EP1975901A1

EP1975901A1 - System and method for radio wave based vehicle-to-vehicle spreading of road traffic information

Info

Publication number: EP1975901A1
Application number: EP07462004A
Authority: EP
Inventors: Attila Bay Zoltán Foundation For Applied Research Török; Lóránt Bay Zoltán Foundation For Applied Research Vajda; Péter Laborczi; Géza Gordos
Original assignee: Bay Zoltan Alkalmazott Kutatasi Kozalapitvany
Current assignee: Bay Zoltan Alkalmazott Kutatasi Kozalapitvany
Priority date: 2007-03-26
Filing date: 2007-03-26
Publication date: 2008-10-01
Anticipated expiration: 2027-03-26
Also published as: ATE426878T1; DE602007000780D1; EP1975901B1

Abstract

The present invention relates to a system and a method for radio wave based vehicle-to-vehicle spreading of road traffic information, wherein each of the vehicles (101-104) is provided with a radio transmitter, a radio receiver, a location positioning device and a message forwarding timer. The method comprises the steps of recognizing, by a first vehicle (101), a road traffic event occurred on a section of a road (105) on which said first vehicle is travelling; generating, by said first vehicle, a piece of road traffic information relating to the road traffic event; generating, by said first vehicle, a first road trajectory description information including at least data for the identification of said road section; generating, by said first vehicle, a first message containing at least a unique identifier for said message, said piece of road traffic information, the location of the vehicle sending the first message, said location being determined by its location positioning device, and said first road trajectory description information; transmitting, by said first vehicle, said first message by radio message spreading; receiving, by at least one second vehicle (102,103,104).

Description

The present invention generally relates to a system and a method for radio wave based vehicle-to-vehicle spreading of road traffic information. The invention further relates to a computer program for carrying out the method according to the invention, as well as a computer program product containing such a computer product.
More particularly, the present invention relates to an ad-hoc radio communication network in which all of the vehicles are provided with a radio transmitter, a radio receiver and location positioning means for identifying the location of the vehicle by absolute coordinates.
In the field of transportation informatics, the so called Intelligent Transportation Systems (ITS) are well known. One of the most important functions of these systems is to prevent road traffic accidents. These systems may, however, play an important role also in spreading of road traffic information and in the coordination of the motion of incidentally formed vehicle convoys. In such systems, communication between the vehicles is typically managed by a message spreading protocol. Because of the message spreading data transmission, these systems have the basic requirement of keeping the extent of flooding of the communication medium on a minimum level.
In message spreading systems, there are known several methods for minimizing the extent of flooding. In our case, those methods are primarily of interest in which the number of the messages to be forwarded are reduced by setting the message forwarding timer to a value inversely proportional to the air line distance between the vehicle sending the message and the vehicle receiving the message. A similar method is disclosed in the paper of Benslimane, "Optimized Dissemination of Alarm Messages in Vehicular Ad-hoc Networks (VANET)", Lecture notes in computer science, ISSN 0302-9743. The method introduced in this paper is based on that vehicles detecting a message previously transmitted by another vehicle (which can be determined, for example, by checking the unique identifier of the packets) stop their message forwarding timer. Thus normally, in the radio zone covered by the radio transmitter of the vehicle sending the message, i.e. in the area within which the transmission of the message sending vehicle can be received, only one vehicle within the particular radio zone with the greatest air line distance from the vehicle sending the message will forward the message. It is obvious, however, that there may exist special traffic situations in which two or more vehicles forward the received message. The advantage of the above mentioned method is that the network is flooded by applying a relatively simple protocol. However, there exist several situations in which this method cannot be used at all, or it can be used only with a rather low level of efficiency. Typically, such a situation is in which a message is to be delivered to vehicles travelling in a sharp band or along a switchback road. In this a case, the extent of flooding is not minimal due to the air line distance between the vehicles, said distance being measured (computed) in a simple way, typically based on GPS (Global Positioning System) coordinates, since the actual topology of the road network is not taken into account for setting the message forwarding timers.
It is an object of the present invention to provide a system and a method wherein during the radio wave based spreading of the road traffic information, the extent of flooding of the network can be kept on an even lower level than before and thereby the efficiency of message forwarding can be further improved.
It is another object of the present invention to efficiently utilize on-board location positioning devices used increasingly wide-spread in vehicles any way, in particular the GPS system, as well as the digital maps in order to minimize the number of message forwards and to deliver the information to an even more number of vehicles concerned. Accordingly, it is a further object of the present invention is to provide a system and a method adapted for recognizing critical zones into which the information otherwise could not reach in the course of normal flooding, and thereby the messages may be reliably forwarded to vehicles being in such critical zones, too.
The present invention is based on the recognition that during spreading the messages, instead of performing a preliminary routing for the message forwards, an ad-hoc communication network is formed of the vehicles, one vehicle being within the radio range of another one, wherein messages are forwarded by flooding the network in such a way that the message forwarding timer of each vehicle is set to a value rather defined as a function of the road distance between the vehicles than the distance measured (computed) along air line therebetween. It is most preferred that the message forwarding timer of the vehicles is set to a value that is inversely proportional to the road distance between the particular vehicles. In this manner, the message forwarding mechanism becomes dependent on the circumstances, which, as compared to the prior art methods, provides an extra information allowing a significant reduction of the number of messages required for the minimal flooding of the network. In the proposed method, however, it is not required for a vehicle that is going to send a message to know either the position or the travelling direction of any other nearby vehicle, i.e. those vehicles being within its radio zone.
According to one aspect of the present invention, there is provided a method for radio wave based vehicle-to-vehicle spreading of road traffic information, wherein each of the vehicles is equipped with a radio transmitter, a radio receiver, a location positioning device and a message forwarding timer. The method comprises the steps of:

recognizing, by a first vehicle, a road traffic event occurred on a section of a road on which said first vehicle is travelling;
generating, by said first vehicle, a piece of road traffic information relating to the road traffic event;
generating, by said first vehicle, a first road trajectory description information including at least data for the identification of said road section;
transmitting, by said first vehicle, a first message by radio message spreading, said first message containing at least a unique identifier for said message, said piece of road traffic information, the location of the vehicle sending the first message, said location being determined by its location positioning device, and said first road trajectory description information;
receiving, by at least one second vehicle, said first message transmitted by said first vehicle or another second vehicle;
determining, by at least one second vehicle out of the second vehicles receiving the first message, based on said first road trajectory description information and the location of said particular second vehicle determined by its location positioning device, if the particular second vehicle is travelling on said road section;
determining, by at least one second vehicle out the second vehicles travelling on said road section, the road distance between said particular second vehicle and the message sending first or second vehicle based on the location of said particular second vehicle determined by its location positioning device and said first road trajectory description information, and subsequently setting the message forwarding timer of said particular second vehicle to a value as a function of the road distance between said particular second vehicle and the message sending first or second vehicle; and
forwarding, by a particular second vehicle, the first message by message spreading when its message forwarding timer has expired.

According to another aspect of the present invention, there is provided a system for radio wave based vehicle-to-vehicle spreading of road traffic information, wherein each of the vehicles is provided with a radio transmitter, a radio receiver, a location positioning device and a message forwarding timer. The system comprises at least one first vehicle and at least one second vehicle, wherein a first vehicle is equipped with means for recognizing a road traffic event on a section of the road on which it is travelling; means for generating a piece of road traffic information relating to the recognized road traffic event; means for generating a first road trajectory description information including at least data for the identification of said road section; and means for generating a first message containing at least a unique identifier of said message, said piece of road traffic information, the location of the message sending vehicle determined by its location positioning device and said first road trajectory description information; whereas a second vehicle is equipped with means for recognizing the travel of the particular second vehicle on said road section, based on the first road trajectory description information and the location of said particular second vehicle, determined by its location positioning device; means for determining the road distance between said particular second vehicle and the message sending first or second vehicle, based on the location of said particular second vehicle determined by its location positioning device, and the first road trajectory description information; and means for setting the message forwarding timer of said particular second vehicle to a value as a function of the road distance between said particular second vehicle and the message sending first or second vehicle.
Finally, in a further aspect of the present invention, there is provided a computer program comprising instructions that, when executed by a computer or processor device forming a part of a first and/or second vehicle of the system according to the invention, enables the computer or processor device to perform any embodiment of the methods according to the invention.
The present invention will become more apparent from the following detailed description of exemplary, but non limiting embodiments with references to the accompanying drawings, in which:

Figures 1a and 1b schematically illustrate various problematic situations of flooding an ad-hoc network of vehicles travelling on a road;
Figures 2a and 2b are flow charts showing the basic steps of the method according to the invention;
Figures 3a and 3b are flow charts showing further steps of various preferred embodiments of the method according to the invention; and
Figure 4 is a block diagram illustrating the basic components of the system according to the invention.

Fig. 1 a shows a road section 105 with respect to which a vehicle 101 intends to transmit a piece of road traffic information for other vehicles 102, 103, 104 travelling behind it, said vehicles having an air line distance d12, d13, d14 from the vehicle 101, respectively. Each of the vehicles 101, 102, 103 has a radio zone (transmission range) 11, 12, 13, respectively. When the ad-hoc network formed of the vehicles 101, 102, 103 and 104 is flooded in a conventional way, the message sent by the vehicle 101 is first forwarded by the vehicle 102 out of the vehicles receiving said message, as d12 > d13, that is the vehicle 102 has the greatest air line distance from the vehicle 101 within its radio zone 11. Subsequently, the message is forwarded by the vehicle 103, since - except the vehicle 101 sending the message - this is the only vehicle that receives the transmission of the vehicle 102. The transmission of the vehicle 103 is, however, also received by the vehicle 104 behind it, thus the message reaches the vehicle 104, too. In this example, three message transmissions were needed for flooding of the ad-hoc network formed of the vehicles 101-104.
According to the present invention, the vehicle that is responsible for forwarding the message is selected based on rather the distance between the vehicles measured (computed) along the road than the distance measured (computed) along air line therebetween. It is assumed for it, however, that every vehicle knows the more or less exact shape of at least the way it has already made, or preferably the actual topology and the absolute positions of the complete road network. In this context, the term "absolute position" or the description of a road section by absolute data means that the particular descriptive parameters of a road section are specified by absolute coordinates originating from a location positioning system like GSM, GPS, Galileo, etc., or other identifiers referring to such absolute coordinates.
According to the present invention, the message sent by the vehicle 101 shown in Fig. 1 a is first forwarded by the vehicle 103, since along the road, the vehicle 103 out of the vehicles 102, 103 receiving the transmission of the vehicle 101 has the greater distance from the vehicle 101, therefore its message forwarding timer will be set to the smaller value. In addition to the vehicle 102, the transmission of the vehicle 103 is received also by the vehicle 104, since both of them are within the radio zone 14 of the vehicle 104. As a result, the message has reached all of the vehicles of the ad-hoc network formed of the vehicles 101-104. In this example, it was enough as few as two message transmissions for flooding the network.
It is obvious that in case of a straight road section, the message forward timing based on the conventional method of measuring air line distances produces the same result as the message forward timing based on measuring the distances along the road. Additionally, one can easily understand that in case of a more complicated road section with even more bends or with branches, the method according to the invention significantly reduces the number of message transmissions required for flooding the ad-hoc network formed of vehicles travelling on a particular road section.
Fig. 1b also illustrates a road section 115 with a sharp bend. On the road section 115, vehicles 111, 112, 113 and 114 are travelling, when the vehicle 111 of them recognizes a road traffic event, in relation to which it desires to deliver road traffic information to the vehicles 112, 113, 114 travelling behind it. As shown in Fig. 1b, each of the vehicles 111, 112, 113 has a radio zone 21, 22, 23, respectively.
In this example, the application of either of a conventional method and the method according to the invention guarantees that first, the vehicle 113 forwards the message transmitted by the vehicle 111. Thereby the message forward process would theoretically stop, since the transmission of the vehicle 113 is received only by vehicles that have already received the former transmission as well. However, on the road section 115, a critical zone 120 (framed with a dashed line) arises into which the message sent by the vehicle 111 will not reach if the conventional flooding based on the measurement of air line distances is used. On the contrary, in the method according to the invention, each of the vehicles 111-113 knows the actual shape and location of the particular road section 115, therefore the vehicle 112 can recognize that the road section 115 has a part not covered by the aggregate radio zone of all former message transmissions, i.e. by a unified area of the radio zones 21 and 23, while said part of the road section is at least partly - or even entirely - within its own radio zone 22. Consequently, this part of the road section forms a critical zone 120. It is obvious that to this end, each of the vehicles 111-113 has to know the aggregate area covered by the radio zones of all vehicles that have transmitted beforehand. Generally, this aggregate area may be easily determined from the absolute positions of the vehicles that have sent a message, the applied radio frequency, the transmission power and other known ambient conditions. In a preferred embodiment of the method according to the invention, subsequently to the recognition of the critical zone 120, the vehicle 112 is also allowed to forward the message of the vehicle 111 within a predetermined period of time after the transmission of the vehicle 113, whereby said message reaches the vehicle 114 travelling in the critical zone 120, too. Hence, flooding of the ad-hoc network formed of the vehicles 111-114 becomes complete, that is the message has been delivered to each of the vehicles forming the network.
As the flow charts of Figs. 2a and 2b illustrate, the method for radio wave based vehicle-to-vehicle spreading of road traffic information, according to the invention, comprises the following main steps.
In the first step S200, a road traffic event occurred on a road section of the way made by a first vehicle 101, 111 is recognized by the first vehicle 101, 111, said road traffic event typically being a kind of emergency, e.g. an accident causing a congested traffic or a road bottleneck, fog, smog, icy conditions, etc., or any other traffic event like travelling time, traffic jam, information on road defects (e.g. dangerous pot-holes), etc.
In the next step S210, a piece of information associated with the road traffic event is generated by the first vehicle 101, 111, said piece of information typically containing a description of the event, the exact location of the event (which is generally the same as the location of the first vehicle 101, 111 at the moment of the recognition of the event), the time of the occurrence of the event or the duration thereof, as well as other important information, e.g. data of the recommended by-pass road. It is obvious for a person skilled in the art that said piece of traffic information may further contain several other kinds of data or information as well.
After generating the road traffic information, a first road trajectory description information is generated by the first vehicle 101, 111 in step S220, said first road trajectory description information containing at least data for identifying said road section. In a particularly preferred embodiment of the method according to the invention, the road trajectory description information of said road section comprises descriptive data originating from an on-board navigation system. If a vehicle is not provided with an on-board navigation system or with other device in which a description of the road network is pre-stored, the road trajectory description information may be produced by said vehicle itself, at least with respect to the way made by it up to that moment. In such a case, the road trajectory description information contains road trajectory descriptive data recorded during the travel of said vehicle.
In an embodiment of the method according to the invention, wherein the road trajectory description information contains road trajectory descriptive data recorded during the travel of the vehicle, the road trajectory is described by sampling the location of the vehicle with a predetermined frequency by means of the location positioning device of the vehicle, and then to the sampled points, at least one parameterizable spline-curve is fitted. The road trajectory is preferably defined by absolute position values identifying one or more point of said road section, and the actual values of the parameters of the at least one spline-curve.
When the road section referred to in the road traffic information is in relation to a single road, the road trajectory description information describes a single continuous (straight or curved) line. However, when the road section referred to in the road traffic information is in relation to a plurality of connecting roads, for example a main road and a secondary road connected thereto, or a road section comprising a cross-roads, the road trajectory description information may describe a plurality of continuous, branching (straight or curved) lines.
In the next step S230 of the method, a first message is generated by the first vehicle 101, 111, said first message containing at least said piece of road traffic information, the location of the vehicle sending the first message, wherein its location is determined by its location positioning device, and the first road trajectory description information. Subsequently, the first message is transmitted by message spreading from the first vehicle 101, 111 in step S235. In the first message, the location of the message sending vehicle is always specified by the absolute location of the vehicle actually sending said message, in the moment of the message sending (which may be either a first transmission or a forward during the spreading process). Preferably, the first message also contains an own unique identifier of the message so that the message can be identified upon the reception thereof. The transmission technique of radio message spreading is well known for a person skilled in the art, moreover, it is not part of the invention, therefore its detailed description is omitted.
If in the radio zone of the first vehicle 101, 111, there is no second vehicle receiving its transmission, the method will finish in step S235, or in a preferred embodiment, the method will continue with the re-transmission of the message.
When in the radio zone of the first vehicle 101, 111, there is a second vehicle that is receiving the first message, the first message is received, in step S240 shown in Fig. 2b, by at least one second vehicle 102-104, 112, 113, and subsequently, in step S250, it is determined, by at least one second vehicle 102-104, 112, 113, from at least the first road trajectory description information specified in the first message and the location of said second vehicle 102-104, 112, 113 determined by its location positioning device, whether said second vehicle 102-104, 112, 113 is travelling on the road section identified in the first message. Step S250 is preferably executed only by those vehicles out of the vehicles receiving the first message that have not forwarded said first message yet. Messages having previously sent by a particular vehicle are recognized by said vehicle through managing a registry of the unique message identifiers.
In the next step S260, at least one second vehicle 102-104, 112, 113 travelling on said road section and receiving the first message determines its road distance from the first or second vehicle 101, 103, 111, 113 sending the message, based on the location of the first or second vehicle 101, 103, 111, 113 sending the first message, wherein said location is specified in the first message, the location of said second vehicle 102-104, 112, 113 and the road trajectory description information.
In order to minimize the extent of flooding, i.e. to minimize the number of message transmissions, the message forwarding timer of all second vehicles 102-104, 112, 113 travelling on said road section and receiving the first message is set, in step S270, to a value as a function of the road distance between the particular second vehicle 102-104, 112, 113 and the first or second vehicle 101, 103, 111, 113 sending the first message, preferably to a value being inversely proportional to said distance. Then, in step S280, the first message is forwarded by radio message spreading from at least one second vehicle 103, 113 when the message forwarding timer of said second vehicle 103, 113 has expired.
In order to avoid simultaneous message transmissions, i.e. to prevent collisions, the first message is only forwarded from a second vehicle 103, 113, in a preferred embodiment of the method according to the invention, if before the expiration of its message forwarding timer, no forward of the first message by another vehicle was detected.
If no forward of the first message by another vehicle is detected in the vehicle 101, 103, 111, 113 for a predetermined period of time, said first message is re-transmitted by the particular vehicle 101, 103, 111, 113, according to a preferred embodiment of the invention. So as to provide the capability of re-transmission of a message, each of the vehicles should have a message re-transmission timer, the value of which is set to a predetermined value upon sending or forwarding a message. Preferably, the value of the message re-transmission timer is determined so that it should be greater than the greatest possible value of the message forwarding timer. Consequently, if the vehicle that has sent a message does not detect the transmission of any other vehicle till the expiration of its message re-transmission timer, it means that no other vehicle was travelling within its radio zone at the moment of transmission of the first message, or the transmissions of other vehicles might have collided - e.g. for certain reasons described below - and therefore they could not be received. In such a situation, the message is re-transmitted after the expiration of the message re-transmission timer in order to increase reliability of the method.
As illustrated in Fig. 2b, instead of the first message sent by a first vehicle, a second vehicle may also receive the first message forwarded by another second vehicle, i.e. in step S240 of the method, the first message may arrive either from a first vehicle that has generated the message, or from a second vehicle that takes part in the spreading of the first message. Flooding of the ad-hoc network formed of vehicles is due to this kind of feed-back.
As mentioned in relation to Fig. 1b before, on the road section associated with the road traffic event, a critical zone 120 may arise into which a message cannot be delivered by flooding during the basic operation. Accordingly, so as to manage such special situations, a preferred embodiment of the method according to the invention also comprises the following steps illustrated in Fig. 3a. In step S300, upon the reception of the first message, an aggregate radio zone covered by all previous transmissions of the first message is determined, and in step S31 0, based on said road section and the aggregate radio zone of the first message, at least one of the second vehicles recognizes that a part of said road section forms a critical zone, at least a part of which extends outside the aggregate radio zone of the first message, but within the radio zone of said second vehicle. Thus in step S320, the message forwarding timer of the at least one second vehicle recognizing the critical zone is set to a predetermined value, and in step S330, the first message is additionally forwarded by this second vehicle as well when its message forwarding timer has expired. The predetermined value to which the message forwarding timer of said second vehicle is set is preferably smaller than the minimum value of the message forwarding timer in the normal operation of the message transmission, wherein said value is inversely proportional to the road distance between the particular vehicles. Consequently, a transmission directed into a critical zone always anticipates the possible normal transmission of the first message. It is obvious that the transmission of a message into a critical zone results in the multiplication of the first message, that is, after sending such a message, two or even more (in the case of more than one critical zone) instances of the first message are propagated at the same time in the network in the course of flooding of the ad-hoc network formed of the vehicles.
If there is a plurality of second vehicles that has recognized a critical zone covered at least partly by its own radio zone, such second vehicles will automatically forward the first message independently of each other and the of vehicle being responsible to forward said message according to the normal operation of the flooding. These quasi immediate message transmissions would, however, occur at the same time with resulting in the collision of the messages, thus frequent re-transmissions would be needed, which led to a significant deterioration of the efficiency of the flooding method according to the invention. To avoid this, forwarding of the first message with such a predetermined, short timing is based on a priority scheme, wherein the vehicle the greatest road distance from the vehicle sending the message is allowed to forward the first message first. Due to this scheme, not only the number of the incidental collisions may be reduced significantly, but also the extent of flooding may be kept on a minimal level. It is obvious for a person skilled in the art that for preventing the transmissions directed into a critical zone from collisions, not only a distance based priority scheme, but also a time divisional medium access or any other collision-free medium access protocol may be similarly applied.
As mentioned before, the road section associated with the road traffic event may include not only a single road, but even a plurality of connecting roads as well. The normal operation of the method according to the invention guarantees that the first message will be propagated along all of the connecting roads at the same time due to the multiplication of the first message, which further increases the efficiency of flooding.
In case the first vehicle generating the first message is not provided with a digital map for obtaining the data to be sent in the first road trajectory description information, the special case may often occur wherein the road trajectory recorded by the first vehicle itself during its travel describes a path in which one or more other road is connected to the road section associated with the road traffic event. In respect that the first vehicle has no information relating to such connecting roads at all, the first message does not contain any data relating to said connecting roads in the first road trajectory description information, thus the road traffic information cannot reach the vehicles travelling along this road section towards the location of the traffic event and being interested in that event. In order to solve this problem, in a preferred embodiment of the method according to the invention, described by referring to the flow chart illustrated in Fig. 3b, in a further step S350, a second vehicle travelling on a connecting road and receiving the first message recognizes that it is travelling on a road section not identified by the first road trajectory description information of the first message but connected to the road section identified by the first road trajectory description information. Subsequently, in step S360, a second road trajectory description information is generated by this second vehicle, said second road trajectory description information containing data for identifying a road section which is partly coincident with the road section specified by the first road trajectory description information. In step S370, a second message is also generated by said second vehicle, wherein said second message contains at least the road traffic information of the first message, the location of the vehicle sending the second message, wherein its location is determined by its location positioning device, and the second road trajectory description information. Next, in step S380, the second message is sent by said second vehicle in the same way as a first message. In step S390, the second message is received by at least one further second vehicle travelling within the radio zone of the former second vehicle sending the second message, on a connecting road specified in the second message. In step S395, the second message is re-transmitted and/or forwarded, in the same way as a first message, by at least one further second vehicle travelling on the road section specified by the second road trajectory description information.
Hence, the second message carries the same road traffic information as that one carried by the first message, but the road section associated with the traffic event is partly different in the second message, therefore the second message tends to be propagated along the connecting road independently of the first message. The second message is spread for the vehicles travelling on the road section specified by the second road trajectory description information in the same manner as a first message is spread.
In case neither is the vehicle travelling on the connecting road provided with a digital map and accordingly, this vehicle knows only the road trajectory of the way it has made, a condition of generating the second message is that this vehicle should change to the road section specified by the first road trajectory description information. Thereby said second vehicle will be able to recognize the partial coincidence of the two road sections based on a comparison made between the first road trajectory description information of the first message and the road trajectory recorded by itself. Consequently, said second vehicle becomes capable of generating and sending a second message.
An alternative embodiment of the method according to the invention further comprises the step of presenting the road traffic information of the first message for the driver of each second vehicle in a visible, audible or other sensible way. Audible presentation of the road traffic information may be carried out, for example, by announcing the information by human voice by using an appropriate electronic device, e.g. through loudspeakers accommodated in the passenger room. Visible presentation of the road traffic information may be carried out, for example, by displaying it in a textual and/or graphical form on the dashboard or on the display of an on-board navigation system.
In a further embodiment of the method according to the invention, an automatic intervention into the driving of the second vehicle receiving the message is performed based on the first and/or second message (with keeping the driving safety in view), by means of a suitably programmed processor device. Depending on the content of the road traffic information, said intervention may include braking down the vehicle, switching on the emergency stop lights, switching on the headlamps, etc.
In the following, the components of the system for carrying out the method according to the invention will be described with reference to Figs. 1a, 1b and 4. The system 400 according to the invention comprises vehicles 101-104, 111-114, each of said vehicles being provided with a radio transmitter 401, a radio receiver 402, a location positioning device 403 and a message forwarding timer 404. As shown in Fig. 4, the system 400 according to the invention comprises at least one first vehicle 101, 111 equipped with means 410 for recognizing a road traffic event on a section of the road along it is travelling, means 412 for generating a piece of road traffic information relating to the recognized road traffic event, means 414 for generating a first road trajectory description information including at least data for the identification of at least said road section and means 416 for generating a first message containing at least said piece of road traffic information, location of the message sending vehicle determined by its location positioning device 403, and the first road trajectory description information. As mentioned before, in terms of functionality, the first vehicle 101, 111 operates as the source of the road traffic information.
Additionally, the system 400 further comprises at least one second vehicle 102-104, 112-114 equipped with means 420 for recognizing the travel of the particular second vehicle 102-104, 112-114 on said road section, based on the first road trajectory description information and the location of said particular second vehicle 102-104, 112-114 determined by its location positioning device, means 422 for determining the road distance between said particular second vehicle 102-104, 112-114 and the message sending first or second vehicle 101-104, 111-114, based on the location of said particular second vehicle 102-104, 112-114 determined by its location positioning device 403 and the first road trajectory description information, and means 424 for setting the message forwarding timer 404 of said particular second vehicle 102-104, 112-114 to a value as a function of the road distance between said particular second vehicle 102-104, 112-114 and the message sending first or second vehicle 101-104, 111-114. In the most preferred embodiment of the system according to the invention, the message forwarding timer is set by said means 424 to a value being inversely proportional to the road distance between the particular vehicles.
It should be noted that although Fig. 4 illustrates only one first vehicle and one second vehicle, it is obvious that the system according to the invention may comprise any number of first vehicle and second vehicle.
In accordance with the method of the invention, a preferred embodiment of the system 400 comprises at least one second vehicle 102-104, 111-114 further equipped with means for determining an aggregate radio zone covered by all of the previous transmissions of a particular first message, means for recognizing a critical zone based on the road section identified by the road traffic information of the first message and the aggregate radio zone associated with said particular first message, means for setting the message forwarding timer 404 of said second vehicle 102-104, 112-114 to a predetermined value, and means for initiating, after expiration of its message forwarding timer 403, the forward of the first message independently of the transmissions of other vehicles.
In another preferred embodiment of the system 400 according to the invention, at least one of the second vehicles 102-104, 112-114 may further comprise means for recognizing a situation wherein said particular second vehicle 102-104, 112-114 is travelling on a road section not specified by the first road trajectory description information of the first message but connected to said road section specified by the first road trajectory description information, means for generating a second road trajectory description information containing data for the identification of a road section partly coincident with the road section specified by the first road trajectory description information, means for generating a second message containing at least the road traffic information of the first message, the location of said particular second vehicle 102-104, 112-114 determined by its location positioning device and the second road trajectory description information, and means for initiating the transmission of the second message from said particular second vehicle 102-104, 111-114 in the same way as a first message.
In yet another preferred embodiment of the system 400 according to the invention, a second vehicle 102-104, 112-114 may comprise means for presenting the road traffic information of the first message for the driver of the vehicle in a visible or audible way and/or means for performing automatic intervention into the driving of the vehicle in response to the first message and/or the second message.
It is obvious for a person skilled in the art that the various means 410-424 used in the system 400 according to the invention, as well as all of the other means used in the preferred embodiments of the method according to the invention may be implemented separately, in a partly or entirely integrated form, or by software and/or by hardware. The means out of said means 410-424 that are actually used in a vehicle are preferably integrated in a single processor device being suitably programmed. Accordingly, the present invention also relates to a computer program comprising instructions that, when executed by a computer or a processor device arranged in a first vehicle and/or a second vehicle in any embodiment of the system according to the invention, enables the computer or the processor device to carry out any embodiment of the method according to the invention. The present invention further relates to a computer program product comprising said computer program, wherein said computer program product is stored on any kind of computer-readable data storing medium.

Claims

A method for radio wave based vehicle-to-vehicle spreading of road traffic information, wherein each of the vehicles is provided with a radio transmitter, a radio receiver, a location positioning device and a message forwarding timer, said method comprising the steps of:
recognizing, by a first vehicle, a road traffic event occurred on a section of a road on which said first vehicle is travelling (S200),

generating, by said first vehicle, a piece of road traffic information relating to the road traffic event (S210),

generating, by said first vehicle, a first road trajectory description information including at least data for the identification of said road section (S220),

generating, by said first vehicle, a first message containing at least a unique identifier for said message, said piece of road traffic information, the location of the vehicle sending the first message, said location being determined by its location positioning device, and said first road trajectory description information (230),

transmitting, by said first vehicle, said first message by radio message spreading (S235),

receiving, by at least one second vehicle, said first message transmitted by said first vehicle or another second vehicle (S240),

determining, by at least one second vehicle out of the second vehicles receiving the first message, based on said first road trajectory description information and the location of said particular second vehicle determined by its location positioning device, whether the particular second vehicle is travelling on said road section (S250),

determining, by at least one second vehicle out the second vehicles travelling on said road section, the road distance between said particular second vehicle and the message sending first or second vehicle based on the location of said particular second vehicle determined by its location positioning device and said first road trajectory description information (S260), and subsequently setting the message forwarding timer of said particular second vehicle to a value defined as a function of the road distance between said particular second vehicle and the message sending first or second vehicle (S270), and

forwarding, by said particular second vehicle, the first message by radio message spreading when its message forwarding timer has expired (S280).
The method of claim 1, characterized in that the message forwarding timer of the second vehicle is set to a value being inversely proportional to the road distance between the particular second vehicle and the message sending first or second vehicle.
The method of claim 1 or 2, characterized in that said first message is forwarded by said second vehicle only if no forward of the first message by another vehicle was detected before the expiration of its message forwarding timer.
The method of any one of claims 1 to 3, characterized in that said method further comprises the steps of:
providing each of said first and second vehicles with a message re-transmission timer,

upon sending the first message, setting the message re-transmission timer of the message sending first or second vehicle to a predetermined value,

re-transmitting said first message by said first or second vehicle if no forward of the first message by a second vehicle has been detected before the expiration of its message re-transmission timer.
The method of any one of claims 1 to 4, characterized in that said method further comprises the steps of:
determining, by a second vehicle, an aggregate radio zone covered by all of the previous transmissions of a particular first message (S300),

based on the road section identified by the road traffic information of the first message and said aggregate radio zone associated with said particular first message, recognizing by at least one second vehicle that a part of said road section is outside said aggregate radio zone, but within the radio zone of said particular second vehicle, wherein said part of the road section constitutes a critical zone (S310),

setting the message forwarding timer of at least one second vehicle recognizing said critical zone to a predetermined value, said value being smaller than the minimum value of the message forward timing (S320), and

additionally forwarding the first message by said particular second vehicle when its message forwarding timer has expired (S330).
The method of claim 5, characterized in that if there is a plurality of second vehicles recognizing a critical zone, the first message will be transmitted by such a second vehicle with said predetermined timing according to a priority scheme, wherein the vehicle with a greater road distance from the message sending vehicle is allowed to forward the first message sooner.
The method of any one of claims 1 to 6, characterized in that said method further comprises the steps of:
recognizing, by a second vehicle receiving said first message, a situation wherein said particular second vehicle is travelling on a road section not specified by the first road trajectory description information of the first message, but connected to said road section specified by the first road trajectory description information (S350),

generating, by said particular second vehicle, a second road trajectory description information containing data for the identification of a road section partly coincident with the road section specified by the first road trajectory description information (S360),

generating, by said particular second vehicle, a second message containing at least the road traffic information of the first message, the location of said particular second vehicle determined by its location positioning device and said second road trajectory description information (S370),

transmitting said second message by said particular second vehicle in the same way as the first message (S380),

receiving said second message by at least one further second vehicle (S390), and

forwarding and/or re-transmitting said second message, in the same way as the first message, by at least one further second vehicle travelling on the road section specified by the second road trajectory description information (S395).
The method of any one of claims 1 to 7, characterized in that said first or second road trajectory description information is an identifier of said road section obtained from a digital map, or a piece of road trajectory description information recoded during the travel of the vehicle.
System (400) for radio wave based vehicle-to-vehicle spreading of road traffic information, wherein each of the vehicles is provided with a radio transmitter (401), a radio receiver (402), a location positioning device (403) and a message forwarding timer (404), characterized in that said system comprising:
at least one first vehicle (101, 111) equipped with

means (410) for recognizing a road traffic event on a section of the road on which it is travelling,

means (412) for generating a piece of road traffic information relating to the recognized road traffic event,

means (414) for generating a first road trajectory description information including at least data for the identification of said road section, and

means (416) for generating a first message containing at least a unique identifier of said message, said piece of road traffic information, location of the message sending vehicle determined by its location positioning device (403) and said first road trajectory description information,
and at least one second vehicle (102-104, 112-114) equipped with
means (420) for recognizing the travel of the particular second vehicle (102-104, 112-114) on said road section, based on the first road trajectory description information and the location of said particular second vehicle (102-104, 112-114) determined by its location positioning device (403),

means (422) for determining the road distance between said particular second vehicle (102-104, 112-114) and the message sending first or second vehicle (101-104, 111-114), based on the location of said particular second vehicle (102-104, 112-114) determined by its location positioning device (403), and the first road trajectory description information, and

means (424) for setting the message forwarding timer (404) of said particular second vehicle (102-104, 112-114) to a value as a function of the road distance between said particular second vehicle (102-104, 112-114) and the message sending first or second vehicle (101-104, 111-114).
The system of claim 9, characterized in that the message forwarding timer (404) is set to a value being inversely proportional to the road distance between said particular second vehicle (102-104, 112-114) and the message sending first or second vehicle (101-104, 111-114).
The system of claim 9 or 10, characterized in that at least on second vehicle (112) further comprises
means for determining an aggregate radio zone covered by all of the previous transmissions of a particular first message,
means for recognizing a critical zone, based on the road section identified by the road traffic information of the first message and said aggregate radio zone associated with said particular first message, wherein the critical zone is defined as a part of said road section being outside said aggregate radio zone, but within the radio zone of said particular second vehicle (112),
means for setting the message forwarding timer (404) of said particular second vehicle (112) recognizing said critical zone to a predetermined value, said value being smaller than the minimum value of the message forward timing, and
means for initiating an additional forward of the first message independently of the transmission of any other vehicle (101-104, 111-114) when the message forwarding timer (404) of said particular second vehicle (112) has expired.
The system of any one of claims 9 to 11, characterized in that at least one second vehicle receiving said first message further comprises
means for recognizing a situation wherein said particular second vehicle is travelling on a road section not specified by the first road trajectory description information of the first message, but connected to said road section specified by the first road trajectory description information,
means for generating a second road trajectory description information containing data for the identification of a road section partly coincident with the road section specified by said first road trajectory description information,
means for generating a second message containing at least the road traffic information of said first message, the location of said particular second vehicle determined by its location positioning device, and said second road trajectory description information, and
means for initiating the transmission of said second message by said particular second vehicle, in the same way as said first message.
The system of any one of claims 9 to 12, characterized in that at least one second vehicle (102-104, 112-114) further comprises means for presenting said road traffic information of said first message for the driver of said vehicle (102-104, 112-114) in a visible or audible way.
Computer program comprising instructions that, when executed by a computer or a processor device arranged in a first and/or second vehicle of the system according to any one of claims 9 to 13, enables the computer or the processor device to perform the method of any one of claims 1 to 8.