Control station device

Abstract

This control station device controls a communication link of a satellite network that is constituted by a plurality of satellites each having a plurality of laser communication terminals. The control station device calculates prediction data pertaining to demand for communications between all pairs of the satellites, updates data pertaining to a visible link on the basis of the positions and speeds of the satellites and the directions of laser beams emitted from the laser communication terminals of the satellites, determines the communication link, on the basis of the prediction data pertaining to the demand for the communications and the data pertaining to the visible link, so as to improve the network total throughput in the future, and controls the laser communication terminals of the satellites so as to form the determined communication link.

Description

Control station device

[0001] The present invention relates to a control station device.

[0002] With the spread of satellite communications, there has been remarkable development in recent years of low earth orbit (LEO) satellite networks, which are advantageous for increasing capacity. In LEO satellite networks, particularly from the perspective of network technology, the main controls are "link control," which determines which satellites to establish communication links with for a given group of satellites (position, velocity), and "route control," which determines which route data should flow through within the communication network created based on the link control.

[0003] Regarding link control, the problem of how to form inter-satellite links in a dynamically changing satellite network has long been known as the "dynamic topology control" problem. Prior art related to the "dynamic topology control" problem has devised link control based on information on the physical layer, such as the inter-satellite distance and the transmission capacity limit (Shannon limit) according to the distance (Non-Patent Document 1).

[0004] I. Leyva-Mayorga et al., “Inter-Plane Inter-Satellite Connectivity in Dense LEO Constellations”, IEEE Trans. Wireless Communications, Vol. 20, No. 6, pp. 3430-3443 (2021).

[0005] In satellite communications, the distribution of communication demand (traffic distribution) is spatially non-uniform. To take into account the non-uniformity of traffic distribution in link control, it is important to include feedback not only from the physical layer but also from the routing layer. This is because the degree of link congestion is determined as a result of routing a given traffic, and it is important to form links to reinforce congested links.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a control station device that can set up communication links that maintain high network performance even when traffic distribution is non-uniform.

[0007] According to an aspect of the present invention, a control station device controls the communication links of a satellite network consisting of multiple satellites, each having multiple laser communication terminals, and calculates predicted data of communication demand between all pairs of satellites, updates visible link data based on the position and velocity of the satellites and the direction of the laser beam emitted from the laser communication terminals possessed by the satellites, determines the communication links based on the predicted data of communication demand and the visible link data so as to improve the total network throughput in the future, and controls the laser communication terminals possessed by the satellites to form the determined communication links.

[0008] According to the present invention, even when traffic distribution is non-uniform, it is possible to set up communication links that can achieve higher network performance than the prior art.

[0009] 1 is a diagram showing the overall configuration of a satellite network according to a first embodiment of the present invention; FIG. 2 is a diagram showing a Walker Delta constellation, which is an example of a typical orbital arrangement of a satellite constellation system; FIG. 3 is a diagram showing a Walker Star constellation, which is an example of a typical orbital arrangement of a satellite constellation system; FIG. 4 is a diagram showing the configuration of a control station device according to a first embodiment of the present invention, together with the configuration of a LEO satellite; FIG. 5 is a diagram showing the configuration of a link control unit according to a first embodiment of the present invention; FIG. 6 is a diagram explaining the direction of a unit vector indicating the eigencoordinate system of a LEO satellite; FIG. 7 is a diagram explaining a visible link set; FIG. 8 is a diagram explaining a set of visible LCT pairs; FIG. 9 is a diagram showing the configuration of an additional link calculation unit according to a first embodiment of the present invention; FIG. 10 is a diagram showing a flow of updating communication links according to a first embodiment of the present invention; FIG. 11 is a diagram showing a flow of a graph update step according to a first embodiment of the present invention; FIG. 12 is a diagram showing Example 1 of the present invention; FIG. 13 is a diagram showing Example 2 of the present invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the following embodiments do not limit the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In the following description, the symbol "→" indicates a vector and is placed above a symbol (e.g., x, y, z, etc.). In the following description, the symbol "·" attached to a "velocity vector" indicates a time derivative and is placed above the symbol "→" (this is different from the symbol "·" that is placed between two vectors and indicates the dot product of these vectors, such as "→ζ·→x").

[0011] First Embodiment A first embodiment of the present invention will be described below with reference to FIGS.

[0012] [Satellite Network] As shown in Figure 1, the satellite network NW includes a plurality of LEO satellites LS and a plurality of ground stations (control stations) ES on the Earth E. As shown in Figure 1, the satellite network NW may also include a GEO satellite GS or an MEO satellite MS. The ground stations (control stations) ES have a control station device (described below).

[0013] A LEO satellite is a satellite that orbits the Earth in a low Earth orbit (LEO), a MEO satellite is a satellite that orbits the Earth in a medium Earth orbit (MEO), and a GEO satellite is a satellite that orbits the Earth in a geostationary Earth orbit (GEO).

[0014] A low Earth orbit (LEO) is an orbit at an altitude of approximately 2,000 km or less above the Earth's surface. A medium Earth orbit (MEO) is an orbit at an altitude of approximately 2,000 km to approximately 36,000 km above the Earth's surface. A geostationary Earth orbit (GEO) is an orbit at an altitude of approximately 36,000 km above the Earth's surface.

[0015] GEO satellites in geostationary orbit (GEO) orbit the GEO at approximately the same speed as the Earth's rotation. GEO satellites are relatively stationary when viewed from any location on Earth. GEO satellites can continue to observe approximately the same area on Earth. In contrast, MEO satellites in medium orbit (MEO) or low orbit (LEO) orbit the GEO at a different speed than the Earth's rotation because their orbits are lower than those of geostationary orbit (GEO). For example, a LEO satellite orbits the Earth in approximately one and a half hours.

[0016] LEO satellites orbit in a lower orbit than MEO satellites. In other words, LEO satellites are closer to the Earth's surface than MEO satellites. This allows LEO satellites to observe the Earth's surface with greater precision than MEO satellites. Furthermore, when ground stations on Earth communicate with LEO satellites, they can use radio waves with lower output than MEO satellites. On the other hand, the area on Earth over which LEO satellites can observe and communicate from a specific position in orbit is narrower than that of MEO satellites. For example, the time period over which a specific ground station on Earth can communicate with a LEO satellite is approximately 10 minutes.

[0017] In order to use LEO satellites to perform observations and communications over a wide area on Earth, low-earth orbit satellite constellation systems are used in which multiple LEO satellites are operated in cooperation as a single unit. A low-earth orbit satellite constellation system uses several to several tens of LEO satellites. A large-scale low-earth orbit satellite constellation system uses hundreds to several thousand LEO satellites. For the sake of explanation, only three LEO satellites, LS1, LS2, and LS3, are shown in Figure 1.

[0018] 2A and 2B show examples of typical orbital configurations for a satellite constellation system. The thick solid line represents the Earth. The thick dotted line represents the equator. An X represents the North Pole. The thin solid lines represent multiple orbits in each configuration. The black and white circles and arrows represent adjacent LEO satellites and their orbital directions. While FIGS. 2A and 2B show a case with five orbital planes, this is not limiting.

[0019] Figure 2A shows an example of a constellation known as a Walker Delta constellation. Figure 2A is a perspective view of the Earth's axis tilted from the vertical of the page. In a Walker Delta constellation, each LEO satellite orbits in a circular orbit at the same altitude. The orbital planes of each LEO satellite are equally spaced above the Earth's equatorial plane. Each orbital plane has the same orbital inclination.

[0020] Figure 2B is an example of a constellation called a Walker Star constellation. Figure 2B is a plan view seen from the north pole side, with the Earth's axis parallel to the vertical direction of the page. In a Walker Star constellation, each LEO satellite orbits on a circular orbit at the same altitude. The orbital planes of each LEO satellite are equally spaced on the Earth's equatorial plane. Each orbital plane includes the Earth's axis. The Walker Star constellation is a special constellation compared to the Walker Delta constellation, which can have orbital inclination angles other than 90 degrees.

[0021] 2A and 2B, in both the Walker Delta and Walker Star constellations, adjacent orbital planes intersect at higher latitudes, so the relative direction from a LEO satellite in one orbital plane (e.g., a black circle) to a LEO satellite in an adjacent orbital plane (e.g., an open circle) changes in almost opposite directions at higher latitudes.

[0022] Returning to Figure 1, in a low-earth-orbit satellite constellation system, in order to link multiple LEO satellites, attempts are being made to enable communication between LEO satellites themselves, in addition to between ground stations and LEO satellites. In particular, to enable high-capacity communication of more than gigabits per second, research and development has been conducted and demonstrated on inter-satellite communication using light (optical satellite communication) instead of radio waves.

[0023] In optical satellite communications, a laser communication terminal (LCT) is mounted on each LEO satellite, and the LEO satellites are connected to each other using collimated laser light transmitted and received by the laser communication terminal (LCT).

[0024] Optical satellite communications can use a wider bandwidth than radio wave communications, allowing for larger-capacity communications. Furthermore, because collimated laser light is used, the risk of interference and interception is reduced. Furthermore, compared to optical communications on the ground, because communications are conducted in space, there is no risk of communication quality being affected by weather.

[0025] Fig. 1 shows a laser beam LB used in optical satellite communications. For the sake of explanation, Fig. 1 only shows a laser beam LB12 between LEO satellites LS1 and LS2 and a laser beam LB23 between LEO satellites LS2 and LS3. In addition to the laser beam LB, Fig. 1 also shows radio waves RW used for communications between the earth station ES and the GEO satellite GS or MEO satellite MS.

[0026] 1, the only LEO satellite LS within communication range of earth station ES1 is LS1, and earth station ES1 can only communicate with LEO satellite LS1 using radio waves RW1. The only LEO satellite LS within communication range of another earth station ES2 is LS3, and the other earth station ES2 can only communicate with LEO satellite LS3 using radio waves RW2. LEO satellite LS2 is not within communication range of either earth station ES1 or ES2.

[0027] Even in such a case, the individual LEO satellites LS can perform optical satellite communications with each other, allowing all of the LEO satellites LS to quickly share data sent from the ground stations ES. This allows multiple LEO satellites LS to be linked and operated as a single unit, enabling observation and communication over a wide area on Earth.

[0028] 1, it is also possible to first communicate from earth station ES1 to GEO satellite GS or MEO satellite MS using radio wave RW3, and then from GEO satellite GS or MEO satellite MS to each of LEO satellites LS1, LS2, or LS3 using radio wave RW4, RW5, or RW6, respectively. In this case, too, by each of the LEO satellites LS performing optical satellite communications, data sent from earth station ES can be quickly shared by all of the LEO satellites LS.

[0029] In FIG. 1, radio waves RW are used for communication between the earth station ES and the GEO satellite GS or MEO satellite MS, but light may be used instead of radio waves.

[0030] [Control Station Device] In a low-earth orbit satellite constellation system, there are many candidates for a pair of LEO satellites to establish an optical satellite communication link (communication link). Control (link control) of which pair of LEO satellites to establish a communication link with significantly affects the throughput of the low-earth orbit satellite constellation system. In the present invention, link control is performed in a control station device possessed by a ground station (control station).

[0031] 3, the control station device 1 includes a satellite orbit manager OM, a traffic manager TM, a route controller PC, and a link controller LC. The LEO satellites LS each include a command transmitter / receiver CT, and laser communication terminals (LCTs) LCT_1, ..., LCT_K. ｉ For the sake of explanation, FIG. 3 shows only the i-th LEO satellite LSi as a representative of all the LEO satellites LS. ｉ is the number of laser communication terminals (LCTs) on board the i-th LEO satellite LSi.

[0032] The satellite orbit management unit OM manages time series data related to the motion of each LEO satellite. The time series data includes position vector data and velocity vector data. The satellite orbit management unit OM references and records the time series data of each LEO satellite that has actually been observed, as necessary. The satellite orbit management unit OM predicts and records future time series data for a certain period of time (typically about 30 minutes, but not limited to this) using orbit calculations. The satellite orbit management unit OM sends the time series data related to the motion of each LEO satellite to the link control unit 10.

[0033] The traffic management unit TM manages time series data related to traffic distribution. The traffic management unit TM refers to and records time series data of actually observed traffic distribution as necessary. The traffic management unit TM predicts and records future time series data up to a certain time (typically about 30 minutes, but not limited to this). The traffic management unit TM sends the time series data related to traffic distribution to the link control unit 10.

[0034] The satellite orbit manager OM and the traffic manager TM refer to external data D1 as necessary. D1 is, for example, GPS observation data or data supplied by an Internet provider.

[0035] The route control unit PC refers to data relating to communication demands (communication requests), allocates the communication demands to the communication links updated by the link control unit 10 (described later), and updates the available capacity of the communication links.

[0036] The routing controller PC refers to external data D2 as needed. D2 is data supplied by, for example, an Internet provider.

[0037] The link control unit 10 updates the communication link data based on time series data related to the motion of each LEO satellite and time series data related to traffic distribution. The link control unit 10 transmits a communication command based on the updated communication link data to the command transmission / reception unit CT of the LEO satellite LSi by radio waves RW. The communication command is transmitted to the laser communication terminals (LCT) LCT_1, ..., LCT_K of the LEO satellite LSi.ｉ For each of the laser beams LB_1, . . . , LB_K, ｉ is used to indicate whether or not to perform optical satellite communication.

[0038] The command transmission / reception unit CT receives communication commands from the link control unit 10 of the control point device 1. The command transmission / reception unit CT receives communication commands from the laser communication terminals (LCT) LCT_1, ..., LCT_K. ｉ Send a communication command to

[0039] Laser communication terminals (LCT) LCT_1, ..., LCT_K ｉ , LB_K are directed to other LEO satellites in response to the received communication command. ｉ Laser communication terminals (LCT) LCT_1, ..., LCT_K ｉ The LEO satellite receives a laser beam emitted from another LEO satellite, thereby enabling optical satellite communications between LEO satellites.

[0040] 4, the link control unit 10 includes a data management unit 110, a communication link calculation unit 120, a coordinate calculation unit 130, a visible link calculation unit 140, and a communication link command unit 150. The link control unit 10 performs link control. As already mentioned, link control has a significant impact on the throughput of a low-earth orbit satellite constellation system.

[0041] [Data Management Unit] The data management unit 110 manages time-series data required for link control. The time-series data managed by the data management unit 110 includes a node set V, a traffic matrix Λ, a visible link set F, and a communication link set E. The node set V, the visible link set F, and the communication link set E have a hierarchical data structure in which data for the elements of the sets further includes data representing the attributes of each element. The data management unit 110 also manages control parameter data X.

[0042] [Node Set] A node set V is a set of nodes v representing each LEO satellite. ｉ (i=1,...,K) １ , ..., v ｉ , ..., vＫ} A node is a point representation of a LEO satellite.

[0043] Node V ｉ is the position vector of the LEO satellite →r ｉ (t), LEO satellite velocity vector → r ｉ (t), intrinsic coordinate system (→ x ｉ , →y ｉ , →z ｉ ), Laser Communication Terminal (LCT) v on LEO satellites ｉ，ｋ (k=1,...,4) as attributes. Position vector of LEO satellite →r ｉ (t) is the time series data of a three-dimensional vector that indicates the position of a specific point (e.g., the center of gravity) of the LEO satellite. The velocity vector →r ｉ (t) is r ｉ This is time series data that represents the time derivative of (t). The time series data also includes future values ​​calculated by trajectory calculation. In the following, the argument time t may generally be omitted.

[0044] As shown in FIG. 5A, the intrinsic coordinate system (→x ｉ , →y ｉ , →z ｉ ) are three unit vectors that represent the coordinate axes of the coordinate system fixed to the LEO satellite. The unit vector (→x ｉ , →y ｉ , →z ｉ ) are set along the pitch, yaw, and roll directions of the LEO satellite, respectively. For convenience of explanation, the yaw direction will be explained first.

[0045] The Yaw direction is the direction from the LEO satellite to the center of the Earth. Unit vector → y ｉ is set in the Yaw direction. The Roll direction is the velocity vector of the LEO satellite, →r ｉ (t) is a direction parallel to the unit vector z ｉ is set in the Roll direction. Therefore, the unit vector → y ｉ and → z ｉ The plane that is spanned by the unit vector →x is the orbital plane of the LEO satellite. ｉ is a unit vector (→x ｉ , →yｉ , →z ｉ ) is set to form a right-handed system. The pitch direction is the unit vector →x ｉ Therefore, the pitch direction is perpendicular to the orbital plane.

[0046] Laser communication terminal (LCT) on LEO satellites ｉ，ｋ (k=1, . . . , 4) is the LCT reference vector →ξ, which indicates the direction of the reference axis of the emitted laser beam. ｉ，ｋ (k=1,...,4) are respectively +→x ｉ , -→x ｉ , + → z ｉ , -→ z ｉ The LEO satellite is equipped with a laser communication terminal (LCT) v ｉ，１ , v ｉ，２ The laser communication terminal (LCT) v is always oriented perpendicular to the orbital plane. ｉ，３ , v ｉ，４ The attitude of the LEO satellite is controlled so that it always faces parallel to the orbital plane. ｉ，ｋ The direction of the laser beam emitted from (k=1,...,4) is determined by the LCT reference vector →ξ ｉ，ｋ within a given angle range (maximum angle Θ ｍａｘ ) can be driven.

[0047] Laser communication terminal (LCT) on LEO satellites ｉ，ｋ (k=1,...,4) is the beam pointing state σ ｉ，ｋ , beam direction angle unit vector → μ ｉ，ｋ The beam direction state σ ｉ，ｋ is a laser communication terminal (LCT) v ｉ，ｋ indicates whether the beam pointing state σ is pointing at any of the laser communication terminals (LCT) of other LEO satellites, or is pointing at none of the laser communication terminals (LCT) of other LEO satellites (standby state). ｉ，ｋ Specifically, σ is the set given by ｉ，ｋ = {v ｊ，ｌ (Laser Communication Terminal (LCT) v ｉ，ｋ Ga Vｊ，ｌ ) = φ (when not pointing at any other Laser Communication Terminal (LCT))

[0048] Beam direction angle unit vector → μ ｉ，ｋ is a laser communication terminal (LCT) v ｉ，ｋ LEO satellite (node) to which ｉ From the laser communication terminal (LCT) v ｉ，ｋ LEO satellite (node) to which other laser communication terminal (LCT) pointed by belongs (in FIG. 5A, v ｊ ) is expressed as a unit vector pointing to the eigencoordinate system (→x ｉ , →y ｉ , →z ｉ ) is expressed as follows. ｉ，ｋ =(→ζ ｉ，ｊ ・→x ｉ , →ζ ｉ，ｊ ・→y ｉ , →ζ ｉ，ｊ ・→z ｉ ) ｔ

[0049] [Traffic Matrix] The traffic matrix Λ is the traffic matrix for each LEO satellite (node ​​v ｉ (i=1, . . . , K)) The traffic matrix Λ is expressed as a K×K matrix.

[0050] The demand for communications is higher in areas with a larger population, so there tends to be a higher demand for communications at lower latitudes on the Earth.

[0051] [Visible Link Set] The visible link set F is the set of visible links for each LEO satellite (node ​​v ｉ (i = 1, ..., K)) １，２ , ..., f ｉ，ｊ , ...}.

[0052] As shown in FIG. 5B, the visible link f ｉ，ｊ is the node v ｉ and node v ｊ Here, the visible link f shown in FIG. ｉ，ｊ The height of the LEO satellite (node) v from the ground surface is called the link altitude.ｉ V of transmitted light from ｊ When the received light intensity at the LEO satellite (node) v becomes smaller than a predetermined value, ｉ is v ｊ Therefore, it becomes invisible (hereinafter, this may be expressed as "invisible at the satellite level").

[0053] Visible Link f ｉ，ｊ is the directional unit vector →ζ ｉ，ｊ , received light level estimate P ｉ，ｊ , link disconnection time τ ＳＡＴ ｉ，ｊ , the set of visible LCT pairs H ｉ，ｊ Link utilization rate ｆ The directional unit vector →ζ ｉ，ｊ is the node v ｉ From node v ｊ is a unit vector pointing to →ζ ｉ，ｊ = (→r ｊ　 - →r ｉ ) / |→r ｊ　 - →r ｉ | is given by

[0054] Received light level estimate P ｉ，ｊ is the LEO satellite (node) v ｉ From LEO satellite (node) v ｊ When a laser beam is transmitted to the LEO satellite (node) v ｊ The estimated received light level P is calculated as the product of the transmission power, the transmission / reception optical antenna gain, and the free space loss. ｉ，ｊ [Unit: dBm] decreases as the link altitude decreases. When the link altitude becomes smaller than a predetermined threshold (a constant determined by system requirements, for example, 80 km), P ｉ，ｊ →It becomes -∞.

[0055] Link disconnection time τ ＳＡＴ ｉ，ｊ is the received light level estimate P ｉ，ｊ is the minimum receivable power P ｍｉｎThis is the future time when the satellite will be invisible at the satellite level (i.e., the time when the satellite will be invisible at the satellite level) and is calculated (predicted) based on the time series data of the position vector and velocity vector of the LEO satellite (node).

[0056] A set of visible LCT pairs H ｉ，ｊ is the LEO satellite (node) v ｉ A laser communication terminal (LCT) v ｉ，ｋ Within the range that can be covered by the laser beam from (the range that can drive the direction), the LEO satellite (node) v ｊ exists, and LEO satellite (node) v ｊ A laser communication terminal (LCT) v ｊ，ｌ Within the range that can be covered by the laser beam from (the range that can drive the direction), the LEO satellite (node) v ｉ (hereinafter, this may be expressed as "visible at the LCT level"). ｉ，ｋ and v ｊ，ｌ is a set of pairs with H ｉ，ｊ Specifically, ρ is defined by the following equation (1): ｉ，ｊ，ｋ is the set given by the following equation (2) using (see FIG. 5C).

[0057]

[0058]

[0059] H ｉ，ｊ Element h of ｉ ｋ , ｊ ｌ is the cleavage time τ of the LCT level ｉ ｋ , ｊ ｌ The LCT level cutoff time τ ｉ ｋ , ｊ ｌ is ρ ｉ，ｊ，ｋ ρ ｊ，ｉ，ｌ is the future time when the value of the LEO satellite (node) changes from 1 to 0 (and therefore becomes invisible at the LCT level), and is calculated (predicted) based on the time series data of the position vector and velocity vector of the LEO satellite (node).

[0060] The link utilization rate wf is the number of visible links f ｉ，ｊ The visible link f is calculated from the results of predicting the frequency of use of the link f up to a certain time in the future. ｉ，ｊ (The algorithm for calculating this will be described later.)

[0061] [Communication Link Set] The communication link set E is a set of links (communication links) that are actually used for communication and are selected from the visible link set F. １，２ , ..., e ｉ，ｊ , ...}. Communication link e ｉ，ｊ is the node v ｉ From node v ｊ The communication link set E is updated by selecting a new link e from among the elements (links) of the set F\E obtained by removing the communication link set E from the visible link set F at a certain time, where both nodes of the link have a laser communication terminal (LCT) in standby mode. ｉ，ｊ Specifically, the communication link e ｉ，ｊ is selected from the candidate link set Fc given by the following equations (3) and (4).

[0062]

[0063]

[0064] Communication link set e ｉ，ｊ is the available capacity (traffic volume) on the link c ｉ，ｊ , link down time T ｄｏｗｎ ｉ，ｊ , link-up time T ｕｐ ｉ，ｊ as an attribute.

[0065] Link utilization capacity (traffic volume) c ｉ，ｊ is updated every time a communication link is updated by the route control unit PC (see FIGS. 3 and 4) allocating communication demands to the communication links (described later). ｉ，ｊ is the maximum link capacity c ｍａｘ The following is the result.

[0066] Link down time Tｄｏｗｎ ｉ，ｊ is the predicted time until link down, which is determined by reflecting both the visibility at the satellite level and the visibility at the LCT level. Specifically, it is given by the following equation (5).

[0067]

[0068] Link-up time T ｕｐ ｉ，ｊ is the current beam direction → μ ｏｐｒ ｉ，ｋ , the other direction as the target (LCT direction target direction) → μ ｔｇｔ ｉ，ｋ The beam pointing penalty is determined by the time required to change the beam direction from ｂｅａｍ is given by the following equation (6).

[0069]

[0070] The control parameters X are parameters required for calculations to update the communication link, and include, for example, the update interval Δt.

[0071] 4, when updating the communication links, the communication link calculation unit 120 calculates links to be deleted and links to be added by referring to the data in the data management unit 110. The communication link calculation unit 120 has a deleted link calculation unit 121 and an added link calculation unit 122.

[0072] 6, the additional link calculation unit 122 has an input / output unit 1221, an initialization unit 1222, a link utilization prediction unit 1223, and a link determination unit 1224. Data from the data management unit 110 is input to the input / output unit 1221. The input / output unit 1221 outputs data to the data management unit 110. Before calculating the links to be added, the initialization unit 1222 initializes the candidate link set F at that time. ｃ , and calculate the link utilization rate w for each element (link) of the candidate link set Fc. ｆThe link utilization prediction unit 1223 predicts the link utilization rate wf for each element (link) of the candidate link set Fc based on future traffic prediction. The link determination unit 1224 initializes the candidate link set Fc. ｃ Among them, link utilization rate w ｆ The additional links are determined in descending order of their value.

[0073] [Coordinate Calculation Unit] Returning to Figure 4, when updating a communication link, the coordinate calculation unit 130 refers to the data in the data management unit 110 and calculates the LEO satellite's inherent coordinate system, LCT reference vector, and LCT pointing target direction. The coordinate calculation unit 130 has a satellite coordinate calculation unit 131, an LCT coordinate calculation unit 132, and an LCT pointing calculation unit 133. The coordinate calculation unit 130 calculates the LEO satellite's inherent coordinate system. The LCT coordinate calculation unit 132 calculates the LCT reference vector. The LCT pointing calculation unit 133 calculates the LCT pointing target direction.

[0074] [Visible Link Calculation Unit] When updating a communication link, the visible link calculation unit 140 refers to the data in the data management unit 110 and calculates whether the link of a LEO satellite pair has visibility at the satellite level and whether it has visibility at the LCT level. The visible link calculation unit 140 has a satellite-level visible link calculation unit 141 and an LCT-level visible link calculation unit 142. The satellite-level visible link calculation unit 141 calculates visibility at the satellite level. The LCT-level visible link calculation unit 142 calculates visibility at the LCT level.

[0075] [Communication Link Command Unit] Each time the communication link is updated, the communication link command unit 150 refers to the data in the data management unit 110 and sends commands to each LEO satellite so that the communication link updated by the communication link calculation unit 120 is realized.

[0076] [Method of Updating a Communication Link] Hereinafter, a method of updating a communication link will be described with reference to FIGS.

[0077] As shown in Fig. 7, the flow of updating a communication link includes a prediction step S1, a graph update step S2, and a command step S3. The communication link is repeatedly updated at predetermined time intervals Δt (t = ..., nΔt, (n+1)Δt, ...). Fig. 7 shows the flow at a certain time (for example, t = nΔt).

[0078] [Prediction Step S1] In prediction step S1, time series data (including position vector and velocity vector data) related to the motion of each LEO satellite up to a certain time in the future and time series data related to future traffic distribution are predicted. The satellite orbit management unit OM (see Figures 3 and 4) predicts the time series data related to the motion of each LEO satellite. The traffic management unit TM (see Figures 3 and 4) predicts the time series data related to future traffic distribution. The satellite orbit management unit OM and traffic management unit TM refer to external data D1 as necessary. The satellite orbit management unit OM and traffic management unit TM send the predicted time series data to the data management unit 110 of the link control unit 10.

[0079] [Graph Update Step S2] In the graph update step S2, the visibility graph and the communication graph are updated. The visibility graph is a simple undirected graph G(V, F) consisting of a node set V and a visible link set F. The communication graph is a simple undirected graph G(V, E) consisting of a node set V and a communication link set E. The link control unit 10 updates the elements v ｉ The visibility graph is updated based on the data of the position vector and the velocity vector, which are attributes of the link control unit 10. The link control unit 10 updates the communication graph based on the link utilization rate wf calculated based on the traffic information Λ and the visibility graph.

[0080] [Command Step S3] In command step S3, a command is sent to each LEO satellite so that the updated communication link is realized (see FIGS. 3 and 4). The command transmitter / receiver CT of the LEO satellite receives the communication command from the link control unit 10 (communication link command unit 150) of the control station device 1. The command transmitter / receiver CT sends the communication command to the laser communication terminals (LCTs) LCT_1, ..., LCT_K. ｉLaser communication terminals (LCT) LCT_1, ..., LCT_K transmit communication commands to ｉ , LB_K are directed to other LEO satellites in response to the received communication command. ｉ Laser communication terminals (LCT) LCT_1, ..., LCT_K ｉ receives the laser beam emitted from the other LEO satellite, thereby establishing an updated communication link.

[0081] After the command step S3 at a certain time (for example, t=nΔt) is completed, and before the command step S1 at the next time (for example, t=(n+1)Δt) is started, the route controller PC (see FIGS. 3 and 4) allocates communication demands to communication links, thereby updating the utilization capacity (traffic volume) c on the link.

[0082] The communication demand is given as information on the node (satellite) that is the starting point of the communication, the node that is the end point, a given transmission capacity [bps], and a given transmission time. Allocating the communication demand to a communication link means calculating a route connecting the node that is the starting point of the communication and the node that is the end point of the communication from among link candidates that are not interrupted for the given transmission time, and allocating data to that route at the given transmission capacity for the given transmission time.

[0083] [Flow of Graph Update Step S2] As shown in FIG. 8, the graph update step S2 includes a first step S21, a second step S22, a third step S23, a fourth step S24, a fifth step S25, a sixth step S26, a seventh step S27, and an eighth step S28.

[0084] Each step will be described below with reference to Fig. 4. In Fig. 4, arrows with numbers in parentheses correspond to the steps described above. The numbers in parentheses correspond to the numbers of each step.

[0085] [First Step S21] In the first step S21, the satellite coordinate calculation unit 131 of the coordinate calculation unit 130 calculates the unique coordinate system (→x ｉ , →y ｉ , →z ｉ) data. The satellite coordinate calculation unit 131 receives data of node set V (time series data related to the movement of each LEO satellite) from the data management unit 110. The satellite coordinate calculation unit 131 calculates data of the unique coordinate system of each LEO satellite based on the received data. The satellite coordinate calculation unit 131 sends the calculated data of the unique coordinate system of each LEO satellite to the data management unit 110. The data management unit 110 updates the data of node set V.

[0086] [Second Step S22] In the second step S22, the LCT coordinate calculation unit 132 of the coordinate calculation unit 130 calculates the LCT reference vector →ξ ｉ，ｋ The LCT coordinate calculation unit 132 receives data for node set V (time series data related to the motion of each LEO satellite) from the data management unit 110. The LCT coordinate calculation unit 132 calculates data for the LCT reference vector of each LEO satellite based on the received data. The LCT coordinate calculation unit 132 sends the calculated data for the LCT reference vector of each LEO satellite to the data management unit 110. The data management unit 110 updates the data for node set V.

[0087] [Third Step S23] In the third step S23, the satellite-level visible link calculation unit 141 of the visible link calculation unit 140 calculates data for the visible link set F. The satellite-level visible link calculation unit 141 receives data for the node set V (time-series data on the movement of each LEO satellite) from the data management unit 110. Based on the received data, the satellite-level visible link calculation unit 141 calculates the visible link set F for the LEO satellite (node) v. ｉ From V ｊ Directed unit vector to →ζ ｉ，ｊ Next, the satellite level visible link calculation unit 141 calculates the received light level estimate P ｉ，ｊ Next, the satellite level visible link calculation unit 141 calculates the received light level estimate P ｉ，ｊ is the minimum receivable power P ｍｉｎ If the link altitude is greater than a predetermined threshold, the LEO satellite (node) v ｉ and v ｊ The link with element f of the visible link set F ｉ，ｊAfter performing the above process for all LEO satellite (node) pairs, the satellite-level visible link calculation unit 141 sends the elements of the obtained visible link set F and the corresponding pointing unit vector and received light level estimate data to the data management unit 110. The data management unit 110 updates the data of the visible link set F.

[0088] [Fourth Step S24] In the fourth step S24, the LCT level visible link calculation unit 142 of the visible link calculation unit 140 calculates data of the visible link set F. The LCT level visible link calculation unit 142 receives data of the node set V (time series data on the motion of each LEO satellite) and data of the visible link set F from the data management unit 110. The LCT level visible link calculation unit 142 calculates the data of each element f of the visible link set F. ｉ，ｊ For the set of visible LCT pairs H ｉ，ｊ The LCT level visible link calculation unit 142 calculates all elements f ｉ，ｊ The set of visible LCT pairs for ｉ，ｊ The data is sent to the data management unit 110. The data management unit 110 updates the data of the visible link set F.

[0089] [Fifth Step S25] In the fifth step S25, the deleted link calculation unit 121 of the communication link calculation unit 120 determines a link to be deleted from the existing communication links. The deleted link calculation unit 121 receives data of the visible link set F and the communication link set E from the data management unit 110. The deleted link calculation unit 121 compares the visible link set F with the communication link set E. If there is an element (link) of the communication link set E that is not included in the visible link set F, the deleted link calculation unit 121 determines that this element (link) is a link to be deleted. The deleted link calculation unit 121 calculates the laser communication terminal (LCT) pair (v ｉ，ｋ , v ｊ，ｌ ) for the beam pointing state σ ｉ，ｋ , σ ｊ，ｌ Specifically, update σ ｉ，ｋ , σ ｊ，ｌ The link deletion calculation unit 121 calculates the updated beam direction state σｉ，ｋ , σ ｊ，ｌ The data of node set V is sent to the data management unit 110. The data management unit 110 updates the data of node set V.

[0090] [Sixth Step S26] In the sixth step S26, the additional link calculation unit 122 of the communication link calculation unit 120 determines a link to be added to the existing communication links. The additional link calculation unit 122 receives data on the traffic matrix Λ, the node set V, the visible link set F, the communication link set E, and the control parameter X from the data management unit 110. The additional link calculation unit 122 determines the laser communication terminal (LCT) pair h of the link to be added according to a specific algorithm (described later). ｉ ｋ , ｊ ｌ = (v ｉ，ｋ , v ｊ，ｌ The additional link calculation unit 122 calculates the laser communication terminal (LCT) pair h ｉ ｋ , ｊ ｌ = (v ｉ，ｋ , v ｊ，ｌ ) for the beam pointing state σ ｉ，ｋ , σ ｊ，ｌ Specifically, update σ ｉ，ｋ , σ ｊ，ｌ respectively, {v ｊ，ｌ}, {v ｉ，ｋ}. The additional link calculation unit 122 calculates the updated beam direction state σ ｉ，ｋ , σ ｊ，ｌ The data of node set V is sent to the data management unit 110. The data management unit 110 updates the data of node set V.

[0091] [Seventh Step S27] In the seventh step S27, the LCT direction calculation unit 133 of the coordinate calculation unit 130 calculates the LCT direction target direction. The LCT direction calculation unit 133 receives data on the node set V and the communication link set E from the data management unit 110. The LCT direction calculation unit 133 calculates the LCT direction target direction for all the laser communication terminals (LCTs) v ｉ，ｋ For beam pointing state σ ｉ，ｋ is not an empty set φ, the beam pointing angle unit vector →μ ｔｇｔｉ，ｋ The LCT direction calculation unit 133 sends the calculated beam direction angle unit vector to the data management unit 110. The data management unit 110 updates the data of the node set V.

[0092] [Eighth Step S28] In the eighth step S28, the communication link command unit 150 transmits a command to each LEO satellite. The communication link command unit 150 receives the beam pointing state σ of each LEO satellite from the data management unit 110. ｉ，ｋ , and the beam pointing angle unit vector of the LCT pointing target direction → μ ｔｇｔ ｉ，ｋ The communication link command unit 150 transmits commands to each LEO satellite based on the received data.

[0093] The commands that the communication link command unit 150 sends to each LEO satellite are dynamically set for each time step that updates the communication link, allowing for more flexible control than a method in which commands are sent to each LEO satellite based on a predetermined plan.

[0094] For example, even if the plan must be changed suddenly due to some emergency such as equipment failure, appropriate communication network control can be automatically performed in accordance with the above-described flow of graph update step S2. Furthermore, control can be performed regardless of the details of the orbital arrangement of the satellite constellation system (whether it is a Walker Star type or a Walker Delta type).

[0095] [Algorithm of Sixth Step S26] The algorithm of the sixth step S26 will be described below with reference to FIG. ｃ Among them, link utilization rate w ｆ The additional links are determined in descending order of their value.

[0096] First, data on the traffic matrix Λ, node set V, visible link set F, communication link set E, and control parameter X are input to input / output unit 1221 of additional link calculation unit 122 from data management unit 110 .

[0097] Next, the initialization unit 1222 of the additional link calculation unit 122 calculates a candidate link set Fc at that time. The initialization unit 1222 initializes the link utilization rate wf for each element (link) of the candidate link set Fc (setting all to zero).

[0098] Next, the link usage prediction unit 1223 calculates the candidate link set F ｃ For each element (link) of ｆ Make predictions.

[0099] As mentioned above, in both the Walker Delta constellation and the Walker Star constellation (see FIGS. 3A and 3B ), the relative direction from a LEO satellite orbiting in one orbital plane to a LEO satellite orbiting in an adjacent orbital plane changes in almost the opposite direction at higher latitudes. Therefore, switching of the beam pointing direction (link switching) used for inter-satellite communications occurs at higher latitudes. On the other hand, as mentioned above, communication demand tends to be higher at lower latitudes around the Earth.

[0100] Taking these points into consideration, in this embodiment, when a link switch occurs on the high-latitude side, information on future traffic predictions on the low-latitude side is fed back to calculate the link utilization rates of candidate links, and the candidate link with the highest link utilization rate is selected as the communication link.

[0101] Specifically, for each time step (forward time step) obtained by discretizing the time from the current time to a certain time ahead, the link utilization prediction unit 1223 allocates the predicted communication demand at each time on the visibility graph (a simple undirected graph G(V, F) consisting of a node set V and a visible link set F) based on the traffic prediction information. ｃ For each element (link) of the network, the congestion degree (the size of the allocated communication capacity) of each link is calculated as the link utilization rate w ｆ This is how the link utilization rate of the candidate link is calculated.

[0102] Next, the link determination unit 1224 selects the link utilization rate w from the elements (links) of the candidate link set Fc. ｆ The additional links are determined in descending order of the number of links. The additional links may be determined by a greedy method or by other methods.

[0103] Finally, the input / output unit 1221 outputs data of the determined additional link to the data management unit 110 .

[0104] As described above, the control station device of this embodiment is a control station device that controls the communication links of a satellite network consisting of multiple satellites, each having multiple laser communication terminals, and calculates predicted data of communication demand between all pairs of satellites, updates visible link data based on the position and velocity of the satellites and the direction of the laser beam emitted from the laser communication terminals possessed by the satellites, determines the communication links based on the predicted data of communication demand and the visible link data so as to improve the total network throughput in the future, and controls the laser communication terminals possessed by the satellites to form the determined communication links.

[0105] Furthermore, as described above, when updating the visible link data, the control station device of this embodiment determines that one satellite and another satellite are visible to each other if another satellite is present within a range in which the emission direction of a laser beam from one laser communication terminal possessed by one satellite can be driven, and the one satellite is present within a range in which the emission direction of a laser beam from another laser communication terminal possessed by the other satellite can be driven.

[0106] Furthermore, as described above, the control station device of this embodiment allocates the communication demand to the visible link based on the forecast data of the communication demand over a future time period from the current time to a certain time ahead, and the value obtained by accumulating and adding the size of the allocated communication capacity over the future time period is used as the future utilization rate.

[0107] According to this embodiment, even when the traffic distribution is non-uniform, it is possible to set up a communication link that can achieve higher network performance than the conventional technology.

[0108] Second Embodiment A second embodiment of the present invention will be described below, with explanations of parts common to the first embodiment of the present invention being omitted.

[0109] In the first embodiment of the present invention, in the fifth step S25 of the graph update step S2, if there is an element (link) of the communication link set E that is not included in the visible link set F, the deleted link calculation unit 121 determines that element (link) is a link to be deleted. In the second embodiment of the present invention, even if an element (link) of the communication link set E is included in the visible link set F, the deleted link calculation unit 121 determines that the link should be deleted if it is determined that the link should be deleted based on other criteria. For example, if the utilization capacity (traffic volume) on the link, which is an attribute of the communication link, is zero, the deleted link calculation unit 121 determines that the link is a link to be deleted.

[0110] According to this embodiment, even when traffic distribution is non-uniform, it is possible to set communication links that maintain high network performance. Furthermore, it is possible to delete communication links that are not being used at all, thereby further improving communication efficiency.

[0111] Third Embodiment A third embodiment of the present invention will be described below, and a description of parts common to the first embodiment of the present invention will be omitted.

[0112] In the first embodiment of the present invention, the deleted link calculation unit 121 updates the beam direction state σ in the fifth step S25 of the graph update step S2, and the added link calculation unit 122 updates the beam direction state σ in the sixth step S26. ｉ，ｋ , σ ｊ，ｌ In the third embodiment of the present invention, the deleted link calculation unit 121 and the added link calculation unit 122 further transmit the updated beam pointing state σ ｉ，ｋ , σ ｊ，ｌ The data is sent to the communication link command unit 150.

[0113] This embodiment allows for establishing communication links that maintain high network performance even when traffic distribution is non-uniform, and also allows commands to be sent to each LEO satellite more quickly to establish updated communication links.

[0114] <Fourth embodiment> A fourth embodiment of the present invention will be described below, and a description of parts common to the first embodiment of the present invention will be omitted.

[0115] In the first embodiment of the present invention, the link determination unit 1224 determines an additional link from among the elements (links) of the candidate link set Fc in descending order of the link utilization rate wf. In the fourth embodiment of the present invention, the LCT level disconnection time τ ｉ ｋ , ｊ ｌ The laser communication terminal (LCT) pair h that maximizes ｉ ｋ , ｊ ｌ = (v ｉ，ｋ , v ｊ，ｌ )

[0116] According to this embodiment, even if the traffic distribution is non-uniform, it is possible to set up a communication link that maintains high network performance. Furthermore, since the laser communication terminal (LCT) pair that is visible for the longest time at the LCT level is selected, the communication network can be made more stable.

[0117] [Examples] Examples 1 and 2 of the present invention will be described below with reference to Figures 9A and 9B. Examples 1 and 2 are the results of numerical simulations of communication network throughput for a Walker Delta constellation (see Figure 3A) and a Walker Star constellation (see Figure 3B), respectively, using a control station device according to the first embodiment of the present invention. The numerical simulations for Examples 1 and 2 were both performed under the following conditions:

[0118] Number of LEO satellites (nodes) in the satellite constellation system: 80 Update interval Δt: 60 seconds Number of LCTs per LEO satellite (node): 4 Beam driving range Θmax: 90° Beam driving speed θbeam: 4° / sec Transmission power: 2.5 W Minimum receivable power Pmin: -26 dBm Maximum link capacity cmax: 100 Gbps Number of forward time steps: 6 Time interval between forward time steps: 300 seconds

[0119] Example 1 FIG. 9A shows the results for a Walker Delta constellation.

[0120] The top row shows the response of the average total throughput to traffic intensity, compared with the results of a conventional method that does not use the present invention. The average total throughput is the average total throughput over the entire simulation time. For all traffic intensities, the results of the present invention exceed the results of the method that does not use the present invention. It is clear that the present invention improves the performance of a communication network.

[0121] The bottom graph shows the time evolution of total throughput at a specific traffic intensity indicated by the red arrow in the top graph. Total throughput improves by 7% on average, with momentary improvements of up to 50%. Total throughput also improves 80% of the time.

[0122] Example 2 Figure 9B shows the results for a Walker Star type constellation. The explanations for the upper and lower rows are the same as those for Figure 9A. Again, as in Figure 9A, an improvement in total throughput is observed. It is clear that the present invention improves the performance of communication networks.

[0123] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

[0124] For example, the device of the present invention can be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0125] For example, in the first embodiment of the present invention, the number of LCTs that each LEO satellite has is set to four, but the number of LCTs is not limited to this number.

[0126] For example, in the first embodiment of the present invention, the orbital arrangement of the satellite constellation is a Walker Star type constellation or a Walker Delta type constellation, but it is not limited to this arrangement.

[0127] For example, in the first embodiment of the present invention, the satellites that make up the satellite constellation are LEO satellites, but this is not limiting and they may also be MEO satellites.

[0128] REFERENCE SIGNS LIST 1 control station device 10 link control unit 110 data management unit 120 communication link calculation unit 121 deleted link calculation unit 122 added link calculation unit 130 coordinate calculation unit 140 visible link calculation unit 150 communication link command unit

Claims

1. A control station device that controls the communication links of a satellite network consisting of multiple satellites, each having multiple laser communication terminals, which calculates forecast data of communication demand between all pairs of satellites, updates visible link data based on the positions and velocities of the satellites and the directions of laser beams emitted from the laser communication terminals possessed by the satellites, determines the communication links based on the forecast data of communication demand and the visible link data so as to improve the total network throughput in the future, and controls the laser communication terminals possessed by the satellites to form the determined communication links.

2. A control station device as described in claim 1, wherein, in updating the visible link data, if another satellite is present within a range in which a laser beam from a laser communication terminal possessed by one satellite can be driven to steer its emission direction, and if the one satellite is present within a range in which a laser beam from another laser communication terminal possessed by the other satellite can be driven to steer its emission direction, the one satellite and the other satellite are determined to be visible to each other.

3. A control station device as described in claim 1 or 2, which allocates communication demand to the visible link based on forecast data of the communication demand over a future time period from the current time to a certain time ahead, and calculates the future utilization rate as the cumulative sum of the allocated communication capacity over the future time period.

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