JPS60187140A - Automatic frequency correcting system - Google Patents

Abstract

PURPOSE:To attain the use of a crystal having low frequency stability by using a crystal oscillator for transmitting and receiving a pilot signal in common at the transmission/reception section in an earth station transceiver using a pilot signal and correcting automatically the transmission frequency. CONSTITUTION:An earth station transmission section Tx is provided with a pilot signal oscillator 5 and the reception section Rx is provided with a pilot receiver P oscillating the frequency in response to the frequency fluctuation of the said pilot signal returned via a satellite SAT. The pilot receiver P includes a voltage controlled oscillator 19 and its oscillated output is inputted to a phase synchronizm oscillator 4 of the transmission section Tx as a reference frequency. The pilot signal oscillator 5 and the reference crystal oscillator 7 of the pilot reciever P are used in common. As a result, since the output frequency of the receiver P is made independent of the frequency fluctuation of the crystal oscillator 7, the crystal oscillator 7 with low frequency stability is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic frequency correction method for a maritime satellite communications earth station.

(Prior art) Conventionally, maritime satellite communications have adopted a narrowband 5cPC communication system, so fluctuations in the local oscillation frequency of the satellite repeater are large compared to the channel spacing, and no frequency correction is required. Met. In particular, in communication from land to a ship station, a method has been adopted in which frequency correction is performed on the shore station side in order to simplify the equipment of the ship station. As the negative column, there is a system as shown in FIG.

In FIG. 1, 1 is a modulator, 2 and 3 are mixers, 4, 5, and 6 are phase-locked oscillators, 7.8 is a crystal oscillator, 9 is a power amplifier, 1o is a duplexer, 11 is a low noise amplifier, 12 is a mixer, 13 is a phase synchronized oscillator, 14
is a crystal oscillator, 15 is a demodulator, 16 is a phase detector, 1T
is a mixer, 181d is a loop amplifier, 19 is a voltage controlled oscillator, and 2o.

21 is a phase synchronized oscillator, and 22 is a crystal oscillator.

In addition, ful, n is the transmitting carrier wave, and ``di~n'' is the receiving carrier wave. For example, in Inmarsat Sinutem, the channel spacing is 25 KHz, whereas the maximum frequency fluctuation of the satellite repeater is approximately 25 KHz. The frequency is ±55KHz.Therefore, it was necessary to perform some kind of frequency correction.

Referring to FIG. 1, the operation of frequency correction will now be described. A phase synchronized oscillator 4 in the IF band small output mixer 2 of the modulator 1
After tI, the signal is mixed with the output of the phase-locked oscillator 6 synchronized with the output of the crystal oscillator 8 in the mixer 3, and the frequency is converted to the 6GTTz band. This 6 GHz band signal is amplified by a power amplifier 9, passes through a duplexer 10, and is transmitted from the antenna to the satellite. The output of the phase-locked oscillator 5 synchronized with the output of the crystal oscillator T is also frequency-converted to the 6 GHz band by the mixer 3, and is used as a pilot signal for frequency correction. (
For example, fu, ) is allocated and transmitted to the satellite.

These signals are received by the satellite at the reception frequency fdl-n (1,5Q
The frequency is converted to the T (z band) band and transmitted from the satellite to the coast station and ship station again.

The signal received at the coast station is supplied to the low-noise amplifier 11 via the duplexer 10 and amplified, and then mixed in the mixer 12 with the output of the phase-locked oscillator 13 synchronized with the output of the crystal oscillator 14, and then sent to the IF The demodulator 15 converts the frequency into
supplied to A part of the IF band signal is supplied to the pilot receiver for frequency correction (the part surrounded by the broken line), and is compared with the difference output of the mixer 17 in the phase detector 16, and a DC voltage according to the phase error is generated. is output. This direct current voltage is applied to the voltage controlled oscillator 1g through a second loop amplifier 18'fF forming a phase locked circuit, and controls its output frequency. The output of the voltage controlled oscillator 19 is multiplied by N by the phase synchronized oscillator 21 and supplied to the mixer 17 . The output of the crystal oscillator 22 is the phase synchronized oscillator 20
is multiplied by M, mixed with the output of the phase synchronized oscillator 21 in the mixing i17, and the difference frequency is supplied to the phase detector 16.

A part of the output of the voltage controlled oscillator 19 is supplied as a reference signal to the phase synchronized oscillator 40 of the transmitting section.

Here, assuming that the local oscillation frequency of the satellite repeater fluctuates by ΔF, all the signals at reception frequencies f・d, -□ similarly fluctuate by ΔF, so that the received pilot wave (f'
dt) also varies by ΔF, and the input frequency (denoted fp) of the pilot receiver also varies by ΔF. If the center frequency of the pressure-controlled oscillator 19 is fv and the output frequency of the crystal oscillator 22 is fr, then in the phase synchronization state, both input frequencies of the phase detector 16 are equal, so the following equation is obtained.
Ru.

(a) When there is no frequency fluctuation - =frXM-fvXN=:fp* @ -1ll (b)
When fr fluctuates by ΔF: f r XM-(f v-1-yx ) × N= f
p−+−Nyu・e12) However, yl is the amount of correction from the center frequency fv of the voltage controlled oscillator 19.

When yl is subtracted from equations 11) and 2, we get ΔF 7t=--1...Fist (3). Therefore, when the frequency of the pilot receiving device fluctuates by ΔF, the output frequency of the voltage controlled oscillator 19 decreases by ΔF/N. Since the output of the voltage controlled oscillator 19 is multiplied by N by the phase-locked oscillator 4 (the same multiplier as that of the phase-locked oscillator 21 is selected), the output frequency of the phase-locked oscillator 4 is lowered by ΔF. As a result, the communication signal, which is the sum frequency of the modulator 1 and the phase-locked oscillator 4, has a frequency lowered by ΔF and is transmitted to the satellite.

Since this communication signal is subject to frequency fluctuation by the amount ΔF of the satellite repeater, the receiving frequencies (fd!~.) exactly cancel each other out and are always kept at a constant frequency.

Therefore, the ship station can receive signals without using a complicated AFc device.

However, this method detects the frequency fluctuations that the pilot signal receives on the satellite by comparing it with the reference crystal oscillator inside the pilot receiver, so the pilot signal inserted into the transmitter 4β section itself fluctuates. Then, the received pilot signal undergoes an additional fluctuation by that amount. As a result, the pilot receiving device also detects this extra frequency variation, and the communication signal ends up undergoing unnecessary frequency correction. For this reason, very high frequency stability is required for the pilot signal. For example, in Inmarsat Synutem, ±100
It is specified to be within Hz. If a crystal oscillator with a constant tank is used to obtain frequency stability on the order of 1o, the disadvantage is that the size becomes large and the power consumption increases.

(Object of the Invention) The object of the present invention is to operate a plurality of mixers by a phase-locked oscillator controlled by a crystal oscillator, and a phase-locked oscillator controlled by a pressure-controlled oscillator to form a phase control loop. In the pilot receiving device of the communication earth station device, the transmitting/receiving section is formed by the feedback loop, and the signal is mixed and amplified and connected to communicate with other stations.
The above drawbacks are eliminated by sharing the biloft crystal oscillator in the transmitter as the reference oscillator for the phase-locked oscillator.
The object of the present invention is to provide an automatic frequency correction scheme that can be implemented using a crystal oscillator with low frequency stability.

(Structure of the invention) The automatic frequency correction method according to the present invention is a modulator.

It includes first to third mixers, first to fourth phase-locked oscillators, first to third crystal oscillators, a power amplifier, two low-noise amplifiers, and a demodulator. This is an improvement on the method achieved by

In the present invention, after the output of the modulator is mixed with the output signal of the first phase-locked oscillator in the first combiner and converted into a first intermediate frequency signal 17, the output signal of the first crystal oscillator is The output signal of the second phase direction 1tJi oscillator synchronized with the output signal is added as a pilot signal, and the first intermediate frequency Iμ is synchronized with the output 4r< of the second crystal oscillator in the second mixer. The signal is mixed with the output signal of the third phase-locked oscillator, converted into a transmission frequency band signal, amplified by a power amplifier, and supplied to the antenna.The antenna receives the reception signal returned from the satellite repeater and generates low noise. It is amplified by an amplifier, mixed with the output signal of the fourth phase synchronized oscillator synchronized with the output signal of the crystal oscillator @3 in the third mixer, converted into a reception IF band signal, and supplied to the demodulator and received. This was realized in a satellite communications earth station that configured a feedback loop to extract a received pilot signal from a part of the IF band signal, detect frequency fluctuations from the received pilot signal, and correct the transmitted frequency.

In accordance with the present invention: 1. In the above, the phase detector is used.

Loop amplifier, 1% pressure controlled oscillator, rabbit, 4th and 5th
This was realized by comprising a phase-locked oscillator and a fourth mixer.

The phase detector is used to perform a complete phase comparison between the received pilot signal and the output signal of the fourth mixer.

The loop amplifier is for amplifying the output voltage of the phase detector.

The voltage controlled oscillator outputs a signal whose frequency is controlled by the output voltage of the loop amplifier, and forms a feedback loop with the first phase locked oscillator.

The fourth phase synchronized oscillator is used to obtain an N-multiplied wave synchronized with the output signal of the voltage controlled oscillator.

The fifth phase-locked oscillator continues oscillation in synchronization with the phase controlled by the output signal of the first crystal oscillator.

The mixer 4 is for mixing the output signals of the fourth and fifth phase synchronized oscillators and applying the mixture to the phase detector.

(Example) Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 d1 shows an embodiment for realizing the automatic frequency correction method according to the present invention. In FIG. 2, elements having the same functions as those in FIG. 1 are given the same reference numerals.

Next, the operation of the implementation shown in FIG. 2 will be explained.

In FIG. 2, the configuration is exactly the same as in FIG. 1 except for the pilot receiving device (the part surrounded by the broken line), so its operation will be omitted.

In addition, the pilot receiving device includes a phase synchronized oscillator-20.
The pilot crystal oscillator 7 of the transmission section 48 is also used as a reference oscillator, but other than this, it is exactly the same as in FIG. Therefore, if there is no frequency fluctuation in the crystal oscillator 7, it is clear that the above equations (112 to (3)) hold true.

Next, assuming that the frequency of the crystal oscillator 70 fluctuates by Δf, the phase-locked oscillator 5 multiplies the fluctuation by M (selected to be the same as the multiplication number of the phase-locked oscillator 20), and the transmitting pilot frequency is MΔf. only changes. Furthermore, if the frequency of the satellite repeater fluctuates by ΔF, all signals at the received frequency fd, ~n fluctuate by ΔF, and therefore the received pilot signal (fdl) fluctuates by (ΔF + MΔf), resulting in as the input frequency of the pilot wound device (
fp) also changes by (ΔF+MΔf). Assuming that the center frequency of the voltage controlled oscillator 19 is fv and the output frequency of the crystal oscillator 7 is ffr, the phase detector 16 . Since both input frequencies are equal in phase, the following equation can be obtained.

(e) ΔF=0. When △f=o: f r XM −f v XN= f p @−14
1(d)ΔF=0. When △f is 0: (fr+△f) XM - (fv+l) XN
=fp+MΔf . . . Φ dispute (5) However, y2 is the amount of correction from the center frequency fv of the voltage controlled oscillator 19.

(e) For ΔF\O2△fpe0: (fr-)-△f)XM (fv-1-y3)xN=f
p+△F+Mmuf...(6)ゝ However, y3
is the amount of correction from the frequency fv of the voltage controlled oscillator 19σ).

In the corner stand of (d), y2 is calculated from equation (4) and equation (51).
Then, y2-0・contact...(7) Since the frequency of the voltage controlled oscillator 19 does not change even if the frequency of the crystal oscillator T changes, the communication signal will not undergo unnecessary frequency correction. do not have. In addition, in the case of (e), formula (4) and clause (61) are used.

If we set ΔF, ----181 υ, even if the frequency of the crystal oscillator T changes, it is possible to obtain the exact same amount of correction for the group as shown in Figure 1.

Therefore, as described above, the reception frequency fd, . . . from satellites other than the pilot signal can always be kept constant.

(Effects of the Invention) As described above, the present invention operates a plurality of mixers using a phase-locked oscillator controlled by a crystal oscillator and a phase-locked oscillator controlled by a voltage-controlled oscillator forming one phase control loop. The feedback loop thus formed forms a transmitting/receiving section, mixes and amplifies the signal, and transmits it as a reference oscillator for a phase synchronized oscillator after the pilot receiving device of the school earth station equipment is connected to communicate with other stations. (When sharing the pilot crystal oscillator, Ij
), the frequency of the pilot crystal oscillator in the transmitter functions to obtain an accurate correction amount regardless of the amount of frequency fluctuation, so a crystal oscillator with low frequency stability can be used, and it is small, low power consumption, This has the effect that the device can be configured at a low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a mechanism for implementing a conventional automatic frequency correction method. FIG. 2 is a block diagram showing an embodiment of the automatic frequency correction method according to the present invention. ，
6, 13, 20.21... Fist phase synchronized oscillator 7.8, 14.22... - Crystal oscillator 9... Box, force amplifier 10... Brancher 11... Low noise Amplifier 15, fist, demodulator 16, phase detector 18, fist, loop amplifier 19, voltage controlled oscillator.

Claims (1)

[Claims] A modulator, first to third mixers, first to fourth phase-locked oscillators, and first to third crystal oscillators. It includes a power amplifier, a low noise amplifier, and a demodulator, and mixes the output of the modulator with the output signal of the first phase-locked oscillator in the first mixer to generate a first intermediate frequency signal. After converting the first intermediate frequency signal into , the output signal of the second crystal oscillator is mixed with the output signal of the third phase-locked oscillator, converted into a transmission frequency band E signal, amplified by the power amplifier, and supplied to the antenna. , the received signal returned from the satellite repeater is received in the antenna and amplified by the low noise amplifier, and the fourth phase synchronization is synchronized with the output signal of the third crystal oscillator in the third mixer. Receive mixed with oscillator output signal■
The F-band signal is doubled and supplied to the demodulator, and the received Byron is extracted from a part of the received 11i' band signal. (The % sign is extracted and the frequency fluctuation is detected from the received pilot signal to correct the transmission frequency. An automatic frequency correction method in a satellite communication earth station configured with a feedback loop as shown in FIG. A loop amplifier for amplifying the output type rF'y of the detector, outputting a signal whose frequency is controlled by the output voltage of the loop amplifier, and supplying the feedback loop to the first phase-locked oscillator. a fourth phase synchronized oscillator for obtaining an N-multiple wave synchronized with the output signal of the voltage controlled oscillator, and an output signal of the first crystal oscillator. a fifth phase-to-phase 1υ1 oscillator for continuing oscillation in synchronization with the phase of the phase shifter; An automatic frequency correction method characterized by comprising a device.