JPH057919B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a satellite broadcast joint reception system that receives satellite broadcast television signals using a common antenna and distributes them to receiving terminals via a coaxial cable or the like. [Technical background of the invention and its problems] A satellite broadcasting system broadcasts television signals transmitted from an earth station to general viewers (individual households, communal broadcast directly to recipients). Not only will you be able to receive high-quality video and audio without interference, you will also have a channel separate from the terrestrial channel, making it possible to broadcast nationwide at the same time. Satellite broadcasting is also considered as a broadcasting medium for new types of broadcasting services in the future, such as teletext, audio-only broadcasting, and high-definition TV, and is expected to become the core of so-called new media. Digitalization of the audio signal transmission method for television satellite broadcasting is being considered, and adoption is being considered in countries around the world. Japan has decided to be the first in the world to digitize the audio signal transmission method for television satellite broadcasting, and plans to implement this from Satellite Broadcasting No. 2 (BS-2). By digitizing the audio signal transmission method, you can enjoy high-quality audio during broadcasting just like you would with a digital audio disk, and you can also multiplex audio broadcasts other than TV audio, or transfer extra transmission bits to facsimile or static transmission. It can be used for other multiplex broadcasts such as images, making it possible to transmit data that can respond to the diversification of the information society. The audio signal transmission method that Japan and many other countries are trying to adopt is called the "audio PCM subcarrier method," and as shown in Figure 1, audio subcarrier 2 (5.727272MHz) is frequency-division multiplexed onto video signal 1. 4-phase differential phase modulation (hereinafter referred to as 4-phase DPSK) is a PCM-encoded audio signal.
This is a method called (Differential Phase Shift Keying). The transmission specifications shown in the table below are used as a method for PCM encoding and multiplexing audio signals.

[Purpose of the invention]

An object of the present invention is to provide a satellite broadcasting joint reception system that enables joint reception of high quality and no loss of information with a relatively simple facility configuration and not demanding performance requirements. [Summary of the Invention] This invention converts received satellite broadcast television signals into VSB-AM signals for each channel,
Furthermore, a conversion device is installed to convert the audio subcarrier into a signal in a frequency band different from this VSB-AM signal, and the signals obtained by these conversion devices are transmitted to the receiving terminal device via a transmission path including a coaxial cable, etc., and received. The terminal device is characterized in that it selects a desired channel signal from each of the VSB-AM signal and the audio subcarrier signal from the received signal in conjunction with each other. That is, for the voice subcarrier, VSB−
To enable high quality and unimpaired transmission of information by transmitting in a frequency band different from that of the AM signal, and to deal with the fact that the transmission frequency band of the VSB-AM signal and this audio subcarrier signal are different. By linking the channel selection of these two signals on the receiving terminal device side, it is possible to extract signals of the same channel for the video signal and the PCM audio signal. [Effects of the Invention] According to the present invention, unlike a system in which a satellite broadcast television signal is transmitted to a receiving terminal device in the form of an FM signal, both the VSB-AM signal and the audio subcarrier signal are transmitted with large losses. In addition, the performance conditions required for facilities such as transmission lines and various transmission equipment are relaxed, and existing equipment can be used effectively. Even in the case of new construction, the technical and economic burden can be kept to a minimum. Furthermore, since the audio subcarrier signal modulated by the PCM audio signal is transmitted in a frequency band different from that of the VSB-AM signal, information on all audio channels can be reproduced, and high-quality audio due to PCM can be reproduced. It becomes possible to play. It is also of course possible to extract independent data bits. [Embodiment of the Invention] Figure 2 shows a schematic configuration of a satellite joint reception system according to an embodiment of the present invention, which is roughly divided into a head end section A, a transmission path B, and a receiving terminal device C. ing. In the head end section A, a satellite broadcast television signal in the 12 GHz band (SHF) is received by a receiving antenna 11 such as a parabola, amplified by a low noise amplifier in an outdoor unit 12, and then an intermediate frequency signal (FM signal) of approximately 1 GHz is received. ). This intermediate frequency signal is distributed and supplied by a distributor 13 to a converter 14 installed for each channel. The converter 14 converts the intermediate frequency signal from the distributor 13 into channels.
It converts into a VSB-AM signal and also converts the audio subcarrier therein into a signal in a frequency band different from that of the VSB-AM signal, and is configured as shown in FIG. 3, for example. The converter 14 in FIG. 3 can be roughly divided into FM-
It consists of an AM converter 31, a remodulator 35 and an audio subcarrier converter 39. The input intermediate frequency signal 30 of the satellite broadcast television signal is
The tuner circuit 32 in the FM-AM converter 31 selects a specific channel (referred to as X) determined for each converter 14, and the limiter/FM demodulator 33 converts the baseband video signal and audio The signal (PSK) is demodulated. Audio signal is further PSK
The signal is guided to a demodulator/PCM decoder 34, where baseband audio signals for two channels are restored. The baseband video signal obtained by the FM-AM converter 31 is sent to the IF modulator 36 in the remodulation device 35.
is converted into a 50MHz band VSB-AM signal by At this time, the IF modulator 36 also has an FM-
Two channels of baseband audio signals obtained by the AM converter 31 are supplied through the audio multiplex modulator 37, and this audio signal is multiplexed onto the VSB-AM signal. The output of the IF modulator 36 is converted by a frequency converter 38 into a signal similar to that used in current television broadcasting.
It is converted into a high frequency signal of any channel in the VHF or UHF band or mid-band. The VSB-AM thus obtained by the remodulation device 35
An example of the frequency spectrum of the signal is shown in FIG. Reference numeral 41 denotes a video signal consisting of a VSB-AM signal, and two channels of audio signals consisting of an FM signal are multiplexed above it. On the other hand, the audio signal obtained by the limiter/FM demodulator 33 is further converted into a signal in a frequency band such as a mid-band by an audio subcarrier. As mentioned above, the audio signals in the television satellite broadcasting that is planned to be implemented in Japan have two modes, A and B. In the A mode, audio signals with an audio bandwidth of 15 KHz are transmitted through four channels. Of these four channels, the remodulator 35 described above can only transmit the first and second audio channels (stereo or bilingual), which are television audio, and can transmit the third and fourth audio channels and independent data bits. Can not. In addition, in the B mode, the audio signal is only on two channels for television, but the audio bandwidth is 20 KHz, and the remodulation device 35 described above has an audio bandwidth of 15 KHz, so good transmission cannot be achieved. Of course, independent data bits in B mode cannot be transmitted either. However, by providing the audio subcarrier converter 39 as shown in FIG. 3, it is possible to transmit the third and fourth audio channels and independent data bits in the A mode, and also to transmit the two channels of audio in the B mode. It can enable high quality transmission of signals and transmission of independent data bits. The VSB-AM signal and audio subcarrier signal for each channel thus obtained by the converter 14 are guided to the transmission path B as shown in FIG. 2, mixed for all channels in the mixer 17, and then Cable 16, amplifier 17 and splitter/brancher 1
9, etc., and is transmitted to the receiving terminal device C. The frequency spectrum of this transmission signal is shown in FIG.
51 and 52 are VSB, similar to 41 and 42 in Figure 4.
-AM signal and two channels of audio signals multiplexed thereto; 53 is an audio subcarrier signal; In this case, the audio carrier signal 53 includes a VSB-AM signal 51 including a video signal and an audio signal 52.
It goes without saying that it is necessary to arrange the frequencies so that they do not overlap (including signals of other channels) and also do not overlap with audio subcarrier signals of other channels. The receiving terminal device C consists of an indoor unit 20, a television receiver 21, an audio device 22, an additional information processing device 23, etc. connected to this as appropriate.
The indoor unit 20 is configured as shown in FIG. 6, for example. That is, the signal 60 transmitted through the transmission path B is first input to the separation filter 61, and after frequency separation of the VSB-AM signal and the audio subcarrier signal consisting of the PSK signal, the signal 60 is sent to the video tuner circuit 62 and the audio subcarrier signal consisting of the PSK signal, respectively. The signal is guided to an audio tuner circuit 63. The video tuner circuit 62
A desired channel signal is selected from the VSB-AM signal and converted to, for example, the 13th channel frequency band (center frequency 473 MHz) of the UHF television band. Since this signal has the same format as current television broadcasting, it can be received through the antenna terminal of the television receiver 21. At this time, since two channels of audio are multiplexed in the television signal of the 13th channel using the television audio multiplexing method, the audio can be reproduced by the speaker built into the television receiver 21. The reasons for converting the VSB-AM signal to the 13th channel frequency band in this way are that the adjacent channels are far apart, so there is less spurious interference, and that the 13th channel frequency band is currently not in use. Home VCRs, which are not expected to be used for some time in the future, use the first or second channel, so they can be connected to satellite broadcasting receivers without any problems. On the other hand, the audio tuner circuit 63 selects a desired channel signal from the input audio subcarrier signal and supplies it to the PSK demodulator/PCM decoder 65.
An analog audio signal is extracted from the PSK demodulator/PCM decoder 65 and supplied to the audio device 22. In addition, the PSK demodulator/PCM decoder 65
Since the entire bit stream after error correction and correction can be extracted from the PCM signal processing section, independent data bits can be supplied to the additional information processing device 23, such as a facsimile device. Here, the video tuner circuit 62 and the audio tuner circuit 63 are controlled by an interlocking channel selection control device 64 so that they select the same channel in conjunction. FIG. 7 shows a specific example of the interlocking tuning control device 64, in which the tuner circuits 62 and 63 are of a so-called electronic tuning type using varactor diodes as tuning elements. That is, when one of the tuning switches 70 is pressed, the channel number to be received is displayed on the channel display 72 through the channel selector 71, and VHF is sent from the band selector 73 to the video tuner circuit 62.
low band (V _L ), high band (V _H ) and
A band switching voltage is provided for switching the UHF band. Furthermore, under the control of the channel selector 71, tuning voltages V _T1 and V _T2 (varactor bias voltages) are supplied from the tuning voltage generation circuits 74 and 75 to the video system and audio system tuner circuits 62 and 63. In this case, the tuning voltage generating circuits 74 and 75 preset the tuning voltage of each channel using, for example, a potentiometer, and the channel selector 71 generates the tuning voltage of the same channel specified by the channel selection switch 70. Tuning voltage generation circuits 74 and 75 feed back information on the corresponding channel of the generated tuning voltage to channel selector 71. In this way, the tuning of the video and audio tuner circuits 62 and 63 can be linked. If the tuner circuits 62 and 63 are not electronically tuned but are mechanical switch-based tuning devices, the respective tuning switches may be mechanically interlocked. Next, some other embodiments of this invention will be described. FIG. 8 shows another example of the configuration of the indoor unit 20, in which a PLL frequency synthesizer is used to link the tuning of the video and audio tuner circuits. That is, the VSB-AM signal separated by the separation filter 61 is tuned through the mixer 81, and the audio subcarrier signal is tuned through the mixer 82. Here, the mixer 82 is supplied with a local oscillation signal from a voltage controlled oscillator (VCO) 84 controlled by a PLL circuit 83, and the mixer 81 is supplied with a local oscillation signal from a voltage controlled oscillator (VCO) 84 controlled by a PLL circuit 83.
The transmitted signal is supplied as a local oscillation signal. In the case of this embodiment, the transmission frequency on transmission line B is that the video system (VSB-AM signal) is hyperband,
The audio system (audio subcarrier signal) is selected for the mid-band. An example of the frequency relationship at this time is shown in the table below.

[Table] For channels after channel 3, the video system uses 6MHz steps and the audio system uses 2MHz steps. By appropriately selecting the transmission frequency in this manner, it is possible to link video and audio channel selection using a PLL frequency synthesizer using the same VCO. In addition, in the case of the above frequency relationship, the output of mixer 81 is 58.75MHz, so
It is converted into a 13ch (473MHz) signal through an RF modulator 86. Further, the output of the mixer 81 is taken out as a video output and audio output by a video demodulator 87 and an audio demodulator 88 as required, and is supplied to a receiver equipped with video and audio input terminals. On the other hand, mixer 8
The output of 2 is extracted by PSK demodulator/PCM decoder 65 in the same manner as before as an analog audio signal and the entire bit stream. Figure 9 shows an example in which the video system and audio system selection are linked using a PLL frequency synthesizer as in Figure 8, but the transmission frequencies are video system (VSB-AM signal) and audio system (audio system). Both subcarrier signals) are transmitted on separate channels using mid-bands. In this case, if the transmission channel of the VSB-AM signal is Xch and its center frequency is _fX , the VCO 94 (473-
If _a local oscillation signal of f
VSB-AM signals can be extracted directly. Incidentally, the VCO 94 is controlled by the PLL circuit 83 as in the case of FIG. On the other hand, the transmission center frequency f′ _X of the audio subcarrier signal
is chosen, for example, f′ _X = (473−f _X /2−5.73) MHz. In this way, the local oscillation signal of ( ₄₇₃ -f . In this way, by designing a system that has a certain relationship between the local oscillation frequencies of the video and audio tuner circuits, the local oscillation signals of both tuner circuits can be generated in tandem from the same oscillation source (VCO94). This simplifies the circuit configuration. Figure 10 shows a VSB that can satisfy these conditions.
- An example of channel allocation of transmission frequencies for AM signals and audio subcarrier signals (PSK) is shown. Another method of interlocking the tuning of the video and audio tuner circuits in the indoor unit 20 in the receiving terminal device C is as shown in FIG.
Identification signal 11 is placed in the audio band part above the VSB-AM signal 51 and in the vicinity of the audio subcarrier signal 53.
One possible method is to insert 1,112. FIG. 12 shows an embodiment to which such a method is applied, in which an identification signal generator 1 that generates the identification signals 111 and 112 is provided on the conversion device 14 side shown in a.
21 is provided, and these identification signals 111 and 112 are
It is inserted in the IF modulator 36 and audio subcarrier converter 39. In this case, on the indoor unit 20 side shown in b, the identification signal 111 is extracted from the output of the video tuner circuit 62 via the video demodulator 124 and the audio demodulator 125, and the identification signal 111 is extracted from the output of the audio tuner circuit 63 by the signal separation circuit 126. The identification signal 112 is separated and extracted by the comparison circuit 12.
7, compare both identification signals 111 and 112, and make sure that they match, that is, the selected VSB-AM
The PLL circuit 123 that obtains the local oscillation signal of the audio tuner circuit 63 is controlled so that the audio subcarrier signal corresponding to the signal is tuned. This invention can be implemented with various other modifications; for example, the transmission frequency of the audio subcarrier signal may be in the VHF or UHF band, in addition to the mid-band.
A frequency in a frequency band different from that of the AM signal may be used, or a modulation method other than PSK may be used for transmission.
Further, the VSB-AM signal and the audio subcarrier signal may be transmitted using separate transmission paths without being mixed. Furthermore, the VSB-AM signal may be transmitted without multiplexing narrowband audio subcarriers (audio signals for two channels).

[Brief explanation of drawings]

FIG. 1 is a diagram showing the frequency spectrum of a baseband signal of a satellite broadcast television signal using the audio PCM subcarrier system, and FIG. 2 is a schematic configuration diagram of a satellite broadcast joint reception system according to an embodiment of the present invention.
Fig. 3 is a diagram showing an example of the configuration of the conversion device, and Fig. 4 is a diagram showing an example of the configuration of the conversion device.
VSB-AM that multiplexes audio signals for channels
Figure 5 shows the frequency spectrum of the signal.
A diagram showing the transmission frequency spectrum of a VSB-AM signal and an audio subcarrier signal, FIG. 6 is a diagram showing an example of the configuration of an indoor unit in the receiving terminal equipment, and FIG. 7 is a diagram showing the configuration of the interlocking channel selection control device in FIG. 6. , FIG. 8 and FIG. 9 are diagrams showing other configuration examples of the indoor unit, FIG. 10 is a diagram showing a specific example of channel allocation of transmission frequencies in the example of FIG. 9, and FIG. FIGS. 12a and 12b are diagrams showing frequency spectra for explaining the insertion method. FIGS. 12a and 12b are diagrams showing an example of the configuration of a converter and an indoor unit to which the method of FIG. 11 is applied. A...Head end, B...Transmission path, C...Receiving terminal device, 11...Antenna, 14...Conversion device, 16...Coaxial cable, 20...Indoor unit, 31...FM-AM converter, 35...Remodulation device, 39...Audio subcarrier converter, 62...Video tuner circuit, 63...Audio tuner circuit, 64...Interlocked tuning control device, 74, 75...
Tuning voltage generation circuit, 81, 82... mixer, 83
...PLL circuit, 84...VCO, 85...3 transmitters, 91, 92...Mixer, 93...PLL circuit,
94...VCO, 95...1/2 frequency divider, 121...
Identification signal generator, 127...comparison circuit.

Claims (1)

[Claims] 1. An audio subcarrier modulated with a PCM audio signal,
In a joint reception system for satellite broadcast television signals that are frequency-division multiplexed on video signals, the television signals are VSB-based for each channel.
- A conversion device that converts the audio subcarrier into an AM signal and a signal in a frequency band different from this VSB-AM signal, and the VSB- obtained by each of these conversion devices.
A transmission path for transmitting AM signals and audio subcarrier signals, and a receiving terminal that selects signals of the same desired channel in conjunction with each of the VSB-AM signals and audio subcarrier signals transmitted via this transmission path. A satellite broadcasting joint reception system comprising: a device; 2. The satellite broadcasting community reception system according to claim 1, wherein the conversion device multiplexes the audio signal restored from the audio subcarrier into the VSB-AM signal and outputs the multiplexed signal. 3. The transmission path mixes and transmits the VSB-AM signal and audio subcarrier signal from the conversion device, and the receiving terminal device mixes and transmits the VSB-AM signal and audio subcarrier signal transmitted via the transmission path. 2. The satellite broadcasting joint reception system according to claim 1, wherein the satellite broadcasting joint reception system selects a channel after frequency-separating the signal. 4. The satellite broadcasting system according to claim 1 or 3, wherein the receiving terminal device converts the selected VSB-AM signal to the frequency of a predetermined television channel and outputs the same. receiving system. 5. The receiving terminal device uses electronically tuned tuner circuits for tuning the VSB-AM signal and the audio subcarrier signal, and generates tuning voltages in conjunction with each other to be supplied to each of these tuner circuits. Claims 1 and 3, which are
The satellite broadcasting joint reception system according to any one of Items 1 and 4. 6. A patent characterized in that the receiving terminal device uses a PLL frequency synthesizer to interlock and generate local oscillation signals for tuning VSB-AM signals and audio subcarrier signals from the same oscillation source. A satellite broadcasting community reception system according to any one of claims 1, 3, and 4. 7. The conversion device outputs the VSB-AM and audio subcarrier signals with channel identification signals added to them, and the receiving terminal device compares the channel identification signals added to both signals and determines whether each channel identification signal is 2. The satellite broadcasting joint reception system according to claim 1, wherein the satellite broadcasting joint reception system performs channel selection so that the channels match.