FR2899420A1 - Gateway for receiving e.g. video on demand type television service, has asymmetric digital subscriber line modem receiving service and determines data representing time division, and access point encapsulating data into radio frame - Google Patents

Abstract

The gateway has an asymmetric digital subscriber line (ADSL) modem receiving a digital video broadcast service e.g. digital video broadcasting-handheld (DVB-H) service. The modem determines data representing a time division and encapsulates service frames in a frame comprising the data. A wireless LAN access point transmits the frame with the data to a digital audio/video terminal e.g. mobile telephone. The access point encapsulates data concerning selected stream received from the modem, into a radio frame (252) for diffusing the data on a wireless LAN. Independent claims are also included for the following: (1) a method for diffusing a digital video service (2) a method for receiving digital video/audio.

Description

Gateway for the reception of television broadcasting services

  digital, terminal and corresponding methods.

1. Field of the invention

  The present invention relates to the field of digital terrestrial television (DVB or English Digital Video Broadcast). More specifically, the invention relates to the broadcasting and reception of DVB-H (DVB-Handheld) services associated with portable terminals. 2. Technological background. DVB is defined in particular in ETSI EN 301 192 (Digital Video Broadcasting (DVB), DVB specification for data broadcasting or DVB data broadcasting) and TR 101 190 (Digital Video Broadcasting (DVB)). Implementation guidelines for DVB terrestrial services Transmission aspects or directives of DVB terrestrial services - aspects relating to the transmission. In particular, DVB-H is specified in ETSI EN 302 304 (Digital Video Broadcasting (DVB), Transmission System for Handheld Terminals (DVB-H) or transmission system for hand-held terminals) and TR 102 377 (Digital Video Broadcasting (DVB), DVB-H Implementation Guidelines or Implementation Guidelines). According to the state of the art, a DVB-H television service (for example of the type of live television or VOD type of English Video On Demand or video on demand) can be downloaded. Figure 1 schematically illustrates a DVB-H network infrastructure for the transmission of a DVB-H video service to a terminal 10 according to the H264 standard in QCIF (Common Intermediate Format Quart or common intermediate format corresponding to a 176x144 resolution).

  The infrastructure includes: - an IP 13 backbone; a video coder 14 receiving data from a receiver 140 and code (or transcode) video streams being transmitted (in English life channels); servers respectively of VOD 150, EPG 151, and a gate 152; a cellular network 12; a DVB-H network 11; and the terminal 10. The servers 14 and 150 to 152 transmit DVB-H services to the terminal 10 via the IP network 13 and the DVB-H network 11. The average throughput of the entire service is equal to about 250 kbit / s. The service gathers several IP streams (or Internet Protocol): one for video, one for audio and, possibly, other services (eg session description (according to SDP protocol).

  The DVB-H network 11 comprises in particular: an IP encapsulation module 110 (or IPE of the English IP Encapsulation) of the DVB-H type; a core network DVB-H 111; and a transmitter 112.

  The module 110 DVB-H IPE receives the streams 160 broadcast (English multicast) IP network 13 according to a protocol of the type RTP (English Real Time Protocol or real-time protocol) on UDP / IP (from the English User Datagramm Protocol over IP). According to their configuration, the module 110 transmits them to the core network 111 by grouping the streams belonging to the same service in the form of an MPEGTS (Motion Picture Expert Group - Transport Stream) stream and encapsulates them in a frame 161. with time division (or time-slice) by adding error correction information (or FEC of English Forward Error Correction) and signaling information according to the DVB-H standard. The transmission rate is generally high and can reach, for example, 10Mbits / s. The MPEG-TS stream 161 is transmitted to the transmitter 112 via the core network 111. The transmitter 112 then transmits it over a DVB-H radio channel the MPEG-TS stream to the terminal 10. The terminal 10 then analyzes the DVB-H signaling information present in the stream 16, associates an IP address with an MPEG-TS address and can then read all the IP packets associated with this address and reconstruct the different flows 160 originally issued. The cellular network 12 is 3G (that is to say, third generation) and comprises in particular: a gateway 120 of GGSN cellular network; a core network 121; and a transmitter 122 (for example a base station).

  The terminal 10 is able to exchange control data with the transmitter 122 enabling interactivity with the service provider, the video type data passing through the DVB-H transmitter 112. Such an infrastructure has the drawback of not be accessible when the terminal is not able to correctly receive the signals transmitted by the transmitters 112 and 122.

  3. Summary of the invention. The invention aims to overcome these disadvantages of the prior art. More particularly, the invention aims to allow reception of digital television services when receiving DVB-H signals via a DVB-H radio transmitter is not possible or difficult, especially inside buildings, while by allowing a saving of energy of the terminal. For this purpose, the invention proposes a gateway comprising means for receiving first frames of a digital video broadcasting service via, for example, a wired network, characterized in that it comprises: means for determining data representative of a temporal division; encapsulation means of each of the first service frames in a second frame comprising said data representative of a temporal division; and means for transmitting over a wireless local area network of each second frame to a digital audio / video terminal. According to a particular characteristic, said gateway comprises means for inserting the data representative of a temporal division in each second frame according to a session description protocol. According to a particular characteristic, said session description protocol is of the SAP-SDP type.

  According to particular features, the means for receiving first frames of a digital video broadcasting service are associated with a wired network or a wireless network.

  According to a particular characteristic, said wired network is a broadband network that notably allows the transmission of a video stream. According to one particular characteristic, said wireless network is of the IEEE 802.11, Hiperlan, IEEE802.15 or IEEE802.16 type in a private or public LAN type configuration (for example of the hot-spot type). According to a particular characteristic, said gateway comprises means for detecting a power saving mode of a destination terminal of said second frames so as to transmit each second frame when the destination terminal is in listening mode. According to a particular characteristic, said service is of the DVB-H type. According to a particular characteristic, each second frame comprises a destination address corresponding to a single terminal.

  According to a particular characteristic, each second frame comprises a destination address corresponding to several terminals. The invention also relates to a terminal which comprises: - means for receiving second frames comprising data representative of a temporal division, the second frames being transmitted on a wireless local area network; and means for extracting first service frames from said second frames. The invention also relates to a method for broadcasting digital video services comprising a step of receiving first frames of a digital video broadcasting service via, for example, a wired network, characterized in that it comprises: a step determining data representative of a temporal division; a step of encapsulation of each of the first service frames in a second frame comprising said data representative of a temporal division; and a step of transmitting on a wireless local area network of each second frame to a digital audio / video terminal.

  The invention also relates to a digital audio / video reception method, characterized in that it comprises: a step of receiving second frames comprising data representative of a temporal division, the second frames being transmitted on a local network without wire; and a step of extracting first service frames from said second frames.

  4. List of figures. The invention will be better understood, and other features and advantages will become apparent on reading the description which follows, the description referring to the appended drawings in which: FIG. 1 schematically illustrates an infrastructure, known per se, of network DVB-H allowing the transmission of a DVB-H video service to a terminal; Figure 2 is a schematic block diagram of an infrastructure of a network implementing a particular embodiment of the invention; FIG. 3 presents an infrastructure of a network according to an alternative embodiment of the invention; Figures 4 and 5 illustrate the structure of a frame transmitted by access point of the network of Figure 2; FIG. 6 shows the exchanges between elements of the network of FIG. 2; Figures 7 and 8 illustrate the structure respectively of a terminal and an access point of the network of Figure 2; Figures 9 and 10 describe algorithms implemented in the elements of Figures 7 and 8; FIG. 11 depicts an algorithm implemented in a terminal of the network of FIG. 3; Figure 12 is a schematic block diagram of an infrastructure of a network implementing an alternative embodiment of the invention; and FIG. 13 shows the exchanges between elements of the network of FIG. 12.

  5. Detailed description of the invention. FIG. 2 presents a schematic block diagram of an infrastructure of a network 2 embodying a particular embodiment of the invention with an infrastructure combining elements DVB-H, xDSL (of English x SDSL or x-Digital Subscriber Line or Digital Subscriber Line-x and Wireless Local Area Network (WLAN).

  The network infrastructure 2 includes: - a service provider-specific IP 13 backbone that interconnects the service provider elements - an IP 23 backbone that connects an ADSL network to the IP 13 network; a video encoder 14 receiving data from a receiver 140; servers respectively of VOD 150, EPG (Electronic Program Guide) 151 or ESG (electronic service guide or electronic service guide according to the terminology DVB-H), and a portal internet (or web portal which is an http / html or wap server allowing interaction with the DVB-H service provider) 152; a DVB-H network 11 an IP router 26 which makes it possible to interconnect the IP networks 13 and 23 - a broadband network (for example of the ATM type) 22; a BAS (Broadband access server) element which belongs to the ADSL structure and which interconnects the broadband network 22 and the IP network 23; a DSLAM module 210; an access network 211; - an ADSL 2120 modem; a WLAN access point 2121 (grouped in a gateway 212 with the modem 2120); and a terminal 20 preferably mobile and for example of the PDA or mobile phone type. The network 2 comprises elements 13, 150 to 152 similar to the elements of the infrastructure 1 which have the same references. The portal 152 and the servers 150 and 151 are connected to the network 13.

  The servers 14 and 150 to 152 transmit DVB-H services to the terminal 20 via the IP network 13 and the DVB-H network 11 when the terminal is in an area covered by the transmitter 112 and more generally the network 11.

  When the terminal 20 is not able to correctly receive the signals transmitted by the transmitter 112 (and / or possibly via a not shown cellular network) the terminal 20 receives a DVB stream 252 via a local area network connected to the network 22. According to different variants of the invention, the terminal 20 connects to the wireless local area network on detecting a bad reception of the DVB-H stream via the DVB-H (and or cellular) network, on detection of the presence of a local network (the local network can be privileged by parameterization or request of the user), on request of the user. The ATM network 22 is connected to the video encoder 14 and receives a video stream from the encoder 14 which it transmits to the DSLAM module 210. The DSLAM module 210 duplicates and sends IP packets relating to the selected streams to the modem 2120 via the network 211 The WLAN access point 2121 receives the data concerning the selected streams of the modem 2120, formats them by encapsulating them in a radio frame 252 for broadcasting on a wireless local area network where the terminal 20 is located, which can thus receive the radio frame 252 which is intended for it. FIG. 4 shows the control data 430 (per service) transmitted according to an IP broadcast protocol (SAP-SDP or Session Annunciation Protocol) by the access point 2121 to the terminal 20. They are preferably transmitted in a manner regular and are not likely to change frequently. The data 430 comprises the following elements (which are specified in the DVB-H standard): indication 431 of use of one-bit temporal division; indication 432 of the 2-bit error correction; size 433 of the 3-bit MPE frame; maximum duration 434 of a burst (amount of information transmitted in a time slot); and - maximum 435 average rate of service.

  FIG. 6 shows the exchanges between the video coder 14, the DSLAM module 210, the ADSL modem 2120, the access point 2121 and the terminal 20.

  The video coder 14 transmits to the DSLAM module 210, frames 60 (or 250 in FIG. 2) containing a video stream according to a multicast protocol of the RTP / UDP type. This transmission is systematic or, preferably, initiated when at least one DSLAM requires a digital audio / video service. When the terminal 20 can not correctly receive the data via the DVB-H network 11, it transmits a request 61 to the DSLAM module 210. The request 61 is of the IGMP (or Internet Group Management Protocol) type. internet) and includes the IP address of the desired video stream to select the corresponding service. The address of the desired video stream can be determined via a prior HTTP point-to-point connection to the web portal 152 or through a stream from the EPG server 151 (which corresponds to a stream with a known address of the terminal 20). Following receipt of the request 61, the DSLAM module 210 duplicates the video stream contained in the frames corresponding to the IP address of the desired stream and transmits it to the modem 2129 in the form of an xDSL stack (xDSL English). stack) 62, for example of the ATM / AAL5 / ADSL type. Next, the ADSL modem 2120 extracts from the stack 62 the video stream and encapsulates it in a frame 63 of the IP broadcast type (IP multicast frame of the RTP / UDP type) which it transmits to the WLAN access point 2121. , the access point 2121 encapsulates in a wireless frame 64 as illustrated with reference to FIG. 5. The access point 2121 encodes the frame to protect the frame against transmission errors between the point of access. access 3021 and the terminal 20 (the terminal 20 implementing the corresponding decoder to correct any transmission errors). The access point 2121 also implements a temporal division (or time slicing in English) compatible with the wireless transmission protocol between the access point and the terminal 20. This protocol is for example of the IEEE802.11 type or Hiperlan type II. The modem 2120 and the access point 2121 are implemented in two separate physical units (for example component or electronic card). According to an alternative embodiment, the modem 2121 and the access point 2120 are implemented in a single physical unit, for example in the form of a residential ADSL gateway (English residential gateway).

  The invention makes it possible to retain the energy conservation possibilities offered by DVB-H for the terminals. The power consumption reduction according to the invention is performed by time division when the packets are transmitted by the access point 2120 on a wireless local area network. An increase in reliability is also achieved by the addition of Forward Error Correction (FEC) data in the radio frames.

  The frame 64 comprises: control data 54 specific to the wireless transmission (for example data enabling equalization of the radio signal and data describing the frame 64 (for example length, source address and destination address); FEC error correction and time division, - an IP multicast address 52 corresponding to the service requested by the terminal 20 for the selected service, - data specific to the RTP / UDP protocol, and - video stream data 50 corresponding to the video stream required by the terminal 20. In the MAC (or Medium Access Control) layer, an address corresponding to the only destination terminal (unicast and non-multicast) is used. There are several terminals, the packet is duplicated and transmitted over the wireless network to each terminal in unicast MAC mode According to an alternative embodiment of the invention, (especially when transmission between the access point 2121 and the terminal 20 is assumed to be of good quality) no error correction data is inserted into the frame 64. In point-to-point connection, an acknowledgment mechanism is advantageously implemented. (And possibly retransmission frames unacknowledged within a predetermined time) whether or not error correction data, which secures the connection and thus improve the quality of service.

  MPEG-TS is not required for transporting video in a WLAN, unlike DVB-H. Preferably, the data format 53 corresponds to the format defined by the DVB-H standard in order to simplify the implementation of the terminal 20 which comprises means for receiving a DVB-H stream. According to an alternative embodiment, the data 53 does not correspond to the format defined by the DVB-H standard. In particular, the FEC data can be specified according to the characteristics of the transmission channel on the wireless local area network. Preferably, according to the invention, the transmission of the data on the local network uses FEC and time division data in the same format as that implemented within the framework of the MPEG DVB-SI standard applied to DVB-H. , for information of the same nature. According to the invention, advantageously, the session description format is compatible with the SDP protocol, an SDP stream carrying the useful session parameters for the coders / decoders, the time division of the DVB-H type and a description of FEC. In order to implement a temporal division and FEC compatible with that of the DVB-H standard, the FEC error correction and temporal division data encoded in an SDP frame are formatted according to the table of FIG. the columns 40 to 42 respectively represent the meaning of each field, its size in number of bits and an identifier) comprise: a flag which indicates whether the temporal division 433 is implemented on 1 bit; an FEC field 434 indicates whether a correction mechanism is implemented on 2 bits; a size 436 of the 3-bit MPE frame; a maximum duration 437 of a burst (which corresponds to a set of packets of elements transmitted sequentially) (thanks to the maximum duration of the indicated burst, if the terminal does not receive the end of burst signal after this maximum duration, it knows that the link is cut off and can try to switch to the DVB-H network if the cut corresponds to an out of reach of the WLAN or wait for a user request, if the cut corresponds to an end of stream transmission on the 8-bit ADSL network); a maximum average bit rate on 4 bits; a 4-bit time-division and FEC identification, and 35-and N-byte 440 identifier selection on 8N bits. The wireless network is preferably compatible with an IEEE 802.11x standard (where x is a version of the standard and is, for example, a, b, g ...). These standards define a mode of energy saving (or PS of English power saving). During a first or new association, the terminal 20 indicates to the access point 3021 the period or the listening interval, that is to say the time elapsed between two plays. This time is expressed in the number of periods of control frames called beacon. A beacon control frame is a management frame issued periodically by the access point 3021. The corresponding period is a configuration parameter of the access point 3021. It is a multiple of 10 ms which corresponds to the minimum value of At such as specified in the DVB-H standard (10ms At 40s). Also, the listening interval is calculated by the terminal 20 and corresponds to the DVB-H At parameter indicated in the data header 53 of a received frame. FIG. 7 schematically illustrates the terminal 20. The terminal 7 comprises, interconnected by an address and data bus 203: a microprocessor 200 (or CPU); a non-volatile memory of the ROM type (of the English Read Only Memory) 201; a random access memory or RAM (Random Access Memory 20) 202; a module 204 for receiving the signal received on the WLAN wireless network; a module 205 for receiving the signal received on the DVBH (or 3G) network; and an interface 206 transmitting the received images to the audio / video application (eg for display or recording). Moreover, each of the elements illustrated in FIG. 7 is well known to those skilled in the art. These common elements are not described here. It will be observed that the word register used in the description designates in each of the memories mentioned, as well a low capacitance memory area (a few binary data) or a high capacity memory zone (for storing an entire program or all or part of the representative data of a received audio / video service). The ROM 201 comprises in particular: a program prog 2010;

  The algorithms implementing the steps of the method described below are stored in the ROM 205 associated with the terminal 20 implementing these steps. On power up, the microprocessor 20 loads and executes the instructions of these algorithms.

  The random access memory 202 comprises in particular: in a register 2020, the operating program of the microprocessor 200 charged to power up the terminal 20; a multicast IP address corresponding to a service required in a register 2021; a listening interval value (or beacon) in a register 2022; one or more audio / video frames received in a register 2023; and audio / video data corresponding to the requested service in a register 2024. FIG. 8 schematically illustrates access point 2121. The access point 2121 comprises, interconnected by an address and data bus 83: a microprocessor 80 (or CPU); a non-volatile ROM type memory (of the English Read Only Memory) 81; a random access memory or RAM (Random Access Memory) 82; a module 84 for transmitting the signal received on the WLAN wireless network; and a module 85 for receiving the signal on the wired network. Moreover, each of the elements illustrated in FIG. 8 is well known to those skilled in the art. These common elements are not described here.

  It is observed that the word register used in the description designates in each of the memories mentioned, as well a memory area of low capacity (a few binary data) a large memory area (for storing an entire program or all or part of representative data of a received audio / video service).

  The ROM 81 includes in particular: a prog 810 program;

  The algorithms implementing the steps of the method described below are stored in the ROM 810 associated with the access point 2121 implementing these steps. On power-up, the microprocessor 80 loads and executes the instructions of these algorithms.

  The RAM 82 comprises in particular: in a register 820, the operating program of the microprocessor 80 charged at powering up the access point. a multicast IP address corresponding to a required service in a register 821; a listening interval value (or beacon) in a register 822; one or more audio / video frames received in a register 823; and audio / video data corresponding to the requested service in a register 824. FIG. 9 illustrates a reception algorithm implemented in the access point 2121. During a first step 90, the access point 2121 initializes the different transmission and reception parameters. Then, during a step 91, it receives an IGMP request from the terminal 20, which it retransmits to the modem 2120, during a step 92. Then, during a step 93, the access point 2121 receives multicast IP frames from the modem 2120 corresponding to ADSL frames received from the DSLAM. Then, during a step 94, it carries out an encapsulation of the MPE type in a wireless frame 64 as illustrated with reference to FIG. 5. During the step 95, the configuration information of the temporal and possible FEC encoding are retrieved.

  The MPE-FEC header then contains the real-time parameters useful for the terminal 20 to perform the inverse time division and the FEC decoding if necessary. Then, during a step 96, the access point 2121 receives from the terminal 20 a PS-POLL type control frame with a bit indicating that the terminal 20 leaves the energy saving mode. The access point 2121 then transmits to the terminal 20, the MPE-type frames 64 stored in its corresponding buffers.

  FIG. 10 illustrates a reception algorithm implemented in the terminal 20. During a first step 100, the terminal 20 initializes the different reception parameters. Then, during a step 101, it checks whether it correctly receives a DVB-H stream from the DVB-H network. If so, assuming that the DVB-H network has priority over the WLAN (by setting, constructing or indicating the user), in a step 102, the terminal 20 receives a DVB-H stream of the DVB-H network. When the terminal 20 no longer receives DVB-H streams, step 101 is repeated. If not, the terminal 20 does not receive or badly (i.e., with much error) a DVB-H stream or the user has requested a switch to the WLAN. step 103, the terminal receives an audio-video stream from the WLAN after request.

  Step 103 begins with a step 1030, during which the terminal 20 transmits to the WLAN access point 2121 a DVB-H stream request in the form of an IGMP request (request 61). The multicast IP address can be determined in advance (for example during the initialization phase or prior reception via the DVB-H network (thanks to an EPG list) or ADSL (via http or through a list EPG)). In addition, during step 1030, the terminal receives the general information (corresponding to the data 430 illustrated in FIG. 4) on the time division and MPE-FEC as configured by the access point. Then, during a test 1031, the terminal 20 checks whether it can receive WLAN radio frames (This step can be performed at any time (and in particular before step 1030)). If no (the WLAN signal is not received or is received with too much error, or the user has requested a switch to the DVB-H network), step 103 ends and step 101 is reiterated. If so (the WLAN signal can be received correctly), in a step 1032, the terminal 20 waits and receives the entire DVB-H burst which corresponds to several frames received via the WLAN with a own address address (or unicast) to the terminal 20. Then, during a step 1033, the terminal 20 processes the data 35 contained in IEEE802.11 frames received and corresponding to a burst. During this step, any transmission errors are corrected using FEC data. Having received a first burst, the terminal 20 can implement the energy saving mode of the WLAN according to the MPE parameters contained in the burst. Then, during a step 1034, on the basis of the information At contained in the MPE header (the other MPE part including the IP frame information) the terminal transmits to the access point 2121 a signaling frame mentioning the listening interval and telling him that he is entering a power saving mode. The terminal 2121 then goes to sleep. Then, during a step 1035 (after expiration of a timer corresponding to the listening interval), the terminal 20 wakes up (listening mode) and, during a step 1036, it goes on standby a beacon frame which comprises a TIM (or traffic indication map) which indicates the number of incoming frames stored in the access point 2121, to the terminal 20. Then, during in a step 1037, the terminal 20 transmits to the access point 2121 a control frame of the PS-POLL type with a bit indicating that the terminal 20 leaves the power saving mode so that the access point 2121 can empty the corresponding buffers and resume the transmission of frames to the terminal at the maximum rate. FIG. 3 presents a schematic block diagram of an infrastructure of a network 3 implementing a variant of the network 2, the ATM network intended for a gateway for home use being replaced, more generally, by an IP network. to provide public access. The elements common to the networks 2 and 3 bear the same references and, unless otherwise indicated, are connected in the same way.

  The network infrastructure 3 includes: - an IP 13 network backbone; an IP 23 network backbone; a video encoder 14 receiving data from a receiver 140; servers respectively of VOD 150, EPG 151, and an internet portal 152; a DVB-H network; an IP router that makes it possible to interconnect the IP networks 13 and 23; an IP network 31; a BAS element which interconnects the IP network 31 and the IP23 network; a router 300; an access network 211; a wired local public network (or LAN hot spot) 301; a DVB-H WPE interface (Wireless LAN Protocol encapsulator) 3020; a WLAN access point 3021 (grouped in a gateway 302 with the interface 3020); and - a terminal 20.

  The interface 3020 implements the mechanisms of time division, FEC and encapsulation MPE in a manner similar to the implementation of the access point 2121. The access point 3021 is thus, preferably, a standard access point. When the terminal 20 is not able to correctly receive the signals transmitted by the transmitter 112 (and / or possibly via a not shown cellular network) the terminal 20 receives a DVB stream 252 via a local area network connected to the network 31. According to different variants of the invention, the terminal 20 connects to the wireless local area network on detecting a bad reception of the DVB-T stream via the DVB-T (and or cellular) network, on detection of the presence of a local network (the local network can be privileged by parameterization or request of the user), on request of the user. The IP network 31 is connected to the video encoder 14 and receives a video stream from the encoder 14 which it transmits to the router 300. The router 300 duplicates and sends IP packets relating to the selected streams to the interface 3020 via the network 301. The WLAN access point 3021 receives the selected stream data from the interface 3020, formats it by encapsulating it in a radio frame 322 for broadcast on a wireless local area network where the terminal 20 can be located. thus receive the radio frame 322 which is intended for it. Figure 11 illustrates a reception algorithm implemented in the terminal 20 when connected to an access point 3021.

  Steps 100, 101 and 102 are similar to those described with reference to FIG. 10 and have the same references. In particular, during step 100, in MAC multicast mode, the access point 3021 has been configured with a delivery traffic indication (DTIM) period initialized to 1 (which corresponds to the number of beacon periods during which the access point 3021 stores the frames). A step 1100 replaces the step 103. It implements steps 1030, 1031, 1032 similar to those of FIG. 10 and which have the same references, the frames being transmitted to or received from the access point 3021. in the affirmative (the WLAN signal can be received correctly), during a step 1032, the terminal 30 waits and receives the entire DVB-H burst which corresponds to several frames received via the WLAN network with an address of MAC multicast recipient. Then, during a step 1133, the terminal 20 processes the data contained in the IEEE802.11 frames received and corresponding to a burst. The received frames are, moreover, in multicast mode as soon as several terminals are connected to the access point (and not with a single reception address corresponding to that of the terminal 20). The operations performed during step 1133 are also similar to those performed by step 1033. Then, during a step 1134, on the basis of information At contained in the header MPE (the other part MPE comprising the information relating to the IP frame) the terminal transmits to the access point 3021 a signaling frame mentioning the listening interval and indicates that it enters a power saving mode. The terminal 20 then goes to sleep. It is at the access point to memorize the packet frames during a time At and to send the frames at the maximum rate.

  Then, during a step 1135 (after expiration of a timer corresponding to the listening interval), the terminal 20 wakes up (listening mode) and, during a step 1136, it goes on standby a beacon frame which comprises a DTIM which indicates the number of multicast frames stored in the access point 3021, to the terminal 20. Then, during a test 1137, the terminal 20 checks whether it has also received a unicast package for himself.

  If not, test 1031 is repeated. If so, during a step 1037, the terminal 20 transmits to the access point 2121 a control frame of the PS-POLL type with a bit indicating that the terminal 20 leaves the energy saving mode of so that the access point 3021 can empty the corresponding buffers and resume the transmission of frames to the terminal at the maximum rate. FIG. 12 presents a schematic block diagram of an infrastructure of a network 124 implementing a particular embodiment of the invention with an infrastructure based on a DVB-H network and a wireless local area network (or WLAN). English Wireless Local Area Network). The network infrastructure 124 comprises in particular: an IP 13 network backbone; a video encoder 14 receiving data from a receiver 140; servers respectively of VOD 150, EPG 151, and an internet portal 152; the DVB-H network 11 - an IP router 26 which makes it possible to interconnect the IP networks 20 and 23; - a DVB-H 1231 gateway; a WLAN access point 3021 (grouped in a gateway 123 with the gateway 1231); and a terminal 20 preferably mobile and for example PDA-type or mobile phone. The network 124 comprises elements 13, 23, 14, 140, 150 to 152, 11, 26 and 20 similar to the elements of the network 2 which have the same references and will not be further described. When the terminal 20 is not able to correctly receive the signals transmitted by the transmitter 112 (and / or possibly via a not shown cellular network) the terminal 20 receives a DVB stream 252 via a local area network connected to the network 11 According to various variants of the invention, the terminal 20 connects to the wireless local area network on detecting a bad reception of the DVB-T stream via the DVB-T (and cellular) network, on detection of the presence of a local network (the local network can be privileged by parameterization or request of the user), on request of the user.

  The DVB-H network 11 is connected to the video encoder 14 and receives a video stream 125 from the encoder 14 which it transmits to the gateway 123. The gateway 1231 duplicates and sends IP packets relating to the selected streams to the WLAN access point 3021 similar to the access point 2120 previously described. The WLAN access point 2120 receives the data relating to the selected streams of the gateway 1231, formats them by encapsulating them in a radio frame 252 for broadcasting on a wireless local area network where the terminal 20 is located which can thus receive the radio frame 252 which is intended for it.

  The control data 430 (per service) transmitted according to an IP broadcast protocol (SAP-SDP) by the gateway 123 to the terminal 20 are also illustrated in FIG. 4. FIG. 13 shows the exchanges between the video coder 14, the gateway 1231, the access point 3021 and the terminal 20.

  The video coder 14 transmits to the gateway 1231 via the DVB-H network 11, frames 130 (or 125 in FIG. 12) containing a video stream according to a multicast protocol of the RTP / UDP type. This transmission is systematic or, preferably, initiated when at least one gateway requires a digital audio / video service. When the terminal 20 can not correctly receive the data via the DVB-H network 11 in direct connection, it transmits a request 131 to the gateway 1231. The request 131 is of the IGMP (or Internet Group Management Protocol) type. Internet group management) and includes the IP address of the desired video stream to select the corresponding service. The address of the desired video stream can be determined via a prior HTTP point-to-point connection to the web portal 152 or through a stream from the EPG server 151 (which corresponds to a stream with a known address of the terminal 20). Following receipt of the request 131, the gateway 1231 duplicates the video stream contained in the frames corresponding to the IP address of the desired stream and encapsulates the video stream in a frame 132 of the IP broadcast type (RTP / multicast IP frame). UDP) that it transmits to the WLAN access point 3021. Thus, during this operation, the gateway 1231 also performs a filter since it extracts from the received IP stream only the streams requested by the IGMP request 131. Then the access point 3021 performs the transmission operations in a manner similar to the access point 2121 and in particular encapsulation in a wireless frame 64 as illustrated with reference to FIG. 3021 access has a structure similar to that of the access point 2121 illustrated with reference to Figure 8. Of course, the invention is not limited to the embodiments described above. In particular, the embodiment described with reference to FIG. 3 also applies, according to a variant of the invention, to a home network (use of the WPE interface and of a standard wireless access point ).

  Furthermore, the invention applies to any type of reception of digital video streams transmitted in particular by ADSL, DVB (in particular DVBT, DVB-H, DVB-S) that is encapsulated in frames with data representative of a time division, these frames being transmitted over a wireless local area network to a digital audio / video terminal.

Claims (15)

  Gateway (212, 302, 123) comprising means for receiving first frames (2120, 3020, 1231) of a digital video broadcasting service, characterized in that it comprises: data determination means representative of a temporal division (2120, 3020, 1231); encapsulation means (2120, 3020, 1231) of each of the first service frames in a second frame comprising said data representative of a temporal division; and - transmission means (2121, 3021) on a wireless local area network of each second frame to a digital audio / video terminal.   2. Gateway according to claim 1, characterized in that said gateway comprises means for inserting data representative of a temporal division in each second frame according to a session description protocol.   Gateway according to claim 2, characterized in that said session description protocol is of the SAP-SDP type.   4. Gateway according to any one of claims 1 to 3, characterized in that the means for receiving first frames of a digital video broadcast service are associated with a wired network (211).   5. Gateway according to any one of claims 1 to 3, characterized in that the means for receiving first frames of a digital video broadcast service are associated with a wireless network (301, 111).   6. Gateway according to any one of claims 1 to 5, characterized in that said wireless network is of the IEEE 802.11, Hiperlan, IEEE802.15 or IEEE802.16 type.   7. Gateway according to any one of claims 1 to 6, characterized in that said gateway comprises means for detecting a power saving mode of a destination terminal of said second frames so as to transmit each second frame when the receiving terminal is in listen mode.   8. Gateway according to any one of claims 1 to 7, characterized in that said service is of the DVB-H type.   9. Gateway according to any one of claims 1 to 8, characterized in that each second frame comprises a destination address corresponding to a single terminal.   10. Gateway according to any one of claims 1 to 8, characterized in that each second frame comprises a destination address corresponding to several terminals.   11. Gateway according to any one of claims 1 to 10, characterized in that it comprises means for determining audio / video terminals and filtering means of the first service frames received, only the service frames intended for one of said determined terminals being encapsulated by said encapsulation means. 30   12. Gateway according to any one of claims 1 to 11, characterized in that the means for receiving first frames of a digital video broadcast service are associated with a long-distance wireless broadcast network.   13. Digital audio / video terminal (20), characterized in that it comprises: - second frame receiving means comprising data representative of a temporal division, the second frames being transmitted on a wireless local area network; and means for extracting first service frames from said second frames.   14. A method of broadcasting digital video services comprising a step of receiving first frames of a digital video broadcasting service, characterized in that it comprises:   A step of determining data representative of a temporal division; an encapsulation step (94) of each of the first service frames in a second frame comprising said data representative of a temporal division; and a transmission step (96) on a wireless LAN of each second frame to a digital audio / video terminal. 15. Digital audio / video reception method, characterized in that it comprises: a step of receiving second frames comprising data representative of a temporal division, the second frames being transmitted on a wireless local area network; and a step of extracting first service frames from said second frames. 30