JPH0754917B2 - Frequency control method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a communication system, and particularly to earth station equipment and earth frequency control device of a satellite communication system for extracting a communication signal based on a frequency of a certain reference signal. Frequency control method.

[Background of the Invention]

The conventional earth station for satellite communication has a frequency control function only on the receiving side. For this reason, if the frequency that is the reference of the pilot signal and the transmission frequency is deviated, or if there is a frequency deviation during transmission, there is no means to correct and the communication state deteriorates, or communication becomes impossible. .

[Object of the Invention]

An object of the present invention is to provide a frequency control method that enables communication by correcting the frequency of a signal to be transmitted even if the reference frequency of the signal to be transmitted is deviated from the reference signal of the signal to be transmitted. It is in.

[Outline of Invention]

In order to achieve the above object, in the present invention, according to the difference between the pilot signal frequency transmitted from the local station to the transmitting side and obtained from the frequency of the carrier signal received via the satellite and the frequency of the pilot signal actually received. The feature is that a frequency control function for correcting the frequency of the carrier signal to be transmitted is added.

Example of Invention

 An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram of a first embodiment of an earth station for satellite communication according to the present invention. The modulator / demodulator 10 is a modulator / demodulator.
It is composed of 20,30,40,50. In each modulator, the transmission data 21, 31, 41, 51 from the data terminal device is modulated and input to the combiner 70 as carrier waves 23, 33, 43, 53. Synthesizer 70
Then, the carrier waves 23, 33, 43, 53 from the respective modulators / demodulators are combined and input as the carrier wave 80 into the transmission frequency control device 100 in the intermediate frequency common unit 90. The intermediate frequency common unit 90 may include a transmission / reception output control function, but it is omitted here.

In the transmission frequency control device 100, the frequency of the carrier wave 80 is changed according to the signal 110 from the frequency deviation detection device 350, and the changed carrier wave 120 is input to the up converter 130. Here, in the frequency deviation detection device 350, both the pilot signal, which is the reference frequency of the satellite communication system, and the signal emitted from the local station and received by the local station are taken in as the signal 230, and the deviation of the frequency deviation between the two signals is taken. Therefore, the signal 110 relating to the change of the transmission frequency is output.

The up-converter 130 performs frequency conversion in order to increase the frequency of the modified carrier wave 120 to be emitted toward the satellite, and inputs the carrier wave 140 to the high-power amplifier 150. The high-power amplifier amplifies the carrier wave 140 until it can be output to the satellite. The antenna 170 emits the carrier wave 160 from the high-power amplifier as a radio wave 300 toward the satellite.

The above is the outline of the transmission method. Next, the case of reception will be described.

In the case of reception, the antenna 300 receives the radio wave 300 from the satellite and inputs it as the carrier wave 180 to the low noise amplifier 190.
The low noise amplifier amplifies a weak signal from the satellite and inputs it to the down converter 210. The down converter converts the frequency of the signal 200 into a frequency that can be handled by the modulation / demodulation device 10, and inputs it to the reception frequency control device 250 in the intermediate frequency common unit 90. The reception frequency control device 250 inputs the signal 230 before the reception frequency control to the frequency deviation detection device 350. In the frequency deviation detector 350, a pilot signal is extracted from the signal 230, the difference between the frequency of this signal and the frequency of the pilot signal obtained from the reference frequency signal 295 in the earth station modulator / demodulator 10 is obtained, and this difference is related to this difference. Signal information 24
It is input as 0 to the reception frequency control device 250. In the reception frequency control device 250, based on the signal 240, frequency conversion is performed so that all the carrier waves 220 are matched with the reference frequency signal 295.
Therefore, the frequency of the entire carrier wave 220 is corrected by the difference between the frequency of the pilot signal received from the satellite and the frequency of the pilot signal obtained from the reference frequency signal 295, and is input to the duplexer 270 as the carrier wave 260.

The demultiplexer 270 outputs the carrier wave 260 separately to each of the modulator / demodulators 20, 30, 40, 50. Carriers 24,34,44,5
4 is demodulated and transmitted to the data terminal device side as received data 22, 32, 42, 52.

The above is the outline of the satellite communication earth station system to which the frequency control method according to the present invention is applied. In this, the parts other than the transmission frequency control function in the intermediate frequency common unit 90 can be realized by the conventional device or method. Is. Next, the transmission frequency control function, which is the main part of the present invention, will be described.

FIG. 2 is a diagram showing in detail the part that controls the transmission frequency in the intermediate frequency common unit 90.

Here, the intermediate frequency common unit 90 handles signals in the 70 MHz band,
The frequency of the pilot signal is 69.955 MHz, and the frequencies between the channels including the pilot signal are 45 KHz apart.

First, the frequency deviation detection function will be described. The channel detector 930 in the frequency deviation detecting device 350 extracts the radio wave transmitted from the local station from the signal 230 based on the signal 290 indicating the channel transmitted by the local station. This signal,
In other words, the frequency of the pilot signal is obtained based on the carrier signal transmitted from the local station (hereinafter referred to as a folded carrier signal) extracted from the received signal 230 and is input to the frequency change signal generator 870 as the signal 950. For example, if the channel number used for transmission at the local station is 3, the carrier signal of that channel is 45 KHz x 3 = 135 KHz with respect to the pilot signal.
There should be a frequency difference of. Therefore, in this case, the frequency of the pilot signal (the frequency of the signal 950) calculated based on the folded carrier signal is (the frequency of the folded carrier signal) -135 KHz. That is, the signal 950
Is obtained by creating a difference frequency signal between the extracted folded carrier signal and the signal of 45 KHz × (used channel number). If the signal transmitted from the own station has a plurality of channels, one channel is randomly selected. The channel detector 930 also extracts a pilot signal from the received signal 230 and inputs it as a signal 940 to the frequency change signal generator 870.

Here, as the reception frequency control function in the frequency deviation detection device 350, the difference between the frequency of the pilot signal 940 and the frequency of the pilot signal obtained by the reference signal 295 is obtained by the reception frequency deviation detector 920, and information on the difference is obtained. 240 outputs are made.

Next, the frequency change signal generator 870 obtains the difference between the frequency of the extracted pilot signal 940 and the frequency of the signal 950. If the time difference is 22.5 KHz or more, the content is transmitted to the earth station operator by the signal 900 and is input to the transmission blocking device 85 to block the transmission of the carrier wave 80. If the difference between the signals 950 and 940 is ± 22.5 KHz or less, the information regarding the change of the transmission frequency is input to the transmission frequency control device 100 as the signal group 110. The details of the signal group 110 will be described later.

In the transmission frequency control device 100, the carrier wave is
The signal 80 is corrected by the difference between the signal 940 and the signal 950, and the frequency is changed so that it becomes the transmission frequency based on the pilot signal actually broadcast to each earth station via the satellite.

The transmission frequency control device 100 is configured to generate a reference frequency for frequency conversion, a 10 KHz reference frequency generator 50.
0, 3KHz reference frequency generator 520, 1KHz reference frequency generator 54
0 and reference frequency generators 500, 520, 54 according to signal group 110
20KHz generator 700, 10KHz generator 710, 9KHz generator 720, 6KHz generator 73 that outputs the signal from 0 by 1x, 2x or 3x
0, 3 KHz generator 740, 2 KHz generator 750, 1 KHz generator 760, synthesizer 830 for synthesizing signals of each frequency, and frequency adder 850 for acting the synthesized signal on carrier wave 80 and outputting it. Consists of 840.

The frequency is changed according to the signal group 110. Each frequency generator 700-760, frequency adder 850, frequency subtractor 8
40 is a 20KHz generation signal 600, 10KHz generation signal 610, 9KHz generation signal 620, 6KHz generation signal 630, 3KHz generation signal 640, 2KHz generation signal 650, 1KHz generation signal 660 and frequency addition signal 810,
Each of them operates when the frequency subtraction signal 820 is output.

The signal group 110 is a group of signals 600 to 660, 810, 820, and each signal is output from the frequency change signal generator 870. Since the transmission frequency is changed based on the pilot signal 940 received from the satellite, if the frequency of the signal 950 is smaller than that of the signal 940, the frequency addition signal 810
When the frequency of the signal 950 is higher than that of the signal 940, the frequency subtraction signal 820 is output. If the difference between the pilot signal 940 and the signal 950 is 22.5 KHz or less,
From the frequency generated signals 600 to 660,
A combination that generates a signal having a frequency of 1 KHz or less is searched for and output to the transmission frequency control device 100.

However, here, the receivable frequency range of each earth station is the case where the modulator / demodulator is less than ± 1 KHz.If the receivable frequency range is other than that, the transmission frequency is adjusted according to that value. The configuration inside the control device 100 may be changed.

Next, the relationship between the carrier waves 80, 120 and 220 will be described with reference to FIGS. Here, for simplification of explanation, it is assumed that the carrier wave 220 received from the satellite has only two signals, a pilot signal and a carrier signal transmitted from the own station and received by the own station.

3 shows the relationship between the frequency F of the carrier wave 80 and the output P, FIG. 4 shows the relationship between the frequency F of the carrier wave 220 and the output P, and FIG. 5 shows the carrier wave 1
It is a figure showing the relation between frequency F of 20 and output P. Also,
3 to 4, F _Pt is the frequency of the pilot signal obtained from the reference frequency in the earth station modulator / demodulator 10, F _Ct
Is the frequency of the carrier signal obtained from the reference frequency of the earth station modulator / demodulator 10, F _CT is before the transmission frequency control (carrier wave 80)
Of the carrier signal, F _CT ′ is the frequency of the carrier signal after transmission frequency control (carrier 120), and F _PR is the frequency of the carrier signal before reception frequency control (carrier 220).

Since the frequency F _CT of the carrier signal on the carrier wave 80 is the signal immediately after being output from the modulator / demodulator, as shown in FIG. 3, F _CT = F _Ct .

As shown in FIG. 4, the difference between the pilot signal frequency F _Pt obtained from the reference frequency in the earth station modulator / demodulator 10 and the pilot signal frequency F _PR received from the satellite is ΔF _P = | F _Pt −F
_PR | and consider the case where the difference between the frequency F _{Ct of the} carrier signal obtained from the reference frequency and the frequency F _{CR of the} carrier signal received from the satellite is ΔF _C = | F _Ct −F _CR |. In this case, the frequency F _CT of the carrier signal of the carrier wave 80 is frequency-converted by the transmission frequency control device 100 by ΔF _P + ΔF _C = | (F _Pt −F _PR ) − (F _Ct −F _CR ) | It becomes the frequency F _CT ′ of the carrier signal of. The relationship between F _Pt , F _CT ′ and F _Ct at this time is shown in FIG. From the above results, it is generally known that the frequency F _Ctn (n: carrier signal number) of the carrier signal before being subjected to the transmission frequency control is changed by the transmission frequency control device 100 as in the following equation.

F _CT ′ _n = F _Ctn − {(F _Pt −F _PR ) − (F _Ctn −F _CRn )} Next, the operation of the frequency change signal generator 870 will be described using a specific example.

In FIG. 6, the pilot signal extracted from the received signal
It is assumed that the frequency of the 940 is 69.9403 MHz, and the frequency of the pilot signal 950, which is obtained from the folded carrier signal transmitted from the local station and received by the local station, is 69.957 MHz. In this case, since the frequency of the pilot signal 940 is lower, the frequency subtraction signal 820 is output. Further, since the difference between the signal 940 and the signal 950 is 16.7 MHz, the 10 KHz generation signal 610, the 6 KHz generation signal 630, and the 1 KHz generation signal 660 are output, respectively. With the above signals, the carrier signals of carrier wave 80 are all reduced in frequency by 17 Kz and output as carrier wave 120. From this, it can be seen that the frequency of the transmitted signal falls within ± 1 KHz from the value based on the frequency of the pilot signal received from the satellite.

In the satellite communication system, the method of extracting the carrier signal from the received signal is to extract the frequency of each carrier signal based on the frequency of the pilot signal received from the satellite, as described above. Therefore, if the reference of the pilot signal and the reference of the carrier signal are deviated, it becomes impossible to perform reception.

As for the place where the frequency shifts, the transmitter, satellite,
Three receivers are possible. Since the pilot signal and the carrier signal pass through the same path for the satellite and the receiving device, the frequency deviation of both signals is the same. Therefore, the cause of the frequency deviation is the frequency shift received from the transmitter. According to the present embodiment, since there is an action and effect that makes the frequency shift received at the time of transmission of the carrier signal almost the same as that of the pilot signal, the frequency shift received by the pilot signal and the carrier signal becomes the same throughout the whole transmission and reception, There is no deterioration of the reception state or unreceivable state due to the deviation.

Next, for comparison with the above-described embodiment of the present invention, a reference example will be described in which frequency correction is performed based on the deviation between the frequency of the reference signal of the own station and the frequency of the received reference signal.

FIG. 7 is a block diagram of the reference example, which is a reference frequency generator.
The point that 2900 is provided is different from FIG.

Only the parts different from FIG. 1 will be described below.

In each of the modulator / demodulators 20, 30, 40, 50, the transmission data 21, 31, 41, 51 from the data terminal device is modulated based on the earth station reference frequency signal 292, and the carrier waves 23, 33, 43, 53 is input to the synthesizer 70.

Here, in the frequency deviation detection device 350, the pilot signal 230, which is the reference signal for satellite communication, and the reference frequency generator 290.
The difference from the earth station reference frequency signal 291 from 0 is determined.

In the case of reception, the reception frequency controller 250 divides the carrier wave 220 into a carrier signal and a pilot signal, and
230 is input to the frequency deviation detector 350. The frequency deviation detection device 350 obtains the difference between the frequency of the pilot signal obtained from the earth station reference frequency signal 291 and the frequency of the received pilot signal, and inputs the signal 240 relating to this difference to the reception frequency control device 250. In the reception frequency control device 250,
Based on the signal 240, all the carrier waves 220 are frequency-changed in the direction of matching with the earth station reference frequency. Therefore, carrier wave 22
The entire frequency of 0 is corrected by the difference between the frequency of the received pilot signal and the frequency of the pilot signal obtained from the signal 291, and is input to the demultiplexer 270 as the carrier wave 260. Here, the pilot signal 230 is a signal before the reception frequency control.

The part of the intermediate frequency common unit 90 excluding the transmission frequency control device 100 can be realized by a conventional device. Next, the transmission frequency control device 100 will be described.

FIG. 8 is a diagram showing in detail the internal configuration of the transmission frequency control device 100 in the intermediate frequency common unit 90 and the connection with peripheral devices.

The deviation between the pilot signal 230 and the earth station reference frequency signal 291 is detected by the frequency deviation detector 350. First, a signal of 69.955 MHz which is the frequency of the pilot signal is generated from the earth station reference frequency signal 291. Next, the pilot signal 230 received from the satellite is fetched, and the difference from the pilot signal frequency generated from the earth station reference frequency signal 291 is obtained. At this time, if the difference is ± 22.5 KHz or more, the content is transmitted to the earth station operator by the signal 900, and the emission of the radio wave is stopped.

When the difference from the earth station reference frequency is ± 22.5 KHz or less with reference to the pilot signal 230, the content is transmitted to the transmission frequency control device 100 by the signal group 110.

In the transmission frequency control device 100, as described above, the carrier wave 80 is changed by the signal group 110 from the earth station reference frequency to the frequency based on the pilot signal.

The configuration of the transmission frequency control device 100 is as shown in FIG.

The output of the signal 110 is performed by the frequency change signal generator 870 in the frequency deviation detection device 350. Signal 810 if the deviation between pilot signal 230 and earth station reference frequency signal 291 is positive
Occurs, and if negative, signal 820 is generated. If the absolute value of the deviation is 22.5 KHz or more, the content is transmitted to the earth station operator by the signal 900, and the transmission of the radio wave is stopped.

If the absolute value of the deviation is 22.5 KHz or less, each frequency generation signal 600
Among 660, the combination of frequency generation signals whose difference from the absolute value of the deviation is ± 1 KHz or less is searched for and the signal is output. As a result, the difference between the reference frequency of the transmitter and the reference frequency of the pilot signal 230 is ± 1
It becomes possible to set the frequency to KHz or less, and it becomes possible to prevent the deterioration of the communication state caused by the deviation of the reference frequency between the transmission signal and the pilot signal. Here, the receivable frequency range of each earth station is ±
Considering the case of 1 KHz or less, and if the receivable frequency range is not ± 1 KHz or less, the configuration in the transmission frequency control device 100 shown in FIG. 8 may be changed according to the value. .

Next, a reference example will be described based on a specific example.

In FIG. 9, the frequency of the pilot signal 230 is 69.9403.
It is assumed that the frequency of the pilot signal obtained from the earth station reference frequency signal 291 is 69.957 MHz. In this case, since the frequency of the pilot signal 230 is lower, the frequency subtraction signal 820 is output. In addition, the difference between the pilot signal 230 and the frequency of the pilot signal obtained from the earth station reference frequency signal 291 is 16.7 KHz.
The generated signal 630 and the 1 KHz generated signal 660 are output respectively.
By the above signals, each device shown by the diagonal lines in FIG. 9 operates.

As a result, each frequency signal of 10 KHz, 6 KHz, and 1 KHz is input to the synthesizer 830 to be a 17 KHz signal that is input to the synthesizer 830. .

When the carrier frequency of the carrier wave 80 is 71.170 MHz, the carrier frequency of the carrier wave 120 is 71.153 MHz and is transmitted. From this, it can be seen that radio waves can be emitted with an error of ± 1 KHz or less based on the frequency of the pilot signal received from the satellite.

In the reference example described above, the frequency deviation of the pilot signal extracted from the received signal is detected based on the frequency of the reference signal of the own station, and the frequency of the carrier signal to be transmitted is corrected in accordance with the frequency deviation. ing. Therefore, the frequency difference between the pilot signal and the carrier signal at the time of reception can be set to a desired value if both the pilot signal and the carrier signal have the same frequency error at the time of signal transmission and at the time of relay by the satellite. Therefore, the communication signal can be correctly received at the receiving station based on the pilot signal. However, the above condition does not always hold in general. In particular, when the pilot transmitting station and the carrier signal transmitting station are separate, both signal paths are different until reaching the satellite. It usually does not hold. In such a case, in this reference example, accurate transmission frequency control cannot be performed, and there is a possibility that the reception state may deteriorate or the reception state may occur.

On the other hand, in the embodiment of the present invention described above, the difference between the pilot signal frequency obtained from the frequency of the carrier signal transmitted from the own station and received via the satellite and the frequency of the actually received pilot signal is calculated. Since the frequency of the carrier signal to be transmitted is corrected accordingly, the frequency difference between the carrier signal and the pilot signal at the time of reception can be maintained at a desired value even when the pilot transmitting station and the carrier signal transmitting station are separate. . That is, the transmission signal reaches the receiving station with the channel frequency that controls the frequency difference from the broadcast pilot signal. Therefore, at the receiving station,
Communication signals can always be correctly received based on the pilot signal.

〔The invention's effect〕

According to the present invention, a signal (carrier signal) for communicating with a pilot signal which is a reference signal in a satellite communication system.
Since it is possible to make the same frequency deviation received at the time of transmission and reception, there is an effect of preventing the deterioration of the reception state and the occurrence of the unreceivable state caused by the frequency deviation. Further, by correcting the frequency of the carrier signal based on the frequency of the pilot signal, there is an effect that the carrier signal is correctly extracted and communication is enabled.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the satellite communication earth station equipment according to the present invention, and FIG. 2 is a block showing the frequency control unit of the satellite communication earth station equipment of FIG. Configuration diagram, FIG. 3 is a diagram showing the relationship between the frequency and the output of the signal before the transmission frequency control, FIG. 4 is a diagram showing the relationship between the frequency and the output of the signal before the reception frequency control, FIG. 5 is the transmission frequency control FIG. 6 is a diagram showing the relationship between the subsequent frequency and output, FIG. 6 is a diagram showing input / output signals in the frequency change signal generator, and FIG. 7 is a reference of the earth station equipment for satellite communication for comparison with the embodiment of the present invention. A block configuration diagram showing an example, FIG. 8 is a block configuration diagram showing the frequency control unit of the satellite communication earth station equipment of FIG. 7, and FIG. 9 is a satellite communication earth station equipment of FIG. It is a block configuration diagram showing a transmission frequency control unit.

Front page continuation (72) Inventor Nobuyuki Fujikura 1099 Ozenji, Aso-ku, Kawasaki-shi, Kanagawa Inside Hitachi Systems Development Laboratory, Inc. (72) Inventor Tsutomu Nakamura 1099, Ozen-ji, Aso-ku, Kawasaki, Kanagawa Prefecture Hitachi System Development Laboratory (72) Inventor Kosuke Shinnai 1099, Ozenji Temple, Aso-ku, Kawasaki City, Kanagawa Prefecture Hitachi Ltd. System Development Laboratory (56) Reference JP-A-60-187140 (JP, A) JP-A-60 -185437 (JP, A) JP-A-59-158137 (JP, A)

Claims (1)

[Claims] 1. A specific channel is assigned to a pilot signal, a data transmitting station transmits data using another channel having a predetermined frequency difference from the specific channel, and a data receiving station relays a satellite. In the communication system for receiving the signal, the data transmitting station extracts the pilot signal and the carrier signal of the data transmitted from the own station and relayed by the satellite from the received signal, and transmits the data used by the own station. Of the channel number and the extracted carrier signal to calculate a pilot signal frequency having the predetermined frequency difference with respect to the frequency of the extracted carrier signal, and the calculated pilot signal frequency and the pilot signal extracted from the received signal. Derive the difference from the frequency and use the reference frequency signal of the local station and the channel number of the data transmission used by the local station as the basis. Frequency control method characterized by controlling the carrier frequency of the transmitted signal by correcting in accordance with the difference obtained by deriving a carrier frequency of the transmission signal generated.