WO2009149730A1

WO2009149730A1 - Method and system for information dissemination in a communication network

Info

Publication number: WO2009149730A1
Application number: PCT/EP2008/004769
Authority: WO
Inventors: Wenhui Zhang; Roberto Baldessari
Original assignee: Nec Europe Ltd.
Priority date: 2008-06-13
Filing date: 2008-06-13
Publication date: 2009-12-17

Abstract

A method for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET), wherein the communication network comprises a multitude of communication nodes (4) and wherein the communication among said communication nodes (4) is performed by way of sending and receiving multicast broadcast messages, is characterized in that additional communication nodes - infrastructure elements (2) - are provided, said infrastructure elements (2) performing the steps of receiving messages from at least two of said communication nodes (4), generating a new message - aggregation message - into which information retrieved from the received messages is included, and broadcasting said generated aggregation message. Furthermore, a corresponding system for information dissemination is disclosed.

Description

METHOD AND SYSTEM FOR INFORMATION DISSEMINATION IN A COMMUNICATION NETWORK

The present invention relates to a method and a system for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET), wherein the communication network comprises a multitude of communication nodes and wherein the communication among said communication nodes is performed by way of sending and receiving multicast broadcast messages.

Information dissemination in mobile communication networks is a crucial task, especially in vehicular communication networks, like VANETs (Vehicular Ad hoc NETworks). VANETs are highly dynamic networks in which motor vehicles equipped with appropriate communication devices, in general called on-board units, act as communication nodes. The functionality of such wireless networks is typically directed to safety, travelling comfort and on-board entertainment applications. In this context, a reliable strategy to deliver messages to vehicles, for instance to all vehicles located in a certain geographical area, is needed. First and foremost, this holds true with respect to periodic safety messages, i.e. each communication node needs to send periodic messages to inform its status to all neighbouring nodes. For instance, such messages are used by cooperative awareness applications.

The simplest strategy for information dissemination is the so-called flooding mechanism. Flooding means that the information to be delivered is broadcast by a communication node, and each communication node that receives the information broadcasts it again, and so on. However, flooding creates a large overhead and a high amount of packet collisions, what is known as the .broadcast storm problem'.

Another problem that is observed in WLAN-based VANETs is that the reception probability of messages, which are sent by each mobile communication node to periodically inform its status to all neighbouring communication nodes within a certain area, becomes very low when the radio propagation environment is unfavourable. This is especially true in urban environments where tall buildings often shadow route intersections, route turning points, etc. For example, packets sent by the communication node will often not be received by another communication node nearby if there is no Line-of-Sight (LoS) communication path between them. In addition, messages can get lost due to the hidden node problem.

Existing solutions use either mobile communication nodes or so called Road Side Units (RSU) to relay packets. For instance, in EP 1 788 749 A1 a method and an apparatus for vehicle-to-vehicle multi-hop broadcast communication is disclosed according to which an efficient form of flooding is applied in order to disseminate information among communication nodes. When a vehicle receives a message, it calculates the distance from the sender based on the transmitted position data. A time when the received packet shall be retransmitted is calculated on the basis of the calculated distance from the sender. In principle, the larger the node's distance from the sender, the shorter is the node's waiting time for retransmission. However, using mobile nodes to relay periodic messages or forward information of other periodic messages may have a lot of redundancy and the relayed packets make also easily get lost.

Using an RSU to relay periodic messages is more reliable than using mobile nodes according to the method described above. RSUs are devices located close to roads which provide for various infrastructure services within the network. RSUs are typically equipped with means for sending and receiving broadcast messages as well as with processing means for message analysis. However, using RSUs for packet relay is not efficient since each received (periodic) message might be relayed. This will lead to congestion when there are a large number of mobile communication nodes sharing limited radio resources in vehicular environments.

It is therefore an object of the present invention to improve and further develop a method and a system of the initially described type for information dissemination in a communication network in such a way that by employing mechanisms that are readily to implement the reception probability of periodic messages is improved and network load is reduced.

In accordance with the invention, the aforementioned object is accomplished by a method comprising the features of claim 1. According to this claim, such a method is characterized in that additional communication nodes - infrastructure elements - are provided, said infrastructure elements performing the steps of receiving messages from at least two of said communication nodes, generating a new message - aggregation message - into which information retrieved from the received messages is included, and broadcasting said generated aggregation message.

Furthermore, the aforementioned object is accomplished by a system comprising the features of independent claim 16. According to this claim, such a system is characterised in that the communication network comprises additional communication nodes - infrastructure elements -, said infrastructure elements comprising reception means for receiving messages from at least two of said communication nodes, processing means for generating a new message - aggregation message - as well as for retrieving information from the received messages and including the retrieved information into said aggregation message, and broadcasting means for broadcasting said generated aggregation message.

According to the invention it has first been recognized that by the implementation of infrastructure elements, which act as additional communication nodes, problems of the above mentioned kind with respect to packet loss can be alleviated. To this end, the infrastructure elements are configured to receive packets from at least two of the communication nodes of the network. The infrastructure elements are further configured to generate a new message which is referred to as aggregation message as the infrastructure elements retrieve information contained in the received messages and include this information into the aggregation message. In a next step the aggregation message is broadcasted and can thus be received by the communication nodes of the network positioned within the transmission range of the infrastructure element. By concentrating information from messages from more than one communication node, preferably from a multitude of communication nodes, in one single message - the aggregation message - the efficiency of the dissemination process is significantly enhanced. Furthermore, by aggregating information from multiple packets into a single message, the number of packets transmitted over the air is reduced. Consequently, network load is reduced which again increases packet reception probability. Preferably, the infrastructure elements are installed at places that allow for Line-of- Sight (LoS) communication with communication nodes positioned in different directions of e.g. a road intersection. For instance, infrastructure elements may be disposed at road intersections in such way that the infrastructure elements cover at least road segments within two different directions of the intersection.

Advantageously, the infrastructure elements are disposed in a height above the ground which exceeds the height of conventional motor vehicles acting as communication nodes. By arranging the infrastructure elements sufficiently high, in general, a better radio propagation environment is achieved.

According to a preferred embodiment, the infrastructure elements are integrated into Road Side Units (RSU). Such collocation is advantageous as there are already existing VANETs in which RSUs are employed and which could be used to implement the infrastructure elements' functionality. Thus, no additional device would have to be provided. Alternatively or additionally, the infrastructure elements may be collocated with other conventional infrastructure elements. For instance, the infrastructure elements could be collocated with traffic light equipment. It is important to note, that the functionality of the infrastructure elements can coexist with other infrastructure-to-vehicle communication functions generally provided by a RSU, including for example traffic light signal broadcasting. Of course, a separate installation of infrastructure elements is also possible.

Advantageously the communication nodes include means for position determination. This means may, for instance, include a GPS (Global Positioning System) receiver.

According to a preferred embodiment, the infrastructure elements extract only predefined information from the messages received from communication nodes and integrate them into an aggregation message. The parts of information which are integrated into the aggregation message may include, for example, the communication nodes' ID, position, speed, heading direction, etc. The specific selection of the information elements which are integrated into the aggregation messages may be changed and may be adapted to the respective situation. Since not all information contained in the messages received from communication nodes is included into the aggregation message, the size of the aggregation message is smaller than the total size of all received messages. Insofar, network load is again reduced.

With respect to highly flexible applications, it may be provided that the infrastructure elements select communication nodes according to predefined selection rules, wherein only information originating from the selected communication nodes is included into the aggregation messages. For instance, the predefined selection rules may be based on the position of a communication node within a predefined geographical area. Moreover, the infrastructure elements may be configured to forward their generated aggregation messages only into a predefined geographical area. The predefined geographical area may be defined by way of e.g. an opening angle. For instance, according to a specific embodiment it may be provided that an infrastructure element is disposed at a corner of a road intersection. It is configured to receive messages from vehicles heading towards the intersection from a first road. The corresponding aggregation messages generated by the infrastructure element are then only forwarded to nodes heading towards the intersection from a second road, wherein both roads may run essentially perpendicular to each other and may be shadowed against each other by tall buildings or the like.

As regards short delays with respect to information dissemination it may be provided that the infrastructure elements generate and broadcast the aggregation messages periodically at a certain frequency. However, the infrastructure elements may include means to immediate forward a received message in case the message is a critical safety message. Preferably, the infrastructure elements include means for buffering information contained in messages received from communication nodes. Thus, it is possible to buffer information received by the infrastructure elements from communication nodes at least between the transmissions of two successive aggregation messages. In this context it proves to be advantageous that information elements included in the messages sent by the communication nodes carry a timestamp so that a correct allocation of buffered information can easily be performed. According to a preferred embodiment, the frequency of generating and broadcasting the aggregation messages is chosen dependent on the frequencies of messages received by the infrastructure elements from the communication nodes. In particular, it is possible to set the aggregation message frequency equal to the highest periodic message transmission frequency of all communication nodes from which the infrastructure elements receives periodic messages. When the communication node with the highest periodic message frequency leaves the transmission range of the infrastructure element, the aggregation message frequency may be reduced accordingly. On the other hand, when a communication node with a higher periodic message frequency than the actual one enters the transmission range of the infrastructure element, the aggregation message frequency may be increased accordingly. Furthermore, it is possible to adaptively change the frequency of generating and broadcasting aggregation messages dependent on the actual channel load. By adapting the aggregation message generation and broadcasting frequency as described, the maximum delay of forwarding periodic message information can be efficiently controlled. As mentioned already above, in case of critical messages, e.g. with respect to safety concerns, an immediate forwarding may be provided.

With respect to a decrease of redundancy in the aggregation messages it may be provided that the geographical positions of communication nodes are included into the aggregation messages in form of relative positions with respect to the infrastructure element. Instead of using latitude and longitude coordinates, this may reduce the size of the aggregation message.

As the infrastructure elements are subject to media access contention from many areas, it may be provided that the aggregation messages sent by the infrastructure elements are assigned a higher priority than periodic messages sent by communication nodes in order to improve the channel access probability of the infrastructure elements. In particular in IEEE 802.11 p systems the priority may be set at the MAC (Media Access Control) layer. Since IEEE 802.11 p supports different priorities at the MAC layer, aggregation packets at an infrastructure element may be assigned a higher priority than periodic messages from communication nodes. This means, with high priority, packets from infrastructure elements will have a shorter waiting time than periodic messages sent by communication nodes. In addition, such priority setting may be implemented at the network layer by giving high priority to aggregation messages at network layer.

There are several ways how to design and further develop the teaching of the present invention in an advantageous way. To this end, it is to be referred to the patent claims subordinate to patent claims 1 and 16 and to the following explanation of a preferred example of an embodiment of the invention, illustrated by the figure on the other hand. In connection with the explanation of the preferred example of an embodiment of the invention by the aid of the figure, generally preferred embodiments and further developments of the teaching will be explained. In the drawings:

Fig. 1 illustrates a generation and broadcasting process of an aggregation message according to an embodiment of the present invention,

Fig. 2 illustrates a scheduling process of aggregation message generation at an infrastructure element according to an embodiment of the present invention, and

Fig. 3 illustrates schematically an example of aggregation message generation from received periodic messages according to an embodiment of the present invention.

Fig. 1 illustrates an application scenario of the present invention at a road intersection 1 in a VANET. A total of four infrastructure elements 2 are arranged in the area of the intersection 1 , wherein the infrastructure elements 2 are collocated with traffic light assemblies 3. More specifically, at each corner of the intersection 1 an infrastructure element 2 is disposed within a height of approximately 3 meters above the ground. Thus, the infrastructure elements 2 are installed at places with sufficiently high radio propagation quality into different directions of the intersection 1. Vehicles 4 are equipped with on-board units and function as communication nodes of the VANET. In the following, the functional principle of the present invention will be described by means of the infrastructure element 2a disposed at the upper left corner of the intersection 1. In the specific scenario shown in Fig. 1 the infrastructure element 2a receives periodic messages from two vehicles 4a, 4b heading towards the intersection 1 from the left side. This is indicated by the continuous line arrows. For the sake of simplicity, only two such vehicles are depicted in Fig. 1. In real scenarios, however, the infrastructure element 2a will typically receive periodic messages from many more vehicles. The infrastructure element 2a retrieves information from the periodic messages received from the nodes 4a, 4b and generates an aggregation message into which the retrieved information is included. The aggregation messages are generated periodically and are broadcast with a certain frequency. In this way, other vehicles (in the specific case shown vehicles 4c, 4d, and 4e), which have lower probability to directly receive periodic messages from the two transmitting vehicles 4a, 4b, will receive the aggregation messages from the infrastructure element 2a with high reception probability. This is indicated by the dashed line arrows. In particular, the reception probability for nodes 4c and 4d is improved as their might be no direct Line-of-Sight communication between these vehicles on the one hand and vehicles 4a, 4b on the other hand due to shadowing buildings placed at the corners of the intersection 1.

By aggregating information from multiple packets into a single message, the number of packets transmitted over the air is significantly reduced. In particular, mobile communication nodes are not required any longer to relay periodic messages or forward information of periodic messages. Each vehicle only has to send periodic messages containing its status information and is getting informed about the other communication nodes' status by receiving aggregation messages from the infrastructure elements 2. Consequently, redundancy is reduced and losses of packets are widely reduced. Good overall performance is achieved with favourable installation locations for the infrastructure elements 2.

Fig. 2 illustrates schematically the process of periodic message information aggregation and scheduling at an infrastructure element. Node 1 sends periodic messages at a certain frequency, the messages being indicated by the white bars along the time axis. Node 2 sends periodic messages with the same frequency as node 1 , the messages of node 2 being indicated by the hatched bars. On the other hand, node 3 sends periodic messages with a lower frequency than nodes 1 und 2, the messages of node 3 being indicated by the black bars.

All periodic messages transmitted by node 1 , node 2 and node 3 are received by an infrastructure element. The infrastructure element retrieves information from the received messages and integrates them into a new aggregation message. In the specific embodiment of Fig. 2 the aggregation messages are sent with the same frequency as the periodic messages of nodes 1 and 2. As nodes 1 and nodes 2 send periodic messages at a higher frequency than node 3, there are aggregation messages which do not contain any information from node 3.

As can be obtained from Fig. 2, the white bars, the hatched bars and the dark bars of the aggregation messages are shorter than the respective bars of the periodic messages of the single nodes. This indicates that the infrastructure element does not necessarily include all information contained in the messages received from the communication nodes into the aggregation message. According to predefined rules, which may be adapted to specific environments and/or situations, the infrastructure element is configured to include only relevant status information of the single nodes into the aggregation message. Consequently, the size of the aggregation messages is smaller than the total size of all packets received from the single communication nodes. This helps to reduced network load, which in return helps to further increase packet reception probability.

Fig. 3 illustrates schematically an example of aggregation message generation from periodic messages of three communication nodes, which are node 1 , node 2 and node 3. The periodic messages each include a header as well as a data part carrying the actual payload of the message. In the embodiment shown in Fig. 3 the data part includes a number of n data fields filled with information elements IE1 ... IEn.

The infrastructure element receives the periodic messages from node 1 , node 2 and node 3, retrieves certain information elements IE from these messages according to predefined algorithms and integrates these information elements into a new message, the aggregation message. In the specific embodiment illustrated in Fig. 3, the first information element IE is extracted from each of the three periodic messages, i.e. IE11 , IE21 and IE31. The retrieved information elements IE11 , IE21 and IE31 are then integrated into the aggregation message. The information elements IE11 , IE21 and IE31 may e.g. refer to the geographical position or the heading direction of the communication nodes 1 , 2 and 3, respectively.

Although according to the embodiment information is retrieved from the data fields of the periodic messages, it is to be noted, that information may also be extracted from the header, e.g. in cases in which the position information of the nodes is included in the header of the periodic messages. Various approaches are possible depending on the specific packet format of the periodic messages.

Many modifications and other embodiments of the invention set forth herein will come to mind the one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

C l a i m s

1. Method for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET), wherein the communication network comprises a multitude of communication nodes (4) and wherein the communication among said communication nodes (4) is performed by way of sending and receiving multicast broadcast messages, c h a r a c t e r i z e d i n that additional communication nodes - infrastructure elements (2) - are provided, said infrastructure elements (2) performing the steps of receiving messages from at least two of said communication nodes (4), generating a new message - aggregation message - into which information retrieved from the received messages is included, and broadcasting said generated aggregation message.

2. Method according to claim 1 , wherein only predefined information elements are extracted from received messages and integrated into said aggregation messages.

3. Method according to claim 2, wherein said predefined information elements include communication node's (4) status information, in particular the communication's node (4) ID and/or position and/or heading direction and/or speed.

4. Method according to claim 1 or 2, wherein said predefined information elements include a timestamp.

5. Method according to any of claims 1 to 4, wherein said infrastructure elements (2) select communication nodes (4) according to predefined selection rules, wherein only information originating from said selected nodes is included into said aggregation messages.

6. Method according to claim 5, wherein said predefined selection rules are based on the position of communication nodes (4) within a predefined geographical area.

7. Method according to any of claims 1 to 6, wherein said infrastructure elements (2) broadcast said aggregation messages only to predefined geographical areas.

8. Method according to any of claims 1 to 7, wherein said infrastructure elements (2) generate and broadcast said aggregation messages periodically at a certain frequency.

9. Method according to any of claims 1 to 8, wherein the frequency of generating and broadcasting said aggregation messages is chosen dependent on the frequencies of messages received by said infrastructure elements (2) from communication nodes (4).

10. Method according to any of claims 1 to 9, wherein the frequency of generating and broadcasting said aggregation messages is set equal to the highest frequency of all communication nodes (4) from which said infrastructure element (2) receives periodic messages.

11. Method according to any of claims 1 to 10, wherein the frequency of generating and broadcasting said aggregation messages is adaptively changed dependent on channel load.

12. Method according to any of claims 1 to 11 , wherein critical messages received from communications nodes (4) are immediately forwarded by said infrastructure elements (2).

13. Method according to any of claims 1 to 12, wherein the geographical position of communication nodes (4) are included into said aggregation messages in form of relative positions with respect to said infrastructure element (2).

14. Method according to any of claims 1 to 13, wherein said aggregation messages are assigned at the MAC (Media Access Control) layer a higher priority than messages from communication nodes (4).

15. Method according to any of claims 1 to 14, wherein said aggregation messages are assigned at the network layer a higher priority than messages from communication nodes (4).

16. System for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET), wherein the communication network comprises a multitude of communication nodes (4), wherein said communication nodes (4) include means for sending and receiving multicast broadcast messages in order to perform communication among each other, c h a r a c t e r i z e d i n that the communication network comprises additional communication nodes - infrastructure elements (2) -, said infrastructure elements (2) comprising reception means for receiving messages from at least two of said communication nodes (4), processing means for generating a new message - aggregation message - as well as for retrieving information from the received messages and including the retrieved information into said aggregation message, and broadcasting means for broadcasting said generated aggregation message.

17. System according to claim 16, wherein said infrastructure elements (2) are installed at places that allow for line-of-sight communication with communication nodes (4) positioned in different directions.

18. System according to claim 16 or 17, wherein said infrastructure elements (2) are disposed in a height above the ground which exceeds the height of communication nodes (4) in form of conventional vehicles.

19. System according to any of claims 16 to 18, wherein said infrastructure elements (2) are integrated into RSUs (Road-Side Units).

20. System according to any of claims 16 to 19, wherein said infrastructure elements (2) are collocated with other conventional infrastructure elements, like traffic light equipment.

21. System according to any of claims 16 to 20, wherein said communication nodes (4) include means for position determination.

22. System according to any of claims 16 to 21 , wherein said infrastructure elements (2) are configured to integrate only predefined information elements into said aggregation messages.

23. System according to any of claims 16 to 22, wherein said infrastructure elements (2) are configured to receive messages originating from a predefined geographical area.

24. System according to any of claims 16 to 23, wherein said infrastructure elements (2) are configured to forward said aggregation messages into a predefined geographical area.

25. System according to claim 23 or 24, wherein said predefined geographical areas are defined by way of an opening angle.

26. System according to any of claims 16 to 25, wherein said infrastructure elements (2) are configured to select communication nodes (4) according to predefined rules, wherein only information originating from said selected nodes are included into said aggregation messages.

27. System according to any of claims 16 to 26, wherein said infrastructure elements (2) include means for buffering information contained in messages received from communication nodes (4).

28. System according to any of claims 16 to 27, wherein said infrastructure elements (2) are configured to adaptively change the frequency of generating and broadcasting said aggregation messages dependent on channel load.