JP3033176B2 - AFC device for satellite communication earth station - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AFC device for a satellite communication earth station, and more particularly to an AFC device for a satellite communication earth station used for a wireless device for performing satellite communication with a mobile object. .

[Conventional technology]

Generally, a transmission frequency correcting means in a mobile satellite communication system in the case where an earth station and a mobile unit communicate with each other via a satellite is a system configuration diagram shown in FIG. 3 and an earth station shown in FIG.
The transmission frequency correction unit 25 of the transmission device provided in 21 will be described. Normally, when communication is performed between the earth station 21 and the satellite 23, even if it is a geostationary satellite, since the satellite orbit has a daily change of about 24 hours, there is a frequency error due to the Doppler shift. Correction of this frequency error is performed by a reference station on the earth.
The reference pilot signal transmitted via satellite from 24
21 receives and corrects the transmission frequency. Earth station 21
The transmission frequency correction unit 25 (4th
3) receives a received signal having the above-mentioned reference pilot signal from an input terminal 26A, and demodulates the reference pilot signal by a reception frequency conversion device 26. The AFC device 27 determines the frequency of the transmission signal to be transmitted to the satellite 23 based on the reference pilot signal.
To apply AFC, calculate the Doppler shift frequency and create a frequency correction signal. The transmission frequency conversion device 28 receives the frequency correction signal, corrects the oscillation frequency of the transmission local oscillator, and sends out an accurate transmission signal that has been subjected to Doppler correction or the like in advance from the output terminal. Returning to FIG. 3, this transmission signal is transmitted to a moving body 22 such as an aircraft via a satellite 23. Here, the transmission frequency between the satellite 23 and the mobile unit 22 naturally causes a large Doppler shift. Although the Doppler shift between the earth station 21 and the satellite 23 is small compared to the large Doppler shift, the Doppler shift is corrected in advance by the transmission frequency correction unit 25 in order to reduce the burden on the correction of the large Doppler shift between the satellite and the aircraft. .

Conventionally, as this type of AFC device 27, as shown in FIG. 2, an input terminal 5A for inputting a reference pilot signal and a built-in voltage controlled oscillator (VCO) based on the reference pilot signal are phase-locked. AFC circuit 2 for generating a reference signal having a good S / N ratio, a frequency counter 2 for counting the frequency of this reference signal, and also for counting the frequency of a voltage controlled crystal oscillator (VCXO) 6 for a transmission signal described later, AFC circuit 5 The Doppler shift of the satellite and the fluctuation of the local oscillator of the satellite transponder are calculated from the latitude and longitude of the reference station and the earth station and the orbit inclination of the satellite based on the reference signal of, and the frequency error between the earth station and the satellite is added in advance. The CPU 3 for transmitting a correction signal for performing the correction, the source of the local oscillation signal of the transmission signal, and the output of the VCXO 6 and the VCXO 6 for oscillating the signal of the frequency corrected by the above-described correction signal are transmitted to the transmission frequency converter 28 shown in FIG. Send out to Force terminal 7A
, Which also branches to the frequency counter 2 for counting the correction frequency. The storage circuit 4 stores the data of the frequency of the above-mentioned reference pilot signal at predetermined time intervals for at least 24 hours.

[Problems to be solved by the invention]

In the above-mentioned conventional AFC device for a satellite communication earth station, the data of the frequency error of the reference pilot signal is periodically sampled and stored in a storage circuit for 24 hours, and then the Doppler shift period of the satellite and the satellite repeater are used. Since the fluctuation of the local oscillator is calculated and the frequency is corrected, if an error occurs in the reference pilot signal, the sampling data is lost until recovery, the frequency error cannot be calculated, and after the pilot signal is recovered. Had the disadvantage of having to wait 24 hours.

[Means for solving the problem]

An AFC device for a satellite communication earth station according to the present invention is an earth station for receiving a reference pilot signal transmitted from a reference station for satellite communication via a satellite, performing phase synchronization based on the reference pilot signal, and creating a reference signal. An AFC circuit, a voltage-controlled oscillator for generating a transmission signal transmitted from the earth station to the satellite, a frequency counter for counting the frequency of the reference signal and the frequency of the transmission signal, and the frequency counter Connected, calculates the Doppler shift of the satellite and the variation of the local oscillator of the satellite transponder based on the reference signal, and supplies the voltage-controlled oscillator as frequency correction data for adding a frequency error between the earth station and the satellite in advance. Processing means for transmitting, at least at predetermined time intervals the frequency correction data
A storage circuit for storing for 24 hours, and a timer circuit for counting the time from when the reference pilot signal is no longer received until the reception of the reference pilot signal is restored, wherein the processing means is configured such that the reference pilot signal is If not received, read out the frequency correction data stored 24 hours ago from the storage circuit and supply it to the voltage control transmitter, and read out the frequency correction data stored 24 hours ago from the storage circuit The time when the normal AFC operation is to be started after the restoration of the pilot signal is determined based on the time counted by the timer circuit and the time counted by the timer circuit, and the time is switched to the normal frequency correction time.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. First
In the figure, the same reference numerals in FIG. 2 perform the same configuration and operation. That is, in this embodiment, the timer circuit 1 is added.

Next, the operation of this embodiment will be described. Now, a case where the reference pilot signal from the reference station 24 cannot be received due to some abnormality will be described. As described above, the frequency error due to the Doppler shift of the satellite takes a sine curve with one cycle of about 24 hours, and the value changes in the same manner as the previous day.
Focusing on the fact that the change in the frequency error of the local oscillator of the satellite repeater per day is very small and almost the same as the previous day, even if the received reference pilot signal has an abnormality, It is possible to take out the frequency correction data and continue the AFC function. further,
By adding a timer circuit 5 that accurately recognizes the time until the received reference pilot signal is restored, the reference pilot signal can be calculated from the correction time every 24 hours using the previously stored correction data. The switching to the correction time started after the signal restoration can be accurately performed. Therefore, it is possible to cope with a long-term abnormality of the pilot signal.

〔The invention's effect〕

As described above, the present invention can accurately recognize the time required for recovery even if an abnormality occurs in a received reference pilot signal by adding a timer circuit and changing the control method accompanying the timer circuit. The switching from the use time of the frequency correction data before the time to the regular frequency correction time can be accurately performed, and the AFC function can be continued.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a conventional AFC device for a satellite communication earth station, FIG. 3 is a general system configuration diagram, and FIG. FIG. 3 is a configuration diagram of a frequency correction unit. 1 ... timer circuit, 2 ... frequency counter, 3 ... CP
U, 4 ... Memory circuit, 5 ... AFC circuit, 6 ... VCXO, 7 ...
... branch circuit, 21 ... earth station, 22 ... mobile object, 23 ... satellite, 24 ... reference station, 25 ... transmission frequency correction unit.

Claims (1)

(57) [Claims] An AFC circuit of an earth station for receiving a reference pilot signal transmitted from a reference station for satellite communication via a satellite, and performing phase synchronization based on the reference pilot signal to generate a reference signal; A voltage-controlled oscillator for generating a transmission signal to be transmitted from a station toward the satellite; a frequency counter for counting the frequency of the reference signal and the frequency of the transmission signal; and Processing means for calculating the Doppler shift of the satellite and the fluctuation of the local oscillator of the satellite transponder based on the frequency control data, and transmitting the frequency error data to the voltage-controlled oscillator as frequency correction data for adding a frequency error between the earth station and the satellite in advance; At least 24 frequency correction data at predetermined time intervals
A storage circuit for storing time; and a timer circuit for counting a time from when the reference pilot signal is not received until reception of the reference pilot signal is restored, wherein the processing unit receives the reference pilot signal. If not, read the frequency correction data stored 24 hours ago from the storage circuit and supply it to the voltage control transmitter, and read the frequency correction data stored 24 hours ago from the storage circuit AFC device for a satellite communication earth station, wherein a time to start a normal AFC operation after the restoration of the pilot signal is determined based on a time and a time counted by the timer circuit, and the time is switched to a normal frequency correction time. .