Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04H—BROADCAST COMMUNICATION
  • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
  • H04H20/28—Arrangements for simultaneous broadcast of plural pieces of information

Definitions

• the field of the invention is that of communication systems, and more specifically that of communication systems for the transmission of multimedia content to portable terminals via digital broadcasting networks.
• the DVB-H standard is an example of a digital terrestrial broadcasting standard for the transmission of content to portable terminals, in which medium speed audio / video IP streams of the order of
• 300-500kbs are transmitted on radio channels whose flow is greater by an order of magnitude (5-20Mbs).
• the streams are sent by bursts of limited duration (typically 100ms ) using the entire bandwidth allocated to DVB-H on the channel.
• the flow of a service (or elementary flow) average flow 500kbs can be achieved by repeating every 2 seconds bursts of 100ms.
• the terminal can then simply listen to the channel intermittently (100 ms every 2 seconds), which saves 95% of the power consumption of its radio circuit.
• Streams broadcast in DVB-H are characterized by a variable bit rate which originates from the encoding techniques. Indeed, at each change of scene, a main image of large size is sent. This main image is followed by images containing the differences with respect to the main image, and which therefore have a smaller size.
• the optimal support of these variable-rate streams in a burst transmission context is an important technical and economic issue for the development of Mobile TV services.
• the burst transmission mechanism is characterized by a signaling that allows the terminal to announce the times when it will have to be listening to receive bursts.
• the implementation of this signaling is described in particular in document ETSI EN 301 192: “Digital Video Broadcasting (DVB); DVB specification for data broadcasting ", in particular paragraph 9:” Time slicing and MPE-FEC ".
• IP datagrams are encapsulated in MPE (Multi-Protocol Encapsulation) sections, which are themselves transported in MPEG-2 packets.
• MPE Multi-Protocol Encapsulation
• a salvo is characterized by:
• bit rate used for its transmission Bb (Burst Bandwidth" in b / s);
• the number of services (or elementary streams) passed at a given moment is known.
• the bursts of a service can be of fixed size (identical or different from one service to another) or variable, which will pose in a different way the problem of the calculation of the delta-t fields.
• bursts are of fixed size, it is easy to calculate the delta-t of each MPE section from the durations of the various services remaining to be sold, the number of MPEG-2 packets already transmitted in the burst and the dedicated flow on the channel to the transmission of bursts.
• bursts will also facilitate the hand-over mechanisms for which the same contents are available from one cell to another in different frequencies.
• phase shift based on the impossibility of rendering isochronous the arrival and the processing of IP datagrams in the various encapsulators IPE ("IP Encapsulator"), consists in ordering differently from one IPE to another the bursts of the various services so as to allow a changing cell terminal to avoid losing IP datagrams and to find in the new cell some of the IP datagrams already received.
• IP Encapsulator IP Encapsulator
• One method commonly used in the state of the art is to delay data forgiveness to obtain a complete view of the bursts between the current burst and the next salvo of the same service. A "posterior" calculation of the delta-t is then performed.
• the object of the invention is to propose a technique for the flow of VBR streams that can both benefit from the advantages of the variable size policy (no bandwidth waste) and the advantages of the fixed size policy (absence additional delay in transmission, facilitation of frequency shift handover).
• the invention proposes, according to a first aspect, a method for generating a data stream comprising a plurality of elementary streams temporally cut to be transmitted in the form of bursts, at least one time indicator indicating in a burst of an elementary flow the start time of the next burst of the same elementary stream, the method comprising the steps according to which: - at the latest at the emission of a burst, the starting time of the next burst of the same elementary stream, and the time stamp of the burst is informed as a function of the predicted departure time for the next burst, - at the predicted departure time, the start of transmission of the next burst is forced, even if a salvo another elementary stream is then being transmitted, and in this case then a multiplex transmission of said next burst with said burst of another elementary stream being transmitted.
• Some preferred, but not limiting, aspects of this method are the following: during the multiplex transmission of said next burst with said burst of another elementary stream being transmitted, x% of the bandwidth allocated to the transmission of the data stream is allocated to said next burst and (100-x)% of said bandwidth is allocated to said burst of another elementary stream being transmitted;
• the multiplex transmission is implemented until the end of the transmission of said burst of another elementary stream; - The multiplex transmission is implemented for a limited time;
• a level of service is guaranteed for each elementary stream, and the start time of a burst of an elementary stream is predicted to correspond to each elementary stream its guaranteed level of service;
• the guaranteed level of service for a basic stream is a guaranteed level of service for the transmission of each of the bursts of the elementary stream;
• the guaranteed level of service for the transmission of a burst is a guaranteed number of packets for the transmission of burst data; the predicted start time of the next burst corresponds to the sum of the number of packets guaranteed for the transmission of the bursts of each of the elementary flows;
• the guaranteed level of service for an elementary stream corresponds to the average, minimum or maximum level of service of a variable-sized elementary stream
• a burst comprising a plurality of sections, the header of each section comprising a time indicator indicating the starting time of the first section of the next burst of the same elementary stream, for each section the duration is calculated between the date of transmission of the section and the predicted departure time, and information is provided on the temporal indicators of the sections with the said calculated durations;
• the data stream is a DVB-H compatible stream.
• the invention relates to a device for processing a data stream comprising a plurality of elementary streams temporally cut to be transmitted in the form of bursts, and comprising means for implementing the method according to the first aspect. of the invention.
• FIG. 1 represents the delta-t temporal indicators contained in the header of each of the MPE sections of a burst of an elementary stream to indicate the departure time of the first section of the next burst of the same elementary stream.
• FIG. 2a shows a burst transmitted alone on the transmission channel according to the usual method
• FIGS. 2b and 2c show a burst transmitted in accordance with the invention using the possibility of multiplexing during part of the transmission of the burst
• FIG. 3 is a diagram illustrating the transmission of the bursts of different elementary flows in accordance with a possible implementation of the method according to the first aspect of the invention.
• the invention is based on a transmission system in which a data stream comprises a plurality of ES elementary stream services or streams (temporally sliced) to be transmitted in the form of bursts.
• a data stream comprises a plurality of ES elementary stream services or streams (temporally sliced) to be transmitted in the form of bursts.
• a preferred, but not limiting, example of such a system is a system compatible with the DVB-H standard.
• VBR Very Bit Rate
• a VBR flow is characterized by its average flow Vav, its maximum flow Vmax, and its minimum flow Vmin.
• the invention proposes to use the possibility of multiplexing bursts of different elementary streams on the transmission channel.
• the DVB-H standard actually allows multiplexing of bursts.
• a 500kbps average rate service can be sent on a 10Mbps channel with bursts of 100ms duration repeated every two seconds. If we consider two services of the same type, we can send them sequentially, each occupying 10Mbs of the channel for 100ms, or multiplex them at the MPEG-2 or MPE level so that each service will have a duration Bd of 200ms and will occupy 5Mbs on average.
• FIG. 1 shows the time indicators contained in the header of each of the MPE sections of a burst B, j of an elementary stream ES, (burst No. j of the service No.
• the burst B 1J of the elementary stream ES 1 comprises five sections MPE S1 -S5.
• a time-delta-t indicator S1 -delta-t S5 is indicated in the header of each section S1 -S5, to indicate therein a time information relating to the departure time t IJ + i of the first section of the next burst B IJ + i of the same elementary stream ES 1 .
• these temporal indicators can only be filled in after knowing the effective start time of the next burst, which requires having waited for the instant t IJ + i to obtain a complete view of the bursts between the current salvo and the next salvo.
• the temporal indicators (delta-t S1 -delta- t S5) of the sections of a salvo are given at the latest during the constitution of the salvo, on the basis of a prediction of time from the next burst of the same elemental stream.
• the departure time t IJ + i of the next burst B IJ + i of the same elementary stream ES 1 is predicted, and informs the time indicator (s) of the burst B 1J as a function of the predicted departure time for the next burst B IJ + i.
• FIG. 2a shows a burst B1 transmitted alone on the transmission channel according to the usual method, this burst being characterized by a rectangle of dimensions Bb (bandwidth), Bd (duration)
• FIGS. 2b and 2c show a burst B1 transmitted in accordance with the invention, using the multiplexing possibilities during part of the transmission of the burst.
• the burst B1 is characterized by a figure of the same surface as that of FIG. 2a
• FIG. 2b illustrates a general case
• FIG. 2c represents a particular case in which the figure characterizing the salvo B1 is composed of a right triangle T1 (whose right-angle forming cathets are Bd and d1), a rectangle R (of dimensions Bb, d2) and a triangle T2 (whose catheters forming the right angle are Bd and d3).
• the transmission of the burst B1 is broken down into three periods.
• a first period of duration d1 initiated at the start time t0 predicted for the transmission of B1 at most during the transmission of the previous burst of the same stream, during which the burst B1 and a salvo BO of the previous elementary stream are transmitted from multiplexed way on the channel.
• a second period d2 during which the burst B1 is transmitted alone on the channel.
• the distribution of the departure times t, j can be chosen arbitrarily, or, as will be presented hereinafter, with a spacing between the starting times of two consecutive bursts (t i + 1).
• j - t, j ) Ni * T translating a level of service associated with the different services. It will be understood that in the context of the invention, it is important that the departure times t IJ + i are predicted from burst n ° j of the same service n ° i.
• each elementary stream is guaranteed a level of service.
• the starting times of the successive bursts of the different services are then predicted so as to be distributed so as to guarantee the level of service associated with each elementary stream.
• Guaranteeing a given level of service for the transmission of a burst can for example consist in guaranteeing a number of MPEG packets for the transmission of the burst (or in other words to guarantee a duration for the transmission of the burst, that is to say this corresponds to the time required to transmit the guaranteed number of packets).
• the guaranteed level of service for an elementary stream can be set arbitrarily. It may also correspond to the average, minimum or maximum level of service of a VBR elementary stream.
• this level of service can be modulated during the transmission, for example to take into account the rates actually recorded for each of the elementary flows.
• the average number of packets per burst of the elementary stream itself derived from the average bit rate (Vav) of the elementary stream VBR, or
• Vmin the minimum number of packets per burst of the elementary stream, itself derived from the minimum bit rate (Vmin) of the elementary stream VBR, or
• the transport stream will be of type Bi ⁇ 0> B 2 , o, B 3 , o, Bi, i, B 2 , i, B 3 , i, Bi ⁇ 2 > B 2 , 2, B 3 , 2, --- - B 1J , where B 1J represents the burst n ° j of the elementary flow n ° i.
• a guaranteed level of service is associated with an elementary stream by guaranteeing a number of packets for the transmission of bursts of this elementary stream. For example, we can choose to guarantee:
• N1 40 packets for the transmission of each of the bursts of the elementary stream n ° 1;
• N2 30 packets for the transmission of each of the bursts of the elementary stream n ° 2;
• the start time t I J + i of the next burst B I J + i of the same elementary stream ES 1 is predicted on the basis of Guaranteed service levels, and the time-delta-t of the burst B 1J is reported as a function of the predicted departure time for the next burst B IJ + i.
• the predicted departure time corresponds to the sum N of the guaranteed packet numbers N1, N2, N3 for transmitting a burst of each of the elementary streams.
• the predicted departure times t, j are thus spaced by a duration reflecting the service levels guaranteed to the various services.
• T represents the transmission time of an MPEG-2 packet on the BP MAX whole of the assigned bandwidth BP. to the transmission of the data stream.
• the predicted departure time corresponds to the moment at which the next burst should begin to be issued in the event that in the meantime, each of the bursts was transmitted alone on the channel (or at least only on the part of the channel allocated to the DVB-H) respecting the level of service that has been associated with it.
• the start time t IJ + i of the burst B iJ + i is located at N * T seconds of the departure time t ,,, of the burst B 1J . It is actually considered that the bursts of the three elementary streams to be transmitted before the next burst of the stream ES 1 will each be successively transmitted using the guaranteed number of packets.
• Bursts consisting of a plurality of sections S1-S5 are considered in the following.
• force predicted start time t IJ + i, the start of transmission of the next burst B IJ + i, including whether a burst of another elementary stream is then in progress of transmission.
• a multiplex transmission of said next burst with said burst of another elementary stream being transmitted is carried out.
• the elementary streams have transmitted, in the interval between the transmission starts t, j , t IJ + i, two consecutive bursts B 1J , B 1, J + 1 of the same elementary stream ES 1, plus that what was allocated to them (for example an arbitrary service level, or a level of service corresponding to the average service level of a VBR stream), a multiplex transmission is carried out.
• the burst Bi 0 (burst n ° 0 of the service n ° 1) is still in progress of transmission.
• the start of the burst B 2 , o is then forced at t 2 , o, and a multiplex transmission is carried out on the part of the channel allocated to the transmission of the data stream (this part having a bandwidth BPMAX) of burst B 20 with burst Bi, 0 .
• a burst of another service is no longer being transmitted to the predicted departure time, there is no need to perform a multiplex transmission. This case is represented in FIG. 3 for the transmission of the bursts B 2, i and Bi 2 which are transmitted from the outset to t 2 , i and t i, 2 only on the channel, with the complete BP MAX bandwidth.
• the multiplex transmission may for example consist, as represented in FIG. 3, in allocating x% of the bandwidth BP MAX to the incoming burst whose transmission is forced to its predicted departure time and (100-x)% from the bandwidth BP MAX to the burst still being transmitted.
• the distribution of the bandwidth BP MAX between bursts can of course be carried out according to different schemes, for example as this is shown schematically in Figure 2c by providing a linear increase in the bandwidth allocated to the incoming burst.
• the multiplex transmission is implemented until the end of the transmission of the burst of another elementary stream still being transmitted to the start time of a burst.
• the multiplex transmission is implemented during a limited time W
• the invention implements an "a priori" calculation of the temporal indicator (s) delta-t during the constitution of the burst.
• the invention thus has the advantage over a policy of bursts of variable size not to introduce delay in the transmission of bursts. It thus benefits from the advantages of a fixed size policy, such as the facilitation of hand-over by phase-shift, and the absence of any additional delay in the issue.
• the invention makes it possible, with respect to the fixed size policy set to maximum, to make better use of the bandwidth resource.
• the invention is of course not limited to the method described above, but extends to an electronic device comprising software and / or hardware means configured to implement this method.
• This device typically resumes the functions of an IP encapsulator
• IP Encapsulator receiving IP streams, splitting them temporally, calculating intra-burst FEC protection, encapsulating IP packets and embedding them in the transport stream.
• the means for encapsulating the IP packets and embedding them in the transport stream are configured to, at the most at the time of issuing a burst, predict the starting time of the next burst of the same elementary stream, to inform the time indicator (s) of this burst, and to force at the start time predicts the transmission of the next burst, including if a burst of another elementary stream is then being transmitted.

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Time-Division Multiplex Systems (AREA)
• Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
• Data Exchanges In Wide-Area Networks (AREA)

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• 2007
  • 2007-07-06 FR FR0756329A patent/FR2918531B1/fr not_active Expired - Fee Related
• 2008
  • 2008-06-27 WO PCT/EP2008/058311 patent/WO2009007261A2/fr not_active Ceased
  • 2008-06-27 EP EP08774472A patent/EP2174433A2/de not_active Withdrawn

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