material layer according to the mode of transmission which makes it possible any decoder DVB to find the received programs. By definition, it enriches the standards used for the digital transmission without reinventing the wheel. The various digitised channels (of television mainly, but also radio) are multiplexed: they are separate in audio, videos, data, cut out out of packages, the various packages, coming from one or more sources, are transmitted in series, by using technique FIFO.
A program of TV is thus composed of the flow of the video component, of the flow of the audio component, the flow of the French subtitles, the flow of the English subtitles, etc Each one of these packages is called elementary flow and is stamp of a single number of identification, or Packet IDentifier (PID). At output of the multiplexor thus either a MPTS containing is several programs, or a SPTS containing only one program. Tables DVB are used to define each one of these elementary flows, and to associate them the ones with the others.
MPEG2 PSI (Program Specific information)
PID Abbr Name Description
0x0000 STALEMATE Program Association Counts List the PMT and the NIT
0x0001 CAT Conditional Association Counts Provides information on the system of Conditional Access, as well as the localisation of the EM
0xnnnn PMT Program Map Counts Identify and indicates the localisation of the flows contained in each service, as well as the localisation of the PCR for each service
DVB IF (Service Information)
PID Abbr Name Description
0x0010 NIT Network Information Counts Provides information about the physical network
0x0011 SDT Service Description Counts Described the services of the system
0x0011 BEATS Bouquet Association Counts Described the services of a bouquet (is thus not limited to only one network).
0x0012 EIT Event Information Counts Described the events of the services: for example name of the event, time of departure, duration, etc
0x0014 TDT Time Definition Counts Provides information over the date and the hour to format UTC.
0x0014 EARLY Time offset Counts Provides information over the date and the hour to format UTC, as well as the time zone.
Characteristic
PMT
One can find one or more PMT by TS.Mais it is either one, or the other. If there are several PMT in a TS, there will be as much as services present.
NIT and SDT
The NIT and the SDT provide various information, according to whether the table transmits information of flow Transport Stream current, or that of other flows TS present on the network. One speaks then about NIT Actual or SDT Actual for the flow on which the decoder is syntonised.
EIT
Because of the amount of information to be transported, table EIT is divided into several subdivisions.
EIT actual p ⁄ f provides information on the events present and following for this stream Transport
EIT actual sch provides future information on the upcoming events on this Stream Transport
Descriptors
To make it possible the decoder to effectively manage elementary flows, a series of descriptors are defined by DVB, and are included in the tables. These descriptors define for example the type of video elementary flow (MPEG2, MPEG4), the type of audio elementary flow (MPEG1, MPEG2), but also the language of the audio, or even the type of the service.
Service type
DVB defines also which is the type of each service. Indeed, it appeared useful, not to say necessary, to be able to classify the services according to the content-type, in order to allow, inter alia, a better layout of the services with the specific applications present on the decoder of the final customer.
List the most current services
Type Definition
0x01 Digital television service
0x02 Digital radio sound service
0x03 Teletext service
0x06 Mosaic service
0x11 MPEG-2 HD digital television service
0x16 MPEG-4 SD digital television service
0x19 MPEG-4 HD digital television service
Classification
For a simplified navigation, the user has a numerical remote control allowing to call a chain by his number. If no classification is defined, it is consequently impossible to reconstitute the service for the majority of the decoder, even if some of them make it possible to associate an audio PID and a video PID with a PID PMT.
To make the economy of classification (1 to 999 defined by the standard) it is possible to use an application which will make a list of the programs by type and will offer a page of navigation. It is the case for the majority of the radio applications and the interactive applications. But there remains always possible to assign a number for a digital radio, even an application.
Backward channel
The backward channel is the means implemented to allow the application of a certain number of interactive services.
For example to allow the televiewers to react on a subject on line by the addition of a window raising a multi-choice question.
But also, the backward channel makes it possible to question the decoder on its state, or the access card conditional, and well of others still, like the statistics TV rating.
In the majority of the European countries, it is interdict to use the backward channel on a specific customer to obtain information of marketing from them. However, for, or more simply improvement maintenance actions of the services, specific surveys are carried out by sector to polish the implementation of new services.
A certain number of standards DVB define, or rather supplement, the existing specifications for the backward channel.
This backward channel can be any transmission resource, even if today the operators satellite use the telephone, while the operators cable use the modem DATA OVER CABLE SERVICE INTERFACE SPECIFICATION, whereas operators ADSL have by defect a bidirectional connexion.
Standards
In order to provide a specific standard to each technology of transmission, a standard exists for each one of them in order to ensure a perfect transmission of the data since its point of origin to the decoder of the final customer, by respecting specific specificities to each media of transport.
In addition to defining the manner of transporting a flow DVB of a point has towards a point B, several other standards define the interactivity, the subtitles, the Conditional Access and well of others.
Therefore, for a given network, several standards will be applied to conform to the standard.
The list of the standards is organised by fields of application.
List standards of version 10 in the month of August 2007
Standards Description
Transmission
DVB-S Satellite transmission
DVB-S2 Satellite transmission version 2
DVB-C Transmission cables
DVB-CS Satellite transmission
DVB-T Terrestrial transmission
DVB-T2 Terrestrial transmission version 2
DVB-H Portable receiver
DVB-SH Portable receiver transmission by satellite
DVB-MDS Multipoint satellite transmission
DVB-DSNG Temporary satellite transmission
Multiplexing
DVB-SI Definition of the tables
DVB-DATA Diffusion of the data
DVB-SSU Upgraded software of the receivers
DVB-TVA Personal digital recorder
DVB-GSE Generic data
Encoding of the sources
DVB-MPEG Use of a system MPEG2
Subtitling
DVB-SUB Subtitles
Interactivity
DVB-NIP Interactive service, protocol not specified
DVB-RCC Interactive service by cable
DVB-RCP Interactive service by switched network
DVB-RCD Interactive service by DECT
DVB-RCL Interactive service by LMDS
DVB-RCG Interactive service by GSM
DVB-RCCS Interactive service by satellite
DVB-RCS Interactive service by satellite
DVB-RCT Interactive service by terrestrial transmission
DVB-RCGPRS Interactive service by GPRS
MHP
DVB-MHP Multi-media platform
DVB-PCF Contents with the format for portable
Content protection ⁄ Rights management
DVB-CPCM Content protection ⁄ Rights management
Interfacing
DVB-PDH Network PDH
DVB-SDH Network SDH
DVB-ATM Network ATM
DVB-HAN Network HAN
DVB-HLN Network HLN
DVB-CI Interface common for the Conditional Access
DVB-PI Interface for CATV ⁄ SMATV and ASI
DVB-IRDI Interface input ⁄ output decoder
Protocol Internet
DVB-IPTV By IP network
DVB-IPDC IP datacast on network DVB-H
Conditional Access
DVB-CSAS Support of encryption and the Conditional Access
DVB-SIM Simulcrypt
Analyses and measures
DVB-M And flows DVB ⁄ MPEG measure analyse
DVB-C
Standard DVB-C is the application of standard DVB to the rope drives.
This standard takes account of the characteristics of a transmission on cable:
The tape available is reduced: 8 MHz, one thus will need an important spectral effectiveness
The signal is protected and amplified, the signal report ⁄ ratio with noise is good
The disturbances are due to the echoes caused by a bad adaptation of the socket user.
To obtain a good spectral effectiveness, one uses a modulation QAM-64 associated with a linear equaliser or DFE based on the criterion with the zero-sustained pressure in order to cancel the intersymbol interference.
Standard DVB-C is not compatible with standard DVB-T. However, Philips, Technisat, Loewe, Sony, Metz,... market in Europe of the TV with mixed tuner DVB-T ⁄ DVB-C integrated, which avoids external receivers DVB-C for the chains of TV in light (or encrypted, with common interface). With the Benelux countries, JVC markets also a series of TV LCD but only MPEG-2.
In France, the television sets manufactured as from 2009 to see itself applying logo HD-TV, must necessarily decode MPEG-4 HD and have a tuner TNT HD (DVB-T), but the manufacturers anticipate while installing in more famous mixed tuner DVB-T/DVB-C.
DVB-T
DVB-T for Digital Video Broadcasting - Terrestrial is a standard of diffusion of digital television by terrestrial microwave links. It is about the one of the standards of the family DVB which includes ⁄ understands standards of diffusion of digital television by various means. The DVB-T defines the method of transmission of the televised services (audio, video and data), it uses a modulation OFDM with a concatenation of the coding of channel.
Principle
This standard takes account of the characteristics of a hertzian transmission:
tape available reduced: 8 MHz in TV
strong attenuation on the level of the receiver, the signal report/ratio with noise (SNR) is limited to approximately 18,6 dB
interference with the adjacent channels
Important interference (IIS) Intersymbol related to long multitrajets (distance from important propagation)
presence of impulsive noise (due to the engines, electrical equipment).
For a traditional modulation, one would be limited by the SNR to a QPSK-6 or QAM-25 and the IIS would extend on several hundreds from symbols. It is thus preferable to use a modulation of the type OFDM.
In fact, the possible presence of strong echoes due to the bad acceptance requirements (not released antennas) imposes the COFDM.
Standard DVB-T makes it possible to put in network place isofréquence synchronous, which makes it possible to save the frequencies by using the same frequency for transmitters which cover adjacent zones. This principle of network requires a temporal and frequential perfect synchronisation of all the transmitters of the network and is completely transparent for the receiver.
Alternatives
The T-DMB uses a temporal interlacing which allows a better correction of the fast fadings and thus a mobile use. On the other hand, the tape used is narrower and the reduced spectral effectiveness because of the recourse to a modulation QPSK.
ATSC is used in North America.
ISDB-T is used in South America.
DVB-H
The DVB-H is a numerical system of broadcasting intended for a reception on mobile terminal. Principal competing technologies of the DVB-H are the T-DMB and the ISDB-T.
Technical description
DVB-H are a standard of transmission video worked out by project DVB and published by the ETSI or CENELEC. DVB-H is an adaptation of the DVB-T, the system for numerical terrestrial television (TNT), with the requirements of the receivers of pocket. DVB-H offers a channel going down to high banc usable such as it is or in complement from the mobile telecommunication networks.
The video codec used is MPEG-4 AVC. The possible audio codecs are AAC, HE-AAC, HE-AAC v2.
Numerical modulation COFDM makes it possible to resist the echoes and thus to reinforce the mobile reception.
The technique of multiplexing per time interval makes it possible to reduce electricity consumption for the small terminals, radio the reception part having to function only during the time interval reserved for the selected program.
Each time interval includes datagrams IP which can contain up to 2 Mbits of data including the elements of control of a Reed-Solomon code.
System DVB-H was validated by the ETSI and is advised by the EBU.
Although specified for fixed or slow receivers (pedestrians) the DVB-H would function correctly in vehicles up to 70 km ⁄ h, according to the operator.
Standard DVB-H describes only the part of transmission of this system imagined by DVB without indicating the means of exploitation of the IP-based service thus transported. Within this framework, DVB proposes a series of specifications known as IP DataCast (DVB-IPDC), concurrent specifications of standard BCAST of the OMA (Open Mobile Alliance).
It should be noted that the mobile emissions (DVB-H) are emitted in vertical polarisation particularly in the great agglomerations because they are received better in this mode of polarity.
Specifications Datacast IP
Specifications IPDC over DVB-H thus describe a whole of components which aim at allowing the deployment of an commercial offer of mobile television based on the Internet Protocol. Indeed, it is probable that such an offer will may find it very beneficial to draw advantage from the bidirectional possibilities of symmetrical communication and of the advanced system of invoicing offered by the mobile telephone networks. Accordingly, DVB-IPDC defines a hybrid system on television combining a network of one-way broadcasting adapted numerical mobile with a bidirectional mobile communication network of type GPRS or UMTS.
DVB-IPDC is composed of a number of individual specifications which taken together form a complete system. The points approached are: the architecture of the system, the description of the principal use cases, the transport and the interpretation of metadata on the system (tables PSI ⁄ SI), the electronic guide of programs used for the discovery and selection of services, the system of purchase and protection of services, protocols of distribution of the contents (content delivery protocol, CDP).
DVB-IPDC was initially developed to be used with DVB-H on the level of the physical layer, but it is now expected that the system can be used with different systems DVB of digital television mobile (like DVB-SH), and even generally like roadbase of any system containing IP.
The majority of the specifications were approved right now by the ETSI. The whole of the documents is freely downloadable on the site.
Frequencies
DVB-H is conceived to work in the following wavebands:
VHF-III (174-230 MHz) in cohabitation with the DVB-T and the T-DAB
UHF-IV ⁄ V (470-830 MHz) in cohabitation with the DVB-T
Bandage L (range from 1,452 to 1,492 GHZ) This frequency band is used today for the T-DAB and the S-DAB
Chains DVB-H can coexist with chains DVB-T in the same multiplexing. However certain conditions are necessary so that this compatibility is assured. It is necessary that the field of signal DVB-T is much more important because one passes from a reception by fixed antenna of roof to a reception on a small antenna with any gain. It is necessary also that the modulation is changed because the technical choices of the modulation are for a fixed reception whereas is needed a mobile reception.
The cohabitation between the DVB-T and the DVB-H on channels is difficult to realise because there is such a difference of field between the fixed reception of roof and the mobile reception in an flat which receivers DVB-T find desensitised. The standard specifying the manufacture of the receivers indicates that the differential of field should not exceed 29 dB whereas in the case of figure DVB-H ⁄ DVB-T, the differential is of 39 dB at least. In spite of the difference between DVB-H and DVB-T, receivers DVB-T can display the level and the quality of reception, when they detect an emission DVB-H, but cannot, in general, not memorise the signal. At the time of an automatic search, they jump this signal. Certain apparatuses DVB-T memorise multiplexing DVB-H, by regarding it as radio, but do not decode the chains.
DVB-S
Standard DVB-S (Digital Video Broadcasting - Satellite) is the application of standard DVB to the transmissions by satellite.
This standard takes account of the characteristics of a satellite transmission:
The tape available is relatively broad: 36 MHz,
Channel of the type AWGN
Signal strongly attenuated and dominated by the noise
Transmission in hot line.
It is thus necessary to use an effective transmission with weak signal report ⁄ ratio with noise: one uses a modulation QPSK associated with advanced codes: an effective convolutif coding to reduce the error rate followed by a entrelacor and a Reed-Solomon code.
Manufacturers market in Europe of televisions with mixed tuners DVB integrated. These apparatuses make it possible to the televiewers to receive directly without external receiver the chains of TV in light (or encrypted with interface common DVB-CI), by satellite, in MPEG4 AVC or MPEG2, HD or SD.
DVB-S2
The DVB-S2 is the most recent standard as regards transmission of the multimedia contents by satellite. It was conceived, inter alia, to replace existing standard of diffusion of the digital video by satellite, the DVB-S. The DVB-S2 was developed in 2003, and was ratified by the ETSI in March 2005. It is based on the DVB-S and the standard used by the SNG.
The new standard will cover as a range of services much wider as the only diffusion such as the interactive services with a way return via satellite. In this case and for the users general public, the way return is ensured thanks to another standard, like the DVB-RCS. Standard DVB-S2 also makes it possible to carry out communications point-have-point or point-have-multi-point during the occasional transmissions of certain events.
in order to guaranty the quality of service required by the various applications and to exploit the spectral resources in a more effective way, the DVB-S2 adopts at the same time an adaptive coding and an adaptive constellation. thus, and for a given service, the form of wave evolves/moves in a dynamic way according to the conditions of propagation. Four diagrams of modulation are then proposed, these diagrams are given by the QPSK, 8PSK, 16 aPSK and 32 aPSK, the setting forms of it being ensured by a filter of root of Cosine Raised with roll-off of 0.2,0.25 or 0.35. In the case of the modulations 16aPSK and 32aPSK the report ⁄ ratio of the radii between the various under-constellations is adapted to the rates of coding so ensuring of better performances in power.
increase in the flow
The DVB-S is a relatively old protocol (1997), conceived to take into account rather important technical limitations, in particular in terms of noise of phase in the receivers.
Such limitations being exceeded today, one of the PALs of standard DVB-S2 is to increase transmission rate, by allowing the use of more powerful modulations for example. The DVB-S2 also profits from the last innovations in terms of coding thanks to the use of codes LDPC.
A satellite main issue of the transmissions is that the quality of the channel is very dependent on the weather to which the receiver is subjected, as well as distance from the satellite (in the case of satellites not-geostationary). For example the transmission is better in clear weather than in rainy weather. In the case of a not-geostationary satellite, the transmission is much better when the satellite is with the zenit that when it is at the horizon.
These variations in the quality of the channel thus oblige has to dimension a system of transmission according to the worst possible conditions: the system is under optimal the remainder of time. This sub-optimal use concerns however more than 90% of the use of the system.
The DVB-S2 thus envisages systems of adaptive modulation and coding, which makes it possible to modify the parameters of transmission (modulation and coding) according to the parameters running of transmission. One speaks about VCM and aCM.
Interactive services
The DVB-S2 envisages systems of interactive services.
Modulation
The modulations used for standard DVB-S2 are of the modulations of the aPSK type. These modulations have constant envelopes, which makes it possible as well as possible to dimension the amplifiers embarked in the satellites and thus to gain an invaluable place and a mass.
The modulations used are the modulations QPSK, 8PSK, 16aPSK and 32aPSK.
Coding
Coding adopted channel is a concatenation of a code in block of type BCH and of a code LDPC with a process of iterative decoding. The size of the entrelacor is of 64800.
Weave DVB-S2
In protocol DVB-S2, the data are transmitted in the forms of frames. thus, between two frames, the modulation and coding can be modified, which makes it possible to set up systems of aCM or VCM.
A frame is thus made up:
Of a header: symbols transmitted thanks to a very robust modulation (PI ⁄ 2-BPSK). These symbols transmit information of modulation and coding on the part given of the frame. Thanks to the robust modulation employed, these symbols can be used by the receiver to synchronise itself (in symbols, phase and frequency).
Of a part given. Two types of frames can be used: normal frames (64 800 bits) or short frames (16 200 bits). it should be noted that they are the sizes of frames out of bits after coding, the decoded binary frames will thus have variable sizes according to coding used. The number of symbols of the physical frame will depend him on the modulation used.
modes of compatibility with the DVB-S
The DVB-S2 envisages a mode of compatibility to be able to start has to be deployed by using the same receivers as those deployed for the DVB-S. In this case, receivers DVB-S will be able to continue has to be used with the same performances, while receivers DVB-S2 will profit from an increased efficiency (use of a constellation 8PSK instead of a simple QPSK). In this case, transmission DVB-S2 is not done to the maximum of the possibilities.
Performances
The table summarises the performances of the various diagrams which the standard proposes. no loss related on the imperfections of the channel or the nonlinear amplifiers is taken into account during the bench-marking. This loss is function of the adopted constellation but also of the mode of transmission: mono-carrying mode or multi-carrying mode.
Table 13 of the standard describes various configurations DVB-S2 with the C ⁄ N necessary for a transmission QEF.
Modcod C ⁄ N(dB) Spectral effectiveness (dB)
QPSK 1 ⁄ 4 -2,35 0,363143
QPSK 1 ⁄ 3 -1,24 0,486258
QPSK 2 ⁄ 5 -0,30 0,586573
QPSK 1 ⁄ 2 1,00 0,732487
QPSK 3 ⁄ 5 2,23 0,880224
QPSK 2 ⁄ 3 3,1 0,979445
QPSK 3 ⁄ 4 4,03 1,101831
QPSK 4 ⁄ 5 4,68 1,1757
QPSK 5 ⁄ 6 5,18 1,225676
QPSK 8 ⁄ 9 6,2 1,308482
QPSK 9 ⁄ 10 6,42 1,324898
8PSK 3 ⁄ 5 5,50 1,31851
8PSK 2 ⁄ 3 6,62 1,467136
8PSK 3 ⁄ 4 7,91 1,650461
8PSK 5 ⁄ 6 9,35 1,83597
8PSK 8 ⁄ 9 10,69 1,960009
8PSK 9 ⁄ 10 10,98 1,984598
16aPSK 2 ⁄ 3 8,97 1,953479
16aPSK 3 ⁄ 4 10,21 2,197575
16aPSK 4 ⁄ 5 11,03 2,344904
16aPSK 5 ⁄ 6 11,61 2,444579
16aPSK 8 ⁄ 9 12,89 2,609735
16aPSK 9 ⁄ 10 13,13 2,642475
32aPSK 3 ⁄ 4 12,73 2,74318
32aPSK 4 ⁄ 5 13,64 2,927087
32aPSK 5 ⁄ 6 14,28 3,051509
32aPSK 8 ⁄ 9 15,69 3,25767
32aPSK 9 ⁄ 10 16,05 3,298539
The diversity of the diagrams of coding channel and modulation makes it possible standard DVB-S2 to adapt has a broad field of application from which the requirements are different.
In the case of the services of diffusion of the video and the high-definition video, the new standard allows a gain of 25% and 30% in spectral effectiveness compared to the equivalent existing standards.
The adoption of a form of adaptive wave in the case of an interactive transmission point-have-point is much more interesting. The exchanges of the relative informations to the channel of propagation make it possible to select the constellation and the rate of coding most appropriate to the conditions of propagation. This solution improves the capacity of a transpondor edge of a factor which varies between 100% and 200%. In addition to the gain obtained in capacity, the adaptive connexion makes it possible to guaranty a better availability of the system. The exchange of the relative informations in the conditions of propagation can be carried out is via the satellite even or through a terrestrial infrastructure.

execution time customer :
runtime server : 1.046 seconds