CN114679212B - Topology control method and system for satellite network - Google Patents

Topology control method and system for satellite network Download PDF

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CN114679212B
CN114679212B CN202011572897.7A CN202011572897A CN114679212B CN 114679212 B CN114679212 B CN 114679212B CN 202011572897 A CN202011572897 A CN 202011572897A CN 114679212 B CN114679212 B CN 114679212B
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CN114679212A (en
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李钊
胡振东
李静玲
张远
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Xidian University
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Abstract

The invention discloses a topology control method and a system thereof for a satellite network, wherein the method comprises the following steps: the system comprises a plurality of satellite nodes, the ground station determines the size of a topological time slot according to the time required by the satellite to complete the establishment and disassembly operation of an inter-satellite link, and uniformly divides the orbit running period of a satellite network by taking the topological time slot as an interval to obtain an initial topological snapshot sequence corresponding to the topological time slot; selecting topological structures corresponding to adjacent topological time slots from the initial topological snapshot sequence for comparison, and performing duplicate removal degeneracy if the topological structures are the same to obtain a duplicate removal degenerated topological snapshot sequence; setting a preset threshold of the difference degree of the topological structure, eliminating the difference in the topological structure by a method of adding a small amount of redundant public edges for the topological snapshot with the difference degree of the topological structure smaller than the preset threshold in the topological snapshot sequence after duplication removal degeneracy, merging the topological snapshots, and finally obtaining the topological snapshot sequence after redundancy addition degeneracy.

Description

Topology control method and system for satellite network
Technical Field
The invention belongs to the field of satellite network topology control, and particularly relates to an offline topology control method, in particular to a topology control method and system of a satellite network.
Background
The nodes in the satellite network have high-speed mobility, and the position coordinates, inter-satellite links, connection states and the like of the satellite nodes are changed along with time, so that the connection relation between the satellite nodes is complex and changeable, and therefore the network connection between the satellite nodes needs to be optimized by adopting a topology control technology. According to different processing modes of topology information, the topology control of the satellite network can be divided into two modes of online topology control and offline topology control. The online topology control means that the satellite node generates or adjusts the topology structure of the satellite network in real time, and when the emergency similar to the failure of the satellite node is met, the online topology control can respond in time so as to ensure the overall performance of the network. The off-line topology control refers to that a ground station calculates the topology connection relation in the whole satellite network operation period in advance according to the orbit parameters of the satellite nodes, and uploads and injects calculation results to each satellite node so as to realize the topology control of the whole satellite network.
For topology control of satellite networks, ye N et al propose Ye N, zhu Z, liu J, et al distributed Cluster-based Fault-tolerant Topology Control for Space Information Networks [ C ]. IEEE International Conference on Cyber-Enabled Distributed Computing and Knowledge Discovery,2010:210-217. This Cluster distributed Fault-tolerant topology control algorithm applied to spatial information networks first performs local topology discovery, then nodes in a single Cluster construct k-connected topologies in the clusters by adjusting transmit power to form k optimal vertex disjoint paths to nodes in the vicinity thereof, and then calculate the topology of any two adjacent clusters as weighted bipartite graphs, selecting the best matching node as a boundary node therein, thereby establishing the topology between the clusters. Huang J et al, supra, et al, an optimized snapshot division strategy for satellite network in GNSS J IEEE Communications Letters,2016,20 (12): 2406-2409. This snapshot splitting strategy applied to global navigation satellite systems (Global Navigation Satellite System, GNSS) first divides the period of a satellite network into a series of visibility slices (Visibility Slices) according to the visibility law of the satellite network (i.e., the time window in which data communication between periodically existing satellites and ground stations is possible), and then merges adjacent ones of the visibility slices into a topological snapshot according to the duration of the visibility slices and the number of ground stations. The above processing method for the topology snapshot does not consider the problem that the snapshot with the same topology structure occupies too much space on the satellite, so that the processing method has a large limitation in practical application.
The problems of the prior art are: excessive topology snapshot time interval can cause that the topology cannot accurately correspond to the current network state, so that the data transmission performance of the network is damaged; excessively small topological snapshot dividing time intervals can generate a large number of topological snapshots with the same or similar structures in the running period of the satellite, so that the data storage space of the satellite is excessively occupied; moreover, too frequent topology adjustment operation generates more on-board resource consumption and affects the continuity of data transmission in the task execution process.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides an offline topological degeneracy (Duplicates Removal and Redundancy Increase based Offline Topology Simplification and Merging, DR/RI-OTSM) method based on de-duplication and redundancy.
Difficulty and meaning for solving the technical problems: in the off-line topology control, a large number of topology snapshots with the same or similar structures can be generated, how to measure the difference degree among the topology snapshots, a merging strategy of the topology snapshots is provided, and the on-board storage space is saved by reducing the number of the topology snapshots, so that the method is a problem worthy of research.
The method is realized by firstly uniformly dividing the regression period of a satellite network into topological snapshot sequences, and then performing deduplication degeneracy on adjacent snapshots with the same topological structure; and then, aiming at the topology sequence obtained by duplication elimination and degeneration, redundant degeneration is added to adjacent snapshots with the topology structure difference lower than a preset threshold, namely, the purposes of merging topology snapshots with low difference degree, further reducing the number of stored snapshots on the satellite and the frequency of network topology adjustment are achieved by adding a small amount of redundant links, so that the topology of the satellite cluster has better stability and environmental adaptability, and the consumption of satellite resources caused by frequent topology switching is avoided.
Further, the offline topological degeneracy method based on de-duplication and redundancy addition comprises the following steps:
(1) The satellite network comprises L satellite nodes, and the orbit running period of the satellite is T. The ground station determines the dividing time interval delta T of the topological time slot according to the time required by the establishment and disassembly operation of the inter-satellite links between satellites, evenly divides the orbit running period T of the satellite network by the time interval delta T, and marks the nth time interval obtained by division as the topological time slot p n ；
(2) The ground station calculates each topology time slot p n The relative distance between the inner satellites is used for obtaining a distance matrix D n Distance matrix D by using minimum spanning tree algorithm MST n Processing to obtain a topology time slot p n Topology junction of corresponding satellite networkConstructing a topology snapshot sequence S by using the topology structure of the satellite network corresponding to all topology time slots;
(3) In the topology snapshot sequence S, selecting the topology structures corresponding to adjacent topology time slots for comparison, if the topology structures are the same, merging the adjacent topology time slots, removing repeated topology snapshots with the same topology structure, and updating the topology snapshot sequence; if the topological structures are different, sequentially selecting the topological structures corresponding to the subsequent adjacent time slots for comparison until the topological structures of all the topological time slots are compared, and obtaining a topology snapshot sequence S after duplication removal and degeneracy DR ；
(4) Setting a preset threshold eta of the difference degree of the topological structure, and for S DR Adjacent snapshots with the difference degree smaller than eta in the topological structure are eliminated by adding redundant public edges, the adjacent snapshots after the difference are eliminated are combined, and a topological snapshot sequence S of the satellite network after redundancy degeneration is obtained RI 。
Further, the step (1) specifically includes:
(1a) The ground station determines the dividing time interval delta t of the topological time slot according to the time required by the establishment and the disassembly operation of the inter-satellite links between satellites. Δt time length adjusted by topology
Figure BDA0002858151780000031
And topology maintenance duration t γ The common components are as follows:
Figure BDA0002858151780000032
at a length of
Figure BDA0002858151780000033
All satellites synchronously perform topology adjustment, and the time required for the satellites to perform topology adjustment is calculated according to the following formula:
Figure BDA0002858151780000034
wherein t is q Time t for searching and capturing target for satellite-borne antenna r Adjusting the time for tracking the target for the satellite-borne antenna;
(1b) The earth station sets the orbit period T of the satellite network at time intervals
Figure BDA0002858151780000035
Evenly dividing to obtain the time length of +.>
Figure BDA0002858151780000041
Topological time slot p n Wherein->
Figure BDA0002858151780000042
Figure BDA0002858151780000043
Representing a round up->
Figure BDA0002858151780000044
Representing a set of integers.
Further, the step (2) specifically includes:
(2a) The ground station at each time t according to the respective satellite n Calculating the v of any two satellites in the network containing L satellites i And v j Euclidean distance d between i,j Where i+.j and i, j ε {1, …, L, …, L }, and storing the calculation result in an L×L distance matrix D n In (a) and (b);
(2b) Distance matrix D n As an input parameter of the minimum spanning tree algorithm MST, a time t is calculated n Topology snapshot s of a satellite network of (a) n The topology snapshot indicates the network topology connection relationship to adjoin matrix A n Form store of A n The elements of the ith row and the jth column in the table are marked as epsilon i,j ，ε i,j The element value of (a) indicates whether a link exists between satellite nodes, when epsilon i,j When=1, it indicates node v i And v j There is a link between, when epsilon i,j When = ≡, node v is indicated i And v j No link exists between the two topology snapshot sequences, and in the orbit running period T of the satellite network, the topology structures of the satellite network corresponding to all topology time slots form a topology snapshot sequence S, and the elements in the S are recorded as S n 。
Further, the step (3) specifically includes:
(3a) Ground station selects adjacent topology snapshots s n Sum s n+x Corresponding adjacent matrix A n And A n+x Performing element-by-element exclusive OR
Figure BDA0002858151780000045
Calculation of (i) wherein->
Figure BDA0002858151780000046
And initializing x=1, if the calculation result +.>
Figure BDA0002858151780000047
Snapshots should be deleted from topology snapshot sequence S n+x Reserving snapshot s n And updates the topology snapshot sequence s≡s- { S n+x -and x≡x+1; if->
Figure BDA0002858151780000048
Then snapshot s is preserved n Sum s n+x And updating n++1 and x++1, continuing the comparison operation until all snapshot elements in the sequence S are traversed, thereby obtaining a topology snapshot sequence S after duplicate removal degeneracy DR ；
(3b) For transient interval [ t ] with delta topology time slots n ,t n+δ ]Topology snapshot s within ξ Sum s ψ Performing comparison and inspection to solve the problem of topology oscillation caused by repeated change of topology structure due to relative position change among satellites, wherein ζ<ψ and ζ, ψ ε [ n, n+δ ]]If there is a snapshot s ξ Sum s ψ Is identical in topology, s is deleted ξ To s ψ All snapshots in between, reserve s ξ And update S DR ←S DR -{s ξ ,…,s ψ Then from snapshot s ψ+1 The next round of comparison checking is continued until the sequence S DR Is traversed.
Further, the step (4) specifically includes:
(4a) Determining a preset threshold eta of the difference degree of the topological structure, and comparing S with DR Neighboring topology snapshots s in (1) n Sum s m Corresponding adjacent matrix A n And A m Performing element-by-element exclusive OR
Figure BDA0002858151780000051
Calculation by calculating matrix->
Figure BDA0002858151780000052
F-norm of (F-norm)
Figure BDA0002858151780000053
Wherein sigma i,j Representation matrix Q n The ith row and the jth column of the matrix are used for obtaining the number of the elements with the value of 1 in the matrix, and if the operation result is I Q n || F Not equal to 0, then there is Q between the topologies of neighboring snapshots n || F The difference between the two sides is that Q is used n || F And/2 characterizes the degree of difference between the snapshots.
(4b) Select S DR Topology snapshot s in (a) n Sum s m Corresponding adjacent matrix A n And A m Performing bitwise exclusive OR operation to obtain
Figure BDA0002858151780000054
Wherein m is>n, calculate matrix Q n F-norm Q of (2) n || F Judging whether or not the Q is satisfied n || F /2<η, if the inequality is true, redundant degeneracy is added to the topology snapshot, otherwise continuing at S DR Is selected from s m Checking adjacent follow-up topology snapshots; in the pair of snapshots s n Sum s m In the case of redundancy addition degeneracy, the matrix Q is used n Index of elements with median 1, will adjoin matrix a n And A m Has thereinThe element value of the same index is set to 1 to make snapshot s n Sum s m The topology of (3) is the same; next, snapshot s will be taken m From a sequence of topology snapshots S DR Delete and update the topology snapshot sequence to S DR ←S DR -{s m Continuing to S DR The rest elements in the sequence are operated as above until all snapshot elements are traversed, and finally the redundant and degenerate topological snapshot sequence S is obtained RI 。
The invention aims to provide a topology control method of a satellite network, which is suitable for degenerate optimization of generated topology snapshots when offline topology control is carried out on the satellite network.
In summary, the invention has the advantages and positive effects that: according to the invention, a dynamic topological connection relation of a satellite network in an orbit running period is converted into a quasi-static topological connection relation in a topological snapshot sequence mode, after duplication elimination and degeneration are carried out on adjacent snapshots with the same topological structure, redundancy and degeneration are further carried out on the adjacent snapshots with the topological structure difference lower than a preset threshold, the purposes of merging topological snapshots with low difference degree, further reducing the number of stored snapshots on the satellite and the frequency of network topology adjustment are achieved by adding a small amount of redundant links, so that the topology of the satellite cluster has better stability and environmental fitness, and the resource consumption on the satellite caused by frequent topology switching is avoided.
The invention is not only suitable for topology control of low orbit satellites, but also suitable for topology control of micro-nano satellite clusters, and the ground station can effectively reduce the number of topology snapshots and save the on-satellite data storage space after performing deduplication and redundancy degeneracy on the topology snapshots.
Drawings
FIG. 1 is a schematic diagram of a topology control method of a satellite network of the present invention;
FIG. 2 is a schematic diagram of a system model of a satellite network of the present invention;
FIG. 3 is a flow chart diagram of a topology control method of the satellite network of the present invention;
FIG. 4 is a diagram of the deduplication degeneracy of a topological snapshot sequence of the present invention;
FIG. 5 is a schematic diagram of the topology snapshot sequence plus redundancy degeneracy of the present invention;
FIG. 6 is a schematic diagram of the deduplication, redundancy-added degeneracy efficiency of a topology snapshot of the present invention.
Detailed Description
The present invention will be described in detail with reference to examples below in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Aiming at the demands of the satellite network for connectivity and adaptability, the invention provides a topology control method of the satellite network, improves the degeneracy efficiency of the topology snapshot of the satellite network, and can solve the problems that the topology snapshot occupies too much data storage space of the satellite and the satellite network frequently carries out topology structure adjustment.
The principle of application of the invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the topology control method of the satellite network provided by the embodiment of the invention includes the following steps:
step 101, a satellite network includes L satellite nodes, and an orbit running period of a satellite is T. The ground station determines the dividing time interval delta T of the topological time slot according to the time required by the establishment and disassembly operation of the inter-satellite links between satellites, evenly divides the orbit running period T of the satellite network by the time interval delta T, and marks the nth time interval obtained by division as the topological time slot p n ；
Step 102, the ground station calculates each topological time slot p n The relative distance between the inner satellites is used for obtaining a distance matrix D n Distance matrix D by using minimum spanning tree algorithm MST n Processing to obtain a topology time slot p n The topology structure of the corresponding satellite network forms a topology snapshot sequence S by the topology structure of the satellite network corresponding to all topology time slots;
step 103, in the topology snapshot sequence S, selecting the topology structures corresponding to adjacent topology time slots for comparison, and merging if the topology structures are the sameAdjacent topology time slots, removing repeated topology snapshots with the same topology structure, and updating a topology snapshot sequence; if the topological structures are different, sequentially selecting the topological structures corresponding to the subsequent adjacent time slots for comparison until the topological structures of all the topological time slots are compared, and obtaining a topology snapshot sequence S after duplication removal and degeneracy DR ；
The topology structures in this embodiment are the same, which means that the connection relations between nodes in the network are the same. Satellite nodes in adjacent topology snapshots may have different coordinates, the distance between nodes may be different, but the order of connection between nodes should be the same.
104, setting a preset threshold eta of the difference degree of the topological structure, and performing S DR Adjacent snapshots with the difference degree smaller than eta in the topological structure are eliminated by adding redundant public edges, and then adjacent snapshots after the difference elimination are combined to obtain a redundant and degenerate topological snapshot sequence S RI 。
It should be noted that, the redundant common edge in this embodiment may be understood as a redundant (or, redundant) link, which refers to a link newly added based on the original network topology.
The principle of application of the invention is further described below with reference to the accompanying drawings.
Fig. 2 is a schematic diagram of a system model of the satellite network according to the present invention. The system model used by the invention consists of 16 Low Earth Orbit (LEO) satellites, the satellites run in a cluster mode, the running orbits of satellite nodes are all circular (the eccentricity e=0), and the influence of the perturbation forces from other celestial bodies is ignored.
The satellite orbit is generally determined by a coordinate system of the satellite orbit, a common equatorial inertial coordinate system is adopted, the origin of the coordinate is located at the earth center, an equatorial plane is taken as a reference plane, an X axis points to a level spring point, a Y axis rotates 90 degrees from the X axis to the east in the equatorial plane, and a Z axis points to the north pole perpendicular to the equatorial plane. The coordinate system describes the orbital motion of the cluster satellite by adopting the kepler orbit root, and comprises six parameters of a semi-long axis a, an eccentricity e, an orbit inclination angle theta, an ascending intersection point right ascent angle omega, a near-place amplitude angle omega and a plane near-point angle M, so that the kepler orbit root can be expressed as a six-dimensional vector form:
K＝[a eθΩωM] (3)
wherein the semi-major axis a is the sum of the earth radius and the satellite orbit altitude.
As shown in fig. 3, the topology control method of the satellite network provided by the embodiment of the invention specifically includes the following steps:
step 1, a ground station determines a division time interval delta T of a topological time slot according to the time required by the establishment and disassembly operations of an inter-satellite link between satellites, evenly divides an orbit operation period T of a satellite network by the time interval delta T, and marks an nth time interval obtained by division as a topological time slot p n 。
One topology time slot is divided into two stages of topology adjustment and topology maintenance, and a network topology structure of the topology maintenance stage is called a topology snapshot. When the topology structure of the satellite network is changed, firstly, the inter-satellite links need to be built or removed in a topology adjustment stage, and then the satellite network enters a topology maintenance stage to keep the adjusted network topology until the next topology adjustment stage. Thus, the partition time interval Δt of the topology time slot is adjusted in length by the topology
Figure BDA0002858151780000081
And topology maintenance duration t γ The common components are as follows:
Figure BDA0002858151780000082
at a length of
Figure BDA0002858151780000083
All satellites synchronously perform topology adjustment, and the time required for the satellites to perform topology adjustment is calculated according to the following formula:
Figure BDA0002858151780000084
wherein t is q Time t for searching and capturing target for satellite-borne antenna r The time to track the target is adjusted for the satellite borne antenna.
With the known position coordinates of the target satellite, the search acquisition time t of the satellite-borne antenna to the target q Can be controlled typically within 10 ms. Because the distance between satellites in the network is relatively short when the satellites operate in cluster mode, the time t for tracking the target is adjusted by the satellite-borne antenna r Typically within a few hundred milliseconds. From the above, the total time required for the satellite clusters to make topology adjustments and maintain a stable topology for communication is typically less than 1s. Therefore, when the satellite network is subjected to offline topology control, the division interval delta t of the topology time slots is not smaller than
Figure BDA0002858151780000085
The operating period T of the satellite network is +.>
Figure BDA0002858151780000086
After uniform division, a length of time of +.>
Figure BDA0002858151780000087
Topological time slot p n Wherein->
Figure BDA0002858151780000088
Figure BDA0002858151780000089
Representing a round up->
Figure BDA00028581517800000810
Representing a set of integers.
And step 2, calculating the topological connection relation between satellites in each topological time slot, and generating a topological snapshot sequence.
The ground station at each time t according to the respective satellite n Calculating the position coordinates of any two satellites v in a network containing 16 satellites i And v j Euclidean distance d between i,j Wherein i+.j and i j ε {1, …)L, …, L }, and storing the calculation result in a 16 x 16 distance matrix D n In, it should be noted that D n The main diagonal element value of (2) is ≡infinity; the distance between satellites is used as a weight value to obtain a distance matrix D n Distance matrix D by using MST algorithm n Processing, calculating the topological connection relation between satellites in each topological time slot and using an adjacent matrix A n Form store of A n The elements of the ith row and the jth column in the table are marked as epsilon i,j ，ε i,j The element value of (a) indicates whether a link exists between satellite nodes, when epsilon i,j When=1, it indicates node v i And v j There is a link between, when epsilon i,j When = ≡, node v is indicated i And v j No link exists between the two topology snapshot sequences, and in the orbit running period T of the satellite network, the topology structures of the satellite network corresponding to all topology time slots form a topology snapshot sequence S, and the elements in the S are recorded as S n 。
And 3, comparing topological structures in adjacent topological time slots, and performing duplication removal degeneracy on the topological snapshot.
(3a) The ground station performs deduplication degeneracy on the topology snapshot sequence S, namely selects adjacent topology snapshots S n Sum s n+x Corresponding adjacent matrix A n And A n+x Performing element-by-element exclusive OR
Figure BDA0002858151780000091
Calculation of (i) wherein->
Figure BDA0002858151780000092
And x=1 is initialized. If the calculation result->
Figure BDA0002858151780000093
Snapshots should be deleted from topology snapshot sequence S n+x Reserving snapshot s n And updates the topology snapshot sequence s≡s- { S n+x -and x≡x+1; if->
Figure BDA0002858151780000094
Then snapshot s is preserved n Sum s n+x And updating n++1 and x++1, continuing the comparison operation until all snapshot elements in the sequence S are traversed, thereby obtaining a topology snapshot sequence S after duplicate removal degeneracy DR 。
(3b) For transient interval [ t ] with delta topology time slots n ,t n+δ ]Topology snapshot s within ξ Sum s ψ Performing comparison and inspection to solve the problem of topology oscillation caused by repeated change of topology structure due to relative position change among satellites, wherein ζ<ψ and ζ, ψ ε [ n, n+δ ]]If snapshot s exists ξ Sum s ψ The topology structures of the two are identical, which shows that topology concussion exists in the transient region, and s is deleted ξ To s ψ All snapshots in between, reserve s ξ And update S DR ←S DR -{s ξ ,…,s ψ Then from snapshot s ψ+1 The next round of comparison checking is continued until the sequence S DR Is traversed.
As can be seen from fig. 4, from the time slot p 0 To time slot p 5 Has the same topological structure, so that the topological snapshot s obtained after duplicate removal and degeneracy 0 Is maintained for a period of time of
Figure BDA0002858151780000101
The time length is required to pass before the snapshot>
Figure BDA0002858151780000102
And performing topology adjustment. Similarly, degenerate topology snapshots s 6 Sum s n-7 (degenerated by 11 and 8 consecutive topological time slots respectively) are +.>
Figure BDA0002858151780000103
And->
Figure BDA0002858151780000104
Meanwhile, the time length is required to be longer before each snapshot>
Figure BDA0002858151780000105
Performing topologyAnd (5) adjusting.
Step 4, S in the topology snapshot deduplication sequence DR And (3) performing redundancy degeneracy on the snapshots with the same topological structure.
(4a) A preset threshold eta of the degree of difference of the topological structure is determined. For S DR Neighboring topology snapshots s in (1) n Sum s m Corresponding adjacent matrix A n And A m Performing element-by-element exclusive OR
Figure BDA0002858151780000106
Calculation by calculating matrix->
Figure BDA0002858151780000107
F-norm of (F-norm)
Figure BDA0002858151780000108
Wherein sigma i,j Representation matrix Q n The i-th row and the j-th column elements) in the matrix to obtain the number of the elements with the value of 1 in the matrix. If the operation result is Q n || F Not equal to 0, then there is Q between the topologies of neighboring snapshots n || F The difference between the two sides is that Q is used n || F And/2 characterizes the degree of difference between the snapshots.
(4b) Select S DR Topology snapshot s in (a) n Sum s m Corresponding adjacent matrix A n And A m Performing bitwise exclusive OR operation to obtain
Figure BDA0002858151780000109
Wherein m is>n, calculate matrix Q n F-norm Q of (2) n || F Judging whether or not the Q is satisfied n || F /2<η, if the inequality is true, redundant degeneracy is added to the topology snapshot, otherwise continuing at S DR Is selected from s m Adjacent subsequent topology snapshots are checked. In the pair of snapshots s n Sum s m In the case of redundancy addition degeneracy, the matrix Q is used n Index of elements with median 1, will adjoin matrix a n And A m The element value with the same index in (1) is set to be fastS. photo n Sum s m Is identical in topology. Next, snapshot s will be taken m From a sequence of topology snapshots S DR Delete and update the topology snapshot sequence to S DR ←S DR -{s m Continuing to S DR The rest elements in the sequence are operated as above until all snapshot elements are traversed, and finally the redundant and degenerate topological snapshot sequence S is obtained RI 。
Fig. 5 gives an illustration of the topology snapshot sequence plus redundancy degeneracy. Because of the deduplication degeneracy of the resulting snapshot sequence S in FIG. 4 DR Adjacent topology snapshot s in (a) 0 Sum s 6 There are two different edges (epsilon) 4,11 And epsilon 8,9 ) According to the rule of adding redundancy degeneracy, for snapshot s 0 Sum s 6 Respectively adding redundant edges epsilon 4,11 And epsilon 8,9 The two redundant topologies have the same structure and can be further degenerated. The result of adding redundancy degeneracy is shown in FIG. 5, and the degenerated topology snapshot is still s 0 The topology adjustment time length is as follows
Figure BDA0002858151780000111
But the duration of the topology maintenance s phase is increased to +.>
Figure BDA0002858151780000112
The application effect of the present invention will be described in detail with reference to simulation.
1. Simulation conditions:
for the evaluation of the performance of the present invention we assume that 16 LEO satellites are operated in cluster mode, the orbit of the satellite nodes are all circular (eccentricity e=0), and the influence of the perturbation forces from other celestial bodies is ignored. Each satellite is provided with an array antenna with the same beam width and adjustable orientation, and different beams are formed in different directions by adopting a space division multiplexing technology to cover different satellite nodes. In the inter-satellite communication process, each satellite always transmits signals with maximum transmission power to ensure the same maximum transmission distance.
TABLE 1 Kepler orbital root number and random bias range for micro-nano satellite network
Parameter type Initial value Random bias range
Semi-long axis a (km) 7800 ±10
Track inclination angle theta (°) 95 ±3
Intersection point of ascending and right angle is omega (°) 275 ±3
Near-spot amplitude angle ω (°) 175 ±3
Flat angle M (°) 180 ±3
According to the number of kepler orbits and the random bias range thereof shown in table 1, the orbit parameters of 16 satellites are set, and the simulation duration is 60 minutes. The 16 satellites synchronously travel in a circular orbit of about 1500km above earth from the ground in a trunked mode, with a relative distance between the satellites of about 100-1000 km.
2. The simulation content:
note |s| as the initial snapshot number, |s DR And I is the number of snapshots after duplicate removal and degeneracy, |S RI And i is the number of snapshots after redundancy addition, then the deduplication degeneracy efficiency α and redundancy addition degeneracy efficiency β can be defined as:
Figure BDA0002858151780000121
and
Figure BDA0002858151780000122
as shown in fig. 6, Δt=1s, η=3, and l takes different values, the proposed DR/RI-OTSM is degenerate for the topology snapshot. L is respectively 8, 16, 32 and 64, the simulation times are set to be 100, the simulation time length of each simulation is set to be 60 minutes, 3601 snapshots generated by each simulation are processed by the method, the efficiency of duplicate removal degeneracy and redundancy addition degeneracy of the snapshots is obtained, and the average value of efficiency samples obtained by 100 simulations is obtained. As shown, as L increases, α and β decrease gradually. And the efficiency of adding redundancy degeneracy is significantly better than that of removing redundancy degeneracy. This is because, given a simulation duration, on the premise of generating the same number of topology snapshots, as the number of satellite nodes in the network increases, the number of edges included in the topology increases accordingly, resulting in more various topology structures of the snapshots, i.e., the number of topology snapshots with the same structure decreases, resulting in a reduction in the efficiency of deduplication degeneracy. For the snapshot sequence after de-duplication degeneracy, since the degree of difference between adjacent topological snapshots becomes more remarkable along with the increase of the number of nodes, the redundancy-added degeneracy cannot degenerate the snapshots exceeding the preset threshold under the limitation of the preset threshold η=3 of the degree of difference (i.e. when L is larger, the sequence S DR The number of difference edges of adjacent snapshots in (a) is greater than a preset threshold of degree of difference η=3 with a higher probability), so that the redundancy-added degeneracy efficiency also decreases with an increase in L.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (5)

1. The topology control method of the satellite network is suitable for a topology control system of the satellite network and is characterized by comprising the following steps:
the satellite network comprises L satellite nodes, and the orbit running period of the satellite is T; the ground station determines the dividing time interval delta T of the topological time slot according to the time required by the establishment and disassembly operation of the inter-satellite links between satellites, evenly divides the orbit operation period T of the satellite network by the time interval delta T, and marks the nth time interval obtained by division as the topological time slot p n ；
Step (2) the ground station calculates each topological time slot p n The relative distance between the inner satellites is used for obtaining a distance matrix D n Distance matrix D by using minimum spanning tree algorithm MST n Processing to obtain a topology time slot p n The topology structure of the corresponding satellite network forms a topology snapshot sequence S by the topology structure of the satellite network corresponding to all topology time slots;
step (3) in the topology snapshot sequence S, selecting the topology structures corresponding to the adjacent topology time slots for comparison, if the topology structures are the same, merging the adjacent topology time slots, removing repeated topology snapshots with the same topology structure, and updating the topology snapshot sequence; if the topological structures are different, sequentially selecting the topological structures corresponding to the subsequent adjacent time slots for comparison until the topological structures of all the topological time slots are compared, and obtaining a topology snapshot sequence S after duplication removal and degeneracy DR ；
Step (4) setting a preset threshold eta of the difference degree of the topological structure, and for S DR Adjacent snapshots with the difference degree smaller than eta in the topological structure are eliminated by adding redundant public edges, and then adjacent snapshots after the difference elimination are carried outMerging to obtain topological snapshot sequence S of satellite network after redundancy degeneracy RI 。
2. The topology control method of a satellite network according to claim 1, wherein said step (1) comprises:
(1a) The ground station determines the dividing time interval delta t of the topological time slot according to the time required by the establishment and the disassembly operation of the inter-satellite links between satellites, and the time length of delta t adjusted by the topology
Figure FDA0004129788560000011
And topology maintenance duration t γ The common components are as follows:
Figure FDA0004129788560000021
at a length of
Figure FDA0004129788560000022
All satellites synchronously perform topology adjustment, and the time required for the satellites to perform topology adjustment is calculated according to the following formula:
Figure FDA0004129788560000023
wherein t is q Time t for searching and capturing target for satellite-borne antenna r Adjusting the time for tracking the target for the satellite-borne antenna;
(1b) The earth station sets the orbit period T of the satellite network at time intervals
Figure FDA0004129788560000024
Evenly dividing to obtain the time length of +.>
Figure FDA0004129788560000025
Topological time slot p n Wherein->
Figure FDA0004129788560000026
Representing a round up->
Figure FDA0004129788560000027
Representing a set of integers.
3. The topology control method of a satellite network according to claim 1, wherein said step (2) comprises:
(2a) The ground station at each time t according to the respective satellite n Calculating the v of any two satellites in the network containing L satellites i And v j Euclidean distance d between i,j Where i+.j and i, j ε {1, …, L, …, L }, and storing the calculation result in an L×L distance matrix D n In (a) and (b);
(2b) Distance matrix D n As an input parameter of the minimum spanning tree algorithm, the time t is calculated n Topology snapshot s of a satellite network of (a) n The topology snapshot indicates the network topology connection relationship to adjoin matrix A n Form store of A n The elements of the ith row and the jth column in the table are marked as epsilon i,j ，ε i,j The element value of (a) indicates whether a link exists between satellite nodes, when epsilon i,j When=1, it indicates node v i And v j There is a link between, when epsilon i,j When = ≡, node v is indicated i And v j No link exists between the two topology snapshot sequences, and in the orbit running period T of the satellite network, the topology structures of the satellite network corresponding to all topology time slots form a topology snapshot sequence S, and the elements in the S are recorded as S n 。
4. A topology control method of a satellite network according to claim 3, wherein said step (3) comprises:
(3a) Ground station selects adjacent topology snapshots s n Sum s n+x Corresponding adjacent matrix A n And A n+x Performing element-by-element exclusive OR
Figure FDA0004129788560000028
Calculation, wherein n, < >>
Figure FDA0004129788560000029
And initializing x=1, if the calculation result +.>
Figure FDA0004129788560000031
Snapshots should be deleted from topology snapshot sequence S n+x Reserving snapshot s n And updates the topology snapshot sequence s≡s- { S n+x -and x≡x+1; if->
Figure FDA0004129788560000032
Then snapshot s is preserved n Sum s n+x And updating n++1 and x++1, continuing the comparison operation until all snapshot elements in the sequence S are traversed, thereby obtaining a topology snapshot sequence S after duplicate removal degeneracy DR ；
(3b) For transient interval [ t ] with delta topology time slots n ,t n+δ ]Topology snapshot s within ξ Sum s ψ Performing comparison and inspection to solve the problem of topology oscillation caused by repeated change of topology structure due to relative position change among satellites, wherein ζ < ψ and ζ, ψ e [ n, n+delta ]]If there is a snapshot s ξ Sum s ψ Is identical in topology, s is deleted ξ To s ψ All snapshots in between, reserve s ξ And update S DR ←S DR -{s ξ ,…,s ψ Then from snapshot s ψ+1 The next round of comparison checking is continued until the sequence S DR Is traversed.
5. A topology control method of a satellite network according to claim 3, wherein said step (4) comprises:
(4a) Determining a preset threshold eta of the difference degree of the topological structure, and comparing S with DR Neighboring topology snapshots s in (1) n Sum s m Corresponding toAdjacency matrix A n And A m Performing element-by-element exclusive OR
Figure FDA0004129788560000033
Calculation by calculating matrix->
Figure FDA0004129788560000034
F-norm of (F-norm)
Figure FDA0004129788560000035
Wherein sigma i,j Representation matrix Q n The ith row and the jth column of the matrix are used for obtaining the number of the elements with the value of 1 in the matrix, and if the operation result is I Q n || F Not equal to 0, then there is Q between the topologies of neighboring snapshots n || F The difference between the two sides is that Q is used n || F 2, characterizing the difference degree between the snapshots;
(4b) Select S DR Topology snapshot s in (a) n Sum s m Corresponding adjacent matrix A n And A m Performing bitwise exclusive OR operation to obtain
Figure FDA0004129788560000036
Wherein m is greater than n, calculate matrix Q n F-norm Q of (2) n || F Judging whether or not the Q is satisfied n || F And/2 < eta, if the inequality is true, adding redundancy degeneracy to the topology snapshot, otherwise continuing at S DR Is selected from s m Checking adjacent follow-up topology snapshots; in the pair of snapshots s n Sum s m In the case of redundancy addition degeneracy, the matrix Q is used n Index of elements with median 1, will adjoin matrix a n And A m The element value with the same index in (1) is set to make snapshot s n Sum s m The topology of (3) is the same; next, snapshot s will be taken m From a sequence of topology snapshots S DR Delete and update the topology snapshot sequence to S DR ←S DR -{s m Continuing to S DR The rest of the elements in the list are operated on until all snapshot elements are obtainedTraversing to finally obtain the topological snapshot sequence S after redundancy degeneration RI 。/>
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