Method and device for communicating from a first vehicle to a second vehicle, regarding a geographical position in a critical traffic situation.

Abstract

The present invention relates to a method and device for communicating the geographical location of a critical traffic situation from a first vehicle to a second vehicle. If at least two received alert messages (31) correspond to the same critical traffic situation (32), then the method determines (33) parameters of a second elliptical probability density function representing an intersection between at least two first elliptical probability density functions whose parameters are included in said at least two received alert messages. An alert message is then transmitted (34). This transmitted alert message includes the identifier designating said same critical traffic situation carried by one of said at least two received alert messages and the parameters of the second elliptical probability density function. (See Figure 3 for abbreviations.)

Description

Title of the invention: Method and device for communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation. Technical field

[0001] The present invention relates to the broadcasting of an alert message between vehicles when a critical traffic situation occurs. In particular, the present invention relates to a method and device for communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation. Technological background

[0002] It is widely known that contemporary vehicles can communicate with each other by incorporating communication systems implementing a technology known by the acronym V2X.

[0003] V2X technology allows either direct communication between vehicles (this is called V2V communication), or communication between vehicles via a communication infrastructure (this is called V2I communication), or communication between a vehicle and pedestrians (this is called V2P communication).

[0004] The primary interest of these communications is to optimize traffic management, reduce accidents and improve road safety. V2X communication follows standardized protocols (called ITS-G5) which have been standardized by ETSI (European Telecommunications Standards Institute). For more details on the ITS-G5 standard, the reader can refer to the article by Mohamed Aymen Labiod, Contribution to the improvement of video transmissions in vehicular ad-hoc networks (VANET), Doctoral thesis defended on July 5, 2019, Valenciennes, 2019, 134 pages.

[0005] Two main types of cooperative messages in ITS G5 are used: these are CAM messages (from the English Cooperative Awareness Message) and DENM messages (from the English Decentralized Environmental Notification Message).

[0006] CAM messages are intended to enable cooperative awareness, i.e., to locate vehicles or cooperative infrastructure in real time relative to each other, and to report the position and status of vehicles. CAM messages are transmitted regularly by vehicles, and all vehicles within range can receive and process them. The CAM message architecture is composed of mandatory data and conditional data which must be specified depending on the sender of the message.

[0007] DENM messages are alert messages that are intended to be broadcast over a geographical area. They are only issued during an unexpected event such as the occurrence of a critical traffic situation. Triggering is automatic or automated (involving the various sensors present on the vehicle), or may result from a manual signal from an agent (driver or manager) via a human-machine interface embedded in the vehicle. DENM messages are defined by a header and a set of containers comprising different sets of unit fields to be completed.

[0008] V2X technology is a communication technology that allows the vehicle to communicate with its environment. It is considered as an alert system and an additional sensor capable of providing specific information to navigation and / or AD AS systems (Advanced Driver Assistance Systems). Cooperative message broadcasting (CAM / DENM) is therefore a means that can be used to locate distant vehicles that are not visible to the Cameras / Radars / Lidars embedded in the vehicle.

[0009] In the context of V2X technology, when a vehicle detects a critical traffic situation (an accident, an obstacle on the road, a congested traffic situation, etc.), it generates a DENM message containing information on the nature of this critical traffic situation and information on the vehicle such as the speed and direction of the vehicle or the geographical position of the vehicle. This geographical position of the vehicle, called GPS position, is obtained by a receiver of a satellite positioning system, called GNSS (Global Navigation Satellite System), for example a receiver of a GPS (Global Positioning System) or Galileo system and / or an antenna of such a receiver.

[0010] The DENM message is then transmitted by the vehicle to other vehicles within range (nearby) via V2X communication. These other vehicles can use this received DENM message to make a real-time decision on how to react to the critical traffic situation indicated by the received DENM message. For example, vehicles can adjust their speed or change lanes to avoid an accident or congestion on the road.

[0011] These other vehicles then relay this DENM message via V2X communication until the message has been received by all vehicles within range. This relay process can be done multiple times, allowing DENM messages to reach a greater number of vehicles. The objective is to increase the probability that vehicles are informed of the critical traffic situation and can make decisions accordingly.

[0012] The transmission of DENM messages between vehicles may vary depending on the specifications of the communication system used. For example, some communication systems may limit the number of relays to avoid saturation of V2X communication. Others may include methods for selecting the most appropriate vehicles to relay the messages. But the relay process is fundamentally the same, with the vehicles relaying the DENM messages they receive.

[0013] Several problems may arise when relaying DENM messages via V2X communication. For example, since DENM messages are encapsulated in packets and may be transmitted over a wireless communication network that may be disrupted, some of the packets may be lost due to congestion in the wireless communication network and / or interference with other wireless devices. Transmission quality may also be degraded, for example, due to the distance between vehicles, the presence of obstacles such as buildings or trees, or interference with other wireless technologies. Overload of the communication network may also occur due, for example, to too many DENM messages being sent.DENM message synchronization issues can also occur, i.e., DENM messages may be received late or not at all, which can affect the efficiency of V2X communication. Errors in the data carried by DENM messages can also occur during the transmission of DENM messages, which can lead to misinterpretation of the information or even wrong decisions being made by vehicles.

[0014] One of the problems to be solved is to define an efficient DENM message communication method to compensate for the problems mentioned above and communicate DENM messages carrying precise GPS positions, with a reduced confidence interval, from the location of a critical traffic situation to all vehicles within range via V2X communication.

[0015] Data fusion methods implemented by AD AS systems (Advanced Driver Assistance Systems) are known for locating a vehicle. The location of the vehicle is obtained, for example, by merging a GPS position obtained from a receiver of a satellite positioning system, data from an odometer and / or an inertial unit, data from a radar sensor, etc. These fusion algorithms can be used to increase the accuracy of the location of a vehicle at a given time.

[0016] Indeed, data fusion involves combining data from multiple information sources to obtain a more accurate geographic position. This may involve correcting errors and / or resolving conflicts between the information sources, as well as taking into account uncertainties associated with each source to obtain a combined geographic position with reduced uncertainty.

[0017] Methods for aggregating GPS positions are also known. Aggregating GPS positions is different from data fusion because aggregation involves collecting multiple GPS positions without correcting or merging them together. Aggregating GPS positions can thus be used to improve the accuracy of locating a vehicle on average over a given period, but does not correct individual errors in GPS positions as can a method for merging data from multiple sources.

[0018] By the DENM message relay mechanism, a vehicle can receive DEMN messages from several vehicles for the same critical traffic situation. Given the GPS position errors due to the problems mentioned, the GPS positions corresponding to the same critical traffic situation may not be the same in all the relayed DENM messages.

[0019] One of the problems solved by the present invention is to reduce the uncertainty of GPS positions, which can vary depending on environmental conditions and measurement errors. This can lead to inconsistencies in the information shared between vehicles and bias the behaviors of the vehicles based on this shared information.

[0020] Another problem being solved is to relay DENM messages efficiently in V2X communication networks. DENM messages must be transmitted quickly and with high reliability to ensure optimal road safety.

[0021] In addition, when multiple vehicles detect a critical traffic situation and send DENM messages, it may be difficult to determine whether these are the same or different situations. This may result in duplicate messages or delays in decision-making by other vehicles receiving these DENM messages.

[0022] Summary of the present invention

[0023] An object of the present invention is to solve at least one of the problems of the technological background described above.

[0024] Another object of the present invention is to improve the DENM message relay mechanism via V2X communication.

[0025] Another object of the present invention is to optimize traffic management, reduce accidents and improve road safety.

[0026] According to a first aspect, the present invention relates to a method of communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation, said method being implemented by at least one processor of the first vehicle, said method comprising the following steps: - reception, by the first vehicle, of at least two alert messages sent by two different vehicles, each alert message received comprising an identifier designating a critical traffic situation and parameters of a first probability density function of elliptical shape representative of a geographical position of said critical traffic situation and of an error of said geographical position; - verification that said at least two alert messages received correspond to the same critical traffic situation by comparing the identifiers carried by said at least two alert messages received; - if said at least two alert messages received correspond to the same critical traffic situation then determining parameters of a second elliptical-shaped probability density function representing an intersection between at least two first elliptical-shaped probability density functions whose parameters are included in said at least two alert messages received; and sending an alert message comprising the identifier designating said same critical traffic situation carried by one of said at least two alert messages received and the parameters of the second elliptical-shaped probability density function; - otherwise, relay said at least two alert messages received.

[0027] The objective of the present invention is to improve the accuracy of GPS positions transmitted in DENM messages by vehicles via V2X communication. These vehicles are capable of detecting critical traffic situations and transmitting DENM messages to alert nearby vehicles via V2X communication. These messages are relayed to reach a larger number of vehicles and ensure real-time decision-making by these vehicles which can be autonomous. However, the accuracy of GPS positions can be affected by random errors, in particular when several GPS positions must be aggregated to determine the precise geographical position of a critical traffic situation. The proposed communication method determines whether the received DENM messages correspond to the same critical traffic situation by comparing identifiers carried by said received DENM messages.If these received DENM messages correspond to the same critical traffic situation then the accuracy of the geographical position of said same critical traffic situation is improved by aggregating. GPS positions carried by at least two received DENM messages while respecting the requirements of V2X communication, in terms of transmission time, bandwidth and latency, which improves road safety and traffic management.

[0028] The present invention is also advantageous because it avoids relaying all DENM messages which correspond to the same critical traffic situation, which makes it possible to reduce duplicate messages and delays in decision-making by the vehicles receiving these messages.

[0029] This can improve road safety and traffic management by providing more accurate and reliable information to drivers and automated driving systems, thereby reducing the risk of accidents and improving traffic flow.

[0030] According to a variant, said at least two first probability density functions and the second probability density function of elliptical shape are each modeled as a Gaussian distribution having as parameters a mean value which defines a geographical position of a critical traffic situation and a variance or standard deviation which limits an error around the mean value.

[0031] According to a variant, the mean value of the Gaussian distribution modeling the second elliptical-shaped probability density function defines a geographical position of said same critical traffic situation and the variance or standard deviation limits an error around said mean value, said mean value and said variance or standard deviation being the parameters of the second elliptical-shaped probability density function.

[0032] According to a variant, the Gaussian distribution modeling the second probability density function of elliptical shape is obtained by a product of the Gaussian distributions modeling said at least two first probability density functions.

[0033] According to a variant, the intersection between said at least two first probability density functions of elliptical shape is calculated by solving an integral of said product of the Gaussian distributions.

[0034] According to a variant, the intersection between said at least two first probability density functions of elliptical shape is calculated using a so-called Monte-Carlo method.

[0035] According to a second aspect, the present invention relates to a device for communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation, the device comprising a memory associated with a processor configured for implementing the steps of the method according to the first aspect of the present invention.

[0036] According to a third aspect, the present invention relates to a vehicle, for example of automobile type, comprising a device as described above according to the second aspect of the present invention.

[0037] According to a fourth aspect, the present invention relates to a computer program which comprises instructions adapted for executing the steps of the method according to the first aspect of the present invention, in particular when the computer program is executed by at least one processor.

[0038] Such a computer program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0039] According to a fifth aspect, the present invention relates to a computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the method according to the first aspect of the present invention.

[0040] On the one hand, the recording medium may be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a ROM memory, a CD-ROM or a microelectronic circuit type ROM memory, or a magnetic recording means or a hard disk.

[0041] Furthermore, this recording medium may also be a transmissible medium such as an electrical or optical signal, such a signal being able to be conveyed via an electrical or optical cable, by conventional or hertzian radio or by self-directed laser beam or by other means. The computer program according to the present invention may in particular be downloaded from an Internet-type network.

[0042] Alternatively, the recording medium may be an integrated circuit in which the computer program is incorporated, the integrated circuit being adapted to perform or to be used in performing the method in question. Brief description of the figures

[0043] Other characteristics and advantages of the present invention will emerge from the description of the particular and non-limiting exemplary embodiments of the present invention below, with reference to the appended figures 1 to 3, in which:

[0044] [Fig.l] schematically illustrates a road environment 1, according to a particular and non-limiting exemplary embodiment of the present invention;

[0045] [Fig.2] schematically illustrates a device configured to communicate from a first vehicle to a second vehicle a geographical position of a critical traffic situation, according to a particular and non-limiting exemplary embodiment of the present invention;

[0046] [Fig.3] illustrates a flowchart of the different steps of a method of communication from a first vehicle to a second vehicle, of a geographical position of a critical traffic situation, according to a particular and non-limiting exemplary embodiment of the present invention.

[0047] Description of the examples of embodiment

[0048] A method and a device for communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation will now be described in what follows with joint reference to Figures 1 to 3. The same elements are identified with the same reference signs throughout the description which follows.

[0049] The problems related to the relay of DENM messages mentioned above induce errors in the GPS positions carried by these DENM messages.

[0050] These errors can be represented by elliptical-shaped probability density functions in DENM messages whose parameters (shape, size) depend on several factors, in particular the quality of the received GPS signal, the environment and atmospheric disturbances.

[0051] The present invention considers the intersection of these elliptical-shaped probability density functions which is defined as a region where the elliptical-shaped probability density functions overlap and as a region in which the actual geographical position of a critical traffic situation is most likely. Using the parameters of these elliptical-shaped probability density functions, the parameters of a new elliptical-shaped probability density function are determined. This new elliptical-shaped probability density function represents a geographical position of the critical traffic situation with a reduced location error compared to that represented by the elliptical-shaped probability density functions defined by the parameters carried by received DENM messages.

[0052] [Fig.l] schematically illustrates a road environment 1, according to a particular and non-limiting exemplary embodiment of the present invention.

[0053] Suppose that a critical traffic situation occurs, for example an accident of a vehicle 103, and that the vehicles 104 and 105 detect this critical traffic situation.

[0054] A first vehicle 101 carries a device 200 described in relation to [Fig.2]. The device 200 is configured to implement a method of communication from the first vehicle 101 to a second vehicle 102, of a geographical position of the critical traffic situation.

[0055] [Fig.l] illustrates the case where a communication process between vehicles 101 and 102 uses V2V communication to relay DENM messages received by the vehicle 101 but a similar case could be illustrated using V2P or V2I communication involving a communication infrastructure not shown in [Fig.l].

[0056] In a first operation of the communication process, the device 200 receives at least two alert messages, in this case the two DENM messages referenced DENM4 and DENM5 transmitted by the vehicles 104 and 105.

[0057] The received alert message DENM4 comprises an identifier ID designating the critical traffic situation (accident of vehicle 103) and parameters of a first probability density function of elliptical shape representative of a geographical position of said critical traffic situation and of an error of said geographical position.

[0058] The received alert message DENM5 comprises the identifier ID and parameters of a first probability density function of elliptical shape representative of a geographical position of said critical traffic situation and of an error of said geographical position.

[0059] In a second operation, the device 200 verifies that said at least two alert messages received, in this case the two messages DENM4 and DENM5, correspond to the same critical traffic situation by comparing the identifiers carried by said at least two alert messages received, in this case by comparing the identifiers carried by the messages DENM4 and DENM5.

[0060] If said at least two alert messages received, in this case the two messages DENM4 and DENM5, correspond to the same critical traffic situation, that is to say that the identifiers carried by said at least two alert messages received are identical, then in a third operation, the device 200 determines parameters of a second probability density function of elliptical shape representing an intersection between at least two first probability density functions of elliptical shape whose parameters are included in said at least two alert messages received, and in a fourth operation, an alert message is sent, said sent alert message comprising the identifier ID designating said same critical traffic situation carried by one of said at least two alert messages received and the parameters of the second probability density function of elliptical shape.

[0061] According to the example of [Fig.l], the messages DENM4 and DENM5 carry the same identifier ID. The device 200 then determines parameters of a second elliptical-shaped probability density function representing an intersection between the first two elliptical-shaped probability density functions whose parameters are carried by the alert messages DENM4 and DENM5 received. The device 200 then sends an alert message comprising the identifier ID designating the critical traffic situation carried by the DENM4 (or DENM5) message and the parameters of the second elliptical probability density function.

[0062] If said at least two alert messages received, in this case the two messages DENM4 and DENM5, do not correspond to the same critical traffic situation, that is to say the identifiers carried by said at least two alert messages received are different, in a fifth operation, the device 200 relays said at least two alert messages received, that is to say it transmits the alert messages DEM4 and DENM5 received.

[0063] According to a variant, said at least two first probability density functions and the second probability density function of elliptical shape are each modeled as a Gaussian distribution having as parameters a mean value which defines a geographical position of a critical traffic situation and a variance or standard deviation which limits an error around the mean value.

[0064] When two independent GPS position measurements are made, each with an error represented by a Gaussian function, the aggregate distribution of the two measurements can be modeled as a new Gaussian distribution whose mean and variance depend on the properties of the individual Gaussian distributions.

[0065] According to a variant, the mean value of the Gaussian distribution modeling the second elliptical-shaped probability density function defines a geographical position of said same critical traffic situation and the variance or standard deviation limits an error around said mean value, said mean value and said variance or standard deviation being the parameters of the second elliptical-shaped probability density function.

[0066] In general, when two independent GPS positions are aggregated, the variance of the new Gaussian distribution (second elliptical-shaped probability density function) is generally smaller than the variance of the individual Gaussian distributions (first elliptical-shaped probability density functions), which can result in an improvement in the accuracy of a vehicle's GPS position.

[0067] This property of variance can be demonstrated mathematically as follows.

[0068] When the probability density functions representative of geographical positions of critical traffic situations and errors of said geographical positions are modeled by Gaussian distributions of mean and standard deviation ü (of variance <7-), these probability density functions are given by:

[0069] f ( X ) = —*ex

[0070]

[0071]

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[0075]

[0076]

[0077]

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[0085] As an example, the resulting probability density function f(x) of the product of three probability density functions fr / 2, f3 representing error probabilities of three GPS positions of vehicle 105 taken by vehicles 101, 102 and 103 is given by: with j the mean and standard deviation of the probability density function fp ) the mean and standard deviation of the probability density function f2 and (T / ) 'average and standard deviation of the probability density function / 3. Using Bayes' theorem, we can calculate the probability density function f(z) for an aggregated GPS position z as follows: f ( vv v- ut - P 1xk 1 * f 1 J vH -¼ A3hJ / (¾)^¾)^¾) where Ai? x2' A3 are the GPS positions of vehicles 101, 102 and 103 and f ( jq ), / ( X2 ), f ( X3 ) are the probability densities of the GPS positions of vehicles 101, 102 and 103. Assuming that the GPS positions of the vehicles are independent and their distribution is normal, the probability densities f ( x^, ) z = 1, ..., 3 can be written as: f ( xk ) =—jz= *exp^5^> Substituting the probability densities into the previous equation, we obtain: / ( Z ) — eXP eXP eXP where <7? is the variance of the aggregated GPS position, given by: * / + / *0-^72 ^2 By reducing, we obtain the probability density function of the aggregated GPS position by: OR A / 2 + (722 *<732+ --+^7 (AM)2 _ P 7 ~ Qfcr^) with i and j having indices from 0 to Nl. The probability density functions can be represented graphically by ellipses and the probability density function of the aggregated GPS position (second probability density function) can then be calculated by calculating an intersection between these two ellipses.

[0086] According to a variant, if the probability density functions representative of GPS positions and their errors are represented by Gaussian distributions, the aggregation of the two GPS positions, that is to say the obtaining of the Gaussian distribution of the second probability density function of elliptical shape, is a product of these Gaussian distributions modeling the first probability density functions in the sense that the distribution of the aggregated GPS position is the statistical distribution resulting from the aggregation of the information of the GPS positions.

[0087] According to a variant, to calculate the intersection between two ellipses (first two probability density functions according to the example of [Fig.l]) representing two Gaussian distributions, the following integral can be solved: [°O88i 10¼ ( [y 1 ) pv, ( [ y ] ) Kl -

[0089] with pv(X) the density of a normal distribution £ j and S a covariance matrix.

[0090] The statistical distribution resulting from the aggregation of the information from the two GPS positions is then given by:

[0091] p (X) =— 2.” j S j

[0092] with X = [xy] the aggregated GPS position and x — [ r $ 1 an aggregated GPS position L ' JY' L v' jvj estimated.

[0093] According to a variant, the intersection between said at least two first probability density functions of elliptical shape is calculated using a so-called Monte-Carlo method.

[0094] This variant is advantageous because it is inexpensive in terms of computing resources.

[0095] [Fig.2] schematically illustrates a device 2 configured to communicate from a first vehicle 101 to a second vehicle 102, from a geographical position of a critical traffic situation, according to a particular and non-limiting exemplary embodiment of the present invention. The device 2 corresponds for example to a device on board the vehicle 101, for example a computer.

[0096] The device 2 is for example configured for the implementation of the operations described with regard to [Fig. 1] and / or the steps of the method described with regard to [Fig. 3]. Examples of such a device 2 include, but are not limited to, on-board electronic equipment such as an on-board computer of a vehicle, an electronic calculator such as an ECU (“Electronic Control Unit”), a smartphone, a tablet, a laptop. The elements of the device 2, individually or in combination, can be integrated into a single circuit integrated, in several integrated circuits, and / or in discrete components. The device 2 can be produced in the form of electronic circuits or software (or computer) modules or even a combination of electronic circuits and software modules.

[0097] The device 2 comprises one (or more) processor(s) 20 configured to execute instructions for carrying out the steps of the method and / or for executing the instructions of the software(s) embedded in the device 2. The processor 20 may include integrated memory, an input / output interface, and various circuits known to those skilled in the art. The device 2 further comprises at least one memory 21 corresponding for example to a volatile and / or non-volatile memory and / or comprises a memory storage device which may comprise volatile and / or non-volatile memory, such as EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic or optical disk.

[0098] The computer code of the embedded software(s) comprising the instructions to be loaded and executed by the processor is for example stored in the memory 21.

[0099] According to various particular and non-limiting embodiments, the device 2 is coupled in communication with other similar devices or systems and / or with communication devices, for example a TCU (from the English “Telematic Control Unit” or in French “Telematic Control Unit”), for example via a communication bus or through dedicated input / output ports.

[0100] According to a particular and non-limiting exemplary embodiment, the device 2 comprises a block 22 of interface elements for communicating with external devices, for example a remote server or the “cloud”, other nodes of the ad hoc network. The interface elements of the block 22 comprise one or more of the following interfaces: - RF radio frequency interface, for example Wi-Fi® type (according to IEEE 802.11), for example in the 2.4 or 5 GHz frequency bands, or Bluetooth® type (according to IEEE 802.15.1), in the 2.4 GHz frequency band, or Sigfox type using UBN (Ultra Narrow Band) radio technology, or LoRa in the 868 MHz frequency band, LTE (Long-Term Evolution), LTE-Advanced; - USB interface (from the English “Universal Serial Bus” or “Universal Serial Bus” in French); - HDMI interface (from the English “High Definition Multimedia Interface” or “High Definition Multimedia Interface” in French); - LIN interface (from the English “Local Interconnect Network”, or in French “Réseau local interconnected”).

[0101] Data is for example loaded to the device 2 via the interface of the block 22 using a Wi-Fi® network such as according to IEEE 802.11, an ITS G5 network based on IEEE 802.1 Ip or a mobile network such as a 4G (or 5G) network based on the LTE (Long Term Evolution) standard defined by the 3GPP consortium, in particular an LTE-V2X network.

[0102] According to another particular and non-limiting embodiment, the device 2 comprises a communication interface 23 which makes it possible to establish communication with other devices (such as other computers of the on-board system) via a communication channel 24. The communication interface 23 corresponds for example to a transmitter configured to transmit and receive information and / or data via the communication channel 24. The communication interface 23 corresponds for example to a wired network of the CAN (from the English “Controller Area Network” or in French “Réseau de contrôles”) type, CAN FD (from the English “Controller Area Network Flexible Data-Rate” or in French “Réseau de contrôles à débit de données flexible”), FlexRay (standardized by the ISO 17458 standard) or Ethernet (standardized by the ISO / IEC 802-3 standard).

[0103] According to a particular and non-limiting exemplary embodiment, the device 2 can provide output signals to one or more external devices, such as a display screen 25, touch-sensitive or not, one or more speakers 26 and / or other peripherals 27 (projection system) via output interfaces 28, 29 and 30 respectively. According to a variant, one or other of the external devices is integrated into the device 2.

[0104] [Fig.3] illustrates a flowchart of the different steps of a method of communication from the first vehicle 101 to the second vehicle 102, of a geographical position of a critical traffic situation, according to a particular and non-limiting exemplary embodiment of the present invention. The method is for example implemented by a device on board the vehicle 101 or by the device 2 of [Fig.2],

[0105] In a first step 31, at least two alert messages are received. Said at least two alert messages are sent by two different vehicles, each alert message received comprising an identifier designating a critical traffic situation and parameters of a first probability density function of elliptical shape representative of a geographical position of said critical traffic situation and of an error of said geographical position.

[0106] In a second step 32, it is verified that said at least two alert messages received correspond to the same critical traffic situation by comparing the identifiers carried by said at least two alert messages received.

[0107] If said at least two alert messages received correspond to the same situation critical traffic situation then parameters of a second elliptical probability density function are determined. Said second elliptical probability density function represents an intersection between at least two first elliptical probability density functions whose parameters are included in said at least two received alert messages. ; An alert message is sent. Said alert message comprises the identifier designating said same critical traffic situation carried by one of said at least two received alert messages and the parameters of the second elliptical probability density function.

[0108] If said at least two alert messages received do not correspond to the same critical traffic situation then said at least two alert messages received are relayed.

[0109] According to a variant, the variants and examples of the operations described in relation to [Fig.l] apply to the steps of the method of [Fig.3].

[0110] Of course, the present invention is not limited to the exemplary embodiments described above but extends to a method of communication from a first vehicle to a second vehicle, of a geographical position of a critical traffic situation which would include secondary steps without thereby departing from the scope of the present invention. The same would apply to a device configured for the implementation of such a method.

[0111] The present invention also relates to a vehicle, for example an automobile or more generally an autonomous land-based motor vehicle, comprising the device 2 of [Fig.2].

Claims

Claims

1. Method for communicating from a first vehicle (101) to a second vehicle (102), a geographical position of a critical traffic situation, said method being implemented by at least one processor of the first vehicle (101), said method comprising the following steps: - reception (31), by the first vehicle (101), of at least two alert messages (DENM4, DENM5) transmitted by two different vehicles (104, 105), each received alert message (DENM4, DENM5) comprising an identifier designating a critical traffic situation and parameters of a first elliptical-shaped probability density function representative of a geographical position of said critical traffic situation and of an error of said geographical position;- verification (32) that said at least two alert messages received correspond to the same critical traffic situation by comparison of the identifiers carried by said at least two alert messages received; - if said at least two alert messages received correspond to the same critical traffic situation then determination (33) of parameters of a second probability density function of elliptical shape representing an intersection between at least two first probability density functions of elliptical shape whose parameters are included in said at least two alert messages received; and transmission of an alert message comprising the identifier designating said same critical traffic situation carried by one of said at least two alert messages received and the parameters of the second probability density function of elliptical shape; - otherwise, relaying (35) said at least two alert messages received.;

2. The method of claim 1, wherein said at least two first probability density functions and the second elliptical-shaped probability density function are each modeled as a Gaussian distribution having as parameters a mean value that defines a geographic position of a critical traffic situation and a variance or standard deviation that bounds an error around the mean value.

3. A method according to claim 2, wherein the average value of the Gaussian distribution modeling the second elliptical-shaped probability density function defines a geographical position of said same critical traffic situation and the variance or standard deviation limits an error around said mean value, said mean value and said variance or standard deviation being the parameters of the second elliptical-shaped probability density function.

4. The method of claim 3, wherein the Gaussian distribution modeling the second elliptical-shaped probability density function is obtained by a product of the Gaussian distributions modeling said at least two first probability density functions.

5. The method of claim 4, wherein the intersection between said at least two first elliptical-shaped probability density functions is calculated by solving an integral of said product of Gaussian distributions.

6. Method according to claim 5, for which the intersection between said at least two first probability density functions of elliptical shape is calculated from a so-called Monte Carlo method.

7. Computer program comprising instructions for implementing the method according to any one of the preceding claims, when these instructions are executed by a processor.

8. A computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the method according to one of claims 1 to 6.

9. Device (2) for communicating from a first vehicle to a second vehicle, a geographical position of a critical traffic situation, said device (2) comprising a memory (21) associated with at least one processor (20) configured for implementing the steps of the method according to any one of claims 1 to 6.

10. Vehicle (101) comprising the device (6) according to claim 9.

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