JPH02280423A - Transmission power control system using superimposing modulation - Google Patents

Abstract

PURPOSE:To keep excellent line quality with simple constitution for a great number of small sized earth stations by informing reception signal quality information due to superimposing modulation from a small sized earth station to a relay earth station and applying compensation control against rainfall attenuation with the relay earth station centralizingly. CONSTITUTION:The result of measuring the quality of the reception signal affected due to rainfall attenuation or the like at groups of small sized earth stations A1-An, B1-Bn is informed to the relay earth station 2 by using superimposing modulation and the transmission power of the relay earth station 2 to the small sized earth stations A1-An, B1-Bn is controlled within a range set in advance. Then the operation to incorporate the result of measurement result of the quality of the reception signal to the substantial transmission signal is not required, and the system is easily applied also to the existing small sized earth station installation, and the system cost is made inexpensive.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a transmission power control method in a satellite communication system, and is particularly applicable to communication between small earth stations using a frequency band accompanied by rainfall attenuation. This paper relates to an effective 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 to 12/14 GHz>) is seen as a promising future low-cost satellite communication system.

As described above, when a frequency band of 10 GHz or more is used in a satellite communication line, rain attenuation becomes a major problem in line operation. Measures to prevent this are especially important for small earth stations that operate at low elevation angles.

Conventionally, a space diversity method and a transmission power control method have been considered as rain attenuation countermeasures.

The space diversity method prepares two antennas, installs them far enough away from each other so that they are not affected by rain at the same time, and maintains the line while selecting the one with the least rain attenuation of the two antennas. This is a method to do so.

In addition, transmission power control methods usually control the transmission power of the local station by referring to the reception information of the earth station concerned, such as the beacon signal level, or the reception signal quality measured by the small earth station is used to control the transmission power of the relay earth station. There is a transmission power control method (Japanese Patent Application No. 60-200517') in which notification is made along with the transmission signal.

Communication methods between small earth stations include direct communication between small earth stations via satellites, and methods in which a relay earth station is used to receive and demodulate signals from the small earth station via the relay earth station or satellite.・There is a method in which the signal is re-modulated and transmitted to the other party's small earth station via a satellite. In the latter method using a relay earth station, the signal from the small earth station is received by the large antenna of the relay earth station, so the reception C/N at the relay earth station (
Although the signal power to noise power ratio (signal power to noise power ratio) is sufficiently large, it is difficult to secure a sufficiently high margin against rain attenuation on the side of a small earth station that receives signals from a relay earth station with a small antenna.

(Problem to be Solved by the Invention) Using the above-mentioned space diversity method as a rain attenuation countermeasure for a small earth station has a problem in terms of the cost of duplicating equipment. Further, the aforementioned transmission power control method has a drawback in that a part of the original transmission signal is used to report received signal quality information, and the device requires some modification.

Therefore, the present invention enables the relay earth station to easily add functions to the device, and to maintain the reception level of the small earth station almost constant regardless of changes in the environment such as rainfall, without using a part of the transmitted signal. The purpose of this study is to provide a method for controlling the transmission power of

(Means for Solving the Problems) The present invention measures the quality of received signals affected by rain attenuation, etc. at each small earth station, and reports the results to a relay earth station using superimposed modulation. This method maintains good received signal quality by controlling the transmission power of the station to the small earth station within a preset value range, and its feature is that superimposed modulation is used to transmit received signal quality information to the small earth station. This is where the information is sent from to the relay earth station.

This method is extremely easy to add functions to existing small earth station equipment, and is also extremely easy to maintain, operate, and monitor.

Compared to conventional methods, the present invention does not require any operations to incorporate the measurement results of the received signal quality into the original transmitted signal, and is a method that can be easily applied to existing small earth station equipment. The purpose is to provide an effective and inexpensive transmission power control method that can be applied to communication between small earth stations.

(Structure and operation of the invention) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram for explaining a communication system between small earth stations via relay earth stations to which the present invention is applied. In the figure, 1 is a satellite, 2 is a relay earth station, and 3 to 8 are small earth stations. In addition, the uplink from the earth station to satellite 1,
The line from satellite 1 toward the earth station is called the downlink. Also,
It is assumed that communication between each small earth station is set using a frequency division method.

In this configuration, the relay earth station 2 receives a plurality of signals from each of the small earth stations 3 to 8 via the satellite 1, demodulates these signals independently, re-modulates them, and transmits them to the satellite 1. In addition, as a configuration to which the present invention is applied, in addition to the configuration in which there is one satellite as shown in FIG.
A configuration is also conceivable in which the earth station 5 is connected to the satellite 1, the earth stations 6 to 8 are connected to other satellites (not shown), and an earth station having two antennas connected to each satellite is interposed as the relay earth station 2. Since the technical idea of the present invention is not changed no matter which configuration is adopted, the following explanation will proceed using the configuration shown in FIG. 1 as an example.

In such a configuration, in order to reduce the communication cost of the small earth station, the small earth station is generally configured with a small antenna and a low-power transmitter, so the margin of transmission level or reception level for line operation ( margin) is small.

In particular, the reception level has little margin because the satellite transmission output per channel is small and the reception antenna gain is also small. Therefore, the downlink signal quality of the small earth station deteriorates first due to rainfall.

Therefore, in the transmission power control at the relay earth station in the present invention, the signal quality measured at each small earth station is reported to the relay earth station using superimposed modulation, and the transmission power of the relay earth station to the small earth station is adjusted. The goal is to control.

In the following description, for convenience of explanation, a communication example will be used in which the relay earth station 2 intervenes in the communication between the small earth station 3 and the small earth station 6.

(Example 1) This is a first embodiment of the present invention.

The operation of this system will be described in detail below, taking as an example superimposed modulation using BPSK (two-phase digital phase keying) for -order modulation and ±45'' ps for secondary modulation.

First, the superimposition modulation method on the small earth station side will be explained below.

FIG. 2 shows a block diagram of a device for generating the superimposed modulated waves at a small earth station.

10 is a primary modulation digital baseband signal such as voice, data, facsimile, etc.; 11 is a BPSK modulator; 12 is a BPS output signal of the modulator 11; and 13 is a secondary modulation representing signal quality information measured at a small earth station. The digital baseband signal 14 is a PSK modulator for generating a phase deviation of ±45'' according to the signal of the secondary modulation digital baseband signal 13, and 15 is the output signal of the PSK modulator 14.

The secondary modulated digital baseband signal 13 is signal quality information such as the reception C/N (signal power to noise power ratio) of the small earth station and the bit error rate, and its transmission speed is the same as that of the primary modulated digital baseband signal lO much lower than.

FIG. 3 shows a phase diagram of a modulated wave.

FIG. 3(a) shows the output 12 of the BPSK modulator 11
Figures (b) and 3 (C) respectively show examples of the output 15 of the modulator 14 at PS when the secondary modulation digital baseband signal 13 is 1°Zll□''. That is,
In the modulator 14, the BPSK wave of (0 @, 180') is converted into a BPSK wave of (0 @, 180'), and when the low speed secondary modulation digital baseband signal is '1° (+45', +225°)
, and when the signal is “0°° (-45°, +135°
@) PSK wave is used.

Then, PSK modulated twice (superimposed) in this way
The output 15 of modulator 14 is transmitted from the small earth station to the relay earth station.

Next, a method for extracting a signal from the superimposed modulated carrier wave on the relay earth station side and controlling the transmission output for the small earth station will be explained.

FIG. 4 is a block diagram of a device related to transmission power control at a relay earth station.

Here, 20-22. 20°-22° represents the input signal of each channel, 23-25. 23°-25° is the PSK demodulator for the secondary modulation signal of the small earth station, 26
~28, 26°~28° is the BPSKI modulator for the primary modulation signal of the earth station, 29~31.29'~31'
(iPsK modulator, 32 to 34; 32' to 34' are variable attenuators; 35 to 37 degrees; 35 to 37 degrees represent the output of each channel.

Further, 38 is a control circuit for the variable attenuator.

FIG. 5 shows the PSK demodulators 23 to 25, 23' in FIG.
It is a block diagram of 25 degrees.

40 represents an input signal, 41 is a doubler circuit, 42 is a phase detection circuit, and 43 is the output of the phase detection circuit 42, that is, small earth station received signal quality information.

Next, the operation of this device will be explained.

The superimposed modulated carrier wave from the small earth station 3 enters the device as an input signal 20. The PS demodulator 23 demodulates the digital baseband signal used for secondary modulation in the small earth station 3 and detects small earth station received signal quality information. In the PSK demodulator 23, Fig. 3(b) and (C)
The superimposed modulated wave as shown in FIG. 5 becomes the input signal 40 in FIG.
In response to FIGS. 3(b) and 3(c) showing 1'O, outputs of +90° and -90° are respectively outputted to the phase detection circuit 42 as shown in FIG. The phase detection circuit 42 is +9
0° and -90° are determined, and small earth station received signal quality information, which is a secondary modulated digital baseband signal, is detected and output to the control circuit 38. The control circuit 38 uses the difference between a preset signal quality reference value and the received signal quality information of the small earth station to adjust the variable attenuator 3 for the small earth station.
2'' is controlled so that the above-mentioned difference is reduced.

Note that in the case where the earth station received signal quality information is differentially encoded and transmitted, a differential phase detector may be used in place of the phase detector 42.

Further, the primary modulated digital baseband signal in the input signal 20 is demodulated into BPS by the demodulator 26, and
and a variable attenuator 32, a transmitter (not shown)
, and is transmitted to the small earth station 6 in FIG. 1 via the satellite 1.

On the other hand, the transmission signal from the small earth station 6 is received by the relay earth station as an input signal of 20 degrees as shown in FIG.
demodulated by the modulator 29, and then modulated by the variable attenuator 3.
The signal is relayed from 2' via a transmitter via a satellite and received by a small earth station 3. In this case, the small earth station received signal quality information is always included in the output of the PSK demodulator 23° in FIG. 4, and the control circuit 38 calculates the difference between the preset signal quality reference value and the signal quality. is used to control the attenuation amount of the variable attenuator 32 so that the above-mentioned difference is reduced.

(Embodiment 2) FIG. 7 shows a second embodiment of the present invention, in which a superimposed modulated wave is transmitted to a small earth station when BPSK is used as the -order modulation and ASK (digital amplitude modulation) is used as the secondary modulation. 54 is an amplitude modulator;
55 is the output of the amplitude modulator 54, and the other parts are the same as in FIG.

FIG. 8 shows a phase diagram of the modulator output 55, where, for example, the secondary modulated digital baseband signal 13 representing the small earth station received signal quality information measured at the small earth station is 1.

In the case of BPSK with amplitude C1 as shown in Fig. 8(a)
When the wave is 0'°, the amplitude CD is as shown in Figure 8(b).
The BPSK waves are superimposed and modulated using ASK modulation, respectively, and sent to the relay earth station. The transmission power control of the relay earth station is performed by the demodulators 23 to 25 and 23° to 25' for the secondary modulated digital baseband signal in FIG.
Except for being an SK demodulator, the configuration is otherwise exactly the same as that shown in FIG. 4, and its operation is also the same as described above. In FIG. 9, the input signal 60 is as shown in FIG.
This is a superimposed modulated signal containing small earth station received signal quality information corresponding to 22'. 61 is a carrier wave regeneration circuit for extracting a carrier wave component from the input signal 60, and 62 is a synchronous detection circuit for detecting a small earth station received signal quality information signal from the input signal 60 using the carrier wave component generated by the regeneration circuit. A circuit 63 is a level detection circuit for detecting the level of the output of the detection circuit. Output 6 of level detection circuit 63
4 is proportional to the secondary modulated wave amplitudes C1 and CO in FIG. 8, so that the secondary modulated digital baseband signal can be demodulated to AS.

In addition, in Fig. 9, the ASK demodulator without 61 and 62 (
The digital baseband signal can also be demodulated using an asynchronous ASK demodulator (called an asynchronous ASK demodulator).

(Example 3) A third embodiment of the present invention will be described.

Figure 10 shows FSK as secondary modulation in a small earth station.
This figure shows a circuit configuration for generating a superimposed modulated wave when using (digital frequency modulation). Here, 7
4 indicates the carrier frequency of the output 12 (BPSK modulated wave) of the BPSK modulator according to ++ 1 ++ and “0” 9 of the signal quality information 13, for example, fO+Δf and fO−Δf, respectively.
75 is the output of the frequency modulator 74. Other details are the same as in FIG. 2.

However, fO is the carrier frequency of the output 12 of the BPSK modulator 11.

The configuration of the control device for transmitting power of the relay earth station for the superimposed modulated wave is the same as that in FIG. 4, except that the demodulators 23 to 25 and 23' to 25 in FIG. 4 have the configuration shown in FIG. 11. The operation is also the same as that described in FIG. 11th
In the figure, 80 is a modulated wave superimposed on primary modulated BPS from a small earth station of secondary modulated FSX, 81 is a doubling circuit for removing BPSK of primary modulation from the superimposed modulated wave, and 82
83 is a frequency discriminator, and 83 is a frequency discriminator, and the discriminator output 84 is +Δf and It takes a value proportional to −Δf and is received signal quality information at a small earth station. As a result, the secondary modulated digital baseband signal is demodulated.

In addition, in the embodiments so far, phase modulation,
Although the case where amplitude modulation and frequency modulation are applied individually has been described, it is obvious that the present method also operates when a combination of these modulations is used as secondary modulation. In addition, -order modulation is not limited to BPS, but also other polyphase PSK, AS,
It is also possible to use FSK.

Although an example of transmission power control via a relay earth station has been described above, it goes without saying that the same concept can be applied to communication between small earth stations that does not involve a relay earth station. In this case, on the receiving side, it is necessary to decode information regarding rain attenuation from the partner earth station, and it is also necessary that the small earth station has sufficient transmission power.

Although Fig. 1 shows an example of communication between a small earth station group (A) and a small earth station group (B), communication is also performed within each small earth station group via relay earth stations. If the relay earth station has antenna equipment that can connect to two satellites, wide range communication between small earth stations can be realized via the two satellites, and the present invention described above naturally applies to these methods. Needless to say, it can also be applied to.

In addition, in the description of the embodiment, a case has been described in which satellite communication is configured between small earth stations via a relay earth station, but the present invention is applicable not only to the above embodiment but also to large earth stations (central earth stations). It can also be applied to satellite communication systems between small earth stations and small earth stations. For example, if the Kanmon Earth Station cannot be accessed by land line due to geographical conditions, or if it is economically more advantageous to access the central earth station directly via satellite than via land line, the above-mentioned method may be used. A satellite communication link between a central earth station and a small earth station may be configured. In such a configuration, if the central earth station is provided with the function of a relay earth station as explained in the previous embodiment, the central earth station can perform the transmission power control according to the present invention in exactly the same way as in the previous embodiment. It is clear that it is possible to force a functional operation to take place.

(Effects of the Invention) As described above, according to the present invention, compensation control for rain attenuation is performed centrally by the relay earth station, so many small earth stations can maintain good line quality despite having a simple configuration. can.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a satellite communication system according to the present invention, and FIG.
3 and 3 are diagrams of a BPSK-PSK superimposed modulated wave generation circuit and its phase vector, FIG. 4 is a block diagram of the basic relay earth station device configuration according to the present invention, and FIGS. 5 and 6 are two diagrams. The phase vector diagrams of the demodulator for the next modulation and the output of the doubler circuit of the demodulator, FIGS. 7, 8, and 9 are BPSK.
- Explanatory diagram related to ASK superimposed modulation wave generation and demodulation, Part 1
FIG. 0 and FIG. 11 are explanatory diagrams related to generation and demodulation of superimposed modulated waves in BPSK-FS. 1...Satellite, 2...Relay earth station, 3-8
...small earth station, 10...-time modulated digital baseband signal, 11
...BPSK modulator, 12... Output of BPSK modulator, 13... Secondary modulation digital baseband signal, 14... PSK modulator, 15... Output of PSK modulator, 20 to 22 and 20゛-22'...input signal at the relay earth station, 23-25 and 23゛-25゛...PSK demodulator for the secondary modulation signal, 26-28 and 26'-28゛...- BPSK demodulator for time modulated signal, 29~31 and 29゛~31°...modulator, 32~
34 and 32°~34'...variable attenuator, 35~3
7 and 35' to 37°...Output of variable attenuator, 38
...Control circuit, 40...Input signal, 41...2 multiplier circuit, 4
2... Phase detection circuit, 43... Phase detection circuit output, 54... Amplitude modulator, 55... Amplitude modulator output, 60... Input signal, 61... Carrier wave regeneration circuit, 62 ... Synchronous detection circuit, 63 ... Level detection circuit, 64 ... Level detection circuit output, 74 ... Frequency modulator, 75 ... Frequency modulator output, 80 ... Input signal, 81. ...Doubling circuit, 82...Band-pass amplitude limiter, 83...Frequency discriminator, 84...Frequency discriminator output, A1-An...Small earth station group, Bl-Bn... Small earth station group.

Claims (1)

[Claims] A relay earth station that relays the communication is interposed in the satellite communication between small earth stations, and after the relay earth station receives the signal from the small earth station via the satellite and performs signal reproduction processing. , in a transmission power control method applied to a satellite communication system in which the signal is transmitted to a partner small earth station via a satellite, each of the small earth stations uses the downlink signal from the satellite to transmit the signal of the signal. The quality is measured, and using the received signal quality information created from the measurement results, the carrier wave modulated by the transmission signal in the first modulator is further superimposed modulated in the second modulator, and the small earth station A modulated wave is transmitted, and the relay earth station detects received signal quality information of the small earth station from the received superimposed modulated wave, and adjusts the signal quality to a preset reference value according to the signal quality. A transmission power control method characterized by controlling the transmission output to a small earth station within a preset value range.