Wireless communication device and activation method

Abstract

A wireless communication device in a wireless communication system having one or more communication devices installed on the ground and a mobile wireless communication device, the wireless communication device comprising an activation signal generation unit that generates an activation signal for activating the one or more communication devices, a distribution unit that distributes the activation signal generated by the activation signal generation unit, one or more frequency change addition units for applying a frequency change to the activation signal distributed by the distribution unit, and a transmission unit that transmits an activation signal to which a frequency change was applied by the one or more frequency change addition units.　

Description

[Technical Field]

[0001] The present invention relates to a wireless communication device and a startup method. [Background technology]

[0002] With the development of IoT (Internet of Things) technology, the installation of IoT terminals equipped with various sensors in various locations is being considered. IoT terminals may be installed in places where it is difficult to install base stations, such as on marine buoys, ships, and mountainous areas. Therefore, a system has been proposed in which data collected by IoT terminals installed in various locations is relayed to base stations installed on the ground by relay devices installed on low-earth orbit satellites.

[0003] Because IoT devices are powered by batteries, they need to operate in a power-saving manner to extend battery life. Therefore, in a satellite sensing platform, in order to realize a battery life of years for IoT devices, it is necessary for the IoT device to transmit uplink data when it detects that a low-earth orbit satellite has arrived in the sky. One possible way for an IoT device to detect that a low-earth orbit satellite has arrived in the sky is to observe downlink signals from a low-earth orbit satellite to the ground, as in the technology described in Non-Patent Document 1 (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] F. Shu, X. Zhang, T. Kondo, “Development of correlator model for differential VLBI observations of satellites”, 2008 International Conference on Microwave and Millimeter Wave Technology, ICMMT2008 Proceedings, Vol.1, pp.443-446, April 2008. Summary of the Invention [Problem to be solved by the invention]

[0005] However, because low-earth orbit satellites move at high speeds, downlink signals transmitted from low-earth orbit satellites experience intra-frame Doppler shifts. Therefore, IoT devices installed in locations where Doppler shifts exceed the allowable demodulation range cannot demodulate the downlink signal, even if the downlink signal reception level is high. This problem occurs not only with signals transmitted from low-earth orbit satellites, but also with signals transmitted from wireless communication devices moving in the sky.

[0006] In view of the above circumstances, the present invention aims to provide a technology that can activate a communication device installed on the ground even when a Doppler change occurs in a signal transmitted from a wireless communication device moving in the sky. [Means for solving the problem]

[0007] One aspect of the present invention is a wireless communication device in a wireless communication system having one or more communication devices installed on the ground and a mobile wireless communication device, the wireless communication device comprising: a start-up signal generation unit that generates a start-up signal for starting the one or more communication devices; one or more frequency change imparting units that impart a frequency change to the start-up signal generated by the start-up signal generation unit; and a transmission unit that transmits the start-up signal with the frequency change imparted to the one or more frequency change imparting units.

[0008] One aspect of the present invention is a startup method performed by a wireless communication device in a wireless communication system having one or more communication devices installed on the ground and a mobile wireless communication device, the startup method including generating a startup signal for starting the one or more communication devices, changing the frequency of the generated startup signal, and transmitting the startup signal with the changed frequency. [Effects of the Invention]

[0009] According to the present invention, it is possible to activate a communication device installed on the ground even when a Doppler shift occurs in a signal transmitted from a wireless communication device moving in the sky. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an overview of a wireless communication system according to the present invention. [Figure 2] 10 is a schematic diagram showing a Doppler change within a frame caused by processing in the present invention and the state within the frame when received by a terminal station. FIG. [Figure 3] 10 is a schematic diagram showing a Doppler change within a frame caused by processing in the present invention and the state within the frame when received by a terminal station. FIG. [Figure 4] 10 is a schematic diagram showing a Doppler change within a frame caused by processing in the present invention and the state within the frame when received by a terminal station. FIG. [Figure 5] 10 is a schematic diagram showing a Doppler change within a frame caused by processing in the present invention and the state within the frame when received by a terminal station. FIG. [Figure 6] 1 is a configuration diagram of a wireless communication system according to an embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of an assignment table according to the embodiment. [Figure 8] 10 is a sequence diagram showing a flow of a terminal station startup process performed by the wireless communication system according to the embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (overview) Fig. 1 is a diagram for explaining an overview of a wireless communication system 1 according to the present invention. As shown in Fig. 1, the wireless communication system 1 according to the present invention has at least a mobile relay station 2 and one or more terminal stations 3. Fig. 1 shows, as an example, a case in which two terminal stations 3-1 and 3-2 are provided. The terminal station 3-1 and the terminal station 3-2 are located in different areas. For example, the terminal station 3-1 is located in area A1, and the terminal station 3-2 is located in area A2.

[0012] Because the mobile relay station 2 moves at high speed, an intra-frame Doppler shift occurs when the activation signal transmitted from the mobile relay station 2 is received by the terminal station 3 located in each area. The activation signal is a signal for activating the terminal station 3. If an intra-frame Doppler shift occurs in the activation signal, some of the terminal stations 3 located in each area may not be able to demodulate and decode the activation signal. For example, even if the activation signal transmitted from the mobile relay station 2 is received by the terminal station 3-1 located in area A1 and the terminal station 3-2 located in area A2, different intra-frame Doppler shifts occur in the activation signal received by each terminal station 3, and depending on the installation location of the terminal station 3, the activation signal may not be able to be demodulated and decoded.

[0013] Therefore, in the mobile relay station 2 of the present invention, when transmitting an activation signal, each activation signal is multiplexed and transmitted with an intra-frame frequency change appropriate for each area on the ground as seen from the mobile relay station 2 (for example, areas A1, A2, and A3 in FIG. 1). The intra-frame frequency change appropriate for each area is assumed to be determined in advance based on the altitude of the mobile relay station 2 (more specifically, the moving speed of the mobile relay station 2, which is determined by the altitude), the downlink transmission frequency, and the positions of the mobile relay station 2 and the area.

[0014] More specifically, the mobile relay station 2 distributes the activation signal, applies a frequency change appropriate for each area to each of the distributed activation signals, and then combines and transmits the combined signals. This allows the terminal station 3 to be activated even if an intra-frame Doppler change occurs in the activation signal transmitted from the mobile relay station 2.

[0015] For example, if the altitude of mobile relay station 2 is 570 km and it is desired to activate terminal station 3 in an area directly below mobile relay station 2 (area A3 in FIG. 1) with a 400 MHz band activation signal, mobile relay station 2 can transmit the activation signal with a frequency change of approximately 130 Hz / s, thereby enabling terminal station 3 to demodulate and decode the activation signal. Furthermore, if it is desired to activate terminal station 3 in an area approximately 300 km away from directly below mobile relay station 2, mobile relay station 2 can transmit the activation signal with a frequency change of approximately 90 Hz / s, thereby enabling terminal station 3 to demodulate and decode the activation signal.

[0016] 2 to 5 are schematic diagrams showing the Doppler change within a frame that occurs when processing according to the present invention is performed, and the state within the frame when the signal is received by the terminal station 3. As shown in FIG. 2, it is assumed that the mobile relay station 2 transmits an activation signal that is a combination of activation signals 51 and 52. Activation signal 51 represents a signal in which a frequency change value F1 has been added to activate the terminal station 3-1 located in area A1, and activation signal 52 represents a signal in which a frequency change value F2 has been added to activate the terminal station 3-2 located in area A2. Here, frequency changes F1 and F2 are frequency change values ​​appropriate for each area, determined in advance based on the altitude and downlink transmission frequency of the mobile relay station 2.

[0017] The activation signal received by the terminal station 3-1 located in area A1 undergoes a Doppler shift as shown in FIG. 3. As a result, the activation signal received by the terminal station 3-1 located in area A1 is in the state shown in FIG. 4. FIG. 5 shows the example shown in FIG. 4 viewed on the frequency axis. Although activation signals with different frequency changes will interfere with each other, due to the intra-frame Doppler shift, only activation signal 51 with the frequency change appropriate for area A1 is emphasized, as shown in FIG. 5, while activation signal 52 with the other frequency change is spread in frequency. Therefore, it can be seen that activation signal 51 with the frequency change F1 value can be demodulated and decoded. As a result, terminal station 3-1 can be activated.

[0018] 2 to 5, the terminal station 3-1 located in area A1 has been mainly described, but the same applies to the terminal station 3-2 located in area A2. For example, the terminal station 3-2 located in area A2 experiences a Doppler shift different from the Doppler shift occurring in the activation signal received by the terminal station 3-1 located in area A1. In this case, when the activation signal is received by the terminal station 3-2 located in area A2, the activation signal to which the frequency change F2 has been applied is emphasized, and the activation signal 51 to which the other frequency change has been applied is spread in frequency. Therefore, the activation signal 52 to which the value of the frequency change F2 has been applied can be demodulated and decoded. As a result, the terminal station 3-2 can be activated.

[0019] Fig. 6 is a configuration diagram of a wireless communication system 1 according to an embodiment. The wireless communication system 1 has a mobile relay station 2, one or more terminal stations 3, and a base station 4. The wireless communication system 1 may have any number of mobile relay stations 2, terminal stations 3, and base stations 4. It is assumed that the number of terminal stations 3 is large. Fig. 6 shows a case where the wireless communication system 1 has two terminal stations 3-1 and 3-2. In the following description, when there is no need to distinguish between the terminal stations 3-1 and 3-2, they will simply be referred to as terminal station 3.

[0020] The mobile relay station 2 is an example of a wireless communication device mounted on a moving body, and whose communication area changes over time. When the mobile relay station 2 reaches the sky above a data collection area, it transmits an activation signal to activate the terminal station 3. The data collection area is an area for collecting data acquired by the terminal station 3. The mobile relay station 2 determines whether it has reached the sky above the data collection area based on, for example, orbit information of the mobile relay station 2 and time information.

[0021] The mobile relay station 2 in this embodiment is provided on a LEO (Low Earth Orbit) satellite. The altitude of a LEO satellite is 2000 km or less, and it orbits the Earth once in approximately 1.5 hours. The terminal station 3 and base station 4 are installed on the Earth, such as on land or sea. Hereinafter, a radio signal transmitted from the terminal station 3 to the mobile relay station 2 will be referred to as a terminal uplink signal, and a signal transmitted from the mobile relay station 2 to the terminal station 3 and base station 4 will be referred to as a downlink signal.

[0022] Because a mobile relay station 2 mounted on a LEO satellite communicates while moving at high speed, the time during which each terminal station 3 and base station 4 can communicate with the mobile relay station 2 is limited. Specifically, from the ground, the mobile relay station 2 passes overhead every few minutes. The terminal station 3 collects and stores data such as environmental data detected by sensors. The terminal station 3 transmits a terminal uplink signal containing the collected data at a timing when communication with the mobile relay station 2 is possible. As the mobile relay station 2 moves above the Earth, it receives terminal uplink signals transmitted from each of the multiple terminal stations 3. The mobile relay station 2 accumulates the data received from the terminal station 3 via the terminal uplink signal and wirelessly transmits the accumulated data to the base station 4 via a downlink signal at a timing when communication with the base station 4 is possible. The base station 4 acquires the data collected by the terminal station 3 from the received downlink signal.

[0023] The mobile relay station 2 has an antenna used for wireless communication with the terminal station 3 and an antenna used for wireless communication with the base station 4. Therefore, the mobile relay station 2 can perform wireless communication with the terminal station 3 and wireless communication with the base station 4 in parallel.

[0024] Mobile relay stations can be mounted on geostationary satellites, drones, or unmanned aerial vehicles such as HAPS (High Altitude Platform Station). However, although relay stations mounted on geostationary satellites have a wide ground coverage area (footprint), their high altitude means that the link budget for IoT devices installed on the ground is very small. On the other hand, relay stations mounted on drones or HAPS have a high link budget but a narrow coverage area.

[0025] Furthermore, drones require batteries, and HAPS require solar panels. In this embodiment, a mobile relay station 2 is mounted on a LEO satellite. Therefore, the link budget is kept within the limits, and since LEO satellites orbit outside the atmosphere, there is no air resistance and fuel consumption is low. The footprint is also larger than when a relay station is mounted on a drone or HAPS.

[0026] The terminal station 3 collects data such as environmental data detected by a sensor. The terminal station 3 is activated based on an activation signal transmitted from the mobile relay station 2, and transmits the collected data to the mobile relay station 2 wirelessly. For example, when the mobile relay station 2 instructs the terminal station 3 on transmission timing, the terminal station 3 wirelessly transmits the collected data to the mobile relay station 2 at the instructed transmission timing. The terminal station 3 is one aspect of a communication device.

[0027] The base station 4 receives the data collected by the terminal station 3 from the mobile relay station 2 .

[0028] The terminal station 3 and the base station 4 are installed at specific locations on the earth, such as on land or sea.

[0029] The configuration of each device will be explained. The mobile relay station 2 includes one antenna 21, a terminal communication unit 22, a storage unit 23, a control unit 24, a base station communication unit 25, and one antenna 26. The mobile relay station 2 may include multiple antennas 21. When configured in this manner, the mobile relay station 2 performs reception processing using MIMO (multiple-input and multiple-output).

[0030] Terminal communication unit 22 has transceiver 221, terminal signal demodulator 222, activation signal generator 223, distributor 224, frequency variation assigners 225-1 to 225-N (N is an integer equal to or greater than 1), and combiner 226. Note that when there is only one frequency variation assigner 225, terminal communication unit 22 does not need to have distributor 224 and combiner 226.

[0031] The transmitting / receiving unit 221 receives a terminal uplink signal via the antenna 21. In this manner, the transmitting / receiving unit 221 communicates with one or more terminal stations 3 via the antenna 21.

[0032] The terminal signal demodulation unit 222 demodulates the terminal uplink signal received by the transmission / reception unit 221 and stores the demodulation result in the storage unit 23. For example, if the demodulation result includes data collected by the terminal station 3, the terminal signal demodulation unit 222 stores the demodulation result in the storage unit 23.

[0033] The demodulation performed by the terminal signal demodulation unit 222 includes, for example, frequency conversion for converting an RF (Radio Frequency) signal received by the transmission / reception unit 221 into a baseband signal, and frame detection for detecting an uplink signal transmitted from the terminal station 3. Furthermore, for example, when digital processing is performed by the terminal signal demodulation unit 222, the terminal signal demodulation unit 222 performs analog-to-digital conversion.

[0034] The activation signal generating unit 223 generates an activation signal for activating a plurality of terminal stations 3 .

[0035] The distribution unit 224 distributes the activation signal generated by the activation signal generation unit 223 .

[0036] Frequency change applying units 225-1 to 225-N apply frequency changes to the activation signals distributed by distribution unit 224. Frequency change applying units 225-1 to 225-N are arranged in parallel, and apply different frequency changes to the activation signals distributed by distribution unit 224.

[0037] The synthesis unit 226 synthesizes the excitation signals to which the frequency changes have been applied, to generate a synthesized excitation signal.

[0038] Storage unit 23 stores at least orbit information 231, received data 232, and an assignment table 233. Orbit information 231 is information relating to the orbit of the LEO satellite on which mobile relay station 2 is mounted, and is information that makes it possible to obtain, for example, the position, speed, and moving direction of the LEO satellite at any time. Received data 232 is data collected by terminal station 3, and is data to be transmitted to base station 4. Assignment table 233 is a table in which the value of the frequency change to be assigned by frequency change assignment units 225-1 to 225-N is registered for each area.

[0039] FIG. 7 is a diagram showing an example of the assignment table 233 in the embodiment. The assignment table 233 has multiple records indicating information regarding the value of frequency change assigned to each area. Each record has values ​​for the area, the distance from the mobile relay station, and the assigned change frequency. The area value indicates a region determined according to the distance from the mobile relay station 2. The value of the distance from the mobile relay station indicates the distance from a reference position, which is directly below the mobile relay station 2. The value of the assigned change frequency is the value of frequency change assigned to the activation signal by the frequency change assigning units 225-1 to 225-N. The assigned change frequency is 0 Hz / s or higher. The reason for setting the assigned change frequency to 0 Hz / s or higher is that activation may be possible in some areas even without an assigned frequency change value (even with the activation signal generated by the activation signal generating unit 223 as is). Therefore, by assigning a value of 0 Hz / s, which does not substantially change the frequency of the activation signal, it is possible to activate terminal stations 3 located in areas where activation is possible without assigning a frequency change value. The number of areas registered in the assignment table 233 is equal to or less than the number of frequency change assignment sections 225-1 to 225-N.

[0040] 7, the assignment table 233 associates an assigned change frequency with each area. For example, the top row of the assignment table 233 associates an area "A1," a distance "D1" from the mobile relay station, and an assigned change frequency "F1." This indicates that the area that is a distance "D1" away from the reference position is area "A1," and that the frequency change value assigned to the activation signal to activate the terminal station 3 located in area "A1" is "F1."

[0041] 7, the assignment table 233 associates frequency change values ​​to be assigned to the activation signal in order to activate the terminal stations 3 located in each area. By assigning these frequency change values ​​to the activation signal, the terminal stations 3 located in each area as seen from the reference position can be activated.

[0042] The control unit 24 is configured using a processor such as a CPU (Central Processing Unit) and a memory. The control unit 24 executes a program to realize the functions of the operation control unit 241 and the setting unit 242. Some or all of these functional units may be realized by hardware (including circuitry) such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array), or may be realized by a combination of software and hardware. Some of these functions do not need to be pre-installed in the mobile relay station 2, and may be realized by installing an additional application program in the mobile relay station 2.

[0043] The operation control unit 241 refers to the orbit information 231 and the time information and determines whether the location where the LEO satellite carrying the mobile relay station 2 is currently located is above a data collection area. If it is a data collection area, the operation control unit 241 instructs the setting unit 242 to acquire a frequency change value and instructs the terminal communication unit 22 to send an activation signal. On the other hand, if it is not a data collection area, the operation control unit 241 does nothing in particular.

[0044] In response to an instruction from the operation control unit 241, the setting unit 242 refers to the assignment table 233 and sets the value of the frequency change to be assigned by each frequency change assigning unit 225-n for each frequency change assigning unit 225-n. Specifically, the setting unit 242 first reads out the assignment table 233 from the storage unit 23. Next, the setting unit 242 refers to the read assignment table 233 and acquires the value of each assigned change frequency for each area. This value of the assigned change frequency is the value to be set in the frequency change assigning unit 225-n. The setting unit 242 sets the acquired value of each assigned change frequency for each area to a different frequency change assigning unit 225-n. This allows each frequency change assigning unit 225-n to assign a different frequency change value.

[0045] The base station communication unit 25 reads out the received data stored in the storage unit 23 from the data storage unit 23 as data to be transmitted to the base station 4. The base station communication unit 25 encodes and modulates the transmission data to generate a base station downlink signal. The base station communication unit 25 transmits the base station downlink signal from the antenna 26.

[0046] The terminal station 3 includes a data storage unit 31, a transceiver unit 32, a demodulator unit 33, a startup control unit 34, and an antenna 35. In order to reduce power consumption, the terminal station 3 is in a sleep state except for some functions until it receives a startup signal from the mobile relay station 2. Here, the some functions are, for example, the data storage unit 31, the transceiver unit 32, the demodulator unit 33, and the startup control unit 34 shown in FIG. 2. The terminal station 3 may include multiple antennas 35.

[0047] The data storage unit 31 stores environmental data detected by the sensors. The transmitter / receiver 32 communicates with the mobile relay station 2. For example, the transmitter / receiver 32 receives a downlink signal transmitted from the mobile relay station 2. For example, the transmitter / receiver 32 reads environmental data from the data storage unit 31 as terminal transmission data in response to an instruction from the communication control unit 33. The transmitter / receiver 32 wirelessly transmits, from the antenna 35, a terminal uplink signal in which the read terminal transmission data is set.

[0048] The transceiver 32 transmits and receives signals using, for example, LPWA (Low Power Wide Area). LPWA includes LoRaWAN (registered trademark), Sigfox (registered trademark), LTE-M (Long Term Evolution for Machines), NB (Narrow Band)-IoT, etc., but any wireless communication method can be used. The transceiver 32 may transmit and receive signals to and from other terminal stations 3 using time division multiplexing, OFDM (Orthogonal Frequency Division Multiplexing), etc. The transceiver 32 may perform beamforming of signals to be transmitted from the multiple antennas 35 using a method predetermined for the wireless communication method used.

[0049] The demodulation unit 33 demodulates the downlink signal received by the transceiver unit 32. The downlink signal received by the transceiver unit 32 is a signal obtained by combining an activation signal to which different frequency conversions have been applied and an activation signal to which no frequency conversion has been applied. Depending on the distance between the mobile relay station 2 and the terminal station 3, a Doppler shift occurs in the downlink signal.

[0050] The activation control unit 34 switches from the sleep state to the activation state in response to an activation signal included in the downlink signal demodulated by the demodulation unit 33 .

[0051] The base station 4 is equipped with an antenna 41. The base station 4 converts the terminal downlink signal received by the antenna 41 into an electrical signal, and then demodulates and decodes it to obtain received waveform information. The base station 4 performs reception processing for the terminal uplink signal indicated by the received waveform information. At this time, the base station 4 performs reception processing using the wireless communication method used by the terminal station 3 for transmission, and obtains the terminal transmission data.

[0052] The operation of the wireless communication system 1 will now be described. Fig. 8 is a sequence diagram showing the flow of the startup process of the terminal station 3 performed by the wireless communication system 1 in the embodiment. In the example shown in Fig. 8, the terminal station 3-1 is located in area A1, and the terminal station 3-2 is located in area A2.

[0053] The operation control unit 241 determines that the current position of the mobile relay station 2 is above a data collection area (step S101). The operation control unit 241 instructs the setting unit 242 to acquire a frequency change value, and instructs the terminal communication unit 22 to transmit an activation signal. In response to the instruction from the operation control unit 241, the setting unit 242 refers to the assignment table 233 and acquires the value of the assigned change frequency (e.g., assigned change frequencies "F1", "F2", . . .) for each area (e.g., areas "A1", "A2", . . .) (step S102).

[0054] The setting unit 242 sets the value of the imparted change frequency for each acquired area to each frequency change adding unit 225-n (step S103). For example, the setting unit 242 sets the value "F1" of the imparted change frequency for the acquired area "A1" to the frequency change adding unit 225-1, and sets the value "F2" of the imparted change frequency for the acquired area "A2" to the frequency change adding unit 225-2.

[0055] Initiation signal generation unit 223 generates an activation signal in response to an instruction from operation control unit 241 (step S104). Initiation signal generation unit 223 outputs the generated activation signal to distribution unit 224. Distribution unit 224 receives the activation signal as input. Distribution unit 224 distributes the activation signal input (step S105). As a result, the activation signal is input to each frequency change applying unit 225.

[0056] Each frequency change imparting unit 225 imparts the value of the imparted variation frequency set by setting unit 242 to the inputted activation signal (step S106). Each frequency change imparting unit 225 outputs the activation signal to which the value of the imparted variation frequency has been imparted to combining unit 226. The activation signal outputted from each frequency change imparting unit 225-n is inputted to combining unit 226.

[0057] The combining unit 226 combines the input activation signals to generate a combined activation signal (step S107). The combining unit 226 outputs the generated combined activation signal to the transmitting / receiving unit 221. The transmitting / receiving unit 221 transmits the combined activation signal output from the combining unit 226 as a downlink signal via the antenna 21 (step S108). The downlink signal transmitted from the mobile relay station 2 is received by the terminal stations 3-1 and 3-2 located within the reach of the radio waves transmitted from the mobile relay station 2 (steps S109, S110).

[0058] The transmitter / receiver 32 of the terminal station 3-1 outputs the received downlink signal to the demodulator 33. The demodulator 33 of the terminal station 3-1 demodulates the downlink signal (step S111). Here, the downlink signal includes multiple activation signals to which different frequency changes have been applied. Although the signals to which different frequency changes have been applied will interfere with each other, due to the intra-frame Doppler shift, only the signal to which a frequency change appropriate for the area has been applied is emphasized, and the other signals to which a frequency change has been applied are spread in frequency. The demodulator 33 of the terminal station 3-1 located in area "A1" can demodulate the activation signal to which the applied change frequency "F1" has been applied.

[0059] The activation control unit 34 of the terminal station 3-1 controls the terminal station 3-1 to change from the sleep state to the activation state based on the activation signal demodulated by the demodulation unit 33 (step S112). The transceiver unit 32 of the terminal station 3-1 transmits a terminal uplink signal based on the environmental data stored in the data storage unit (step S113).

[0060] The transceiver 32 of the terminal station 3-2 outputs the received downlink signal to the demodulator 33. The demodulator 33 of the terminal station 3-2 demodulates the downlink signal (step S114). The demodulator 33 of the terminal station 3-2 located in area "A2" can demodulate the activation signal to which the assigned change frequency "F2" is assigned. The activation controller 34 of the terminal station 3-2 controls the terminal station 3-2 to change from a sleep state to an activated state based on the activation signal demodulated by the demodulator 33 (step S115). The transceiver 32 of the terminal station 3-2 transmits a terminal uplink signal based on the environmental data stored in the data storage unit (step S116).

[0061] This allows the mobile relay station 2 to receive terminal uplink signals transmitted from each terminal station 3. Note that the mobile relay station 2 repeatedly executes the processes from step S102 to step S108 while it is above the data collection area.

[0062] In the wireless communication system 1 configured as described above, the mobile relay station 2 applies a frequency change to the activation signal and transmits the activation signal with the frequency change. As a result, even if a Doppler shift occurs in the activation signal received by the terminal station 3 installed on the ground, the activation signal is emphasized by the Doppler shift because the frequency change is appropriate for that area. This allows the activation signal to be demodulated in the terminal station 3. As a result, the terminal station 3 can be activated. In this way, in the wireless communication system 1, it is possible to activate the terminal station 3 installed on the ground even if a Doppler shift occurs in the signal transmitted from the mobile relay station 2 moving in the sky.

[0063] Furthermore, in the wireless communication system 1, the activation signal generated by the activation signal generation unit 223 is distributed by the distribution unit 224 and output to each of the multiple frequency change applying units 225. The activation signals to which the multiple frequency change applying units 225 have applied frequency changes are then combined by the combination unit 226 and transmitted. This allows the activation signals to be combined and transmitted. Although activation signals to which different frequency changes have been applied will interfere with each other, due to intra-frame Doppler shift, in the orbit signal received by the terminal stations 3 located in each area, only the activation signal to which the frequency change appropriate for that area has been applied is emphasized, and the activation signals to which the other frequency changes have been applied are frequency spread. Therefore, the terminal stations 3 located in each area can demodulate the activation signal and become activated.

[0064] A modification of the wireless communication system 1 will now be described. In the above-described embodiment, the mobile relay station 2 is configured to determine whether or not it is above a data collection area based on the orbit information 231 and time information. The mobile relay station 2 may be configured to determine whether or not it is above a data collection area using other methods. Specifically, the mobile relay station 2 may obtain the start and end times of data collection from the terminal station 3 through uplink communication from the base station 4, and determine that it is above the data collection area from the start time to the end time.

[0065] In the above-described embodiment, the mobile relay station 2 activates the terminal stations 3 located in each area within the radio wave coverage area. However, the mobile relay station 2 may be configured to activate the terminal stations 3 located in a specific area. As shown in FIG. 7 , the assignment table 233 stores the value of the assigned frequency change for each area. Therefore, the mobile relay station 2 only needs to assign the value of the assigned frequency change corresponding to the area in which the terminal station 3 is to be activated to the activation signal and transmit the signal. Specifically, when an instruction to activate the terminal station 3 located in a specific area is input, the setting unit 242 first refers to the assignment table 233 and acquires the value of the assigned frequency change corresponding to the specific area. For example, if the specific area is one area, the setting unit 242 refers to the assignment table 233 and acquires the value of the assigned frequency change corresponding to the one specific area. Next, the setting unit 242 sets the acquired value of the assigned frequency change to all the frequency change assignment units 225. As a result, the combined activation signal generated by the combination unit 226 includes an activation signal to which only the value of the assigned frequency change corresponding to the specific area is assigned. The transmitting / receiving unit 221 then transmits the generated combined activation signal. This further emphasizes the activation signal for the specific area. As a result, the terminal stations 3 located in the specific area can demodulate and decode the activation signal more reliably. As a result, only the terminal stations 3 located in the specific area can be activated. Therefore, terminal stations 3 that do not need to be activated are not activated, and power consumption can be reduced. Note that the number of specific areas may be one or more. For example, if there are two specific areas (e.g., areas A1 and A2), the setting unit 242 refers to the assignment table 233 and acquires the values ​​of the assigned frequency change corresponding to the two specific areas. Next, the setting unit 242 sets each of the acquired values ​​of the assigned frequency change in the frequency change assignment unit 225. At this time, the setting unit 242 may set each of the acquired values ​​of the assigned frequency change in the frequency change assignment unit 225 equally or at a predetermined ratio.When the number of frequency change imparting units 225 is four and the acquired values ​​of the imparted variation frequency are set equally to the frequency change imparting units 225, the setting unit 242 sets the value of the imparted variation frequency corresponding to area A1 to frequency change imparting units 225-1 to 2, and sets the value of the imparted variation frequency corresponding to area A2 to frequency change imparting units 225-3 to 4. When the number of frequency change imparting units 225 is four and the acquired values ​​of the imparted variation frequency are set to frequency change imparting units 225-2 to 225-3, and sets the value of the imparted variation frequency corresponding to area A2 to frequency change imparting unit 225-4, and so on, in accordance with the ratio.

[0066] In the above-described embodiment, the mobile relay station 2 is configured to assign a value of 0 Hz / s to the activation signal in the frequency change assigning unit 225 in order to activate the terminal station 3 located in an area where activation is possible without assigning a frequency change value. In this case, N frequency change assigning units 225 are required to assign a frequency change value to each of the activation signals distributed to N routes by the distributor 224. Alternatively, the mobile relay station 2 may be configured to include (N-1) frequency change assigning units 225, and one of the N routes distributed by the distributor 224 may be a route that directly connects the distributor 224 and the combiner 226 (a route that does not pass through the frequency change assigning unit 225). In other words, the mobile relay station 2 may be configured to assign frequency change values ​​to (N-1) activation signals among the activation signals (N activation signals) distributed to N routes by the distributor 224 by the (N-1) frequency change assigning units 225, and directly input one activation signal to the combiner 226. In this case, the (N-1) frequency change assigning units 225 assign a frequency value other than 0. Then, the activation signal distributed by the distribution unit 224 and directly input to the synthesis unit 226 becomes an activation signal for activating terminal stations 3 located in areas where activation is possible without assigning a frequency change value. By configuring in this way, the configuration of the mobile relay station 2 can be reduced compared to the configuration of the above-described embodiment.

[0067] In the above embodiment, the mobile body on which the mobile relay station is mounted is described as a LEO satellite, but it may also be a geostationary satellite or other flying body that flies in the sky, such as a drone or HAPS.

[0068] Some or all of the processing performed by the mobile relay station 2 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to implement the function. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system.

[0069] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or a medium that stores a program for a fixed period of time, such as a volatile memory within a computer system that serves as a server or client in such a case. The program may also be one that realizes part of the above-mentioned functions, or one that can realize the above-mentioned functions in combination with a program already stored in the computer system, or one that can be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0070] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0071] The present invention can be applied to a technology for communicating with a mobile object equipped with a mobile relay station. [Explanation of symbols]

[0072] 1...wireless communication system, 2...Mobile relay station, 3...Terminal station, 4...Base station, 21...antenna, 22...Terminal communication unit, 23…Storage section 24...Control unit, 25...Base station communication unit, 26...antenna, 31...data storage unit, 32...Transmitter / receiver, 33...Demodulation section, 34...Demodulation section, 35...antenna, 41...antenna, 221...Transmitter / receiver, 222...terminal signal demodulation unit, 223…Start signal generation unit 224...Distribution section 225-1 to 225-N...Frequency change applying section 226...Synthesis section 241...Motion control unit, 242...Settings section

Claims

1. 1. A wireless communication device in a wireless communication system having one or more ground-based communication devices and a mobile wireless communication device, a wake-up signal generation unit that generates a wake-up signal for activating the one or more communication devices; one or more frequency change applying units that apply a frequency change to the activation signal generated by the activation signal generating unit to pre-compensate for time fluctuations of Doppler shift; a transmitter that transmits an activation signal with a frequency change applied to the one or more frequency change applying units; Equipped with the one or more frequency change imparting units are a plurality of frequency change imparting units, a distributor that distributes the activation signal generated by the activation signal generator and outputs the distribution signal to each of the plurality of frequency change applying units; a synthesizing unit that synthesizes the activation signals to which the frequency changes have been applied by the plurality of frequency change applying units; Furthermore, the transmitting unit transmits the activation signal after being combined by the combining unit; At least some of the plurality of frequency change applying units apply the same frequency change to the activation signal distributed by the distribution unit in accordance with a set ratio. Wireless communication device.

2. a setting unit that sets the value of the frequency change provided by the one or more frequency change providing units for each of the one or more frequency change providing units, the setting unit sets the value of the frequency change set for each terrestrial area seen from the wireless communication device for each of the one or more frequency change applying units. The wireless communication device of claim 1 .

3. when an instruction to activate the one or more communication devices installed in a specific area is input, the setting unit sets the value of the frequency change corresponding to the specific area in the one or more frequency change applying units. The wireless communication device according to claim 2 .

4. 1. A startup method performed by a wireless communication device in a wireless communication system having one or more ground-based communication devices and a mobile wireless communication device, the method comprising: generating a wake-up signal to wake up the one or more communication devices; a frequency change is applied to the generated activation signal to pre-compensate for time fluctuations of the Doppler shift; Transmitting an activation signal with a frequency change; Distributing the generated activation signal and outputting it to a plurality of frequency change imparting units that impart the frequency change to the activation signal, combining the activation signals to which the frequency changes have been applied by the plurality of frequency change applying units; Send the combined activation signal, At least some of the plurality of frequency change applying units apply the same frequency change to the distributed activation signal in accordance with a set ratio. How to start.

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