Information transmission method of adaptive access mechanism based on traffic flow density

Abstract

The invention relates to an information transmission method of an adaptive access mechanism based on traffic flow density, which comprises the following steps that: in a cellular network coverage area, a base station broadcasts network configuration parameters to all vehicle users in the area; in a time slot tG, delimiting a selection window and identifying candidate channel resources in the selection window; defining a sensing window, and performing resource screening on the candidate channel resources in the selection window by using the sensing window; selecting a part of channel resources with relatively lowest average reference signal strength indication in the sensing window as residual candidate channel resources L2, and checking whether the residual candidate channel resources L2 are available or not; and calculating a channel busy rate (CBR). According to the invention, the MODE2 access mechanism is adaptively adjusted according to different traffic flow densities. According to the method, an efficient access mode can be selected to improve the transmission rate; and when the traffic flow is high, the access mode is switched to a more robust access mode so as to enhance the transmission reliability and the anti-interference capability.

Description

Technical Field

[0001] The present invention relates to the field of 3GPP NR V2X communication technology, and in particular to an information transmission method of an adaptive access mechanism based on vehicle flow density. Background Art

[0002] As an extension of the Internet of Things, the Internet of Vehicles can assist the development of smart cities. The Internet of Vehicles relies on vehicle-to-vehicle communications to allow vehicles to communicate with other vehicles in real time. In this context, cellular vehicle-to-everything (C-V2X) communication has become an important technology to achieve the goal of the Internet of Vehicles. Currently, there are two versions of C-V2X, Long Term Evolution-V2X (LTE-V2X) and New Radio-V2X (NR-V2X). Today, applications in the Internet of Vehicles are developing towards the requirements of high reliability and low latency. LTE-V2X cannot really meet the needs of future applications. For this reason, NR-V2X is designed to supplement LTE-V2X. 5GNR-V2X supports advanced driving use cases, higher throughput and automation levels. As a key component of 5G technology, NR-V2X makes full use of its advantages of high bandwidth, low latency and high reliability to provide a solid technical foundation for communication between vehicles. This technology not only enhances the vehicle's ability to assist in traffic management, but also expands the scope of non-safety applications. For example, NR-V2X can be used for vehicle platooning, extended sensors, advanced driving, remote driving, and cooperative collision avoidance. Together, these applications promote the advancement of autonomous driving and intelligent transportation systems, and drive the comprehensive development of connected transportation.

[0003] The access mechanism is an important part of the 5GNR-V2X physical layer, which enables efficient data transmission and communication between connected vehicles in real time. By using advanced modulation schemes and coding techniques, it can optimize data transmission rate and reliability, thereby ensuring low-latency and stable communication even when vehicles are driving at high speeds or in complex environments.

[0004] 3GPP defines two access mechanisms for 5GNR-V2X sidelink communications: MODE1 and MODE2. In MODE1, the base station schedules and allocates resources to vehicles in a centralized manner. In MODE2, vehicles autonomously manage, configure, and schedule resources in a decentralized manner without the assistance of the base station. MODE2 can meet the requirements of low latency and high reliability of service quality in communications. Due to the flexibility of the MODE2 access mechanism, it has broad application prospects, but it still faces many challenges in actual deployment. For example, as the traffic density increases, periodic beacon messages will occupy the entire control channel and cause channel congestion.

[0005] MODE2 allows connected vehicles to autonomously select their transmission resources using Semi-Persistent Scheduling (SPS) and Dynamic Scheduling (DS) schemes. The SPS scheme is a periodic reservation of resources and is suitable for periodic messages of fixed size, while DS is a non-reserved scheme that requires the mandatory selection of new transmission resources for each generated message and is suitable for non-periodic messages. The SPS scheduling scheme can use Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM) and turbo coding modulation and coding schemes (MCS) to transmit information. In addition, 5G NR-V2X MODE2 also introduces some new features, such as support for unicast and multicast communications, novel feedback channels, and new control channel designs. These features will provide more flexible, reliable and higher throughput V2X services for advanced driving use cases. This not only improves the intelligence level of vehicles, but also lays the foundation for realizing autonomous driving and vehicle-to-everything (V2X) applications, making information exchange between vehicles and between vehicles and infrastructure more efficient and accurate.

[0006] On the other hand, 5G NR-V2X MODE2 is more flexible in parameter design compared to LTE-V2X MODE4. In terms of the physical layer, MODE2 supports a wider range of subframe time slots, subcarrier spacing, and coding modulation schemes, which enables it to adapt to a wider range of communication needs; in terms of resource allocation, MODE2 supports a more refined resource reservation interval (Resource Reservation Interval, RRI), allowing any integer between 1 millisecond and 99 milliseconds, which provides vehicles with greater flexibility to adapt to different eV2X business needs and characteristics. MODE2 also introduces the function of the re-evaluation mechanism to better cope with changes in transmission messages and undetected interference problems between vehicles, providing greater resource management flexibility.

[0007] However, with the continuous evolution of Internet of Vehicles technology, the amount of sensory data that connected vehicles need to process is growing exponentially, and the complexity of intelligent driving algorithms is also rising rapidly. This not only brings huge pressure on data processing and computing to connected vehicles, but also places an excessive burden on communication networks. In the face of this challenge, a more intelligent access mechanism technology is urgently needed to dynamically adjust transmission parameters under different communication conditions, optimize the transmission efficiency of information, ensure the efficient transmission of information, and improve the comprehensive performance of intelligent connected vehicles. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide an information transmission method based on an adaptive access mechanism of vehicle flow density, which can improve the data transmission efficiency and reliability in a vehicle networking environment.

[0009] The technical solution adopted by the present invention is an information transmission method of an adaptive access mechanism based on vehicle flow density, the method comprising the following steps:

[0010] S1. In the coverage area of ​​the cellular network, the base station broadcasts its network configuration parameters to all vehicle users in the area, wherein the network configuration parameters include the number of sub-channels in the network, the time-frequency resource size of the sub-channels, the semi-persistent scheduling period T, and the sub-channel reselection probability p; the vehicle users continuously monitor the sub-channels in the cellular network, record the received signal power value strength on the sub-channels, and save them;

[0011] S2, in time slot t G , the vehicle user defines the selection window as: [t G +T1,t G +T2], and identify candidate channel resources within the selection window; wherein T1 represents the processing time for the vehicle user to select the candidate channel resources, T1≤4; T2 represents the delay time for the vehicle user to send a data packet, T 2min ≤T2≤100,10≤T 2min ≤20 or 20≤T2≤100, where T 2min Indicates the minimum delay time for vehicle users to send data packets;

[0012] S3, defining a perception window, wherein the perception window is: [t G -1000,t G ], using the perception window to screen the candidate channel resources in the selection window, screening out the channel resources that may have been previously reserved by other vehicle users and the channel resources previously reserved by the user, and obtaining the remaining candidate channel resources L1 after screening;

[0013] S4, selecting the portion of channel resources with the lowest average reference signal strength indicator in the perception window from the remaining candidate channel resources L1 as the remaining candidate channel resources L2, and the number of the remaining candidate channel resources L2 is ≥ 20% of the number of candidate channel resources in the selection window;

[0014] S5, executing the evaluation mechanism to check whether the remaining candidate channel resources L2 are available; if available, transmitting data on the remaining candidate channel resources L2; ​​if not available, returning to step S2 and executing again;

[0015] S6. For the excluded resources and total channel resources in the selection window, calculate the channel busy rate CBR. When CBR≥0.8, use the coding modulation access mechanism of QPSK-r0.5 for data transmission; when 0.5≤CBR<0.8, use the coding modulation access mechanism of QPSK-r0.7 for data transmission; when CBR<0.5, use the coding modulation access mechanism of 16QAM-r0.5 for data transmission.

[0016] The beneficial effects of the present invention are as follows: the present invention adaptively adjusts the MODE2 access mechanism according to different vehicle flow densities. By real-time monitoring of vehicle flow and network load conditions, the relevant configuration parameters of the MODE2 access mechanism are dynamically adjusted to match current communication needs. When the communication network is overloaded, the scheme can effectively reduce the complexity and bit error rate of data transmission, optimize the use of network resources, and ensure efficient data transmission and system stability. When the vehicle flow is low, the method of the present invention can select an efficient access method to increase the transmission rate; when the vehicle flow is high, it switches to a more robust access method to enhance the reliability and anti-interference capability of the transmission.

[0017] Preferably, in step S3, the specific process of using the perception window to screen the candidate channel resources in the selection window includes the following steps:

[0018] S3.1. First, search for the time slot T in which the information was transmitted before in the perception window. N , and for each time slot T where information is transmitted N Perform traversal and calculate the time slot T N +q·RRI i Whether it is within the selection window, where RRI i Represents the total resource reservation interval, q represents an integer, when RRI i ≥100, q=1; if time slot T N +q·RRI i Within the selection window, exclude the time slot T N +q·RRI i Channel resources;

[0019] S3.2, secondly, for the time slot T in the selection window, N +q·RRI i Each remaining time slot T F Traverse and calculate T at the same time F +j·RRI TX , where j is a constant, 1≤j≤10·ReselectionCounter-1, and ReselectionCounter is a reselection counter. If T F+j·RRI TX and T N +q·RRI i If they are equal, then the time slot T is directly excluded. F Channel resources;

[0020] S3.3, finally, exclude the candidate channel resources that may be occupied by other vehicles, find the corresponding transmission block TB through the side chain control information received by the vehicle user, and measure the reference signal received power RSRP on the TB for judgment. If the RSRP is higher than the set threshold, exclude the candidate channel resources;

[0021] S3.4. Summarize the remaining candidate channel resources to obtain the remaining candidate channel resources L1 after screening. If the number of remaining candidate channel resources L1 does not meet the requirement that the number of remaining candidate channel resources L1 is ≥ 20% of the candidate channel resources in the selection window, increase the set threshold described in step S3.3 by 3dB and return to step S3.3 for screening.

[0022] Preferably, in step S4, the average reference signal strength indicator is a time slot T in the perception window. TX -Measured at T·j.

[0023] Preferably, in step S6, the expression for calculating the channel busy rate CBR is:

[0024] Among them, N E represents the total number of channel resources excluded in the selection window, and N represents the total number of channel resources in the selection window;

[0025]

[0026] Where, 0≤n≤2; λ represents the information data packet generation frequency, and its value is 10Hz or 20Hz; S represents the number of subchannels in each time slot; S PSR It represents the average number of vehicles that the vehicle can perceive in the selection window;

[0027]

[0028] Among them, β represents the traffic density, that is, how many vehicles are there per meter; PSR represents the information packet perception rate; P t represents the vehicle's transmitted signal power, which is 20dBm or 23dBm; PL represents the path loss in the channel; P SEN Indicates the perceived power threshold of vehicle users, which is -90.5dBm. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of sub-channelization of an adaptive access mechanism in the method of the present invention;

[0030] Figure 2 A schematic diagram of channel resources in a sensing window and a selection window in the present invention;

[0031] Figure 3 It is a schematic diagram of the re-evaluation mechanism in the present invention;

[0032] Figure 4 This is a PDR comparison diagram when the vehicle flow rate is high in the simulation experiment of the present invention;

[0033] Figure 5 It is a PDR comparison diagram when the traffic volume is low in the simulation experiment of the present invention. DETAILED DESCRIPTION

[0034] The invention will be further described below with reference to the accompanying drawings and in combination with specific implementations, so that those skilled in the art can implement the invention with reference to the description. The protection scope of the invention is not limited to the specific implementations.

[0035] The present invention improves the 5G NR-V2X MODE2 mechanism by using an adaptive access mechanism. The access mechanism includes a scheme that is dynamically adjusted based on the real-time network environment. The vehicle automatically selects the most appropriate access mechanism scheme based on the channel quality and communication requirements. It has the following advantages:

[0036] In the access mechanism selection stage, the present invention introduces the channel busy ratio (CBR) as a standard for adaptive selection.

[0037] In the resource allocation stage, differentiated sub-channelization schemes are set for different MCSs according to different access mechanisms. This differentiated resource allocation strategy helps to improve the reliability of information transmission.

[0038] In addition, the present invention improves the SPS scheme of 5G NR-V2X MODE2, allowing vehicles to adaptively select the most appropriate coding and modulation method according to the channel busy rate, which effectively reduces data packet conflicts and significantly improves the performance of NR-V2X.

[0039] The following is a detailed description of the adaptive access mechanism and resource allocation strategy:

[0040] In the present invention, in 5G NR-V2X MODE2, we first define two sub-channelization schemes: adjacent PSCCH+PSSCH and non-adjacent PSCCH+PSSCH. Figure 1As shown in Figure 1, the sidelink control information (SCI) is transmitted in the PSCCH, and the transport blocks (TB) are transmitted in the PSSCH. If the SCI and TB are adjacent, the subchannel is defined as the resource block for transmitting SCI+TB, and this scheme is defined as the adjacent PSCCH+PSSCH scheme. For the non-adjacent PSCCH+PSSCH scheme, Figure 1 As shown in , the entire channel is divided into two resource pools. The upper resource pool only transmits SCI, and the lower resource pool only transmits TB. SCI and TB are not adjacent. In this case, the sub-channel is defined as the resource blocks that transmit TB. Figure 1 As shown, for adjacent PSCCH+PSSCH, SCI and TB are transmitted in adjacent resource blocks (RBs). For each SCI+TB transmission, SCI occupies the first two RBs of the subchannel used for transmission, and TB is transmitted in the RB after SCI. For non-adjacent PSCCH+PSSCH, RBs are divided into multiple resource pools, one pool is dedicated to transmitting SCI, each SCI occupies two RBs, and the second pool is only used to transmit TB.

[0041] In C-V2X, TB can use QPSK or QAM for transmission, while SCI always uses QPSK modulation. Therefore, for the first sub-channelization scheme, we use QPSK-r0.5 or QPSK-r0.7 coding modulation; for the second sub-channelization scheme, we use 16QAM-r0.5 coding modulation for TB transmission. Under the same bandwidth, when using these three MCS, each time slot contains 3, 4, and 6 sub-channels respectively, and each sub-channel occupies 16, 12, and 8 RBs respectively. However, the coding modulation method of 16QAM-r0.5 is more sensitive to noise and interference, and has a higher bit error rate, so it needs to be used in an environment with better channel conditions; the coding modulation method of QPSK-r0.5 has a stronger error correction capability and is more resistant to noise and interference, so it performs well in a poor channel environment; the coding modulation method of QPSK-r0.7 balances the information transmission rate and error correction capability, and is suitable for most communication applications under medium conditions, but its error correction capability is weaker than that of QPSK-r0.5. The following introduces the specific steps of an information transmission method based on an adaptive access mechanism of vehicle flow density of the present invention:

[0042] Step 1: Within the coverage area of ​​the cellular network, the base station broadcasts its network configuration parameters to all vehicle users (VUE) within the area, wherein the network configuration parameters include the number of sub-channels within the network, the size of the time-frequency resources of the sub-channels, the semi-persistent scheduling period T, and the sub-channel reselection probability p; the vehicle users continuously monitor the sub-channels within the cellular network, record the received signal power value strength on the sub-channels and save it; in addition, when the vehicle is not within the coverage area of ​​the cellular network, the vehicle users use a set of pre-configured parameters to replace the network configuration parameters that need to be configured.

[0043] Step 2: Define the selection window (SW) and identify candidate resources; G , the vehicle user needs to reserve a subchannel to send data packets of periodic services; the vehicle user defines the selection window as: [t G +T1,t G +T2], and identify candidate channel resources within the selection window; wherein T1 represents the processing time for the vehicle user to select the candidate channel resources, T1≤4; T2 represents the delay time for the vehicle user to send a data packet, when the vehicle transmits 10 data packets, or 20 data packets, or 50 data packets per second, the corresponding maximum delay PDB is 100ms, 50ms, 20ms, respectively, T 2min ≤T2≤100,10≤T 2min ≤20, or 20≤T2≤100, and T2 must be set so that t G +T2 meets the maximum delay requirement for transmitting TB;

[0044] Step 3: Define the perception window, the perception window is: [t G -1000,t G ], using the perception window to perform resource screening on the candidate channel resources in the selection window, screening out the channel resources that may have been previously reserved by other vehicle users and the channel resources previously reserved by the user, and obtaining the remaining candidate channel resources L1 after screening;

[0045] Step 4: select the channel resources with the lowest average RSSI in the sensing window from the remaining candidate channel resources L1 as the remaining candidate channel resources L2, and the number of the remaining candidate channel resources L2 is ≥ 20% of the number of candidate channel resources in the selection window;

[0046] Step 5: Execute the evaluation mechanism to check whether the remaining candidate channel resource L2 is available; if available, transmit data on the remaining candidate channel resource L2; if not available, return to step S2 and execute again;

[0047] Step six, for the excluded resources and total channel resources in the selection window, calculate the channel busy rate CBR, when CBR ≥ 0.8, use the coding modulation access mechanism of QPSK-r0.5 for data transmission; when 0.5 ≤ CBR < 0.8, use the coding modulation access mechanism of QPSK-r0.7 for data transmission; when CBR < 0.5, use the coding modulation access mechanism of 16QAM-r0.5 for data transmission; the excluded resources in the selection window refer to the part of resources that are screened out in the selection window after step four, that is, the part of resources that are not selected as L2 in the remaining candidate channel resources L1 after screening.

[0048] In the above steps, after step 4, the remaining candidate channel resources L2 are created. At this time, a resource is randomly selected from L2, such as Figure 3 As shown, assuming that we select the blue primary resource in time slot m, VUE will continue to sense the transmission of other UEs in time slot m and execute step 2 again to check whether the selected resource is available. VUE will execute step 2 at n' and define a new selection window [n'+T1,n'+T2'], where T2' represents the delay time for vehicle users to send data packets, T2min≤T2'≤PDB-(n'-n), where n is the time slot that VUE wants to define the selection window when executing step 2 for the first time, and PDB is the maximum delay time for transmitting TB; if the primary resource is not excluded in the new selection window, the data packet is transmitted on the primary resource. If the primary resource is excluded, steps 3 and 4 are executed to select a new resource.

[0049] Furthermore, in step S3, the specific process of using the perception window to perform resource screening on the candidate channel resources in the selection window includes the following steps:

[0050] S3.1. First, search for the time slot T in which the information was transmitted before in the perception window. N , because the vehicle is transmitting information in time slot TN, and since the vehicle communication process is half-duplex, the vehicle cannot receive information in this time slot and cannot know the resource occupancy of other vehicles and the reservation status in the selection window. Therefore, every possible resource reservation interval (RRI) should be traversed, that is, for every time slot T where information has been transmitted, N Perform a traversal and calculate T at the same time N +q·RRI i Whether it is within the selection window, where RRI iRepresents the total resource reservation interval, q represents an integer, when RRI i ≥100, q=1; if T N +q·RRI i Within the selection window, exclude the time slot T N +q·RRI i Channel resources;

[0051] S3.2. Next, for each remaining time slot T in the selection window, F Traverse and calculate T at the same time F +j·RRI TX , where j is a constant, 1≤j≤10·ReselectionCounter-1, and ReselectionCounter is a reselection counter. The value of the reselection counter varies depending on the resource reservation interval. For example, when RRI is greater than or equal to 100ms, ReselectionCounter is randomly selected between 5 and 15. If T F +j·RRI TX and T N +q·RRI i If they are equal, then the time slot T is directly excluded. F resources;

[0052] S3.3. Finally, exclude the candidate channel resources that may be occupied by other vehicles, find the corresponding transmission block TB through the received side chain control information and measure the reference signal received power RSRP on TB for judgment. If the RSRP is higher than the set threshold, exclude the candidate channel resources;

[0053] S3.4. Summarize the remaining candidate channel resources to obtain the remaining candidate channel resources L1 after screening. If the number of remaining candidate channel resources L1 does not meet the requirement that the number of remaining candidate channel resources L1 is ≥ 20% of the candidate channel resources in the selection window, increase the set threshold described in step S3.3 by 3dB and return to step S3.3 for screening.

[0054] Further, in step S4, the average reference signal strength indication is the time slot T in the perception window TX -T·j, if the semi-persistent scheduling period T is 100ms, then the average reference signal strength indication expression is:

[0055] Further, in step S6, the expression for calculating the channel busy rate CBR is:

[0056] Among them, N Erepresents the total number of channel resources excluded in the selection window, and N represents the total number of channel resources in the selection window;

[0057]

[0058] Where, 0≤n≤2; λ represents the frequency of generating information data packets, which can be 10Hz or 20Hz; S represents the number of subchannels in each time slot; S PSR It represents the average number of vehicles that the vehicle can perceive in the selection window;

[0059]

[0060] Among them, β represents the traffic density, that is, how many vehicles are there per meter; PSR represents the information packet perception rate; P t represents the vehicle's transmitted signal power, which is 20dBm or 23dBm; PL represents the path loss in the channel; P SEN Indicates the perceived power threshold of vehicle users, which is -90.5dBm.

[0061] Each time VUE transmits a TB, the reselection counter (RC) in SCI will be reduced by 1. When RC is 0, VUE repeats steps 2 to 5 with probability 1-p to re-reserve the sub-channel, and continues to occupy the previously reserved sub-channel to send service data packets with probability p. Where p∈[0,0.8], if the resources occupied by the TB to be transmitted are greater than the previously reserved sub-channel or the delay time of the TB to be transmitted is greater than 100 time slots, it is necessary to reselect the sub-channel.

[0062] The following is a specific simulation experiment to illustrate the superiority of the information transmission method of the adaptive access mechanism based on vehicle flow density proposed by the present invention.

[0063] The scenario of the simulation experiment is selected from the 3GPP Manhattan urban scenario simulated by MATLAB. The position of the vehicle in the Manhattan urban scenario is deployed on the road according to the spatial Poisson distribution process, and the vehicle travels at a constant speed in the lane. The coordinates of the vehicle at 10s are extracted, and the traffic density is set to 0.1vehicle / m and 0.3vehicle / m respectively to simulate the change of traffic density in the real driving scenario. For the simulation parameters and deployment of each experiment, we set a receiving vehicle and a sending vehicle, the total channel access bandwidth is 20MHz, the subcarrier spacing is 30kHz, and the specific simulation parameters are specified in Table 1. In order to further evaluate the performance of the scheme proposed in the present invention, we use the unimproved conventional Mode2 transmission mechanism as the Baseline, compare the packet acceptance rates under the two schemes (Baseline and the scheme of the present invention) and analyze the performance of the improved scheme.

[0064] Table 1 Simulation parameters

[0065]

[0066] exist Figures 4 to 5 In the figure, the comparison results between the method of the present invention and the conventional Mode 2 under different traffic density are shown. It can be clearly seen from the comparative analysis that the adaptive access mechanism proposed in this paper always shows better performance regardless of whether it is under low traffic density or high traffic density. When the traffic volume is low, this scheme selects an efficient access method to increase the transmission rate, and when the traffic volume is high, it switches to a more robust access method to enhance the reliability and anti-interference ability of the transmission. In addition, with the increase of traffic density, the advantages of this mechanism become more obvious. When the channel environment is poor, the sender can choose an access method with lower modulation complexity and higher anti-noise interference ability to ensure that the information can be more reliably transmitted to the receiver and improve the stability of the system. The simulation experimental results show that the adaptive access mechanism can effectively improve network performance and optimize resource utilization when dealing with different traffic conditions, thereby providing strong support for the realization of intelligent transportation systems.

Claims

1. An information transmission method based on an adaptive access mechanism of vehicle flow density, characterized in that: The method comprises the following steps: S1. In the coverage area of ​​the cellular network, the base station broadcasts its network configuration parameters to all vehicle users in the area, wherein the network configuration parameters include the number of sub-channels in the network, the time-frequency resource size of the sub-channels, the semi-persistent scheduling period T, and the sub-channel reselection probability p; the vehicle users continuously monitor the sub-channels in the cellular network, record the received signal power value strength on the sub-channels, and save them; S2, in time slot t G , the vehicle user defines the selection window as: [t G +T1,t G +T2], and identify candidate channel resources within the selection window; wherein T1 represents the processing time for the vehicle user to select the candidate channel resources, T1≤4; T2 represents the delay time for the vehicle user to send a data packet, T 2min ≤T2≤100,10≤T 2min ≤20 or 20≤T2≤100, where T 2min Indicates the minimum delay time for vehicle users to send data packets; S3, defining a perception window, wherein the perception window is: [t G -1000,t G ], using the perception window to screen the candidate channel resources in the selection window, screening out the channel resources that may have been previously reserved by other vehicle users and the channel resources previously reserved by the user, and obtaining the remaining candidate channel resources L1 after screening; S4, selecting the portion of channel resources with the lowest average reference signal strength indicator in the perception window from the remaining candidate channel resources L1 as the remaining candidate channel resources L2, and the number of the remaining candidate channel resources L2 is ≥ 20% of the number of candidate channel resources in the selection window; S5, executing the evaluation mechanism to check whether the remaining candidate channel resources L2 are available; if available, transmitting data on the remaining candidate channel resources L2; ​​if not available, returning to step S2 and executing again; S6. For the excluded resources and total channel resources in the selection window, calculate the channel busy rate CBR. When CBR≥0.8, use the coding modulation access mechanism of QPSK-r0.5 for data transmission; when 0.5≤CBR<0.8, use the coding modulation access mechanism of QPSK-r0.7 for data transmission; when CBR<0.5, use the coding modulation access mechanism of 16QAM-r0.5 for data transmission.

2. The information transmission method of the adaptive access mechanism based on vehicle flow density according to claim 1 is characterized by: In step S3, the specific process of using the perception window to screen the candidate channel resources in the selection window includes the following steps: S3.

1. First, search for the time slot T in which the information was transmitted before in the perception window. N , and for each time slot T where information is transmitted N Perform traversal and calculate the time slot T N +q·RRI i Whether it is within the selection window, where RRI i Represents the total resource reservation interval, q represents an integer, when RRI i ≥100, q=1; if time slot T N +q·RRI i Within the selection window, exclude the time slot T N +q·RRI i All candidate channel resources within; S3.2, secondly, for the time slot T in the selection window, N +q·RRI i Each remaining time slot T F Traverse and calculate T at the same time F +j·RRI TX , where j is a constant, 1≤j≤10·ReselectionCounter-1, and ReselectionCounter is a reselection counter. If T F +j·RRI TX and T N +q·RRI i If they are equal, then the time slot T is directly excluded. F Channel resources; S3.3, finally, exclude the candidate channel resources that may be occupied by other vehicles, find the corresponding transmission block TB through the side chain control information received by the vehicle user, and measure the reference signal received power RSRP on the TB for judgment. If the RSRP is higher than the set threshold, exclude the candidate channel resources; S3.

4. Summarize the remaining candidate channel resources to obtain the remaining candidate channel resources L1 after screening. If the number of remaining candidate channel resources L1 does not meet the requirement that the number of remaining candidate channel resources L1 is ≥ 20% of the candidate channel resources in the selection window, increase the set threshold described in step S3.3 by 3dB and return to step S3.3 for screening.

3. The information transmission method of the adaptive access mechanism based on vehicle flow density according to claim 2 is characterized by: In step S4, the average reference signal strength indicator is the time slot T in the perception window. TX -Measured at T·j.

4. The information transmission method of the adaptive access mechanism based on vehicle flow density according to claim 3 is characterized by: In step S6, the expression for calculating the channel busy rate CBR is: Among them, N E represents the total number of channel resources excluded in the selection window, and N represents the total number of channel resources in the selection window; Where, 0≤n≤2; λ represents the information data packet generation frequency, and its value is 10Hz or 20Hz; S represents the number of subchannels in each time slot; S PSR It represents the average number of vehicles that the vehicle can perceive in the selection window; Among them, β represents the traffic density, that is, how many vehicles are there per meter; PSR represents the information packet perception rate; P t represents the vehicle's transmitted signal power, which is 20dBm or 23dBm; PL represents the path loss in the channel; P SEN Indicates the perceived power threshold of vehicle users, which is -90.5dBm.

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