CN110224723B - Design method of unmanned aerial vehicle-assisted backscatter communication system - Google Patents
Design method of unmanned aerial vehicle-assisted backscatter communication system Download PDFInfo
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Abstract
The invention belongs to the technical field of communication, and relates to a design method of an unmanned aerial vehicle-assisted backscatter communication system. According to the invention, a reader with high cost is not required to be deployed on the ground to collect data of the Internet of things equipment, and the unmanned aerial vehicle is adopted as the flexibly movable information receiver. Compared with the existing transmission protocol of unmanned aerial vehicle hovering-communication-flying, the transmission protocol design of flying-while-communication provided by the invention has the advantages that the utilization efficiency of system energy is obviously improved on the premise of ensuring the throughput requirement and the energy collection requirement of each backscattering device, and the problem of high-efficiency data collection of a large amount of passive devices in the Internet of things is solved.
Description
Technical Field
The invention belongs to the technical field of communication, and relates to a design method of an unmanned aerial vehicle-assisted backscatter communication system.
Background
The internet of things is an important application scene of 5G and future mobile communication systems, various internet of things devices generally have strict requirements on energy, cost, complexity and the like, and passive devices will occupy an important position in the future internet of things. The backscattering communication is a passive communication technology and has great application value in the Internet of things. Conventional backscatter systems, such as radio frequency identification systems, comprise two major parts, a backscatter device and a reader. The passive backscatter devices are usually passive devices, the circuit structure is simple, limited functions such as data acquisition, data storage, backscatter transmission and the like can be completed, and the cost is greatly lower than that of active communication devices; the reader reads the data of the backscattering equipment by detecting the received backscattering signals. The backscatter device can use a part of the received radio frequency signal to collect energy to meet the normal work of the circuit of the backscatter device; and the rest part is used as a carrier wave, and self information is modulated on the carrier wave signal and is transmitted to the reader in a backscattering mode.
The unmanned aerial vehicle has the characteristics of high maneuverability, high flexibility, easiness in immediate deployment, small influence of landforms and the like, and has shown unique superiority in various fields. In the aspect of wireless communication, after a natural disaster occurs or in an emergency, ground communication system equipment is possibly damaged to cause abnormal work, and an unmanned aerial vehicle can be used for providing instant communication service; by utilizing the characteristic of easy instant deployment, the unmanned aerial vehicle can also enlarge the coverage area of the original communication system and reduce the cost caused by unnecessary laying of ground communication network nodes. Compared with the traditional ground communication system, the unmanned aerial vehicle provided with the chip, the device and the equipment with the communication function can better avoid obstacles in the air by utilizing the high maneuverability and the high flexibility of the unmanned aerial vehicle, change the relative distance and the position between the unmanned aerial vehicle and the ground communication equipment, further improve the quality of a wireless channel and improve the communication performance.
In particular, in the conventional ground backscatter communication system, the reader integrates the functions of a carrier transmitter and an information receiver, and is limited by the extremely low efficiency of downlink energy transmission, the coverage area of a single reader is very limited, and a plurality of readers are needed in a large-range deployment scene, so that the networking cost is extremely high; the unmanned aerial vehicle technique can perfectly compensate the shortcoming of high cost, and a great deal of advantages of the unmanned aerial vehicle can be utilized to realize the information collection of the backscattering equipment in a large range.
Disclosure of Invention
The invention provides an unmanned aerial vehicle auxiliary backscattering communication system with an unmanned aerial vehicle as an information receiver, and relates to a system composition structure, a working principle and a transmission protocol, unmanned aerial vehicle path design and a system resource allocation method, so as to solve the problem of high-efficiency data collection of a large number of passive devices in the ground Internet of things. The invention provides an unmanned aerial vehicle-assisted backscatter communication system, which is particularly suitable for information collection tasks of sensors/tags of large-scale ground Internet of things.
The technical scheme adopted by the invention is as follows: the unmanned aerial vehicle auxiliary backscattering communication system consists of a plurality of ground radio frequency excitation sources, a plurality of ground backscattering devices and an unmanned aerial vehicle; wherein the content of the first and second substances,
each ground radio frequency excitation source is provided with 1 transmitting antenna for transmitting radio frequency signals and providing carrier waves and energy for backscattering equipment;
each ground backscatter device is provided with 1 antenna, one part of received radio frequency signals is used for energy collection, the other part of the received radio frequency signals is used for reflection, and self data are modulated on the part of the received radio frequency signals and then reflected to the unmanned aerial vehicle;
the unmanned aerial vehicle is provided with a chip, a device or equipment which can be used for communication, and the unmanned aerial vehicle is provided with 1 receiving antenna which can receive a signal reflected by the ground backscatter equipment and then demodulate the signal to acquire data of the ground equipment.
The basic working principle of the unmanned aerial vehicle-assisted backscatter communication system is that the unmanned aerial vehicle can communicate with different backscatter devices in a Time Division Multiplexing (TDMA) access mode during air flight. As shown in fig. 3, the corresponding transmission protocol of "edge flashing communication" includes the following steps:
s11: the signal excitation source transmits a radio frequency signal;
s12: the ground equipment which is not communicated with the unmanned aerial vehicle is in an energy collection mode, collects energy by receiving signals transmitted by the excitation source, and does not perform backscattering;
s13, using a part of received signals for energy collection by using backscattering equipment which establishes communication with the unmanned aerial vehicle, and modulating the other part of signals as carriers and then performing backscattering;
s14, the unmanned aerial vehicle communicates with the backscattering equipment on the ground one by one, decodes and collects data information of the unmanned aerial vehicle.
And S15, after the task is finished, the unmanned aerial vehicle returns to the terminal.
Further, the excitation source in step S11 is an active device, the location distribution thereof may be arbitrary, and the emission power thereof cannot exceed the peak value PmaxThe flight path design and system resource allocation are carried out on line;
the backscatter devices in step S12 are passive devices with arbitrary location distribution, and the energy collected by the backscatter devices in the task period must meet the minimum energy requirement E set by the systemminSo that the passive device has sufficient energy to maintain the proper operation of the internal circuitry.
A known energy conversion efficiency η exists when the energy collection is performed by the backscatter device in the step S13; when signal reflection is carried out, the power reflection coefficient can be optimized in resource allocation;
in step S14, the drone is accessed by Time Division Multiple Access (TDMA)The unmanned aerial vehicle is accessed one by one, and the uplink throughput of each backscattering device in a task period must ensure the minimum requirement Qmin；
In step S15, the drone completes the task of data collection and reaches the end point. The unmanned aerial vehicle flies along a path designed strictly under the line, the relative position of the path design (including the flying path and the flying speed) and ground equipment and QminClosely related, also under-line.
The invention also comprises an unmanned aerial vehicle path design and system resource allocation method, sets an optimization target to maximize the Energy Efficiency (EE) of the system, and jointly optimizes the access matrix from the ground backscatter equipment to the unmanned aerial vehicle
Power reflection coefficient of backscatter device
The transmit power distribution P of the excitation source, and the flight path Q of the drone. The corresponding optimization problem is the following (P2).
q (0) ═ q (n). formula (6i)
Wherein, formula (6a) is the minimum throughput constraint of each backscatter device, formula (6b) is the minimum collected energy constraint of each backscatter device, formula (6c) is the constraint that only one BD is accessed to the drone at any time, formula (6d) is the 0/1 value constraint of the access indicator variable, formula (6e) is the transmit power constraint of each radio frequency excitation source, formula (6f) is the value range constraint of the power reflection coefficient of each backscatter device, formula (6g) is the maximum speed limit for the drone flight, and formula (6h) is the constraint that the drone flies back to the starting point after completing the mission.
The problem (P2) solving concept includes, but is not limited to, the following methods. The problem (P2) is a non-Convex Optimization problem including coupling variables and non-Convex constraint functions, and can be solved by an efficient iterative algorithm using an alternating Optimization (e.g., Block Coordinate descent) technique and a Convex approximation Optimization (e.g., Successive Convex Optimization) technique, respectively.
The invention has the beneficial effects that: according to the invention, a reader with high cost is not required to be deployed on the ground to collect data of the Internet of things equipment, and the unmanned aerial vehicle is adopted as a flexibly movable information receiver. Compared with the existing transmission protocol of unmanned aerial vehicle hovering-communication-flying, the transmission protocol design of flight-while-communication provided by the invention obviously improves the utilization efficiency of system energy on the premise of ensuring the throughput requirement and the energy collection requirement of each backscattering device, and solves the problem of high-efficiency data collection of a large amount of passive devices in the Internet of things.
Drawings
FIG. 1: a structural block diagram of an unmanned aerial vehicle-assisted backscatter communication system;
FIG. 2: a block diagram of a backscatter device;
FIG. 3: an unmanned aerial vehicle 'edge flash communication' transmission protocol flow chart;
FIG. 4: a system energy efficiency simulation diagram under the path and resource optimization scheme;
FIG. 5: each backscattering device is accessed to a time slot number simulation graph of the unmanned aerial vehicle;
FIG. 6: flight path simulation diagram of unmanned aerial vehicle.
Detailed Description
The invention is described in detail below with reference to the drawings and simulation examples so that those skilled in the art can better understand the invention.
As shown in fig. 1, the drone assisted backscatter communication system includes M ground radio frequency excitation sources, K ground backscatter devices, and one drone. Each ground radio frequency excitation source is provided with 1 transmitting antenna for transmitting radio frequency signals and providing carrier waves and energy for the backscatter devices; each ground backscatter device is provided with 1 antenna, one part of received radio frequency signals is used for energy collection, the other part of the received radio frequency signals is used for reflection, and self data are modulated on the part of the received radio frequency signals and then are reflected to the unmanned aerial vehicle; the unmanned aerial vehicle flies at a certain fixed height and is provided with a communication chip, a device or equipment, the unmanned aerial vehicle is provided with 1 receiving antenna which can receive signals reflected by the ground backscatter equipment, and then the receiving antenna demodulates the signals to acquire data of the ground equipment. The backscattering equipment is connected into the unmanned aerial vehicle in a TDMA mode, and only one backscattering equipment can communicate with the unmanned aerial vehicle in one time slot. In a task period T, the drone needs to collect data information of all backscatter devices, and guarantee the minimum throughput and minimum collected energy requirement of each backscatter device, and finally the drone returns to a certain place (such as a starting point).
As shown in fig. 2, each of the backscatter devices includes:
a backscatter antenna for receiving and reflecting radio frequency signals in an environment;
the switch load is used for changing the load impedance of the antenna and realizing the backscatter modulation;
the microcontroller is used for controlling the communication process of the backscattering equipment;
a signal processor for basic signal processing by the backscatter device, such as decoding of control signals;
an energy harvester for harvesting energy from the radio frequency signal in the environment and using it to replenish the battery powering all modules in the backscatter device.
Other modules, including battery, memory, sensing.
The backscatter device modulates its received radio frequency signal by switching the load impedance to change the amplitude and/or phase of its backscatter signal, and the backscatter signal is received and ultimately decoded by the drone.
The basic working principle of the unmanned aerial vehicle-assisted backscatter communication system provided by the invention is that the unmanned aerial vehicle can communicate with different backscatter devices in an access mode of Time Division Multiplexing (TDMA) during air flight. As shown in fig. 3, the corresponding transmission protocol of "edge flashing communication" includes the following steps:
s11: the signal excitation source transmits a radio frequency signal;
s12: the ground equipment which is not communicated with the unmanned aerial vehicle is in an energy collection mode, collects energy by receiving signals transmitted by the excitation source, and does not perform backscattering;
s13, using a part of received signals for energy collection by using backscattering equipment which establishes communication with the unmanned aerial vehicle, and modulating the other part of signals as carriers and then performing backscattering;
s14, the unmanned aerial vehicle communicates with the backscattering equipment on the ground one by one and collects data information of the unmanned aerial vehicle;
and S15, after the task is finished, the unmanned aerial vehicle returns to the terminal.
Further, the excitation source in step S11 is an active device, the location distribution thereof may be arbitrary, and the emission power thereof cannot exceed the peak value PmaxAnd can be optimized by the resource allocation method, it is worth mentioning that the system resource allocation of the present invention is performed on-line (described in detail later);
the backscatter devices in step S12 are passive devices with arbitrary location distribution, and the energy collected by the backscatter devices in the task period must meet the minimum energy requirement E set by the systemminSo that the passive device has sufficient energy to maintain the proper operation of the internal circuitry. The excitation source and the backscattering exist in a pair, any backscattering equipment can only receive the signal emitted by the excitation source closest to the backscattering equipment, and the signals from other excitation sources can be ignored;
a known energy conversion efficiency η exists when the energy collection is performed by the backscatter device in the step S13; when signal reflection is carried out, the power reflection coefficient can be optimized in resource allocation;
in step S14, the drones are connected to each other in a TDMA manner, and the uplink throughput of each backscatter device in a task period must ensure the minimum requirement Qmin. Relative position and Q of unmanned aerial vehicle's route design and ground equipmentminAre closely related;
in step S15, the drone completes the task of data collection and reaches the end point. The unmanned aerial vehicle flies along a path designed strictly under the line, the relative position of the path design (including the flying path and the flying speed) and ground equipment and QminClosely related, also performed under-line;
in the following, a signal processing flow in a data sending phase is introduced in detail, and then an optimization method for a flight path of the unmanned aerial vehicle and system resource allocation is provided.
The backscatter devices are each paired with its nearest excitation source, with set for excitation source m
Represents a set of backscatter devices paired with it, wherein
And q (t) ═ x (t), y (t)]TRespectively, the position of the mth excitation source and the kth backscatter device, and the drone, on a two-dimensional plane. The channels from the excitation source to the backscatter device and from the backscatter device to the drone are all modeled as free space path losses, where βm,k(t)＝β0/(H2+||wk-q(t)||2) Denotes the channel gain, β, of the k-th backscatter device to its paired m-th excitation source0Is the path loss constant of the wireless channel in unit distance (i.e. 1 meter), H is the fixed height (in meters) of the unmanned aerial vehicle flight, betak(t)＝β0/||wk-um||2Representing the channel gain of the kth backscatter device to the drone. In addition, Pm(t) represents the transmission power of the mth excitation source, and the transmission power vectors of all the excitation sources are denoted as P (t) ═ P1(t),…,Pm(t)]。
Represents the power reflection coefficient of the kth backscatter device paired with the mth excitation source at time t, and the power reflection coefficients of all backscatter devices on the surface are recorded as
Eta for energy collection efficiency of kth backscatter devicem∈[0,1]And (4) showing. Thus throughout the task cycleWithin T, the energy collected by the kth backscatter device is:
at time t, with a binary variable am,k(t)∈[0,1]，
Indicating whether a k-th backscatter device paired with an m-th excitation source establishes a communication link with the drone, wherein am,k(t) ═ 1 indicates that it is communicating with the drone, otherwise am,k(t) is 0. By means of matrices
As an indicator variable it is indicated whether all backscatter devices on the ground are in communication with the drone. Because the ground equipment and the unmanned aerial vehicle are accessed in a TDMA (time division multiple access) mode, at most one ground backscatter equipment communicates with the unmanned aerial vehicle at any time t, namely the constraint is required to be met
Additive white Gaussian noise Power at UAV Signal receiver is σ2. The throughput per bandwidth (bit/Hz) of the kth backscatter device over the entire task period T can be expressed as:
the energy consumption of the unmanned aerial vehicle comprises communication energy consumption and propulsion energy consumption, but the communication energy consumption in an actual system is far less than the propulsion energy consumption. Wherein the communication energy consumption is related to the signal processing and communication circuit operation; the propulsion energy consumption is used to keep the drone hovering or flying in the air, related to the speed of the drone, its own attributes and environmental factors. V (t) represents the flight speed of the drone, and the propulsion power of the drone may be represented as:
other parameters P in equation (3)0,
Pi，v0，d0θ, s and A are fixed parameters in the Energy consumption model of the drone (see references "Y. Zeng, J. xu, and R. Zhang," Energy minimization for Wireless communication with road-running UAV, "IEEE Transactions on Wireless Communications, vol.18, No.4, pp.2329-2345, April 2019" and "A.R.S. Bramwell, G.Done, and D.Balmford, Bramwell's Helicopter Dynamics,2 ed. American Institute of Aeronous&Ast (aiaa),2001 "), relating to the drone's own attributes and environment.
For the communication system designed by the present invention, in a task cycle, considering the swallowing and spitting amount of all ground backscatter devices, the transmitting power of all ground excitation sources and the propulsion Energy consumption of the unmanned aerial vehicle, the Energy Efficiency (EE) of the communication system can be expressed as:
furthermore, the invention also provides an optimization method of the flight path and the resource allocation scheme. And with the aim of maximizing the energy efficiency of the system, jointly optimizing four groups of variables, including an access matrix A (t) from the ground backscatter devices to the unmanned aerial vehicle, a power reflection coefficient B (t) of the backscatter devices, the transmission power distribution P (t) of the excitation source and a flight path q (t) of the unmanned aerial vehicle. The specific optimization problem (P1) is as follows:
q (0) ═ q (t) (equation 5h)
Wherein, formula (5a) is the minimum throughput constraint of each backscatter device, formula (5b) is the minimum collected energy constraint of each backscatter device, formula (5c) is the constraint that only one BD is accessed to the drone at any time, formula (5d) is the 0/1 value constraint of the access indicator variable, formula (5e) is the transmit power constraint of each radio frequency excitation source, formula (5f) is the value range constraint of the power reflection coefficient of each backscatter device, formula (5g) is the maximum speed limit for the drone flight, and formula (5h) is the constraint that the drone flies back to the starting point after completing the mission.
The problem (P1) is a non-convex optimization problem that includes coupling variables, continuous-time integrals, and non-convex constraint functions. To make the problem (P1) easier to handle, the invention first discretizes the problem in timeI.e. to disperse the operation period T into N time slots, each time slot having a length TsT/N; when N is sufficiently large, the problem after discretization is a good approximation of the original problem and can be expressed as (P2):
q (0) ═ q (n) (equation 6i)
Similar to the problem (P1), equation (6a) of the problem (P2) is the minimum throughput constraint per backscatter device, equation (6b) is the minimum collected energy constraint per backscatter device, equation (6c) is the constraint that only one BD is guaranteed to access the drone at any time, equation (6d) is the 0/1 value constraint for the access indicator variable, equation (6e) is the transmit power constraint per rf excitation source, equation (6f) is the value range constraint for the power reflection coefficient per backscatter device, equation (6g) is the maximum speed limit for the drone to fly, and equation (6h) is the constraint that the drone flies back to the starting point after completing the mission.
The problem (P2) is still a non-Convex Optimization problem including coupling variables and non-Convex constraint functions, and can be solved by an efficient iterative algorithm using an alternating Optimization (e.g., Block Coordinate descent) technique and a Convex approximation Optimization (e.g., Successive Convex Optimization) technique, respectively.
The beneficial effects of the present invention are verified by simulation experiments, considering that K ═ 40 Backscatter Devices (BDs) are randomly distributed at 112 × 112m2And M-16 signal excitation sources are distributed in the region. Unmanned aerial vehicle's flying height sets up to H10 meters, unmanned aerial vehicle's maximum flying speed VmaxThe additive white Gaussian noise power of the unmanned aerial vehicle receiver is sigma2-90 dBm. The task period of the unmanned aerial vehicle is T-90 s, the unmanned aerial vehicle is divided into N-360 time slots, and the length of each time slot is TsT/N is 0.45s, and the maximum transmitting power of the excitation source is set to be Pmax6W, beta in the 900MHz band0The convergence threshold of the resource allocation optimization algorithm is 10 ∈ 30dB-4Setting the energy conversion efficiency of all ground backscatter devices to ηkSet the minimum requirement for the energy collected by all backscatter devices, and its throughput minimum requirement to be the same at 0.5,
the convergence algorithm converged up to 20 times in the simulation.
To facilitate comparison of performance, consider an existing "hover-communicate-re-fly" baseline scheme: i.e. the drone hovers in turn at K positions, communicating with only a single backscatter device at each position. The hover position and hover time are obtained by an optimization method.
FIG. 4 shows the fixation
The maximum energy efficiency obtained by optimization and the minimum throughput requirement to be met by the backscatter apparatus
The relationship of variation between them. Compared with the benchmark scheme of 'hover-communication-re-flight', the design scheme of 'communication while flying' can improve the energy efficiency of the system by at least 200%. Even in that
In time, the system energy efficiency under the scheme of the invention is slightly attenuated to be 0.243, but compared with the system energy efficiency of the 'hover-communication-re-flight' scheme, the system energy efficiency is 0.085, and the improvement is still very remarkable.
FIG. 5 shows the fixation
When the values are respectively 1bit/Hz, 2bit/Hz and 4bit/Hz, the number of the time slots of each backscattering device accessed to the unmanned aerial vehicle in the scheme designed by the invention is increased. Fig. 6 shows an unmanned flight path designed by the present invention. As can be seen from fig. 5 and 6, the number of time slots for the ground backscatter devices to be connected to the drones is not equal, and generally, the longer the time for the backscatter devices near the excitation source is, for example, the 3 rd backscatter device, 15 th backscatter device, 21 th backscatter device, and 30 th backscatter device in the figure. In addition, the relative position distribution between the backscatter devices and the excitation source directly affects the flight trajectory of the drone. For example, the nth time slot is 190-235 time slots in fig. 6, when the minimum throughput requirement of the backscatter device is small
To maximize system energy efficiency, the drone flies toward the 30 th backscatter device and then flies away. As the minimum throughput requirements of backscatter devices increase,
2bit/Hz, 4bit/Hz, this flight tendency of the drone will be weakened, otherwise the minimum throughput requirement of each backscatter device cannot be guaranteed.
Claims (1)
1. A design method of an unmanned aerial vehicle-assisted backscatter communication system is characterized in that the unmanned aerial vehicle-assisted backscatter communication system consists of a plurality of ground radio frequency excitation sources, a plurality of ground backscatter devices and an unmanned aerial vehicle; wherein the content of the first and second substances,
each ground radio frequency excitation source is provided with 1 transmitting antenna for transmitting radio frequency signals, and the radio frequency signals can provide carrier waves and energy for the backscatter equipment;
each ground backscatter device is provided with 1 antenna, one part of received radio frequency signals is used for energy collection, the other part of the received radio frequency signals is used for reflection, and the ground backscatter devices modulate data of the ground backscatter devices onto the signals used for reflection and then reflect the data to the unmanned aerial vehicle;
the unmanned aerial vehicle is provided with a chip, a device or equipment for communication, and the unmanned aerial vehicle is provided with 1 receiving antenna which can receive signals reflected by the ground backscatter equipment and then demodulate the signals to obtain data of the ground equipment;
the unmanned aerial vehicle communicates with different ground backscatter devices in the air flight period in a time division multiplexing access mode, and the transmission protocol of the unmanned aerial vehicle and the ground backscatter devices in the flight process is as follows:
s11: a ground radio frequency excitation source transmits a radio frequency signal;
s12: the ground backscatter devices which are not communicated with the unmanned aerial vehicle are in an energy collection mode, collect energy by receiving signals transmitted by a ground radio frequency excitation source, and do not perform backscatter;
s13, using a part of received signals for energy collection by ground backscattering equipment which establishes communication with the unmanned aerial vehicle, and modulating the other part of signals as a carrier wave and then performing backscattering;
s14, the unmanned aerial vehicle communicates with the ground backscattering equipment one by one, decodes and collects data information of the unmanned aerial vehicle;
s15, after the task is finished, the unmanned aerial vehicle returns to the terminal point;
the ground radio frequency excitation source is active equipment, the position distribution is random, and the transmitting power can not exceed a set peak value PmaxAnd can be optimized;
the ground backscatter devices are passive devices with arbitrary position distribution, and the energy collected by the backscatter devices in the mission period must meet the minimum energy requirement E set by the systemmin；
A known energy conversion efficiency eta exists when the ground backscatter device collects energy; when signal reflection is carried out, the power reflection coefficient can be optimized in resource allocation;
the unmanned aerial vehicle is accessed into the unmanned aerial vehicle one by one in a time division multiple access mode, and the uplink throughput of each backscattering device in a task period must ensure the minimum requirement Qmin；
The method also comprises an unmanned aerial vehicle path design and system resource allocation method, sets an optimization target to maximize the energy efficiency EE of the system, and jointly optimizes the access matrix from the ground backscatter equipment to the unmanned aerial vehicle
Power reflection coefficient of backscatter device
The transmission power distribution P of the excitation source and the flight path Q of the unmanned aerial vehicle establish the following optimization problems:
q (0) ═ q (n). formula (6i)
Where equation (6b) is the minimum throughput per backscatter device
Constraint, equation (6c) is the lowest collected energy per backscatter device
Constraint, equation (6d) is a constraint that ensures that only one ground backscatter access drone is available at any one time, and equation (6e) is an access droneAnd (3) inputting 0/1 value constraint of the indicator variable, wherein the formula (6f) is the maximum transmission power P of each radio frequency excitation sourcemaxAnd (3) constraining, wherein a formula (6g) is a value range constraint of the power reflection coefficient of each backscattering device, and a formula (6h) is a maximum speed V of the flight of the unmanned aerial vehiclemaxLimiting, wherein a formula (6i) is a constraint that the unmanned aerial vehicle flies back to the starting point after completing the task;
n is the number of time slots after the dispersion of the operation period T, and the length of each time slot is TsT/N, M is the number of ground radio frequency excitation sources, k refers to k backscatter devices,
representing a set of ground backscatter devices paired with an mth ground radio frequency excitation source, binary variable am,k(n)∈[0,1]Indicating whether a k-th backscatter device paired with an m-th excitation source at an nth time slot establishes a communication link with the drone, wherein am,k(n) ═ 1 indicates that it is communicating with the drone, otherwise am,k(n)＝0，βm,kChannel gain, β, for the k-th backscatter device to its paired m-th excitation source0Is the path loss constant, u, of the radio channel over a unit distancemAnd wkRespectively representing the position of the m-th excitation source and the k-th backscatter device and the drone on a two-dimensional plane, Pm(n) represents the transmission power of the mth excitation source, bm,k(n) represents the power reflection coefficient of the kth backscatter device paired with the mth excitation source during time slot n, H is the fixed altitude at which the drone is flying, q (n) represents the central position of the drone during time slot n, σ2Power of additive white Gaussian noise at UAV Signal receiver, V (n) flight speed of unmanned aerial vehicle, P0,
Pi，v0，d0θ, s and a are fixed parameters in the unmanned aerial vehicle energy consumption model, and η is the energy collection efficiency of the ground backscatter devices.
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