阅读说明：本技术 一种智能超表面与中继的协作系统辅助无人机通信方法 (Auxiliary unmanned aerial vehicle communication method of intelligent super-surface and relay cooperation system ) 是由 唐冬 李一聪 黄高飞 赵赛 郑晖 刘贵云 于 2021-09-13 设计创作，主要内容包括：本发明涉及一种智能超表面与中继的协作系统辅助无人机通信方法,其包括建立两阶段的传输协议和信道模型；获得智能超表面与中继协作系统辅助无人机数据采集速率与中继接收与发送的两阶段的时间分配系数、智能超表面的两阶段的相位和无人机的位置之间的关系；优化中继接收与发送的两阶段的时间分配系数、智能超表面的两阶段的相位和无人机的位置；部署智能超表面和中继,使智能超表面、中继与无人机、传感器节点之间建立视距通信链路。解决了当RIS部署在接近地面用户的位置时,RIS辅助无人机通信带来的性能提升极大受限的问题。本发明具有提升部署在接近地面用户位置的RIS辅助无人机通信性能的效果。(The invention relates to an intelligent super-surface and relay cooperative system auxiliary unmanned aerial vehicle communication method, which comprises the steps of establishing a two-stage transmission protocol and a channel model; acquiring the relation between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle; optimizing time distribution coefficients of two stages of relay receiving and transmitting, phases of two stages of intelligent super-surface and positions of the unmanned aerial vehicle; and deploying the intelligent super surface and the relay to establish a line-of-sight communication link between the intelligent super surface and the relay and between the unmanned aerial vehicle and the sensor node. The problem of when the RIS deploys in the position that is close to ground user, the performance that the communication of the supplementary unmanned aerial vehicle of RIS brought promotes very big restriction is solved. The invention has the effect of improving the communication performance of the RIS auxiliary unmanned aerial vehicle deployed at the position close to the ground user.)

1. An intelligent super-surface and relay cooperative system auxiliary unmanned aerial vehicle communication method is characterized by comprising the following steps:

the method comprises the steps of sending data to a relay and an unmanned aerial vehicle based on an intelligent super-surface auxiliary sensor node, decoding and forwarding the data to the unmanned aerial vehicle based on the intelligent super-surface auxiliary relay, and meanwhile, establishing a transmission protocol and a channel model of two stages when the sensor node reflects signals to the unmanned aerial vehicle through the intelligent super-surface;

establishing a relation between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the relay receiving and sending two stages, the phase of the intelligent super surface and the position of the unmanned aerial vehicle according to the transmission protocol and the channel model of the two stages;

the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super-surface and relay cooperation system reaches the maximum value, and the time distribution coefficient of two stages of relay receiving and transmitting, the phase of the two stages of the intelligent super-surface and the position of the unmanned aerial vehicle are optimized;

deploying the intelligent super surface and the relay according to the optimized time distribution coefficient of the two phases of relay receiving and transmitting, the phase of the two phases of the intelligent super surface and the position of the unmanned aerial vehicle, so that a line-of-sight communication link is established among the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node.

2. The intelligent super surface and relay cooperative system assisted drone communication method of claim 1, wherein the step of optimizing relay reception and transmission two-phase time allocation coefficients comprises:

the position of the unmanned aerial vehicle and the phases of the two stages of the intelligent super surface are preset, so that the intelligent super surface and relay cooperation system assists the solving that the data acquisition rate of the unmanned aerial vehicle reaches the maximum value to be converted into a linear programming problem and solved, and the time distribution coefficients of the two stages of receiving and sending of the relay are optimized and updated.

3. The intelligent hypersurface and relay collaboration system assisted drone communication method of claim 1 wherein the step of optimizing the phase of the two phases of the intelligent hypersurface comprises:

the position of the unmanned aerial vehicle is preset, the time distribution coefficient of the relay receiving and sending phases is optimized, the intelligent super surface and the relay cooperation system is used for assisting the solving that the data acquisition rate of the unmanned aerial vehicle reaches the maximum value to be converted into a convex semi-definite planning problem through a semi-definite relaxation method, and the phases of the intelligent super surface in the two phases are optimized and updated.

4. The cooperative system assistant unmanned aerial vehicle communication method of claim 3, wherein based on the preset unmanned aerial vehicle position, a convex optimization solver and a Gaussian randomization method are adopted to solve the phase of the phase in which the sensor node reflects the signal to the unmanned aerial vehicle through the intelligent super surface while the intelligent super surface assistant relay decodes and forwards the data to the unmanned aerial vehicle.

5. The cooperative system-assisted unmanned aerial vehicle communication method of claim 4, wherein based on the optimized time distribution coefficient of the two phases of receiving and transmitting by the relay, the decoding and forwarding data by the intelligent super-surface assisted relay to the unmanned aerial vehicle, and the phase of the sensor node reflecting the signal to the unmanned aerial vehicle through the intelligent super-surface and the preset position of the unmanned aerial vehicle, a convex optimization solver and a Gaussian randomization method are adopted to solve the phase of transmitting the data to the relay and the unmanned aerial vehicle by the intelligent super-surface assisted sensor node.

6. The intelligent hyper-surface and relay collaboration system assisted drone communication method of claim 1, wherein the step of optimizing the location of the drone comprises:

based on the optimized time distribution coefficient of the two stages of relay receiving and sending and the optimized phase of the two stages of the intelligent super surface, the solution that the data acquisition rate of the intelligent super surface and the relay cooperation system for assisting the unmanned aerial vehicle reaches the maximum value is converted into the relation problem of the departure angle and the path loss in the array response of the unmanned aerial vehicle position and the communication link from the intelligent super surface to the unmanned aerial vehicle, the solution is solved, and the position of the unmanned aerial vehicle is optimized and updated.

7. The method for assisting unmanned aerial vehicle communication by the cooperation system of intelligent super surface and relay as claimed in claim 6, wherein when solving the problem of the relationship between the unmanned aerial vehicle position and the departure angle and path loss in the array response from the intelligent super surface to the unmanned aerial vehicle communication link, the finite region successive optimization-successive convex approximation algorithm is adopted to successively solve the locally optimal unmanned aerial vehicle position in a small region, and convex approximation is performed by the successive convex approximation method until the fractional growth of the objective function value is smaller than a preset threshold value, so as to obtain the optimal position solution of the unmanned aerial vehicle.

8. The cooperative system assisted drone communication method of any one of claims 1 to 7, wherein the deploying intelligent super surface, relays, drones and sensor nodes, the step of establishing line-of-sight communication links between the intelligent super surface, relays and drones and sensor nodes comprises:

when no direct communication link exists between the unmanned aerial vehicle and the sensor node, presetting the ground position of the sensor node in a building;

locating the relay in an area outside a building;

combining the positions of the sensor nodes and the relays to enable at least 2 intelligent super surfaces to be vertically placed on the surface of a building;

meanwhile, based on the optimized position of the unmanned aerial vehicle, a line-of-sight communication link is established among the intelligent super-surface, the relay, the unmanned aerial vehicle and the sensor node.

9. A computer device comprising a memory, a processor and a computer program stored in the memory and run on the processor, the processor when executing the computer program implementing the steps of the intelligent hyper-surface and relay collaboration system assisted drone communication method of any one of claims 1-8.

10. A computer-readable storage medium, characterized in that it stores a computer program which, when executed by a processor, implements the steps of the intelligent hyper-surface and relay collaboration system assisted drone communication method of any one of claims 1 to 8.

Technical Field

The invention relates to the technical field of communication, in particular to an intelligent communication method for an unmanned aerial vehicle assisted by a cooperation system of a super surface and a relay.

Background

The development and application of 5G technology have brought new vision to mobile communication, and also brought new challenges, such as rapid increase of data traffic demand, serious influence of millimeter wave communication by occlusion, and the like. Particularly, for the unmanned aerial vehicle data acquisition system who is applied to smart city, because of city building, trees and people etc. to the adverse effect of communication environment, in addition unmanned aerial vehicle's mobility is also limited to the improvement of communication performance, especially in the unmanned aerial vehicle communication scene that is furnished with millimeter wave communication, the influence that the barrier sheltered from and brings is more serious. Subject to the above limitations, the drone needs to fly at a higher altitude to maintain a higher LoS (Line of Sight) probability, which also results in a larger communication loss.

Recently, a technology named "RIS (Intelligent super Surface)" has been proposed and rapidly received attention of researchers. The RIS technology is considered as a key technology of the future 6G due to its characteristics of low cost, easy deployment, and changeable communication environment.

In general, an RIS is an array plane composed of a large number of passive reflective elements, each of which can be independently controllable to change the amplitude or phase of an incident signal. At present, many researches and examples prove that the intelligent super-surface has remarkable improvements in spectrum efficiency, communication coverage rate, reliability and the like. Therefore, by deploying the RIS and skillfully designing the reflection, the signal propagation environment can be flexibly reconfigured, so that the degree of freedom of unmanned aerial vehicle communication is further improved, and a better communication connection can be kept when a direct communication link is shielded.

And because the reflection link when the RIS assists the unmanned aerial vehicle to communicate also has loss, in order to reduce the influence of loss, generally deploy RIS near transmitting terminal or receiving end. If consider when deploying the RIS in the position of being close ground user, because the position of unmanned aerial vehicle is changeable, can't obtain the fixed position of being close unmanned aerial vehicle, then still face the problem that has the sheltering from between unmanned aerial vehicle and the RIS, lead to the performance promotion that the communication of the supplementary unmanned aerial vehicle of RIS brought very limited.

With respect to the related art in the above, the inventors consider that there is a drawback that the performance improvement by the RIS assisted drone communication is greatly limited when the RIS is deployed at a position close to a ground user.

Disclosure of Invention

In order to improve the performance of communication of the RIS auxiliary unmanned aerial vehicle deployed at a position close to a ground user, the invention provides an intelligent super-surface and relay cooperative system auxiliary unmanned aerial vehicle communication method.

In a first aspect, the invention provides an intelligent super-surface and relay cooperative system-assisted unmanned aerial vehicle communication method, which has the characteristic of improving the communication performance of an RIS-assisted unmanned aerial vehicle deployed at a position close to a ground user.

The invention is realized by the following technical scheme:

an intelligent super-surface and relay cooperative system assisted unmanned aerial vehicle communication method comprises the following steps:

the method comprises the steps of sending data to a relay and an unmanned aerial vehicle based on an intelligent super-surface auxiliary sensor node, decoding and forwarding the data to the unmanned aerial vehicle based on the intelligent super-surface auxiliary relay, and meanwhile, establishing a transmission protocol and a channel model of two stages when the sensor node reflects signals to the unmanned aerial vehicle through the intelligent super-surface;

establishing a relation between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the relay receiving and sending two stages, the phase of the intelligent super surface and the position of the unmanned aerial vehicle according to the transmission protocol and the channel model of the two stages;

the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super-surface and relay cooperation system reaches the maximum value, and the time distribution coefficient of two stages of relay receiving and transmitting, the phase of the two stages of the intelligent super-surface and the position of the unmanned aerial vehicle are optimized;

deploying the intelligent super surface and the relay according to the optimized time distribution coefficient of the two phases of relay receiving and transmitting, the phase of the two phases of the intelligent super surface and the position of the unmanned aerial vehicle, so that a line-of-sight communication link is established among the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node.

The present invention in a preferred example may be further configured to: the step of optimizing the time distribution coefficient of the two stages of relay receiving and transmitting comprises the following steps:

the position of the unmanned aerial vehicle and the phases of the two stages of the intelligent super surface are preset, so that the intelligent super surface and relay cooperation system assists the solving that the data acquisition rate of the unmanned aerial vehicle reaches the maximum value to be converted into a linear programming problem and solved, and the time distribution coefficients of the two stages of receiving and sending of the relay are optimized and updated.

The present invention in a preferred example may be further configured to: the step of optimizing the phase of the two phases of the smart metasurface comprises:

the position of the unmanned aerial vehicle is preset, the time distribution coefficient of the relay receiving and sending phases is optimized, the intelligent super surface and the relay cooperation system is used for assisting the solving that the data acquisition rate of the unmanned aerial vehicle reaches the maximum value to be converted into a convex semi-definite planning problem through a semi-definite relaxation method, and the phases of the intelligent super surface in the two phases are optimized and updated.

The present invention in a preferred example may be further configured to: on the basis of the preset position of the unmanned aerial vehicle, a convex optimization solver and a Gaussian randomization method are adopted to solve the phase of the stage that the sensor node reflects signals to the unmanned aerial vehicle through the intelligent super surface while the intelligent super surface auxiliary relay decodes and forwards data to the unmanned aerial vehicle.

The present invention in a preferred example may be further configured to: based on the optimized time distribution coefficients of the relay receiving and sending phases, the intelligent super-surface auxiliary relay decodes and forwards data to the unmanned aerial vehicle, and meanwhile, the phase of the sensor node to the unmanned aerial vehicle through the intelligent super-surface reflection signal and the preset position of the unmanned aerial vehicle are solved by adopting a convex optimization solver and a Gaussian randomization method, and the phase of the intelligent super-surface auxiliary sensor node sending the data to the relay and the unmanned aerial vehicle is solved.

The present invention in a preferred example may be further configured to: the step of optimizing the position of the drone comprises:

based on the optimized time distribution coefficient of the two stages of relay receiving and sending and the optimized phase of the two stages of the intelligent super surface, the solution that the data acquisition rate of the intelligent super surface and the relay cooperation system for assisting the unmanned aerial vehicle reaches the maximum value is converted into the relation problem of the departure angle and the path loss in the array response of the unmanned aerial vehicle position and the communication link from the intelligent super surface to the unmanned aerial vehicle, the solution is solved, and the position of the unmanned aerial vehicle is optimized and updated.

The present invention in a preferred example may be further configured to: and when solving the relation problem of the departure angle and the path loss in the array response of the unmanned aerial vehicle position and the communication link from the intelligent super surface to the unmanned aerial vehicle, adopting a finite region successive optimization-continuous convex approximation algorithm to successively solve the position of the locally optimal unmanned aerial vehicle in a small region, and performing convex approximation through a continuous convex approximation method until the fraction increment of the objective function value is smaller than a preset threshold value to obtain an optimal position solution of the unmanned aerial vehicle.

The present invention in a preferred example may be further configured to: the step of deploying an intelligent super-surface, a relay, a drone and a sensor node such that a line-of-sight communication link is established between the intelligent super-surface, the relay and the drone, the sensor node comprises:

when no direct communication link exists between the unmanned aerial vehicle and the sensor node, presetting the ground position of the sensor node in a building;

locating the relay in an area outside a building;

combining the positions of the sensor nodes and the relays to enable at least 2 intelligent super surfaces to be vertically placed on the surface of a building;

meanwhile, based on the optimized position of the unmanned aerial vehicle, a line-of-sight communication link is established among the intelligent super-surface, the relay, the unmanned aerial vehicle and the sensor node.

In a second aspect, the present invention provides a computer device with features to enhance communication performance of an RIS assisted drone deployed near a ground user location.

The invention is realized by the following technical scheme:

a computer device comprising a memory, a processor and a computer program stored in the memory and running on the processor, the processor when executing the computer program implementing the steps of the above-described intelligent hyper-surface and relay collaboration system assisted drone communication method.

In a third aspect, the present invention provides a computer-readable storage medium having features to enhance communication performance of a RIS-assisted drone deployed proximate to a ground user location.

The invention is realized by the following technical scheme:

a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the above-described intelligent hyper-surface and relay collaboration system assisted drone communication method.

In summary, the present invention at least includes the following beneficial technical effects:

1. based on respective characteristics of the RIS and the relay, the communication between the UAV and the ground user is assisted by deploying the cooperation system of the RIS and the relay, so that the RIS can establish an additional communication link and can assist in enhancing the SN or the communication between the UAV and the relay, the communication speed between the unmanned aerial vehicle with a variable position and the ground sensor node reaches the maximum value, the cooperative assistance effect of the relay and the intelligent super surface in the communication is exerted to the maximum extent, the problem that the unmanned aerial vehicle cannot collect the data of the ground sensor node due to obstruction in the application scene of data collection of the unmanned aerial vehicle in the urban complex environment is solved, and the data collection speed is greatly improved;

2. by optimizing the position of the unmanned aerial vehicle, the position of the unmanned aerial vehicle can be flexibly changed aiming at different channel states so as to improve the communication quality;

3. through decoding and forwarding of the active relay, the number of elements required by the RIS can be reduced, and the deployment cost is reduced.

Drawings

Fig. 1 is a schematic diagram of RIS assisted communication.

Fig. 2 is a schematic diagram of a system for assisting a drone in communication with a cooperative system of an intelligent super surface and a relay according to an embodiment of the present invention.

Fig. 3 is a schematic flow chart of a method for assisting a drone in communication by a collaboration system of an intelligent super-surface and a relay according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of the communication process between the collaboration system of relay and RIS and the SN and UAV to establish the LoS link.

Detailed Description

The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In addition, the term "and/or" herein is only one kind of association relationship describing an associated object, and means that there may be three kinds of relationships, for example, a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship, unless otherwise specified.

The scenario of communication between the RIS assisting base station/wireless access point, the user, as shown in fig. 1, creates an additional communication link between the base station and the user by deploying the RIS. In the figure, Θ is a reflection coefficient of RIS, and h, G, and G respectively represent a channel gain from base station to RIS, a channel gain from RIS to user, and a channel gain from base station to user.

In this communication scenario, the total channel gain H received by the ue can be represented as H ═ G + G^HAnd thetah, the channel can be reconfigured by adjusting the reflection coefficient theta of the RIS, so as to achieve the effect of expected enhancement or reduction of the communication performance. Due to the special composition and principle of the RIS, compared with other similar technologies such as relay and backscatter communication, the RIS has the advantages of low cost, low energy consumption, high efficiency and the like.

There have been some studies comparing: the difference in performance between passive RIS and active relays, the conclusion indicates that, despite the above advantages, passive RIS requires the deployment of a large number of reflective elements to achieve performance comparable to that of conventional active relays, which undoubtedly increases the deployment cost; also with the increase of reflective elements, the channel of RIS assisted wireless communication becomes more challenging. Therefore, how to balance the roles and locations of both RIS and relay in a communication system is a question worth discussing.

Moreover, by the development of unmanned aerial vehicle technology, unmanned aerial vehicle communication technology also receives the extensive attention of researchers. Generally speaking, unmanned aerial vehicles can bring very big degree of freedom for communication design because of its mobility and flexibility. With the rise of the internet of things technology, interconnection among large-scale equipment is also a hot spot for future network research and application, and unmanned aerial vehicle communication can also play an important role in the internet of things technology.

Although the probability of LoS can be improved by the high mobility of the unmanned aerial vehicle, the mobility of the unmanned aerial vehicle is limited to the improvement of the communication performance due to the severe influence of urban buildings, trees, people and the like on the communication environment, and especially in the communication scene of the unmanned aerial vehicle with millimeter wave communication, the influence caused by the shielding of obstacles is more serious. Subject to the above limitations, the drone may need to fly at a higher altitude to maintain higher LoS performance, which also results in greater communication loss. Therefore, through deploying the RIS, with the degree of freedom that further improves unmanned aerial vehicle communication for unmanned aerial vehicle also can keep better communication connection when direct communication link is sheltered from.

And because the RIS assists the unmanned aerial vehicle to communicate, two distances form the product path loss, wherein the two distances comprise the receiving power of the user and the distance d from the transmitting end to the RIS_SIAnd distance d from RIS to receiver_ID. Specifically, the "product path loss" formed by the two distances is inversely proportional to the product of the two distances, | E²∝(d_SId_ID)^-1Where E represents the product path loss. Therefore, to reduce the impact of the product path loss, the RIS is typically deployed near the transmitting end or the receiving end. However, for the unmanned aerial vehicle communication system assisted by the RIS, since the position of the unmanned aerial vehicle is changeable, a fixed position close to the unmanned aerial vehicle cannot be obtained, and if the RIS is deployed at a position close to a ground user, the problem that the unmanned aerial vehicle and the RIS are shielded still is encountered, so that the performance improvement brought by the aid of the RIS is very limited.

At present, few researches on using the RIS to assist the relay to improve the communication rate of the conventional relay system are carried out, but the important point is that the RIS is used to improve the conventional relay without considering the cooperation of the conventional relay and the conventional relay, and specifically, only the RIS is used to assist the relay and a communication link between a transmitting end and a receiving end is considered, and the RIS itself can assist the connection between the transmitting end and the receiving end. The influence caused by the position change of the unmanned aerial vehicle is not considered by other relay and RIS cooperative systems.

In conclusion, the functions of the RIS and the relay are coordinated, the RIS and the relay form a cooperation system to assist the unmanned aerial vehicle in carrying out data acquisition tasks on the ground sensor nodes, and the unmanned aerial vehicle has great research value.

The embodiments of the present invention will be described in further detail with reference to the drawings attached hereto.

Referring to fig. 2, a system for deploying an RIS and relay cooperation to assist a rotorcraft UAV (Unmanned aerial vehicle) in uplink communication with an SN (Sensor Node) on the ground, for example, a system for deploying a UAV to perform data acquisition tasks on an SN in a specific area, and a system for an intelligent super surface and relay cooperation system to assist a drone in communication are shown in fig. 2. Before the UAV performs a data acquisition task, the SN position of the ground is preset, and the UAV cannot establish a direct communication link with the SN. Specifically, the SN is located in a building, a half-duplex decode-and-forward relay is placed outside the building, the RIS array is deployed on the building surface near the building, and the RIS is vertically deployed on the building surface by facing the relay and the SN considering the reflection path of the RIS. The deployment of relays and RIS makes it possible to establish a LoS link between relay and RIS based collaboration systems and SN and UAV.

Referring to fig. 3, an embodiment of the present invention provides an intelligent super-surface and relay cooperative system-assisted unmanned aerial vehicle communication method, and main steps of the method are described as follows.

S1, when the nodes send data to the relay and the unmanned aerial vehicle based on the intelligent super-surface auxiliary sensor and decode and forward the data to the unmanned aerial vehicle based on the intelligent super-surface auxiliary relay, the nodes reflect signals to the unmanned aerial vehicle through the intelligent super-surface, and establish a transmission protocol and a channel model of two stages;

s2, obtaining the relation between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the relay receiving and sending two stages, the phase of the intelligent super surface and the position of the unmanned aerial vehicle according to the transmission protocol and the channel model of the two stages;

s3, enabling the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system to reach the maximum value, and optimizing the time distribution coefficient of the two stages of relay receiving and transmitting, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle;

and S4, deploying the intelligent super surface and the relay according to the optimized time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle, and establishing a line-of-sight communication link among the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node.

Specifically, S1, the stage of sending data to the relay and the unmanned aerial vehicle based on the intelligent super-surface auxiliary sensor node and the stage of decoding and forwarding the data to the unmanned aerial vehicle based on the intelligent super-surface auxiliary relay, and the stage of sending a signal to the unmanned aerial vehicle by the sensor node through the intelligent super-surface reflection signal, wherein the specific steps of establishing a two-stage transmission protocol and a two-stage channel model are described as follows.

The RIS assisted SN sends the data to the relay and, at the same time, forwards the data to the UAV for reception. Assuming that the RIS is made up of M passive reflecting elements each with a distance d between them, the positions of all the reflecting elements can be considered the same, denoted w, since the size of the reflecting elements and the mutual spacing are much smaller than the communication distance_I＝[X_I,Y_I,Z_I]^T. The reflection coefficient of the RIS includes two parts, namely, reflection amplitude and reflection phase, and most of the current research on the RIS assumes that the reflection amplitudes of all elements are 1, i.e., the reflection amplitude is full emission, and for simplifying the model, we also adopt the assumption that the reflection phase can be expressed as:

wherein the phase of each reflective element is required to satisfy a constraintThe SN, the relay and the UAV are all single antennas, the relay is a half-duplex decoding forwarding relay, data is received at a first hop, and data is sent at a second hop. The position coordinates of the SN and the relay may be represented as w, respectively_S＝[X_S,Y_S,0]^T，w_R＝[X_R,Y_R,Z_R]^T. UAV flies at fixed altitude H, the position of which may be denoted as w_U＝[q,H]^TWherein q is [ x, y ═ y]. To simplify the problem, we consider the UAV to suspend to start receiving data after flying to a specific location, and therefore optimize only for the location where the system's optimal communication rate is obtained.

Referring to fig. 4, a communication process of establishing a LoS link between a cooperation system of a relay and a RIS and an SN and a UAV is divided into two stages, namely, a first stage in which an intelligent super-surface assisted sensor node transmits data to the relay and the unmanned aerial vehicle, a second stage in which the sensor node reflects signals to the unmanned aerial vehicle through an intelligent super-surface while the intelligent super-surface assisted sensor node decodes and forwards the data to the unmanned aerial vehicle. In the first phase, the relay is in a data receiving state, and the RIS assisted SN sends data to the relay and the UAV; in the second phase, the relay is in the data sending state, and the SN can still reflect the signal to the UAV through the RIS while the relay decodes and forwards the data to the UAV. The communication rate of the system can be improved by adjusting alpha, assuming that the time proportion allocated in the first stage and the second stage is alpha and 1-alpha respectively, namely the received time allocation coefficient alpha and the transmitted time allocation coefficient 1-alpha, wherein alpha is more than or equal to 0 and less than or equal to 1.

Further, byRespectively SN-RIS (SN to RIS), RIS-Relay (RIS to Relay), SN-Relay (SN to Relay), RIS-UAV (RIS to UAV), Relay-UAV (Relay to UAV) baseband equivalent channels, the channels of Relay-RIS and RIS-Relay satisfy G according to channel reciprocity_IR＝G_RI。

Due to flexibility of RIS deployment and mobility of UAV, all the above channels are modeled as Rician fading channels, taking baseband equivalent channel of SN-RIS as an example, there are:

wherein the content of the first and second substances,rho is the reference distance d for the path loss between SN and RIS₀1m of path loss, d_SIIs the distance between SN and RIS, κ is the path loss exponent,is the channel gain coefficient, beta, between SN and RIS_SIIs a Rician factor, LoS componentArray response, φ, for SN signaling RIS_SI＝|X_S-X_I|/d_SIAs cosine of AoA (angle of arrival), NLoS componentCSCG (Complex Gaussian circular symmetric variables) modelable as zero mean Unit variance, i.e.

S2, according to the two-stage transmission protocol and the channel model, the concrete steps of obtaining the relationship between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system, the time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle are described as follows.

Fixing the transmitting power of SN to P_SThe transmission power of the relay is fixed to P_RIn addition, defineIs the phase of the RIS in the first phase, whereinIn the same way, v₂＝[v_2,1,…,v_2,M]Is the phase of the second phase and is,the reflected phase constraint is converted into a constant modulus constraint

The communication link of the first stage comprises S-R and S-U, wherein S-R refers to a composite link of SN-RIS-relay and SN-relay, S-U refers to a reflection cascade link of SN-RIS-UAV, and according to the channel model in (2), the SNR (Signal-to-Noise Ratio) of the S-R composite link is as follows:

whereinσ²Is the noise power. The SNR of the S-U reflection cascade link is as follows:

whereinTherefore, according to equation (3), the rate of data received by the relay in the first stage is:

from equation (4), the data rate received by the UAV in the first stage is:

the communication link in the second phase includes R-U and S-U, where R-U refers to the composite link of relay-RIS-UAV and relay-UAV, and S-U refers to the reflective cascade link of SN-RIS-UAV, and similar to the first phase, the SNR of R-U and S-U can be obtained as follows:

wherein the content of the first and second substances,thus, the rate at which the UAV of the second stage receives data is:

in the communication model for establishing the LoS link between the cooperative system of relays and RIS and the SN and UAV, assuming that the transmission of data is in a rate-free encoding manner, the data is received at the UAV in the form of energy accumulation, so the communication rate of the system can be expressed as:

C＝min{αC_R,1,αC_U,1+(1-α)C_U,2} (10)

it is to be noted that C is satisfied for the establishment of the above expression_R,1≥C_U,1I.e. gamma_SR≥γ_SU1In practice, the above preconditions may generally hold, since UAVs fly over cities, subject to distance.

The communication rate expression of the system reflects the relationship between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle.

S3, the specific steps of enabling the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system to reach the maximum value, and optimizing the time distribution coefficient of the two stages of relay receiving and transmitting, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle are described as follows.

Under the scene that a cooperation system comprising a two-stage relay and an RIS assists the UAV to acquire data of a ground SN, the intelligent super-surface and relay cooperation system assists the data acquisition rate of the UAV by jointly optimizing the two-stage time distribution of the two-stage relay receiving and forwarding, the two-stage phase of the RIS and the optimal communication position of the UAV. Thus, the following optimization problem is obtained:

P1:

s.t.0≤α≤1, (12)

wherein, the variables to be optimized are time distribution coefficient factors alpha of two phases of relay and RIS phase v_iAnd UAV location q.

Specifically, in solving the problem P1, since the optimization objective is to optimize the variables α, v_iAnd q coupling is not a concave function and cannot be directly solved, and constant modulus constraint (13) is difficult to directly process, so that the original non-convex problem is decomposed into three subproblems to be solved by adopting an alternative optimization method. Specifically, we need to optimize four variables α, v₁,v₂And q, optimizing the other variable by giving two variables to obtain an updated optimized variable, and iteratively updating all optimized variables by alternately solving to finally approach to an optimal solution. Three subproblems are expressed as follows:

sub-problem P2: giving the position of the UAV and the RIS phase, and optimizing a time distribution coefficient alpha;

sub-problem P3: optimization of RIS phase v given UAV position and time distribution coefficients_i；

Sub-problem P4: the UAV position q is optimized given the time allocation coefficients and RIS phase.

Specifically, the step of optimizing the time distribution coefficient α is described below.

At a given pointUAV position q and RIS phase v_iWhen, the original question P1 can be converted into:

P2:

the P2 problem is also the LP (Linear programming) problem, let:

from formulae (6) and (9), it is readily demonstrated that: c is not less than 0_U,1≤C_U,2Thus, A₁With respect to monotonous decrease of α, A₂With respect to a monotone not increasing, while A₁(0)＝0,A₂(0)＝C_U,2,A₁(1)＝C_R,1,A₂(1)＝C_U,1Thus A₁(0)≤A₂(0),A₁(1)≥A₂(1) Optimum time distribution coefficient alpha^*Should satisfy A₁(α^*)＝A₂(α^*) A closed solution can be obtained:

further, the RIS phase v is optimized_iThe steps of (a) are described below.

According to the preset UAV position q and the optimized time distribution coefficient factor α, the original problem P1 can be converted into:

P3：

s.t.(13).

the RIS phase optimization of the second stage can be performed first, and the P3 problem can be further split into:

P3.1：

s.t.

the general formula (9) is as follows:

wherein the content of the first and second substances,t＝1，

whileThe constant modulus constraint (18) then translates into:

applying SDR (semi-deterministic relaxation) method to relax the rank 1 constraint, the P3.1 problem can be transformed as follows:

P3.2:

s.t.

the P3.1 problem is a convex semi-definite programming problem and can be solved by a convex optimization solver, such as a CVX tool.

In general, P3.2 generally cannot directly obtain a solution satisfying the rank 1 constraint, namely rank (V)₂) Not equal to 1, which means that the solution obtained by P3.2 is only an upper bound of P3.1, where a high rank solution obtained by Gaussian randomization method is requiredI.e., a solution of rank greater than 1, is processed to obtain the desired solution of rank 1.

Specifically, the obtained high rank is solved by V first₂Performing eigenvalue decomposition, i.e. V ═ U Σ U^HWherein U ═ e₁,...,e_M+1],Σ＝diag(λ₁,...,λ_M+1) Then generating several Gaussian random variables r corresponding to severalThe solution chosen to maximize the value of the objective function is our solutionConstruction of the RIS phaseWherein [ x ]]_(1:M)A vector of the first M elements of x is represented to obtain the phase of the second phase.

After the optimization solution obtains the phase of the second stage, the P3 problem can be rewritten as:

P3.3:

s.t.αC_R,1(v₁)≥η, (25)

αC_U,1(v₁)+(1-α)C_U,2≥η, (26)

similar to the second stage of the optimization solution, P3.3 is rewritten as:

P3.4:

s.t.

wherein the content of the first and second substances, t＝1，C_U,2solved according to given UAV position and previous step P3.1Thus obtaining the product. Similar to the RIS phase solution of the second stage, the P3.4 problem is a convex semi-definite programming problem, which can be obtained by a convex optimization solver, such as a CVX tool, where the obtained solution is generally high-rank, and the phase of the first stage can be obtained by applying the gaussian randomization method

In general, based on the preset unmanned aerial vehicle position and the optimized time distribution coefficient, the solution that the communication speed of the intelligent super surface and the relay cooperation system reaches the maximum value is converted into a convex semi-definite planning problem through a semi-definite relaxation method, and the phases of the intelligent super surface in the second stage and the first stage are sequentially solved. The phase of the second stage is solved based on the preset position of the unmanned aerial vehicle, and a time distribution coefficient is not needed at the moment; and further, solving the phase of the first stage based on the phase obtained by the second stage solution, the preset unmanned aerial vehicle position and the optimized time distribution coefficient. Further, the step of optimizing the UAV position q is described below.

Based on the optimized time distribution coefficient factor α and the optimized phases of the RIS two phases, the original problem P1 can be transformed as:

P4:

for optimization of UAV position, P4 may be further rewritten as:

P4.1:

according to equations (6) and (9), the change in UAV position affects both AoD (departure angle) and pathloss, i.e., φ, in the array response of the RIS-UAV link_IU＝|X_I-x|/d_IU(q) andthe coupling between the two can not be solved directly, and therefore, the problem is solved by proposing an LRO (Limited Region Optimization) method. That is, an initial UAV position q is given₀Then, in a limited area of the position, optimizing to obtain a local optimal UAV position q₁，||q₁-q₀| ≦ Δ, Δ is chosen small enough to make the AoD of the array response approximately constant, so in this iteration, the position optimization of the UAV only affects the amount of path loss, while the array response is considered constant. By analogy, we further optimize with a limited region of the iteratively updated UAV location to obtain a locally optimal solution. For a given feasible UAV location q_lThe limited area constraint is:

||q-q_l||≤Δ (35)

this time is:

substituting it into equations (6) and (9) yields:

similarly, there are:

thus, the P4.1 problem can be rewritten as:

P4.2:

s.t.||q-q_l||≤Δ (42)

the P4.2 problem cannot be solved directly because the objective function is non-convex, and the relaxation variables mu and tau are introduced, so that the following optimization problem is considered:

P4.3:

s.t.||q-q_l||≤Δ, (44)

d_IU(q)≤μ, (45)

d_RU(q)≤τ. (46)

note that to make the P4.3 problem equivalent to the P4.2 problem, its optimal solution requires a guaranteed constraint (45)) And (46) are taken equally. For the P4.3 problem, the objective function and constraints (45) and (46) are both non-Convex and cannot be directly solved, we adopt SCA (sequential Convex Approximation) method, specifically, we apply the objective function and constraints (45) and (46) in { mu., (mu.)_l,τ_lFind the first order Taylor expansion at the place, have:

wherein

Thus, according to (47) - (50), the P4.3 problem can be approximated as:

P4.4:

s.t.||q-q_l||≤Δ, (52)

the P4.4 problem is a convex optimization problem and can be solved by a convex optimization solver (such as a CVX tool).

Therefore, when the UAV position is optimized, the problem that the objective function is difficult to solve due to the change of the UAV position is solved based on the LRO method. By successively solving for locally optimal UAV positions in small areas, it is guaranteed that in each solution, AoD can be seen as approximately constant. And then, carrying out convex approximation on the non-convex problem by adopting an SCA method, and continuously iterating to approximate an optimal solution. The specific iterative process can refer to the following LRO-SCA algorithm flow:

1. initialization variable q₀,μ₀,τ₀Setting a threshold value zeta and calculating an initial objective function value, wherein the iteration times l is 0;

2. from { q_l,μ_l,τ_lSolving the P4.4 problem, and updating to obtain { q }_l+1,μ_l+1,τ_l+1}；

3. Updating the iteration times l as l +1, and updating the objective function value;

4. skipping to the step 2, and sequentially executing the step 2-3;

5. ending the iteration until the fraction increment of the objective function value is smaller than a threshold value zeta;

6. and outputting the optimization solution q.

In summary, the algorithm flow for optimizing the time distribution coefficients of the two stages of relay receiving and transmitting, the phases of the two stages of intelligent super-surface and the position of the drone can be described as follows:

1. initializing variablesSetting a threshold epsilon and calculating an initial objective function value when the iteration number r is 0;

2. from givenSolving the P2 subproblem, and updating to obtain alpha^r+1；

3. Given by { q^r,α^r+1Solve the P3.2 sub-problem, moreIs newly obtained

4. From givenSolving the P3.4 sub-problem and updating to obtain

5. From givenSolving the P4.4 subproblem (LRO-SCA algorithm), and updating to obtain q^r+1；

6. Updating the iteration times r to r +1, and updating the objective function value;

7. skipping to the step 2, and sequentially executing the steps 2-6;

8. ending the iteration until the fraction increment of the objective function value is smaller than a threshold epsilon;

9. output variable optimization solution { q, v }₁,v₂,α}。

And S4, deploying the intelligent super surface and the relay according to the optimized time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle, and establishing a line-of-sight communication link among the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node.

And then deploying the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node, so that the step of establishing a line-of-sight communication link between the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node comprises the following steps:

when no direct communication link exists between the unmanned aerial vehicle and the sensor node, presetting the ground position of the sensor node in the building;

locating the relay in an area outside the building;

combining the positions of the sensor nodes and the relays to enable at least 2 intelligent super surfaces to be vertically placed on the surface of a building;

meanwhile, based on the optimized position of the unmanned aerial vehicle, a line-of-sight communication link is established among the intelligent super-surface, the relay, the unmanned aerial vehicle and the sensor node.

In this embodiment, the number of the intelligent super surfaces vertically placed on the building surface may range from [145,155], and specifically may be 150.

In the embodiment, the relay and intelligent super-surface-based cooperation system considers respective characteristics of the RIS and the relay, and the cooperation system for deploying the RIS and the relay assists the communication between the UAV and the ground user, so that the RIS can establish an additional communication link and can assist in enhancing the SN or the communication between the UAV and the relay, the communication rate of the unmanned aerial vehicle with the variable position and the ground sensor node is assisted to reach the maximum value, and the cooperative assistance effect of the relay and the intelligent super-surface in the communication is exerted to the maximum degree. The problem that the unmanned aerial vehicle cannot collect node data of the ground sensor due to obstruction in an application scene of data acquisition of the unmanned aerial vehicle in a complex urban environment is solved; simultaneously, through optimizing unmanned aerial vehicle's position, can change unmanned aerial vehicle's position to different channel state in a flexible way to improve communication quality. Compared with the traditional active relay forwarding system, the embodiment obviously improves the communication rate of relay forwarding by the aid of the RIS. For example, under the conditions that the transmission signal-to-noise ratio is 50dB and the number of reflecting elements is 64, the speed of the relay and intelligent super-surface cooperative system is improved by 4.2dB compared with the traditional relay forwarding system; compared with a general wireless system only deploying the RIS auxiliary communication, the number of elements required by the RIS can be reduced through decoding and forwarding of the active relay, and the deployment cost is reduced. For example, when the transmission signal-to-noise ratio is 30dB, to achieve a communication rate of 2bps/Hz, the RIS and relay cooperative system requires only 118 reflective elements, whereas the RIS-only assisted scheme requires 196 reflective elements to achieve.

It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

In one embodiment, a computer device is provided, which may be a server. The computer device includes a processor, a memory, a network interface, and a database connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program when executed by a processor implements an intelligent hyper-surface and relay cooperative system assisted drone communication method.

In one embodiment, a computer-readable storage medium is provided, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the following steps when executing the computer program:

s1, when the nodes send data to the relay and the unmanned aerial vehicle based on the intelligent super-surface auxiliary sensor and decode and forward the data to the unmanned aerial vehicle based on the intelligent super-surface auxiliary relay, the nodes reflect signals to the unmanned aerial vehicle through the intelligent super-surface, and establish a transmission protocol and a channel model of two stages;

s2, obtaining the relation between the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system and the time distribution coefficient of the relay receiving and sending two stages, the phase of the intelligent super surface and the position of the unmanned aerial vehicle according to the transmission protocol and the channel model of the two stages;

s3, enabling the data acquisition rate of the unmanned aerial vehicle assisted by the intelligent super surface and relay cooperation system to reach the maximum value, and optimizing the time distribution coefficient of the two stages of relay receiving and transmitting, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle;

and S4, deploying the intelligent super surface and the relay according to the optimized time distribution coefficient of the two stages of relay receiving and sending, the phase of the two stages of the intelligent super surface and the position of the unmanned aerial vehicle, and establishing a line-of-sight communication link among the intelligent super surface, the relay, the unmanned aerial vehicle and the sensor node.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, databases, or other media used in embodiments provided herein may include non-volatile and/or volatile memory.

It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-mentioned division of the functional units and modules is illustrated, and in practical applications, the above-mentioned function distribution may be performed by different functional units and modules according to needs, that is, the internal structure of the system is divided into different functional units or modules to perform all or part of the above-mentioned functions.