Unmanned aerial vehicle auxiliary relay system power control method based on statistical knowledge

Abstract

The invention discloses an unmanned aerial vehicle auxiliary relay system power control method based on statistical knowledge, and belongs to the technical field of wireless communication, and the method comprises the steps: initializing the peak transmitting power and average transmitting power of a source node A and an air unmanned aerial vehicle relay R, initializing the outage probability limit and the rate at which the A transmits data information to a destination node B through the R, dividing the flight time delta of the unmanned aerial vehicle into 2I time slots; the unmanned aerial vehicle relay and the ground source node obtain statistical knowledge of the system; solving the optimization problem to obtain an identification vector of a time slot capable of being used for communication from A to B, the transmitting power of A and the transmitting power of R; and finally, controlling the transmitting power of the source node and the transmitting power of the aerial unmanned aerial vehicle relay according to the obtained result. The probability line-of-sight link condition between the unmanned aerial vehicle and the ground node and the large-scale and small-scale fading effects are jointly considered, the transmitting power of the source node and the unmanned aerial vehicle relay is optimally controlled, and more data information can be transmitted.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communication, and particularly to a power control method for an unmanned aerial vehicle (UAV)-assisted relay system based on statistical knowledge. Background Art

[0002] At present, a large number of literatures have studied the performance optimization problems of relay communication systems when UAVs are used as mobile relays, such as maximizing communication capacity, spectral efficiency, or power efficiency. In the process of studying these optimization problems, it is often considered that there is a line-of-sight (LoS) link between the UAV and the ground node. In fact, the existence of a LoS link between the UAV and the ground node is conditional, which is specifically related to factors such as the communication environment, the flight altitude of the UAV, and the elevation angle between the UAV and the ground node. Therefore, in fact, there is a LoS link between the UAV and the ground node with a certain probability. In addition, the communication between the UAV and the ground node is also affected by large-scale and small-scale fading. At present, for the research on UAV-assisted relay communication, there is a lack of joint consideration of the probabilistic LoS link situation, large-scale and small-scale fading effects between the UAV and the ground node. On the other hand, the UAV flies in the air and has high mobility. Therefore, for UAV-assisted air-to-ground or ground-to-air communication, it is difficult for the transmitter to accurately obtain real-time channel knowledge. Because, even if the transmitter obtains real-time channel knowledge through traditional channel estimation, due to the fast movement characteristics of the UAV, the channel characteristics will change accordingly. Therefore, the power control method based on traditional real-time channel knowledge is not applicable to UAV-assisted air-to-ground or ground-to-air communication. Therefore, it is necessary to provide a power control method for a UAV-assisted relay system that jointly considers the probabilistic LoS link situation, large-scale and small-scale fading effects between the UAV and the ground node to maximize the communication capacity. Summary of the Invention

[0003] The technical solution of the present invention provides a solution significantly different from the prior art for the technical problem that the prior art solution is too single. Specifically, it provides a power control method for a UAV-assisted relay system based on statistical knowledge, which jointly considers the probabilistic LoS link situation, large-scale and small-scale fading effects between the UAV and the ground node, and optimally controls the transmission powers of the source node and the UAV relay in the UAV relay system. Under the conditions of meeting the peak and average transmission power limitations of the source node and the UAV relay, and satisfying the outage probability requirement of the destination node, the data information received by the destination node is maximized.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0005] A power control method for a UAV-assisted relay system based on statistical knowledge, comprising the following steps:

[0006] S1. Initialize the peak transmit power of the source node A and the aerial UAV relay R and initialize the average transmit power of A and R and initialize the outage probability limit P out and the rate r at which A sends data information to the destination node B through R AB , and divide the flight time Δ of the UAV into 2I time slots;

[0007] S2. The UAV relay R and the ground source node A obtain the statistical knowledge of the system;

[0008] S3. The UAV relay R and the ground source node A solve the optimization problem composed of equations (19a)-(19g) to obtain the identification vector J of the time slots that can be used for communication from A to B * , the transmit power of A and the transmit power of R where, i ∈ J * ,

[0009]

[0010]

[0011] In equation (19a), P A =[P A (1), P A (3), …, P A (2I - 1)] and P R =[P R (2), P R (4), …, P R (2I)] are the vectors composed of the transmit powers of A and R in each time slot respectively; as shown in equation (19g), J is a subset of the set {1, 2, …, I}; |J| represents the size of J, that is, the number of elements in J, and is also the number of time slots that can be used for communication from the source node A to the destination node B; r AB is the rate at which A sends data information to B through R; and J * are the optimal values of P A , P R and J respectively; in equation (19b), p out (2i) is the outage probability of the destination node B in the 2i-th time slot, and P out is the outage probability limit; equation (19b) means that when i ∈ J, the outage probability of the destination node B in the 2i-th time slot needs to be less than or equal to the outage probability limit P out ; equations (19c) and (19d) give the peak transmit power limits of the nodes, where, PA (2i - 1) represents the transmission power of node A at the (2i - 1)-th time slot, P R (2i) represents the transmission power of relay R at the 2i-th time slot, and are the maximum transmission power limits of A and R respectively; Equations (19e) and (19f) give the average transmission power limits of the nodes, where I represents half of the total number of time slots, that is, the number of time slots during which A or R can send data information, and is also the number of time slots for communication from source node A to destination node B. and are the average transmission power limits of A and R respectively;

[0012] S4. According to the results obtained in step S3, control the transmission power of source node A and the transmission power of the aerial UAV relay R.

[0013] Furthermore, in step S2, the statistical knowledge of the system includes: the location information of the source node and the destination node, the statistical information of the air - ground channel, the flight trajectory information of the UAV relay, and the information transmission rate r from the source to the destination node AB and the outage probability limit P of the destination node out .

[0014] Furthermore, the location information of the source node and the destination node includes: A is located at [0, 0] in the two - dimensional coordinate system, and B is located at [0, l AB where l AB is the distance between A and B; the antenna position of source node A is q A = [0, 0, h A , and the antenna position of destination node B is q B = [l AB , 0, h B , where h A is the antenna height of A, and h B is the antenna height of B.

[0015] Furthermore, the statistical information of the air - ground channel includes: the large - scale channel power between A and R at the (2i - 1)-th time slot and in the υ link state the large - scale channel power between R and B at the 2i - th time slot and in the θ link state the fading parameter of the small - scale channel power between A and R at the (2i - 1)-th time slot and in the υ link state the mean value of the small - scale channel power between A and R at the (2i - 1)-th time slot and in the υ link state the fading parameter of the small - scale channel power between R and B at the 2i - th time slot and in the θ link state the mean value of the small - scale channel power between R and B at the 2i - th time slot and in the θ link state The probability of a υ link occurring between A and R in the (2i - 1)-th time slot The probability of a θ link occurring between R and B in the 2i-th time slot where i ∈ {1, 2, …, I}, υ, θ ∈ {LoS, NLoS}

[0016] Furthermore, the flight trajectory information of the UAV relay includes: the speed V of the UAV is constant during flight, the flight time is Δ, the position of the UAV at time t is q(t), and the position of the UAV antenna is the same as that of the UAV, which is q(t), where 0 ≤ t ≤ Δ

[0017] Furthermore, in step 3, the specific solution process includes:

[0018] S3-1. Let the transmission power of A in the (2i - 1)-th time slot be That is, Let the transmission power of R in the 2i-th time slot be That is, Then, calculate the outage probability p out (2i), where i ∈ {1, 2, …, I}

[0019] S3-2. Let k = 0, then, check the magnitude of the outage probability value calculated in step S3-1; if p out (2i) ≤ P out holds, then let k = k + 1, Next, put into ; otherwise, let where i ∈ {1, 2, …, I}

[0020] S3-3. If Let Then, jump to step S3-8; otherwise, jump to step S3-4

[0021] S3-4. Use the "CONTOURC" function in Matlab to calculate the contour of p out (2i) at P out , then return the contour matrix. Next, in the contour matrix, find the combination with the minimum sum of the transmission powers of A and R, and denote it as and where

[0022] S3-5. If and hold, then let where Then, jump to step S3-8; otherwise, jump to step S3-6;

[0023] S3-6. If and hold, All elements in will be sorted in ascending order according to the value of and hold, All elements in will be sorted in ascending order according to the value of and hold, All elements in will be sorted in ascending order according to the value of Then, jump to step S3-7;

[0024] S3-7. If holds and or holds, where Let And let where i ∈ J * ;

[0025] S3-8. The algorithm ends.

[0026] Furthermore, in step S3-1, the outage probability p out (2i) of the destination node B is calculated according to equations (16), (17) and (18);

[0027]

[0028] where c AR (2i - 1) is the channel capacity from the ground source node A to the UAV relay R in the (2i - 1)-th time slot, c RB (2i) is the channel capacity from the UAV relay R to the ground destination node B in the 2i-th time slot, r AB is the rate at which A sends data information to B through R, Pr[c AR (2i - 1) ≥ r AB , c RB (2i) ≥ r AB represents the probability that c AR (2i - 1) ≥ r AB and c RB (2i) ≥ r AB occur simultaneously;

[0029]

[0030] In Equations (17) and (18), \(i\in\{1,2,\ldots,I\}\), \(\upsilon,\theta\in\{LoS,NLoS\}\) represent the LoS or NLoS link conditions. is the probability of a \(\upsilon\) link occurring between A and R in the \((2i - 1)\)-th time slot. is the probability of a \(\theta\) link occurring between R and B in the \(2i\)-th time slot. \(\Gamma(x)\) is the Gamma function, \(\Gamma(x,y)\) is the incomplete Gamma function, \(r\) AB is the rate at which A sends data information to B through R, \(f\) AR (x) is the probability density function of the small-scale channel power between A and R in the \((2i - 1)\)-th time slot, \(f\) RB (x) is the probability density function of the small-scale channel power between R and B in the \(2i\)-th time slot, \(P\) A (2i - 1) is the transmission power of A in the \((2i - 1)\)-th time slot, \(P\) R (2i) is the transmission power of R in the \(2i\)-th time slot. is the large-scale channel power between A and R in the \((2i - 1)\)-th time slot and in the \(\upsilon\) link state. is the large-scale channel power between R and B in the \(2i\)-th time slot and in the \(\theta\) link state, \(\sigma\) 2 is the average power of the Gaussian white noise. represents the fading parameter of the small-scale channel power between A and R in the \((2i - 1)\)-th time slot and in the \(\upsilon\) link state. is the mean value of the small-scale channel power between A and R in the \((2i - 1)\)-th time slot and in the \(\upsilon\) link state. represents the fading parameter of the small-scale channel power between R and B in the \(2i\)-th time slot and in the \(\theta\) link state. is the mean value of the small-scale channel power between R and B in the \(2i\)-th time slot and in the \(\theta\) link state.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The method provided by the present invention is based on the statistical knowledge of the system, jointly considers the probabilistic line-of-sight link conditions, large-scale and small-scale fading effects between the UAV and the ground nodes, optimally controls the transmission powers of the source node and the UAV relay, and maximizes the data information transmitted from the source to the destination node under the conditions of meeting the destination node outage probability limit, the peak and average transmission power limits of the source and the UAV relay. Simulation experiments also show that this optimization method can achieve more data information transmission under the condition of meeting the destination node outage probability limit.

[0033] The present invention will be explained in detail below in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0034] Figure 1Schematic diagram of the UAV-assisted three-node relay communication system of the present invention;

[0035] Figure 2 Graph of the destination node outage probability result under the first straight track in the embodiment;

[0036] Figure 3 Graph of the destination node outage probability result under the second straight track in the embodiment;

[0037] Figure 4 Graph of the destination node outage probability result under the third straight track in the embodiment;

[0038] Figure 5 Graph of the destination node outage probability result under the first circular track in the embodiment;

[0039] Figure 6 Graph of the destination node outage probability result under the second circular track in the embodiment;

[0040] Figure 7 Graph of the destination node outage probability result under the third circular track in the embodiment. Detailed implementation manners

[0041] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0043] As Figure 1 shown, a UAV-assisted three-node relay communication system, in which a ground source node A sends data information to a ground destination node B through a UAV relay R. It is assumed that there is no direct link between node A and node B; A is located at [0, 0] in the two-dimensional coordinate system, and B is located at [0, l AB where l AB is the distance between A and B; the antenna height of A is h A , and the antenna height of B is h B, the antenna height of R is the same as the flight height of the UAV. Assume that the UAV flies along a pre-specified trajectory q(t) and flies from the starting position q s to the ending position q e within Δ time, that is, the flight time is Δ, 0 ≤ t ≤ Δ. The speed V of the UAV during flight is constant, and the position of the UAV at time t is q(t). It should be noted that since the UAV flies along a pre-specified trajectory, q(t) is known. During flight, the UAV acts as a half-duplex decode-and-forward (HD-DF) relay to forward data information from the ground source node A to the ground destination node B. The antenna position of the source node A is q A = [0, 0, h A , and the antenna position of the destination node B is q B = [l AB , 0, h B , and the position of the UAV antenna is the same as that of the UAV, which is q(t). Here, assume that q(0) = q s , q(Δ) = q e . Therefore, at time t, the distances between the UAV antenna and the antennas of the ground source node A and the ground destination node B can be written as

[0044] d AR (t) = ||q(t) - q A || (1)

[0045] d RB (t) = ||q(t) - q B || (2)

[0046] In the HD-DF (half-duplex frequency-division multiple access) operating mode, any node in the system cannot receive signals while transmitting signals; similarly, any node in the system cannot transmit signals while receiving signals. Since there is no direct link between the ground source node A and the ground destination node B, the ground source node A needs two-hop transmission (two time slots) to transmit data information to the ground destination node B through the aerial UAV relay R. Here, the flight time Δ of the UAV is divided into 2I time slots, and the length of each time slot is τ = Δ / 2I. Assume that the length τ of each time slot is small enough, and the position of the UAV (UAV antenna) is approximately unchanged within each time slot. In addition, it should be noted that although the entire flight time Δ of the UAV relay has 2I time slots, since one communication from A to B requires two time slots, the total number of time slots available for A to B communication is I.

[0047] Thus, in the i-th time slot, i∈{1,2,…,2I}, the position of the drone (drone antenna) can be recorded as q(i), which can be calculated by substituting t=iτ into q(t); at the end of the last time slot, the position of the drone (drone antenna) q(2I) is equal to q e , t=2Iτ can also be substituted into q(t) to calculate q(2I). In this way, in the odd time slot, that is, the 2i-1 time slot, i∈{1,2,…,I}, the ground source node A transmits data information to the drone relay R; the drone relay R forwards the data information received from A to the ground destination node B in the next even time slot, that is, the 2i time slot, i∈{1,2,…,I}.

[0048] In the 2i-1th time slot, the ground source node A transmits a unit power signal x A (2i-1), then the signal y received by the drone relay R R (2i-1) can be written as

[0049]

[0050] Among them, υ∈{LoS,NLoS} is used to represent the line of sight (LoS) or non-line of sight (NLoS) link situation, P A (2i-1) is the transmission power of the ground source node A, is the large-scale channel power between A and R at the 2i-1th time slot and link state υ, is the small-scale channel gain between A and R at the 2i-1 time slot and link state v, z R (2i-1) is the Gaussian white noise received by R, and its average power is σ 2 .here, It can be written as

[0051]

[0052] Among them, υ∈{LoS,NLoS} is used to represent the LoS and NLoS link conditions, represents the unit distance channel power of the large-scale channel in the link state υ, d AR (2i-1) is the distance between the antennas of A and R in the 2i-1 time slot, which can be calculated by substituting t=(2i-1)τ into equation (1). υ is the channel fading index of the large-scale channel between A and R when a link v appears in the 2i-1 time slot, usually a constant in [2, 4] and α LoS <α NLoS It should be noted that: By probability appears, i.e., the probability of appearance is the probability of appearance is which can be calculated by Equation (5).

[0053]

[0054] In Equation (5), h A is the height of Antenna A, h R (2i - 1) is the antenna height of the UAV relay R at the (2i - 1)-th time slot. Specifically, it can be obtained by substituting t = (2i - 1)τ into q(t). η 1 and η 2 are constants, and their specific values are related to the terrain over which the UAV flies. is the elevation angle between A and R at the (2i - 1)-th time slot.

[0055] For the small-scale channel gain in Equation (3) adopting the Nakagami-m model, the small-scale channel power, i.e., obeys the Gamma distribution, and its probability density function can be written as:

[0056]

[0057] In Equation (6), represents the fading parameter taking positive integer values, where υ ∈ {LoS, NLoS} is used to represent the LoS or NLoS link situation. Usually is the mean value in the υ link state, and Γ(x) is the Gamma function.

[0058] Thus, at the end of the (2i - 1)-th time slot, the ratio of the useful signal power received by the UAV relay R to the noise power, i.e., the signal-to-noise ratio, is shown in Equation (7).

[0059]

[0060] In the (2i - 1)-th time slot, the channel capacity from the ground source node A to the UAV relay R is:

[0061]

[0062] In the 2i-th time slot, the UAV relay R encodes and modulates the data information received from A in the (2i - 1)-th time slot into a unit power signal x R (2i), and then transmits it to the ground destination node B with power P R (2i). At the end of the 2i-th time slot, the signal received by the ground destination node B is

[0063]

[0064] where θ ∈ {LoS, NLoS} is used to represent LoS and NLoS link conditions, and P R (2i) is the transmission power of R, is the large-scale channel power between R and B in the 2i-th time slot and θ link state, is the small-scale channel gain between R and B in the 2i-th time slot and θ link state, z B (2i) is the Gaussian white noise received by B, and its average power is σ 2 . The large-scale channel power here can be written as

[0065]

[0066] where θ ∈ {LoS, NLoS} is used to represent LoS and NLoS link conditions, represents the per-unit-distance channel power of the large-scale channel in the θ link state, d RB (2i) is the distance between the antennas of R and B in the 2i-th time slot, which can be specifically calculated by substituting t = 2iτ into Equation (2). α θ is the channel fading exponent of the large-scale channel between R and B when the θ link occurs in the 2i-th time slot, usually taking a constant within [2, 4] and α LoS < α NLoS . It should be noted that: appears with probability , that is, the probability of appearance is the probability of appearance is which can be calculated from Equation (11).

[0067]

[0068] In Equation (11), h B is the height of the B antenna, h R (2i) is the antenna height of R in the 2i-th time slot, which can be specifically calculated by substituting t = 2iτ into q(t). η 1 and η 2 are constants, and their specific values are related to the terrain over which the UAV flies, is the elevation angle between R and B in the 2i-th time slot.

[0069] For the small-scale channel gain in Equation (9), if the Nakagami-m model is adopted, then the small-scale channel power here follows a Gamma distribution, and its probability density function can be written as:

[0070]

[0071] Among them, represents the fading parameter taking positive integer values in the θ link state, where θ ∈ {LoS, NLoS} is used to represent the LoS or NLoS link situation. Usually is the mean value in the θ link state, and Γ(x) is the Gamma function.

[0072] At the end of the 2i-th time slot, the ratio of the useful signal power received by the ground destination node B to the noise power, that is, the signal-to-noise ratio is:

[0073]

[0074] Therefore, in the 2i-th time slot, the channel capacity from the UAV relay R to the ground destination node B is

[0075]

[0076] In this way, through the transmission in two time slots (the 2i - 1-th and 2i-th time slots), the channel capacity that the destination node can obtain is

[0077] c B (2i) = min[c AR (2i - 1), c RB (2i)] (15)

[0078] Among them, min(x, y) represents the minimum value operation.

[0079] For the destination node B, it is required that the probability of outage is less than or equal to P out . It should be noted that: the prerequisite for the destination node not to have an outage is that neither the link from the source node A to the UAV relay R nor the link from the UAV relay R to the destination node B has an outage. Assume that the source node A sends data information to the destination node at a constant rate r AB through the UAV relay R. In the 2i-th time slot, i ∈ {1, 2, …, I}, the probability of outage p out (2i) can be written as

[0080]

[0081] Among them, Pr[c AR (2i - 1) ≥ r AB , c RB (2i) ≥ r AB represents the probability that c AR (2i - 1) ≥ r AB and c RB (2i) ≥ r AB occur simultaneously. According to the requirements of the destination node B, p out(2i) ≤ P out needs to be satisfied, where i ∈ {1, 2, …, I}. The following equations (17) and (18) respectively give Pr[c AR (2i - 1) ≥ r AB and Pr[c RB (2i) ≥ r AB . Therefore, substituting equations (17) and (18) into equation (16) gives the probability p out (2i) of outage at the destination node B in the 2i-th time slot, where i ∈ {1, 2, …, I}.

[0082]

[0083] In equations (17) and (18), i ∈ {1, 2, …, I}, υ, θ ∈ {LoS, NLoS} represent LoS or NLoS link conditions, is the probability of a υ link occurring between A and R in the (2i - 1)-th time slot, is the probability of a θ link occurring between R and B in the 2i-th time slot, Γ(x) is the Gamma function, Γ(x, y) is the incomplete Gamma function, r AB is the rate at which A sends data information to B through R, f AR (x) is the probability density function of the small-scale channel power between A and R in the (2i - 1)-th time slot, f RB (x) is the probability density function of the small-scale channel power between R and B in the 2i-th time slot, P A (2i - 1) is the transmit power of A in the (2i - 1)-th time slot, P R (2i) is the transmit power of R in the 2i-th time slot, is the large-scale channel power between A and R in the (2i - 1)-th time slot and in the υ link state, is the large-scale channel power between R and B in the 2i-th time slot and in the θ link state, σ 2 is the average power of the additive white Gaussian noise, represents the fading parameter of the small-scale channel power between A and R in the (2i - 1)-th time slot and in the υ link state (taking positive integer values), is the mean of the small-scale channel power between A and R in the (2i - 1)-th time slot and in the υ link state, represents the fading parameter of the small-scale channel power between R and B in the 2i-th time slot and in the θ link state (taking positive integer values), is the mean of the small-scale channel power between R and B in the 2i-th time slot and in the θ link state.

[0084] Given the knowledge of channel statistics (including the statistical information of large-scale fading, small-scale fading, and the probability information of the occurrence of line-of-sight links), the flight trajectory of the UAV relay (including the position of the UAV relay antenna), and the positions of the source and destination nodes (including the positions of the source and destination node antennas), the problem of transmit power control for the ground source node and the UAV relay node is studied. The goal is to maximize the data information received by the destination node within Δ time under the constraint of the outage probability P out This problem can be written as an optimization problem consisting of equations (19a), (19b), (19c), (19d), (19e), (19f), and (19g).

[0085]

[0086]

[0087] In equation (19a), P A =[P A (1), P A (3), …, P A (2I - 1)] and P R =[P R (2), P R (4), …, P R (2I)] are the vectors composed of the transmit powers of A and R in each time slot respectively; as shown in equation (19g), J is a subset of the set {1, 2, …, I}; |J| represents the size of J, that is, the number of elements in J, which is also the number of time slots available for communication from the source node A to the destination node B; r AB is the rate at which A sends data information to B through R; and J * are the optimal values of P A , P R , and J respectively. In equation (19b), p out (2i) is the outage probability of the destination node B in the 2i-th time slot, and P out is the outage probability limit; equation (19b) means that when i ∈ J, the outage probability of the destination node B in the 2i-th time slot needs to be less than or equal to the outage probability limit P out ; equations (19c) and (19d) give the peak transmit power limits of the nodes, where P A (2i - 1) represents the transmit power of node A in the (2i - 1)-th time slot, and P R (2i) represents the transmit power of the relay R in the 2i-th time slot, and They are the maximum transmit power limits of A and R respectively; Equations (19e) and (19f) give the average transmit power limits of the nodes, where I represents half of the total number of time slots, that is, the number of time slots during which A or R can send data information, and is also the number of time slots for communication from the source node A to the destination node B. and They are the average transmit power limits of A and R respectively.

[0088] Observing Equations (16), (17) and (18), it can be found that: the outage probability p out (2i) of node B in the 2i-th time slot is a monotonically decreasing function of P A (2i - 1) and P R (2i). Therefore, first assume that A and R both use the maximum power to send data information in each time slot, and then calculate the outage probability of node B in each time slot. It should be noted that: the outage probability of node B calculated at this time is the minimum value of the actual outage probability. Next, check the magnitudes of the outage probabilities calculated for each time slot. If p out (2i) > P out , then the 2i - 1-th time slot and the 2i-th time slot are not used to send data information, that is, the transmit power of A in the 2i - 1-th time slot is 0, and the transmit power of R in the 2i-th time slot is 0; for all i (i ∈ {1, 2,..., I}) that satisfy p out (2i) ≤ P out , combine them into a vector If for all i ∈ {1, 2,..., I}, p out (2i) > P out , then is an empty set. If is an empty set, it means that the optimization problem composed of Equations (19a), (19b), (19c), (19d), (19e), (19f) and (19g) has no feasible solution. In this case, A and R will be in the idle state and do not send any data information. If is non-empty, then write as

[0089]

[0090] where represents the size of , that is, the number of elements in represents the i-th element in and For A and R, in addition to having to satisfy the peak transmit power limit, they also need to satisfy the average transmit power limit. For this reason, it is necessary to solve the optimization problem composed of Equations (21a) and (21b).

[0091]

[0092] In formula (21a), P A (2i - 1) represents the transmission power of node A in the (2i - 1)-th time slot, P R (2i) represents the transmission power of relay R in the 2i-th time slot. is the vector given by the above formula (20), and the elements therein are the identifiers of the time slots that can satisfy the outage probability limit of the destination node when A and R transmit data information with the maximum power. P A = [P A (1), P A (3), …, P A (2I - 1)] and P R = [P R (2), P R (4), …, P R (2I)] are respectively the vectors composed of the transmission powers of A and R in each time slot. and are respectively the optimal values of P A and P R under the constraint condition of formula (21b). In formula (21b), p out (2i) is the outage probability of the destination node B in the 2i-th time slot, and P out is the outage probability limit of the destination node. The optimization problem composed of formula (21a) and formula (21b) can be solved by calculating the contour lines of the outage probability p out (2i) of the destination node B. Specifically: regard p out (2i) as a function of P A (2i - 1) and P R (2i), where use the "CONTOURC" function in Matlab to calculate the contour lines of p out (2i) at P out , and then return the contour line matrix. Then, in the contour line matrix, find the combination with the minimum sum of the transmission powers of A and R, and denote it as and where Finally, all of and are respectively composed into vectors and Next, compare and with and respectively. Specifically, it can be divided into the following four cases.

[0093] Case 1: If and hold, then A and R send data information at power and respectively in the (2i - 1)-th time slot and the 2i-th time slot, where

[0094] Case 2: If and hold, all elements in will be sorted in ascending order according to the value of

[0095] Case 3: If and hold, all elements in will be sorted in ascending order according to the value of

[0096] Case 4: If and hold, all elements in will be sorted in ascending order according to the value of

[0097] It should be noted that: when , and always hold, that is to say, is included in Case 1 above. Therefore, for Case 2, Case 3 and Case 4 above, holds.

[0098] Due to the limitation of the average transmission power, for Case 2, Case 3 and Case 4 above, only the first n time slots in the sorted that meet the average transmission power limit can be used to realize the communication from A to B, and the subsequent time slots will not be available for the communication from A to B, where

[0099] According to the above discussion, a method is given to solve the optimization problem composed of equations (19a), (19b), (19c), (19d), (19e), (19f) and (19g) as follows.

[0100] Step 1: Initialize the peak transmission powers of the source node A and the aerial UAV relay R and Initialize the average transmission powers of A and R and Initialize the interruption probability limit P out and the rate r at which A sends data information to B through R AB , divide the flight time Δ of the UAV into 2I time slots;

[0101] Step 2: Obtain or calculate system statistical knowledge, including: the large-scale channel power between A and R in the (2i - 1)-th time slot and the υ link state the large-scale channel power between R and B in the 2i-th time slot and the θ link state the fading parameter of the small-scale channel power between A and R in the (2i - 1)-th time slot and the υ link state (where its value is a positive integer), the mean value of the small-scale channel power between A and R in the (2i - 1)-th time slot and the υ link state the fading parameter of the small-scale channel power between R and B in the 2i-th time slot and the θ link state (where its value is a positive integer), the mean value of the small-scale channel power between R and B in the 2i-th time slot and the θ link state the probability of the υ link occurring between A and R in the (2i - 1)-th time slot the probability of the θ link occurring between R and B in the 2i-th time slot where i ∈ {1, 2, …, I}, υ, θ ∈ {LoS, NLoS};

[0102] Step 3: Let the transmission power of A in the (2i - 1)-th time slot be that is,[[]] Let the transmission power of R in the 2i-th time slot be that is,[[]] Then, calculate the interruption probability p of the destination node B according to equations (16), (17) and (18)[[]] out (2i), where i ∈ {1, 2, …, I};

[0103] Step 4: Let[[]] k = 0, then, check the magnitude of the interruption probability value calculated in Step 3; if p[[]] out (2i) ≤ P[[]] out holds, then let k = k + 1,[[]] then put[[]] into[[]] otherwise, let[[]] where i ∈ {1, 2, …, I};

[0104] Step 5: If[[]] let[[]] Then, jump to Step 10; otherwise, jump to Step 6;

[0105] Step 6: Use the "CONTOURC" function in Matlab to calculate pout (2i) The contour line at P out , then return the contour matrix. Next, in the contour matrix, find the combination with the minimum sum of the transmission powers of A and R, and denote it as and where

[0106] Step 7: If and hold, then let where Then, jump to Step 10; otherwise, jump to Step 8;

[0107] Step 8: If and hold, All elements in will be sorted in ascending order according to the value of and hold, All elements in will be sorted in ascending order according to the value of and hold, All elements in will be sorted in ascending order according to the value of Then, jump to Step 9;

[0108] Step 9: If holds, and or holds, where Let And, let where i ∈ J * ;

[0109] Step 10: The algorithm ends.

[0110] Example: As Figure 1 shown, the UAV relay R flies along the predetermined orbit q(t) for a flight time of Δ, that is, 0 ≤ t ≤ Δ. During the flight, it acts as a half-duplex decode-and-forward relay to forward data information from the ground source node A to the ground destination node B. The rate at which A sends data information to B through R is r AB .

[0111] Before the UAV relay conducts an official flight, the UAV relay R and the ground source node A obtain the statistical knowledge of the system, including: the location information of the source node and the destination node (including the location information of the antennas of the two nodes), the statistical information of the air-ground channel (including the statistical information of large-scale fading and small-scale fading and the probability information of the occurrence of line-of-sight links), the flight trajectory information of the UAV relay (including the location information of the antenna of the UAV relay), as well as the information transmission rate from the source to the destination node and the outage probability limit of the destination node.

[0112] Then, for the optimization problem composed of equations (19a), (19b), (19c), (19d), (19e), (19f) and (19g), the UAV relay R and the ground source node A obtain the identification vector J of the time slots that can be used for communication from A to B through the method of the present invention * , the transmission power of A and the transmission power of R where, i ∈ J * , If then during the entire flight process of the UAV, both the ground source node A and the UAV relay remain in a silent state and do not send or forward any data information. If During the period when the UAV relay R flies from the starting position along the predetermined orbit to the termination position, when i ∈ J * , the source node A sends data information to R with power in the (2i - 1)-th time slot, R executes the decode-and-forward protocol, and then, in the 2i-th time slot, forwards the data information to the destination node with power ; when i ∈ {1, 2, …, I} but , both the source node A in the (2i - 1)-th time slot and the UAV relay in the 2i-th time slot remain in a silent state, that is, they do not send or forward any data information.

[0113] For the optimization method proposed by the present invention, the present invention conducts simulation experiments and compares them with the scheme in which the source node and the UAV relay always transmit with an average power. The experimental environment is the Matlab environment. Table 1 gives the parameter values in the simulation experiments.

[0114] Table 1

[0115]

[0116] Figure 2 , Figure 3 , Figure 4 respectively give the outage probabilities of the destination node under three straight-line orbits. The situations of the three straight-line orbits are as follows: 1) The first straight-line orbit, the UAV flies from the starting position q s = [0, 0, 100] to the termination position q e= [l AB , 0, 150]; 2) The second straight-line orbit, where the UAV flies from the starting position q s = [900, -100, 100] to the termination position q e = [100, 100, 100]; 3) The third straight-line orbit, where the UAV flies from the starting position q s = [l AB / 2, -400, 100] to the termination position q e = [l AB / 2, 400, 100]. In the case of the three straight-line orbits, the rate at which the source node A sends data information to the destination node B through the UAV relay R is r AB = 10 -3 bit / s·Hz. The flight speed of the UAV relay is V = 50 m / s. Table 2 gives the ratio of the number of time slots available for communication from A to B to the total number of time slots, and the total transmission power of A and B. Here, "the method of the present invention" means the outage probability of the destination node calculated after power control of the nodes using the derived outage probability formula for the method of the present invention; "average power transmission" means the outage probability of the destination node calculated using the derived outage probability formula for the case where the nodes always send data information at the average power; "simulation" means the outage probability of the destination node obtained by computer simulation.

[0117] From Figure 2 , Figure 3 , Figure 4 it can be seen that "the method of the present invention" does not occupy all time slots for communication from A to B. The reason is that the channel quality of some time slots cannot reach the required outage probability limit. For these time slots with channel quality not reaching the required outage probability limit, the method of the present invention will not be used to send data information to save energy consumption. Although the "average power transmission" scheme always sends data information, in the case of the first and second straight-line orbits, only 25% and 22.5% of the time slots are available for communication from A to B respectively (see Table 2 for details). Using the method of the present invention, in the case of the first and second straight-line orbits, 65% and 72.5% of the time slots are available for communication from A to B respectively, and can meet the required outage probability limit (see Figure 2 and Figure 3 ), and at the same time, A and B consume less power. For the first straight-line orbit, using the method of the present invention, A and R consume 56.88% and 88.10% of the power of the "average power transmission" scheme respectively. For the second straight-line orbit case, using the method of the present invention, A and R consume 92.27% and 91.79% of the power of the "average power transmission" scheme respectively. For the third straight-line orbit case, the "average power transmission" scheme has no time slots that can meet the required outage probability limit (see Figure 4and Table 2), although at this time A and R always transmit data information using average power. However, using the method of the present invention, 25% of the time slots can be used for communication from A to B. In this case, A and R respectively consume only 93.97% and 12.55% of the power of the "average power transmission" scheme (see Table 2). In addition, Figure 2 、 Figure 3 and Figure 4 show that the calculated outage probability is very close to the computer simulation results, indicating the correctness of the derived outage probability expression.

[0118] Table 2 Ratio of the number of time slots available for communication from A to B to the total number of time slots and the total transmission power of A and B

[0119]

[0120] Figure 5 、 Figure 6 、 Figure 7 respectively give the outage probabilities of the destination node 82.4962 under three circular orbits. The situations of the three circular orbits are as follows: 1) The first circular orbit, the UAV flies one week clockwise from the starting position q s =[l AB / 2 - r, 0, 100]; 2) The second circular orbit, the UAV flies one week clockwise from the starting position q s =[0, 0, 100]; 3) The third circular orbit, the UAV flies one week clockwise from the starting position q s =[l AB - 2r, 0, 100]. In the cases of the three circular orbits, the radius r of the circular orbit for the UAV relay flight is 200 m, the flight speed of the UAV relay is V = 50 m / s, the flight altitude is constant at 100 m, and the rate at which the source node A sends data information to the destination node B through the UAV relay R is r AB =5×10 -4 bit / s·Hz.

[0121] From Figure 5 、 Figure 6 and Figure 7 it can be seen that the "method of the present invention" does not occupy all time slots to send data information, which depends on the quality of the communication links involved. Although the "average power transmission" scheme always sends data information, in the cases of the first and third circular orbits, only 42.5% and 17.5% of the time slots are available for communication from A to B (see Table 2). Using the method of the present invention, in the cases of the first and third circular orbits, 60% and 77.5% of the time slots are available for communication from A to B (see Figure 5 、 Figure 7and Table 2), and consume less power. For the first circular orbit, using the method of the present invention, A and R consume 92.56% and 33.33% of the power of the "average power transmission" scheme respectively. For the third circular orbit, using the method of the present invention, A and R consume 35.22% and 99.60% of the power of the "average power transmission" scheme respectively. For the second circular orbit, there are no available time slots for the "average power transmission" scheme (see Figure 6 and Table 2), although A and R always use their average power to send data information. However, using the method of the present invention, in the case of the second circular orbit, 22.5% of the time slots can be used for communication from A to B (see Figure 6 and Table 2). At this time, A and R only consume 26.96% and 9.28% of the power of the "average power transmission" scheme respectively. In addition, Figure 5 , Figure 6 and Figure 7 show that the calculated outage probability is very close to the computer simulation results, further proving the correctness of the derived outage probability expression.

[0122] The above has described the present invention by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as such non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A power control method for an unmanned aerial vehicle assisted relay system based on statistical knowledge, characterized in that: The steps include: S1, Initialize the peak transmission power of the source node A and the aerial drone relay R and Initialize the average transmit power of A and R and Initialization interruption probability limit P out and the rate r at which A sends data information to the destination node B via R AB , divide the UAV’s flight time Δ into 2I time slots; S2, UAV relay R and ground source node A acquire statistical knowledge of the system; S3, the drone relay R and the ground source node A solve the optimization problem composed of equations (19a)-(19g) to obtain the identification vector J of the time slot that can be used for communication from A to B * , the transmission power of A and the transmitting power of R Where i∈J * , In formula (19a), P A =[P A (1),P A (3),…,P A (2I-1)] and P R =[P R (2),P R (4),…,P R (2I)] are vectors composed of the transmission power of A and R in each time slot; as shown in formula (19g), J is a subset of the set {1,2,…,I}; |J| represents the size of J, that is, the number of elements in J, which is also the number of time slots that can be used for communication from source node A to destination node B; r AB is the rate at which A sends data information to B via R; and J * P A , P R and the optimal value of J; in formula (19b), p out (2i) is the outage probability of the destination node B in the 2i time slot, P out is the interruption probability limit; Formula (19b) indicates that when i∈J, the interruption probability of the destination node B in the 2i time slot must be less than or equal to the interruption probability limit P out ; Equations (19c) and (19d) give the peak transmit power limits of the nodes, where P A (2i-1) represents the transmission power of node A in the 2i-1 time slot, P R (2i) represents the transmission power of relay R in the 2ith time slot, and are the maximum transmit power limits of A and R respectively; Equations (19e) and (19f) give the average transmit power limits of the nodes, where I represents half of the total number of time slots, that is, the number of time slots in which A or R can send data information, and is also the number of time slots for communication from source node A to destination node B. and are the average transmit power limits of A and R respectively; S4. According to the result obtained in step S3, control the transmission power of the source node A and the transmission power of the aerial drone relay R.

2. According to claim 1, a power control method for a UAV-assisted relay system based on statistical knowledge, characterized in that: In step S2, the statistical knowledge of the system includes: the location information of the source node and the destination node, the statistical information of the air-ground channel, the flight trajectory information of the drone relay, and the information transmission rate r from the source to the destination node AB and the interruption probability limit P of the destination node out .

3. The power control method of a UAV-assisted relay system based on statistical knowledge according to claim 2 is characterized in that: The location information of the source node and the destination node includes: A is located at [0, 0] in the two-dimensional coordinate system, and B is located at [0, l AB ], where l AB is the distance between A and B; the antenna position of source node A is q A =[0, 0, h A ], the antenna position of the destination node B is q B =[l AB ,0,h B ],h A is the antenna height of A, h B is the antenna height of B.

4. The power control method of a UAV-assisted relay system based on statistical knowledge according to claim 2, characterized in that: The statistical information of the air-ground channel includes: the large-scale channel power between A and R in the 2i-1 time slot and the v link state Large-scale channel power between R and B at the 2i time slot and θ link state Fading parameters of the small-scale channel power between A and R at the 2i-1 time slot and link state v The mean value of the small-scale channel power between A and R at the 2i-1 time slot and link state v Fading parameters of the small-scale channel power between R and B at the 2i time slot and the θ link state The mean value of the small-scale channel power between R and B at the 2i time slot and the θ link state The probability of a υ link occurring between A and R in the 2i-1 time slot The probability of a θ link between R and B in the 2ith time slot Among them, i∈{1,2,…,I}, υ,θ∈{LoS,NLoS}.

5. The power control method of a UAV-assisted relay system based on statistical knowledge according to claim 2, characterized in that: The flight trajectory information relayed by the drone includes: the speed V of the drone is constant during flight, the flight time is Δ, the position of the drone at time t is q(t), the position of the drone antenna is the same as the position of the drone, q(t), 0≤t≤Δ.

6. The power control method of a UAV-assisted relay system based on statistical knowledge according to claim 1, characterized in that: In step 3, the specific solution process includes: S3-1, let A's transmission power in the 2i-1th time slot be Right now, Let the transmission power of R in the 2ith time slot be Right now, Then, calculate the outage probability p of the destination node B out (2i), where i∈{1,2,…,I}; S3-2. Order k=0, then check the value of the interruption probability calculated in step S3-1; if p out (2i)≤P out If it holds, let k = k + 1, Then Put in Otherwise, let Here i∈{1,2,…,I}; S3-3, if make Then, jump to step S3-8; otherwise, jump to step S3-4; S3-4. Calculate p using the "CONTOURC" function in Matlab out (2i) In P out The contour line at , and then return to the contour line matrix, then, in the contour line matrix, find the combination with the minimum transmission power and R, and record it as and in, S3-5, if and If established, then in, Then, jump to step S3-8; otherwise, jump to step S3-6; S3-6, if and Established, All elements in The values ​​of are sorted from small to large. If and Established, All elements in The values ​​of are sorted from small to large. If and Established, All elements in The values ​​of are sorted from small to large, where Then, jump to step S3-7; S3-7, if Established, and or Established, among which, make And, let Where i∈J * ; S3-8, the algorithm ends.

7. The power control method of a UAV-assisted relay system based on statistical knowledge according to claim 6, characterized in that: In step S3-1, the outage probability p of the destination node B is calculated according to equations (16), (17) and (18): out (2i); Among them, c AR (2i-1) is the channel capacity from the ground source node A to the drone relay R in the 2i-1th time slot, c RB (2i) is the channel capacity from the drone relay R to the ground destination node B in the 2ith time slot, r AB is the rate at which A sends data information to B via R, Pr[c AR (2i-1)≥r AB ,c RB (2i)≥r AB ] means c AR (2i-1)≥r AB and c RB (2i)≥r AB Probability of simultaneous occurrence; In equations (17) and (18), i∈{1,2,…,I},υ,θ∈{LoS,NLoS} represents the LoS or NLoS link situation. is the probability of a υ link occurring between A and R in the 2i-1 time slot, is the probability of a θ link appearing between R and B in the 2i time slot, Γ(x) is the Gamma function, Γ(x,y) is the incomplete Gamma function, r AB is the rate at which A sends data information to B via R, f AR (x) is the probability density function of the small-scale channel power between A and R in the 2i-1 time slot, f RB (x) is the probability density function of the small-scale channel power between R and B in the 2i time slot, P A (2i-1) is the transmission power of A in the 2i-1th time slot, P R (2i) is the transmit power of R in the 2ith time slot, is the large-scale channel power between A and R at the 2i-1th time slot and link state υ, is the large-scale channel power between R and B at the 2i time slot and the θ link state, σ 2 is the average power of Gaussian white noise, represents the fading parameter of the small-scale channel power between A and R at the 2i-1th time slot and υ link state, is the mean value of the small-scale channel power between A and R in the 2i-1th time slot and link state υ, represents the fading parameter of the small-scale channel power between R and B at the 2i time slot and the θ link state, is the mean value of the small-scale channel power between R and B in the 2ith time slot and the θ link state.

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