EP0676872A1 - Cyclical and cellular data radio broadcasting - Google Patents

Abstract

The method involves selective data transmission in a number N of diffusion regions (Zn,Zn+1). Each region includes a data transceiver which operates in relation to a network distribution centre. The distribution centre successively transmits a common data packet (BDc) and N regional data packets (BDn,BDn+1) associated with the N regions during a first period (PRm-1). Each transceiver detects the common packet and the specific packet for that region and retransmits the information during a second period (PRm). The messages transmitted by all the regional transmitters are synchronised. <IMAGE>

Description

The present invention relates 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 network distribution head, 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.

In a given territory, an information system for road vehicles moving in this territory fulfills various functions such as collecting information, formatting and disseminating it.

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 which will be received by the user, for example: "Works 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 "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 by 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 the 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 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 cellular data broadcasting network. and cyclical.

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 be broadcast repeatedly during a second period following the first period said message, the messages broadcast by all the receiving / broadcasting means being synchronous.

Advantageously, the common data packet sent 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 predetermined number of 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 the messages broadcast have 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 following 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 removing the video signal frame, so as to transmit 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 stores the zone changes, for example to control and limit the frequency of these changes relative to the duration of the 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 sent by the distribution head.

• la figure 1 est un schéma d'un réseau de diffusion d'informations routières mettant en oeuvre le procédé selon l'invention;
• la figure 2 est un bloc-diagramme schématique de la tête de distribution du réseau d'informations routières;
• la figure 3 est un diagramme temporel d'une ligne de suppression de trame vidéo émise par la tête de distribution vers des moyens récepteurs/diffuseurs du réseau;
• la figure 4 est un diagramme temporel de plusieurs trames de signal vidéo multiplexé avec des paquets de données établis par la tête de distribution;
• la figure 5 est un bloc-diagramme d'un moyen récepteur/diffuseur du réseau d'informations routières; et
• la figure 6 est un diagramme temporel de la diffusion de messages pendant plusieurs périodes de renouvellement par deux moyens récepteurs/diffuseurs.

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:

• FIG. 1 is a diagram of a network for broadcasting road information implementing the method according to the invention;
• FIG. 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 transmitted by the distribution head to receiver / broadcast means of the network;
• FIG. 4 is a time diagram of several frames of multiplexed video signal with data packets established by the distribution head;
• FIG. 5 is a block diagram of a receiver / broadcaster means of the traffic information network; and
• FIG. 6 is a time diagram of the broadcasting of messages during several renewal periods by two receiving / broadcasting means.

With reference to FIG. 1, a traffic information broadcasting network comprises a network distribution head TD, and a plurality of receiver / broadcast means RD _1,1 to RD _{N, JN} defining N broadcast zones Z₁ to Z _N , N and JN being whole numbers.

In order not to overload Figure 1, six diffusion zones Z₁, Z _n-1 , Z _n , Z _{n + 1} , Z _N-1 and Z _N were represented, the index n being between 1 and N.

The N diffusion zones cover a road axis AR and partially overlap two by two. Each diffusion zone Z _n comprises Jn receiver / diffusers means defining with different frequencies, the integer 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 the CCITT X.25 recommendation.

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 + 1 data blocks are successively a data block common to all zones and N zone data blocks associated respectively with the N zones Z₁ to Z _N. 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 road axis AR is always located in at least one of the diffusion zones Z₁ to Z _N. 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 a television channel transmitter EM.

The depacketizer / demultiplexer DD receives via the transmission artery AT, N + 1 digital multiplexed channels V _c and V₁ to V _N according to the X.25 packet transmission mode. The digital channel V _c supports the information common to all the zones, and the digital channel V _n supports the information specific to the zone Z _n .

The depacketizer / demultiplexer DD depackets and demultiplexes the X.25 packets then identifies the packets so as to reconstruct the N + 1 digital channels V _c and V₁ to V _N at parallel outputs.

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 free portions of the video signal through the multiplexer MX1.

With reference to FIG. 3, a frame blanking signal line L _n produced by the multiplexer MX1 successively comprises a line synchronization interval SC then a data packet pd _n associated with the broadcasting area Z _n and contained in the PA active portion of the line. The data packet Pd _n comprises a header and _n with 8 bytes and a data block bd _n having a maximum length of 32 bytes. The header and _n includes a synchronization burst used by the receiver / broadcast means RD _{n, 1} to RD _{n, Jn} associated with the zone Z _n , as well as a length indicator IL _n of the data block bd _n and an identifier I _n of the digital channel V _n , and consequently of the diffusion zone Z _n .

The header and _c associated with a common data packet pd _c also includes, in a manner analogous to the header and _n , the synchronization burst as well as a length indicator IL _c of the data block bd _c relating to information common to the zones and supported by the channel V _c and a common identifier I _c .

The N + 1 packets formed in buffer memory in the coupler C, namely the first packet pd _c with the header and _c and the data block bd _c then the packets pd₁ to pd _N associated with the channels V₁ to V _N and in zones Z₁ to Z _N are successively read in the coupler so that these packets are introduced into the active parts of the line blanking lines, for example at the rate of three lines per video frame as illustrated in FIG. 4.

Thus during a period of renewal of information PR, a first video frame TV₁ comprises the line L _c containing the packet pd _c and the lines L₁ and L₂ containing the packets pd₁ and pd₂ respectively, and so on until a last frame video TV _k which comprises at least one of the lines L _N-2 , L _N-1 and L _N containing the packets pd _n-2 , pd _n-1 and pd _n .

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 renewal period PR defines in the distribution head TD a period during which the information disseminated by the means RD _1,1 to RD _{N, JN} remain respectively unchanged.

The signal resulting from the multiplexing of the N + 1 packets pd _c and pd₁ to pd _N and from the video signal SV is transmitted to the television channel transmitter EM.

Knowing that all the receiving / broadcasting means RD _1,1 to RD _{N, JN} have similar structures, one means RD _{n, j} of them included in the zone Z _n is described below with reference to FIG. 5 .

In the receiver / diffuser means RD _{n, 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. A block extractor EX receives in baseband the video signal from the receiver RV in order to recognize the packets pd _c and pd _n during each renewal period PR among the video frames carrying in particular the N + 1 packets. The extractor circuit EX detects the packets pd _c and pd₁ to pd _N by means of the synchronization bursts and identifies the packets pd _c and pd _n by means of the common identifier and the channel identifier Vn. These identifications make it possible to extract the data block bd _c and the data block bd _n accompanied by the corresponding block length indicators. The recognition of the packet pd _c 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 / diffuser means RD _{n, j} .

The data blocks bd _c and bd _n and the corresponding length identifiers IL _c and IL _n are applied to a formatting circuit CF which processes them to form second data blocks BD _c and BD _n in a format compatible with subsequent broadcasting to mobile receivers in vehicles. The blocks BD _c and BD _n are applied successively to a first input of a multiplexer MX2.

A CET header formation means essentially constituted by a programmable read-only memory PROM forms a message header AND _n applied to a second input of the multiplexer MX2. The PROM memory stores in particular an area identifier IZ _n associated with the area Z _n and frequency characteristics, such as the digitized transmission frequencies of the receiver / broadcast means RD _n-1,1 to RD _{n-1, J (n -1)} and RD _{n + 1.1} to RD _{n + 1, J (n + 1)} included in the geographically neighboring zones Z _n-1 and Z _{n + 1} .

The header AND _n with the blocks BD _c and BD _n are thus multiplexed by the multiplexer MX2 to be applied to a first input of another multiplexer with three inputs MX3.

A message stuffing circuit CB fills with stuffing bits the end of the message M _n to be broadcast by the receiver / broadcaster RD _{n, 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 AND _n , and receives the data block length identifiers IL _c and IL _n from the extractor EX. The circuit CB calculates the difference DIF = LM - (LE + IL _c + IL _n ) expressing the number of bits forming a stuffing sequence SB _n to be introduced at the end of the message M _n .

The stuffing bits are applied to a second input of the multiplexer MX3 which transmits in series a message M _n = [AND _n , BD _c , BD _n , SB _n ] 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 PR _m , in one of the memories, for example MM1, is read cyclically a first message M _{n, m} which has been formed by the means RD _{n, j} during a period PR _m-1 preceding said period PR given renewal PR _m , while a second message M _{n, m + 1} modified more or less with respect to the first message N _{n, m} 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 PR _{m + 1} succeeding the given renewal period PR _m , the message M _{n, m + 1} previously written in memory MM2 is read cyclically. As shown in FIG. 5, the receiver / broadcaster RD _{n, j} comprises at output a transmitter EF with transmission antenna AE which frequency modulates each digital message M _n read cyclically in one of the memories MM1 and MM2 during a period PR, and more generally the messages M _n read alternately in the memories MM1 and MM2 at the 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 M _{n, m-1} , M _{n, m} and M _{n, m + 1} that the blocks BD _c and BD _n were respectively different, that is to say that '' at each PR renewal period, the information contained in the bd _c and bd _n blocks of the packets sent by the TD distribution head differ significantly in content and length.

In addition, it has been assumed, according to a variant, that each message M _n relating to the broadcasting area Z _n included a block of local information BIL _n . This local information is received locally in a CIL circuit included in each of the receiver / broadcast means RD _{n, j} in the zone Z _n , 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 from sources located near the zone Z _n . In this case, according to predetermined criteria and preprogrammed in the CIL circuit, this determines the length LL _n of the block BIL _n according to the difference DIF = LM - (LE + IL _c + IL _n ), so that LL _n is less than or equal to DIF. When LL _n is less than said difference DIF, the complement DIF - LL _n is signaled by the local information formatting circuit CIL to the stuffing circuit CB which produces stuffing bits in number corresponding to DIF-LL _n . Thus, according to this variant, when local information is also to be broadcast, the multiplexer MX3 receives by a third input the serialized block BIL _n established by the circuit CIL in order to introduce it into the message to be constituted M _n , between the block BD _n and a stuffing bit sequence SB _n , as shown in Figure 6.

In FIG. 6 are also shown messages M _{n + 1, m-1} , M _{n + 1, m} and M _{n + 1, m + 1} established simultaneously in the receiver / broadcast means RD _{n + 1.1} to RD _{n + 1, J (n + 1)} included in the zone Z _{n + 1} during PR _m-2 , PR _m-1 and PR _m renewal periods and distributed cyclically during PR _m-1 , PR _m and PR _{m + 1} periods, respectively.

It has been assumed that no local information corresponding to a block BIL _n is to be broadcast during the period PR _m .

It appears that all the messages broadcast in all the zones Z₁ to Z _N are synchronous; for example, the header AND _n , AND _{n + 1} of the first messages M _{n, m} , M _{n + 1, m} at the start of a renewal period PR _m is synchronous with the header and _c in the common packet pd _c which is received by all the receiver / broadcast means, which is included in a video frame line L _c by the distribution head TD during the period PR _m and which relates to common information to be broadcast during the next renewal period PR _{m + 1} .

Thus, from one message to another, the headers AND _n , AND _{n + 1} and the common data blocks BD _c 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 diffusion zones, as indicated in ZR _{n-1, n} between zones Z _n-1 and Z _n and ZR _{n, n + 1} between zones Z _n and Z _{n + 1} , the invention provides on board of a vehicle maintaining reception of minimum information constituted by the common block BD _c .

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 just before receiving 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 M _n , M _{n + 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 blocks of data bd _c and bd₁ to bd _N to be transmitted, some of which are very long, can be distributed in the two, three or more, active image parts of several lines for suppressing successive video frames. In this case the header and _c of a common packet pd _c sent during a period PR _m also contains a length indicator IM _{m + 1} for the messages M _{n, m + 1} , M _{n + 1, m + 1} to be broadcast during the following period PR _{m + 1} , this indicator IM _{m + 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 PR _{m + 1} , the duration of which is proportional to (NL.IM _{m + 1} ).

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 header and _c of common packet pd _c .

Claims (9)

1 - Method for broadcasting data in N broadcasting areas (Z₁ to Z _N ) each comprising at least one data receiver / broadcaster means (RD _1.1 to RD _{N, JN} ) in relation to a network distribution head ( TD), where N is a positive integer, characterized in that the distribution head successively transmits a common data packet (pd _c ) and N zone data packets (pd₁ to pd _N ) associated respectively with the N zones during a first predetermined period (PR _m-1 ) and in that each receiving / broadcasting means (RD _{n, j} ) in each (Z _n ) of the broadcasting areas detects identifiers (I _c , I _n ) in the common packet (pd _c ) and in a respective one (pd _n ) of said N zone packets so as to establish a message (M _{n, m} ) having a predetermined length (LM) as a function of the common and zone packets (pd _c , pd _n ) and repeatedly broadcast during a second period (PR _m ) succeeding the first period said mess age (M _{n, m} ), the messages broadcast by all the receiving / broadcasting means (RD _1.1 to RD _{N, JN} ) being synchronous. 2 - A method of broadcasting data according to claim 1, characterized in that the common data packet (pd _c ) sent by the distribution head (TD) during a period, contains a synchronization word (and _c , burst) , and the 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 common data packet (pd _c ) sent by the distribution head (TD) during a first period (PR _m ) contains a message length indicator (IM _{m + 1} ), and the messages (M _{1, m + 1} , M _{N, m + 1} ) broadcast by the receiver / broadcast means during the following period (PR _{m + 1} ) have a length dependent on this indicator, the same message being repeated a predetermined number of times in each period. 4 - A method of broadcasting data according to any one of claims 1 to 3, characterized in that the messages (M₁ to M _N ) broadcast respectively by all the receiving / broadcasting means during a period respectively contain a stuffing sequence ( SB₁ to SB _N ) such that all the messages broadcast have the same length (LM). 5 - Method according to any one of claims 1 to 4, characterized in that the common data packet (pd _c ) transmitted by the distribution head (TD) during a first period (PR _m ) contains a repetition indicator message (NL _{m + 1} ) and the messages (M _{1, m + 1} to M _{N, m + 1} ) broadcast by the receiving / broadcasting means during the following period (PR _{m + 1} ) are repeated a number of times dependent of said repetition indicator (NL _{m + 1} ) during the following period (PR _{m + 1} ). 6 - A method of broadcasting data according to any one of claims 1 to 5, characterized in that the distribution head (TD) multiplexes the common data packet (pd _c ) and the N area data packets (pd₁ from _N ) with a video signal (SV), inserting them into the lines of frame removal from the video signal, so as to transmit them on a television channel. 7 - A method of broadcasting data according to any one of claims 1 to 6, characterized in that each message (M _n ) broadcast by a receiver / broadcaster means (RD _{n, 1} to RD _{n, Jn} ) associated with a broadcast area (Z _n ) contains an area identifier (IZ _n , ET _n ). 8 - Method according to any one of claims 1 to 7, characterized in that each message (M _n ) broadcast by a given receiver / broadcaster means (RD _1.1 to RD _{n, Jn} ) associated with a broadcast area (Z _n ) contains operating characteristics (ET _n ), such as frequency, of receiving / broadcasting means geographically close to said given receiving / broadcasting means. 9 - A method of broadcasting data according to any one of claims 1 to 8, characterized in that the receiver / broadcaster means include in the message (M _n ) to be broadcast, following information (BD _c , BD _n ) established as a function of said common packets (pd _c ) and of zone (pd _n ), a block (BIL _n ) established as a function of local information received via a local transmission means (MTL).

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