FR2718586A1 - Cyclic and cellular data dissemination. - Google Patents

Abstract

Data is selectively broadcast in N broadcast zones (Zn; Zn + 1) each comprising at least one data receiver / broadcaster in relation to a network distribution head. The distribution head sends successively a common data packet (BDc) and N zone data packets (BDn; BDn + 1) associated with the N zones during a first period (PRm - 1). Each receiver / broadcaster in each of the zones detects the common packet and the respective one of the N zone packets so as to establish a message (Mn, m; Mn + 1, m) as a function of these two packets and to broadcast repeatedly the message for a second period (PRm). The messages broadcast respectively by all the receiving / broadcasting means are synchronous. The broadcasting zones cover, for example, a road axis so that a receiver on board a vehicle permanently picks up information contained in the common packet and, depending on its location, local information.

Description

The present invention relates to

  generally to the dissemination of information from a network of transmitters to mobile receivers. The invention relates more particularly to a method of broadcasting data broadcast by data receiving / broadcasting means distributed in N broadcasting areas and in relation to a head of

  network distribution, where N is a positive integer.

  Such a method is used in a road information system intended for users, in particular mobiles such as road vehicles. The information useful for road vehicles belongs to three categories: endogenous information, that is to say generated by different sensors on the vehicle, information on board and stored on a storage medium, and finally exogenous information relating to the user environment. This last category covers in particular road traffic information intended for road vehicles. This information concerns for example the state of the roads, the location of works, and the availability in the car parks of a city. On a given territory, an information system for road vehicles moving on this territory fulfills various functions such as collecting information, setting

in form and dissemination of these.

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  The dissemination of information is organized into messages passing through an RDS (Radio Data Service) telecommunications system. A message includes a header containing information on the message itself and a data field containing the actual information that will be received by the user, for example: "Work on

road A at junction B ".

  The RDS system is based on a frequency modulation (FM) sound broadcasting network. An FM transmitter has a relatively short range, of some tens of kilometers; the RDS system therefore uses a network of transmitters, distributed geographically and frequently, so that each point of a given territory is covered by at least one given transmitter, without being "scrambled" by the others. The territory is therefore divided into a finite number of diffusion zones, partially overlapping. A mobile receiver moving within the coverage area of a given transmitter receives traffic information by being tuned to the frequency of this transmitter. Thanks to the RDS system, the transmitter regularly transmits to the receiver the frequencies of the geographically neighboring transmitters which broadcast the same program. The mobile receiver automatically compares the level of power received on these different frequencies. When the mobile receiver reaches the overlap area of two or more transmitters, it automatically switches to the frequency with the highest power level. In addition, the RDS system offers a useful bit rate available per transmitter, for an application of the type "broadcasting of information messages

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  "which is limited and on the order of 100 bit / s. This speed is much lower than the amount of information relating to the territory covered

through the broadcasting system.

  This amount of information is high since the information system is only of economic interest if the territory covered is large to cover a large number of users, and also because of the very nature of traffic information which is " slowly variable ". Indeed, a given piece of information is relevant for a certain period, with possible modifications of this information, and must be repeated at regular intervals during this period, so that it reaches a maximum of users. The dissemination of information is cyclical. It is therefore not possible to disseminate all of the information concerning the territory throughout the territory. In order for a given user at a given point in the territory to receive the information that is useful to him, the information sent to him must be sorted. This sorting is carried out by means of cellularization or

regionalization of information.

  The territory is therefore divided into a finite number of dissemination areas. A broadcasting area is a part of territory for which a set of information can be defined which is of interest to any user located at any point in the area. A broadcast area includes at least one transmitter that broadcasts information relevant to the area and different from information from

neighboring areas.

  When a mobile receiver moves in a broadcast overlap area relating to two or

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  more transmitters and when the topography of the territory causes successive and brief variations in the levels of power received, a switching device in the receiver automatically changes the reception frequency in burst; the receiver then alternates between a synchronization search and a data acquisition procedure. Data acquisition is disrupted, which leads to loss of information during the

  crossing of the overlap area.

  The present invention aims to provide a data broadcasting method which minimizes the loss of information when a mobile receiver switches from one transmitter to another, in order to be implemented in particular in a data broadcasting network.

cellular and cyclic.

  To this end, a method of broadcasting data in N broadcasting areas each comprising at least one data receiver / broadcaster means in relation to a network distribution head, where N is a positive integer, is characterized in that the head distribution system successively transmits a common data packet and N zone data packets respectively associated with the N zones for a first predetermined period and in that each receiver / broadcaster means in each of the broadcasting zones detects identifiers in the common packet and in a respective one of said N zone packets so as to establish a message having a predetermined length as a function of the common and zone packets and to broadcast repeatedly during a second period following the first period said message, the messages broadcast by all the

  receiving / diffusing means being synchronous.

  Advantageously, the common data packet transmitted by the distribution head during a period contains a synchronization word, and the synchronization of the messages broadcast by the receiver / broadcast means during said one period.

  depends on this synchronization word.

  According to another characteristic, the common data packet sent by the distribution head during a first period contains a message length indicator, and the messages broadcast by the receiver / broadcast means during the following period have a length dependent on this indicator, the same message being repeated a number of

  predetermined times in each period.

  Advantageously, the messages broadcast respectively by all the receiving / broadcasting means during a period respectively contain a stuffing sequence such that

  all broadcast messages are the same length.

  In another aspect of the invention, the common data packet sent by the distribution head during a first period contains a message repetition indicator and the messages broadcast by the receiver / broadcast means during the following period are repeated a number of times dependent on said indicator of repetitions during the

next period.

  According to another characteristic of the invention, the distribution head multiplexes the common data packet and the N zone data packets with a video signal, by inserting them into the lines

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  frame removal of the video signal, so that

  broadcast them on a television channel.

  Each message broadcast by a receiver / broadcaster means may contain a zone identifier. Thus, a mobile receiver receiving the messages memorizes the zone changes, for example to control and limit the frequency of these

  changes to the length of messages.

  According to a variant of the invention, the receiver / broadcaster means include in the message to be broadcast, following information established as a function of said common and zone packets, a block established as a function of local information received via a means of local transmission. Local information supplements the information issued by the

distribution head.

  Other characteristics and advantages of the present invention will appear more clearly on

  reading the following description of several

  preferred embodiments of the invention with reference to the corresponding appended drawings in which: - Figure 1 is a diagram of a network for broadcasting road information implementing the method according to the invention; - Figure 2 is a schematic block diagram of the distribution head of the road information network; FIG. 3 is a time diagram of a line for suppressing a video frame sent by the distribution head to receiver / broadcast means of the network; FIG. 4 is a time diagram of several frames of video signal multiplexed with

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  data packets established by the distribution head; - Figure 5 is a block diagram of a receiver / broadcaster means of the road information network; and FIG. 6 is a time diagram of the broadcasting of messages during several periods of

  renewal by two receiving / diffusing means.

  With reference to FIG. 1, a traffic information broadcasting network comprises a network distribution head TD, and a plurality of receiver / broadcast means RD1,1 to RDN, JN defining N broadcast zones Z1 to ZN, N and JN

being whole numbers.

  In order not to overload Figure 1, six diffusion zones Z1, Zn-l, Zn, Zn + l, ZN-1 and ZN have been represented, the index n being between 1 and N. The N diffusion zones overlap an AR road axis and partially overlap two by two. Each diffusion zone Zn comprises Jn receiver / diffusers means defining with different frequencies, the whole Jn possibly being equal to 1, 2, 3

or 4 for example.

  The distribution head receives traffic information through a data transmission route. This transmission route is an X.25 link, which transmits data in the form of

  packets conforming to CCITT recommendation X.25.

  After processing, which will be detailed below, the distribution head TD transmits N + 1 data blocks to the plurality of receiver / broadcast means distributed in the N broadcast areas. The N + l data blocks are successively a data block common to all

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  zones and N zone data blocks associated respectively with the N zones Z1 to ZN. The data transmitted by the distribution head is formatted into data packets multiplexed to a video signal in a television channel. Each receiver / broadcaster means processes the data packets in the television channel to extract the information contained in the common block and the block associated with the respective broadcasting zone in order to distribute them cyclically in the form of repetitive messages. The messages broadcast by all the receiving / broadcasting means are synchronous. A vehicle moving on the rear AR axis is always located in at least one of the diffusion zones Z1 to ZN. The vehicle user then accesses the information through a dedicated receiver placed in the vehicle. Such a receiver comprises for example a display screen on which the information contained in a message is displayed and therefore in the common block and the associated block. With reference to FIG. 2, the network distribution head TD essentially comprises a depacketizer / demultiplexer DD, a digital channel coupler C, a video-data multiplexer MX1, and

  an EM television channel transmitter.

  The depacketizer / demultiplexer DD receives via the transmission route AT, N + 1 digital channels multiplexed Vc and V1 to VN according to the packet X.25 transmission mode. The digital channel Vc supports the information common to all the zones, and the digital channel Vn supports the

  information specific to the Zn zone.

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  The DD depacketizer / demultiplexer depackets and demultiplexes X.25 packets then identifies the packets so as to reconstruct them at outputs

  the N + 1 digital channels Vc and V1 to VN parallel.

  The N + 1 digital channels are transmitted to the coupler C which produces a digital packet frame. Each packet contains the data of a digital channel. The packet frame is time multiplexed with a video signal by the

multiplexer MX1.

  The multiplexer MX1 uses the resources available in a video signal SV constituted by time intervals unoccupied by the image itself. These time intervals correspond to the free active portion in the few lines of the video frame suppression signal, this free portion succeeding the line synchronization signal in each line. The packets formed by the coupler C are inserted respectively and successively in these portions

  free of the video signal through the multiplexer MX1.

  With reference to FIG. 3, a frame suppression signal line Ln produced by the multiplexer MXl successively comprises a line synchronization interval SC then a data packet pdn associated with the broadcasting area

  Zn and contained in the active portion PA of the line.

  The pdn data packet comprises an 8-byte etn header and a bdn data block having a maximum length of 32 bytes. The etn header includes a synchronization burst used by the receiver / broadcast means RDn 1 to RDn, Jn associated with the zone Zn, as well as a length indicator ILn of the data block bdn and an identifier In of the

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  digital channel Vn, and consequently of the broadcasting zone Zn 'The header etc associated with a common data packet pdc also includes, in a manner analogous to the etn header, the synchronization burst as well as an indicator of length ILc of the data block bdc relating to the information common to the zones and supported by the channel Vc and a

common identifier Ic.

  The N + 1 packets formed in buffer in the

  coupler C, namely the first packet Pdc with the

  head etc and the data block bdc then the packets pd1 to pdN associated with the channels V1 to VN and to the zones Z1 to ZN are read successively in the coupler so that these packets are introduced into the active parts of the lines of suppression of frame, for example at the rate of three lines per video frame

as shown in figure 4.

  Thus, during a period of renewal of information PR, a first video frame TV1 comprises the line Lc containing the packet Pdc and the lines L1 and L2 respectively containing the packets pd1 and pd2, and so on until a last video frame TVk which includes at least one of the lines LN_2, LN_1 and LN containing the pdn_2 packets,

Pdn_1 and pdn.

  According to the example illustrated, the integer N is between 3 (K-1) and 3K, and the renewal period PR is at least greater than K periods of video frame. The PR renewal period defines in the distribution head TD a period during which the information disseminated by the means

  RD1,1 to RDN JN remain unchanged respectively.

  il 2718586 The signal resulting from the multiplexing of the N + 1 packets pdc and pd1 to pdN and the video signal SV is

  transmitted to the TV channel transmitter EM.

  Knowing that all the receiver / distributor means RD1,1 to RDN, JN have similar structures, one means RDnj of them included in the zone Zn is described below with reference to the

figure 5.

  In the receiver / diffuser means RDn, j, a video receiver RV receives by an antenna ANT the video signal emitted by the distribution head TD. A synchronization circuit CS connected to the receiver recovers the video frame synchronization and the line synchronization for the recognition and the processing of the received video frames. An EX block extractor receives the video signal from the RV receiver in baseband in order to recognize the Pdc and pdn packets during each PR renewal period among

  video frames carrying in particular the N + l packets.

  The extractor circuit EX detects the Pdc and pd1 to pdN packets by means of the synchronization bursts and identifies the Pdc and pdn packets by means of the common identifier and the channel identifier Vn. These identifications make it possible to extract the data block bdc and the data block bdn accompanied by the corresponding block length indicators. Recognition of the packet Pdc by the extractor EX also contributes to synchronizing a time base BT producing various clock signals to control subsequent operations in the other circuits of the receiver / broadcast means RDn, j The data blocks bdc and bdn and the corresponding length identifiers ILc and ILn

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  are applied to a formatting circuit CF which processes them to form second data blocks BDc and BDn in a format compatible with subsequent broadcasting to mobile receivers in vehicles. The BDc and BDn blocks are applied successively to a first entry of a

MX2 multiplexer.

  A CET header formation means essentially constituted by a programmable read-only memory PROM forms a message header ETn applied to a second input of the multiplexer MX2. The PROM memory stores in particular an area identifier IZn associated with the area Zn and frequency characteristics, such as the digitized transmission frequencies of the receiver / broadcast means RDn_, 11 to RDnl, J (n_1) and RDn + 1.1 to RDn + l, J (n + l) included in the geographically neighboring zones Zn-1 and Zn + l1 The ETn header with the BDc and BDn blocks are thus multiplexed by the multiplexer MX2 to be applied to a first input d 'another

MX3 three-input multiplexer.

  A message stuffing circuit CB fills with stuffing bits the end of the message Mn to be broadcast by the receiver / broadcaster RDn, j, knowing that the message has a predetermined length LM, expressed in number of bits. Thus, the circuit CB contains in programmable read-only memory the message length LM and the constant length LE of the message header ETn, and receives the data block length identifiers ILc and ILn from the extractor EX. The circuit CB calculates the difference DIF = LM - (LE + ILc + ILn) expressing the number of bits forming a stuffing sequence SBn to be introduced at the end of the

message Mn.

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  The padding bits are applied to a second input of the multiplexer MX3 which transmits in series a message Mn = [ETn, BDc, BDn, SBn] to be written in one of two parallel RAM message memories MM1 and MM2. Indeed, as illustrated in FIG. 6, during a given renewal period PRm, in one of the memories, for example MM1, is read cyclically a first message Mnm which has been formed by the means RDnj during a period PRm_1 preceding said PR period of renewal given PRm, while a second message Mnm + 1 modified more or less compared to the first message Mnm is formed by means of the circuits EX, CF, CET and CB to be finally written in the second message memory MM2 . During the renewal period PRm + 1 succeeding the given renewal period PRmi the message Mn, m + l previously written in memory MM2 is read cyclically. As shown in FIG. 5, the receiver / diffuser means RDn, j comprises at output an emitter EF with emission antenna AE which frequency modulates each digital message Mn read cyclically in one of the memories MM1 and MM2 during a period PR , and more generally the messages Mn read alternately in the memories MM1 and MM2 at

respective periods PR.

  In practice, a PR renewal period is between 3 and 5 minutes, and a message has

  a duration of a few tens of seconds.

  In FIG. 6, it has been assumed in the messages Mn, m-1, Mn, m and Mn, m + l that the blocks BDc and BDn were respectively different, that is to say that at each renewal period PR , the information contained in the bdc and bdn blocks of

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  packets sent by the TD distribution head differs

notably in content and length.

  In addition, it has been assumed, according to a variant, that each message Mn relating to the broadcasting area Zn included a block of local information BILn. This local information is received locally in a CIL circuit included in each of the receiver / broadcast means RDnj in the zone Znt through a local transmission means MTL. This MTL means can be a local broadband cable network, with a dedicated telephone line, or even more simply a user telephone line, transmitting local information coming from sources located near the zone Zn. In this case, according to predetermined and preprogrammed criteria in the CIL circuit, the latter determines the length LLn of the block BILn according to the difference DIF = LM - (LE + ILc + ILn), so that LLn is less than or equal at DIF. When LLn is less than said difference DIF, the complement DIF - LLn is signaled by the local information formatting circuit CIL to the stuffing circuit CB which produces stuffing bits in number corresponding to DIF-LLn. Thus, according to this variant, when local information is also to be broadcast, the multiplexer MX3 receives by a third input the serialized block BILn established by the circuit CIL in order to introduce it into the message to be constituted Mn, between the block BDn and a sequence of

  stuffing bit SBn, as shown in figure 6.

  In FIG. 6 are also shown messages Mn + l, m-1, Mn + 1, m and Mn + l, m + 1 established simultaneously in the receiver / broadcast means RDn + 1.1 to RDn + l, J ( n + l) included in zone Zn + 1

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  during renewal periods PRm_2, PRm_1 and PRm and broadcast cyclically during the periods

  PRm_1, PRm and PRm + 1, respectively.

  It has been assumed that no local information corresponding to a BILn block is to be broadcast during

the PRm period.

  It appears that all the messages broadcast in all the zones Z1 to ZN are synchronous; for example, the header ETn, ETn + 1 of the first messages Mnm, Mn + lm at the start of a period of n, mnlm renewal PRm is synchronous with the header etc in the common packet Pdc which is received by all receiving / broadcasting means, which is included in a video frame line Lc by the distribution head TD during the period PRm and which relates to common information to be broadcast during the period

next renewal PRm + 1.

  Thus, from one message to another, the headers ETn, ETn + 1 and the common data blocks BDC are respectively synchronous. When a dedicated mobile receiver on board a vehicle automatically switches in frequency intermittently during the crossing of a diffusion overlap zone relating to two receiving / diffusing means, and more particularly to two associated receiving / diffusing means with two distinct broadcasting zones, as indicated in ZRn_1, n between zones Zn-1 and Zn and ZRnn + 1 between zones Zn and Zn + lt the invention ensures on board a vehicle the maintenance of reception of minimum information consisting of

the common block BDC.

  In addition, the frequency switching in a mobile receiver constituting the implementation of the method according to the invention is carried out systematically at the start / end of the cycle, for example

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  just before the reception of the header of a message so that the reception of the common block of the next message received with the new frequency is not

  disturbed by frequency switching.

  According to other variants, instead of the length of the messages Mn, Mn + 1 and the duration of the periods PR being constant, these are variable and composed by the distribution head as a function in particular of the length of the data blocks bdc and bd1 to bdN to be transmitted, some of which are very long, can be distributed in the two, three or more, active image parts of several successive video frame suppression lines. In this case, the header etc of a common packet Pdc sent during a period PRm also contains a length indicator IMm + l for the messages Mn, m + l, Mn + l, m + 1 to be broadcast during the period following PRm +, this indicator IMm + 1 being written in memory in the circuits CB and CIL in place of the length LM according to the embodiment described above. The time base BT in each receiver / broadcaster means controls NL readings of the same messages in one of the memories MM1 and MM2 during the period PRm + 1, the duration of which is proportional to (NL.IMm + 1) To According to yet another variant, the number NL of message repetitions is programmed by the distribution head at each renewal period, and

  is included in the pdc common packet etc header.

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Claims (8)

  1 - Method for broadcasting data in N broadcasting areas (Z1 to ZN) each comprising at least one data receiver / broadcaster means (RD1,1 to RDNJN) in relation to a network distribution head (TD), o N is a positive integer, characterized in that the distribution head successively transmits a common data packet (Pdc) and N zone data packets (pd1 to pdN) associated respectively with the N zones during a first predetermined period (PRm_1) and in that each receiving / broadcasting means (RDn, j) in each (Zn) of the broadcasting zones detects identifiers (Ic, In) in the common packet (Pdc) and in a respective one (pdn) of said N zone packets so as to establish a message (Mn, m) having a predetermined length (LM) as a function of the common and zone packets (pdc, Pdn) and to broadcast repeatedly during a second period (PRm) succeeding the first period said message ( Mn m), the messages broadcast by all receiving / broadcasting means (RD1,1 to RDNJN) being synchronous.   2 - A method of broadcasting data according to claim 1, characterized in that the common data packet (pdc) transmitted by the distribution head (TD) during a period, contains a synchronization word (etc, burst), and synchronization of the messages broadcast by the receiver / broadcast means during said one period   depends on this synchronization word.   3 - A method of data dissemination according to claim 1 or 2, characterized in that the 18 2718586   common data packet (Pdc) sent by the distribution head (TD) during a first period (PRm) contains a message length indicator (IMm + l), and the messages (Ml, m + 1, MNm + i) broadcast by the receiving / broadcasting means during the following period (PRm + i) have a length dependent on this indicator, the same message being repeated one   predetermined number of times in each period.   4 - Data dissemination process in accordance with   any one of claims 1 to 3,   characterized in that the messages (M1 to MN) broadcast respectively by all the receiving / broadcasting means during a period respectively contain a stuffing sequence (SB1 to SBN) such that all the messages broadcast have the same length (LM).   - Process according to any one of   claims 1 to 4, characterized in that the package   common data (Pdc) emitted by the distribution head (TD) during a first period (PRm) contains a message repetition indicator (NLm + i) and the messages (Ml, m + l to MN, m + l) broadcast by the receiving / broadcasting means during the following period (PRm + i) are repeated a number of times depending on said repetition indicator   (NLm + i) during the following period (PRm + i).   6 - Data dissemination process in accordance with   any one of claims 1 to 5,   characterized in that the distribution head (TD) multiplexes the common data packet (pdc) and the N area data packets (pd1 to pdN) with a video signal (SV), inserting them into the lines of 19 2718586   frame removal of the video signal, so that   broadcast them on a television channel.   7 - Data dissemination process in accordance with   any one of claims 1 to 6,   characterized in that each message (Mn) broadcast by a receiver / broadcaster means (RDn, 1 to RDnJn) associated with a broadcast area (Zn) contains a zone identifier (IZn, ETn).   8 - Process according to any one of   claims 1 to 7, characterized in that each   message (Mn) broadcast by a given receiver / broadcaster means (RD1,1 to RDn, Jn) associated with a broadcast area (Zn) contains operating characteristics (ETn), such as frequency, of geographically neighboring receiver / broadcasters of said given receiver / diffuser means.   9 - Data dissemination process in accordance with   any one of claims 1 to 8,   characterized in that the receiving / broadcasting means include in the message (Mn) to be broadcast, following information (BDc, BDn) established as a function of said common packets (Pdc) and of zone (Pdn), a block (BILn ) established on the basis of local information received via a means of local transmission (MTL).