Radio wave propagation evaluation device and radio wave propagation evaluation method

Abstract

The purpose of the present invention is to provide a technology for appropriately estimating or evaluating radio wave reception intensity without requiring a large number of man-hours in an area where there are a large number of shielding and reflecting objects.　To this end, a radio wave propagation evaluation device according to the present invention includes a means for creating, using a first computer simulation, first model terrain data with which statistical properties substantially matching those of the sample measured values are obtained, the sample measured values indicating the relationship between a reception position and reception power in an evaluation area. The device may further include: a means for adding a dynamic object to the first model terrain data to create second model terrain data; and a means for outputting radio wave reception intensity in the evaluation area by performing a second computer simulation using the second model terrain data.

Description

Radio Wave Propagation Evaluation Apparatus and Radio Wave Propagation Evaluation Method

[0001] The present invention relates to a radio wave propagation evaluation apparatus and a radio wave propagation evaluation method.

[0002] In a wireless communication system using radio waves, since the reception intensity of radio waves greatly affects communication quality, in order to achieve stable operation, it is necessary to evaluate the installation location and number of wireless stations, etc. prior to introduction. Ideally, it is certain to temporarily install a wireless station in the planned introduction area and evaluate the radio wave intensity through actual measurement. However, if there are objects (shielding and reflecting objects) with shielding and reflection properties for radio waves in the planned introduction area, it is not realistic to evaluate under all conditions because it requires a very large amount of man-hours.

[0003] Japanese Patent Application Laid-Open No. 2001-99880

[0004] Techniques for calculating and evaluating the reception intensity of radio waves by computer simulation based on terrain data have also been conventionally used. Although there is a possibility of reducing man-hours compared to actual measurement, in an environment where there are a very large number of shielding and reflecting objects, such as a railway vehicle base, factory, or warehouse, there is a problem that the man-hours required to create accurate terrain data become extremely large.

[0005] For example, in Patent Document 1, terrain data that is a prerequisite for computer simulation is generated from building design data, and the radio wave intensity is calculated using electromagnetic field analysis. Although accurate results can be obtained if all terrain data including materials can be accurately generated, on the other hand, electromagnetic field analysis takes an enormous amount of calculation time.

[0006] On the other hand, there is a method called ray tracing that performs calculations by treating radio waves in the same way as light. It is known that this method can perform calculations in a much shorter time than electromagnetic field analysis. However, in an environment where there are many relatively small objects as described above, there is a problem that appropriate results cannot be obtained even if accurate terrain data is given.

[0007] An object of the present invention is to provide a technique for appropriately estimating or evaluating the radio wave reception intensity without requiring a large amount of man-hours in an evaluation area with a very large number of such shielding and reflecting objects.

[0008] To solve the above-mentioned problems, one representative radio wave propagation evaluation device of the present invention includes means for creating first model terrain data using first computer simulation, which obtains statistical properties that substantially match the statistical properties of sample measured values, using sample measured values ​​that show the relationship between the receiving position and the received power in the evaluation area.

[0009] According to the present invention, a technique can be provided for appropriately estimating or evaluating radio wave reception strength in evaluation areas with a very large number of shielding and reflecting objects, without requiring significant manpower. Other problems, configurations, and effects not mentioned above will be clarified by the following description of embodiments.

[0010] Figure 1 shows an example of an evaluation area where sample measurements are performed. Figure 2 shows an example of the relationship between the receiving position and received power obtained by sample measurements. Figure 3 shows an example of the evaluation flow in the radio wave propagation evaluation device of Example 1. Figure 4 shows an example of the arrangement of shielding and reflecting objects within the evaluation area. Figure 5 shows an example of the results of a radio wave propagation simulation. Figure 6 shows an example of second model terrain data. Figure 7 shows an example of the evaluation flow in the radio wave propagation evaluation device of Example 2.

[0011] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to these embodiments. In the drawings, identical parts are denoted by the same reference numeral. When there are multiple components having the same or similar functions, different subscripts may be used with the same reference numeral. Furthermore, when it is not necessary to distinguish between these multiple components, the subscripts may be omitted.

[0012] Furthermore, while terms such as "first," "second," etc., may be used in this disclosure to describe various elements or components, it will be understood that these elements or components should not be limited by these terms. These terms are used solely to distinguish one element or component from another. Accordingly, the first element or component described below may also be called the second element or component without departing from the teaching of the concept of the present invention.

[0013] Furthermore, the position, size, shape, and extent of each component shown in the drawings may not represent the actual position, size, shape, and extent in order to facilitate understanding of the invention. For this reason, the present invention is not necessarily limited to the position, size, shape, and extent disclosed in the drawings.

[0014] First, let's explain the terms commonly used in this embodiment. (Characteristics of shielding and reflecting materials) In this disclosure, the characteristics of shielding and reflecting materials refer to the attributes of an object that affect radio wave intensity and radio wave quality. For example, this includes the shape, size, density, dielectric constant, refractive index, etc. of an object.

[0015] (Statistical Properties) In this disclosure, statistical properties mean radio wave propagation characteristics that can be treated statistically (based on the concept of median and spread). For example, this includes the distribution of received signal strength of a mobile station with respect to distance from a radio station.

[0016] (Random) In this disclosure, "random" means random numbers with a predetermined density. For example, this includes defining a number of meshes in a plane, each with a predetermined side length, and randomly placing objects within each mesh.

[0017] (Dynamic Objects) In this disclosure, dynamic objects are a general term for objects that can enter and exit the evaluation area, and include, for example, railway vehicles if the evaluation area is a railway depot, or cargo if the evaluation area is a warehouse.

[0018] <Sample Measurement> Before describing Example 1, we will explain the sample measurement, which is a prerequisite for the evaluation flow of Example 1, using Figure 1.

[0019] Figure 1 shows an example of an evaluation area where sample measurements are taken. Sample measurements are taken in the measurable area 23 (shaded area) within the entire evaluation area 20. The measurable area 23 is the range within the evaluation area 20 where measurements can be taken. For example, if the target area is a railway depot, this includes the service deck; if it is a factory or warehouse, it includes passageways, etc.

[0020] Sample measurements are performed after the specifications of the wireless system under evaluation (wireless communication standards, specifications of wireless equipment, antenna specifications, frequency band, etc.), the placement of wireless stations (transmitting stations), and the location of mobile stations (measuring instruments) have been determined based on actual implementation. The measurement is then performed by transmitting radio waves from the wireless stations and measuring the received power when the mobile stations receive them. If there are multiple candidate locations for wireless stations, measurements are performed for each candidate location. The same applies if there are multiple candidate locations for mobile stations, but it is desirable to place a number of mobile stations sufficient to grasp the statistical properties. One possible method for this is to move a measuring instrument mounted on a cart comprehensively within the evaluation area and take measurements at predetermined intervals (20 ms).

[0021] Furthermore, there are no particular limitations on the specific measurement methods used between radio stations and mobile stations; any measurement method can be adopted. In addition, sample measurements can be performed not only in two dimensions but also in three dimensions.

[0022] Figure 2 shows an example of the relationship between reception location and received power obtained through sample measurements. The graph in Figure 2 summarizes the results of receiving radio waves transmitted from one radio station at multiple mobile stations. The horizontal axis represents the distance between the radio station and the mobile station (reception location), and the vertical axis represents the power measured by the mobile station (received power). Each dot in the graph in Figure 2 corresponds to the measured value by the mobile station.

[0023] (Example 1) Figure 3 shows an example of the evaluation flow in the radio wave propagation evaluation device of Example 1. In this example, steps 10 to 13 are the flow for creating the first model terrain data, step 14 is the flow for creating the second model terrain data, and steps 15 and 16 are the flow for outputting the radio wave reception strength in the evaluation area. Each flow will be described in order below.

[0024] <Flowchart for creating the first model terrain data> The flowchart for creating the first model terrain data will be explained below.

[0025] Step 10 involves creating model terrain data to be used in the radio wave propagation simulation described later. The model terrain data created here does not need to accurately reflect the actual terrain data. In this embodiment, shielding and reflecting objects 21 are randomly placed within the evaluation area 20 to create the model terrain data. The shielding and reflecting objects 21 have characteristics that affect radio wave propagation, such as the shape, size, density, dielectric constant, and refractive index of the object. At least one of these can be adjusted.

[0026] Figure 4 shows an example of the arrangement of shielding and reflecting objects within the evaluation area. In the evaluation area 20 of Figure 4, one radio station (not shown) is placed, along with numerous shielding and reflecting objects 21 placed randomly. An example of randomly placing the shielding and reflecting objects 21 is to place cylinders with a diameter of 1 m at an average distance of 3 m between each cylinder. The model terrain data created in step 10 combines the arrangement of shielding and reflecting objects 21 in the evaluation area 20 with the above-mentioned characteristics set for the shielding and reflecting objects 21.

[0027] In step 11, a radio wave propagation simulation is performed on the model terrain data created in step 10. The radio wave propagation simulation calculates the received power for multiple receiving positions within the model terrain data using computer simulation. It is preferable that the specifications of the wireless system in the radio wave propagation simulation be the same as those of the sample measurement. Furthermore, the receiving positions (locations of mobile stations) can be set by dividing the evaluation area into a mesh, for example. In that case, the received power intensity will be simulated for each mesh.

[0028] While ray tracing is a suitable computer simulation method for radio wave propagation, other simulation methods can also be employed.

[0029] Figure 5 shows an example of the results of a radio wave propagation simulation. The graph in Figure 5 summarizes the results of receiving radio waves transmitted from a radio station at multiple receiving locations. The horizontal axis represents the distance between the radio station and the receiving location, and the vertical axis represents the power measured at the receiving location (received power). Each dot in the graph in Figure 5 corresponds to the simulated value at the receiving location.

[0030] In step 12, the statistical properties of the measured values ​​of the mobile station obtained from the sample measurements are compared with the statistical properties of the simulated values ​​of the receiving position obtained from the radio wave propagation simulation in step 11. The statistical properties compared here can be set according to the desired design performance, and may be, for example, the average received power for each distance, or a value such as the 95% worst-case value.

[0031] In this embodiment, the statistical properties of the measured values ​​of the mobile station obtained from the sample measurements, and the statistical properties of the simulated values ​​of the receiving position obtained from the radio wave propagation simulation in step 11, are modeled using the following equation (1).

[0032] Equation (1) uses the distance d from the radio station as a parameter, where Pr is the received power, Pt is the transmitted power, Gt is the transmitting antenna gain, Gr is the receiving antenna gain, λ is the wavelength, d is the distance from the transmitting station, and α and β are coefficients. The first and second terms of equation (1) are free propagation attenuation terms that decrease according to the square law with respect to the distance from the radio station, and the third term is a term to consider additional attenuation due to the effects of reflection and scattering that occur at a constant rate with respect to the distance from the transmitting station. The coefficients α and β are mathematically modeled by determining them using methods such as the least squares method.

[0033] The curve shown in Figure 2 is an example of a model equation (statistical properties) that mathematically models the measured values ​​using equation (1), and the curve shown in Figure 5 is an example of a model equation (statistical properties) that mathematically models the simulated values ​​using equation (1). In this embodiment, these two model equations are used to compare and evaluate whether the statistical properties related to the measured values ​​and the statistical properties related to the simulated values ​​are in approximate agreement. For example, the curve showing the 95% worst-case scenario in Figure 2 (indicated as "worst") is compared to the curve showing the 95% worst-case scenario in Figure 5 (indicated as "worst").

[0034] In step 13, the comparison results from step 12 are evaluated. If the comparison results are not determined to be approximately identical, the process returns to step 10, and at least one of the characteristics of the shielding / reflecting objects 21, such as the shape, size, density, dielectric constant, or refractive index of the object, is adjusted similarly for all shielding / reflecting objects 21, and steps 10 through 13 are repeated.

[0035] There are no particular restrictions on how the characteristics are adjusted here, but for cases where the relationship between the characteristics of the shielding / reflecting material 21 and the coefficients of equation (1) is known, such as the fact that increasing the density of the shielding / reflecting material 21 increases α and decreasing the density decreases α, or that increasing the dielectric constant decreases α and decreasing the dielectric constant increases α, or that the size and density of the shielding / reflecting material 21 are related to β, adjustments may be made by referring to such matters.

[0036] If the comparison result is determined to be a near-identical match, this model terrain data becomes the first model terrain data, and the process proceeds to step 14. Note that the method for determining near-identical match is not limited, and may be used as appropriate, for example, by using a known curve similarity evaluation method.

[0037] By creating this first model terrain data, it is possible to obtain terrain data with radio wave propagation characteristics that closely match those of actual terrain data, even without creating terrain data that accurately reflects actual obstructions and reflectors, and even in areas where it is not possible to place a mobile station and take measurements in sample measurements. Therefore, radio wave reception strength can be appropriately estimated or evaluated over the entire range of the evaluation area without requiring a large amount of effort.

[0038] <Flowchart for creating the second model terrain data> Next, we will explain the flowchart for creating the second model terrain data.

[0039] In step 14, a second model terrain data set is created by placing dynamic objects within the evaluation area 20 of the first model terrain data obtained in step 13.

[0040] Figure 6 shows an example of the second model terrain data. In Figure 6, 22-1, 22-2, and 22-3 represent dynamic objects. Multiple patterns of arrangement for dynamic objects are predetermined to reflect actual conditions. In addition, predetermined values ​​are set for characteristics that affect radio wave intensity and quality for the dynamic objects, but these characteristic values ​​should be set according to the actual conditions of the dynamic objects (for example, according to the type and length of the railway vehicles).

[0041] <Flowchart for outputting radio wave reception strength in the evaluation area> Next, we will explain the flowchart for outputting radio wave reception strength in the evaluation area.

[0042] In step 15, the radio wave propagation simulation is performed again on the second model terrain data obtained in step 14, and the results are output. The results of the radio wave propagation simulation are, for example, the received power intensity at each location within the evaluation area.

[0043] In step 16, it is determined whether the second model terrain data has been created for all the placement patterns of the dynamic objects. If the second model terrain data has been created for all the placement patterns of the dynamic objects, the evaluation flow of this embodiment ends. Otherwise, return to step 14 and repeat steps 14 to 16 for the remaining placement patterns of the dynamic objects.

[0044] By creating the second model terrain data in this way, placing dynamic objects on it, and performing radio wave propagation simulations, it becomes possible to appropriately estimate or evaluate the radio wave reception intensity without requiring a large amount of labor even under conditions where the dynamic objects exist in various placement patterns.

[0045] This embodiment can reproduce the statistical properties of the received power even when the arrangement of the shielding and reflecting objects does not match the actual environment, so it is suitable as an evaluation technique for the arrangement of wireless stations, etc. Also, when the target area is a railway base and one of the communication devices is mounted on a train, according to the technology of the present invention, there is also an excellent feature that it is possible to evaluate the received power on the track of the train that has not been actually measured based on the measurement results in the service deck where it is easy to actually measure.

[0046] (Embodiment 2) FIG. 7 is a diagram showing an example of an evaluation flow in the radio wave propagation evaluation apparatus of Embodiment 2. The difference from Embodiment 1 is that step 17 is added between step 14 and step 15. Since the other steps are the same as those in Embodiment 1, the description is omitted.

[0047] In step 17, an interference source is further arranged on the second model terrain data with dynamic objects arranged in step 15. Here, an interference source is something that exists within the evaluation area and interferes with the wireless station when communicating using the same frequency band as the wireless station, such as another system that uses Wi-Fi (2.4 GHz band). Since the type, number, arrangement, etc. of the interference sources can be grasped through a preliminary survey in the evaluation area, it is advisable to arrange them in accordance with the actual situation.

[0048] Next, in step 15, in addition to the radio wave propagation simulation shown in step 15 of Example 1, a radio wave propagation simulation will also be performed by placing an interference source that emits radio waves on the second model terrain data.

[0049] In Example 1, the received power of the target signal is evaluated. However, if interference waves are present, interference power is necessary to evaluate the reception quality. In Example 2, by adding the interference source in step 17, it becomes possible to calculate not only the received power of the target signal but also the received power of the interference waves, enabling the evaluation of the signal-to-interference power ratio, i.e., the signal quality of the received signal.

[0050] (Modifications) Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the present invention. Possible embodiments of the present invention are described below, but are not limited thereto.

[0051] (Aspect 1) A radio wave propagation evaluation device for evaluating the radio wave reception strength in an evaluation area, characterized by comprising means for creating first model terrain data using first computer simulation, which obtains statistical properties substantially consistent with the statistical properties of sample measured values, using sample measured values ​​that show the relationship between reception position and received power in the evaluation area.

[0052] (Aspect 2) A radio wave propagation evaluation device according to Aspect 1, further comprising: means for adding dynamic objects to the first model terrain data to create a second model terrain data; and means for outputting the radio wave reception strength in the evaluation area using the second model terrain data with a second computer simulation.

[0053] (Aspect 3) A radio wave propagation evaluation device according to either aspect 1 or 2, wherein the means for creating the first model terrain data using the first computer simulation is characterized by placing shielding and reflecting objects on the model terrain data that forms the basis of the first model terrain data.

[0054] (Aspect 4) A radio wave propagation evaluation device according to any one of aspects 1 to 3, wherein the means for creating the first model terrain data using a first computer simulation is such that the statistical properties of the model terrain data created in the process of the first computer simulation and the statistical properties of the sample measured values ​​are determined to be substantially the same by comparing their respective mathematical models, and the mathematical model includes one or more of the following: a square law attenuation term that takes into account the effect of free propagation attenuation, an exponential attenuation term that takes into account attenuation due to reflection and scattering of radio waves, and an adjustment constant term.

[0055] (Aspect 5) A radio wave propagation evaluation device according to either aspect 3 or 4, wherein the means for creating the first model terrain data using a first computer simulation is characterized by adjusting the characteristics of shielding and reflecting objects placed in the model terrain data in order to match the statistical properties of the model terrain data created in the process of the first computer simulation with the statistical properties of the measured sample values.

[0056] (Aspect 6) A radio wave propagation evaluation device according to any one of aspects 2 to 5, wherein the means for creating the second model terrain data further comprises means for adding interference sources.

[0057] (Aspect 7) A radio wave propagation evaluation method for evaluating the radio wave reception strength in an evaluation area, comprising a procedure for creating first model terrain data using first computer simulations, which obtain statistical properties that substantially match the statistical properties of sample measured values, using sample measured values ​​that show the relationship between reception position and received power in the evaluation area.

[0058] (Aspect 8) A radio wave propagation evaluation method according to aspect 7, further comprising: a step of adding dynamic objects to the first model terrain data to create a second model terrain data; and a step of outputting the radio wave reception strength in the evaluation area using the second model terrain data with a second computer simulation.

[0059] (Aspect 9) A radio wave propagation evaluation method according to either aspect 7 or 8, characterized in that, in the procedure for creating the first model terrain data using a first computer simulation, shielding and reflecting objects are placed on the model terrain data that forms the basis of the first model terrain data.

[0060] (Aspect 10) A radio wave propagation evaluation method according to any one of aspects 7 to 9, wherein in the procedure for creating the first model terrain data using a first computer simulation, the statistical properties of the model terrain data created in the process of the first computer simulation and the statistical properties of the sample measured values ​​are determined to be substantially identical by comparing their respective mathematical models, and the mathematical model includes one or more of the following: a square law attenuation term that takes into account the effect of free propagation attenuation, an exponential attenuation term that takes into account attenuation due to reflection and scattering of radio waves, and an adjustment constant term.

[0061] (Aspect 11) A radio wave propagation evaluation method according to either aspect 9 or 10, wherein in the procedure for creating the first model terrain data using a first computer simulation, the characteristics of the shielding and reflecting objects placed in the model terrain data are adjusted in order to substantially match the statistical properties of the model terrain data created in the process of the first computer simulation with the statistical properties of the sample measured values.

[0062] (Aspect 12) A radio wave propagation evaluation method according to any one of aspects 8 to 11, characterized in that the step of creating the second model terrain data further includes a step of adding interference sources.

[0063] 20: Evaluation area 21: Obstructions / reflective objects 22: Dynamic objects 23: Measurable area

Claims

1. A radio wave propagation evaluation device for evaluating the radio wave reception strength in an evaluation area, characterized by comprising means for creating first model terrain data using first computer simulations, which obtain statistical properties substantially consistent with the statistical properties of the sample measured values, using sample measured values ​​that show the relationship between the reception position and the received power in the evaluation area.

2. A radio wave propagation evaluation device according to claim 1, further comprising: means for adding dynamic objects to the first model terrain data to create a second model terrain data; and means for outputting the radio wave reception strength in the evaluation area using the second model terrain data with a second computer simulation.

3. A radio wave propagation evaluation device according to claim 1 or 2, wherein the means for creating the first model terrain data using the first computer simulation is characterized by placing shielding and reflecting objects on the model terrain data that forms the basis of the first model terrain data.

4. A radio wave propagation evaluation device according to claim 1 or 2, wherein the means for creating the first model terrain data using a first computer simulation is such that the statistical properties of the model terrain data created in the process of the first computer simulation and the statistical properties of the sample measured values ​​are determined to be substantially identical by comparing their respective mathematical models, and the mathematical model includes one or more of the following: a square law attenuation term that takes into account the effect of free propagation attenuation, an exponential attenuation term that takes into account attenuation due to reflection and scattering of radio waves, and an adjustment constant term.

5. A radio wave propagation evaluation device according to claim 3, wherein the means for creating the first model terrain data using a first computer simulation is characterized by adjusting the characteristics of the shielding and reflecting objects placed in the model terrain data in order to match the statistical properties of the model terrain data created in the process of the first computer simulation with the statistical properties of the sample measured values.

6. A radio wave propagation evaluation device according to claim 2, wherein the means for creating the second model terrain data further comprises means for adding interference sources.

7. A radio wave propagation evaluation method for evaluating the radio wave reception strength in an evaluation area, characterized by comprising a procedure for creating first model terrain data using first computer simulations, which obtain statistical properties that substantially match the statistical properties of sample measured values, using sample measured values ​​that show the relationship between reception position and received power in the evaluation area.

8. A radio wave propagation evaluation method according to claim 7, further comprising: a step of adding dynamic objects to the first model terrain data to create a second model terrain data; and a step of outputting the radio wave reception strength in the evaluation area using the second model terrain data with a second computer simulation.

9. A radio wave propagation evaluation method according to claim 7 or 8, characterized in that, in the step of creating the first model terrain data using a first computer simulation, shielding and reflecting objects are placed on the model terrain data that forms the basis of the first model terrain data.

10. A radio wave propagation evaluation method according to claim 7 or 8, wherein in the step of creating the first model terrain data using a first computer simulation, the statistical properties of the model terrain data created in the process of the first computer simulation and the statistical properties of the sample measured values ​​are determined to be substantially identical by comparing their respective mathematical models, and the mathematical model includes one or more of the following: a square law attenuation term that takes into account the effect of free propagation attenuation, an exponential attenuation term that takes into account attenuation due to reflection and scattering of radio waves, and an adjustment constant term.

11. A radio wave propagation evaluation method according to claim 9, wherein the procedure for creating the first model terrain data using a first computer simulation is characterized by adjusting the characteristics of the shielding and reflecting objects placed in the model terrain data in order to substantially match the statistical properties of the model terrain data created in the process of the first computer simulation with the statistical properties of the measured sample values.

12. A radio wave propagation evaluation method according to claim 8, characterized in that the step of creating the second model terrain data further includes a step of adding interference sources.

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