Method for selecting return flight height of unmanned aerial vehicle under scene that wind speed and wind direction change along with height

Abstract

The invention provides an unmanned aerial vehicle homeward flight height selection method in a scene that wind speed and wind direction change along with height. The method comprises the following steps: acquiring position information of a landing point and a homeward flight point of an unmanned aerial vehicle; vertically dividing the return space of the unmanned aerial vehicle into a plurality of wind layers; classifying each wind layer according to the included angle between the wind direction and the X-axis positive axis to obtain a wind layer set with an X-axis positive velocity component and a wind layer set without an X-axis positive velocity component; one wind layer is selected from the wind layer set one by one to serve as a level flight wind layer, and other crossing wind layers are combined to form a return flight path; carrying out flight total energy consumption calculation and average data transmission rate calculation on each homeward flight path; and calculating the ratio of the total flight energy consumption to the average data transmission rate, and selecting the return path with the maximum ratio of the total flight energy consumption to the average data transmission rate for return flight.

Description

Technical Field

[0001] The present invention belongs to the technical field of UAV return flight technology in wireless communication, and specifically relates to a method for selecting the return flight altitude of a UAV in a scenario where the wind speed and direction vary with altitude. Background Art

[0002] Wind speed is one of the key factors affecting the flight stability and safety of UAVs. During the flight mission of a UAV, if an unexpected situation occurs or communication with the ground base station is lost, and at the same time affected by the wind speed, the flight state of the UAV may become more complex and dangerous. The UAV autonomous return flight technology can automatically make a decision to return when the UAV encounters an unexpected situation, and plan a safe return path based on current meteorological information such as wind speed and direction. This technology not only relies on positioning technologies such as GPS and Beidou, but also needs to combine technologies such as wind speed measurement, flight control system, and autonomous navigation algorithm to ensure that the UAV can safely return under complex meteorological conditions. Therefore, under complex meteorological conditions such as wind speed, the UAV return flight technology is of great significance for ensuring the safety of UAVs and improving the reliability and efficiency of flight missions. Summary of the Invention

[0003] Object of the Invention: To solve the problem of path selection for a UAV to return in a scenario where the wind speed and direction vary with altitude, the present invention proposes a method for selecting the return flight altitude of a UAV in a scenario where the wind speed and direction vary with altitude.

[0004] Technical Solution: A method for selecting the return flight altitude of a UAV in a scenario where the wind speed and direction vary with altitude, comprising the following steps:

[0005] Obtain the position information of the UAV landing point and the return point;

[0006] Establish a spatial Cartesian coordinate system according to the position information of the return point and the landing point;

[0007] Under the established spatial Cartesian coordinate system, vertically divide the UAV return space into multiple wind layers. In the same wind layer, the wind speed and direction are consistent and are horizontal winds, and the wind direction and wind speed are different between different wind layers;

[0008] Classify each wind layer according to the angle between the wind direction and the positive X-axis to obtain a set Ξ of wind layers with a positive X-axis velocity component and a set Ψ of wind layers without a positive X-axis velocity component; the wind layers in the set Ξ of wind layers can be used as crossing wind layers or as level flight wind layers, and the wind layers in the set Ψ of wind layers can only be used as crossing wind layers;

[0009] During the process of returning from the return point to the landing point, the UAV needs to select a wind layer in the set Ξ of wind layers as the level flight wind layer, and other wind layers as the crossing wind layers;

[0010] Select a wind layer from the wind layer set Ξ one by one as the level flight wind layer, and combine other crossing wind layers to form |Ξ| return paths; calculate the total flight energy consumption E and the average data transmission rate R for each return path;

[0011] Select the one with the maximum return path for the return flight.

[0012] Furthermore, classifying each wind layer according to the angle between the wind direction and the positive X-axis to obtain the wind layer set Ξ with a positive X-axis velocity component and the wind layer set Ψ without a positive X-axis velocity component specifically includes:

[0013] Assume that in wind layer i, the wind direction is represented by the angle α between the wind direction and the positive X-axis i to characterize;

[0014] If 0 ≤ α i ≤ 90°, this wind layer belongs to the wind layer set Ξ with a positive X-axis velocity component;

[0015] If 90° < α i ≤ 180°, this wind layer belongs to the wind layer set Ψ without a positive X-axis velocity component.

[0016] Furthermore, the calculation of the total flight energy consumption E for each return path specifically includes:

[0017] Define the wind layer where the return point is located as wind layer 0; the wind layer where the landing point is located as wind layer end;

[0018] Assume that the UAV flies along the middle line of the wind layer in the wind layer;

[0019] For the return path with wind layer j selected as the level flight wind layer, j ∈ Ξ and j ≠ 0, the calculation of the total flight energy consumption E includes:

[0020] Calculate the crossing energy consumed by the UAV when crossing wind layer 0 from the return point;

[0021] Calculate the crossing energy consumed by the UAV when successively crossing other crossing wind layers to reach wind layer j;

[0022] Calculate the energy consumed by the UAV to fly to the middle line of wind layer j;

[0023] Calculate the energy consumed by the UAV during level flight in wind layer j;

[0024] Calculate the crossing energy consumed by the UAV when successively crossing other crossing wind layers to reach wind layer end;

[0025] Calculate the crossing energy consumed by the UAV when crossing wind layer end to reach the landing point;

[0026] For the return path with the selected wind layer j as the level flight wind layer, where j = 0 and 0 ∈ Ξ, the total flight energy consumption E is calculated as follows:

[0027] Calculate the energy consumed by the UAV when crossing wind layer 0 from the return point;

[0028] Calculate the energy consumed by the UAV during level flight in wind layer 0;

[0029] Calculate the energy consumed by the UAV when successively crossing other crossing wind layers to reach wind layer end;

[0030] Calculate the energy consumed by the UAV when crossing wind layer end to reach the landing point;

[0031] For the return path with the selected wind layer j as the level flight wind layer, where j = 0 and 0 ∈ Ξ and end = 0, the total flight energy consumption E is calculated as follows:

[0032] Calculate the energy consumed by the UAV during level flight in wind layer 0;

[0033] Calculate the energy consumed by the UAV when reaching the landing point in wind layer 0.

[0034] Furthermore, in wind layer i, its wind speed is denoted as v i , and the angle between the wind direction and the positive X-axis is denoted as α i , assuming that the flight speed of the UAV remains at v at any time during the return flight, and v > v i ; the height of each wind layer is denoted as H i , and i represents wind layer i;

[0035] Assume that the UAV crosses wind layer i, and the energy consumed by the UAV when crossing wind layer i is expressed as:

[0036]

[0037] where P is the flight power of the UAV, and H i is the height of wind layer i; v i,z is the speed of the UAV in the Z-axis direction in wind layer i;

[0038] When i ∈ Ξ, v i,y = v i sinα i is the component of the wind speed v i in the Y-axis direction;

[0039] When i ∈ Ψ,

[0040] Furthermore, the energy consumed by the UAV when crossing wind layer 0 from the return point is expressed as:

[0041]

[0042] In the formula, represents the crossing energy consumed by the UAV to cross the wind layer 0 upward from the return point, represents the crossing energy consumed by the UAV to cross the wind layer 0 downward from the return point, P is the flight power of the UAV, and H 0,1 is the distance from the return point to the uppermost layer of the wind layer 0, and H 0,-1 is the distance from the return point to the lowermost layer of the wind layer 0, and v 0,z is the speed of the UAV in the Z-axis direction in the wind layer 0.

[0043] Furthermore, the energy consumed by the UAV to fly to the midline of the wind layer j is expressed as:

[0044]

[0045] In the formula, P is the flight power of the UAV, and H j represents the height of the wind layer j, and v i,y = v i sinα i is the component of the wind speed v i along the Y-axis direction; v represents the flight speed of the UAV; during the process of crossing the flight layer j to reach the midline, the UAV has no X-axis displacement;

[0046] The energy consumed by the level flight is expressed as:

[0047]

[0048] Among them, D j represents the distance of the UAV flying horizontally in the wind layer j, represents the speed of the UAV flying horizontally along the positive X-axis, and is expressed as: α j represents the angle between the wind direction in the wind layer j and the positive X-axis;

[0049] The crossing energy consumed by the UAV to cross the wind layer end to reach the landing point is expressed as:

[0050]

[0051] Among them, respectively represent the crossing energies consumed by the UAV to cross the wind layer end downward and upward to reach the landing point, and H end,1 is the distance from the landing point to the uppermost layer of the wind layer end, and H end,-1 is the distance from the landing point to the lowermost layer of the wind layer end, and v end,z is the speed of the UAV in the Z-axis direction in the wind layer end.

[0052] Further, the calculation of the average data transmission rate R specifically includes:

[0053] Divide the return process into multiple time intervals Δt, and assume that the channel gain from the UAV to the landing point remains unchanged within the time interval Δt;

[0054] Set that in wind layer i, the wind speed is denoted as v i , and the angle between the wind direction and the positive X-axis is denoted as α i ; in wind layer j, the wind speed is denoted as v j , and the angle between the wind direction and the positive X-axis is denoted as α j ;

[0055] For crossing wind layer i ∈ Ξ, its crossing time is defined as: v i,z is the speed of the UAV along the Z-axis direction in wind layer i, and H i represents the height of wind layer i; during the crossing, is divided into sub-time intervals, and the change in the X-axis coordinate of each sub-time interval is: Δx i = v i cosα i Δt, and the change in the Z-axis coordinate is: v i,y = v i sinα i is the component of the wind speed v i along the Y-axis direction; v represents the flight speed of the UAV;

[0056] For crossing wind layer i ∈ Ψ, its crossing time is defined as During the crossing, is divided into sub-time intervals, and the change in the Z-axis coordinate of each sub-time interval is:

[0057] For crossing wind layer i ∈ Ξ and crossing wind layer i ∈ Ψ, if the UAV crosses wind layer i downward, then the coordinate of the UAV on the Z-axis is subtracted by Δz in each sub-time interval i ; if the UAV crosses the wind layer upward, then the coordinate of the UAV on the Z-axis is added by Δz in each sub-time interval i ;

[0058] For the level flight wind layer j ∈ Ξ, its level flight time is defined as During the level flight, is divided into sub-time intervals, and the change in the X-axis coordinate of each sub-time interval is: represents the speed of the UAV flying horizontally along the positive X-axis, expressed as:

[0059] According to the coordinate change amount of each sub - time period in the return path, obtain the channel gain value between the UAV and the landing point in any sub - time period;

[0060] According to the channel gain value between the UAV and the landing point in any sub - time period, obtain the total data volume of this return path;

[0061] Divide the total data volume by the total flight time to obtain the average data transmission rate of this return path.

[0062] Further, the step of selecting one wind layer from the wind layer set Ξ as the level - flight wind layer one by one, combining with other crossing wind layers to form |Ξ| return paths; calculating the total energy consumption E and the average data transmission rate R for each return path is replaced by the following steps:

[0063] Set that in wind layer j, the wind speed is denoted as v j and the angle between the wind direction and the positive X - axis is denoted as α j ;

[0064] For the wind layers in the wind layer set Ξ that are higher than the wind layer where the return point is located, calculate the Q value according to the following formula:

[0065]

[0066] For the wind layers in the wind layer set Ξ that are lower than the wind layer where the return point is located, calculate the Q value according to the following formula:

[0067]

[0068] In the formula, H i represents the height of wind layer i;

[0069] Sort the Q values of all wind layers in the wind layer set Ξ from large to small, and select the wind layers corresponding to the first few Q values;

[0070] One by one, take the wind layers corresponding to the first few Q values as the level - flight wind layers, combine with other crossing wind layers to form multiple return paths; calculate the total energy consumption E and the average data transmission rate R for each return path.

[0071] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0072] (1) The method of the present invention focuses on the UAV return method in the scenario where the wind speed and direction vary with height. The space is divided into wind layers with different heights. In each wind layer, the wind in the horizontal direction has the same wind speed and consistent wind direction, and the wind directions and speeds of different wind layers are different. It solves the problem of path selection for UAVs to return in the scenario where the wind speed and direction vary with height, physically conforms to the realistic application scenario and can be effectively applied to engineering practice;

[0073] (2) The method of the present invention conducts in-depth theoretical analysis and application exploration on the communication technology from the return point to the landing point in the scenario where the wind speed and direction vary with height, and provides a solution with low flight energy consumption. Description of the Drawings

[0074] Figure 1 It is a schematic diagram of the scenario of the UAV return height selection method proposed by the present invention in the scenario where the wind speed and direction vary with height;

[0075] Figure 2 It is a schematic flow diagram of the UAV return height selection method proposed by the present invention in the scenario where the wind speed and direction vary with height. Detailed Embodiments

[0076] The technical solution of the present invention will be further elaborated below in conjunction with the drawings and embodiments. As Figure 1 and Figure 2 shown, this embodiment proposes a UAV return height selection method in the scenario where the wind speed and direction vary with height. Assume that the UAV is at point O at the return point and point E at the landing point; the main steps are as follows:

[0077] Step 1: Obtain the position information of the UAV landing point and return point; for simplicity of expression, the return point is point O and the landing point is point E. The position information of point E needs to be recorded before the UAV takes off. Point O refers to the position where the UAV receives the user's return instruction or triggers the system's automatic return instruction due to reasons such as less remaining energy.

[0078] Step 2: Establish a spatial Cartesian coordinate system according to the position information of the return point and the landing point; without loss of generality, this embodiment takes point O as the origin (0, 0, 0) of the spatial Cartesian coordinate system, and the coordinates of point E are denoted as (x end , y end , z end ). The projection of the line connecting point O and point E on the horizontal plane is used as the positive axis of the X-axis. Therefore, y end = 0, and the horizontal distance from point O to point E is x end . Therefore, in this spatial Cartesian coordinate system, the coordinates of point E are (x end , 0, z end ).

[0079] Step 3: Considering the scenario where the wind speed and direction vary with height, under the established spatial Cartesian coordinate system, the return space of the UAV is vertically divided into multiple wind layers. In the same wind layer, the wind speed and direction are consistent and horizontal, and the wind direction and speed are different between different wind layers. For ease of description, in wind layer i, the wind speed is denoted as v i , the angle between the wind direction and the positive X-axis is α i , and the height is H i of the wind layer.

[0080] Step 4: In the wind layer, the UAV will be affected by its wind speed and direction when passing through it. Since the wind direction is random, in this embodiment, each wind layer is classified according to the angle between the wind direction and the positive X-axis. If 0 ≤ α i ≤ 90°, this wind layer belongs to the set Ξ of wind layers with a positive X-axis velocity component. If 90° < α i ≤ 180°, this wind layer belongs to the set Ψ of wind layers without a positive X-axis velocity component. The wind layers in the set Ξ of wind layers can be used as traversing wind layers or as level flight wind layers, and the wind layers in the set Ψ of wind layers can only be used as traversing wind layers;

[0081] Step 5: During the process of returning from the return point to the landing point, the UAV needs to select a wind layer from the set Ξ of wind layers as the level flight wind layer, which can effectively utilize the wind speed to push the UAV to fly along the positive X-axis towards point E, thereby achieving the purpose of reducing flight energy consumption. Before reaching the level flight wind layer, the UAV needs to pass through multiple traversing wind layers in sequence. The flight of the UAV along the positive X-axis direction not only exists in the selected level flight wind layer, but also in some traversing wind layers, the UAV can also use the positive X-axis wind speed component to push the UAV to fly along the positive X-axis. The level flight layer can be higher than the wind layer where point E is located, can be lower than the wind layer where point E is located, or can be in the same wind layer as point E. Point O can be higher than point E, can be lower than point E, or can be in the same wind layer as point E.

[0082] Step 6: Select a wind layer from the set Ξ of wind layers one by one as the level flight wind layer, and combine with other traversing wind layers to form |Ξ| return paths; after receiving the return command at point O, the UAV selects the level flight wind layer for return, not only considering the energy consumption during return, but also considering the communication problem at point E. Therefore, it is necessary to calculate the total flight energy consumption E and the average data transmission rate R for each return path.

[0083] Now, further analysis is made on the calculation of the total flight energy consumption E.

[0084] Since the UAV selects the return wind layer at point O, it can enter a certain wind layer by ascending or descending, and then fly straight towards point E in that wind layer. Subsequently, when approaching point E, the UAV needs to descend or ascend its altitude to achieve a precise landing at point E.

[0085] Divide the wind layers that the UAV can fly (descend or ascend) to during the return journey according to their respective wind speeds and directions. Since point O is the coordinate origin, the wind layer it is in is defined as wind layer 0. Therefore, the wind layers above it are denoted as wind layer 1 to wind layer M, and the wind layers below it are denoted as wind layer -1 to wind layer -N. In wind layer 0, the distances from point O to its uppermost and lowermost layers are H 0,1 and H 0,-1 , so there is H 0,1 +H 0,-1 =H0. Since z end is known, the wind layer where point E is located is also known, denoted as wind layer end. The distances from point E to the uppermost and lowermost layers of its wind layer end are H end,1 and H end,-1 . To ensure that the UAV does not fall or rise to other wind layers due to vertical jitter or the like when flying horizontally in a certain wind layer, it is assumed that the UAV flies along the middle line in that wind layer, and it is assumed that the flight speed of the UAV remains v at any moment during the return journey. In this embodiment, it is assumed that the wind speed of any wind layer is less than the airspeed of the UAV, that is, v>v i .

[0086] For the return path with wind layer j selected as the horizontal flight wind layer, j + Ξ and j≠0, calculate the total flight energy consumption E j including: calculating the crossing energy consumed by the UAV to cross wind layer 0 upward (j>0) or downward (j<0) from point O, calculating the crossing energy consumed to cross other crossing wind layers in sequence to reach wind layer j, calculating the energy consumed by the UAV to fly to the middle line of wind layer j, and calculating the energy consumed by the UAV to fly horizontally in wind layer j Calculating the crossing energy consumed by the UAV to cross other crossing wind layers upward (end>j) or downward (end<j) in sequence to reach wind layer end, and calculating the crossing energy consumed by the UAV to cross wind layer end to reach the landing point.

[0087] For the return path with wind layer j selected as the horizontal flight wind layer, j = 0 and 0∈Ξ, calculate the total flight energy consumption E0 including: calculating the crossing energy consumed by the UAV to cross wind layer 0 upward (end>0) or downward (end<0) from point O, and calculating the energy consumed by the UAV to fly horizontally in wind layer 0 Calculate the energy consumed by the UAV to sequentially cross other wind layers upward (end > 0) or downward (end < 0) to reach the wind layer end, and calculate the energy consumed by the UAV to cross the wind layer end and reach the landing point.

[0088] For the return path with the selected wind layer j as the level flight wind layer, where j = 0 and 0 ∈ Ξ and end = 0, calculate the total flight energy consumption E, including: calculating the energy consumed by the UAV during level flight in wind layer 0 Calculate the UAV upward (z end > 0) or downward (z end < 0) energy consumed to reach the landing point in wind layer 0.

[0089] When the UAV crosses the wind layers in the wind layer set Ψ, part of the UAV's airspeed counteracts the wind speed of this wind layer, and the remaining speed components are used for the UAV's flight in the vertical direction.

[0090] When the UAV crosses the wind layers in the wind layer set Ξ, part of the UAV's airspeed counteracts the component of the wind speed of this wind layer on the Y-axis, and the remaining speed components are used for the UAV's flight in the vertical direction.

[0091] The details are as follows.

[0092] When 0 ≤ α i ≤ 90°, the wind speed v i , can be decomposed into the component along the positive X-axis as: v i,x = v i cosα i ; the component along the Y-axis is: v i,y = v i sinα i . v i,y will cause the UAV to deviate from the return direction. Therefore, the UAV needs to use its own airspeed to offset it. Furthermore, the speed of the UAV along the Z-axis can be obtained as: And v i,x is in the same direction as the UAV's return direction. Therefore, the UAV can use this component for horizontal flight to achieve the purpose of saving energy. Its horizontal flight distance is: Among them, is the time consumed by the UAV to cross wind layer i.

[0093] When 90° < α i ≤ 180°, The speed of the UAV along the Z-axis is: At this time, the UAV has no speed component on the positive X-axis, and it has no horizontal displacement on the wind layer where 90° < α i ≤ 180° in order to quickly gain altitude or descend.

[0094] Based on the above analysis, it can be known that the energy consumed by the UAV to cross the wind layer i is expressed as:

[0095]

[0096] where P is the flight power of the UAV, and H i is the height of the wind layer i; v i,z is the velocity of the UAV in the Z-axis direction in the wind layer i.

[0097] In particular, the energy consumed by the UAV to cross the wind layer 0 upward and downward is expressed as:

[0098]

[0099] In the formula, represents the energy consumed by the UAV to cross the wind layer 0 upward from the return point, represents the energy consumed by the UAV to cross the wind layer 0 downward from the return point, and v 0,z is the velocity of the UAV in the Z-axis direction in the wind layer 0.

[0100] For the purpose of solving energy, the wind speed on the selected wind layer should have a component on the positive axis of the X-axis. If the UAV chooses to fly horizontally in the wind layer j ∈ Ξ, the energy consumed by the UAV to fly to the midline of the wind layer j is expressed as:

[0101]

[0102] Since 0 ≤ α j ≤ 90°, then:

[0103]

[0104] where is the velocity of the UAV flying horizontally along the positive axis of the X-axis.

[0105] It can be obtained that:

[0106]

[0107] Also, since v > v j and there is:

[0108]

[0109] Furthermore, the energy consumed by the UAV to fly to the midline of the wind layer j can be expressed as:

[0110]

[0111] where D jIndicates the horizontal flight distance of the UAV in wind layer j.

[0112] It should be noted that during the process of crossing the horizontal flight wind layer j to reach the middle line, the UAV has no displacement in the X-axis direction.

[0113] Specifically, when the UAV approaches point E, it will cross the wind layer end. Therefore, the crossing energies consumed for the UAV to cross the wind layer end downward and upward to reach the landing point are respectively expressed as:

[0114]

[0115] where v end,z is the speed of the UAV in the Z-axis direction in the wind layer end.

[0116] Since the UAV can choose to ascend or descend to reach the selected horizontal flight wind layer at the initial stage of the return flight, the following nine cases are analyzed for energy:

[0117] Case 1: If the UAV chooses to descend and the UAV chooses to perform a horizontal flight return in wind layer j and end < j, its energy consumption can be expressed as:

[0118]

[0119] where the horizontal flight distance of the UAV in wind layer j is:

[0120]

[0121] Case 2: If the UAV chooses to descend and the UAV chooses to perform a horizontal flight return in wind layer j and end > j, its energy consumption can be expressed as:

[0122]

[0123] where the horizontal flight distance of the UAV in wind layer j is:

[0124]

[0125] Case 3: If the UAV chooses to descend and the UAV chooses to perform a horizontal flight return in wind layer j and end = j, its energy consumption can be expressed as:

[0126]

[0127] where the horizontal flight distance of the UAV in wind layer j is:

[0128]

[0129] Case 4: If the UAV chooses to ascend and the UAV chooses to perform a horizontal flight return in wind layer j and end < j, its energy consumption can be expressed as:

[0130]

[0131] Among them, the distance that the UAV flies horizontally in wind layer j is:

[0132]

[0133] Case 5: If the UAV chooses to ascend and the UAV chooses to fly horizontally and return in wind layer j and end > j, its energy consumption can be expressed as:

[0134]

[0135] Among them, the distance that the UAV flies horizontally in wind layer j is:

[0136]

[0137] Case 6: If the UAV chooses to ascend and the UAV chooses to fly horizontally and return in wind layer j and end < j, its energy consumption can be expressed as:

[0138]

[0139] Among them, the distance that the UAV flies horizontally in wind layer j is:

[0140]

[0141] Case 7: If the UAV chooses wind layer 0 (provided that 0 ≤ α i ≤ 90°) to fly horizontally and return and end > 0, its energy consumption can be expressed as:

[0142]

[0143] Among them, the distance that the UAV flies horizontally in wind layer 0 is:

[0144]

[0145] Case 8: If the UAV chooses wind layer 0 (provided that 0 ≤ α i ≤ 90°) to fly horizontally and return and end < 0, its energy consumption can be expressed as:

[0146]

[0147] Among them, the distance that the UAV flies horizontally in wind layer 0 is:

[0148]

[0149] Case 9: If the UAV chooses wind layer 0 (provided that 0 ≤ α iFly horizontally back at ≤ 90°) and end = 0, and its energy consumption can be expressed as:

[0150]

[0151] Wherein, The horizontal flight distance of the UAV in wind layer 0 is D0 = x end .

[0152] Now, further analysis and explanation of the communication problem are given.

[0153] During the process of the UAV returning from point O to point E, the return process is divided into multiple time intervals Δt. Since the time interval Δt is small, within each time interval Δt, because the UAV runs a short distance, it can be assumed that the channel gain at the E point remains unchanged during this period.

[0154] The path loss of the wireless transmission of the UAV at point O depends on the distance-based fading and the fading based on the line-of-sight (LoS) probability. The LoS occurrence probability of the additional path loss between nodes p and q is given by:

[0155]

[0156] Wherein, c0 and d0 depend on the environmental variables, and these environmental variables are constants; is the elevation angle of the air-to-ground wireless transmission link, h is the vertical height between the UAV and point E, is the horizontal distance between nodes p and q.

[0157] Therefore, the channel gain between nodes p and q is defined as:

[0158]

[0159] Wherein, ρ0 is the unit channel gain value (known); and are the line-of-sight LoS and non-line-of-sight NLoS (Non Line of Sight) occurrence probabilities of the additional path loss between nodes p and q (known), and there is Ω LoS and Ω NLoS respectively represent the additional path losses of the LoS and NLoS links (known), and satisfy Ω LoS << Ω NLoS ; D p,q is the distance between nodes p and q.

[0160] Therefore, if the displacement of the UAV in each sub-time period during the return process from point O to point E is known, the channel gain value between the UAV and point E in any sub-time period can be obtained.

[0161] For wind layer \(i\in\Xi\), its crossing time is defined as: During the crossing, it can be divided into sub - time periods, and the change in the X - axis coordinate of each sub - time period is: \(\Delta x\) i \(=v\) i \(\cos\alpha\) i \(\Delta t\), and the change in the Z - axis coordinate is:

[0162] For wind layer \(i\in\Psi\), its crossing time is defined as During the crossing, it can be divided into sub - time periods, and the change in the Z - axis coordinate of each sub - time period is:

[0163] It should be noted that when considering wind layer \(i\in\Xi\) and wind layer \(i\in\Psi\), if the UAV descends through the wind layer, then the Z - axis coordinate of the UAV in each sub - time period needs to subtract \(\Delta z\) i ; otherwise, it should be added. At the same time, only when crossing the wind layer in \(\Xi\), the UAV has a horizontal displacement in the positive X - axis direction.

[0164] For wind layer \(j\in\Xi\), its level - flight time is defined as During the level - flight, it can be divided into sub - time periods, and the change in the X - axis coordinate of each sub - time period is:

[0165] Based on the above analysis, according to the information such as the wind speed, wind direction of the UAV crossing and level - flying through the wind layer, and the positions of each wind layer, and combining the above 9 flight situations, the channel gain of each sub - time period during the UAV's return flight from point O to point E can be obtained. Furthermore, the total data volume \(T\) of choosing wind layer \(j\in\Xi\) for return flight can be obtained j , \(T\) j Divided by the total flight time, the average data transmission rate \(R\) of the UAV choosing wind layer \(j\in\Xi\) for return flight can be obtained j .

[0166] From the UAV return - flight altitude selection method in the scenario where the wind speed and wind direction change with altitude given above, it can be seen that the UAV needs to calculate the total flight energy \(E\) and the average data transmission rate \(R\) for \(|\Xi|\) level - flyable wind layers at point O. If the vertical height of each wind layer becomes smaller, it will increase the number of wind layers to be calculated, thus affecting the performance of the system. Based on the above analysis and combining the characteristics of the scenario where the wind speed and wind direction change with altitude studied in this embodiment, a low - complexity return - flight altitude selection method is given, which specifically includes:

[0167] In the wind layers of the wind layer set Ξ, the UAV uses the wind speed in the positive X-axis direction in the horizontal direction to assist in flight, so as to achieve the purpose of reducing energy consumption. Therefore, in the wind layer set Ξ, the wind layers with higher X-axis speed components have obvious advantages in reducing energy consumption. In addition, it is also necessary to consider that the greater the vertical distance from the wind layer to point O, the higher the energy consumption for crossing. At the same time, the wind layers in the wind layer set Ξ are helpful for the UAV to move in the positive X-axis direction, but the wind layers in the wind layer set Ψ are not helpful for the UAV to move in the positive X-axis direction and consume energy for crossing.

[0168] Therefore, define the ratio of the X-axis speed component of the wind layer in the wind layer set Ξ to the total height of the wind layer in the wind layer set Ψ as the Q value. For the wind layers in the wind layer set Ξ that are higher than the wind layer where the return point is located, calculate the Q value according to the following formula:

[0169]

[0170] For the wind layers in the wind layer set Ξ that are lower than the wind layer where the return point is located, calculate the Q value according to the following formula:

[0171]

[0172] Sort the Q values of all wind layers in the wind layer set Ξ from largest to smallest. The larger the Q j , the greater the X-axis speed component in the wind layer or the smaller the total height of the wind layer in the wind layer set Ψ.

[0173] According to parameters such as the computing power of the system or the delay time for the UAV to execute the return command, etc., it can be set to only calculate the Q j values of the first few level flight wind layers so as to avoid calculating for all wind layers in the set Ξ .

[0174] Step 7: Select the return path with the largest to return, and thus complete the selection of the UAV return height ∈ in the scenario where the wind speed and direction change with height, and effectively reduce the computational complexity of the method: *

[0175]

Claims

1. A method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with altitude, characterized in that: The following steps are involved: Get the location information of the drone landing point and return point; According to the location information of the return point and the landing point, a spatial Cartesian coordinate system is established; In the established spatial Cartesian coordinate system, the return space of the UAV is vertically divided into multiple wind layers. In the same wind layer, the wind speed and wind direction are consistent and horizontal wind, while the wind direction and wind speed between different wind layers are different. Each wind layer is classified according to the angle between the wind direction and the positive axis of the X-axis, and a wind layer set Ξ with a positive velocity component of the X-axis and a wind layer set Ψ without a positive velocity component of the X-axis are obtained; the wind layers in the wind layer set Ξ can be used as passing wind layers or as level flight wind layers, and the wind layers in the wind layer set Ψ can only be used as passing wind layers; When returning from the return point to the landing point, the drone needs to select one wind layer from the wind layer set Ξ as the level flight wind layer, and the other wind layers as the crossing wind layers; Select one wind layer from the wind layer set Ξ one by one as the level flight wind layer, and combine it with other crossing wind layers to form |Ξ| return paths; Calculate the total flight energy consumption E and average data transmission rate R for each return route; Choose the one with the largest Return along the return path.

2. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 1, characterized in that: The wind layers are classified according to the angle between the wind direction and the positive axis of the X-axis to obtain a set of wind layers Ξ with a positive velocity component of the X-axis and a set of wind layers Ψ without a positive velocity component of the X-axis, specifically including: Assume that in wind layer i, the wind direction is represented by the angle between the wind direction and the positive axis of the X axis as α i to characterize; If 0≤α i ≤90°, the wind layer belongs to the wind layer set Ξ with a positive velocity component along the X axis; If 90°<α i ≤180°, the wind layer belongs to the wind layer set Ψ without positive velocity component of X-axis.

3. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 1, characterized in that: The calculation of the total energy consumption E for each return flight path specifically includes: The wind layer where the return point is located is defined as wind layer 0; the wind layer where the landing point is located is defined as wind layer end; Assume that the UAV flies along the middle line of the wind layer in the wind layer; For the return path of selecting wind layer j as the level flight wind layer, j∈Ξ and j≠0, the calculation of the total flight energy consumption E includes: Calculate the energy consumed by the drone to pass through wind layer 0 from the return point; Calculate the crossing energy consumed by the UAV to pass through other wind layers in sequence to reach wind layer j; Calculate the energy consumed by the drone to fly to the middle line of wind layer j; Calculate the energy consumed by the UAV in level flight at wind layer j; Calculate the crossing energy consumed by the UAV to pass through other wind layers in sequence and reach the end of the wind layer; Calculate the energy consumed by the drone to pass through the wind layer end and reach the landing point; For the return path of selecting wind layer j as the level flight wind layer, j = 0 and 0∈Ξ, the calculation of the total flight energy consumption E includes: Calculate the energy consumed by the drone to pass through wind layer 0 from the return point; Calculate the energy consumed by the drone in level flight at wind layer 0; Calculate the crossing energy consumed by the UAV to pass through other wind layers in sequence and reach the end of the wind layer; Calculate the energy consumed by the drone to pass through the wind layer end and reach the landing point; For the return path of selecting wind layer j as the level flight wind layer, j = 0 and 0∈Ξ and end = 0, the calculation of the total flight energy consumption E includes: Calculate the energy consumed by the drone in level flight at wind layer 0; Calculate the energy consumed by the drone to reach the landing point at wind layer 0.

4. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 3, characterized in that: Set in wind layer i, the wind speed is recorded as v i , the angle between the wind direction and the positive axis of the X-axis is denoted as α i , assuming that the UAV flight speed is maintained at v at any time during the return flight, and v>v i ; The height of each wind layer is recorded as H i , i represents wind layer i; Assuming that the UAV passes through wind layer i, the energy consumed by the UAV passing through wind layer i is expressed as: Among them, P is the flight power of the UAV, H i is the height of wind layer i; v i,z is the speed of the UAV along the Z axis in wind layer i; When i∈Ξ, v i,y =v i sinα i is the wind speed v i The component along the Y axis; When i∈Ψ, 5. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 3, characterized in that: The energy consumed by the UAV when passing through wind layer 0 from the return point is expressed as: In the formula, It indicates the energy consumed by the drone to pass through wind layer 0 upward from the return point. It represents the energy consumed by the drone to pass through wind layer 0 from the return point downward, P is the flight power of the drone, H 0,1 H is the distance between the return point and the top layer of wind layer 0. 0,-1 v is the distance between the return point and the lowest wind layer 0, 0,z is the speed of the drone along the Z axis in wind layer 0.

6. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 3, characterized in that: The energy consumed by the UAV to fly to the middle line of wind layer j is expressed as: Where P is the flight power of the UAV, H j represents the height of wind layer j, v i,y =v i sinα i is the wind speed v i The component along the Y axis direction; v represents the flight speed of the UAV; during the period of crossing the flight layer j to reach the middle line, the UAV has no X axis displacement; The energy consumed in the level flight is expressed as: Among them, D j It represents the distance that the UAV flies level in wind layer j. Indicates the speed of the drone flying horizontally along the positive X-axis, expressed as: α j It represents the angle between the wind direction in wind layer j and the positive axis of X axis; The energy consumed in passing through the wind layer end to reach the landing point is expressed as: in, They represent the energy consumed in passing through the wind layer end downward and upward to reach the landing point, respectively. end,1 H is the distance between the landing point and the uppermost layer of the wind layer end. end,-1 v is the distance between the landing point and the lowest layer of the wind layer end, end,z is the speed of the drone along the Z axis in the wind layer end.

7. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 1, characterized in that: The calculation of the average data transmission rate R specifically includes: The return process is divided into multiple time intervals Δt, assuming that the channel gain from the UAV to the landing point remains unchanged within the time interval Δt; Set in wind layer i, wind speed is recorded as v i , the angle between the wind direction and the positive axis of the X-axis is denoted as α i ; In wind layer j, the wind speed is recorded as v j , the angle between the wind direction and the positive axis of the X-axis is denoted as α j ; For the crossing wind layer i∈Ξ, the crossing time is defined as: v i,z is the speed of the UAV along the Z axis in wind layer i, H i represents the height of wind layer i; during the crossing, Divided into sub-time periods, the X-axis coordinate change of each sub-time period is: Δx i =v i cosα i Δt, the change in Z-axis coordinate is: v i,y =v i sinα i is the wind speed v i The component along the Y axis; v represents the flight speed of the drone; For the wind layer i∈Ψ, the crossing time is defined as During the crossing, Divided into sub-time periods, and the Z-axis coordinate change in each sub-time period is: For crossing wind layer i∈Ξ and crossing wind layer i∈Ψ, if the UAV passes through wind layer i downward, the coordinate of the UAV on the Z axis is subtracted by Δz in each sub-time period. i ; If the UAV passes through the wind layer upward, then the coordinate of the UAV on the Z axis is added with Δz in each sub-time period i ; For the level flight wind layer j∈Ξ, the level flight time is defined as During level flight, Divided into sub-time periods, the X-axis coordinate change of each sub-time period is: Indicates the speed of the drone flying horizontally along the positive X-axis, expressed as: According to the coordinate change in each sub-time period in the return path, the channel gain value between the UAV and the landing point in any sub-time period is obtained; According to the channel gain value between the UAV and the landing point in any sub-time period, the total data volume of the return path is obtained; Divide the total data volume by the total flight time to get the average data transmission rate for the return path.

8. The method for selecting the return altitude of a UAV in a scenario where the wind speed and wind direction vary with the altitude according to claim 1, characterized in that: The method of selecting one wind layer from the wind layer set Ξ as the level flight wind layer one by one and combining it with other crossing wind layers to form |Ξ| return paths; and calculating the total flight energy consumption E and the average data transmission rate R for each return path is replaced by the following steps: Set in wind layer j, wind speed is recorded as v j , the angle between the wind direction and the positive axis of the X-axis is denoted as α j ; For the wind layer in the wind layer set Ξ that is higher than the wind layer where the return point is located, the Q value is calculated according to the following formula: For the wind layer in the wind layer set Ξ that is lower than the wind layer where the return point is located, the Q value is calculated according to the following formula: In the formula, H i represents the height of wind layer i; Sort the Q values ​​of all wind layers in the wind layer set Ξ from large to small, and take the wind layers corresponding to the first few Q values; The wind layers corresponding to the first few Q values ​​are used as level flight wind layers one by one, and combined with other crossing wind layers to form multiple return paths; the total flight energy consumption E and the average data transmission rate R are calculated for each return path.

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