WIRELESS COMMUNICATION SYSTEM, COMMUNICATION APPARATUS AND WIRELESS COMMUNICATION METHOD

In a wireless communication system including a first communication device, one or more second communication devices disposed around the first communication device, and a relay device that moves, the second communication device includes a second reception unit that attempts to receive a radio wave in a predetermined band and measures reception strength, and a second transmission unit that transmits, to the first communication device, reception result information indicating a peripheral radio wave condition based on the reception strength measured by the second reception unit, and the first communication device includes a first reception unit that attempts to receive a radio wave in the predetermined band and measures reception strength, a determination unit that determines a band to be used for transmission of data to the relay device on a basis of a peripheral radio wave condition based on the reception strength measured by the first reception unit and the peripheral radio wave condition based on the reception result information transmitted from the second transmission unit, and a first transmission unit that transmits the data to the relay device using the band determined by the determination unit.

TECHNICAL FIELD

The present invention relates to a wireless communication system, a communication apparatus and a wireless communication method.

BACKGROUND ART

With the development of Internet of Things (IoT) technology, it has been studied to install IoT terminals including various sensors in various places. The IoT terminals may be installed in a place where installation of a base station is difficult, such as on a buoy or on a ship in the sea or in a mountainous area. Therefore, to collect data obtained by the IoT terminals installed in various places, a technology of causing a relay device mounted on a low earth orbit satellite (LEO) to relay transmission of data from the IoT terminals to the base station has been studied.

Many IoT terminals are installed on the ground. Therefore, there is a technology in which a low earth orbit satellite receives a plurality of low power wide area (LPWA) terminal signals transmitted at the same timing with a plurality of antennas and separates the signals into signals for the respective IoT terminals. As a result, the number of IoT terminals accommodated in the low earth orbit satellite can be increased.

Conventionally, an IoT terminal receives a radio wave of a specific frequency for a certain period in communication with a low earth orbit satellite. In a case where the IoT terminal confirms that there are no other terminals interfering with each other, the IoT terminal transmits data to the low earth orbit satellite. However, in a case where a plurality of IoT terminals is located outside a signal coverage, the IoT terminals cannot mutually recognize that radio wave interference occurs, and a hidden terminal problem that causes interference or the like may occur.

In response to such a hidden terminal problem, the technology described in Non Patent Literature 1 controls data transmission timing by transmitting and receiving request to send (RTS)/clear to send (CTS), which are control signals, and prevents occurrence of radio wave interference.

CITATION LIST

Non Patent Literature

Non Patent Literature 1: S. Khurana, et al., “Effect of hidden terminals on the performance of IEEE 802.11 MAC protocol”, Proceedings 23rd Annual Conference on Local Computer Networks, IEEE, pp. 12-20, October 1998.

SUMMARY OF INVENTION

Technical Problem

However, in a case where communication is performed between the IoT terminal and the low earth orbit satellite, even if the control signal is transmitted from the IoT terminal to the low earth orbit satellite, the control signal does not reach another IoT terminal from the low earth orbit satellite thereafter. Therefore, in this case, the technology using the control signals such as RTS/CTS as described above cannot be applied, and there is a problem that prevention of occurrence of radio wave interference is difficult.

In view of the above circumstances, an object of the present invention is to provide a wireless communication system, a communication apparatus and a wireless communication method capable of further reducing occurrence of radio wave interference.

Solution to Problem

The first aspect of the present invention is a wireless communication system including a first communication device, one or more second communication devices disposed around the first communication device, and a relay device that moves, the second communication device including: a second reception unit that attempts to receive a radio wave in a predetermined band and measures reception strength; and a second transmission unit that transmits, to the first communication device, reception result information indicating a peripheral radio wave condition based on the reception strength measured by the second reception unit; and the first communication device including: a first reception unit that attempts to receive a radio wave in the predetermined band and measures reception strength; a determination unit that determines a band to be used for transmission of data to the relay device on a basis of a peripheral radio wave condition based on the reception strength measured by the first reception unit and the peripheral radio wave condition based on the reception result information transmitted from the second transmission unit; and a first transmission unit that transmits the data to the relay device using the band determined by the determination unit.

Further, the second aspect of the present invention is a communication device including a first communication unit and one or more second communication units disposed around the first communication unit, and configured to perform communication with a relay device that moves, the second communication unit including: a second reception unit that attempts to receive a radio wave in a predetermined band and measures reception strength; and a second transmission unit that transmits, to the first communication unit, reception result information indicating a peripheral radio wave condition based on the reception strength measured by the second reception unit; and the first communication unit including a first reception unit that attempts to receive a radio wave in the predetermined band and measures reception strength; a determination unit that determines a band to be used for transmission of data to the relay device on a basis of a peripheral radio wave condition based on the reception strength measured by the first reception unit and the peripheral radio wave condition based on the reception result information transmitted from the second transmission unit; and a first transmission unit that transmits the data to the relay device using the band determined by the determination unit.

Further, one aspect of the present invention is a wireless communication method by a first communication device, one or more second communication devices disposed around the first communication device, and a relay device that moves, the wireless communication method including: by the second communication device, a second reception step of attempting to receive a radio wave in a predetermined band and measuring reception strength; by the second communication device, a second transmission step of transmitting, to the first communication device, reception result information indicating a peripheral radio wave condition based on the reception strength measured by the second reception step; by the first communication device, a first reception step of attempting to receive a radio wave in the predetermined band and measuring reception strength; by the first communication device, a determination step of determining a band to be used for transmission of data to the relay device on a basis of a peripheral radio wave condition based on the reception strength measured by the first reception step and the peripheral radio wave condition based on the reception result information transmitted by the second transmission step; and by the first communication device, a first transmission step of transmitting the data to the relay device using the band determined by the determination step.

Further, one aspect of the present invention is a wireless communication method by a communication device that includes a first communication unit and one or more second communication units disposed around the first communication unit, and performs communication with a relay device that moves, the wireless communication method including: by the second communication unit, a second reception step of attempting to receive a radio wave in a predetermined band and measuring reception strength; by the second communication unit, a second transmission step of transmitting, to the first communication unit, reception result information indicating a peripheral radio wave condition based on the reception strength measured by the second reception step; y the first communication unit, a first reception step of attempting to receive a radio wave in the predetermined band and measuring reception strength; by the first communication unit, a determination step of determining a band to be used for transmission of data to the relay device on a basis of a peripheral radio wave condition based on the reception strength measured by the first reception step and the peripheral radio wave condition based on the reception result information transmitted by the second transmission step; and by the first communication unit, a first transmission step of transmitting the data to the relay device using the band determined by the determination step.

Advantageous Effects of Invention

According to the present invention, it is possible to further reduce occurrence of radio wave interference.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a basic data transmission configuration among terminal stations, a mobile relay station, and a base station by a wireless communication system of an embodiment will be described.

[Basic Configuration of Wireless Communication System]

FIG.1is a configuration diagram of a wireless communication system1according to an embodiment. The wireless communication system1includes a mobile relay station2, terminal stations3, and a base station4. Each of the numbers of mobile relay stations2, terminal stations3, and base stations4included in the wireless communication system1is arbitrary, but it is assumed that there is a large number of terminal stations3.

The mobile relay station2is an example of a relay device that is mounted on a mobile object and has a communicable area that moves over time. The mobile relay station2is provided in, for example, a low earth orbit (LEO) satellite. The LEO satellite has an altitude of 2000 km or less and orbits in the air over the earth once every about 1.5 hours. The terminal station3and the base station4are installed on the earth, for example, on the ground or on the sea. The terminal station3is, for example, an IoT terminal. The terminal station3collects data such as environmental data detected by a sensor and wirelessly transmits the collected data to the mobile relay station2.FIG.1illustrates only two terminal stations3.

The mobile relay station2receives data transmitted from each of the plurality of terminal stations3with a wireless signal while moving above the earth. The mobile relay station2accumulates the received data and wirelessly and collectively transmits the accumulated data to the base station4at timing at which communication with the base station4is possible. The base station4receives the data collected by the terminal stations3from the mobile relay station2.

As the mobile relay station, use of a relay station mounted on a geosynchronous satellite, a drone, or an unmanned aerial vehicle such as a high altitude platform station (HAPS) is conceivable. However, the relay station mounted on a geosynchronous satellite has a wide coverage area (footprint) on the ground, but has an extremely small link budget with respect to the IoT terminals installed on the ground because its altitude is high. Meanwhile, the relay station mounted on a drone or a HAPS has a high link budget, but has a narrow coverage area. Moreover, a battery is necessary in a drone and a solar panel is necessary in a HAPS.

In the present embodiment, the mobile relay station2is mounted on the LEO satellite. Thus, the link budget falls within a limit, and, in addition, the LEO satellite has no air resistance and has low fuel consumption because the LEO satellite orbits outside the atmosphere. In addition, the footprint is also larger than that in a case where a relay station is mounted on a drone or a HAPS.

The mobile relay station2mounted on the LEO satellite performs communication while moving at a high speed. Therefore, a time zone in which each terminal station3or base station4can communicate with the mobile relay station2is limited. Specifically, seen from the ground, the mobile relay station2passes through the sky in about ten minutes. Further, wireless communication schemes having various specifications are used in the terminal stations3.

Accordingly, the mobile relay station2receives a terminal uplink signal from the terminal station3within coverage at a present position during movement and stores waveform data of the received terminal uplink signal. The mobile relay station2wirelessly transmits a base station downlink signal in which the waveform data of the terminal uplink signal is set to the base station4at the timing when the base station4is in the coverage. The base station4demodulates the base station downlink signal received from the mobile relay station2to obtain the waveform data of the terminal uplink signal. The base station4demodulates and decodes the terminal uplink signal represented by the waveform data to obtain terminal transmission data that is data transmitted by the terminal station3.

Hereinafter, configurations of the mobile relay station2, the terminal station3, and the base station4will be described.

As illustrated inFIG.1, the mobile relay station2includes an antenna21, a terminal communication unit22, a data storage unit23, a base station communication unit24, and an antenna25.

The terminal communication unit22includes a reception unit221and a received waveform recording unit222. The reception unit221receives the terminal uplink signal through the antenna21. The received waveform recording unit222samples a received waveform of the terminal uplink signal received by the reception unit221, and generates waveform data indicating a value obtained by the sampling. The received waveform recording unit222writes, in the data storage unit23, received waveform information in which reception time of the terminal uplink signal in the antenna21and the generated waveform data are set. The data storage unit23stores the received waveform information written by the received waveform recording unit222.

The base station communication unit24transmits the received waveform information to the base station4with the base station downlink signal of any wireless communication scheme. The base station communication unit24includes a storage unit241, a control unit242, a transmission data modulation unit243, and a transmission unit244. The storage unit241stores transmission start timing calculated in advance on the basis of orbit information of the LEO satellite on which the mobile relay station2is mounted and a position of the base station4. The orbit information of the LEO satellite is information from which a position, a velocity, a movement direction, and the like of the LEO satellite at any time can be obtained. The transmission time may be represented by, for example, an elapsed time from the transmission start timing. The control unit242controls the transmission data modulation unit243and the transmission unit244to transmit the received waveform information to the base station4at the transmission start timing stored in the storage unit241. The transmission data modulation unit243reads the received waveform information from the data storage unit23as transmission data, and modulates the read transmission data to generate the base station downlink signal. The transmission unit244converts the base station downlink signal from an electrical signal into a wireless signal, and transmits the wireless signal from the antenna25.

As illustrated inFIG.1, the terminal station3includes a data storage unit31, a transmission unit32, and one or a plurality of antennas33.

The data storage unit31stores sensor data and the like. The transmission unit32reads the sensor data from the data storage unit31as the terminal transmission data and wirelessly transmits the terminal uplink signal in which the read terminal transmission data is set from the antenna33.

The transmission unit32transmits the signal by low power wide area (LPWA), for example. Examples of the LPWA include LoRaWAN (registered trademark), Sigfox (registered trademark), long term evolution for machines (LTE-M), and narrow band (NB)-IoT, but any wireless communication scheme can be used. The transmission unit32may perform transmission with another terminal station3by time division multiplexing, orthogonal frequency division multiplexing (OFDM), or the like.

The transmission unit32determines a channel and transmission timing to be used by the local station to transmit the terminal uplink signal by a method determined in advance in the wireless communication scheme to be used. Alternatively, the transmission unit may perform beam formation of signals transmitted from the plurality of antennas33on the basis of the method determined in advance in the wireless communication scheme to be used.

As illustrated inFIG.1, the base station4includes an antenna41, a reception unit42, a base station signal reception processing unit43, and a terminal signal reception processing unit44.

The reception unit42converts a terminal downlink signal received through the antenna41into an electrical signal. The base station signal reception processing unit43demodulates and decodes the received signal converted into the electrical signal by the reception unit42to obtain the received waveform information. The base station signal reception processing unit43outputs the received waveform information to the terminal signal reception processing unit44.

The terminal signal reception processing unit44performs reception processing for the terminal uplink signal indicated by the received waveform information. At this time, the terminal signal reception processing unit44acquires the terminal transmission data by performing the reception processing by the wireless communication scheme used by the terminal station3for transmission. The terminal signal reception processing unit44includes a terminal signal demodulation unit441and a terminal signal decoding unit442.

The terminal signal demodulation unit441demodulates the waveform data and outputs a symbol obtained by the demodulation to the terminal signal decoding unit442. The terminal signal demodulation unit441may perform, for a signal indicated by the waveform data, processing of compensating for a Doppler shift of the terminal uplink signal received by the antenna21of the mobile relay station2, and then perform the demodulation. The Doppler shift applied to the terminal uplink signal received by the antenna21is calculated in advance on the basis of the position of the terminal station3and the orbit information of the LEO on which the mobile relay station2is mounted. The terminal signal decoding unit442decodes the symbol demodulated by the terminal signal demodulation unit441to obtain the terminal transmission data transmitted from the terminal station3.

[Basic Operation of Wireless Communication System]

Hereinafter, a basic operation of the wireless communication system1will be described below.FIG.2is a flowchart illustrating processing of the wireless communication system1in a case where an uplink signal is transmitted from the terminal station3.

The terminal station3obtains data detected by an internally or externally provide sensor (not illustrated) as needed, and writes the obtained data in the data storage unit31(step S111). The transmission unit32reads sensor data from the data storage unit31as the terminal transmission data. The transmission unit32wirelessly transmits the terminal uplink signal in which the terminal transmission data is set from the antenna33at the transmission start timing obtained in advance on the basis of the orbit information of the LEO satellite on which the mobile relay station2is mounted (step S112). The terminal station3repeats the processing from step S111.

The reception unit221of the mobile relay station2receives the terminal uplink signal transmitted from the terminal station3(step S121). Depending on the wireless communication scheme of the terminal stations3serving as transmission sources, there are some cases where the terminal uplink signal is received from only one terminal station3by time division at the same frequency, or there are some cases where the terminal uplink signals are simultaneously received from a plurality of terminal stations3at the same frequency. The received waveform recording unit222writes, in the data storage unit23, the received waveform information that associates the waveform data representing the waveform of the terminal uplink signal received by the reception unit221with reception time (step S122). The mobile relay station2repeats the processing from step S121.

FIG.3is a flowchart illustrating processing of the wireless communication system1in a case where the base station downlink signal is transmitted from the mobile relay station2. When having detected that current time is the transmission start timing stored in the storage unit241, the control unit242included in the base station communication unit24of the mobile relay station2instructs the transmission data modulation unit243and the transmission unit244to transmit the received waveform information (step S211).

The transmission data modulation unit243reads the received waveform information accumulated in the data storage unit23as the transmission data, modulates the read transmission data, and generates the base station downlink signal. The transmission unit244wirelessly transmits the base station downlink signal generated by the transmission data modulation unit243through the antenna25(step S212). The mobile relay station2repeats the processing from step S211.

The antenna41of the base station4receives the base station downlink signal from the mobile relay station2(step S221). The reception unit42converts the base station downlink signal received by the antenna41into the received signal of the electrical signal and outputs the received signal to the base station signal reception processing unit43. The base station signal reception processing unit43demodulates the received signal, and decodes the demodulated received signal (step S222). The base station signal reception processing unit43outputs the received waveform information obtained by the decoding to the terminal signal reception processing unit44.

The terminal signal reception processing unit44performs the reception processing for the terminal uplink signal indicated by the waveform data included in the received waveform information (step S223). Specifically, the terminal signal demodulation unit441specifies the wireless communication scheme used by the terminal station3to transmit the terminal uplink signal on the basis of information specific to the wireless communication scheme included in the received signal indicated by the waveform data. The terminal signal demodulation unit441demodulates the received signal indicated by the waveform data in accordance with the specified wireless communication scheme, and outputs the symbol obtained by the demodulation to the terminal signal decoding unit442.

The terminal signal decoding unit442decodes the symbol input from the terminal signal demodulation unit441by the specified wireless communication scheme to obtain the terminal transmission data transmitted from the terminal station3. Note that the terminal signal decoding unit442can also use a decoding scheme with a large calculation load, such as successive interference cancellation (SIC). The base station4repeats the processing from step S221.

[Configuration of Wireless Communication System Related to Interference Detection]Hereinafter, a configuration of the wireless communication system1related to interference detection will be described. In communication with the mobile relay station2, the terminal station3in the present embodiment attempts to receive a radio wave of a specific frequency for a certain period in advance before transmitting desired data to the mobile relay station2. The terminal station3transmits data to the mobile relay station2in a case of confirming that there are no other terminal stations3interfering with each other on the basis of a reception result.

Further, in the wireless communication system1according to the present embodiment, one or more periphery detection stations8are installed around each terminal station3(a communication apparatus). Similarly to the terminal station3, the periphery detection station8also attempts to receive a radio wave of a specific frequency for a certain period in advance. The periphery detection station8transmits the reception result to the terminal station3. The terminal station3checks whether there are other terminal stations3that interfere with each other in consideration of not only the reception result in the local device but also the reception results in the one or more periphery detection stations8. As a result, the terminal station3can confirm whether there are other terminal stations3that interfere with each other on the basis of the reception results in a wider range.

With such a configuration, in the wireless communication system1according to the present embodiment, the terminal station3can detect the other terminal stations3interfering with each other with higher accuracy. As a result, the wireless communication system1according to the present embodiment can further reduce the occurrence of radio wave interference in the communication between the mobile relay station2and the terminal station3.

Note that, in the present embodiment, the periphery detection station8is a wireless station for exclusive use for reception dedicated to attempting to receive the radio wave of a specific frequency and transmitting the reception result to the terminal station3, but the present embodiment is not limited thereto. For example, each of the periphery detection stations8may be configured to appropriately function as the terminal station3that transmits and receives data to and from the mobile relay station2.

FIG.4is a diagram illustrating an example of a positional relationship among the terminal station3and the periphery detection stations8. As illustrated inFIG.4, the plurality of periphery detection stations8is installed at predetermined intervals at positions on a substantially concentric circle centered on the position of the terminal station3, for example. As a result, the terminal station3can check whether there are other terminal stations3that interfere with each other on the basis of a reception state in a wider range.

Note that the positional relationship among the terminal station3and the periphery detection stations8is not limited to that illustrated inFIG.1. For example, there may be a shield that shields radio waves such as undulations of terrain, an obstacle that reflects radio waves such as a building, or the like around the terminal station3. In such a case, the periphery detection station8is desirably arranged at an appropriate position according to intensity of transmission and reception of the radio waves, the modulation method, and the type of interference source (pulse wave, white noise, or the like).

Note that communication between the periphery detection station8and the terminal station3may be either wireless communication or wired communication.

Hereinafter, configurations of the terminal station3and the periphery detection station8related to interference detection will be described.FIG.5is a block diagram illustrating functional configurations of the terminal station3and the periphery detection station8related to interference detection. Note thatFIG.5illustrates only a functional configuration related to interference detection, and description of other functional configurations is omitted. That is, the terminal station3further has the functional configuration illustrated in the block diagram ofFIG.5in addition to the functional configuration illustrated in the block diagram ofFIG.1. Note that, inFIG.5, functional units common to those inFIG.1are denoted by the same reference numerals, and description thereof may be omitted.

As illustrated inFIG.5, the terminal station3includes the transmission unit32, the antenna33, a reception unit34, a periphery detection station control unit35, and a peripheral radio wave condition determination unit36.

The transmission unit32acquires a periphery detection request output from the periphery detection station control unit35. The periphery detection request is a request signal for causing the periphery detection station8to receive, for a certain period of time, a band desired to be used by the terminal station3for data transmission to the mobile relay station2. The transmission unit32transmits the acquired periphery detection request to the periphery detection station8via the antenna33.

Further, in a case where it is not determined by the peripheral radio wave condition determination unit36that a reception level has exceeded a predetermined threshold in the terminal station3and the periphery detection station8over a certain period, the transmission unit32transmits desired data to the mobile relay station2using the above-described band desired to be used.

The reception unit34attempts to receive the band desired to be used for transmission of data to the mobile relay station2for a certain period. The reception unit34outputs information indicating a reception result to the peripheral radio wave condition determination unit36.

Furthermore, the reception unit34receives each piece of reception result information transmitted from one or more periphery detection stations. The reception result information is information indicating a result of reception using the band desired to be used, which has been attempted by the periphery detection station8in response to the above-described periphery detection request. The reception unit34outputs the received reception result information to the peripheral radio wave condition determination unit36.

The periphery detection station control unit35transmits the periphery detection request to each of the one or more periphery detection stations8via the transmission unit32and the antenna33, for example, at timing when the terminal station3and the mobile relay station2become able to communicate with each other.

The peripheral radio wave condition determination unit36acquires, from the reception unit34, information indicating the reception result of reception by the reception unit34in the band desired to be used for transmission of data to the mobile relay station2and the reception result information acquired from each of the one or more periphery detection stations. The peripheral radio wave condition determination unit36determines whether the reception level has not exceeded a predetermined threshold in the terminal station3or the periphery detection station8over a certain period on the basis of the acquired information. In the case where it is determined that the reception level has not exceeded the predetermined threshold in the terminal station3and the periphery detection station8over the certain period, the peripheral radio wave condition determination unit36causes the transmission unit32to transmit desired data to the mobile relay station2using the above-described band desired to be used.

Furthermore, as illustrated inFIG.5, the periphery detection station8includes an antenna81, a reception unit82, a periphery detection request processing unit83, a peripheral radio wave condition transmission unit84, and a transmission unit85.

The reception unit82receives the periphery detection request transmitted from the terminal station3through the antenna81. The reception unit82outputs the received periphery detection request to the periphery detection request processing unit83.

The periphery detection request processing unit83acquires the periphery detection request output from the reception unit82. The periphery detection request processing unit83attempts to receive the band desired to be used for transmission of data to the mobile relay station2for a certain period through the reception unit82and the antenna81on the basis of the acquired periphery detection request.

The periphery detection request processing unit83determines whether the reception level has not exceeded a predetermined threshold over a certain period. The periphery detection request processing unit83outputs the reception result information indicating the result of the determination to the peripheral radio wave condition transmission unit84.

The peripheral radio wave condition transmission unit84acquires the reception result information output from the periphery detection request processing unit83. The peripheral radio wave condition transmission unit84transmits the acquired reception result information to the terminal station3via the transmission unit85and the antenna81.

[Operations of Terminal Station and Periphery Detection Station Related to Interference Detection]

Hereinafter, operations of the terminal station3and the periphery detection station8related to interference detection will be described. First, an example of an operation of a conventional terminal station related to interference detection will be described for easy understanding of the description.

FIG.6is a flowchart illustrating an operation of a conventional terminal station related to interference detection. The operation of the conventional terminal station illustrated in the flowchart ofFIG.6is started at timing when the conventional terminal station and a mobile relay station becomes able to communicate with each other.

First, the conventional terminal station attempts to receive a band desired to be used for transmission of data to the mobile relay station for a certain period (step $901).

Next, the conventional terminal station measures a reception level and determines whether the measured reception level has exceeded a predetermined threshold (step S902).

Next, in a case where it is determined that the reception level has not exceeded the predetermined threshold over the certain period (step S902: NO), the conventional terminal station transmits desired data to the mobile relay station using the above-described band desired to be used (step S903). As described above, the operation of the conventional terminal station related to interference detection illustrated in the flowchart ofFIG.6ends.

Hereinafter, an example of operations related to interference detection of the terminal station3and the periphery detection station8of the wireless communication system1according to the present embodiment will be described.FIG.7is a flowchart illustrating operations of the terminal station3and the periphery detection station8related to interference detection. The operations of the terminal station3and the periphery detection station8illustrated in the flowchart ofFIG.7are started at timing when the terminal station3and the mobile relay station2become able to communicate with each other, for example.

First, the periphery detection station control unit35of the terminal station3transmits the periphery detection request to each of the one or more periphery detection stations8via the transmission unit32and the antenna33(step S301).

Next, the reception unit34of the terminal station3attempts to receive the band desired to be used for transmission of data to the mobile relay station2for a certain period through the antenna33(step S302). The reception unit34outputs the information indicating the reception result to the peripheral radio wave condition determination unit36. Furthermore, the reception unit34waits for reception of the reception result information transmitted from the periphery detection station8.

Next, the reception unit82of the periphery detection station8waits for reception of the periphery detection request transmitted from the terminal station3in step S301described above (step S401).

In the case of receiving the periphery detection request transmitted from the terminal station3via the antenna81(step S402: YES), the reception unit82of the periphery detection station8outputs the received periphery detection request to the periphery detection request processing unit83. The periphery detection request processing unit83attempts to receive the band desired to be used for transmission of data to the mobile relay station2for a certain period through the reception unit82and the antenna81(step S403).

Next, the periphery detection request processing unit83of the periphery detection station8determines whether the reception level has not exceeded a predetermined threshold over a certain period. The periphery detection request processing unit83outputs the reception result information indicating the result of the determination to the peripheral radio wave condition transmission unit84. The peripheral radio wave condition transmission unit84transmits the acquired reception result information to the terminal station3via the transmission unit85and the antenna81(step S404). As described above, the operation of the periphery detection station8related to interference detection illustrated in the flowchart ofFIG.7ends.

Next, the reception unit34of the terminal station3receives each piece of the reception result information transmitted from the one or more periphery detection stations (step S303). The reception unit34outputs the acquired reception result information to the peripheral radio wave condition determination unit36.

Next, the peripheral radio wave condition determination unit36of the terminal station3determines whether the reception level has not exceeded the predetermined threshold in the terminal station3or the periphery detection station8over a certain period on the basis of the reception result of the reception by the reception unit34in the band desired to be used for transmission of data to the mobile relay station2and the reception result indicated by the reception result information acquired from each of the one or more periphery detection stations (step S304). Next, in the case where it is not determined that the reception level has exceeded the predetermined threshold in the terminal station3and the periphery detection station8over the certain period (step S304, NO), the transmission unit32of the terminal station3transmits the desired data to the mobile relay station2using the above-described band desired to be used (step S305). As described above, the operation of the terminal station3related to interference detection illustrated in the flowchart ofFIG.7ends.

As described above, the wireless communication system1according to the present embodiment includes the one or more periphery detection stations8installed around the terminal station3. To determine the band to be used for transmission of data to the mobile relay station2, the terminal station3checks in advance whether the band desired to be used interferes with other terminal stations3. At this time, the terminal station3performs the check by attempting to receive the band desired to be used for a certain period.

Furthermore, the terminal station3causes not only the own device to perform the check but also the one or more periphery detection stations8installed around the local device to perform reception and check in the band desired to be used. The terminal station3collects the reception result information from the one or more periphery detection stations8. As a result, the terminal station3can check whether the band desired to be used interferes with other terminal stations3on the basis of a reception status in a wider range. Therefore, the wireless communication system1according to the present embodiment can further reduce the occurrence of radio wave interference in the communication between the mobile relay station2and the terminal station3.

Further, in the wireless communication system1according to the present embodiment, it is not necessary to use a control signal for controlling transmission timing such as RTS and CTS, for example. Thereby, it is possible to suppress the occurrence of radio wave interference even in the wireless communication system having the time zone in which the mobile relay station2and the terminal station3communicate with each other is limited.

Further, according to the above-described embodiment, the mobile relay station stores and accumulates information of the received signal waveform without demodulating the radio terminal uplink signal received from the terminal station, and performs wireless transmission at timing when communication with the base station is possible. The base station performs the reception processing such as demodulation and decoding of the terminal uplink signal indicated by the received signal waveform in the mobile relay station. Thus, a non-regenerative relay scheme that does not depend on the communication scheme can be applied to the wireless communication system using a low earth orbit satellite.

In addition, since non-regenerative relay is performed, the mobile relay station does not need to implement a wireless communication scheme used for the terminal station. For example, in a case where a terminal station that performs communication by using a new wireless communication scheme is added, a change to the mobile relay station is not necessary, and the only change to be made is to add the wireless communication scheme to the base station installed on the ground. It is therefore possible to simultaneously accommodate various IoT systems, and it is also possible to easily deal with an update of the IoT systems according to the above-described embodiment.

In addition, according to the above-described embodiment, since processing for a large Doppler shift applied to each terminal station can be performed by the base station instead of the mobile relay station, it is not necessary to implement, in the mobile relay station, a complicated nonlinear operation for compensating for the Doppler shift.

Note that, in the above embodiment, the case where the mobile object on which the mobile relay station is mounted is an LEO satellite has been described. However, the mobile object may be another flying object capable of flying, such as a geostationary satellite, a drone, or a HAPS.

Note that the mobile relay station2may transmit the base station downlink signals through the plurality of antennas25. For example, multiple input multiple output (MIMO) may be used to transmit the base station downlink signals. In this case, the mobile relay station2can collectively transmit the data, which have received from the plurality of terminal stations3and accumulated with good quality, in a short time at timing when communication with the base station4is possible.

Note that the mobile relay station2may receive the terminal uplink signals using a plurality of antennas21. For example, the mobile relay station2may receive the terminal uplink signal received from the terminal station3by diversity reception, MIMO reception, or the like. In this case, the mobile relay station2can improve the link budget between the mobile relay station2and the terminal station3.

According to the above-described embodiment, the wireless communication system includes a first communication device, one or more second communication devices arranged around the first communication device, and a relay device that moves. For example, the wireless communication system is the wireless communication system1in the embodiment, the first communication device is the terminal station3in the embodiment, the second communication device is the periphery detection station8in the embodiment, and the relay device is the mobile relay station2in the embodiment.

The second communication device includes a second reception unit and a second transmission unit. The second reception unit attempts to receive a radio wave in a predetermined band and measures reception strength. The second transmission unit transmits, to the first communication device, reception result information indicating the peripheral radio wave condition based on the reception strength measured by the second reception unit. For example, the predetermined band is a band desired to be used by the terminal station3in the embodiment to transmit data to the mobile relay station2, the second reception unit is the reception unit82of the periphery detection station8in the embodiment, and the second transmission unit is the transmission unit85of the periphery detection station8in the embodiment.

The first communication device includes a first reception unit, a determination unit, and a first transmission unit. The first reception unit attempts to receive a radio wave in a predetermined band and measures reception strength. The determination unit determines a band to be used for transmission of data to the relay device on the basis of the peripheral radio wave condition based on the reception strength measured by the first reception unit and the peripheral radio wave condition based on the reception result information transmitted from the second transmission unit. The first transmission unit transmits the data to the relay device using the band determined by the determination unit. For example, the first reception unit is the reception unit34in the embodiment, the determination unit is the peripheral radio wave condition determination unit36in the embodiment, and the first transmission unit is the transmission unit32in the embodiment.

Note that the first transmission unit transmits request information for causing the second reception unit to receive a radio wave in a predetermined band. In this case, the second reception unit receives the radio wave in the predetermined band when receiving request information. For example, the request information is the periphery detection request in the embodiment.

Note that the first transmission unit transmits the request information at timing when the first reception unit and the second reception unit can communicate with the relay device. For example, the timing when communication is possible is timing when the mobile relay station2according to the embodiment passes over the terminal station3and the periphery detection station8.

Note that the relay device may be included in a low earth orbit satellite, and the first communication device and the second communication device may be installed on the earth.

Note that the wireless communication system may further include a third communication device. For example, the third communication device is the base station4in the embodiment. In this case, the relay device includes a relay device transmission unit. For example, the relay device transmission unit is the transmission unit244in the embodiment. The relay device transmission unit transmits data acquired from the first communication device to the third communication device at timing when communication with the third communication device is possible. For example, the timing when communication is possible is timing when the mobile relay station2according to the embodiment passes over the base station4.

A part or the whole of the configuration of the wireless communication system1in the above-described embodiment may be implemented by a computer. In that case, a program for implementing this function may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read and executed by a computer system to implement this function. Note that the “computer system” mentioned herein includes an OS and hardware such as peripheral devices. Also, the “computer-readable recording medium” is a portable medium such as a flexible disk, a magneto-optical disc, a ROM, or a CD-ROM, or a storage device such as a hard disk embedded in the computer system. Further, the “computer-readable recording medium” may include a medium that dynamically holds the program for a short time, such as a communication line in a case where the program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds the program for a certain period of time, such as a volatile memory inside a computer system serving as a server or a client in that case. Also, the foregoing program may be for implementing some of the functions described above, may be implemented in a combination of the functions described above and a program already recorded in a computer system, or may be implemented with a programmable logic device such as a field programmable gate array (FPGA).

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to the embodiment, and includes design and the like within a range not departing from the gist of the present invention.

REFERENCE SIGNS LIST

1Wireless communication system

2Mobile relay station

8Periphery detection station

22Terminal communication unit

23Data storage unit

24Base station communication unit

31Data storage unit

35Periphery detection station control unit

36Peripheral radio wave condition determination unit

43Base station signal reception processing unit

44Terminal signal reception processing unit

83Periphery detection request processing unit

84Peripheral radio wave condition transmission unit

222Received waveform recording unit

243Transmission data modulation unit

44Terminal signal demodulation unit

442Terminal signal decoding unit