JPS6376593A - Signal transmission system and its generating device - Google Patents

Abstract

PURPOSE:To contrive improvement of the stability of the orthogonality of signals in the transmission and the reception of an orthogonal multiplex signal by modulating a carrier wave with a multiplex signal other than a video signal securing the orthogonality against the video signal, and transmitting the result. CONSTITUTION:A video signal carrier wave which is phase-shifted by approximately ninety degrees by a phase shifter 11 is modulated by a digital modulation circuit 12 by using a digital-coded voice, and its output is supplied to an adder 13 where it is added with a video transmission signal. As a result, a carrier wave for video is modulated orthogonally with the video signal and the digital- coded sound, signal. By the phase detector 17 incorporated in a circuit 16 to monitor the orthogonality, the phase difference between the video signal output of an amplitude modulation circuit 6 and the output of a digital modulation circuit 12, then an arithmetic circuit 18 calculates the difference between the phase difference and a prescribed phase difference in order that the phase shifter 11 is controlled through a low-pass filter 19. As a result, the orthogonal multiplex can be executed more stably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multiplex transmission system, and more particularly to a transmission signal generating device effective for multiplexing digitally encoded audio and the like onto a video signal and transmitting the multiplexed signal.

[Conventional technology]

The method of multiplexing digitally encoded PCM audio and video signals is reported in the Satellite Broadcasting Receiving Technology Study Group Report, Part 1, "Satellite Broadcasting Receivers," edited by the Radio Technology Association, published in June 1981. However, PCM is applied to the current NTSC video signal using a 5.7272MHz subcarrier.
Since the audio is multiplexed, it does not meet the bandwidth of current terrestrial television broadcasting, making it difficult to use for terrestrial television broadcasting.

On the other hand, regarding the possibility of multiplex transmission for current terrestrial television broadcasting, the Japan Broadcasting Corporation Network's Broadcasting Technology Book 2, "Broadcasting Methods," was published by the Japan Broadcasting Publishing Association in January 1980.
, pages 205 to 208, but there is no description of a method that can secure a transmission capacity of approximately 1 megapint/second for transmitting two channels of high-quality audio.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, there was no method for multiplex transmission of high-quality audio signals in the current terrestrial television broadcasting. An object of the present invention is to provide a signal generation device for multiplexing transmission of other signals on an amplitude modulated signal, and in particular, to provide a signal generation device for multiplexing transmission of other signals to an amplitude modulated signal, and in particular, to provide a signal generation device for transmitting signals such as high quality digitally encoded audio signals for current television broadcasting. The object of the present invention is to provide a signal transmission method for multiplex transmission and a generation device effective for generating the signal.

[Means for solving problems]

The above object is achieved by modulating the orthogonal components of the amplitude modulated carrier wave with another signal. In particular, in the case of a video signal that undergoes vestigial sideband amplitude modulation, signals such as audio signals that are digitally encoded within the transmission band of both sidebands of the carrier wave have an orthogonal relationship with the video signal of the carrier wave. This is achieved by modulating and transmitting the signal.

Further monitoring of the orthogonality relationship is achieved by providing a monitoring period in which the orthogonally modulated signal has a certain determined signal.

[Effect]

Residual Sideband Amplitude-modulated video signal carrier wave has both sidebands and is a general amplitude-modulated band (DSB)
Since the carrier wave is modulated so that the video signal and the audio signal have an orthogonal relationship, the influence of the audio signal on the reproduced video signal can be reduced. By making the degree of modulation of the audio signal lower than that of the video signal, it is possible to reduce the influence of the audio signal on the video signal reproduced by envelope detection.

Furthermore, since the audio signal is reproduced by synchronous detection, the orthogonally modulated video signal is not demodulated, and the influence is reduced.

In current terrestrial television broadcasting, the band with both sidebands of vestigial sideband amplitude modulation is approximately 1.5 MFlz, which is approximately 1 h.
It is possible to transmit two channels of digitally encoded high quality audio at i bits/second (for example, 12 bits x 2 channels x 32 sampling x 1.3 redundancy - IMbps).

Furthermore, since the monitoring period can be used to confirm and maintain orthogonality on the modulation side and to ensure orthogonality of the demodulation circuit on the reception side, the stability of transmission and reception can be improved.

Furthermore, since both the frequency and the modulation method are different from the current FM audio signal, they do not affect each other and are compatible.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a transmitter for multiplex transmission of digitally encoded audio signals to the current terrestrial transmission television. 1 is a video signal processing circuit, 2 to 4 are video signal input terminals,
5 is a carrier wave generator, 6 is an amplitude modulation circuit, 7 is an audio signal input terminal for digitally encoding and transmitting, and 8 is an analog signal input terminal.
Digital conversion circuit (hereinafter abbreviated as ADC), 9 is a digital signal processing circuit, 10 is a low-pass filter, 11 is a phase shifter, 12 is a digital modulation circuit, 13 is an adder, 14
is a VSB filter for residual sideband amplitude modulation, 15 is an antenna, dish is an orthogonality monitoring circuit, 17 is a phase detection circuit, 1
8 is an arithmetic circuit, and 19 is a low-pass filter.

B and G input from video input terminals 2 and 3.4.

The B video signal is subjected to luminance signal processing 1 in video signal processing circuit 1.
Processing such as color difference signal processing is performed, a synchronization signal is added, and the signal is input as a video transmission signal to an amplitude modulation circuit 61C. The amplitude modulation circuit 6 amplitude-modulates the output of the carrier wave generator 5 with the video transmission signal, limits the band to the television broadcast band by the VSB filter 14, and transmits it from the antenna 15. The above is the same as conventional terrestrial television broadcasting.

Next, the high quality audio added to the adder 13 will be described below.

The analog audio signal to be multiplexed and transmitted is converted into a digital signal by the ADC 8 in addition to the audio signal input terminal 7 which digitally encodes and transmits the signal. Next, in addition to the digital signal processing circuit 9, processing such as idle addition and interleaving for detecting and correcting errors occurring during transmission is performed. Next, unnecessary high-frequency components are removed through a low-pass filter 10 suitable for the transmission rate of the digital code. This digitally encoded audio is modulated by a digital modulation circuit 12 using a video signal carrier wave whose phase is shifted by approximately 90 degrees via a phase shifter 11 . The output is added to an adder 13 and added to the video transmission signal. As a result, the video carrier wave is modulated in an orthogonal relationship with the video signal and the digitally encoded audio signal. The phase detector 17 built in the orthogonality monitoring circuit detects the phase difference between the output of the amplitude modulation circuit 6 and the output of the digital modulation circuit 12 of the video signal, and the arithmetic circuit 18 detects the phase difference from the predetermined phase difference. Stable orthogonal multiplexing can be achieved by calculating the shift of the signal and controlling the phase shifter 11 via the low-pass filter 19.

According to this embodiment, there is an effect that the audio signal digitally encoded on the carrier wave of the video signal can be multiplexed and transmitted stably orthogonally to the video signal.

FIG. 2 shows another embodiment of the present invention in which conventional FM audio is multiplexed in addition to the digitally encoded audio signals described above, taking into consideration compatibility with the conventional system.

The same symbols as in FIG. 1 have the same functions. 20 is an adder, 2
1 is an audio input terminal for FM modulation, 22 is a carrier wave generator for audio, 23 is an FM modulation circuit, 24 is a matrix circuit in the video signal processing circuit, and 25 is a luminance signal section.

26 is a color difference signal processing circuit, and 27 is an NTSC signal format generation circuit.

In FIG. 2, the PCM audio signal processing and video signal processing are the same as in FIG. 1. In the video signal processing circuit 1, the input three primary color signals of R, G, and H are divided into a luminance signal and a color difference signal by a matrix 24, and after each is processed by a luminance signal processing circuit 25 and a color difference signal processing circuit 26, NTSC generation is performed. A circuit 27 converts it into a video transmission signal. Now, the audio signal of the audio input terminal 21 newly added in this circuit is transmitted to the FM modulation circuit 23, which converts the carrier wave from the audio carrier generation circuit 22 into FM.
M modulation is performed and the output signal is applied to the adder 20. The adder 20 outputs a VSB signal including an amplitude modulated video signal and a digitally modulated digitally encoded audio signal.
The output signal of the filter 14 and the FM modulated audio signal are added, and the output is transmitted from the antenna 15.

FIG. 3 shows the modulated spectrum, and FIG. 4 shows a vector diagram of the modulation state of the video signal of the video carrier wave and the digitally encoded audio signal. In FIG. 3, reference numeral 51 indicates the spectrum of the video signal after the VSB filter, 52 indicates the spectrum of the FM-modulated audio signal, and 53 indicates the spectrum of the digitally encoded audio signal. Here, since the video signal spectrum 51 and the digitally encoded audio signal spectrum 52 are orthogonally multiplexed, they are shown divided into two stages in FIG.

Further, the digitally encoded audio signal has a transmission rate of IM bits/second, and the spectrum is shown when the carrier wave is modulated with a transmission roll-off rate of 0.5.

In Figure 3, for the video carrier wave '1: -0,75
The spectrum below h river Z is attenuated by a VSB filter that performs residual sideband amplitude modulation.

Up to 4.2 MHz, a video signal exists in a spectrum near 4.5 MHz in which an audio carrier wave is FM modulated.

Since both sidebands are transmitted for ±0.75 MFJz with respect to the video carrier wave, it can be considered as general amplitude modulation (DSB). When a signal within ±0.75 MELZ orthogonal to the carrier wave having both sidebands is modulated with amplitudes @A and -A corresponding to digital codes 1 and 0, the carrier wave vector becomes the video signal. When is set to 1, a) s<tf
Aainωct (11, where ωC is the angular frequency of the carrier wave.

It is.

Let us now consider interference from a digitally encoded audio signal to a received video signal. The video signal detection circuit is ■ωc
For those that are synchronously detected at t, only the coefficient of ■ωct (that is, only the video signal) is reproduced and does not cause interference, regardless of the value of A.

Further, in the case where the video signal detection circuit performs envelope detection, interference can be reduced by lowering the value of A below 1.

For example, if A is 0.1, N = 1.005 in J, and compared to 1, a signal of 0.005 (approximately -46 dB) will have an effect, but if the S/N ratio of the video signal is 40 dB or more, it is practical. I think there is no problem.

On the other hand, interference with the digitally encoded audio from the video signal can be eliminated by demodulating only the components orthogonal to the carrier wave in the synchronous detection circuit 15, as shown in FIG. Considering the signal level to noise ratio (hereinafter referred to as SN ratio),
Assuming that the SN ratio of the video signal is 40 dB at a practical level, the bandwidth is the transmission bandwidth IM of the digitally encoded audio signal.
Hz, the S/N ratio of the digitally encoded audio signal is 46 dB, but if the modulation level A is set to 0.
If it is set to 1, the transmission SN ratio will be about 26 dB.

On the other hand, even if we consider the relationship between the S/N ratio and bit error rate of the f digital signal using a general binary signal, the S/N ratio is 17.4.
It is 10 in dB. When the SN ratio of a video signal is 40 dB, the transmission SN ratio of a digitally encoded audio signal is 26 dB, which is a practically sufficient value for digital signal transmission.

Let us now consider the monitoring circuit. The transmission signal is modulated by the video signal as shown in equation (1) (2) ωct component and ωc modulated by the digitally encoded audio signal
There is a t component, but if it is modulated into amplitudes A and -A by digital codes 1 and 0, the phase difference of the plane ωct will be 190°
and +90° are related to the digital code, so the phase difference can be determined after knowing whether the digital code is 1 or 0. An explanatory vector diagram is shown in FIG. 61 is a reference phase, 62 is a quadrature phase, 63 is a vector of amplitude A, 64 is a vector of amplitude -A, 65 and 66 are reference phases 61 of vectors 63 and 64.
It is a component of As shown in the figure, the phase difference ψ from the quadrature phase
When the output of the digital modulation circuit 12 is shifted and modulated with amplitudes of A and -A, components 65 and 66 of the reference phase 61 can be detected by synchronous detection or the like. The absolute value of this component is related to the phase difference ψ, and the polarity matches the polarity of A and -A corresponding to digital codes 1 and O, so the phase difference ψ is determined by the absolute value of the component of the digital code and reference phase 61. Can be detected.

Still another embodiment of the invention is shown in FIG. Components with the same symbols as in FIG. 2 indicate the same functions. The difference from Figure 2 is that
The input of the monitoring circuit is the output of the adder 13 and the carrier wave generator 5.
The phase relationship of the orthogonally multiplexed signals output from the adder 13 is monitored based on the phase of the carrier wave. A vector diagram of multiplexed signals is shown in FIG. 7 to explain the operation. 67 is a video signal vector, 68
is a composite vector of vector 67 and vector 63, 69 is a composite vector of vector 67 and vector 64, 70 is a component of vector 680 reference phase 61, 71 is vector 69
This is a component of the 0 reference phase 61. Video signal vector 71
Vectors 68 and 69 represent composite vectors of vectors 63 and 64 of phase difference ψ deviation amplitudes A and -A from the orthogonal phase. This vector is the output signal of adder 13. In order to monitor the orthogonality of this signal, a phase difference is detected using the output of the carrier wave generator 5 as a reference. For example, when a component of the reference phase 61 is extracted by phase detection such as synchronous detection, vector 68 becomes vector 70. The vector 69 becomes a vector 71, and the difference between the vectors 7° and 71 is proportional to the phase difference ψ, and by knowing this difference, the phase difference ψ can be found. In this case, the difference between the vectors 70 and 71 differs depending on the amplitude of the video signal vector 67 and the amplitudes A and -A of the orthogonal components even when the phase difference ψ is the same. It is also possible to improve the accuracy of detecting the phase difference ψ by fixing the digital code constant and fixing the amplitude of the orthogonal component to A or -A. An example thereof is shown in FIG. 72 is an example of a baseband video signal waveform using color par as an example;
73 is a digital code transmission lock, and 74 is an example of digital code transmission data.

Video signal waveform example 72 is a horizontal synchronization signal, a sword rover burst,
They are white, yellow, cyan, green, magenta, red, and blue, and square frames such as color bursts indicate color subcarriers. During the horizontal synchronization signal period of this video signal, the video carrier wave is 100% amplitude modulated. The transmission rate of the digital code to be multiplexed is 1λ
The digital code changes to 1 in synchronization with one clock 73 of 1M port 2 when ff1ps is set. At this time, processing is performed by the digital signal processing circuit 9 to generate a digital code transmission data example 74 in which 3 data within the horizontal synchronization signal period are fixed as O and 3 data within the next horizontal synchronization signal period are fixed as 1. do. As a result, the 3 data within the horizontal synchronization signal period repeat the signs 1 and O, that is, the amplitude of the orthogonal component, A and -A every horizontal period, so if there is a phase difference ψ, the vectors 70 and 71 in FIG. 6 is repeated, it is also possible to change the control by the digital signal processing circuit 9 to the control by the horizontal synchronizing signal on the video signal processing circuit. Furthermore, as described above, detecting the phase difference within the horizontal synchronization signal period has nothing to do with the video signal.
This has the effect of stably monitoring orthogonality.

Next, FIG. 9 shows an example of a receiver that demodulates a transmission signal according to the present invention. 101 is an antenna, 102 is a high frequency amplification circuit, 103 is a frequency conversion circuit, 104 is a reproduction filter for a receiver of a VSB transmitted signal, 105 is an intermediate frequency amplification circuit, 106 is a video signal detection circuit, and 107 is a video signal amplification circuit. 108 is a color difference signal demodulation circuit, 109 is a primary color signal demodulation circuit, 110 is a cathode ray tube, 111 is an audio intermediate frequency amplification circuit, 112 is an audio FM detection circuit, 113 is an audio signal output terminal, 114 & is a band pass filter, 115 is a 117 is a phase detection circuit; 118 is a video signal stable period detection circuit; 11 is a synchronous detection circuit;
9 is a changeover switch, 120 is a low-pass filter, 121
is a voltage controlled oscillator, 122 is a code identification circuit, 123 is a clock regeneration circuit, 124 is a digital signal processing circuit,
125 is a digital-to-analog conversion circuit (hereinafter abbreviated as DAC), 126 is an output terminal for the digitally encoded and transmitted audio signal, 127 is a synchronous detection circuit, and 128 is a π/
2 phase shifter.

129 is an average value circuit.

A television signal input from an antenna 101 is amplified by a high frequency amplification circuit 102, frequency converted to an intermediate frequency for demodulation by a frequency conversion circuit 103, and amplified by an intermediate frequency amplification circuit 105 via a reproduction filter 104 for a receiver. . Tuning is performed by changing the local oscillation frequency of the frequency conversion circuit 1030. Regarding the video signal band from the signal amplified by the intermediate frequency amplification circuit 105, the video signal detection circuit 10
6, and from the luminance signal output from the video signal amplification circuit 107 and the color difference signal output from the color difference signal demodulation circuit 108, the primary color signal demodulation circuit 109 obtains three colors of R, G, and B, and displays them on the cathode ray tube 110. .

On the other hand, the audio signal band is amplified by an audio intermediate frequency amplification circuit 111 and detected and demodulated by an audio FM detection circuit 112 to obtain an audio signal at an audio signal output terminal 113. The above is the same as a conventional television receiver.

In addition to the above, in order to demodulate the digitally encoded audio signal, the digitally encoded audio signal band multiplexed and transmitted from the output of the frequency conversion circuit 103 is selected and amplified by the bandpass filter 114, and the synchronous detection circuit 115 In this step, a signal synchronized with the carrier wave regenerated by the carrier wave regeneration circuit is used to detect and demodulate a signal modulated with a component orthogonal to the amplitude modulation component of the carrier wave. A code identification circuit 122 converts the resulting signal into a digital code at a point with a low error rate, and a digital signal processing circuit 124 detects and corrects errors occurring during transmission using an error detection and correction code. The clock regeneration circuit 123 is a synchronous detection circuit 115
This circuit extracts the transmission lock from the output signal of the synchronous detection circuit 115, and is necessary for digitally encoding the output signal of the synchronous detection circuit 115 at a point where the error rate is low (the so-called maximum aperture of the eye pattern).

The digital signal after error detection and correction is sent to the DAC 125.
The output terminal 126 converts the signal into an analog signal, converts it back into an audio signal, digitally encodes it, and outputs the transmitted audio signal at the output terminal 126. On the carrier wave regeneration circuit, the phase difference between the carrier wave that is the output of the band pass filter 114 and the output of the voltage controlled oscillator 121 is detected by the phase detection circuit 117, and the phase difference between the carrier wave that is the output of the band pass filter 114 and the output of the voltage controlled oscillator 121 is detected by the phase detection circuit 117. Negative feedback is provided to the voltage controlled oscillator 121. The output of the voltage controlled oscillator 121 becomes a reproduced carrier wave, which becomes a carrier wave for detection by the synchronous detection circuit 115. Here, the period during which the modulation of the carrier wave by the video signal is stable, such as the horizontal synchronization signal period of the video signal, is calculated by π/2 from the output of the voltage controlled oscillator 121.
A stable period detection circuit 118 detects a video signal detected by a synchronous detection circuit 127 using a signal phase-shifted by π/2 using a phase shifter 128, and controls a changeover switch 119.

Furthermore, when receiving a transmission signal that inverts the orthogonal multiplexed signal every 1,000 periods of the horizontal synchronization signal period as shown in FIG. It is possible to reduce the influence of orthogonally multiplexed signals and synchronize with the video signal carrier wave in the horizontal synchronization signal period.

Another embodiment of the invention is shown in FIG. 150 is an equalizer circuit, and the same symbols as in FIG. 6 indicate the same functions. The intermediate frequency regeneration filter of the receiver may cause asymmetry in both sidebands of amplitude modulation, resulting in deterioration of the orthogonality of the orthogonally multiplexed signal. In order to reduce the deterioration of the orthogonality, an equalizer circuit 150 having characteristics opposite to those of the reproduction filter of the receiver is provided, so that the orthogonality can be better maintained during video signal detection in the receiver.

〔Effect of the invention〕

According to the present invention, the phase difference between orthogonally multiplexed signals or the phase difference of multiplexed signals after orthogonally multiplexing can be detected by the monitoring period or the monitoring circuit, so the stability of orthogonality in transmitting or receiving orthogonally multiplexed signals can be detected. There is an effect that can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of one embodiment of the present invention, Fig. 2 is a block diagram of another embodiment of the present invention, Fig. 3 is a Nuvector diagram for explaining the present invention, and Fig. 4 is a block diagram of another embodiment of the present invention. FIG. 5 is a vector diagram for explaining the present invention. FIG. 6 is a configuration diagram of still another embodiment of the present invention. FIG. 7 is a vector diagram for explaining the present invention. , FIG. 8 is a diagram of an example of a transmission signal of the present invention, FIG. 9 is a configuration diagram of an embodiment of a receiver for implementing the invention, and FIG. 10 is a configuration diagram of another embodiment of the invention.
It is a diagram. 8...ADC. 9... Digital signal processing circuit, 11... Phase shifter, 12... Digital modulation circuit, 13... Adder, 16... Monitoring circuit, 17
...Phase detection circuit, 150...Equalizer. Parable 'IR's 3rd Figure 4- Figure Atsushi S Figure 1 / 7th Concave R aJ
=D-to1111

Claims (1)

[Claims] 1. In a television transmission system in which a carrier wave is modulated in vestigial sideband amplitude with a video signal and transmitted, the carrier wave is a multiplexed signal other than the video signal and has an orthogonal relationship with the video signal. A signal transmission method characterized by modulated transmission. 2. A signal transmission system according to claim 1, characterized in that the multiplexed signal is a digitally encoded signal and a code with a small DC component is used. 3. Signal transmission according to claim 1, characterized in that a modulation monitoring period is provided in which the multiplexed signal is modulated at a constant level within a constant period during which the modulation level is constant, such as a horizontal synchronization signal period of a video signal. method. 4. In claim 3, the multiplex signal level in the modulation monitoring period is set to the same level with opposite phases for each modulation monitoring period, thereby suppressing the average DC component in the modulation monitoring period. A signal transmission method characterized by a signal. 5. An apparatus for generating a transmission signal according to the transmission method according to claim 1, which comprises a carrier wave generation circuit that generates the transmitted carrier wave, a phase shifter that generates orthogonal components of the carrier wave, and the carrier wave generation circuit. a first modulation circuit that amplitude-modulates the output of the circuit with the video signal; a second modulation circuit that modulates the output of the phase shifter with the multiplexed signal; and combining the output signals of the first and second modulation circuits. 1. A signal transmission generation device comprising: a mixing circuit for detecting the outputs of the first and second modulation circuits; and a monitoring circuit for detecting the phase of the outputs of the first and second modulation circuits and monitoring the phase difference between them.