Network optimization method and system based on railway ray tracing wireless coverage prediction

Abstract

The present invention belongs to the technical field of railway wireless propagation prediction, and specifically provides a network optimization method and system based on railway ray tracing wireless coverage prediction, wherein the method includes: first, in a coordinate system, the BIM design model is integrated with the three-dimensional survey map; then the map elements of the integrated map are classified, and electromagnetic parameters are assigned to different materials in the map, and the model is lightweighted to obtain the basic environmental model after the railway is built; finally, the basic environmental model and the built railway building model are synthesized into a railway simulation environment model, and wireless network planning is carried out. The scheme is based on high-precision survey maps and three-dimensional design models, accurately reflects the railway environment after construction, and accurately obtains the prediction results of wireless signal coverage along the railway. At the same time, the lightweight processing of the survey map and the BIM model also ensures the computational efficiency of the wireless coverage prediction; and greatly improves the accuracy and robustness of the wireless coverage prediction.

Description

Technical Field

[0001] The present invention relates to the technical field of railway wireless propagation prediction, and more specifically, to a network optimization method and system based on railway ray tracing wireless coverage prediction. Background Art

[0002] The traditional railway wireless network planning and design process is: first, the wireless network planning and design is carried out according to the preliminary planned railway horizontal and vertical sections, and then the field survey is carried out to obtain a grid electronic map with an accuracy of 20 meters to 50 meters. The preliminary wireless site and network parameters are determined through the simulation of the wireless network planning software based on the empirical propagation model, and then the on-site survey is carried out to determine the final construction drawing design of the wireless base station site and antenna configuration and other design contents. This wireless network planning method and design process has the following three problems: First, traditional wireless network planning and simulation are based on independent simulation software. If you want to obtain more accurate radio wave propagation prediction results, you need to correct the existing empirical wireless propagation model or modify the parameters of the empirical propagation model to perform wireless propagation prediction. This work requires field testing, so it cannot be carried out in the survey and design stage. Field testing conditions are only possible when the railway project is basically completed; second, the grid electronic map required by the traditional wireless network planning (radio wave propagation prediction) software is not accurate enough, and it is impossible to describe the impact of the actual terrain on the propagation of radio wave signals in detail and accurately, and the high-precision three-dimensional digital map lacks an interface with traditional commercial software; third, the traditional digital map only enters basic information such as the center line of the line and bridges and tunnels, and usually does not load and use the railway BIM design results, especially does not simulate the environment after the railway is built in the survey and design stage, and accurately carry out wireless coverage prediction based on the terrain and landforms after the railway is built. The accuracy of radio wave propagation prediction is not high, and it is easy to have design defects such as coverage blind spots caused by improper planning and design or site selection. In summary, the design of traditional wireless communication systems can only be fully determined in the final stage of the project. During this period, due to the lack of comprehensive and detailed evaluation and optimization methods, the wireless base station site selection is improper, resulting in frequent adjustments to the design site, insufficient wireless coverage or network quality defects, which may greatly affect the project investment and even the quality of the project. In the current process of bidding and construction of projects only after the synchronous design of the pre-station and post-station construction drawings is completed, it is a major problem to provide accurate site design in the design stage.

[0003] To solve the above problems, the China Railway Construction Electrification Bureau and the Beijing Jiaotong University team simulated the completed railway in the preliminary design stage to plan the wireless network. They carried out a pilot project of 900MHz GSM-R wireless network optimization technology based on the railway BIM model in the construction of the four electric systems of the Beijing-Xiong Railway. They used the ray tracing method to predict the propagation of radio waves on a simplified BIM model, optimize the preset azimuth and elevation angles of the base station antenna, and shorten the construction and commissioning cycle. They also applied for a number of patents, such as: a method for obtaining channel information by ray tracing for reflected or scattered propagation, patent authorization number: 201910424428.1; a method, device and computer equipment for predicting field strength, patent authorization number: 201910620032.4; a method and device for predicting high-speed rail network coverage based on machine learning and ray tracing, patent authorization number: 202010072957.2, etc. However, this pilot study was simply based on BIM model data, without considering the impact of the surrounding original geographical environment. Railways, especially high-speed railways, frequently pass through cities and mountainous areas during the planning process. The impact of the surrounding original terrain on the signal (mainly obstruction) is sometimes even greater than the railway building itself. Therefore, simply simulating the surrounding terrain, or even only considering the BIM design model, cannot obtain accurate simulation results in most railway environments. Relevant research based on high-precision environmental data needs to be further promoted. Summary of the invention

[0004] The present invention aims to solve the technical problem that the existing technology simply simulates the surrounding terrain, or even only considers the BIM design model, but cannot obtain accurate simulation results in most railway environments.

[0005] The present invention provides a network optimization method based on railway ray tracing wireless coverage prediction, comprising the following steps:

[0006] S1, obtain the three-dimensional survey map and BIM design model of the railway;

[0007] S2, integrates the BIM design model with the 3D survey map in one coordinate system;

[0008] S3, classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built;

[0009] S4, generating a completed railway building model;

[0010] S5, synthesize the basic environment model and the completed railway building model into a railway simulation environment model, and carry out wireless network planning.

[0011] Preferably, the S1 specifically includes: a three-dimensional survey map obtained by oblique photography or laser radar technology.

[0012] Preferably, the S2 specifically includes:

[0013] S21, placing the BIM design model on the corresponding position of the three-dimensional survey map;

[0014] S22, deleting the overlapping areas of the model areas corresponding to the roadbed, cutting, tunnel entrance and newly built slope protection in the railway three-dimensional design and the three-dimensional survey map from the three-dimensional survey map to obtain a fused high-precision survey map.

[0015] Preferably, the S22 specifically includes:

[0016] The terrain and objects in the fused high-precision survey map are classified and marked with different colors; the classified model areas are vegetation cover, soil, cement road surface, water surface, and surrounding buildings.

[0017] Preferably, S3 specifically includes: model areas of vegetation coverage, soil, cement pavement, water surface, and surrounding buildings, which are re-mapped and marked with different colors, so that the mapping relationship between electromagnetic parameters of different colors and materials can be established for subsequent simulation calculations to complete the electromagnetic parameter assignment process.

[0018] Preferably, the model lightweighting in S3 specifically includes: reducing the resolution and the number of model facets by vertex thinning of the survey map model that has been corrected and classified and assigned environmental electromagnetic parameters, so as to reduce the amount of ray tracing simulation calculations at the back end.

[0019] Preferably, the S4 specifically includes:

[0020] All internal structure information and small-scale design information on the exterior surface in the BIM design model are removed, leaving a simplified building exterior surface design model;

[0021] After extracting the model facade, classify the different material elements of the model and re-map them with different colors. The same material as the environment base model is mapped with the same color as the former.

[0022] The building exterior surface design model is mesh-simplified and further lightweighted using the edge folding algorithm to obtain the completed railway building model.

[0023] Preferably, S5 specifically includes: deploying base stations along the railway, setting the site parameters of the base station's transmission power, antenna height, gain, number, antenna azimuth and downtilt angle, forming a preset site location and site parameters, and then using a ray tracing method to analyze the rationality of the wireless network planning and design.

[0024] Preferably, the ray tracing method specifically comprises:

[0025] Set the radio wave transmitting point Tx and all the receiving points Rx that need to be calculated, find the Rx farthest from Tx, and set the maximum propagation distance threshold; calculate the center point of all triangular face elements in the model, and when the sum of the two distances from the center point to the selected Rx and Tx is greater than the threshold, delete the face element to obtain the environment model within the simulation range;

[0026] In the environment model within the simulation range, determine the visibility of all remaining model face elements to all Rx and Tx, delete all faces that are invisible to both Tx and Rx, and construct an environment model A for direct, transmitted, and reflected light;

[0027] At the same time, in the environment model within the simulation range, all vertices in each pair of Tx-Rx Fresnel zones are determined, and the face elements whose vertices are not in the zone are deleted to form the diffraction environment model B; then, the same-plane face elements in the environment model A and the environment model B are merged to determine whether the normal vectors of each two adjacent faces and the vertical distance from Tx to the plane where the face element is located are exactly the same, and the two adjacent faces with the same conditions are merged, and the face elements are expanded into polygons to form the final simplified simulation environment model A and simplified simulation environment model B;

[0028] Environmental model A is used to calculate direct radiation, transmission, and reflection in the environment, and environmental model B is used to calculate diffraction in the environment. The received electric field multipath components of each Rx are saved in complex form, and all electric field multipath components received by the same Rx are coherently superimposed to obtain the wireless coverage prediction simulation results of all observation points.

[0029] The present invention also provides a network optimization system based on railway ray tracing wireless coverage prediction, the system is used to implement a network optimization method based on railway ray tracing wireless coverage prediction, comprising:

[0030] The fusion module is used to obtain the 3D survey map and BIM design model of the railway, and fuse the BIM design model with the 3D survey map in one coordinate system;

[0031] The network planning module is used to classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built; and generate a completed railway building model; then the basic environmental model and the completed railway building model are combined into a railway simulation environment model, and wireless network planning is carried out.

[0032] Beneficial effects: The network optimization method and system based on railway ray tracing wireless coverage prediction provided by the present invention include: first, in a coordinate system, the BIM design model is integrated with the three-dimensional survey map; then, the map elements of the integrated map are classified, and electromagnetic parameters are assigned to different materials in the map, and the model is lightweighted to obtain the basic environmental model after the railway is built; finally, the basic environmental model and the completed railway building model are synthesized into a railway simulation environment model, and wireless network planning is carried out. The scheme is based on high-precision survey maps and three-dimensional design models to accurately reflect the railway environment after construction, and uses ray tracing technology to use a more accurate wireless propagation simulation method in the early stage of railway design to more accurately obtain the prediction results of wireless signal coverage along the railway, and on this basis, wireless network planning is carried out. At the same time, the lightweight processing of the survey map and the BIM model also ensures the computational efficiency of the wireless coverage prediction; and greatly improves the accuracy and robustness of the wireless coverage prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a network optimization method based on railway ray tracing wireless coverage prediction provided by the present invention;

[0034] Figure 2 Generate a flow chart for the environment basic model provided by the present invention;

[0035] Figure 3 A flow chart for generating a completed railway building model provided by the present invention. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0037] like Figure 1 As shown, the network optimization method based on railway ray tracing wireless coverage prediction provided by the embodiment of the present invention includes the following steps:

[0038] S1, obtain the three-dimensional survey map and BIM design model of the railway;

[0039] S2, integrates the BIM design model with the 3D survey map in one coordinate system;

[0040] S3, classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built;

[0041] S4, generating a completed railway building model;

[0042] S5, synthesize the basic environment model and the completed railway building model into a railway simulation environment model, and carry out wireless network planning.

[0043] The specific technical problems to be solved in this implementation plan are as follows:

[0044] 1. Acquisition of the completed railway ray tracing environment model. Combining high-precision survey maps with BIM technology, the terrain in the survey map is modified accordingly based on the design model, and the modified survey map and BIM design model are lightweighted respectively. Before the completion of the railway, a ray tracing three-dimensional environment model of the completed railway is simulated and generated;

[0045] 2. Carry out ray tracing simulation calculations based on the preset base station locations and site parameters, and adjust and optimize the wireless network planning and design according to the calculation results, effectively improving the accuracy and robustness of the wireless network planning scheme and the quality of engineering design before the railway is built;

[0046] 3. Simplify the environment model for ray tracing characteristics. Reduce the number of map faces by distinguishing the visibility of emission and model faces, distinguishing faces within the emission-receiving Fresnel zone, and simplify the railway ray tracing three-dimensional environment model map to improve the efficiency of ray tracing calculations.

[0047] The specific implementation process of this technical solution is as follows:

[0048] (1) Through railway survey and design work, high-precision three-dimensional railway topographic survey maps (referred to as "three-dimensional survey maps") and BIM design models of new railway facilities (referred to as "BIM design models") are obtained. High-precision three-dimensional survey maps are mainly obtained through oblique photography or laser radar (LiDAR) technology.

[0049] (2) Integration of BIM design model and 3D survey map. First, unify the model coordinate system, unify the BIM design model and 3D survey map to the same projection coordinate system, and delete the overlapping parts of the survey map with the design model, mainly including the survey map model area corresponding to the roadbed, road cutting, tunnel entrance and newly built slope protection in the design model.

[0050] (3) Generate an environmental basic model. The environmental basic model is mainly an environmental information model other than the main building structure of the railway, mainly including the surrounding natural terrain including mountains, vegetation, etc., as well as artificial buildings including houses and roads.

[0051] First, based on the fused 3D survey map, different map elements are classified and processed, including vegetation coverage, soil, cement road surface, water surface, surrounding buildings and other model areas, and re-mapped with different colors. Later simulation calculations will establish a mapping relationship between electromagnetic parameters of different colors and materials to complete the electromagnetic parameter assignment process;

[0052] Secondly, after completing the classification of map elements, the model resolution is reduced by vertex thinning to reduce the model complexity, and the basic model of the environment after the railway is built is derived.

[0053] (4) Generate a completed railway building model. The railway building model refers to all BIM design models of the entire railway line except for the internal structure design of the tunnel. The three-dimensional environment model required for railway section wireless coverage prediction based on ray tracing only needs to extract the model's outer surface information. However, in the railway BIM design process, since it needs to meet the technical requirements of multiple disciplines, its model design content is far more than the actual needs of the communication system design, which creates a meaningless system calculation burden on the ray tracing calculation. Therefore, it is necessary to remove all the internal structure information and the small-sized design information on the outer surface in the BIM design model, leaving a simplified building exterior surface design model; after extracting the model facade, classify the different material elements of the model, mainly into glass, masonry wall, metal wall, etc., and re-map and mark them with different colors. It should be noted that the same material as the environmental basic model needs to be mapped and marked with the same color as the former. After completing the above operations, the building exterior surface design model is meshed, and the building exterior surface design model is further lightweight using the edge folding algorithm to obtain the completed railway building model.

[0054] (5) After obtaining the basic model of the environment after construction and the railway building model, they can be synthesized into a railway simulation environment model and wireless network planning can be carried out, that is, base stations (site locations) are deployed along the railway, and the base station transmission power, antenna height, gain, number, antenna azimuth, downtilt angle and other site parameters are set to form preset site locations and site parameters. Ray tracing technology is then used to analyze the rationality of the wireless network planning and design.

[0055] The ray tracing method requires separate calculations for each transmitting antenna. Considering that the amount of calculation for each transmitting antenna is relatively large, it is necessary to further simplify the built railway simulation environment model according to the requirements of the ray tracing algorithm during the calculation process, remove model elements that will not affect the ray tracing calculation results, and reduce the computational complexity of the simulation process.

[0056] Specifically, the simplification process first sets the radio wave transmitting point Tx and all the receiving points Rx that need to be calculated in the model, finds the Rx farthest from Tx, and sets the maximum propagation distance threshold. Calculate the center point of all triangular face elements in the model. When the sum of the two distances from the center point to the selected Rx and Tx is greater than the threshold, delete the face element to obtain the environment model within the simulation range.

[0057] In the environment model within the simulation range, determine the visibility of all remaining model face elements to all Rx and Tx, delete all faces that are invisible to both Tx and Rx, and construct an environment model A for direct, transmitted, and reflected light.

[0058] At the same time, all vertices in each pair of Tx-Rx Fresnel zones are determined in the environment model within the simulation range, and the face elements whose vertices are not in the zone are deleted to form the diffraction environment model B.

[0059] Then, the same-plane face elements in environment model A and environment model B are fused to determine whether the normal vectors of every two adjacent faces and the vertical distance from Tx to the plane where the face element is located are exactly the same. The two adjacent faces with the same conditions are fused, and the face elements are expanded into polygons to form the final simplified simulation environment model A and simplified simulation environment model B.

[0060] (7) The simplified environment model A and the simplified simulated environment model B are respectively imported into the ray tracing algorithm. The environment model A is used to calculate the direct radiation, transmission, and reflection in the environment, and the environment model B is used to calculate the diffraction in the environment. The received electric field multipath components of each Rx are saved in complex form, and all the electric field multipath components received by the same Rx are coherently superimposed to obtain the wireless coverage prediction simulation results of all observation points.

[0061] (8) Based on the wireless simulation prediction results, the rationality of the wireless network planning and design (station location and site parameters) is judged. The judgment rule can be to determine whether there is an area in the wireless coverage area where the minimum receiving level does not meet the relevant railway standards, or other network technical indicators (such as rate) do not meet the regulatory requirements. If there is, the wireless network planning and design (station location and site parameters) is adjusted and the ray tracing simulation calculation is performed again. If not, the calculation is completed and the wireless network planning results, i.e., the station location and site parameters, are output.

[0062] Figure 1 The overall flow chart of the present invention is described. The present invention as a whole can be divided into two parts for description, namely, obtaining the railway environment simulation model after completion and ray tracing wireless network planning calculation.

[0063] The first part of the present invention is to obtain a simulation model of the railway environment after completion, that is, to generate a simulation model of the railway environment after completion suitable for the ray tracing algorithm based on the three-dimensional survey map and the BIM design model. After obtaining the two original models (the three-dimensional survey map and the BIM design model), first unify the coordinate systems of the two models; use the BIM design model as a reference for the three-dimensional survey map and delete the overlapping areas; then perform lightweight and model material processing to generate an environmental basic model. The specific method is shown in the process Figure 2 ; First, simplify the 3D model mesh of the BIM design model, then process the model material to generate the completed railway building model. For specific methods, see the process Figure 3 After obtaining the basic environment model and the railway building model, the two processed models are integrated into a unified environment model, that is, the railway environment simulation model after completion.

[0064] After obtaining the completed railway environment simulation model, we will enter the content of ray tracing wireless network planning calculation based on the lightweight model. It is necessary to load the preset railway wireless network planning scheme, and after determining the current base station radio wave transmission point Tx and all receiving points Rx that need to be calculated, further simplify the model.

[0065] First, find the Rx farthest from Tx and set the maximum propagation distance threshold. Calculate the center point of all triangular face elements in the model. When the sum of the two distances from the center point to the selected Rx and Tx is greater than the threshold, delete the face element to obtain the environment model within the simulation range. In the environment model within the simulation range, determine the visibility of all remaining model face elements to all Rx and Tx, delete all faces that are not visible to Tx and Rx, and form an environment model A for direct, transmitted, and reflected. At the same time, determine all vertices in the Fresnel zone of each pair of Tx-Rx in the environment model within the simulation range, delete all face elements whose vertices are not in the area, and form an environment model B for diffraction.

[0066] After that, the environmental model A and the environmental model B are processed separately, and the same-plane surface elements in the model are fused to form the final simplified simulation environment model (environmental model A and environmental model B), which is used to import the ray tracing simulation algorithm to perform wireless propagation coverage prediction and obtain the wireless coverage prediction simulation results of all observation points.

[0067] After obtaining the simulation results of wireless coverage prediction for the railway section, the wireless coverage results of all wireless base stations and repeaters in the section are integrated to judge the rationality of the wireless network planning and design. The judgment rule can be to determine whether there is an area in the wireless coverage area of ​​the section where the minimum receiving level does not meet the relevant railway standards, or other network technical indicators (such as rate) do not meet the requirements of the specification. If so, adjust the wireless network planning and design, and re-perform ray tracing simulation calculations. If not, complete the calculation and output the wireless network planning results.

[0068] Figure 2 The flow chart of generating the basic model of the railway environment after completion based on the 3D survey map is described. First, the fused 3D survey map is obtained based on the initial 3D survey map and the BIM design model; then, different map elements are classified and the map materials are assigned through different color map identification methods; after completing the classification of map elements, the model resolution is reduced by vertex thinning to reduce the model complexity, and the basic model of the railway environment after completion is derived.

[0069] Figure 3 This paper describes the flow chart of generating the railway building model after the railway is completed based on the BIM design model. First, the building facade of the three-dimensional design model is extracted, and all internal structures including the building internal housing construction design and building structure design are deleted; the different material elements of the model are classified and re-mapped with different colors. It should be noted that the same material as the environmental basic model needs to be mapped with the same color as the former; after completing the above operations, the grid is simplified to obtain the railway building model after completion.

[0070] In a specific implementation scenario:

[0071] 1. Export the completed railway simulation environment model

[0072] (1) Through the preliminary railway survey and design work, high-precision 3D survey maps and BIM design models are obtained, and the coordinate system of the 3D model is unified.

[0073] (2) High-precision survey maps mainly refer to three-dimensional survey maps obtained through oblique photography or LiDAR technology. However, these maps are not directly applicable to ray tracing simulation calculations. First, they need to be integrated with the three-dimensional design results. Secondly, electromagnetic parameters need to be assigned to different materials in the map and the model needs to be lightweight in order to effectively adapt to the ray tracing simulation algorithm.

[0074] (3) During the actual construction process, the original terrain may change to a large extent, especially for railway sections passing through mountainous areas. The completed railway may involve leveling the mountains or excavating rock walls. Therefore, it is necessary to integrate high-precision survey maps with BIM design models so that they can present the completed railway environment as realistically as possible.

[0075] (4) To integrate the BIM design model with the 3D survey map, the BIM design model must first be placed at the corresponding position on the 3D survey map to serve as a reference model for correcting the 3D survey map.

[0076] (5) The BIM design model and the 3D survey map are integrated, and the overlapping areas between the model areas corresponding to the roadbed, cutting, tunnel entrance, and newly built slope protection in the railway 3D design and the 3D survey map are deleted from the 3D survey map to obtain a fused high-precision survey map.

[0077] (6) Assigning electromagnetic parameters to the map is mainly to classify the terrain and objects of the fused high-precision survey map into model areas such as vegetation cover, soil, cement road surface, water surface, and surrounding buildings, and mark them with different colors. Electromagnetic parameters are assigned by mapping different colors to corresponding material parameters in the ray tracing simulation algorithm to obtain a phased map model.

[0078] (7) The map is lightweighted by thinning the vertices of the survey map model that has been corrected and classified and assigned environmental electromagnetic parameters, thereby reducing the resolution and greatly reducing the number of model face elements, thereby reducing the amount of ray tracing simulation calculations in the back end.

[0079] (8) The lightweight processing of the BIM design model is mainly divided into two steps. First, the model facade is identified and extracted to obtain the building exterior surface design model. Then, the building exterior surface design model is further lightweighted by mesh simplification through the edge folding algorithm.

[0080] (8) The three-dimensional environment model required for railway section wireless coverage prediction based on ray tracing only needs to extract the model's outer surface information. However, in the railway BIM design process, since it needs to meet the technical requirements of multiple disciplines, its model design content is far more than the actual needs of communication system design, which creates a meaningless system calculation burden for ray tracing calculations. Therefore, it is necessary to remove all internal structure information and small-scale design information on the outer surface in the BIM design model, leaving a simplified building outer surface design model.

[0081] (9) The processed three-dimensional survey map model is combined with the BIM design model to form a unified built railway simulation environment model.

[0082] 2. Ray tracing wireless network planning optimization based on lightweight model

[0083] (1) Load the preset railway wireless network planning scheme, deploy base stations (site locations) along the railway, set the base station's transmission power, antenna height, gain, number, antenna azimuth, downtilt angle and other site parameters, and form preset site locations and site parameters. In this embodiment, it is a section of a tunnel entrance section of the railway, and a base station (or repeater) needs to be set at a suitable position outside the tunnel entrance at both ends of the section.

[0084] (2) Perform ray tracing wireless coverage prediction calculations on the two tunnel entrance base stations respectively. Set the radio wave transmission point Tx and all receiving points Rx that need to be calculated in the model. Tx is the designed base station or repeater antenna position, and Rx is the roof antenna position along the railway. Therefore, Rx can be set to points along the railway that are 4.5 meters above the track surface and at a certain distance.

[0085] (3) Find the Rx farthest from Tx and set the maximum propagation distance threshold. Calculate the center points of all triangular face elements in the model. When the sum of the two distances from the center point to the selected Rx and Tx is greater than the threshold, delete the face element to obtain the environment model within the simulation range.

[0086] (4) In the environment model within the simulation range, determine the visibility of all remaining model facets to all Rx and Tx. The visibility of the model facet relative to Tx (Rx) is determined by the following method: the center point of the triangular facet is P, and the facet normal vector is Then there is

[0087]

[0088] By means of loop testing or matrix building, the visibility of the model face elements of the model Tx and all Rx is judged, and the visible face element numbers are recorded respectively. Then, the intersection of all the recorded results is calculated to find the face element numbers that are invisible to both Tx and Rx, and all the face elements with corresponding numbers are deleted from the model to form an environmental model A for direct, transmitted, and reflected light.

[0089] (5) To construct the diffraction environment model B, it is necessary to determine all vertices within the Fresnel zone of the farthest pair of Tx-Rx in the environment model within the simulation range. That is, find all model vertices within the Fresnel ellipsoid with Tx and Rx as the focus, and delete all the face elements whose vertices are not within the area. The Fresnel zone here can be determined according to the actual calculation requirements to determine the order of the Fresnel zone. To determine whether the model face element vertex is within the Fresnel zone, the following formula can be used for calculation:

[0090]

[0091] Where n is the order of the Fresnel zone, λ is the wavelength of the radio wave, d1 and d2 are the distances from the foot of the perpendicular from the model vertex to the Tx-Rx line segment to Tx and Rx respectively. When the length of the perpendicular from the model vertex to the Tx-Rx line segment is less than Rn, the vertex can be considered to be in the Fresnel zone.

[0092] (6) The environmental model A and the environmental model B are processed separately, and the same-plane face elements in the model are merged to determine whether the normal vectors of every two adjacent faces and the vertical distance from Tx to the plane where the face element is located are exactly the same. The two adjacent faces with the same conditions are merged, and the face elements are expanded into polygons to form the final simplified simulation environment model (environmental model A and environmental model B), which is used to import the ray tracing simulation algorithm and perform wireless propagation coverage prediction.

[0093] (7) Based on the mirror image ray tracing algorithm, the wireless signal reception strength of each observation point is calculated, and a signal coverage simulation curve along the railway is generated. The ray tracing algorithm calculates the multipath components such as direct, transmitted, reflected and diffracted that can be received by each observation point in the map. Direct, transmitted and reflected calculations are performed in environmental model A, and diffraction calculations are performed in environmental model B. The two parts of the calculation results obtained at each observation point are coherently superimposed. The receiving paths of all observation points along the line are uniformly displayed on the complete map.

[0094] (8) After completing the wireless propagation coverage prediction in this environment, the results are observed to determine whether the current wireless network planning scheme is reasonable. If there are areas where the minimum receiving level does not meet the railway-related standards, or other network technical indicators (such as rate) do not meet the regulatory requirements, it is necessary to adjust the preset site location and site parameters, and then re-perform ray tracing simulation calculations. If it is verified that there is no unreasonable design, the calculation is completed and the wireless network planning results are output.

[0095] The present invention is used to perform ray tracing wireless coverage prediction and network planning optimization calculation. It can not only simulate the railway environment after completion and perform relatively accurate wireless propagation prediction in the design stage when the railway has not yet been built, but also reduce the computational complexity of multiple calculations in the same environment by classifying and filtering out irrelevant items in the map according to the ray tracing calculation characteristics, effectively improve the overall computing efficiency, and help improve the accuracy and robustness of wireless network planning solutions and the quality of railway wireless system engineering design.

[0096] The embodiment of the present invention further provides a network optimization system based on railway ray tracing wireless coverage prediction, the system is used to implement a network optimization method based on railway ray tracing wireless coverage prediction, including:

[0097] The fusion module is used to obtain the 3D survey map and BIM design model of the railway, and fuse the BIM design model with the 3D survey map in one coordinate system;

[0098] The network planning module is used to classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built; and generate a completed railway building model; then the basic environmental model and the completed railway building model are combined into a railway simulation environment model, and wireless network planning is carried out.

[0099] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A network optimization method based on railway ray tracing wireless coverage prediction, characterized in that: The following steps are involved: S1, obtain the three-dimensional survey map and BIM design model of the railway; S2, integrates the BIM design model with the 3D survey map in one coordinate system; S3, classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built; S4, generating a completed railway building model, specifically including: All internal structure information and small-scale design information on the exterior surface in the BIM design model are removed, leaving a simplified building exterior surface design model; After extracting the model facade, classify the different material elements of the model and re-map them with different colors. The same material as the environment base model is mapped with the same color as the former. The building exterior surface design model is meshed and further lightweighted using the edge folding algorithm to obtain the completed railway building model; S5, synthesizing the basic environment model and the completed railway building model into a railway simulation environment model, and carrying out wireless network planning, specifically including: deploying base stations along the railway, setting the site parameters of the base station transmission power, antenna height, gain, number, antenna azimuth angle and downtilt angle, forming a preset site location and site parameters, and then using a ray tracing method to analyze the rationality of the wireless network planning and design; the ray tracing method specifically includes: Set the radio wave transmitting point Tx and all the receiving points Rx that need to be calculated, find the Rx farthest from Tx, and set the maximum propagation distance threshold; calculate the center point of all triangular face elements in the model, and when the sum of the two distances from the center point to the selected Rx and Tx is greater than the threshold, delete the face element to obtain the environment model within the simulation range; In the environment model within the simulation range, determine the visibility of all remaining model face elements to all Rx and Tx. The visibility of model face elements relative to Tx and Rx is determined by: the center point of the triangular face element is P, and the face element normal vector is Then there is By loop testing or building a matrix, the visibility of the model facets of the model Tx and all Rx is judged, and the visible facet numbers are recorded respectively. Then, the intersection of all the recorded results is calculated to find the facet numbers that are invisible to both Tx and Rx, and all the facets with corresponding numbers are deleted from the model to form the environment model A for direct, transmitted, and reflected images. At the same time, in the environment model within the simulation range, all vertices in each pair of Tx-Rx Fresnel zones are determined, and the face elements whose vertices are not in the zone are deleted to form the diffraction environment model B. Whether the face element vertices of the model are in the Fresnel zone can be calculated according to the following formula: Where n is the order of the Fresnel zone, λ is the wavelength of the radio wave, d1 and d2 are the distances from the foot of the perpendicular from the model vertex to the Tx-Rx line segment to Tx and Rx respectively. When the length of the perpendicular from the model vertex to the Tx-Rx line segment is less than Rn, the vertex can be considered to be in the Fresnel zone; then the same-plane face elements in the environment model A and the environment model B are fused to determine whether the normal vectors of each two adjacent faces and the vertical distance from Tx to the plane where the face element is located are exactly the same, and the two adjacent faces with the same conditions are fused, and the face element is expanded into a polygon to form the final simplified simulation environment model A and simplified simulation environment model B; Environmental model A is used to calculate direct radiation, transmission, and reflection in the environment, and environmental model B is used to calculate diffraction in the environment. The received electric field multipath components of each Rx are saved in complex form, and all electric field multipath components received by the same Rx are coherently superimposed to obtain the wireless coverage prediction simulation results of all observation points.

2. The network optimization method based on railway ray tracing wireless coverage prediction according to claim 1 is characterized in that: The S1 specifically includes: a three-dimensional survey map obtained by oblique photography or laser radar technology.

3. The network optimization method based on railway ray tracing wireless coverage prediction according to claim 1 is characterized in that: The S2 specifically includes: S21, placing the BIM design model on the corresponding position of the three-dimensional survey map; S22, deleting the overlapping areas of the model areas corresponding to the roadbed, cutting, tunnel entrance and newly built slope protection in the railway three-dimensional design and the three-dimensional survey map from the three-dimensional survey map to obtain a fused high-precision survey map.

4. The network optimization method based on railway ray tracing wireless coverage prediction according to claim 3 is characterized in that: The S22 specifically includes: The terrain and objects in the fused high-precision survey map are classified and marked with different colors; the classified model areas are vegetation cover, soil, cement road surface, water surface, and surrounding buildings.

5. The network optimization method based on railway ray tracing wireless coverage prediction according to claim 1 is characterized in that: The S3 specifically includes: model areas of vegetation coverage, soil, cement road surface, water surface, and surrounding buildings, which are re-mapped and marked with different colors so that the mapping relationship between electromagnetic parameters of different colors and materials can be established for subsequent simulation calculations to complete the electromagnetic parameter assignment process.

6. The network optimization method based on railway ray tracing wireless coverage prediction according to claim 1, characterized in that: The model lightweighting in S3 specifically includes: reducing the resolution and the number of model facets by vertex thinning of the survey map model that has been corrected and classified and assigned environmental electromagnetic parameters, so as to reduce the amount of ray tracing simulation calculations at the back end.

7. A network optimization system based on railway ray tracing wireless coverage prediction, characterized in that: The system is used to implement the network optimization method based on railway ray tracing wireless coverage prediction according to any one of claims 1 to 6, comprising: The fusion module is used to obtain the 3D survey map and BIM design model of the railway, and fuse the BIM design model with the 3D survey map in one coordinate system; The network planning module is used to classify the map elements of the fused map, assign electromagnetic parameters to different materials in the map, and lightweight the model to obtain the basic environmental model after the railway is built; and generate a completed railway building model; then the basic environmental model and the completed railway building model are combined into a railway simulation environment model, and wireless network planning is carried out.

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