JPS6160024A - Receiver - Google Patents

Abstract

PURPOSE:To attain transmission of the least information even at the worst reception state by using the normal 1st transmission mode and the 2nd transmission mode transmitting data even if the reception state is worse, detecting the mode in response to the reception state to switch the reception circuit. CONSTITUTION:An FM demodulation output is given to an input terminal 21, and since it is only at the 1st mode that the video signal is transmitted, a synchronizing signal is extracted from a synchronous separator circuit 25 only at the 1st mode. Just after a DC voltage is fed to a power terminal 32, an inverter 35 outputs H level by the operation of a capacitor 34, and after a prescribed time, its output is inverted, an output of an inverter 36 is fed to switch circuits 34, 41, fed to an FM demodulator as a switching signal of a loop filter and the switch circuits 37, 41 change over the reception mode. Thus, when the synchronizing signal is extracted, an output level of a diode 28 brings the mode to the 1st mode reception state for a prescribed time from application of power. When no synchronizing signal is detected from the synchronizing separator circuit 25, on output of the inverter 36 goes to H, and the switch circuits 37, 41 select the 2nd mode reception state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving device applied to an information transmission system using satellite communication.

[Conventional technology]

When information is transmitted using satellite communication, it is possible to instantly transmit information over a wide area. For this reason, an information transmission system using satellite communication is convenient, for example, when it is desired to instantly transmit information such as product pictures and inventory data from a head office to sales offices scattered over a wide area.

In satellite communications, an artificial satellite receives radio waves sent from a transmitting station on the ground, converts them to a predetermined frequency, amplifies them to a level that allows direct reception, and then transmits them to the target area. The radio waves used for satellite communication are sub-millimeter waves in the SHF (super high frequency) band.

Radio waves with short wavelengths, such as those in the SHF band, are attenuated greatly during dense fog or rain. For this reason, in conventional information transmission systems using satellite communications, in cases such as heavy rain, a lot of noise appears in the images and many errors occur in the data. In the worst case, the video will be interrupted and all information will be lost along with the video.

[Problem that the invention seeks to solve]

Therefore, when the reception condition is poor like this, it may be possible to use a transmission mode that is resistant to noise in addition to the normal transmission mode so that only the minimum amount of information can be transmitted.

However, if there is more than one transmission mode, a problem arises in that it is necessary to detect which transmission mode is on the receiving side, and the mode of the receiving device must be switched depending on the mode.

Therefore, in addition to the first transmission mode in which video signals, audio and data are sent, and the second reception mode in which data can be reliably sent even when reception conditions are poor and there is a lot of noise, the present invention provides two reception modes. The purpose is to provide a receiving device that can transmit the minimum amount of information even in bad weather. Another object of the present invention is to provide a receiving device that can automatically switch modes with a simple circuit configuration without using pilot signals. Still another object of the present invention is to set the receiving state to the first transmission mode with high probability immediately after power is turned on when the circuit operation is not stable;
It is an object of the present invention to provide a receiving device that can reduce the adverse effects caused by switching the receiving mode.

[Means for solving problems]

The present invention provides a first transmission mode (clear sky mode) in which a video signal and a signal obtained by modulating a subcarrier of a predetermined frequency on the high frequency side of the video signal with audio and/or data are FM-modulated and transmitted; In a satellite communication receiving device having a second transmission mode (save mode) in which voice and/or data is FM modulated and transmitted, the received signal is frequency-converted and the frequency-converted signal is converted to FM.
an FM demodulator 15 that performs 4x modulation, a first means for extracting audio and/or data in a first transmission mode to which the output of the FM demodulator 15 is supplied, respectively; and audio in a second transmission mode. and/or second means for retrieving data 4
2.43, a circuit 37.41 for selecting the output of the first means and the output of the second means, and a detection means 34.35 for detecting the rise of the power supply, and the output of the detection means 34.35 This receiving device controls a selection circuit to select a first transmission mode for a predetermined period of time from when the power is turned on.

[Effect]

In addition to the first transmission mode in which video signals, audio signals, and data are sent, a second transmission mode is used that allows data to be sent reliably even when reception conditions are poor and there is a lot of noise. information can be sent reliably. Second
In this transmission mode, no video signal is sent, only audio and data. Therefore, the two modes can be switched by detecting the synchronization signal in the video signal, switching to the first mode if the synchronization signal is detected, and switching to the second mode if the synchronization signal cannot be detected. is done automatically.

The normally transmitted mode is clear sky mode.

However, for several seconds after the power is turned on, the circuit is unstable and synchronization separation is not performed properly, so the receiver is set to save mode reception state. In the save mode reception state, no video signal processing is performed. For this reason, if the state is switched to the clear sky mode reception state after the synchronization signal is separated several seconds after the power is turned on, it will take time to start processing the video signal. Therefore, after the power is turned on, the clear sky mode reception state is set for a predetermined period of time.

〔Example〕

An embodiment of the invention will be described below with reference to the drawings. In this embodiment, in addition to the normal mode (hereinafter referred to as clear sky mode) in which video signals, audio, and data are sent, there is also a Error mode (
Two transmission modes (hereinafter referred to as save mode) are used.

These two transmission modes will be explained in detail below. The clear sky mode is a mode in which a video signal F and four-phase PSK modulated audio and data signals F2 are sent, as shown in the spectrum diagram of FIG. 2A. The save mode is approximately 2 M as shown in the spectrum diagram in Figure 2B.
This is a mode in which only the audio and data signals F3 in the llz band are sent.

The video signal F sent in clear sky mode is an analog color video signal with the highest frequency Br.

is, for example, 4.5M1lz. The audio signal has, for example, two channels and is converted into PCM. The sampling frequency fs of the audio signal is, for example, 48 kllz, and the number of quantization bits is 16 bits. This PCM audio signal is encoded as shown in FIG. 3 together with additional data used for transmitting inventory information, for example. The additional data is, for example, a maximum of 24 bits, and
Since the M data has a quantization bit number of 16 bits and two channels, it is 32 bits. Before and after these additional data and PCM data, for example, 1 bit of 5YNC bit and 7-bit parity of (63,56) BC:H code are attached.

The 4-phase PSK modified audio and data signal Ft sent in clear sky mode is frequency-divided into a video signal by the coded additional data and audio data digital signals as shown in Figure 3 above. For example, 5.7 multiplexed
The subcarrier of 27M1lz is subjected to four-phase PSK modulation.

4-phase PSK modulation means, for example, that data is divided into 2 bits each, and when the phase (11) of a sine wave corresponding to each of the divided 2 bits is (sin θ
+cosθ), (01) (sinθ−Cosθ)
, (10) when (cosθ−5inθ), (
This is a modulation method in which (-sin θ - COS θ) is determined when 00), and these sine waves of corresponding phases are switched according to each 2-bit data.

In the save mode, 4-phase PSK modulation is not performed, and only the voice and data signals F'S are FM modulated and transmitted.

From the transmitting side on the ground, in clear sky mode, the second
A composite signal of the video signal F shown in FIG.
The frequency is converted to 4GHz and output to the artificial satellite. In the save mode, the audio and data signal F3 shown in FIG. 2B is FM modulated and frequency converted to, for example, 14Gl(z) and output to the artificial satellite.

The radio waves sent from the transmitting side are received by the artificial satellite, converted to, for example, 12 GI (z), amplified to power that can be directly received by the receiving side, and output.

Unlike the clear sky mode, the save mode transmits only one audio and data signal, so it does not require enough power to transmit a video signal. In addition, the save mode has a narrower transmission band than the clear sky mode, and the triangular noise peculiar to FM modulation is reduced to a low frequency. For this reason, in save mode, the C/N ratio! As shown in FIG. 5, the error rate of voice and data signals is reduced even when the noise is high. In Fig. 5, the horizontal axis shows the C/N ratio of the received input, and the vertical axis shows the error rate. The white triangle shows the error rate in clear sky mode, and the white circle dot shows the error rate. is the error rate in save mode. Therefore, even if transmission is difficult in clear sky mode, by using save mode, necessary data and audio other than video signals can be reliably transmitted.

FIG. 1 and FIG. 6 show an embodiment of the present invention, and this embodiment is designed so that the output from the satellite can be received both in clear sky mode and in save mode. .

In FIG. 6, reference numeral 1 indicates an antenna composed of a parabolic main reflector, a sub-reflector, and an electromagnetic horn. A circularly polarized wave generator 2 is connected to the electromagnetic horn of the antenna 1.

The circularly polarized wave generator 2 has a configuration in which, for example, a dielectric material is inserted into a circular waveguide at an angle of 45'' with respect to the plane of polarization of the linearly polarized wave.The circularly polarized wave received by the antenna 1 is The circularly polarized wave generator 2 converts the wave into a linearly polarized wave, and the transmission path is changed from a rectangular waveguide to a coaxial cable by passing through a converter (not shown).Then, the received signal is sent to the SHF amplifier 3. The mixer 4 is supplied with a local oscillation signal from the first local oscillator 5,
A first intermediate frequency signal appears at the output of mixer 4. The output of this mixer 4 is supplied to a first intermediate frequency amplifier 6. The device from this antenna 1 to the first intermediate frequency amplifier 6 is installed outdoors.

This outdoor unit is coupled to the indoor unit via a coaxial cable 7. Reference numeral 8 indicates a first intermediate frequency amplifier of the indoor unit, and its output is passed through a variable bandpass filter 9 to select a desired wave, which is then sent to a mixer 10.
supplied to This mixer 10 includes a second local oscillator 1
1 and a second intermediate frequency signal is obtained at its output. This second intermediate frequency signal is transmitted to the second intermediate frequency band pass filter 12' and the second intermediate frequency amplifier 1.
3 and a limiter 14 to an FM demodulator 15. The FM demodulator 15 is a PLL demodulator, and the characteristics of the loop filter can be switched depending on the mode. The FM demodulated output by the FM demodulator 15 is sensed from the output terminal 16.

This FM demodulation output is sent from the input terminal 21 in FIG. 1 to a low-pass filter 22, a band-pass filter 23, and a low-pass filter 24, respectively. The signal is supplied to the switch circuit 37.

A video signal is sent only in clear sky mode, and no video signal is sent in save mode. Therefore, the synchronization signal is extracted from the sync separation circuit 25 only when the received signal is in the clear sky mode, and the sync signal is not extracted from the sync separation circuit 25 when the received signal is in the save mode.

The output of the synchronization separation circuit 25 is connected to an integration circuit 26 for noise removal.
The signal is supplied to the amplifier amplifier 27 via. The output of buffer amplifier 27 is supplied to diode 28 .

The cathodes of the diodes 28, 29, and 30 are commonly connected, and this common connection point is connected to the input terminal of the inverter 36. With this diode 28°29.30,
An OR gate is configured.

A terminal 31 is connected to the anode of the diode 29,
An antenna setting mode signal is supplied from the terminal 31. The antenna setting mode is a mode for setting the direction of the antenna in the best direction. When the antenna setting mode signal is supplied and the antenna setting mode is set, the antenna input signal level will be displayed as a bar graph on the screen,
The peak value of this input signal level is held and displayed.

A series connection of a resistor 33 and a capacitor 34 is inserted between the power supply terminal 32 and the ground, and a connection point between the resistor 33 and the capacitor 34 is connected to an input terminal of an inverter 35 . A cathode of a diode 30 is connected to the output terminal of this inverter 35. Immediately after the DC voltage is applied to the power supply terminal 32,
Due to the charging current flowing into the capacitor 34, the voltage at the input terminal of the inverter 35 is low, and a high level output is supplied from the inverter 35 to the diode 30.

When a certain period of time, for example 2 to 3 seconds, has passed and charge is stored in the capacitor 34, the input voltage of the inverter 350 increases and the output of the inverter 35 is inverted.

Therefore, the level of the anode of the diode 30 becomes low level.

The output of the inverter 36 is supplied to switch circuits 37 and 41 as well as to a mode display circuit 44. Although not shown, the output of the inverter 36 is supplied to the FM demodulator 15 as a loop filter switching signal.

Switch circuits 37 and 41 switch reception modes. When the output of the inverter 36 is at low level, the input terminal 37A and the output terminal 37B of the switch circuit 37
is connected, the input terminal 41A and the output terminal 41B of the switch circuit 41 are connected, and a clear 4 chi mode reception state is entered. At this time, the mode display circuit 44 displays that it is in the clear sky mode reception state. Also, at this time, the loop filter of the FM demodulator 15 is switched to have characteristics for clear sky mode.

An OR gate is formed by diodes 28, 29, and 30. Therefore, when the synchronization signal is extracted, the level of the anode of the diode 28 becomes high level,
Clear sky mode reception status is established. Further, when setting the direction of the antenna, a high-level antenna setting mode signal is supplied to the diode 29, and the clear sky mode reception state is always set. Further, for several seconds after the power is turned on, the level of the diode 30 is at a high level, so that the clear sky mode reception state is established.

In the clear sky mode reception state, video signals and audio,
Data output is retrieved as follows.

The FM demodulated output from the input terminal 21 is passed through the low-pass filter 2.
2 and a bandpass filter 23, and a color video signal F1 appears at the output of the lowpass filter 22. This color video signal F1 is taken out from the output terminal 46 via the switch circuit 37.

A four-phase PSK modulated audio and data signal F2 appears from the output of the bandpass filter 23. The output of the bandpass filter 23 is supplied to a demodulation circuit 38 and also to a bit clock recovery circuit 39. A bit clock reproducing circuit 39 reproduces a bit clock synchronized with the received data, and the output of the bit clock reproducing circuit 39 is supplied to a demodulating circuit 38 and a latch 40. The demodulation circuit 38 performs 4-phase PSK demodulation, and the output of the demodulation circuit 38 is supplied to the latch 40. PCM audio output and data are taken out from the output of the latch 40, and the output of the latch 40 is supplied to the signal processing circuit 45 via the switch circuit 41.

A signal processing circuit 45 performs signal processing such as error correction, and the PCM audio output and data are taken out from an output terminal 47. Although not shown, the PCM audio output and data are separated, and the PCM audio output is D/A converted to form an audio signal.

When no synchronization signal is detected from the synchronization separation circuit 25, the level of the anode of the diode 28 is low.

Therefore, when the synchronization signal is not detected, the output of the inverter 36 becomes high level.

When the output of the inverter 36 becomes high level, the input terminal 37C and the output terminal 37B of the switch circuit 37 are connected, and the input terminals 41C and 41B of the switch circuit 41 are connected, and a save mode reception state is entered. At this time, the mode display circuit 44 displays that it is in the save mode reception state, and the loop filter of the FM demodulator 15 is switched to have characteristics for the save mode.

In the save mode reception state, audio and data output are extracted as follows.

The FM demodulated output from the input terminal 21 is passed through the low-pass filter 2.
4. Audio and data signals F are obtained from the output of the low-pass filter 24 , and the output of the low-pass filter 24 is supplied to the latch 43 and also to the bit clock recovery circuit 42 . Hint clock regeneration circuit 4
2, the bit clock synchronized with the received data is regenerated,
The output of bit clock recovery circuit 42 is supplied to latch 43. PCM audio output and data are taken out from the output of the launch 43, and the output of the latch 43 is sent to the switch circuit 41.
The signal is supplied to the signal processing circuit 45 via.

A signal processing circuit 45 performs signal processing such as error correction, and the PCM audio output and data are taken out from an output terminal 47. Although not shown, the PCM audio output and data are separated, and the PCM audio output is D/A converted to form an audio signal.

As described above, in this embodiment, automatic switching between clear sky mode and save mode is performed by detecting a synchronization signal. The reason why the clear sky mode is always set for a predetermined period of time after the power is turned on is to ensure that this automatic switching is performed reliably.

In other words, the normally transmitted mode is the clear sky mode. However, for a few seconds after the power is turned on, the circuit is unstable and synchronization separation is not performed normally, so the receiver is set to the save mode reception state. In the save mode reception state, no video signal processing is performed. For this reason, if the state is switched to the clear sky mode reception state after the synchronization signal is separated several seconds after the power is turned on, it will take time to start processing the video signal. Therefore, after the power is turned on, the clear sky mode reception state is set for a predetermined period of time.

〔Effect of the invention〕

According to this invention, in addition to the first transmission mode in which video signals, audio, and data are sent, it is possible to receive the second transmission mode in which data is reliably sent even when reception conditions are poor and there is a lot of noise. Therefore, it is possible to realize a receiving device that can transmit the minimum amount of information even in bad weather. Further, according to the present invention, since the transmission mode is detected from the synchronization signal, automatic switching of the transmission mode can be performed with a simple circuit configuration without inserting a pilot signal. Furthermore, since the clear sky mode is always set for a predetermined period of time after the power is turned on, the mode can be switched reliably.

[Brief explanation of drawings]

FIG. 1 is a partial block diagram of an embodiment of the present invention, FIG. 2 is a spectrum diagram used to explain clear sky mode and save mode, FIG. 3 is a route map used to explain voice and data signals, and FIG. 5 is a vector diagram used to explain four-phase PSK modulation, FIG. 5 is a graph showing the effects of clear sky mode and save mode, and FIG. 6 is a block diagram of a part of an embodiment of the present invention. 15: FM demodulator, 25: Synchronization separation circuit, 28°2
9.30? Diode, 32: Power supply terminal, 34: Capacitor, 37, 41: Sui Nochi circuit.

Claims (1)

[Claims] A signal obtained by modulating a video signal and a subcarrier of a predetermined frequency on the high frequency side of the video signal with audio and/or data is an FM signal.
In a satellite communication receiving device having a first transmission mode in which the voice and/or data is modulated and transmitted, and a second transmission mode in which the voice and/or data is FM modulated and transmitted, the received signal is frequency-converted and FM demodulated. a first means for extracting the audio and/or data in the first transmission mode and the audio and/or data in the second transmission mode to which outputs of the receiving and demodulating means are respectively supplied. , a circuit for selecting the output of the first means and the output of the second means, and a detection means for detecting the rise of the power supply, and the selection circuit according to the output of the detection means. The receiving device is configured to select the first transmission mode for a predetermined period of time from the time when the power is turned on.