Wireless communication system, wireless communication device, wireless communication method, and program for wireless communication

Abstract

Provided is a wireless communication system including: a transmission station 10 that is provided with a multi-beam antenna 12 for generating a plurality of beams 18-1, 18-2 to be emitted at fixed angles θ1, θ2 with respect to a directivity direction 14; and a reception station 22 that performs wireless communication using a plurality of antennas 20-1, 20-2. The transmission station 10 selects a transmission object antenna to which the plurality of beams are to be emitted, from among the plurality of antennas 20-1, 20-2. The directivity direction 14 is controlled to a specific direction that places the transmission object antenna within the coverage of the plurality of beams. A transmission signal is emitted from the multi-beam antenna 10 in a state in which the directivity direction 14 matches the specific direction. Among simultaneously placed antennas including one or more antennas 20-1, 20-2 simultaneously placed in the coverage of the plurality of beams, one that generates the maximum transmission capacity is selected as the transmission object antenna.

Description

Wireless communication system, wireless communication device, wireless communication method, and wireless communication program

[0001] This disclosure relates to a wireless communication system, a wireless communication device, a wireless communication method, and a wireless communication program, and in particular to a wireless communication system, a wireless communication device, a wireless communication method, and a wireless communication program that are suitable for maximizing the transmission capacity of spatial multiplexing transmission using a multi-beam antenna with a fixed beam direction.

[0002] Low Earth Orbit (LEO), which is an orbit around the Earth at an altitude of 2,000 km or less, is closer to the Earth's surface than Geostationary Earth Orbit (GEO). Therefore, using LEO for wireless communications offers various benefits. For example, the distance between the satellite and the ground station (GW: Gateway) is less than one-tenth of that when using GEO, significantly reducing propagation delay. Furthermore, the shorter propagation distance reduces propagation loss, enabling the power consumption of the transmitting station (MS: Moving Station) onboard the satellite to be reduced. This also makes it easier to miniaturize satellites and GWs, which is expected to reduce facility costs.

[0003] Unlike GEO satellites, LEO satellites are characterized by constantly moving when viewed from the ground. Therefore, in order to provide continuous service using LEO satellites, it is necessary to launch multiple satellites to provide comprehensive coverage to the entire service area. In particular, to provide global services, it is essential to deploy a satellite constellation orbiting the Earth.

[0004] In order to increase the communication capacity of terrestrial terminals and the number of terminals accommodated in communication services using LEO satellites, it is necessary to increase the capacity of the feeder link lines connecting the satellites and ground stations. To expand the capacity of the feeder link, it is desirable to use high frequency bands that enable broadband communication. In particular, for satellite-based communications, the use of the Ka band in the 20-30 GHz band and the Q / V band in the 40-50 GHz band is being considered.

[0005] These bands are significantly affected by rain attenuation, so it is necessary to build a system that can tolerate communication interruptions during rain. As a countermeasure against rain, for example, site diversity, which uses multiple antennas remotely located to prevent all satellites from being affected by rain at the same time, is being considered.

[0006] Typically, the MS and GW communicate using a single antenna. However, to further increase the capacity of the feeder link, a technology has been developed that utilizes spatial multiplexing transmission between multiple antennas (MIMO: Multiple-Input Multiple-Output) for satellite communications. Hereafter, this type of communication will be referred to as satellite MIMO.

[0007] In communications using satellite MIMO, the MS and GW are in a line-of-sight environment with no obstructions. In this case, high spatial correlation occurs in the multiple paths formed between the multiple antennas on the MS side and the multiple antennas on the GW side. As a result, it becomes difficult to properly separate the signals received by each of the multiple antennas on the GW, which is an issue.

[0008] Non-Patent Document 1 below states that antenna placement is an important factor in improving transmission capacity in a line-of-sight environment. More specifically, Non-Patent Document 1 discloses that, because satellite MIMO communications are performed in a line-of-sight environment and with a long transmission / reception distance, multiple antennas (hereinafter referred to as gateway antennas) placed on the ground can be placed far apart to form multiple channels with low correlation. In this case, MIMO transmission using multiple channels with low correlation is possible by connecting the remotely placed gateway antenna to the base station by wire.

[0009] One form of satellite MIMO is a technology in which multiple antennas capable of forming multi-beams are installed on an MS, and parallel transmission using multi-beams is established between the MS and multiple antennas on the ground. To realize such satellite MIMO, a satellite antenna capable of forming multi-beams and pointing control is required. Known methods for pointing control of satellite antennas are mechanical drive and electronic scanning.

[0010] The following non-patent document 2 discloses a mechanically driven tracking method. Specifically, this document discloses a method of using a highly directional antenna such as a parabolic antenna to mechanically adjust the angle of the antenna itself to control the direction of the antenna relative to a receiving station. Since mechanically driven tracking can be achieved simply by controlling the antenna angle, it has the advantage of being easier to achieve low cost and low power consumption compared to electronically controlled methods.

[0011] On the other hand, forming multiple beams using highly directional antennas requires the installation of multiple antennas whose angles can be adjusted mechanically. In this case, due to the constraints of the installation area on the satellite, each antenna must be made smaller. However, miniaturizing the antenna reduces the gain of each individual antenna. As a result, there is a risk that the conditions under which link calculations can be carried out will be reduced.

[0012] Non-Patent Document 3 below discloses a tracking technique using electronic scanning. In this technique, an array antenna equipped with many antenna elements with wide directivity is used. The excitation coefficients of the amplitude and phase of each array element are controlled so that the combined radio waves from all the antenna elements are propagated in the desired direction with high power.

[0013] In this case, since a single array antenna equipped with many small antenna elements can form multiple beams, there is little need for miniaturization due to space constraints on the satellite. However, since each of the many antenna elements must be driven individually, the same number of amplifiers as the antenna elements are required. Therefore, the greater the number of antenna elements, the greater the number of amplifiers required, which creates the problem of increased power consumption compared to mechanically driven systems.

[0014] The following non-patent document 4 discloses a configuration in which the feeder of a parabolic antenna is arrayed in order to form multiple beams while obtaining the receiving gain of the parabolic antenna. Such a parabolic antenna (hereinafter referred to as a "multi-beam parabolic antenna") does not require multiple parabolic antennas to be arranged side by side, and does not require miniaturization, making it possible to form multiple beams without sacrificing antenna gain. In this respect, the configuration described in non-patent document 4 has an advantage in terms of mounting area.

[0015] A. Knopp, R.T. Schwarz, D. Ogermann, C.A. Hofmann and B. Lankl, "Satellite System Design Examples for Maximum MIMO Spectral Efficiency in LOS Channels," IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference, 2008, pp. 1-6. T. Ueno, S. Ukawa, M. Sugita, T. Suzuki, T. Shima and Y. Arikawa, "ALOS-2 On-Orbit Evaluation Results of Satellite Attitude / Antenna Coordinated Control and Antenna Alignment Error Estimation," Proceedings of the 57th Joint Conference on Automatic Control Engineering, 2014, Vol. 57, Session ID 3A01-2, pp. 1882-1887. T. Takahashi et al., "On-Board Calibration Methods for Mechanical Distortions of Satellite Phased Array Antennas," in IEEE Transactions on Antennas and Propagation, vol. 60, no. 3, pp. 1362-1372, March 2012, doi: 10.1109 / TAP.2011.2180303. Mitsuaki Orikasa, and Yoshiyuki Fujino. "Study of Ultra-Multibeam Technology and Beamforming Experiments." National Institute of Information and Communications Technology Research Report 61.1 (2015): 111-118.

[0016] However, in a multi-beam parabolic antenna, the direction of the multiple beams is fixed to the direction of the antenna itself, so the method using a multi-beam parabolic antenna does not allow for flexible control of the direction of each beam, as is the case with electronic scanning using an array antenna.

[0017] Therefore, in order to provide a large transmission capacity to the feeder link while resolving issues such as the limited installation area on the satellite, antenna gain loss, and high power consumption due to a large number of amplifiers, it is desirable to use a multi-beam parabolic antenna and improve the transmission capacity of the feeder link under the constraint that the beam direction is fixed.

[0018] In order to solve the above-mentioned problems, a first object of the present disclosure is to provide a wireless communication system that is suitable for maximizing the transmission capacity of a feeder link while using a multi-beam parabolic antenna and under the constraint that the beam direction is fixed.

[0019] A second object of the present disclosure is to provide a wireless communication device that is suitable for maximizing the transmission capacity of a feeder link while using a multi-beam parabolic antenna and under the constraint that the beam direction is fixed.

[0020] A third object of the present disclosure is to provide a wireless communication method suitable for maximizing the transmission capacity of a feeder link while using a multi-beam parabolic antenna and under the constraint that the beam direction is fixed.

[0021] A fourth object of the present disclosure is to provide a wireless communication program suitable for maximizing the transmission capacity of a feeder link while using a multi-beam parabolic antenna and under the constraint that the beam direction is fixed.

[0022] A first aspect is a wireless communication system including a transmitting station equipped with a multi-beam antenna that generates multiple beams that are radiated at a fixed angle relative to a direction of direction of directionality, and a receiving station that performs wireless communication using multiple antennas, wherein the transmitting station is configured to perform the following processes: selecting a target antenna to be radiated with the multiple beams from among the multiple antennas; controlling the direction of direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the direction of direction coinciding with the specific direction; and it is desirable that the target antenna be the simultaneously accommodating antenna that generates the largest transmission capacity among simultaneously accommodating antennas that include one or more of the antennas that simultaneously fall within the coverage of the multiple beams.

[0023] In addition, a second aspect is a wireless communication device that has a multi-beam antenna that generates multiple beams that are radiated at a fixed angle relative to the directional direction, and that performs wireless communication with a receiving station that uses multiple antennas, and is configured to execute the following processes: selecting a target antenna to be radiated with the multiple beams from among the multiple antennas; controlling the directional direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the directional direction coinciding with the specific direction, and it is desirable that the target antenna be the simultaneously accommodating antenna that generates the largest transmission capacity among simultaneously accommodating antennas that include one or more of the antennas that simultaneously fall within the coverage of the multiple beams.

[0024] Furthermore, a third aspect is a wireless communication method for establishing wireless communication with a receiving station using multiple antennas, using a multi-beam antenna that generates multiple beams that are radiated at a fixed angle with respect to a direction of direction of direction of direction of direction of transmission, comprising the steps of: selecting a target antenna to be radiated with the multiple beams from among the multiple antennas; controlling the direction of direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the direction of direction matching the specific direction. It is preferable that the step of selecting the target antenna of transmission comprises the steps of: searching for simultaneously servicable antennas that include one or more of the antennas that can simultaneously be accommodated within the coverage of the multiple beams; estimating the transmission capacity that can be obtained for each of the simultaneously servicable antennas; and selecting the simultaneously servicable antenna for which the largest transmission capacity is estimated as the target antenna of transmission.

[0025] Furthermore, a fourth aspect is a computer-readable wireless communication program for establishing wireless communication between a transmitting station equipped with a multi-beam antenna that generates multiple beams radiated at a fixed angle with respect to a direction of direction of direction, and a receiving station that performs wireless communication using multiple antennas, the program including a process of causing the transmitting station to execute the following processes: selecting a target antenna to be radiated with the multiple beams from among the multiple antennas; controlling the direction of direction of the multi-beam antenna in a specific direction that brings the target antenna into coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna in a state where the direction of direction matches the specific direction, and it is desirable that the process of selecting the target antenna includes a process of searching for simultaneously accommodating antennas including one or more of the antennas that can simultaneously fit within the coverage of the multiple beams; a process of estimating the transmission capacity that can be obtained for each of the simultaneously accommodating antennas; and a process of selecting the simultaneously accommodating antenna for which the maximum transmission capacity is estimated as the target antenna.

[0026] According to the first to fourth aspects, while using a multi-beam parabolic antenna, it is possible to provide the feeder link with the largest possible transmission capacity under the constraint that the beam direction is fixed.

[0027] 1 is a diagram for explaining the configuration of a wireless communication system according to a first embodiment of the present disclosure. It is a block diagram for functionally explaining the configurations of the transmitting station and the ground station shown in FIG. 1. It is a diagram showing a state in which the distance between GW antennas is greater than the coverage width of the beam emitted by the transmitting station shown in FIG. 1. It is a diagram showing a state in which the transmitting station shown in FIG. 1 has aligned the central axis of the beam with a single GW antenna. It is a diagram showing a state in which two GW antennas are contained within the coverage of the beam emitted by the transmitting station shown in FIG. 1. It is a diagram showing a state in which the transmitting station shown in FIG. 1 has aligned the central axis of the beam with one of two GW antennas that are contained within the coverage to avoid the influence of inclement weather. It is a diagram showing a state in which the transmitting station shown in FIG. 1 has selected a combination that is expected to have the maximum propagation capacity from among combinations of GW antennas that are contained within the coverage of the beam and radiates the beam. It is a diagram showing a state in which three GW antennas are contained within the coverage of the beam emitted by the transmitting station shown in FIG. 1. It is a diagram showing a state in which the transmitting station shown in FIG. 1 has selected two of the three GW antennas that are contained within the coverage to radiate the beam to avoid the influence of inclement weather. 10 is a flowchart for explaining the flow of processing executed in each of the transmitting station and the ground station shown in Fig. 1. FIG. 11 is a flowchart for explaining the details of step 102 shown in Fig. 10.

[0028] First Embodiment [Configuration of First Embodiment] (Overall Configuration) Fig. 1 is a diagram for explaining the configuration of a wireless communication system according to a first embodiment of the present disclosure. As shown in Fig. 1, the system of this embodiment includes a transmitting station (MS) 10. The MS 10 is a wireless communication device mounted on an airborne platform that constitutes an NTN (Non-Terrestrial Network), such as a LEO satellite or a HAPS (High Altitude Platform Station).

[0029] In this embodiment, the MS 10 is equipped with a multi-beam parabolic antenna 12. The multi-beam parabolic antenna 12 has a parabolic antenna body and an arrayed power feeder, and is capable of emitting multiple beams in a direction fixed relative to the body.

[0030] 1, reference numeral 14 indicates the direction of the central axis of the multi-beam parabolic antenna 12, i.e., the pointing direction of the multi-beam parabolic antenna 12. The arrayed feeder provided in the multi-beam parabolic antenna 12 is set to radiate a first beam 18-1 in a direction 16-1 at an angle θ1 with respect to the pointing direction 14, and to radiate a second beam 18-2 in a direction 16-2 at an angle θ2 with respect to the pointing direction 14. Hereinafter, when there is no need to distinguish between the two beams 18-1 and 18-2, the subscripts of the reference numerals will be omitted and they will be referred to as "beam 18."

[0031] In this embodiment, the multi-beam parabolic antenna 12 generates two beams 18-1 and 18-2, but the present disclosure is not limited to this. The multi-beam parabolic antenna 12 may generate three or more beams.

[0032] As shown in Fig. 1, the system of this embodiment includes multiple GW antennas placed on the ground. Two GW antennas 20-1 and 20-2 are shown as an example in Fig. 1. Hereinafter, when there is no need to distinguish between the two, the subscripts of the reference symbols will be omitted and they will be referred to as "GW antennas 20." The multiple GW antennas 20 are installed at sufficient distances so that multiple channels with low spatial correlation can be formed between them and the MS 10.

[0033] The GW antenna 20 is connected to a receiving station 22 via a wired or wireless path. The receiving station 22 includes an interference compensation unit 24 and a demodulation unit 26. The interference compensation unit 24 performs processing to compensate for the influence of interference superimposed on the signals received by each of the GW antennas 20. The demodulation unit 26 also performs equalization processing and demodulation processing to demodulate signals transmitted using the MIMO transmission technique.

[0034] (Details of the Transmitting Station MS) Fig. 2 is a block diagram for functionally explaining the configuration of the MS 10 and the ground station (GW) 60 included in the system of this embodiment. The function of each block shown in Fig. 2 may be implemented in circuitry or processing circuitry including a general-purpose processor programmed to realize the function, an application-specific processor, an integrated circuit, an ASIC (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), a conventional circuit, and / or a combination thereof. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. The processor may also be a programmed processor that executes a program stored in a memory.

[0035] In this specification, a circuit, a "part," a "unit," or a "means" refers to hardware that is programmed to implement a described function or that implements that function, and may be any hardware disclosed herein or any hardware that is programmed to implement the described function or that is known to execute that program.

[0036] If the hardware is a processor, which is considered to be a type of circuitry, then the circuitry, "part" or "unit" or "means" is the combination of the hardware and software used to configure the hardware and / or processor.

[0037] 2, the MS 10 includes a modulation unit 30. The signal processed by the modulation unit 30 is then processed by a transmission amplitude / phase control unit 32 and provided to the multi-beam parabolic antenna 12 from a signal transmission unit 34. The multi-beam parabolic antenna 12 radiates two beams 18 that propagate the transmission signal, directed at fixed angles θ1 and θ2 with respect to the pointing direction 14.

[0038] The multi-beam parabolic antenna 12 includes a signal receiving unit 36 ​​for processing received signals. The signal receiving unit 36 ​​provides the received signals to a reception amplitude / phase control unit 38. The reception amplitude / phase control unit 38 provides information about the received signals to a demodulation unit 40 and also feeds back the information to the transmission amplitude / phase control unit 32.

[0039] The demodulator 40 performs a predetermined demodulation process on the received signal to restore the data transmitted from the ground. The transmission amplitude and phase controller 32 reflects the fed back information in subsequent control.

[0040] The reception amplitude / phase control unit 38 also provides information about the received signal to a received power calculation unit 42. The received power calculation unit 42 calculates the power of the received signal and provides the result to a directivity direction control unit 44.

[0041] The MS 10 is provided with a GW antenna position estimator 46. The GW antenna position estimator 46 estimates the relative positions of the individual GW antennas 20 as seen from the MS 10 based on pre-stored position information of each GW antenna 20 and the current position of the MS 10. The estimated position information is provided to a transmission target GW antenna selector 48.

[0042] The transmission target GW antenna selector 48 extracts from all GW antennas 20 those that can be covered by the MS 10 from its current location. If there are multiple GW antennas 20 that can be covered, the transmission target GW antenna selector 48 further selects from these antennas a combination that maximizes the transmission capacity of the feeder link and determines these as the transmission targets. The determination of the transmission target GW antenna selector 48 is provided to the directivity direction control unit 44.

[0043] The pointing direction control unit 44 is further provided with an estimate of the current position of the MS 10 from a station position estimator 50, and with an estimate of the current attitude of the MS 10 from a station attitude estimator 52. The pointing direction control unit 44 generates a drive signal for controlling the pointing direction 14 of the beam 18 based on the above-mentioned various pieces of information it has received.

[0044] The drive signal generated by the directivity direction control unit 44 is provided to the antenna drive unit 54. The antenna drive unit 54 has a mechanism for mechanically driving the body of the multi-beam parabolic antenna 12. The multi-beam parabolic antenna 12 is mechanically driven by the antenna drive unit 54 to change its attitude so as to achieve the desired directivity direction 14.

[0045] (Details of the Ground Station Gateway) The Gateway 60 includes multiple Gateway antennas 20 installed at sufficient intervals. Signals received by the Gateway antennas 20 are provided to a signal receiving unit 62 via a wired or wireless path. These signals are then subjected to interference compensation processing and demodulation processing within the receiving station 22 as described with reference to FIG. 1.

[0046] The signal receiving unit 62 also provides the received signals received from each GW antenna 20 to a received power calculation unit 64. The received power calculation unit 64 calculates the received power for each received signal and provides the result to a directivity direction control unit 66. Based on the information on the received power, the directivity direction control unit 66 generates a drive signal for each GW antenna 20 that received a signal, in order to obtain a directivity direction that maximizes the receiving sensitivity.

[0047] The drive signal generated by the directivity direction control unit 66 is provided to an antenna drive unit 68-i provided for each GW antenna 20. For example, the drive signal for the GW antenna 20-1 is provided to the antenna drive unit 68-1. Furthermore, the drive signal for the GW antenna 20-2 is provided to the antenna drive unit 68-2. Hereinafter, when there is no need to distinguish between the individual antenna drive units, the subscripts of the reference symbols will be omitted and they will be referred to as "antenna drive units 68."

[0048] The GW antenna 20 has a parabolic antenna body similar to the multi-beam parabolic antenna 12. All of the GW antennas 20 can change their direction of orientation by being mechanically driven by the corresponding antenna driving unit 68. However, in the present disclosure, the GW antenna 20 may be a phased array antenna capable of electronic scanning, rather than being mechanically driven.

[0049] The GW 60 further includes a modulation unit 70 that modulates the transmission data. The signal that has been modulated as desired by the modulation unit 70 is provided to a signal transmission unit 72. The signal transmission unit 72 causes each of the GW antennas 20 designated as transmission antennas to transmit an uplink signal directed toward the MS 10.

[0050] [Operation of First Embodiment] (Situation when one GW antenna fits within the coverage) Fig. 3 shows a situation in which the distance between the two GW antennas 20-1 and 20-2 is greater than the coverage width of the two beams 18 emitted by the multi-beam parabolic antenna 12. In this case, even if the direction of direction 14 of the multi-beam parabolic antenna 12 is aligned with the midpoint 74 between the two GW antennas 20-1 and 20-2, sufficient reception power cannot be obtained from either of them.

[0051] 4 shows a state in which the multi-beam parabolic antenna 12 has its direction of orientation 14 aligned with one of the GW antennas 20-2. In this embodiment, the multi-beam parabolic antenna 12 is configured so that an overlapping region occurs between the two beams 18-1 and 18-2. This overlapping region is large enough to accommodate a single GW antenna 20. Therefore, when the multi-beam parabolic antenna 12 aligns its direction of orientation 14 with the GW antenna 20-2, the GW antenna 20-2 is accommodated in the overlapping region.

[0052] In this embodiment, the MS 10 has the function of achieving spatial multiplexing transmission by transmitting different signals on each of the two beams 18. However, under the circumstances shown in Fig. 4, the MS 10 employs a transmit diversity technique in which the same signal is transmitted on the two beams 18. More specifically, the MS 10 shown in Fig. 4 employs an in-phase combining transmission technique in which the transmission phases of the two beams 18 are controlled so that a signal strengthened by in-phase combining reaches the GW antenna 20-2. In-phase combining transmission can achieve higher communication robustness compared to single-beam transmission in which only one of the two beams 18 is used.

[0053] When implementing in-phase combining transmission, the MS 10 notifies the receiving station 22 that it will use this technique prior to starting communication. Upon receiving this notification, the receiving station 22 performs demodulation processing in the same manner as in the case of SISO (Single-Input Single-Output) transmission, without implementing interference compensation or the like for MIMO transmission. This establishes high-quality wireless communication between the MS 10 and the receiving station 22.

[0054] (Situation in which two GW antennas are simultaneously within the coverage of a beam) FIG. 5 shows a situation in which two beams 18 each cover two GW antennas 20. In this case, the MS 10 can deliver sufficient transmission power to both GW antennas 20 by aligning the pointing direction 14 of the multi-beam parabolic antenna 12 with the midpoint 74 between the two GW antennas 20. Furthermore, in this embodiment, the two GW antennas 20 are positioned sufficiently far apart, so channel correlation for each antenna is sufficiently suppressed. Therefore, the MS 10 shown in FIG. 5 transmits two types of signals with the same frequency but different content using the two beams 18, performing 2x2 MIMO spatial multiplexing transmission. Regarding interference between adjacent beams with the same frequency, as shown in the figure, the SINR (Signal-to-Interference-plus-Noise Ratio) characteristics can be improved by performing known interference compensation and equalization processing followed by demodulation processing. In the figure, "r" indicates the received signal, and "s'" indicates the signal after equalization.

[0055] 6 shows a situation in which one of two GW antennas 20 within its coverage is affected by bad weather, so the multi-beam parabolic antenna 12 aligns its pointing direction 14 with the other GW antenna 20. Even if both GW antennas 20 are within the coverage of two beams 18, if an event occurs in one of the GW antennas 20 that causes a degradation in communication characteristics, the MS 10 stops spatial multiplexing transmission and performs in-phase combined transmission toward the other GW antenna 20.

[0056] The Ka band (uplink 30 GHz, downlink 20 GHz) and higher frequency bands used in satellite communications enable wideband communications, but are susceptible to the effects of rain attenuation. For this reason, as shown in Figure 6, if rain is detected in the area of ​​the GW antenna 20-2, a situation may arise in which the desired communication quality cannot be obtained between the GW antenna 20-2 and the MS 10. The MS 10 acquires severe weather information such as rain and geomagnetic storms for each area in which the GW antenna 20 is located that falls within its coverage area, and excludes GW antennas 20 that are affected by severe weather from the transmission targets.

[0057] In a situation where both GW antenna 20-1 and GW antenna 20-2 are within the coverage area, if GW antenna 20-2 is excluded from the transmission target, only GW antenna 20-1 will be the transmission target. In this case, the MS 10 aligns its pointing direction 14 with GW antenna 20-1 and performs in-phase combined transmission toward GW antenna 20-1, which is accommodated in the overlapping area of ​​beam 18, in the same way as in the case described with reference to Figures 3 and 4. This realizes the best communication environment under the circumstances shown in Figure 6, and maximizes transmission capacity.

[0058] (A situation where there are three GW antennas that can communicate) Figure 7 shows a situation where the number of GW antennas 20 that can communicate with the MS 10 is greater than the number of beams 18 emitted by the multi-beam parabolic antenna 12. More specifically, Figure 7 shows a situation where the following conditions are met: (1) The multi-beam parabolic antenna 12 generates two beams 18. (2) There are three GW antennas 20 in the area where communication with the MS 10 is possible. (3) The maximum number of GW antennas 20 that can simultaneously fit within the coverage of two beams 18 is two.

[0059] 7, there are a maximum of three cases (3C2 = 3) in which 2 × 2 MIMO multiplex transmission is possible using two beams 18. From these three cases, MS 10 selects the case that maximizes transmission capacity, taking into consideration the predicted position of GW antenna 20 and contour information of the beam coverage.

[0060] The predicted values ​​of transmission capacity can be compared, for example, based on the following formula: where Nr is the number of receiving antennas, Nt is the number of transmitting antennas, and σ ｎ ２ represents the received noise power, and Pt represents the transmitted power.

[0061]

[0062] In the specific arrangement shown in FIG. 7 , i.e., an arrangement in which three GW antennas 20 are arranged side by side, 2×2 MIMO multiplex transmission is possible in two cases: when two GW antennas 20-1 and 20-2 are the transmission targets, and when two GW antennas 20-2 and 20-3 are the transmission targets. FIG. 7 shows an example in which the latter case is selected as the transmission target as a result of a comparison of transmission capacity. In this case, the MS 10 aligns the direction 14 of the multi-beam parabolic antenna 12 with the midpoint 76 between the GW antennas 20-2 and 20-3. Thereafter, 2×2 MIMO multiplex transmission is performed between the MS 10 and the receiving station 22, as in the case shown in FIG. 5. As a result, the best communication environment under the circumstances shown in FIG. 7 is realized, and transmission capacity is maximized.

[0063] (Situation in which three GW antennas are simultaneously within the coverage of a beam) Figure 8 shows a situation in which three GW antennas 20 are simultaneously within the coverage of two beams 18 emitted by the MS 10. In the situation shown in Figure 8, each of the three GW antennas 20 can receive at least one of the two beams 18. In this case, the MS 10 controls the pointing direction 14 of the multi-beam parabolic antenna 12 toward the midpoint (center of gravity) 78 of the three GW antennas 20.

[0064] In the situation shown in Figure 8, the MS 10 has two transmitting antennas and the ground station has three receiving antennas, enabling 2x3 MIMO multiplexing transmission. In the case of 2x3 MIMO, interference cancellation between adjacent channels can be performed in the same way as in the case of 2x2 MIMO. Specifically, as shown in Figure 8, the SINR characteristics can be improved by performing known interference cancellation and equalization processing using a 3x2 matrix followed by demodulation processing. This realizes the best communication environment under the situation shown in Figure 8 and maximizes transmission capacity.

[0065] 9 shows a situation in which one of three GW antennas 20 that simultaneously fall within the coverage of a beam 18 is affected by bad weather, so the multi-beam parabolic antenna 12 transmits only to the other two GW antennas 20. Even if all three GW antennas 20 simultaneously fall within the coverage of two beams 18, if an event that causes degradation of communication characteristics occurs in some of them, the MS 10 will exclude the GW antenna 20 where the event is occurring from the transmission targets.

[0066] Specifically, in the present embodiment, when the GW antenna 20-3, out of the three within the coverage area, is affected by bad weather, the MS 10 transmits only to the two GW antennas 20-1 and 20-2, which are expected to function normally.The pointing direction 14 of the multi-beam parabolic antenna 12 is then aligned with the midpoint 80 between them, and 2x2 MIMO multiplex communication is performed, as in the case shown in Figure 5.This realizes the best communication environment under the conditions shown in Figure 9, and maximizes transmission capacity.

[0067] 9 illustrates a situation in which only GW antenna 20-3 of the three GW antennas 20 is affected by bad weather, but the present disclosure is not limited to this. That is, if two of the three GW antennas 20 are affected by bad weather, the MS 10 excludes those two from the transmission targets and transmits only to the remaining GW antenna 20. In this case, as in the case shown in FIG. 6, the MS 10 performs in-phase combined transmission, and the receiving station 22 performs demodulation processing similar to that in the case of SISO.

[0068] [Processing Flow Executed in First Embodiment] Fig. 10 is a flowchart for explaining the processing flow executed in each of the MS 10 and the GW 60 in this embodiment. More specifically, the left side of Fig. 10 shows the processing flow executed in the MS 10. Furthermore, the right side of Fig. 10 shows the processing flow executed in the GW 60.

[0069] (Processing flow of MS 10) As shown in the area on the left side of Fig. 10, MS 10 first predicts its own position and the position of the GW antenna 20 as seen from itself (step 100). The absolute positions (latitude, longitude, etc.) of all GW antennas 20 are registered in MS 10 in advance. MS 10 also has a function to detect its own position. After detecting its own position, MS 10 predicts the position of each GW antenna 20 relative to itself based on that position and the absolute position of the GW antenna 20.

[0070] Next, the MS 10 selects, from among all the GW antennas 20, a GW antenna 20 to be used as a transmission target in order to obtain the maximum transmission capacity (step 102).

[0071] 11 is a flowchart for explaining the details of step 102. First, based on the location information obtained in step 100, GW antennas 20 that are currently capable of communicating with the MS 10 are extracted from all GW antennas 20 (step 140). Hereinafter, the GW antennas 20 extracted here will be referred to as "communication-capable antennas."

[0072] Next, a process is executed to exclude bad weather antennas from the antennas capable of communication extracted in step 140 (step 142). Specifically, first, weather information relating to the installation areas of the antennas capable of communication is acquired from outside. Next, based on the acquired weather information, antennas capable of communication that are in an environment that has a non-negligible impact on communication quality are recognized as bad weather antennas. Finally, the antennas capable of communication excluding the bad weather antennas are determined as "transmission candidate antennas."

[0073] Next, using the transmitting candidate antennas determined in step 142 as a population, a search is made for a set of GW antennas 20 that can be simultaneously accommodated in the two beams 18 emitted by the multi-beam parabolic antenna 12 (step 144). For example, in the situation shown in Fig. 3, each of the GW antennas 20-1 and 20-2 is recognized as a "simultaneous accommodated antenna." Also, in the situation shown in Fig. 5, for example, a set of the GW antennas 20-1 and 20-2 is recognized as a "simultaneous accommodated antenna."

[0074] Next, one of the "simultaneous accommodating antennas" identified in the search in step 144 is set as the target for propagation capacity estimation (step 146).

[0075] Next, it is determined whether the simultaneously accommodating antennas set as the estimation target include a plurality of GW antennas 20 (step 148).

[0076] As a result, if it is determined that the simultaneously accommodated antennas include multiple antennas, the center points of those antennas (see Figures 3, 5, 7 and 8) are virtually determined as the directional direction 14 of the multi-beam parabolic antenna 12 (step 150).

[0077] Furthermore, MIMO transmission is virtually selected as the communication method between MS 10 and GW 60 (step 152).

[0078] After the above process is completed, the transmission capacity that can be secured between the target simultaneous access antenna and the MS 10 is estimated using the virtually set directivity direction 14 and the virtually selected communication method (step 154).

[0079] When the estimation of the transmission capacity is completed, it is determined whether or not the estimation of the transmission capacity has been completed for all the simultaneously accommodating antennas searched for in step 144 (step 156). As a result, if it is determined that the estimation has not been completed for all the antennas, the processing from step 146 onwards is executed again.

[0080] If it is determined in step 148 above that the simultaneously accommodating antennas set as the processing target do not include multiple antennas, it can be determined that the simultaneously accommodating antennas are a single GW antenna 20. In this case, the direction toward the GW antenna 20 is virtually determined as the directivity direction 14 of the multi-beam parabolic antenna 12 (step 158).

[0081] In this case, SISO transmission is then virtually selected as the communication method between the MS 10 and the GW 60 (step 160).

[0082] Thereafter, in step 154, the transmission capacity that can be secured by the current estimation target is estimated in the same manner as above.

[0083] As the above process is repeated, if it is determined in step 156 that all estimations have been completed, the maximum transmission capacity is extracted from all the estimated transmission capacities (step 162).

[0084] Then, the extracted simultaneously accommodating antenna that generates the maximum transmission capacity is selected as the best transmission target to be selected under the current situation (step 164).

[0085] 10 again, the explanation will be continued. After completing the selection of the GW antenna 20 that maximizes the transmission capacity through the above process, the MS 10 next performs coarse adjustment of the pointing direction 14 (step 104). The coarse adjustment is performed based on the location information predicted in the above step 100.

[0086] Next, a process is executed to receive the beacon transmitted from the GW antenna 20 determined as the transmission target (step 106).

[0087] Fine adjustment of the pointing direction 14 is then performed based on information obtained from the received beacons (step 108).

[0088] Thereafter, the MS 10 generates data for downlink (step 110), and transmits a signal carrying that data from the multi-beam parabolic antenna 12 to the GW antenna 20 that is the transmission target (step 112).

[0089] (Processing flow of GW 60) As shown in the area on the right side of Fig. 10 , the GW 60 first predicts the position of each GW antenna 20 and the position of the MS 10 as seen from each GW antenna 20 (step 120). The absolute positions (latitude, longitude, etc.) of all GW antennas 20 are registered in advance in the GW 60. The GW 60 also has a function for detecting the position of the MS 10. After detecting the position of the MS 10, the GW 60 predicts the relative positions of the two based on that position and the positions of each GW antenna 20.

[0090] Next, based on the relative positional relationship predicted in step 120, coarse antenna adjustment is performed to orient the direction of the GW antenna 20 toward each MS 10 (step 122).

[0091] Furthermore, each of the GW antennas 20 transmits a beacon toward the MS 10 (step 124).

[0092] Next, fine adjustment of the direction of pointing is performed on each of the GW antennas 20 (step 126). This fine adjustment may be performed based on the strength of the beacon signal or the like received by each of the GW antennas 20 from the MS 10, for example.

[0093] Thereafter, when any of the GW antennas 20 receives a transmission signal from the MS 10, the GW 60 sequentially performs processes such as channel estimation (step 128), equalization (step 130), demodulation (step 132), and data recovery (step 134) to process the transmission signal.

[0094] According to the above process, the MS 10 can control the direction 14 of the multi-beam parabolic antenna 12 so as to obtain the maximum transmission capacity under the constraint that the beam direction is fixed. Therefore, according to the system of this embodiment, it is possible to provide the feeder link with a sufficiently large transmission capacity while sufficiently suppressing the antenna installation area and power consumption in the MS 10.

[0095] [Variations of the First Embodiment] In the first embodiment described above, the multi-beam parabolic antenna 12 is mounted on the MS 10, which moves relative to the GW antenna 20. However, the present disclosure is not limited to this. For example, the multi-beam parabolic antenna 12 may be mounted on a transmitting station, whose relative position with respect to the receiving antenna does not change. Even in this case, a situation may arise in which some receiving antennas cannot maintain sufficient sensitivity due to changes in the environment between the transmitting station and the receiving antennas. For this reason, a technique for selecting an antenna that generates the maximum transmission capacity from among multiple receiving antennas and setting it as the transmission target may be used in combination with such a transmitting station.

[0096] 10 Transmitting station (MS) 12 Multi-beam parabolic antenna 14 Direction of beam 18, 18-1, 18-2 Beam 20, 20-1, 20-2, 20-3 GW antenna 22 Receiving station 60 Ground station (GW) 74, 76, 78, 80 Center point

Claims

1. A wireless communication system including a transmitting station equipped with a multi-beam antenna that generates multiple beams that are radiated at a fixed angle relative to the directional direction, and a receiving station that performs wireless communication using multiple antennas, wherein the transmitting station is configured to perform the following processes: select a target antenna from the multiple antennas to be radiated with the multiple beams; control the directional direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiate a transmission signal from the multi-beam antenna with the directional direction coinciding with the specific direction, and the target antenna is the simultaneously radiated antenna that generates the largest transmission capacity among simultaneously radiated antennas that include one or more of the antennas that are simultaneously within the coverage of the multiple beams.

2. A wireless communication device that has a multi-beam antenna that generates multiple beams that are radiated at a fixed angle relative to the directional direction and that performs wireless communication with a receiving station that uses multiple antennas, and is configured to execute the following processes: selecting a target antenna to be radiated with the multiple beams from among the multiple antennas; controlling the directional direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the directional direction coinciding with the specific direction, wherein the target antenna is the simultaneously accommodating antenna that generates the largest transmission capacity among simultaneously accommodating antennas that include one or more of the antennas that simultaneously fit into the coverage of the multiple beams.

3. A wireless communication method for establishing wireless communication with a receiving station using multiple antennas, using a multi-beam antenna that generates multiple beams that are radiated at a fixed angle relative to the direction of directionality, comprising the steps of: selecting a target antenna from the multiple antennas to be radiated with the multiple beams; controlling the direction of direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the direction of direction matching the specific direction, wherein the step of selecting the target antenna comprises the steps of: searching for simultaneously servicable antennas including one or more of the antennas that can simultaneously fit within the coverage of the multiple beams; estimating the transmission capacity that can be obtained for each of the simultaneously servicable antennas; and selecting the simultaneously servicable antenna for which the largest transmission capacity is estimated as the target antenna.

4. A computer-readable wireless communication program for establishing wireless communication between a transmitting station equipped with a multi-beam antenna that generates multiple beams radiated at a fixed angle relative to the directional direction, and a receiving station that performs wireless communication using multiple antennas, the program including a program that causes the transmitting station to execute the following processes: selecting a target antenna from among the multiple antennas to be radiated with the multiple beams; controlling the directional direction of the multi-beam antenna in a specific direction that brings the target antenna into the coverage of the multiple beams; and radiating a transmission signal from the multi-beam antenna with the directional direction coinciding with the specific direction, wherein the process of selecting the target antenna includes a process of searching for simultaneously accommodating antennas including one or more of the antennas that can simultaneously fit within the coverage of the multiple beams; estimating the transmission capacity that can be obtained for each of the simultaneously accommodating antennas; and selecting the simultaneously accommodating antenna for which the maximum transmission capacity is estimated as the target antenna.

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