CN117240339A - Satellite optical network routing algorithm research method under space debris interference - Google Patents

Abstract

The invention discloses a satellite optical network routing algorithm research method under space debris interference, and relates to the technical field of satellite optical network routing. The invention analyzes the characteristics of satellite network, comprehensively considers the situations of space debris position, short invalidation of inter-satellite links, link propagation delay and the like, calculates the communication cost between adjacent satellites according to the visibility and link state information of the adjacent satellites and by adding direction judgment, dynamically calculates an effective path, improves the communication success rate and reduces rerouting caused by link faults.

Description

Satellite optical network routing algorithm research method under space debris interference

Technical Field

The invention relates to the technical field of satellite optical network routing, in particular to a satellite optical network routing algorithm research method under space debris interference.

Background

Space debris refers to the product of human space activities, including rocket bodies and Wei Xingti for completing tasks, rocket ejections and the like, and is a main pollution source of space environment. In recent years, more and more space activities lead to a rapid increase in the number of on-orbit spacecrafts, and a series of space experiments generate more and more space fragments, so that more serious pollution is caused to the space environment. The data show that by the beginning of 2020, space debris with a diameter of more than 10cm is nearly 3 tens of thousands; dangerous space debris between 1 cm and 10cm in diameter is over 90 tens of thousands. Meanwhile, compared with microwave communication, laser communication has the advantages of high transmission rate, large transmission capacity, high speed, good confidentiality, low power consumption of terminal equipment and the like, and becomes a necessary choice of future satellite networks. In order to cover the world, future satellite optical networks will be composed of tens of thousands of satellites in the near-earth orbit, and satellite nodes perform line-of-sight communication through point-to-point or point-to-multipoint laser links.

The conventional distance vector routing and link state routing algorithms cannot be applied to Low-Earth-Orbit (LEO) satellite networks with high-speed changes. Thus, e.ekici proposes a routing algorithm for virtual nodes that cover a feature point with an polar-orbiting satellite constellation, converting the routing problem between mobile satellite nodes into a stable routing problem between virtual nodes. The literature proposes a virtual topology algorithm (DT-DVTR) which discretizes the system period of the satellite network into discrete snapshots, but the two routing calculation methods cannot adapt to the real-time dynamics of the satellite network. The literature uses link propagation delay and link queuing delay as link cost metrics and proposes an adaptive routing scheme, but does not take into account the information of the network itself.

When the network is blocked by fragments, the data packet cannot continue to be transmitted forwards due to the breakage of the communication path, and the problem that the data packet needs to be rerouted or is solved by adopting a certain dynamic routing strategy is solved. The method has the advantages of high cost, low timeliness and no good recovery capability for fault burst and recovery. Based on the method, the FSA-based dynamic fault-tolerant routing method proposed by LuY et al is used for processing node faults in a two-dimensional grid, and the effect of using a boundary diffusion and forwarding protocol on a polar orbit satellite constellation is good, but the construction of a fault area is complex, the variety is various, the information of the boundary needing flooding diffusion is more, and the calculation complexity is higher. The literature proposes a satellite network link state routing scheme (SLSR). Node and link failure abnormality is handled by collecting node and link failure information in real time, but the overhead of information flooding is far greater than that of the original link state algorithm. Qi et al propose a distributed survivor routing algorithm (DSRA-MCIO) suitable for a jumbo constellation with inclined orbits, which selects a minimum overhead to determine a main path and a plurality of standby paths between each pair of satellite node pairs based on the regularity of the constellation network topology, and according to a failure recovery mechanism, reduces the end-to-end delay and signaling overhead when a link fails, but the data packet is easily forwarded to a non-optimal scheme due to early change of topology, thereby generating a larger overhead. Zhao Yang proposes a probability distribution datagram routing algorithm based on logical distance, which measures the importance degree of a certain link fault by analyzing the influence of the link fault on the minimum hop count of the network, ensures that data advance along the least influenced direction of the failed link as much as possible on the premise of the minimum hop count, considers load balancing and improves the resistance to the link failure, but cannot cope with the real-time link fault in the network, so that a new solution to the above problems is required.

Disclosure of Invention

The invention aims to provide a satellite optical network routing algorithm research method under space debris interference.

In order to achieve the above purpose, the present invention provides the following technical solutions: the method for researching the satellite optical network routing algorithm under the interference of the space debris at least comprises the following steps:

establishing an LEO constellation network structure, dividing a polar orbit constellation into P orbit planes, wherein each orbit plane has the same inclination angle and the same number of Q satellites, and P multiplied by Q satellites are totally arranged, all satellites have the same orbit height, the same numbers of different orbit planes are positioned on the same horizontal plane, all orbit planes form two intersecting points in the north-south poles, each node can establish 4 inter-satellite laser links, and an ISL can acceptably point, acquire and track and keep the links under the condition of no interference;

establishing a space debris movement model, using a kepler model to approximate the simulation, and analyzing the relative position relationship between the debris and the satellite along with the time change to perform inter-satellite visibility analysis;

a dynamic routing algorithm is adopted on the basis of the LEO constellation network structure, so that the method is better suitable for high-speed dynamic changes of constellation topology and link information;

the link state routing algorithm of the dynamic routing algorithm is selected, the link state algorithm is improved by collecting link state information in real time and adding a direction influencing factor and a direction enhancing index, the link cost is estimated again by utilizing inter-satellite visibility, the direction of a data packet in each hop is further influenced, the link interruption caused by space fragment shielding is avoided, a proper link can be selected to meet the communication requirement, the communication time delay is reduced, the communication success rate of a communication system is improved, and the stability of the network communication quality is enhanced.

Preferably, in the establishing the LEO constellation network structure, for a polar orbit satellite network topology structure, two satellites in orbit are at a distance L _v Equal length throughout, expressed as:

wherein R is the orbit radius, Q is the number of satellites on the same orbit surface;

distance L between two satellites in orbit _h Is changed along with the movement of the node, and the following steps are obtained:

L _h ＝b×cos(lat)

wherein lat is the dimension in which the track surface is located,p is the number of track surfaces for the distance between track surfaces, and it can be seen that the track distance is shortened with increasing latitude;

abstracting the polar orbit constellation structure into a network model structure;

to distinguish each satellite node, it is assigned a unique address, using<m，n>Represents the earth logical address of a satellite, where m is the orbital plane number and n is the number of the satellite in the same orbital plane, and the path from the source satellite A to the destination satellite B can be defined as P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) consists of a sequence of nodes:

P(＜m ₀ ,n ₀ ＞,＜m _I ,n _I ＞)＝{＜m ₀ ,n ₀ ＞,...,＜m _i ,n _i ＞,...＜m _I ,n _I ＞}

wherein < m _i ,n _i The address of the node passing through at present is represented by the number of the current satellite, i represents the number of the current satellite, and each hop added on the path can change m or n by a numerical value of 1;

a shortest hop-count path set between two points in the two-dimensional network comprises a longitudinal connection set and a transverse connection set;

mapping to a low-orbit satellite scene, wherein longitudinal connection is a longitudinal inter-satellite link in a track plane, and transverse connection is a lateral inter-satellite link between track planes; so that the number of path hops between source-destination A, B satellites H (P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) is defined as:

preferably, the building of the space debris movement model at least comprises the following steps:

the earth is considered as a mass celestial body of one point, and the mass of an object moving around the earth is negligible;

neglecting higher-order effects in the earth gravitational field and the environmental disturbance, expressing a motion equation by a non-inertial reference system ECEF system, and calculating to obtain the position and the speed of the space debris through six elements of the orbit;

solving by using a kepler model based on an initial position and a speed created for the space debris;

in the near-focus coordinate system, the position r of the space debris can be obtained according to the motion law of the celestial body _p And velocity v _p The method comprises the following steps:

where a is the semi-major axis, e is the eccentricity,for true near-earth angle, GM is the constant of the gravitational force, and the value is 398603 multiplied by 10 ⁹ m ³ /s ² ；

The position and velocity are scaled to the ECEF system, any point can be expressed in (x, y, z), and for the spatial debris, the scaled coordinates are expressed as:

x＝(cosl*cosω-sinl*sinω*cosθ _i ,-coslsinω-sinl*cosω*cosθ _i ,sinl*sinθ _i )

y＝(sinl*cosω+cosl*sinω*cosθ _i ,-sinl*sinω+cosl*cosω*cosθ _i ,-cosl*sinθ _i )

z＝(sinω*sinθ _i ,cosω*sinθ _i ,cosθ _i )

where l is the equatorial longitude of the intersection point, ω is the near-to-point radial angle, θ _i Is the track inclination angle;

the equation of the coordinates after conversion is brought in to obtain R= [ x, y, z]Bringing R into the formula to obtain the position R of the space debris in the ECEF system _E Equation of (v) and velocity v _E The formula of (2) is as follows:

r _E ＝R*r _p

v _E ＝R*v _p

the relationship between position and velocity and time is obtained by fourth-order Longgar-Kutta numerical integration of the equation, as shown in the following equation:

wherein, t is _n Time is expressed as y _n Representing the position and velocity of the chip at a certain moment, where r is _E Equation of (v) and velocity v _E The numerical value in the formula (I) is denoted as y _n ＝(r _E (1),v _E (1),r _E (2),v _E (2),r _E (3),v _E (3) Updating and iterating the position and the speed along with the change of time, and analyzing the relative position relationship between fragments and satellites along with the change of time to perform inter-satellite visibility analysis.

Preferably, the derivation of the dynamic routing algorithm at least includes the following steps: determining a direction influence factor, determining a direction enhancement index A, determining a link cost and realizing a routing decision algorithm.

Preferably, the determining the direction influencing factor at least includes the steps of:

according to the inter-satellite link direction, four influence factors are provided, which are respectively represented by N, S, W, E, and the initial values of the influence factors are all 0;

the direction influence factors are assigned only at the beginning of a task in the process of one-time task transmission, and are used for assisting in direction judgment in the forwarding process of the data packet, so that the transmission is prevented from being trapped into circulation due to the formation of a loop;

the known propagation direction is divided into straight line propagation and oblique line propagation, wherein the straight line propagation address < m, n > only changes one value, and the oblique line propagation causes both values in < m, n > to change;

giving direction factor and satellite address according to the relative position relation of source satellite and destination satellite<m，n>Correspondence between m and n, the variation of m and n being defined by n _t And m _t Representation, record n _t ＝n _i -n _o ，m _t ＝m _i -m _o ；

Wherein < m _o ,n _o Is the address of the source node, < m _i ,n _i Is the address of the destination node.

Preferably, the determining the direction-enhancing index a includes at least the steps of:

according to the network characteristic structure, the whole system network is disassembled into single node elements in the shape of a single crossroad;

obtaining the position sum of fragments obtained by the relation of the position and the speed and time through the fourth-order Longer lattice-Kutta numerical integration of the equation, obtaining the visibility data between satellites by judging whether the two satellites and the fragments are collinear at the current moment, and introducing a direction enhancement index A _i ，A _i Is an array of satellite visibility values in four directions, visible 1 and invisible 0, A _i Representing i ε { N, W, S, E };

each node A _i The value of the data packet is refreshed in t, and the data packet is used for assisting in accounting the link cost to judge the forwarding direction of the next hop of the data packet.

Preferably, the determining the link cost includes at least the following steps:

selecting a proper index to describe the cost of a network communication link according to a network optimization theory, and selecting a link cost measure capable of reflecting the dynamic property of the network through the continuous change of topology to timely reflect the state of a laser link;

the link cost L is set as follows:

wherein,delta epsilon is infinitesimal, l (A, B) is the end-to-end distance, d (A, B) is the end-to-end propagation delay, +.>c is the speed of light;

under the condition that a certain direction influence factor is the same as the enhancement index of the direction, the link cost is very low, and the direction indicated by the direction influence factor is selected preferentially;

when the direction influencing factor and the direction enhancement index of a certain direction are different, a path with lower transmission delay is selected when the path is to be bypassed.

Preferably, the implementation of the routing decision algorithm at least comprises the following steps:

initializing, namely obtaining an adjacent matrix of a satellite network topology corresponding to initial time according to the topology of a polar orbit satellite network, wherein the adjacent matrix comprises visibility among satellites and longitude and latitude parameters of the satellites;

secondly, satellite addressing and parameter determining, namely, distributing unique unchanged logic addresses < m, n > for each satellite, obtaining the value of a direction influence factor according to the address relation between a source satellite and a destination satellite, and not changing in the transmission process;

thirdly, calculating L (t) of link cost, and obtaining visibility, direction enhancement index, direction influence factor and link distance among satellites at the current moment by considering shielding of fragments on the satellites to obtain four link cost at the moment when a data packet reaches a certain point;

fourthly, selecting a route, and utilizing the cost in the third step to perform Dijkstra algorithm to find the shortest forwarding path between the two satellites at the current time delta t;

and fifthly, circularly executing, namely repeatedly executing the third step and the fourth step when the data arrives at the next satellite until the destination node is reached, ending the transmission, and outputting a path, a total transmission delay and a total hop count.

Compared with the prior art, the invention has the beneficial effects that:

the invention analyzes the characteristics of satellite network, comprehensively considers the situations of space debris position, short invalidation of inter-satellite links, link propagation delay and the like, calculates the communication cost between adjacent satellites according to the visibility and link state information of the adjacent satellites and by adding direction judgment, dynamically calculates an effective path, improves the communication success rate and reduces rerouting caused by link faults.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic diagram of an polar orbit constellation structure according to the present invention;

FIG. 2 is a schematic diagram of a two-dimensional topology of a polar orbiting satellite network of the present invention;

FIG. 3 is a diagram illustrating the data propagation direction of a source-destination node according to the present invention;

FIG. 4 is a schematic diagram of a single-node element according to the present invention;

FIG. 5 is a flow chart of the DEI-LS algorithm of the present invention;

FIG. 6 is a diagram of a 48/6/30 constellation model of the present invention;

FIG. 7 is a diagram of the motion trajectories of satellites in a polar orbit satellite network according to the present invention;

FIG. 8 is a schematic view of the movement state of the fragments at a certain moment in the present invention;

fig. 9 is a schematic diagram of the availability of 95 links in the network at a certain time according to the present invention;

FIG. 10 is a schematic diagram of link costs of satellite No. 21 and four adjacent satellites according to Dijkstra algorithm of the present invention;

FIG. 11 is a schematic diagram of link costs of satellite No. 21 and four adjacent satellites in the DEI-LS algorithm of the present invention;

FIG. 12 is a schematic diagram of the number of hops routed between satellite No. 21 and satellite No. 25 according to the present invention;

FIG. 13 is a diagram of the number of hops between satellite 21 and satellite 55 according to the present invention;

FIG. 14 is a schematic diagram of transmission delays of satellite No. 21 and satellite No. 25 according to the present invention;

fig. 15 is a schematic diagram of transmission delays of satellite 21 and satellite 55 according to the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.

Embodiment one:

according to the method, the characteristics of the satellite network are analyzed, the situations of space debris positions, short invalidation of inter-satellite links, link propagation delay and the like are comprehensively considered, according to the visibility of adjacent satellites and link state information, direction judgment is added, the communication cost between the adjacent satellites is calculated, an effective path is dynamically calculated, the communication success rate is improved, and rerouting caused by link faults is reduced.

Referring to fig. 1-5, the method for researching the satellite optical network routing algorithm under the interference of space debris at least comprises the following steps:

establishing an LEO constellation network structure, dividing a polar orbit constellation into P orbit planes, wherein each orbit plane has the same inclination angle and the same number of Q satellites, and P multiplied by Q satellites are totally arranged, all satellites have the same orbit height, the same numbers of different orbit planes are positioned on the same horizontal plane, all orbit planes form two intersecting points in the north-south poles, each node can establish 4 inter-satellite laser links (ISI), and an ISL can be directed, acquired and tracked (PAT) maintaining link acceptably under the condition of no interference;

a space debris motion model is built, a plurality of space debris gathered around a low-orbit satellite rotates around the earth, so that the kepler model is used for approximate simulation, and the kepler model is used for analyzing the relative position relationship between the debris and the satellite along with the change of time and carrying out inter-satellite visibility analysis;

a dynamic routing algorithm is adopted on the basis of the LEO constellation network structure, so that the method is better suitable for high-speed dynamic changes of constellation topology and link information;

the method is characterized in that the method comprises the steps of selecting a link state routing algorithm of a dynamic routing algorithm, collecting link state information in real time, adding a Direction Influencing Factor (DIF) and a Direction Enhancing Index (DEI) to improve the link state algorithm, re-estimating link cost by using inter-satellite visibility, further influencing the direction pointing of a data packet in each hop, avoiding link interruption caused by space fragment shielding, selecting a proper link to meet communication requirements, reducing communication delay, improving the communication success rate of a communication system and enhancing the stability of network communication quality.

In the establishment of the LEO constellation network structure, for a polar orbit satellite network topology structure, the distance L between two satellites in orbit _v Equal length throughout, expressed as:

wherein R is the orbit radius, Q is the number of satellites on the same orbit surface;

distance L between two satellites in orbit _h Is changed along with the movement of the node, and the following steps are obtained:

L _h ＝b×cos(lat)

wherein lat is the dimension in which the track surface is located,p is the number of track surfaces for the distance between track surfaces, and it can be seen that the track distance is shortened as the latitude increases;

according to the disclosure, in the large-scale low-orbit satellite networking method and performance evaluation, the polar orbit constellation structure can be abstracted into a network model structure as shown in fig. 2;

to distinguish each satellite node, it is assigned a unique address, using<m，n>Represents the earth logical address of a satellite, where m is the orbital plane number and n is the number of the satellite in the same orbital plane, and the path from the source satellite A to the destination satellite B can be defined as P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) consists of a sequence of nodes:

P(＜m ₀ ,n ₀ ＞,＜m _I ,n _I ＞)＝{＜m ₀ ,n ₀ ＞,...,＜m _i ,n _i ＞,...＜m _I ,n _I ＞}

wherein < m _i ,n _i The address of the node passing through at present is represented by the number of the current satellite, i represents the number of the current satellite, and each hop added on the path can change m or n by a numerical value of 1;

a shortest hop-count path set between two points in the two-dimensional network comprises a longitudinal connection set and a transverse connection set;

mapping to a low-orbit satellite scene, wherein longitudinal connection is a longitudinal inter-satellite link in a track plane, and transverse connection is a lateral inter-satellite link between track planes; so that the number of path hops between source-destination A, B satellites H (P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) is defined as:

the building of the space debris movement model at least comprises the following steps:

the earth is considered as a mass celestial body of one point, and the mass of an object moving around the earth is negligible;

neglecting higher-order effects in the earth gravitational field and the environmental disturbance, expressing a motion equation by a non-inertial reference system ECEF system, and calculating to obtain the position and the speed of the space debris through six elements of the orbit;

solving by using a kepler model based on an initial position and a speed created for the space debris;

in the near-focus coordinate system, the position r of the space debris can be obtained according to the motion law of the celestial body _p And velocity v _p The method comprises the following steps:

where a is the semi-major axis, e is the eccentricity,for true near-earth angle, GM is the constant of the gravitational force, and the value is 398603 multiplied by 10 ⁹ m ³ /s ² ；

The position and velocity are scaled to the ECEF system, any point can be expressed in (x, y, z), and for the spatial debris, the scaled coordinates are expressed as:

x＝(cosl*cosω-sinl*sinω*cosθ _i ,-coslsinω-sinl*cosω*cosθ _i ,sinl*sinθ _i )

y＝(sinl*cosω+cosl*sinω*cosθ _i ,-sinl*sinω+cosl*cosω*cosθ _i ,-cosl*sinθ _i )

z＝(sinω*sinθ _i ,cosω*sinθ _i ,cosθ _i )

where l is the equatorial longitude of the intersection point, ω is the near-to-point radial angle, θ _i Is the track inclination angle;

the equation of the coordinates after conversion is brought in to obtain R= [ x, y, z]Bringing R into the formula to obtain the position R of the space debris in the ECEF system _E Equation of (v) and velocity v _E The formula of (2) is as follows:

r _E ＝R*r _p

v _E ＝R*v _p

the relationship between position and velocity and time is obtained by fourth-order Longgar-Kutta numerical integration of the equation, as shown in the following equation:

wherein, t is _n Time is expressed as y _n Representing the position and velocity of the chip at a certain moment, where r is _E Equation of (v) and velocity v _E The numerical value in the formula (I) is denoted as y _n ＝(r _E (1),v _E (1),r _E (2),v _E (2),r _E (3),v _E (3) Updating and iterating the position and the speed along with the change of time, and analyzing the relative position relationship between fragments and satellites along with the change of time to perform inter-satellite visibility analysis.

The routing algorithm research of the low orbit satellite network is carried out based on the network structure shown in fig. 2, and a dynamic routing algorithm is adopted in order to better adapt to the high-speed dynamic change of constellation topology and link information. The method is characterized in that the method comprises the steps that the blocking of fragments in a network is different from the situation of node faults needing to be repaired, space fragments are only temporarily caused to be in an invisible state, a link state routing algorithm of a dynamic routing algorithm is selected, the link state algorithm is improved by collecting link state information in real time and adding a Direction Influencing Factor (DIF) and a Direction Enhancement Index (DEI), the inter-satellite visibility is utilized to re-estimate the cost of a link, the direction pointing of a data packet in each hop is influenced, the link interruption caused by the blocking of the space fragments is avoided, and a proper link can be selected. The dynamic algorithm utilizes the real-time state of the link, can meet the communication requirement, reduce the communication delay, improve the communication success rate of a communication system and enhance the stability of the network communication quality.

The derivation of the dynamic routing algorithm comprises at least the following steps: determining a direction influence factor, determining a direction enhancement index A, determining a link cost and realizing a routing decision algorithm;

the determining the direction influence factor at least comprises the following steps:

according to the inter-satellite link direction, four influence factors are provided, which are respectively represented by N, S, W, E, and the initial values of the influence factors are all 0;

the direction influence factors are assigned only at the beginning of a task in the process of one-time task transmission, and are used for assisting in direction judgment in the forwarding process of the data packet, so that the transmission is prevented from being trapped into circulation due to the formation of a loop;

the known propagation directions are divided into straight line propagation and oblique line propagation as shown in fig. 3, the straight line propagation address < m, n > changes only one value, and the oblique line propagation causes both values in < m, n > to change;

based on the relative position relation between the source satellite and the destination satelliteDirection factor and satellite address<m，n>Correspondence between m and n, the variation of m and n being defined by n _t And m _t Representation, record n _t ＝n _i -n _o ，m _t ＝m _i -m _o ；

The change in the direction influencing factor for the two propagation directions is shown in tables 1 and 2, where < m _o ,n _o Is the address of the source node, < m _i ,n _i The address of the destination node;

TABLE 1 propagation in straight line direction

TABLE 2 diagonal propagation

Continuous table 2

The determining the direction enhancement index a comprises at least the following steps:

according to the network characteristic structure, the whole system network is disassembled into single node elements in the shape of a single crossroad, as shown in fig. 4;

obtaining the position sum of fragments obtained by the relation of the position and the speed and time through the fourth-order Longer lattice-Kutta numerical integration of the equation, obtaining the visibility data between satellites by judging whether the two satellites and the fragments are collinear at the current moment, and introducing a direction enhancement index A _i ，A _i Is an array of satellite visibility values in four directions, visible 1 and invisible 0, A _i Representing i ε { N, W, S, E };

each node A _i Refreshing the values of the data packet in t, and helping to calculate the link cost to judge the forwarding direction of the next hop of the data packet;

the determining the link cost at least comprises the following steps:

selecting a proper index to describe the cost of a network communication link according to a network optimization theory, and selecting a link cost measure capable of reflecting the dynamic property of the network through the continuous change of topology to timely reflect the state of a laser link;

the link cost L is set as follows:

wherein,delta epsilon is infinitesimal, l (A, B) is the end-to-end distance, d (A, B) is the end-to-end propagation delay, +.>c is the speed of light;

under the condition that a certain direction influence factor is the same as the enhancement index of the direction, the link cost is very low, and the direction indicated by the direction influence factor is selected preferentially;

when the direction influence factors and the direction enhancement indexes of a certain direction are different, a path with lower transmission delay is selected when a path is to be bypassed;

the routing decision algorithm implementation at least comprises the following steps:

the satellites are uniformly distributed on each orbital plane of the polar orbit constellation so that the longitudinal inter-satellite distances within the orbital planes are uniform. In polar orbit constellations, the shortest propagation delay path belongs to the smallest hop path. Therefore, the purpose of the research is to utilize direction judgment to select a link distance and a transmission delay as indexes to influence link cost and select a path with better transmission performance under the condition that the link is temporarily unavailable due to space debris interference, and take the hop count as the quality of evaluating communication performance.

Initializing, namely obtaining an adjacent matrix of a satellite network topology corresponding to initial time according to the topology of a polar orbit satellite network, wherein the adjacent matrix comprises visibility among satellites and longitude and latitude parameters of the satellites;

secondly, satellite addressing and parameter determining, namely, distributing unique unchanged logic addresses < m, n > for each satellite, obtaining the value of a direction influence factor according to the address relation between a source satellite and a destination satellite, and not changing in the transmission process;

thirdly, calculating L (t) of link cost, and obtaining visibility, direction enhancement index, direction influence factor and link distance among satellites at the current moment by considering shielding of fragments on the satellites to obtain four link cost at the moment when a data packet reaches a certain point;

fourthly, selecting a route, and utilizing the cost in the third step to perform Dijkstra algorithm to find the shortest forwarding path between the two satellites at the current time delta t;

and fifthly, circularly executing, namely repeatedly executing the third step and the fourth step when the data arrives at the next satellite until the destination node is reached, ending the transmission, and outputting a path, a total transmission delay and a total hop count.

The dynamic route implementation flow is shown in fig. 5.

Embodiment two:

referring to fig. 6-15, the present embodiment is used for further disclosing simulation verification on the premise of the above embodiment, so that the simulation result shows that in the environment where space debris exists, the DEI-LS routing algorithm can better satisfy the theoretical minimum hop count without sacrificing the communication quality, the hop count is 14% lower than that of the conventional Dijkstra algorithm, the transmission delay is 17% lower, and the proposed algorithm can better promote the communication performance when coping with space debris shielding.

Simulation environment setting:

this section builds a network model of the Walker48 constellation (constellation parameters 48/6/30:1400 km) on the satellite simulation software STK, with the environmental parameters shown in table 3. All satellite nodes included in the constellation network are shown in fig. 6, the motion trajectories of the respective satellites are shown in fig. 7, and the polar boundaries are 70 °.

TABLE 3 simulation Environment parameter settings

According to the literature MaZ, zhao Y, wang W, et al adaptive Snapshot Routing Based on Space Debris Risk Perception in Satellite Optical Networks [ C ]// International Conference on Optical Network Design and modeling IEEE,2021.9492513, authors divide the impact of the patches on the link into three risks, classifying 3% of the patches by machine learning will put the link in a high risk state, and based on the number of patches with a size of 3 ten thousand patches exceeding 10cm, 1000 space patches in the simulation environment are set for simplifying the calculation, tracking them, and if the two satellites are collinear, the link is considered to be blocked from communication, and no more distinction is made. Fig. 8 shows the positions of 1000 fragments obtained by simulation at a certain time.

The track of the fragments is irregular, there may be a plurality of fragments interfering with the same link, if tracking is performed from the fragment angle, the visibility between satellites can be judged according to the obtained position and velocity vector, and fig. 9 is a diagram showing the availability of 95 links in the network at a certain moment, at which time, the dead links occupy about 10% in the whole network due to the fragment shielding.

In order to analyze the influence of the relative position relation of the source and the destination satellites on the routing performance, communication tasks of the No. 21 satellite and the No. 25 satellite and communication tasks of the No. 21 satellite and the No. 55 satellite are selected, the simulation time is 15 minutes, and the tasks are transmitted once every other minute.

Fig. 10 and 11 show the link costs of the satellite 21 communicating with four adjacent satellites at the start time of performing co-orbit transmission and off-orbit transmission by comparing the DEI-LS algorithm with the Dijkstra algorithm, respectively, and it can be seen that the obtained link costs are not exactly the same even when the same satellite node performs different task transmission due to the introduction of the direction influencing factor and the direction enhancing index. For Dijkstra's algorithm, only the link distance is considered as an indicator.

For the DEI-LS algorithm, when the satellites on the same orbit surface carry out linear propagation (21-25), the communication with the satellites No. 31 and No. 11 is not the transmission direction of the theoretical shortest path, and the link cost is the sum of the link distance and the transmission delay; the satellite number 28 and the satellite number 22 are both the transmission directions of the theoretical shortest path, but the cost of the link number 28 is much lower than that of the link number 22, and the result of direction selection can be seen that the link in the transmission direction of the satellite number 22 can be blocked by space debris.

When the satellite with the different orbit surface carries out oblique line propagation (21-55), the direction influencing factors E and S are 1, the communication with the satellite 28 and the satellite 11 is not the transmission direction of the theoretical shortest path, and the link cost is the sum of the link distance and the transmission delay; and satellites No. 31 and No. 22 are the transmission directions of the theoretical shortest path, and the cost of both links is very low, which proves that no shielding can occur, so that the transmission direction with lower time delay is preferentially selected.

Fig. 12 and 13 show the change in the number of hops over route for two transmissions, respectively, for the DEI-LS algorithm compared to the conventional Dijkstra algorithm. The simulation result shows that the DEI-LS algorithm has fewer hops than the Dijkstra algorithm no matter whether the source satellite and the destination satellite are in the same orbit, and can be well maintained to the theoretical minimum hops even if the routing hops of the Dijkstra algorithm are increased, and the average hops of the DEI-LS algorithm are 20% lower than those of the Dijkstra algorithm.

The transmission delays of two task propagation of the same track and different track are shown in the following figures 14 and 15, and in the same track plane transmission, the average transmission delay of the DEI-LS algorithm is 20% lower than that of the traditional Dijkstra algorithm; in the transmission of the different channel surface, the average transmission delay of the DEI-LS algorithm is 13% lower than that of the traditional Dijkstra algorithm.

In consideration of time-varying changes of space debris and topology of LEO constellation, an environment model of space debris causing inter-satellite laser link interruption is established in a satellite laser communication system, and an improved link state routing algorithm (DEI-LS) with direction enhancement is provided, wherein the algorithm analyzes inter-satellite visibility through real-time debris positions, performs direction enhancement forwarding when debris is shielded, and can effectively avoid a fault link without affecting communication quality. The simulation is compared with the traditional Dijkstra algorithm, so that the routing hop count of the algorithm can be basically consistent with the theoretical minimum hop count, the hop count is reduced by 14% compared with the Dijkstra algorithm, and the transmission delay is reduced by 17%. The link state routing algorithm with the enhanced direction, which is proposed by considering the influence of space debris, can better solve the network instability condition caused by link interruption on the premise of not influencing the communication quality.

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 characteristics 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.

Claims (8)

1. The method for researching the satellite optical network routing algorithm under the interference of space debris is characterized by comprising the following steps of: at least comprises the following steps:

establishing an LEO constellation network structure, dividing a polar orbit constellation into P orbit planes, wherein each orbit plane has the same inclination angle and the same number of Q satellites, and P multiplied by Q satellites are totally arranged, all satellites have the same orbit height, the same numbers of different orbit planes are positioned on the same horizontal plane, all orbit planes form two intersecting points in the north-south poles, each node can establish 4 inter-satellite laser links, and an ISL can acceptably point, acquire and track and keep the links under the condition of no interference;

establishing a space debris movement model, using a kepler model to approximate the simulation, and analyzing the relative position relationship between the debris and the satellite along with the time change to perform inter-satellite visibility analysis;

a dynamic routing algorithm is adopted on the basis of the LEO constellation network structure, so that the method is better suitable for high-speed dynamic changes of constellation topology and link information;

the link state routing algorithm of the dynamic routing algorithm is selected, the link state algorithm is improved by collecting link state information in real time and adding a direction influencing factor and a direction enhancing index, the link cost is estimated again by utilizing inter-satellite visibility, the direction of a data packet in each hop is further influenced, the link interruption caused by space fragment shielding is avoided, a proper link can be selected to meet the communication requirement, the communication time delay is reduced, the communication success rate of a communication system is improved, and the stability of the network communication quality is enhanced.

2. The method for researching a satellite optical network routing algorithm under the interference of space debris according to claim 1, wherein the method comprises the following steps: in the establishment of the LEO constellation network structure, for a polar orbit satellite network topology structure, the distance L between two satellites in orbit _v Equal length throughout, expressed as:

wherein R is the orbit radius, Q is the number of satellites on the same orbit surface;

distance L between two satellites in orbit _h Is changed along with the movement of the node, and the following steps are obtained:

L _h ＝b×cos(lat)

wherein lat is the dimension in which the track surface is located,p is the number of track surfaces for the distance between track surfaces, and it can be seen that the track distance is shortened with increasing latitude;

abstracting a polar orbit constellation structure into a network model structure;

to distinguish each satellite node, it is assigned a unique address, using<m，n>Represents the ground logical address of a satellite, where m is the orbital plane number and n is the number of the satellite in the same orbital plane, the path from the source satellite A to the destination satellite BCan be defined as P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) consists of a sequence of nodes:

P(＜m ₀ ,n ₀ ＞,＜m _I ,n _I ＞)＝{＜m ₀ ,n ₀ ＞,...,＜m _i ,n _i ＞,...＜m _I ,n _I ＞}

wherein < m _i ,n _i The address of the node which passes through at present is represented by the number of the current satellite, i represents the number of the current satellite, and each hop added on the path can change one of m and n by a value of 1;

a shortest hop-count path set between two points in the two-dimensional network comprises a longitudinal connection set and a transverse connection set;

mapping to a low-orbit satellite scene, wherein longitudinal connection is a longitudinal inter-satellite link in a track plane, and transverse connection is a lateral inter-satellite link between track planes; so that the number of path hops between source-destination A, B satellites H (P (< m) ₀ ,n ₀ ＞,＜m _I ,n _I >) is defined as:

3. the method for researching a satellite optical network routing algorithm under the interference of space debris according to claim 1, wherein the method comprises the following steps: the building of the space debris movement model at least comprises the following steps:

the earth is considered as a mass celestial body of one point, and the mass of an object moving around the earth is negligible;

neglecting higher-order effects in the earth gravitational field and the environmental disturbance, expressing a motion equation by a non-inertial reference system ECEF system, and calculating to obtain the position and the speed of the space debris through six elements of the orbit;

solving by using a kepler model based on an initial position and a speed created for the space debris;

in the near-focus coordinate system, the position r of the space debris can be obtained according to the motion law of the celestial body _p And velocity v _p The method comprises the following steps:

where a is the semi-major axis, e is the eccentricity,for true near-earth angle, GM is the constant of the gravitational force, and the value is 398603 multiplied by 10 ⁹ m ³ /s ² ；

The position and velocity are scaled to the ECEF system, any point can be expressed in (x, y, z), and for the spatial debris, the scaled coordinates are expressed as:

x＝(cosl*cosω-sinl*sinω*cosθ _i ,-coslsinω-sinl*cosω*cosθ _i ,sinl*sinθ _i )

y＝(sinl*cosω+cosl*sinω*cosθ _i ,-sinl*sinω+cosl*cosω*cosθ _i ,-cosl*sinθ _i )

z＝(sinω*sinθ _i ,cosω*sinθ _i ,cosθ _i )

where l is the equatorial longitude of the intersection point, ω is the near-to-point radial angle, θ _i Is the track inclination angle;

the equation of the coordinates after conversion is brought in to obtain R= [ x, y, z]Bringing R into the formula to obtain the position R of the space debris in the ECEF system _E Equation of (v) and velocity v _E The formula of (2) is as follows:

r _E ＝R*r _p

v _E ＝R*v _p

the relationship between position and velocity and time is obtained by fourth-order Longgar-Kutta numerical integration of the equation, as shown in the following equation:

wherein, t is _n Time is expressed as y _n Representing the position and velocity of the chip at a certain moment, where r is _E Equation of (v) and velocity v _E The numerical value in the formula (I) is denoted as y _n ＝(r _E (1),v _E (1),r _E (2),v _E (2),r _E (3),v _E (3) Updating and iterating the position and the speed along with the change of time, and analyzing the relative position relationship between fragments and satellites along with the change of time to perform inter-satellite visibility analysis.

4. A method for studying a satellite optical network routing algorithm under the interference of space debris according to claim 3, wherein: the derivation of the dynamic routing algorithm comprises at least the following steps: determining a direction influence factor, determining a direction enhancement index A, determining a link cost and realizing a routing decision algorithm.

5. The method for researching a satellite optical network routing algorithm under space debris interference according to claim 4, wherein the method comprises the following steps: the determining the direction influence factor at least comprises the following steps:

according to the inter-satellite link direction, four influence factors are provided, which are respectively represented by N, S, W, E, and the initial values of the influence factors are all 0;

the direction influence factors are assigned only at the beginning of a task in the process of one-time task transmission, and are used for assisting in direction judgment in the forwarding process of the data packet, so that the transmission is prevented from being trapped into circulation due to the formation of a loop;

the known propagation direction is divided into straight line propagation and oblique line propagation, wherein the straight line propagation address < m, n > only changes one value, and the oblique line propagation causes both values in < m, n > to change;

giving direction factor and satellite address according to the relative position relation of source satellite and destination satellite<m，n>Correspondence between m and n, the variation of m and n being defined by n _t And m _t Representation ofRecord n _t ＝n _i -n _o ，m _t ＝m _i -m _o ；

Wherein < m _o ,n _o Is the address of the source node, < m _i ,n _i Is the address of the destination node.

6. The method for researching a satellite optical network routing algorithm under space debris interference according to claim 5, wherein the method comprises the following steps: the determining the direction enhancement index a comprises at least the following steps:

according to the network characteristic structure, the whole system network is disassembled into single node elements in the shape of a single crossroad;

obtaining the position sum of fragments obtained by the relation of the position and the speed and time through the fourth-order Longer lattice-Kutta numerical integration of the equation, obtaining the visibility data between satellites by judging whether the two satellites and the fragments are collinear at the current moment, and introducing a direction enhancement index A _i ，A _i Is an array of satellite visibility values in four directions, visible 1 and invisible 0, A _i Representing i ε { N, W, S, E };

each node A _i The value of the data packet is refreshed in t, and the data packet is used for assisting in accounting the link cost to judge the forwarding direction of the next hop of the data packet.

7. The method for researching a satellite optical network routing algorithm under space debris interference according to claim 6, wherein the method comprises the following steps: the determining the link cost at least comprises the following steps:

selecting a proper index to describe the cost of a network communication link according to a network optimization theory, and selecting a link cost measure capable of reflecting the dynamic property of the network through the continuous change of topology to timely reflect the state of a laser link;

the link cost L is set as follows:

wherein,delta epsilon is infinitesimal, l (A, B) is the end-to-end distance, d (A, B) is the end-to-end propagation delay, +.>c is the speed of light;

under the condition that a certain direction influence factor is the same as the enhancement index of the direction, the link cost is very low, and the direction indicated by the direction influence factor is selected preferentially;

when the direction influencing factor and the direction enhancement index of a certain direction are different, a path with lower transmission delay is selected when the path is to be bypassed.

8. The method for researching a satellite optical network routing algorithm under space debris interference according to claim 7, wherein: the routing decision algorithm implementation at least comprises the following steps:

initializing, namely obtaining an adjacent matrix of a satellite network topology corresponding to initial time according to the topology of a polar orbit satellite network, wherein the adjacent matrix comprises visibility among satellites and longitude and latitude parameters of the satellites;

secondly, satellite addressing and parameter determining, namely, distributing unique unchanged logic addresses < m, n > for each satellite, obtaining the value of a direction influence factor according to the address relation between a source satellite and a destination satellite, and not changing in the transmission process;

thirdly, calculating L (t) of link cost, and obtaining visibility, direction enhancement index, direction influence factor and link distance among satellites at the current moment by considering shielding of fragments on the satellites to obtain four link cost at the moment when a data packet reaches a certain point;

fourthly, selecting a route, and utilizing the cost in the third step to perform Dijkstra algorithm to find the shortest forwarding path between the two satellites at the current time delta t;

and fifthly, circularly executing, namely repeatedly executing the third step and the fourth step when the data arrives at the next satellite until the destination node is reached, ending the transmission, and outputting a path, a total transmission delay and a total hop count.