CN110493749A - A kind of car networking greedy routing method based on track search - Google Patents

Abstract

The present invention relates to the field of intelligent transportation, in particular to a greedy routing method for Internet of Vehicles based on path exploration, which includes planning multiple routing paths as alternative paths according to a digital map when a source vehicle responds to a data request, and the source vehicle sends a probe to the destination vehicle package determines the transmission delay of each alternative path, and calculates the connectivity of each road segment according to the road segment connectivity model; the destination vehicle comprehensively considers the data transmission delay and the connectivity of the road segment, selects the optimal routing path, and The path replies to the source vehicle with a reply packet; the source vehicle writes the sequence ID of the road section passed by the selected routing path into the header of the data packet, and then the vehicles in the path use the greedy algorithm to forward the data packet to the destination vehicle hop by hop; this method proposes multiple Jump greedy search mechanism to avoid data being forwarded to vehicles trapped in routing holes. On the other hand, this method proposes a variable greedy search radius mechanism to reduce the occurrence of link interruptions.

Description

A Greedy Routing Method for Internet of Vehicles Based on Path Exploration

technical field

The invention relates to the field of intelligent transportation, in particular to a greedy routing method for Internet of Vehicles based on path exploration.

Background technique

Under the demand of building and developing new cities, the intelligent transportation system, as an important project of the smart city, provides a certain direction for the redevelopment and re-layout of the urban environment. The intelligent transportation system will determine the development trend of future transportation. It will effectively and integrate more mature data communication transmission concepts, traffic management methods, wireless sensor networks, vehicle control theory and new generation computer network technology into the entire ground traffic management system. The establishment of a real-time, accurate and efficient comprehensive transportation management system that plays a role in a large area and in all directions, and cross-field cooperation is becoming the trend of the entire industry.

Vehicle Ad-hoc Networks (VANET) is an emerging technology that integrates a new generation of wireless networks into vehicles, aiming to enable communication between vehicles to improve road safety and provide essential services. As a special mobile ad hoc network, VANET plays an important role in the development of intelligent transportation and smart city. The VANET mainly includes two types of applications, security warning and entertainment services. Safety warning messages, such as collision warnings and front vehicle speed change warnings, are transmitted in the form of broadcasts, which have high requirements for time delay. Entertainment services, such as file sharing and video requests for specific road sections, are implemented through multi-hop unicast routing, which has certain delay tolerance characteristics. The method proposed by the invention is a multi-hop unicast routing algorithm applied to inter-vehicle entertainment services.

For the routing algorithms of the Internet of Vehicles that have been proposed so far, they can be classified from different perspectives. According to different addressing methods, the algorithms can be divided into topology-based routing algorithms, geographical location-based routing algorithms and map-based routing algorithms. In the multi-hop unicast routing of the Internet of Vehicles, routing algorithms based on geographic location, such as Greedy Perimeter Stateless Routing (GPSR), etc., have the characteristics of low routing overhead and strong adaptability, and are very suitable for application In the highly dynamic Internet of Vehicles routing environment. However, routing protocols based on geographic location do not consider the particularity of urban scenes and the dynamics of road traffic. In the rapidly changing vehicle topology, it is easy to forward data packets to areas with routing holes and generate many redundant forwardings, resulting in relatively The problem of long data transmission delay and high packet loss rate.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the present invention proposes a greedy routing method for Internet of Vehicles based on path exploration, which specifically includes the following steps:

S1: The vehicle listens to the data requests of other vehicles; the vehicle that responds to the data request is called the source vehicle, and the vehicle that initiates the data request is called the destination vehicle;

S2: When the source vehicle responds to the data request, the source vehicle searches the local routing table to see if there is a route section sequence to the destination vehicle, if there is, go to S8, otherwise go to S3;

S3: Planning multiple routing paths according to the digital map as alternative paths;

S4: The source vehicle sends a detection packet to each alternative path;

S5: When the destination vehicle receives the detection packet, calculate the data transmission delay of each path according to the data information in the detection packet, and calculate the connectivity of each road section according to the road section connectivity model;

S6: Comprehensively consider the data transmission delay and the connectivity of the road section, select the optimal routing path, and reply a reply packet to the source vehicle according to the selected routing path;

S7: Determine whether the source vehicle has received a reply message within t time of sending the detection packet, if received, go to S8; if not, return to step S4;

S8: The source vehicle writes the sequence ID of the road segment passed by the selected routing path into the header of the data packet, and the source vehicle uses a greedy algorithm to forward the data packet to the destination vehicle according to the routing path.

Further, considering the data transmission delay and the connectivity of the road section comprehensively, the selected routing path includes:

Among them, M(I _S , _{ID )} is the set of alternative paths from the source vehicle to the destination vehicle; r is the optimal path in the set of alternative paths for the vehicle; G(r) is the comprehensive consideration of the data transmission delay and the connectivity of road sections The objective function of ; D(r) is the path delay; P _C (e _i ) is the connectivity probability of the link on the path; n is the number of links on the path.

Further, the source vehicle uses the greedy algorithm to forward the data packet to the destination vehicle according to the routing path including:

S81. Formulate beacon messages exchanged between vehicles; whether the current vehicle has a data packet to be forwarded, and if so, whether there is a target vehicle in the neighbor list of the current vehicle, and if so, directly send the data packet to the target vehicle;

S82, if there is no target vehicle in the neighbor table of the current vehicle, then judge whether there is a vehicle at the intersection in the neighbor table of the current vehicle, if so, proceed to step S83; otherwise proceed to step S84;

S83. Judging whether there is a vehicle on the next section of the path in the neighbor table of the current vehicle, if there is, forwarding to the vehicle on the next path, otherwise forwarding to the vehicle at the intersection to complete the data forwarding;

S84. Determine the greedy search radius according to the current road maximum speed limit and forwarding vehicle speed, and calculate the distance between the neighbor vehicle and the target vehicle according to the location information of the neighbor vehicle in the neighbor table;

S85. Arrange in ascending order according to the distance between the neighbor vehicle and the target vehicle, and filter the neighbor vehicles according to the arrangement;

S86. During the screening process, if the distance between the current vehicle and the neighbor vehicle is less than the search radius, send a search packet to the neighbor vehicle to determine whether the neighbor vehicle has a next hop;

S87. If the neighbor vehicle has a next hop, the current vehicle sends the data packet to the neighbor vehicle;

S88. If no neighboring vehicle meeting the screening condition is found after screening all the neighboring vehicles, wait for t1 time, and return to S84 to recalculate the greedy search radius.

In the common geographical location-based routing protocol, the present invention selects the locally optimal forwarding vehicle for each forwarding, which may cause the problem of routing holes. Vehicles; on the other hand, in the Internet of Vehicles, because of the high-speed mobility of vehicles, link interruptions are prone to occur when using geographical location-based routing protocols to transmit data. This method proposes a variable greedy search radius mechanism to reduce the chain Occurrence of road interruption.

Description of drawings

Fig. 1 is a flow chart of the source vehicle exploring a routing path and sending a data packet before sending a data packet in the present invention;

Fig. 2 is a schematic diagram of unstable connectivity in the link connectivity model;

Fig. 3 is a schematic diagram of stable connectivity in the link connectivity model;

Fig. 4 is the flow chart of a forwarding vehicle forwarding data packets in the determined routing path;

Figure 5 is a schematic diagram of greedy search and forwarding;

Fig. 6 is a schematic diagram of variable greedy search.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The present invention proposes a greedy routing method for the Internet of Vehicles based on path exploration, as shown in Figure 1, specifically comprising the following steps:

S1: The vehicle listens to the data requests of other vehicles; the vehicle that responds to the data request is called the source vehicle, and the vehicle that initiates the data request is called the destination vehicle;

S2: When the source vehicle receives the data request response, the source vehicle searches the local routing table to see if there is a route section sequence to the destination vehicle, if there is, go to S8, otherwise go to S3;

S3: Planning multiple routing paths according to the digital map as alternative paths;

S4: The source vehicle sends a detection packet to each alternative path;

S5: When the destination vehicle receives the detection packet, calculate the data transmission delay of each path according to the data information in the detection packet, and calculate the connectivity of each road section according to the road section connectivity model;

S6: Comprehensively consider the data transmission delay and the connectivity of the road section, select the optimal routing path, and reply a reply packet to the source vehicle according to the selected routing path;

S7: Judging whether the source vehicle has received a reply message within t time of sending the detection packet, if received, then go to S8; if not received, then return to step S4; preferably, t=2s;

S8: The source vehicle writes the sequence ID of the road segment passed by the selected routing path into the header of the data packet, and the source vehicle uses a greedy algorithm to forward the data packet to the destination vehicle according to the routing path.

When the source vehicle cannot directly send data packets to the destination vehicle, it is necessary to plan the routing path from the source vehicle to the destination vehicle according to the digital map as an alternative route set. The alternative route set includes finding the path from the source vehicle to the destination vehicle based on the digital map The path with the fewest intersections is taken as the shortest path, and the path from the source vehicle to the destination vehicle has twice the number of intersections in the shortest path.

In the present invention, three types of packets need to be sent, including the detection packet sent by the source vehicle to the destination vehicle, the reply packet sent by the destination vehicle to the source vehicle after receiving the detection packet, and the data packet sent by the source vehicle after receiving the reply packet. The exploration packet sent by the source vehicle to the destination vehicle is shown in Table 1, including 32 bytes, of which the first to second bytes are the type of the exploration packet; the third to fifth bytes are the number of alternative paths, namely The number of exploration packets sent by the source vehicle; the 6th to 8th bytes are the routing path number explored by the exploration packet; the 9th to 16th bytes are the ID sequence of the road section that the exploration packet will pass through, including the location of the source vehicle and the destination vehicle road section; the 17th to 24th bytes record the sending time of the exploration packet; the 25th to 32nd bytes record the number of hops that the exploration packet is forwarded from the source vehicle to the destination vehicle; and the IP address of the destination vehicle, the ID number of the destination vehicle , the IP address of the source vehicle and the ID number of the source vehicle are written in the header of the reply packet.

Table 1 Format of detection packet

The type indicates the type of the packet. When the value of the type is 1, it means a detection packet; when the value is 2, it means a reply packet; when the value is 3, it means a data packet;

The number of routes is the number of routes recorded in the set of alternative routes of the source vehicle, that is, the number of routing routes planned according to the digital map, and also the number of detection packets sent;

The path number is the number of the routing path explored by the record discovery package, that is, each candidate path has a path number;

The ID sequence of the road section to be passed is the ID sequence of the road section to be passed by the specified route search package, including the road section where the source vehicle and the destination vehicle are located;

The sending time of the exploration packet is to record the sending time of the exploration packet, so as to calculate the transmission delay of the path after the exploration packet reaches the destination vehicle;

The multi-hop forwarding hop count counter records the hop count of the discovery packet being forwarded from the source vehicle to the destination vehicle.

The link connectivity model divides the connectivity of vehicles in the two-way lane into stable connection and unstable connection. If there is only a vehicle in the opposite lane within the communication range of the vehicle carrying data, it is an unstable connection, otherwise it is stable. Connection; in the two-way lane road section, the road section connectivity model divides the connectivity of vehicles in the process of driving in the two-way lane into stable connection and unstable connection. The following two situations are used to calculate the connection probability of the road section as shown in Figure 2-3 The road in the same direction refers to the road that is consistent with the driving direction of the preceding vehicle, that is, road 1 in FIGS.

Case 1: Unstable connectivity

As shown in Figure 2, the direction of probe packet transmission is from i to j, vehicle ni is driving on road 1 and needs to transmit a probe packet, and there is no communicable vehicle on road 1 within the communication range R of vehicle ni, at this time In an unstable connection, it is necessary to use a vehicle on the reverse road 2 (for example, vehicle nj) to transmit packets.

If K represents a random variable of the number of vehicles on a section of road, K follows a Poisson distribution, and the distribution law is:

Among them, P(K=k) represents the probability that there are k vehicles in the range of R, ρ(t) is the density of vehicles on the road section at time t, n(t) is the number of vehicles on the road section at time t, and L is two The length of the road segment between intersections.

The distance between any two consecutive vehicles obeys the exponential distribution, and the probability that the distance between vehicle ni and vehicle ni+1 on road 1 is greater than the maximum communication range R of vehicle ni is:

Among them, ρ ₁ (t) is the vehicle density on road 1 at time t; i is the number of vehicles with distance greater than R in road 1.

When this happens, the probability that vehicle ni needs to forward packets with the help of vehicles on road 2 is:

Among them, ρ ₂ (t) is the vehicle density of road 2 at time t, Indicates the rounding down, and x _i represents the distance between the ith vehicle without the same direction vehicle within the communication range and the nearest same direction vehicle in the direction of data packet transmission.

Let the variable M represent the number of disconnected links on road 1, then there are m disconnected links, and the probability that each disconnected link is connected through road 2 is:

Among them, n ₁ (t) represents the number of vehicles on road 1 at time t, and n ₁ (t)-1 is the number of links on road 1, then the probability of m disconnected links is:

In the case that there is at least one disconnected link on road 1, the connection probability of the road segment at time t, that is, the connection probability of unstable connection is expressed as:

Case 2: Stable connectivity

As shown in Figure 3, within the communication range of the vehicle, at least one vehicle on road 1 provides a relay for data forwarding, that is, the distance X between vehicle ni+1 and vehicle ni+2 is smaller than the communicable range R of vehicle ni+1 , then it is a stable connection, that is, the connection probability of stable connection is expressed as:

To sum up the above two situations, the connectivity rate of the vehicle at time t is expressed as:

Now the transmission delay of each routing path has been known according to the detection packet, that is, the destination vehicle calculates the data transmission delay of the path and the connectivity of the road section through the time when the detection packet is sent and the time when the destination vehicle receives the detection packet. The optimal routing path is selected by combining the connectivity of the road section and the transmission delay of the routing path, expressed as:

Among them, _M (I _S , ID ) is the set of alternative paths from source vehicle _IS to destination vehicle ID; r is the optimal path in the set of vehicle alternative paths; _G (r) is the comprehensive consideration of data transmission delay and the objective function of the connectivity of the link; D(r) is the path delay; P _C (e _i ) is the connectivity probability of the link on the path; n is the number of links on the path.

Table 2 Format of reply packet

The destination vehicle needs to inform the source vehicle of the selected routing path through a reply packet. After receiving the detection packet, the destination vehicle replies to the source vehicle. The format of the reply packet is shown in Table 2, including 32 bytes, of which the first to second bytes It is the type of the discovery packet; the 3rd to 5th bytes are the number of the selected path; the 6th to 8th bytes are the number of the received path; the 9th to 16th bytes are the ID sequence of the road section that the reply packet will pass through, including The road section where the source vehicle and the destination vehicle are located, the ID sequence of the road section to be passed in the reply packet is the ID sequence of the selected optimal routing path to pass through the road section; the 17th to 24th bytes record the transmission delay of each path; the 25th byte ~32 bytes record the number of hops that the reply packet is forwarded from the destination vehicle to the source vehicle; and write the information of the IP address of the destination vehicle, the ID number of the destination vehicle, the IP address of the source vehicle, and the ID number of the source vehicle in the reply The header of the package.

Wherein, the number of the selected path records the number of the selected path, that is, the optimal routing path selected based on the transmission delay of each routing path and the connectivity of the road section;

Received route number is when the destination vehicle is ready to send a reply message to the source vehicle, write the numbers of all route exploration packets received from the same source vehicle into this field;

The transmission delay of each path records the transmission delay corresponding to each path, and the format is (path number, transmission delay).

As shown in Figure 4, the source vehicle uses the greedy algorithm to forward the data packet to the destination vehicle according to the routing path, including:

S81. Formulate beacon messages exchanged between vehicles; whether the current vehicle has a data packet to be forwarded, and if so, whether there is a target vehicle in the neighbor list of the current vehicle, and if so, directly send the data packet to the target vehicle;

S82, if there is no target vehicle in the neighbor table of the current vehicle, then judge whether there is a vehicle at the intersection in the neighbor table of the current vehicle, if so, proceed to step S83; otherwise proceed to step S84;

S83. Judging whether there is a vehicle on the next section of the path in the neighbor table of the current vehicle, if there is, forwarding to the vehicle on the next path, otherwise forwarding to the vehicle at the intersection to complete the data forwarding;

S84. Determine the greedy search radius according to the current road maximum speed limit and forwarding vehicle speed, and calculate the distance between the neighbor vehicle and the target vehicle according to the location information of the neighbor vehicle in the neighbor table;

S85. Arrange in ascending order according to the distance between the neighbor vehicle and the target vehicle, and filter the neighbor vehicles according to the arrangement;

S86. During the screening process, if the distance between the current vehicle and the neighbor vehicle is less than the search radius, send a search packet to the neighbor vehicle to determine whether the neighbor vehicle has a next hop;

S87. If the neighbor vehicle has a next hop, the current vehicle sends the data packet to the neighbor vehicle;

S88. If no neighbor vehicle meeting the screening conditions is found after screening all neighbor vehicles, wait for t1 time, return to S84 and recalculate the greedy search radius; preferably, the present invention selects the waiting time as t1=1s;

Wherein, the vehicle within the vehicle search range is referred to as the vehicle's neighbor vehicle.

The beacon message is a message periodically broadcast between vehicles. In the present invention, the format of the beacon message is as shown in Table 3, including the vehicle speed, the vehicle direction, the ID number of the road section where the vehicle is located, and the vehicle is located at the intersection. The judgment flag bit and the position coordinates of the vehicle; and write the IP address of the vehicle and the ID number of the vehicle in the header of the beacon message.

Table 3 Vehicle beacon message format

Wherein, the driving direction of the vehicle is represented as an intersection number pair, (the intersection number that the vehicle leaves, the intersection number that the vehicle moves towards);

The ID of the road section where the vehicle is located: it can be obtained by combining the digital map and GPS positioning on the vehicle. If the vehicle is at an intersection, the ID of the road section where the vehicle is located is the number of the intersection where the vehicle is located;

The judgment sign position of the vehicle at the intersection. If it is at the intersection, the sign position is 1, otherwise it is 0; when the vehicle is driving on the road section, due to the restrictions of the buildings on both sides of the city, the vehicle cannot receive the beacon message of the vehicle on other road sections , when the number of link IDs in the beacon message received by the vehicle is greater than or equal to 3, it means that the vehicle is at an intersection, and this field of the beacon message is set to 1;

The location coordinates of the vehicle are obtained according to the digital map and GPS positioning, and may be longitude and latitude coordinates.

As shown in Figure 5, according to the greedy routing algorithm of GPSR, within the communication range of node S, because the distance between node C and destination node D is closer than the distance between node B and destination node D, C will be selected as The next hop forwards the node, but there is no node within the communication range of C that is closer to D than C and D, so the GPSR protocol will use the right-hand forwarding rule to forward the data to B, and then forwarded by B, But this increases the number of forwarding hops and time delay; so in the present invention, the node writes whether there is a next-hop vehicle as a field into the beacon information, and the node S first selects the node C according to the distance, but through C's beacon information knows that C has no next hop, so check the second nearest node B, and node B has a next hop, so send the data to B.

The present invention redefines the communication distance between the two vehicles in order to reduce the probability that the vehicle leaves the communication range of the sending vehicle when transmitting data. As shown in Figure 6, Rmax is the maximum communication range of S. According to the greedy algorithm, S must be within Rmax Find the next hop vehicle within the range, but the present invention narrows the search range of S by formulating the search radius, so that S is not forwarded to E but forwarded to B with a smaller search range. The search radius of the present invention is expressed as:

Among them, R _i is the greedy search radius of the current vehicle i; V _max is the maximum speed of the vehicle on the road; V _i is the speed of the current vehicle i; t _rb is the time it takes for the next hop vehicle to receive the data after sending the data; M _b is the size of the data packet transmitted by the vehicle; r _b is the data packet transmission rate; x _b is the data transmission time between two vehicles, generally x _b → 0, which can be ignored.

For common geographic location-based routing protocols, local optimal forwarding vehicles are selected for each forwarding, which may cause routing holes. This method proposes a multi-hop greedy search mechanism to avoid data being forwarded to vehicles trapped in routing holes.

In the Internet of Vehicles, due to the high-speed mobility of vehicles, link interruptions are prone to occur when using geographic location-based routing protocols to transmit data. This method proposes a variable greedy search radius mechanism to reduce the occurrence of link interruptions .

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. A greedy routing method for Internet of vehicles based on path exploration is characterized by comprising the following steps:

s1: the vehicle monitors data requests of other vehicles; the vehicle responding to the data request is called a source vehicle, and the vehicle initiating the data request is called a target vehicle;

s2: when the source vehicle responds to the data request, the source vehicle searches whether a route road section sequence reaching the destination vehicle exists in the local route table, if so, the S8 is carried out, otherwise, the S3 is carried out;

s3: planning a plurality of routing paths according to the digital map to be used as alternative paths;

s4: the source vehicle sends a detection packet to each alternative path;

s5: when the target vehicle receives the detection packet, calculating the data transmission time delay of each path according to the data information in the detection packet, and calculating the connectivity of each road section according to the road section connectivity model;

s6: comprehensively considering data transmission delay and road section connectivity, selecting an optimal routing path, and replying a reply packet of a source vehicle according to the selected routing path;

s7: judging whether the source vehicle receives the reply message within t times of sending the detection packet, and if so, turning to S8; if not, returning to step S4;

s8: and the source vehicle writes the road section sequence ID passed by the selected routing path into the head of the data packet, and forwards the data packet to the destination vehicle according to the routing path by using a greedy algorithm.

2. The routing method of claim 1, wherein the planning of the plurality of routing paths according to the digital map as the alternative paths comprises finding a path from the source vehicle to the destination vehicle through the minimum intersection as the shortest path according to the digital map, and then taking a path with the intersection number less than or equal to twice the intersection number of the shortest path in the path from the source vehicle to the destination vehicle and the shortest path together as the alternative paths to form the alternative path set.

3. The routing method for the greedy routing in the internet of vehicles based on the path exploration, according to claim 1, is characterized in that a detection packet sent by a source vehicle to a destination vehicle and a reply packet replied by the destination vehicle to the source vehicle after receiving the detection packet both comprise 32 bytes, wherein the 1 st to 2 nd bytes are types of the exploration packet; the 3 rd to 5 th bytes are the number of the alternative paths, namely the number of the exploration packets sent by the source vehicle; the 6 th byte to the 8 th byte are routing path numbers explored by the exploration packet; the 9 th byte to the 16 th byte is an ID sequence of a road section to be passed by the exploration packet, and the ID sequence comprises the road section where the source vehicle and the target vehicle are located; recording the sending time of the exploration packet by 17 th to 24 th bytes; recording the hop number of the exploration packet forwarded from the source vehicle to the target vehicle by 25-32 bytes;

after receiving the detection packet, the destination vehicle replies a reply packet of the source vehicle, wherein the reply packet comprises 32 bytes, and the 1 st byte to the 2 nd byte is the type of the detection packet; the 3 rd to 5 th bytes are the serial numbers of the selected paths; the 6 th byte to the 8 th byte is a received path number; the 9 th byte to the 16 th byte is an ID sequence of a road section to be passed by the reply packet, and comprises the road section where the source vehicle and the destination vehicle are located; recording the transmission delay of each path by 17-24 bytes; and recording the hop number of the reply packet forwarded from the destination vehicle to the source vehicle by 25-32 bytes.

4. The routing method for greedy routing in internet of vehicles based on path exploration according to claim 1, wherein calculating connectivity of each road segment according to a road segment connectivity model comprises: the road section communication model divides the communication condition of the vehicles in the running process of the bidirectional lane into stable connection and unstable connection, if only vehicles exist on a reverse lane in the communication range of the vehicles carrying data, the connection is unstable, otherwise, the connection is stable; connectivity of road segmentsExpressed as:

wherein,representing connectivity of the road segment when the connectivity is unstable;indicating connectivity of the road segment when the connectivity is stable.

5. The routing method for greedy routing in internet of vehicles based on path exploration, according to claim 4, wherein connectivity of road segments during unstable connectivityTo representComprises the following steps:

wherein,representing the probability that there are m broken links, each broken link being connected by a vehicle traveling in reverse;representing the probability of m broken links in the road; m is the number of links disconnected at time t; n is₁(t) represents the number of vehicles on the same road at time t; n is₁(t) -1 represents the total number of links on the same-direction road at time t.

6. The routing method for greedy routing in internet of vehicles based on path exploration, according to claim 1, wherein connectivity of road segments during stable connectivityExpressed as:

where ρ is₁(t) vehicle density on road segment 1; r is the maximum communication radius between two vehicles; l is the length of the section between two intersections.

7. The routing method for greedy routing in internet of vehicles based on path exploration according to claim 1, wherein the selecting of the routing path comprehensively considers data transmission delay and connectivity of the road sections comprises:

wherein, M (I)_S,I_D) A source vehicle to destination vehicle alternative path set is obtained; r is the optimal path in the vehicle alternative path set; g (r) is an objective function comprehensively considering data transmission delay and connectivity of a road section; d (r) is the path delay; p_C(e_i) The connection probability of the road sections on the path; n is the number of segments on the path.

8. The routing method of claim 1, wherein forwarding the data packet to the destination vehicle according to the routing path by the source vehicle using a greedy algorithm comprises:

s81, making a beacon message exchanged between vehicles; whether the current vehicle has a data packet to be forwarded or not, if so, whether the current vehicle has a destination vehicle or not in a neighbor table of the current vehicle, and if so, directly sending the data packet to the destination vehicle;

s82, if the neighbor list of the current vehicle does not have the target vehicle, judging whether the neighbor list of the current vehicle has the vehicle at the intersection, if so, executing the step S83; otherwise, performing step S84;

s83, judging whether a vehicle of a next road section in the path exists in the neighbor list of the current vehicle, if so, forwarding the vehicle to the vehicle of the next path, otherwise, forwarding the vehicle to the vehicle at the intersection, and finishing data forwarding;

s84, determining a greedy search radius according to the highest speed limit and the forwarded vehicle speed of the current road, and calculating the distance between the neighbor vehicle and the target vehicle according to the position information of the neighbor vehicle in the neighbor table;

s85, arranging according to the distance between the neighbor vehicle and the target vehicle in an ascending order, and screening the neighbor vehicles according to the arrangement;

s86, in the screening process, if the distance between the current vehicle and the neighbor vehicle is less than the search radius, sending a search packet to the neighbor vehicle to determine whether the neighbor vehicle has the next hop;

s87, if the neighbor vehicle has the next hop, the current vehicle sends the data packet to the neighbor vehicle;

and S88, if all the screened neighbor vehicles do not find the neighbor vehicles meeting the screening condition, waiting for t1 moments, and returning to S84 to recalculate the greedy search radius.

9. The greedy routing method based on internet of vehicles for path exploration according to claim 8, wherein the beacon message exchanged between vehicles is vehicle information shared between vehicles on the same road section, and the beacon message comprises the IP address of the vehicle, the ID number of the vehicle, the driving direction of the vehicle, the ID number of the road section where the vehicle is located, the judgment mark position of the vehicle at the intersection, and the position coordinates of the vehicle, wherein the driving direction of the vehicle is an intersection number pair consisting of the intersection number from which the vehicle leaves and the intersection number to which the vehicle drives; the ID of the road section where the vehicle is located is obtained through a digital map on the vehicle and GPS positioning, and if the judgment zone bit of the vehicle located at the intersection is 1, the ID of the road section where the vehicle is located is the number of the intersection where the vehicle is located; and when the number of the road section IDs in the beacon message received by the vehicle is more than or equal to 3, determining that the vehicle is positioned at the intersection, and setting the judgment mark position of the vehicle positioned at the intersection as 1, otherwise, setting the judgment mark position as 0.

10. The routing method for greedy routing in internet of vehicles based on path exploration according to claim 8, wherein calculation of greedy search radius comprises:

wherein R is_iSearching the radius for the greedy of the current vehicle i; v_maxIs the maximum speed of the vehicle on the road; v_iIs the speed of the current vehicle i; t is t_rbFor the next hop after sending dataThe time it takes for the vehicle to receive the data; m_bThe size of the data packet transmitted for the vehicle; r is_bSending a rate for the data packet; x is the number of_bIs the data transfer time between two vehicles.