Patent Application
20250105916
The present invention relates to a communication apparatus, a communication system, a communication method, and a program.
With the development of Internet of Things (IoT) technology, it has been studied to install IoT terminals including various sensors in various places. For example, it is also assumed that the IoT is used to collect data of a place where it is difficult to install a base station, such as a buoy or a ship on the sea or a mountainous area. Meanwhile, there is a technology of wirelessly communicating with a communication apparatus on the ground by using an unmanned aerial vehicle (UAV) or a geostationary satellite (see, for example, Non Patent Literature 1).
The channel capacity of a relay device and a communication apparatus changes depending on the environment in which the communication apparatus is installed. For example, in a case where communication apparatuses are provided in an urban area, since there are many competing communication apparatuses, there is a possibility that the channel capacity decreases due to signal collision. In addition, for example, in a case where the communication apparatus is provided in a mountain area, the channel capacity may be reduced because the viewing angle is narrow due to an obstacle such as a forest.
In view of the above circumstances, an object of the present invention is to provide a communication apparatus, a communication system, a communication method, and a program capable of improving communication efficiency according to an environment in which the communication apparatus is installed.
A first aspect of the present invention is a communication apparatus that transmits data to a relay device that performs communication while moving, the communication apparatus including: an acquisition unit that acquires environment information indicating an installation environment of the communication apparatus; a scheme specifying unit that specifies a transmission scheme of the data on the basis of relational data indicating a relationship between the environment information and the transmission scheme and the acquired environment information; and a transmission unit that transmits the data to the relay device on the basis of the specified transmission scheme.
A second aspect of the present invention is a communication system, including: a relay device that performs communication while moving; and a plurality of communication apparatuses according to the above aspect, in which the environment information of at least one of the plurality of communication apparatuses is different from the environment information of another communication apparatus.
A third aspect of the present invention is a communication method of a communication apparatus that transmits data to a relay device that performs communication while moving, the communication method including: a step of acquiring environment information indicating an installation environment of the communication apparatus; a step of specifying a transmission scheme of the data on the basis of relational data indicating a relationship between the environment information and the transmission scheme and the acquired environment information; and a step of transmitting the data to the relay device on the basis of the specified transmission scheme.
According to the at least one aspect described above, communication efficiency can be improved according to the environment in which the communication apparatus is installed.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The mobile relay station 2 is an example of a relay device that performs communication while moving. The mobile relay station 2 is provided in, for example, a low earth orbit (LEO) satellite. The LEO satellite has an altitude of 2000 km or less and moves around the earth once every about 1.5 hours. The terminal station 3 and the base station 4 are installed on the earth such as on the ground or on the sea. The terminal station 3 is, for example, an IoT terminal. The terminal station 3 collects data such as environmental data detected by a sensor and wirelessly transmits the collected data to the mobile relay station 2. In the drawing, only two terminal stations 3 are illustrated. The mobile relay station 2 receives the data transmitted from each of the plurality of terminal stations 3 via radio signals while moving above the earth and wirelessly transmits the received data to the base station 4. The base station 4 receives the data collected by the terminal station 3 from the mobile relay station 2.
As the mobile relay station 2, it is conceivable to use a relay station mounted on a geostationary satellite or an unmanned aerial vehicle such as a drone, or a high altitude platform station (HAPS). However, a relay station mounted on a geostationary satellite has a wide coverage area (footprint) on the ground, but has a very small link budget with respect to IoT terminals installed on the ground because its altitude is high. On the other hand, in the case of a relay station mounted on a drone or a HAPS, the link budget is high, but the coverage area is small. Furthermore, the drone requires a battery, and the HAPS requires a solar panel. In the present embodiment, the mobile relay station 2 is 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 moves around the outside of the atmosphere. In addition, the footprint is larger than that in the case of the relay station mounted on the drone or the HAPS.
However, the mobile relay station 2 mounted on the LEO satellite performs communication while moving at a high speed, and thus a Doppler shift occurs in radio signals. In addition, the relay station mounted on the LEO satellite has a smaller link budget than a case where a relay station is mounted on a drone or a HAPS. Therefore, the mobile relay station 2 receives radio signals from the terminal stations 3 through a plurality of antennas and transmits the radio signals to the base station 4 through a plurality of antennas. Communication quality can be improved by a diversity effect and beamforming effect of communication using the plurality of antennas. In the present embodiment, there will be described an example where the mobile relay station 2 relays radio signals received from the terminal stations 3 through the plurality of antennas to the base station 4 by multiple input multiple output (MIMO). Note that a method of relaying to the base station 4 may be other than MIMO.
A configuration of each device will be described.
The mobile relay station 2 includes a plurality of first antennas 21, a terminal communication unit 22, a base station communication unit 23, and a plurality of second antennas 24. The first antenna 21 is used for communication with the terminal station 3. The second antenna 24 is used for communication with the base station 4. The terminal communication unit 22 includes a storage unit 221, a reception schedule determination unit 222, a reception unit 223, a combining unit 224, and a spectrum conversion unit 225.
The storage unit 221 stores position data of the terminal station 3 and orbit data of the LEO satellite. The position data of the terminal station 3 is indicated by, for example, latitude and longitude. The orbit data of the LEO is data from which a position, speed, moving direction, and the like of the LEO satellite at an arbitrary time can be obtained. The storage unit 221 has a storage area for storing spectral data of a terminal uplink signal received from the terminal station 3.
The reception schedule determination unit 222 specifies a timing at which a signal is received from each terminal station 3 on the basis of the position data of the terminal station 3 and the orbit data stored in the storage unit 221. The reception unit 223 receives a signal via the plurality of first antennas 21. The combining unit 224 combines a plurality of signals received by the reception unit 223 via the plurality of first antennas 21 according to a predetermined combination parameter. The combination parameter is indicated by, for example, an offset of a phase and amplitude of each first antenna 21. Note that the combination parameter may be obtained on the basis of the signal reception timing and the positional relationship between the mobile relay station 2 and the communication counterpart terminal station 3 at the reception timing, or may be a constant value at all times. The combining unit 224 reproduces a terminal uplink signal by combining the signals.
The spectrum conversion unit 225 converts the signal combined by the combining unit 224 into a frequency spectrum. The spectrum conversion unit 225 obtains a frequency spectrum of the received signal by fast Fourier transform (FFT), for example. The spectrum conversion unit 225 records spectral data indicating the generated frequency spectrum in the storage unit 221. The spectral data is indicated by a combination of a frequency and power of the frequency.
The base station communication unit 23 transmits spectral data indicating a waveform of the terminal uplink signal received by the terminal communication unit 22 to the base station 4 by MIMO. The base station communication unit 23 includes a storage unit 231, a transmission schedule determination unit 232, a control unit 233, a MIMO communication unit 234, a data generation unit 235, and a transmission data modulation unit 236.
The storage unit 231 stores a communication time zone with the base station 4 obtained in advance from a position of the base station 4 and an orbit of the LEO satellite. In addition, the storage unit 231 stores in advance a weight of a base station downlink signal transmitted from each second antenna 24 for each transmission time in the communication time zone. The transmission time may be indicated by, for example, a time elapsed from a transmission start timing. The weight for each transmission time is calculated on the basis of the orbit data of the LEO satellite and the position of each antenna station 41.
The transmission schedule determination unit 232 determines a transmission time zone for each spectral data on the basis of the number of pieces of the spectral data stored in the storage unit 221 and the communication time zone. For example, the transmission schedule determination unit 232 determines a transmission time of each piece of the spectral data by dividing the length of the communication time zone by the number of pieces of the spectral data and determines the transmission time zone of each piece of the spectral data by separating the communication time zone by the transmission time.
The control unit 233 issues an instruction on the weight for each transmission time read from the storage unit 231 to the MIMO communication unit 234. The MIMO communication unit 234 establishes MIMO communication with the base station 4 according to a predetermined protocol.
The data generation unit 235 converts the spectral data stored in the storage unit 221 into a parallel signal. The transmission data modulation unit 236 modulates the spectral data converted into the parallel signal. The modulated parallel signal is weighted with the weight instructed from the control unit 233 and is transmitted from each second antenna 24 as a base station downlink signal.
The terminal station 3 includes a data storage unit 31, a setting unit 32, an acquisition unit 33, a condition specifying unit 34, a correction unit 35, a transmission unit 36, and one or a plurality of antennas 37. The terminal station 3 is an example of a communication apparatus that transmits data to the relay device. The data storage unit 31 stores sensor data, environment information, relational data, and the orbit data of the LEO satellite. The environment information is information indicating an installation environment of the terminal station 3 set from the outside. The environment information has values of, for example, a mountain area, the sea, a rural area, an urban area, and the like. The relational data indicates a relationship between the environment information and the transmission scheme. For example, the relational data is a table in which each value of the environment information is associated with the transmission scheme. The transmission method is indicated by a multi-value number, the number of bits of an error correction code, and transmission power. Note that, in other embodiments, an error detection code may be used instead of the error correction code.
In the relational data, an environment with a relatively small channel capacity is associated with a transmission scheme with higher transmission quality, and an environment with a relatively large channel capacity is associated with a transmission scheme with higher transmission efficiency. For example, since the viewing angle is narrow due to the presence of trees and the like in a mountain area, there is a high possibility that the channel capacity becomes small compared to that on the sea with few obstacles. In addition, for example, in an urban area, since the existence density of communication apparatuses in the area is high, there is a high possibility that the channel capacity becomes small as compared with that in a rural area in which the existence density of communication apparatuses is low.
Specifically, in the relational data, a transmission scheme having a small multi-value number is associated with an environment with a small channel capacity. The larger the multi-value number, the larger the amount of information per symbol, and the higher the transmission efficiency. On the other hand, the smaller the multi-value number, the lower a symbol error rate and the higher the transmission quality. In addition, in the relational data, a transmission scheme having a large number of bits of the error correction code is associated with an environment with a small channel capacity. The shorter the error correction code, the larger the information amount of the payload with respect to a data frame, and the higher the transmission efficiency. On the other hand, the longer the error correction code, the larger the number of bits in which the error can be corrected, and the higher the transmission quality. Note that in a case where the error detection code is used, the transmission scheme in which the number of bits of the error detection code is large is associated with the environment with a small channel capacity in the relational data. The shorter the error detection code, the larger the information amount of the payload with respect to a data frame, and the higher the transmission efficiency.
In addition, in the relational data, a large transmission power is associated with an environment with a large amount of noise. For example, since there are more communication equipment used on the ground in the urban area than in the rural area, the SN ratio is relatively high. Thus, the probability of occurrence of an error can be reduced by increasing the transmission power and reducing the SN ratio.
The setting unit 32 receives setting of environment information and relational data from the outside. For example, when the terminal station 3 is installed, the setting unit 32 receives the setting of the environment information by an input device, which is not illustrated, included in the terminal station 3. In addition, for example, the terminal station 3 may receive an update of the environment information from a management device, which is not illustrated. For example, the management device may monitor a communication environment such as a congestion status and a communication frequency of communication between the mobile relay station 2 and the terminal station 3 for each area, update the environment information of each terminal station 3 when the communication environment changes, and transmit the updated environment information to each terminal station 3. In addition, for example, the setting unit 32 receives an update of the relational data stored in the terminal station 3 by a management device, which is not illustrated. The environment information set in the setting unit 32 varies depending on the installation environment of the terminal station 3. Installation information different from that of another terminal station 3 is set in at least one of the plurality of terminal stations 3 included in the wireless communication system 1. On the other hand, the relational data set in the setting unit 32 is the same data in all the terminal stations 3 included in the wireless communication system 1.
The setting unit 32 causes the data storage unit 31 to store the value of the environment information and the relational data received from the outside. Note that, in a case where the installation environment of the terminal station 3 is subsequently changed due to the relocation of the terminal station 3 or the like, the environment information is reset by the user.
The acquisition unit 33 acquires the value of the environment information from the data storage unit 31. The condition specifying unit 34 refers to the relational data stored in the data storage unit 31 and specifies the transmission scheme associated with the value of the environment information acquired by the acquisition unit 33. In addition, the condition specifying unit 34 specifies the transmission time zone of the terminal uplink signal and the elevation angle of the LEO satellite for each time in the transmission time zone on the basis of the orbit information of the LEO satellite stored in the data storage unit 31.
The correction unit 35 corrects the transmission scheme specified by the condition specifying unit 34 on the basis of the elevation angle. The lower the elevation angle, the lower the separation performance of the terminal uplink signal in the mobile relay station 2. Accordingly, the correction unit 35 corrects the transmission scheme so that the lower the elevation angle, the higher the transmission quality. For example, in a case where the elevation angle is lower than a predetermined value, the correction unit 35 reduces the number of units of the multi-value number and increases the number of units of the number of bits of an error correction code. On the other hand, in a case where the elevation angle is higher than a predetermined value, the correction unit 35 increases the number of units of the multi-value number and reduces the number of units of the number of bits of an error correction code. In addition, the lower the elevation angle, the higher the SN ratio because the distance between the mobile relay station 2 and the terminal station 3 is longer. Accordingly, the correction unit 35 corrects the transmission scheme so that the lower the elevation angle, the larger the transmission power. For example, the correction unit 35 corrects the transmission power by multiplying the transmission power specified by the condition specifying unit 34 by a coefficient that increases as the elevation angle decreases.
The transmission unit 36 wirelessly transmits, from the antenna 37, the terminal uplink signal in which the sensor data stored in the data storage unit 31 is set as terminal transmission data according to the transmission time zone specified and the transmission scheme corrected by the correction unit 35. The transmission unit 36 may give notification of the transmission scheme of the terminal uplink signal using a preamble. The transmission unit 36 transmits the signal by, for example, low power wide area (LPWA). 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. In addition, the transmission unit 36 may perform transmission with another terminal station 3 by time-division multiplexing, orthogonal frequency division multiplexing (OFDM), MIMO, or the like. The transmission unit 36 determines a channel to be used by the own station to transmit the terminal uplink signal and a transmission timing by a method determined in advance in a wireless communication scheme to be used. In addition, the transmission unit 36 may perform beam formation of the signals to be transmitted from the plurality of antennas 37 by a method determined in advance in the wireless communication scheme to be used.
The base station 4 includes a plurality of antenna stations 41, a MIMO reception unit 42, a base station signal reception processing unit 43, and a terminal signal reception processing unit 44.
Each antenna station 41 is arranged at a position far from another antenna station 41 so as to increase a difference in an angle of arrival of a signal from each of the plurality of second antennas 24 of the mobile relay station 2. Each antenna station 41 converts a base station downlink signal received from the mobile relay station 2 into an electric signal and outputs the electric signal to the MIMO reception unit 42.
The MIMO reception unit 42 aggregates the base station downlink signals received from the plurality of antenna stations 41. The MIMO reception unit 42 stores a weight for each reception time with respect to the base station downlink signal received by each antenna station 41 on the basis of the orbit data of the LEO satellite and the position of each antenna station 41. For example, the reception time may be indicated by a time elapsed from a reception start timing. The MIMO reception unit 42 multiplies the base station downlink signal input from each antenna station 41 by the weight corresponding to the reception time of the base station downlink signal and combines the reception signals multiplied by the weights. Note that the same weight may be used regardless of the reception time. The base station signal reception processing unit 43 demodulates and decodes the combined reception signal, thereby obtaining demodulation information. The base station signal reception processing unit 43 outputs the demodulation information to the terminal signal reception processing unit 44.
The terminal signal reception processing unit 44 performs reception processing of the terminal uplink signal. The terminal signal reception processing unit 44 decodes a symbol of the terminal uplink signal from the spectral data indicated by the demodulation information, thereby obtaining the terminal transmission data transmitted from the terminal station 3. That is, the terminal signal reception processing unit 44 decodes the symbol of the terminal uplink signal by converting the frequency domain waveform indicated by the spectral data into the time domain waveform.
Operation of the wireless communication system 1 will be described.
The terminal station 3 acquires data detected by a sensor, which is not illustrated, provided outside or inside and writes the acquired data to the data storage unit 31 (step S102). The acquisition unit 33 acquires the environment information from the data storage unit 31 (step S103). The condition specifying unit 34 specifies the transmission scheme (multi-value number, the number of bits of error correction code, and transmission power) associated with the value of the environment information acquired in step S103 from the relational data stored in the data storage unit 31 (step S104). In addition, the condition specifying unit 34 specifies the transmission time zone of the terminal uplink signal and the elevation angle of the LEO satellite in each time in the transmission time zone on the basis of the orbit data of the LEO satellite stored in the data storage unit 31 (step S105).
The transmission unit 36 of the terminal station determines whether the current time is included in the transmission time zone of the uplink signal specified by the condition specifying unit 34 (step S106). When the transmission unit 36 determines that the current time is not included in the transmission time zone of the uplink signal (step S106: NO), the terminal station 3 returns the processing to step S101.
On the other hand, when the transmission unit 36 determines that the current time is included in the transmission time zone of the uplink signal (step S106: YES), the correction unit 35 corrects the transmission scheme on the basis of the elevation angle of the LEO satellite at the current time such that the lower the elevation angle, the higher the transmission quality, and the larger the transmission power (step S107). The transmission unit 36 reads the sensor data from the data storage unit 31, sets the read sensor data as terminal transmission data, and sets the terminal transmission data in the terminal uplink signal of the transmission scheme corrected in step S107. The transmission unit 36 wirelessly transmits the terminal uplink signal in which the terminal transmission data is set through the antenna 37 (step S108). The terminal station 3 returns the processing to step S106. As a result, the terminal station 3 continuously transmits the uplink signal during the transmission time zone.
The transmission schedule determination unit 232 determines whether the current time is included in the communication time zone with the base station 4 by referring to the storage unit 231 (step S125). When the current time is not included in the communication time zone with the base station 4 (step S125: NO), the processing returns to step S121. On the other hand, when the current time is included in the communication time zone with the base station 4 (step S125: YES), the transmission schedule determination unit 232 determines a transmission time of each spectral data on the basis of the number of pieces of the spectral data stored in the storage unit 221 and the length of the communication time zone with the base station 4 (step S126).
The data generation unit 235 performs parallel conversion on the spectral data stored in the storage unit 221, and the transmission data modulation unit 236 modulates the parallel-converted spectral data. The MIMO communication unit 234 weights the transmission data modulated by the transmission data modulation unit 236 with the weight issued from the control unit 233 and generates a base station downlink signal to be transmitted from each second antenna 24. The MIMO communication unit 234 transmits each generated base station downlink signal from the second antenna 24 by MIMO (step S127). When transmitting all the spectral data stored in the storage unit 221, the mobile relay station 2 returns the processing to step S121.
The terminal signal reception processing unit 44 decodes a symbol of the terminal uplink signal indicated by the spectral data, thereby obtaining the terminal transmission data transmitted from the terminal station 3 (step S143). Note that the terminal signal reception processing unit 44 can also use a decoding method having a large calculation load, such as successive interference cancellation (SIC). The base station 4 repeats the processing from step S141.
As described above, according to the first embodiment, the terminal station 3 specifies the transmission scheme of the data to the mobile relay station 2 on the basis of the relational data indicating the relationship between the environment information and the transmission scheme and the environment information indicating the installation environment of the terminal station 3. As a result, the terminal station 3 can improve the communication efficiency according to the environment in which the terminal station 3 is installed by setting an appropriate transmission scheme for each installation environment as the relational data.
In addition, according to the first embodiment, the terminal station 3 corrects the specified transmission scheme on the basis of the orbit information of the mobile relay station 2. Since the magnitude of the channel capacity of the terminal station 3 and the mobile relay station 2 can be predicted from the orbit information of the mobile relay station 2, the terminal station 3 can further improve the communication efficiency by correcting the transmission scheme on the basis of the orbit information. Note that, in another embodiment, the terminal station 3 may communicate with the mobile relay station 2 without correcting the specified transmission scheme.
The terminal station 3 according to the second embodiment further includes a positioning unit 38 in addition to the configuration of the first embodiment. In addition, in the second embodiment, information stored in a data storage unit 31 and processing of an acquisition unit 33 included in the terminal station 3 are different from those of the first embodiment. The positioning unit 38 specifies the position of the terminal station 3 on the ground with the GNSS.
The data storage unit 31 according to the second embodiment stores map information indicating the relationship between the position on the ground and the value of the environment information instead of the setting information of the first embodiment. The map information is data in which an area indicated by a combination of latitude and longitude is associated with a value of environment information of the area. The setting unit 32 may receive an update of the map information. The acquisition unit 33 acquires the value of the environment information associated with the position of the terminal station 3 measured by the positioning unit 38 from the map information.
As described above, the terminal station 3 according to the second embodiment acquires the environment information on the basis of the map information indicating the relationship between the position on the ground and the environment information and the measured position of the own station. As a result, the terminal station 3 can adapt to the change in the installation environment without resetting the environment information.
The terminal communication unit 22 of the mobile relay station 2 according to the third embodiment includes a terminal signal reception processing unit 226 instead of the spectrum conversion unit 225 of the first embodiment. Similarly to the terminal signal reception processing unit 44 of the first embodiment, the terminal signal reception processing unit 226 decodes a symbol of the terminal uplink signal and obtains sensor data transmitted from the terminal station 3. The terminal signal reception processing unit 226 reads the transmission scheme from the preamble of the terminal uplink signal transmitted from the terminal station 3, and decodes the terminal uplink signal on the basis of the transmission scheme. The storage unit 221 according to the third embodiment stores the sensor data received by the terminal signal reception processing unit 226. The data generation unit 235 of the base station communication unit 23 converts the sensor data into a parallel signal.
Since the sensor data decoded from the terminal uplink signal is superimposed on the base station downlink signal transmitted by the mobile relay station 2, the base station signal reception processing unit 43 of the base station 4 can obtain the sensor data by decoding the base station downlink signal. Thus, the base station 4 according to the third embodiment may not include the terminal signal reception processing unit 44.
As described above, according to the above-described embodiments, the terminal station 3 acquires the environment information indicating the installation environment of the own station, and specifies the data transmission scheme on the basis of the relational data indicating the relationship between the environment information and the transmission scheme and the acquired environment information. As a result, the terminal station 3 can improve the communication efficiency according to the installation environment.
The terminal station 3 includes a processor, a memory, an auxiliary storage device, and the like connected by a bus and executes a program to function as a device including the acquisition unit 33 and the condition specifying unit 34. Examples of the processor include a central processing unit (CPU), a graphic processing unit (GPU), and a microprocessor.
The program may be recorded on a computer-readable recording medium. The computer-readable recording medium is a storage device such as a magnetic disk, a magneto-optical disk, an optical disk, or a semiconductor memory, for example. A relay program may be transmitted via an electrical communication line.
Note that all or some of the functions of the terminal station 3 may be implemented by using a custom large scale integrated circuit (LSI) such as an application specific integrated circuit (ASIC) or a programmable logic device (PLD). Examples of the PLD include a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). Such an integrated circuit is also included in the examples of the processor.
Although embodiments have been described in detail with reference to the drawings, specific configurations are not limited to the above-described configurations, and various design changes and the like can be made thereto. That is, in other embodiments, the order of the above-described processing may be changed as appropriate. In addition, part of the processing may be executed in parallel.
The terminal station 3 according to the above-described embodiments may be formed with a single computer, or the components of the terminal station 3 may be disposed to be divided into a plurality of computers, and the plurality of computers may function as the terminal station 3 in cooperation with each other.
According to the above-described embodiments, the multi-value number, the error correction code, and the transmission power are changed according to the environment information of the terminal station 3, but it is not limited thereto. For example, in other embodiments, at least one of the multi-value number, the error correction code, and the transmission power may be changed according to the environment information. In addition, in other embodiments, the transmission scheme other than the multi-value number, the error correction code, and the transmission power may be different.
In the above-described embodiments, the mobile relay station 2 is mounted on the LEO satellite, but it is not limited thereto. For example, the mobile relay station 2 according to other embodiments may be mounted on another flying object such as a geostationary satellite, a drone, or a HAPS. In addition, in the above-described embodiments, the mobile relay station 2 moves above the earth, and the terminal station 3 and the base station 4 are provided on the earth, but the wireless communication system 1 according to other embodiments may use a celestial body other than the earth, such as the moon.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/001753 | 1/19/2022 | WO |
