CN113242566A - Unmanned aerial vehicle base station selection method under shielding effect - Google Patents

Abstract

The present invention studies and discusses the shading problem of buildings in dense urban areas, and proposes a method for selecting a base station of an unmanned aerial vehicle under shading effect. If it is not zero, according to the dense urban environment parameters and penetration loss factor, determine the occlusion of the link between the user and the UAV base station within the connectable range and the penetration loss of the link. The user selects the nearest UAV base station that is not blocked by buildings within the connectable range as the serving UAV base station. When there is no UAV base station that is not blocked by buildings, select the nearest unmanned base station that is once blocked by buildings. The base station is used as the serving base station. When the coverage of a single UAV base station is small, that is, when the UAV antenna angle is small, based on the proposed UAV base station selection method considering the occlusion effect, the service of the UAV base station considering the occlusion effect to users will be reduced. Effectively increase coverage.

Description

A selection method of UAV base station under occlusion effect

technical field

The present invention relates to the technical field of wireless communication, in particular to the communication of unmanned aerial vehicles in the future fifth generation mobile communication (Beyond 5th Generation, B5G) and sixth generation mobile communication (6th Generation, 6G).

Background technique

Facing the explosive growth of mobile data traffic in the future, UAV communication, as one of the main research directions for B5G to expand the communication space, has received extensive attention from academia and industry. Ground sites often have a long deployment period and high cost, which makes the existing ground site deployment solutions unsuitable for highly dynamic business scenarios (such as heating scenarios with large capacity requirements and blind repair scenarios with high coverage requirements). The goal of accessing the site on demand by the spatial and temporal distribution of ground mobile users. Because UAVs have the characteristics of low cost, rapid deployment, and wide coverage, they can be used as air base stations to provide communication services for ground users. To meet the needs of rapid communication recovery in disaster areas, as an effective supplement to ground base station communication is the main research direction of future mobile communication.

In the future mobile communication system, UAV as a base station for wireless communication service is a technology that can meet high complexity and dynamic data requirements. Compared with the existing ground cell and satellite communication, UAV base station communication has the following advantages: better mobility makes it possible to quickly deploy sites on demand, because the links between ground users and macro stations are mostly line-of-sight ( The line-of-sight (LOS) path increases the capacity of data transmission. UAV base station communication is mostly used for blind and heating scenarios, that is, to provide services for areas where ground base stations are not deployed and traditional communication is interrupted, or to provide good link performance and capacity improvement in areas with dense users. In addition, UAV base stations use beams to serve users, which can effectively improve link quality and user capacity.

Since UAV base stations are often used in heating scenarios and ground mobile users are densely distributed in urban scenarios, based on the actual wide beam model, the beam pitch angle and deployment height of the UAV base station will directly affect the beam coverage of the UAV base station. In addition, when analyzing the changes of UAV channel conditions in urban environment, the occlusion effect of buildings and the penetration loss caused by them need to be considered.

SUMMARY OF THE INVENTION

The present invention studies and discusses the shading problem of buildings in dense urban areas, and proposes a method for selecting a base station of an unmanned aerial vehicle under shading effect. If it is not zero, the user selects the nearest UAV base station that is not blocked by buildings within the connectable range as the serving UAV base station. The UAV base station that is occluded once by the object is used as the service base station.

The UAV base station selection method considering the occlusion effect of the present invention comprises the following steps:

Step 200: Determine the range of the UAV base station that the user can connect to according to the UAV deployment parameters and antenna configuration.

的关系表达式如下The wide-beam UAV base station is deployed at a height h from the ground in a dense urban area, and the antenna angle is set to θ, θ∈(0, π/2). Considering the influence of the UAV’s antenna angle on the beam gain, the UAV base station Beam gain G and beam azimuth

The relational expression is as follows

Among them, the side lobe gain of the beam is approximately 0, so the UAV base station can only provide services to users within the coverage of the beam, and the signal strength outside the coverage of the beam is almost zero. Therefore, the range of the wide-beam UAV base station that the user can connect to is a circular area with the user as the center and a radius of htanθ.

Step 210: Determine the occlusion situation of the link between any user and the UAV base station within the connectable range through three-dimensional space occlusion modeling according to the obtained dense urban environment parameters, introduce a penetration loss factor, and obtain the penetration of the link. loss.

According to the distribution of the number of blocked buildings, the penetration loss S of the link between the user and the UAV base station is determined, and its calculation formula is:

S=γ ^K' ,

Among them, γ is the power loss ratio after the signal passes through a building in a certain area, that is, the penetration loss factor. Both the user's useful signal and the interfering signal need to consider the influence of building blockage. For large buildings with multiple walls and mmWave beam scenarios with more severe penetration loss through buildings, γ=0, assuming that all buildings are impenetrable. The invention studies the beam model of the wide beam. In the urban environment, the building will block the beam of the UAV base station, the penetration loss of the building is small, but it will still affect the user, that is, γ>0.

Both the user's useful signal and the interfering signal need to consider the shading effect of the building.

In the above formula, K' is the number of blocked buildings on the connection between the UAV base station and the user's three-dimensional space, and K' obeys the Poisson distribution, and the expression is:

Among them, R is the distance from the user to the horizontal projection of the UAV base station; p=λE[L]E[W] is the normalized urban density obtained from the building density λ, E[L] and E[W] are respectively The average length and width of the building, p=0 when there is no building on the ground, p=1 when the building completely covers the ground; β is related to the average length and width of the building and the building density, expressed as:

η is the building blockage probability in three-dimensional space, and the calculation formula is:

为用户和无人机基站水平投影连线上对应位置处的建筑恰好阻塞用户与该无人机基站信道的高度。对建筑物的高度分布函数f_H(h′_b)从地面到

高度处进行积分，即得到在二维空间建筑物阻塞用户和无人机基站水平投影连线但三维空间无法阻塞用户与该无人机基站信道的概率，进而得到三维空间的建筑物阻塞概率η。Among them, the upper limit of points

The building at the corresponding position on the horizontal projection connection between the user and the UAV base station is just the height that blocks the channel between the user and the UAV base station. The height distribution function f _H (h' _b ) for the building from the ground to

Integrate at the height, that is, the probability that the building blocks the horizontal projection connection between the user and the UAV base station in the two-dimensional space, but the three-dimensional space cannot block the channel between the user and the UAV base station, and then obtains the building blocking probability η in the three-dimensional space .

Among them, the height distribution function f _H (h′ _b ) of the building is expressed as follows, considering that it obeys the Rayleigh distribution with the average height of the building as the characteristic value,

h_b为一定范围内建筑物的平均高度。in,

h _b is the average height of buildings within a certain range.

P _{K'=0} =e ^-η(βx+p/4) corresponds to a signal that does not experience penetration loss. When the penetration loss factor is large, it is considered that the probability of K' being greater than 1 is small, and the huge penetration loss of the signal passing through two or more buildings has a negligible impact on the user.

Step 220: According to the above-determined occlusion of the link between the user and the UAV base station within a connectable range and the penetration loss of the link, the UAV base station is selected, and the user service base station is determined. The rules for the selection method of UAV base stations considering the occlusion effect are as follows:

When there is a UAV base station with LOS path within the user's connectable range htanθ, the user is served by the beam of the UAV base station with LOS path, that is, there is no penetration loss of useful signals. The user selects the UAV base station with the largest RSRP as its serving base station. At this time, the user is served by the nearest LOS UAV base station. The remaining UAV base stations within the connectable range are interfering base stations. UAV base stations or UAV base stations with NLOS paths.

In this case, the beam of the UAV in the distance Htanθ is not blocked by buildings, that is, the LOS path from the service UAV to the user, and the horizontal projection x of the connection between the user and the base station of the service UAV The paths from other UAV base stations to users are blocked by buildings, so the probability density function expression is obtained as:

Among them, μ is the deployment density of UAV base stations, and the expression of U(x) is:

When there is no UAV base station with LOS path within the user's connectable range htanθ, the user is served by the UAV base station beam with non-line-of-sight (NLOS) path, that is, the useful signal has penetration loss. The huge penetration loss of the signal passing through two or more buildings has a negligible impact on the user. At this time, the user selects the nearest UAV base station that is blocked by the building once as the service base station, and can connect to other UAV base stations within the range. It is an interfering base station, and the interfering base stations are all UAV base stations of NLOS path.

In this case, the paths from the beams of all UAVs to the user within the Htanθ distance are blocked by buildings, and the UAV with the closest distance is selected as the service UAV of the user, that is, the service UAV to the user. is NLOS diameter, then the probability density function is

beneficial effect

Aiming at the situation that the user-UAV base station link may be blocked by dense urban buildings, the UAV base station signal received by the user may have penetration loss, and a method for selecting the UAV base station under the blocking effect is proposed. Based on the existing wide beam model, the antenna angle and deployment height of the UAV base station will affect the coverage of a single UAV base station. In urban environments, buildings will block the beam of the UAV base station. When the UAV base station is used, the penetration loss of the building is small, but it will still affect the user. Therefore, when there is no UAV base station with LOS path within the user's connectable range, the user selects the nearest UAV base station that is blocked by the building once. drone base station service.

For the selection of UAV base stations considering the occlusion effect, there are two cases of LOS path UAV and UAV base stations blocked by buildings as user service UAV base stations. The beam coverage performance of the user-centric UAV base station network in the urban environment is analyzed. When the coverage of a single UAV base station is small, that is, when the UAV antenna angle is small, the UAV base station blocked by buildings is considered. The service to users will effectively increase the coverage.

Description of drawings

Fig. 1 is the unmanned aerial vehicle base station network scene diagram considering the occlusion effect of the present invention;

Fig. 2 is the algorithm implementation flow chart of the present invention;

Fig. 3 is the variation relation diagram of the signal-to-interference ratio (Signal-to-Interference Ratio, SIR) coverage rate with the angle of the drone antenna under the selection of the unmanned aerial vehicle base station considering the occlusion effect of the present invention;

FIG. 4 is a graph showing the relationship between the SIR coverage and the ratio of the UAV/average building height under different penetration losses of the present invention.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Aiming at the scene where buildings are occluded in dense urban areas, the present invention proposes a method for selecting a UAV base station under the occlusion effect. The network model diagram is shown in FIG. 1 . Considering the actual coverage model of the wide beam, that is, the influence of the antenna angle of the UAV on the beam gain, the UAV base station can only provide services to users within the coverage of the beam, and the signal strength outside the coverage of the beam is almost zero. Therefore, the coverage of a single drone will be affected by the deployment height and antenna angle of the drone base station. Accordingly, the range that users can connect to the drone base station is limited by the deployment height and antenna angle of the drone base station.

Obtain the environmental parameters of dense urban areas, including building height distribution, average length and width, and density, establish a three-dimensional space building blocking model, and obtain the distribution of the number of blocked buildings K' on the three-dimensional space connection between the UAV base station and the user. The penetration loss factor is introduced, and the penetration loss S of the link between the user and the UAV base station is determined according to the distribution of the number of blocked buildings. Both the user's useful signal and the interfering signal need to consider the influence of building blockage.

Based on the different occlusion of the link between the user and the UAV base station within the range of the UAV base station that the user can connect to, two types of users are given in Figure 1: the user who can connect to the UAV base station and has a LOS path UAV and Users who do not have LOS path UAVs can be connected to the UAV base station. For the two types of users shown in Figure 1, the corresponding UAV base station selection strategy is given according to the situation, including:

For users who can connect to the UAV base station with LOS path UAV, the user can be served by the LOS path UAV base station beam, that is, the useful signal has no penetration loss. The user selects the nearest LOS UAV base station as the serving base station.

For users who can connect to the UAV base station without LOS path UAV, the user can only be served by the NLOS path UAV base station beam, that is, the useful signal has penetration loss. The huge penetration loss of the signal passing through two or more buildings has a negligible impact on the user. At this time, the user selects the nearest UAV base station that is blocked by the building once as the serving base station.

The algorithm flow of the present invention is shown in accompanying drawing 2, and its concrete implementation steps are:

Step 300: Determine the range of the UAV base station that the user can connect to according to the UAV deployment parameters and antenna configuration.

Step 310: Determine the occlusion situation of the link between any user and the UAV base station within the connectable range through three-dimensional space occlusion modeling according to the obtained dense urban environment parameters, introduce a penetration loss factor, and obtain the penetration of the link. loss.

Step 320: According to the above-determined occlusion of the link between the user and the UAV base station within the connectable range and the penetration loss of the link, the UAV base station is selected, and the user service base station is determined.

The simulation results are shown in Fig. 3 and Fig. 4, and the SIR coverage performance index of the network is studied under the UAV base station selection scheme considering the occlusion effect of the present invention. The SIR threshold is set to -5dB, the range of antenna angle is θ∈(0,π/2), the hanging height of UAV is 150m, and the average height of buildings is 100m. In addition, the penetration loss factor in Figure 3 is set to 0.1, the density of UAV base stations in Figure 4 is set to 30/km ² , and the urban density p is 0.4. Based on the above simulation parameters, Figures 3 and 4 study the relationship between network SIR coverage and antenna angle, UAV density, penetration loss factor, and urban density.

Figure 3 shows the relationship between the wide-beam UAV base station network coverage and the UAV antenna angle under different UAV densities and urban densities. It can be seen from the figure: 1) When the UAV-related parameters and building-related parameters are determined, the UAV base station beam coverage first increases and then decreases with the change of the UAV base station antenna angle. The reason is that when the UAV deployment height is determined, the UAV beam pitch angle will become the only variable that affects the beam coverage of a single UAV. With the increase of the beam pitch angle, more users will be located in the UAV base station. When the beam coverage increases to a certain limit and continues to increase, the increase in beam interference between UAVs reduces the signal-to-interference ratio of users, resulting in a decrease in coverage. Therefore, in urban scenarios, when the density and deployment height of UAV base stations are determined, in order to improve the coverage rate of the UAV group beam, it is necessary to adjust the antenna angle of the UAV base station to an appropriate angle. 2) The UAV density μ affects the optimal UAV base station antenna angle. The smaller the UAV density, the larger the UAV base station antenna angle that achieves the highest coverage. The reason is that when the density of drones is small, a single drone needs a larger beam coverage to meet the coverage of all users. 3) The increase in urban density will lead to a decrease in the coverage of the UAV network, and the optimal UAV antenna angle changes less when the UAV density is high (eg μ=120/km ² ). The hour decreases more obviously with the increase of urban density (eg μ=30/km ² ). The reason is that when the density of drones is high, the coverage rate is less affected by the urban density, and the reduction is small; and when the density of drones is low, the coverage rate is greatly affected by buildings, which is also reflected in the most Excellent drone antenna angle. When the UAV antenna angle increases to a certain value, continuing to increase the antenna angle will reduce the user's signal-to-interference ratio, and the increase in urban density will affect the service UAV signal coverage, and the beams between UAV base stations will be affected. The interference is reduced, and the service drone signal is more seriously affected than in the case of less urban density.

Figure 4 depicts the total coverage rate P _c of the UAV base station of the present invention with different penetration loss factors and the coverage rate P _c1 when only considering the LOS path UAV base station within the range of the user-connectable UAV base station. Changes in the angle of the antenna of the machine. It can be seen from the figure: 1) Analysis of the impact of penetration loss factor: when γ=0.1, the coverage rate is higher than that when γ=0.5. After the density of UAVs is sufficient to cover the limited urban area, the increase of penetration loss factor While improving the coverage capability of a single UAV base station, it also increases the beam interference of other UAV base stations. At this time, the influence of the latter on the coverage rate leads to the reduction of the SIR value of most users, which reduces the coverage rate. 2) Comparative analysis of the total coverage rate P _c and the coverage rate P _c1 when only considering the LOS path UAV base station within the range of the user-connectable UAV base station: considering the LOS path UAV and the unmanned aerial vehicle blocked by buildings. There are two situations in which man-machine serves as a user to serve UAV. When the coverage of a single UAV base station is small, as shown in Figure 4, when the UAV antenna angle is small (θ<1rad), consider the UAV base station blocked by buildings Services to users will greatly improve coverage. 3) Comparative analysis of coverage changes with γ=0: when the coverage of a single UAV base station is small, as shown in Figure 4, when the UAV antenna angle is small (θ<0.8rad), the present invention, namely penetration loss When it is not 0, the coverage is much greater than the coverage when γ=0, but with the increase of the coverage of a single UAV base station, the coverage of the present invention is smaller than the coverage when γ=0, and the coverage when γ=0 The rate peak may be higher than the coverage peak when γ>0. The reason is that when the coverage of a single drone is limited, if the blocked drone beam can serve users, it will greatly improve the coverage of the drone base station network, but as the coverage of a single drone base station increases. Large, the UAV base station network is sufficient to cover the entire area, and there will be other UAVs serving users who were blocked by buildings and cannot get the beam service of the UAV base station; when γ=0, there are no unmanned aerial vehicles blocked by buildings. Therefore, when the coverage of a single UAV base station is large enough, the coverage rate is higher than the coverage rate in this chapter, and the coverage peak value may be larger.

Those of ordinary skill in the art should realize that the above embodiments are only used to illustrate the present invention, not as a limitation of the present invention, as long as the changes and modifications to the above embodiments are within the scope of the present invention within the protection scope of the present invention.

Claims (5)

1. A method for selecting a base station of an unmanned aerial vehicle under an occlusion effect is characterized by comprising the following steps: the wide-beam unmanned aerial vehicle base station is deployed in a dense urban area, the coverage range of a single unmanned aerial vehicle base station is limited, and the range in which a user can be connected with the unmanned aerial vehicle base station is determined according to the deployment height and the beam width of the unmanned aerial vehicle base station; acquiring environmental parameters of dense urban areas, introducing a penetration loss factor, establishing a three-dimensional space building blocking model according to urban building distribution parameters as a power loss proportion of signals passing through a building, and determining penetration loss according to the blocking model and the penetration loss factor; according to whether the unmanned aerial vehicle base station with the LOS path exists in the connectable range of the user, the user selects the nearest LOS unmanned aerial vehicle base station to serve or the nearest unmanned aerial vehicle base station which is shielded once by a building as a service base station.

2. The method according to claim 1, wherein the wide-beam drone base station is deployed in a dense urban area at a height h from the ground, the antenna angle is set to θ, the drone base station is considered to be only able to provide service to users within the beam coverage range in consideration of the influence of the drone antenna angle on the beam gain, and the farthest distance of the user connectable wide-beam drone base station is htan θ if the signal intensity outside the beam coverage range is almost zero.

3. The method according to claim 1, wherein the dense urban environment parameters including building position distribution, height distribution, average length, width and density are obtained, a three-dimensional space building blocking model is established, distribution of the number K' of blocking buildings on a three-dimensional space connection line of an unmanned aerial vehicle base station and a user is obtained, and the expression is as follows:

wherein, R is the distance from the user to the horizontal projection of the unmanned aerial vehicle base station, p is the normalized city density obtained by the building density lambda, beta is the parameter related to the average length and width of the building and the building density, eta is the building blocking probability of the three-dimensional space, and the calculation formula is as follows:

wherein f is_H(h'_b) As a function of the height distribution of the building.

4. A method according to claims 1 and 3, characterized in that a penetration loss factor γ is introduced, and the penetration loss S of the user and drone base station links is determined from the distribution of the number of blocked buildings, calculated as:

S＝γ^K’，

both the user's useful signal and the interfering signal need to take into account the effects of building blockage.

5. The method of claims 1, 2 and 4, wherein the link status of the user due to building occlusion is in two cases, and accordingly, the base station selection scheme of the drone considering the occlusion effect comprises:

when the unmanned aerial vehicle base station with the LOS path exists in the connectable range h tan theta of the user, the user is served by the unmanned aerial vehicle base station beam with the LOS path, namely, the useful signal has no penetration LOSs, the user selects the unmanned aerial vehicle base station with the maximum RSRP as the service base station, the user is served by the nearest LOS unmanned aerial vehicle base station at the moment, and the rest unmanned aerial vehicle base stations in the connectable range are interference base stations;

when the unmanned aerial vehicle base station with the LOS path does not exist in the connectable range h tan theta of the user, the user is served by the unmanned aerial vehicle base station beam with the NLOS path, namely, the useful signal has penetration LOSs, the influence of the penetration LOSs of the signal passing through the buildings twice or more on the user can be ignored, and the user selects the nearest unmanned aerial vehicle base station which is shielded once by the buildings as the service base station.

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