CN110913402A - High-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation - Google Patents
High-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation Download PDFInfo
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Abstract
The invention provides an unmanned aerial vehicle ad hoc network clustering method with high coverage efficiency for jointly optimizing communication and formation, which comprises the following steps: obtaining a packet error rate of single-hop transmission according to a free space path loss model of communication between unmanned aerial vehicles, and providing an end-to-end multi-hop delay model based on the packet error rate; defining coverage area efficiency and coverage width efficiency, and providing a coverage efficiency model to evaluate the coverage performance of the unmanned aerial vehicle group; converting the unmanned aerial vehicle coverage efficiency problem under the time delay constraint into a minimized objective function problem with a time delay penalty term by a penalty function method; according to the provided iterative optimization algorithm based on the block coordinate descent method, the optimal cluster head set of the unmanned aerial vehicle cluster, the optimal position and the optimal power of each unmanned aerial vehicle are obtained, so that the maximum coverage of the unmanned aerial vehicle cluster to the area is realized under the constraint condition that the communication time delay requirement and the power requirement among the unmanned aerial vehicles are met.
Description
Technical Field
The invention belongs to the field of unmanned aerial vehicle ad hoc network system architecture, and particularly relates to a high-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation.
Background
Because unmanned aerial vehicle has advantages such as small, mobility is strong, low in cost, deployment convenience, unmanned aerial vehicle is more and more extensive in military use and civilian field's application, for example, reconnaissance, accurate agriculture, disaster management and environmental monitoring etc.. In the development process of the unmanned aerial vehicle technology, people gradually realize that the task completion reliability of a single unmanned aerial vehicle is not high enough, and the complex work task is difficult to complete due to the limitation of factors such as energy, capacity and load of the single unmanned aerial vehicle, so that the cooperative operation of multiple unmanned aerial vehicles becomes a trend. With the development of technologies such as electronics and communication, unmanned aerial vehicles tend to be miniaturized, and large-scale unmanned aerial vehicle clusters represented by swarms are receiving wide attention from the industry and academia.
In the face of complex tasks and dynamic uncertain environments, communication interruption, operation failure and other emergency situations sometimes occur in unmanned aerial vehicle clusters, and therefore, in the face of various possible future environments and application requirements, the unmanned aerial vehicle clusters are required to be capable of intelligently judging working environments, behaviors of the unmanned aerial vehicles are automatically adjusted and controlled to guarantee completion of working tasks, and therefore the unmanned aerial vehicles become important development directions of large-scale unmanned aerial vehicle clusters. In order to realize autonomous control, an unmanned aerial vehicle ad hoc network capable of providing efficient and flexible inter-machine communication becomes a key, however, a series of challenges are brought to resource allocation, channel access, network routing and the like of the unmanned aerial vehicle ad hoc network in a large scale, and clustering of an unmanned aerial vehicle cluster can meet the challenges brought by large-scale unmanned aerial vehicles.
Among the numerous applications of drones, area coverage is one of the most common and important applications, such as reconnaissance of a certain area, data acquisition, or providing network services to ground users. In order to meet mission requirements, the drone network needs to perceive the area as efficiently as possible. In drone ad hoc networks, autonomous clustering and data transfer require that drones remain close enough to maintain network connectivity, which may severely reduce the coverage efficiency of the drone swarm. And in order to reduce coverage overlap, dispersing the drones will reduce the communication quality between drones. Most of the known methods for clustering unmanned aerial vehicles do not consider the coverage efficiency and communication problems of the unmanned aerial vehicle cluster. Therefore, it is very important to study maximization of area coverage performance while securing communication requirements.
Disclosure of Invention
The invention aims to provide a high-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation aiming at the defects or problems in the prior art.
The technical scheme of the invention is as follows: a high coverage efficiency unmanned aerial vehicle ad hoc network clustering method jointly optimizing communication and formation considers that N unmanned aerial vehicles reconnaissance a certain area, and the network structure of the unmanned aerial vehicle ad hoc network is G (N, Q, P, H, M), wherein N is a node set, Q is a node position vector set, P is a power set, H is a cluster head set, and M is a cluster member set, and the coverage efficiency of the unmanned aerial vehicle cluster is maximized under the time delay and power constraint through the joint optimization of cluster heads, positions and power of the unmanned aerial vehicle cluster; the high-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation comprises the following steps:
step 3, converting the unmanned aerial vehicle coverage efficiency problem under the time delay constraint into a minimized objective function problem with a time delay penalty term by a penalty function method;
step 4, clustering based on a clustering algorithm optimization structure of a greedy algorithm to obtain a better cluster head set;
step 5, obtaining a local optimal position according to the relative position of the optimal structure of the position optimization algorithm based on the steepest descent algorithm;
step 7, based on the optimization algorithms in the steps 4, 5 and 6, carrying out iterative optimization on the optimization algorithms by adopting a structural optimization algorithm of a block coordinate descent algorithm idea, so that the coverage efficiency of the unmanned aerial vehicle group to the area is maximized under the constraint condition of meeting the communication time delay requirement and the power requirement among the unmanned aerial vehicles;
in step 1, a packet error rate of single-hop transmission is obtained according to a free space path loss model of communication between unmanned aerial vehicles, and an end-to-end multi-hop delay model, a time delay model sigma, is provided based on the packet error rate of single-hop transmissionijIs defined as:
whereinThe average single-hop time delay from the K-1 hop to the K hop in the shortest path from the unmanned aerial vehicle i to the unmanned aerial vehicle j is represented, K represents the total shortest path hop number from the unmanned aerial vehicle i to the unmanned aerial vehicle j, tau represents the round-trip time of single-hop communication, and an、gnIs a parameter that is independent of the transmission mode,representing the signal to interference plus noise ratio of the channel. Considering the UAV communication link as a line-of-sight link, the information power gain h transmitted from node i to node jijIs defined asWhere ρ is0Is the unit distance channel gain, qiIs the location vector of node i, qjIs the position vector of node j, dijIs the distance between node i and node j. The signal-to-interference-and-noise ratio of the channel is expressed asWhere No represents noise, by2Is obtained as2As ambient noise, IijFor interference, hijFor the power gain of information transmitted from node I to node j, IiFor a set of interfering nodes, Pi、PzRepresenting the transmission power of node i and node z. Assuming that the MAC protocol used in the network is TDMA, each node transmits information independently and randomly at each time slot with a probability r. Thus, interference IijIs desired to beThe SINR at this expected interference may be approximated asBased on the channel SINR formula, the single-hop packet error rate of the node i transmitting information to the node j can be expressed asAverage single-hop delay from node i to node j isTherefore, the time delay sigma corresponding to the shortest path from the node i to the node j can be obtainedijIf there is no communication path from node i to node j, then σ is definedij=∞。
Defining coverage area efficiency and coverage width efficiency in the step 2, and providing a coverage efficiency model to evaluate the coverage performance of the unmanned aerial vehicle group;
the coverage area efficiency is defined as:wherein N represents the total number of drones,r represents the coverage radius of each unmanned aerial vehicle, S (G) represents the coverage area of the unmanned aerial vehicle cluster under the structure G, and S (G) is defined asWherein s isijRepresents the overlapping coverage area of UAV i and UAV j, and is divided into sijIs defined asdijRepresenting the distance between drone i and drone j.
The coverage width efficiency is defined as:wherein We(G) The coverage width of the unmanned aerial vehicle perpendicular to the speed direction under the structure G is represented, and W is usede(G) Is defined asWherein u isκ(i)Is the value of the i-th unmanned aerial vehicle position vector projection to the velocity vertical direction, k is the sequence in the node set and satisfies
Based on the coverage area efficiency and the coverage width efficiency, the coverage area efficiency can be defined as:wherein α ∈ [0,1 ]]α can be selected according to the specific application.
In step 3, considering the time delay constraint between the leader node and the cluster head and the time delay constraint between the cluster members, modeling the problem of maximized coverage efficiency as follows:
0≤Pi≤Pmax,wherein σHUpper bound value, sigma, for the time delay of leader node and cluster head nodeMIs the upper limit constraint value, P, of the time delay of the cluster member node and the cluster head nodemaxIs an upper bound for transmission power. Adopting a penalty function method to convert the unmanned aerial vehicle coverage efficiency problem under the delay constraint into a minimized objective function problem with a delay penalty term, wherein the problem can be modeled as a minimized model as follows:
s.t.Pi≤Pmax
wherein λ is1,λ2,λ3> 0 is the corresponding penalty term coefficient, Δ1,Δ2,Δ3Is a penalty term, δ, corresponding to the delay constraintijAnd deltaiIs a delay constraint penalty function, which is defined as follows:
if the time delay sigmaijSatisfy corresponding timeThe delay upper bound is then δ ij0, otherwise δij>0 has a penalty on latency. If the node is not communicated with the leader node, the time delay is infinite, and the distance between the node i and the leader node is used as a penalty item.
In step 4, according to clustering of the clustering algorithm optimization structure based on the greedy algorithm, the current unmanned aerial vehicle position Q is givenlTransmission power PlAnd cluster head HlWhere l refers to the number of iterations, the goal is optimized by adding or deleting cluster heads, i.e., to find a cluster head set H satisfying J (Q)l,Pl,H)<J(Ql,Pl,Hl) This cluster head set H is the found better cluster head set, and the details are as follows:
4.1, deleting cluster heads: from HlFinding an optimal cluster head i and changing the optimal cluster head i into a cluster member to reduce the target function J most, if the optimal cluster head i cannot be found to reduce the target function J, keeping the optimal cluster head i unchanged;
4.2, adding cluster heads: finding a non-cluster-head node J to reduce the target function J to the maximum after the non-cluster-head node J is changed into a cluster head, and if the non-cluster-head node J cannot be found, keeping the target function J unchanged;
in step 5, according to the relative position of the position optimization algorithm optimization structure based on the steepest descent algorithm, a local optimal position is obtained, and the gradient of the objective function J on Q is firstly calculatedWherein l refers to the number of iterations, then the position Q is updated by using the steepest descent algorithm,wherein the content of the first and second substances,
in step 6, optimizing the transmission power of the structure according to the power optimization algorithm based on the steepest descent algorithm to obtain better power, determining the reduction or increase of the node power according to the gradient of J to P, and firstly calculating the gradientWherein l is iteration number, updating power P by using a steepest descent method,wherein λ>0 andto satisfy the constraint Pi≤Pmax,Can order Pl+1←min{Pmax,Pl+1};
In step 7, the structural optimization algorithm is proposed according to the idea based on the block coordinate descent algorithm, iterative optimization is carried out on the algorithms in step 4, step 5 and step 6, the optimal cluster head set of the unmanned aerial vehicle cluster, the optimal position and the optimal power of each unmanned aerial vehicle are obtained, and the unmanned aerial vehicle cluster can cover the area to the maximum extent under the constraint condition that the communication time delay requirement and the power requirement among the unmanned aerial vehicles are met; in order to optimize the structure G ═ of the unmanned aerial vehicle ad hoc network (N, Q, P, H, M), the selection, relative position and transmission power of the cluster heads will be optimized simultaneously, and the cluster member set is determined by Q, P, H; in the structure optimization algorithm proposed based on the block coordinate descent algorithm idea, the current structure G is given at each stepl=(Ql,Pl,Hl) Wherein l refers to the number of times of the first iteration, and the optimized structure G is obtained by the following stepsl+1The method comprises the following steps:
5.1 optimizing the Structure (Q) by clustering Algorithml,Pl,Hl) To obtain a better cluster head set Hl+1;
5.2 optimizing the Structure (Q) by means of a position optimization Algorithml,Pl,Hl+1) To obtain a locally preferred position Ql+1;
5.3 optimizing the Structure (Q) by means of a Power optimization Algorithml+1,Pl,Hl+1) To a more optimal power Pl+1;
5.4, passing aboveStep(s) to obtain a more optimal structure Gl+1=(Ql+1,Pl+1,Hl+1) Repeating the above step pair Gl+1Optimizing until | | JL+1-JLThe value of | < epsilon, wherein epsilon is used for judging whether the algorithm is converged or not, and the value is e-6。
The technical scheme provided by the invention has the following beneficial effects:
the high-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method based on joint optimization communication and formation takes the maximized coverage efficiency as a target under the constraint of considering communication delay and power, and converts the maximized coverage efficiency problem under the constraint of delay into a minimized target function problem with a delay punishment item by adopting a punishment function method. In order to meet the communication time delay requirement and the power requirement between unmanned aerial vehicles and simultaneously maximize the coverage efficiency, an iterative optimization algorithm based on a block coordinate descent method is developed to simultaneously optimize the selection, the relative position and the transmission power of a cluster head.
Drawings
Fig. 1 is a schematic diagram of an unmanned aerial vehicle ad hoc network reconnaissance system according to the present invention;
FIG. 2 is a schematic diagram of the coverage width of the unmanned aerial vehicle cluster according to the present invention;
FIG. 3(a) is a schematic diagram of an initial networking architecture of the unmanned aerial vehicle cluster according to the present invention;
FIG. 3(b) is a schematic diagram of the networking architecture after the optimization of the unmanned aerial vehicle cluster of the present invention;
FIG. 4 is a graph of experimental simulation results of the relationship between coverage efficiency and the number of unmanned aerial vehicles under different coverage radii;
FIG. 5 is a diagram of experimental simulation results of the relationship between coverage efficiency and the number of UAVs according to different time delay constraints;
FIG. 6 is a diagram of a simulation result of a relationship between the number of nodes and the coverage efficiency under different powers according to the present invention;
FIG. 7(a) is a graph of experimental simulation results of relationship between the number of nodes and the number of cluster heads under different time delay constraints;
fig. 7(b) is a graph of the experimental simulation result of the relationship between the number of nodes and the number of cluster heads under different powers.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the high-coverage unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation, provided by the invention, N unmanned aerial vehicles are used for reconnaissance of a certain area, and the network structure of the unmanned aerial vehicle ad hoc network is recorded as G (N, Q, P, H, M), wherein N is a node set, Q is a node position vector set, P is a power set, H is a cluster head set, and M is a cluster member set.
In the problem of large-scale unmanned aerial vehicle ad hoc network clustering applied to reconnaissance coverage, the optimization problem of communication performance and coverage performance exists, and the following challenges specifically exist: 1) in an unmanned aerial vehicle ad hoc network, autonomous cluster and data transmission require that an unmanned aerial vehicle maintain a close enough distance to maintain network connection, which may seriously reduce the coverage efficiency of an unmanned aerial vehicle cluster; 2) in order to reduce coverage overlap, dispersing the drones reduces the communication quality between the drones; 3) the larger transmission power of the unmanned aerial vehicle consumes more energy and causes a communication interference problem to other nodes, and if the transmission power is too small, the signal strength is small, so that the transmission power needs to be optimized on the premise of not exceeding the maximum power limit.
Specifically, the high-coverage-rate unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation comprises the following steps:
in step 1, a packet error rate of single-hop transmission is obtained according to a free space path loss model of communication between unmanned aerial vehicles, and an end-to-end multi-hop delay model, a time delay model sigma, is provided based on the packet error rate of single-hop transmissionijIs defined as:
whereinThe average single-hop time delay from the k-1 hop to the k hop in the shortest path from the unmanned aerial vehicle i to the unmanned aerial vehicle j is represented, k represents the total shortest path hop number from the unmanned aerial vehicle i to the unmanned aerial vehicle j, tau represents the round-trip time of single-hop communication, and an、gnIs a parameter that is independent of the transmission mode,representing the signal to interference plus noise ratio of the channel. Considering the UAV communication link as a line-of-sight link, the information power gain h transmitted from node i to node jijIs defined asWhere ρ is0Is the unit distance channel gain, qiIs the location vector of node i, qjIs the position vector of node j, dijIs the distance between node i and node j. The signal-to-interference-and-noise ratio of the channel is expressed asWhere No represents noise, by2Is obtained as2As ambient noise, IijFor interference, hijFor the power gain of information transmitted from node I to node j, IiFor a set of interfering nodes, Pi、PzRepresenting the transmission power of node i and node z. Assuming that the MAC protocol used in the network is TDMA, each node transmits information independently and randomly at each time slot with a probability r. Thus, interference IijIs desired to beThe SINR at this expected interference may be approximated asSingle-hop error of node i transmitting information to node j based on channel signal-to-interference-and-noise ratio formulaThe packet rate can be expressed asAverage single-hop delay from node i to node j isTherefore, the time delay sigma corresponding to the shortest path from the node i to the node j can be obtainedijIf there is no communication path from node i to node j, then σ is definedij=∞。
Defining coverage area efficiency and coverage width efficiency in the step 2, and providing a coverage efficiency model to evaluate the coverage performance of the unmanned aerial vehicle group;
the coverage area efficiency is defined as:wherein N represents the total number of the unmanned aerial vehicles, R represents the coverage radius of each unmanned aerial vehicle, S (G) represents the coverage area of the unmanned aerial vehicle cluster under the structure G, and S (G) is defined asWherein s isijRepresents the overlapping coverage area of UAV i and UAV j, and is divided into sijIs defined asdijRepresenting the distance between drone i and drone j.
The coverage width efficiency is defined as:wherein We(G) The coverage width of the unmanned aerial vehicle perpendicular to the speed direction under the structure G is represented, and W is usede(G) Is defined asWherein u isκ(i)Is the value of the i-th unmanned aerial vehicle position vector projection to the velocity vertical direction, k is the sequence in the node set and satisfies
Based on the coverage area efficiency and the coverage width efficiency, the coverage area efficiency can be defined as:wherein α ∈ [0,1 ]]α can be selected according to the specific application.
In step 3, considering the time delay constraint between the leader node and the cluster head and the time delay constraint between the cluster members, modeling the problem of maximized coverage efficiency as follows:
0≤Pi≤Pmax,wherein σHUpper bound value, sigma, for the time delay of leader node and cluster head nodeMIs the upper limit constraint value, P, of the time delay of the cluster member node and the cluster head nodemaxIs an upper bound for transmission power. Adopting a penalty function method to convert the unmanned aerial vehicle coverage efficiency problem under the delay constraint into a minimized objective function problem with a delay penalty term, wherein the problem can be modeled as a minimized model as follows:
s.t.Pi≤Pmax
wherein λ is1,λ2,λ3> 0 is the corresponding penalty term coefficient, Δ1,Δ2,Δ3Is a penalty term, δ, corresponding to the delay constraintijAnd deltaiIs a delay constraint penalty function, which is defined as follows:
if the time delay sigmaijSatisfying the corresponding upper time delay constraint is δ ij0, otherwise δij>0 has a penalty on latency. If the node is not communicated with the leader node, the time delay is infinite, and the distance between the node i and the leader node is used as a penalty item.
In step 4, according to clustering of the clustering algorithm optimization structure based on the greedy algorithm, the current unmanned aerial vehicle position Q is givenlTransmission power PlAnd cluster head HlWhere l refers to the number of iterations, the goal is optimized by adding or deleting cluster heads, i.e., to find a cluster head set H satisfying J (Q)l,Pl,H)<J(Ql,Pl,Hl) This cluster head set H is the found better cluster head set, and the details are as follows:
4.1, deleting cluster heads: from HlFinding an optimal cluster head i and changing the optimal cluster head i into a cluster member to reduce the target function J most, if the optimal cluster head i cannot be found to reduce the target function J, keeping the optimal cluster head i unchanged;
4.2, adding cluster heads: finding a non-cluster-head node J to reduce the target function J to the maximum after the non-cluster-head node J is changed into a cluster head, and if the non-cluster-head node J cannot be found, keeping the target function J unchanged;
optimizing the junction according to a steepest descent algorithm-based position optimization algorithm in step 5Obtaining the relative position of the structure, obtaining the local optimal position, firstly calculating the gradient of the target function J on QWherein l refers to the number of iterations, then the position Q is updated by using the steepest descent algorithm,wherein the content of the first and second substances,
in step 6, optimizing the transmission power of the structure according to the power optimization algorithm based on the steepest descent algorithm to obtain better power, determining the reduction or increase of the node power according to the gradient of J to P, and firstly calculating the gradientWherein l is iteration number, updating power P by using a steepest descent method,wherein λ>0 andto satisfy the constraint Pi≤Pmax,Can order Pl+1←min{Pmax,Pl+1};
In step 7, the structural optimization algorithm is proposed according to the idea based on the block coordinate descent algorithm, iterative optimization is carried out on the algorithms in step 4, step 5 and step 6, the optimal cluster head set of the unmanned aerial vehicle cluster, the optimal position and the optimal power of each unmanned aerial vehicle are obtained, and the unmanned aerial vehicle cluster can cover the area to the maximum extent under the constraint condition that the communication time delay requirement and the power requirement among the unmanned aerial vehicles are met; in order to optimize the structure G ═ (N, Q, P, H, M) of the drone ad hoc network, the selection of cluster heads, relative positions and transmission powers, cluster members, will be optimized simultaneouslyThe set is determined by Q, P, H; in the structure optimization algorithm proposed based on the block coordinate descent algorithm idea, the current structure G is given at each stepl=(Ql,Pl,Hl) Wherein l refers to the number of times of the first iteration, and the optimized structure G is obtained by the following stepsl+1The method comprises the following steps:
5.1 optimizing the Structure (Q) by clustering Algorithml,Pl,Hl) To obtain a better cluster head set Hl+1;
5.2 optimizing the Structure (Q) by means of a position optimization Algorithml,Pl,Hl+1) To obtain a locally preferred position Ql+1;
5.3 optimizing the Structure (Q) by means of a Power optimization Algorithml+1,Pl,Hl+1) To a more optimal power Pl+1;
5.4 obtaining a better structure G by the above stepsl+1=(Ql+1,Pl+1,Hl+1) Repeating the above step pair Gl+1Optimizing until | | JL+1-JLThe value of | < epsilon, wherein epsilon is used for judging whether the algorithm is converged or not, and the value is e-6。
The invention discloses an unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation and having high coverage efficiency, and figure 1 shows a scene of unmanned aerial vehicle ad hoc network clustering for maximizing coverage efficiency under time delay constraint.
Fig. 3(a) (b) are the structure diagrams of the unmanned aerial vehicles before and after optimization, respectively, considering that 15 unmanned aerial vehicles reconnaissance the area. In fig. 3(b), a node a is a leader node, a square node is a cluster head node, the remaining circle nodes are cluster member nodes, an arrow on the node a indicates a moving direction of the unmanned aerial vehicle cluster, a dotted circle indicates a coverage area, a dotted line between the nodes indicates a link between two adjacent nodes, numbers on the node a and the node E indicate a time delay from the leader node to the cluster head, other numbers in the figure indicate a time delay from the cluster head to the cluster member, and a diagonal dotted line indicates a coverage width. As can be seen from fig. 3(a), initially most nodes are isolated nodes, and the calculated coverage area efficiency and coverage width efficiency are 0.76 and 0.34, respectively. After optimization, as shown in fig. 3(b), 3 clusters are obtained, the cluster heads are respectively a node a, a node K and a node E, and the coverage area efficiency and the coverage width efficiency are respectively 0.84 and 0.37. It can be seen that due to communication delay constraint, nodes are covered by a certain overlap, and after the scheme designed by the invention is adopted to optimize the unmanned aerial vehicle ad hoc network structure, the coverage performance is improved.
Fig. 4 is a graph of a relationship between the number of nodes and the coverage performance under different coverage radii, where the coverage radii are sequentially increased by 20, 50, 80, and 110, and the coverage efficiencies when the number of nodes under different radii is 10, 20, 30, 40, and 50 are respectively recorded, and it can be seen that the coverage efficiency of the system decreases with the increase of the coverage radius of the nodes, and also decreases with the increase of the number of nodes. This is because the delay constraints limit the distance and number of communication hops between drones, while increasing the coverage radius results in more overlapping coverage.
FIG. 5 is a graph of the relationship between the number of nodes and the coverage efficiency under different delay constraints, where σ is (σ)H,σM) To represent a delay constraint, where σHUpper bound value, sigma, for the time delay of leader node and cluster head nodeMFour kinds of delay constraints are considered for the upper limit constraint values of the time delay of the cluster member node and the cluster head node, wherein σ is (2,3), σ is (4,6), σ is (6,9) and σ is (8,12), the coverage efficiency when the number of nodes is 10, 20, 30, 40 and 50 under different time delay combinations is recorded, and it can be seen that the coverage efficiency is increased along with the increase of the time delay threshold value, because the larger the time delay threshold value is, the larger the inter-unmanned aerial vehicle distance can meet the time delay constraint.
Fig. 6 is a graph of a relationship between the number of nodes and coverage efficiency under different powers, and considering static power and optimized power, in a scenario of setting static power, the power of the nodes is independently and randomly generated by normal distribution, and the standard deviation is 10, and it is expected that the cases of 30 mW, 60 mW, and 90mW are considered respectively. For an optimized power scene, the node power is randomly and independently taken from 20-100 mW in a uniformly distributed manner, and it can be seen that in some cases, the coverage efficiency is increased along with the increase of the power, because the larger the power is, the larger the distance between the nodes can be under the same time delay constraint, and after the power of the nodes is optimized by adopting the scheme designed by the invention, the nodes can have better coverage efficiency under the lower power.
Fig. 7(a) is a relationship diagram of the number of nodes and the number of cluster heads under four different delay constraints, and it can be seen that the smaller the delay constraint threshold, the greater the number of cluster heads, and more clustering results, because the larger the cluster size, the greater the delay between cluster heads and cluster members will also increase, and the delay constraint threshold limits the cluster size. Fig. 7(b) shows that, when the delay constraint is σ ═ 2,3, the influence of power optimization on the number of cluster heads is considered, and it can be seen that the optimized power reduces the number of cluster heads, because the connection and interference between nodes can be better considered when the scheme designed by the present invention is used to optimize the node power, under the same delay constraint, higher connectivity and less interference between nodes can be achieved, so that more nodes can be accommodated in the cluster, and the number of clusters is reduced.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (8)
1. An unmanned aerial vehicle ad hoc network clustering method with high coverage efficiency for jointly optimizing communication and formation is characterized in that: considering that N unmanned aerial vehicles reconnaissance a certain area, and recording the network structure of the unmanned aerial vehicle ad hoc network as G ═ N, Q, P, H and M, wherein N is a node set, Q is a node position vector set, P is a power set, H is a cluster head set, and M is a cluster member set;
the high-coverage-efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation comprises the following steps:
step 1, obtaining a packet error rate of single-hop transmission according to a free space path loss model of communication between unmanned aerial vehicles, and providing an end-to-end multi-hop delay model based on the packet error rate;
step 2, defining coverage area efficiency and coverage width efficiency, and providing a coverage efficiency model to evaluate the coverage performance of the unmanned aerial vehicle group;
step 3, converting the unmanned aerial vehicle coverage efficiency problem under the time delay constraint into a minimized objective function problem with a time delay penalty term by a penalty function method;
step 4, clustering based on a clustering algorithm optimization structure of a greedy algorithm to obtain a better cluster head set;
step 5, obtaining a local optimal position according to the relative position of the optimal structure of the position optimization algorithm based on the steepest descent algorithm;
step 6, obtaining more optimal power according to the transmission power of the power optimization algorithm optimization structure based on the steepest descent algorithm;
and 7, based on the optimization algorithms in the steps 4, 5 and 6, carrying out iterative optimization on the optimization algorithms by adopting a structural optimization algorithm of a block coordinate descent algorithm idea, so that the coverage efficiency of the unmanned aerial vehicle group to the area is maximized under the constraint condition of meeting the communication time delay requirement and the power requirement among the unmanned aerial vehicles.
2. The high coverage efficiency unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation according to claim 1, wherein in step 1, a packet error rate of single-hop transmission is obtained according to a free space path loss model of communication between unmanned aerial vehicles, and an end-to-end multi-hop delay model, a time delay model sigma, is provided based on the packet error rate of single-hop transmissionijIs defined as:
whereinThe average single-hop time delay from the K-1 hop to the K hop in the shortest path from the unmanned aerial vehicle i to the unmanned aerial vehicle j is represented, K represents the total shortest path hop number from the unmanned aerial vehicle i to the unmanned aerial vehicle j, tau represents the round-trip time of single-hop communication, and an、gnIs a parameter that is independent of the transmission mode,representing the signal to interference plus noise ratio of the channel.
3. The unmanned aerial vehicle ad hoc network clustering method for high coverage efficiency combined optimization of communication and formation according to claim 1, wherein coverage area efficiency and coverage width efficiency are defined in step 2, and a coverage efficiency model is proposed to evaluate the coverage performance of the unmanned aerial vehicle cluster;
the coverage area efficiency is defined as:wherein N represents the total number of the unmanned aerial vehicles, R represents the coverage radius of each unmanned aerial vehicle, S (G) represents the coverage area of the unmanned aerial vehicle cluster under the structure G, and S (G) is defined asWherein s isijRepresenting the overlapping coverage area of drone i and drone j;
the coverage width efficiency is defined as:wherein We(G) Representing the coverage width of the unmanned aerial vehicle under the structure G in the direction vertical to the speed direction;
4. The method for clustering unmanned aerial vehicle ad hoc networks with high coverage efficiency by jointly optimizing communication and formation according to claim 1, wherein the unmanned aerial vehicle coverage efficiency problem under the delay constraint is converted into a minimization objective function problem with a delay penalty term by a penalty function method in step 3, and the problem is modeled as a minimization model as follows:
s.t.Pi≤Pmax
wherein λ is1,λ2,λ3> 0 is the corresponding penalty term coefficient, Δ1,Δ2,Δ3Is a penalty term, δ, corresponding to the delay constraintijAnd deltaiIs a delay constraint penalty function, which is defined as follows:
5. the unmanned aerial vehicle ad hoc network clustering method capable of jointly optimizing communication and formation and having high coverage efficiency according to claim 1, wherein in step 4, a current unmanned aerial vehicle position Q is given according to clustering of a clustering algorithm optimization structure based on a greedy algorithmlTransmission power PlAnd cluster head HlWhere l refers to the number of iterations, the goal is optimized by adding or deleting cluster heads, i.e.Find satisfying J (Q)l,Pl,H)<J(Ql,Pl,Hl) The cluster head set H is a more optimal cluster head set, and specifically, the following is performed:
4.1, deleting cluster heads: from HlFinding an optimal cluster head i and changing the optimal cluster head i into a cluster member to reduce the target function J most, if the optimal cluster head i cannot be found to reduce the target function J, keeping the optimal cluster head i unchanged;
4.2, adding cluster heads: finding a non-cluster head node J makes the objective function J reduce most after it becomes a cluster head, and if not, it remains unchanged.
6. The unmanned aerial vehicle ad hoc network clustering method for jointly optimizing communication and formation and having high coverage efficiency according to claim 1, wherein in step 5, a local optimal position is obtained according to a relative position of an optimization structure of a position optimization algorithm based on a steepest descent algorithm, and a gradient of an objective function J on Q is first calculatedWherein l refers to the number of iterations, then the position Q is updated by using the steepest descent algorithm,wherein the content of the first and second substances,
7. the method according to claim 1, wherein the optimal power is obtained in step 6 by optimizing the transmission power of the structure according to a power optimization algorithm based on a steepest descent algorithm, the decrease or increase of the node power is determined according to the gradient of J to P, and the gradient is first calculatedThe power P is updated using the steepest descent method,wherein λ>0 andto satisfy the constraintCan order Pl+1←min{Pmax,Pl+1}。
8. The unmanned aerial vehicle ad hoc network clustering method with high coverage efficiency for jointly optimizing communication and formation according to claim 1, wherein in step 7, the algorithms in step 4, step 5 and step 6 are iteratively optimized according to a structural optimization algorithm proposed based on the idea of a block coordinate descent algorithm to obtain an optimal cluster head set of an unmanned aerial vehicle cluster, an optimal position and optimal power of each unmanned aerial vehicle, so that under the constraint condition of meeting the communication delay requirement and power requirement among the unmanned aerial vehicles, the maximum coverage of the unmanned aerial vehicle cluster on an area is realized; in order to optimize the structure G ═ of the unmanned aerial vehicle ad hoc network (N, Q, P, H, M), the selection, relative position and transmission power of the cluster heads will be optimized simultaneously, and the cluster member set is determined by Q, P, H; in the structure optimization algorithm proposed based on the block coordinate descent algorithm idea, the current structure G is given at each stepl=(Ql,Pl,Hl) Wherein l is the number of iterations, the optimized structure G is obtained by the following stepsl+1The method comprises the following steps:
5.1 optimizing the Structure (Q) by clustering Algorithml,Pl,Hl) To obtain a better cluster head set Hl+1;
5.2 optimizing the Structure (Q) by means of a position optimization Algorithml,Pl,Hl+1) To obtain a locally preferred position Ql+1;
5.3 optimizing the Structure (Q) by means of a Power optimization Algorithml+1,Pl,Hl+1) To a more optimal power Pl+1;
5.4 obtaining a better structure G by the above stepsl+1=(Ql+1,Pl+1,Hl+1) Repeating the above step pair Gl+1Optimizing until | | JL+1-JLAnd | | is less than epsilon, wherein epsilon is used as a threshold for judging whether the algorithm converges or not.
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