Road traffic information transmission system based on roadside communication

Abstract

The application discloses a road traffic information transmission system based on roadside communication and belongs to the technical field of intelligent traffic communication. The system comprises a vehicle terminal, a plurality of roadside communication base stations, an edge computing node and a central management platform. The vehicle terminal sends a transmission frame carrying a vehicle identifier and traffic state data to the currently accessed roadside communication base station when the channel is idle. The edge computing node compresses the vehicle trajectory data in the net data and encapsulates the traffic state data as a to-be-uploaded data packet. The central management platform establishes a data routing table according to the vehicle identifier and the roadside communication base station number in the to-be-uploaded data packet, and distributes the to-be-uploaded data packet to a downstream roadside communication base station. The system can utilize multiple base stations to receive copies for verification and merging in the overlapping coverage area, and distribute data to the downstream base stations along the driving direction of the vehicle.

Description

Technical Field

[0001] This invention relates to the field of intelligent transportation communication technology, specifically to a road traffic information transmission system based on roadside communication. Background Technology

[0002] Roadside communication-based road traffic information transmission systems generally include vehicle-mounted terminals, roadside communication base stations, edge computing nodes, and a central management platform. Vehicle-mounted terminals collect vehicle identification and traffic status data and transmit them wirelessly to roadside communication base stations. The roadside communication base stations forward the received data to edge computing nodes for aggregation processing, and then the central management platform stores and distributes the data. In actual road environments, vehicles traveling along the road sequentially cross the coverage areas of multiple roadside communication base stations, and there are often overlapping coverage areas between adjacent base stations. When a vehicle is in this overlapping area, the wireless signal propagation path is affected by roadside buildings, large vehicles, or terrain undulations. Transmission frames received by a single base station may experience bit errors or loss due to signal strength fluctuations. When a vehicle switches from its original serving base station to an adjacent base station, the original serving base station's receiving link is broken while the adjacent base station has not yet completed its connection, making it difficult for a single base station to obtain a complete transmission frame. Although adjacent base stations may simultaneously capture signals from the same vehicle-mounted terminal, they process them independently, without exchanging and verifying the copies of the received transmission frames, resulting in insufficient utilization of multiple received copies. On the central management platform side, the aggregated vehicle traffic status data needs to be distributed to roadside communication base stations for use by downstream vehicles or roadside equipment. Existing distribution methods are mostly based on network-wide broadcasting, fixed base station sets, or static subscription relationships. These methods fail to calculate the downstream roadside communication base stations a vehicle will pass by based on the current roadside communication base station number and road topology, resulting in data transmission haphazardness, delayed information acquisition by downstream base stations, and unrelated base stations undertaking unnecessary data reception and processing tasks. It is necessary to address the insufficient reliability of frame reception in overlapping coverage areas of adjacent base stations and the lack of adaptive routing for vehicle travel direction in the central management platform's data distribution. Summary of the Invention

[0003] This invention addresses the problems in existing technologies, such as insufficient reliability of single-base station receiving and transmitting frames in overlapping coverage areas of adjacent roadside communication base stations, and the lack of adaptive routing for data distribution by the central management platform based on vehicle travel direction. It provides a road traffic information transmission system based on roadside communication. By having the primary and auxiliary service base stations in overlapping coverage areas of adjacent base stations collaboratively receive, verify, and merge data, complete net data is generated. The central management platform establishes a data routing table based on vehicle identification and roadside communication base station numbers, determines the downstream set of roadside communication base stations based on road topology, and distributes data packets to be uploaded, thereby improving the reliability and timeliness of road traffic information transmission.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a road traffic information transmission system based on roadside communication, including an on-board terminal, multiple roadside communication base stations, edge computing nodes, and a central management platform. The on-board terminal is used to send transmission frames carrying vehicle identification and traffic status data to the currently accessed roadside communication base station when the communication channel is idle. The roadside communication base station is used to determine the primary serving base station and the secondary serving base station when it detects that the on-board terminal is located in the coverage overlap area of ​​two adjacent roadside communication base stations. The secondary serving base station sends its received transmission frames to the primary serving base station through a wired interface. The primary serving base station verifies and merges the two transmission frames into net data. The edge computing nodes are used to compress the vehicle trajectory data in the net data and encapsulate the compressed trajectory data and the traffic status data in the net data into a data packet to be uploaded. The central management platform is used to receive the data packet to be uploaded, establish a data routing table based on the vehicle identification and roadside communication base station number in the data packet to be uploaded, and distribute the data packet to be uploaded to downstream roadside communication base stations. The system improves wireless transmission reliability by using dual base stations in overlapping areas to collaboratively receive and verify data, reduces the amount of data transmitted back through edge computing compression, and achieves orderly distribution of traffic information to downstream base stations through a data routing table.

[0005] As a technical solution of the present invention, the vehicle-mounted terminal includes a channel listening unit, a frame construction unit, and a transmission unit. The channel listening unit continuously samples the energy of the communication channel before transmitting a transmission frame, and determines that the channel is idle when the sampled value is lower than a preset threshold. The frame construction unit generates a transmission frame based on the vehicle identifier, traffic state data, and the current time. The frame header of the transmission frame includes a vehicle identifier field, a message type field, and a timestamp field. The transmission unit immediately transmits the transmission frame when the channel is idle, calculates a backoff time based on the priority identifier in the message type field when the channel is not idle, and triggers the channel listening unit to resample after the backoff time expires. This solution enables the vehicle-mounted terminal to adjust its backoff strategy according to message priority in channel contention scenarios, reducing collisions and ensuring the timely transmission of high-priority messages.

[0006] Furthermore, the roadside communication base station includes an overlap detection unit, a service negotiation unit, and a merging execution unit. The overlap detection unit determines whether the vehicle-mounted terminal is within the coverage overlap area of ​​two adjacent roadside communication base stations based on the surrounding base station identifier list reported by the vehicle-mounted terminal. The service negotiation unit exchanges the received signal strength indication value and current queue load between the two adjacent roadside communication base stations, and determines the primary and secondary serving base stations according to a priority rule of larger received signal strength indication value and smaller current queue load. The merging execution unit receives a copy of the transmission frame sent by the secondary serving base station through the wired interface from the primary serving base station, verifies and merges the received transmission frame and the copy of the transmission frame to generate net data. This scheme dynamically determines the primary and secondary base stations based on signal strength and load status, avoiding overload of a single base station and improving the efficiency of data merging in overlapping areas.

[0007] Furthermore, the merging execution unit includes a frame-by-frame alignment subunit, a byte comparison subunit, and a check selection subunit. The frame-by-frame alignment subunit aligns the locally received transmission frames with the replica transmission frames sent by the auxiliary serving base station according to the start identifier, generating an aligned first sequence and a second sequence. The byte comparison subunit performs a byte-by-byte XOR operation on the first and second sequences to obtain the difference byte distribution. The check selection subunit, when the difference byte distribution is zero, randomly selects one sequence as the net data; when the difference byte distribution is not zero, it extracts the frame check sequences from both sequences for cyclic redundancy check (CRC), selecting the sequence that passes CRC as the net data; if both sequences pass CRC, the sequence with the earlier reception time is selected as the net data. This method improves the accuracy of the net data by utilizing dual-replica difference comparison and check selection without increasing additional transmission overhead.

[0008] Furthermore, the edge computing node includes a trajectory point extraction unit, a thinning unit, and a packaging unit. The trajectory point extraction unit extracts a sequence of vehicle trajectory points with timestamps from the net data. The thinning unit iterates through the trajectory points in the sequence, starting from the starting point, calculating the difference in direction angle and distance between the current trajectory point and the previous retained point. If both the direction angle difference and the distance difference exceed the distance change threshold, the current trajectory point is retained as a feature point; otherwise, it is discarded, generating a compressed trajectory point sequence. The packaging unit associates the compressed trajectory point sequence with the traffic status data in the net data and adds the roadside communication base station number and collection time interval from the data source, generating a data packet to be uploaded. This scheme retains the characteristics of vehicle trajectory changes while removing redundant trajectory points, reducing the amount of data transmission between the edge computing node and the central management platform.

[0009] Furthermore, the central management platform includes a routing table construction unit, a topology matching unit, and a distribution execution unit. The routing table construction unit establishes a data routing table with the vehicle identifier as the key and the roadside communication base station number sequence as the value, based on the vehicle identifier and roadside communication base station number in the data packet to be uploaded. The topology matching unit determines the set of downstream roadside communication base stations along the vehicle's travel direction based on pre-stored road topology data and updates the data routing table with this set. The distribution execution unit, according to the data routing table, sequentially sends the data packet to be uploaded to each roadside communication base station in the downstream roadside communication base station set via a wired transmission link and receives confirmation of receipt from each roadside communication base station. This scheme enables traffic information to be distributed in advance to base stations along the vehicle's travel direction, improving the timeliness of downstream base stations' response to target vehicles or road condition information.

[0010] As one technical solution of the present invention, the vehicle-mounted terminal includes an authentication code generation unit. This unit, when generating a transmission frame, concatenates vehicle identification, traffic status data, and the current timestamp into data to be signed, and calculates a message authentication code using a session key shared with the roadside communication base station. The message authentication code is then appended to the end of the transmission frame. The roadside communication base station includes an authentication code verification unit. This unit, upon receiving the transmission frame, verifies the message authentication code using the shared session key. If verification passes, the transmission frame is accepted; if verification fails, the transmission frame is discarded, and a retransmission instruction is sent to the vehicle-mounted terminal. This solution protects the integrity of the transmission frame and authenticates its origin through the message authentication code, reducing the risk of unauthorized or tampered data entering the system.

[0011] As a technical solution of this invention, the roadside communication base station includes a multi-level queue scheduling unit. This unit maintains multiple priority queues. When multiple transmission frames sent by vehicle terminals are received, each transmission frame is inserted into its corresponding priority queue based on the message type field in its frame header. The multi-level queue scheduling unit retrieves transmission frames from the multiple priority queues in descending order of priority for transmission. When multiple transmission frames exist in a queue of the same priority, the vehicle identifier field of each transmission frame is hashed, and the retrieval order is determined based on the hash value. This solution provides differentiated scheduling for different types of messages in multi-vehicle concurrent scenarios. Simultaneously, within the same priority, the hash-distributed selection order reduces the latency concentration that might result from a fixed order.

[0012] As a technical solution of this invention, the edge computing node includes a cross-section fusion unit. This unit acquires multiple net data sets from multiple roadside communication base stations and, based on the roadside communication base station number and collection time interval in each net data set, groups the net data sets belonging to the same road cross-section into the same fusion group. The cross-section fusion unit then performs a weighted summation of the average vehicle speeds in the traffic state data within the multiple net data sets in the fusion group. The weight is the number of trajectory points in the corresponding net data set, resulting in the fused average vehicle speed for the cross-section. This average vehicle speed is then used as the traffic state data for that road cross-section and uploaded to the central management platform along with the data packet to be uploaded. This solution achieves a more stable cross-section traffic state through multi-base station data fusion, reducing the impact of single-base station data fluctuations on platform-side judgment.

[0013] As a technical solution of this invention, the central management platform includes a data lifecycle management unit. This unit sets a lifecycle period for each data packet to be uploaded in the data routing table and records the number of requests from downstream roadside communication base stations for the data packet to be uploaded within that lifecycle period. At the end of the lifecycle period, if the number of requests is zero, the data packet to be uploaded is deleted from storage, and a data deletion notification is sent to the edge computing node that generated the data packet. This allows the edge computing node to delete its locally stored copy of the data packet to be uploaded based on the data deletion notification. This solution reduces the invalid data usage of the central management platform and edge computing nodes by cleaning up traffic data without downstream demand based on requests.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: Within the overlapping coverage area of ​​adjacent roadside communication base stations, the overlap detection unit determines that the vehicle is in the overlapping coverage area based on the list of surrounding base station identifiers reported by the vehicle terminal. The service negotiation unit exchanges received signal strength indication values ​​and current queue loads between adjacent base stations, and determines the primary serving base station and the secondary serving base station according to the priority rule of the larger received signal strength indication value and the smaller queue load. The secondary serving base station sends the received transmission frames to the primary serving base station through the wired interface. The primary serving base station merges the transmission frames and transmission frame copies received locally. The merging execution unit first aligns the two transmission frames according to the starting identifier, performs an XOR operation on the first sequence and the second sequence byte by byte to obtain the difference byte distribution; when the difference byte distribution is zero, one sequence is randomly selected as the net data; when the difference byte distribution is not zero, the frame check sequences in the two sequences are extracted for cyclic redundancy check, and the sequence that passes the cyclic redundancy check is selected as the net data; if both sequences pass the cyclic redundancy check, the sequence with the earlier reception time is selected as the net data. The above method obtains multiple received copies of the same transmission frame from adjacent base stations, transmits the copies using wired interfaces without consuming wireless channel resources, and selects the correct sequence through byte comparison and cyclic redundancy check, reducing frame loss and bit errors caused by signal fading, obstruction, or handover when receiving data from a single base station, thus ensuring the integrity and accuracy of the net data entering the edge computing node. After receiving the data packet to be uploaded from the edge computing node, the central management platform establishes a data routing table with the vehicle identifier as the key and the roadside communication base station number sequence as the value, based on the vehicle identifier and the roadside communication base station number in the data packet; according to the pre-stored road topology data, it determines the set of downstream roadside communication base stations that the vehicle corresponding to the vehicle identifier travels through in the direction of travel, and updates this set to the data routing table; the distribution execution unit sends the data packet to be uploaded sequentially to each roadside communication base station in the downstream roadside communication base station set through the wired transmission link according to the data routing table, and receives the confirmation information returned by each base station. This method binds data routing to the vehicle's direction of travel and road topology, enabling vehicle traffic status data to be transmitted in advance along the travel path to the coverage area of ​​the base station to be entered. This avoids irrelevant base stations receiving and caching unnecessary data as in broadcast or fixed list distribution methods, shortens the time for downstream base stations to obtain vehicle status information, and reduces wired link transmission redundancy and base station processing overhead. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0016] Figure 1 This is a schematic diagram of a road traffic information transmission system based on roadside communication. Figure 2 This is a schematic diagram of the structure of an edge computing node; Figure 3 This is a diagram showing the received signal strength indication values ​​and received signal strength difference thresholds between the primary serving base station and the secondary serving base station; Figure 4 This is a schematic diagram illustrating the changes in the direction angle difference and distance difference of the vehicle trajectory point sequence; Figure 5 It is a curve showing the load change of each priority queue in a multi-level queue scheduling system. Detailed Implementation

[0017] 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 embodiments of the present invention, not all embodiments. 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.

[0018] See Figure 1 This invention provides a road traffic information transmission system based on roadside communication, including an on-board terminal, multiple roadside communication base stations, edge computing nodes, and a central management platform. When the communication channel is idle, the on-board terminal sends transmission frames carrying vehicle identification and traffic status data to the currently accessed roadside communication base station. When a roadside communication base station detects that the on-board terminal is located in the coverage overlap area of ​​two adjacent roadside communication base stations, it determines a primary serving base station and an auxiliary serving base station. The auxiliary serving base station sends its received transmission frames to the primary serving base station via a wired interface. The primary serving base station verifies and merges the two transmission frames into net data. The edge computing nodes compress the vehicle trajectory data in the net data and encapsulate the compressed trajectory data and the traffic status data in the net data into a data packet to be uploaded. The central management platform receives the data packet to be uploaded, establishes a data routing table based on the vehicle identification and roadside communication base station number in the data packet, and distributes the data packet to downstream roadside communication base stations.

[0019] In practice, the vehicle-mounted terminal includes a channel listening unit, a frame construction unit, and a transmission unit.

[0020] Before sending a transmission frame, the channel eavesdropping unit continuously samples the energy of the communication channel. Within a preset sampling window, the channel eavesdropping unit samples the energy of the received signal on the communication channel and uses the average energy of all sampling points within the preset sampling window as the sample value. The channel eavesdropping unit compares the sample value with a preset threshold. When the sample value is lower than the preset threshold, the channel eavesdropping unit determines that the communication channel is idle. When the sample value is not lower than the preset threshold, the channel eavesdropping unit continues sampling. The preset threshold and the preset sampling window duration are obtained by the vehicle terminal from the downlink configuration message received by the roadside communication base station when accessing the roadside communication base station.

[0021] The frame construction unit generates a transmission frame based on the vehicle identifier, traffic status data, and the current time. The vehicle identifier is a unique code assigned to the vehicle-mounted terminal when registering with the roadside communication base station. Traffic status data includes vehicle speed, location information, and direction of travel. The frame construction unit writes the vehicle identifier into the vehicle identifier field in the frame header of the transmission frame, the message type into the message type field in the frame header of the transmission frame, and the current time into the timestamp field in the frame header of the transmission frame. The message type field has two values: high-priority message type and low-priority message type. The frame construction unit determines the value of the message type field based on the emergency braking flag in the traffic status data. When the emergency braking flag is set, the message type field value corresponds to a high-priority message type; when the emergency braking flag is not set, the message type field value corresponds to a low-priority message type.

[0022] The transmitting unit immediately transmits a transmission frame when the channel listening unit determines that the communication channel is idle. When the channel listening unit determines that the communication channel is not idle, the transmitting unit reads the priority identifier from the message type field in the frame header of the transmission frame and calculates the backoff time based on the priority identifier. The backoff time calculation formula is: ;

[0023] Among them, T backoff N represents the backoff time, in milliseconds; slot T represents the number of backoff slots, and its value is a positive integer; slot The duration of the backoff time slot is indicated in milliseconds. It is determined by the time slot configuration parameters received by the vehicle terminal from the roadside communication base station when it accesses the roadside communication base station, and the value is a fixed value.

[0024] The sending unit internally stores a priority backoff configuration table, where N represents the number of backoff slots corresponding to high-priority message types. slot The value is 2, representing the number of backoff slots N corresponding to low-priority message types. slotThe value is 5. The reason for setting the number of backoff slots for high-priority message types to 2 is that high-priority transmission frames require short backoff times. The backoff time corresponding to 2 backoff slots is within the allowable access delay range of high-priority transmission frames, and the receiver has sufficient processing time after the high-priority transmission frame is sent. The reason for setting the number of backoff slots for low-priority message types to 5 is that low-priority transmission frames are allowed longer access delays. The backoff time corresponding to 5 backoff slots is higher than the high-priority backoff time, so that high-priority transmission frames can access the communication channel before low-priority transmission frames when the communication channel is not idle.

[0025] The transmitting unit queries the priority backoff configuration table based on the priority identifier to obtain the number of backoff slots N. slot The transmitting unit will send N slot With T slot Multiply to get the retreat time T backoff During the retreat time T backoff After completion, the transmitting unit triggers the channel listening unit to resample.

[0026] In practice, roadside communication base stations include an overlap detection unit, a service negotiation unit, and a merging execution unit.

[0027] The overlap detection unit determines whether the vehicle-mounted terminal is located within the coverage overlap area of ​​two adjacent roadside communication base stations based on the surrounding base station identifier list reported by the vehicle-mounted terminal. During communication, the vehicle-mounted terminal periodically scans the received roadside communication base station broadcast signals, parses the roadside communication base station identifiers in the broadcast signals, and forms a surrounding base station identifier list. The vehicle-mounted terminal reports the surrounding base station identifier list to the currently accessed roadside communication base station through an extended field in the uplink transmission frame. The overlap detection unit extracts the surrounding base station identifier list from the uplink transmission frame and checks whether the list contains the identifier of the currently accessed roadside communication base station and at least one adjacent roadside communication base station identifier. When the surrounding base station identifier list contains both the identifier of the currently accessed roadside communication base station and an adjacent roadside communication base station identifier, the overlap detection unit determines that the vehicle-mounted terminal is located within the coverage overlap area of ​​two adjacent roadside communication base stations. The adjacent roadside communication base station identifiers are determined by the roadside communication base stations according to a pre-stored base station adjacency table, which records the correspondence between each roadside communication base station and its adjacent counterparts.

[0028] The service negotiation unit exchanges its received signal strength indication (RSI) and current queue load between two adjacent roadside communication base stations. The RSI is obtained by the roadside communication base station measuring the received power of the transmission frames sent by the vehicle-mounted terminal; the RSI value is a quantized value of the transmission frame signal strength measured by the roadside communication base station's receiving link. The current queue load is obtained by the roadside communication base station counting the number of transmission frames waiting to be sent in the queue. The service negotiation unit sends a negotiation request message between the two adjacent roadside communication base stations via a wired interface, carrying its own RSI and current queue load. After obtaining the RSI and current queue load of the other roadside communication base station, the two adjacent roadside communication base stations determine the primary and secondary serving base stations according to a priority rule that the higher the RSI and the lower the current queue load. The specific determination rules are as follows: Compare the received signal strength (RSS) indicators of the same transmission frame sent by the same vehicle-mounted terminal received by two adjacent roadside communication base stations. If the absolute value of the difference between the two RSS indicators exceeds a preset RSS threshold, the roadside communication base station with the larger RSS indicator is selected as the primary serving base station, and the other roadside communication base station is selected as the secondary serving base station. If the absolute value of the difference between the two RSS indicators does not exceed the preset RSS threshold, compare the current queue load of the two roadside communication base stations, and select the roadside communication base station with the smaller current queue load as the primary serving base station, and the other roadside communication base station as the secondary serving base station. If the current queue load of the two roadside communication base stations is equal, select the primary serving base station according to the roadside communication base station number from smallest to largest, and the other roadside communication base station as the secondary serving base station. The preset RSS threshold is configured by the roadside communication base stations to avoid frequent switching of the primary serving base station due to small fluctuations in the RSS indicator value.

[0029] The merging execution unit receives copies of transmission frames sent by the auxiliary serving base station via a wired interface from the primary serving base station, and verifies and merges the received transmission frames and their copies to generate net data. After receiving a transmission frame from the vehicle-mounted terminal, the auxiliary serving base station encapsulates it into a wired frame and sends it to the primary serving base station via the wired interface. The primary serving base station receives copies of the transmission frames sent by the auxiliary serving base station via the wired interface, while retaining its own received transmission frames. The merging execution unit includes a frame-by-frame alignment subunit, a byte comparison subunit, and a verification selection subunit.

[0030] The frame-by-frame alignment subunit aligns the received transmission frames with the copies of transmission frames sent by the auxiliary serving base station according to the start identifier, generating an aligned first sequence and a second sequence. The start identifier is the start-of-frame delimiter in the transmission frame header, which is a fixed bit sequence. The frame-by-frame alignment subunit searches for the start-of-frame delimiter in the received transmission frames, starting from the frame header, and uses the position of the first bit of the start-of-frame delimiter as the start position of the received transmission frame. Similarly, the frame-by-frame alignment subunit searches for the start-of-frame delimiter in the copies of transmission frames sent by the auxiliary serving base station, starting from the frame header, and uses the position of the first bit of the start-of-frame delimiter as the start position of the copies of transmission frames sent by the auxiliary serving base station. The frame-by-frame alignment subunit uses the start position of the received transmission frames as the start position of the first sequence and the start position of the copies of transmission frames sent by the auxiliary serving base station as the start position of the second sequence, aligning the first bit of the first sequence with the first bit of the second sequence, and then aligning subsequent bits sequentially.

[0031] The byte comparison subunit performs a byte-by-byte XOR operation on the first and second sequences to obtain the difference byte distribution. The byte comparison subunit maintains a difference byte distribution list, initially empty. The byte comparison subunit sequentially reads bytes at the same offset from the first and second sequences, and performs an XOR operation on the byte at offset m in the first sequence and the byte at offset m in the second sequence, where m increments from 0. When the XOR result is non-zero, the byte comparison subunit records the offset m in the difference byte distribution list. When the XOR result is zero, the byte comparison subunit does not record the offset m. After traversing all bytes of the first and second sequences, the byte comparison subunit obtains the difference byte distribution list.

[0032] When the difference byte distribution list is empty, the verification selection subunit determines that the first sequence and the second sequence are identical byte-by-byte. The verification selection subunit then selects either sequence as the net data, choosing the first sequence. When the difference byte distribution list is not empty, the verification selection subunit extracts the frame check sequence from the first sequence and the frame check sequence from the second sequence for cyclic redundancy check (CRC). The frame check sequence is the CRC field in the end of the transmitted frame. The frame check sequence is calculated by the vehicle terminal when generating the transmitted frame by performing CRC on the frame header and net payload data. The verification selection subunit performs CRC calculation on the data in the frame header and net payload fields of the first sequence to obtain the first CRC result. It then compares the first CRC result with the frame check sequence in the first sequence. If the first CRC result matches the frame check sequence in the first sequence, the first sequence passes the CRC check; otherwise, it fails the CRC check. The verification selection subunit performs cyclic redundancy check (CRC) calculations on the data in the frame header and payload fields of the second sequence to obtain a second CRC result. This second CRC result is then compared with the frame check sequence in the second sequence. If the second CRC result matches the frame check sequence in the second sequence, the second sequence is considered to have passed CRC. If the second CRC result does not match the frame check sequence in the second sequence, the second sequence is considered to have failed CRC. When the first sequence passes CRC and the second sequence fails CRC, the verification selection subunit selects the first sequence as the payload. When the first sequence fails CRC but the second sequence passes CRC, the verification selection subunit selects the second sequence as the payload. When both the first and second sequences pass CRC, the verification selection subunit selects the sequence with the earlier reception time as the payload. The reception time is determined by the reception time of the transmitted frame recorded by the primary serving base station and the reception timestamp appended by the secondary serving base station when sending a copy of the transmitted frame through the wired interface. When neither the first nor the second sequence passes CRC, the verification selection subunit discards both sequences and sends a retransmission instruction to the vehicle terminal. The final net data generated by the verification selection sub-unit is sent to the edge computing node.

[0033] See Figure 3 In the figure, the horizontal axis represents the transmission frame number, ranging from 0 to 500, and the vertical axis represents the received signal strength indication value, in dBm. The figure shows the received signal strength indication value curve of the primary serving base station (blue solid line), the received signal strength indication value curve of the secondary serving base station (red dashed line), the absolute value curve of the difference between the received signal strength indication values ​​(green dotted line), and the preset received signal strength threshold (purple dashed line).

[0034] As can be seen from the blue solid line and red dashed line, the received signal strength indication curves of the primary serving base station and the secondary serving base station show a relatively consistent trend, and both are within the range of -85dBm to -65dBm. This indicates that both adjacent roadside communication base stations received signals from the vehicle-mounted terminal's transmission frames, satisfying the prerequisite for the overlap detection unit in this embodiment to determine the coverage overlap area. The fluctuations in the curves reflect the dynamic changes in the wireless channel environment.

[0035] The green dotted line represents the absolute value of the difference between the received signal strength indication values ​​of the primary serving base station and the secondary serving base station. This value consistently falls within the range of 0 to 3 dBm and remains below the preset received signal strength threshold (approximately 5 dBm) indicated by the purple dashed line in the figure. According to the aforementioned embodiment, when the absolute value of the difference between the received signal strength indication values ​​of the two roadside communication base stations does not exceed the preset threshold, the current queue load of the two base stations should be compared to determine the primary serving base station and the secondary serving base station. The data in the figure shows that the current signal strength difference is small, meeting this condition.

[0036] In specific implementation, please refer to Figure 2 The edge computing node includes a trajectory point extraction unit, a thinning unit, an encapsulation unit, and a cross-section fusion unit.

[0037] The trajectory point extraction unit extracts a sequence of vehicle trajectory points with timestamps from the net data. The net data is sent to the edge computing node via a wired interface from the roadside communication base station. The net data includes vehicle identification, timestamp, location information, and traffic status data. The trajectory point extraction unit reads the net data line by line, using the vehicle identification field as the vehicle identifier, the timestamp as the timestamp, and the longitude and latitude coordinates as the location coordinates. The unit creates a trajectory point record for each trajectory point, containing the vehicle identifier, timestamp, longitude, and latitude coordinates. The unit sorts all trajectory point records corresponding to the same vehicle identifier in ascending order of timestamp, forming a sequence of vehicle trajectory points with timestamps. The first trajectory point in the sequence is the starting point.

[0038] The thinning unit iterates through the vehicle trajectory point sequence, starting from the starting point, calculating the difference in orientation angle and distance between the current trajectory point and the previous retained point. The starting point is designated as the first retained point. Starting from the second trajectory point in the sequence, the thinning unit treats each trajectory point as the current trajectory point. Based on the longitude and latitude coordinates of the current trajectory point and the previous retained point, the thinning unit calculates the distance difference between them. This distance difference is calculated using spherical distance methods, with the unit being meters. The thinning unit also calculates the orientation angle of the current trajectory point relative to the previous retained point, and calculates the difference in orientation angle between them. This difference is calculated as the absolute value of the difference between the two orientation angles, with the unit being degrees. The direction change threshold is configured by the edge computing node during initialization, and its value is 15 degrees. This value is chosen because changes in vehicle direction at road intersections or sharp bends typically exceed 15 degrees; changes less than 15 degrees do not affect traffic state analysis results. The distance change threshold is also configured by the edge computing node during initialization, and its value is 20 meters. This value is chosen because the interval between adjacent trajectory points on urban roads is typically 5 to 10 meters. 20 meters exceeds the maximum interval between adjacent trajectory points; when the distance difference exceeds 20 meters, it indicates a significant vehicle displacement, and the current trajectory point needs to be retained as a feature point.

[0039] The thinning unit retains the current trajectory point as a feature point when both the direction angle difference and the distance difference exceed the direction change threshold; it discards the current trajectory point when neither the direction angle difference nor the distance difference exceeds the distance change threshold. After traversing all trajectory points in the vehicle trajectory point sequence, the thinning unit arranges the starting point and all feature points in ascending order of timestamps to generate a compressed trajectory point sequence.

[0040] The encapsulation unit associates the compressed trajectory point sequence with the traffic state data in the net data. The encapsulation unit extracts traffic state data from the net data, which includes vehicle speed, direction of travel, and emergency braking signs. The encapsulation unit matches the vehicle identifiers in the compressed trajectory point sequence with the vehicle identifier field in the net data, and associates the successfully matched compressed trajectory point sequences with the traffic state data in the net data to form an associated data record. The encapsulation unit adds the roadside communication base station number and collection time interval of the data source to the associated data record. The roadside communication base station number of the data source is determined by the roadside communication base station number extracted from the net data by the edge computing node, and the collection time interval is determined by the timestamps of the first and last trajectory points in the compressed trajectory point sequence, including the start and end times. The encapsulation unit encapsulates the associated data record, after adding the roadside communication base station number and collection time interval, into a data packet to be uploaded.

[0041] The cross-section fusion unit acquires multiple net data sets from multiple roadside communication base stations and groups net data sets belonging to the same road cross-section into the same fusion group based on the roadside communication base station number and collection time interval in each net data set. The cross-section fusion unit reads the roadside communication base station number and collection time interval from each net data set, grouping net data sets with the same roadside communication base station number and overlapping collection time intervals into the same fusion group. The same road cross-section represents the set of net data sets within the same collection time interval and coverage area of ​​the same roadside communication base station. The cross-section fusion unit performs a weighted summation of the average vehicle speeds from the traffic state data within multiple net data sets in the fusion group, with the weight being the number of trajectory points in the corresponding net data set. The cross-section fusion unit counts the number of trajectory points in the vehicle trajectory data of each net data set; the number of trajectory points in the vehicle trajectory data is determined by the number of trajectory points in the net data set. The formula for calculating the average vehicle speed of the fused cross-section is: ;

[0042] Among them, V merge The average vehicle speed of the fused cross-section is expressed in kilometers per hour; U represents the total number of net data points within the same fusion group, taking a positive integer value, obtained by counting the net data points within the fusion group using the cross-section fusion unit; n u This represents the number of trajectory points in the vehicle trajectory data of the u-th net data set, taking a positive integer value. It is obtained by the cross-section fusion unit counting the number of trajectory points from the vehicle trajectory data in the corresponding net data set; v u The average vehicle speed in the traffic status data of the u-th net data is expressed in kilometers per hour and is a non-negative real number. It is obtained by reading the average vehicle speed from the traffic status data of the corresponding net data by the cross-section fusion unit; u represents the sequence number of the net data in the fusion group, with a value from 1 to U.

[0043] The cross-section fusion unit uses the fused average vehicle speed as the traffic status data for the corresponding road cross-section. The cross-section fusion unit sends the fused average vehicle speed to the encapsulation unit, which encapsulates the fused average vehicle speed as traffic status data into the data packet to be uploaded, and sends the data packet to be uploaded to the central management platform through the uplink communication interface of the edge computing node.

[0044] See Figure 4 In the graph, the horizontal axis represents the trajectory point number, the left side of the vertical axis represents the direction angle difference in degrees, and the right side represents the distance difference in meters. The blue dashed curve represents the trend of the direction angle difference between adjacent trajectory points in the vehicle trajectory point sequence, the green solid curve represents the trend of the distance difference between adjacent trajectory points, the red dashed line is the direction change threshold (15 degrees), and the purple dashed line is the distance change threshold (20 meters).

[0045] As shown in the graph, the direction angle difference value mostly remains below the 15-degree direction change threshold, with occasional peaks exceeding this threshold. This indicates that the vehicle's direction changes are primarily concentrated within 15 degrees, with a few trajectory points exhibiting significant direction changes, potentially corresponding to road intersections or sharp bends. The distance difference curve generally fluctuates below the 20-meter distance change threshold, but several peaks exceeding 20 meters appear, indicating trajectory points where the vehicle has undergone significant displacement. The peak values ​​of the direction angle difference and distance difference values ​​mostly do not completely overlap, suggesting that direction and distance changes complement each other in determining trajectory point thinning.

[0046] According to the thinning unit configuration in the above embodiment, when the direction angle difference exceeds 15 degrees and the distance difference exceeds 20 meters, the trajectory point is determined as a feature point and retained; when the direction angle difference does not exceed 15 degrees or the distance difference does not exceed 20 meters, the trajectory point is discarded. The threshold lines for the direction angle difference and distance difference in the figure clearly indicate the determination threshold of the thinning unit, helping to ensure that the trajectory point is retained only when the vehicle trajectory undergoes a significant change in direction and a large change in distance, thereby effectively compressing the amount of trajectory data.

[0047] In practice, the central management platform includes a routing table construction unit, a topology matching unit, a distribution execution unit, and a data lifecycle management unit.

[0048] The central management platform receives data packets uploaded by edge computing nodes via a receiving interface. These packets contain a vehicle identification field, a roadside communication base station number field, a data collection time interval field, a compressed trajectory point sequence, and traffic status data. The routing table construction unit parses the vehicle identification and roadside communication base station number from the data packets. The roadside communication base station number is added by the edge computing node when encapsulating the data packets. The routing table construction unit checks if an entry with the vehicle identification as the key already exists in the data routing table. If no entry exists, the unit creates a new entry with the vehicle identification as the key and the sequence containing the roadside communication base station number as the value. If an entry already exists, the unit appends the roadside communication base station number from the current data packet to the end of the existing sequence, maintaining the chronological order of the numbers.

[0049] The topology matching unit determines the set of downstream roadside communication base stations along the vehicle's travel direction based on pre-stored road topology data. Road topology data is stored in the central management platform's database and includes roadside communication base station numbers, location coordinates, adjacent roadside communication base station numbers, and road direction information. The topology matching unit reads the vehicle's travel direction from the data packet to be uploaded, based on the vehicle's identification; this direction is provided by the travel direction field in the traffic status data. Starting with the currently accessed roadside communication base station number, the topology matching unit determines the set of downstream roadside communication base stations along the vehicle's travel direction based on the adjacent roadside communication base station numbers and road direction information in the road topology data. The topology matching unit updates the determined set of downstream roadside communication base stations in the entry corresponding to the vehicle's identification in the data routing table, appends each roadside communication base station number in the downstream set to the roadside communication base station number sequence, and marks the receiving order corresponding to each roadside communication base station number.

[0050] The distribution execution unit, based on the data routing table, sequentially sends the data packet to be uploaded to each roadside communication base station in the downstream roadside communication base station set via a wired transmission link. The distribution execution unit reads the roadside communication base station number sequence corresponding to the vehicle identifier in the data routing table, and sequentially extracts the numbers marked as downstream roadside communication base stations from the sequence. The distribution execution unit establishes a connection with the corresponding roadside communication base station via the wired transmission link and sends the data packet to be uploaded completely to the corresponding roadside communication base station via the wired transmission link. After sending the data packet, the distribution execution unit waits for an acknowledgment of receipt from the corresponding roadside communication base station. The acknowledgment of receipt includes the corresponding roadside communication base station number and a reception status code. When the distribution execution unit receives the acknowledgment of receipt, it records the reception status of the corresponding roadside communication base station as "received" in the data routing table. If the distribution execution unit does not receive an acknowledgment of receipt within the preset acknowledgment timeout period, it retransmits the data packet to be uploaded to the corresponding roadside communication base station, with the number of retransmissions not exceeding the preset maximum number of retransmissions.

[0051] The data lifecycle management unit sets a lifetime for each data packet to be uploaded in the data routing table. Each data packet to be uploaded corresponds to a routing table entry, and the data lifecycle management unit sets a lifetime field for each routing table entry. The lifetime length is calculated using the following formula: ;

[0052] Where, D lifetime t represents the duration of survival, expressed in minutes, and is a non-negative real number. deadline This indicates the data destruction time of the data packet to be uploaded. The value is a date and time value in seconds. It is obtained by adding a preset data retention period to the end of the data packet's collection time interval, as determined by the central management platform. The preset data retention period is 3600 seconds (60 minutes). The reason for choosing 3600 seconds is that road traffic status data loses its real-time nature after 60 minutes, and downstream roadside communication base stations do not require more than 60 minutes of traffic status data. creation This indicates the time when the data packet to be uploaded was generated. The value is a date and time value in seconds, which is read by the central management platform from the timestamp field of the data packet to be uploaded.

[0053] The data lifecycle management unit records the number of requests made by downstream roadside communication base stations for data packets to be uploaded during the lifecycle period. Each downstream roadside communication base station sends a data request message to the central management platform during the lifecycle period. This message includes the identifier of the data packet to be uploaded and the requesting roadside communication base station number. Upon receiving the data request message, the data lifecycle management unit finds the corresponding routing table entry based on the identifier of the data packet to be uploaded and increments the request count counter. The initial value of the request count counter is 0. At the end of the lifecycle period, the data lifecycle management unit checks the request count. When the request count is zero, the data lifecycle management unit deletes the data packet to be uploaded from storage and sends a data deletion notification to the edge computing node that generated the data packet. The data deletion notification includes the identifier of the data packet to be uploaded. Upon receiving the data deletion notification, the edge computing node finds a locally stored copy of the data packet to be uploaded based on the identifier and deletes the copy from its local storage. When the request count is not zero, the data lifecycle management unit maintains the storage of the data packet to be uploaded and continues to reserve storage space for it after the lifecycle period ends. The retention period is configured by the central management platform.

[0054] In implementation, the vehicle-mounted terminal includes an authentication code generation unit. When generating a transmission frame, the authentication code generation unit concatenates the vehicle identifier, traffic status data, and current timestamp into data to be signed. The vehicle identifier is assigned by the roadside communication base station during vehicle terminal registration and is a fixed-length string. Traffic status data includes vehicle speed, location information, and direction of travel, and is collected by sensors inside the vehicle-mounted terminal. The current timestamp is provided by the vehicle-mounted terminal's internal clock module and represents the time the transmission frame was generated. The authentication code generation unit concatenates the vehicle identifier, traffic status data, and current timestamp into the data to be signed in the order of vehicle identifier first, traffic status data in the middle, and current timestamp last. The authentication code generation unit uses a shared session key with the roadside communication base station to calculate the message authentication code for the data to be signed. The shared session key is obtained by the vehicle-mounted terminal and the roadside communication base station through key negotiation during the initial authentication process. The shared session key is generated by the roadside communication base station and sent to the vehicle-mounted terminal through an encrypted channel; the shared session key is a fixed-length random binary sequence. When calculating the message authentication code, the authentication code generation unit performs a hash calculation on the shared session key and the data to be signed to obtain the message authentication code. The authentication code generation unit adds the message authentication code to the end of the transmission frame, and the length of the message authentication code field in the end of the frame is determined by the output length of a preset hash function.

[0055] In some embodiments, the roadside communication base station includes an authentication code verification unit. After receiving a transmission frame, the authentication code verification unit verifies the message authentication code using a shared session key. The authentication code verification unit extracts the message authentication code field from the end of the transmission frame to obtain the received message authentication code. The authentication code verification unit extracts the vehicle identification field from the frame header of the transmission frame and traffic status data and current timestamp fields from the payload of the transmission frame. The authentication code verification unit concatenates the vehicle identification, traffic status data, and current timestamp into verification signature data in the order of vehicle identification first, traffic status data in the middle, and current timestamp last. The authentication code verification unit performs a hash calculation on the verification signature data using the shared session key to obtain a locally calculated message authentication code. The authentication code verification unit compares the received message authentication code with the locally calculated message authentication code bit by bit. When the received message authentication code and the locally calculated message authentication code are completely identical, the authentication code verification unit determines that the verification is successful, accepts the transmission frame, and sends the transmission frame to the subsequent processing flow. When there is a discrepancy between the received message authentication code and the locally calculated message authentication code, the authentication code verification unit determines that the verification has failed, discards the transmission frame, and sends a retransmission instruction to the vehicle terminal. The retransmission instruction is sent to the vehicle terminal by the roadside communication base station through the downlink control channel, and includes the transmission frame sequence number and the retransmission reason code.

[0056] In practical implementation, the roadside communication base station also includes a multi-level queue scheduling unit. This unit maintains multiple priority queues, the number of which is set by the roadside communication base station in its configuration file. These priority queues include high-priority queues, normal-priority queues, and low-priority queues. When the multi-level queue scheduling unit receives transmission frames from multiple vehicle-mounted terminals, it inserts each transmission frame into the corresponding priority queue based on the message type field in the frame header. The unit reads the message type field from the frame header and queries a priority mapping table based on the priority identifier in the message type field. This priority mapping table records the correspondence between priority identifiers and priority queues. When the priority identifier in the message type field corresponds to high priority, the multi-level queue scheduling unit inserts the transmission frame into the high-priority queue; when it corresponds to normal priority, it inserts the frame into the normal-priority queue; and when it corresponds to low priority, it inserts the frame into the low-priority queue.

[0057] The multi-level queue scheduling unit retrieves transmission frames from multiple priority queues in descending order of priority for transmission. The unit first checks if the high-priority queue is empty; if not, it retrieves the transmission frame from the high-priority queue for transmission. If the high-priority queue is empty, the unit checks if the ordinary-priority queue is empty; if not, it retrieves the transmission frame from the ordinary-priority queue for transmission. If the ordinary-priority queue is empty, the unit checks if the low-priority queue is empty; if not, it retrieves the transmission frame from the low-priority queue for transmission. When multiple transmission frames exist in a queue of the same priority, the multi-level queue scheduling unit hashes the vehicle identification field of each transmission frame and determines the retrieval order based on the hash value. The hash calculation formula is: ;

[0058] Among them, H queue This represents the queue scheduling hash value, which is a fixed-length binary string output by a preset hash function; H hash This indicates the default hash function, which uses the SM3 algorithm and has an output length of 256 bits; V id This represents the vehicle identification field, with a fixed-length string value assigned by the roadside communication base station.

[0059] The multi-level queue scheduling unit calculates the queue scheduling hash value for each transmission frame in the same priority queue, arranges the queue scheduling hash values ​​in ascending order, and retrieves transmission frames sequentially according to the sorted order for transmission. When two queue scheduling hash values ​​are the same, the multi-level queue scheduling unit compares the reception timestamps of the two transmission frames, retrieving the transmission frame with the earlier reception timestamp first. The multi-level queue scheduling unit then sends the retrieved transmission frame to the next level processing unit.

[0060] See Figure 5 In the graph, the horizontal axis represents the scheduling rounds, ranging from 0 to 500, and the vertical axis represents the number of transmission frames to be sent in the queue, in units of frames. The graph shows four curves: high-priority queue, normal-priority queue, low-priority queue, and total queue load, which correspond to the queuing status of the vehicle terminal's transmission frames in the multi-level queue scheduling unit of the roadside communication base station.

[0061] The high-priority queue curve is represented by a solid blue line. The number of transmitted frames fluctuates between 5 and 18 frames. Overall, it maintains a low and relatively stable queue length, indicating that high-priority message type transmission frames can be processed and sent quickly, which meets the design requirements of the multi-level queue scheduling unit in the above embodiment for short backoff time slots and priority scheduling of high-priority queues.

[0062] The curve for the normal priority queue is represented by a red dashed line. The number of transmitted frames ranges from approximately 8 to 23, which is significantly higher than that of the high priority queue. The fluctuation range is also large, indicating the backlog of the normal priority queue when the communication load changes. This reflects that the waiting time for normal priority message type transmission frames in the queue is relatively long.

[0063] The low-priority queue curve is represented by a green dotted line. It has the lowest number of transmitted frames, which is basically maintained between 2 and 12 frames. Although the number is small, the low-priority queue has a lower processing priority than the high-priority queue. In the above embodiment, the large number of backoff slots makes its queuing waiting time longer.

[0064] The total queue load curve is represented by a purple dotted line. Its value is the sum of the number of frames transmitted by each priority queue. The fluctuation range is between 20 and 50 frames, and it shows an overall periodic fluctuation trend, reflecting the total load status of the roadside communication base station in different scheduling rounds for processing transmission frames.

[0065] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A road traffic information transmission system based on roadside communication, characterized in that, include: Vehicle-mounted terminals, multiple roadside communication base stations, edge computing nodes, and a central management platform; The vehicle-mounted terminal is used to send transmission frames carrying vehicle identification and traffic status data to the currently accessed roadside communication base station when the communication channel is idle; When a vehicle-mounted terminal is detected to be located in the overlapping coverage area of ​​two adjacent roadside communication base stations, the roadside communication base station determines the primary service base station and the secondary service base station. The secondary service base station sends the received transmission frames to the primary service base station through a wired interface. The primary service base station verifies and merges the two transmission frames into net data. Edge computing nodes are used to compress vehicle trajectory data in the net data and encapsulate the compressed trajectory data and traffic status data in the net data into a data packet to be uploaded; The central management platform is used to receive the data packets to be uploaded, establish a data routing table based on the vehicle identifier and roadside communication base station number in the data packets to be uploaded, and distribute the data packets to be uploaded to downstream roadside communication base stations.

2. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The vehicle-mounted terminal includes a channel listening unit, a frame construction unit, and a transmission unit; The channel listening unit is used to continuously sample the energy of the communication channel before sending the transmission frame, and to determine that the channel is idle when the sampled value is lower than a preset threshold. The frame construction unit is used to generate the transmission frame based on the vehicle identifier, the traffic status data and the current time. The frame header of the transmission frame includes a vehicle identifier field, a message type field and a timestamp field. The sending unit is used to immediately send the transmission frame when the channel is idle, calculate the backoff time according to the priority identifier in the message type field when the channel is not idle, and trigger the channel listening unit to resample after the backoff time ends.

3. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The roadside communication base station includes an overlap detection unit, a service negotiation unit, and a merging execution unit; The overlap detection unit is used to determine whether the vehicle terminal is in the coverage overlap area of ​​two adjacent roadside communication base stations based on the list of surrounding base station identifiers reported by the vehicle terminal. The service negotiation unit is used to exchange the received signal strength indication value and the current queue load between two adjacent roadside communication base stations, and to determine the primary service base station and the secondary service base station according to the priority rule of the larger received signal strength indication value and the smaller the current queue load. The merging execution unit is used to receive a copy of the transmission frame sent by the auxiliary service base station through the wired interface from the primary service base station, and to verify and merge the transmission frame received locally and the copy of the transmission frame to generate the net data.

4. The road traffic information transmission system based on roadside communication according to claim 3, characterized in that, The merging execution unit includes a frame-by-frame alignment subunit, a byte comparison subunit, and a check selection subunit; The frame-by-frame alignment subunit is used to align the transmission frames received by the local unit with the copies of transmission frames sent by the auxiliary service base station according to the start identifier, and generate the aligned first sequence and second sequence. The byte comparison subunit is used to perform an XOR operation on the first sequence and the second sequence byte by byte to obtain the difference byte distribution; The verification selection subunit is used to select one sequence as the net data when the difference byte distribution is zero, and when the difference byte distribution is not zero, extract the frame verification sequence from the two sequences respectively for cyclic redundancy check, and select the sequence that passes the cyclic redundancy check as the net data. If both sequences pass the cyclic redundancy check, the sequence with the earlier reception time is selected as the net data.

5. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The edge computing node includes a trajectory point extraction unit, a thinning unit, and an encapsulation unit; The trajectory point extraction unit is used to extract a sequence of vehicle trajectory points with timestamps from the net data; The thinning unit is used to traverse the trajectory points sequentially from the starting point in the vehicle trajectory point sequence, calculate the difference in direction angle and distance between the current trajectory point and the previous retained point, and retain the current trajectory point as a feature point when the difference in direction angle exceeds the direction change threshold and the difference in distance exceeds the distance change threshold; otherwise, the current trajectory point is discarded to generate a compressed trajectory point sequence. The encapsulation unit is used to associate the compressed trajectory point sequence with the traffic status data in the net data, and add the roadside communication base station number and collection time interval of the data source to generate the data packet to be uploaded.

6. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The central management platform includes a routing table construction unit, a topology matching unit, and a distribution execution unit; The routing table construction unit is used to establish a data routing table with the vehicle identifier as the key and the roadside communication base station number as the value, based on the vehicle identifier in the data packet to be uploaded and the roadside communication base station number; The topology matching unit is used to determine the set of downstream roadside communication base stations that the vehicle corresponding to the vehicle identifier passes through according to the pre-stored road topology data, and update the set of downstream roadside communication base stations to the data routing table. The distribution execution unit is used to send the data packet to be uploaded sequentially to each roadside communication base station in the downstream roadside communication base station set through a wired transmission link according to the data routing table, and to receive confirmation of receipt returned by each roadside communication base station.

7. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The vehicle-mounted terminal includes an authentication code generation unit. The authentication code generation unit is used to concatenate the vehicle identifier, the traffic status data, and the current timestamp into data to be signed when generating the transmission frame, and to calculate a message authentication code for the data to be signed using a session key shared with the roadside communication base station, and to add the message authentication code to the end of the transmission frame. The roadside communication base station includes an authentication code verification unit. After receiving the transmission frame, the authentication code verification unit uses a shared session key to verify the message authentication code. If the verification is successful, the transmission frame is accepted; if the verification fails, the transmission frame is discarded and a retransmission instruction is sent to the vehicle terminal.

8. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The roadside communication base station includes a multi-level queue scheduling unit, which is used to maintain multiple priority queues. When receiving transmission frames sent by multiple vehicle terminals, the multi-level queue scheduling unit inserts each transmission frame into the queue of the corresponding priority according to the message type field in the frame header of each transmission frame. The multi-level queue scheduling unit is used to retrieve transmission frames from the multiple priority queues in descending order of priority for transmission. When there are multiple transmission frames in the same priority queue, the vehicle identification field of each transmission frame is hashed, and the retrieval order is determined according to the size of the hash value.

9. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The edge computing node includes a cross-section fusion unit, which is used to obtain multiple net data from multiple roadside communication base stations, and divide the net data belonging to the same road cross-section into the same fusion group according to the roadside communication base station number and collection time interval in each net data. The cross-section fusion unit is used to perform a weighted summation of the average vehicle speed in the traffic state data of multiple net data within the fusion group. The weight is the number of trajectory points in the corresponding net data to obtain the fused cross-section average vehicle speed. The cross-section average vehicle speed is then used as the traffic state data of the road cross-section and uploaded to the central management platform along with the data packet to be uploaded.

10. The road traffic information transmission system based on roadside communication according to claim 1, characterized in that, The central management platform includes a data lifecycle management unit, which is used to set a lifecycle period for each data packet to be uploaded in the data routing table, and to record the number of requests made by the downstream roadside communication base station to the data packet to be uploaded within the lifecycle period; The data lifecycle management unit is used to delete the data packet to be uploaded from storage when the number of requests is zero at the end of the lifecycle period, and send a data deletion notification to the edge computing node that generated the data packet to be uploaded, so that the edge computing node deletes the locally stored copy of the data packet to be uploaded according to the data deletion notification.

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