JP2013048421A - Method for information dissemination in communication network, communication node and communication method thereof, and communication network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET).SOLUTION: A communication network 1 comprises a plurality of communication nodes N which are aware of the respective geographical position, and the dissemination process is initiated by one of the nodes, an originator node O, by sending a unicast message that includes information to be disseminated to a specific node, a first forwarder node F1, within a relevant area RA in which the information is to be disseminated. Other nodes C1, C2, and C3 in the relevant area RA, which receive the message sent by the originator node O to the first forwarder node F1, elect a forwarder node, respectively, and perform a unicast retransmission of the message to the elected forwarder node on the basis of a timer-based contention process.

Description

  The present invention relates to an information distribution method in a communication network, preferably a vehicular ad hoc network (VANET). Here, the communication network has a plurality of communication nodes that are aware of their geographical location, and the distribution process involves the relevant area in which information is to be distributed from one of those nodes (the originating node). It starts by sending a unicast message containing the information to be delivered to a specific node (first forwarding node) within.

  Information distribution in mobile communication networks is an important issue, especially in vehicle communication networks such as VANET (vehicular ad hoc network), the trust to deliver messages to all vehicles located within a geographical area. A strategy that can be done is necessary. This is especially true for safety information messages related to dangerous events such as traffic accidents and ice formation.

  The simplest strategy for information distribution is the so-called flooding mechanism. Flooding means that information to be delivered is broadcast from a certain node, each node receiving the information broadcasts it again, and so forth. However, flooding causes large overhead and multiple packet collisions, which is known as the “broadcast storm problem”. There are proposals to solve this problem, but the delay in receiving information to be delivered has not been addressed adequately. However, particularly in VANET, safety-related information may be important, so a short delay is required.

  In the case of vehicle movement, there is PBR (Position-Based Routing) as another more advanced method particularly applied to the main road environment. The PBR uses the geographical location of the communication node to determine in which direction the message should be forwarded. For this purpose, the conventional PBR protocol uses beacon messages to allow each node to notify all neighboring nodes of its address and geographical location via wireless broadcast. When a node receives such a beacon message from an adjacent node, the node stores its address and position in its adjacent node table. When a node should transfer a packet, the node uses the table to determine an adjacent node that is a transfer destination for the packet to go to the final destination. Typically, this determination is based on a geometric heuristic by selecting neighboring nodes that minimize the residual distance to the destination. This process is known as greedy forwarding. Location-based routing is a fairly fast mechanism, but due to its unicast, point-to-point nature, it has drawbacks with respect to, for example, fading effects and robustness against packet loss due to packet collisions. So far, PBR is only suitable for a limited range due to the severe propagation conditions and the possibility of high channel loads in the vehicle environment.

  In addition, contention-based forwarding (referred to as CBF) has been proposed to perform unicast packet forwarding. Unlike PBR, CBF does not require transmission of beacon messages. Instead, the node broadcasts data packets received by all nodes within its communication range. Of the receiving nodes, the actual forwarding node is selected by a distributed timer based contention process. According to this process, the optimal node forwards the packet, and forwarding by all other receiving nodes is suppressed. In the general two-dimensional case with random waypoint mobility, CBF has been shown to perform better than PBR. The superiority of CBF performance is most apparent when mobility is high.

  However, it turns out that CBF is disadvantageous because of the delay entering the delivery process by a timer-based contention mechanism. Especially for trunk roads, communication nodes move at high speeds, and the delivery of life-related safety information is extremely important, so CBF is not an appropriate solution.

  Accordingly, an object of the present invention is to minimize propagation delay and significantly improve robustness against uncertainty by using an easy-to-implement mechanism in the information distribution method in the communication network as described above. Improvement and further development.

  According to the invention, the above object is achieved by a method according to claim 1. As described in claim 1, the method includes a method in which other nodes in a related area that have received a message transmitted from an originating node to a first forwarding node each elect a forwarding node and enter a timer-based contention process. Based on this, unicast retransmission of a message to a selected forwarding node is performed.

  As first recognized by the present invention, a pure PBR mechanism for information delivery does not meet the requirements needed for special situations such as life-threatening safety applications. It is further recognized that the disadvantages of PBR are caused by the purely unicast nature of this procedure. Unicast means that the message is sent over the broadcast medium with a specific destination address in the header. In some situations and configurations, this can cause excessive packet collisions. Therefore, according to the present invention, the node that receives the message transmitted from the originating node to the first forwarding node does not discard the message. In fact, each of these nodes selects a suitable forwarding node and retransmits the message to the chosen forwarding node based on a timer-based contention process. Note that these forwarding nodes may be the same as or different from the first forwarding node selected by the originating node.

  The combination of unicast location-based routing and contention-based forwarding ensures highly robust information delivery against uncertainties such as collision and propagation phenomena. The method according to the invention provides redundancy such that messages that are not correctly transmitted from the originating node to the first forwarding node are not lost and are retransmitted by the appropriate neighboring nodes.

  The method according to the invention is ideal for applications in high mobility situations with severe propagation conditions and high channel loads. However, as will be apparent to those skilled in the art, the present invention is not limited to such applications. In fact, the method according to the present invention is applicable to any communication network as described above where reliable and efficient information distribution is important.

  Advantageously, the relevant area where information is to be distributed is specified by the originating node according to the type of information to be distributed. In general, the originating node attempting to deliver a message is aware of the relevant situation and can therefore specify a relevant area where the information delivered can be important. For example, it is assumed that the transmission node detects a traffic accident on a main road with multiple lanes on one side. In this case, the related area can be designated by the calling node as an area extending from the accident site in a direction opposite to the traveling direction by a length of, for example, 500 to 1000 meters. In the case of a single lane local road, the relevant area can be designated as an area extending from the accident site in both directions of the road.

  Advantageously, the relevant area is included in the message sent by the originating node. This allows all nodes involved in the distribution process to be notified about the relevant area and take this information into account.

  In another advantageous aspect, the originating node specifies at least one information propagation direction based on the relevant area. In the above example relating to traffic accidents, the information propagation direction is optimally corresponding to the extended part of the road in one or both directions of travel. In the case of an intersection, the information propagation direction may correspond to the extended portion of the branching path. When the related area is basically circular, the transmitting node can specify a total of four information propagation directions, each divided by 90 °, for example.

  The information propagation direction can be used as a basis for the originating node to select as the first forwarding node a node that has a high (preferably highest) positive progress towards the propagation direction. Because of this election process, the originating node can specify a forwarding area and only nodes within this forwarding area can be included in the forwarding node election process. The transfer area may be limited to a range showing a predetermined message reception probability. The size of the transfer area may be reduced as the message relevance increases. In any case, the specific SINR (signal to interference noise ratio) and transmission power of the participating nodes may be taken into account.

  As a preferred embodiment, the first forwarding node also designates a forwarding area after receiving the message, and designates the node having the highest or at least a high positive progress toward the propagation direction in the forwarding area as the second forwarding node. Elected as. Thereafter, the first forwarding node sends a message to the second forwarding node, and so on. This message transfer process can be repeated until the end of the relevant area is reached. Note that this forwarding scheme does not include any additional delay at any hop. Advantageously, message retransmission based on a timer-based contention process is performed after each message transfer process to the next transfer node. That is, each time a message is transferred from one forwarding node to the next using the unicast location-based forwarding method, each node that receives this message selects its own forwarding node and uses a timer-based contention. Resend the message to each forwarding node based on the process.

  With respect to the node being aware of its geographical location, the communication node preferably has means for determining its current location. For example, in VANET, energy consumption and miniaturization are not important features, so the node may be equipped with a navigation system such as a GPS system.

  Also, the communication node can be provided with updated information regarding the geographic location of neighboring nodes. For this purpose, beacon messages periodically transmitted by the communication node in connection with other safety mechanisms can be used. This suppresses additional overhead that hinders the wireless medium (radio broadcast). With pre-transmission of status messages, each node informs all its neighbors (ie, nodes within a single hop transmission range) of its address and geographic location via wireless broadcast. Each node includes, for example, an adjacent node table in which this information is updated. The beacon transmission frequency may be adapted to the degree of mobility in the network. The status message may include additional information regarding parameters such as speed and direction of movement of each node.

  Advantageously, all communication nodes operate in promiscuous mode. As a result, all messages, including unicast messages, are received by all nodes within the communication range of the message transmission node as if they were transmitted in the broadcast mode. As a result, the maximum number of nodes can participate in the contention process.

  In a preferred embodiment, the contention process is performed as follows.

  Each node that receives a message sent by the originating node or any forwarding node can start a timer. For each node, a contention period that is inversely proportional to the distance the node is moving forward in the propagation direction is set for the message transmission node. That is, the greater the distance between the node and each forwarding node, the shorter the contention period. As soon as the end of the contention period of the node is reached, the node can retransmit the message in broadcast mode to the next selected forwarding node. In this way, not only is redundancy achieved, but at the same time, the node with the longest distance advanced in the propagation direction will retransmit the message first. This keeps the delay introduced by the contention process to a minimum.

  In order to stop the contention process, a maximum number of retransmissions can be set for each node. In this regard, each node can run a counter that increases each time the node receives a message. The contention process can be interrupted when the counter of one of the nodes involved in the contention process reaches the maximum number of retransmissions. The value of the maximum number of retransmissions can be specified by the transmission node according to the type of information to be distributed. For traffic applications (generally non-critical), setting this maximum value to 1, for example, causes only one additional node to resend the message in addition to each forwarding node. The more sensitive the application is, the higher the maximum value can be selected. For example, in the case of a safety application, the maximum value may be set to 3 or a larger value.

  As an additional or alternative parameter, the size of the transfer area may be taken into account when specifying the maximum number of retransmissions. In general, the larger the size of the transfer area, the higher the value of the maximum number of retransmissions. As a result, a decrease in the message reception probability due to an increase in the transfer area can be compensated by making the contention process redundant.

  In the case of network division within a related area, there may be a case where information to be distributed does not completely reach the related area. However, it can be said that it is a design matter whether, for example, a temporary danger should be notified to a node in a related area. If the network is partitioned and the information is “valid” for a relatively long period of time, a node that does not receive a retransmission from the propagation direction stores that information and forwards it when a new neighboring node is detected Good.

  There are various possibilities for implementing the invention in an advantageous manner. To this end, reference is made to the claims subordinate to claim 1, while referring to the following description of preferred embodiments of the invention, illustrated by the drawings. In describing preferred embodiments of the present invention with reference to the drawings, preferred general embodiments and variations thereof in accordance with the teachings of the present invention will be described.

It is a schematic diagram of embodiment which applied the information delivery method in the communication network by this invention.

  Further details will be described with reference to the drawings. FIG. 1 schematically shows a part of the communication network 1. In the specific embodiment shown, the communication network 1 is a vehicle ad hoc network (VANET) and includes a plurality of vehicles that act as communication nodes N of the communication network 1. In this specification, the terms vehicle and node are used as synonyms in the context of this example. Nodes N support wireless technology and can exchange information with each other by radio broadcast. Specifically, FIG. 1 shows a situation of a main road having roadways 2 and 3 in which two operation directions are separated from each other by a guardrail 4.

  The vehicle O detects a danger on the road. For example, the vehicle O encounters an accident or detects the formation of rain ice. After detecting the dangerous event, the vehicle O immediately starts an information distribution process to notify the other vehicle N. For this purpose, the vehicle O (hereinafter referred to as the calling node O) designates a relevant area (RA). A related area is a geographical area where information to be delivered by the originating node O may be relevant to other nodes N. For example, in the case of rain / ice detection, there is a very high possibility that rain / ice is also present on the roadway in the opposite direction. Therefore, it is assumed that the related area extends from the transmission node O in both directions. In the embodiment shown in FIG. 1, the originating node O has encountered an accident. Since this information is only important for the following vehicle (because the direction of travel is separated by the guardrail 4), the relevant area extends only from the originating node O in the direction opposite to the direction of travel. The length of the related area may be set according to the average speed of the communication node N. In the case of a highway, this length can be set in the range of 500 to 2000 meters.

  In the following description, it is assumed that all the nodes N are aware of the positions of the surrounding nodes N by transmitting periodic status messages (beacons) including position, speed, direction, and the like. It is also assumed that transmissions by any node N span the entire width of the road and all nodes N are set to promiscuous mode. Promiscuous mode means that each node N, in principle, receives all messages sent by any other node within its communication range.

  In the next step after designating the relevant area where the information is to be delivered, the originating node O generates a message containing the information to be delivered. In general, the information to be distributed includes the type of danger detected, its location, and a time stamp. Next, the calling node O designates a forwarding area FA (forwarding area). The transfer area FA is a kind of robust range with a sufficiently high probability of receiving a message, which may cause interference with other nodes and wireless cards necessary to correctly decode the transmitted signal. It is determined in consideration of the specific SINR (signal to interference noise ratio) defined. As a result, the transfer area is smaller than the deterministic / ideal communication range CR (communication range). This improves the reliability and sufficiency of the delivery process. Actually, the size of the transfer area FA may be determined according to the traffic volume, average speed, transmission power of the transmission node O, importance of the application, and the like.

  Rapid distribution of information is performed by a unicast location-based scheme. This method selects a known node having the highest (or at least higher) positive progress in the information propagation direction in the transfer area FA. The selected node is called the first forwarding node F1, to which the message is forwarded by the originating node N. This mechanism is repeated as long as there are enough Node Ns with full connectivity until the relevant area is fully covered. That is, the first forwarding node F1 designates a new forwarding area, and forwards the message to the second forwarding node F2 having the highest (or at least higher) positive progress in the information propagation direction within the area. For clarity, the second forwarding node F2 and subsequent forwarding nodes Fn are not shown in FIG. Unlike contention schemes where there is an additional delay at each hop, this type of transfer is very fast.

  Due to the fading phenomenon and the possibility of collision (collision) that exist in the vehicle environment, the reliability of the delivery method is improved by retransmitting the message by broadcast. The retransmission mechanism uses the contention period to improve reliability. After all the nodes C1, C2, C3 located in the forwarding area FA have received the delivered message (not just the message designated to forward the message in the previous unicast location-based forwarding scheme), Start a timer-based contention period. In order to improve cooperation between nodes, the contention area can be designated as a circle centered on the node and having the same radius as the transfer area FA. The node contention period can be set to be inversely proportional to the distance traveled in the propagation direction relative to the transmitting node. That is, the closer the node is to each forwarding node F1, F2,..., Fn, the shorter the contention period. In the example shown in FIG. 1, the contention period of the node C1 is shorter than the contention period of the node C2, and the contention period of the node C2 is shorter than the contention period of the node C3. The node that has reached the end point of the contention period retransmits the message using the address of the forwarding node selected by that node as the destination address. In the example shown in FIG. 1, the node C1 may select the node P as a forwarding node. This is because this node has the highest positive progress toward the propagation direction as seen from node C1.

  In order to control the repetition and superposition of transmission to the medium, a node receiving a message from a node located within its robust range stops its contention process if it is running. In order to improve reliability, a maximum number of retransmissions may be set for each node. In that case, the contention process is resumed after each (delivered message) receive or send event until a predetermined maximum value is reached.

  To summarize, a specific example of the procedure is as follows.

  1. A vehicle (source node) detects a threat to safety and selects a relevant area for distribution.

  2. The originating node selects the “next forwarding node”, that is, the node having the highest geographical progress in the delivery direction within the forwarding area from its neighbor table.

3. The originating node sends a broadcast message that includes:
-Related area for distribution-Your location-ID of "next forwarding node"

4). a. The “next forwarding node” immediately forwards the message to the new “next forwarding node”.
b. All other message receiving nodes in the "forwarding area" initiate a contention period that is inversely proportional to the distance traveled.

5. a. When the contention period ends,
Send a message with the ID of “next forwarding node”
• Resume contention (up to a specific maximum number of times).
b. If a message is received a number of times equal to a certain maximum value,
・ Stop contention.

  Based on the above description and accompanying drawings, those skilled in the art will be able to conceive of many variations and other embodiments of the present invention. Accordingly, it is to be understood that the invention is not limited to the specific embodiments disclosed, and that variations and other embodiments are included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive sense only and are not intended to be limiting.

Claims (24)

In definitive information distributing method in a communication network, said communication network (1) has a plurality of communication nodes to be aware of the geographical location of the self (N),
Is one originating node of said plurality of nodes (O) is, to the first transfer node information is a specific node associated area (RA) to be delivered (F1), the information to be distributed It sends a unicast message containing,
The originating node (O) of the first transfer node from another node (C1, C2, C3) in said associated area (RA) receiving the message sent to the (F1) is, in each relevant area Selecting a forwarding node that is a specific node, and performing unicast retransmission of the message to the elected forwarding node based on a timer-based contention process;
An information distribution method in a communication network.   The method according to claim 1, characterized in that the relevant area (RA) is specified by the originating node (O) according to the type of information to be distributed.   The method according to claim 1 or 2, characterized in that the associated area (RA) is included in the message transmitted by the originating node (O).   The method according to any one of claims 1 to 3, characterized in that the originating node (O) specifies at least one information propagation direction based on the associated area (RA).   The origination node (O) designates a forwarding area (FA), and a node having a positive progress that is highest or at least high in the forwarding direction in the forwarding area (FA) is a first forwarding node. 5. The method according to claim 1, wherein the method is selected as (F1).   After the first forwarding node (F1) receives the message, the first forwarding node (F1) designates a forwarding area, and within the forwarding area, a node having the highest or at least a positive progress toward the propagation direction is designated as the first forwarding node (F1). 6. A method according to claim 5, characterized in that it is elected as two forwarding nodes.   The method according to claim 6, characterized in that the message transfer process is repeated until the end of the relevant area (RA) is reached.   8. The method of claim 7, wherein retransmission of the message based on a timer-based contention process is performed after each message forwarding process to the next forwarding node.   9. Method according to any one of claims 1 to 8, characterized in that the communication node (N) comprises means for determining its geographical location.   10. Method according to any one of the preceding claims, characterized in that the communication node (N) is provided with updated information regarding the geographical location of neighboring nodes.   11. Method according to any one of the preceding claims, characterized in that the communication node (N) sends periodic status messages.   The method according to claim 11, characterized in that the status message includes information on parameters such as speed, direction of movement, etc. of each communication node (N).   The method according to any one of claims 1 to 12, characterized in that the communication node (N) operates in promiscuous mode.   A contention period is set for each communication node (C1, C2, C3) that receives the message transmitted by the originating node (O) or any forwarding node (F1), and the contention period is: 14. A method according to any one of the preceding claims, characterized in that it is inversely proportional to the forward distance of the nodes (C1, C2, C3) in the propagation direction with respect to the sending node (O, F1) of the message.   Each communication node (C1, C2, C3) that receives the message transmitted by the originating node (O) or any forwarding node (F1) starts a timer after receiving the message. 15. A method according to any one of claims 1 to 14.   16. Method according to claim 14 or 15, characterized in that each communication node (C1, C2, C3) retransmits the message in broadcast mode as soon as it reaches the end of its contention period.   17. A method according to any one of the preceding claims, characterized in that each communication node (N) operates a counter that increases each time the node (N) receives the message.   18. The contention process is interrupted when a counter of one of the communication nodes (C1, C2, C3) involved in the contention process reaches a predetermined maximum value. The method described.   The value of the maximum number of retransmissions is specified by the originating node (O) according to the type of information to be distributed and / or according to the size of the forwarding area (FA). Item 19. The method according to Item 18.   20. The method according to claim 18 or 19, wherein the value of the maximum number of retransmissions is set to 1 for a traffic application and set to a value of 3 or more for a safety application.   21. A method as claimed in any preceding claim, wherein the communication network is a vehicular ad hoc network (VANET).   A communication node in a communication network (1) comprising a plurality of communication nodes (N) that recognizes their geographical location,
  If it is the originating node (O), it sends a unicast message containing the information to be delivered to the first forwarding node (F1) which is a specific node in the relevant area (RA) where the information is to be delivered,
  If the message transmitted from the originating node (O) to the first forwarding node (F1) is received, a forwarding node that is a specific node in the related area is selected and based on a timer-based contention process. Unicast retransmission of the message to the selected forwarding node,
  A communication node characterized by that.   A communication method of a communication node in a communication network (1) composed of a plurality of communication nodes (N) that recognizes its own geographical position,
  If the communication node is the originating node (O), a unicast message containing information to be distributed to the first forwarding node (F1), which is a specific node in the relevant area (RA) where the information is to be distributed Send
  When the communication node receives the message transmitted from the originating node (O) to the first forwarding node (F1), it selects a forwarding node that is a specific node in the related area, and performs timer-based contention. Performing a unicast retransmission of the message to a selected forwarding node based on a process;
  A communication method for a communication node.   A communication network (1) comprising a plurality of communication nodes (N) that recognizes their geographical location,
  The originating node (O), which is one of the plurality of nodes, should be delivered from the first forwarding node (F1), which is a specific node in the relevant area (RA) where information is to be delivered Send a unicast message with information,
  Other nodes (C1, C2, C3) in the related area (RA) that received the message transmitted from the originating node (O) to the first forwarding node (F1) Selecting a forwarding node that is a specific node, and performing unicast retransmission of the message to the elected forwarding node based on a timer-based contention process;
  A communication network characterized by that.

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