Patent Description:
For wireless communication between a helicopter moving in a wide area and a ground station, a helicopter-installed satellite communication system has been put to practical use in which a communication apparatus installed in the helicopter and the ground station perform communication via a communication satellite. In the helicopter-installed satellite communication system, signals are intermittently blocked by rotor blades of the helicopter because the rotor blades are present on a communication path in midair between the communication apparatus installed in the helicopter and the communication satellite. A conventional helicopter-installed satellite communication system assigns a different frequency to each user. Each user occupies a specific frequency in time to perform communication. However, with increasing communication demand, it is desired that the helicopter-installed satellite communication system apply time-division multiplexing with high frequency utilization efficiency. Furthermore, to improve interconnectivity between the helicopter-installed satellite communication system and another system, it is desirable that the helicopter-installed satellite communication system can adopt a general-purpose communication apparatus conforming to standardization instead of a unique communication scheme.

To this problem, Patent Literature <NUM> discloses a technique to improve reliable transmission against blocking due to rotor blades by duplicating a transmission signal, delaying a duplicate signal, and transmitting the two-wave transmission signals so that the signal can be transmitted and received through space between the rotor blades. Patent Literature <NUM> discloses techniques for improving data rates at mobile terminals that are subject to periodic channel interruptions in a beyond-line-of-sight communication system. Patent Literature <NUM> discloses a helicopter satellite communication method which allows reception of a burst signal intermittently transmitted from a helicopter while avoiding interruptions due to rotary wings.

However, the above conventional technique has a problem that under conditions where the rotor-blade blocking rate is high, it is a possibility that both of the two-wave transmission signals may be blocked by the rotor blades.

The present disclosure has been made in view of the above. It is an object of the present disclosure to provide a base station that can improve the reliable transmission of signals under conditions where blocking by rotor blades occurs in wireless communication using time-division multiplexing.

In order to solve the above problem and achieve the object, the present disclosure is a base station according to claim <NUM>.

Further aspects are disclosed in the dependent claims.

The base station according to the present disclosure achieves the effect of being capable of improving the reliable transmission of signals under conditions where blocking by the rotor blades occurs in wireless communication using time-division multiplexing.

Hereinafter, a terminal, a base station, a control circuit, a storage medium, and a communication method according to embodiments of the present disclosure will be described in detail with reference to the drawings.

<FIG> is a diagram illustrating a configuration example of a communication system <NUM> according to a first embodiment. The communication system <NUM> includes a terminal <NUM>, a relay station <NUM>, and a base station <NUM>. In the communication system <NUM>, the terminal <NUM> and the base station <NUM> are wirelessly connected via the relay station <NUM> to transmit and receive data and the like. The terminal <NUM> is a communication apparatus installed in a machine having rotor blades, specifically, a helicopter (not illustrated). The relay station <NUM> is a communication apparatus that relays wireless communication performed by the terminal <NUM> and the base station <NUM>. The relay station <NUM> may be a communication satellite or a mobile object staying in the air at a high altitude. Hereinafter, a case where the relay station <NUM> is a communication satellite will be described as an example. The base station <NUM> is a communication apparatus installed on the ground. The base station <NUM> may be a communication apparatus fixed on the ground or a movable communication apparatus. The communication system <NUM> is a helicopter-installed satellite communication system in which the terminal <NUM> and the base station <NUM> perform wireless communication via the relay station <NUM>.

In the following description, in the communication system <NUM>, communication from the base station <NUM> to the terminal <NUM> via the relay station <NUM> is referred to as a forward link, and communication from the terminal <NUM> to the base station <NUM> via the relay station <NUM> is referred to as a return link.

Next, configurations and operations of the terminal <NUM> and the base station <NUM> will be described. <FIG> is a block diagram illustrating a configuration example of the terminal <NUM> according to the first embodiment. The terminal <NUM> includes a rotor blade state monitoring unit <NUM>, a transceiver <NUM>, and a data processing unit <NUM>. The rotor blade state monitoring unit <NUM> monitors a rotor blade state by measuring the timing at which the rotor blades of the helicopter block a communication path in midair between the relay station <NUM> and the terminal <NUM>. The transceiver <NUM> transmits, to the base station <NUM>, the rotor blade state, a resource request for requesting radio resources, and data etc. using radio resources allocated from the base station <NUM>. The transceiver <NUM> receives, from the base station <NUM>, data, resource notification of the allocation of radio resources in response to a resource request, etc. The data processing unit <NUM> performs management of data to be transmitted to the base station <NUM>, encoding and modulation of data to be transmitted to the base station <NUM>, demodulation and decoding of data received from the base station <NUM>, etc..

<FIG> is a block diagram illustrating a configuration example of the base station <NUM> according to the first embodiment. The base station <NUM> includes a transmission control unit <NUM>, a transceiver <NUM>, and a data processing unit <NUM>. When there is a resource request from the terminal <NUM>, the transmission control unit <NUM> determines radio resources to be allocated to the terminal <NUM>, using the rotor blade state etc. The transceiver <NUM> transmits data, resource notification of the allocation of radio resources in response to a resource request, etc. to the terminal <NUM>. The transceiver <NUM> receives the rotor blade state, a resource request for requesting radio resources, data, etc. from the terminal <NUM>. The data processing unit <NUM> performs management of data to be transmitted to the terminal <NUM>, encoding and modulation of data to be transmitted to the terminal <NUM>, demodulation and decoding of data received from the terminal <NUM>, etc..

First, operations of the terminal <NUM> and the base station <NUM> at the time of a forward link will be described. <FIG> is a diagram illustrating operations of the terminal <NUM> and the base station <NUM> at the time of a forward link according to the first embodiment. First, in the terminal <NUM>, the rotor blade state monitoring unit <NUM> monitors the rotor blade state. Specifically, the rotor blade state monitoring unit <NUM> measures the timing at which the rotor blades block a communication path in midair between the relay station <NUM> and the terminal <NUM> as the monitoring of the rotor blade state. The blocking timing is, specifically, a blocking cycle, a blocking time, a blocking rate, the temporal stability of the blocking time, or the like. The temporal stability is, for example, variance. The rotor blade state monitoring unit <NUM> can measure the blocking timing by a combination of existing techniques, using the attitude of the helicopter, position information, detected information on the rotor blades, the position of the relay station <NUM> that is a communication satellite, etc. The timing at which the rotor blades block a communication path in midair between the relay station <NUM> and the terminal <NUM>, that is, the rotor blade state includes at least one of the above-described blocking cycle, blocking time, blocking rate, or temporal stability of the blocking time.

The transceiver <NUM> of the terminal <NUM> transmits the timing at which the rotor blades block a communication path in midair between the relay station <NUM> and the terminal <NUM> measured by the rotor blade state monitoring unit <NUM> as the rotor blade state to the base station <NUM> via the relay station <NUM>. Communication between the terminal <NUM> and the base station <NUM> is performed via the relay station <NUM> as described above. However, hereinafter, in order to simplify the description, the description "via the relay station <NUM>" will be omitted in the following description. When the rotor blade state is transmitted to the base station <NUM>, in a case where radio resources for an individual return link, for example, a transmission possible time, a frequency, or the like has been allocated from the transmission control unit <NUM> of the base station <NUM> to the terminal <NUM>, the transceiver <NUM> transmits the rotor blade state at a time without blockage by the rotor blades during the transmission possible time of the allocated radio resources. In a case where radio resources for an individual return link have not been allocated from the transmission control unit <NUM> of the base station <NUM> to the terminal <NUM>, the transceiver <NUM> may transmit the rotor blade state, using radio resources allocated to contention-based random access or the like which have been determined by the transmission control unit <NUM> in advance.

In the base station <NUM>, the transceiver <NUM> receives the rotor blade state from the terminal <NUM>. The transmission control unit <NUM> determines the number of times that data to be transmitted to the terminal <NUM> on a forward link managed by the data processing unit <NUM> is duplicated and the transceiver <NUM> successively transmits the date, that is, the number of successive transmissions, based on the data amount of the data to be transmitted to the terminal <NUM> on the forward link, the rotor blade state, a wireless communication rate satisfying a desired communication quality, a required data error rate, etc. The desired communication quality is, for example, an error rate. The required data error rate is, for example, a packet error rate. For example, when the transceiver <NUM> can transmit successively without any gaps in time, the transmission control unit <NUM> determines the number of successive transmissions so that the following condition is satisfied that (the time of blocking by the rotor blades) < (the radio frame length) × (the number of successive transmissions). In other words, for example, when the transceiver <NUM> can transmit successively without any gaps in time, the transmission control unit <NUM> determines the number of successive transmissions so that the time of blocking by the rotor blades is smaller than a value obtained by multiplying the radio frame length by the number of successive transmissions. The radio frame length is the length of a radio frame used to transmit data. This allows the terminal <NUM> to receive at least one radio frame, that is, at least one piece of data at a time without blocking by the rotor blades.

When the transceiver <NUM> is only allowed to transmit successively at the Internet Protocol (IP) packet level by a black box, the transceiver <NUM> may not be able to successively transmit data without any gaps in time. In this case, the transmission control unit <NUM> determines the number of successive transmissions so that the following condition is satisfied that {<NUM>-(the rate of blocking by the rotor blades)^(the number of successive transmissions)} > (a desired error rate). In other words, the transmission control unit <NUM> determines the number of successive transmissions so that a value obtained by subtracting, from <NUM>, a value represented by a power with the rate of blocking by the rotor blades as "the base" and the number of successive transmissions as "the exponent" is greater than a desired error rate. The transceiver <NUM> duplicates and transmits an IP packet for the number of successive transmissions that satisfies {<NUM>-(the rate of blocking by the rotor blades) ^ (the number of successive transmissions)} > (the desired error rate). This allows the terminal <NUM> to receive a radio frame, that is, data with a probability higher than or equal to the desired error rate. Furthermore, because the rotor blade state may vary depending on the attitude of the helicopter in which the terminal <NUM> is installed, when determining the number of successive transmissions, the transmission control unit <NUM> may multiply the number of successive transmissions by a correction coefficient based on the stability of the rotor blade state, for example, the variance of the blocking cycle, the blocking rate, or the like so as to correct the number of successive transmissions. For example, when the variance is large, the transmission control unit <NUM> makes a correction to increase the number of successive transmissions, thereby allowing an improvement in the reliable transmission of data from the base station <NUM> to the terminal <NUM>. The transceiver <NUM> duplicates and successively transmits data to the terminal <NUM> for the number of successive transmissions determined by the transmission control unit <NUM>.

In the terminal <NUM>, the transceiver <NUM> receives data from the base station <NUM>. The data processing unit <NUM> demodulates and decodes the data received by the transceiver <NUM>, and transmits an acknowledgement to the base station <NUM> via the transceiver <NUM>.

When the transceiver <NUM> of the base station <NUM> receives an acknowledgement from the terminal <NUM> while successively transmitting data, the transceiver <NUM> of the base station <NUM> may stop successively transmitting the data since further successive transmission of the data is unnecessary. Furthermore, because the transceiver <NUM> of the terminal <NUM> may redundantly receive two or more pieces of the same data successively transmitted from the base station <NUM>, the transceiver <NUM> may check the received data for duplication and discard data that is a duplicate of received data.

In a case where the terminal <NUM>, the relay station <NUM>, and the base station <NUM> conform to a mobile phone standard, for example, the 3rd Generation Partnership Project (3GPP), the base station <NUM> can successively transmit data by setting DL_REPETITION_NUMBER defined in 3GPP to the number of successive transmissions determined above. In a case where the terminal <NUM>, the relay station <NUM>, and the base station <NUM> conform to Digital Video Broadcasting (DVB)-Satellite-Second Generation (S2) or DVB-Satellite-Second Generation Extensions (S2X), the above-described radio frame is a PLFRAME, and the base station <NUM> may duplicate and successively transmit a PLFRAME. That is, the transceiver <NUM> of the base station <NUM> duplicates and successively transmits a PLFRAME defined in DVB-S2 or DVB-S2X for the number of successive transmissions.

<FIG> is a flowchart illustrating the operation of the terminal <NUM> at the time of a forward link according to the first embodiment. In the terminal <NUM>, the rotor blade state monitoring unit <NUM> monitors the rotor blade state (step S101). The transceiver <NUM> transmits the rotor blade state to the base station <NUM> (step S102). The transceiver <NUM> receives data from the base station <NUM> (step S103). The data processing unit <NUM> transmits an acknowledgement to the base station <NUM> via the transceiver <NUM> (step S104).

<FIG> is a flowchart illustrating the operation of the base station <NUM> at the time of a forward link according to the first embodiment. In the base station <NUM>, the transceiver <NUM> receives the rotor blade state from the terminal <NUM> (step S301). The transmission control unit <NUM> determines the number of successive transmissions at the time of transmitting data to the terminal <NUM> (step S302). The transceiver <NUM> transmits the data to the terminal <NUM> for the number of successive transmissions determined by the transmission control unit <NUM> (step S303). The transceiver <NUM> receives an acknowledgement from the terminal <NUM> (step S304). At this time, the transceiver <NUM> stops successively transmitting the data if the transceiver <NUM> is successively transmitting the data (step S305).

Next, operations of the terminal <NUM> and the base station <NUM> at the time of a return link will be described. <FIG> is a diagram illustrating operations of the terminal <NUM> and the base station <NUM> at the time of a return link according to the first embodiment. Similarly to the case of performing communication on a forward link, in the terminal <NUM>, the rotor blade state monitoring unit <NUM> monitors the rotor blade state. The data processing unit <NUM> monitors the data rate of data to be transmitted by the terminal <NUM>. Then, the transceiver <NUM> transmits, to the base station <NUM>, the rotor blade state and a resource request for requesting radio resources necessary for satisfying the data rate. The radio resources requested in the resource request are radio resources when the terminal <NUM> transmits the data on a return link, and are, for example, a time, a frequency, a transmission rate, the amount of storage of data in a buffer, or the like. Here, by setting a transmission rate requested in the resource request to, for example, a value obtained by dividing the data rate by (<NUM>-the blocking rate), the terminal <NUM> can request a higher transmission rate when the blocking rate is higher, to transmit desired data in a non-blocking interval. The value obtained by dividing the data rate by (<NUM>-the blocking rate) is also referred to as a value obtained by dividing the data rate by a value obtained by subtracting the blocking rate from <NUM>. In a case where information requested in the resource request is not the transmission rate, the terminal <NUM> may request, as information requested in the resource request, a value obtained by converting the transmission rate into information equivalent to the transmission rate such as a time or a frequency, or a value obtained by converting the transmission rate into the amount of storage of data that is the amount of data that can be transmitted in a unit time. Similarly to the base station <NUM> at the time of a forward link, when the rate of blocking by the rotor blades varies depending on the attitude of the helicopter in which the terminal <NUM> is installed, the transceiver <NUM> of the terminal <NUM> may multiply the transmission rate by a correction coefficient, based on the stability of the rotor blade state.

In the base station <NUM>, the transceiver <NUM> receives the rotor blade state and the resource request from the terminal <NUM>. The transmission control unit <NUM> determines a time in which the terminal <NUM> can transmit on a return link, based on the rotor blade state and the resource request, and allocates radio resources for the terminal <NUM> to transmit the data. The transceiver <NUM> transmits the radio resources allocated by the transmission control unit <NUM> as resource notification to the terminal <NUM>. To prevent the resource notification itself from being blocked by the rotor blades, the transceiver <NUM> may determine the number of successive transmissions of the resource notification, based on the rotor blade state and successively transmit the resource notification.

In the terminal <NUM>, when the transceiver <NUM> receives the resource notification from the base station <NUM>, the transceiver <NUM> returns an acknowledgement to the resource notification to the base station <NUM>. The transceiver <NUM> extracts the data to be transmitted from the data processing unit <NUM>. When a time, a frequency, or the like in which the terminal <NUM> can transmit on a return link is allocated as the radio resources by the resource notification from the base station <NUM>, the transceiver <NUM> transmits the data to the base station <NUM> at a time without blockage by the rotor blades in the time or the frequency in which transmission is possible.

<FIG> is a flowchart illustrating the operation of the terminal <NUM> at the time of a return link according to the first embodiment. In the terminal <NUM>, the rotor blade state monitoring unit <NUM> monitors the rotor blade state (step S111). The transceiver <NUM> transmits, to the base station <NUM>, the rotor blade state and a resource request for requesting necessary radio resources (step S112). Upon receiving resource notification from the base station <NUM> (step S113), the transceiver <NUM> transmits an acknowledgement to the base station <NUM> (step S114). The transceiver <NUM> extracts data to be transmitted from the data processing unit <NUM> and transmits the data based on the resource notification (step S115).

<FIG> is a flowchart illustrating the operation of the base station <NUM> at the time of a return link according to the first embodiment. In the base station <NUM>, the transceiver <NUM> receives the rotor blade state and a resource request from the terminal <NUM> (step S311). Based on the rotor blade state and the resource request, the transceiver <NUM> allocates radio resources to the terminal <NUM> (step S312), and transmits resource notification to the terminal <NUM> (step S313). The transceiver <NUM> receives an acknowledgement from the terminal <NUM> (step S314), and then receives data from the terminal <NUM> (step S315).

Next, a hardware configuration of the terminal <NUM> will be described. In the terminal <NUM>, the transceiver <NUM> is communication equipment. The rotor blade state monitoring unit <NUM> and the data processing unit <NUM> are implemented by processing circuitry. The processing circuitry may be a processor that executes a program stored in memory and the memory, or may be dedicated hardware. The processing circuitry is also referred to as a control circuit.

<FIG> is a diagram illustrating a configuration example of processing circuitry <NUM> when a processor <NUM> and memory <NUM> implement processing circuitry included in the terminal <NUM> according to the first embodiment. The processing circuitry <NUM> illustrated in <FIG> is a control circuit and includes the processor <NUM> and the memory <NUM>. When the processing circuitry <NUM> consists of the processor <NUM> and the memory <NUM>, each function of the processing circuitry <NUM> is implemented by software, firmware, or a combination of software and firmware. The software or firmware is described as a program and stored in the memory <NUM>. In the processing circuitry <NUM>, the processor <NUM> reads and executes the program stored in the memory <NUM>, thereby implementing the functions. That is, the processing circuitry <NUM> includes the memory <NUM> for storing the program that results in the execution of the processing in the terminal <NUM>. This program can be said to be a program for causing the terminal <NUM> to perform the functions implemented by the processing circuitry <NUM>. This program may be provided by a storage medium in which the program is stored, or may be provided by another means such as a communication medium.

The program can be said to be a program that causes the terminal <NUM> to perform a first step in which the rotor blade state monitoring unit <NUM> monitors the rotor blade state by measuring the timing at which the rotor blades block a communication path in midair between the relay station <NUM> and the terminal <NUM>, and a second step in which the transceiver <NUM> transmits the rotor blade state to the base station <NUM> and transmits data using radio resources allocated from the base station <NUM>.

Here, the processor <NUM> is, for example, a CPU, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a digital signal processor (DSP), or the like. The memory <NUM> corresponds, for example, to nonvolatile or volatile semiconductor memory such as random-access memory (RAM), read-only memory (ROM), flash memory, an erasable programmable ROM (EPROM), or an electrically EPROM (EEPROM) (registered trademark), or a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a digital versatile disc (DVD), or the like.

<FIG> is a diagram illustrating an example of processing circuitry <NUM> when dedicated hardware constitutes the processing circuitry included in the terminal <NUM> according to the first embodiment. The processing circuitry <NUM> illustrated in <FIG> corresponds, for example, to a single circuit, a combined circuit, a programmed processor, a parallel-programmed processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination of these. The processing circuitry may be implemented partly by dedicated hardware and partly by software or firmware. Thus, the processing circuitry can implement the above-described functions by dedicated hardware, software, firmware, or a combination of these.

The hardware configuration of the base station <NUM> is the same as the hardware configuration of the terminal <NUM>. In the base station <NUM>, the transceiver <NUM> is communication equipment. The transmission control unit <NUM> and the data processing unit <NUM> are implemented by processing circuitry. The processing circuitry may be a processor that executes a program stored in memory and the memory, or may be dedicated hardware.

As described above, according to the present embodiment, the terminal <NUM> monitors the rotor blade state and transmits the rotor blade state to the base station <NUM>. In a case of forward-link communication, the base station <NUM> determines the number of successive transmissions of data based on the rotor blade state and successively transmits the data for the number of successive transmissions. In a case of return-link communication, the base station <NUM> allocates radio resources with which the terminal <NUM> can transmit data, based on the rotor blade state. The terminal <NUM> transmits the data at a timing without blockage by the rotor blades in the allocated radio resources. Consequently, in wireless communication using time-division multiplexing, the terminal <NUM> and the base station <NUM> can improve the reliable transmission of signals such as data and resource notification, under conditions where blockage by the rotor blades occurs.

In the first embodiment, the base station <NUM> allocates radio resources to the terminal <NUM>, considering radio waves being blocked by the rotor blades, so that the base station <NUM> successively transmits data on a forward link, and the terminal <NUM> transmits data only in a non-blocking interval on a return link. However, the first embodiment, in which radio resources are redundantly allocated, has a problem of low frequency utilization efficiency. Therefore, a second embodiment will describe a method to achieve communication that avoids blockage by the rotor blades without allocating redundant radio resources.

<FIG> is a block diagram illustrating a configuration example of a terminal 10a according to the second embodiment. The terminal 10a includes the rotor blade state monitoring unit <NUM>, the transceiver <NUM>, the data processing unit <NUM>, and a synchronizer <NUM>. The terminal 10a is obtained by adding the synchronizer <NUM> to the terminal <NUM> of the first embodiment illustrated in <FIG>. <FIG> is a block diagram illustrating a configuration example of a base station 30a according to the second embodiment. The base station 30a includes the transmission control unit <NUM>, the transceiver <NUM>, the data processing unit <NUM>, and a synchronizer <NUM>. The base station 30a is obtained by adding the synchronizer <NUM> to the base station <NUM> of the first embodiment illustrated in <FIG>. The synchronizer <NUM> of the terminal 10a and the synchronizer <NUM> of the base station 30a manage times to uniquely determine transmission and reception timings by correcting a delay difference due to the geometry of the terminal 10a and the base station 30a. That is, the synchronizer <NUM> of the terminal 10a and the synchronizer <NUM> of the base station 30a correct a delay difference in the transmission or reception of data etc. between the terminal 10a and the base station 30a. A state in which synchronization between the synchronizer <NUM> of the terminal 10a and the synchronizer <NUM> of the base station 30a is achieved is, for example, a state in which timing alignment in 3GPP is established.

<FIG> is a diagram illustrating operations of the terminal 10a and the base station 30a according to the second embodiment. The synchronizer <NUM> of the terminal 10a and the synchronizer <NUM> of the base station 30a manage times with predetermined slot numbers, and have grasped a delay difference Δd due to the geometry. In the example of <FIG>, the delay difference Δd corresponds to <NUM> slots. A time at which the base station 30a receives data etc. transmitted by the terminal 10a in slot S01 after the delay difference Δd is slot S01 at the base station 30a. The delay difference Δd when data etc. are transmitted from the base station 30a to the terminal 10a is also <NUM> slots. Thus, in order for the terminal 10a to receive data etc. in slot S11, the base station 30a can transmit the data etc. in slot S06.

First, in the terminal 10a, the rotor blade state monitoring unit <NUM> monitors a rotor blade state. The transceiver <NUM> transmits the rotor blade state to the base station 30a. Here, as in the first embodiment, the rotor blade state is a blocking cycle, a blocking time, a blocking rate, the temporal stability of the blocking time, or the like. The blocking cycle and the blocking time are associated with slot numbers. <FIG> is a diagram illustrating an example in which information on the rotor blade state is associated with slot numbers in the terminal 10a according to the second embodiment. For example, a format of a communication start time, a communication possible period, and a blocking cycle is defined, and the communication start time is associated with slot S01, the communication possible period with two slots, and the blocking cycle with five slots. Although not illustrated in <FIG>, the blocking time can be obtained by (the blocking cycle)-(the communication possible period) = (three slots). In the second embodiment, the rotor blade state transmitted from the terminal 10a to the base station 30a includes at least one of the communication start time, the communication possible period, and the blocking cycle. In a case where the present embodiment is implemented based on 3GPP standards, the communication start time may be adapted to drxStartOffset in 3GPP, the communication possible period to onDurationTimer in 3GPP, and the blocking cycle to DRXcycle in 3GPP.

At the time of transmission of the rotor blade state to the base station 30a, when radio resources for an individual return link, for example, a transmission possible time, a frequency, or the like has been allocated by the transmission control unit <NUM> of the base station 30a to the terminal 10a, the transceiver <NUM> transmits the rotor blade state at a time without blockage by the rotor blades among the allocated radio resources. When radio resources for an individual return links have not been allocated by the transmission control unit <NUM> of the base station 30a to the terminal 10a, the transceiver <NUM> may transmit the rotor blade state, using radio resources allocated to contention-based random access or the like which have been determined by the transmission control unit <NUM> in advance.

In the base station 30a, the transceiver <NUM> receives the rotor blade state from the terminal 10a. The transmission control unit <NUM> estimates a period during which the terminal 10a can receive data etc., that is, a communication possible period during which communication is not blocked by the rotor blades, from the data amount of data to be transmitted to the terminal 10a on a forward link managed by the data processing unit <NUM>, the rotor blade state, etc. The transceiver <NUM> transmits the forward-link data to the terminal 10a so that the terminal 10a can receive the forward-link data during the communication possible period estimated by the transmission control unit <NUM>. When the transceiver <NUM> has received a resource request for a return link from the terminal 10a, the transmission control unit <NUM> determines resource allocation for the terminal 10a to transmit data in the communication possible period. The transceiver <NUM> transmits resource notification for providing a notification of radio resources allocated by the transmission control unit <NUM> so that the terminal 10a can receive the resource notification during the communication possible period.

In the terminal 10a, the transceiver <NUM> receives the data and the resource notification from the base station 30a. The data processing unit <NUM> transmits an acknowledgement to the received data to the base station 30a via the transceiver <NUM>. When there is data to be transmitted on a return link and resource notification has been received from the base station 30a, the transceiver <NUM> transmits the data to the base station 30a using radio resources allocated by the resource notification.

In the present embodiment, since the terminal 10a and the base station 30a can grasp the state of the rotor blades at a time at which they are synchronized with each other, the same processing as that of common intermittent transmission and reception can be performed. Thus, the terminal 10a can stop transmitting and receiving functions in a period other than an interval for intermittent transmission and reception, that is, other than the communication possible period. For example, if the terminal 10a manages a standby state with states such as Active, Idle, and Dormant, the terminal 10a may transition to the Idle mode in a period other than the communication possible period.

<FIG> is a flowchart illustrating the operation of the terminal 10a according to the second embodiment. In the terminal 10a, the rotor blade state monitoring unit <NUM> monitors the rotor blade state (step S121). The transceiver <NUM> transmits the rotor blade state to the base station 30a (step S122). The transceiver <NUM> receives data and resource notification from the base station 30a (step S123). The data processing unit <NUM> transmits an acknowledgement to the data to the base station 30a via the transceiver <NUM>, and transmits data using radio resources allocated by the resource notification (step S124).

<FIG> is a flowchart illustrating the operation of the base station 30a according to the second embodiment. In the base station 30a, the transceiver <NUM> receives the rotor blade state from the terminal 10a (step S321). The transmission control unit <NUM> estimates a reception possible period at the terminal 10a (step S322). The transceiver <NUM> transmits data so that the terminal 10a can receive the data in the reception possible period, and transmits resource notification when a resource request for a return link has been received from the terminal 10a (step S323). The transceiver <NUM> receives an acknowledgement to the transmitted data and data from the terminal 10a (step S324).

Note that the base station 30a may perform control combining the intermittent transmission and reception method described in the present embodiment with the successive transmission method described in the first embodiment. <FIG> is a flowchart illustrating another example of the operation of the base station 30a according to the second embodiment. In the base station 30a, the transceiver <NUM> receives the rotor blade state from the terminal 10a (step S331). The transmission control unit <NUM> determines whether or not the rotor blade state is stable (step S332). The transmission control unit <NUM> determines the stability of the rotor blade state by, for example, comparing the variance of the blocking rate, the blocking cycle, or the like with a predetermined threshold. When the rotor blade state is stable (step S332: Yes), the synchronizer <NUM> determines a synchronization state between the base station 30a and the terminal 10a (step S333). When the base station 30a and the terminal 10a are in a synchronized state (step S333: Yes), the transceiver <NUM> determines that the intermittent communication control described in the second embodiment is possible, and applies the intermittent communication mode (step S334). When the rotor blade state is not stable (step S332: No) or when the base station 30a and the terminal 10a are not in a synchronized state (step S333: No), the transceiver <NUM> determines that the successive transmission control described in the first embodiment is possible, and applies the successive transmission mode (step S335). Thus, when the rotor blade state is stable and synchronization with the terminal 10a is established, the transceiver <NUM> transmits data to the terminal 10a so that the terminal 10a can receive the data during the communication possible period. Otherwise, the transceiver <NUM> successively transmits data to the terminal 10a.

As illustrated in <FIG>, when there are a plurality of relay stations <NUM> and a plurality of base stations 30a with which the terminal 10a can communicate, the terminal 10a may monitor the rotor blade state for the plurality of relay stations <NUM> and transmit the individual rotor blade state to the respective base stations 30a. <FIG> is a diagram illustrating a configuration example of a communication system 50a according to the second embodiment. The communication system 50a includes the terminal 10a, two relay stations <NUM>, and two base stations 30a. When the terminal 10a can communicate with different base stations 30a via different relay stations <NUM>, in the terminal 10a, the rotor blade state monitoring unit <NUM> monitors the rotor blade state for each base station 30a. The transceiver <NUM> sets the base station 30a with which the rotor blade state is the most stable and the terminal 10a is in synchronization, as a communication target. Consequently, the terminal 10a can improve frequency utilization efficiency and communication reliability. In <FIG>, the numbers of the relay stations <NUM> and the base stations 30a are two, which is an example. The numbers of the relay stations <NUM> and the base stations 30a may be three or more.

As described above, according to the present embodiment, the terminal 10a includes the synchronizer <NUM>, and the base station 30a includes the synchronizer <NUM>. In a state where the terminal 10a and the base station 30a are time-synchronized, the terminal 10a transmits the rotor blade state associated with slot numbers to the base station 30a. The base station 30a performs communication only in rotor-blade non-blocking intervals in the same manner as in intermittent communication. Furthermore, the base station 30a can control switching between the intermittent communication mode and the successive transmission mode, based on the stability of the rotor blade state, the synchronization state, etc. Consequently, the terminal 10a and the base station 30a can improve the reliable transmission of signals, for example, data, resource notification, etc. while preventing redundant radio resource allocation even under conditions where blockage by the rotor blades occurs. In the second embodiment, the terminal 10a and the base station 30a can improve frequency utilization efficiency as compared with the terminal <NUM> and the base station <NUM> of the first embodiment.

Claim 1:
A base station (<NUM>) in a communication system in which a terminal (<NUM>) to be installed in a machine having rotor blades and the base station (<NUM>) transmit and receive data to and from each other via a relay station (<NUM>), the base station (<NUM>) comprising:
a transceiver (<NUM>) to receive, from the terminal (<NUM>), a rotor blade state that is a result of measurement by the terminal (<NUM>) of timing at which the rotor blades block a communication path in midair between the relay station (<NUM>) and the terminal (<NUM>); and
a transmission control unit (<NUM>) to determine radio resources to be allocated to the terminal (<NUM>), using the rotor blade state;
characterized in that the transmission control unit (<NUM>) determines, based on said rotor blade state, a number of successive transmissions for which data to be transmitted on a forward link is duplicated and successively transmitted, and the transceiver (<NUM>) successively transmits the data to the terminal (<NUM>) for the number of successive transmissions.