JPS6321369B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a multi-beam satellite communication system that uses a frequency band with large rainfall attenuation, and when there is rain in a certain spot beam irradiation area, ) In order to compensate for the attenuation of radio waves due to rain, the transmission of spot beams is switched to an on-board high-output transmitter that uses a newly established frequency band, thereby securing a rain margin. It is related to.

In satellite communications that use frequencies in the 30/20 GHz band, radio waves are attenuated by rain, and there is a high possibility that the line will be disconnected during rain.

Therefore, in order to avoid line disconnections, it is necessary to increase or decrease the transmission power depending on the degree of rain attenuation, or to increase the transmission power in advance so that the line will not be disconnected until a certain level of rain attenuation occurs. Must be. This power increase is called the rain margin.

In the uplink from the earth to the satellite, attenuation can be compensated for by increasing or decreasing the transmission power of the earth station in accordance with the amount of attenuation caused by rain.

On the other hand, in the downlink from the satellite to the earth, it is not easy to control the increase or decrease of the transmission power of the transmitter onboard the satellite. It is designed with this in mind.

For this reason, when looking at the equipment on board the satellite, it continues to transmit at high power levels that would not be necessary under clear skies.As a result, in the case of a multi-beam system, the number of transmitting tubes corresponding to the number of beams is also required. It has the drawbacks of being large, consuming large amounts of power, making the equipment large and heavy, and having a high failure rate.

Furthermore, if the transmission power of the satellite-mounted transmitter is increased by considering only attenuation due to rain, there is a drawback that interference will occur with other spot beams using the same frequency in the same area.

In a multi-beam satellite communication system, the present invention switches the transmission frequency for some of the multi-beams that have been attenuated by rain to a frequency set in advance for transmission power control, thereby creating a traveling wave tube with a large transmission output. We have realized downlink transmission power control for transmission using This is to reduce the size and weight, and the drawings will be explained in detail below.

As shown in Figure 1, the currently used multi-beam satellite communication system has service areas 2, 7, and 8 that are each handled by one satellite.For example, if we look at service area 2 of satellite 12, This area is also divided into small areas (small circular areas as shown by numbers 14 and 15, hereinafter referred to as spot areas) that are irradiated with multiple spot beams, and communication is carried out between each spot area using the satellite. This is done on a time-sharing basis via .

The frequencies used are not as different as the number of spot areas;
The transmission capacity is increased by repeatedly using a frequency that is used in a certain spot area and is also used in other spot areas that are sufficiently distant from that spot area.

To prevent interference between spots using the same frequency, the beam width should be narrowed sufficiently.
Relative separation angle α _D (=/ ₀ , where: Separation from the main axis of the antenna At the same time, the beam width is narrowed so that the beam angle is _φ0 : antenna half-width), and the spot areas that use the same frequency are set apart, so that the interference between the beams is -20 to -30 dB in the design. There is.

Figure 2 shows the satellite antenna radiation pattern shown in the World Consultative Committee on Radio (CCIR) Report 558. In this figure, if the relative separation angle is 3 or more, the antenna gain can be -20 dB. I understand.

Therefore, even within the same service area, 2
If the two spot areas are separated by a relative separation angle of 3 when viewed from the satellite antenna, a C/N of -20 dB can be obtained even at the same frequency, and no interference will occur.

If the relative separation angle is 3 or more with respect to the service areas of other satellites, no interference problem will occur.
Since this value can normally be obtained for the service area of adjacent satellites, it is not necessary to make the distance between two satellites extremely far apart in order to prevent interference.

FIG. 3 shows an example of repeated use of frequencies and arrangement of spot areas. Figure a shows the three frequencies ₁ to ₃ , Figure b shows the four frequencies ₁ to ₄ , and Figure c shows the four frequencies 1 to 4.
This is an example in which seven types of frequencies ₁ to ₇ are used and placed at each spot.

In the above system, suppose, for example, that there was rain in the spot area 14 of FIG. 1, causing attenuation, so the transmission power was increased by 10 dB in the satellite onboard transmitter. And same as spot area 14
4', the C/N due to interference before transmitting power increase is
If it were 20 dB, this C/N would drop to 10 dB due to an increase in transmission power. This value is close to the required C/N value for a two-phase signal, and is 3 dB short of the required value for a four-phase signal.

In the 30/20 GHz band, a rain margin of 10 to 15 dB is often secured, so it is possible that the interference between beams will be even greater than the above.

In this way, in a system that repeatedly uses frequencies, it is possible to compensate for the attenuation caused by rain by simply increasing the transmission power of the spot beam that illuminates the spot area with rainfall.
This can lead to problems of interference with other spot areas on the same frequency.

Therefore, in the present invention, a method is used in which a satellite is equipped with a high-power transmitter that transmits at a frequency different from the frequency used within the service area, and which can be switched to use during rainy days. .

Referring to FIG. 1, an embodiment of the present invention will be described in the case where rain occurs on the spot beam 14. Considering that the diameter of the spot beam 14 is approximately 50 to 150 km (depending on the number of spot beams, that is, the diameter of the satellite antenna), the diameter of the adjacent spot beam 15 is
The probability of rain occurring simultaneously within the same period is considered to be sufficiently small.

Fig. 4 shows an example of the frequency configuration of the embodiment of the present invention, and shows the 3.5 GHz band (17.7 to 21.2 GHz) of the 20 GHz band.
A frequency arrangement that uses all of the frequencies is adopted. Carrier waves 20 at frequency ₁ to carrier waves 26 at frequency ₇ correspond to the frequencies within service area 2 of satellite 12 in Figure 1, and the power used to transmit these carrier waves is a low value that satisfies the standards for clear weather. It is.
The carrier wave 27 with frequency ₈ is, for example, spot beam 1.
When rain attenuation occurs in 4, carrier wave ₂ of frequency 2
1 is a new frequency carrier transmitted by the spot beam 14 at high power with a rain margin.

Since the frequencies are different in this way, even if high power transmission is performed, it is possible to secure a rain margin without increasing inter-beam interference with other spot beams.

FIG. 5 shows an example of the configuration of an on-board repeater for realizing the present invention. In the embodiment shown in the figure, the signal 2 from the earth station reaching the satellite receiving antenna 28 is
9 is the frequency of 30GHz band F1, F2...F7
The signal is focused by receiving horns 30 to 33, amplified by low noise amplifiers 34 to 37, and frequency converted to 1F or baseband by receiving frequency converters 38 to 41. This signal is connected via a satellite onboard switch 42 to transmit frequency converters 44-48. A switching pattern for this satellite-mounted switch 42 is set by a switch control unit 43 on the satellite.

The baseband signal or 1F signal from _{the satellite onboard switch 42 is frequency-converted by transmission frequency converters 44-48 to the frequencies of high-frequency signals 1-8 .} This signal is amplified by the on-board traveling wave tubes 49 to 53, radiated from the horns 54 to 57, reflected by the antenna mirror surface 58, and irradiated onto the intended service area on the ground.

The on-board traveling wave tubes 49 to 52, which amplify the carrier waves of frequencies ₁ to ₇ in the 20 GHz band, are used when the downlink service area is sunny. Since no margin is required, it is smaller than the on-board traveling wave tube 53 used during rain (for example, 7 to 12 dB).
Transmit with power (e.g. 1W).

As a result, when paying attention to the series of spot beams 14 during clear weather, the connection point of the satellite onboard switching device 42 is the point A 59, which is closed, the onboard traveling wave tube 50 is used, and the high frequency Switcher 6
2 is closed on the traveling wave tube 50 side.

Assuming that rain has occurred in the earth station area within the spot beam 14 in the service area 2 of FIG. 43, where it issues a command to change the connection point of the satellite onboard switch 42 from point A 59 to point B 60. As a result, it is connected to the on-board traveling wave tube 53 of high output. At the same time, the contact of the high frequency switch 62 is switched from point C 66 to point D 67, and the contact of switch 65 is connected to point E 68. As a result, a large power (for example, 20 W) is transmitted from the earth station horn 55 in the spot beam 14.
Rain attenuation can be compensated for. This control is
A high frequency switching device control unit 6 that sends information on the occurrence of rain to the satellite and controls the switching device in response to this information.
9.

Because of this configuration, even when rain attenuation occurs on other spot beams, the switch control unit 43 and high frequency switch control unit 69 switch the satellite-mounted switch 42, etc. It becomes possible to deal with rainfall attenuation.

If the on-board traveling wave tube used in the explanation has more output, the line will not be disconnected even if the rain attenuation is large, and the operating rate will improve, and the C/N will increase, making it possible to use multiphase. As a result, the fourth
It is possible to narrow the band of the carrier wave 27 shown in the figure (for example, if the band is changed from two phases to four phases, the band is halved).

In the frequency allocation example shown in FIG. 4, the newly added carrier wave 27 is placed at the upper end of the band, but it may also be placed at the center of the band for reasons such as the receiver bandwidth of the earth station.

In this way, in the multi-beam system, unlike the case of a single beam with a wide half-width, it is easy to obtain a sufficient relative separation angle between the antennas of adjacent satellites, so interference with adjacent satellites is rarely a problem. Therefore, when adopting the method of the present invention, it is not necessary to increase the distance between adjacent orbits (the distance represented by θ ₁ and θ ₂ in FIG. 1) compared to the conventional method.

In addition, inter-beam interference between multiple beams can be avoided by using different frequencies, and reuse can be achieved by repeating frequencies as in the past.

The example in Figure 5 describes an example in which there is one onboard high-output transmitter, but this number depends on factors such as the difference in the probability of simultaneous rainfall depending on the region, the required annual line operating rate, and the size of the multi-beam spot. Therefore, there is an optimal value, and the number is determined based on that.

In the present invention, the earth station receiving section requires a demodulation section for one of carrier waves ₁ to ₇ and carrier wave ₈ used during rain, but compared to the equipment scale of the entire earth station, _the The proportion of the demodulated portion for the carrier wave is small, and the problem of complicating the device configuration does not occur.

As explained above, in a satellite communication system that uses a multi-beam with a sharp antenna beam by using a large antenna, high power transmission is performed using a newly created frequency band, which can cause interference with neighboring satellites. It becomes possible to deal with rain attenuation without inter-beam interference.

As a result, compared to the conventional method that is equipped with a traveling wave tube that has an output that satisfies the rain margin and always transmits a high output power, when it is sunny, the transmission output is approximately 10 dB, although it varies depending on the method. Only a small amount of power needs to be transmitted, reducing the power consumption of the satellite, the size and weight of the equipment, and, in turn, helping to reduce the failure rate of the traveling wave tube section and other components.

Furthermore, it is possible to downsize the bulb and power supply of the mounted traveling wave tube, and in conjunction with the above-mentioned reduction in power consumption, the number of mounted repeaters can be increased, and the system transmission capacity can be increased.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a satellite communication system using multi-beams to which the present invention is applied, Fig. 2 is a diagram showing a radiation pattern of an antenna onboard a satellite, and Fig. 3 is a diagram showing an example of frequency repetition use of the multi-beam system. 4 is a diagram showing an example of frequency allocation according to an embodiment of the present invention,
FIG. 5 is a diagram showing an example of a repeater configuration in an embodiment of the present invention. 2, 7, 8... Satellite system service area, 12, 16, 17... Multi-beam satellite, 1
3... Satellite antenna, 14, 14', 15, 18,
19...Spot beam and spot area irradiated by the spot beam, 20-27...Carrier waves with frequencies _1-8 , ₂₈ , 58...Large antenna mounted on the satellite, 30-33, 54-57...Horn, 34-37...Low noise amplifier, 38-41...
...Receiving frequency converter, 42...Satellite onboard switching device,
43...Switcher control unit, 44-48...Transmission frequency converter, 49-53...Onboard traveling wave tube for amplifying and transmitting frequencies ₁ to ₈ , 61-65...High frequency switching device, 59...Contact A, 60...Contact B, 66...
...Contact C, 67...Contact D, 68...Contact E, 6
9...High frequency switching device control section.

Claims (1)

[Claims] 1. In the multi-beam satellite communication system, in which communication is performed by switching between multiple spot beams on a satellite in a time-division manner, interference occurs on the satellite with the frequency assigned to each spot beam as a frequency for communication during clear weather. A transmitting frequency converter that generates a carrier wave of a different frequency, a transmitting power amplifier that amplifies the carrier wave to enough transmitting power to ensure sufficient line quality even in the presence of attenuation due to rain, and a transmitting power amplifier that generates a carrier wave of a different frequency. a switching device capable of switching a received signal from another area on the ground to be supplied to a spot beam directed to an input terminal of the transmission frequency converter; and a switching device control section for controlling the switching device. a high frequency switch for supplying the output of the transmission power amplifier to a horn that forms a spot beam directed toward the rainy area, and a high frequency switch control section that controls the high frequency switch; When it rains in an area irradiated by a specific spot beam and the radio waves are attenuated, the signal to be transmitted to the area is transmitted to the specific spot beam via the transmitting frequency converter and the transmitting power amplifier. A transmission power control system for satellite communication, characterized in that it is possible to switch the power to be supplied to a forming horn.