Communication system

Abstract

One aspect of the present invention is a wireless communication system in which a wireless signal, the wireless signal being transmitted from a terminal station device that includes a first transmitter, which is a transmitter for transmitting the wireless signal, and that uses the first transmitter to transmit the wireless signal to a mobile body capable of receiving the wireless signal, is received by the mobile body. The wireless communication system comprises: the mobile body; at least one terminal station device; and a schedule transmitting device that includes a second transmitter, which is a transmitter for transmitting schedule information indicating the position at which the mobile body is scheduled to be present at each point in time, and transmits the schedule information to the terminal station device by using the second transmitter at a preset time. The terminal station device acquires, on the basis of the schedule information, a time at which the mobile body passes through a position through which the mobile body is scheduled to pass and where communication between the terminal station device and the mobile body is possible, and transmits the wireless signal by using the first transmitter so that the wireless signal reaches said position at the acquired time.

Description

communication systems

[0001] The present invention relates to communication systems.

[0002] For example, wireless communication may be performed between a terminal station device and a mobile object such as a satellite for the purpose of collecting data, etc. (see Non-Patent Document 1). In this case, a technique has been considered to realize data transmission between the terminal station device and the mobile object, in which the mobile object transmits a signal (hereinafter referred to as a "data transmission start signal") to the terminal station device to notify the start of data transmission, and the terminal station device transmits data to the mobile object wirelessly after receiving the signal.

[0003] Kohei Suzaki, et al. "Laboratory Experimental Evaluation of Terminal Activation Area Control Technology Using Doppler Fluctuation Compensation for Satellite IoT Platforms." IEICE Conferences Archives. The Institute of Electronics, Information and Communication Engineers, 2023.

[0004] However, mobile objects often move irregularly and at high speeds. Therefore, in technology where transmission begins after receiving a data transmission start signal, the terminal station device must be constantly activated to receive the data transmission start signal. As a result, power is consumed even while waiting for the data transmission start signal, which may arrive at any time.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique for reducing the power consumption required for communication.

[0006] One aspect of the present invention is a wireless communication system in which a mobile unit receives a wireless signal transmitted from a terminal station device having a first transmitter that transmits a wireless signal to a mobile unit capable of receiving the wireless signal, the terminal station device comprising the mobile unit, one or more of the terminal station devices, and a second transmitter that transmits schedule information indicating the location where the mobile unit is expected to be at each time, and a schedule transmission device that transmits the schedule information to the terminal station device using the second transmitter at a predetermined time, the terminal station device obtaining, based on the schedule information, the time at which the mobile unit will pass a location where the mobile unit is expected to pass and where communication between the terminal station device and the mobile unit is possible, and transmitting the wireless signal using the first transmitter so that the wireless signal will arrive at the location at the obtained time.

[0007] The present invention makes it possible to reduce the power consumption required for communication.

[0008] 1 is an explanatory diagram illustrating a communication system according to an embodiment. A diagram illustrating an example of the hardware configuration of a terminal station device according to an embodiment. A diagram illustrating an example of the hardware configuration of a schedule transmission device according to an embodiment. A flowchart illustrating an example of the flow of processing executed in the communication system according to an embodiment. A flowchart illustrating an example of the flow of processing executed by each terminal station device according to a modified example. A diagram illustrating an example of a circular area with a radius r according to a modified example. A diagram illustrating the relationship between the communication available time rate and the distance from the center of the area according to a modified example. A first explanatory diagram illustrating an example of frequency channel transition according to a modified example. A second explanatory diagram illustrating an example of frequency channel transition according to a modified example. A first explanatory diagram illustrating the possibility of congestion according to a modified example. A second explanatory diagram illustrating the possibility of congestion according to a modified example. A first explanatory diagram illustrating the demodulation success rate according to a modified example. A second explanatory diagram illustrating the demodulation success rate according to a modified example.

[0009] 1 is an explanatory diagram illustrating a communication system 100 according to an embodiment. The communication system 100 is a wireless communication system including a terminal station device 1 and a mobile object 2. The communication system 100 includes one or more terminal station devices 1.

[0010] The terminal station device 1 includes a first transmitter 10, which is a transmitter that transmits a radio signal. The radio signal carries information to be transmitted, such as data to be transmitted to a mobile object 2. The terminal station device 1 transmits the radio signal to the mobile object 2 using the first transmitter 10. The mobile object 2 is capable of receiving the radio signal transmitted by the first transmitter 10. In the communication system 100, the mobile object 2 receives the radio signal transmitted by the first transmitter 10.

[0011] The communication system 100 includes a terminal station device 1 and a mobile object 2, as well as a schedule transmitting device 3. The schedule transmitting device 3 includes a second transmitter 30, which is a transmitter that transmits schedule information. The schedule information is trajectory information of the mobile object 2. In other words, the schedule information is information that indicates the planned location of the mobile object 2 at each time. The schedule transmitting device 3 transmits the schedule information to the terminal station device 1 using the second transmitter 30 at a preset time.

[0012] <Details of Timing of Transmission of Radio Signal by Terminal Station Device 1> The terminal station device 1 acquires the communication available time based on the schedule information. The communication available time is the time when the mobile unit 2 passes a position where the mobile unit 2 is scheduled to pass and where communication between the terminal station device 1 and the mobile unit 2 is possible (hereinafter referred to as the "communication available position"). The terminal station device 1 then transmits the radio signal using the first transmitter 10 so that the radio signal arrives at the communication available position at the acquired time (i.e., the communication available time).

[0013] <Example of Effect of Communication System 100> An example of effect of the communication system 100 will be described. The communication system 100 includes a schedule transmission device 3. Therefore, in the communication system 100, the terminal station device 1 does not need to receive a data transmission start signal from the mobile object 2, and does not receive the data transmission start signal. The data transmission start signal is a signal that notifies the start of data transmission. Since the terminal station device 1 does not receive the data transmission start signal, it does not need to start up and wait for the arrival of the data transmission start signal. This reduces the power consumption required for communication.

[0014] <Another Example of the Effect of the Communication System 100> Consider a situation in which the mobile object 2 is a small satellite, HAPS, or the like in the sky or space, and the terminal station device 1 is located on the ground. In such a case, if a technology for transmitting a data transmission start signal in the same frequency band as a terrestrial LPWA (Low Power Wide Area Network) is used, line of sight from the sky would result in interference over a wide area with similar terrestrial systems. On the other hand, with the communication system 100, there is no need to transmit a data transmission start signal from the mobile object 2 to the terminal station device 1, and therefore such interference problems do not occur.

[0015] <Example of Terminal Station Device 1> The terminal station device 1 may be located on the ground, underground, on water, underwater, in the sky, or in space. The terminal station device 1 is, for example, a sensor. When the terminal station device 1 is such a sensor, the wireless signal transmitted by the terminal station device 1 carries data acquired by the terminal station device 1. In other words, the information to be transmitted is, for example, data acquired by the terminal station device 1 through sensing. The terminal station device 1 does not necessarily have to be a sensor, and may be a device that acquires information transmitted from a mobile terminal such as a smartphone. In such a case, the information to be transmitted is, for example, information transmitted by the mobile terminal.

[0016] <Example of Mobile Object 2> The terminal station device 1 may be located on the ground, underground, on the water, underwater, in the sky, or in space. The mobile object 2 may be, for example, a High Altitude Platform Station (HAPS), a small satellite, or another mobile object such as a car, an airplane, a ship, or a submarine.

[0017] <Example of Schedule Transmission Device 3> The schedule transmission device 3 is, for example, a geostationary satellite. A geostationary satellite is a device that has a function of relaying communication signals from the ground, etc., and is capable of simultaneous communication with multiple devices. When the schedule transmission device 3 is a geostationary satellite, the schedule transmission device 3 may acquire schedule information from the mobile object 2 via an antenna, such as a parabolic antenna. Note that the schedule transmission device 3 does not necessarily have to exist in the sky or space like a satellite. The schedule transmission device 3 may exist on the ground, underground, on water, or underwater. In such cases, the schedule transmission device 3 may transmit schedule information to the terminal station device 1 via a wired or wireless connection.

[0018] When the schedule transmission device 3 is located on the ground, underground, on water or underwater and obtains schedule information from the mobile body 2, and the mobile body 2 is in the sky or space, the schedule transmission device 3 may obtain schedule information from the mobile body 2, for example, by radio.

[0019] It should be noted that the schedule transmission device 3 does not necessarily need to obtain the schedule information from the mobile object 2. The schedule information may be input to the schedule transmission device 3 in advance, for example, before the manager of the mobile object 2 starts the operation of the mobile object 2.

[0020] 2 is a diagram showing an example of the hardware configuration of the terminal station device 1 in the embodiment. The terminal station device 1 includes a control unit 11 including a processor 91 such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an NPU (Neural Network Processing Unit) and a memory 92, which are connected via a bus, and executes a program. The terminal station device 1 functions as a device including the control unit 11, an interface unit 12, and a storage unit 13 by executing the program.

[0021] More specifically, the processor 91 reads out a program stored in the storage unit 13 and stores the read out program in the memory 92. The processor 91 executes the program stored in the memory 92, whereby the terminal station device 1 functions as a device including the control unit 11, the interface unit 12, and the storage unit 13.

[0022] The control unit 11 controls the operation of each functional unit included in the terminal station device 1. The control unit 11 executes, for example, a communication available time acquisition process. The communication available time acquisition process is a process of estimating a communication available time based on schedule information. The control unit 11 executes, for example, a wireless signal transmission process. The wireless signal transmission process is a process of controlling the operation of the first transmitter 10 to cause the first transmitter 10 to transmit a wireless signal so that the wireless signal reaches a communication available position at the communication available time.

[0023] In the communication available time acquisition process, the communication available time may be estimated using any known process. For example, a format of satellite orbit information called Two Line Element (TLE) may be used. The passage time can be calculated by combining the orbital inclination angle, right ascension of the ascending node, and the terminal's latitude and longitude information.

[0024] The control unit 11 acquires, for example, information stored in the storage unit 13. Specifically, the process of acquiring information stored in the storage unit 13 is a read process.

[0025] The interface unit 12 includes a communication interface 120. The communication interface 120 includes a communication device for connecting the terminal station device 1 to an external device. Each communication device included in the communication interface 120 communicates with the external device via wired or wireless communication. An example of the external device is the schedule transmission device 3. In this case, the communication interface 120 acquires schedule information by communicating with the schedule transmission device 3. The information acquired by the communication interface 120 is output to the control unit 11 or the memory unit 13.

[0026] The communication interface 120 is configured to include a first transmitter 10 as one of the communication devices. Therefore, the terminal station device 1 is equipped with the first transmitter 10. In communication with an external device using the first transmitter 10, the external device is a mobile object 2.

[0027] The interface unit 12 may be configured to include an input interface 121. The input interface 121 may be configured as an input device such as a mouse, keyboard, or touch panel, or may be configured as an interface that connects these input devices to the terminal station device 1. In this way, the input interface 121 accepts input of various information to the terminal station device 1 via the input device such as a mouse, keyboard, or touch panel.

[0028] It should be noted that the various types of information that can be input to the communication interface 120 of the interface unit 12 do not necessarily have to be input to the communication interface 120 of the interface unit 12 , but may be input to the input interface 121 of the interface unit 12 .

[0029] The interface unit 12 may be configured to include an output interface 122. The output interface 122 may include a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display, and a speaker. The output interface 122 may be configured as an interface that connects these display devices or speakers to the terminal station device 1. In this way, the output interface 122 outputs information. Therefore, the output interface 122 may output information input to the communication interface 120 or the input interface 121, for example, as an image or sound.

[0030] The storage unit 13 is configured using a computer-readable storage medium device (non-transitory computer-readable recording medium) such as a magnetic hard disk device or a semiconductor storage device. The storage unit 13 stores various information related to the terminal station device 1. The storage unit 13 stores, for example, various information generated by the operation of the control unit 11. The storage unit 13 may exist on a cloud, for example. The storage unit 13 stores, for example, schedule information. The storage unit 13 stores, for example, communication possible times obtained based on the schedule information.

[0031] 3 is a diagram showing an example of the hardware configuration of the schedule transmission device 3 in an embodiment. The schedule transmission device 3 has a control unit 11 including a processor 93 such as a CPU, GPU, or NPU, and a memory 94, which are connected by a bus, and executes a program. By executing the program, the schedule transmission device 3 functions as a device including a control unit 31, an interface unit 32, and a storage unit 33.

[0032] More specifically, the processor 93 reads out the program stored in the storage unit 13 and stores the read out program in the memory 94. When the processor 93 executes the program stored in the memory 94, the schedule transmission device 3 functions as a device including a control unit 31, an interface unit 32, and a storage unit 33.

[0033] The control unit 31 controls the operation of each functional unit included in the schedule transmission device 3. The control unit 31 acquires, for example, schedule information. The schedule information may be acquired from the mobile object 2 via the interface unit 32, or may be read from schedule information previously stored in the storage unit 33.

[0034] The control unit 31 executes, for example, a schedule transmission process. The schedule transmission process is a process of transmitting schedule information to the terminal station device 1 using the second transmitter 30 at a preset time. The control unit 31 acquires, for example, information stored in the memory unit 33. Specifically, the process of acquiring the information stored in the memory unit 33 is a read process.

[0035] The interface unit 32 is configured to include a communication interface 320. The communication interface 320 is configured to include a communication device for connecting the schedule transmission device 3 to an external device. Each communication device included in the communication interface 320 communicates with the external device via wired or wireless communication. The external device is, for example, a device that has transmitted schedule information. In such a case, the communication interface 320 acquires the schedule information by communicating with the device that has transmitted the schedule information. The device that has transmitted the schedule information is, for example, the mobile object 2. The information acquired by the communication interface 320 is output to the control unit 31 or the memory unit 33.

[0036] The communication interface 320 is configured to include the second transmitter 30 as one of the communication devices. Therefore, the schedule transmission device 3 is equipped with the second transmitter 30. The external device in the communication with the external device using the second transmitter 30 is the terminal station device 1.

[0037] The interface unit 32 may be configured to include an input interface 321. The input interface 321 may be configured as an input device such as a mouse, keyboard, or touch panel, or may be configured as an interface that connects these input devices to the schedule transmission device 3. In this way, the input interface 321 accepts input of various information to the schedule transmission device 3 via an input device such as a mouse, keyboard, or touch panel.

[0038] It should be noted that the various types of information that can be input to the communication interface 320 of the interface unit 32 do not necessarily have to be input to the communication interface 320 of the interface unit 32 , but may be input to the input interface 321 of the interface unit 32 .

[0039] The interface unit 32 may be configured to include an output interface 322. The output interface 322 may include a display device such as a CRT display, a liquid crystal display, or an organic EL display, and a speaker. The output interface 322 may be configured as an interface that connects these display devices or speakers to the schedule transmission device 3. In this way, the output interface 322 outputs information. Therefore, the output interface 322 may output information input to the communication interface 320 or the input interface 321, for example, as an image or sound.

[0040] The storage unit 33 is configured using a computer-readable storage medium device (non-transitory computer-readable recording medium) such as a magnetic hard disk device or a semiconductor storage device. The storage unit 33 stores various information related to the schedule transmission device 3. The storage unit 33 stores, for example, various information generated by the operation of the control unit 31. The storage unit 33 may exist on, for example, a cloud. The storage unit 33 stores, for example, schedule information.

[0041] 4 is a flowchart showing an example of the flow of processing executed in the communication system 100 in this embodiment. The control unit 31 of the schedule transmission device 3 acquires schedule information (step S101). Here, the control unit 31 of the schedule transmission device 3 acquires the schedule information, for example, from the mobile object 2. If the schedule information has been previously stored in the storage unit 33, the control unit 31 of the schedule transmission device 3 may acquire the schedule information by reading it from the storage unit 33.

[0042] Next, the control unit 31 of the schedule transmitting device 3 transmits the schedule information to the terminal station device 1 at a preset time using the second transmitter (step S102). That is, the control unit 31 of the schedule transmitting device 3 executes a schedule transmission process.

[0043] Next, the control unit 11 of the terminal station 1 receives the transmitted schedule information (step S103). Next, the control unit 11 of the terminal station 1 estimates the communication available time based on the schedule information (step S104). That is, the control unit 11 of the terminal station 1 executes the communication available time acquisition process.

[0044] Next, the control unit 11 of the terminal station device 1 executes a wireless signal transmission process (step S105). That is, the control unit 11 of the terminal station device 1 controls the operation of the first transmitter 10 to cause the first transmitter 10 to transmit the wireless signal so that the wireless signal reaches the communication position at the communication available time.

[0045] <Regarding the Timing of Wireless Signal Transmission> The timing of wireless signal transmission will now be described in more detail. The terminal station device 1 estimates the communication available time by executing a communication available time acquisition process. The communication available time is the time when communication is possible if the wireless signal reaches the communication available position at that time. It is not sufficient for the terminal station device 1 to start preparing to transmit a wireless signal at the communication available time. It is also not sufficient for the terminal station device 1 to start transmitting a wireless signal at the communication available time.

[0046] This is because transmitting a wireless signal requires time for starting up a device related to the transmission of the wireless signal, such as reading transmission information and setting transmission settings, and the propagation speed of the wireless signal is finite. Specifically, the device related to the transmission of the wireless signal is the first transmitter.

[0047] The communication system 100 configured in this manner includes the schedule transmitting device 3. Therefore, as described in <Example of effect achieved by the communication system 100>, the power consumption required for communication is reduced.

[0048] (Variant Example) <First technique for further improving communication stability in variant example> In the communication system 100, the timing, frequency or code division at which a signal carrying schedule information is transmitted from the schedule transmitting device 3 to the terminal station device 1 may be timing corresponding to one or more areas that are the result of dividing the space in which the terminal station device 1 exists according to a predetermined rule.

[0049] This technology will be explained in more detail below. First, a situation will be described in which schedule information for a moving object 2 is broadcast from a schedule transmission device 3 to terminal station devices 1. In this situation, multiple terminal station devices 1 are activated simultaneously during a period around the time when the moving object 2 passes. In this case, the moving object 2 receives radio signals simultaneously, and the signals may become a source of interference with each other.

[0050] For example, when a terminal station device 1 transmits a radio signal at the time when a mobile unit 2 is closest to the terminal station device 1, multiple terminal station devices 1 located close to the terminal station device 1 simultaneously transmit radio signals. In this case, the correlation of the propagation paths from the terminal station device 1 to the mobile unit 2 becomes high, making it difficult for the mobile unit 2 to separate the arriving radio signals.

[0051] Therefore, consider a communication system 100 in which the following first and second processes are executed. In the first process, a terminal station device 1 transmits a radio signal including signal information to a mobile unit 2, and the control unit 31 of the schedule transmission device 3 aggregates the signal information received by the mobile unit 2 and stores it as a database. The signal information is information about the radio signal. The information about the radio signal may include, for example, a frequency channel, received power, a modulation / demodulation method, a spreading code, time, or location information of the terminal station device 1 that is the sender. The time and location information may be obtained based on schedule information, for example.

[0052] The second process is a process in which the control unit 31 of the schedule transmitting device 3 acquires information (hereinafter referred to as "area information") indicating how frequently or with what parameters the terminal station devices 1 in each area transmit signals for each area divided according to a predetermined rule such as division by mesh (hereinafter referred to as "division rule"). The parameter may be, for example, a frequency channel or a packet length.

[0053] The area information is obtained based on a database of signal information. That is, the area information is obtained based on a collection of signal information. More specifically, the area information is obtained by statistically treating the database of signal information. Note that the area is the area in which the terminal station device 1 is located.

[0054] When the first process and the second process are performed, information for each area is stored in the schedule transmitting device 3. Therefore, the control unit 31 can transmit the schedule information according to the area based on the area information. For example, the control unit 31 does not transmit the schedule information simultaneously regardless of the area, but transmits the schedule information at a timing according to the area in accordance with a predetermined rule based on the area information.

[0055] For example, the control unit 31 may transmit the schedule information at a frequency according to the area, rather than using the same frequency regardless of the area. Note that the frequency here refers to the frequency of a signal carrying the schedule information. For example, the control unit 31 may transmit the schedule information at a code division according to the area, rather than using the same code division regardless of the area.

[0056] By doing so, the amount of schedule information that can be sent increases, and it becomes possible to divide the communication area visible from the movement (flight route) of the mobile unit 2 into finer mesh areas.

[0057] Note that when transmitting the schedule information, the control unit 31 does not necessarily need to transmit only the schedule information. In addition to the schedule information, the control unit 31 may also transmit communication stability information, which is information regarding the stability of communication, such as information indicating the possibility of congestion (hereinafter referred to as "congestion possibility information") and information indicating the demodulation success rate.

[0058] For clarity, the definitions of the congestion probability and the demodulation success rate will be described later, so please refer to them as appropriate. The congestion probability information may include, for example, information on the number of terminal station devices 1 that can be accommodated, collected in the area defined by the mobile object 2.

[0059] Fig. 5 is a flowchart showing an example of the flow of processing executed by each terminal station 1 in the modified example. More specifically, Fig. 5 is a flowchart showing an example of the flow of processing executed by the terminal station 1 when the terminal station 1 receives schedule information and congestion possibility information.

[0060] The control unit 11 of the terminal station device 1 acquires schedule information and congestion possibility information (step S201). Next, the control unit 11 determines whether the congestion possibility N is equal to or less than a predetermined threshold Th (step S202). If the congestion possibility N is equal to or less than the predetermined threshold Th (step S202: YES), the control unit 11 controls the operation of the first transmitter 10 to transmit a wireless signal toward the moving object 2 (step S203). After step S203, the terminal station device 1 transitions to a sleep state (step S204). The sleep state is defined as a resting state until the next orbit schedule information is acquired.

[0061] On the other hand, if the congestion possibility N is not equal to or less than the predetermined threshold Th (step S202: NO), the control unit 11 performs an autonomous transmission permission probability calculation (step S205). The autonomous transmission permission probability calculation is a process in which a probability is set for each terminal station device 1 and calculations are performed randomly according to that probability. The probability is arbitrarily set by the control unit 11 in the autonomous transmission permission probability calculation based on the priority of the information to be transmitted, etc. If transmission permission is granted with the set probability as a result of the autonomous transmission permission probability calculation (step S205: YES), the process of step S203 is executed. On the other hand, if transmission permission is not granted as a result of the autonomous transmission permission probability calculation (step S205: NO), the process of step S204 is executed.

[0062] The calculation using the congestion possibility information in the process of FIG. 5 may be performed independently by the control unit 11 of each terminal station device 1 .

[0063] <Second Technique for Further Stable Communication in Modification> Consider a situation where the schedule transmission device 3 is a geostationary satellite. In such a case, there may be a huge number of terminal station devices 1 within the terrestrial visible (communicable) range of the schedule transmission device 3. In this case, in the communication system 100, each terminal station device 1 operates independently, and the communication available time calculated from the obtained orbit information is such that, if the terminal station devices 1 are located in nearly the same location, there is almost no difference in the relative communication available start time, resulting in communication occurring at almost the same time and causing interference. Therefore, the terminal station devices 1 may wait within the calculated communication available time range of the mobile unit 2 using random backoff, thereby dispersing the signal transmission timing.

[0064] However, within the area formation range of the mobile body 2, the communication time is longest when the orbit passes directly above the terminal station device 1, but the problem arises that the communication time during which the mobile body 2 passes becomes shorter the greater the shortest distance from the orbit.

[0065] Therefore, the control unit 11 of the terminal station device 1 can acquire location information of the device itself, and may be activated at an activation time (or frequency or code) determined for each area to which the device itself belongs, to acquire information from the schedule transmission device 3. When location information is stored in advance in the storage unit 13, for example, the acquisition of location information of the device itself may be a process of acquiring the location information of the device itself stored in the storage unit 13. The location information of the device itself may be acquired, for example, by communication with a device that is a source of the location information, or by GPS (Global Positioning System, Global Positioning Satellite).

[0066] Furthermore, the control unit 11 of the terminal station device 1 may acquire information indicating the possibility of congestion, and may execute a process of not transmitting with a certain probability if the congestion possibility indicated by the acquired information indicating the possibility of congestion exceeds a threshold. More specifically, the control unit 11 of the terminal station device 1 may execute a process of not transmitting a wireless signal to the mobile unit 2 with a certain probability if the congestion possibility indicated by the information indicating the possibility of congestion exceeds a threshold, based on the information indicating the possibility of congestion. This reduces the congestion rate per channel and increases the demodulation success rate throughout the system. The threshold in this case is calculated using information indicating the available communication time from the terminal station device 1 to the mobile unit 2.

[0067] <<Example of a Situation in Which Transmission is Not Performed Probability>> An example of a situation in which transmission is not performed probability will be described. For example, a terminal station device 1 located at a position d = 0.8r or greater can avoid collisions by not transmitting, but this reduces transmission opportunities, resulting in a deterioration in the accommodation rate of the entire system. Therefore, in communication system 100, schedule transmission device 3 grasps location information from the transmission signals of each terminal station device 1 collected by mobile object 2, and presents each terminal station device 1 with the congestion probability N within a certain area range.

[0068] Then, a predetermined threshold value multiplied by the communication available time rate 1 / r from the terminal station device 1 is set as a threshold value Th, and when the congestion possibility N exceeds this threshold value Th, each terminal station device 1 is controlled so as not to transmit with a certain probability. Note that r is the radius of the circle when the area is circular.

[0069] Fig. 6 is an explanatory diagram illustrating an example of a circular area of ​​radius r in a modified example. The area in the example of Fig. 6 is an area of ​​radius r centered at point A. In Fig. 6, the area is a region within a plane spanned by the X-axis and Y-axis. In the example of Fig. 6, a mobile unit 2 is located directly above point A (in the Z-axis direction in Fig. 6). Since the mobile unit 2 is located directly above point A, in this case, the terminal station device 1 that can communicate with the mobile unit 2 is the terminal station device 1 located within the circular area of ​​radius r centered at point A.

[0070] In addition to point A, point B is also shown in Figure 6. The distance between point A and point B is d, which is shorter than r. According to Pythagoras' theorem, it is possible to define distance l as the square root of the difference between the square of r and the square of d.

[0071] 7 is an explanatory diagram illustrating the relationship between the communication time rate and the distance from the center of the area in a modified example. The communication time rate is defined as the time rate obtained by dividing the communication time of the mobile unit 2 as seen from the terminal station device 1 when the mobile unit 2 moves parallel to the ground line directly below the track of the mobile unit 2 by a distance d, by the maximum communication time. The maximum communication time is the time from when the transmitted signal from the terminal station device 1 reaches the mobile unit 2 at a receivable level to when it becomes unreceivable, assuming that the mobile unit 2 passes directly above the terminal station device 1.

[0072] Assuming that the receivable antenna pattern of the mobile unit 2 is circular, the available communication time rate is equivalent to the value obtained by dividing the distance l shown in Fig. 6 by the distance r. More specifically, Fig. 7 is a diagram showing an example of the relationship between the position within the area shown in Fig. 6 and the available communication time rate. Fig. 7 shows that the available communication time rate decreases as the distance from the center of the area (i.e., point A) increases.

[0073] The control unit 11 of each terminal station device 1 may control the transmission of a wireless signal based on the priority. For example, the control may be performed such that the priority of the wireless signal transmission of a terminal station device 1 that transmitted a wireless signal to a mobile object 2 at the previous timing is lowered. Note that the higher the priority, the higher the probability of transmitting a wireless signal. Also, for example, if the data to be carried by the wireless signal is data that requires quick response, the control may be performed such that the priority of the wireless signal transmission is increased.

[0074] The control of the transmission of wireless signals based on priority may be, for example, a control to perform retransmission when the congestion probability N is significantly lower than the threshold value Th. This control improves redundancy and reliability.

[0075] <Third Technique for Further Stabilizing Communication in Modification> When the congestion possibility exceeds a threshold, the control unit 11 of the terminal station device 1 may execute a process of transitioning to a frequency channel with a lower congestion possibility. That is, when the congestion possibility exceeds a predetermined threshold, the control unit 11 may execute a process of changing the frequency channel of a radio signal to be transmitted to the mobile object 2 to another frequency channel with a lower congestion possibility. As a result, the radio signal is transmitted to the mobile object 2 on the frequency channel after the transition.

[0076] The frequency channel to which the user is to transition may be a frequency channel randomly determined by the control unit 11 from among multiple frequency channel candidates with a lower probability of congestion, or may be a frequency channel determined by the control unit 11 in accordance with a predetermined rule.

[0077] Since the schedule transmission device 3 simultaneously broadcasts the congestion probability for each frequency channel to a large number of terminal station devices 1, it is difficult to send a channel transition command to each individual terminal station device 1. The terminal station device 1 may calculate a transition probability for itself from the received congestion probability, and control the parameters to transition according to the probability so that the expected transmission probabilities are uniform. Note that this frequency channel may be a spread code, etc. Note that "calculated by the terminal station device 1" means that the control unit 11 of the terminal station device 1 performs the calculation.

[0078] 8 is a first explanatory diagram illustrating an example of frequency channel transition in a modified example. Fig. 8 shows that a portion exceeding the total channel capacity or a portion exceeding the average value for each frequency channel when viewed as the entire communication system 100 is transitioned to another frequency channel. The total channel capacity is a value set for each frequency channel by, for example, (communication available time) / (average transmission signal length of terminal station device 1).

[0079] Note that Figure 8 includes images D101 and D102. Image D101 shows the congestion probability of the total channel capacity for each frequency channel estimated from the previous transmission signal of terminal station device 1 collected by mobile station 2. On the other hand, image D102 shows the congestion probability of the total channel capacity for each frequency channel after a transition based on probability. Note that "60%, " "70%, " "40%, and "110%" shown in image D101 in Figure 8 respectively represent the congestion probabilities of frequency channels 1 to 4 indicated by the congestion possibility information. Therefore, in the example of Figure 8, the congestion possibility information indicates that the congestion probability of frequency channel 1 is 60%, the congestion possibility information indicates that the congestion probability of frequency channel 2 is 70%, the congestion possibility information indicates that the congestion probability of frequency channel 3 is 40%, and the congestion possibility information indicates that the congestion probability of frequency channel 1 is 110%.

[0080] The definition of "excess of average value" in Fig. 8 is the excess over the average of the congestion probabilities when the total channel capacity of each frequency channel is the same. The definition of "excess of total channel capacity" in Fig. 8 is the excess over 100% of the total channel capacity.

[0081] 9 is a second explanatory diagram illustrating an example of frequency channel transition in the modified example. In the example of FIG. 8, for example, frequency channel 4 transitions to frequency channel 1 with a probability of 10%.

[0082] <Fourth technique for further improving communication stability in the modified example> When the congestion level is below a certain level, the communication system 100 can determine to some extent which terminal station devices 1 were unable to communicate based on terminal numbers, location information, etc. Therefore, not only the congestion status such as the number of terminals, but also the demodulation success rate for each area is estimated and transmitted. When the demodulation success rate is low or the possibility of congestion (congestion rate) is high, priority is assigned to each terminal station device 1, and the terminal station device 1 having high-priority data transmits. For terminal station devices 1 with low priority, control is performed such that transmission is not performed on the first pass, but rather the priority is increased depending on the number of times transmission was not possible, and transmission is performed on the second pass or later.

[0083] Here, the communication system 100 grasps, specifically, means that the schedule transmitting device 3 acquires the location and frequency channel information for each area of ​​the terminal station device 1 that has been successfully demodulated.

[0084] In this manner, in the communication system 100, the control unit 11 may autonomously determine whether its own device (terminal station device 1) should operate with priority based on communication stability information such as the demodulation success rate sent from the schedule transmission device 3, and control its own device (terminal station device 1) itself in accordance with the determination. That is, based on the communication stability information, the terminal station device 1 may determine the priority and autonomously decide whether to operate. Note that the terminal station device 1 with a high priority may be fixedly set in advance based on the importance of the data to be transmitted, etc.

[0085] In addition, the control unit 11 may perform an operation such as shifting a terminal station device 1 with a high priority to an available frequency channel. The control unit 11 may also perform redundancy control such as retransmitting two or more times within the same path using multiple channels and multiple spreading codes. In the control unit 31 of the schedule transmission device 3, if a terminal station device 1 that is assumed to be present within the area from past received data fails to demodulate two, three, ... consecutively, it is counted as a failed terminal. Because this is a broadcast method, it is difficult to notify each of the huge number of terminal station devices 1 of the success or failure of communication, but it is possible to distribute the statistical number of failed terminals.

[0086] Therefore, the control unit 11 calculates the probability of consecutive failures two, three, etc., based on the interference probability of the terminal station device 1 itself from two times before, three times before, etc. When the terminal station device 1 transmits a signal and receives the latest schedule information again from the schedule transmission device 3, the demodulation success rate is updated, and if the success rate is not equal to or greater than a threshold value (e.g., 90% success), the control unit 11 may determine the priority of the information, and then the terminal station device 11 may transmit the same data. Note that the success rate may be calculated and distributed by estimation only for terminal station devices 1 with high priority. Note that the calculation and distribution of this success rate are performed by the schedule transmission device 3.

[0087] <Regarding the possibility of congestion> The following description will be given taking as an example a case where the moving body 2 is a flying moving body. Fig. 10 is a first explanatory diagram for explaining the possibility of congestion in the modified example. Fig. 11 is a second explanatory diagram for explaining the possibility of congestion in the modified example.

[0088] By matching the flight path of the mobile unit 2 with the time period when the mobile unit 2 received the wireless signal, the control unit 31 estimates the number of terminals accommodated in the surrounding area where the mobile unit 2 was flying. The number of terminals is estimated by recording the number of terminals received during the previous movement. For example, if only the previous value is used, the control unit 31 estimates the number of terminals in Area 1h2a1 and Area 2h2a2 of Flight 2 as 10, 12, etc. using the values ​​of h1a1 and h1a1.

[0089] An example of areas is shown in Fig. 10. In Fig. 10, the reference numeral D103 indicates a moving object 2. In Fig. 11, an example of the relationship between Flights 1 to 4 and areas is shown.

[0090] It may also be estimated using only the previous value, or it may be possible to use the average value of the values ​​of h1, h2, ..., or to calculate the variance, standard deviation, etc. and perform statistical processing. The above estimated number of terminals is used as the numerator and the terminal capacity limit set in the system is used as the denominator to estimate the possibility of congestion (congestion rate). The interference collision probability may also be calculated from the congestion rate and compared with a threshold. The interference collision probability may be calculated using a statistical approach that calculates queues such as Poisson arrivals.

[0091] Let the congestion probability (congestion rate) be λ, and the probability that no event occurs (no transmission from other terminal station devices 1) during time T is P(0) = e －λＴ The time T during which the radio signal is transmitted is expressed as T Ｄ It is sufficient that no wireless signal is transmitted by other terminal station devices 1 during this time, and the communication system 100 calculates a probability threshold in advance, and the control unit 11 determines whether the distributed interference collision probability 1-P(0) is high or low. The process of calculating the probability threshold by the communication system 100, specifically, is executed by the control unit 31.

[0092] <Regarding Demodulation Success Rate> Fig. 12 is a first explanatory diagram illustrating the demodulation success rate in the modified example. Fig. 13 is a second explanatory diagram illustrating the demodulation success rate in the modified example. To obtain the demodulation success rate, in addition to the congestion rate, the communication system 100 grasps the terminal IDs present in the area and records them in a database. This process is specifically performed by the control unit 31. The terminal ID is an identifier of each terminal station device 1 assigned in advance to each terminal station device 1.

[0093] The next time the mobile unit 2 passes through the area above the terminal station device 1, the control unit 31 compares the IDs of terminals that are collected and successfully demodulated with the terminal IDs that should actually exist, and calculates the demodulation success rate.

[0094] With regard to terminal IDs, taking into consideration that the terminal station device 1 may move, if a terminal ID is not included in IDs that have been successfully demodulated for a certain period of time, it is deleted from the database. This process is performed by the control unit 31. Furthermore, if the same terminal ID is found in another location, the control unit 31 updates the area database and determines whether the terminal station device 1 has moved. The parameter for the number of transmitting terminals also changes depending on the movement of the terminal station device 1, the frequency of transmission, and the like. For this reason, the control unit 31 may retain data for a long period of time and calculate the number of transmitting terminals roughly using long-term trends based on time, etc.

[0095] An example of the relationship between flights and areas is shown in Fig. 12. Fig. 13 shows an example of the relationship between Flight 1 and Flight 2 and areas.

[0096] The terminal station device 1 may be implemented using a plurality of information processing devices communicably connected via a network. In this case, the processes executed by the control unit 11 may be distributed among the plurality of information processing devices.

[0097] The schedule transmission device 3 may be implemented using a plurality of information processing devices connected to each other via a network. In this case, the processes executed by the control unit 31 may be distributed among the plurality of information processing devices.

[0098] All or part of the functions of the communication system 100, the terminal station device 1, and the schedule transmission device 3 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

[0099] Although an embodiment of the present invention has been described in detail above 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.

[0100] 100...Communication system, 1...Terminal station device, 2...Mobile object, 3...Schedule transmission device, 10...First transmitter, 30...Second transmitter, 11...Control unit, 12...Interface unit, 13...Memory unit, 120...Communication interface, 121...Input interface, 122...Output interface, 320...Communication interface, 321...Input interface, 322...Output interface, 31...Control unit, 32...Interface unit, 33...Memory unit, 91...Processor, 92...Memory, 93...Processor, 94...Memory

Claims

1. A wireless communication system in which a mobile unit receives a wireless signal transmitted from a terminal station device that is equipped with a first transmitter that transmits a wireless signal to a mobile unit capable of receiving the wireless signal, the terminal station device comprising: the mobile unit; one or more of the terminal station devices; and a schedule transmitting device that is equipped with a second transmitter that transmits schedule information indicating the expected location of the mobile unit at each time, and that transmits the schedule information to the terminal station device using the second transmitter at a preset time, wherein the terminal station device obtains, based on the schedule information, the time at which the mobile unit will pass a location where the mobile unit is expected to pass and where communication between the terminal station device and the mobile unit is possible, and transmits the wireless signal using the first transmitter so that the wireless signal will arrive at the obtained location at the time.

2. The communication system according to claim 1, wherein the timing, frequency or code division of the signal carrying the schedule information transmitted from the schedule transmitting device to the terminal station device is timing according to one or more areas resulting from dividing the space in which the terminal station device exists in accordance with a predetermined rule.

3. The communication system according to claim 1, wherein the schedule transmission device transmits communication stability information, which is information relating to the stability of communication, to the terminal station device in addition to the schedule information.

4. The communication system according to claim 3, wherein the terminal station autonomously judges the priority level based on the communication stability information and decides whether to operate.

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