JP7635005B2 - Satellite communication device, its transmitter and transmission method - Google Patents

Description

This embodiment relates to a satellite communication device, its transmitter, and a transmission method.

VSAT (Very Small Aperture Terminals) devices are communication devices for communicating with geostationary satellites, with relatively small antenna apertures. These VSAT devices have become even smaller in recent years, and are now available in not only vehicle-mounted but also portable types, and their mobility has led to their use in disaster sites and other locations. They are also often used in conjunction with mobile communications infrastructure. By connecting communication terminals such as telephones and TVs to the respective MODEMS (Modulator-Demodulators) of these VSAT devices, communication via satellite lines becomes possible, and communication such as telephone calls, video conferences, and e-mails can be carried out between control stations and disaster sites, or between disaster sites in general.

The main components of the VSAT device are a MODEM connected to a transmitting and receiving antenna via a transmitter and receiver, which include frequency converters such as a BUC (Block Up-Converter) for transmission and an LNC (Low Noise block down-Converter) for reception.

In VSAT equipment, the MODEM output level is usually adjusted first when establishing satellite communications. If the reception level changes significantly during operation, the MODEM output level may be changed manually, but once operation has begun, it is common not to change the MODEM output level.

In response to this, some recent MODEMs are equipped with a test function that changes the output level at irregular intervals to determine the BUC's P1dB (1 dB gain compression point: an output characteristic that indicates the linearity of a linear amplifier, and represents the output level at which the gain drops by 1 dB relative to the ideal characteristic of the gain line) in order to ensure communication quality.

In contrast, existing transmitters are designed on the assumption that the MODEM will not change its output level during operation, and are not equipped with a function to adjust the output power. For this reason, if the P1dB of the BUC of the transmitter is large compared to the output power approved by application (hereinafter referred to as the applied power), when the output level of the MODEM, i.e. the input level of the BUC, is increased by the test function during operation of the MODEM, the output power of the BUC will exceed the applied power, resulting in the transmission of illegal radio waves.

JP 2012-95196 A Japanese Patent Application Laid-Open No. 6-104777 Japanese Patent Application Laid-Open No. 5-191184

As described above, in conventional ultra-small satellite communication devices, when a modem with a test function is used that changes the output level irregularly during operation to obtain the P1dB output characteristic of the upconverter in the transmitter, if the P1dB of the upconverter is large compared to the applied power, radio waves that exceed the applied power are transmitted.

The objective of this embodiment is to provide a satellite communications device, a transmitter and a transmission method thereof that can control the output power so that it does not exceed the applied power, and can suppress the transmission of radio waves that exceed the applied power, even when a modem with a test function that changes the output level irregularly during operation to determine the output characteristics of the upconverter of the transmitter is used.

In order to solve the above problems, the satellite communication device according to this embodiment includes a modem, a transmitter, an antenna, and a receiver. The modem has a modulation/demodulation function for modulating communication data from a communication terminal into an intermediate frequency band communication signal, transmitting and outputting the signal, and demodulating the intermediate frequency band communication signal obtained by receiving radio waves from a communication satellite and outputting the signal to the communication terminal, and a test function for irregularly changing the output level of the communication signal to be transmitted and outputted to obtain transmission output characteristics. The transmitter includes an up-converter that converts an intermediate frequency band communication signal output from the modem to a radio frequency band, a variable attenuator that attenuates an input level of the up-converter by an attenuation amount according to a command, an amplifier that power-amplifies and outputs the communication signal converted to the radio frequency band by the up-converter, a detector that detects a power value of the output power-amplified by the amplifier, and an output controller that compares the detected power value detected by the detector with a power upper threshold, and when the detected power value exceeds the power upper threshold, instructs the variable attenuator to increase the attenuation amount stepwise from an initial setting value until the detected power value falls below the power upper threshold, and after the detected power value falls below the power upper threshold, instructs the variable attenuator to return the attenuation amount stepwise to the initial setting value. The antenna transmits the radio frequency band communication signal output from the transmitter to a communication satellite and receives the radio frequency band communication signal from the communication satellite. The receiver amplifies the radio frequency communication signal received by the antenna, converts it to an intermediate frequency band, and outputs it to the modem.

FIG. 1 is a diagram showing an example of a satellite communication system to which an embodiment is applied. FIG. 2 is a plan view showing the external configuration of a satellite communication device used in a fixed station of the satellite communication system shown in FIG. 1 as a first embodiment. FIG. 3 is a block diagram showing a schematic configuration of the main body of the satellite communication device shown in FIG. FIG. 4 is a block diagram showing the configuration of a communication processing system and a control processing system of the satellite communication device shown in FIG. FIG. 5 is a block diagram showing the configuration of a transmitter used in the satellite communication device shown in FIG. FIG. 6 is a flowchart showing a control process for limiting the output power to the requested power in the transmission output controller of the transmitter shown in FIG. FIG. 7 is a plan view showing the outer configuration of a satellite communication device used in a vehicle-mounted station or a portable station of the satellite communication system shown in FIG. 1 as a second embodiment. FIG. 8 is a block diagram showing the configuration of a signal processing system and a control processing system of the satellite communication device shown in FIG.

The following describes the embodiment with reference to the drawings.

A satellite communication system is equipped with multiple earth stations that communicate with each other via satellites in geostationary orbit. This satellite communication system is applied as a wide-area disaster prevention radio system, for example, to the disaster prevention systems of wide-area local governments such as prefectures. Specifically, live images captured at disaster sites can be transmitted from the satellite communication device via satellite links to earth stations in prefectural capitals, etc. This allows the situation of the disaster to be known quickly and accurately.

Figure 1 is a diagram showing an example of a satellite communications system to which an embodiment is applied. This system is formed around a communications satellite SAT in geostationary orbit at its core. On the ground side, fixed stations FS1 to FSn are installed in places such as prefectural capitals. Vehicle-mounted station MS1 or portable station MS2 can also be installed at disaster sites. Fixed stations FS1 to FSn, vehicle-mounted station MS1, and portable station MS2 each have a communications satellite device, and are capable of communicating with each other via the communications satellite SAT.

For example, video footage of the disaster site can be sent via satellite to the main base (fixed station FS1) and other bases (fixed stations FS2 to FSn) to help grasp the disaster situation. In addition, satellite lines can be used for VoIP (Voice over IP) calls and video conferences to share information between related departments and hold disaster response discussions.

This type of system is often constructed as part of a local government's disaster prevention system. The method of allocating lines to satellite communication equipment is called DAMA (Demand Assignment Multiple Access). Control stations installed at several locations on the ground are responsible for controlling DAMA.

(First embodiment)
Fig. 2 is a plan view showing the external configuration of a fixed type satellite communication device 10 used as a fixed station of the satellite communication system shown in Fig. 1 as a first embodiment, where (a) is a top view, (b) is a side view of (a) seen from the top in the figure, (c) is a side view of (a) seen from the bottom in the figure, (d) is a side view of (a) seen from the left in the figure, and (e) is a bottom view. The satellite communication device 10 shown in Fig. 2 is a so-called VSAT device, and is composed of a main body section 20 and an antenna section 30, and although details are not shown, the antenna direction of the antenna section 30 is fixed in a state facing the communication satellite SAT.

The main body 20 contains a signal processing board 21 housed in a housing 22, to which electronic components such as a power switch 23, a power connector 24, a LAN connector 25, and a transmission/reception monitor 26 are attached, and the signal processing board 21 is connected to each electronic component inside the housing 22.

The power switch 23 is a switch that controls the start and stop of the device by turning the power on and off. The power connector 24 is a connector that is connected to an AC 100V power line, and turns the connection to the power line on and off according to the on/off operation of the power switch 23. The LAN connector 25 is a connector that is connected to a wireless or wired network. The transmit/receive monitor 26 is a display that monitors and displays the power value of the signal distributed from the communication signal during transmission and reception.

The antenna unit 30 is a planar transmitting/receiving antenna in which an antenna board 31, on which antenna elements are arranged in an array, is housed in a radome 32. The power supply end of the antenna board 31 is connected to the RF transmitting/receiving end of the signal processing board 21 of the main body unit 20.

Figure 3 is a block diagram showing the general configuration of the main body 20 of the satellite communication device 10 shown in Figure 2.

In FIG. 3, the signal processing board 21 of the main body 20 includes a MODEM 211, a wireless unit 212, a processor 213, a two-way distributor (two types for transmission and reception) 214, a filter 215, and an AC/DC converter 216.

MODEM 211 is a modulation/demodulation unit connected to LAN connector 25. MODEM 211 modulates communication data from a communication terminal connected to LAN connector 25, generates a baseband IF band communication signal, outputs it to wireless unit 212, inputs the IF band communication signal from wireless unit 212, demodulates the communication data, and outputs it to the communication terminal.

The radio unit 212 frequency-converts (up-converts) the baseband IF band communication signal sent from the MODEM 211 to an RF band signal using the BUC, power-amplifies the signal, and sends it to the antenna section 20. The radio unit 212 also low-noise-amplifies the RF band communication signal received from the communication satellite SAT by the antenna section 30, and frequency-converts (down-converts) the signal to a baseband IF band signal using the LNC, and sends it to the MODEM 211.

The processor 213 is composed of an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and is a control unit that controls the signal processing of the MODEM 211 and the wireless unit 212.

The two-way distributor 214 distributes the communication signal from the MODEM 211 to the wireless unit 212 and the communication signal from the wireless unit 212 to the MODEM 211 into two signals and sends them to the transmission/reception monitor 26.

The filter 215 is a filter that cuts out noise components that are mixed in from the AC 100V power line connected to the power connector 24.

The AC/DC converter 216 is a conversion unit that converts the AC 100V AC voltage input through the filter 215 into a DC voltage, adjusts the voltage appropriately, and supplies it to the MODEM 211, the wireless unit 212, the processor 213, the 2-way distributor 214, and the transmission/reception monitor 26.

Figure 4 is a block diagram showing the configuration of the communication processing system and control processing system of the satellite communication device 10 shown in Figure 2.

In FIG. 4, a Wi-Fi (registered trademark for wireless LAN) router 200 is connected to the LAN connector 25 to which the MODEM 211 is connected. As a result, the MODEM 211 is wirelessly connected to communication terminals such as a notebook PC 201, a VoIP phone 202, and a tablet 203 through the Wi-Fi router 200. The MODEM 211 has a modulation/demodulation function that modulates communication data from the communication terminal, generates a baseband IF band communication signal, outputs the signal to the wireless unit 212 via the 2-way distributor 214, inputs the IF band communication signal supplied from the wireless unit 212 via the 2-way distributor 214, demodulates the communication data, and outputs the signal to the communication terminal, and a test function that irregularly changes the output level to determine the output characteristics of the frequency conversion.

The radio unit 212 sends the baseband IF band communication signal sent from the MODEM 211 via the 2-way distributor 214 to the transmitter 2121. The transmitter 2121 is equipped with a BUC that frequency converts (up-converts) the IF band communication signal to an RF band signal. The transmitter 2121 power amplifies the RF band communication signal obtained by frequency converting the IF band communication signal from the MODEM 21 using the BUC, and sends it to the antenna section 30 via the RF branch/combiner 2122. The antenna section 30 sends the RF band communication signal output from the radio unit 212 toward the communication satellite SAT.

The antenna unit 30 also receives an RF band communication signal transmitted from the communication satellite SAT and sends the RF band communication signal to the radio unit 212. The radio unit 212 sends the RF band communication signal received by the antenna unit 30 from the communication satellite SAT to the receiver 2123 via the RF branch/combiner 2122. The receiver 2123 is equipped with an LNC that frequency converts (down-converts) the RF band communication signal to a baseband IF band signal. The receiver 2123 performs low-noise amplification on the RF band communication signal from the antenna unit 30, frequency converts it to an IF band communication signal using the LNC, and sends it to the MODEM 211 via the two-way distributor 214. The MODEM 211 demodulates the communication data from the input baseband IF band communication signal and sends it to the designated communication terminal indicated in the demodulated data. This enables data communication via the communication satellite SAT.

Here, in order to ensure communication quality, MODEM 211 is equipped with a test function that changes the output level at irregular intervals and determines the P1dB of the BUC in transmitter 2121. In this case, if the P1dB of the BUC being used is large compared to the applied power, when MODEM 211 increases the output level, it will send out radio waves that exceed the applied power. Therefore, in this embodiment, transmitter 2121 is equipped with a function that suppresses the output power to below the applied power.

Figure 5 is a block diagram showing the specific configuration of the transmitter 2121.

In FIG. 5, the transmitter 2121 is a transmitter that amplifies the IF band communication signal from the MODEM 211 with a predetermined gain using the first stage amplifier T1, and further attenuates the signal based on a control signal that specifies the amount of attenuation using a digital variable attenuator (DATT) T2, and outputs the signal to the BUC. The BUC is composed of a middle stage amplifier T3 and a mixer T4. The BUC amplifies the IF band communication signal from the variable attenuator T2 with a predetermined gain using the middle stage amplifier T3, mixes the IF band communication signal with a local oscillation signal LO in the mixer T4, frequency converts (up-converts) the signal to an RF band communication signal, and outputs the signal to the final stage amplifier T5. The final stage amplifier T5 power-amplifies the RF band communication signal from the BUC with a predetermined gain, and outputs the signal to the antenna unit 30 via the splitter T6. Here, the splitter T6 splits a part of the input RF band communication signal and sends it to the RF power detector T7. The RF power detector T7 receives the RF band communication signal branched by the brancher T6, periodically detects its power, and notifies the transmission output controller T8 of the power value. When the processor 213 gives the transmission output controller T8 an operation command when the communication line is connected, the attenuation amount of the variable attenuator T2 is set to the initial value.

Figure 6 is a flowchart showing the control process for limiting the output power to the requested power in the transmission output controller T8.

In FIG. 6, when an RF detection power value (hereinafter, the detection power value) Pd detected by the RF power detector T7, for example, in units of seconds, is input (step S11), the transmission output controller T8 compares the detection power value Pd with a previously registered upper allowable value (hereinafter, the upper limit threshold) Pref for the applied power, and determines whether the detection power value Pd exceeds the upper limit threshold Pref (step S12).

In step S12, if the detected power value Pd exceeds the upper threshold Pref (YES), the transmission output controller T8 increases the attenuation of the variable attenuator T2 by 0.5 dB from the initial setting value (next time, the previous setting value) (step S13), reduces the power of the IF band communication signal before upconversion, controls the detected power value Pd of the RF band communication signal after upconversion to be equal to or lower than the upper threshold Pref, and waits (1 second) for input of the next detected power value Pd (step S14).

In step S12, while the detected power value Pd is below the upper threshold Pref (NO), the transmission output controller T8 determines whether the attenuation amount of the variable attenuator T2 is the initial setting value (step S15).

If it is the initial setting value (YES) in step S15, the process waits (1 second) for the input of the next detected power value Pd (step S16) and returns to step S11.

In step S15, if the attenuation of the variable attenuator T2 is not the initial setting value (NO), the transmission output controller T8 reduces the attenuation of the variable attenuator T2 by 0.5 dB (step S17), proceeds to step S16, and thereafter gradually returns it to the initial setting value in 0.5 dB steps.

On the other hand, in step S12, if the detected power value Pd exceeds the upper threshold Pref (YES), the transmission output controller T8 increases the attenuation of the variable attenuator T2 (step S13) to reduce the power of the IF band communication signal before upconversion, and controls so that the detected power value Pd of the RF band communication signal after upconversion is equal to or lower than the upper threshold Pref. Then, the controller waits for one second (step S14) and returns to step S11.

That is, in this embodiment, the MODEM 211 and the transmitter 2121 are configured not to perform mutually coordinated control. The transmitter 2121 normally converts the IF band communication signal output from the MODEM 211 to an RF signal using the BUC, amplifies it with a predetermined gain, and transmits it to the antenna unit 30. Therefore, whether the IF output level of the MODEM 211 has changed is detected by detecting the RF output level inside the transmitter 2121. Since the IF output level of the MODEM 211 changes irregularly, the RF output level of the transmitter 2121 is constantly detected. When the RF output level of the transmitter 2121 exceeds a set upper threshold level, the attenuation amount of the digital variable attenuator T2 inside the transmitter 2121 is controlled so that the RF output level does not exceed the set threshold level.

As described above, according to the satellite communication device of this embodiment, when the MODEM 211 is equipped with a function for changing the output level at irregular intervals to obtain the P1dB of the BUC in the transmitter 2121, if it is detected that the output power of the transmitter 2121 exceeds the upper threshold for the applied power when the output level of the MODEM 211 is increased, the power of the IF band communication signal before upconversion is reduced, and the detected power value Pd of the RF band communication signal after upconversion is controlled to be equal to or lower than the upper threshold value Pref for the applied power, thereby reliably suppressing the transmission of radio waves that exceed the applied power.

Note that while the test function is being executed, the MODEM 211 does not actually measure the power of the transmitter 2121, but rather communicates with the control station to simply check the C/N ratio. In other words, when the RF communication signal output from the transmitter 2121 increases by 1 dB, the C/N ratio also increases by 1 dB where linearity is achieved. This is noted, and the C/N ratio is simply taken as the output power of the transmitter 2121 to find the point of P1dB. For this reason, even if the output power of the transmitter 2121 is suppressed while the test function of the MODEM 211 is being executed, this does not affect the processing of the test function of the MODEM 2121.

Second Example
FIG. 7 is a side plan view showing the exterior of a portable satellite communication device 40 used in the vehicle-mounted station MS1 or the portable station MS2 of the satellite communication system shown in FIG. 1 as a second embodiment, and FIG. 8 is a functional block diagram showing the communication processing system and the control processing system of the satellite communication device 40 shown in FIG. 7.

The satellite communication device 40 is a so-called VSAT device, and also functions as a satellite capture device. Its size is compact enough for the user to carry it around, and its weight is kept low. This satellite communication device 40 can be carried to a disaster site, for example, and used as an emergency communication station.

The satellite communication device 40 includes a main body unit 50 that modulates and demodulates communication signals, an azimuth angle control unit 60 that controls the antenna azimuth angle at the top of the main body unit 50, an elevation angle control unit 70 that controls the antenna elevation angle at the top of the main body unit 50, a polarization angle control unit 80 that controls the antenna polarization angle, a radio unit 90 that transmits and receives communication signals, and an antenna unit 100 that is integrated with the radio unit 90 and transmits and receives radio waves to and from the communication satellite SAT using a flat antenna.

The main body 50 has a signal processing board 51 housed in a housing 52, and a LAN connector 53 is attached to the side of the housing 52. Furthermore, a position sensor 54, a tilt sensor 55, and a memory 56 are provided inside. In addition, three or more support legs 57 are provided on the bottom surface of the housing 51.

The signal processing board 51 includes a MODEM 511 as a communication processing system, and a processor (such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit)) 512 as a control processing system.

MODEM 511 is a modulation/demodulation unit that has modulation/demodulation functions and test functions similar to those of MODEM 211 in the first embodiment. MODEM 511 is connected to LAN connector 53, modulates communication data from a communication terminal connected to LAN connector 53, generates a baseband IF band communication signal, outputs it to wireless unit 90, inputs the IF band communication signal from wireless unit 90, demodulates the communication data, and outputs it to the communication terminal.

The processor 512 is composed of an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor 512 has a function to control the signal processing of the MODEM 511 and the radio unit 90, as well as a function to execute a pointing control process S1 that controls the pointing direction of the antenna unit 100, a satellite capture process S2 that captures radio waves from the communication satellite SAT, and a line control process S3 that connects a communication line with the communication satellite SAT.

The position sensor 54 is a sensor that acquires position information (e.g., latitude and longitude) of the installation location of the satellite communication device 40, for example, by using a Global Positioning System (GPS). The position information acquired by the position sensor 54 is passed to the processor 512.

The tilt sensor 55 is a sensor that acquires tilt information including the amount of tilt of the main body 50 at the installation location. The amount of tilt can be acquired, for example, by using an acceleration sensor to detect the gravitational acceleration of the Earth at the installation location. Information such as the amount of tilt can be used as an index showing the attitude of the satellite communication device 40. The acquired tilt information is passed to the processor 512.

Memory 56 is a storage unit that stores tilt information 561 and a satellite target angle table 562. Tilt information 561 is tilt information sensed by tilt sensor 55. Satellite target angle table 562 is a table that associates terrestrial position information (e.g., latitude, longitude) sensed by position sensor 54 with satellite target angles (azimuth, elevation, polarization) of a communications satellite SAT to be captured. For example, the latitude of Sapporo, Hokkaido, is 141.4° and the longitude is 43.1°, and it is shown that at this position, the target angles (azimuth, elevation, polarization) of a certain communications satellite SAT are (151.2°, 36.1°, 10.4°).

Each of the three or more support legs 57 has a height adjustment mechanism. When installing the satellite communication device 40, the height of each of the three or more support legs 57 is adjusted so that the reference plane (the upper surface of the turntable 61 described below) is horizontal.

The azimuth control unit 60 includes a turntable 61 and an azimuth control unit 62. The azimuth control unit 62 includes an azimuth control motor controller 621 and an azimuth control motor 622.

The turntable 61 is arranged on the upper part of the housing 52 of the main body 50 so as to be freely rotatable around a rotation axis (azimuth axis or AZ (Azimuth) axis) A1. The azimuth angle control motor 622 is engaged with the turntable 61. The azimuth angle control motor control unit 621 drives and controls the azimuth angle control motor 622, thereby rotating the turntable 61 to a specified antenna azimuth angle.

The elevation angle control unit 70 includes a support column 71, a bearing 72, and an elevation angle control unit 73.

The support column 71 supports the housing of the polarization angle control unit 80 from both sides, and physically connects the main body unit 50 and the rear housing of the radio unit 90 through the polarization angle control unit 80. The bearing 72 is disposed on the upper surface of the turntable 61, and one end of the support column 71 is attached so as to be freely rotatable around a rotation axis (elevation axis or EL (Elevation) axis) A2. The elevation angle control unit 73 includes an elevation angle control motor controller 731 and an elevation angle control motor 732 inside. The rotation axis of the elevation angle control motor 732 is engaged with the bearing 72. The elevation angle control motor controller 731 drives and controls the elevation angle control motor 732, thereby rotating the support column 71 around the rotation axis A2 to a specified antenna elevation angle.

The polarization angle control unit 80 includes a coupler 81 and a polarization angle control unit 82. The coupler 81 connects the housing of the polarization angle control unit 82 to the rear surface of the integrated unit of the radio unit 90 and the antenna unit 100 so that the housing can rotate freely around a rotation axis (polarization axis or POL (Polarization) axis) A3. The polarization angle control unit 82 includes a polarization axis control motor control unit 821 and a polarization axis control motor 822 inside.

The rotating shaft of the polarization angle control motor 822 is engaged with the coupler 81. The polarization angle control motor control unit 821 drives and controls the polarization angle control motor 822, thereby allowing the coupler 81 to rotate to a specified antenna polarization angle.

The wireless section 90 includes a housing 91 that is integrated with the rear of the antenna section 100, and is housed therein a wireless unit 92, two 2-way splitters 93, a transmission/reception monitor 94, and a received radio wave intensity detector 95.

The wireless unit 92 has the same configuration as the wireless unit 212 of the first embodiment, and includes a transmitter 921, an RF branch/combiner 922, and a receiver 923. The baseband intermediate frequency band (hereinafter, IF band) signal sent from the MODEM 511 of the main body 50 is frequency-converted to a radio frequency band (hereinafter, RF band) signal by the BUC of the transmitter 921 and output to the antenna unit 100, and the RF band signal from the antenna unit 100 is frequency-converted to an IF band signal by the LNC of the receiver 923 and output to the MODEM 511. The specific configuration of the transmitter 922 is the same as that of the transmitter 2121 of the first embodiment shown in FIG. 4, so a description thereof will be omitted here.

The 2-way distributor 93, like the 2-way distributor 214 in the first embodiment, distributes the communication signal from the MODEM 511 to the wireless unit 92 and the communication signal from the wireless unit 92 to the MODEM 511 in two directions and sends them to the transmission/reception monitor 94.

The transmit/receive monitor 94 is a display that monitors and displays the power value of the signal distributed from the communication signal during transmission and reception, similar to the transmit/receive monitor 26 in the first embodiment.

The received radio wave intensity detector 95 detects the received radio wave intensity from the antenna reception signal obtained by the receiver 923 of the wireless unit 92 and sends it to the processor 512 of the main body 50.

The antenna unit 100 is a planar transmitting/receiving antenna, similar to the antenna unit 30 of the first embodiment, in which an antenna substrate 101 on which antenna elements are arranged in an array is housed in a radome 102.

The power supply terminal of the antenna board 101 is connected to the RF transmitting/receiving terminal of the radio section 90. That is, the antenna section 100 transmits an RF band communication signal output from the radio unit 92 toward the communication satellite SAT, receives an RF band communication signal transmitted from the communication satellite SAT, and transmits the RF band communication signal to the radio unit 92.

Here, the size of the antenna unit 100 is, for example, 50 cm x 50 cm. In addition to the planar antenna shown in the figure, for example, a parabolic antenna can also be used. The antenna unit 100 is designed to have a sharp directivity in order to minimize energy loss of radio waves. For this reason, the satellite communication device 40 is equipped with an azimuth angle control unit 60, an elevation angle control unit 70, and a polarization angle control unit 80 as an antenna pointing control system for accurately aligning the azimuth angle (AZ), elevation angle (EL), and polarization angle (POL) to the communication satellite SAT, which are three different axes.

The following describes how to connect a communication line to a communication satellite SAT after the satellite communication device 40 configured as above has been installed at a desired location.

When the main body unit 50 is started, the processor 512 performs a pointing control process S1 to point the antenna of the antenna unit 100 toward the communication satellite SAT, and a satellite capture process S2 to capture radio waves from the communication satellite SAT and adjust the pointing direction so that the radio wave strength is at a sufficient level. After that, a line control process S3 connects a communication line with the communication satellite SAT and communicates with the communication terminal. The processing contents of the pointing control process S1, the satellite capture process S2, and the line control process S3 will be explained in order below.

First, in the above-mentioned pointing control process S1, the direction of the communication satellite SAT is determined by referring to the satellite target angle table 562 in the memory 56 based on the position information sensed by the position sensor 54 and the tilt information stored in the memory 56, and the azimuth angle control unit 60, the elevation angle control unit 70, and the polarization angle control unit 80 are instructed to have the target azimuth angle, elevation angle, and polarization angle. The azimuth angle control unit 60 receives the target azimuth angle instruction, and drives and controls the azimuth angle control motor 622 by the azimuth angle control motor controller 621 to rotate the turntable 61 around the A1 axis, and align the antenna azimuth angle with the target azimuth angle. The elevation angle control unit 70 receives the target elevation angle instruction, and drives and controls the elevation angle control motor 732 by the elevation angle control motor controller 731 to rotate the support column 71, the end of which is attached to the bearing 72, around the rotation axis A2, and align the antenna elevation angle with the target elevation angle. Upon receiving the target polarization angle instruction, the polarization angle control unit 80 drives and controls the polarization angle control motor 822 using the polarization angle control motor controller 821 to rotate the coupler 81 around the rotation axis A3 and align the antenna polarization angle with the target polarization angle.

Here, in the above-mentioned pointing control process S1, the elevation angle of the antenna unit 100 is changed in conjunction with the rotation of the antenna unit 100 in the azimuth direction. At this time, the tilt information 561 of the satellite communication device 40 sensed by the tilt sensor 55 is referenced, and the elevation angle of the antenna unit 100 is changed so that the elevation angle of the antenna unit 100 is constant regardless of the tilt of the main body unit 50. The elevation angle of the antenna unit 100 corresponding to the rotation angle of the antenna unit 100 in the azimuth direction at this time is calculated based on the tilt information 561. In addition, the rotation speed of the elevation angle control motor 732 corresponding to the calculated elevation angle is calculated.

In other words, in the above pointing control process S1, a 360-degree search is performed in the azimuth direction, the tilt of the satellite communication device 40 is measured by the tilt sensor 55, and tilt information is obtained. Then, based on the tilt information, an equation for calculating a simple elevation axis angle (ELVSAT) is derived from a linear algebra three-dimensional rotation equation. Furthermore, this is simplified to a six-point sampling algorithm. This relaxes the restrictions on software implementation and makes it possible to reliably capture satellites using minimal resources.

In this case, the elevation (ELSAT) between the satellite communication device 40 and the satellite SAT is calculated from the position information of the satellite communication device 40, and the inclination of the satellite communication device 40 is corrected so that a 360-degree search can always be performed at the same elevation angle (ELSAT). In this way, it is possible to capture the satellite SAT without relying on a direction sensor.

Next, in the satellite capture process S2, the radio wave reception strength detected by the radio wave reception strength detector 95 of the radio unit 90 is monitored, the angle at which the reception strength of the received signal is at its peak is detected, and the azimuth angle, elevation angle, and polarization angle of the antenna unit 100 are instructed to the azimuth angle control unit 60, elevation angle control unit 70, and polarization angle control unit 80, so that radio waves from the target communications satellite SAT are captured with sufficient gain.

In addition, in the line control process S3, after the satellite capture process S2 is completed, a communication line connection instruction is sent to the MODEM 511, the transmitter 921, and the receiver 922, and a communication line is established between the communication terminal connected to the MODEM 511 and the communication satellite SAT.

In the above configuration, the communication process after the communication line is established and the control process for limiting the output power in the transmission output controller T8 of the transmitter 921 to the requested power are the same as those in the first embodiment, so their explanation will be omitted here.

That is, in this embodiment, the MODEM 511 and the transmitter 921 are configured not to control each other in cooperation. The transmitter 921 normally converts the IF band communication signal output from the MODEM 511 to an RF signal using the BUC, amplifies it with a predetermined gain, and sends it to the antenna unit 100. Therefore, whether the IF output level of the MODEM 511 has changed is detected by detecting the RF output level inside the transmitter 921. Since the IF output level of the MODEM 511 changes irregularly, the RF output level of the transmitter 921 is constantly detected. When the RF output level of the transmitter 921 exceeds a set upper threshold level, the attenuation amount of the digital variable attenuator T2 inside the transmitter 921 is controlled so that the RF output level does not exceed the set threshold level.

As described above, according to the satellite communication device 40 of this embodiment, when the MODEM 511 is equipped with a function for changing the output level at irregular intervals to obtain the P1dB of the BUC in the transmitter 921, if it is detected that the output power of the transmitter 921 exceeds the upper limit threshold for the applied power when the output level of the MODEM 511 is increased, the power of the IF band communication signal before upconversion is reduced, and the detected power value Pd of the RF band communication signal after upconversion is controlled to be equal to or lower than the upper limit threshold value Pref for the applied power, thereby reliably suppressing the transmission of radio waves that exceed the applied power.

In this embodiment, too, while the MODEM 511 is executing the test function, it does not accurately measure the power of the transmitter 921, but rather communicates with the control station to simply check the C/N ratio. In other words, when the RF communication signal output from the transmitter 921 increases by 1 dB, the C/N ratio also increases by 1 dB where linearity is achieved. This is noted, and the C/N ratio is simply taken as the output power of the transmitter 921, and the point of P1dB is found. For this reason, even if the output power of the transmitter 921 is suppressed while the MODEM 511 is executing the test function, this does not affect the processing of the MODEM 511's test function.

The present invention is not limited to the above-described embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

SAT...communication satellite, FS1-FSn...fixed station, MS1...vehicle station, MS2...portable station,
10...Satellite communication device (VSAT device),
20...Main body, 21...Signal processing board, 211...MODEM, 212...Radio unit, 2121...Transmitter, T1...First stage amplifier, T2...Variable attenuator (DATT), T3...Middle stage amplifier, T4...Mixer, T5...Final stage amplifier, T6...Split, T7...RF power detector, T8...Transmission output controller, 2122...RF splitter/combiner, 2123...Receiver, 213...Processor, 214...2-way splitter, 215...Filter, 216...AC/DC converter, 22...Housing, 23...Power switch, 24...Power connector, 25...LAN connector, 26...Transmission/reception monitor,
30: antenna unit, 31: antenna board, 32: radome, 200: Wi-Fi router, 201: notebook PC, 202: VoIP phone, 203: tablet,
40: satellite communication device (VSAT device), 50: main body, 51: signal processing board, 511: MODEM, 512: processor, S1: pointing control processing, S2: satellite capture processing, S3: line control processing, 52: housing, 53: LAN connector, 54: position sensor, 55: tilt sensor, 56: memory, 561: tilt information, 562: satellite target angle table, 57: support leg,
60: Azimuth angle control section, 61: Turntable, 62: Azimuth angle control unit, 621: Azimuth angle control motor controller, 622: Azimuth angle control motor,
70: elevation angle control section, 71: support column, 72: bearing, 73: elevation angle control unit, 731: elevation angle control motor controller, 732: elevation angle control motor,
80: polarization angle control unit, 81: coupler, 82: polarization angle control unit, 821: polarization axis control motor control unit, 822: polarization axis control motor,
90: radio section, 91: housing, 92: radio unit, 921: transmitter, 922: RF branch/combiner, 923: receiver, 93: 2-way distributor, 94: transmission/reception monitor, 95: received radio wave intensity detector,
100: antenna portion, 101: antenna substrate, 102: radome.

Claims (3)

a modem having a modulation/demodulation function for modulating communication data from a communication terminal into an intermediate frequency band communication signal, transmitting and outputting the signal, and demodulating the intermediate frequency band communication signal obtained by receiving radio waves from a communication satellite and outputting the signal to the communication terminal, and a test function for irregularly changing the output level of the communication signal to be transmitted and outputted, to determine transmission output characteristics;
a variable attenuator for attenuating an input level of the upconverter by an attenuation amount according to a command, an amplifier for power-amplifying and outputting the communication signal converted to the radio frequency band by the upconverter, a detector for detecting a power value of the output power-amplified by the amplifier, and an output controller for comparing the detected power value detected by the detector with a power upper limit threshold, and when the detected power value exceeds the power upper limit threshold, for instructing the variable attenuator to increase the attenuation amount stepwise from an initial setting value until the detected power value falls below the power upper limit threshold, and for instructing the variable attenuator to return the attenuation amount stepwise to the initial setting value after the detected power value falls below the power upper limit threshold;
an antenna that transmits a radio frequency band communication signal output from the transmitter to a communication satellite and receives a radio frequency band communication signal from the communication satellite;
a receiver for amplifying the radio frequency communication signal received by said antenna, converting it to an intermediate frequency band, and outputting it to said modem. A transmitter for use in a satellite communication device using a modem having a modulation/demodulation function for modulating communication data from a communication terminal into an intermediate frequency band communication signal, transmitting and outputting the signal, and demodulating the intermediate frequency band communication signal obtained by receiving radio waves from a communication satellite and outputting the signal to the communication terminal, and a test function for irregularly changing the output level of the communication signal to be transmitted and outputted,
an up-converter for converting an intermediate frequency band communication signal output from the modem into a radio frequency band;
a variable attenuator for attenuating the input level of the up-converter by an attenuation amount according to a command;
an amplifier that amplifies the power of the communication signal converted into a radio frequency band by the upconverter and outputs the amplified signal;
a detector for detecting a power value of the output amplified by the amplifier;
and an output controller that compares the detected power value detected by the detector with a power upper threshold, and when the detected power value exceeds the power upper threshold, instructs the variable attenuator to increase the attenuation amount in steps by a constant amount from an initial setting value until the detected power value falls below the power upper threshold, and after the detected power value falls below the power upper threshold, instructs the variable attenuator to return the attenuation amount to the initial setting value in steps by a constant amount . A transmission method for a transmitter used in a satellite communication device using a modem having a modulation/demodulation function for modulating communication data from a communication terminal into an intermediate frequency band communication signal, transmitting and outputting the signal, and demodulating the intermediate frequency band communication signal obtained by receiving radio waves from a communication satellite and outputting the signal to the communication terminal, and a test function for irregularly changing the output level of the communication signal to determine transmission output characteristics, comprising:
The transmitter includes:
a frequency conversion step of converting an intermediate frequency band communication signal output from the modem into a radio frequency band by an up-converter;
an attenuation step of attenuating an input level of an intermediate frequency band communication signal from said modem by a variable attenuator according to an instruction;
an amplifying step of amplifying the power of the communication signal converted into the radio frequency band in the frequency converting step by an amplifier and outputting the amplified communication signal;
a detection step of detecting a power value of the output amplified by the amplifier by a detector;
and an output control step of: comparing, by an output controller, the detected power value detected by the detector with a power upper threshold; and, when the detected power value exceeds the power upper threshold, instructing the variable attenuator to increase the attenuation amount in steps by a constant amount from an initial setting value until the detected power value falls below the power upper threshold; and, after the detected power value falls below the power upper threshold, instructing the variable attenuator to return the attenuation amount to the initial setting value in steps by a constant amount .

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