JP2700972B2 - Pilot signal and its signal-to-noise ratio detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a very small earth station for satellite communication (hereinafter referred to as VSAT: Very Small Apertu).
and a signal-to-noise ratio (C / N) detection circuit used in the pilot signal.

[0002]

2. Description of the Related Art Conventionally, for example, a system shown in FIG. 3 is known as a VSAT system.

Referring to FIG. 3, a VSAT system of this type includes a plurality of VSAT stations 12 and 13 in addition to a pilot station 11, and the VSAT stations 12 and 13 are connected to a pilot station 11 via a communication satellite 14. And a VSA via the communication satellite 14
T stations 12 and 13 communicate with each other.

Incidentally, the VSAT station 12 and the VSAT station 1
It is known that the C / N of the received signal in each of the VSAT stations 12 and 13 changes when performing mutual communication with the VSAT 3 due to external conditions such as weather. On the other hand, the transmission signal from each of the VSAT stations 12 and 13 is generally frequency-converted by the communication satellite 14 and sent to another VSAT station. The received signal frequencies at stations 12 and 13 are shifted. That is, the quality of the received signal at the VSAT station is deteriorated due to the various factors described above (this leads to deterioration of communication quality).

Therefore, as described above, the pilot station 1
1 transmits a pilot signal (unmodulated signal) to each VS
The AT satellites 12 and 13 receive this pilot signal and detect its frequency and C / N to obtain the communication satellite 1
4 and the rate of deterioration of the C / N between the VSAT stations 12 and 13 can be known. That is, the VSAT stations 12 and 13 use the pilot signal to automatically control the frequency (AFC: Automatic Freq).
UPC, and detects the C / N of the pilot signal to control transmission output (UPC: Uplin).
k Power Control).

As described above, in the conventional VSAT station, a pilot signal detection circuit for detecting the pilot signal frequency and a C / N for detecting the C / N of the pilot signal are provided.
N detection circuits are provided, and these detection circuits have, for example, the configuration shown in FIG.

Referring to FIG. 2, an antenna 21 is connected to a demodulator 23 and an IF amplifier (hereinafter simply referred to as an amplifier) 24 via a down converter 22.
1 is amplified by an amplifier 24, and is transmitted through a power splitter 25 to a pilot signal detector 26.
And the noise detection unit 27.

The pilot signal detector 26 has a narrow band pass filter 26a, and the pilot signal is band-limited by the narrow band filter 26a. That is,
The narrow band pass filter 26a passes only the pilot signal. This pilot signal is sent to a limiting amplifier 26b, where it is amplified to a predetermined level, and is amplified as an amplified pilot signal by an AFC circuit (not shown).
Given to. Thus, the AFC circuit knows the presence or absence of the pilot signal and executes the frequency control. On the other hand, the amplified pilot signal is provided to a signal detector 26c, where the signal is frequency-detected. The frequency detection value is AF
It is sent to the C circuit. The AFC circuit controls the frequency so that the pilot signal frequency becomes a predetermined frequency based on the frequency detection value.

In the noise detector 27, first, the FM detector 27
In step a, noise on the pilot signal is detected to obtain a noise signal. This noise signal is provided to the signal converter 27d via the low-frequency amplifier 27b and the bandpass filter 27c, where it is converted into a signal (for example, a voltage signal) corresponding to the noise level. This voltage signal is supplied to a UPC circuit (not shown), and the UPC circuit controls the transmission output according to the voltage signal level.

[0010]

As described above, in the conventional VSAT station, pilot signal detection and C / N detection are performed by independent circuits, respectively, and two detection circuits (analog circuits) must be provided. Therefore, there is a problem that the circuit scale becomes large.

Further, in the C / N detection, no consideration is given to the frequency shift of the pilot signal, so that C
/ N is difficult to detect. Similarly, there is a problem that it is difficult to accurately detect a pilot signal because no consideration is given to noise in pilot signal detection. That is, the conventional VS
Since the AT station performs pilot signal detection and C / N detection independently, there is a problem that frequency deviation and noise interfere with each other and accurate detection is difficult.

An object of the present invention is to reduce the circuit scale,
It is another object of the present invention to provide a detection circuit capable of accurately detecting a pilot signal and its C / N.

[0013]

According to the present invention, there are provided a plurality of satellite communication earth stations and a pilot station, wherein the satellite communication earth stations communicate with each other via a communication satellite, and further include the satellite communication earth station. An earth station receives a pilot signal from the pilot station via the communication satellite, performs automatic frequency control, and is used in a satellite communication system that performs transmission output control. The earth station detects the pilot signal and detects a signal of the pilot signal. A detection circuit that detects the noise-to-noise ratio, receives the pilot signal, compares a phase of the pilot signal with a phase of a control signal to generate a phase error signal, and based on the phase error signal, A voltage controlled oscillator for controlling the phase of the control signal, and a position for outputting a pilot signal detection signal when the phase error indicated by the phase error signal is zero. A pilot signal detection unit including a synchronization detection circuit; and a noise detection unit that receives the phase error signal and detects the signal-to-noise ratio according to the phase error signal, and a pilot signal and a signal thereof. A noise-to-noise ratio detection circuit is obtained.

[0014]

According to the present invention, when phase synchronization of a pilot signal is established in a phase locked loop constituted by a phase comparator and a voltage controlled oscillator, a pilot signal detection signal is output from the phase locked comparator, Since the noise level, that is, the signal-to-noise ratio is detected by the phase error signal provided from the comparator, the detection of the pilot signal and the detection of the C / N are performed by substantially one system, so that the circuit scale is reduced. Can be downsized. Further, mutual interference between the frequency error and the noise can be removed, and the pilot signal detection and the C / N detection can be accurately performed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Referring to FIG. 1, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The pilot signal from amplifier 24 is first provided to pilot signal detecting section 31. After the pilot signal is band-limited by the narrow band filter 31a, it is amplified by the limiting amplifier 31b and input to the phase comparator 31c. The control signal is supplied from the voltage controlled oscillator 31d to the phase comparator 31c, and the phase comparator 31c generates a phase error between the pilot signal and the control signal, and outputs the phase error signal. This phase error signal is applied to a voltage controlled oscillator 31d after unnecessary frequency components are removed by a low-pass filter 31e. The voltage control oscillator 31d performs phase control (frequency control) of the control signal so that the phase error indicated by the phase error signal becomes zero. That is, in the voltage controlled oscillator 31d, the phase of the control signal and the phase of the pilot signal are matched.

Here, the output of the low-pass filter 31e, that is, the phase error signal is equivalent to a noise signal that has passed through the narrow-band filter 31a together with the pilot signal. That is,
This indicates the C / N of the pilot signal.

By the way, when the frequency error of the pilot signal is equal to or less than a predetermined value, the pilot signal passes through the narrow band filter 31a and the phase comparator 31
c, the voltage is controlled by a phase-locked loop composed of a voltage-controlled oscillator 31d and a low-pass filter 31e. The above phase error signal is supplied to the synchronization detector 31f. When the phase error signal is zero, the synchronization detector 31f determines that synchronization has been established, and outputs the pilot signal detection signal to the AFC.
Send to circuit (not shown). On the other hand, the output of the voltage controlled oscillator 31d, that is, a control signal is separately provided to the AFC circuit. The AFC circuit knows the establishment of the synchronization by the pilot signal detection signal and controls the frequency based on the control signal at this time.

On the other hand, the phase error signal is supplied to the noise detection section 32, and after being amplified by the low frequency amplifier 32a, unnecessary frequency components are further removed by the bandpass filter 32b and sent to the signal converter 32c as a noise signal. . Signal converter 3
At 2c, the noise signal is converted into, for example, a voltage signal according to the level of the noise signal, that is, according to the C / N, and transmitted to a UPC circuit (not shown). Then, the UPC circuit performs transmission output control based on the voltage signal.

[0020]

As described above, in the present invention, since the pilot signal is detected by using the phase locked loop, and then the C / N detection is performed, the system is practically one system and the circuit scale is small. There is an effect that can be made. Further, there is an effect that the interference between the circuits can be considered, and the pilot signal and the C / N can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a pilot signal and its C / N detection circuit according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional pilot signal and its C / N detection circuit.

FIG. 3 is a diagram schematically showing a micro earth station system for satellite communication.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Pilot station 12, 13 VSAT station 14 Communication satellite 21 Antenna 22 Down converter 23 Demodulator 24 IF amplifier 25 Power splitter 26 Pilot signal detector 27 Noise detector 31 Pilot signal detector 32 Noise detector

Claims (1)

(57) [Claims] 1. A satellite communication earth station comprising: a plurality of satellite communication earth stations; and a pilot station. The satellite communication earth stations communicate with each other via communication satellites. Used in a satellite communication system for performing automatic frequency control and transmitting output control by receiving via the communication satellite, and detecting the pilot signal and detecting a signal-to-noise ratio of the pilot signal, Receiving the pilot signal,
A phase comparator that generates a phase error signal by comparing the phase of the pilot signal with the phase of the control signal, a voltage-controlled oscillator that controls the phase of the control signal based on the phase error signal, and the phase error signal A pilot signal detection unit including a phase synchronization detection circuit that outputs a pilot signal detection signal when the phase error is zero, receives the phase error signal, and sets the signal-to-noise ratio according to the phase error signal. A pilot signal and a signal-to-noise ratio detection circuit, comprising: a noise detection unit for detecting the pilot signal.