JPH04355522A - Satellite communication system - Google Patents

Abstract

PURPOSE:To build up a satellite communication system having an expanded transmission band in which reception power is made constant. CONSTITUTION:The satellite communication system makes communication between a ground station arranged to a specific service area 6 on the earth 1 and plural communication satellites 4a-4d arranged on different orbits 8a-8d. The communication antenna 5a (5b-5d) of a common structure is mounted on each communication satellite (4a-4d) and the transmission band of a prescribed frequency in response to the altitude of the orbit is assigned to the communication antenna of each communication satellite. Thus, all the transmission bands of the system is expanded. The system includes plural communication satellites 4b-4d arranged on different elliptic orbits 8b-8d and assigns the transmission band of a frequency proportional to the altitude of the remotest point on the elliptic orbit to each communication satellite, thereby making substantially the reception power of the ground station constant over the entire transmission band.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication system for communicating between a ground station and a plurality of communication satellites placed in different orbits. This satellite communication system can be used for land mobile satellite communication, millimeter wave personal satellite communication, high-definition satellite broadcasting, etc., for example.

0002

[Background Art] In a typical conventional satellite communication system, so-called geostationary communication satellites are widely used, which are placed in a circular orbit along the earth's equator and are stationary relative to a specific service area on the earth. It had been. However, when geostationary communication satellites are used, although a sufficient angle of elevation can be obtained in relatively low latitude areas, the angle of elevation becomes significantly small in high latitude areas, which may cause communication problems.

On the other hand, in recent years, a system has been proposed in which a plurality of communication satellites are placed in different orbits to perform communication on a global scale. This type of satellite communication system is described, for example, in the document "Technical C
Haracteristics of a Pers
onal Communication Mobi
le Satellite System”CCI
There is the Motorola Iridium system disclosed in R IWP 8/14-52 (August 1, 1990). This system launches a total of 77 communication satellites on multiple orbits that intersect with each other, and is intended to perform personal communications on a global scale. 7 shows a communication satellite arrangement of the Iridium system according to FIG. 6; As shown,
Around Earth 1, there are orbits (orbits) set at equal longitude intervals.
A plurality of communication satellites 3a, 3b,..., 3n arranged in circular orbits 2a, 2b,..., 2n are orbiting regularly. These communication satellites are interconnected and cover the entire earth at any given time, making it possible to communicate with all regions around the clock.

0004

[Problem to be Solved by the Invention] However, in the Iridium system described above, in order to maintain substantially uniform received power over the entire earth, the frequency transmission bandwidth used for communication is compared to that of a geostationary communication satellite. Then, it is very narrow and limited to, for example, the L band. Therefore, there is a problem that the communication line capacity is small and it becomes impossible to cope with an increase in the number of ground stations.

[0005]

[Means for Solving the Problems] In view of the above-mentioned problems of the conventional technology, the present invention provides a satellite communication system that has a wide frequency transmission bandwidth and can sufficiently cope with an increase in the number of users. With the goal. To achieve this objective, the present invention basically employs a satellite communication system for communicating between a ground station and a plurality of communication satellites placed in different orbits. As a characteristic part, each communication satellite is equipped with a communication antenna having a common structure, and each communication satellite's communication antenna is assigned a transmission band of a predetermined frequency according to its orbit altitude. With this configuration, it is possible to widen the total transmission band compared to the conventional technology. That is, this satellite communication system includes multiple communication satellites placed in different elliptical orbits,
Each communications satellite is assigned a transmission band with a frequency proportional to its elliptical orbit apogee altitude. With such a configuration,
It becomes possible to make the received power at the ground station substantially constant over the entire transmission band. In addition to the communications satellites located in elliptical orbits, the system may also include additional communications satellites located in geosynchronous orbits. In such a system, for example, a communication satellite in a geostationary orbit is assigned the C band, and a communication satellite in an inner elliptical orbit closest to the earth is assigned UHF band.
It is possible to allocate an L band to a communication satellite on the next intermediate elliptical orbit, and to allocate an S band to a communication satellite on the farthest outer elliptical orbit. Each communication satellite to which a specific frequency transmission band is assigned according to its orbital altitude is equipped with a common communication antenna, for example, a mesh reflector type communication antenna with an aperture diameter of 6 mφ class.

Alternatively, as another embodiment, communications satellites in geostationary orbits are assigned the Ku band, communications satellites in inner elliptical orbits are assigned the UHF band, communications satellites in intermediate elliptical orbits are assigned the L band, and communications satellites in intermediate elliptical orbits are assigned the L band; The S band can also be assigned to communication satellites in elliptical orbits. In such a case, each communication satellite is commonly equipped with a reflector type communication antenna having an aperture diameter of 2 mφ class, for example.

[0007] More preferably, a pair of reflector type communication antennas having a large aperture diameter and a small aperture diameter are mounted on a communication satellite in a geostationary orbit, the C band and the Ku band are simultaneously assigned, and the antenna is placed in an elliptical orbit. The communication satellite is equipped with at least one of the pair of communication antennas.
A system including a mixture of different types of antennas may also be used. In such a case, a 6 mφ class antenna can be used as the large aperture communication antenna, and a 2 mφ class antenna can be used as the small aperture communication antenna.

[0008] Generally, it is suitable to use a reflector antenna having the same aperture diameter as a communication antenna having a common structure mounted on each communication satellite. This reflecting mirror antenna has a mirror surface made of a metal wire mesh having a mesh spacing sufficiently smaller than the minimum transmission band wavelength of the present satellite communication system, for example.

[0009]

According to the present invention, by allocating different frequency transmission bands to a plurality of communication satellites, the usable transmission bandwidth of the communication system as a whole can be made larger than before. When allocating a frequency transmission band to each communication satellite, it is set appropriately according to the satellite orbit altitude, that is, the distance between the ground station and the communication satellite, so the received power at the ground station is virtually constant over the entire transmission band. It is possible to do this. Generally, as recognized in the field of electromagnetic wave propagation, received power is inversely proportional to the square of the orbit altitude and proportional to the square of the transmission frequency. Therefore, by allocating high-frequency transmission bands to communication satellites located far away and low-frequency transmission bands to communication satellites located close to each other, it is possible to keep the received power constant across the entire system. .

[0010] Furthermore, a plurality of communication satellites are equipped with communication antennas having a common structure. Since there is no need to prepare a different communication antenna for each communication satellite, it is possible to save the construction cost of the entire system. As a communication antenna having this common structure, for example, a reflector antenna made of a metal wire mesh having a mesh spacing sufficiently smaller than the minimum transmission band wavelength of this communication system can be used, and effective transmitting and receiving effects can be achieved over the entire transmission band. can play.

The satellite communication system according to the present invention includes communication satellites placed in a plurality of elliptical orbits having different apogee altitudes relative to a specific region. Unlike a geostationary orbit, which is set along the equator, an elliptical orbit allows the inclination angle to be freely set for a specific region, such as a high latitude region, and the elevation angle relative to the communication satellite can be set sufficiently large. Therefore, it is possible to construct a satellite communication system without communication failure.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic overall view showing a first embodiment of a satellite communication system according to the present invention. This system consists of ground stations located in a specific service area 6 located on the surface of the earth 1, and mutually different orbits 8a, 8b, 8.
A plurality of communication satellites 4a, 4b, 4 located at c and 8d
This is to carry out space communications between spacecraft C and C4D. Although a total of four communication satellites are used in this embodiment, the present invention is not limited to this. Each communication satellite 4a to 4d is equipped with a communication antenna 5a to 5d having a common structure. A transmission band of a predetermined frequency is assigned to the communication antenna of each communication satellite according to its orbit altitude, that is, its distance from the service area 6. The system has three different apogee altitudes or apogee distances.
It includes three communication satellites 4b, 4c and 4d arranged in three elliptical orbits 8b, 8c and 8d. By allocating a transmission band with a frequency proportional to the altitude of the apogee to the communication satellite on this elliptical orbit, the received power at the ground station located in the service area 6 can be made substantially constant over the entire transmission band. I'm trying to make it happen. The system further includes an additional communications satellite 4a placed in a geostationary orbit 8a having a different orbital altitude than the three elliptical orbits 8b to 8d mentioned above. The communication satellite 4a fixed on this geostationary orbit further shares other frequency transmission bands. Although this system can be constructed from only a plurality of communication satellites in an elliptical orbit, the scope of use or application is further expanded by including communication satellites in a geostationary orbit. In addition, the system can include communications satellites located in other orbits in addition to elliptical and geostationary orbits.

As mentioned above, each communication satellite 4a to 4d
are equipped with communication antennas 5a to 5d having a common structure. As such a communication antenna, for example, a reflector antenna having the same aperture diameter can be used. This reflector antenna has a mirror surface made of a metal wire mesh having a mesh spacing sufficiently smaller than the minimum transmission band wavelength of the satellite communication system. The microstructure of such a metal wire mesh is shown in FIG. This mesh is made of metal wires 9 knitted in a net shape, and the mesh spacing S is set to be sufficiently small compared to the wavelength of the electromagnetic waves, so that the incident electromagnetic waves are substantially
% efficiency.

FIG. 3 is a schematic perspective view of the reflector type communication antenna equipped with the metal wire mesh shown in FIG. 2. As shown in the figure, the present reflector antenna includes a curved reflecting surface 10 made of metal mesh. Furthermore, curved reflective surface 1
A primary radiator 11 is attached to the zero focal position. The transmitted electromagnetic waves radiated from the primary radiator 11 are efficiently reflected by the mesh reflecting surface 10 and radiated toward the ground service area. Conversely, the electromagnetic waves transmitted from the ground station are reflected by the curved reflecting surface 10 and then transmitted to the primary radiator 1.
It is converged in the direction of 1. The curved reflective surface 10 has the same aperture diameter and the same mesh spacing S for all communication satellites.

Returning to FIG. 1 again, the method of allocating frequency transmission bands to individual communication satellites will be explained. The purpose of this allocation is to make the received power at the receiving antennas of ground stations located in the service area substantially constant.

Generally, Friis's transmission formula is applied to electromagnetic wave propagation phenomena. This is expressed by the following relational expression (1). Wr=Wt/(16π)2×(λ/d)
2 GtGr ...... (1) In relational expression (1), Wr is reception power, Wt is transmission power, Gr is reception antenna gain, Gt is transmission antenna gain, λ is transmission wavelength, and d is transmission antenna and reception antenna. is the distance between Now, assuming that the aperture diameter of the transmitting antenna is Dt and the aperture diameter of the receiving antenna is Dr, the following relational expressions (2) and (3) hold between the antenna gain and the aperture diameter. Gt=(πDt/λ)2……
………………………………… (2) Gr.
=(πDr/λ)2 …………………………………
...... (3) Next, by substituting relational expressions (2) and (3) into relational expression (1), the following relational expression (4) is obtained. Wr=π2 Wt/16×(Dt/d)2
×(Dr/λ)2… (4)

The relational expression (4) thus obtained will be applied to the satellite communication system of the present invention shown in FIG. In this case, Wr represents the received power of the ground station located in service area 6,
Wt represents the transmission power of the transmitting antennas 5a to 5d mounted on the individual communication satellites 4a to 4d, Dt represents the aperture diameter of the transmitting antenna, and d represents the distance between the ground station and each communication satellite, that is, the orbit. Dr represents the altitude, Dr represents the aperture diameter of the receiving antenna of the ground station, and λ represents the wavelength of electromagnetic waves used for space communication. In this system, antennas 5a mounted on individual communication satellites 4a to 4d
Since they have a common structure, the parameters Wt and Dt are constant. Further, the parameter Dr is also constant. Therefore, the relational expression (4
), the received power Wr at the ground station is inversely proportional to the square of the orbit altitude and inversely proportional to the square of the wavelength. Alternatively, it is proportional to the square of the transmission frequency. That is, the higher the orbit altitude, the lower the received power, and conversely, the higher the transmission frequency, the higher the received power. That is, the orbit altitude and the transmission frequency are in a complementary relationship to each other. Using this complementary relationship, it is possible to keep the received power approximately constant over the entire transmission band of this system.

For example, in the satellite communication system shown in FIG.
S-band (
2.5GHz) and L band (1.5GHz) to the antenna 5c mounted on the communication satellite 4c on the intermediate elliptical orbit 8c.
z), and the UHF band (0.8 GHz) is assigned to the antenna 5d mounted on the communication satellite 4d on the inner elliptical orbit 8d. These transmission frequency bands are applicable to communications to fixed ground stations or mobile ground stations. Each orbital altitude is set in order to keep the received power of all these different transmission frequency bands constant. Now, geostationary satellite 4
Let R be the orbital altitude of a. At this time, the orbit altitude of the outer communication satellite 4b, that is, the distance between the apogee of the outer elliptical orbit 8b and the service area 6 on the earth, is set to R/1.6, and the elliptical orbit altitude of the intermediate satellite 4c is set to R/2. .7, and the orbit altitude of the inner communication satellite 4d is set to R/5. Antenna 5a to 5 mounted on each communication satellite 4a to 4d, respectively
When the received power Wr is calculated by applying relational expression (4) to d, all values become constant. That is, the ground station located in the service area 6 can receive all the transmitted electromagnetic waves of the C band, S band, L band, and UHF band with the same receiving power using a receiving antenna having a predetermined aperture diameter. When each transmission band is allocated in this way, it is preferable that each communication satellite is commonly equipped with a mesh reflector type communication antenna of, for example, 6 mφ class.

Instead of the above example, Ku
The outer communication satellite 5b may be assigned the S band, the intermediate communication satellite 4c may be assigned the L band, and the inner communication satellite 4d may be assigned the UHF band. In this case as well, the altitude of each satellite orbit is set so as to keep the received power on the ground constant according to relational expression (4). Further, as a transmitting antenna mounted on each satellite, for example, a reflector type communication antenna with an aperture diameter of 2 mφ class can be used.

Next, an example of a ground station located in the service area 6 will be shown with reference to FIG. In this example, a mobile ground station mounted on a truck 12 is shown. A mobile antenna 13 is installed on the roof of the truck 12. This antenna 13 receives and/or transmits electromagnetic waves to individual communication satellites. When considering transmission, the mobile antenna 13 has a radiation pattern 14 directed toward a stationary communications satellite in a geostationary orbit, and a radiation pattern 15 directed toward a communications satellite in an elliptical orbit. If the service area 6 is set in a relatively high latitude region on the earth, the angle of elevation relative to the geostationary satellite will be small, so the cone angle of the radiation pattern 14 will be large. On the other hand, for communication satellites on elliptical orbits, the inclination angle of the elliptical orbit can be set to suit a specific service area, so the angle of elevation can be increased. Therefore, the cone angle of the radiation pattern 15 can be made small.

Finally, FIG. 5 is a schematic overall view showing a second embodiment of the satellite communication system according to the present invention. Similar to the first embodiment shown in FIG. 1, this system also includes four communication satellites. Satellite 4a is placed in a geostationary orbit 8a, satellite 4k is placed in an outer elliptical orbit 8k, satellite 4n is placed in an intermediate elliptical orbit, and satellite 17m is placed in an inner elliptical orbit 8m. The geostationary satellite 4a has a pair of reflector type communication antennas 5a and 1 having a large aperture diameter and a small aperture diameter.
It is equipped with 6a. The large aperture antenna 5a has a C band (
4 GHz), and the Ku band (12 GHz) is assigned to the small aperture antenna 16a. That is,
The large aperture antenna 5a is for relatively low frequencies, and typically a mesh reflector type communication antenna of 6 mφ class is used. On the other hand, the small aperture communication antenna 16a is designed for relatively high frequencies, for example, a small reflector antenna of 2 mφ class is used, and the ratio of the aperture diameter to the wavelength is determined to be constant.

On the other hand, a communication satellite on an elliptical orbit is equipped with at least one of a large aperture antenna and a small aperture antenna. Specifically, the outer elliptical orbit 8k
The upper satellite 4k is equipped with a large aperture antenna 5k assigned to the L band, and the satellite 4n placed in an intermediate elliptical orbit 8n is equipped with a large aperture antenna 5n assigned to the UHF band. A 17m small communication satellite placed in an 8m inner elliptical orbit is equipped with a 16m small aperture antenna assigned to the S band. In this example as well, since each orbital altitude is appropriately set according to the above-mentioned relational expression (4), the ground station located in service area 6 receives substantially the same received power over the entire transmission band of the system. Can receive electromagnetic waves.

In both the first and second embodiments described above, the systems are constructed using four communication satellites, but the system is not limited to this. The number of communication satellites can be appropriately selected depending on the type of transmission band used. Further, in the embodiments described above, only one communication satellite is placed in each elliptical orbit, but the invention is not limited to this. For example, in order to enable 24-hour communication in a specific service area, a plurality of communication satellites may be arranged in the same elliptical orbit.

[0024]

As explained above, according to the present invention, a plurality of communication satellites equipped with communication antennas having a common structure are arranged on different elliptical orbits, and the distance between the apogee of each elliptical orbit and the ground service area is determined. A frequency transmission band proportional to the distance from the satellite is allocated to each communication satellite. Therefore, since the satellite communication system according to the present invention has a transmission bandwidth expanded compared to the conventional one, the number of communication lines can be increased, and the effect is that it can sufficiently cope with an increase in the number of users. There is. Another advantage is that the ground station can receive electromagnetic waves with the same reception power over the entire transmission band. Furthermore, by mounting a communication antenna having a common structure on a plurality of communication satellites, there is an effect that the construction cost of the entire system can be reduced. In addition, since transmission and reception are carried out via communication satellites orbiting on an elliptical orbit, there is the advantage that communication can be carried out even to areas behind a specific service area. A further advantage is that inter-satellite communication is also possible via the ground station.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a first embodiment of a satellite communication system according to the present invention.

FIG. 2 is an enlarged view showing the mesh structure of a mesh reflector type communication antenna mounted on a communication satellite.

FIG. 3 is a perspective view showing a common mesh reflector type communication antenna mounted on a communication satellite.

FIG. 4 is a schematic perspective view showing a ground station consisting of a mobile body.

FIG. 5 is a schematic diagram showing a second embodiment of the satellite communication system according to the present invention.

FIG. 6 is a schematic diagram showing a conventional satellite communication system.

[Explanation of symbols]

Claims (3)

[Claims] Claim 1: In a satellite communication system for communicating between a ground station and a plurality of communication satellites placed in different orbits, each communication satellite is equipped with a communication antenna having a common structure, It includes multiple communication satellites placed in different elliptical orbits, and by assigning each communication satellite a transmission band with a frequency proportional to its elliptical orbit apogee altitude, the received power at the ground station can be distributed over the entire transmission band. A satellite communication system characterized by a substantially constant value. 2. A satellite communication system according to claim 1, characterized in that it includes an additional communication satellite placed in a geostationary orbit different from an elliptical orbit. 3. The communication antenna having a common structure mounted on each communication satellite is a reflector antenna having the same aperture diameter, and is a metal wire mesh having a mesh spacing sufficiently smaller than the minimum transmission band wavelength of the satellite communication system. 3. The satellite communication system according to claim 1, further comprising a mirror surface made of.