JP2020205504A - Communication device, communication method, and program - Google Patents

Abstract

To provide a communication device, a communication method, and a program that can further increase the speed and capacity of data transmission.SOLUTION: A communication device includes a transmission unit that modulates data by using a plurality of carrier waves and transmits the modulated data to a ground station, and a control unit that derives surplus power generated when the data is transmitted by the transmission unit, and determines, for each of the plurality of carriers, at least one of a coding rate of an error correction code for the data and a modulation method of the data according to the derived surplus power, and the control unit determines the power required when the transmission unit transmits the data, for each carrier wave, according to at least one of the coding rate and the modulation method determined for the carrier wave.SELECTED DRAWING: Figure 2

Description

The present invention relates to communication devices, communication methods, and programs.

When an artificial satellite orbiting the earth communicates with a radio base station on the ground (hereinafter referred to as a ground station), it is the angle between the line connecting the ground station and the artificial satellite and the horizontal plane with respect to the ground station. The lower the elevation angle, the longer the propagation distance of radio waves between the ground station and the artificial satellite, and the greater the attenuation of radio waves due to free space loss. Normally, in the line design of data communication from an artificial satellite to a ground station, the antenna mounted on the artificial satellite and the transmission of radio waves are performed under the conditions where the line establishment is the lowest, that is, the elevation angle during operation is the lowest. Various parameters such as power are determined and fixed. Therefore, in the operation where the elevation angle is high, the propagation distance is shorter than when the elevation angle is low, so that the ground station may generate extra power (hereinafter referred to as surplus power) exceeding the received power required for establishing the communication line. ..

As described above, there are known techniques for further increasing the speed and capacity of data transmission under the condition that surplus power is generated (see, for example, Patent Documents 1 and 2). For example, Patent Document 1 describes a technique for changing the coding method of an error correction code or changing the modulation method in response to changes in the communication environment such as precipitation attenuation and free space loss, as planned in advance. Is disclosed. By adopting such a method, the frequency utilization efficiency of communication between the artificial satellite and the ground station is maximized.

International Publication No. 2016/174774 Japanese Unexamined Patent Publication No. 58-150343

However, in the conventional technology, when switching the coding rate or modulation method of the error correction code based on the surplus power that can be generated according to the elevation angle of the artificial satellite during operation, CCSDS (Consultative Committee for Space Data System) ) And ETSI (European Telecommunications Standards Institute), etc., the standardized coding rate and modulation method are finite, and the maximization of frequency utilization efficiency is not sufficient. As a result, it was not possible to transmit a large amount of data at high speed. Further, such a problem is not limited to spacecraft such as artificial satellites, but is common to all mobile bodies that communicate with ground stations such as aircraft and drones flying over the ground.

The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a communication device, a communication method, and a program capable of further increasing the speed and capacity of data transmission. It is one of.

One aspect of the present invention occurs when data is error-corrected, encoded and modulated using a plurality of carriers, and the modulated data is transmitted to a ground station, and when the data is transmitted by the transmission unit. A control unit that derives surplus power and determines at least one of the coding rate of the error correction code for the data and the modulation method of the data for each of the plurality of carriers according to the derived surplus power. The control unit is a communication device that determines the power required for the transmission unit to transmit data for each carrier according to at least one of the coding rate and the modulation method determined for each carrier.

According to one aspect of the present invention, it is possible to further increase the speed and capacity of data transmission.

It is a figure which shows an example of the communication system 1 including the communication apparatus which concerns on embodiment. It is a figure which shows an example of the structure of the communication device 100 which concerns on embodiment. It is a figure which shows an example of the structure of the transmission part 110. It is a figure which shows an example of the change of the free space loss with respect to the elevation angle. It is the figure which compared the method of this embodiment and the conventional method. It is a figure which shows typically the power distribution for each carrier. It is a flowchart which shows an example of the flow of a series of processing by the communication apparatus 100 which concerns on embodiment. It is a figure which shows an example of the signal space diagram of QAM.

Hereinafter, embodiments of the communication device, communication method, and program of the present invention will be described with reference to the drawings. The communication device in this embodiment is typically mounted on an artificial satellite orbiting the earth. Further, the communication device is not limited to an artificial satellite, and may be mounted on other spacecraft such as a space probe and a space station, or may be mounted on a mobile body such as an aircraft or a drone that moves over the ground. Hereinafter, as an example, a communication device will be described as being mounted on an artificial satellite.

FIG. 1 is a diagram showing an example of a communication system 1 including a communication device according to an embodiment. The communication system 1 includes, for example, an artificial satellite SAT equipped with a communication device and a ground station 200. The artificial satellite SAT is typically an artificial satellite that observes the earth using radio waves, infrared rays, and visible light, but it transmits a communication satellite that relays a signal transmitted from a ground station 200 or a radio signal. It may be another type of artificial satellite, such as a navigation satellite.

For example, since the artificial satellite SAT is navigating along the orbit around the earth according to a predetermined operation schedule (navigation schedule), the relative position of the artificial satellite SAT as seen from the ground station 200, that is, the artificial satellite. The elevation angle of the SAT fluctuates with time, and the propagation distance according to the elevation angle is uniquely determined. The free space loss according to the propagation distance is larger as the elevation angle is lower and the propagation distance is longer, and is smaller as the elevation angle is higher and the propagation distance is shorter. For example, the ground station 200 receives and analyzes the information observed by the artificial satellite, and transmits a signal to the artificial satellite.

FIG. 2 is a diagram showing an example of the configuration of the communication device 100 according to the embodiment. The communication device 100 includes, for example, a transmission unit 110, a reception unit 120, a control unit 130, an observation sensor 140, and a storage unit 150. In outer space where the artificial satellite SAT navigates, the power of the communication device 100 is supplied exclusively by solar power generation, and the amount of power generated is finite, so that the maximum amount of power that can be consumed by the communication device 100 is limited. Works in an environment.

The transmission unit 110 transmits data to the ground station 200 using radio waves in a frequency band (for example, centimeter wave or millimeter wave) used in telemetry or the like.

FIG. 3 is a diagram showing an example of the configuration of the transmission unit 110. As shown in the illustrated example, the transmitter 110 includes N transmitters (transmitter circuits) 112, an adder 114, an amplifier 116, and an antenna 118. For example, the nth transmitter 112-n includes a coding unit 112-n-1, a modulation unit 112-n-2, and a transmission power control unit 112-n-3. n is any natural number greater than or equal to 1 and less than or equal to N.

The coding unit 112-n-1 encodes the data stored in the storage unit 150 at the coding rate instructed by the control unit 130.

The modulation unit 112-n-2 modulates the data encoded by the coding unit 112-n-1 by the modulation method instructed by the control unit 130.

The transmission power control unit 112-n-3 outputs the data modulated by the modulation unit 112-n-2 with the transmission power instructed by the control unit 130. In the following, the coded and modulated data will be referred to as a "signal".

The data input from the storage unit 150 to the transmitter 112 is handled in a desired information unit (for example, a bit). The data may be data in which one data is divided and parallelized by serial-parallel conversion, or may be data that is input independently from the storage unit. Each of the plurality of transmitters 112 has a different carrier phase or frequency from each other. Hereinafter, it is assumed that the modulation method is phase modulation, and the carrier frequencies are different from each other.

The adder 114 adds the signals modulated by each transmitter 112 and outputs them to the amplifier 116.

The amplifier 116 amplifies the power of the signals added by the adder 114. The antenna 118 irradiates the signal amplified by the amplifier 116 as radio waves toward the ground. The antenna 118 may be composed of a plurality of antennas such as a phased array antenna whose directivity can be controlled.

The receiving unit 120 receives radio waves in a frequency band such as those used for telecommands from the ground station 200. The telecommand is a command sent from the ground station 200 to give a command to the artificial satellite SAT.

The control unit 130 derives the surplus power of the radio wave transmitted by the antenna 118 based on the time of the operation schedule of the artificial satellite SAT, and according to the surplus power, the error correction code for each of the plurality of transmitters 112. Determine the code rate, modulation method, and transmission power of. Then, the control unit 130 transmits the control information indicating the determined coding rate, the modulation method, and the transmission power to the transmission unit 110.

The control unit 130 is realized by, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit) executing a program stored in the storage unit 150. Further, the control unit 130 may be realized by hardware such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), or FPGA (Field-Programmable Gate Array), or collaboration between software and hardware. May be realized by. Further, the program referenced by the processor may be stored in the storage unit 150 in advance, or is stored in a removable storage medium such as a DVD or a CD-ROM, and the storage medium is a drive of the communication device 100. It may be installed in the storage unit 150 by being attached to the device.

In the artificial satellite SAT, it is recommended to transmit data from the artificial satellite SAT to the ground station 200 by using a coding rate and a modulation method conforming to a standard defined by CCSDS or ETSI. However, as described above, as the elevation angle of the artificial satellite SAT increases, the propagation distance becomes shorter, so that the extra power exceeding the minimum power required to guarantee that the data transmitted from the artificial satellite SAT can be restored by the ground station 200 is exceeded. Power, that is, surplus power is generated.

Therefore, the control unit 130 derives the elevation angle of the artificial satellite SAT from the time in consideration of the fact that the artificial satellite SAT is orbiting the earth, and further derives the surplus power from the derived elevation angle. For example, the control unit 130 may derive the surplus power directly from the time by referring to the table or the relational expression in which the surplus power is associated with the time of the operation schedule, or at the time of the operation schedule. On the other hand, the surplus power is indirectly derived from the time by referring to the table or relational expression with which the elevation angle is associated and the table or relational expression with which the surplus power is associated with the elevation angle. May be good.

For example, the control unit 130 may derive surplus power based on the information output from the observation sensor 140 described later when the artificial satellite SAT is orbiting along the orbit, or the reception unit 120 may derive the surplus power. It may be derived based on the telecommand received from the ground station 200. Alternatively, the information output from the observation sensor 140 and the telecommand received from the ground station 200 by the receiving unit 120 may be combined and derived.

For example, in the standard DVB-S2 (Digital Video Broadcasting Satellite Second Generation) defined by ETSI, the signal power to noise power spectral density ratio (Es / N ₀ ) per symbol at Frame Error Rate (FER) = 1E-5 is analyzed. When the coding rate of the error correction code is 5/6 and the modulation method is QPSK (Quadrature Phase Shift Keying), Es / N ₀ is 5.18 [dB], and the coding rate of the error correction code is Is 5/6 and the modulation method is 8PSK, Es / N ₀ is described as 9.35 [dB].

Es represents the energy per code (symbol), N ₀ represents the noise power spectral density per 1 [Hz], and Es / N ₀ is the energy Es per code with respect to the noise power spectral density N ₀ . Represents the ratio of. That is, a modulation method in which the information transmission rate ([bit] / [s]) per bandwidth 1 [Hz] is large in order to ensure that the ground station 200 on the receiving side can normally demodulate the modulated data. (Modulation method with higher frequency utilization efficiency) means that it is necessary to increase the transmission power.

FIG. 4 is a diagram showing an example of a change in free space loss with respect to an elevation angle. As shown in the figure, the larger the elevation angle, that is, the closer the artificial satellite SAT is to directly above the ground station 200, the shorter the propagation distance between the artificial satellite SAT and the ground station 200, so that the free space loss decreases. Therefore, even if the transmission power is reduced when the elevation angle is large, it means that Es / N ₀ satisfies the required value.

The observation sensor 140 is a sensor that observes the earth by detecting radio waves, infrared rays, visible light, etc. that are emitted or reflected from the ground. The observation sensor 140 is, for example, an antenna that receives radio waves, a camera that detects visible light or infrared rays emitted from the ground surface, and the like. The observation sensor 140 converts a signal indicating the observation result into a data format that can be used by the control unit 130, and then outputs the signal to the control unit 130.

The storage unit 150 is realized by, for example, an HDD (Hard Disc Drive), a flash memory, an EEPROM (Electrically Erasable Programmable Read Only Memory), a ROM (Read Only Memory), a RAM (Random Access Memory), or the like. The storage unit 150 stores, for example, data to be transmitted to the ground station 200.

(Explanation of how to determine the modulation method)
Hereinafter, the details of the method of determining the modulation method according to the surplus power will be described. First, N carriers (carrier waves) arranged on the frequency axis, that is, N carriers having different frequencies from each other are defined as carrier 1, carrier 2, ..., carrier n, ..., Carrier N. N is a natural number of 2 or more. Hereinafter, an example in which the modulation method is variable will be described for the sake of simplicity, but the same applies when the coding rate of the error correction code is variable or both the coding rate and the modulation method are variable. ..

When transmitting observation data on a single carrier without carrier division (N = n = 1), the reception C required to switch to the digital modulation system of the modulation order of ^{2 2} from ^{m m + 1} (e.g., 8PSK from QPSK) / N ₀ ((C / N ₀ ) _{n, m + l} ) [antilogarithm] is expressed as in the mathematical formula (1).

Here, C represents the received signal power, and N ₀ represents the noise power spectral density. Further, (C / N ₀ ) _{m + l} represents the received C / N ₀ (received signal power to noise power spectral density ratio) required for the modulation method of degree 2 ^{m + 1} .

On the other hand, in the present embodiment, the order of the modulation method of n carriers is switched from 2 ^m to 2 ^{m + 1} , and the order of the modulation method of (Nn) carriers remains at 2 ^m. The received C / N ₀ ((C / N ₀ ) _{n, m + l} ) [antilogarithm] required for the above is expressed by the formula (2).

Here, n is a natural number of 1 or more and N or less. Further, (C / N ₀ ) _m represents the reception C / N ₀ required for the modulation method having a degree of 2 ^m . _{Further, {(C / N 0)} m + 1 - (C / N 0) m} is representative of the amount of increase of the receiving C / _{N 0} required to switch to the ^{2 m + 1} the order of the modulation scheme for all carriers from ^{2 m} There is. In the present embodiment, the amount of increase in reception C / N ₀ required when switching the modulation method at the ratio of n / N can be controlled. Therefore, when the order of the modulation method for only n carriers is switched from 2 ^m to 2 ^{m + 1} , the modulation method can be switched with a smaller reception C / N ₀ as the number of divisions N of the carriers is increased.

When the modulation order of the modulation method of n carriers is switched from 2 ^m to 2 ^{m + 1} , the frequency utilization efficiency η _{n, m + 1} [bit / s / Hz] is expressed by the mathematical formula (3).

FIG. 5 is a diagram comparing the method of the present embodiment with the conventional method. As shown in the figure, the frequency utilization efficiency η, which was conventionally fixed until the required C / N ₀ of the next modulation method is reached, is gradually improved according to the number of carrier divisions N as shown in equation (3). As a result, the transmission capacity of the communication device 100 can be increased.

The reception C / N ₀ of each carrier increases as the elevation angle θ rises, and decreases as the elevation angle θ decreases. Therefore, the control unit 130 increases the output power of only the carrier 1 and decreases the output power of the other carriers at the timing when the reception C / N ₀ increases and exceeds a certain value.

In this case, the received C / N ₀ (surplus power is generated) is further increased by the increase due to the increase in the elevation angle θ and the aggregated output power, so that the control unit 130 is the carrier 1 in which the power is concentrated. The modulation method of is redetermined to a higher-order modulation method that requires a high requirement C / N ₀ , or is redetermined to a modulation method having a high coding rate.

At this time, the surplus power of the carrier 1 becomes 0. On the other hand (under the condition that the total output power is constant), the output power of the carriers other than the carrier 1 is reduced by the output power operation, but the received C / N ₀ is increased by the increase of the elevation angle θ, so that amount is offset. To do. As a result, the requirement C / N ₀ required to maintain the original coding rate / modulation method is satisfied. That is, the control unit 130 maintains the modulation method of the other carrier that divides the power into the carrier 1 without changing it.

As the elevation angle θ increases, the control unit 130 switches the coding rate or modulation method in the order of carrier 2, carrier 3, ..., Carrier N, so that all carriers move to the next coding rate or modulation method. During the period until switching, the coding rate / modulation method can be densely switched by the number of divisions N of the carriers. As a result, a large amount of data can be transmitted while reducing the surplus power for each elevation angle θ.

When transmitting with only one carrier without carrier division, the required C / N ₀ of the digital modulation method having a modulation order of 2 ^m and a modulation order of 2 ^{m + 1} is expressed by mathematical formulas (4) and (5).

Here, P is the output power of the transmitter, G is the total gain from the transmitter amplifier, the transmission / reception antenna gain, the power supply loss, and other devices, θ is the elevation angle during operation, and L (θ) is free space propagation according to the elevation angle θ. It is a loss. In the artificial satellite SAT that orbits the earth in low earth orbit, L (θ) increases as the elevation angle θ rises and decreases as the elevation angle θ falls. Further, θ _m is an elevation angle at which the minimum reception C / N ₀ required to switch to a modulation method having a modulation order of 2 ^m is obtained, and θ _{m + 1} is the minimum required to switch to a modulation method having a modulation order of 2 ^{m + 1.} This is the elevation angle at which reception C / N ₀ is obtained.

The noise power spectral density N ₀ is generally determined by the equipment configuration of the ground station, is not zero, and can always be regarded as constant even if the elevation angle θ changes. Therefore, by multiplying both sides by N ₀ , the formula (4) , (5) can be expressed by converting them into units of received power as in the formulas (6) and (7). Hereinafter, the format of the received power C will be described as in the equations (6) and (7).

Here, the difference ΔL of the free space loss corresponding to the modulation order of 2 ^m and the modulation order of 2 ^{m + 1} is defined as in the equation (8).

At this time, the required received power having a modulation order of 2 ^{m + 1} can be expressed as in the equation (9) by using the difference ΔL of the free space loss.

On the other hand, when the carrier is divided into N pieces, the symbol rate per carrier is 1 / N, and the required received power per carrier is also l / N. Therefore, the required received power with a modulation order of 2 ^{m + 1} per carrier. Can be expressed as in the formula (10).

Therefore, the difference ΔL of the free space loss per carrier required to switch the order of the modulation method from 2 ^m to 2 ^{m + 1} is also ΔL / N.

(Distribution of surplus electricity for each carrier)
Hereinafter, how to allocate the surplus power to each carrier will be described with reference to the figure. FIG. 6 is a diagram schematically showing power distribution for each carrier. In the illustrated example, N = 3, and the case where the modulation method is changed from QPSK to 8PSK is shown.

If you do not carrier division unlike this embodiment, in order to switch the order of the modulation scheme from 2 ^m to 2 ^{m + 1,} the difference in free space loss was necessary to reach a [Delta] L. That is, it was necessary for the elevation angle to rise to θ _{m + 1} .

On the other hand, when the carriers are divided into N pieces as in the present embodiment, the difference in free space loss per carrier required for switching is ΔL / N, so that each carrier is before the elevation angle rises to θ _{m + 1.} The surplus power generated in the carriers can be aggregated in one carrier. Therefore, when the difference in free space loss reaches ΔL / N, the control unit 130 may redetermine the modulation method to a higher-order modulation method that requires a high reception power C in advance of only the carrier 1. Alternatively, the modulation method with a high coding rate may be redetermined. After allocating the surplus power, the surplus power of each carrier becomes 0.

Similar to the carrier 1, the control unit 130 performs the same processing on the carriers 2, 3, ..., N to determine the modulation method. In this way, the power is concentrated on some carriers and the modulation method of the carriers that have concentrated the power is switched. Therefore, as the number N of carriers increases, the difference in free space loss required for switching increases linearly. I will go. Assuming that the difference in free space loss required to switch the carriers up to the nth carrier to the higher-order modulation method in advance is ΔL _n , the relationship between ΔL _n and ΔL is expressed by the equation (11).

Multiplying both sides of the formula (6) by GP gives the formula (12).

The mathematical formula (12) can be transformed like the mathematical formula (13).

Thus it is possible to derive the received power C necessary for switching the order of the modulation scheme of the n carriers from 2 ^m to 2 ^{m + 1} to.

In (power operation ends up to N-th) when the switching has been completed carrier modulation method up to N-th, the order of the modulation scheme of all carriers are switched from 2 ^m to 2 ^{m + 1.} The elevation angle at this time is θ _{m + 1} . After that, the phase shifts to the switching phase from the modulation order 2 ^{m + 1} to 2 ^{m + 2,} and the above operation is repeated thereafter.

Next, the value of the output power of the transmission unit 110 that is actually operated will be described. The received powers C _{1, m + 1} required when switching the order of the modulation method of one carrier from 2 ^m to 2 ^{m + 1} can be expressed by dividing into two terms as shown in the equation (14).

The first term of the formula (14) represents the received power of the carrier 1, and the second term represents the total received power of the carrier 2 to the carrier N. Further, each received power can be classified into a required received power having a modulation order of 2 ^{m + 1} and 2 ^m , surplus power due to an increase in elevation angle θ, and the amount of power distributed by power operation. From the equation (14), for the carrier 1, the required received power of the modulation order 2 ^{m + 1} can be satisfied by adding the received power in total ((N-1) ΔLGP / N ² ) by the power operation, and the carrier 2 From this, it can be seen that the required received power of 2 ^m can be maintained for the carrier N even if the received power is deducted (ΔLGP / N ² ) by the power operation.

Similarly, the received powers Cn _{and m + 1} required when switching the modulation order of the modulation method of n carriers from 2 ^m to 2 ^{m + 1} are as shown in Equation (15).

Even when switching from the order 2 ^m of the modulation method of n carriers to 2 ^{m + 1} , the carriers 1 to n are modulated by adding the received power ((Nn) ΔLGP / N ² ) by power operation. The required received power of order 2 ^{m + 1} can be satisfied. Further, it can be seen that the required received power of 2 ^m can be maintained even if the received power (nΔLGP / N ² ) is deducted from the carrier n + l for the carrier N by the power operation.

Thus, deriving the amount of operation of the power operation required when switching the reception power C _{n, m + 1,} and the modulation scheme necessary for switching the modulation order of the modulation scheme of the n carriers from 2 ^m to 2 ^{m + 1} showed that.

(Processing flow of communication device)
Hereinafter, a series of processing flows by the communication device 100 according to the embodiment will be described with reference to a flowchart. FIG. 7 is a flowchart showing an example of a flow of a series of processes by the communication device 100 according to the embodiment.

First, the control unit 130 determines the initial value of the elevation angle θ based on the operation plan (step S100).

Next, the control unit 130 sets the initial value (m = mо) of the modulation order (step S102). Here, mо is the minimum value of the modulation order that can be set by the transmitter 112.

Next, the control unit 130 sets an initial value (n = 1) of the number of carriers whose modulation method is to be switched (step S104).

Next, the control unit 130 determines whether or not the elevation angle θ is maximum (step S106). When the elevation angle θ is the maximum, the control unit 130 ends the process of this flowchart.

On the other hand, when the elevation angle θ has not reached the maximum, the control unit 130 continues the processing of this flowchart. The control unit 130 determines whether or not the received power C [antilogarithm] satisfies the mathematical formula (16) (step S108). If the received power C does not satisfy the equation (16), the elevation angle θ is increased (step S110). As the elevation angle θ increases, the difference in free space propagation loss increases for each carrier, and the received power also increases accordingly.

On the other hand, when the received power C satisfies the mathematical formula (16), the control unit 130 performs an operation of distributing the output power (steps S112 to S116). Specifically, the control unit 130 reduces the output power of the carrier other than the target carrier for which the modulation method is switched (step S112), and aggregates the reduced power into the output power of the target carrier (step S114). As a result, the received power C satisfies the required received power (C _{m + 1} ) having a modulation order of 2 ^{m + 1} due to the increase in power distributed from other carriers in addition to the signal power originally possessed by the target carrier. The modulation method of the target carrier is switched to the next modulation method (the modulation method having the next highest order) (step S116). On the other hand, the other carriers satisfy the original required received power ( _Cm ) because the originally possessed signal power is increased by the increase of the elevation angle θ even in the state where the signal power is lowered. Therefore, the control unit 130 maintains the current modulation method without changing the modulation method of other carriers. After switching the modulation method of the target carrier, the surplus power of all carriers becomes zero.

Next, the control unit 130 switches the number of target carriers from n to n + 1 (step S118). Next, the control unit 130 determines whether or not all carriers from 1 to N have been selected as processing targets (step S120), and when all carriers have not yet been selected as processing targets, that is, n ≦ In the case of N, the above processes from step S106 to step S118 are repeatedly executed.

On the other hand, when all carriers from 1 to N are selected as processing targets, that is, when n> N, the control unit 130 shifts to the next modulation method switching phase (2 ^{m + 1} to 2 ^{m + 2} ) (step S122). .. The control unit 130 returns the process to S104 and initializes the number of carriers to be switched in the modulation method to n = 1.

The control unit 130 repeats the processes of steps S104 to S122 from 2 ^m to 2 ^{m + 1} , 2 ^{m + 1} to 2 ^{m + 2} , ..., Until the maximum elevation angle is reached. When the maximum elevation angle is reached, the processing of this flowchart ends.

In the above flowchart, a control example when the elevation angle θ rises has been described, but when the elevation angle θ decreases, the modulation method is switched by performing the operation opposite to that when the elevation angle θ rises. To do. In this case, the operation is continued until the minimum elevation angle is reached, and the process ends when the minimum elevation angle is reached.

Further, in the above flowchart, the method of determining the elevation angle θ based on the operation plan has been described as an example, but the elevation angle θ may be determined based on the actually received received power C, or two determination methods. May be used together.

According to the embodiment described above, the communication device 100 mounted on the artificial satellite SAT (an example of a mobile body) modulates data using a plurality of carriers, transmits the modulated data to a ground station, and transmits the data. The surplus power generated during transmission was derived, and at least one of the coding rate of the error correction code for the data and the data modulation method was determined for each of the plurality of carriers according to the surplus power, and was determined for each carrier. Since the power required for transmitting data is determined for each carrier according to at least one of the coding rate and the modulation method, it is possible to further increase the speed and capacity of data transmission.

The transmission capacity is further increased when the surplus power at the time of switching between the coding rate and the modulation method is taken into consideration. This surplus power may be recorded separately from the propagation loss as surplus power for maintaining communication quality even when the predicted reception C / N ₀ contains an error due to an error in orbit determination accuracy. Therefore, the method of the present embodiment can be applied to the surplus power due to switching as well as the surplus power due to propagation loss.

Further, when the required transmission capacity is the same, by applying the method of the present embodiment, the required transmission capacity can be achieved with a lower reception power as compared with the conventional example. As a result, for example, the conventional TWTA (Traveling Wave Tube Amplifier) can be changed to a lower cost and lower mass SSDA (Solid State Power Amplifier), and the system resources of the satellite can be significantly reduced. ..

(Modification example)
Hereinafter, a modified example of the above-described embodiment will be described. In the above-described embodiment, APSK (Amplitude & Phase Shift Keying) has been exemplified as the switching modulation method, but the present invention is not limited to this, and other modulation methods may be used. For example, QAM (Quadrature Amplitude Modulation) may be used.

FIG. 8 is a diagram showing an example of a signal space diagram of QAM. The illustrated example shows a 16QAM signal space diagram. When QAM is adopted as the modulation method, the modulation method may be switched between 16QAM, 32QAM, 64QAM, and so on according to the fluctuation of the elevation angle θ.

Further, the communication device 100 of the above-described embodiment is also applicable to a communication system using Adaptive Coding & Modulation (ACM) technology and a communication system using multi-channel. Here, a practical example for a communication system using ACM technology will be described. ACM is a technology that adaptively changes the error correction coding rate and modulation method in response to changes in the communication environment such as rainfall attenuation and free space loss, and when line conditions fluctuate due to rainfall attenuation, etc. (surplus in fine weather) When power is generated), by switching the coding rate / modulation method according to the received signal, the optimum coding rate / modulation method can be applied according to the change.

Conventionally, when the fluctuation amount of the line condition is not enough for the surplus power required to switch the modulation order of the modulation method from 2 ^m to 2 ^{m + 1} , the coding rate / modulation method cannot be switched. Therefore, by applying the technique of the present embodiment, the required C / N ₀ required when switching the coding rate / modulation method is subdivided. As a result, it becomes possible to switch the coding rate / modulation method according to more detailed fluctuations in the line condition, and as a result, it becomes possible to improve the transmission rate and the reliability of the communication line (improve the operating rate).

Further, the technique of the present embodiment can be used in combination with a common amplification technique as exemplified in Patent Document 2. In the case of wideband transmission by one user alone, such as the earth observation satellite direct transmission system, until now, transmission was mainly performed by one carrier in order to reduce device resources, but it seems that it is allocated in the Ka band. In the case of 1.5 [GHz] wideband transmission, the application of multi-carrier common amplification is required because there is a limit to the frequency band supported by one carrier for both the modulator and demodulator in the current device technology. When the multi-carrier common amplification is applied, the amplifier gain of all carriers is constant, so that it is impossible to make the amplifier output of each carrier variable when the amplifier input power is constant. Therefore, in the present invention, by adopting a method of controlling the power of the modulator output unit before the amplifier input, it is possible to make the amplifier input power of each carrier variable, and the on-board resources of the device are reduced by the multi-carrier common amplification. At the same time, this method makes it possible to maximize the communication system 1 and increase the transmission capacity.

The embodiment described above can be expressed as follows.
A transmitter that modulates data using a plurality of carrier waves and transmits the modulated data to a ground station.
Storage that stores programs and
With a processor,
When the processor executes the program,
Derivation of surplus power generated when the data is transmitted by the transmitter
At least one of the code rate of the error correction code for the data and the modulation method of the data is determined for each of the plurality of carriers according to the derived surplus power.
The power required for the transmitter to transmit data is determined for each carrier wave according to at least one of the coding rate and the modulation method determined for each carrier wave.
A communication device that is configured to.

Although the embodiments for carrying out the present invention have been described above using the embodiments, the present invention is not limited to these embodiments, and various modifications and substitutions are made without departing from the gist of the present invention. Can be added.

100 ... communication device, 110 ... transmitter, 120 ... receiver, 130 ... control, 140 ... observation sensor, 150 ... storage, 200 ... ground station, SAT ... artificial satellite

Claims (10)

A transmitter that modulates data using a plurality of carrier waves and transmits the modulated data to a ground station.
The surplus power generated when the data is transmitted by the transmission unit is derived, and at least one of the coding rate of the error correction code for the data and the modulation method of the data is set according to the derived surplus power. It is equipped with a control unit that determines each of the carriers of
The control unit determines the power required for the transmission unit to transmit data for each carrier wave according to at least one of the coding rate and the modulation method determined for each carrier wave.
Communication device. The control unit derives the surplus power based on the elevation angle seen from the ground station.
The communication device according to claim 1. The control unit derives the elevation angle based on the time of the operation schedule of the mobile body, and derives the surplus power based on the derived elevation angle.
The communication device according to claim 2. The control unit
As the surplus power becomes larger, the modulation method of the data is determined to be a modulation method having a larger amount of information that can be transmitted.
Alternatively, the larger the surplus power, the smaller the coding rate is determined.
The communication device according to any one of claims 1 to 3. The control unit determines the first modulation method using a part of the plurality of carrier waves to be a modulation method having a larger amount of information that can be transmitted than the second modulation method using another carrier wave.
The transmission unit compares the transmission power of the first data modulated by the first modulation method with the transmission power of the second data modulated by the second modulation method within the range of the surplus power. To increase
The communication device according to any one of claims 1 to 4. The transmission unit increases the transmission power of the first data and decreases the transmission power of the second data within the range of the surplus power.
The communication device according to claim 5. The transmission unit calculates the power required for the transmission unit to transmit data for each carrier wave so that the decrease in the transmission power of the second data becomes the increase in the transmission power of the first data. decide,
The communication device according to claim 6. Mounted on mobiles with limited available power,
The communication device according to any one of claims 1 to 7. A computer mounted on a mobile body including a transmitter that modulates data using a plurality of carrier waves and transmits the modulated data to a ground station
The surplus power generated when the data is transmitted by the transmission unit is derived, and the surplus power is derived.
At least one of the code rate of the error correction code for the data and the modulation method of the data is determined for each of the plurality of carriers according to the derived surplus power.
The power required for the transmitter to transmit data is determined for each carrier according to at least one of the coding rate and the modulation method determined for each carrier.
Communication method. A computer mounted on a mobile body including a transmitter that modulates data using a plurality of carrier waves and transmits the modulated data to a ground station.
The process of deriving the surplus power generated when the data is transmitted by the transmitter, and
A process of determining at least one of the code rate of the error correction code for the data and the modulation method of the data according to the derived surplus power for each of the plurality of carrier waves.
A process of determining the power required for the transmission unit to transmit data according to at least one of the coding rate and the modulation method determined for each carrier wave, and a process of determining the power required for each carrier wave.
A program to execute.

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