EP0695051B1 - Digital satellite transmission system - Google Patents

Description

The present invention relates to a system digital satellite transmission including a link sending digital information to the satellite, said satellite re-transmitting a multiplex resignation.

The DTVB standard for television broadcasting by satellite was described in the Union publication European Broadcasting Company of January 94, entitled "Specification of the" Baseline Modulation / Channel Coding System "for Digital Multiprogramme Television by Satellite "(V4 / MOD-B, DTVB 1110, GT V4 / MOD 252).

This standard implements the transmission satellite multiprogram using MPEG-2 standard for audio and video compression and multiplexing. For the definition of this MPEG-2 standard, we will refer to the publication of International Standardization Organization (ISO) entitled "MPEG-2 Systems Working Draft "(ISO / IEC JTC1 / SC20 / WG11, NO501, MPEG93, July 1993).

The DTVB standard implicitly assumes that the different TV channels are routed to a single earth station for their multiplexing. The multiplexed data stream, called the data stream transport, is then transmitted to the satellite by a common uplink after inserting information redundancy for signal protection.

This need to transport each channel from television with a common uplink, also called contribution link, generates costs additional resulting from a part of the implementation from this contribution link land station and secondly from the routing of signals to this earth station from various transmitters land.

The present invention relates to a system allowing the elimination of this bond of contribution, in particular in the context of the implementation artwork of the satellite transmission of digital television that can be received directly at home of a user.

French Patent Application FR 2 498 034 (WESTERN ELECTRIC) describes a two-way TDMA system in which multiplexing is entirely carried out at on board the satellite. The present invention also has for aim of simplifying the on-board multiplexer, in the case of an application on digital television.

The invention thus relates to a system digital satellite transmission including a link sending digital information to the satellite, said satellite re-transmitting a multiplex emission as defined in claim 1.

The implementation of the invention thus allows to simplify the on-board multiplexer module, since a part of the channel adaptation function is performed by individual issuers.

At least one said individual transmitter can be a ground station. Thus, each ground station transmits directly towards the satellite, which allows elimination of the contribution link. It is not incidentally not necessary that all transmitters individual are ground stations.

Said connection is advantageously a connection multiplex transmitting a multiplex transmit signal which is preferably a modulated analog signal, preferably in phase, for the transport of said information digital. The multiplex signal advantageously comprises packets each of which carries information from one single program.

The adaptation block of the first type is by example a scrambling block and / or an encoding block external.

At least one individual transmitter can have a device for receiving the transmission multiplex and a clock extracting device providing a signal clock of the individual transmitter. This provides simply a clock that has no drift relative to the clock of the satellite that powers among other things the multiplexer module.

1) une pluralité de branches en parallèle, dont chacune reçoit à son entrée un signal analogique démultiplexé par un démultiplexeur analogique, lequel fait partie de l'architecture embarquée sur le satellite, chaque branche en parallèle comprenant successivement :

a) un filtre passe-bande,

b) un convertisseur analogique-numérique,

c) un démodulateur en bande de base,

d) une mémoire tampon attaquant une entrée d'un multiplexeur embarqué.

2) ledit multiplexeur embarqué,

3) un convertisseur numérique-analogique,

4) un modulateur du signal analogique fourni par le convertisseur numérique-analogique,

5) un mélangeur fournissant un signal d'émission satellite multiplexée.

According to a preferred embodiment, the on-board multiplexer module successively comprises:

1) a plurality of branches in parallel, each of which receives at its input an analog signal demultiplexed by an analog demultiplexer, which is part of the architecture on board the satellite, each branch in parallel successively comprising:

a) a bandpass filter,

b) an analog-digital converter,

c) a baseband demodulator,

d) a buffer memory attacking an input of an on-board multiplexer.

2) said on-board multiplexer,

3) a digital-analog converter,

4) a modulator of the analog signal supplied by the digital-analog converter,

5) a mixer providing a multiplexed satellite transmission signal.

The multiplexer module includes advantageously, downstream of the on-board multiplexer and in upstream of the digital-analog converter, a generator at least one channel adaptation block of a second type requiring exchange of information between programs different. An adapter block of the second type can be for example an interleaving block and / or a block internal encoding.

The modulator of said analog signal is advantageously a phase modulator with several states, preferably a four-state phase modulator (0 °, 90 °, 180 °, 270 °), each of the values representing a dibinary (QPSK).

• la figure 1 représente un schéma fonctionnel d'un système selon l'invention ;
• la figure 2 représente un flux de transport numérique selon le standard MPEG-2 ;
• la figure 3 illustre la configuration connue mettant en oeuvre une liaison de contribution ;
• la figure 4 illustre la transmission effectuée selon l'invention sans liaison de contribution ;
• la figure 5 représente le diagramme fonctionnel d'une adaptation de canal connue en soi ;
• la figure 6 représente l'adaptation de canal modifiée selon un mode de réalisation préféré de l'invention ;
• la figure 7 représente le diagramme fonctionnel d'une liaison ascendante selon un mode de réalisation préféré de l'invention ;
• la figure 8 illustre le découpage en canaux d'une liaison ascendante selon l'invention ;
• la figure 9 représente un schéma fonctionnel d'un bloc multiplexeur embarqué selon un mode de réalisation préféré de l'invention ;
• la figure 10 représente diverses configurations d'implantation de ce module multiplexeur dans l'architecture du satellite ;
• et la figure 11 un mode de réalisation préféré de la figure 10.

Other characteristics and advantages of the invention will appear better on reading the description which follows, given by way of nonlimiting example, in conjunction with the drawings in which:

• FIG. 1 represents a functional diagram of a system according to the invention;
• FIG. 2 represents a digital transport stream according to the MPEG-2 standard;
• FIG. 3 illustrates the known configuration implementing a contribution link;
• FIG. 4 illustrates the transmission carried out according to the invention without contribution link;
• FIG. 5 represents the functional diagram of a channel adaptation known per se;
• FIG. 6 represents the modified channel adaptation according to a preferred embodiment of the invention;
• FIG. 7 represents the functional diagram of an uplink according to a preferred embodiment of the invention;
• FIG. 8 illustrates the division into channels of an uplink according to the invention;
• FIG. 9 represents a functional diagram of an on-board multiplexer block according to a preferred embodiment of the invention;
• FIG. 10 represents various configurations of implantation of this multiplexer module in the architecture of the satellite;
• and FIG. 11 a preferred embodiment of FIG. 10.

According to FIG. 1, a transmission system according to the invention comprises a certain number of ground stations E ₁ , E ₂ , E ₃ , E ₄ , etc. ... provided with transmitting antennas A ₁ , A ₂ , A ₃ , A ₄ , etc ... transmitting with a so-called "low" speed towards a SAT satellite, which receives all of these emissions by a single AR receiving antenna. According to this system, the stations E ₁ , E ₂ , E ₃ , E ₄ , etc., which are arranged on the ground in different geographical positions send their signals independently of each other to the SAT satellite which acts as an answering machine for the transmission of one or more digital television programs. Each ground station E ₁ , E ₂ , E ₃ , E ₄ , etc. transmits a signal corresponding to at least one television program. A multiplex MMUX module integrated into the architecture of the SAT satellite performs processing on the signals received by the reception antenna AR from the ground stations E ₁ , E ₂ , E ₃ , E ₄ , etc. so as to generate a single multiplex signal transmitted by the transmission antenna AE towards terrestrial receivers intended for individual users, or buildings, provided with satellite reception antennas. The signal transmitted by the transmitting antenna AE of the satellite SAT comprises a multiprogram television signal in which the transmissions of the ground stations E ₁ , E ₂ , E ₃ , E ₄ , etc. or of only some of them they are multiplexed.

The downlink constituted by the emissions from the AE transmit antenna is performed from preferably according to the standard of television programs DTVB satellite mentioned above.

With this system, we have freed ourselves from the Contribution link of Prior Art.

The uplinks E ₁ , E ₂ , E ₃ , E ₄ , etc. emit signals conforming to the MPEG-2 standard according to which the audio, video and possibly data signals are multiplexed and compressed to form an elementary stream. PES package.

The MPEG-2 transport stream is shown at FIG. 2. It comprises a succession of packets P1, P2, P3, P4, etc ... A packet has a data segment PES which combines video, audio and aforementioned data and which is preceded by a header successively comprising a synchronization byte SYNC, usually one byte, one indication segment packet transport error message TPEI, a PSI segment packet start indication, TP segment transport priority indication, a PID segment, a TSC scrambling control segment, an AFC segment of adaptation signal control, a CC segment of continuity counter and an AF adaptation field. For more details, we will refer to the definition of MPEG-2 standard.

In systems using the MPEG-2 standard, it may for example be envisaged that the ground stations E ' ₁ , E' ₂ , E ' ₃ , E' ₄ , etc ... transmit their video information V ' ₁ , V ' ₂ , V' ₃ , V ' ₄ , etc. audio A' ₁ , A ' ₂ , A' ₃ , A ' ₄ , etc ... and data D' ₁ , D ' ₂ , D' ₃ , From ₄ to a transport multiplexer TRMUX forming part of the contribution link LC which is arranged on the ground and which transmits the multiplex towards a satellite which then only retransmits it as it is for the domestic users.

According to the configuration of the invention as illustrated in FIG. 4, each transmitter E ₁ , E ₂ , E ₃ , E ₄ is provided with its own transport multiplexer TRMUX1, TRMUX2, TRMUX3, TRMUX4, etc. which multiplexes the video, audio and data data, respectively V ₁ , A ₁ , D ₁ for the transmitter E ₁ , V ₂ , A ₂ , D ₂ for the transmitter E ₂ , V ₃ , A ₃ , D ₃ for the 'transmitter E ₃ , V ₄ , A ₄ , D ₄ for the transmitter E ₄ , etc. Each of these multiplexed signals is transmitted by the antennas A ₁ , A ₂ , A ₃ , A ₄ , etc. direction of the SAT satellite in which they will be. processed by the MMUX multiplexer module to produce the transmit multiplex grouping the programs corresponding to the transmitters E ₁ , E ₂ , E ₃ , E ₄ , etc. in the direction of the antennas of the receivers of the domestic users.

Each transport package carries information from a single program. The transport multiplexer of rank p TRMUX _p performs a certain number of functions to enable it to calculate the values inserted in the header of the packet. It generates this header and if necessary adds enough PES data to reach a length of 188 bytes. The transport multiplexer TRMUX _p operates at a lower bit rate than the transport multiplexer TRMUX incorporated in the contribution link LC of FIG. 3. In the case of a television type broadcast, the information bit rate is known and remains stable for a given program, which allows the generation of transport packets channel by channel as shown in Figure 4.

Since there is no need to exchange information between the TRMUX _p transport multiplexers arranged in the individual transmitters E ₁ , E ₂ , E ₃ , E ₄ , etc., these multiplexers can be arranged separately on the ground in each of the transmitting stations, while the MMUX multiplexer module is, in turn, incorporated into the architecture of the SAT satellite.

In addition, it is interesting to limit the the functions performed by the module are no longer possible MMUX multiplexer. It is indeed more interesting to keep as many functions as possible at the station level even if it means increasing the radiated power effective isotropic ("EIRP") rather than carrying a full MPEG-2 multiplexer.

This is illustrated in Figures 5 and 6.

Figure 5 shows a diagram functional of the channel adaptation, known per se, according to the MPEG-2 standard. This channel adaptation includes firstly a scrambling function performed by a EMB scrambler to obtain energy dispersion then an external coding carried out by an external encoder EXENC, an interleaving performed by a device of interlacing INT, an internal encoding carried out by a INENC internal encoder and finally such modulation that a QPSK four-state phase modulation performed by a MOD modulator, the signal leaving the modulator MOD can then be directed to the transmitting antenna AE of SAT satellite.

This adaptation has the known function of protect the downlink intended for a user domestic against satellite channel faults.

According to the invention, there are a certain number of blocks of the adaptation channel on the earth stations E ₁ , E ₂ , E ₃ , E ₄ , etc. These blocks are those which execute functions which, as well as the Applicant highlighted, do not require a mutual exchange of information between different programs. This is how the scrambling and external coding functions can be placed on the ground while the interleaving and internal coding functions remain located on the SAT satellite.

In addition, since the ground stations perform EXENC external coding, this allows protection against uplink errors, resulting in a decrease in power effective isotropic radiated EIRP of stations land.

The functional diagram of a transmitter E _p is represented in FIG. 7. It comprises a video encoder ENCV _p of video signals V _p , an audio encoder ENCA _p of audio signals A _p and a data encoder ENCD _p of data D _p providing PES packets to as many inputs of a TMUX _p transport multiplexer. The compression of video, audio and data data is carried out in a known manner in the three aforementioned encoders. Since the allocation of the channel is fixed or almost fixed, there is no need to collect other PES data from other channels supplying the same satellite. Consequently, the transport multiplexer TMUX _p generates the header which corresponds to the processing of PES data at its input, that is to say corresponding to the only channel which interests it and produces the transport packet TP in the MPEG-2 format.

UWPR processor reverses word sign unique header of the package according to the standard DTVB standard frame organization.

A CU control logic unit controlled by a reference clock H supervises this inversion as well as the energy dispersal process which is produced by the EMB scrambling unit. Internal coding is made by an RS processor according to a Reed-Solômon code with parameters (204, 188, 8). This encoding Reed-Solomon performed before QPSK modulation performed by the MOD modulator and the transmission carried out by the EM transmitter.

The carrier frequency of the signal emitted by the antenna A _p does not require frequency stability better than 10 ppm. It is therefore possible to use a local oscillator. However, given that a said transmitting station E _p generally has a control receiver REC, we take advantage of the existence of this receiver REC to extract a system clock therefrom from the downlink signal supplied by the satellite SAT so as to lock the reference clock H which supplies, in addition to the control unit CU and the RS modules, the multiplexer TMUX _p and the modulator MOD.

It will be noted, as will be shown more in detail later, that in the MMUX multiplexer module of the SAT satellite, buffers are put in works upstream of the on-board multiplexer to allow correction of residual errors and errors due to the Doppler phenomenon, before multiplexing and emission by the AE antenna.

FIG. 8 illustrates the distribution of the channels of the SAT satellite. A group of N transmitting stations E _p (with N = 6) shares a satellite responder R _p in the frequency domain (FDMA). The total capacity of the transmitter is distributed equally among the stations. In other words, if R _d megabit / s are available on the downlink, that is to say for satellite transmission, each station E _{p will} transmit R _u = R _d / N megabit / s. The allocation of the resource is generally static, that is to say that a station is authorized to transmit only on a certain frequency which is allocated to it.

For example, FIG. 8 illustrates the case of a satellite presenting several answering machines having a bandwidth of 33 MHz and which are assigned to the multiprogram digital television broadcast. One of the responders R _p has six carriers corresponding to six transmitters E _p transmitting on a band of approximately 5 MHz and each having a rate R _u of 6 megabits / s for a total information rate of the downlink RD = 36 megabits / s.

Figure 9 shows a block diagram of the MMUX on-board multiplexer module. The signal at 12 GHz provided by the AR receiver antenna of the SAT satellite is supplied to the input of an IMUX input demultiplexer which is part of the architecture of the satellite and that is located upstream of the MMUX multiplexer module properly said.

The MMUX multiplexer module has at its input an MEL1 input mixer which receives at an input on the one hand the output signal of the input demultiplexer IMUX and at its other input a signal supplied by a MUL1 multiplier from a reference clock embedded HR. In accordance with the example in the figure 8 the multiplexer module has been shown in a configuration corresponding to six terrestrial transmitters. Consequently, the output signal of the mixer MEL1 is introduced to the respective inputs of six amplifiers respectively A1 to A6 whose output feeds surface acoustic wave ("SAW") filters respectively F1 to F6. Such filters have the advantage of being compact, light in weight and have very good rejection characteristics. These filters are adjusted to match the six channels shown in Figure 8. The output signal filters F1 to F6 is then introduced at the input of analog to digital converters respectively referenced CAN1 to CAN6 and clocked by the clock of HR reference. These analog-to-digital converters perform 8-bit conversion at one frequency sampling which is roughly double the carrier bandwidth of 11 million of samples / second for a bandwidth of 5MHz. Note that the conversion could also be performed with a 6-bit converter without the quantization distortion is too large. The output of converters CAN1 to CAN6 is introduced at the input of digital product detectors DP1 to DP6. These detectors convert the respective signals in the complex domain by Hilbert transform of well known way in the field of treatment digital. The signals provided by the detectors DP1 to DP6 are introduced at the input of a circuit NTP1 to interpolation and filtration respectively NTP6. The purpose of interpolation is to allow a adapted and precise filtering. This filtering is carried out by a finite impulse response FIR filter, that is to say a non-recursive digital filter. Interpolation and adaptive filtering are driven by the clock signal delivered by the RH clock with a multiplication of frequency by 4 achieved by the multiplier circuit MUL2. The signals supplied by circuits MP1 to MP6 are then demodulated into baseband by as many demodulators respectively DEM1 to DEM6 which carry out known manner the coherent demodulation of the modulated signal in phase with four QPSK states. They include means to cover the digital phase and the cadence. The demodulators advantageously include a signal level for controlling a low-pass filter to perform an automatic control loop of the gain of amplifiers A1 to A6 so as to use at best of their possibilities the converters analog-digital CAN1 to CAN6.

Buffers M1 to M6 are interposed between DEM1 to DEM6 demodulators and the multiplexer embedded.

• réaliser le multiplexage séquentiel des paquets fournis par les mémoires M1 à M6 ;
• insertion de paquets dits "de remplissage" en cas de mauvais fonctionnement d'une ou plusieurs liaisons ascendantes. Un drapeau spécialement prévu dans l'en-tête du paquet peut être mis en oeuvre pour alerter le récepteur au sol.

The on-board multiplexer has the following functions:

• carry out the sequential multiplexing of the packets supplied by the memories M1 to M6;
• insertion of so-called "filling" packets in the event of malfunction of one or more uplinks. A flag specially provided in the header of the packet can be used to alert the receiver on the ground.

The multiplexer is clocked from the RH clock whose frequency is multiplied by one MUL3 multiplier.

• un circuit d'entrelacement INT qui réalise un entrelacement par convolution conformément au standard DTVB. La profondeur d'entrelacement est de 12 octets et sa structure correspond au mode de fonctionnement de Forney. Il nécessite une mémoire interne de 9000 bits ;
• un encodeur interne INENC qui réalise un encodage par convolution, également selon le standard DTVB. Sa structure est relativement simple ;
• un convertisseur numérique-analogique de type sigma-delta avec une cadence de conversion d'environ 26MHz ;
• un modulateur pour réaliser une modulation de phase QPSK à quatre états. Il comporte, en bande de base, deux filtres de mise en forme en cosinus et une conversion à une fréquence intermédiaire f_IF ;
• un mélangeur MEL2, auquel un circuit multiplexeur MEL5 forment un signal de 12GHz dérivé de l'horloge de référence RH

The on-board multiplexer output signals supply successively:

• an INT interleaver circuit which performs convolutional interleaving in accordance with the DTVB standard. The interleaving depth is 12 bytes and its structure corresponds to the operating mode of Forney. It requires an internal memory of 9000 bits;
• an internal INENC encoder which performs convolutional encoding, also according to the DTVB standard. Its structure is relatively simple;
• a digital-analog converter of the sigma-delta type with a conversion rate of approximately 26 MHz;
• a modulator for performing QPSK phase modulation with four states. It comprises, in baseband, two cosine shaping filters and a conversion to an intermediate frequency f _IF ;
• a mixer MEL2, to which a multiplexer circuit MEL5 form a 12 GHz signal derived from the reference clock RH

• soit directement après un multiplexeur d'entrée IMUX comme représenté à la figure 9 et à la figure 10 (option 1). Dans ce cas, en cas de défaillance d'un amplificateur à tube à ondes progressives TWTA_p utilisé pour la réémission par l'antenne AE, le signal peut être envoyé à un autre amplificateur TWTA, mais il n'est pas possible d'effecteur une réallocation de fréquence puisque le module MMUX est lié à un multiplexeur d'entrée particulier IMUX ;
• soit après la matrice de commutation d'entrée MCE et avant l'amplificateur CAMP_p qui alimente l'amplificateur de puissance TWTA_p (option 2). Dans ce cas, une nouvelle allocation de fréquence est possible, grâce au réseau MCE qui peut affecter des signaux d'un multiplexeur d'entrée quelconque au module MMUX ;
• soit au niveau de la matrice MCE (option 3), ce qui permet à la fois une nouvelle allocation de fréquence et un changement d'amplificateur TWTA ; ceci nécessite par contre d'adapter la matrice MCE, par exemple en la dédoublant en une matrice MCE1 en amont du module MMUX, et une matrice MCE2 en aval du module MMUX.

The MMUX multiplexer module can be arranged:

• either directly after an IMUX input multiplexer as shown in Figure 9 and Figure 10 (option 1). In this case, in the event of failure of a TWTA _p traveling-wave tube amplifier used for retransmission by the AE antenna, the signal can be sent to another TWTA amplifier, but it is not possible to effect frequency reallocation since the MMUX module is linked to a particular IMUX input multiplexer;
• either after the input switching matrix MCE and before the amplifier CAMP _p which supplies the power amplifier TWTA _p (option 2). In this case, a new frequency allocation is possible, thanks to the MCE network which can assign signals from any input multiplexer to the MMUX module;
• either at the level of the MCE matrix (option 3), which allows both a new frequency allocation and a change of TWTA amplifier; this however requires adapting the MCE matrix, for example by splitting it into an MCE1 matrix upstream of the MMUX module, and an MCE2 matrix downstream of the MMUX module.

We have represented the case of a SAT satellite with a single MMUX module. Of course, it is one or more other responders from the be assigned to such reception and that a module be associated with them accordingly MMUX multiplexer.

Claims (11)

1. Multichannel digital satellite television transmission system with channel matching, according to the DTVB standard, comprising an uplink for sending digital information to the satellite, the said satellite having a transmission multiplex retransmitter, the said uplink comprising a plurality of individual transmitters (E₁ ... E₄), each of which has a means for transmitting a multiplex transmission signal at a first rate corresponding to at least one television programme and the retransmitter of the satellite (SAT) comprising an on-board multiplexer module (MMUX) having a means for combining the said transmission signals in order to form the said transmission multiplex at a second rate higher than the first rate, characterised in that at least one individual transmitter (E₁ ... E₄) comprises a multiplexer for at least the audio and visual signals of at least one television programme and in that the said individual transmitter (E₁ ... E₄) comprises a generator of at least one channel matching unit, according to the DTVB standard, which is a first type not requiring any information exchange between different programmes.
2. System according to Claim 1, characterised in that at least one said individual transmitter (E₁ ... E₄) is a ground station.
3. System according to Claim 1, characterised in that the multiplex transmission signal is an analogue signal modulated for transporting the said digital information.
4. System according to one of Claims 1 to 3, characterised in that the multiplex signal comprises packets, each of which transports the information of only one program.
5. System according to Claim 1, characterised in that a said matching unit of the first type is a scrambling unit.
6. System according to one of Claims 1 or 5, characterised in that a said matching unit of the first type is an external encoding unit.
7. System according to one of the preceding claims, characterised in that at least one individual transmitter (E₁ ... E₄) comprises a reception device (REC) of the transmission multiplex supplied by the satellite and a clock extraction device using the said transmission multiplex, supplying a clock signal of the said individual transmitter.
8. System according to one of the preceding claims, characterised in that the multiplexer module comprises successively:

   1) a plurality of branches in parallel, each of which receives at its input an analogue signal demultiplexed by an analogue demultiplexer, each parallel branch comprising successively:

   a) a band-pass filter (F₁ ... F₆),

   b) an analogue to digital converter (CAN1 ... DEM6),

   c) a base-band demodulator (DEM1 ... DEM6),

   d) a buffer (M1 ... M6) driving an input of an on-board multiplexer;

   2) the said on-board multiplexer,

   3) a digital to analogue converter (CNA),

   4) a modulator (MOD) for the analogue signal supplied by the digital to analogue converter (CNA),

   5) a mixer (MEL2) supplying a multiplexed satellite transmission signal.
9. System according to Claim 8, characterised in that the multiplexer module (MMUX) comprises, downstream of the on-board multiplexer and upstream of the digital to analogue converter (CNA), a generator of at least one channel matching unit of a second type requiring an exchange of information between different programmes.
10. System according to Claim 9, characterised in that a said matching unit of the second type is an interleaving unit.
11. System according to one of Claims 9 or 10, characterised in that a said matching unit of the second type is an internal encoding unit.

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