JP5283184B2 - Satellite communication system and frequency characteristic correction method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a satellite communication system and its frequency characteristic correction method which can reduce bit error, while being able to avoid change of signal strength resulting from radio wave interference between a satellite mounting antenna and a ground antenna. <P>SOLUTION: The satellite communication system 100 is provided with a satellite 1 which revolves around the earth, a ground station 2 installed on a ground, and communications are performed between the artificial satellite 1 and the ground station 2. Even if the reception strength in the ground station 2 is changed, a correction circuit (a digital filter) corrects so as to make the frequency characteristic uniform in the occupied frequency band of the reception signal power in the ground station 2, by interposing a mounting device loaded on the artificial satellite 1, in a radio wave radiation zone from the satellite mounting antenna 5 loaded on the artificial satellite 1. The correction circuit is mounted in either or both a receiver 9 of the ground station 2 or a transmitter 4 of the artificial satellite 1. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a satellite communication system used for communication between an artificial satellite and a ground station and a frequency characteristic correction method thereof.

  For example, as shown in FIG. 20, the satellite communication system includes a receiving station (ground station) installed on the earth 200 with an artificial satellite 201 that orbits the earth center P of the earth 200 around the orbit R. ) Communications are performed by propagating radio waves between the terrestrial antenna 203 and the satellite-mounted antenna 204 of the artificial satellite 201 while tracking with the terrestrial antenna (parabolic antenna or the like) 203 of 202.

  When the artificial satellite 201 is operated in a solar synchronous orbit, a mornia orbit, etc., its orbit position changes as shown at times t1, t2, t3,... Shown in FIG. Therefore, the receiving station 202 controls the elevation angle and azimuth angle of the ground antenna 203 so that the ground antenna 203 always faces the satellite-mounted antenna 204 of the artificial satellite 201.

  As a control method for directly facing the ground antenna 203 to the artificial satellite 201, a method (program for predicting the position of the artificial satellite 201 at a certain time in advance by some method and controlling the direction of the ground antenna 203 to the predicted position. Tracking) and a method of receiving the signal transmitted from the artificial satellite 201 by the ground antenna 203 and controlling the elevation angle and the azimuth angle of the ground antenna 203 so that the intensity of the received signal is maximized.

  The automatic tracking method includes a step track method, a conical scan method, and the like that are performed by using the intensity of the received signal received by the ground antenna 203, and these methods are adopted for artificial satellites that are operated in the solar synchronous orbit. . In these systems, the received signal power is changed by a method of changing the elevation angle, azimuth angle, or horn attachment angle of the beam of the ground antenna 203 (antenna scan), and the changed elevation angle, azimuth angle, or horn attachment is changed. By repeating the directing of the terrestrial antenna 203 to the elevation angle, azimuth angle, or horn mounting angle at which the received signal power is maximized from the change in the received signal power with respect to the angle, the terrestrial antenna 203 faces the artificial satellite 201. Yes.

  In addition, satellite-mounted antennas that are controlled based on other tracking methods have also been proposed, as seen from artificial satellites in all time zones during orbiting based on the boresight direction on the orbit already known in advance. A shaped beam former that calculates a beam shape factor that covers the whole earth area in advance and shapes the antenna beam into a beam shape that covers the whole earth area as viewed from the artificial satellite based on the beam shape factor, and the shaped beam A beam antenna that radiates the beam from the former toward the earth is provided so as not to cause a blind spot in the cover area viewed from the artificial satellite (see, for example, Patent Document 1).

JP 2005-269384 A

However, the conventional antenna control method has the following problems.
(1) Changes in received signal strength due to changes in signal strength due to rainfall, changes in signal strength due to the influence of radio wave shielding between the satellite 201 and the ground antenna 203, etc. If a change in signal strength caused by a cause other than the mounting angle is included, the ground antenna 203 cannot be controlled to face the artificial satellite 201 correctly. For this reason, it is necessary to remove as much as possible the change in signal intensity that occurs outside the elevation angle, azimuth angle, or horn attachment angle.

(2) Also, in recent years, the physical shape of satellite-mounted devices mounted on artificial satellites has become complicated, and therefore, when countermeasures for signal interference with satellite-mounted devices are not sufficient, the space between the satellite and the ground antenna 203 is not sufficient. Some of the satellite-mounted equipment that intervenes in the radio wave may cause radio wave interference. For example, as shown in FIG. 21A, the satellite-mounted device 206 is in a positional relationship between the satellite-mounted antenna 204 and the ground antenna 203, or as shown in FIG. When the satellite-mounted device 206 enters the radiation range of the mounted antenna 204 to the ground antenna 203, the beam pattern of the satellite-mounted antenna 204 becomes different from that measured by the antenna alone. This phenomenon occurs when the beam directing center direction of the satellite-mounted antenna 204 is changed, or by signal interference between the satellite-mounted device 206 and the satellite-mounted antenna 204 having a complicated shape.

(3) When the data rate transmitted from the artificial satellite to the ground exceeds 100 to 300 Mbit / sec, the occupied frequency band for transmitting the data becomes several hundred MHz or more. In order to communicate data between an artificial satellite and a terrestrial antenna without error, it is necessary to use an antenna having uniform frequency characteristics in the occupied band of radio waves used for the communication. However, if the problem as shown in FIG. 21 occurs, the frequency characteristics in the occupied band of the radio wave used for communication cannot be kept uniform, so that the data received by the ground antenna has more bit errors than usual. The problem of being included arises.

  Accordingly, an object of the present invention is to prevent changes in signal strength due to radio wave interference between the satellite mounted antenna and the ground antenna by making the frequency characteristics of the received signal uniform. Another object of the present invention is to provide a satellite communication system capable of reducing bit errors and a frequency characteristic correcting method thereof.

  To achieve the above object, the present invention according to claim 1 is a satellite communication system that performs communication between an artificial satellite orbiting the earth and a ground station installed on the earth. Even if the reception intensity at the ground station changes due to the installation of the equipment mounted on the artificial satellite in the radiation area of the radio wave from the satellite antenna, the occupied frequency band of the received signal power received at the ground station Satellite communication characterized in that a correction circuit for correcting a reception signal of the ground station or a transmission signal of the artificial satellite so that frequency characteristics are uniform is provided in at least one of the ground station and the artificial satellite Provide a system.

  According to a second aspect of the present invention, in the satellite communication system according to the first aspect, the correction circuit is a digital filter that makes the frequency characteristic uniform by using a variable value of an angle of the antenna mounted on the satellite as a parameter. It is provided in the receiver of the ground station.

  According to a third aspect of the present invention, in the satellite communication system according to the second aspect, the digital filter is provided in a demodulation unit of the receiver.

  According to a fourth aspect of the present invention, in the satellite communication system according to the second aspect, the digital filter is provided between a down converter and a receiving unit of the receiver.

  According to a fifth aspect of the present invention, in the satellite communication system according to the second aspect, the correction circuit includes a plurality of digital signals that make the frequency characteristics uniform by using fixed values of different angles of the satellite-mounted antenna as parameters. A filter is provided between the downconverter and the receiving unit of the receiver of the ground station, and one of the plurality of digital filters that has the least bit error at the time of reception is selected.

  According to a sixth aspect of the present invention, in the satellite communication system according to the first aspect, the correction circuit performs a fast Fourier transform on a signal input to the digital filter, and the fast Fourier transform unit. And a digital filter for making the frequency characteristic uniform based on a result of processing by a Fourier transform unit and a variable value of the angle of the satellite-mounted antenna, and is provided in the receiver of the ground station.

  According to a seventh aspect of the present invention, in the satellite communication system according to the first aspect, the correction circuit is a digital filter that corrects a frequency characteristic of a transmission signal of a transmitter mounted on the artificial satellite, and the transmission circuit It is provided in the machine.

  According to an eighth aspect of the present invention, in the satellite communication system according to the seventh aspect, the digital filter is provided between a modulation unit provided in the transmitter and an up-converter. To do.

  In order to achieve the above-mentioned object, the present invention according to claim 9 is characterized in that a satellite-mounted device mounted on the artificial satellite interferes with radio wave radiation from the artificial satellite to the earth ground station. The receiver of the ground station is grasped from the operation status of the satellite, and the frequency characteristics of the occupied frequency band of the received signal power in the ground station are uniform according to the angle of the satellite-mounted antenna mounted on the satellite. A frequency characteristic correction method for a satellite communication system is provided, wherein the frequency characteristic of the received signal is corrected.

  According to a tenth aspect of the present invention, in the frequency characteristic correction method for the satellite communication system according to the ninth aspect, the correction of the received signal is based on an angular constant of a satellite-mounted antenna mounted on the artificial satellite. This is performed by allowing the received signal to pass through a digital filter to be changed.

  In order to achieve the above object, the present invention according to claim 11 is directed to the possibility that a satellite-mounted device mounted on the artificial satellite interferes with radiation of a radio wave from the artificial satellite to a ground station on the earth. Ascertained from the operation status of the artificial satellite, and installed in the artificial satellite so that the frequency characteristics of the occupied frequency band of the received signal power in the ground station are uniform according to the angle of the antenna mounted on the artificial satellite. There is provided a frequency characteristic correction method for a satellite communication system, wherein a frequency characteristic of a transmission signal is corrected by a transmitter.

  According to a twelfth aspect of the present invention, in the frequency characteristic correction method of the satellite communication system according to the eleventh aspect, the correction of the transmission signal is based on an angle constant of a satellite-mounted antenna mounted on the artificial satellite. This is performed by allowing the transmission signal to pass through a digital filter to be changed.

  According to the present invention, it is possible to prevent a change in signal intensity due to radio wave interference between a satellite-mounted antenna and a ground antenna, and to reduce bit errors.

1 is a block diagram showing a communication system according to a first embodiment of the present invention. The occupied frequency band spectrum and bit error occurrence status in each part of the communication system according to the first embodiment are shown, (a) is the occupied frequency band spectrum of the transmission power of the transmitter of the artificial satellite, (b) is the artificial satellite 1 is a diagram illustrating an evaluation of an occupied frequency band spectrum of the gain of a satellite-mounted antenna, (c) an occupied frequency band spectrum of a gain of a ground antenna, and (d) an evaluation of a bit error occurrence state of a receiver of the ground station. It is a figure explaining the coordinate definition of an artificial satellite. It is a figure which shows the boresight direction gain Gtx ((theta) ax, (theta) ay, (theta) bx, (theta) by) of the satellite side antenna at the time of the directional center direction ((theta) ax, (theta) ay) = (0,0) of a satellite mounting antenna. It is a figure which shows the antenna gain change used for correction | amendment of the received signal power of the tracking reception system in consideration of the radio wave interference by the artificial satellite equipment. It is a figure which shows an example of the state which the satellite mounting apparatus of the artificial satellite rotated. It is a figure explaining the radio wave interference with the beam direction of a satellite-mounted antenna, and a satellite-mounted apparatus. It is a block diagram which shows the structure of the demodulation part of the receiver of a ground station. It is a block diagram which shows the detail of a digital filter. It is a block diagram which shows the structure of the receiver of the ground station which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the receiver of the ground station which concerns on the 3rd Embodiment of this invention. The receiver of the ground station which concerns on the 4th Embodiment of this invention, and its modification are shown, (a) is a block diagram which shows 4th Embodiment, (b) shows the modification of (a). It is a block diagram. It is a block diagram which shows the structure of the receiver of the ground station which concerns on the 5th Embodiment of this invention. It is a characteristic view which shows two of the filter characteristics for making electric power energy spectrum distribution of an occupation band constant. It is a characteristic view which shows two other filter characteristics for making the electric energy spectrum distribution of an occupation band constant. It is a block diagram which shows the structure of the transmitter of the artificial satellite which concerns on the 6th Embodiment of this invention. It is a block diagram which shows the structure of the transmitter of the artificial satellite which concerns on the 7th Embodiment of this invention. It is a block diagram which shows the structure of the transmitter of the artificial satellite which concerns on the 8th Embodiment of this invention. It is a block diagram which shows the structure of the transmitter of the artificial satellite which concerns on the 9th Embodiment of this invention. It is a figure which shows an example of a satellite communication system. It is a figure which shows the condition where a satellite mounting apparatus interposes between the antenna of a satellite, and a ground antenna.

[First Embodiment]
(Configuration of satellite communication system)
FIG. 1 is a block diagram showing a communication system according to the first embodiment of the present invention. The satellite communication system 100 includes an artificial satellite 1 that circulates in outer space on the earth around the earth's center and a ground station 2 that is installed on the earth and receives radio waves from the artificial satellite 1. Yes. The artificial satellite 1 is an earth observation satellite, for example. In the present embodiment, the ground station 2 is a receiving station.

  The artificial satellite 1 includes a receiver 3 that receives radio waves from a ground transmitting station (not shown), a transmitter 4 that transmits transmission data to be transmitted to the ground station 2, and receives radio waves from the ground side and from the transmitter 4. A satellite-mounted antenna 5 that radiates the transmission output as a radio wave, an observation device 6 that observes the earth environment and the like, and a controller 7 that controls the entire artificial satellite 1. The satellite-mounted antenna 5 is a gimbal control antenna, for example, and a plurality of antennas may be mounted. The control unit 7 includes all the controls in the artificial satellite 1 such as attitude control and power supply control.

  The transmitter 4 performs a modulation unit 10 that performs phase modulation (PSK: Phase Shift Keying) or the like on a transmission target signal, and converts a transmission signal from the modulation unit 10 into a transmission target frequency band (for example, a GHz band). A converter 11 and a transmitter 12 that feeds a high-frequency output obtained by power amplification of the transmission signal from the up-converter 11 to the satellite-mounted antenna 5 are provided.

  The ground station 2 includes a ground antenna 8 that receives radio waves from the artificial satellite 1 and a receiver 9 that processes a signal received by the ground antenna 8. The ground antenna 8 is, for example, a Cassegrain antenna, and includes a tracking device (not shown) that tracks the artificial satellite 1. The receiver 9 includes a down converter 13 that converts a received signal from, for example, a gigahertz (GHz) band to a lower frequency band, and a demodulator 14 that demodulates an output signal of the down converter 13.

(Operation of satellite communication system)
Next, the operation of the satellite communication system 100 will be described. The artificial satellite 1 modulates observation data from the observation device 6 and a response signal to a signal (for example, a command from the ground) received by the receiver 3 by the modulation unit 10 of the transmitter 4 to generate a modulated signal. This modulated signal is converted to a desired frequency in the GHz band by the up-converter 11 and further subjected to power amplification and the like by the transmitter 12 and then fed to the satellite-mounted antenna 5. The satellite-mounted antenna 5 transmits the high-frequency power from the transmission unit 12 toward the earth as a radio wave.

  The ground station 2 receives the radio wave from the satellite-mounted antenna 5 by the ground antenna 8. The received signal is converted into a low frequency band by the down converter 13 and further demodulated by the demodulator 14 to output a demodulated signal. Further, the demodulated signal is processed by a circuit (not shown) for transmission to a communication line on the ground side.

  Here, the transmission output of the satellite 1 is Ptx [dBm], the passive circuit loss is Ptxl [dB], the gain of the satellite-mounted antenna 5 is Gtx [dBi], the polarization loss is Lpo [dB], and the free space loss is When LFs [dB], environmental absorption loss is Laa [dB], rain attenuation loss is Lra [dB], and ground station antenna gain is Grx [dBi], the received signal power Pr at the ground antenna 8 is given by Equation (1). It is done.

(Equation 1)
Pr = Ptx + Ptxl + Gtx + Lpo + LFs + Laa + Lra + Grx
... (1)

  As described above, when the observation device (satellite-mounted device) 6 enters the radio wave radiation range of the satellite-mounted antenna 5 of the artificial satellite 1 with respect to the ground antenna 8, the received signal power Pr received by the ground antenna 8 decreases. However, as is clear from the above equation (1), the received signal power Pr can be corrected by increasing the antenna gain Gtx. Such correction is performed in the demodulator 14 described later in the first embodiment.

  FIG. 2 shows the occupied frequency band spectrum and the occurrence of bit errors in each part of the communication system according to the first embodiment. (A) is the occupied frequency band spectrum of the transmission power of the artificial satellite transmitter. ) Is the occupied frequency band spectrum of the gain of the satellite-mounted antenna of the artificial satellite, (c) is the occupied frequency band spectrum of the gain of the ground antenna, and (d) is a diagram showing the evaluation of the bit error occurrence status of the receiver of the ground station. is there.

  Since the transmission power of the transmitter 4 mounted on the artificial satellite 1 is not affected by the outside, the occupied frequency band spectrum is in an ideal state as shown in [A] and [B] of FIG. . When the ground station 2 is also in an ideal reception state, its occupied frequency band spectrum is in an ideal state as shown in [A]. The gain of the satellite-mounted antenna 5 is as shown in FIG. 2B when a change in signal strength or interference with the observation device 6 occurs due to the poor antenna mounting position described in the above problem. Characteristics deteriorate. Furthermore, if the same problem occurs, the received signal power (Pr) of the ground antenna 8 also deteriorates the characteristics of the occupied frequency band spectrum as shown in FIG. Therefore, the deteriorated characteristics as shown in [B] of FIGS. 2B and 2C can be made ideal characteristics as shown in [A] of FIGS. 2B and 2C. If possible, the above problems can be solved.

  When a problem occurs, the received signal power of the terrestrial antenna 8 becomes as shown in [B] of FIG. 2C, so that the receiver 9 of the ground station 2 receives the antenna gain shown in [A] of FIG. 2B. It is made on the assumption that it is transmitted from the satellite-mounted antenna 5 depending on the characteristics. When such a receiver 9 receives and demodulates the signal, it is known that many bit errors are included.

  FIG. 3 is a diagram for explaining the coordinate definition of the artificial satellite. The coordinates X, Y, and Z of the artificial satellite 1 with respect to the earth 200 are defined as shown in FIG. Here, X is the traveling direction of the artificial satellite 1 in the satellite orbit direction R, and the traveling direction is positive. Y is a direction orthogonal to the direction X. Z is the center direction of the earth 200, and the earth center (center) direction is positive.

The satellite-mounted antenna 5 has angles of the pointing center direction as θax and θay. The angles θax and θay are determined based on information provided from the operator (owning organization or the like) of the artificial satellite 1. Note that when the satellite-mounted antenna 5 does not have a movable mechanism, the angles θax and θay are fixed values. Further, the boresight angles (viewing angles) θbx and θby when the ground antenna 8 is viewed from the artificial satellite 1 are obtained as follows.
(I) The position of the artificial satellite 1 is obtained by orbit prediction calculation.
(Ii) The position of the ground antenna 8 is given.
(Iii) θbx and θby are obtained from the three-dimensional coordinate positions given by (i) and (ii) above.

  The boresight angles θbx and θby at a certain time can be obtained from the information (i) and (ii). Specifically, a table for time is prepared in advance as follows, and necessary constants are read as shown in Table 1 with reference to time at the time of reception.

  The antenna gain Gtx ′ (θax, θay, θbx, θby) of the satellite mounted antenna 5 in the θbx and θby directions is given by the following equation (2).

(Equation 2)
Gtx ′ (θax, θay, θbx, θby)
= Gtx (θax, θay, θbx, θby)
+ Gti (θax, θay, θbx, θby) (2)

  FIG. 4 is a diagram illustrating the boresight direction gain Gtx (θax, θay, θbx, θby) of the satellite-mounted antenna when the satellite-mounted antenna has a pointing center direction (θax, θay) = (0, 0). The characteristic of the boresight direction gain Gtx can be known from FIG.

  FIG. 5 is a diagram illustrating a change in antenna gain used for correcting the received signal power Pr of the tracking reception system in consideration of radio wave interference caused by the satellite-mounted device. FIG. 5 shows a boresight angle (θbx, θby) versus antenna gain change Gti (θax, θay, θbx, θby) when the pointing center direction of the satellite-mounted antenna 5 is a certain direction (θax, θay) = (0, 0). ), That is, (θbx, θby) vs. antenna gain change Gti in a certain direction (θax, θay). Gti is obtained in advance for all angles θax, θay, θbx, and θby. Further, Gti for the combination of angles θax, θay, θbx, and θby may be obtained by actual measurement, or may be obtained by computer simulation using the physical shapes of the satellite-mounted antenna 5 and the observation device 6 (satellite-mounted device) as input constants. good.

  When the received signal power Pr received by the ground antenna 8 is obtained according to the above formula (1), first, the directional center direction (θax, θay) of the satellite-mounted antenna 5 and the ground antenna 8 are viewed from the artificial satellite 1. Boresight angles θbx and θby are given, and Gtx (θax, θay, θbx, θby) is obtained as an antenna gain Gtx with respect to the angles θax, θay from FIG.

  Next, the antenna gain change Gti is obtained from FIG. 5 by Gti (θax, θay, θbx, θby). A value obtained by adding Gtx (θax, θay, θbx, θby) and Gti (θax, θay, θbx, θby) is defined as Gtx ′. The received signal power Pr is obtained by substituting this Gtx ′ for Gtx in the above equation (1).

  FIG. 6 is a diagram illustrating an example of a state in which a satellite-mounted device of an artificial satellite has moved. As shown in FIG. 6, when the state of radio wave interference changes due to the movement of the satellite-mounted device 16, the movement direction of the satellite-mounted device 16 is given as the directions θex and θey of the satellite-mounted device 16, and the change of the antenna gain with respect to the movement is given. Gti (θax, θay, θbx, θby, θex, θey) may be used, and Gtx ′ (θax, θay, θbx, θby, θex, θey) may be obtained from Equation (3).

(Equation 3)
Gtx ′ (θax, θay, θbx, θby, θex, θey)
= Gtx (θax, θay, θbx, θby)
+ Gti (θax, θay, θbx, θby, θex, θey) (3)

  FIG. 7 is a diagram for explaining the radio wave interference between the beam direction of the satellite-mounted antenna and the satellite-mounted device. In the above description, Gtx is expressed by the angles θax, θay in the direction of the directional center of the satellite-mounted antenna 5 and the boresight angles θbx, θby when the ground antenna 8 is viewed from the artificial satellite 1, but the beam direction of the satellite-mounted antenna 5 7 and the ground antenna 8 are in the relationship shown in FIG. 7, Gtx and Gti are expressed as an elevation angle (Elevation: El) and an azimuth angle (Azimuth: Az) of the ground antenna, and Gtx (Az, El) and It may be expressed as Gti (Az, El). Further, the direction of the ground antenna 8 may be expressed by an XY method or the like. The boresight angles θbx and θby when the ground antenna 8 is viewed from the artificial satellite 1 are obtained by performing orbit prediction calculation using orbit ephemeris provided by the operator of the artificial satellite 1. And obtained from the result and the position of the ground antenna 8.

  Further, in the above formulas (1) and (2), the case where the satellite-mounted antenna 5 can be varied with respect to the boresight directions θax and θay, and the case where the satellite-mounted device 16 can move in the angles θex and θey directions have been shown. When the satellite-mounted antenna 5 is fixed in a specific direction or when the satellite-mounted device 16 is fixed in a specific direction, the angles θax, θay, θex from the above formulas (1) and (2). , Θey may be excluded.

(Configuration of demodulator)
Next, the configuration of the demodulation unit that corrects the received signal power Pr based on the above-described method will be described. FIG. 8 is a block diagram showing the configuration of the demodulation unit of the receiver of the ground station. The demodulator 14 includes a multiplier 141 to which a received signal and a carrier wave of cosωt are input, an LPF (low-pass filter) 142 that performs band limitation on a multiplication result by the multiplier 141, and an analog signal from the LPF 142 as a digital signal. A / D (analog / digital) converter 143 for conversion, digital filter (correction circuit) 144 for correcting fluctuations in frequency characteristics caused by angles θax, θax, θbx, θbx of satellite mounted antenna 5, digital A D / A (digital / analog) converter 145 that converts the signal from the filter 144 from digital to analog, an LPF 146 that outputs a decoded signal α in which the band of the signal from the D / A converter 145 is limited, and a received signal And a multiplier 147 to which a carrier wave of −sin ωt is input, and multiplication by the multiplier 147 LPF 148 that performs band limitation on the result, A / D converter 149 that converts an analog signal from LPF 148 into a digital signal, and fluctuations in frequency characteristics caused by the angles θax, θax, θbx, and θbx are corrected. Digital filter (correction circuit) 150, a D / A converter 151 for converting a signal from the digital filter 150 from digital to analog, a band of the signal from the D / A converter 151, and a decoded signal β An LPF 152 for output and a filter constant setting table 153 for changing the filter constants of the digital filters 144 and 150 based on the angle constants (θax, θax, θbx, θbx) are provided.

  The filter constant setting table 153 can be constructed using DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array) computer software, or the like.

  In FIG. 8, each of the combination comprising the digital filter 144, the D / A converter 145 and the LPF 146 and the combination comprising the digital filter 150, the D / A converter 151 and the LPF 152 are DFU (Digital Filter Unit). Is configured.

(Configuration of digital filter)
FIG. 9 is a block diagram showing details of the digital filter. The digital filters 144 and 150 are, for example, FIR (Finite Impulse Response) type or IIR (Infinite Impulse Response) type filters and have the same configuration. Therefore, the configuration of the digital filter 144 will be described here. The digital filter 144 includes n delay units 17 _{-1 to} 17 _-n connected in series so as to sequentially delay a signal from the A / D conversion unit 143, an input signal or a delay signal, and a filter constant setting table 153. N multipliers 18 _-1 to 18 _-n for multiplying the parameters h _{0 to} h _n and n adders 19 _{-1 to} 19 -19 for adding the multiplication results of the multipliers 18 _-1 to 18 _{-n. -N} .

Table 2 shows an example of the table contents of the filter constant setting table 153. This filter constant setting table 153 shows parameters h _{0 to} h _n at certain angles θax, θax, θbx, θbx of the satellite mounted antenna 5.

The multiplier _{18 -1} multiplies the parameters _{h 0} from the input signal and the filter constant setting table 153, multiplier ₁₈ -2 _{~ 18 -n} includes one output signal of the delay circuit ₁₇ -2 _{to 17 -n} The parameters h _{1 to} h _n (hereinafter also simply referred to as h) are multiplied. Adder ₁₉ -1 _{~ 19 -n} are connected to sequentially add the multiplier ₁₈ -1 _{~ 18 -n} output signal to the multiplier _{18 -1} by the multiplier _{18 -n} side.

  The characteristics of the digital filters 144 and 150 can be varied by the parameter h from the filter constant setting table 153. The parameter h corresponds to the directional center directions θax and θay of the satellite-mounted antenna 5 and the boresight angles θbx and θby when the ground antenna 8 is viewed from the artificial satellite 1. The filter constant setting table 153 is generated when the angles θax, θay, θbx, θby of the satellite-mounted antenna 5 change with reference to the frequency spectrum of the occupied band measured in a situation where the satellite-mounted equipment is not interfering. Even if the angles θax, θay, θbx, and θby of the satellite mounted antenna 5 change by demodulating the characteristics of the digital filters 144 and 150 so as to amplify or attenuate so as to cancel the frequency spectrum change of the occupied band, demodulation is possible. The frequency spectrum of the occupied band input to the unit 14 is prevented from changing.

  Table 3 shows an example of a table for sequentially changing the characteristics of the digital filters 144 and 150. As shown in Table 3, FIR filter constants are prepared together with time, and filter constants corresponding to reception times are sequentially loaded into the digital filters 144 and 150.

Table 4 shows an example of the contents of constants (Gti) set in the filter constant setting table 153. The filter constant setting table 153 loads the parameters h _{0 to} h _n of the digital filters 144 and 150 to the digital filters 144 and 150, respectively, based on the time. Examples shown in Table 3 shows an angle constants (θax, θay, θbx, θby ) n number of constants in the _(h 0 _{~h n).} In the filter constant setting table 153 that is actually used, parameters h _{0 to} h _n are defined for all combinations of angles θax, θay, θbx, and θby.

(Operation of demodulator)
Next, the operation of the demodulator 14 will be described with reference to FIGS. The signal from the down-converter 13 is input to a multiplier 141 having cos ωt as a carrier wave and a multiplier 147 having −sin ωt as a carrier wave, whereby phase detection is performed. The two signals subjected to phase detection are band-limited by the LPFs 142 and 148 and then input to the digital filters 144 and 150.

In the digital filters 144 and 150, “convolution calculation” is performed on the output signals of the LPFs 142 and 148. In the delay units 17 _{-1 to} 17 _-n shown in FIG. 9, the current input and the past input are obtained, and for these signals, the multipliers 18 _-1 to 18 _-n receive the coefficient h from the filter constant setting table 153. by applying a ₀ to h _n, to obtain a filter output from the adder _{19 -1.}

  The filter constant setting table 153 generates constants at the angles θax, θay, θbx, and θby, and changes the filter constants of the digital filters 144 and 150 based on these constants, so that an ideal frequency as shown in [A] in FIG. The filter characteristics of the digital filters 144 and 150 are corrected so that a band spectrum tram is obtained. The output signals of the digital filters 144 and 150 are converted from digital signals to analog signals by the D / A converters 145 and 151, and the decoded signals α and β are extracted by passing through the LPFs 146 and 152.

(Effects of the first embodiment)
According to the first embodiment, the digital filter 144, 150 is provided in the demodulator 14, and the received signal power Pr is changed by changing the frequency characteristics of the digital filter 144, 150 based on the parameter h from the filter constant setting table 153. Thus, the artificial satellite 1 can be tracked without being affected by changes in signal intensity.

[Second Embodiment]
FIG. 10 is a block diagram showing a configuration of a receiver of the ground station according to the second embodiment of the present invention. In contrast to the first embodiment shown in FIG. 8 in which the DFU 15 is provided in the demodulation unit 14, the present embodiment connects the DFU 15 to the down converter 13, and the receiving unit 20 including the DFU 15 and the demodulation unit 14 includes: A reception filter 154 is connected between the two. The receiving unit 20 is configured by removing the DFU 15 from FIG. The receiving unit 20 may have an analog configuration. In this case, a D / A converter is provided before the receiving unit 20.

  The DFU 15 according to the present embodiment corrects the level within the occupied band of the received signal so as to be equal to the ideal spectrum shown in FIG. The effect obtained by the second embodiment is the same as that of the first embodiment.

[Third Embodiment]
FIG. 11 is a block diagram showing a configuration of a receiver of the ground station according to the third embodiment of the present invention. In the present embodiment, the reception filter 154 and the DFU 15 are interchanged in the second embodiment shown in FIG. The effect obtained by the third embodiment is the same as that of the first embodiment.

[Fourth Embodiment]
FIG. 12 shows a receiver of a ground station and a modification thereof according to the fourth embodiment of the present invention, (a) is a block diagram showing the fourth embodiment, and (b) is a block diagram of (a). It is a block diagram which shows a modification. In this embodiment, in the second embodiment shown in FIG. 10, a plurality of DFUs (DFUs 15A to 15C) are used as correction circuits, and a switch 21 is provided between the DFUs 15A to 15C and the reception filter 154. It is a thing. The switch 21 is controlled to be switched by a control unit (not shown). The input units of the DFUs 15A to 15C are connected in parallel, and one of the three output units is selected by the switch 21 and applied to the reception filter 154. In this case, the parameter h of the digital filter 144 of the DFUs 15A to 15C is set to a different fixed value. In FIG. 12A, the DFUs 15A to 15C may be analog filters.

  The control unit that controls the switch 21 detects the DFU 15A to 15C with the least bit error based on the demodulated signal, and operates the switch 21 to select one of the DFUs 15A to 15C. . As a method of selecting the one having the least bit error, there is a method of determining an error when decoding a Reed-Solomon code included in transmission data by a control unit, or determining an error when decoding a turbo code. .

[Modification of Fourth Embodiment]
The configuration of the receiver 9 shown in FIG. 12B is the same as the configuration shown in FIG. 12A. The filter 154A and the receiving unit 20A are connected in series to the DFU 15A, and the filter 154B and the receiving unit 20B are connected in series to the DFU 15B. A filter 154C and a receiving unit 20C are connected in series to the DFU 15C. The receiving units 20A to 20C are configured by the PSK digital system. In FIG. 12B, the DFUs 15A to 15C may be analog filters.

  In this configuration, the receiving units 20A to 20C operate according to the outputs of the DFU 15A to DFU 15C. However, since the setting values of the DFU 15A to DFU 15C are different from each other, the receiving units 20A to 20C are both the same configuration and the same. Even if it is a specification, the bit errors obtained by the receiving units 20A to 20C are different. Therefore, the control unit (not shown) selects the one having the least bit error among the receiving units 20A to 20C.

(Effect of 4th Embodiment and its modification)
According to the fourth embodiment and its modification, the same effect as that of the first embodiment can be obtained, and the demodulator 14 can be used even when the angles θax, θay, θbx, θby of the satellite mounted antenna 5 change. It is possible to cope with a case where the change in the frequency spectrum of the occupied band input to is not so large, thereby making the filter constant setting table 153 unnecessary.

  Further, when the artificial satellite 1 is an earth observation satellite that performs high-speed communication, even if the fastest device available at present is used, it is difficult to increase the speed with the configuration of the first embodiment shown in FIG. However, according to the configuration of the fourth embodiment, high-speed communication can be easily achieved.

[Fifth Embodiment]
FIG. 13: is a block diagram which shows the structure of the receiver of the ground station based on the 5th Embodiment of this invention. In this embodiment, in FIG. 8 of the first embodiment, an FFT (Fast Fourier Transform) is performed on the output signal of the A / D converter 143 between the A / D converter 143 and the filter constant setting table 153. : Fast Fourier transform) An FFT unit 155 that performs processing is provided. Although only the configuration on the decoded signal α side is shown in FIG. 13, the configuration on the decoded signal β side is the same, and the same as the FFT unit 155 is provided between the A / D converter 149 and the filter constant setting table 153. An FFT unit having a configuration is provided. Here, the configuration and operation on the decoded signal α side will be described, and the description on the decoded signal β side will be omitted.

  In the present embodiment, digital filter 144 has the configuration shown in FIG. 9 and a plurality of filter characteristics for making the power energy spectrum distribution in the occupied band constant. An example thereof is shown in FIGS. 14 and 15 show filter characteristics for making the power energy spectrum distribution in the occupied band constant. 14 and 15, the horizontal axis indicates the normalized frequency of the spectrum obtained by FFT, and the vertical axis indicates the normalized amplitude.

The filter characteristic of the digital filter 144 is Fil. # 1 (FIG. 14A), Fil. # 2 (FIG. 14 (b)), Fil. # 3 (FIG. 15 (a)), Fil. Four types of # 4 ((b) of FIG. 15) are prepared. Nf1, Nf2, Nf3,... Nfn shown in FIG. 14 (a) are amplitudes for a certain frequency. Although four types of filter characteristics are used here, more filters are actually prepared. Fil. # 1 to Fil. The characteristic of # 4 is achieved by changing the value of the filter constant (h ₀ -h _n ) shown in Table 1.

  Next, the operation of the receiver 9 shown in FIG. 13 will be described. The received signal that is an input is digitized by the LPF 142 and the A / D converter 143, and the power energy spectrum (spectrum distribution) of the occupied band is obtained from this signal by the FFT unit 155. The filter constant setting table 153 obtains a constant of the digital filter 144 for setting the difference between the power energy spectrum by the FFT unit 155 and the frequency spectrum of the occupied band measured in an ideal communication state to 0, and this constant is converted to digital. This is applied to the filter 144. Note that angle constants (θax, θay, θbx, θby) are given to the filter constant setting table 153 in order to limit the range in which the digital filter 144 operates or the constants of the digital filter 144.

  The digital filter 144 is provided with the Fil. # 1 to Fil. The power energy spectrum (Prmse) is obtained for all of # 4 by using the constants shown in Equation 4 below. The digital filter 144 employs, as the parameter h of the digital filter 144, a value of which Prms is the smallest value among the four Prms. In Equation 4, n is the number of spectra, Of is a spectrum obtained by reception or FFT, and Sf is a standard spectrum.

  As described above, the digital filter 144 operates so as to always keep the power energy spectrum distribution of the occupied band constant. An output signal of the digital filter 144 is converted from a digital signal to an analog signal by the D / A converter 145, and a signal whose band is limited by the LPF 146 becomes an output signal.

  In the fifth embodiment, when it is not necessary to limit the operation range of the parameters of the digital filter 144, the parameters described above from the filter constant setting table 153 are not used without using the angle constants (θax, θay, θbx, θby). May be output to the digital filter 144.

(Effect of 5th Embodiment)
According to the fifth embodiment, the digital filter 144 corrects the spectrum having the characteristic [B] shown in FIG. 2C to the spectrum having the characteristic [A]. Therefore, even when the direction of the beam pointing center of the satellite-mounted antenna 5 of the artificial satellite 1 is changed or the observation device 6 having a complicated shape is mounted on the artificial satellite 1, the signal caused by the positional relationship of the satellite-mounted antenna 5 Generation of interference or the like can be prevented.

(Correction of frequency characteristics on the satellite side)
Next, when the beam pointing center direction of the satellite-mounted antenna 5 changes, when a part of the observation device 6 mounted on the artificial satellite 1 causes radio wave interference between the artificial satellite 1 and the ground antenna 8. Specifically, an embodiment on the side of the artificial satellite 1 for correcting the spectrum having the characteristic [B] shown in FIG. 2B to the spectrum having the characteristic [A] will be described.

[Sixth Embodiment]
FIG. 16: is a block diagram which shows the structure of the transmitter of the artificial satellite based on the 6th Embodiment of this invention. The present embodiment solves the above problem (3), and changes in frequency characteristics so as to reduce bit errors caused by a change in the gain with respect to the frequency of the satellite-mounted antenna 5 due to radio wave interference. Is provided in the transmitter 4 of the satellite 1 with a correction circuit (DFU 23 described later) and a filter constant setting table 153.

(Configuration of satellite transmitter)
The modulation unit 10 includes an S / P (serial / parallel) conversion unit 101 that converts a baseband signal into a parallel signal, data conversion units 102 and 103 that obtain a PSK signal from the output signal of the S / P conversion unit 101, and data The multiplier 104 that multiplies the signal from the converter 102 and the carrier signal cosωt, the multiplier 105 that multiplies the signal from the data converter 103 and the carrier signal −sinωt, and the multiplication results by the multipliers 104 and 105. An adder 106 for adding the signal, a transmission filter 22 for band-limiting the output signal of the adder 106, a DFU (correction circuit) 23 connected to the transmission filter 22, and the upconverter 11 connected to the DFU 23. And the above-described filter constant for providing an angle constant to the DFU 23 and the transmitter 12 connected to the up-converter 11 A setting table 153. The DFU 23 has the same configuration as the DFU 15 shown in FIG.

(Operation of satellite transmitter)
A baseband signal (input signal) composed of binary values “1” and “0” is converted into a parallel signal by the S / P converter 101. The parallel signals are subjected to gray coding and level conversion (processing to make signals of +1 and −1) by the data conversion units 102 and 103, and a modulated signal is generated. This modulated signal is multiplied by the carrier signal by multipliers 104 and 105 to generate a PSK signal. This PSK signal is input to the DFU 23 through the transmission filter 22.

  The filter constant setting table 153 in the present embodiment is obtained when the angles θax, θay, θbx, and θby of the satellite-mounted antenna 5 change with reference to the frequency spectrum of the occupied band measured in a situation where radio wave interference does not occur. In order to cancel the generated frequency spectrum change of the occupied band, the characteristics of the digital filter in the DFU 23 are sequentially changed so that the signal in the up-converter 11 is amplified or attenuated. Thereby, the change of the frequency spectrum of the occupation band of the receiver 9 received on the ground can be prevented. The modulated signal processed by the DFU 23 is input to the up-converter 11, converted to a desired frequency, and then power-amplified by the transmitter 12 and fed to the satellite-mounted antenna 5.

(Effect of 6th Embodiment)
According to the sixth embodiment, the DFU 23 is provided between the modulation unit 10 and the up-converter 11 so as to cancel the change in the frequency spectrum of the occupied band that occurs when the angle of the satellite-mounted antenna 5 changes. Therefore, it is possible to reduce a bit error that occurs in the receiver 9 of the ground station 2 due to a change in the gain with respect to the frequency of the satellite-mounted antenna 5.

[Seventh Embodiment]
FIG. 17 is a block diagram showing the configuration of the artificial satellite transmitter according to the seventh embodiment of the present invention. This embodiment is obtained by replacing the transmission filter 22 and the DFU 23 in the sixth embodiment shown in FIG. 16, and the other configuration is the same as that of the sixth embodiment. According to the seventh embodiment, the same effect as in the sixth embodiment can be obtained.

[Eighth Embodiment]
FIG. 18 is a block diagram showing a configuration of the artificial satellite transmitter according to the eighth embodiment of the present invention. In this embodiment, in the seventh embodiment shown in FIG. 17, the function of the transmission filter 22 is provided to the DFU 23 so that the transmission filter 22 can be removed, and other configurations are the seventh embodiment. It is the same as the form. According to the eighth embodiment, an effect similar to that of the sixth embodiment can be obtained.

[Ninth Embodiment]
(Configuration of transmitter)
FIG. 19 is a block diagram showing the configuration of the artificial satellite transmitter according to the ninth embodiment of the present invention. In this embodiment, the configuration of the receiver 9 of the ground station 2 of FIG. 13 in the fifth embodiment is applied to the transmitter 4 of the artificial satellite 1, and the FFT unit 155 is removed from the configuration of FIG. It has a configuration. In the artificial satellite 1, since the spectrum distribution of the signal before transmission is known, it is not necessary to measure the spectrum by the FFT unit 155. For this reason, the FFT unit 155 is not provided in this embodiment. However, even if the FFT unit 155 is provided, no inconvenience occurs.

(Transmitter operation)
In the transmitter 4 of FIG. 19, for example, the transmission signal from the modulation unit 10 shown in FIG. 16 is digitized by the LPF 142 and the A / D converter 143 and then applied to the digital filter 144. The filter constant of the digital filter 144 is changed by a filter constant setting table 153 that operates based on angle constants (θax, θay, θbx, θby). As a result, the digital filter 144 operates so as to keep the power energy spectrum distribution of the occupied band always constant, and its output signal is converted from a digital signal to an analog signal by the D / A converter 145 and further band-limited by the LPF 146. The signal is applied to the up-converter 11.

(Effect of 9th Embodiment)
According to the ninth embodiment, a spectrum having a characteristic such as [B] shown in FIG. 2B with respect to a transmission signal by the digital filter 144 on the artificial satellite 1 side has a characteristic such as [A]. Since the spectrum can be corrected, the position of the satellite-mounted antenna 5 is changed even when the beam-directing center direction of the satellite-mounted antenna 5 of the artificial satellite 1 is changed or the observation device 6 having a complicated shape is mounted on the artificial satellite 1. Generation of signal interference or the like due to the relationship can be prevented.

[Other embodiments]
The present invention is not limited to the above embodiments, and various modifications can be made without departing from or changing the technical idea of the present invention. For example, three solutions for radio wave interference caused by satellite-mounted equipment have been shown, but in actual application, it is effective to adopt two of the three, preferably three, simultaneously. Realization is also easy.

DESCRIPTION OF SYMBOLS 1 Artificial satellite 2 Ground station 3 Receiver 4 Transmitter 5 Satellite mounted antenna 6 Observation equipment 7 Control part 8 Ground antenna 9 Receiver 10 Modulation part 11 Up converter 12 Transmission part 13 Down converter 14 Demodulation part 15 DFU (digital filter unit)
15A DFU
15B DFU
15C DFU
16 Satellite mounted equipment 17 _{-1 to} 17 _-n delay unit 18 _-1 to 18 _-n multiplier 19 _{-1 to} 19 _-n adder 20 receiving unit 20A receiving unit 20B receiving unit 20C receiving unit 21 switch 22 transmission filter 23 DFU
DESCRIPTION OF SYMBOLS 100 Satellite communication system 101 S / P conversion part 102 Data conversion part 103 Data conversion part 104 Multiplier 105 Multiplier 106 Adder 141 Multiplier 142 LPF (low pass filter)
143 A / D converter 144 Digital filter 145 D / A converter 147 Multiplier 148 LPF
149 A / D converter 150 Digital filter 151 D / A converter 152 LPF
153 Filter constant setting table 154 Reception filter 154A Reception filter 154B Reception filter 154C Reception filter 155 FFT unit 200 Earth

Claims (12)

In a satellite communication system that performs communication between an artificial satellite orbiting the earth and a ground station installed on the earth,
The received signal received by the ground station even when the reception intensity at the ground station changes due to the installation of the equipment mounted on the artificial satellite in the radiation area of the radio wave from the satellite mounted antenna mounted on the artificial satellite A correction circuit for correcting the reception signal of the ground station or the transmission signal of the artificial satellite so that the frequency characteristics of the occupied frequency band of power are uniform is provided in at least one of the ground station and the artificial satellite. A satellite communication system.   2. The satellite communication system according to claim 1, wherein the correction circuit is a digital filter that makes the frequency characteristic uniform by using a variable value of an angle of the antenna mounted on the satellite as a parameter, and is provided in a receiver of the ground station. A satellite communication system.   3. The satellite communication system according to claim 2, wherein the digital filter is provided in a demodulator of the receiver.   3. The satellite communication system according to claim 2, wherein the digital filter is provided between a down converter and a receiving unit of the receiver.   3. The satellite communication system according to claim 2, wherein the correction circuit includes a plurality of digital filters that equalize the frequency characteristics using fixed values having different angles of the satellite-mounted antenna as parameters. A satellite communication system, which is provided between a converter and a receiving unit, wherein one of the plurality of digital filters having the least bit error during reception is selected.   2. The satellite communication system according to claim 1, wherein the correction circuit includes a fast Fourier transform unit that performs a fast Fourier transform on a signal input to the digital filter, a processing result by the fast Fourier transform unit, and the satellite mounting. A satellite communication system, comprising: a digital filter that makes the frequency characteristics uniform based on a variable value of an antenna angle, and is provided in a receiver of the ground station.   2. The satellite communication system according to claim 1, wherein the correction circuit is a digital filter for correcting a frequency characteristic of a transmission signal of a transmitter mounted on the artificial satellite, and is provided in the transmitter. Satellite communication system.   8. The satellite communication system according to claim 7, wherein the digital filter is provided between a modulation unit provided in the transmitter and an upconverter provided in the transmitter. system.   From the operational status of the artificial satellite, grasp the possibility that the satellite-equipped equipment installed in the artificial satellite will interfere with the radiation of radio waves from the artificial satellite to the earth ground station. A satellite communication system characterized in that the frequency characteristic of the received signal is corrected by the receiver of the ground station so that the frequency characteristic of the occupied frequency band of the received signal power in the ground station becomes uniform according to the angle. Frequency characteristic correction method.   10. The method of correcting a frequency characteristic of a satellite communication system according to claim 9, wherein the received signal is corrected by applying a digital filter whose frequency characteristic is changed based on an angle constant of a satellite-mounted antenna mounted on the artificial satellite. A method for correcting frequency characteristics of a satellite communication system, characterized in that the frequency characteristic correction is performed by passing the signal.   From the operational status of the artificial satellite, grasp the possibility that the satellite-equipped equipment installed in the artificial satellite will interfere with the radiation of radio waves from the artificial satellite to the earth ground station. Satellite communication characterized in that the frequency characteristics of the transmission signal are corrected by a transmitter mounted on the artificial satellite so that the frequency characteristics of the occupied frequency band of the received signal power in the ground station become uniform according to the angle. System frequency characteristics correction method.   12. The frequency characteristic correction method for a satellite communication system according to claim 11, wherein the transmission signal is corrected by applying a digital filter whose frequency characteristic is changed based on an angle constant of an antenna mounted on the satellite to the transmission signal. A method for correcting frequency characteristics of a satellite communication system, characterized in that the frequency characteristic correction is performed by passing the signal.

Images