JP7657760B2 - Non-geostationary satellite communication system, adjustment device and program for adjusting communication delay in non-satellite communication system - Google Patents

Description

This disclosure relates to a technique for adjusting communication delays in communications via non-geostationary satellite communications systems.

Patent Document 1 and Patent Document 2 disclose a non-geostationary satellite communication system using low earth orbit (LEO) satellites, which are non-geostationary satellites. Unlike geostationary orbit (GEO) satellites, non-geostationary satellites appear to move from the Earth's surface.

Non-Patent Document 1 also discloses a congestion control algorithm called BBR (Bottleneck Bandwidth and Round-trip Propagation Time). BBR is a congestion control algorithm that focuses on the fact that an increase in queuing delay in a transfer device that transfers packets transmitted and received between communication devices is observed by the communication device as an increase in round-trip delay (RTT), and adjusts the window size according to the RTT.

Special Publication No. 2020-507992 Special table 2019-532598 publication

Cardwell, et. al. , "BBR: Congestion-based congestion control: Measuring bottleneck bandwidth and round-trip propagation time", ACM Queue, 14(5), pp. 20-53, 2016

Figure 1 shows an example of communication in a non-geostationary satellite communication system. In the following description, "non-geostationary satellite" is also referred to simply as "satellite". Earth stations 80 and 81 communicate with satellites 90 and 91. Although only two satellites 90 and 91 are shown in Figure 1, in a non-geostationary satellite communication system, multiple satellites are used, and the satellites are positioned so that one or more satellites are always visible at any point on the Earth's surface. Because non-geostationary satellites appear to move from the Earth's surface, the satellites with which earth stations 80 and 81 communicate are switched over time.

As shown in FIG. 1, a signal transmitted by ground station 80 is received by ground station 81 via satellites 90 and 91. Here, communication delay D1 in the section between ground station 80 and satellite 90 (hereinafter referred to as the uplink section) changes as the distance between ground station 80 and satellite 90 changes over time. In addition, when the satellite communicating with ground station 80 is switched from satellite 90 to another satellite, communication delay D1 in the uplink section also changes. The same applies to communication delay D2 in the section between satellite 91 and ground station 81 (hereinafter referred to as the downlink section).

Many satellites in the non-geostationary satellite communication system orbit on multiple orbits. Here, when satellite 90 and satellite 91 orbit on the same orbit, the communication delay D3 in the section between satellite 90 and satellite 91 (hereinafter, space section) is constant. However, when satellite 90 and satellite 91 orbit on different orbits, the distance between satellite 90 and satellite 91 changes over time, and therefore the communication delay D3 in the space section changes over time. Note that in FIG. 1, there are two satellites involved in the communication in the space section, but depending on the positional relationship between ground station 80 and ground station 81, there may be one or three or more satellites involved in the communication. In summary, in the non-geostationary satellite communication system, the distance of the section from the transmitting ground station 80 to the receiving ground station 81 (hereinafter, referred to as the system section) changes over time, and therefore the communication delay in the system section changes over time.

BBR is a congestion control method that assumes that delays other than queuing delay (e.g., delays based on distance) are constant, and treats an increase in RTT as an increase in queuing delay. However, in non-geostationary satellite communication systems, the distance between system sections fluctuates, so when BBR is applied, an increase in RTT due to fluctuations in the distance between system sections is treated as an increase in queuing delay and controlled, making it impossible to perform congestion control with precision.

This disclosure provides a technique for suppressing variations in delays other than queuing delays in communications via non-geostationary satellite communications systems.

According to one aspect of the present disclosure, a coordination device for a non-geostationary satellite communication system includes a determination means for determining a maximum value of a communication delay in a transmission section for a packet transmitted from a first ground station to a second ground station via one or more non-geostationary satellites, estimating a communication delay of the packet in transmission through the transmission section based on a processing time of the packet in the non-geostationary satellite communication system to obtain an estimated value, and determining an amount of delay to be given to the packet based on the maximum value and the estimated value, and a delay means for giving the packet a delay of the delay amount determined by the determination means, wherein the determination means determines whether the packet is a first type packet or a second type packet based on information stored in a header of the packet, and determines the amount of delay if the packet is the first type packet, and the delay means gives the packet a delay of the delay amount if the determination means determines that the packet is the first type packet .

According to the present disclosure, it is possible to suppress fluctuations in delays other than queuing delays in communications via non-geostationary satellite communications systems.

FIG. 1 is a diagram showing an example of communication in a non-geostationary satellite communication system. 1 is a system block diagram of a non-geostationary satellite communication system according to one embodiment. FIG. 2 is a block diagram of a coordination device according to one embodiment. FIG. 1 is a diagram showing an example of fluctuation in communication delay due to fluctuation in communication distance in a non-geostationary satellite communication system. 1 is a system block diagram of a non-geostationary satellite communication system according to one embodiment. 1 is a system block diagram of a non-geostationary satellite communication system according to one embodiment. 1 is a system block diagram of a non-geostationary satellite communication system according to one embodiment.

The embodiments are described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions are omitted.

First Embodiment
Fig. 2 is a system configuration diagram of a non-geostationary satellite communication system according to this embodiment. In Fig. 2, a satellite system 3 includes a plurality of non-geostationary satellites. A ground station 1 transmits a radio signal to the satellite system 3. A ground station 2 receives a radio signal from the satellite system 3. In the following description, the ground station 1 is the transmitting side and the ground station 2 is the receiving side, but the ground station 1 can also be the receiving side and the ground station 2 can also be the transmitting side. The non-geostationary satellite communication system may include a plurality of ground stations different from the ground stations 1 and 2, but the configuration of each ground station is similar.

The radio device 10 of the ground station 1 receives a transmission packet from a transmitting communication device (not shown) and transmits a radio signal based on the transmission packet to the satellite system 3. The radio signal is a signal that carries the transmission packet, that is, a signal that includes the transmission packet. The transmitting communication device may transmit the transmission packet directly to the radio device 10, or may transmit the transmission packet to the radio device 10 via a data network.

The satellite system 3 transmits the radio signal received from the ground station 1 to the radio device 20 of the ground station 2. The satellite system 3 may determine the ground station that transmits the radio signal based on the destination of the transmission packet carried by the radio signal. Alternatively, the satellite system 3 may determine that the ground station that transmits the radio signal is the ground station 2 based on the identifier of the ground station 2 that the radio device 10 stores in the header of the radio signal. In this case, the radio device 10 determines the ground station that transmits the transmission packet based on the destination of the transmission packet, and stores the identifier of the determined ground station in the header of the radio signal. The satellite system 3 relays the radio signal between non-geostationary satellites as necessary. The radio device 20 transmits the transmission packet obtained by demodulating the received radio signal to the adjustment device 5.

Figure 3 is a configuration diagram of the adjustment device 5. The delay amount determination unit 51 first determines the maximum communication delay Dmax due to the distance of the system section from the ground station 1 to the ground station 2. As described above, the distance of the system section varies with time, and the communication delay due to the distance also varies with time. Figure 4 shows an example of the change in communication delay over time due to the change in the distance of the system section. As shown in Figure 4, the communication delay varies between a minimum value Dmin and a maximum value Dmax. The maximum communication delay Dmax can be determined based on the orbital information of each non-geostationary satellite in the satellite system 3, the position of the ground station 1 (e.g., latitude, longitude, altitude), and the position of the ground station 2. The orbital information of the non-geostationary satellite includes information indicating the relationship between the time and the position of the non-geostationary satellite. The orbital information and the position of the ground station 2 are known to the adjustment device 5. Therefore, the method of determining the position of the ground station 1 will be described below.

The delay amount determination unit 51, for example, acquires the position of the ground station 1 from the wireless device 10. In this case, the wireless device 10 includes position information indicating the position of the ground station 1 in the header of the transmission packet or the header of the wireless signal. It is also possible to configure the wireless device 10 to acquire an identifier of the wireless device 10 instead of acquiring information directly indicating the position of the ground station 1 (latitude, longitude, altitude) itself from the wireless device 10. In this case, a database indicating the relationship between the identifier of the ground station and the position information indicating the position of the ground station for each ground station is provided in the adjustment device 5. Alternatively, the adjustment device 5 is configured so that the adjustment device 5 can access the database. The delay amount determination unit 51 can determine the position of the ground station 1 by referring to the database based on the identifier of the ground station 1 acquired from the wireless device 10. It is to be noted that the delay amount determination unit 51 acquires the information included in the header of the wireless signal from the wireless device 20.

In this embodiment, the maximum value Dmax is a constant value regardless of time once the transmitting ground station and the receiving ground station are determined. Therefore, for example, a database showing the relationship between the identifiers of other ground stations and the maximum value Dmax with the other ground stations can be provided inside or outside the adjustment device 5, and the maximum value Dmax can be determined by referring to the database.

The delay amount determination unit 51 further determines the distance over which the received transmission packet is transmitted in the system section, and estimates or determines the communication delay Dact based on the distance. For this purpose, the wireless device 10 includes a predetermined time (hereinafter, processing time) within the processing period of the transmission packet at the ground station 1 in the header of the transmission packet or the header of the wireless signal. The processing time may be, for example, the reception time of the transmission packet at the wireless device 10 or the transmission time of the wireless signal corresponding to the transmission packet. The processing time may also be a predetermined time between the reception time and the transmission time. The delay amount determination unit 51 determines the distance of the system section when the transmission packet is transported in the system section based on the processing time, the orbit information, the position of the ground station 1, and the position of the ground station 2, and determines the communication delay Dact based on the determined distance.

The delay amount determination unit 51 calculates the period Dadd by subtracting the communication delay Dact from the maximum value Dmax calculated for the transmission packet, and notifies the delay unit 50 of the period Dadd. The delay unit 50 buffers the transmission packet for the period Dadd and then transmits the transmission packet to the receiving communication device or the data network.

With the above configuration, regardless of the time fluctuation of the distance of the system section, the sum of the delay due to the distance of the system section and the delay provided by the delay unit 50 (hereinafter referred to as the system delay) is approximately constant at the maximum value Dmax. Therefore, it is possible to suppress fluctuations in delays other than queuing delay in communications via a non-geostationary satellite communication system. Furthermore, by making the system delay approximately constant, the fluctuations in RTT correspond to the fluctuations in queuing delay, and it is possible to prevent deterioration in the accuracy of congestion control based on the RTT.

<Modification of the first embodiment>
In the above description, the delay amount determination unit 51 determines the communication delay Dact based on the processing time at the ground station 1, the orbit information, the position of the ground station 1, and the position of the ground station 2. However, the difference between the processing time at the ground station 1 and the reception time of the transmission packet at the adjustment device 5 can also be the communication delay Dact. When queuing packets is also performed in the non-geostationary satellite of the satellite system 3, the communication delay Dact obtained in this manner includes the queuing delay in the satellite system 3 in addition to the delay based on the distance of the system section. Therefore, when the queuing delay amount in the satellite system 3 changes significantly and the queuing delay in the satellite system 3 is reflected in the congestion control, it is not preferable to obtain the communication delay Dact in this manner. However, when the change amount of the queuing delay in the satellite system 3 is small or when it is not necessary to reflect the queuing delay in the satellite system 3 in the congestion control, the difference between the processing time and the reception time can be the communication delay Dact.

In the above description, the delay amount determination unit 51 obtained the processing time from the ground station 1. However, the delay amount determination unit 51 can determine the communication delay Dact by using the time when the delay amount determination unit 51 received the transmission packet as the processing time. In this case, the wireless device 1 does not need to include the processing time in the header of the transmission packet or the header of the wireless signal. Since the reception time of the transmission packet in the delay amount determination unit 51 is affected by queuing delay in the satellite system 3, the accuracy of the communication delay Dact obtained by using the reception time as the processing time is lower than the accuracy of the communication delay Dact based on the processing time obtained from the ground station 1. Note that the present disclosure is not limited to using the time when the delay amount determination unit 51 received the transmission packet as the processing time, and any time from when the wireless device 20 received the wireless signal to when the delay amount determination unit 51 received the transmission packet can be used as the processing time.

Second Embodiment
Next, the second embodiment will be described, focusing on the differences from the first embodiment. Fig. 5 is a system configuration diagram of a non-geostationary satellite communication system according to this embodiment. In this embodiment, a delay is applied at the transmitting ground station 1. The coordinating device 5 receives a transmission packet from a transmitting communication device, applies a delay of a period Dadd to the transmission packet, and then transmits the transmission packet to the wireless device 10. The wireless device 10 transmits a wireless signal based on the transmission packet to the satellite system 3. In this embodiment, the receiving wireless device 20 transmits a transmission packet obtained by demodulating the received wireless signal to the receiving communication device or a data network.

The configuration diagram of the adjustment device 5 is the same as that of FIG. 3. The operation of the delay amount determination unit 51 in this embodiment will be described below. As in the first embodiment, the delay amount determination unit 51 determines the maximum value Dmax based on the orbit information, the position of the ground station 1, and the position of the ground station 2. In order to determine the position of the ground station 2, the delay amount determination unit 51 notifies the wireless device 10 of the destination address of the transmission packet and obtains the identifier of the ground station 2 from the wireless device 10. It is also possible to configure the delay amount determination unit 51 to be able to determine the identifier of the ground station 2 that receives the transmission packet based on the destination address of the transmission packet. The adjustment device 5 has a database indicating the relationship between the identifier of the ground station and the position information indicating the position of the ground station for each ground station, or is configured to be able to access the database. The delay amount determination unit 51 determines the position of the ground station 2 by referring to the database based on the identifier of the ground station 2. Also, as in the first embodiment, a database showing the relationship between the identifiers of other ground stations and the maximum value Dmax with the other ground stations may be provided inside or outside the adjustment device 5, and the maximum value Dmax may be determined by referring to the database.

The delay amount determination unit 51 also sets the time when the transmission packet is received as the processing time, determines the distance of the system section based on the processing time, the orbit information, the position of ground station 1, and the position of ground station 2, and determines the communication delay Dact based on the determined distance. The delay amount determination unit 51 obtains a period Dadd by subtracting the communication delay Dact from the maximum value Dmax obtained for the transmission packet, and notifies the delay unit 50 of the period Dadd. The delay unit 50 buffers the transmission packet for the period Dadd and then transmits the transmission packet to the wireless device 10.

In this embodiment, the time when the wireless device 10 transmits a wireless signal to the satellite system 3 is the period Dadd after the time when the coordinating device 5 receives the transmission packet. Therefore, the distance of the system section at the time when the wireless device 10 transmits a wireless signal will differ from the distance of the system section at the processing time when the coordinating device 5 receives the transmission packet, and the system delay will deviate from the maximum value Dmax. However, since the fluctuation period of the distance of the system section is about several tens of minutes, which is sufficiently long compared to the period Dadd, the deviation of the system delay from the maximum value Dmax is small and does not pose a major problem.

In addition, in order to more accurately approximate the system delay to the maximum value Dmax, the period Dadd can be configured to be a variable, the communication delay Dact can be determined for each value of the period Dadd, and the period Dadd can be calculated so that the sum of these values is the maximum value Dmax.

With the above configuration, the system delay is approximately constant at the maximum value Dmax regardless of fluctuations in the distance between system sections. Therefore, fluctuations in delays other than queuing delays can be suppressed in communications via a non-geostationary satellite communications system. Furthermore, by making the system delay approximately constant, fluctuations in RTT correspond to fluctuations in queuing delay, and deterioration of the accuracy of congestion control based on RTT can be prevented.

Third Embodiment
Next, the third embodiment will be described with a focus on the differences from the first and second embodiments. In this embodiment, it is assumed that delay variations due to distance variations in the space section can be ignored, or that distance variations in the space section are ignored. FIG. 6 is a configuration diagram of a non-geostationary satellite communication system according to this embodiment. In this embodiment, delays are given in the transmitting ground station 1 and the receiving ground station 2, respectively. The coordinating device 5 of the ground station 1 receives a transmission packet from the transmitting communication device, and transmits the transmission packet to the wireless device 10 after giving a delay of a period Dadd1 to the transmission packet. The wireless device 10 transmits a wireless signal based on the transmission packet to the satellite system 3. The wireless device 20 transmits a transmission packet obtained by demodulating the received wireless signal to the coordinating device 5 of the ground station 2. The coordinating device 5 of the ground station 2 transmits the received transmission packet to the receiving communication device or a data network after giving a delay of a period Dadd2 to the transmission packet.

The delay amount determination unit 51 of the adjustment device 5 of the ground station 1 holds the maximum communication delay Dmax1 in the uplink section. The delay amount determination unit 51 of the adjustment device 5 of the ground station 1 also acquires the elevation angle of a directional antenna, for example, a parabolic antenna, provided in the wireless device 10 from the wireless device 10. The elevation angle of the parabolic antenna is the elevation angle in the direction in which the wireless signal is transmitted, and is also the direction in which the wireless device 10 sees the non-geostationary satellite with which the wireless device 10 is currently communicating. Therefore, the delay amount determination unit 51 of the adjustment device 5 of the ground station 1 can determine the distance to the non-geostationary satellite with which the wireless device 10 is currently communicating based on the elevation angle, and can therefore estimate the communication delay Dact1 in the uplink section. The delay amount determination unit 51 of the adjustment device 5 of the ground station 1 determines the period obtained by subtracting the communication delay Dact1 from the maximum value Dmax1 as Dadd1.

The delay amount determination unit 51 of the adjustment device 5 of the ground station 2 also holds the maximum communication delay Dmax2 in the downlink section. The delay amount determination unit 51 of the adjustment device 5 of the ground station 2 also acquires the elevation angle of a directional antenna, for example, a parabolic antenna, provided in the wireless device 20 from the wireless device 20. The elevation angle of the parabolic antenna is the elevation angle in the direction in which the wireless signal is received, and corresponds to the direction of the non-geostationary satellite with which the wireless device 20 is currently communicating, as seen from the wireless device 20. Therefore, the delay amount determination unit 51 of the adjustment device 5 of the ground station 2 can determine the distance to the non-geostationary satellite with which the wireless device 20 is currently communicating based on the elevation angle, and can therefore estimate the communication delay Dact2 in the downlink section. The delay amount determination unit 51 of the adjustment device 5 of the ground station 2 determines the period obtained by subtracting the communication delay Dact2 from the maximum value Dmax2 as Dadd2.

With the above configuration, the delay in the uplink and downlink sections is approximately constant, and if delay fluctuations in the space section are ignored, the system delay is approximately constant. Therefore, it is possible to suppress fluctuations in delay other than queuing delay in communications via a non-geostationary satellite communications system. Furthermore, by making the system delay approximately constant, the fluctuations in RTT correspond to the fluctuations in queuing delay, and it is possible to prevent deterioration in the accuracy of congestion control based on RTT.

<Fourth embodiment>
Next, the fourth embodiment will be described, focusing on the differences from the first to third embodiments. In this embodiment, a delay is applied within the satellite system 3. Fig. 7 is a configuration diagram of a non-geostationary satellite communication system according to this embodiment. The wireless device 10 receives a transmission packet from a transmitting communication device and transmits it to the satellite system 3. The satellite system 3 applies a communication delay of a period Dadd to the wireless signal, and then transmits the wireless signal to the wireless device 20. The wireless device 20 transmits a transmission packet obtained by demodulating the received wireless signal to a receiving communication device or a data network.

In this embodiment, each non-geostationary satellite of the satellite system 3 has a coordinating device 5. However, only one non-geostationary satellite applies a delay. As an example, the coordinating device 5 of a non-geostationary satellite that transmits a radio signal to the radio device 20 applies a delay to the radio signal. Alternatively, the coordinating device 5 of a non-geostationary satellite that receives a radio signal from the radio device 10 can be configured to apply a delay to the radio signal. As explained in the first to third embodiments, each non-geostationary satellite has orbit information and information for determining the position of each ground station. Then, the period Dadd is calculated so that the system delay approaches the maximum value Dmax, with the time when the radio signal is received being the processing time.

Fifth Embodiment
Next, the fifth embodiment will be described with a focus on the differences from the first to fourth embodiments. In the first to fourth embodiments, a delay is applied to all transmission packets so as to compensate for the communication delay due to the distance variation of the system section. In this embodiment, a delay is applied selectively to the transmission packets. For example, a configuration can be adopted in which a delay is applied to the transmission packets for the TCP protocol that performs congestion control, and a delay is not applied to the transmission packets for the UDP protocol that does not perform congestion control. Alternatively, a configuration can be adopted in which the adjustment device 5 controls whether or not to apply a delay based on the flag information in the header of the transmission packet, on the premise that the communication device stores flag information indicating whether or not congestion control based on the RTT is performed in the header of the transmission packet. The operation of the adjustment device 5 when applying a delay is the same as that described in the first to fourth embodiments. On the other hand, when no delay is applied, the delay amount determination unit 51 does not need to calculate the period Dadd. In addition, the transmission packets or radio signals are bypassed by the delay unit 50.

Sixth Embodiment
Next, the sixth embodiment will be described with a focus on the differences from the first to fifth embodiments. In the first to fifth embodiments, the adjustment device 5 applies a delay so that the system delay approaches the maximum value Dmax. However, the fluctuation period of the communication distance of the system section is about several tens of minutes, and for example, for packets of communication that ends in about several tens of seconds, the system delay can be made constant without applying a delay that makes the system delay the maximum value Dmax. For this reason, in this embodiment, the delay amount determination unit 51 determines the communication period for each communication, and sets the communication delay based on the maximum value of the distance of the system section within the communication period to the maximum value Dmax.

For example, when the delay amount determination unit 51 detects a packet that sets up a connection such as TCP, it determines the start of communication. The delay amount determination unit 51 then determines the application (HTTP, FTP) based on the port number of the TCP packet, and can determine the communication period by assuming that communication will continue for a period previously set for the determined application. Also, if a maximum period during which communication is possible is determined in advance, the communication period can be set to be the period from the start of communication to a time after the maximum period.

The adjustment device 5 according to the present disclosure can be realized by a program that causes a computer to operate as the adjustment device 5. The program is configured to cause a device having one or more processors to function as the adjustment device 5 when executed by the device. The program can be stored in a computer-readable storage medium or distributed via a network.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

The above configuration makes it possible to suppress fluctuations in delays other than queuing delays in communications via non-geostationary satellite communications systems. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

50: Delay section, 51: Delay amount determination section

Claims (13)

A coordinating device for a non-geostationary satellite communication system, comprising:
a determination means for determining a maximum value of a communication delay in a transport section from a first ground station to a second ground station via one or more non-geostationary satellites, estimating a communication delay of the packet in transport in the transport section based on a processing time of the packet in the non-geostationary satellite communication system to obtain an estimated value, and determining an amount of delay to be given to the packet based on the maximum value and the estimated value;
a delay means for giving the packet a delay of the amount of delay determined by the determination means;
Equipped with
the determining means determines whether the packet is a first type packet or a second type packet based on information stored in a header of the packet, and if the packet is the first type packet, determines the delay amount;
The delay means imparts a delay of the delay amount to the packet when the determination means determines that the packet is the first type packet . The adjustment device is provided in the second ground station,
The coordinating device according to claim 1 , wherein the processing time is included in the packet or a signal including the packet that the second ground station receives from a first non-geostationary satellite of the one or more non-geostationary satellites. The adjustment device is provided in the second ground station,
The coordinating device of claim 1 , wherein the processing time is based on a time when the second ground station receives the packet or a signal including the packet from a first non-geostationary satellite of the one or more non-geostationary satellites. The adjustment device is provided in the first ground station,
The coordinating device of claim 1 , wherein the processing time is based on a time when the first ground station received the packet. the coordinating device is provided on a first non-geostationary satellite among the one or more non-geostationary satellites;
The coordinating device of claim 1 , wherein the processing time is based on a time when the first non-geostationary satellite received a signal including the packet. The coordinating device according to claim 5 , wherein the first non-geostationary satellite is a non-geostationary satellite that receives a signal including the packet from the first ground station, or a non-geostationary satellite that transmits a signal including the packet to the second ground station. The adjustment device is provided in the second ground station,
the processing time is included in the packet or a signal including the packet, which is received by the second ground station from a first non-geostationary satellite among the one or more non-geostationary satellites;
2. The adjustment device according to claim 1, wherein the determination means determines the estimated value based on a difference between the processing time and a time when the second ground station receives the packet or a signal including the packet from the first non-geostationary satellite. 7. The adjustment device according to claim 1, wherein the determination means determines the estimated value based on orbit information indicating a relationship between time and position of the one or more non-geostationary satellites, the position of the first ground station, the position of the second ground station, and the processing time. 7. The adjustment device according to claim 1, wherein the determination means determines the maximum value based on orbit information indicating a relationship between time and position of the one or more non-geostationary satellites, the position of the first ground station, and the position of the second ground station. The adjustment device described in claim 9, wherein the determination means determines a maximum distance of the transportation section based on orbit information indicating a relationship between time and position of the one or more non-geostationary satellites, the position of the first ground station, and the position of the second ground station, and determines the maximum value based on the maximum distance. The adjustment device described in claim 9, wherein the determination means determines a predetermined period including the processing time based on orbit information indicating the relationship between time and position of the one or more non-geostationary satellites, the position of the first ground station, and the position of the second ground station, determines a maximum distance of the transportation section during the predetermined period , and determines the maximum value based on the maximum distance. A program, when executed by one or more processors of an apparatus having one or more processors, causing the apparatus to function as the adjustment apparatus according to any one of claims 1 to 6 . A non-geostationary satellite communication system comprising a plurality of ground stations including a first ground station and a second ground station, and a plurality of non-geostationary satellites,
when the first ground station receives a packet to be transported to the second ground station via a first non-geostationary satellite that communicates with the first ground station among the plurality of non-geostationary satellites, the first ground station estimates a communication delay of the packet in the transport of the first transport section based on a first direction to the first non-geostationary satellite as seen from the first ground station to obtain a first estimated value so that a communication delay in the first transport section from the first ground station to the first non-geostationary satellite becomes a first predetermined value, and gives the packet a delay amount based on a difference between the first predetermined value and the first estimated value;
when the second ground station receives the packet from a second non-geostationary satellite that communicates with the second ground station among the plurality of non-geostationary satellites, the second ground station estimates a communication delay of the packet in the second transport section based on a second direction to the second non-geostationary satellite as seen from the second ground station so that the communication delay in the second transport section from the second non-geostationary satellite to the second ground station becomes a second predetermined value, thereby obtaining a second estimated value, and imparting a delay amount based on a difference between the second predetermined value and the second estimated value to the packet .
Non-geostationary satellite communications systems.

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