Topology optimization device, topology optimization method, and program
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2025-07-01
- Publication Date
- 2026-08-06
Smart Images
Figure JP2025023757_06082026_PF_FP_ABST
Abstract
Description
Topology Optimization Device, Topology Optimization Method, and Program
[0001] The present disclosure relates to a topology optimization device, a topology optimization method, and a program.
[0002] In a satellite constellation, in order to construct an inter-satellite network using multiple satellites orbiting along a circular orbit, the use of free space optical communication with high confidentiality and capable of realizing high-capacity communication has been considered. Since free space optical communication is one-to-one communication, topology design is required to determine which satellites are connected to each other and what kind of inter-satellite network is constructed. On the other hand, Non-Patent Document 1 and Non-Patent Document 2 disclose methods for optimizing the topology of an inter-satellite network.
[0003] In the method described in Non-Patent Document 1, based on a probabilistic combinatorial optimization algorithm, the position and velocity of satellites are calculated for each time, the evaluation of visibility constraints and the minimum inter-satellite distance are calculated, and the evaluation of constraints is performed over the entire time. If a violation occurs, a new solution is searched, and the topology of the inter-satellite network is optimized by repeating until the constraints are satisfied and the stopping condition is satisfied.
[0004] In the method described in Non-Patent Document 2, based on a probabilistic combinatorial optimization algorithm, the position and velocity of satellites are calculated for each time, the evaluation of visibility constraints and communication number constraints and the minimum inter-satellite distance are calculated, a graph is constructed with satellites as nodes and inter-satellite links as edges, and the evaluation of the topology is performed based on the evaluation result of the constraints and the positions between satellites. If a violation occurs, a new solution is searched, and the topology of the inter-satellite network is optimized by repeating until the constraints are satisfied and the stopping condition is satisfied.
[0005] Jian Tai, 6 others, “Topology Optimization Design of LEO Satellite Network”, Cybersecurity and Cyberforensics, July 1, 2019 W. Chengzhuo, 3 others, “Dynamic optimization of laser inter-satellite link network topology based on genetic algorithm”, IEEE International Conference on Electronic Measurement & Instruments, November 1, 2019
[0006] The technologies described in Non-Patent Documents 1 and 2 do not consider the disruption of communication links due to interference between sunlight and optical communication terminals mounted on satellites when optimizing the topology of intersatellite networks. In particular, in satellite constellations in asynchronous solar orbits, the relationship between the orbital plane and the angle of incidence of sunlight changes depending on the time, so the locations where communication links are disrupted also change. There is a risk that the intersatellite links assigned as a topology may actually be disrupted by solar interference, leading to isolation from the intersatellite network and an increased latency.
[0007] This disclosure was made to solve the problems described above, and aims to reduce the risk of satellite isolation from the inter-satellite network and the risk of increased latency in inter-satellite communication within the orbital plane of a free-space optical communication device.
[0008] To achieve the above objective, the topology optimization device according to this disclosure optimizes the topology of an inter-satellite network consisting of multiple satellites orbiting along an orbit and equipped with free-space optical communication devices. The topology optimization device includes an optimization calculation unit. Based on position and velocity information indicating the position and velocity of satellites over a predetermined period of one or more orbits, and solar direction information indicating the history of the incident direction of sunlight, the optimization calculation unit calculates whether it satisfies a solar interference constraint, which is a condition that the angle between the relative direction between satellites and the direction of the sun does not fall within the no-receiving angle of the free-space optical communication device, and a line-of-sight constraint, which is a condition that the shortest distance between the line segments between satellites and the Earth surface is greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored. From among the candidate topologies of the inter-satellite network, it constructs a connection graph in which satellites are used as nodes and pairs of satellites that satisfy the solar interference constraint and line-of-sight constraint are connected as edges. For the constructed connection graph, weights based on the distance between satellites are set on the edges, and based on the connection graph with weights set on the edges, it optimizes the topology of the inter-satellite network using an optimization algorithm.
[0009] According to this disclosure, in inter-satellite communication using free-space optical communication equipment within the orbital plane of a satellite in orbit, optimizing the topology of the inter-satellite network while considering solar interference makes it possible to reduce the risk of satellite isolation from the inter-satellite network and the risk of increased latency.
[0010] Figure showing an example of the functional configuration of the topology optimization device according to Embodiment 1. Flowchart showing the topology optimization process according to Embodiment 1. Figure showing the patrol process on the intersatellite network according to Embodiment 4. Figure showing the patrol process on the adjacency matrix according to Embodiment 4. Flowchart showing the topology optimization process according to Embodiment 4. Figure showing the azimuth angle and elevation angle pattern indicating the communication range of the LCT according to Embodiment 6. Figure showing an example of the hardware configuration of the topology optimization device according to Embodiments 1 to 6.
[0011] The topology optimization apparatus, topology optimization method, and program according to this embodiment will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.
[0012] (Embodiment 1) The configuration of the topology optimization device 1 according to Embodiment 1 will be described with reference to Figure 1. The topology optimization device 1 optimizes the topology of an inter-satellite network that performs inter-satellite communication within the orbital plane of a solar asynchronous orbit. A solar asynchronous orbit is an example of an orbit. The satellite is equipped with a free-space optical communication device (LCT: Laser Communication Terminal) and can connect to other satellites equal to the number of LCTs. The LCT points in the direction of the target satellite as seen from itself, and communication is disconnected if the angle between the direction the LCT points and the sunlight is within the no-receiving angle. Hereinafter, the topology of the inter-satellite network will be referred to as the network topology.
[0013] Figure 1 is a diagram showing an example of the functional configuration of the topology optimization device 1 according to Embodiment 1. As shown in Figure 1, the topology optimization device 1 includes a position velocity information acquisition unit 11 that acquires position velocity information indicating the position and velocity of a satellite over a predetermined period of one or more orbits in an asynchronous solar orbit, a position velocity information storage unit 12 that stores the position velocity information, a solar direction information acquisition unit 13 that acquires solar direction information indicating the history of the incident direction of sunlight, a solar direction information storage unit 14 that stores the solar direction information, an optimization calculation unit 15 that optimizes the network topology based on the position velocity information and the solar direction information, and a network topology output unit 16 that outputs network topology information indicating the optimized network topology.
[0014] The position and velocity information acquisition unit 11 acquires position and velocity information indicating the position and velocity of a satellite within the orbital plane for a predetermined period of one or more orbits in an asynchronous solar orbit, and stores it in the position and velocity information storage unit 12. The solar direction information acquisition unit 13 acquires solar direction information indicating the history of the direction of incident sunlight, and stores it in the solar direction information storage unit 14. The position and velocity information and solar direction information may be acquired, for example, from the satellite, from an external device or system, or input by the user.
[0015] The optimization calculation unit 15 performs optimization processing to optimize the network topology based on position and velocity information and sunlight direction information. Specifically, the optimization calculation unit 15 generates vector variables using random numbers that represent which satellites establish links with which other satellites, and generates initial candidate network topologies. The number of vector variables to be generated is determined by the number of satellites. At this time, in order to generate a solution space that excludes connection candidates that deviate significantly from the line-of-sight constraint, for links within the orbital plane, only a few satellites in front of and behind the current satellite may be selected as connection candidates in advance, and upper and lower limits that take into account not only the number of satellites but also the line-of-sight constraint may be given to the vector variables to be generated.
[0016] The optimization calculation unit 15 calculates an evaluation value for each candidate network topology based on position and velocity information and solar direction information. Specifically, the optimization calculation unit 15 converts the vector variables into an adjacency matrix for each candidate network topology. At each time step, the optimization calculation unit 15 constructs a connection graph based on the adjacency matrix obtained by converting the vector variables, with each satellite as a node and the links between satellites as edges, and weights based on the distance between satellites set for the edges. For the obtained connection graph, it performs a process to calculate an evaluation value based on the weights of the edges and constraint values of pre-set constraints. The optimization calculation unit 15 takes the worst-case value of the final evaluation value, obtained by linearly combining the evaluation value for the connection graph at each time step of a predetermined period and the constraint value as a penalty term, as the evaluation value for the candidate network topology. If there are X constraints, the final evaluation value of the connection graph = evaluation value + constraint value = a1 * value of the evaluation function + a2 * penalty term for constraint 1 + a3 * penalty term for constraint 2 + ... + a(X + 1) * penalty term for constraint X. a1 to a(X+1) are weighting coefficients. In this case, when calculating the final evaluation value by combining the evaluation value and the penalty term, the relative weights of the evaluation value and the penalty term may be changed according to the progress of optimization.
[0017] In the method for constructing a connection graph according to Embodiment 1, first, the direction of sunlight and the positions and velocities of all satellites are calculated. Next, for each pair of satellites, a determination result is calculated to determine whether the following conditions are met: a solar interference constraint, which requires that the angle between the relative direction between satellites and the direction of the sun does not fall within the no-receiving angle of the LCT; and a line-of-sight constraint, which requires that the shortest distance between the line segment between satellites and the Earth's surface is greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored. The entire inter-satellite network is treated as a single connection graph, and a connection graph is constructed by connecting only the pairs of satellites that satisfy the solar interference constraint and the line-of-sight constraint as edges among the candidate network topology.
[0018] The optimization calculation unit 15 uses the candidate network topology for which an evaluation value has been obtained to find a candidate for the next generation network topology by binomial crossover, performs the above processing to calculate the evaluation value of the next generation candidate, and updates the current generation to the candidate with the higher evaluation value among the current generation and next generation candidates. The termination conditions for the iterative process of calculating the evaluation value of the network topology candidate and updating to the candidate with the higher evaluation value are, for example, when the number of iterations of the above process reaches a predetermined number of iterations, when the evaluation value of the candidate becomes smaller than a threshold, when the change in the evaluation value of the candidate is less than a threshold, or when the evaluation value of the candidate becomes smaller than a threshold AND the change in the evaluation value of the candidate is less than a threshold. When the termination conditions are met, the optimization calculation unit 15 terminates the process.
[0019] The network topology output unit 16 outputs network topology information showing the optimized network topology. The network topology information may be output by, for example, displaying it on a screen or transmitting it to a terminal used by the user. Alternatively, the network topology information may be used as information indicating the target satellite for each satellite based on the optimized network topology, and the network topology information may be transmitted to the satellite. In this case, the satellite adjusts the direction of the LCT's aiming direction to the direction of the target satellite based on the received network topology information.
[0020] Here, the flow of the topology optimization process performed by the optimization calculation unit 15 of the topology optimization device 1 will be explained using Figure 2. The topology optimization process shown in Figure 2 starts, for example, when an optimization instruction for the network topology is input to the topology optimization device 1. Before the topology optimization process starts, it is assumed that position velocity information and sunlight direction information are stored in the position velocity information storage unit 12 and the sunlight direction information storage unit 14 of the topology optimization device 1, respectively.
[0021] The optimization calculation unit 15 generates vector variables using random numbers to represent which satellites establish links with which other satellites, and generates initial candidate network topologies (step S11). The optimization calculation unit 15 converts the candidate network topology vector variables into an adjacency matrix (step S12). The optimization calculation unit 15 sets an initial time (step S13). The optimization calculation unit 15 obtains position velocity information and solar direction information for the set time from the position velocity information storage unit 12 and the solar direction information storage unit 14, respectively (step S14). Based on the adjacency matrix obtained by converting the vector variables, the optimization calculation unit 15 constructs a connection graph with each satellite as a node and the links between satellites as edges, and sets weights based on the distance between satellites for the edges (step S15), and calculates evaluation values and constraint values for the obtained connection graph (step S16).
[0022] If evaluation values and constraint values have not been calculated for all time points (step S17; NO), the optimization calculation unit 15 updates the time points (step S18). The process returns to step S14, and steps S14 to S17 are repeated. Once evaluation values and constraint values have been calculated for all time points (step S17; YES), the optimization calculation unit 15 calculates the worst-case value obtained by linearly combining the evaluation values and constraint values for the connection graph at each time point as a penalty term, and uses that value as the evaluation value for the candidate network topology (step S19). If there is an evaluation value for a previous network topology candidate, it updates to a candidate with a higher evaluation value (step S20).
[0023] If the termination condition for the iterative process is not met (step S21; NO), the optimization calculation unit 15 uses the candidate network topology for which the evaluation value was obtained to find the next generation candidate by binomial crossover (step S22), and the process returns to step S17, repeating steps S17 to S21. When the termination condition for the iterative process is met (step S21; YES), the optimization calculation unit 15 terminates the process.
[0024] According to the topology optimization device 1 of Embodiment 1, in inter-satellite communication within the orbital plane of a solar asynchronous orbit using a free-space optical communication device, optimizing the network topology while considering solar interference makes it possible to reduce the risk of satellites becoming isolated from the inter-satellite network and the risk of increased latency.
[0025] (Embodiment 2) In Embodiment 1, the worst-case final evaluation value obtained by linearly combining the evaluation value for the connection graph at each time point in a predetermined period with the constraint value as a penalty term was used as the evaluation value for the network topology candidate. In Embodiment 2, however, a connection component constraint is added to the constraint value as a penalty term, which is conditional on the number of connected components being 1. The differences between Embodiment 2 and Embodiment 1 will be described below.
[0026] The edge weights shall be set based on at least one metric, such as network link stability, communication speed, or communication latency. Alternatively, in evaluating the connection graph, the connection graph weights may be fixed times that simulate the geometric time and number of hops required to transmit the inter-satellite distance. For example, the latency represented by the following equation 1 shall be used as the evaluation value for the connection graph.
[0027]
[0028] In Math 1, let L(i,j) be an edge, c be the speed of light, Tdelay be a fixed delay time due to satellites, and x(i,j) be a binary variable representing the satellites in the path. Let E∈{0,1}(NS×NS) be the binary variable matrix of the adjacency matrix representing the assignment as a search variable. The weight of each edge in the connection graph is L(i,j) / c + Tdelay, and the overall evaluation value of the connection graph is expressed in Math 1.
[0029] Since the connected component of a connection graph can be 1 or greater, the connected component - 1 is added as a constraint value and treated as a penalty term. Note that the connected component constraint is not limited to a penalty term that adds the connected component - 1 as a constraint value; it may also be a penalty term that returns 0 when the connected component = 1 and 1 when the connected component > 1.
[0030] The worst-case scenario of the shortest path problem for all points at an edge can be used as the evaluation value for the connection graph. In this case, if there are unreachable paths, a penalty term is added to the evaluation value, which can be a very large value or a constraint value calculated from the constraints.
[0031] According to the topology optimization device 1 of Embodiment 2, by adding a connected component constraint to the penalty term, which requires that the connected component be 1, it is possible to suppress the isolation of satellites from the inter-satellite network and reduce the possibility that satellites will be unable to transmit information.
[0032] (Embodiment 3) In Embodiment 2, a constraint value with a connection component constraint, which is conditional on the number of connected components being 1, was used as a penalty term, and the final evaluation value was calculated for the connection graph by a linear combination of the evaluation value based on latency and the constraint value of this penalty term. In Embodiment 3, however, a constraint value of the number of communications, which is conditional on the number of LCTs required in the candidate network topology not deviating from the number of LCTs mounted on each satellite, is added to the constraint value used as the penalty term. The differences between Embodiment 3 and Embodiment 2 will be described below.
[0033] In the evaluation function for the connectivity graph, a penalty term is added to the evaluation value based on edge weights, along with a penalty term for when the number of LCTs required for a candidate network topology deviates from the number of LCTs on each satellite. The communication count constraint is, for example, a penalty term that returns 0 if the number of LCTs required for a candidate network topology does not deviate from the number of LCTs on each satellite, and 1 otherwise. The final evaluation value is obtained by linearly combining the evaluation value and the constraint values of each penalty term.
[0034] According to the topology optimization device 1 of Embodiment 3, by adding a communication line limit to the penalty clause, the possibility that a satellite may not be able to establish a link due to an insufficient number of LCTs can be reduced.
[0035] (Embodiment 4) In Embodiment 3, the network topology was evaluated for all orbital planes. In Embodiment 4, when the number of satellites on all orbital planes of multiple asynchronous solar orbits is the same, a connection graph is constructed by setting edge weights for all satellites on all orbital planes from a candidate network topology for one orbital plane of asynchronous solar orbits. A cyclic process is performed to generate a new connection graph by moving the nodes to adjacent orbital planes while keeping the positional relationships of the nodes and the connection relationships of the edges of this connection graph fixed. The cyclic process is repeated to generate a connection graph for all satellites on all orbital planes of asynchronous solar orbits. The cyclic process will be explained using Figure 3. In the example in Figure 3, a new connection graph G2 is generated by moving the nodes to adjacent orbital planes while keeping the positional relationships of the nodes and the connection relationships of the edges of connection graph G1, which connects the nodes of three satellites, fixed. Similarly, a new connection graph G3 is generated by moving the nodes to adjacent orbital planes while keeping the positional relationships of the nodes and the connection relationships of the edges of connection graph G2 fixed.
[0036] As an example of cyclic processing, if the connection graph is represented by the adjacency matrix, the state of the connection graph in the first orbital plane is offset by the number of satellites in the orbital plane, and the entire offset up to the last satellite is used to generate a new connection graph that becomes the connection graph of the adjacent second orbital plane. Weights are set for the edges of the connection graph and the new connection graph, and a calculation is performed to optimize the network topology based on the connection graph with weights set for all edges.
[0037] Specifically, the optimization calculation unit 15 calculates an adjacency matrix for the entire network graph from candidate vector variables of the network topology. At this time, if the number of orbital planes is L, the optimization calculation unit 15 repeats a cyclic process L times in which it replaces the elements of the matrix with the position moved (M, M) when the number of satellites in the orbital plane is M. When the number of satellites in the orbital plane is M, it replaces the elements of the matrix with the position moved (M, M). If the index of each axis at the destination exceeds the number of satellites, it starts from 1. In the example in Figure 4, M = 3, and the element "1" in the matrix of satellites S1 and S2 in the first orbital plane is moved (3, 3) and replaced with "1" in the matrix of satellites S4 and S5 in the second orbital plane. Based on the adjacency matrix obtained by repeating the cyclic process L times, the optimization calculation unit 15 performs the optimization process of Embodiment 3.
[0038] Here, the flow of the topology optimization process performed by the optimization calculation unit 15 of the topology optimization device 1 will be explained using Figure 5. Steps S31 to S38 and S42 to S44 of the topology optimization process shown in Figure 5 are the same as steps S11 to S18 and S20 to S22, respectively, so their explanation will be omitted.
[0039] The optimization calculation unit 15 calculates evaluation values and constraint values for the connection graph for all time points, and then performs a topology traversal process to generate a new connection graph by moving the nodes to adjacent orbital planes while keeping the positional relationships of the nodes in the connection graph and the connection relationships of the edges fixed, and moving the fixed state relatively (step S39). If the termination condition for the traversal process is not met (step S40; NO), the process returns to step S33, and steps S33 to S40 are repeated. If the termination condition for the traversal process is met (step S40; YES), the optimization calculation unit 15 uses the evaluation values for the entire period of the orbital plane traversal to calculate the worst value, average value, or other values obtained from other processes as the evaluation values for the entire period of the traversal of all orbital planes (step S41).
[0040] In embodiments 1 to 3, in asynchronous solar orbits, the direction of sunlight changes by 360° for each orbital plane. Therefore, it is necessary to set the optimal topology using the history of the entire period of several years during which the direction of sunlight changes by 360°. However, according to the topology optimization device 1 of embodiment 4, instead of the direction of sunlight, the topology is evaluated by cycling through it for each orbital plane. Due to the symmetry of the constellation shape, it is only necessary to use the orbital history for a certain period at a certain time, thereby reducing computational cost and data volume.
[0041] (Embodiment 5) In Embodiment 4, for a candidate network topology, a connection graph was constructed for all satellites on the orbital plane of a solar asynchronous orbit by connecting only pairs of satellites that satisfy the solar interference constraint and line-of-sight constraint as edges. However, in Embodiment 5, in addition to the solar interference constraint and line-of-sight constraint, a tracking rate constraint is added, which is a condition that the required angular velocity of the LCT drive mechanism for tracking each other, calculated based on the relative position vector and relative velocity vector between satellites, does not exceed the maximum angular velocity that the LCT drive mechanism can achieve. In addition, a connection graph is constructed by connecting only pairs of satellites that satisfy the solar interference constraint, line-of-sight constraint and tracking rate constraint as edges. The differences between Embodiment 5 and Embodiment 4 will be described below.
[0042] In the method for constructing the connection graph according to Embodiment 5, first, the direction of sunlight and the positions and velocities of all satellites are calculated. Next, for all pairs of satellites, a determination result is calculated to determine whether the following conditions are met: a solar interference constraint, which is that the angle between the relative direction between satellites and the direction of the sun does not fall within the no-receiving angle of the LCT; a line-of-sight constraint, which is that the shortest distance between the line segment between satellites and the Earth's surface is greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored; and a tracking rate constraint, which is that the required angular velocity of the LCT drive mechanism for tracking each other, calculated based on the relative position vector and relative velocity vector between satellites, does not exceed the maximum angular velocity that the LCT drive mechanism can achieve.
[0043] When the relative position vector between satellites is dr and the relative velocity vector is dv, the required angular velocity of the drive mechanism of the LCT for tracking each other's satellites is expressed by the following equation (2).
[0044]
[0045] Regarding the entire satellite network as a single connected graph, among the candidates of the network topology, only the pairs of satellites that satisfy the sunlight interference constraint, the line-of-sight constraint, and the tracking rate constraint are connected as edges to construct a connected graph.
[0046] According to the topology optimization device 1 according to Embodiment 5, by constructing a connected graph with the addition of the tracking rate constraint, it is possible to reduce the possibility that the satellite cannot establish a link because the required angular velocity of the drive mechanism of the LCT for tracking each other's satellites exceeds the allowable tracking angular velocity of the LCT.
[0047] (Embodiment 6) In Embodiment 5, for the candidates of the network topology, only the pairs of satellites that satisfy the sunlight interference constraint, the line-of-sight constraint, and the tracking rate constraint are connected as edges, and a connected graph is constructed for all the satellites on all the orbital planes of the sun-synchronous orbit. However, in Embodiment 6, to the sunlight interference constraint, the line-of-sight constraint, and the tracking rate constraint, a drivable angle constraint is added on the condition that the angle formed by the relative position vector direction and the pointing direction of the reference LCT at the reference mounting angle on the mounting surface is within the drivable angle of the LCT. Only the pairs of satellites that satisfy the sunlight interference constraint, the line-of-sight constraint, the tracking rate constraint, and the drivable angle constraint are connected as edges to construct a connected graph. Hereinafter, the differences from Embodiment 5 of Embodiment 6 will be described.
[0048] In the method for constructing a connection graph according to Embodiment 6, first, the direction of sunlight and the positions and velocities of all satellites are calculated. Next, for all pairs of satellites, a determination result is calculated to determine whether the following conditions are met: a solar interference constraint, which is conditional on the angle between the relative direction between satellites and the direction of the sun not falling within the LCT's no-receiving angle; a line-of-sight constraint, which is conditional on the shortest distance between the line segment between satellites and the Earth's surface being greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored; a tracking rate constraint, which is conditional on the LCT's allowable tracking angular velocity not exceeding a threshold based on the relative position vector and relative velocity vector; and a drivable angle constraint, which is conditional on the angle between the relative position vector direction and the directional direction of the reference LCT at the reference mounting angle on the mounting surface being within the LCT's drivable angle. The entire inter-satellite network is treated as a single connection graph, and among the candidate network topology, only pairs of satellites that satisfy the solar interference constraint, line-of-sight constraint, tracking rate constraint, and drivable angle constraint are connected as edges to construct the connection graph.
[0049] As shown in Figure 6, the driveable angle constraint may be defined as a pattern of azimuth and elevation angles that allows communication in both directions without obstruction by the satellite's structure relative to the LCT's reference pointing direction, and the driveable angle constraint may be determined by whether or not the relative position vector direction is located within this pattern. In the example in Figure 6, the shaded area represents the communication range.
[0050] According to the topology optimization device 1 of Embodiment 6, by constructing a connection graph with a constraint on the driveable angle, it is possible to reduce the possibility that the satellite will not be able to establish a link because the angle between the relative position vector direction and the directional direction of the reference LCT at the reference mounting angle on the mounting surface exceeds the driveable angle of the LCT.
[0051] The hardware configuration of the topology optimization device 1 will be explained using Figure 7. As shown in Figure 7, the topology optimization device 1 includes a temporary storage unit 301, a storage unit 302, a calculation unit 303, an input unit 304, a transmitting / receiving unit 305, and a display unit 306. The temporary storage unit 301, storage unit 302, input unit 304, transmitting / receiving unit 305, and display unit 306 are all connected to the calculation unit 303 via a BUS.
[0052] The calculation unit 303 is, for example, a CPU (Central Processing Unit). The calculation unit 303 executes the processing of the optimization calculation unit 15 according to the control program stored in the storage unit 302.
[0053] The temporary storage unit 301 is, for example, RAM (Random-Access Memory). The temporary storage unit 301 loads the control program stored in the storage unit 302 and uses it as a work area for the calculation unit 303.
[0054] The storage unit 302 is a non-volatile memory such as flash memory, hard disk, DVD-RAM (Digital Versatile Disc - Random Access Memory), or DVD-RW (Digital Versatile Disc - ReWritable). The storage unit 302 pre-stores a program for causing the calculation unit 303 to perform processing of the topology optimization device 1, and also supplies the information stored in this program to the calculation unit 303 according to the instructions of the calculation unit 303, and stores the information supplied from the calculation unit 303. The position velocity information storage unit 12 and the sunlight direction information storage unit 14 are configured in the storage unit 302.
[0055] The input unit 304 is an interface device that connects input devices such as a keyboard, pointing device, and voice input device to the BUS. Information entered by the user is supplied to the calculation unit 303 via the input unit 304. In a configuration in which the user inputs position speed information and sunlight direction information to the position speed information acquisition unit 11 and the sunlight direction information acquisition unit 13, respectively, the input unit 304 functions as the position speed information acquisition unit 11 and the sunlight direction information acquisition unit 13.
[0056] The transmitting / receiving unit 305 is a communication device that communicates with satellite S2. Alternatively, it may be a network termination device or wireless communication device that connects to a network including a communication device that communicates with satellite S2, and a serial interface or LAN (Local Area Network) interface that connects to them. The transmitting / receiving unit 305 functions as a position / velocity information acquisition unit 11, a solar direction information acquisition unit 13, and a network topology output unit 16.
[0057] The display unit 306 is a display device such as an LCD (Liquid Crystal Display) or an organic EL (electroluminescence) display. When the network topology output unit 16 is configured to display network topology information on the screen, the display unit 306 functions as the network topology output unit 16.
[0058] The processing of the position-velocity information acquisition unit 11, position-velocity information storage unit 12, solar direction information acquisition unit 13, solar direction information storage unit 14, optimization calculation unit 15, and network topology output unit 16 of the topology optimization device 1 shown in Figure 1 is performed by a control program that uses resources such as the temporary storage unit 301, calculation unit 303, storage unit 302, input unit 304, transmission / reception unit 305, and display unit 306 for processing.
[0059] Furthermore, the aforementioned hardware configuration and flowchart are examples only and can be changed and modified as needed.
[0060] The core components of the topology optimization device 1, such as the calculation unit 303, temporary storage unit 301, storage unit 302, input unit 304, transmission / reception unit 305, and display unit 306, can be implemented using a standard computer system, rather than a dedicated system. For example, the topology optimization device 1 can be configured by distributing a computer-readable recording medium such as a flexible disk, CD-ROM (Compact Disc - Read Only Memory), or DVD-ROM (Digital Versatile Disc - Read Only Memory) containing a computer program for performing the aforementioned operations, and then installing the computer program on a computer. Alternatively, the topology optimization device 1 can be configured by storing the computer program on a storage device of a server on a communication network such as the Internet, and then downloading it from a standard computer system.
[0061] Furthermore, if the functions of the topology optimization device 1 are realized through a division of labor between the OS (Operating System) and the application program, or through cooperation between the OS and the application program, then only the application program portion may be stored in the recording medium or storage device.
[0062] Furthermore, it is possible to superimpose a computer program onto the carrier wave and provide it via a communication network. For example, the computer program may be posted on a bulletin board system (BBS) on the communication network and provided via the communication network. The system may then be configured to execute the aforementioned processing by starting this computer program and running it under the control of the OS, just like other application programs.
[0063] In embodiments 1 to 6 described above, the topology optimization device 1 exists separately from the satellite, but the satellite may also be equipped with the topology optimization device 1.
[0064] In the embodiments 1 to 6 described above, the topology optimization device 1 includes a position velocity information acquisition unit 11, a position velocity information storage unit 12, a solar light direction information acquisition unit 13, and a solar light direction information storage unit 14. However, the position velocity information acquisition unit 11, the position velocity information storage unit 12, the solar light direction information acquisition unit 13, and the solar light direction information storage unit 14 may be provided by an external device or system.
[0065] Although embodiments 2 to 5 described above have been explained separately, these embodiments may be combined.
[0066] Although a preferred embodiment 1 has been described in detail above, the invention is not limited to the above-described embodiment, and various modifications and substitutions can be made to the above-described embodiment 1 without departing from the scope of the claims.
[0067] Furthermore, this disclosure allows for various embodiments and modifications without departing from its broad spirit and scope. The embodiments described above are for illustrative purposes only and do not limit the scope of this disclosure. That is, the scope of this disclosure is indicated by the claims, not by the embodiments. Various modifications made within the scope of the claims and the equivalent significance of the disclosure are considered to be within the scope of this disclosure.
[0068] This application is based on Japanese Patent Application No. 2025-14117, filed on 30 January 2025. The entire specification, claims, and drawings of Japanese Patent Application No. 2025-14117 are incorporated herein by reference.
[0069] 1 Topology optimization device, 11 Position and velocity information acquisition unit, 12 Position and velocity information storage unit, 13 Solar light direction information acquisition unit, 14 Solar light direction information storage unit, 15 Optimization calculation unit, 16 Network topology output unit, 301 Temporary storage unit, 302 Storage unit, 303 Calculation unit, 304 Input unit, 305 Transmit / receive unit, 306 Display unit, G1, G2, G3 Connection graphs, S1 to Sn Satellites.
Claims
1. A topology optimization device for optimizing the topology of an inter-satellite network of multiple satellites orbiting along a circular orbit and equipped with free-space optical communication devices, comprising: position velocity information indicating the position and velocity of the satellites over a predetermined period of one or more orbits, and solar direction information indicating the history of the incident direction of sunlight, which calculates a determination result of whether the following conditions are met: a solar interference constraint, which is a condition that the angle between the relative direction between the satellites and the direction of the sun does not fall within the no-receiving angle of the free-space optical communication device; and a line-of-sight constraint, which is a condition that the shortest distance between the line segment between the satellites and the Earth surface is greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored; constructs a connection graph from among the candidate topologies of the inter-satellite network, with the satellites as nodes and connecting pairs of the satellites that satisfy the solar interference constraint and the line-of-sight constraint as edges; sets weights based on the inter-satellite distance to the edges of the constructed connection graph; and optimizes the topology of the inter-satellite network using an optimization algorithm based on the connection graph with weights set to the edges.
2. The topology optimization device according to claim 1, wherein the optimization calculation unit adds a connection component constraint to the connection graph, which is conditional on the connection component being 1; sets weights for the edges of the connection graph based on at least one of the indicators of network link stability, communication speed, and communication latency; evaluates the connection graph based on evaluation values based on the weights of the edges of the connection graph and the constraint values of the connection component constraint; and optimizes the topology of the network between satellites using an optimization algorithm.
3. The topology optimization device according to claim 2, wherein the optimization calculation unit, in evaluating the connection graph, adds, in addition to the evaluation value based on the weight of the edges of the connection graph and the constraint value of the connection component constraint, a constraint value of the number of communication lines constraint, provided that the number of required free-space optical communication devices in the candidate topology of the inter-satellite network does not deviate from the number of free-space optical communication devices mounted on each satellite.
4. When the orbit is a solar asynchronous orbit having multiple orbital planes, and the number of satellites is the same for all orbital planes, the optimization calculation unit generates a connection graph for multiple satellites constituting one orbital plane of the solar asynchronous orbit, and while fixing the positional relationship of the nodes and the connection relationship of the edges in the connection graph with weights set on the edges, it generates a new connection graph by moving the fixed state relatively to move the nodes to adjacent orbital planes, it repeats a cyclic process of setting weights on the edges of the new connection graphs, and optimizes the topology of the network between the satellites using an optimization algorithm based on all connection graphs with weights set on all edges, the topology of the network between the satellites according to any one of claims 1 to 3.
5. The topology optimization device according to any one of claims 1 to 4, wherein the satellite is equipped with a free-space optical communication device, and the optimization calculation unit adds a tracking rate constraint to the solar interference constraint and the line-of-sight constraint, provided that the required angular velocity of the drive mechanism of the free-space optical communication device for tracking each other, calculated based on the relative position vector and relative velocity vector between the satellites, does not exceed the maximum angular velocity that the drive mechanism of the free-space optical communication device can achieve, calculates a determination result of whether the solar interference constraint, the line-of-sight constraint and the tracking rate constraint are satisfied, and constructs a connection graph in which pairs of satellites that satisfy the solar interference constraint, the line-of-sight constraint and the tracking rate constraint are connected as edges among the candidate topologies of the inter-satellite network.
6. The topology optimization device according to any one of claims 1 to 5, wherein the satellite is equipped with a free-space optical communication device, and the optimization calculation unit adds a driveable angle constraint to the solar interference constraint and the line-of-sight constraint, which is a condition that the angle between the relative position vector direction and the directional direction of a reference free-space optical communication device at a reference mounting angle on the mounting surface is within the driveable angle of the free-space optical communication device, calculates a determination result of whether or not the solar interference constraint, the line-of-sight constraint and the driveable angle constraint are satisfied, and constructs a connection graph in which pairs of satellites that satisfy the solar interference constraint, the line-of-sight constraint and the driveable angle constraint are connected as edges among the candidate topologies of the inter-satellite network.
7. A topology optimization device that optimizes the topology of an inter-satellite network consisting of multiple satellites orbiting along a circular orbit and equipped with free-space optical communication devices, calculates a determination result based on position and velocity information indicating the position and velocity of the satellites over a predetermined period of one or more orbits, and solar direction information indicating the history of the incident direction of sunlight, to determine whether a solar interference constraint is satisfied, which is conditional on the angle between the relative direction between satellites and the direction of the sun not falling within the no-receiving angle of the free-space optical communication device, and a line-of-sight constraint, which is conditional on the shortest distance between the line segment between satellites and the Earth surface being greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored, among the candidate topologies of the inter-satellite network, constructs a connection graph in which the satellites are nodes and pairs of satellites satisfying the solar interference constraint and the line-of-sight constraint are connected as edges, sets weights based on the inter-satellite distance to the edges of the constructed connection graph, and optimizes the topology of the inter-satellite network using an optimization algorithm based on the connection graph with weights set on the edges.
8. A program that functions as an optimization calculation unit for a computer that optimizes the topology of an inter-satellite network consisting of multiple satellites orbiting in orbit and equipped with free-space optical communication devices, by calculating a determination result based on position and velocity information indicating the position and velocity of the satellites over a predetermined period of one or more orbits, and solar direction information indicating the history of the direction of incident sunlight, to determine whether the solar interference constraint, which is a condition that the angle between the relative direction between satellites and the direction of the sun does not fall within the no-receiving angle of the free-space optical communication device, and the line-of-sight constraint, which is a condition that the shortest distance between the line segments between satellites and the Earth surface is greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored, is satisfied, constructs a connection graph from among the candidate topologies of the inter-satellite network, with the satellites as nodes and connecting pairs of satellites that satisfy the solar interference constraint and the line-of-sight constraint as edges, sets weights based on the inter-satellite distance to the edges of the constructed connection graph, and optimizes the topology of the inter-satellite network using an optimization algorithm based on the connection graph with weights set to the edges.