KR20090056072A - Emergency warning message broadcasting method using range-based relay node selecting method for vehicular ad-hoc network - Google Patents

Abstract

An emergency warning message broadcasting method using a range-based relay node is provided to minimize a message transmission time between terminals by assigning an optimum transmission delay time. An emergency warning message broadcasting method is comprised of the steps: relaying node candidate receives the EWM(Emergency Warning Message)(S2); it is determined whether the received message is the new EWM or not (S4); The location information of a primitive source node included in received EWM and location information of the previous relaying node are extracted, and the location information of the relaying node candidate is obtained through A GPS (S6); The distance between the primitive source node and the relaying node candidate and the distance between the relaying node and the relaying node candidate (S8); and It is determined whether the relaying node candidate is satisfied with the predetermined condition or not (S10).

Description

Emergency Warning Message Broadcasting Method Using Range-based Relay Node Selecting Method for Vehicular Ad-hoc Network

The present invention relates to an emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network. The present invention relates to an area for a vehicle ad hoc network that can reduce end-to-end message propagation delay time and network load regardless of node density. The present invention relates to an emergency alert message broadcasting method using a relay relay node selection algorithm.

VANET (Vehicular Ad-hoc Network, VANET), which is emerging as a core technology of Intelligent Transportation System (ITS) for intelligent vehicles, is based on mobile ad-hoc network (MANET) based on inter-vehicle wireless communication. It is a kind. VANET forms a temporary network through autonomous wireless communication between vehicles without the help of infrastructure such as base stations around the road. This results in smooth traffic flow control, driver safety and convenience, and improved fuel economy and performance.

FIG. 1 is a diagram schematically showing an example of a broadcasting protocol for a VANET according to the prior art, FIG. 2 is a diagram showing a message delivery latency of distance-based EWM broadcasting according to the prior art, and FIG. As an example of the distance-based EWM broadcast according to the prior art, a diagram showing a case where the vehicle density is high and the vehicle density is low.

1 to 3, the VANET is similar to the existing MANET in that autonomous network configuration between mobile nodes is possible. However, for fast and accurate inter-vehicle communication, various special situations that may occur in a vehicle environment, such as high-speed mobility of nodes (hereinafter, referred to simply as nodes in the present invention), a network topology, and a sudden change in node density, must be considered. These features lead to frequent network breaks, short link survival times, low packet arrival rates, and radio interference. Since the network protocols of MANET do not take these features into account, a new network protocol for VANET is required.

VANET's ultimate goal is to improve vehicle and driver safety. To do this, it is necessary to promptly and accurately inform the roadside of dangerous situations so that other vehicles within the hazardous area can cope with the danger in advance. In general, a broadcast method is widely used in such a manner that an emergency warning message (EWM) can be propagated to a plurality of vehicles. Broadcast is a method by which a transmitting node simultaneously delivers a packet to all nodes within a communication range. Flooding, a typical broadcast method, serves as both a transmitting node and a receiving node to propagate an EWM. Although this method is very simple, all nodes participate in packet transmission, resulting in drastic performance degradation due to increased bandwidth and transmission delay time.

VANET and MANET

The commonality between VANET and MANET is that networks are autonomously configured by mobile nodes without the aid of underlying network facilities such as base stations or access points (APs). However, as shown in Table 1, the existing MANET and VANET have different features in many ways. In general, nodes constituting MANET have low change of node density and mobility, and show irregular movement pattern. VANET, on the other hand, has a rapid change in node density, high travel speed of more than 100 km / h, and a relatively regular movement pattern along the road. In addition to these features, VANET not only changes network topology very quickly but also occurs frequently. Frequent changes in network topologies make shorter the life cycle of inter-node communication links. Since most nodes in MANET have limited power resources, the main focus is on the development of MAC and routing protocols to minimize the energy consumption of nodes. In contrast, energy consumption is not a problem because the nodes that make up a VANET use a high-capacity vehicle battery that is continuously recharged.

VANET

The ultimate goal of VANET is to improve driver safety through wireless communication between vehicles. As mentioned above, the broadcast protocol can be used as an effective way for an emergency vehicle to deliver EWM to a number of neighboring vehicles. In case of unicast or multicast method, it is difficult to use EWM delivery method for VANET because EWM receiving node is not known before EWM occurs. Broadcasting has been used primarily as a route discovery mechanism for unicast, and is typically flooded. Flooding is simple to implement, so the message reachability is excellent even in the mobile environment. On the other hand, since all nodes in the network participate in message delivery, the overhead due to message duplication, contention, and collision is very high. In particular, as the number of nodes in the network increases, the network load such as bandwidth and transmission delay time increases rapidly.

The time until the vehicle driver is aware of an emergency and the vehicle comes to a complete stop can be calculated as the sum of princess time and braking time. Gongju time refers to the time until the driver recognizes the emergency situation and starts to apply the brakes. Braking time is the time until the brakes are activated and the vehicle stops completely. According to statistics, Gongju time is 0.7sec ~ 1.5sec, which is the time that a vehicle traveling at 100km / h can travel 19.44m ~ 41.65m. Therefore, when the rear vehicle can receive the EWM including emergency information such as freezing of roads, falling rocks, fog, construction, and accidents from the front vehicle and can reduce princess time, it is necessary to cope with an emergency such as a chain collision. You can greatly improve your skills. However, in order to effectively perform EWM broadcasting through VANET, improvements in transmission latency, network load, and arrival rate must be preceded.

The existing EWM broadcasting protocol proposed for VANET can be classified as shown in FIG. 1. Broadcasting protocol can be divided into flooding, distance-based broadcast, table-based broadcast, and cluster-based broadcast according to node's role and ENode selection method in EWM delivery. Most of them acquire location information through GPS mounted on vehicles.

The flooding-based broadcast scheme proposed a method to reduce the network load by limiting the number of times the nodes participating in the EWM retransmission, but the overhead such as network load and transmission delay due to the characteristics of flooding could not be greatly improved. It was. Flooding-based broadcast protocols include DOLPHIN and I-IBA.

In the distance-based broadcast scheme, only one node of the EWM receiving node in the communication area transmits the EWM in order to reduce network load and transmission delay. At this time, the selection of the forwarding node is based on the distance from the message transmission node. In other words, the waiting time for EWM broadcasting for each forwarding node varies depending on the distance so that the edge node farthest from the message transmitting node can forward the EWM first. The distance-based broadcast technique is suitable for mobile environments because the density of nodes is high and the bandwidth required for EWM transmission is high and the end-to-end message propagation delay is relatively low. However, if the density of the node is low, the end-to-end message propagation delay is long and the message arrival due to network disconnection is inferior. Distance-based broadcast protocols include DDT, RBM, ODAM, and VCWC.

In the table-based broadcast scheme, each node maintains a location list of neighbor nodes, and a transmitting node selects a next EWM forwarding node. The neighbor node list information of each node is maintained by exchanging control messages using a query-response mechanism with neighboring nodes during periodic or EWM occurrence. Table-based broadcast schemes have better overhead, transmission delay, and arrival than flooding. However, if the network topology changes frequently as the mobility of nodes increases, not only the network load but also the end-to-end message delivery delay time increases. This is because, as the mobility of nodes increases, the bandwidth consumption increases as the period of control message exchange between nodes becomes shorter. Typical table-based broadcast protocols include TRADE, SDRP, OAPB, and UMB.

The cluster-based broadcast technique divides a road into clusters of a certain area, selects a cluster header among nodes in a cluster, and broadcasts an EWM through the header. The cluster-based broadcast technique shows relatively good performance when the network topology changes little. However, if the mobility of the node increases, the network topology changes frequently, so the control message for cluster member reconfiguration and cluster header selection increases. Cluster-based broadcast protocols include SIMCOMM and CBLR.

As described above, the broadcast protocol for VANET should solve problems such as transmission delay time and network load. In particular, the broadcast protocol for VANET's EWM transmission needs to be able to quickly notify surrounding vehicles of road hazards. Therefore, minimizing the end-to-end message delivery delay may be important.

 Area Based Relay Node Selection Algorithm

As described above, flooding, table-based broadcast techniques, and cluster-based broadcast techniques cause performance degradation such as network load and end-to-end message delivery delay depending on network topology and node density. On the other hand, the distance-based broadcasting protocol has a problem that the end-to-end message delivery delay time increases because it is difficult to select an efficient edge node when the node density is low.

In the existing distance-based broadcasting protocol, the waiting time for EWM delivery of each node is determined according to the distance from the transmitting node. As shown in FIG. 2, when the nodes v1, v2, and v3 are located as far as D1, D2, and D3 from the EWM transmitting node, each node has a message delivery waiting time inversely proportional to the distance of the EWM transmitting node. That is, the nearest node v1 which EWM from the sending node and have a wait time of the longest t _3, has the wait time for the farthest v3 shortest t _1. Therefore, the waiting time RWT _i for delivering the EWM according to the distance from the EWM transmitting node of each node can be expressed as Equation (1).

Where d is the distance from the EWM transmitting node, RWT _max represents the maximum propagation waiting time, and R is the transmission distance of the EWM transmitting node.

The node receiving the EWM calculates the message delivery waiting time according to the distance for message re-delivery, and only the node whose waiting time expires first broadcasts the message to the nodes in the transmission area. Since the waiting time becomes shorter as the distance increases, the border node farthest in the transmission area of the node broadcasting the EWM transmits the EWM first. At this time, if a node that has already received the EWM receives a duplicate message, the broadcast storm problem is solved by discarding the received EWM message and entering the standby state. However, this method has a problem in that the waiting time of the message is determined according to the distance from the transmitting node, so that the optimal waiting time is not achieved when the node is not located at the edge of the EWM transmitting node.

3 shows an EWM retransmission process through an edge node in the distance-based EWM broadcasting protocol. Each node in the network may serve as one of an original sender node, a relay node, and a relay node candidate. In FIG. 3, an S node that initially makes and broadcasts an EWM becomes a raw transport node, and N1, N2, N3, N4, and N5 nodes that deliver the EWM to other nodes become relay nodes. In Figure 3, the shaded portion represents the new broadcasting area of the relay node, and the nodes located within the shaded area become relay node candidates for EWM delivery. When the vehicle density is high, as shown in Fig. 3A, since there are a large number of relay node candidates in the communication area of each relay node, the probability that the relay candidate node is located at the edge of the communication area increases. Therefore, the EWM propagation delay time can be minimized because it can have an optimized message propagation latency. However, consider a case where the vehicle density is low on the road as shown in FIG. 3B. As shown in the figure, N2 becomes the next relay node of N1 and N3 is determined to be the next relay node of N2. However, since N2 and N3 are not actually located at the edge of the communication area of the EWM transmission node, the EWM propagation latency becomes that long. Thus, the end-to-end message delivery delay time at which the EWM is delivered from the original transmitting node to the last node in the broadcast range is increased.

An object of the present invention is to improve the conventional problems as described above, and to propose an area-based relay node selection algorithm for a vehicle ad hoc network that can reduce end-to-end message propagation delay time and network load regardless of node density. The present invention provides an emergency warning message broadcasting method.

According to a preferred embodiment of the present invention for achieving the above object, in the emergency alert message broadcasting method using the area-based relay node selection algorithm for the vehicle ad hoc network of the present invention, the relay node candidate receives the EWM, A first step of determining whether the received message is a new EWM; A second step of extracting location information of a source transmitting node and location information of a previous relay node included in the received EWM and obtaining location information of the relay node candidate through GPS; Calculating a distance d _{S ,} C between the original transmitting node S and the relay node candidate C and a distance d _{R , C} between the relay node R and the relay node candidate C ; A fourth step of determining whether the relay node candidate C satisfies d _{S , C} ≦ d _{S , D} ; If the relay node candidate is within EWM broadcasting range, determining a EWM propagation latency; And a sixth step of re-delivering the EWM by replacing the position of the previous relay node included in the received EWM message with the position of the relay node candidate when the EWM delivery waiting time expires.

As described above, according to the emergency warning message broadcasting method using the area-based relay node selection algorithm for the vehicle ad hoc network according to the present invention, the area-based relay node selection algorithm is a relay node for transmitting an emergency warning message to the communication area; Even if it is not located at the edge of, it is possible to minimize the end-to-end message delivery delay time by providing an optimal delivery wait time. In addition, since there is no need to exchange control messages for broadcasting emergency alert messages, there is an effect of having a low network load. The proposed algorithm has the effect of reducing the end-to-end message propagation delay even in VANET environment with low node density and short transmission distance.

Hereinafter, an emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a diagram schematically illustrating an area-based relay node selection algorithm according to the present invention, and FIG. 5 is an EWM used in an emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network according to the present invention. 6 is a flowchart illustrating an EWM delivery process of a relay node candidate in an emergency alert message broadcasting method using a region-based relay node selection algorithm for a vehicle ad hoc network according to the present invention, and FIG. In the emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network, the distance between nodes is shown schematically.

4 to 7, the present invention provides a new broadcasting scheme for quickly delivering EWM messages to rear vehicles.

The area-based relay node selection algorithm of the present invention is a method of limiting the number of nodes participating in EWM broadcasting in order to reduce network load and message delivery delay time. The broadcasting protocol using the area-based relay node selection algorithm is based on the location of the vehicle, and delays end-to-end message delivery by selecting only the node with the best waiting time among nodes in the transmission area of the EWM transmission node and delivering the EWM. It can reduce time and network load. In addition, it has a stable performance even in a vehicle environment where the topology changes frequently.

The area-based relay node selection algorithm proposed in the present invention ensures that each node has a minimum propagation latency based on the distance from the EWM transmitting node even if the node is not located at the edge of the communication area. As shown in FIG. 4, when there are relay node candidates of v1, v2, and v3 at D1, D2, and D3 distances from the EWM transmitting node, the maximum propagation latency that each relay node candidate can have is determined by the distance from the EWM transmitting node. Inversely proportional times t ₃ , t ₂ , t ₁ . Each candidate selects a random time τ ₁ , τ ₂ , τ ₃ within the maximum propagation waiting time it can have and uses it as its message propagation waiting time. Thus, the farther the node is from the EWM transmitting node, the greater the probability of having a shorter message propagation time, and a shorter message propagation time, even if the node is not located at the edge of the communication area. In addition, even a node close to the EWM transmitting node may have a short message delivery time. Through the region-based relay node selection algorithm, the message delivery latency RWT _i of each relay node candidate may be expressed as Equation 2.

Where ST _max is the maximum message delivery latency of the relay node candidate.

If all nodes within the range of broadcasting message delivery are v _i , relay nodes r _i , and communication node neighbor nodes of relay nodes n _i , each of these sets V, R, N can be represented by Equation 3 as follows. have.

The EWM propagation delay time T _{s , d} until the original transmitting node broadcasts the first EWM until all nodes in the network receive the EWM can be expressed by Equation 4.

t _com ( ri ) is the calculation time taken for the relay node r _i to process the protocol after receiving the EWM, and t _rwt ( ri ) is the wait time for the EWM delivery of the relay node ri. t _c (ri) is the medium access delay time until the EWM is transmitted from the MAC layer, and the number of neighbor nodes ( E ( ri ) ) and any backoff time ( E ( ri ) ) simultaneously transmitting the EWM in the communication area of the relay node r _i . Δt). Therefore, in case of flooding, there is no t _rwt , but all nodes in the transmission area become relay nodes, so when transmitting EWM at the same time, t _c may increase rapidly due to an increase in message collision and retransmission. On the other hand, the distance-based relay node selection method can minimize the medium access delay ( t _c ) instead of adding EWM propagation waiting time ( t _rwt ) because only one node is determined as a relay node in the communication area. .

Figure 5 shows the message format of the EWM used in the present invention. The EWM message is 250 bytes long and consists of four items: the location of the original sender node, the location of the previous relay node, the scope of delivery of the EWM message, and the forwarded data.

Figure 6 shows the process until the relay node candidate receives the EWM and re-deliver the message. After the relay node candidate receives the EWM (S2), the relay node candidate determines whether the received message is a new EWM (S4), and discards the received EWM if it is already received (S5). Subsequently, the position information of the original transmission node and the position information of the previous relay node included in the received EWM are extracted, and the position information of the relay node candidate itself is obtained through GPS (S6). And calculates a transmission source node S and the distance between the candidate relay node C d _S, and _C, the distance between the relay node and the relay node R candidate C _{R d, C} as shown in Figure 7 (S8). At this time, the relay node candidate C determines whether d _{S , C} ≤ d _{S , D} is satisfied (S10). If the relay node candidate C is out of the EWM brocasting range, the relay node candidate C discards the received EWM and does not attempt to transfer the EWM. If the relay node candidate is within the EWM broadcasting range, the EWM propagation waiting time is determined according to Equation 2 (S12). When the EWM delivery waiting time expires (S14), the position of the previous relay node included in the received EWM message is changed to the position of the relay node candidate itself to re-deliver the EWM (S16). In this way, the zone-based relay node selection algorithm can minimize message waiting time even if the node is away from the edge of the transmission area of the EWM transmitting node. have.

On the other hand, although not shown, the node for the ad hoc network according to the present invention (that is, the vehicle) is an EWM message of the EWM message format of the format as shown in FIG. A communication interface module for performing data transmission and reception with other neighbor nodes and a GPS module for recognizing its location, and an area-based relay node selection algorithm (program) and other operating programs used in the present invention are stored. Controls the operating program storage unit and the device as a whole, but controls to perform all processes of EWM reception and message re-delivery through the area-based relay node selection algorithm, and outputs a control signal for managing the EWM message of the data storage unit. It comprises a central control unit.

       1 is a diagram schematically showing an example of a broadcasting protocol for a VANET according to the prior art.

2 is a diagram illustrating a message delivery waiting time of distance-based EWM broadcasting according to the prior art.

3 illustrates an example of a case where the vehicle density is high and the vehicle density is low as an example of the distance-based EWM broadcast according to the prior art.

4 is a diagram schematically illustrating an area-based relay node selection algorithm according to the present invention.

5 is a diagram illustrating a message format of an EWM used in an emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network according to the present invention.

6 is a flowchart illustrating an EWM delivery process of a relay node candidate in an emergency alert message broadcasting method using an area-based relay node selection algorithm for a vehicle ad hoc network according to the present invention.

7 is a diagram showing the distance between nodes in the emergency alert message broadcasting method using the area-based relay node selection algorithm for the vehicle ad hoc network according to the present invention.

Claims (3)

In the emergency alert message broadcasting method using a region-based relay node selection algorithm for a vehicle ad hoc network in which vehicles are defined as nodes, A first step of the relay node candidate receiving the EWM and determining whether the received message is a new EWM; A second step of extracting location information of a source transmitting node and location information of a previous relay node included in the received EWM and obtaining location information of the relay node candidate through GPS; Calculating a distance d _{S ,} C between the original transmitting node S and the relay node candidate C and a distance d _{R , C} between the relay node R and the relay node candidate C ; A fourth step of determining whether the relay node candidate C satisfies d _{S , C} ≦ d _{S , D} ; If the relay node candidate is within EWM broadcasting range, determining a EWM propagation latency; And a sixth step of re-delivering the EWM by replacing the position of the previous relay node included in the received EWM message with the position of the relay node candidate when the EWM delivery waiting time expires. 2. The method of claim 1, wherein the EWM waiting time of the fifth step is determined according to the following equation: Emergency warning message broadcasting method using the area-based relay node selection algorithm for the vehicle ad hoc network. [Equation 2]

Where ST _max is the maximum message delivery waiting time of the relay node candidate. The EWM message format of claim 1, wherein the EWM message has a length of 250 bytes and consists of four items: the location of the original transmitting node, the location of the previous relay node, the delivery range of the EWM message, and the forwarding data. A method of broadcasting emergency alert messages using area-based relay node selection algorithm for vehicle ad hoc network.

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