JP2013143663A - Satellite diversity system using close range two earth stations - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sufficient diversity effect in the Sat-D system for avoiding line disconnection due to rainfall by receiving signals from two satellites and switching to a line of small rainfall attenuation in the fixed satellite services using such as Ku, Ka band, and to reduce the cost of an entrance line in the conventional SD system.SOLUTION: In order to receive signals containing the same information from first and second satellites, two earth stations located not in the same place but in the places separated about 3-5 km are used. When the rainfall attenuation increases in the sky above one earth station and the threshold of C/N required in the system is exceeded, switching is made to other earth station and to the diversity mode, thus enhancing the availability ratio of line. The two earth stations are located at east and west positions so as to reduce the probability of simultaneous rainfall attenuation in two earth stations, when compared with a case where the two earth stations are located in the north-south direction.

Description

Signals from two satellites using short-range 2 earth stations separated by 3-5 km to avoid attenuation in frequency bands with high rain attenuation such as 14/12 GHz (Ku) band and 30/20 GHz (Ka) band And a satellite diversity (Sat-D) system using a short-distance 2 earth station for improving the line availability by the diversity effect.
Since the launch of fixed satellite communications using the 6/4 GHz band about 40 years ago, many satellites have been launched on the geostationary satellite orbit (GSO), and GSO congestion has become a problem. For this reason, use of the Ku band and the Ka band, which are higher frequency bands, has become popular. In such a frequency band exceeding 10 GHz, attenuation due to rain is large, and a large rain merge is taken into consideration at the time of design, and high performance is required for the earth station antenna and the high power amplifier (HPA device). It is a costly satellite system.
The present invention receives signals of the same information from two satellites when attenuation due to rain occurs, receives signals from satellites with low rain attenuation, and follows other rain attenuations according to the movement of rain clouds that generate rainfall. By applying the Sat-D method of switching and receiving signals from small satellites, it is possible to reduce the time rate of line disconnection.
The conventional Sat-D method seems to be considered in patents such as Hatsuda shown in Patent Document 1 and other papers published by Hatsuda in IEEE (American Institute of Electrical and Electronics Engineers) papers and IEICE journals. In addition, a method has been proposed in which two earth stations are installed at the same point, signals from two satellites are received, and a signal having a high signal strength is employed. In this method, if the distance between two satellites is sufficiently large with respect to the rain clouds generated above the two earth stations, a diversity effect can be obtained and the line operation rate can be improved. However, because the earth station is used at the same point, if the rain area is wide or the distance between two satellites is small, both satellite signals are attenuated and sufficient diversity effect cannot be obtained. Exists.
In the present invention, in order to more effectively avoid rain attenuation, a signal from two satellites is received using a short-distance two earth station separated by 3 to 5 km, and the line operation rate is improved by the diversity effect. A Sat-D system using two short-range earth stations is proposed.
The idea is that the rain area of rain clouds such as cumulonimbus clouds that cause large rain attenuation is generally 3 to 5 km, and the rainfall correlation between earth stations 3 to 5 km away is expected to be very small and probable. This improves the overall line availability of the system.

The satellite communication earth station apparatus using a frequency band with high rain attenuation, such as Ku band, Ka band, etc., has a large rain attenuation. In order to communicate a required circuit channel, a large antenna, An output HPA device is required. For example, if a 150 W HPA device is to be realized in the Ka band, an expensive HPA device using a tube type such as klystron or TWT is required, and the HPA device is expensive, resulting in a significant increase in system cost and an inexpensive satellite. It was a bottleneck for providing services. Further, the Ku-band and Ka-band antennas having a diameter of 10 m are required to have a fine mirror surface accuracy and are expensive.
Up to now, various methods for improving the operating rate have been devised in order to cope with large rain attenuation in frequency bands such as the Ku band and the Ka band. This includes the following methods.
(1) Use of a large antenna and a high-power transmitter,
(2) Improvement by modulation / demodulation method (error correction method, PSK phase number variable method, bit rate variable method, etc.)
(3) Diversity methods (site diversity method (SD method), Sat-D method, time diversity method (TDD method), etc. have been studied.
Among them, various diversity methods are methods that utilize the movement of the rain region, the attenuation of only a limited region, and the like. FIG. 1 shows a block diagram of a configuration of a conventional SD system. As shown in FIG. 1, the same signals 4 and 5 from the satellite 1 are received by the two earth stations 2 and 3 that are separated from each other, and the signal 4 of the earth station that is less affected by the rain 6 and has a strong signal strength is adopted. By doing so, the line deterioration due to the rain 6 is improved. The SD system has already been put to practical use by Intelsat international satellite communications, etc., to receive signals away from the earth station (Yamaguchi Station-Hamada Station) about 100 km and improve the operating rate.
In this SD system, when the earth station interval of about 100 km is taken, the cost of the entrance line between the two earth stations is increased, and the diversity effect is great to increase the system cost, but it is disadvantageous in cost comparison, and the remainder Many have not been put to practical use.
FIG. 2 shows a block diagram of a conventional Sat-D scheme. As shown in FIG. 2, two earth stations 26 and 27 are installed at the same point, and signals 23 and 24 from two satellites 21 and 22 transmitting the same satellite information are received. The operation rate is improved by adopting the signal 24 of the earth station 27 having a small signal strength.

Japanese Patent Laid-Open No. 2008-109557, “Satellite Diversity Device”: Hatsuda et al.'S patent that uses a Luneberg antenna capable of receiving a plurality of satellite signals with one antenna mirror surface to realize a low-cost diversity device It is. This patent uses a Luneberg antenna installed at one point, and is different from the Sat-D system using an earth station about 3 to 5 km away from the present invention.

JP-A-59-85143, “Satellite Communication System”: In a satellite communication system in which a large number of earth stations perform narrow-band communication via satellites using a centralized control request allocation multiple access system, a distance within a certain distance of the earth station is exceeded. At least two remote earth stations are each composed of centralized control means for transmitting centralized control by transmitting a control signal of request allocation multiple access method and pilot transmission means for transmitting pilot signals, etc., and monitoring the propagation loss of pilot signals This is a patent for controlling the sending and stopping of control signals. It is unrelated to the Sat-D scheme of the present invention, which uses an earth station about 3-5 km away.

Japanese Patent Laid-Open No. 05-145457, “Transmission Power Control System Using Site Diversity”: In a TDMA satellite communication system, a transmission power control system using site diversity for controlling transmission power in the uplink, This is a patent that can minimize the transmission power control error while minimizing it. For this reason, it is irrelevant to the Sat-D system of the present invention using an earth station about 3 to 5 km away.

Ku-band, Ka-band, especially Ka-band satellite communication earth stations are expensive for each device, and therefore it is necessary to reduce the cost in consideration of the line parameters and the device cost. In addition, due to rain attenuation, the signal strength from the satellite may not satisfy the predetermined signal power band noise power ratio (C / N) necessary for continuing communication, and at this time, the line is disconnected, Since the reliability of the system is lowered, it is necessary to improve the operation rate by some method.

As a countermeasure, various diversity methods are effective, but each has advantages and disadvantages. Among them, the Sat-D method is considered to be effective, but the conventional method receives signals from two satellites at two earth stations at the same point as shown in FIG. When the distance between the two satellites is narrow or the distance between the two satellites is narrow, there may be a case where a sufficient diversity effect cannot be obtained.
In order to solve this problem, the present invention implements the Sat-D scheme using a short-range earth station that is about 3 to 5 km away, which is a distance having a small rainfall correlation during heavy rain, and achieves sufficient diversity. An effect is obtained.
In general, the rain area when large rain attenuation occurs is cumulonimbus and the like. In many cases, the rain area is relatively narrow, about 3 to 5 km, and this rain area moves slowly with the wind. For this reason, the probability of simultaneous rain attenuation between two earth stations separated by about 3-5 km is sufficiently low, and the diversity effect of the Sat-D method is greatly improved by separating the two earth stations about 3-5 km. It is expected.

The problems that the invention needs to solve can be summarized as follows.
(1) Issues of enhancing the diversity effect of the conventional Sat-D method As shown in Fig. 2, the conventional Sat-D method uses two earth stations at the same point and includes two satellites 21,22. When the signals 23 and 24 are received and the rain region is wide or the orbit interval between the two satellites is narrow, there may be a case where a sufficient diversity effect cannot be obtained. For this reason, some method that can obtain a greater diversity effect is expected.

(2) Measures to increase the cost of the entrance line in the SD system The conventional SD system has a greater diversity effect as the distance between the two earth stations is larger, and the site diversity system 2 earth station that has been put into practical use. The distance between them is as large as about 100 km. The cost of the entrance line at such a distance is high and the operating rate is improved, but it is often disadvantageous when comparing the system cost with other systems.

As means for solving the problems to be solved by the above invention, the following is applied.
(1) Method of increasing the distance between earth stations in order to enhance the diversity effect of the Sat-D system In the conventional Sat-D system, two earth stations are installed at the same point, and two satellites are used. It is conceivable that there may be a problem with the site diversity effect when the signal from the satellite is received and the satellite separation angle is small.
In order to solve this problem, in the present invention, two satellites are provided with a configuration in which they are separated from each other by 3 to 5 km corresponding to the size of the rain area when large rain attenuation occurs and are connected by an entrance line. , The probability that two earth stations will suffer rain attenuation at the same time decreases, and it becomes possible to improve the operating rate of the system.
(2) Measures for increasing cost of entrance line in SD system In the conventional site diversity system, the entrance line is as large as 50 km to 100 km, and the entrance line cost is enormous.
In the present invention, the distance between the two earth stations is about 3 to 5 km, and the cost of the entrance line can be kept sufficiently small. As a result, it is advantageous for cost comparison with other systems, a sufficient diversity effect is obtained, and a system with low cost can be constructed.
In general, considering that the rain area moves from west to east, the two earth stations are arranged east and west, so that the diversity effect can be increased compared to the north-south direction.

  (1) In the frequency band exceeding 10 GHz in the Ku band, the Ka band, etc., the signal attenuation due to rain is large. For this reason, the required system downtime ( For example, 0.5% per year) is secured. For example, in the Ku band, about 10 dB in the 14 GHz band and about 6 dB in the 12 GHz band, and in the Ka band, about 15 dB in the 30 GHz band and about 10 dB in the 20 GHz band, and a line unavailability of 0.5% / year (about 40 hours). ) Can be realized (may vary slightly by region and year). For this rain margin, not only simply increasing the antenna diameter or increasing the transmission power, but also replacing it with a diversity gain due to the diversity effect, even a small earth station can satisfy the required line availability. It becomes possible. This makes it possible to use a small earth station, thereby reducing the system cost.

(2) In the present invention, the line operating rate is improved by taking a distance of about 3 to 5 km between the two earth stations. Compared to a long entrance line like the conventional SD system, the distance between the entrance lines is improved. Since the distance is short, the entrance line cost can be greatly reduced.
(3) In the conventional Sat-D system, if the interval between two satellites is not sufficiently large, sufficient operation rate cannot be improved. In the present invention, by taking a distance of about 3 to 5 km between the two earth stations, the correlation between the two earth stations of the rain attenuation becomes small, so that it is expected that a large diversity effect can be obtained.
(4) In the conventional Sat-D method, two earth stations at the same point are used, but if natural disasters (fire, flood, earthquake, etc.), human disasters (terrorism, war, etc.) occur When a disaster occurs, both the two earth stations go down and the line is completely disconnected. On the other hand, in the Sat-D system of the present invention, since a distance of about 3 to 5 km is taken between two earth stations, there is a high probability that one earth station will not be damaged even if a disaster occurs. It is possible to improve system reliability in system safety management. This is particularly effective for large-scale disasters that are likely to be damaged in the future, such as large-scale earthquakes, large-scale tsunamis, and large-scale international terrorism.
(5) Rain attenuation occurs and the Sat-D system is activated at about 0.5% of the year (1.0% even if margin is expected), and there is no rain attenuation at other times. The line quality is good enough. Other than this time, when the weather is about 99% per year, it is possible to transmit and receive different channels independently of the two earth stations of the Sat-D system. This means that two earth stations can perform communication for two channels in fine weather, and communication for one channel is performed by two earth stations only at about 0.5% of the year. For this reason, in the Sat-D system, it is considered that the reduction in the number of communication channels that can be operated is about 0.5% of the annual rate, and the influence on the effective use of the line is small. Other time rates, except about 0.5% of the year, can transmit normal lines with two earth stations, and increase the number of lines in the system.

The block diagram of the structure of the conventional SD system is shown. The block diagram of the structure of the conventional Sat-D system is shown. The block diagram of the structure of the Sat-D system using two short-distance stations of this invention is shown. The flowchart of the detail of operation | movement of the Sat-D system of this invention is shown.

In the conventional Sat-D method, two earth stations at the same point are used. However, in the present invention, the operation of the Sat-D method is performed by arranging the two earth stations in the east-west direction at a distance of about 3 to 5 km. When the rate is improved and the rain is not attenuated in fine weather, the two earth stations independently transmit and receive another communication channel.
In FIG. 3, rain attenuation 35 occurs, and the same channel from the two satellites 31 and 32 is received by the two earth stations 36 and 37. If the signal 33 from the satellite 31 is attenuated by the rain 35, the earth station 36 When the state close to the line disconnection is reached, the 2 earth station switches to the signal 34 from the satellite 32 having a strong signal strength by the switch 43, and the earth station having a strong signal strength not affected by the rain zone. 37 channels are employed and the receiver 44 demodulates the signal.
When the rain zone moves and the signal strength of the earth station 37 becomes weak, control is performed to switch to the other earth station 36 and continue communication.
Since the two earth stations are about 3 to 5 km away from each other in the east-west direction, the probability of simultaneous attenuation of the two earth stations is lower than that of the same earth station, which makes it possible to improve the line operation rate.
In Japan, most of the rainy areas move almost east and west, and compared to the two earth stations located in the north-south direction, the probability that the rain area covers the two earth stations at the same time is small, and the probability that the line will be disconnected at the same time is small. It is possible to hold down.

A breakthrough is necessary to improve the diversity gain of the conventional Sat-D method and to prevent the cost of the entrance line in the conventional SD method.
In the present invention, as shown in FIG. 3, the two earth stations 36 and 37 are installed in the east-west direction at a distance of about 3 to 5 km to transmit and receive signals from the two satellites 31 and 32. In a state where rain attenuation does not occur in fine weather, the two earth stations 36 and 37 are used to independently receive the two satellites 31 and 32, and perform normal communication channel transmission and reception.
Assume that rain attenuation 35 occurs due to cumulonimbus or the like, and the attenuated signal 33 from the satellite 31 is received by the earth station 36, and the level detection circuit 38 detects that this level has reached a state close to a line disconnection. . At this time, the communication channel is limited, and the shift to the Sat-D diversity communication mode in which one satellite communication is performed with two satellites. Signals 33 and 34 of the same communication channel are transmitted from the two satellites 31 and 32. This signal is received simultaneously by the two earth stations 36 and 37.
The signal level detected by the level detector 38 is compared with the signal detected by the level detection circuit 39 by the comparison circuit 40 when the signal 34 from the satellite 32 is received by the earth station 37.
When the level determination circuit 41 determines that the signal level received by the earth station 37 from the satellite 32 is high, the switching control circuit 42 is driven and the switch 43 is controlled to switch to the earth station 37 side. The received signal is demodulated by the receiver 44.
Since the two earth stations 36 and 37 are separated by about 3 to 5 km in the east-west direction, the probability that the two earth stations 36 and 37 simultaneously receive the rain attenuation 35 is small. When one earth station reaches the rain attenuation approaching the line disconnection, it switches to a mode in which the other earth station transmits and receives.
When it is confirmed that the signal 34 having a strong signal strength that is not affected by the rain region 35 continues to be transmitted / received through the channel of the earth station 37 and the rain region 35 moves and the signal strength becomes weaker, the other signal is received. The control is performed so as to continue the communication by switching to the earth station 36.
When it is detected that the rain zone 35 has passed over both earth stations, the amount of rain attenuation has decreased, and has become a value sufficient to maintain the line, the Sat-D diversity communication mode The configuration is canceled and each earth station returns to the normal mode in which its own channel is transmitted and received. About 99% of the year is this normal mode.

FIG. 4 shows a detailed flowchart of the operation of the Sat-D method of the present invention. In steps S1 and S2, it is determined whether the signal intensity from the satellites 31 and 32 divides a threshold value for satisfying a predetermined line maintenance. If the signal strength from the satellites 31 and 32 does not divide the threshold value for satisfying the predetermined line maintenance in steps S1 and S2, the earth stations 36 and 37 normally operate in steps S3 and S4. Conduct communication. This hour rate is approximately 99% per year.
In step S5 and S6, when the signal strength from the satellites 31 and 32 divides the threshold value for satisfying the predetermined line maintenance, the signal strength from the satellite 31 is compared in step S7. . If the signal intensity from the satellite 31 is high at step S8, the reception is switched to diversity reception at the earth station 36 at step S9, and demodulated by the receiver 40 at step S10. If the signal strength from the satellite 31 is small in step S11, the reception is switched to diversity reception in the earth station 37 in step S12, and demodulated by the receiver 44 in step S13.

(1) As explained so far, as a method for improving the annual unavailability in the fixed satellite communication system using the Ku band, the Ka band, etc., the improvement effect is larger than the conventional Sat-D system ( Diversity gain is large), and line quality can be improved by improving the annual availability factor.
(2) Since a large diversity gain can be obtained, the required values for various parameters (antenna diameter, transmission output, etc.) of the earth station for diversity are relaxed, thereby enabling ultra-small antennas, low-power transmitter output, etc. It becomes possible to operate with. For this reason, the system cost is improved, and an economical and high-performance system can be realized.
(3) Since the length of the entrance line is about 3 to 5 km, the cost of the entrance line can be reduced compared to the cost burden of an expensive entrance line with a length of several tens to 100 km of the conventional SD system. In addition, a comprehensive economic system configuration is possible.
(4) Since the two earth stations perform normal communication by setting the line independently during normal times, communication at the maximum transmission rate at each earth station is possible at most time rates of the year.
(5) When it rains, the satellites 31 and 32 transmit the same signal, and adopt only the signal with strong signal strength to obtain diversity gain, but this time rate is about 0.5% of the year The impact on the overall system capacity reduction is very small.
(6) Since two earth stations are installed at a distance of about 3 to 5 km, even if the earth station is damaged by a natural disaster or human disaster, the probability that the remaining diversity earth stations will be damaged at the same time is reduced. It will be advantageous from the viewpoint of system crisis management.

1: satellite 2, 3, earth station 4, 5: signal from satellite 1, 6: rain attenuation, 7: switch, 8: receiver, 21, 22: satellite, 23: signal from satellite 21, 24: Signal from satellite 22, 25: Rain attenuation, 26, 27: Earth station, 28: Switch, 29: Receiver, 31, 32: Satellite, 33: Signal from satellite 31, 34: Signal from satellite 32 Signal: 35: Rain attenuation, 36, 37: Earth station, 38, 39: Level detection circuit, 40: Comparison circuit, 41: Level determination circuit, 42: Switching control circuit, 43: Switch, 44: Receiver,

Claims (2)

In a satellite communication system that uses a frequency band with high rain attenuation, a point that is about 3 to 5 km away from the same location in order to receive signals containing the same information from the first and second satellites 31 and 32 Configured to use earth stations 36 and 37 arranged in
When the rain attenuation 35 is generated on the line of the earth station 36 and it is detected that the signal level in the level judgment circuit 38 of the earth station 36 has reached a state close to the line disconnection, the level judgment of the other earth station 37 is made. The signal level in the circuit 39 is compared with the comparison circuit 40, the level determination circuit 41 determines that the signal level is close to the line disconnection, the switching control circuit 42 controls the switch 43, and the earth station having a strong signal level 37 to maintain communication by receiving the signal at 37 and demodulating at receiver 44
When the rain attenuation 35 moves and it is detected that the signal level in the level determination circuit 39 of the earth station 37 has reached a state close to a line disconnection, the same control as above is performed, and the signal level is strong. A satellite diversity system using two short-distance earth stations characterized by receiving the signal of the line, In claim 1, the two earth stations 36 and 37 are installed in the east-west direction at a distance of about 3 to 5 km, and are configured to transmit and receive signals from the two satellites 31 and 32. The station 36, 37 is configured to reduce the probability of receiving the rain attenuation 35 at the same time, and when one earth station reaches the rain attenuation near the line disconnection, the other earth station is switched to the mode in charge of transmission / reception. Satellite diversity system using two short-distance earth stations characterized by improving the line utilization rate.