JP7536234B2 - Multi-beam relay communication system - Google Patents

Description

This relates to a multi-beam relay communication system that is mounted on an air vehicle and efficiently shares the same frequency band to enable bidirectional communication between a large number of user terminals distributed over a wide area and a gateway station via a relay communication device with a multi-beam antenna.

Conventionally, there have been hopes for the realization of a relay communication system in which unmanned or manned aircraft are flown at high altitudes of several thousand meters to several tens of kilometers, and used as communication relay bases to provide communication services to user terminals distributed over a wide area from lower altitudes to the ground.

When two-way communication with a user terminal is established through such a relay communication system, a satellite communication system is generally used. In satellite communication systems, a multi-beam antenna that directs antenna beams for transmission and reception in multiple directions at the same time may be used to reuse frequencies for efficient use. Since it is difficult to share one frequency band for both the uplink and downlink in a satellite communication system due to the long communication distance, a frequency division multiplexing method is used that uses different frequency bands for the uplink and downlink. Separate frequency bands are also allocated to the feeder link that connects the satellite to the gateway station and the user link that connects the satellite to the user terminal. In addition, the attitude of a satellite is usually highly stable, and the directivity of the antenna beam generated by the satellite's multi-beam antenna is almost fixed without the need for high-speed control. In addition, while satellite services are available up to about 10 km above the earth's surface and sea level, the altitude of a geostationary satellite is 36,000 km above the equator, so the viewing angle of the service area from the satellite is 20° or less, and even in the case of a low-orbit satellite, the viewing angle is 90° or less. This has the advantage that the difference in communication quality due to differences in relative direction and position from the satellite is small, allowing for more stable relay communication.

Non-Patent Document 1 summarizes the recent trends in satellite communication systems that use the Ka band (30/20 GHz band), and states that currently most satellite communication systems employ a multi-beam communication method to make effective use of frequencies. According to this document, in any Ka-band satellite communication system, different frequency bands are used for the uplink (from the earth station to the satellite) and the downlink (from the satellite to the earth station). Specifically, the 30 GHz band is allocated to the uplink, and the 20 GHz band is allocated to the downlink.

However, with this satellite communications system, geostationary satellites are at an altitude of over 36,000 km above sea level from the equator, and even non-geostationary satellites are at an altitude of 800 to 8,000 km above sea level, meaning that the distances from the earth's surface, sea level, or the sky up to an altitude of about 10 km above sea level that are the targets of the service are extremely long. For this reason, if a time division duplex (TDD) method is adopted, in which communication is performed with a time lag while both sides are synchronized on the same frequency band, it becomes necessary to set a large guard time between the time slots of the uplink and downlink, making it difficult to improve efficiency. This poses the problem that it is difficult to share the same frequency band for the uplink and downlink.

This non-patent document 1 also states that in any satellite system, the user link (between the satellite and the user terminal) and the feeder link (between the satellite and the operator's earth station) require broadband communication lines to avoid interference, or because the feeder link needs to accommodate all communication traffic in the user link. This necessitates the adoption of means to allocate separate frequency bands between these two links, posing the problem of the need for a separate frequency channel for the feeder link in addition to the user link.

Since satellite communication systems move by inertia in a vacuum, disturbances that disturb attitude are extremely small compared to those in the atmosphere, and high-speed correction control of the antenna beam direction is not required. In addition, the viewing angle of the service area of the earth's surface, sea level, or up to about 10 km above sea level as seen from the satellite is a maximum of about ±9° for geostationary satellites, and is within 46° for non-geostationary satellites. Therefore, even if this service area is covered with multiple beams, there is little difference in communication quality between beams, and there is no need for technology to standardize communication quality. Therefore, if this technology is applied to a communication system for user terminals in a service area with a wide angle of ±60° or more, the communication quality for user terminals located on the periphery of the service area will be significantly reduced, and there will be problems in that if a relay communication device is installed on an aircraft flying in the atmosphere, there will be large fluctuations in attitude and direction, and communication quality will also be large at user terminals and gateway stations.

The technology disclosed in Non-Patent Document 2 and Patent Document 1 aims to efficiently use frequencies by equipping one or more unmanned aerial vehicles (drones) with relay communication devices, and using time division multiplexing (TDD) and time division multiple access (TDMA) to share the same frequency band between transmission and reception lines in each communication section consisting of these drones, user terminals, ground control stations, target unmanned aerial vehicles to be controlled, etc.

In the technology disclosed in Non-Patent Document 2 and Patent Document 1, one target unmanned aerial vehicle is serviced by one ground control station, but by increasing the number of time slots and frequency channels, it is possible to expand to allow simultaneous communication connections to multiple target unmanned aerial vehicles. However, an omnidirectional single-beam antenna is used for the relay communication device, and expansion to a communication method compatible with multi-beam antennas is not anticipated, resulting in the problem that it is not possible to increase the spatial frequency utilization efficiency.

JP 2017-228917 A

Ministry of Internal Affairs and Communications document, “Investigative and Examination Materials on Issues Surrounding Satellites,” https://www.soumu.go.jp/main_content/000463131.pdf, January 31, 2017 Kagawa, Ono et al., "Demonstration Experiment of Drone Control and Sensor Data Transmission Using 920MHz Band Multi-hop Wireless Communication System," IEICE Technical Report, vol. 118, no. 344, RCC2018-97, pp. 217-221, December 2018.

The present invention was conceived in consideration of the above-mentioned problems, and its purpose is to provide a multi-beam relay communication system that is mounted on an air vehicle and that efficiently shares the same frequency band to perform two-way communication between a large number of user terminals distributed over a wide area and a gateway station via a relay communication device having a multi-beam antenna.

The multibeam relay communication system according to the first invention comprises a relay communication device mounted on an air vehicle and having a multibeam antenna that generates n antenna beams for transmission and reception for a user link, each of which is directed to n cells, and generates m antenna beams for transmission and reception for a feeder link, each of which is directed to m gateway stations; k user terminals that perform two-way communication with the relay communication device through the user link; and m gateway stations that are connected to a public communication network and perform two-way communication with the relay communication device through the feeder link. The user terminals and the gateway stations form a round-trip communication path through the user link and the feeder link via the relay communication device, and the relay communication device assigns divided frequency bands obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n≧q) to each of the antenna beams so that they are different between adjacent cells in the user link, and assigns the divided frequency bands to each of the gateway stations so that they are different from the divided frequency bands assigned to the antenna beams directing the cell in which the gateway station is included.

The multi-beam relay communication system according to the second invention is the first invention, characterized in that the relay communication device sets the antenna beam diameter generated for the feeder link to be smaller than the antenna beam diameter generated for the user link.

The multibeam relay communication system according to the third invention comprises a relay communication device mounted on an air vehicle and having a multibeam antenna that generates n antenna beams for transmission and reception for a user link, each of which is directed to n cells, and generates m antenna beams for transmission and reception for a feeder link, each of which is directed to m gateway stations; k user terminals that perform two-way communication with the relay communication device through the user link; and m gateway stations that are connected to a public communication network and perform two-way communication with the relay communication device through the feeder link. The user terminals and the gateway stations form a round-trip communication path through the user link and the feeder link via the relay communication device, and the relay communication device classifies the cells into z zones consisting of a plurality of cells, and assigns antenna elements for transmitting and receiving the antenna beams in the multibeam antenna to each zone according to the gain of the two-way communication.

The multi-beam relay communication system according to the fourth invention is characterized in that, in the third invention, the relay communication device assigns divided frequency bands obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n≧q) to each of the antenna beams so that the divided frequency bands are different between adjacent cells in the user link, and assigns the divided frequency bands to each of the gateway stations so that the divided frequency bands are different from the divided frequency bands assigned to the antenna beams pointing to the cell in which the gateway station is included, and assigns antenna elements for transmitting and receiving the antenna beams in the multi-beam antenna according to the gain of the antenna beam generated for the feeder link.

A multi-beam relay communication system according to a fifth aspect of the present invention is characterized in that, in the first aspect, the relay communication device divides the entire frequency band of the user link into f(1) to f(q) (n≧q) and assigns divided frequency bands to each of the antenna beams so that the divided frequency bands are different between adjacent cells in the user link, and assigns the divided frequency bands to each of the gateway stations so that the divided frequency bands are different from the divided frequency bands assigned to the antenna beams pointing to the cell including the gateway station, and further repeatedly generates, for each time segment in the user link, antenna beams corresponding to the coverage of a portion of a group of cells in the entire coverage, and repeatedly generates, for each time segment in the feeder link, antenna beams corresponding to a portion of all of the gateway stations.

According to the present invention having the above-mentioned configuration, a user link is formed between a gateway station, which is connected to a ground network via a relay communication device by wire or wireless and connected to the relay communication device by a feeder link, and a fixed or mobile user terminal that is distributed over a wide area on the ground, sea, or sky at a wide angle from the relay communication device. The relay communication device then assigns divided frequency bands obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n≧q) to each antenna beam so that the divided frequency bands are different between the adjacent cells in the user link, and assigns divided frequency bands to each gateway station so that the divided frequency bands are different from the divided frequency bands assigned to the antenna beams pointing to the cell containing the gateway station. This makes it possible to provide communication services with high frequency utilization efficiency to user terminals distributed over a wide area in areas with poor or no communication infrastructure.

Since such a relay communication system relays communication via a communication relay base at a high altitude, it can comprehensively cover an area with a diameter of several tens of kilometers even in cases where the terrestrial communication infrastructure is poor or where there are mountainous or oceanic areas, making it possible to build a communication infrastructure that is less susceptible to the effects of disasters. For this reason, the relay communication system of the present invention can be expected to be used as a backup network for so-called terrestrial communication networks. In addition, since this relay communication system is mounted on an aircraft, the communication distance to the user terminal is significantly shorter than that of a satellite. Therefore, it has the advantage that high-speed communication can be performed with a smaller transmission output and antenna gain than a satellite line, and communication costs can be reduced accordingly.

FIG. 1 is a diagram showing the overall system configuration of a multi-beam relay communication system to which the present invention is applied. FIG. 2 is a diagram for explaining a block configuration of the relay communication device. FIG. 3 is a diagram for explaining an example in which the entire frequency band of a user link transmitted by a relay communication device is divided into divided frequency bands f(1) to f(q). FIG. 4 is a diagram showing an example in which a cell is formed by an antenna beam in a feeder link overlapping a cell in a user link, and communication is performed while reducing interference between the two links by preventing the divided frequency bands of the user link cell and the feeder link cell from overlapping. FIG. 5 is a diagram showing an example in which a narrower antenna beam diameter is assigned to a gateway station in a feeder link, thereby reducing interference with cells of nearby user links that use the same divided frequency band. FIG. 6 is a diagram showing an example in which a plurality of divided frequency bands of a feeder link are allocated to the same cell. FIG. 7 is a diagram showing an example of allocating antenna elements for transmitting and receiving antenna beams in the multi-beam antenna to each zone consisting of a plurality of cells in accordance with the gain of two-way communication. FIG. 8 is a diagram for explaining a case in which the diameter of an antenna beam generated for a feeder link is set smaller than the diameter of an antenna beam generated for a user link in the example of FIG. FIG. 9 is a diagram showing an example of generating antenna beams for transmission and reception directed to cells in each altitude range. FIG. 10 is a diagram showing an example of a frame configuration when the entire frequency band of the user link and the feeder link is divided into frequency bands f(1) to f(q). FIG. 11 is a diagram showing an example of bidirectional communication of a forward link and a return link based on the frame configuration shown in FIG. FIG. 12 is a diagram showing an example in which one packet to be transmitted or received in a user link or a feeder link is transmitted as divided packets divided into a plurality of time slots or frequency channels. FIG. 13 is a diagram showing an example in which antenna beams corresponding to the coverage of a portion of a group of cells among the entire coverage are generated repeatedly at the same time for each time segment in a user link. FIG. 14 is another diagram showing an example in which antenna beams corresponding to the coverage of a portion of a group of cells among the entire coverage are generated repeatedly at the same time for each time segment in a user link. FIG. 15 is a diagram showing an example in which the service areas of high altitude aircraft or drones are partially overlapped.

Below, we will explain in detail the multi-beam relay communication system to which the present invention is applied, with reference to the drawings.

Figure 1 shows the overall system configuration of a multibeam relay communication system 1 to which the present invention is applied. This multibeam relay communication system 1 is equipped with a relay communication device 2 mounted on an air vehicle and having a multibeam antenna 21, k user terminals 3 that perform bidirectional communication with the relay communication device 2, m gateway stations 4 that perform bidirectional communication with the relay communication device 2, a public communication network 5 connected to the gateway station 4, and a central communication terminal 6 connected to the public communication network 5.

The relay communication device 2 is mounted on a flying object such as a manned or unmanned aircraft, helicopter, airship, or balloon flying at high altitude. The relay communication device 2 generates n transmitting antenna beams and n receiving antenna beams each pointing in n different directions for the user link. The relay communication device 2 also generates m transmitting antenna beams and m receiving antenna beams each pointing in the directions of m gateway stations 4 located in m different directions for the feeder link. Hereinafter, these transmitting antenna beams and receiving antenna beams for the user link and feeder link are collectively referred to as antenna beams for transmission and reception.

As shown in FIG. 2, in addition to the multi-beam antenna 21, the relay communication device 2 includes a user link transceiver 22, a relay unit 23 connected to the user link transceiver 22, a feeder link transceiver 24 connected to the relay unit 23, phase and amplitude control units 25-1 to 25-n connected to the user link transceiver 22, and phase and amplitude control units 26-1 to 26-m connected to the feeder link transceiver 24.

The multi-beam antenna 21 is composed of an array of e small antenna elements 211 that are shared for both transmission and reception. The above-mentioned transmit and receive antenna beams for the user link and feeder link are transmitted and received through each small antenna element 211. The transmit and receive antenna beams generated through these small antenna elements 211 are configured to be directed toward each cell on Earth in the user link. Similarly, the transmit and receive antenna beams generated through these small antenna elements 211 are configured to be directed toward each gateway station 4 on Earth.

The direction of such an antenna beam of the small antenna elements 211 is set by the respective phase and amplitude control units 25-1 to 25-n and 26-1 to 26-m connected to them. The phase and amplitude control units 25-1 to 25-n and 26-1 to 26-m can control the direction of such an antenna beam by respectively setting the phase and amplitude of the power supply signal to the small antenna elements 211 and the received signal of the small antenna elements 211.

Under the control of such phase and amplitude control units 25-1 to 25-n and 26-1 to 26-m, it is possible to set the direction of the antenna beam to multiple different directions simultaneously or in a time-division manner. In addition, even if the attitude or direction of the aircraft, such as an aircraft carrying this relay communication device 2, changes, this can be compensated for, and control can be realized to maintain the direction of the antenna beam in a fixed direction.

The user link transceiver 22 controls two-way communication between k user terminals 3. The user link transceiver 22 actually outputs signals received from the user terminals 3 via the multi-beam antenna 21 to the relay unit 23. It also controls the transmission of signals from the gateway station 4 sent from the relay unit 23 via the multi-beam antenna 21.

The feeder link transceiver 24 controls bidirectional communication between m gateway stations 4. The feeder link transceiver 24 actually outputs signals received from the gateway station 4 via the multibeam antenna 21 to the relay unit 23. It also controls the transmission of signals from the user terminal 3 sent from the relay unit 23 via the multibeam antenna 21.

The relay unit 23 relays the transmission and reception of signals between the user link transceiver unit 22 and the feeder link transceiver unit 24.

The user terminal 3 is a mobile or fixed terminal for individual users to perform wireless communication. Examples of the user terminal 3 include fixed telephones, mobile phones, smartphones, tablet terminals, wearable terminals, and personal computers (PCs), as well as communication terminals mounted on automobiles, aircraft, ships, trains, robots, and various devices. When the user terminal is a mobile terminal, communication is performed in units of cells 7, which are small service areas divided within the entire area. In this user link, n antenna beams for transmission and reception, each directed to one of the n cells 7, are formed through the relay communication device 2. The user terminal 3 communicates with the relay communication device 2 via an antenna beam directed toward the cell 7 to which it belongs.

The gateway station 4 serves as a base station fixed on the ground, but is not limited to this and may be configured as a semi-fixed station whose range of movement is limited to a predetermined range. This gateway station 4 communicates with the relay communication device 2 via antenna beams through a feeder link. The gateway station 4 is connected to a public communication network 5 including an Internet line, and is capable of transmitting information acquired from the Internet to each user terminal 3 by relaying it through the relay communication device 2. The gateway station 4 can also execute various operations for controlling the entire multi-beam relay communication system 1 and the flight of the relay aircraft on which it is mounted, based on instructions and control from a central communication terminal 6 connected via the public communication network 5.

The multi-beam relay communication system 1 configured as described above can configure a round-trip communication path between k user terminals 3 and m gateway stations 4 via one relay communication device 2. This round-trip communication path can also be shared in the same frequency band by time division multiplexing or frequency division multiplexing, or a combination of time division multiplexing and frequency division multiplexing. In addition, it can also be combined with beam division multiplexing provided by the multi-beam antenna 21 to reuse the same frequency channel in a specified frequency band, allowing two-way communication with high frequency utilization efficiency. Specific methods for this are described below.

As shown in FIG. 3, the entire frequency band of the user link transmitted by the relay communication device 2 is divided into divided frequency bands f(1) to f(q). The number of divided frequency bands q here is based on the premise that the relationship n≧q holds in relation to the number n of antenna beams described above.

Any of f(1) to f(q) is assigned to each transmitting and receiving antenna beam generated by the multi-beam antenna 21 so that mutual interference between the antenna beams is minimized. Each antenna beam is formed to be directed to each cell 7 in the user link as shown in FIG. 3, and communication is performed independently between the antenna beams assigned to each cell 7. In particular, when the partial frequency bands of antenna beams directed to adjacent cells 7 overlap, there is a possibility that mutual communication interference will occur. For this reason, at least the divided frequency bands are assigned to the antenna beams directed to adjacent cells 7 so that they are different from each other. As an example of assignment, as shown in FIG. 3, when q is 3, the partial frequency bands f(1), f(2), and f(3) are arranged so that they are different from each other between the antenna beams directed to adjacent cells 7. In the example of FIG. 3, when focusing on one cell 7 to which the partial frequency band f(1) is assigned, this can be realized by alternately arranging the other partial frequency bands f(2) and f(3) in the six cells 7 arranged around it. In the above example, the case where q is 3 has been described, but the present invention is not limited to this. When q is 7, that is, when the partial frequency bands are composed of f(1) to f(7), focusing on one cell 7 to which the partial frequency band f(1) is assigned, the other partial frequency bands f(2) to f(7) can be arranged in the six cells 7 arranged around it. If q is 3 or more, it is possible to adopt various arrangement variations that reduce mutual interference between antenna beams based on the above arrangement example.

In this way, each divided frequency band f(1) to f(q) can be reused between different transmitting antenna beams and different receiving antenna beams, and the number of user terminals 3 that can be accommodated in the user link can be increased in proportion to the number of times the divided frequency band is reused in both the transmitting and receiving antenna beams.

In addition to the method of allocating divided frequency bands in the user link, the present invention may also allocate divided frequency bands in the feeder link in a similar manner. In such a case, the entire frequency band of the feeder link transmitted by the relay communication device 2 is divided into divided frequency bands f(1) to f(q). In terms of equipment costs, it is efficient to set the number of divided frequency bands q so that the relationship m≦q holds in relation to the number m of antenna beams allocated to each gateway station 4 described above, but m>q may also be satisfied.

Any of f(1) to f(q) is assigned to each transmitting and receiving antenna beam generated by the multi-beam antenna 21 so that mutual interference between the antenna beams is minimized. Each antenna beam is formed to be directed to each cell 7 in the feeder link as shown in FIG. 4, and communication is performed independently between the antenna beams assigned to each cell 7. In particular, if the partial frequency bands of antenna beams directed to adjacent cells 7 overlap, there is a possibility that mutual communication interference will occur. For this reason, at least the partial frequency bands are assigned to the antenna beams directed to adjacent cells 7 so that they are different from each other. A specific example of this assignment method may be applied to the user link example described above.

At this time, it is desirable to allocate the partial frequency bands f(1) to f(q) assigned to each antenna beam generated for the feeder link so that mutual interference with the partial frequency bands f(1) to f(q) assigned to the antenna beam for the user link is reduced. For example, as shown in FIG. 4, when focusing on the same cell 7, the partial frequency band f(1) is assigned to the cell 7 in which the partial frequency band assigned through the user link is f(2) in the feeder link. Similarly, the partial frequency band f(2) is assigned to the cell 7 in which the partial frequency band assigned through the user link is f(3) in the feeder link. Similarly, the partial frequency band f(3) is assigned to the cell 7 in which the partial frequency band assigned through the user link is f(1) in the feeder link. This makes it possible to prevent communication interference between the user link and the feeder link in each cell 7 without overlapping the partial frequency bands. Note that there may be cases where the partial frequency band of the user link and the partial frequency band of the feeder link overlap between adjacent cells, but as shown in FIG. 5, in general, in the feeder link, the antenna beam diameter is narrowed and assigned to the gateway station 4. In other words, by setting the antenna beam diameter generated for the feeder link to be smaller than the antenna beam diameter generated for the user link, communication interference between them can usually be prevented even in cases where the partial frequency band of the user link and the partial frequency band of the feeder link overlap between adjacent cells.

Figure 6 shows an example of allocating multiple types of feeder link partial frequency bands to the same cell 7. Even in such a case, when focusing on the same cell 7, it is possible to prevent communication interference between the user link and the feeder link in the same cell 7 by allocating partial frequency bands f(1) and f(3) to the cell 7 whose partial frequency band allocated through the user link is f(2). Similarly, when focusing on another cell 7, it is possible to prevent communication interference between the user link and the feeder link in the same cell 7 by allocating partial frequency bands f(1) and f(2) to the cell 7 whose partial frequency band allocated through the user link is f(3).

In addition, in the present invention, the cells may be classified into z zones consisting of a plurality of cells, and an antenna element for transmitting and receiving the antenna beam of the multi-beam antenna may be assigned to each zone according to the gain of two-way communication. For example, as shown in FIG. 7, the beam antenna is classified into z zones (cell groups) according to the direction of direction to the cell 7 or the communication distance to the cell. In the example of FIG. 7, each cell 7 is grouped into zone 1, which is the closest distance to the relay communication device 2, zone 2, which is a medium distance, and zone 3, which is a long distance. When performing this grouping, the small antenna element 211 to be used in zone 1, the small antenna element 211 to be used in zone 2, and the small antenna element 211 to be used in zone 3 are assigned in advance. The number of small antenna elements 211 for generating antenna beams directed to these is appropriately allocated according to the zone. At this time, the number of small antenna elements 211 to be assigned to a zone that is more likely to have a longer distance to the relay communication device 2 and a lower communication quality and therefore a lower gain, as shown in FIG. 7, may be increased.

In this way, by allocating antenna elements that transmit and receive the antenna beams in the multi-beam antenna according to the gain of two-way communication, it is possible to reduce differences in communication gain and communication quality between zones.

In addition, by appropriately changing the allocation of the small antenna elements 211 used to generate the antenna beam for the feeder link and setting the width of each beam, it is possible to share the same frequency band between the antenna beam in the feeder link and the antenna beam in the user link with little mutual interference.

At this time, as shown in the above-mentioned Figures 4 and 5, the divided frequency bands obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n ≥ q, m ≤ q) are assigned to each antenna beam so as to be different between adjacent cells in the user link. At the same time, as shown in Figure 8, when the divided frequency bands are assigned to each gateway station so as to be different from the divided frequency bands assigned to the antenna beam pointing to the cell 7 containing the gateway station, the antenna beam diameter generated for the feeder link is set smaller than the antenna beam diameter generated for the user link. This makes it possible to reduce communication interference between the two.

The example in Figure 9 shows an example in which n transmission/reception antenna beams directed toward n cells in altitude range (layer) A are generated for a first user link, and n2 transmission/reception antenna beams directed toward n2 spatial regions in altitude range (layer) B are generated for a second user link. Incidentally, altitude range (layer) A is set to a lower altitude than altitude range (layer) B. In addition to these, m transmission/reception antenna beams directed toward m gateway stations 4 are generated for the feeder link, similar to the above.

First, the system includes k user terminals 3 that perform two-way communication with the relay communication device 2 through a first user link. The system also includes a plurality of second user terminals 9 mounted on another flying object that flies at a lower altitude than the flying object on which the relay communication device 2 is mounted and which performs two-way communication through a second user link. The flying object on which the second user terminals 9 are mounted is composed of an unmanned or manned aircraft, helicopter, or the like. Furthermore, the system also includes m gateway stations 4 that perform two-way communication with the relay communication device 2 through a feeder link.

The user terminal 3 and the gateway station 4 form a round-trip communication path through a first user link and a feeder link via the relay communication device 2. The second user terminal 9 and the gateway station 4 form a round-trip communication path through a second user link and a feeder link via the relay communication device 2.

In this case, the first user link and the second user link may be assigned to antenna beams for different altitude ranges so that their communication frequencies are different from each other. Also, the first user link and the second user link may be assigned to antenna beams for different altitude ranges so that their time slots are different from each other. This makes it possible to prevent communication interference between the first user link and the second user link.

In addition, in the present invention, when the entire frequency band of the user link and feeder link that the relay communication device 2 transmits and receives is divided into each divided frequency band f(1) to f(q), communication may be performed based on the frame structure in the following method.

Figure 10 shows an example of the frame structure. It is assumed that the user link and feeder link have a fixed time length and perform bidirectional communication in frame units that are synchronized with each other. Each frame of the user link and feeder link consists of two subframes, divided into an earlier and later subframe in time, and a guard time, which is a predetermined signal-free interval, is added to the end of each subframe. The divided frequency band allocated to the user link is cu, and the divided frequency band allocated to the feeder link is cf.

Here, the communication path from the user terminal 3 to the gateway station 4 via the relay communication device 2 is called a return link. Also, the communication path from the gateway station 4 to the user terminal 3 via the relay communication device 2 is called a forward link. In each frequency channel, the front subframe and the rear subframe are divided into time slots of su1, su2, ... or time slots of sf1, sf2, ....

In this case, in the return link, for example, as shown in FIG. 10, the signal sent from the user terminal 3 through the user link is inserted into the previous subframe of time slot su1. The relay communication device 2 transmits the signal inserted into the previous subframe of time slot su1 to the subsequent subframe of time slot sf4 of the subsequent frame through the feeder link to the gateway station 4.

In the forward link, as shown in FIG. 10, the signal sent from the gateway station 4 via the feeder link is inserted into the previous subframe of time slot sf1. The relay communication device 2 transmits the signal inserted into the previous subframe of time slot sf1 to the subsequent subframe of time slot su4 of the subsequent frame, via the user link, to the user terminal 3.

Signals in other subframes in the user link and feeder link will also be sent in the following frame. The divided frequency band cu constituting the user link may be further divided into multiple or more divided frequency bands, each of which may be superimposed on an antenna beam for transmission and reception. The divided frequency band cf constituting the feeder link may be further divided into multiple or more divided frequency bands, each of which may be superimposed on an antenna beam for transmission and reception.

In this case, in bidirectional communication of the forward link and return link, the frequency bands cu and cf are shared by both the user link and the feeder link, respectively, making it possible to accommodate a large number of user terminals within the communication system.

When such data frames are used to perform bidirectional communication on the forward link and the return link, as shown in FIG. 11, the subframes may be arranged so that the relay communication device 2 transmits on the feeder link at the same timing as the user link and receives on the feeder link at the same timing as the relay communication device 2 receives on the user link. That is, in FIG. 10, a return link data frame on the user link is formed in time slot su1, and a forward link data frame on the feeder link is formed in sf1 at the same timing. This means that, as shown in FIG. 11(a), the timing of transmission from the user terminal 3 to the relay communication device 2 is the same as that of transmission from the gateway station 4 to the relay communication device 2. Similarly, in FIG. 10, a forward link data frame on the user link is formed in time slot su2, and a return link data frame on the feeder link is formed in sf2 at the same timing. This means that, as shown in FIG. 11(b), the timing of transmission from the relay communication device 2 to the user terminal 3 is the same as that of transmission from the relay communication device 2 to the gateway station 4. The relay communication device 2 prevents the transmission timing in the user link from overlapping with the reception timing in the feeder link, and also prevents the reception timing in the user link from overlapping with the transmission timing in the feeder link, making it possible to avoid interference caused by leakage from transmission to reception.

In the present invention, as shown in FIG. 12, one packet, which is a collection of information to be sent on the return link, may be allocated to a single block consisting of one time slot of one frequency channel in one subframe in the user link or feeder link according to the amount of information. In other words, single blocks in the user link or feeder link may be collected to form a divided packet, and one packet may be composed by combining multiple divided packets. One packet may also be divided and allocated to multiple blocks of two or more subframes, two or more frequency channels, and two or more time slots. In other words, two or more blocks in the user link or feeder link may be collected to form a divided packet, and one packet may be composed by combining multiple divided packets. Although it is this one packet that is actually communicated, a communication line that flexibly adapts to the amount of information in one packet that needs to be communicated can be established.

In addition, the present invention may further combine time division when dividing the entire frequency band of the user link transmitted by the relay communication device 2 as shown in FIG. 3 into divided frequency bands f(1) to f(q). As shown in FIG. 13, the relay communication device 2 divides the entire time into d time segments, and in the user link, in the first time segment T1, n (T1) antenna beams corresponding to a part of the coverage area of the entire coverage area of the relay communication device 2 are generated simultaneously. In the example of FIG. 13, antenna beams directed to seven cells are generated simultaneously as the n (T1) antenna beam. Next, in the second time segment T2, n (T2) antenna beams corresponding to another part of the coverage area are generated simultaneously. In the example of FIG. 13, antenna beams directed to six cells are generated simultaneously as the n (T2) antenna beam. This operation is repeated until the total number of beams n corresponding to the entire coverage area (here, n (T1) + n (T2) + ... + n (Td) = n, where Td is the last d-th time segment) is reached.

Similarly, in the feeder link, the relay communication device 2 simultaneously generates m (T1) antenna beams corresponding to a portion of all the gateway stations 4 in time segment T1. Next, in time segment T2, it simultaneously generates m (T2) antenna beams corresponding to another portion of the gateway stations 4, and repeats this process until the total number of beams m (where m (T1) + m (T2) + ... + m (Td) = m) corresponding to all the gateway stations 4 is reached.

In other words, in the user link, for each time segment, antenna beams corresponding to the coverage of a portion of the cell groups within the entire coverage are generated simultaneously and repeatedly, and in the feeder link, for each of the above time segments, antenna beams corresponding to a portion of the gateway stations 4 among all the gateway stations 4 are generated repeatedly.

Each time segment of the user link and feeder link is synchronized with the frame period and subframe period shown in FIG. 10 described above. Then, for each time segment, only a portion of all multi-beams are generated simultaneously, and these are switched in sequence.

This allows the relay communication device 2 to correspond to the entire coverage area of the user link and all gateway stations of the feeder link, while reducing the number of antenna beams that are generated simultaneously. As a result, it is possible to reduce the transmission power of the relay communication device 2, and it is also possible to reduce the inter-beam interference of the user link and the inter-beam interference between the user link and the feeder link.

In this case, in the user link, a gateway station 4 included in a part of the coverage area consisting of multiple cells may be assigned to a time segment different from the time segment of the data frame assigned to that coverage area. For example, in time segment T2, an antenna beam m(T2) corresponding to another part of the gateway stations 4 is generated, but in that time segment T2, the gateway station 4 included in the coverage area of this m(T2) is assigned to a different time segment.

Figure 14 shows another example of the embodiment shown in Figure 13. In this example shown in Figure 14, the switching timing of the time segments T1, T2, T3, ... is aligned with the period of each frame. In the example of Figure 13 described above, the switching timing of the time segments T1, T2, T3, ... is performed within the previous subframe or the next subframe, whereas in Figure 14, it is performed on a frame basis consisting of the previous subframe and the next subframe. By implementing a similar method in this case, it is possible to cover the entire coverage area of the user link and all gateway stations of the feeder link, while reducing the number of antenna beams that are generated simultaneously.

According to the present invention having the above-mentioned configuration, a user link is formed that connects a gateway station 4, which is connected to a ground network via a relay communication device 2 by wire or wireless and connected to the relay communication device 2 by a feeder link, with fixed or mobile user terminals 3 that are distributed over a wide area on the ground, sea or sky and at a wide angle from the relay communication device. This makes it possible to provide communication services with high frequency utilization efficiency to user terminals 3 that are distributed over a wide area in areas where communication infrastructure is poor or non-existent.

Specifically, the same frequency band can be shared between the user link and the feeder link, and between the forward link and the return link, with minimal mutual interference, making it possible to ensure the same communication capacity with a smaller frequency band than before.

In addition, in both the user link and the feeder link, the gain of the multi-beam antenna can be allocated according to the distance and angle seen from the relay communication device 2, making it possible to achieve uniformity by reducing the difference in communication quality between user terminals 3 or between multiple gateway stations 4.

In addition, according to the present invention, by mounting a relay communication device 2 on an aircraft that flies at high altitudes of 10 to 20 km, it becomes possible to realize a multi-connection communication service between many user terminals 3 on the ground, at sea, or in the air (at a lower altitude than the altitude of the relay communication device 2) with a diameter of tens of kilometers or more. Examples of communication data handled by this service include sensor data, audio data, video data, etc., as well as command data and telemetry data for controlling robots and drones, making it possible to realize IoT services over a wide area, including areas with poor or non-existent communication infrastructure.

The multi-beam relay communication system 1 to which the present invention is applied is expected to have lower system construction costs and communication terminal costs than launching a satellite using a rocket or the like, and also has the advantage of being able to provide a communications infrastructure that is resistant to terrestrial disasters. Another advantage of the multi-beam relay communication system 1 is that it can reduce radio wave attenuation and communication delays compared to satellite systems.

In particular, in the multi-beam relay communication system 1 to which the present invention is applied, even if the same frequency band is used between antenna beams, mutual interference can be reduced by creating a certain degree of difference in beam direction, so there is no problem even if the same frequency band is used by multiple beams that are far apart from each other, and it is possible to accommodate more user terminals within a limited frequency range.

In addition, the multi-beam relay communication system 1 to which the present invention is applied electronically controls its antenna beam directivity, so even if the horizontal or vertical orientation of the relay communication device 2 varies over time, the variation is automatically compensated for, minimizing the impact on the quality of communication provided to the user terminal. In other words, the present invention can keep the beam footprint for the ground, sea, and sky constant regardless of the attitude and azimuth variations of an aircraft flying at high altitude.

Furthermore, the multi-beam relay communication system 1 to which the present invention is applied makes it possible to minimize the difference in communication quality between an area directly under an aircraft flying at high altitude and an area on the periphery of a service area far away from the aircraft, by using a gain distribution method based on the pointing direction.

The multi-beam relay communication system 1 to which the present invention is applied has a multi-beam antenna 21 consisting of multiple small antenna elements 211, and the direction of the antenna beam can be set by feeding power to each small antenna element 211 or by appropriately setting the phase of the radio waves received by each small antenna element 211. By performing these operations simultaneously between the directions of multiple antenna beams, it is possible to simultaneously direct and transmit antenna beams in multiple different directions. In addition, by changing the number of small antenna elements 211 used for each antenna beam, the gain of the antenna beam can be freely set. As an alternative to this multi-beam antenna 21, it may be realized by providing a directional antenna (not shown) facing multiple different directions and generating an antenna beam for each directional antenna.

Possible fields in which the multi-beam relay communication system 1 to which the present invention is applied can be applied include backup lines for mobile phone networks and dedicated communication networks, as well as wide-area IoT connections and operation management/control for various sensors, robots, unmanned aerial vehicles, automobiles (including autonomous driving), trains, aircraft, flying vehicles, ships, and human-held terminals. Unmanned aerial vehicles and manned aircraft flying at various altitude ranges can be covered with multi-beams layered for each altitude range.

Furthermore, according to the multi-beam relay communication system 1 to which the present invention is applied, as shown in FIG. 15, the service area can be expanded by flying multiple high-altitude aircraft or unmanned aircraft in the sky. At the same time, by overlapping a portion of the service area of each high-altitude aircraft or unmanned aircraft, each user terminal 3 located in the overlapping area can select the one with the best propagation conditions from among the multiple high-altitude aircraft or unmanned aircraft and communicate with it when radio waves are blocked or attenuated due to buildings or topography on the ground. Therefore, according to the present invention, it is highly useful as a measure to avoid the effects of blocking or attenuation.

REFERENCE SIGNS LIST 1 Multi-beam relay communication system 2 Relay communication device 3 User terminal 4 Gateway station 5 Public communication network 6 Central communication terminal 7 Cell 9 Second user terminal 21 Multi-beam antenna 22 User link transceiver unit 23 Relay unit 24 Feeder link transceiver unit 25 Phase and amplitude control unit 26 Phase and amplitude control unit 211 Small antenna element

Claims (5)

a relay communication device mounted on an airborne vehicle, the relay communication device having a multi-beam antenna for generating n antenna beams for transmission and reception for a user link, the n antenna beams being directed to n cells respectively, and for generating m antenna beams for transmission and reception for a feeder link, the m antenna beams being directed to m gateway stations respectively;
k user terminals that perform bidirectional communication with the relay communication device through the user link;
a number m of gateway stations connected to a public communication network and performing bidirectional communication with the relay communication device through the feeder link;
the user terminal and the gateway station form a round-trip communication path through the user link and the feeder link via the relay communication device;
the relay communication device allocates divided frequency bands, obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n≧q), to each of the antenna beams so as to be different from each other between the adjacent cells in the user link, and allocates the divided frequency bands to each of the gateway stations so as to be different from each other from the divided frequency bands allocated to the antenna beams pointing to the cell including the gateway station. 2. The multi-beam relay communication system according to claim 1, wherein the relay communication device sets an antenna beam diameter for the feeder link to be smaller than an antenna beam diameter for the user link. a relay communication device mounted on an airborne vehicle, the relay communication device having a multi-beam antenna for generating n antenna beams for transmission and reception for a user link, the n antenna beams being directed to n cells respectively, and for generating m antenna beams for transmission and reception for a feeder link, the m antenna beams being directed to m gateway stations respectively;
k user terminals that perform bidirectional communication with the relay communication device through the user link;
a number m of gateway stations connected to a public communication network and performing bidirectional communication with the relay communication device through the feeder link;
the user terminal and the gateway station form a round-trip communication path through the user link and the feeder link via the relay communication device;
The relay communication device classifies a plurality of cells into z zones, and assigns antenna elements for transmitting and receiving the antenna beams of the multibeam antenna to each of the zones according to the gain of the two-way communication. 4. The multibeam relay communication system according to claim 3, wherein the relay communication device allocates divided frequency bands, obtained by dividing the entire frequency band of the user link into f(1) to f(q) (n≧q), to each of the antenna beams so as to be different between adjacent cells in the user link, and allocates the divided frequency bands to each of the gateway stations so as to be different from the divided frequency bands allocated to the antenna beams pointing to the cell including the gateway station, and allocates antenna elements for transmitting and receiving the antenna beams in the multibeam antenna in accordance with a gain of the antenna beam generated for the feeder link. 2. The multi-beam relay communication system according to claim 1, wherein the relay communication device assigns divided frequency bands, obtained by dividing a total frequency band of the user link into f(1) to f(q) (n≧q), to each of the antenna beams so that the divided frequency bands are different between adjacent cells in the user link, and assigns the divided frequency bands to each of the gateway stations so that the divided frequency bands are different from the divided frequency bands assigned to the antenna beams pointing to the cell including the gateway station, and further repeatedly generates, for each time segment in the user link, antenna beams corresponding to coverage areas of a part of cell groups in a total coverage, and repeatedly generates, for each time segment in the feeder link, antenna beams corresponding to a part of all gateway stations.

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