A relay selection method and system for a vehicle-to-vehicle multi-hop cooperative communication system

Abstract

This invention discloses a relay selection method and system for vehicle-to-vehicle multi-hop cooperative communication systems. It constructs a stochastic geometric model of the vehicle network and determines the location and size of candidate relay areas based on a no-relay probability threshold and the communication service quality of relay links. All candidate relay vehicles within the relay selection area are acquired to obtain a candidate relay set. A relay vehicle is selected from the candidate relay vehicles according to a relay selection strategy that guarantees the service quality between the source node and the relay vehicle. The source node sends messages to both the relay vehicle and the destination node. After decoding the message, the relay vehicle forwards it to the next relay vehicle or destination node based on its relative position to the destination node. When the distance between the relay vehicle and the destination node exceeds the communication range, the currently selected relay node is used as the source node after one hop, and this process is repeated until the message is forwarded to the destination node. This invention effectively reduces the number of relay hops, making communication more reliable and reducing latency.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically relating to a relay selection method and system for vehicle-to-vehicle multi-hop cooperative communication systems. Background Technology

[0002] With societal development, the number of vehicles on the road is constantly increasing, and their level of intelligence is also rising, leading to the development of vehicle-to-everything (V2X) systems. V2X systems enable information exchange between vehicles, between vehicles and roads, and between vehicles and people through mutual communication. They are a core component of future intelligent transportation systems, effectively improving road safety, alleviating traffic congestion, and promoting the realization of autonomous driving.

[0003] While the development of the Internet of Vehicles (IoV) brings greater convenience, it also faces many challenges. Firstly, vehicles are faster and change location more frequently than traditional mobile terminals, leading to frequent and rapid changes in the IoV network topology. Secondly, the complex road environment, with numerous vehicles and other obstacles, exacerbates path loss and multipath effects in IoV communication, impacting communication quality. Furthermore, the high speed of vehicles means that communication interruptions or errors can have serious consequences, posing significant challenges to IoV communication.

[0004] The 3rd Generation Partnership Project (3GPP) proposed a cellular vehicle-to-everything (C-V2X) communication solution. C-V2X, in addition to direct communication, supports cooperative communication between vehicles with the assistance of existing infrastructure. That is, when the direct link channel conditions between vehicles are poor, cellular base stations or other vehicles can act as relays, thereby improving communication reliability. However, vehicles, as relay carriers, are highly mobile, but current relay selection schemes lack analysis of the vehicle's random location and do not impose spatial restrictions on relay vehicles, easily leading to situations where the relay vehicle is too close or too far from the source node. If the relay vehicle is too close, the progress per hop will be small, increasing the number of relay hops, resulting in reduced efficiency and increased latency; if the relay vehicle is too far, the source node-relay vehicle link quality will be poor, leading to an increased probability of interruption and more retransmissions.

[0005] There is currently no effective solution to the above problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a relay selection method and system for vehicle-to-vehicle multi-hop cooperative communication systems, which addresses the shortcomings of the prior art and solves the technical problems of high relay hop count, large delay, and low cooperative communication efficiency when the direct link channel conditions of vehicles are poor.

[0007] The present invention adopts the following technical solution:

[0008] A relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system includes the following steps:

[0009] S1. Construct a stochastic geometric model of the vehicle network based on the distribution characteristics of vehicles. In the stochastic geometric model, the source node and the destination node are any nodes in the network. The source node communicates with the destination node in a multi-hop relay manner.

[0010] S2. Based on the random geometric model obtained in step S1, determine the location and size of the candidate relay area according to the no-relay probability threshold and the communication service quality of the relay link;

[0011] S3. Obtain all candidate relay vehicles within the relay selection area to obtain a candidate relay set. If the set is empty, expand the candidate relay radius and repeat step S2. Select a relay vehicle from the candidate relay vehicles according to the relay selection strategy that guarantees the service quality of the source node-relay vehicle.

[0012] S4. The source node sends messages to the relay vehicle and the destination node obtained in step S3, respectively. After the relay vehicle decodes the message, it forwards the message to the next relay vehicle or the destination node according to its relative position with the destination node.

[0013] S5. When the distance between the relay vehicle and the destination node is greater than the communication range, after one hop, the currently selected relay node is used as the source node, and steps S2 to S4 are repeated until the message is forwarded to the destination node.

[0014] Specifically, in step S1, the road system is modeled as having a strength of Poisson process Each straight line Distance from the origin to the foot of the perpendicular to the corresponding line and angle The decisions are independent of each other; based on the process of road formation of a Poisson line, vehicles on the road are modeled as points of density on the Poisson line. One-dimensional Poisson point process The vehicles on each line are independently and identically distributed, and their positions constitute a Poisson-Cox process. .

[0015] Specifically, in step S2, a signal propagation model between the source node and the relay vehicle is constructed. Nakagami-m fading is used to characterize small-scale fading. Different fading environments are simulated by changing the value of m. When m=1, Nakagami-m fading is Rayleigh fading, and the small-scale fading coefficient is... Obtain the parameter as The exponential distribution is used to calculate the mean interference power of the vehicle-to-everything (V2X) system, and then the mean noise power is calculated to obtain the result at a distance of... At this point, the lower bound of the success probability of communication between the source node and the candidate relay vehicle is given if it is within the vehicle's communication range. Within the specified range, the success rate of inter-vehicle communication is greater than the set success probability threshold. ,Right now Therefore, the maximum range that meets the conditions is defined as the vehicle's communication range. .

[0016] Furthermore, the size and location of the candidate relay area are as follows:

[0017]

[0018] in, The vehicle's communication range. The radius of the candidate relay region. This indicates the location of the candidate relay area center.

[0019] Furthermore, the vehicle's communication range for:

[0020]

[0021] in, The signal-to-interference-plus-noise ratio (SIN / N) threshold required for decoding. For vehicle density, For road density, A threshold for the probability of successful communication within the communication range. This represents the probability that a vehicle is active at a given moment and is using the same frequency band as the receiver. From the origin to the road distance, For vehicles perpendicular to the road distance, This is the path loss coefficient. The standard deviation of the noise. This refers to the transmitter's transmission power.

[0022] Specifically, in step S3, using the candidate relay area selected in step S2, all candidate relay vehicles within the relay selection area are obtained, resulting in a candidate relay set. If the corresponding set is empty, the radius of the candidate relay area is expanded and a new candidate relay vehicle is selected; then, the expected signal-to-interference-plus-noise ratio of the signal received by the vehicle is used as a performance indicator of the source node-relay link to select a relay vehicle.

[0023] Furthermore, the vehicle with the highest expected signal-to-interference-plus-noise ratio is selected from the candidate relay vehicle set as the relay. Forwarding a message, i.e.:

[0024]

[0025] in, This refers to the signal-to-interference-plus-noise ratio (SIR) of the signal received by the relay vehicle. Let be the signal-to-interference-plus-noise ratio (SIR) of the i-th vehicle in the candidate relay area.

[0026] Specifically, in step S4, the relay vehicle first decodes the message using a decode-forward method, and then forwards the message to the next relay vehicle or the destination node based on its relative position to the destination node. If the distance is less than the communication range obtained in step S2, the relay vehicle will proceed with the forwarding. If the signal is selected, the message is forwarded directly to the destination node, which then merges and decodes the signals using a selective merging method, ending the transmission; otherwise, the message is forwarded to the next relay.

[0027] Furthermore, the relay vehicle receives signals. Received signal from the destination node They are respectively:

[0028]

[0029]

[0030] in, The transmitter's transmission power, The channel's small-scale fading coefficient. The distance between the transmitter and the receiver. This is the path loss coefficient. and The variances are respectively Gaussian additive white noise.

[0031] Secondly, embodiments of the present invention provide a relay selection system for a vehicle-to-vehicle multi-hop cooperative communication system, comprising:

[0032] The module constructs a stochastic geometric model of the vehicle network based on the distribution characteristics of vehicles. In the stochastic geometric model, the source node and the destination node are any nodes in the network, and the source node communicates with the destination node in a multi-hop relay manner.

[0033] The location module, based on the random geometric model obtained from the construction module, determines the location and size of the candidate relay area according to the no-relay probability threshold and the communication service quality of the relay link;

[0034] The selection module retrieves all candidate relay vehicles within the relay selection area, resulting in a candidate relay set. If the set is empty, the radius of the candidate relays is expanded. The location module is then repeated to select a relay vehicle from the candidate relay vehicles based on the relay selection strategy that ensures the quality of service between the source node and the relay vehicle.

[0035] In the decoding module, the source node sends messages to the relay vehicle and the destination node obtained by the selection module, respectively. After the relay vehicle decodes the message, it forwards the message to the next relay vehicle or the destination node according to its relative position with the destination node.

[0036] The output module, after one hop, uses the currently selected relay node as the source node and repeats this process until the message is forwarded to the destination node.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] A relay selection method for vehicle-to-vehicle multi-hop cooperative communication systems is proposed. Based on the distribution characteristics of vehicles, vehicles are modeled as Poisson-Cox processes, accurately representing their unique dynamic topology. A candidate relay region is then defined, and vehicles are selected as relays within this region. The distribution of vehicles within this region is analyzed and derived. Selecting relays within a specific region allows for more flexible selection based on vehicle distribution, thereby improving the overall performance of the cooperative communication system. Furthermore, optimizing region parameters increases the probability of successful communication, maximizing the progress per hop and reducing the number of relay hops, effectively improving cooperative communication performance. Optimizing the size of the candidate relay region reduces the probability of no relay and decreases the number of retransmissions. Optimizing the location of the candidate relay region ensures that all candidate relay vehicles are within communication range, thus guaranteeing the quality of service. Based on the maximum average received power, the vehicle with the highest signal-to-interference-plus-noise ratio (SIR) among the candidate relay vehicles is selected as the relay vehicle, ensuring the channel condition from the source node to the relay vehicle and reducing the probability of relay vehicle decoding failure.

[0039] Furthermore, due to the high speed and frequent movement of vehicles, their positions change frequently, exhibiting significant randomness. However, vehicles always travel along roads, thus their spatial distribution exhibits certain regularities. The stochastic geometric model in step S1 of this invention uses line processes to represent road positions and point processes to represent vehicle positions, modeling vehicles as Poisson point processes on lines. This model, while using the randomness of Poisson point processes to represent the random movement of vehicles, effectively restricts vehicle positions to different straight lines, thus fully representing the randomness and regularity of vehicle spatial distribution and more accurately describing the spatial topology of the vehicle network. Moreover, the stochastic geometric model facilitates statistical analysis of random networks, thereby benefiting the analysis of vehicle network performance at the system level.

[0040] Furthermore, when the source node chooses to communicate with the destination node using cooperative transmission, we first define a candidate relay area based on the number and distribution characteristics of vehicles, and then select vehicles as relays within this area. In step S2, the radius of the candidate relay area is optimized and adjusted according to road density and vehicle density, thereby limiting the probability of no vehicles in the area, avoiding situations where no next-hop relay can be found, and reducing the number of retransmissions. Moreover, the communication range of vehicles is related to the level of interference in the vehicle network. As the number of vehicles increases, interference in the same frequency band intensifies, reducing the communication range of vehicles. We obtain the lower bound of the communication range of the source node based on the success probability and use this range as the farthest distance of the candidate relay area, ensuring that all candidate relay vehicles are within the communication range of the source node, thus guaranteeing the link service quality between the source node and the relay vehicle. Then, by restricting the center position and radius of the candidate relay area, we avoid situations where the relay vehicle is farther from the destination node than the source node. Therefore, selecting relay vehicles within the candidate relay area can ensure the quality of transmission service while making the message as close to the destination node as possible with each relay, thereby reducing the number of relay hops.

[0041] Furthermore, by optimizing the size of candidate relays, the probability of no vehicles within the candidate relay area can be kept within a set threshold, thereby reducing the number of retransmissions and avoiding situations where relays cannot be found. By adjusting the position of the candidate relay area, the location distribution of relay vehicles can be optimized, so that after each decoding and forwarding of signals, relay vehicles are closer to the destination node, thus improving the progress per hop and increasing communication efficiency.

[0042] Furthermore, by calculating the vehicle interference power, the communication range of the vehicles is obtained, ensuring that all vehicles within the candidate relay area are within the communication range. This guarantees the quality of communication service between the source node and the relay vehicles, thereby reducing the probability of relay vehicles failing to decode signals. Simultaneously, the communication range also determines whether subsequent relay vehicles forward messages to the destination node or seek new relay vehicles to continue forwarding.

[0043] Furthermore, based on the given candidate relay areas, relay vehicles are selected. Relay nodes forward data to the destination node via decoding and forwarding, avoiding noise accumulation. First, all vehicles within the candidate relay areas are considered as candidate relay vehicles. Then, the vehicle with the highest expected signal-to-interference-plus-noise ratio (SNR) is selected as the relay. This scheme maximizes the average success probability of link communication between the source node and the relay vehicle, reducing the probability of decoding errors and thus reducing the number of retransmissions by the relay vehicle. Under this scheme, when selecting relay vehicles, the path between the source node, relay, and destination node is comprehensively considered while ensuring communication service quality, effectively reducing the number of relay hops, thereby making communication more reliable and with lower latency.

[0044] Furthermore, based on the determination of candidate relay areas, all vehicles in the candidate relay areas constitute a candidate relay vehicle set. Within this set, the vehicle with the highest expected signal-to-interference-plus-noise ratio is selected as the relay vehicle to forward messages. This ensures that the average received power of the relay vehicle signal is maximized, thereby increasing the probability of the relay vehicle successfully decoding information.

[0045] Furthermore, when the destination node is within the communication range of the relay vehicle, the relay vehicle directly forwards the signal to the destination node, which can reduce the number of relay hops and ensure communication quality. However, when the relay vehicle is far from the destination node, using a single relay vehicle to forward the signal cannot guarantee the link quality. Therefore, when the distance between the relay vehicle and the destination node exceeds the communication range, the relay vehicle acts as the source node and searches for a new relay, thereby ensuring communication reliability.

[0046] Furthermore, the relay vehicle employs a decode-and-forward scheme. Information can only be successfully decoded and forwarded to subsequent nodes when the signal-to-interference-plus-noise ratio (SNR) of the received signal is greater than a threshold. Therefore, it is necessary to analyze the received signals of the relay vehicle. Simultaneously, the destination node uses selective merging to combine signals received from both the relay vehicle and the source node. Therefore, in addition to the signals forwarded by the relay vehicle, it is also necessary to analyze the signals sent by the source node and select the signal with the higher SNR for decoding.

[0047] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0048] In summary, this invention accurately characterizes the spatial distribution of vehicles by modeling them as Poisson-Cox processes, and analyzes and derives the spatial distribution of relay vehicles in specific areas. Selecting relays within candidate relay areas ensures communication quality throughout the overall cooperative communication transmission process. Optimizing the size of candidate relay areas avoids situations where there are no relays, reducing the number of retransmissions. By calculating and analyzing the communication range of vehicles and optimizing the location of candidate relay areas, the service quality of relay links is guaranteed, while maximizing the progress per hop, ensuring that each relay message forwarding is closer to the destination node, thus reducing the number of relay hops.

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0050] Figure 1 This is a system space model diagram of the present invention;

[0051] Figure 2 This is a schematic diagram of the candidate relay region of the present invention;

[0052] Figure 3This is a simulation diagram showing the success probability of cooperative communication under different schemes of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0055] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0056] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" relationship.

[0057] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0058] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0059] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0060] This invention provides a relay selection method for vehicle-to-vehicle multi-hop cooperative communication systems. By modeling and analyzing vehicle positions, the method optimizes the location and size of candidate relay regions based on the probability of no relay and the probability of success. Then, within the candidate relay regions, a relay vehicle is selected based on the signal-to-interference-plus-noise ratio (SINR). This scheme maximizes per-hop progress while ensuring communication service quality, ensuring that after each relay, the forwarded information is closer to the destination node, effectively reducing the number of relay hops and lowering latency. Simultaneously, it avoids situations where the relay vehicle is farther from the destination node, reducing backpropagation and improving communication efficiency.

[0061] This invention discloses a relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system, comprising the following steps:

[0062] S1. Based on the distribution characteristics of vehicles, construct a stochastic geometric model of the vehicle network, where the source node and the destination node can be any node in the network, and the source node communicates with the destination node in a multi-hop relay manner.

[0063] Considering that roads are typically straight and their layout is often irregular due to factors such as terrain and buildings, we simplify roads to straight lines on a plane and model the road system as having a strength of [missing value]. Poisson process Each straight line The distance from the origin to the foot of the perpendicular to the line and angle The decisions are independent of each other; based on the process of road formation of a Poisson line, vehicles on the road are modeled as points of density on the Poisson line. One-dimensional Poisson point process The vehicles on each line are independently and identically distributed, thus the positions of the vehicles constitute a Poisson-Cox process. This characterizes the randomness of vehicle movement and the regularity of only being able to travel on roads; in the vehicle-to-everything (V2X) network, the source node and destination node are arbitrary nodes in the network. Without loss of generality, it is assumed that the source node is located at the origin and the destination node is located at... The source node first sends the message to the destination node. If the destination node successfully decodes the message, the transmission ends. Otherwise, the source node communicates with the destination node using a multi-hop cooperative transmission method.

[0064] S2. Based on the stochastic geometric model of vehicle-to-everything (V2X) communication, determine the location and size of candidate relay areas according to the no-relay probability threshold and the communication service quality of relay links.

[0065] When the source node selects multi-hop cooperative communication, based on the vehicle random model established in step S1, a candidate relay area is first defined, and the next relay is selected within this area. To balance the progress of each hop with the quality of communication service, the candidate relay area is set as a circle with a center. Located on the line connecting the source node and the destination node, with a radius of circle To achieve better communication quality, optimize the candidate relay area. The parameters are set; the optimization goal is to maximize the progress per hop while ensuring the existence and quality of relay links, thereby reducing the number of relay hops; specifically as follows:

[0066] first, The optimization requirement is to ensure that the probability of no relay vehicle in the candidate relay area is less than the set threshold, so as to avoid the situation where there is no relay.

[0067] Secondly The selection of candidate relay vehicles requires that they are all within the communication range of the source node to ensure communication quality.

[0068] Finally, to avoid the relay vehicle's distance from the destination node being greater than the distance from the source node d to the destination node, let .

[0069] First, optimization is performed based on the probability of no relay vehicles in the candidate relay area. This avoids multiple retransmissions due to the inability to find a relay vehicle. Because of the randomness inherent in vehicle-to-everything (V2X) networks, when the source node requests a multi-hop relay, the number of vehicles within the candidate relay area is random, with a radius of [missing information]. Number of vehicles within the circular area The distribution is as follows:

[0070] (1)

[0071] in, Representing radius Laplace transform of the total length distribution of roads within a circle.

[0072] Since vehicles are constantly moving, it cannot be guaranteed that there will always be a candidate relay vehicle within a candidate relay area of ​​radius R. The probability that the number of candidate relay vehicles is 0 is:

[0073] (2)

[0074] Based on the set relay-free probability threshold To determine the radius of a candidate relay region, the following conditions must be met: In order to maximize the progress of each relay jump, The radius of the candidate relay region can then be obtained. .

[0075] In vehicle communication, communication distance and interference levels are key factors affecting communication performance. Therefore, in step S2, the center position of the candidate relay area is optimized based on the success probability of the relay link under different interference conditions. The selection of candidate relay vehicles ensures that all candidate relay vehicles are within the communication range of the source node, thereby guaranteeing the quality of communication service between the source node and the candidate relay vehicles.

[0076] In step S2, a signal propagation model between the source node and the relay vehicle is first constructed. Considering the general path loss model, in order to characterize the complex channel environment between vehicles, Nakagami-m fading is used to characterize small-scale fading. By changing the value of m, different fading environments can be simulated.

[0077] All vehicles have the same transmission power, and the signal-to-interference-plus-noise ratio (SIR) of the received signal is:

[0078] (3)

[0079] in, The transmitter's transmission power, The channel's small-scale fading coefficient. This represents the distance between the transmitter and the receiver. This is the path loss coefficient. This represents the total interference power at the receiver. This represents the probability that a vehicle is active at a given moment and is using the same frequency band as the receiver. The variance is The power of Gaussian additive white noise.

[0080] The probability of successful vehicle-to-vehicle communication is defined as the probability that the signal-to-interference-plus-noise ratio (SIR) of the signal received by the receiver is greater than a threshold:

[0081] (4)

[0082] When m=1, Nakagami-m fading is Rayleigh fading, and the small-scale fading coefficient is... Obtain the parameter as The exponential distribution of the above equation can be further transformed into:

[0083] (5)

[0084] Due to the function Since it is a convex function, using Jensen's inequality, we get:

[0085] (6)

[0086] With a fixed transmission power, interference is mainly related to the number of interference sources and the distance between the interference sources and the receiver, expressed as follows: Next, we calculate the mean value of the interference power of the vehicle-to-everything (V2X) system. According to Campbell's theorem:

[0087] (7)

[0088] Then calculate the mean of the noise power, since the noise has a variance of... Gaussian additive white noise, yielding:

[0089] (8)

[0090] Therefore, we obtain the distance At this point, the lower bound of the communication success probability between the source node and the candidate relay vehicle is:

[0091] (9)

[0092] If within a certain range Within the vehicle, the success rate of inter-vehicle communication was greater than the set success rate threshold. ,Right now Therefore, the maximum range that meets this condition is defined as the vehicle's communication range.

[0093] As can be seen from formula (9), the success rate of vehicle-to-vehicle communication mainly depends on the communication distance and the degree of interference. When the number of vehicles in the vehicle network system increases, the interference of the system will become more serious, which will reduce the vehicle communication range.

[0094] Based on the parameters of roads and vehicles in the vehicle-to-everything (V2X) system, the communication range of the vehicle is obtained. Solving for the problem, we get:

[0095] (10)

[0096] To ensure communication quality between the source node and the relay vehicle, the center of the candidate relay area cannot exceed [the specified radius]. ,Right now To ensure that after each relay hop, the relay vehicle gets closer to the destination node, Therefore, the size and location of the candidate relay region are obtained.

[0097] S3. Obtain all candidate relay vehicles within the relay selection area to obtain a candidate relay set. If the set is empty, expand the candidate relay radius and repeat step S2. Select a relay vehicle from the candidate relay vehicles according to the relay selection strategy that guarantees the service quality between the source node and the relay vehicle.

[0098] Using the candidate relay area selected in step S2, all candidate relay vehicles within the selected relay area are obtained, resulting in a candidate relay set. If the set is empty, the radius of the candidate relay area is expanded and a new candidate relay vehicle is selected; then the expected signal-to-interference-plus-noise ratio of the signal received by the vehicle is used as a performance indicator of the source node-relay link to select a relay vehicle.

[0099] During message forwarding, the signal-to-interference-plus-noise ratio (SIR) of a vehicle is expressed as:

[0100] (11)

[0101] Furthermore, the vehicle with the highest expected signal-to-interference-plus-noise ratio is selected from the candidate relay vehicle set as the relay. Forwarding a message, i.e.:

[0102] (12)

[0103] generally Since the relays are considered independent and identically distributed with the same mean, the power of the useful signal received by the receiver mainly depends on the path loss. Therefore, the candidate relay vehicle closest to the source node is selected from the set of candidate relay vehicles as the relay. This selection scheme does not require channel estimation and comparison of the advantages and disadvantages of each relay transmission channel, reducing complexity. Furthermore, the relay vehicle selected under this scheme has the highest signal-to-interference-plus-noise ratio (SNR), thus its expected interruption probability is the lowest.

[0104] S4. The source node sends messages to both the relay vehicle and the destination node. After decoding the message, the relay vehicle forwards the message to the next relay vehicle or the destination node according to its relative position to the destination node.

[0105] The source node sends messages to both the relay vehicle and the destination node determined in step S3. The received signals from the relay vehicle and the destination node are as follows:

[0106] (13)

[0107] (14)

[0108] in, The transmitter's transmission power, The channel's small-scale fading coefficients follow an independent, cyclically symmetric complex Gaussian distribution. This represents the distance between the transmitter and the receiver. This is the path loss coefficient. and The variance is Gaussian additive white noise.

[0109] Then, the relay vehicle first decodes the message using a decode-forward method, and then forwards the message to the next relay vehicle or the destination node according to its relative position to the destination node. If the distance is less than the student range obtained in step S2, the relay vehicle will proceed. If the signal is successfully merged, the message is forwarded directly to the destination node, which then merges and decodes the signals using a selective merging method, ending the transmission. Otherwise, the message is forwarded to the next relay.

[0110] S5. After the first hop is completed, the currently selected relay node is used as the source node. The next relay node is selected according to the above relay selection scheme to forward the message. S2 to S4 are repeated until the message is forwarded to the destination node.

[0111] In step S4, if the distance between the relay vehicle and the destination node is greater than the communication range, after one hop, the currently selected relay node is taken as the source node, and the next relay node is selected according to the above relay selection scheme to forward the message. S2 to S4 are repeated until the message is forwarded to the destination node.

[0112] In another embodiment of the present invention, a relay selection system for a vehicle-to-vehicle multi-hop cooperative communication system is provided. This system can be used to implement the above-mentioned relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system. Specifically, the relay selection system for a vehicle-to-vehicle multi-hop cooperative communication system includes a construction module, a location module, a selection module, a decoding module, and an output module.

[0113] The construction module builds a stochastic geometric model of the vehicle network based on the distribution characteristics of vehicles. In the stochastic geometric model, the source node and the destination node are any nodes in the network, and the source node communicates with the destination node in a multi-hop relay manner.

[0114] The location module, based on the random geometric model obtained from the construction module, determines the location and size of the candidate relay area according to the no-relay probability threshold and the communication service quality of the relay link;

[0115] The selection module retrieves all candidate relay vehicles within the relay selection area, resulting in a candidate relay set. If the set is empty, the radius of the candidate relays is expanded. The location module is then repeated to select a relay vehicle from the candidate relay vehicles based on the relay selection strategy that ensures the quality of service between the source node and the relay vehicle.

[0116] In the decoding module, the source node sends messages to the relay vehicle and the destination node obtained by the selection module, respectively. After the relay vehicle decodes the message, it forwards the message to the next relay vehicle or the destination node according to its relative position with the destination node.

[0117] The output module, after one hop, uses the currently selected relay node as the source node and repeats this process until the message is forwarded to the destination node.

[0118] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, the computer program including program instructions, and the processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to implement a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used for the operation of a relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system, including:

[0119] A stochastic geometric model of the vehicle-to-everything (V2X) network is constructed based on the distribution characteristics of vehicles. In this model, the source and destination nodes are arbitrary nodes in the network, and the source node communicates with the destination node via multi-hop relays. Based on the stochastic geometric model, the location and size of the candidate relay area are determined according to the no-relay probability threshold and the communication service quality of the relay link. All candidate relay vehicles within the relay selection area are obtained to form a candidate relay set. If the set is empty, the radius of the candidate relays is expanded. According to the relay selection strategy that ensures the service quality between the source node and the relay vehicle, a relay vehicle is selected from the candidate relay vehicles. The source node sends messages to both the relay vehicle and the destination node. After decoding the message, the relay vehicle forwards it to the next relay vehicle or the destination node based on its relative position to the destination node. When the distance between the relay vehicle and the destination node is greater than the communication range, the currently selected relay node is used as the source node after one hop, and this process is repeated until the message is forwarded to the destination node.

[0120] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory). This computer-readable storage medium is a memory device in a terminal device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and extended storage media supported by the terminal device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device.

[0121] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system in the above embodiments; one or more instructions in the computer-readable storage medium are loaded by the processor and executed as follows:

[0122] A stochastic geometric model of the vehicle-to-everything (V2X) network is constructed based on the distribution characteristics of vehicles. In this model, the source and destination nodes are arbitrary nodes in the network, and the source node communicates with the destination node via multi-hop relays. Based on the stochastic geometric model, the location and size of the candidate relay area are determined according to the no-relay probability threshold and the communication service quality of the relay link. All candidate relay vehicles within the relay selection area are obtained to form a candidate relay set. If the set is empty, the radius of the candidate relays is expanded. According to the relay selection strategy that ensures the service quality between the source node and the relay vehicle, a relay vehicle is selected from the candidate relay vehicles. The source node sends messages to both the relay vehicle and the destination node. After decoding the message, the relay vehicle forwards it to the next relay vehicle or the destination node based on its relative position to the destination node. When the distance between the relay vehicle and the destination node is greater than the communication range, the currently selected relay node is used as the source node after one hop, and this process is repeated until the message is forwarded to the destination node.

[0123] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0124] The probability of successful cooperative communication under this scheme is theoretically analyzed and calculated. Assume the distance between the source node and the destination node is d, which is greater than the communication range between vehicles (d>R). The source node chooses a multi-hop cooperative communication method to communicate with the destination node.

[0125] Based on step S2, candidate relay areas in the vehicle-to-everything (V2X) system parameters and First, calculate the success probability of the source node-relay vehicle link:

[0126] (15)

[0127] Where T represents the signal-to-interference-plus-noise ratio (SINR) threshold. The Laplace transform represents the total interference power.

[0128] As can be seen from formula (15), the success probability of the source node-relay node link mainly depends on the distance distribution of the relay vehicle's location from the edge. and the Laplace transform of the interference power Next, we will calculate them separately.

[0129] First, starting from a single road, we deduce the distribution of the nearest vehicles on that road within the candidate relay area. Based on whether the perpendicular foot of the road to the origin falls within the candidate relay area, the intersection of the road and the candidate relay area is divided into the following two basic cases:

[0130] (a) The foot of the road falls within the candidate relay range;

[0131] (b) The foot of the road falls outside the candidate relay area.

[0132] Since relays can only be selected within the candidate relay area, vehicles located on roads outside the candidate relay area are not considered. Furthermore, if there are no vehicles on the road within the candidate relay area, the distribution of the nearest vehicles on the road is meaningless. Therefore, here, we only consider the condition that there are vehicles on the road within the candidate relay area to derive the spatial distribution of the vehicles closest to the source node.

[0133] In the candidate relay area Within a single fixed road, the spatial distribution of the vehicles closest to the source node is as follows:

[0134] (16)

[0135] in:

[0136]

[0137]

[0138] These represent the edge angle distribution of the vehicle closest to the source node in two different scenarios, with parameters... The angle and chord length of the two points where the line and the circle intersect are respectively determined by the candidate relay region determined in step S2.

[0139] Within the candidate relay region, the spatial distribution of the vehicle closest to the source node on a single random road is as follows:

[0140] (17)

[0141] in, Representative candidate relay area circumference, This represents the probability that there is at least one vehicle on that road. This represents the probability that there is at least one car on a random road. Because the chord lengths at which a straight line intersects a candidate relay region differ at different locations, the probability that the line has a point within that region also differs. Therefore, for a straight line... Need to be multiplied This allows for weighted processing of different straight lines.

[0142] Within the candidate relay region, the probability density distribution of the location of the vehicle closest to the source node (i.e., the selected relay) on all roads is as follows:

[0143] (18)

[0144] The marginal probability density distribution and probability distribution function of the relay vehicle location are as follows:

[0145] (19)

[0146] (20)

[0147] Next, we calculate the Laplace transform of the interference power, assuming that the probability of the vehicle being active at a certain moment and using the same frequency band as the receiver is... .

[0148] The Laplace transform of the total interference power of vehicles on a single road is expressed as:

[0149] (twenty one)

[0150] Furthermore, the Laplace transform of the interference power of all vehicles on the road is:

[0151] (twenty two)

[0152] Furthermore, after the relay vehicle successfully decodes the information, the distance between the relay vehicle and the destination node is... for:

[0153] (twenty three)

[0154] If the distance is less than the vehicle's communication range, the relay vehicle directly forwards the message to the destination node; otherwise, the relay vehicle becomes the new source node, and the distance is used as the new distance between the source and destination nodes. Steps S2 to S5 are repeated. The success probability calculation for subsequent links is the same as for single-hop source node-relay vehicle links. The overall success probability of source node-destination node cooperative communication can be expressed as:

[0155]

[0156] in, This represents the probability of the first relay vehicle successfully communicating with the destination node.

[0157] Simulation verification

[0158] To evaluate the impact of this scheme on cooperative multi-relay systems in vehicle-to-everything (V2X) networks, the following simulation settings were used:

[0159] Path loss coefficient is ;

[0160] Nakagami channel fading parameters are taken ;

[0161] The vehicle's transmission power is 23 dBm;

[0162] The thermal noise power spectral density is -174 dBm / Hz, with a bandwidth of 10 MHz;

[0163] The vehicle density is 20 cars / km;

[0164] The road density is 10 km / km².

[0165] Please see Figure 1 First, a stochastic geometric model of the vehicle-to-everything (V2X) system is constructed, where roads are modeled as randomly distributed straight lines, and vehicles are modeled as randomly distributed points on those lines. Without loss of generality, it is assumed that the source node is located at the origin, and the destination node is located on the x-axis at a distance of d = 400 meters from the source node.

[0166] According to step S2, based on the vehicle's stochastic model, the center position and radius of the candidate relay region are first calculated. A threshold value is set for the probability that the candidate relay region has no relay. The value is 0.95, and the calculation yields... Meters. Let the set success probability threshold be... The value is 0.9, and the probability of co-channel interference is... The signal-to-interference-plus-noise ratio (SIR) threshold for successful decoding is 0.1, and the calculation yields... rice.

[0167] Please see Figure 2 and Figure 3 Based on the location and size of the candidate relay area obtained in step S2, the communication methods of three different schemes in the vehicle-to-everything (V2X) system were compared. Figure 3 As can be seen, direct communication without relays has the lowest success rate. The next best option is selecting the vehicle closest to the source node as the relay. Choosing a relay within the optimized candidate relay area yields the best results. This is because when the source and destination nodes are far apart, the link quality between them is often poor. Relays can replace a poor-quality link with two better-quality links, thus achieving better coverage. While selecting the closest vehicle as the relay ensures the communication quality of the source-relay link, it doesn't restrict the relay's spatial location, potentially leading to the relay vehicle being further away from the destination node, resulting in even worse link quality. Furthermore, increased vehicle density reduces the progress per hop, requiring more relay vehicles and decreasing communication efficiency.

[0168] In summary, this invention provides a relay selection method and system for vehicle-to-vehicle multi-hop cooperative communication systems. Relay vehicles are selected based on distance and success probability. Specifically, a candidate relay vehicle region is set up in the direction from the source node to the destination node, and the vehicle closest to the source node is selected within this region. First, a random model of vehicles is constructed based on their distribution characteristics. Then, by optimizing the size of the candidate relay region, the probability of no relay is limited to a threshold. By calculating the communication range of vehicles at different densities, the position of the center of the candidate relay region is optimized, ensuring the quality of communication from the source node to the relay vehicle. By selecting relay vehicles within the candidate relay region, it is ensured that after each relay, the relay is closer to the destination node, thereby effectively reducing the number of relay hops, reducing latency, and improving the efficiency of cooperative communication. Furthermore, the probability distribution function of the relay vehicle position under this scheme is derived, and the success probability of inter-vehicle cooperative communication under this scheme is theoretically calculated.

[0169] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0170] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0171] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0172] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0173] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0174] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0175] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0176] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0177] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0178] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system, characterized in that, Includes the following steps: S1. Construct a stochastic geometric model of the vehicle network based on the distribution characteristics of vehicles. In the stochastic geometric model, the source node and the destination node are any nodes in the network. The source node communicates with the destination node in a multi-hop relay manner. S2. Based on the stochastic geometric model obtained in step S1, the location and size of the candidate relay area are determined according to the no-relay probability threshold and the communication service quality of the relay link, specifically as follows: A signal propagation model between the source node and the relay vehicle is constructed. Nakagami-m fading is used to characterize small-scale fading. Different fading environments are simulated by changing the value of m. When m=1, Nakagami-m fading is equivalent to Rayleigh fading, and the small-scale fading coefficient is [value missing]. Obtain the parameter as The exponential distribution is used to calculate the mean interference power of the vehicle-to-everything (V2X) system, and then the mean noise power is calculated to obtain the result at a distance of... At this point, the lower bound of the success probability of communication between the source node and the candidate relay vehicle is given if it is within the vehicle's communication range. Within the specified range, the success rate of inter-vehicle communication is greater than the set success probability threshold. ,Right now Therefore, the maximum range that meets the conditions is defined as the vehicle's communication range. ; Vehicle communication range for: in, The signal-to-interference-plus-noise ratio (SIN / N) threshold required for decoding. For vehicle density, For strength, A threshold for the probability of successful communication within the communication range. This represents the probability that a vehicle is active at a given moment and is using the same frequency band as the receiver. From the origin to the road distance, For vehicles perpendicular to the road distance, This is the path loss coefficient. The standard deviation of the noise. This refers to the transmitter's transmission power. The size and location of the candidate relay area are as follows: in, The radius of the candidate relay region. The location of the candidate relay area center; in, The optimization requirement is to ensure that the probability of no relay vehicle in the candidate relay area is less than the set threshold, so as to avoid the situation where there is no relay. The selection of candidate relay vehicles requires that all candidates be within the communication range of the source node to ensure communication quality; to avoid the distance between the relay vehicle and the destination node being greater than the distance between the source node and the destination node, let ; The probability that the number of candidate relay vehicles is 0 is: Based on the set relay-free probability threshold To determine the radius of a candidate relay region, the following conditions must be met: ,make The radius of the candidate relay region is obtained. ; S3. Obtain all candidate relay vehicles within the relay selection area to obtain a candidate relay set. If the set is empty, expand the candidate relay radius and repeat step S2. Select a relay vehicle from the candidate relay vehicles according to the relay selection strategy that guarantees the service quality of the source node-relay vehicle. S4. The source node sends messages to the relay vehicle and the destination node obtained in step S3, respectively. After the relay vehicle decodes the message, it forwards the message to the next relay vehicle or the destination node according to its relative position with the destination node. S5. When the distance between the relay vehicle and the destination node is greater than the communication range, after one hop, the currently selected relay node is used as the source node, and steps S2 to S4 are repeated until the message is forwarded to the destination node.

2. The relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system according to claim 1, characterized in that, In step S1, the road system is modeled as having a strength of Poisson process Each straight line Distance from the origin to the foot of the perpendicular to the corresponding line and angle The decisions are independent of each other; based on the process of road formation of a Poisson line, vehicles on the road are modeled as points of density on the Poisson line. One-dimensional Poisson point process The vehicles on each line are independently and identically distributed, and their positions constitute a Poisson-Cox process. .

3. The relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system according to claim 1, characterized in that, In step S3, using the candidate relay area selected in step S2, all candidate relay vehicles within the relay selection area are obtained, resulting in a candidate relay set. If the corresponding set is empty, the radius of the candidate relay area is expanded and a new candidate relay vehicle is selected; then, the expected signal-to-interference-plus-noise ratio of the signal received by the vehicle is used as a performance indicator of the source node-relay link to select a relay vehicle.

4. The relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system according to claim 3, characterized in that, Select the vehicle with the highest expected signal-to-interference-plus-noise ratio from the set of candidate relay vehicles as the relay. Forwarding a message, i.e.: in, This refers to the signal-to-interference-plus-noise ratio (SIR) of the signal received by the relay vehicle. Let be the signal-to-interference-plus-noise ratio (SIR) of the i-th vehicle in the candidate relay area.

5. The relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system according to claim 1, characterized in that, In step S4, the relay vehicle first decodes the message using a decode-forward method, and then forwards the message to the next relay vehicle or the destination node according to its relative position to the destination node. If the distance is less than the communication range obtained in step S2, the relay vehicle will proceed as planned. If the signal is selected, the message is forwarded directly to the destination node, which then merges and decodes the signals using a selective merging method, ending the transmission; otherwise, the message is forwarded to the next relay.

6. The relay selection method for a vehicle-to-vehicle multi-hop cooperative communication system according to claim 5, characterized in that, Relay vehicle receiving signal Received signal from the destination node They are respectively: in, The transmitter's transmission power, The channel's small-scale fading coefficient. The distance between the transmitter and the receiver. This is the path loss coefficient. and The variances are respectively Gaussian additive white noise.

7. A relay selection system for a vehicle-to-vehicle multi-hop cooperative communication system, characterized in that, include: The module constructs a stochastic geometric model of the vehicle network based on the distribution characteristics of vehicles. In the stochastic geometric model, the source node and the destination node are any nodes in the network, and the source node communicates with the destination node in a multi-hop relay manner. The location module, based on the stochastic geometric model obtained from the construction module, determines the location and size of candidate relay areas according to the no-relay probability threshold and the communication service quality of the relay link, specifically as follows: A signal propagation model between the source node and the relay vehicle is constructed. Nakagami-m fading is used to characterize small-scale fading. Different fading environments are simulated by changing the value of m. When m=1, Nakagami-m fading is equivalent to Rayleigh fading, and the small-scale fading coefficient is [value missing]. Obtain the parameter as The exponential distribution is used to calculate the mean interference power of the vehicle-to-everything (V2X) system, and then the mean noise power is calculated to obtain the result at a distance of... At this point, the lower bound of the success probability of communication between the source node and the candidate relay vehicle is given if it is within the vehicle's communication range. Within the specified range, the success rate of inter-vehicle communication is greater than the set success probability threshold. ,Right now Therefore, the maximum range that meets the conditions is defined as the vehicle's communication range. ; Vehicle communication range for: in, The signal-to-interference-plus-noise ratio (SIN / N) threshold required for decoding. For vehicle density, For strength, A threshold for the probability of successful communication within the communication range. This represents the probability that a vehicle is active at a given moment and is using the same frequency band as the receiver. From the origin to the road distance, For vehicles perpendicular to the road distance, This is the path loss coefficient. The standard deviation of the noise. This refers to the transmitter's transmission power. The size and location of the candidate relay area are as follows: in, The radius of the candidate relay region. The location of the candidate relay area center; in, The optimization requirement is to ensure that the probability of no relay vehicle in the candidate relay area is less than the set threshold, so as to avoid the situation where there is no relay. The selection of candidate relay vehicles requires that all candidates be within the communication range of the source node to ensure communication quality; to avoid the distance between the relay vehicle and the destination node being greater than the distance between the source node and the destination node, let ; The probability that the number of candidate relay vehicles is 0 is: Based on the set relay-free probability threshold To determine the radius of a candidate relay region, the following conditions must be met: ,make The radius of the candidate relay region is obtained. ; The selection module retrieves all candidate relay vehicles within the relay selection area, resulting in a candidate relay set. If the set is empty, the radius of the candidate relays is expanded. The location module is then repeated to select a relay vehicle from the candidate relay vehicles based on the relay selection strategy that ensures the quality of service between the source node and the relay vehicle. In the decoding module, the source node sends messages to the relay vehicle and the destination node obtained by the selection module, respectively. After the relay vehicle decodes the message, it forwards the message to the next relay vehicle or the destination node according to its relative position with the destination node. The output module, after one hop, uses the currently selected relay node as the source node and repeats this process until the message is forwarded to the destination node.

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