JPH02280424A - Transmission power control system - Google Patents

Abstract

PURPOSE:To obtain a line with high reliability and high quality even at production of rainfall attenuation without using any adaptor at a small sized station side by comparing information generated from a signal from a small sized earth station with a preset reference value and controlling the transmission power to the small sized earth station in a preset range. CONSTITUTION:A central station 2 compares a reception signal C/N, a reception level or a pseudo bit error rate from groups of small sized earth stations A1-An, B1-Bn with a preset reference value to obtain the difference of both and estimate the rainfall attenuation in the incoming lines of the groups A1-An, B1-Bn from the difference, references the estimated quantity to control the transmission power from the central station 2 to the groups A1-An, B1-Bn thereby relieving the deterioration in the signal quality due to the rainfall attenuation caused in the outgoing line of the small sized earth stations. Thus, the revision of equipment of the small sized earth stations is not required, the reliability of the satellite communication line is improved and the system is efficiently operated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a transmission power control method in a satellite communication system, and is particularly effective for communication between small earth stations that uses a frequency band that is subject to rainfall attenuation. This is a transmission power control method.

(Conventional technology) In recent years, communication satellites have become larger, digital communication technology has developed,
With the development of communication elements, small earth stations using small antennas are being introduced into satellite communication systems. In particular, a small earth station communication system using the Ku band (11-12/14Gllz) is seen as a promising future low-cost satellite communication system.

By the way, when a frequency band of 10GH2 or more is used in satellite communication, rain attenuation becomes a big problem in line configuration.

Rain attenuation measures are particularly important for small earth stations operating at low elevation angles.

Conventionally, space diversity methods and transmission power control methods have been considered as rain attenuation countermeasures. The space diversity method is a method that maintains line quality by installing two separate antennas far enough in front of each other so that they are not affected by rain at the same time, and selecting the one of the two antennas that is less attenuated by rain. It is. In addition, the transmission power control method is usually a method of controlling the transmission power for the uplink of the own station by referring to the reception information of the earth station, for example, the peak signal level.

(Problem to be solved by the invention) A transmission power control method performed by a central station (including a relay station, hereinafter the same) as a means of improving line quality in a communication system between small earth stations using a frequency band of 10 GIIz or higher includes the following: 1) something that compensates for rainfall attenuation in the uplink of the central station; and 2) a small earth station that measures the received signal quality and sends the information back to the central station, which then uses it to transmit data to the small earth station. There is a closed-loop control method that controls the transmission power so that the received signal quality at the small earth station remains constant.

The latter method is an effective method when it is performed using a line connection method or 5 cpc, but it requires a signal quality measurement circuit on the small earth station side and a change in the format of the signal configuration for transmitting the measurement results to the central station. be. Therefore, it is necessary to change or modify the system device specifications, and it is not possible to reduce the device price.

The present invention has been devised to eliminate the above-mentioned disadvantages.
While an additional device using the conventional technology or closed-loop control method is required on the small earth station side, the present invention does not require any additional equipment on the small earth station side, and only the central station can control fluctuations in the signal quality of the small earth station ( It is characterized by estimating the attenuation (mainly caused by rainfall) and controlling the transmission power from the central station to the small earth station. Furthermore, the present invention achieves the same effect as the closed loop control method described above at the central station, making it possible to provide a highly reliable and high quality line even when rain attenuation occurs.

(Structure and operation of the invention) FIG. 1 is a diagram for explaining a communication system (double hop) between small earth stations via a relay station to which the present invention is applied. In FIG. 1, 1 is a satellite, 2 is a central station, and 3 to 8 are small earth stations. The link from the earth station to the satellite is called the uplink, and the link from the satellite to the earth station is called the downlink.

Communication between small earth stations in this configuration involves the central station 2 receiving multiple signals from each of the small earth stations 3 to 8 via the satellite 1, demodulating these signals independently, and then re-modulating them. By transmitting the signal to the satellite 1, the signal is transmitted to the target small earth station.

Note that as a configuration to which the present invention is applied, in addition to the configuration with one satellite as shown in FIG.
~5 to satellite 1 and 6 to 8 to other satellites (not shown)
A configuration in which an earth station having two antennas connected to the satellites and connected to the respective satellites is interposed as the central station 2 is also conceivable. No matter which configuration is adopted, the technical idea of the present invention is not changed.

By the way, when the same signal from a satellite is received by a micro-earth station and a central station, the central station with a large antenna can receive a much stronger signal, reducing the line margin (in other words, the ability to withstand rain attenuation). is large enough. The transmitter output from the ground to the satellite is 1 for a micro earth station.
A solid-state amplifier of about 3 W is used, and it is possible to obtain satellite power per channel.

Therefore, in a satellite communication system with such a configuration, the downlink has a smaller margin than the uplink, and when it rains, the downlink suffers from signal quality deterioration first.

Incidentally, the service range of satellite communication is generally wide, and it is expected that small earth stations will be distributed over a wide area with different weather conditions.

Therefore, in such a communication system that uses a frequency band of 10 GHz or higher, many small earth stations will not be affected by rain attenuation at the same time, and only some of the earth stations will be significantly affected by rain attenuation. become. If the connection between the central station and the small earth station is configured using a 5cpc line system, the deterioration of the line quality can be alleviated by selectively increasing the transmission power from the central station only for the small earth station that is experiencing rain attenuation. This enables efficient use of satellite power, bandwidth, and central station transmitter output, eliminates variations in reception levels due to satellite radiation patterns, and significantly improves line reliability. can.

(Embodiment 1) An embodiment will be described with reference to FIGS. 2 and 3. First, the configurations of both figures will be explained.

FIG. 2 is a basic equipment block diagram illustrating how the central station performs power control of transmission to the small earth station 3 in FIG. 1 when the small earth station 3 in FIG. Now, an embodiment will be described in which the received signal C/N detected from the received signal from the small earth station received by the central station is used as control information.

In Figure 2, 10 is received BPSK (two-phase phase modulation wave) I
F-fold signal 11 is a BPSK demodulator, 12 is an error correction unit, 1
3 represents a baseband digital signal. Also, 14 is B
2 for creating an unmodulated regenerated carrier wave from a PSK signal
The multiplier section 15 is a C/N measurement section that measures the C/N of the modulated wave. 16 is output information of the C/N measuring section 15, and 17 is a transmission power control section. 26 is a control signal from the transmission power control section 17, which is input to the variable attenuation section 20 where it is modulated by the BPSK modulation section 21. 19 is an IF times signal of the transmission BPSK.

22 is a baseband digital signal that is input to the BPSK modulation section.

Next, a block diagram of the transmission type power control section 17 is shown in FIG. Reference numeral 18 denotes external parameter inputs for setting operating conditions necessary for the transmission power control circuit 17 to control transmission power, including reference C/N, control period,
This includes the maximum value of the control amount, etc.

The reference C/N is set to 18°.

23 is a C/N difference detection section, and 24 is a reference C/N value setting section. Reference numeral 25 denotes a control information creation section, and the output thereof determines the amount of attenuation of the variable attenuation section 20. This amount of attenuation is determined as follows.

Generally, it is known that in the range of 10 to 20 GHz, the amount of rain attenuation increases by about 1.7 times the frequency. Therefore, the difference in C/N from the reference C/N value is A (dB)
Then, the amount of C/N deterioration A' in the downlink is expressed by the following formula (1)
It can be found by In other words, the amount of rain attenuation in the downlink is as follows, where K is the frequency ratio of the downlink and uplink, and fu and fd are the frequencies of the uplink and downlink.

On the other hand, the C/N deterioration due to noise increase can be roughly calculated using the following formula: % where T: System noise temperature during clear weather; Tr: Temperature in a rainy area.

Therefore, the total amount C of C/N deterioration of the micro earth station is given by the following equation (3) in dB value.

C= A' + 1101o D (dB)
(3) By determining the C/N difference A as described above, the total amount C of C/N deterioration in the downlink of the micro earth station can be determined.

Note that if the C/N difference A is negative, the cause may be a cause other than rainfall, such as a level change due to antenna pointing at a micro-earth station or a change in propagation conditions such as scintillation. In this case, the control amount is the negative transmission power control, that is, the transmission power is decreased.

Next, the operation of this circuit shown in FIGS. 2 and 3 will be explained.

The received BPSK IF signal 10 is input to a demodulator 11 of the BPS, passes through an error corrector 12, and is output as a demodulated baseband digital signal 13. On the other hand, BPSK
A part of the IF multiplied signal is branched and input to the doubler 14. The doubler 14 doubles the BPSK signal and converts it into a BPS
It is necessary to convert the K signal to an unmodulated continuous wave and measure the doubled signal C/N.
/N is output to the measuring section 15. The C/N measurement unit 15 measures the signal power to noise power ratio of the input signal, and
N is measured and C/N information 16 is input to the transmission power control section 17, and the reference C/N is 18゛ by the C/N Nth difference detection 3.
The C/N difference between the two is input to the control information creation section 25. The control information creation unit 25 converts the C/N information 16 into (C/N), for example.
N)m, and when the reference C/N18° is (C/N)S, if (C/N)S> (C/N)m, the difference between the two is A.
= (C/N)S-(C/N)+n is control information creation section 2
5, the control information creation section 25 calculates the variable attenuation amount C, and outputs the control signal 26 so as to reduce the attenuation amount of the variable attenuation section 20 by Ao. If A is negative, the control information creation section 25 outputs a control signal that increases the attenuation amount of the variable attenuator 20 by A.

As explained above, in the present invention, the central station receives a BPSK signal from a small earth station via a satellite, and measures the C/N from the received signal. If the transmission power from the small earth station is constant and the satellite repeater operates in a nearly linear region, most of the C/N variation is due to rainfall attenuation that occurs on the propagation path. This is thought to be caused by. Therefore, by referring to this C/N, it is possible to estimate the amount of rain attenuation from the small earth station to the satellite, and from this estimate, it is possible to estimate the amount of rain attenuation for the downlink of the small earth station or for the uplink/downlink. This is possible from the frequency ratio.

As already explained, downlink deterioration at small earth stations is also caused by increased noise that depends on the amount of rainfall attenuation, so the amount of increase in transmission power from the central station is equal to the C/N including the increased noise. Decide to compensate for the amount of deterioration.

In the explanation so far, C/N information is used to create the control signal 26, but in addition to this, a bit error rate depending on the received signal level and C/N may be used.

(Embodiment 2) FIG. 4 is a block diagram of a device for creating a control signal using the reception level.

The level detection section 30 can obtain the reception level by detecting the amplitude component of the reception IF signal 10.

This detection output is output to the level difference detection section 31.

This circuit receives an output from a preset reference reception level 32, detects a level difference between the two, and sends this difference to a control signal generator 25, where a control signal 26 is generated. The other explanations are the same as those in FIG. 2 of the first embodiment.

(Embodiment 3) FIG. 5 is a block diagram of a device that creates a control signal from a pseudo bit error rate.

In the method using the reception level shown in the second embodiment, the reception level fluctuates due to gain fluctuations in the reception system, making it difficult to create a highly accurate control signal.

However, the method of this embodiment provides a higher accuracy than the C/N detection method of the first embodiment.

Several measurement methods have already been proposed as methods for measuring the pseudo bit error rate (for example, Japanese Patent Application No. 57-185).
259). The input signal to the pseudo bit error rate measuring section 40 is the phase detection output of the BPSK demodulating section 11. The output of the pseudo bit error rate measuring section 40 is the bit error rate versus C/
C/N is input to the N converter 41 and corresponds to the bit error rate.
The signal is converted to H and input to the C/N Nth difference detection 3. The subsequent operations are similar to those described in FIGS. 2 and 3 of the above embodiment.

(Embodiment 4) In the explanation up to now, transmission power control for the uplink of the central station has not been mentioned, and it goes without saying that this transmission power control is essential in order to apply the present invention.

In the present invention, as a prerequisite for controlling the transmission power to the partner small earth station by referring to the received signal at the central station, the operation is explained assuming that fluctuations in the received signal level occur on the uplink of the partner small earth station. . Therefore, in order to apply the present invention, it is necessary to eliminate the effects of rain attenuation occurring on the upstream/downstream propagation paths of the central station.

In addition to the signals received from the small earth station mentioned above, the received signals on the downlink include beacon signals transmitted from satellites.

FIG. 6 is a block diagram of an apparatus using a beacon signal.

Reference numeral 50 is an output from an antenna, which passes through a low noise amplifier 51, a beacon signal frequency converter 52 selects a beacon signal, and a beacon signal C/N measuring device 53 converts the beacon signal C/N.
N is measured. The measurement output 54 of the beacon signal C/N measuring device 53 is sent to the transmission power control section 17.

Since the beacon signal is subject to rainfall attenuation only on the downlink of the central station, subtracting the amount of rainfall attenuation received by the beacon signal from the reception level or received C/N of the small earth station will result in the attenuation occurring on the uplink of the small earth station. It is possible to detect level fluctuations.

Note that the amount of rain attenuation of the beacon signal can be determined by referring to the beacon signal level during clear weather or the beacon signal C/N.

On the other hand, the central station's transmission power control amount for the uplink is calculated from the uplink/downlink frequency ratio with reference to the rainfall attenuation measured by the beacon signal, or the central station configures a satellite return loop. In systems where this is possible, the central station transmission power is adjusted so that the difference between the reception level or reception C/N of the beacon signal during clear weather and the reception level or reception C/N of the central station transmission return signal remains almost constant even when it rains. This control makes it possible to control the satellite input level of the signal transmitted from the central station to be constant.

Note that the present invention can be applied in exactly the same way to a system between earth stations (single hop), but in this case, it is applied only to one of the competing earth stations. Furthermore, in either system configuration (single hop or double hop), the amount of control of the transmission power is finite, so the maximum amount of control must be set in advance in the transmission power control circuit.

In the first embodiment described above, the operation was shown using 13PSK as the modulation method, but even if QPSK is used, the handling is exactly the same, and in this case, as shown in FIG.
If the 2-multiplier circuit of 4 is changed to a 4-multiplier circuit, an unmodulated wave can be reproduced. Further, in this example, an example in which a multiplier circuit is used to create a non-modulated wave has been described, but the same effect can be obtained even if a carrier wave reproduction signal using a commonly used Costas loop is used.

Also, when FM is used as the modulation method, it is impossible to use the pseudo bit error circuit shown in Figure 5, but the C/N information in Figure 3 is obtained from the signal from the output of the FM detector. It can be easily created by measuring out-of-band noise. Of course, the method shown in FIG. 4 is also applicable.

Each function of the transmission power control section 17 shown in FIGS. 3 and 4 is as follows.
This can be easily realized by digital processing using a microprocessor or the like. Note that the variable attenuation section 20 needs to include a drive circuit for controlling the variable attenuation section from the control signal 26. Furthermore, if the C/N information or reception level is input as an analog quantity, it is necessary to enable digital processing via an A/D converter.

(Effects of the Invention) As explained above, the present invention allows a central station to compare the received signal C/N, reception level, or pseudo bit error rate from a small earth station with a preset reference value, and calculate the difference between the two. The amount of rainfall attenuation in the uplink of the small earth station is estimated from the difference, the transmission power from the central station to the small earth station is controlled by referring to this estimated amount, and the amount of rainfall attenuation in the uplink of the small earth station is controlled. It is characterized by relieving signal quality deterioration caused by rain attenuation.

Furthermore, in the present invention, the operation of the transmission power control method for rain attenuation countermeasures has been described in which the transmission power from the central station is increased in order to compensate for the attenuation of radio waves caused by rain attenuation. However, the basic operation of the present invention is to detect the signal strength from the small earth station at the central station and perform transmission power control based on the detected signal strength. Therefore, since transmission power control functions for all things that affect the reception strength of radio waves, it is not only effective against rain attenuation, but also against antenna bowing errors due to satellite position drift, scintillation facing that fluctuates extremely slowly, etc. You can expect the same effect.

Furthermore, when the present invention is applied, there is no need to make any changes to the equipment of the small earth station, and furthermore, by adopting the present invention, the reliability of the satellite communication line can be improved and the system can be improved. It becomes possible to operate efficiently.

The present invention can also be applied to normal communication between earth stations without going through a central station.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a satellite communication system according to the present invention, FIG. 2 is a block diagram of a basic device according to the present invention, and FIG. 3 is a block diagram of a transmission power control unit using C/N information. Figure 4 is a block diagram of a device that creates a control signal using the reception level, Figure 5 is a block diagram of a device that creates a control signal using a pseudo error rate, and Figure 6 is a block diagram of a device that measures a beacon signal. It is a diagram. 1...Satellite, 2...Central station, 3-8
...Small earth station, 10...Reception BPSK IF
Double signal 11... BPSK demodulation section, 12... Error correction section, 13... Baseband digital signal, 1
4...2 multiplication part, 15...C/N measurement part,
16... C/N information 17... Transmission power control section, 18... External parameter setting input, 19
...For transmitting BPS IF multiplied signal 20...Variable attenuation section, 22...Baseband digital signal, 23...
C/N difference detection section, 24... reference C/N value setting section,
25... Control signal creation section, 26... Control signal, 30
...Level detection section, 31...Level difference detection section,
32... Reference reception level setting section, 40... Pseudo bit error rate measuring section, 41... Bit error rate to C/N conversion section, 50... Output from antenna, 51... Low noise Amplifier, 52... Frequency converter, 53... Beacon signal C/N measuring device, 54... Beacon signal measuring section output, 55... Frequency converting section. Figure 4

Claims (4)

[Claims] (1) In a satellite communication system that configures a communication line between small earth stations via a central station on the ground, the central station that receives signals from the small earth station uses a reception C created from the signal from the small earth station. /N, the reception level, or the pseudo bit error rate measured from this reception signal is compared with a preset reference value for each information, and from the difference value, the information at the small earth station is determined. Signal power control characterized by estimating fluctuations in downlink signal level or signal quality from a reference value, and controlling transmission power to the small earth station within a preset value range according to this estimated value. method. (2) In a satellite communication system in which earth stations configure a communication line via a satellite, the received C/N, the received level, or this received signal created using the signal received by one of the earth stations forming the line. At least one piece of information in the pseudo bit error rate created from the above is compared with a preset reference value for each piece of information, and from the difference value, it is determined whether there is a change in the signal level or signal quality in the downlink at the other earth station. A transmission power control method characterized in that the transmission power to a partner earth station is controlled within a preset value range according to the estimated value. (3) The central station that performs transmission power control converts the amount of rainfall attenuation caused in the downlink propagation path into a reception level from the small earth station,
Alternatively, the central station is provided with means for excluding from fluctuations in received C/N, and the central station is configured such that the arrival level of the signal transmitted from the central station to the satellite is approximately constant even when the rain attenuation occurs. 2. The transmission power control method according to claim 1, wherein the transmission level is controlled within a preset value range. (4) The earth station that performs transmission power control converts the amount of rain attenuation caused in the downlink propagation path into a reception level from the small earth station,
Alternatively, the earth station is provided with a means for excluding from fluctuations in received C/N, and the earth station is configured such that the arrival level of the signal transmitted from the earth station to the satellite remains almost constant even when the rain attenuation occurs. 3. The transmission power control method according to claim 2, wherein the transmission level is controlled within a preset value range.