JP7395315B2 - Satellite communication device and transmission level control method - Google Patents

Description

Embodiments of the present invention relate to a satellite communication device and a transmission level control method.

Various services such as SNG (Satellite News Gathering) are provided using communication satellites (CS) and broadcasting satellites (BS). This type of satellite relays video/audio signals transmitted via uplink from a ground station or the like in a geostationary orbit, and retransmits them to the ground via downlink. The satellite communicates with equipment on the ground using Ku-band (14GHz/12GHz) radio waves. Since the Ku band is greatly attenuated by raindrops, there is a risk that the satellite link will be disconnected due to clouds or rain. To deal with this, there is a technology called TPC (Transmission Power Control).

TPC is a technology that calculates the amount of rainfall attenuation according to the strength of the reception level on the ground of a reference signal (beacon signal, etc.) transmitted from a satellite with constant power, and corrects the uplink transmission level accordingly. It is. By stabilizing the input level to the satellite transponder using TPC, the downlink reception level on the ground side can also be stabilized.

Japanese Patent Application Publication No. 9-46286 Japanese Patent Application Publication No. 4-275726 Japanese Patent Application Publication No. 5-252084

In recent satellite communication systems, multilevel amplitude phase modulation methods such as 64APSK (Amplitude Phase Shift Keying) and 32APSK are used. Although these systems have a high transmission bit rate, they are vulnerable to rapid fluctuations in the reception level because the amplitude and phase distance between symbols are close. In particular, when the amount of correction of the transmission level by TPC becomes large due to sudden changes in the weather, etc., the demodulation function on the receiving side may not be able to follow the sudden change in signal level, and instantaneous interruption of reception may occur. To avoid this, on the transmitting side, the period of TPC correction is relatively long to suppress sudden changes in the transmission level.

However, slowing down the change in transmission level becomes a problem when it is necessary to reduce the transmission level. That is, if the weather improves rapidly. In such a case, if the increased transmission level cannot be suppressed promptly, the uplink transmission level will exceed the default value. When radio waves with a strength higher than the default value are transmitted to a satellite, an excessive burden is placed on the satellite (transponder, etc.), which can cause performance deterioration of the satellite or serious failure. It is required to be able to suppress the transmission level rapidly.

As described above, satellite communication systems employing TPC have conflicting demands regarding transmission level control, and there is a demand for new technology that can satisfy these demands.
Therefore, it is an object of the present invention to provide a satellite communication device and a transmission level control method that have increased resistance to weather conditions.

According to the embodiment, the satellite communication device includes a modulation section, a transmission signal generation section, a level setting section, a control section, a detection section, and a calculation section. The modulator generates a multilevel modulation signal from the encoded transmission signal. The transmission signal generation unit generates a transmission signal to be transmitted uplink to the artificial satellite from the multilevel modulation signal. The level setting section sets the transmission level of the transmission signal based on the control amount. The control unit repeatedly controls the control amount to the target value in a first period. The detection unit repeatedly detects the reception level of the beacon signal received in the downlink from the artificial satellite. The calculation unit repeatedly calculates the target value in a second period shorter than the first period based on the detected reception level.

FIG. 1 is a diagram showing an example of a satellite communication system to which a satellite communication device according to an embodiment can be applied. FIG. 2 is a conceptual diagram for explaining that the communication environment is affected by weather conditions. FIG. 3 is a conceptual diagram for explaining that a beacon signal is transmitted from the satellite 100. FIG. 4 is a functional block diagram showing an example of a satellite communication device 200 provided in the base station 20. FIG. 5 is a block diagram illustrating an example of data stored in memory 70 and functions implemented by processor 60. FIG. 6 is a diagram showing an example of a setting screen displayed on the LCD panel 90a of the operation unit 90. FIG. 7 is a flowchart illustrating an example of a processing procedure of the satellite communication device 200 according to the embodiment. FIG. 8A is a diagram illustrating an example of the reception level of a beacon signal observed during clear weather. FIG. 8B is a diagram illustrating an example of the reception level of a beacon signal observed when the weather is bad. FIG. 8C is a diagram illustrating an example of the reception level of a beacon signal observed when the weather improves.

A ground-side device (earth station) of a satellite communication system is equipped with TPC equipment or a TPC function to compensate for rainfall attenuation in uplinks. TPC calculates the amount of rain attenuation in the downlink from the reception strength of a signal (such as a beacon signal) transmitted at a constant level from a satellite. Then, based on this value, the amount of rain attenuation in the uplink is determined, and the amount of correction of the transmission power is calculated.

While there are devices that implement the TPC function with dedicated equipment (hardware), there are also cases where TPC is implemented only with software algorithms. This type of device calculates its own transmission level based on the reception level information of the beacon signal, and applies the transmission level to the transmission signal generation unit including the frequency conversion device, thereby performing TPC without the need for dedicated equipment. Realize.

In recent years, satellite communication systems have frequently used multilevel amplitude phase modulation such as 64APSK and 32APSK due to the needs for high image quality, high compression, and narrowband transmission, making them vulnerable to sudden fluctuations in reception levels. I have to say that I am. In addition, with the recent intensification of weather (so-called torrential rain), the possibility of block noise and momentary interruptions is increasing. In particular, in applications such as SNG that handle news materials, noise mixed into the image can ruin the image, and the communication may have to be restarted from the beginning. Techniques that can solve these problems will be described below.

FIG. 1 is a diagram showing an example of a satellite communication system to which a satellite communication device according to an embodiment can be applied. Satellite communication systems include multiple earth stations that communicate with each other via artificial satellites (satellites) in geostationary orbit. This type of system can, for example, transmit live images of a disaster site from a satellite communication device installed at the site and receive them simultaneously at multiple earth stations such as prefectural capitals. This allows the disaster situation to be known quickly and accurately.

In FIG. 1, a signal transmitted uplink from base station 20 to satellite 100 is transmitted downlink from satellite 100 to the ground via satellite 100. The signals relayed by the satellite 100 are received by the vehicle-mounted station 10 and the receiving stations 30 (31 to 3N) on the ground. The in-vehicle station 10 is dispatched to, for example, a disaster site. The base station 20 is installed at a prefectural capital, etc., and the receiving station 30 is installed at a mountainous area, local government, etc. All of the vehicle-mounted station 10, base station 20, and receiving station 30 can include a satellite communication device. In the embodiment, a satellite communication device provided in the base station 20 will be described.

As shown in FIG. 2, when clouds form above the base station 20, the communication link between the base station 20 and the satellite 100 is physically obstructed, and the uplink signal from the base station 20 becomes insufficient. No longer reaches satellite 100 in level. Correspondingly, the power level of the downlink signal also decreases, and there is a possibility that a reception failure will occur at the vehicle-mounted station 10 and the receiving station 30. In order to prevent reception interference, the base station 20 corrects the transmission power by the amount of rain attenuation of the uplink signal and transmits the uplink signal.

As shown in FIG. 3, satellite 100 continuously transmits beacon signals downlink at a defined level. By detecting and constantly monitoring the reception level of this beacon signal, the ground station can grasp the amount of rainfall attenuation between the ground station and the satellite 100. Based on the results, the TPC controls the transmission level of uplink signals.

FIG. 4 is a functional block diagram showing an example of a satellite communication device 200 provided in the base station 20. Satellite communication device 200 includes a transmitter 40, a receiver 50, a processor 60, a memory 70, and an internal bus 80 connecting these. An operating section 90 as a user interface is connected to the internal bus 80, and each function of the satellite communication device 200 can be set from the operating section 90.

The processor 60 is, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and the memory 70 is implemented as, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), or the like. That is, the satellite communication device 200 is a computer equipped with a processor and a memory as hardware.

In FIG. 4, MPEG2-TS (Moving Picture Experts Group 2 - Transport Stream) and H. A transmission signal containing video, audio, data material, etc. encoded by a coding method such as H.265/HEVC (High Efficiency Video Coding) is input to a modulation unit (MOD) 45 of the transmission unit 40 . The modulator 45 generates a multilevel modulation signal such as N-APSK from this transmission signal. Here, N is typically 16, 32, 64, etc., but modulation systems with other multi-level numbers N are also possible. It is also possible to use a method such as QAM (Quadrature Amplitude Modulation).

The multilevel modulated signal is input to an upconverter (U/C) 44 and converted to a frequency for uplink transmission to the satellite 100. This generates a transmission signal.
Here, the up converter 44 includes an attenuator (ATT) 44a. The attenuator 44a sets the transmission level of the transmission signal based on the control amount (TPC correction value (a)) given from the processor 60. The transmission signal is input from the upconverter 44 to the antenna device 41 via a power amplification section (SSPA: Solid State Power Amplifier) 43 and a waveguide switching section 42 . The waveguide switching section 42 is provided so that the antenna device 41 can be shared by a plurality of transmitting sections 40, and can be omitted if there is only one system of transmitting sections 40.

The antenna device 41 includes a FEED 41a that functions as a circulator and an antenna section 41b. The transmission signal from the power amplification section 43 is transmitted via the FEED 41a from the antenna section 41b to the satellite 100 in an uplink manner.

On the other hand, a signal arriving from the satellite 100 via a downlink is received by the antenna section 41b and input to the receiving section 50 via the FEED 41a. This signal is amplified by a reception amplifier (LNC: Low Noise Converter) 51 of the reception section 50, and then distributed to a beacon receiver 53 and a reception device 54 by a distributor 52. The receiving device 54 receives and demodulates various data from the downlink signal.
Beacon receiver 53 constantly monitors the beacon signal from satellite 100 and notifies processor 60 of the beacon signal reception level (b) of the beacon signal.

FIG. 5 is a block diagram illustrating an example of data stored in memory 70 and functions implemented by processor 60.

The processor 60 includes a level setting function 60a, a control function 60b, a detection function 60c, a calculation function 60d, and a set value variable function 60e as processing functions according to the embodiment. These functions are realized by the processor 60 executing instructions written in a program 70a stored in the memory 70. That is, the processor 60 functions as a level setting section, a control section, a detection section, a calculation section, and a set value variable section according to the program 70a.

The level setting function 60a is a function for setting/registering a reference level during clear weather (attenuation amount 0) when operating the TPC. For example, when the beacon level during clear weather is -60 dBm, 20 dB is set as the attenuation reference value (TPC reference value) of the attenuator, and 1.25 is set as the TPC correction coefficient.

The control function 60b controls the attenuator 44a by repeatedly applying the TPC correction value (a) to a separately calculated target value at a preset stability period period (first period). The setting value for the stable period is inputted from the operation unit 90 using a user interface as shown in FIG. 6, for example, and is stored in the memory 70 as the stable period setting value 70b.

The user interface in FIG. 6 is displayed on, for example, an LCD (Liquid Crystal Display) panel 90a of the operation unit 90. The LCD panel 90a displays areas for setting the calculation period, the number of moving averages, the minimum level change amount, and the stable period. Each area is associated with an arrow mark (black △/black ▽), and the numerical value can be increased or decreased by touching the arrow mark. In the embodiment, the stable period setting value is set to 2000 [msec: milliseconds].

The detection function 60c (FIG. 5) of the processor 60 repeatedly detects the reception level (b) of the beacon signal received on the downlink from the satellite 100. The detected value is stored in memory 70 as reception level 70c.

The calculation function 60d calculates the TPC correction value (a) in a calculation cycle (second cycle) shorter than the stable period setting value (first cycle) based on the reception level (b) detected by the detection function 60c. Iteratively calculates the target value. This calculation cycle setting value is input from the operation unit 90 using the LCD screen of FIG. 6, and is stored in the memory 70 as the calculation cycle setting value 70d. In the embodiment, the calculation cycle setting value is set to 800 [msec].
Here, the calculation function 60d calculates the target value based on the moving average value of the reception level (b) over a preset number of samples.

The setting value variable function 60e is a user interface function group for varying various setting values. That is, the setting value variable function 60e displays, on the LCD panel 90a, a user interface for variably setting either or both of the stable period and the calculation cycle. Further, the set value variable function 60e displays on the LCD panel 90a a user interface for setting steps (amounts of change) when controlling the TPC correction value (a) as a control amount to a target value.

As shown in FIG. 6, an area for setting the minimum level change amount is provided on the LCD panel 90a. The set value of the minimum level change amount is input from the operation unit 90 using the LCD screen of FIG. 6, and is stored in the memory 70 as the minimum level change amount set value 70e. In the embodiment, the minimum level change amount setting value is set to 0.5 [dB: decibel]. That is, the TPC correction value (a) is changed in 0.5 dB increments to bring it closer to the target value.

Further, the set value variable function 60e controls the LCD panel 90a to create a user interface for setting the number of samples (moving average number) of the reception level (b) for calculating the target value.

As shown in FIG. 6, an area for setting the moving average number of times is provided on the LCD panel 90a. The set value of the moving average number of times is input from the operation unit 90 using the LCD screen of FIG. 6, and is stored in the memory 70 as the moving average number of times set value 70f. In the embodiment, the moving average number of times setting value is set to 5 [times]. That is, the target value of the TPC correction value (a) is calculated based on the average value of five consecutive samples in time series of the reception level (b) of the beacon signal.

Here, the stable period (first period) and the minimum level change amount are determined on the receiving side of the multi-level modulation signal based on the modulation level N of the multi-level modulation signal generated by the modulation section 45. It is preferable that the settings be made to reduce errors in In other words, by increasing the stability period as the multilevel number N increases, it is possible to suppress sudden changes in TPC correction and reduce shock on the receiving side. The same effect can be obtained because the change in TPC correction can be made gentler by making the minimum level change smaller as the multilevel number N increases. Next, the operation of the above configuration will be explained.

FIG. 7 is a flowchart illustrating an example of a processing procedure of the satellite communication device 200 according to the embodiment. In FIG. 7, the satellite communication device 200 repeatedly acquires the reception level (beacon level) of the received beacon signal (block B1). As a result, a time series of reception levels is obtained as shown in FIGS. 8A to 8C. FIG. 8A shows an example of a beacon level during clear weather, and for example, a beacon level of −60 [dBm] is stably obtained. Here, it is assumed that the period of observation of the beacon level is the calculation period of the control target value, and the number of samples is greater than the number of moving averages. That is, in the embodiment, the beacon level is detected every 800 [msec], and 4 seconds are required for the first time to acquire 5 samples, and after that, the 5 samples are updated at an observation cycle of 800 [msec]. I'll do what I do.

Next, the satellite communication device 200 executes processing to calculate a corrected target value (block B2). In block B2, the satellite communication device 200 calculates the moving average value of the beacon level over five times. For example, in the state of FIG. 8A, the moving average value is -60 dBm, and the maximum beacon level (clear sky level) is obtained. Therefore, the maximum attenuation amount (for example, 20 dB) is set in the attenuator 44a. This 20 dB is the correction target value.

FIG. 8B shows an example of beacon levels observed as the weather worsens. FIG. 8B shows how the beacon level gradually decreases, and for example, a moving average value of -64.0 dBm is calculated. In this case, it is necessary to weaken the attenuation at the attenuator 44a to increase the output level of the transmission signal (attenuation amount DOWN).

Since the beacon level has decreased by 4 dBm from the clear sky level, multiply this by the predetermined coefficient of 1.25 (4 x 1.25 = 5) and subtract this value from 20 dB to obtain the target value of 15.0 dB. . That is, in the case of FIG. 8B, 15.0 dB is calculated as the target value of the attenuation amount of the attenuator 44a. If the moving average value decreases to −70.0 dBm, 20−{(70−60)×1.25}=7.5 dB is calculated as the target value of the attenuation amount of the attenuator 44a. This target value is calculated and updated at intervals of, for example, 800 msec.

Here, the coefficient 1.25 will be explained. That is, the attenuation amount of the beacon level and the attenuation amount of the attenuator 44a usually have different values. This is because the slope of attenuation differs depending on the frequency. For example, it is known that the amount of deterioration calculated using a beacon signal received in the 12 GHz band is corrected approximately 1.25 times in the 14 GHz band, which is the transmission band. In this way, conversion of the amount of attenuation due to the difference in signal attenuation characteristics between the reception band and the transmission band is processed by, for example, the level setting function 60a.

Note that there is a certain relationship between the moving average value and the attenuation amount, and for example, the moving average value and the attenuation amount are stored in the memory 70 in advance in the form of a table. In other words, as the moving average value decreases, the attenuation amount is also fed back in a direction that decreases (output level increases). This correspondence relationship can be calculated in advance by, for example, simulation.

Next, the satellite communication device 200 executes processing to control the TPC level (block B3). This block includes a process of controlling the attenuation amount of the attenuator 44a to the calculated target value, and a process of setting the transmission level of the uplink transmission signal to the satellite 100 based on the attenuation amount of the attenuator 44a. .

That is, as an example, the satellite communication device 200 gradually changes the attenuation amount of the attenuator 44a from 20.0 dB to 15.0 dB in steps of 0.5 dB every 2000 msec. Here, 2000 msec is the stable period shown in FIG. 6, and 0.5 dB is the minimum level change amount.

FIG. 8C shows an example of a beacon level observed as the weather improves. FIG. 8C shows how the beacon level gradually returns to its original level, and for example, a moving average value of -62.0 dBm is calculated. In this case, it is necessary to immediately increase the attenuation at the attenuator 44a so that the output level of the transmission signal does not exceed a predetermined value (attenuation amount UP). In the case of FIG. 8C, 20-{(62-60)×1.25}=17.5 dB is calculated as the target value of the attenuation amount of the attenuator 44a.

In the process from the state shown in FIG. 8B to the state shown in FIG. 8C, the target value of the attenuation amount of the attenuator 44a changes from 15.0 dB to 17.5 dB. Here, too, the satellite communication device 200 gradually changes the attenuation amount of the attenuator 44a from 15.0 dB to 17.5 dB in steps of 0.5 dB every 2000 msec. Then, the procedures of blocks B1 to B3 are repeatedly executed.

As described above, in this embodiment, the attenuation amount of the attenuator 44a is controlled to the control target value relatively slowly and in small steps in the first cycle. By doing this, even when the modulation level of the multilevel modulation signal increases, it is possible to soften the change in signal level, reduce the shock on the receiving side, and suppress the occurrence of transmission errors.

On the other hand, the calculation of the control target value itself is performed faster than the first cycle and is constantly updated. As a guideline, if the attenuation amount is controlled at a cycle of 2000 msec, the target value is calculated repeatedly at a cycle of 800 msec. This makes it possible to follow rapid changes in weather at a sufficiently fast speed and prevent the uplink transmission level from exceeding a predetermined value.

In the existing technology, the algorithm design is such that negative feedback takes effect only when the uplink transmission level exceeds a predetermined value. Therefore, for example, a transmission signal higher than a specified level is transmitted to the satellite 100 for several seconds, which may place an excessive load on the satellite 100.

In contrast, according to the embodiment, the corrected target value for TPC is calculated at high speed using a moving average value and constantly updated. This makes it possible to improve the ability to follow sudden changes in weather. In addition, regarding control to the control target value, by ensuring the minimum amount of level change and stable period that can withstand the multi-level modulation method, it is possible to provide resistance to steep level fluctuations in the received signal. Become.

In other words, according to the embodiment, it is possible to suppress sudden changes in TPC correction and to quickly respond to changes in the weather. Therefore, even with multilevel amplitude phase modulation, stable satellite communication is possible without momentary interruptions. In addition, it is expected that the algorithm will be applied even if multivalue technology advances further in the future. Furthermore, safe satellite communications will be possible even in the face of sudden changes in weather such as torrential rain. By applying the algorithm of the embodiment, it becomes possible to respond to local weather characteristics.
For these reasons, it is possible to provide a satellite communication device and a transmission level control method that have increased resistance to weather conditions.

Note that this invention is not limited to the above embodiments. For example, in the above description, an example was shown in which the functions according to the embodiment are implemented in the base station 20. Instead of this, it is of course possible to implement the functional blocks shown in FIG. 5 in the vehicle-mounted station 10 or the receiving station 30.

Furthermore, it goes without saying that the target value calculation period (800 msec), the number of moving averages (5 times), the minimum level change amount (0.5 dB), and the stable period (2 seconds) can all be set to different values. It flexibly responds to various conditions such as system hardware, multilevel modulation method, weather conditions, etc., and can be applied under a wide range of conditions. For example, if the processor 60 has sufficient capacity, the target value calculation cycle may be shortened to 400 msec, 200 msec, or the like. Furthermore, these values may be set in advance as defaults according to the modulation level N.

Furthermore, it is also possible to switch and set the modulation level N and modulation method even during system operation. In this case, it is preferable for operation to switch the modulation level N and the modulation method between the first news material and the second news material, which are different from each other.

Although an embodiment of the invention has been described, this embodiment is presented by way of example and is not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 10... Vehicle-mounted station, 20... Base station, 30... Receiving station, 40... Transmitting section, 41... Antenna device, 41a... FEED, 41b... Antenna section, 42... Waveguide switching section, 43... Power amplifying section, 44... Up converter, 44a... Attenuator, 45... Modulation unit, 50... Receiving unit, 51... LNC, 52... Distributor, 53... Beacon receiver, 54... Receiving device, 60... Processor, 60a... Level setting function, 60b... Control function , 60c...Detection function, 60d...Calculation function, 60e...Set value variable function, 70...Memory, 70a...Program, 70b...Stable period setting value, 70c...Reception level, 70d...Calculation cycle setting value, 70e...Minimum level change 70f...Moving average frequency setting value, 80...Internal bus, 90...Operation unit, 90a...LCD panel, 100...Satellite, 200...Satellite communication device.

Claims (11)

a modulation unit that generates a multilevel modulation signal from the encoded transmission signal;
a transmission signal generation unit that generates a transmission signal to be transmitted uplink to an artificial satellite from the multilevel modulation signal;
a level setting unit that sets a transmission level of the transmission signal based on a control amount;
a control unit that repeatedly controls the control amount to a target value in a first cycle;
a detection unit that repeatedly detects the reception level of a beacon signal received in downlink from the artificial satellite;
a calculation unit that repeatedly calculates the target value in a second period shorter than the first period based on the detected reception level ,
The first period is set to be longer as the modulation level increases, based on the modulation level of the multilevel modulation signal, in order to reduce errors on the receiving side of the multilevel modulation signal. Satellite communication equipment. The satellite communication device according to claim 1, further comprising a user interface for variably setting at least one of the first cycle and the second cycle. The satellite communication device according to claim 1, wherein the control unit controls the control amount to the target value in each of the first cycles by a variable amount of change . The variation amount is set to be smaller as the modulation level increases, based on the modulation level of the multilevel modulation signal, in order to reduce errors on the receiving side of the multilevel modulation signal. 3. The satellite communication device according to 3 . The satellite communication device according to claim 4, further comprising a user interface for variably setting the amount of change. The satellite communication device according to claim 1, wherein the calculation unit calculates the target value based on a moving average value of the reception level over a variable number of samples . The satellite communication device according to claim 6, further comprising a user interface for variably setting the number of samples . a step of setting a transmission level of a transmission signal generated from a multilevel modulation signal and transmitted in uplink to an artificial satellite based on a control amount;
a process of repeatedly controlling the control amount to a target value in a first cycle;
a step of repeatedly detecting the reception level of a beacon signal received in downlink from the artificial satellite;
a step of repeatedly calculating the target value in a second cycle shorter than the first cycle based on the detected reception level;
Equipped with
The first period is set to be longer as the modulation level increases, based on the modulation level of the multilevel modulation signal, in order to reduce errors on the receiving side of the multilevel modulation signal. Transmission level control method. 9. The transmission level control method according to claim 8, wherein the control amount is a variable amount of change and is controlled to the target value in each of the first cycles . The variation amount is set to be smaller as the modulation level increases, based on the modulation level of the multilevel modulation signal, in order to reduce errors on the receiving side of the multilevel modulation signal. 9. The transmission level control method according to 9. 9. The transmission level control method according to claim 8, wherein the target value is calculated based on a moving average value of the reception level over a variable number of samples .