Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L7/00—Arrangements for synchronising receiver with transmitter
  • H04L7/0091—Transmitter details
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04H—BROADCAST COMMUNICATION
  • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
  • H04H20/65—Arrangements characterised by transmission systems for broadcast
  • H04H20/67—Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W24/00—Supervisory, monitoring or testing arrangements
  • H04W24/02—Arrangements for optimising operational condition
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W56/00—Synchronisation arrangements
  • H04W56/001—Synchronization between nodes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/02—Terminal devices
  • H04W88/04—Terminal devices adapted for relaying to or from another terminal or user

Definitions

• Data synchronization method and device Method and device for generating a data stream, and corresponding computer programs.
• the field of the invention is that of the transmission and broadcasting of information, in particular television, radio or time information data, in a broadcast network comprising at least one fixed reference site, also called a fixed transmitter, and a plurality of broadcast sites.
• a fixed transmitter is for example of long wave transmitter, teleport, or other type.
• the invention relates to the synchronization of the different broadcasting sites, and proposes a technique for compensating for delays due to the geographical positions of the different broadcasting sites, and possibly the variable delays due to the drift of an intermediate transmission equipment. satellite type.
• the invention applies more particularly, but not exclusively, to SFN ("Single Frequency Network") networks, regardless of the broadcast standard used:
• DVB-T or DVB-T2 in English “Digital Video Broadcasting - Terrestrial", in French “digital television broadcasting - Terrestrial”);
• LTE Long Term Evolution
• eMBMS evolved Multimedia Broadcast / Multicast Service, in French “service multimedia broadcast general / multipoint advanced
• TNT digital terrestrial television broadcasting networks
• the invention is not limited, of course, to this particular field of applications, but is of interest for any technique of transmitting or disseminating information that has to deal with a similar or similar problem, and in particular in broadcasting networks the DVB-T standard or the DVB-T2 standard.
• Such digital terrestrial television broadcasting networks are now deployed or being deployed in France, Europe, and several other states of the world.
• These networks can be of MFN ("Multi Frequency Network") type, which means that the different broadcast sites operate at different frequencies, or SFN, or isochronous, which means that Different broadcast sites need to be precisely synchronized in time, frequency, and content.
• MFN Multi Frequency Network
• FIG. 1 illustrates a block diagram of a DVB-T broadcasting system of SFN type implementing a broadcasting of data in the MPEG-2-TS ("Motion Picture Expert Group - Transport Stream") format.
• MPEG-2-TS Motion Picture Expert Group - Transport Stream
• FIG. 1 shows two transmitters 10 and 11 located at two different broadcast sites, each comprising a synchronization module (system SYNC) 101, 111, and a DVB-T modulator 102, 112.
• synchronization 101, 111 is powered by two frequency and time reference signals, for example a signal corresponding to one pulse per second, or 1 pps (for "Puise Per Second"), and a 10 MHz signal resulting from the 1 pps. It is found that there are exactly 10 milions of periods of the frequency reference signal at 10 MHz between two 1 pps pulses.
• These signals can be derived from any reliable reference system 105 and 115, based for example on the American positioning system GPS ("Global Positioning System”), European Galileo, or Russian Glonass.
• GPS Global Positioning System
• European Galileo European Galileo
• Russian Glonass Russian Glonass
• the 10 MHz frequency reference signal can also be used at the head end, via an SFN adapter, to calibrate its output rate, so that it is stable and accurate, as well as by the transmitters of the broadcasting sites to calibrate their bit rate. .
• This reference can also be used by transmitters of broadcast sites to synchronize their transmission frequency, which must be accurate to within 1 Hz in TNT in an SFN for optimal operation.
• the data to be broadcast by each of these transmitters 10, 11 are received in the form of an MPEG-2 TS transport stream (for "MPEG-2 Transport Stream"), originating from a receiver 12 of the transmission sites. broadcast, also playing the role of network adapter ("X Network Adapter").
• the stream M PEG-2 TS of data to be transmitted is constructed by an MPEG-2 multiplexer referenced 13, which performs the framing. Datas.
• Such an MPEG-2 multiplexer is located for example in a national headend, from which are then transported by satellite (in a transport network, also called transmission network) the data to be broadcast by each of the transmitters 10, 11 , dissemination sites.
• the data is processed by an SFN adapter 14, which realizes the time stamping of the frames from the same time and frequency reference system 15 as that 105, 115 which is used by the synchronization modules 101, 111 of the transmitters 10 and 11.
• the adder SFN 14 is the pe n da nt, em issio n, sync modula 101, 111 in reception.
• the SFN adapter is also powered by a frequency reference signal at 10 MHz and by a time reference signal at one pulse per second.
• the data stream is therefore of the MPEG-2 TS type: it is then used to transmit the network adapter 16 ("network adapter TX"), and carried by the intermediate of the transmission or distribution network 17 (for example a satellite transmission network), to the receivers 12 of the broadcasting sites, in order to be made available to the transmitters 10 and 11.
• network adapter TX network adapter 16
• the transmission or distribution network 17 for example a satellite transmission network
• the time marking realized by the SFN adapter 14 consists first of all in building mega-frames and secondly in inserting at any point of each of these mega-frames a mega-initialization packet.
• -trame also called "Mega-frame Initialization Packet", or MIP.
• the MIP packet of the megatram index n is identified by its own PID (for "Packet Identifier” or "packet identifier") and comprises in particular:
• point a two-byte word called "point", which gives the number of data packets (TS packets) between the current MIP and the first TS packet of the next megatram;
• the SFN adapter 14 organizes the data stream 21 into megatrams, and inserts one and only one MIP packet per megatram (MIP n- i for the megatram n-1, MlPn for the megatram n).
• the system SYNC module 101, 102 receives at its input on the one hand the MPEG stream 22 which has been transported in the network, and on the other hand the time references 1 pps. and frequency 10 MHz from, for example, the GPS receiver.
• the system SYNC module 101, 102 finds, thanks to the value STS and pulse 1 pps, when this first packet TS of the next mega-frame is out of the SFN adapter at the head of the network. This corresponds to the time (or time) of transport.
• the system SYNC module 101, 102 derives the broadcast instant, which corresponds to the output time of the SFN adapter at the head end of the network to which is added a controlled delay and co mmun to all us é es transmitters broadcast sites (maximum delay or "Max_Delay", also transported in MIP packets) and a delay that may be specific to each transmitter ("Tx_time_offset").
• This last parameter corresponds to a delay related to the engineering of the broadcasting site.
• the transmitters 10, 11 use the MIP signaling and a time reference (for example a signal 1 pps from a GPS) identical to that used at the transmitter of the headend, to achieve a comparative analysis of the MIP signaling and time stamps STS, and make the decision to delay more or less the received frame, at the output of the transmitter of the broadcast site.
• a time reference for example a signal 1 pps from a GPS
• this deterministic method which is based on the same time reference as the one at the head end, ensures the temporal synchronization of the output signals of the transmitters of the broadcast sites.
• time references 1 pps and frequency 10 MHz are common at all points of the broadcast chain. They are thus deduced, conventionally from a GPS reception.
• the patent application WO2009 / 103638 in the name of TDF proposes a synchronization technique of the different transmitters of a broadcast network, not requiring the use of a reliable time reference (eg from a GPS receiver) ) at each of these issuers.
• This technique makes it possible to use, in the same broadcast network, both transmitters using a time reference from a reliable source, and transmitters using a time reference from the data stream.
• a time offset between two time references obtained according to different techniques is determined at the head end of the network, and a directly modified time marker is transmitted in the data stream sent by the headend to take account of this offset. or this time delay is transmitted to the different emitters of the network, so that the transmitters of the broadcast sites modify their local time reference as a function of this offset.
• the invention proposes a new solution which does not have all of these disadvantages of the prior art, in the form of a data synchronization method, in a broadcasting network comprising at least one fixed transmitter and A variety of broadcast sites.
• the synchronization method implements the following steps, at the level of at least one of the broadcasting sites:
• the invention thus proposes a new solution for the synchronization of the different transmitters of a broadcast network (or a plate of such a network), whatever the geographical position of the different broadcasting sites.
• such a fixed transmitter is a long-wave transmitter (of the type France Inter in France, DCF77 in Germany, MSF in the United Kingdom, - registered trademarks).
• Such an issuer broadcasts time information (date and time) to the different broadcast sites. According to this first example, it is this time information that is re-profiled broadcast site by broadcast site, by modifying the temporal information received at a particular broadcast site to take account of the additional delay related to this broadcast site.
• such a transmitter is a teleport, allowing in particular the transmission of a data stream to a satellite in geostationary orbit.
• no additional delay is applied to the broadcast site associated with the longest travel time from the fixed transmitter, since the absolute delay is, for this broadcasting site, equal to fixed delay.
• the absolute delay is equal to a travel time between the fixed transmitter and the broadcasting site
• the fixed delay is equal to a maximum travel time among the different travel times between the transmitter fixed and each of the network's broadcast sites.
• the absolute delay is equal to a travel time between an intermediate transmission device (and / or broadcast) and the broadcast site
• the fixed delay is equal to a maximum travel time among the different travel times between the intermediate transmission equipment and each of the broadcast sites of the network.
• a p ro c u p e ry, th e r e d i n te rm ed i e r of th e tra n s m e ns is a geostationary satellite.
• the absolute delay corresponds, according to this second embodiment, to the time of travel at bsolu, calculated locally for each deflection site, on the basis of the geographical coordinates of the site (latitude, longitude, altitude) and the nominal position. Satellite geostationary (latitude, longitude, altitude).
• the fixed delay is the maximum delay value at bsol u (travel time) encountered on the network, possibly weighted with the processing time inherent in the satellite receiver.
• This fixed delay is common to all broadcast sites, and in particular allows the 1 pps signals generated at the broadcast sites to be synchronous with a 1 pps signal from a GPS receiver (at the reference position of the satellite, outside of space drifts).
• the data stream comprises at least one field carrying the delay a bsolu
• the obtaining step implements a step of extracting the absolute delay of the data stream.
• the absolute and fixed delays defined previously are static data, it is possible to broadcast them as private data in the data stream.
• the data stream may have a first field carrying the absolute delay associated with the broadcast site S1, a second field carrying the absolute delay associated with the site. S2, and possibly a third field carrying the fixed delay (knowing that this fixed delay is equal to the maximum absolute delay among the absolute delays associated with the diffusion site SI and the diffusion site S2, it is not imperative to the transmit in a separate field).
• the absolute delay associated with the broadcast site SI can be parameterized at a synchronization device of the broadcast site S1
• the absolute delay associated with the broadcast site S2 can be parameterized at the level of a synchronization device S2 broadcast site.
• the fixed delay can be transmitted in the data stream or parameterized at each broadcast site.
• the synchronization method comprises a step of obtaining a time reference, from the recaled flow.
• Such a time reference is for example of type 1 pps, and is synchronous between the different network broadcast sites associated with such a synchronization device.
• the synchronization method comprises a step of obtaining a frequency reference at 10 MHz, from the time reference l pps.
• the broadcasting sites belong to the same SFN-type plate, in which the transmitters use the same transmission frequency.
• the invention relates to a data synchronization device, able to be activated in a broadcast network comprising at least one fixed transmitter and a plurality of broadcast sites, comprising:
• a module for determining an additional delay by subtracting the absolute delay from a fixed delay common to the broadcast sites of the network, the fixed delay corresponding to the maximum absolute delay determined from the geographical positions of the broadcasting sites of the network,
• Such a synchronization device is particularly suitable for implementing the synchronization method described above.
• Such a synchronization device may of course include the various characteristics relating to the synchronization method according to the invention, which can be combined or taken in isolation. Thus, the characteristics and advantages of this synchronization device are the same as those of the synchronization method and are not detailed further.
• such a synchronization device can be integrated into a broadcast site, comprising a receiver and a transmitter that can optionally be combined.
• the invention also relates to a method for generating a data stream, intended to be transmitted in a broadcast network comprising at least one fixed transmitter and a plurality of broadcast sites, implementing the following steps:
• generating a data stream comprising at least one field carrying the absolute delay and at least one field carrying a fixed delay, said fixed delay being common to the broadcast sites of the network and corresponding to the maximum absolute delay determined from the geographical positions of the broadcast sites.
• Such a method of generating a data stream is particularly suitable for developing a data stream intended to be broadcast to the various broadcast sites of the network, as described above.
• such a method of generating a data stream also implements the following steps:
• obtaining a first time reference from an external source; obtaining a second time reference, determined from a first transmission / reception of the data stream;
• the invention thus proposes, according to this embodiment, a new synchronization technique of the different transmitters of a broadcast network, not requiring the use of a reliable time reference (for example from a US positioning system).
• a reliable time reference for example from a US positioning system.
• G PS or European Gal iléo or Russian Glonass at the level of each of these transmitters.
• the first time reference is a pulse per second, derived from a positioning system
• the second time reference is a pulse per second, regenerated from the data stream.
• the temporal offset or said at least one time marker is inserted by replacing a packet of stuffing of the data stream with a phantom packet or a packet of which the signaling does not modify the nature of the flow, that is to say the final service associated with the flow.
• the marking-specific packet or packets inserted in the stream before the transmission can be filtered before the extraction of the time markers, that is to say at the level of each transmitter, for example by overwriting these packets by a stuffing pack. It can be noted that this filtering of the specific packets is deterministic. Thus, in the context of a SFN type network, it does not modify the SFN aspect of the broadcast signal.
• the invention relates to a device for generating a data stream intended to be transmitted in a broadcast network comprising at least one fixed transmitter and a plurality of broadcast sites, comprising:
• a module for generating a data stream comprising at least one field carrying the absolute delay and at least one field carrying a fixed delay, said fixed delay being common to the broadcast sites of the network and corresponding to the maximum absolute delay determined from the geographical positions of the dissemination sites.
• a device for generating a data stream is particularly suitable for implementing the method of generating a data stream described above.
• Such a device may of course include the various features relating to the method of generating a data stream according to the invention, which can be combined or taken in isolation. Thus, the features and advantages of this device are the same as those of the method of generating a data stream and are not detailed further.
• such a device is a headend of a broadcast network.
• the invention also relates to one or more computer programs comprising instructions for implementing a synchronization method and / or a method of generating a data stream as described above when this or these programs are run by a processor.
• This or these programs can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in n ' any other desirable form.
• FIG. 1 already described in relation with the prior art, presents a block diagram of a TNT broadcasting system of the SFN type implementing a broadcasting of the data in the MPEG-2 format;
• FIG. 2 also described in relation to the prior art, illustrates, in the form of a timing diagram, the principle of SFN synchronization implemented in the system of FIG. 1;
• FIGS. 3A and 3B show the main steps of a synchronization method and a method of generating a data stream according to the invention
• FIGS. 4, 5 and 6 illustrate different timing diagrams showing the generation of a 1 pps time reference
• Fig. 7 shows the main steps of a method of generating a data stream implemented to compensate for satellite drift, according to a particular embodiment of the invention
• FIG. 8 presents a technique for generating a frequency reference at 10 MHz
• FIGS. 9 and 10 respectively illustrate examples of a simplified structure of a device for generating a data stream implementing a technique for generating a data stream and a synchronization device implementing a data generation technique. synchronization according to a particular embodiment of the invention
• Figure 11 shows a broadcast channel for DVB-T2 data broadcasting.
• the general principle of the invention is based on the determination of a delay associated with a broadcasting site, because of the travel time associated with this broadcast site, and the compensation of this geographical delay implementation site broadcast by site of broadcasting, which makes it possible to synchronize the different broadcasting sites of a broadcasting network.
• this geographical delay also called absolute delay, makes it possible to compensate for the variations in the transport time of a reference signal between a fixed transmitter (of the long-wave transmitter, teleport, or other type) and the different transmission sites.
• broadcast regardless of the broadcast standard implemented (DVB-T, DVB-T2, DAB, DMB, LTE, ...) ⁇
• FIG. 3A illustrates more precisely the general principle of the synchronization method according to the invention, implemented in a broadcasting network comprising a fixed transmitter supplying at least two distinct broadcasting sites.
• FIG. 3A illustrates the steps implemented in a localized synchronization device at a network broadcast site.
• synchronization devices equip each broadcast site of the network, or of the same network plate, for example an SFN plate.
• Such a synchronization method comprises a first step 31 for obtaining a delay, called absolute delay, determined from the geographical position of the broadcasting site. This gives, at each diffusion site, an absolute delay associated with the diffusion site.
• Such an absolute delay can be calculated at the broadcast site and stored in a memory of the broadcast site, for example in a memory of the synchronization device.
• such an absolute delay can be calculated at the fixed transmitter or a headend connected to the fixed transmitter, and transmitted in a field of the data stream. It is noted that such an absolute delay is determined at least once during the commissioning of the broadcast site, and can then optionally be updated periodically or as a function of a variation of the broadcasting conditions.
• an additional delay obtained for a broadcast site is determined by subtracting the absolute delay associated with this site from a fixed delay common to different dissemination sites of the network.
• the fixed delay is defined as the maximum absolute delay determined from the geographical positions of the network broadcast sites.
• the additional delay corresponds to the difference between the fixed delay and the absolute delay associated with the diffusion site.
• a next step 33 at least one temporal information is recalibrated (if the fixed transmitter broadcasts date and time type information) or at least a portion of a data stream (if the fixed transmitter diffuse data other than time information) taking into account the additional delay. More precisely, during this third step, the additional delay is added to the time information or a portion of the flow of the additional delay is shifted, delivering a recalibrated data stream.
• Also considered according to this example is the introduction of an intermediate transmission equipment such as the Eutelsat 5 ° W (registered trademark) satellite between a fixed teleport type transmitter and the different broadcasting sites. From the satellite lighting zone, it is found that the maximum absolute delay is obtained for the S4 broadcast site. In other words, the travel time of the satellite to the broadcast site S4 is greater than the travel times of the satellite to the broadcast sites S1, S2 and S3 (the travel time from the fixed transmitter to the satellite being identical for these dissemination sites). This maximum absolute delay is also called fixed delay thereafter.
• an intermediate transmission equipment such as the Eutelsat 5 ° W (registered trademark) satellite between a fixed teleport type transmitter and the different broadcasting sites.
• the SI broadcast site is characterized by a minimum value on the absolute path delay.
• the travel time of the satellite to the broadcast site SI is less than the travel times of the satellite to the broadcast sites S2, S3 and S4.
• the reference site is the one that provides the maximum absolute delay (ie the S4 diffusion site according to The example).
• the objective is then to align the absolute delay values on each site with the value of this maximum absolute delay.
• the timing diagram of FIG. 4 illustrates this principle, for the transmission of an MPEG-TS or MPEG2-TS transport stream according to the DVB-T standard.
• the invention is not similar to the DVB-T standard, but makes it possible to compensate for the variations in the transport time between a fixed transmitter and the different broadcasting sites, whatever the broadcasting standard implemented.
• a referenced data stream 41 also called TS transport stream, formed of mega-frames, each mega-frame carrying a mega-frame or MIP initialization packet.
• MIP packet of the n-1 index mega-frame denoted by MIP n- i, is identified by its own PID and notably comprises a word called "pointer".
• the reception on the diffusion site S4 is characterized by a maximum value on the absolute delay (128893.7 ⁇ ). As such, it is not necessary to introduce additional delay to recalibrate the data stream received at the S4 broadcast site.
• the reception on the SI diffusion site is characterized by a minimum value on the absolute delay (125481.5 ⁇ ).
• the data flow is therefore available with a relative advance of 3412.2 ⁇ , corresponding to the difference in the absolute delay values between the S4 and S1 broadcast sites.
• the reception data stream on the IS broadcast site is recalculated by applying an additional delay of 3412.2 ⁇ corresponding to the value of the relative advance.
• the data stream may have a first field carrying the absolute delay associated with the broadcast site S1, a second field carrying the absolute delay associated with the broadcasting site S2, a third field carrying the absolute delay associated with the broadcasting site S3. and a fourth field carrying the absolute delay associated with the S4 scattering site.
• this fourth field therefore carries the fixed delay and it is not necessary to transmit it in a separate field.
• a step of obtaining (34) these different delays by calculation or receiving this information
• a step of generating (35) the data stream comprising these different fields illustrated in FIG. 3B.
• these different values are stored at the level of each broadcasting site that they concern.
• the use of an intermediate transmission equipment is optional. It is therefore possible to define the absolute delay as the travel time between the fixed transmitter and the broadcast site (instead of the travel time between the intermediate transmission equipment and the broadcasting site), and to define the delay. fixed as the maximum travel time between the fixed transmitter and each of the broadcast sites of the network (instead of the maximum travel time between the intermediate transmission equipment and each of the broadcast sites), according to the invention.
• the fixed transmitter is of the long wave transmitter type (France Inter in France, DCF77 in Germany, MSF in the United Kingdom, - registered trademarks), broadcasting temporal information. In this case, we relocate site by site the temporal information.
• an additional delay RI is added to the time conveyed by the time information
• an additional delay R2 is added to the time conveyed by the time information
• an additional reta rd R3 is added to the time conveyed by the time information.
• time references 1 pps rigorously synchronous on each of the broadcasting sites for example from the value STS if one places oneself in the context of the DVB-T standard (or equivalent information if placed in the context of another standard). Indeed, it is recalled that such a time stamp gives the number of periods of 10 MHz between the last pulse 1 reference pps preceding the start of a mega-frame and the beginning of this mega-frame. As illustrated in FIG. 4, it is thus possible to obtain a 1 pps signal generated locally at each broadcast site, from the recalibrated data stream and the value of a synchronization time stamp (STS).
• STS synchronization time stamp
• the relative delays are compensated diffusion site diffusion site, which allows generating time references 1 pps rigorously synchronous on each of the broadcast sites .
• time reference 1 pps thus generated is not necessarily synchronous with a time reference from an external source, such as that delivered by a GPS receiver.
• the satellite is precisely located at its geostationary reference position.
• the timing diagram of FIG. 5 illustrates: the data stream broadcast by the fixed transmitter, referenced 51;
• temporal references 1 pps rigorously synchronous on each of the diffusion sites as explained above.
• a time reference 1 pps synchronous with a time reference 1 pps from a reliable source, such as a GPS receiver.
• the satellite can be drifted around its nominal position.
• the satellite oscillates around its nominal position, with an indicative amplitude of ⁇ 0.05 ° on the value of longitude and ⁇ 40 km on the value of the altitude either vertically or horizontally, but not obliquely.
• This drift affects individually all the diffusion sites, insofar as each absolute delay is affected by a variation obeying a non-constant sinusoidal law.
• FIG. 7 The main steps implemented to compensate for this temporal variation are illustrated in FIG. 7. It is assumed hereinafter that the fixed transmitter is a teleport located in the immediate vicinity of the headend.
• a device for generating a data stream receives as input, on the one hand, the data to be broadcast, and on the other hand a first time reference, obtained from an external source, such as a GPS receiver. It organizes the data in frames, and inserts at least one time marker in the data stream. The stream thus marked passes through an uplink to the satellite, and is then transmitted to the different broadcast sites.
• the headend receives the stream of data transported by the satellite (headend - satellite - headend). From the time marker (s) present in this stream, a second time reference is obtained.
• the first and second time references are then compared during a step 73, to determine a time shift between the first and second time references. Finally, during a step 74, this time shift is transmitted to the different broadcast sites, or else taken into account to modify the time marker (s) in the rest of the data flow transported to the different broadcast sites.
• the modification of the temporal markers makes it possible to compensate, at the head end of the network, the influence of the displacement of the satellite, so as to emulate the reception at the level of the broadcasting sites. It is also possible to transmit this time offset to the different broadcast sites, which can modify their local time reference as a function of this shift.
• these broadcast sites can be of different types, some using a reliable external source for the generation of a time reference (GPS type), others regenerating the time reference from the received data stream, and not therefore not requiring the use of an external reference type GPS.
• this technique is combined with the technique of compensating for geographical delays implemented broadcast site diffusion site, which allows to synchronize the different broadcast sites of a broadcast network and compensate for all variations in transport time between the headend / fixed transmitter and the different broadcast sites, regardless of the broadcast standard implemented (DVB-T, DVB-T2, DAB, DMB , LTE, ).
• the data stream to be broadcast is organized into mega-frames, comprising one or more MIP packets.
• MIP packets carry an STS timing stamp, calculated according to the 1 pps time reference from the GPS receiver, denoted 1 pps (GPS).
• GPS GPS
• the data flow thus constructed is distributed in the transport network.
• the transported data stream is received by the satellite reception means of the headend or the teleport.
• a new 1 pps time reference, denoted 1 pps (TS) is generated from the received data stream.
• the time reference 1 pps (TS) and the time reference 1 pps (GPS) are then compared, determining the time shift ⁇ 1 pps between these two references.
• the information ⁇ 1 pps is determined at the head of the network by comparing the time difference existing through the MIP marker conveyed in the data stream (or ASI stream in satellite reception), with respect to the reference 1 pps from a GPS receiver. It is noted that the receiver of the head of network has a deterministic character, with a processing time identical to that of the receivers arranged on all the broadcasting sites.
• the SFN adapter of the headend modifies the value STS in the MIP packets, taking into account this time shift ⁇ 1 pps.
• the STS previously calculated according to the 1 pps (GPS) time reference, is added to it by adding the time offset, such as:
• variable ⁇ 1 pps corresponds here to the instantaneous variation of travel time caused by the satellite drift, in opposite algebraic value. If the drift of the satellite imposes an extension of the duration of the travel time of "x" ⁇ , the value ⁇ 1 pps will be "-x" ⁇ ,, and vice versa.
• This new value STS ' is inserted in the M IP packets. This time shift is therefore taken into account to modify the time marker (s) in the sequence of the data flow transported to the different broadcasting sites.
• the technique of compensation of the geographical delay is applied on site by site, as illustrated in FIG. 6.
• broadcasting sites which are amputated / shifted fixed delay common to all broadcast sites, to generate at each broadcast site a time reference 1 pps synchronous with the time reference 1 pps (GPS).
• the fixed delay value commu n is retained, as well as the additional delay value to be taken into account for the site concerned (for example 3412.2 ⁇ for the broadcast site SI).
• the STS value contained in the MIP packet originating from the headend is not modified.
• the value ⁇ 1 pps representative of the time difference can be transmitted in a dedicated phantom packet identifier (PI D). This encapsulation allows transparency at the modulator of a downstream broadcast site, and allows its operation by a synchronization device as described above.
• the time offset can thus be inserted in a TS packet having a dedicated PI D, for example by replacing a packet of stuffing of the stream with a packet identified by a ghost PI D, that is to say a packet with a PID. which is not described in the tables and which is not reserved by the standard.
• this time shift is inserted by replacing a packet of stuffing of the stream with a packet whose signaling does not modify the nature of the signal to diffuse.
• the broadcast site knows the time-stamping specific packets (phantom PIDs or packets whose signaling does not modify the nature of the signal to be broadcast).
• This insertion step is for example implemented by a modified MIP inserter.
• an extraction module is provided, making it possible to extract, in the packets specific to the marking, the time offset measured at the head of the network.
• the technique of compensation of the geographical delay is applied site by site, as illustrated in FIG. 6.
• the 1 pps compensated time reference is then aliased to the 1 pps (GPS) time reference, thanks to the time offset compensation ⁇ 1 pps.
• one or more modified temporal marker (s) as described in relation to the first embodiment into one or more marking-specific TS packets.
• these marking-specific packets are identified by a phantom PID or a packet whose signaling does not change the nature of the signal to be broadcast.
• specific tagging packets for example, phantom MIPs
• STS' STS + ⁇ 1 pps
• STS' STS + ⁇ 1 pps
• This insertion step is for example implemented by a slightly modified MIP inserter, to introduce marking-specific packets into the MPEG-TS stream.
• the data flow transported from the headend / teleport to the different broadcast sites therefore has a double time stamp:
• time references 1 pps rigorously synchronous on each of the broadcast sites, which is amputated / shifts the fixed delay common to all broadcast sites, to generate at each broadcast site a time reference 1 pps synchronous with the time reference 1 pps (GPS) .
• the invention is applicable whatever the broadcast standard implemented, from the moment when it is possible to extract the data flow from the time synchronization information, such as a time marker.
• FIG. 8 illustrates an exemplary implementation of the servocontrol of the reference frequency at 10 MHz from the time reference 1 pps generated according to the invention.
• the time reference 1 pps generated according to the invention is filtered 81, then subjected to an oscillator 95, for example of the OCXO type at 10 MHz (in English "Oven Controlled X-tal (Crystal) Oscillator ", in French” Quartz Thermostat Oscillator ").
• the output signal of the oscillator is stored in a register 83, delivering a frequency reference signal at 10 MHz.
• the optimization of the filtering characteristics of the servo loop allow to absorb and smooth variations affecting the reference 1 pps generated according to the invention (from the proposed alternative synchronization module).
• the purpose is to have at the output of reference signals with improved accuracy, conferred in particular by the use of an OCXO type oscillator.
• FIGS. 9 and 10 show, with reference to examples, a simplified structure of a device for generating a data stream and a synchronization device, implementing a technique for generating a data stream. data or synchronization according to an embodiment described above.
• FIGS. 9 and 10 illustrate only one particular way, among several possible, to achieve the various embodiments detailed above.
• the device for generating a data stream comprises a RAM 90, a processing unit 91, equipped for example with a processor, and controlled by a computer program stored in a ROM 92 , implementing the method of generating a data stream according to one embodiment of the invention.
• the code instructions of the computer program 92 are for example loaded into the RAM 90 before being executed by the processor of the processing unit 91.
• the processing unit 91 receives as input data to be disseminated.
• the processor of the processing unit 91 implements the steps of the method of generating a data stream described above, according to the instructions of the computer program 92, to insert the values of the absolute delays associated with the different broadcasting sites. in the data stream.
• the device for generating a data stream the head end comprises, in addition to the memory 90, a module for obtaining at least one absolute delay associated with one of the broadcasting sites and a module for generating data. a data stream comprising at least one field carrying the absolute delay and at least one field carrying a fixed delay, corresponding to the maximum absolute delay. These modules are driven by the processor of the processing unit 91.
• the synchronization device illustrated in FIG. 10, comprises a RAM 93, a processing unit 94, equipped for example with a processor, and controlled by a computer program stored in a ROM 95, implementing the method synchronization according to one embodiment of the invention.
• the code instructions of the computer program 95 are for example loaded into the RAM 93 before being executed by the processor of the processing unit 94.
• the processing unit 94 receives as input a data stream, also called a transport stream.
• the processor of the processing unit 94 implements the steps of the synchronization method to recalibrate the data stream to synchronize the different broadcast sites of the network.
• the synchronization device comprises, in addition to the memory 93, a module for obtaining an absolute delay associated with the broadcasting site, a module for determining an additional delay and a module for resetting the data stream coming from the fixed transmitter. These modules are driven by the processor of the processing unit 94.
• such a synchronization device is integrated with a broadcasting site.
• the synchronization device, the receiver and the transmitter of a broadcast site can be combined within the same equipment.
• FIG. 11 finally presents a broadcasting chain implementing a headend (according to the prior art or as described above) and at least one broadcasting site as described above, for broadcasting a T2-MI data stream according to the DVB-T2 standard.
• the data to be broadcast is framed by a T2-MI gateway 113, delivering a stream of data organized in a frame.
• the temporal marking of the data frames can be implemented by the T2-MI 113 gateway from a 1 pps time reference and a 10 MHz frequency reference from a GPS receiver 114. Possibly, the values of the delays Absolutes associated with the different broadcast sites of the network are inserted into the data stream.
• the T2-M I gateway delivers a T2-MI stream comprising time stamps "timestamps" carried in packets of type (0x, 20) for determining the end of a frame.
• the data stream is then modulated by a DVB-S2 modulator 115, and broadcast through a satellite transmission network 116 to at least one broadcast site.
• the data stream is received by a DVB-S2 receiver 117, and then made available to a synchronization device 118 as described above, to recalibrate the data stream and generate a reference 1 pps and a frequency reference at 10 MHz.
• the thus recalibrated data stream is transmitted to a DVB-T2 modulator 1191 and broadcast by the antenna 1192 of the transmitter 119, using the time and frequency references 1 pps and 10 MHz generated previously.

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Synchronisation In Digital Transmission Systems (AREA)
• Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

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• 2014
  • 2014-04-04 FR FR1453013A patent/FR3019701B1/fr active Active
• 2015
  • 2015-04-03 US US15/301,859 patent/US10341084B2/en not_active Expired - Fee Related
  • 2015-04-03 EP EP15713966.8A patent/EP3127258A1/de not_active Withdrawn
  • 2015-04-03 WO PCT/EP2015/097013 patent/WO2015150587A1/fr active Application Filing

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