Disclosure of Invention
The invention aims to provide an unmanned aerial vehicle data collection method based on minimized information age aiming at the defects of the prior art, and the information age of the data sampled by the sensing node is minimized by balancing the data transmission time and the flight time of the unmanned aerial vehicle, so that the timeliness of the sampled data is ensured.
The technical method adopted by the invention for solving the technical problems comprises the following steps:
(1) based on a data center, M ground sensing nodes and a wireless sensing network of an unmanned aerial vehicle, the data center acquires the positions of the M sensing nodes, sets the flight altitude and the speed of the unmanned aerial vehicle, sets the position of any one sensing node as the horizontal coordinate of a data collection point of the unmanned aerial vehicle, and calculates the data uploading time from all the M sensing nodes to a candidate data collection point of the unmanned aerial vehicle;
(2) according to the data uploading time of the sensing nodes, executing a clustering algorithm, and determining a group of unmanned aerial vehicle data collection points and coordinates thereof, sensing nodes associated with each collection point and an uploading sequence thereof:
(2a) executing a clustering algorithm, dividing all M sensing nodes into K clusters, and associating each cluster of sensing nodes to an unmanned aerial vehicle data collection point;
(2b) adjusting the coordinates of corresponding data collection points of the unmanned aerial vehicle according to the position of each cluster of sensing nodes, and determining the association relationship between each data collection point and which sensing nodes of the unmanned aerial vehicle;
(2c) determining the uploading sequence of the sensing nodes associated with each data collection point, and updating the data uploading time from the sensing nodes to the data collection points;
(3) Executing a path planning algorithm, and determining the optimal flight track of the unmanned aerial vehicle along the data collection point, so that the utility function value of the information age is minimum;
(4) changing the size of the cluster, repeating the steps (2) and (3) until the clustering result is not changed any more, and finding out the coordinates of the data collection points of the unmanned aerial vehicle with the optimal information age, the sensing nodes associated with the data collection points, the uploading sequence and the flight trajectory;
(5) the unmanned aerial vehicle starts from the data center according to the data collection scheme determined in the step (4), accesses the data collection points one by one, stops at each data collection point, establishes a communication link with the associated sensing node, receives and stores data uploaded by the sensing node, and flies back to the data center for data unloading and processing:
(5a) starting from the current position, the unmanned aerial vehicle flies to the next station according to the flight track planned in the step (3);
(5b) if the current position is a data collection point, the unmanned aerial vehicle establishes communication links with the associated sensing nodes one by one according to the uploading sequence of the sensing nodes determined in the step (2), receives sampling data uploaded by the sensing nodes, stores the sampling data in a cache area, and executes the step (5 a); otherwise, the drone offloads the stored sampled data to the data center.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the method, the unmanned aerial vehicle is adopted for relaying data forwarding, and joint optimization is carried out on the data collection point position and the flight path of the unmanned aerial vehicle and the sensing data uploading sequence of the sensing nodes, so that the information age of the sensing nodes is reduced, and the timeliness of the acquired sensing data is ensured.
2. The method of the invention adopts a clustering method to adjust the position of the data collection point of the unmanned aerial vehicle and the distance between the data collection point and the sensing node in advance, effectively balances the data transmission time of all the sensing nodes and the flight time of the unmanned aerial vehicle, and ensures that the information age of the sensing node is not sharply increased along with the increase of the network scale, thereby being suitable for different wireless sensing network scales.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
Referring to fig. 1, the network scenario used in this embodiment includes a data center u
0And M sensing nodes distributed in the two-dimensional plane area and having position coordinates of w
0=(x
0,y
00) and w
S,i=(x
i,y
i0) (i ∈ {1,2,3, …, M }). Each sensing node is assigned an ID serial number, and the position coordinates of the sensing node can be acquired by GPS or other positioning technologies and then transmitted to a data center u in a wireless mode
0The maximum communication range of the sensing node is D
max. The sensing node m samples the monitored object, and encapsulates the sampling data and the time stamp with the length of L
mIn a packet of bits. The unmanned aerial vehicle can fly at a constant speed at the height h and the speed v and can also hover in the air to collect ground node sensing data. According to the position coordinates of each node, the data center u
0Calculating any sensing node m and unmanned aerial vehicle air collection pointA linear distance between k is
Here (x)
k,y
k) The ground coordinates corresponding to the unmanned aerial vehicle collecting point k in the air. When the sensing nodes m upload data to the unmanned aerial vehicle, the ground-air wireless communication links established by the sensing nodes m are easily influenced by factors such as weather and environment, line-of-sight or non-line-of-sight links may occur, so that the wireless signal propagation path loss is different, and the probability of the line-of-sight links is P
LoS(d
m,k) The calculation can be as follows:
where a and b are constants that depend on the environment, the average path loss is calculated:
wherein f iscIs the carrier frequency, c is the speed of light, βLoSAnd betaNLoSRepresenting extra path loss, 1-P, in line-of-sight and non-line-of-sight links, respectivelyLoS(dm,k) Is a non line-of-sight link probability. When the sensing node m is powered by PmData rate R when uploading data packets to the dronem,kCalculated by the following formula:
where B is the communication bandwidth, β is the channel gain at a reference point (e.g., 1 meter from the node), σ2Is the receiver noise power.
Referring to fig. 2, the working steps of this embodiment are as follows:
step 1, initializing data collection parameters of the unmanned aerial vehicle.
Data center u
0Setting values of flying height h and speed v of unmanned aerial vehicle, wherein the flying height h of the unmanned aerial vehicle canTo be set at a maximum value h
maxAnd a minimum value h
minAt any value in between, the flying speed v may be set at 0 to the maximum value v
maxAny value in between. Obtaining the positions of M sensing nodes, setting the position of each sensing node as the horizontal coordinate of a candidate collection point of the unmanned aerial vehicle, and calculating the distance d from the sensing node M to the candidate collection point k of the unmanned aerial vehicle
m,k(M, k e {1,2,3, …, M }), and calculating the average data transmission rate R from the sensing node M to the data collection point k according to the formula
m,kAnd upload time
Setting the clustering weight gamma as zero and the maximum clustering weight gamma as gamma
maxAnd the iteration step size is Δ γ.
Step 2, according to the data transmission time of the sensing node obtained in the step 1
And a clustering weight γ, performing a clustering algorithm based on Affinity Propagation (AP) method.
The specific flow is shown in fig. 3:
(2a) setting the number of initialization iterations t to 0 and setting the maximum number of iterations t
maxIs a larger constant, the correlation coefficient between the sensing nodes m and j
As follows:
first message variable alpham,jIs the message transmitted from the sensing node m to the node j, and the second message variable rhom,jIs a message passed by a sensing node j to a node m, a first message variable alpham,jAnd a second message variable ρm,jAre all initialized to zero, counter tcInitialized to 1, maximum value t of counterc,maxSetting the cluster head set gamma to be a constant, and initializing the cluster head set gamma to be an empty set;
(2b) First elimination in the t-th iterationThe univariate alpham,j(t) and a second message variable ρm,j(t) updates as follows:
wherein N (j) is a neighboring node of the sensing node j, namely the distance between the sensing node j and the sensing node j is less than or equal to the communication range DmaxNode of, N+(j) The method comprises the steps of (1) including a sensing node j and adjacent nodes N (j);
(2c) current new cluster head set ΓnewSetting the message to be an empty set, and if the sum of the first message variable and the second message variable transmitted to the sensing node m by the sensing node m is more than 0, meeting alpham,m(t)+ρm,m(t)>0, the node m is a cluster head, and m is added into the current new cluster head set gammanewExecuting the step (2 d); otherwise, the node m is not a cluster head, and step (2d) is executed.
(2d) If f isnewIf t, the counter is incremented by 1, tc=tc+1, performing step (2 e); otherwise, the counter is cleared, tcAnd (0) updating the cluster head set gamma (gamma)newExecuting the step (2 e);
(2e) if t is
c<t
c,maxAnd t<t
maxUpdating the iteration time t to t +1, and executing the step (2 b); otherwise, the iteration process is terminated, and the association relations between the node m and all the K cluster head nodes j are compared
Find out
Smallest cluster
Dividing the sensing nodes M into the kth cluster, thus dividing the M sensing nodes intoForming a K ═ f | cluster, and recording the nodes in the kth cluster as J
kAssociating them to a data collection point k, performing step (2 f);
(2f) A sensing node set J related to the data collection point k obtained in the step (2e)
k(K-1, …, K) according to node position w
S,i(i∈J
k) Solving the 1-center problem to obtain
Updating optimal position w of data collection point k of unmanned aerial vehicle
kSo that data collection points k to J
kThe maximum distance between each node in the node is minimum;
(2g) obtaining K unmanned aerial vehicle data collection point coordinates w according to the step (2f)
k(K is 1, …, K), recalculating the data uploading time from the sensing node m to the unmanned aerial vehicle collection point K
Set of sensing nodes J associated with data collection point k
kNode upload time in
Sorting from big to small as | J
kUploading sequence V of | sensing nodes
k;
(2h) Calculating the flight time of the unmanned aerial vehicle between any two data collection points k and k' and the flight time from the data collection point k to the data center to obtain etak,k′=v-1dk,k′=v-1||wk-wk′||(k,k′=0,1,...,K);
Step 3, uploading time of the data obtained according to the step (2g)
And the flight time eta of the unmanned aerial vehicle obtained in the step (2h)
k,k′Executing a dynamic planning algorithm, and determining the unmanned aerial vehicle flight track with the maximum node information age utility function:
(3a) calculating the total uploading time of the sensing nodes associated with the data collection point kWorkshop
Calculating the time for the unmanned aerial vehicle to return to the data center for unloading data
The initial data collection point is k equal to 1;
(3b) the set of data collection points other than the starting data collection point K is U ═ 1, …, K \ { K }, listing all subsets of U
The minimum path cost corresponding to the flight paths of the nodes in the S accessed by the unmanned aerial vehicle one by one from the data collection point k is f (k, S), and when the maximum information age of the nodes is taken as a utility function, f (k, S) is iteratively calculated as follows:
wherein f ismax(k, S) is the minimum value of the maximum information age of the flight paths of the nodes in S visited one by the unmanned aerial vehicle from the data collection point k; when the average information age of all nodes is taken as a utility function, f (k, S) is iteratively calculated as follows:
wherein | S | - [ ∑ S | - ]i∈S|JiI is the total number of sensing nodes in S, χiIs the total uploading time f of the sensing nodes associated with the data collection point k obtained in the step (3a)ave(k, S) is the minimum value of the average information age of the flight paths of the nodes in S visited one by the drone from the data collection point k.
(3c) If K is equal to K, all possible flight paths and expenses of the unmanned aerial vehicle are calculated, and step (3d) is executed; otherwise, updating the starting data collection point k to k +1, and executing the step (3 b);
(3d) first stageDetermining the first accessed data collection point U by using the initialized backtracking data collection point set U as {1, …, K } 1=argmink∈Uf (k, U \ k }), and updating the backtracking data collection point set U ═ U \ U }1Determine a second accessed data collection point u2=argmink∈Uf (K, U \ K }), and iterating until U becomes a null set to obtain the K-th accessed data collection point UKFinding out the optimal flight path u ═ u [ u ] of the unmanned plane with the optimal information age0,u1,…,uK,u0];
(3e) Calculating utility function value A of sensing node information ageuIncluding the maximum information age A of the sensing nodemaxAnd mean information age Aave:
Step 4, storing the unmanned aerial vehicle data collection scheme corresponding to the current clustering weight gamma, wherein the scheme comprises unmanned aerial vehicle data collection points K and coordinates w thereof
kAnd each data collection point k is associated with a sensing node set J
kAnd its optimal upload order V
kUnmanned aerial vehicle is along the flight path u of data collection point, utility function value A of sensing node information age
u. Updating the clustering weight gamma-gamma + delta gamma if gamma is less than or equal to gamma
maxExecuting the step 2; otherwise, comparing the utility function values of the information ages of the multiple groups of sensing nodes, and selecting the clustering weight gamma which minimizes the utility function value of the information age
*Determining an optimal unmanned aerial vehicle data collection scheme
(k=1,…,K
*) And
step 5 is executed.
And 5, starting the unmanned aerial vehicle from the data center, and obtaining the optimal unmanned aerial vehicle flight track u according to the steps 2-4 *To get it toThe data collection point is accessed, the sensing data of the related sensing nodes are collected and stored, and the sensing data fly back to the data center for data unloading and processing:
(5a) unmanned plane slave uk(k=0,1,…,K*) Starting from a straight line at a speed v to the next station uk+1;
(5b) If u isk+1Is a data collection point, and step (5c) is executed; otherwise, executing the step (5 g);
(5c) unmanned aerial vehicle collects point u to this data
k+1Associated sensing node
Broadcasting a handshake message, transmitting a confirmation message back after the sensing node receives the handshake message, and establishing the unmanned aerial vehicle and the sensing node
The communication link between the nodes, the order of the initialization uploading node i is 1;
(5d) according to
Specified uploading sequence, unmanned aerial vehicle to sensing node
Broadcasting an uploading instruction message which comprises the ith uploading sensing node
The ID of (1);
(5e) sensing node
After receiving the uploading instruction message, the mobile terminal will
Comparing the node ID with the self ID, if the node ID is the same as the self ID, performing sensing data sampling, packaging the data and the time stamp together in a data packet, and controlling the power P
mUpload data packet to unmanned aerial vehicle, if notThe message is ignored;
(5f) the unmanned aerial vehicle receives and stores a data packet from the sensing node m, and updates an uploading node sequence i to i + 1; if node order is uploaded
Performing step (5 d); otherwise, updating the data collection point sequence number k to k +1, and executing the step (5 a);
(5g) The unmanned aerial vehicle sends handshake information to the data center, after receiving the confirmation information, a communication link is established with the data center, the stored sensing data is transmitted by power P, and the data center receives sensing data packets of all nodes.
The effect of the invention can be further illustrated by simulation:
(1) simulation conditions
The scene used in this embodiment includes a data center with coordinates w0The number of sensing nodes is 19, and the sensing nodes are randomly distributed in a square area with the side length of 2 km. Unmanned aerial vehicle airspeed is 20 meters per second for v, and the fly height is 100 meters for h, and unmanned aerial vehicle and sensing node communication radius are Dmax1000 m, system bandwidth B10 MHz, sensing node transmission power Pm0.1watt, noise power σ2Carrier frequency f of-110 dBmc2GHz, light speed c 3 × 108The channel gain beta of the reference distance point is-60 dB, betaLoS0dB and betaNLoS3dB, environment constant a 9.61 and b 0.16, and packet length Lm1Mbits, maximum number of iterations tmax=105And the maximum value of the counter is tc,maxMaximum clustering weight γ of 100max100 and an iteration step Δ γ of 5.
(2) Emulated content and results
Simulation 1, verifying that the unmanned aerial vehicle data collection scheme generated by the method can enable the sensing node to obtain the minimum maximum information age through data collection point optimization and path planning in a scene of 19 nodes.
FIG. 4 shows that: by adjusting the clustering weight, the number of data collection points of the unmanned aerial vehicle and the coordinates of the data collection points can be changed, on the basis, the maximum information age of the sensing nodes can be effectively reduced by adopting a proper path planning method, the freshness of sensing node perception data is ensured, and the maximum information age index is irrelevant to the node uploading sequence.
Simulation 2, verifying that the unmanned aerial vehicle data collection scheme generated by the method can enable the sensing nodes to obtain the minimum average information age through data collection point adjustment, sensing node uploading sequence optimization and path planning in a scene of 19 nodes.
FIG. 5 shows that: similarly, through adjusting the clustering weight, the number of data collection points and the coordinates of the unmanned aerial vehicle can be changed, on the basis, the average information age of the sensing nodes can be effectively reduced through optimizing the flight track of the unmanned aerial vehicle and the uploading sequence of the sensing nodes, and the freshness of the sensing data of the sensing nodes is ensured.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.