JPH07105940B2 - Transmission signal reproducing method and transmission signal reproducing apparatus - Google Patents

Description

The present invention relates to a multiplex transmission system, and more particularly to a PC for video signals.
The present invention relates to a reproducing method and a reproducing apparatus for receiving a transmission method effective for multiplexing and transmitting M audio signals.

[Conventional technology]

For the method of multiplexing digitally encoded PCM audio signals and video signals, report in "Satellite Broadcast Receiver", Part 1 of the Satellite Broadcasting Receiving Technology Study Group Report, published by the Institute of Radio Engineers of Japan, published in June 1983. However, since the current NTSC video signal is multiplexed with the PCM audio signal by using the 5.7272MHz subcarrier, it does not satisfy the band of the current terrestrial television broadcasting and can not be used for terrestrial television broadcasting. Have difficulty.

On the other hand, the possibility of multiplex transmission to the current terrestrial television broadcasting is discussed from page 205 of the Broadcasting Techniques 2 “Broadcasting Method” edited by the Japan Broadcasting Corporation in January 1983.
Although it is described on page 08, there is no description about a system capable of securing a transmission capacity of about 1 Mbit / sec for transmitting two channels of high quality voice.

[Problems to be solved by the invention]

In the above-mentioned conventional technology, there is no method for multiplex-transmitting a high quality PCM audio signal to the current terrestrial television broadcasting.

It is an object of the present invention to provide a reproducing method and a reproducing apparatus in the case where another signal is multiplex-broadcast with an amplitude-modulated signal, and in particular, a high quality digitally encoded PCM audio signal for current terrestrial television broadcasting. It is an object of the present invention to provide a transmission signal reproducing method and a reproducing apparatus therefor which are effective for receiving a transmission method for multiplex transmission of multiple signals such as

[Means for solving problems]

The above-mentioned object is achieved by modulating the other multiplexed signal by making the carrier wave amplitude-modulated have an orthogonal relationship.

In particular, in the case of a video signal where the residual sideband amplitude is modulated, an orthogonal relationship with the video signal of the carrier wave is generated by a multiplex signal such as a digitally coded PCM audio signal within the transmitted band of both sidebands of the carrier wave. This is achieved by carrying out modulation by transmitting the received signal, and synchronously detecting the received signal with the demodulation signal synchronized with the carrier wave from the received signal to reproduce the multiplexed signal.

[Action]

Remaining sideband Amplitude-modulated video signal Modulates the carrier by having the orthogonal relationship between the video signal and the multiplexed signal by limiting the carrier to the general amplitude-modulated band that has both sidebands. Therefore, the influence of the multiplexed signal on the reproduced video signal can be reduced. By lowering the modulation level of the multiplexed signal to 0.1 or less, which is lower than that of the video signal, it is possible to further reduce the influence of the multiplexed signal on the video signal reproduced by envelope detection. Further, since the multiplex signal is synchronously detected and reproduced, the effect is reduced because the orthogonally modulated video signal is not demodulated.

In the current terrestrial television broadcasting, the band having both sidebands of the residual sideband amplitude modulation is about 1.5 MHz, and the transmission capacity of multiplexed signals can be secured at about 1 Mbit / sec. It is possible to transmit and reproduce two signal channels.

〔Example〕

As an embodiment of the present invention, FIG. 1 shows an example of a receiver when a digitally encoded PCM audio signal is multiplexed and transmitted to a current terrestrial transmission television.

1 is an antenna, 2 is a high frequency amplification circuit, 3 is a frequency conversion circuit, 4 is an intermediate frequency amplification circuit, 5 is a video signal detection circuit,
6 is a video signal amplification circuit, 7 is a color difference signal demodulation circuit, 8 is a primary color signal demodulation circuit, 9 is a cathode ray tube, 10 is an audio intermediate frequency amplification circuit, 11 is an audio FM detection circuit, 12 is an audio signal output terminal,
13 is a band pass filter, 14 is a synchronous detection circuit, 15 is a carrier recovery circuit, 16 is a code identification circuit, 17 is a clock recovery circuit,
18 is a digital signal processing circuit, 19 is a digital / analog conversion circuit (hereinafter abbreviated as DAC), 20 is multiplex-transmitted PCM
It is an output terminal for an audio signal.

The television signal input from the antenna 1 is amplified by the high frequency amplifier circuit 2, frequency-converted to the intermediate frequency for demodulation by the frequency conversion circuit 3, and amplified by the intermediate frequency amplifier circuit 4. The tuning is performed by changing the local oscillation frequency of the frequency conversion circuit 3. The video signal band is detected by the video signal detection circuit 5 from the signal amplified by the intermediate frequency amplification circuit 4,
From the luminance signal output from the video signal amplifier circuit 6 and the color difference signal output from the color difference signal demodulation circuit 7, R, G,
Obtain the three primary colors of B and project them on the cathode ray tube 9.

On the other hand, regarding the audio signal band, the audio intermediate frequency amplifier circuit
The signal is amplified at 10 and detected and demodulated by the audio FM detection circuit 11 to obtain an audio signal at the audio signal output terminal 12. The above is the same as that of the conventional television receiver.

In addition to the above, in order to demodulate the digitally encoded PCM voice signal, the PCM voice signal band multiplexed and transmitted by the bandpass filter 13 is selected from the output of the frequency conversion circuit 3 and amplified, and in the synchronous detection circuit 14, Carrier regeneration circuit
Using the signal synchronized with the carrier reproduced in 15, the signal modulated with the component orthogonal to the amplitude modulation component of the carrier is detected and demodulated. The signal obtained as a result is converted into a digital code by the code identifying circuit 16 at a point where the error rate is small, and the error occurred during transmission is detected and corrected by the digital signal processing circuit 18 using the error detection / correction code. The clock recovery circuit 17 is a circuit for extracting the transmission clock from the signal output from the synchronous detection circuit 14, and digitally encodes the signal output from the synchronous detection circuit 14 at a point where the error rate is small (the so-called maximum opening of the eye pattern). Is necessary for. The digital signal after the error detection and correction is converted into an analog signal by the DAC 19 to be converted into a voice signal, which is obtained at the output terminal 20 of the multiplex-transmitted PCM voice signal.

FIG. 2 shows an embodiment of a transmitter that generates the signal transmitted in the above embodiment. 21 is an audio signal input terminal, 22 is an FM modulator, 23 is an audio signal carrier generator, 24-26 are video signal input terminals, 27 is a matrix circuit, 28 is a luminance signal processing circuit,
29 is a color difference signal processing circuit, 30 is an adding circuit, 31 is a video signal modulator, 32 is a video signal carrier generator, and 33 is multiplex-transmitted.
PCM audio signal input terminal, 34 analog-digital converter (hereinafter abbreviated as ADC), 35 digital signal processing circuit, 36 low-pass filter, 37 90-degree phase shifter, 38 PCM
A voice signal modulator, 39 is an adder, 40 is a VSB filter for vestigial sideband amplitude modulation, 41 is an adder, and 42 is an antenna.

An audio signal from the audio signal input terminal 21 is used to FM-modulate the audio carrier from the audio signal carrier generator 23 in the FM modulator 22. The RGB three primary color signals input to the video input terminals 24 to 26 are divided into a luminance signal and a color difference signal by a matrix 27, processed by a luminance signal processing circuit 28 and a color difference signal processing circuit 29, respectively, and then added by an adder 30. The added signal is used to modulate the carrier wave from the video signal carrier wave generator 32 using the video modulator 31, the VSB filter 40 band-limits it to the television broadcast band, and the adder 41 adds the audio signal to the antenna 42. Send more.

The above is the same as the conventional terrestrial television broadcasting. The following is added to the above signals in order to transmit high quality PCM audio signals.

The multiplexed PCM voice signal is applied to the input terminal 33, the voice signal is converted to a digital signal by the ADC 34, and the digital signal processing circuit 35 adds a code for detecting and correcting an error that occurs during transmission, or interleaves. Unnecessary high-pass components are removed through a low-pass filter 36 suitable for the transmission rate of digital code by performing processing. With this digitally encoded voice, the video signal carrier 90 degrees phase-shifted via the 90-degree phase shifter 37 is modulated by the modulator 38 for the PCM voice signal, and the carrier wave modulated by the video signal by the adder 39. And add. As a result, the video carrier wave is modulated in the orthogonal relationship between the video signal and the PCM audio signal.

The modulated spectrum is shown in FIGS. 3 and 4, and a vector diagram of the modulation state of the video signal of the video carrier and the PCM audio signal is shown in FIG. 43 in FIG. 3 shows the spectrum of the video signal after VSB filtering, 44 shows the spectrum of the FM-modulated audio signal, and 45 of FIG. 4 shows the spectrum of the digitized PCM audio signal. Here, the spectrum of the PCM audio signal has a roll-off rate of 0 at a transmission rate of 1 Mbit / sec.
The spectrum when the carrier wave of the signal of 5 is modulated is shown.

In Fig. 3, VSB is the vestigial sideband amplitude modulation for the spectrum below -0.75MHz with respect to the video carrier.
It is attenuated by the filter. Up to 4.2MHz, there is a spectrum where the audio carrier is FM modulated near the video signal 4.5MHz. Since both sidebands are transmitted at ± 0.75MHz with respect to the image carrier, it can be considered as general amplitude modulation (DSB). If a signal within ± 0.75 MHz orthogonal to the carrier wave having both sidebands is modulated with amplitudes A and -A corresponding to digital codes 1 and 0 as shown in FIG. 4, the carrier wave vector is obtained. When the video signal is 1, cos ωct ± A sin ωct (1) Where ωc is the angular frequency of the carrier.

Expanding equation (1), Is.

Consider the interference from the PCM audio signal to the received video signal. In the case where the video signal detection circuit performs coherent detection with cos ωct, only the coefficient of cos ωct (that is, only the video signal) is reproduced regardless of the value of A, and no interference occurs. In the case where the video signal detection circuit performs envelope detection, lowering the value of A from 1 can reduce interference. For example, if A is 0.1, Therefore, a signal of 0.005 (about -46 dB) is affected compared to 1, but I think that there is no practical problem if the SN ratio of the video signal is 40 dB or more. Furthermore, if A is lowered below 0.1, the influence on the video signal is further reduced.

On the other hand, the interference of the PCM audio signal from the video signal to the detection circuit can be eliminated by demodulating only the component orthogonal to the carrier wave in the synchronous detection circuit 14 as shown in FIG. Considering the signal level to noise ratio (hereinafter referred to as the SN ratio), assuming that the SN ratio of the video signal is 40 dB, the bandwidth is PCM.
Since the transmission bandwidth of voice signals is about 4 times that of 1MHz, PC
The SN ratio of the M audio signal is 46 dB, but when the modulation level A of the PCM audio signal is 0.1, the SN ratio is about 26 dB.

On the other hand, considering the relationship between the SN ratio of a digital signal and the bit error rate as a general binary signal, the SN ratio is 17.4 dB and the bit error rate is 1 × 10 ⁻⁴ . The SN ratio of the video signal is
In the case of 40 dB, the SN ratio of the PCM audio signal is 26 even if A is 0.1.
The value is dB, which is a practically sufficient value for digital signal transmission. Even if A is 0.1, there is a margin of about 10 dB in the SN ratio with respect to the bit error rate of 1 × 10 ^-4 . It turns out that it is enough.

Another embodiment of the present invention is shown in FIG. The received signal is the same as in the case of FIG. 1, and the same reference numerals as those in FIG. 1 indicate the same functions. 3 is a frequency conversion circuit, 46 is a mixing circuit, 47 is a voltage-controlled local oscillator, 48 is a synchronous detector, 49 is a reference signal generator, 50 is a low-pass filter, and 51 is a carrier wave composed of 48 to 50. A reproducing circuit, 52 is an adder, and 53 is a tuning circuit.

1 is different from that shown in FIG. 1 in that it is detected by the synchronous detection circuit 14 in synchronism with a PCM audio signal which is reproduced by the carrier reproduction circuit 15 and is orthogonally modulated with the carrier video signal. In FIG. 6, the modulation of the PCM audio signal is particularly effective when the DC component such as the differential PSK signal is small. Utilizing the orthogonal relationship between the PCM audio signal modulation and the carrier of the video signal, the phase difference between the reference signal generator 49 and the intermediate frequency signal including the carrier is detected by the synchronous detector 48, and the low frequency component is detected. By feeding back to the voltage-controlled local oscillator via the adder 52, the carrier of the intermediate frequency is synchronized with the output of the reference signal generator and the output of the synchronous detector 48 is used as the detection output. The tuning circuit 53 changes the DC voltage at the time of tuning to change the oscillation frequency of the local oscillator 47.

According to the embodiment shown in FIGS. 1 to 6, in the transmitter shown in FIG. 2, digitized PCM voice signal of 1 Mbit / sec in relation to spectrum and vector shown in FIGS. Can be transmitted without interfering with the video and audio signals of the conventional television, and those signals can be reproduced by using the receivers shown in FIGS.

FIG. 7 shows another embodiment of the present invention. In FIG.
Reference numeral 54 is a video synchronous detection circuit, 55 is a phase shifter, and the same reference numerals as those in FIG. 1 indicate the same functions. In the carrier wave reproducing circuit 15, a signal synchronized with the carrier wave is obtained, so that the video signal is synchronously detected using the signal. The output of the carrier wave regenerating circuit 15 is used for demodulating the signal modulated by the quadrature component of the carrier wave by the synchronous detector 14, so that a phase shift of about 90 degrees is required to synchronously detect the video signal. For that purpose, the image is detected by the video synchronous detection circuit 54 via the phase shifter 55. If the phase difference due to the delay time difference between the intermediate frequency amplifier circuit 4 and the band pass filter 13 is a problem, the phase shifter 55
The phase shift amount of can be changed from the set value of 90 degrees.

An embodiment in which the same idea is given in FIG. 6 is shown in FIG. 7 and 8, according to this embodiment, since the synchronous detection can be used for the detection of the video signal, the effect of the orthogonal component on the video reproduction signal can be further reduced.

FIG. 9 shows still another embodiment of the present invention. 56 is a phase shifter, 57 is a band pass filter, and 58 is a PLL circuit.
The same reference numerals as those in the figure indicate the same functions. A carrier wave is extracted from the output of the frequency conversion circuit 3 using a band pass filter 57, a signal synchronized with the carrier wave is obtained by a PLL circuit 58, and a phase shifter 55 is obtained.
And 56 are used to send to the synchronous detection circuit 14 and the video synchronous detection circuit 54. Others are the same as those in FIG. 7, but according to the present embodiment, since the bandpass filter 57 and the PLL circuit 58 are used only for reproducing the signal synchronized with the carrier wave,
Since the influence on other signals can be designed to be small, there is an effect that the influence between the reproduced signals of video and audio can be reduced more stably.

Note that quadrature modulation is performed with A and -A for digital values 1 and 0.
However, it is also possible to transmit in multiple values of three or more.

Also, although the basic sideband component of quadrature modulation is described within the band of transmission of both sidebands of vestigial sideband amplitude modulation, if it is allowed a little deterioration of the error rate in digital transmission, it is partly out of the band. Off-line transmission is also possible.

〔The invention's effect〕

According to the present invention, a carrier for amplitude modulation has a quadrature relationship with the above-mentioned modulation and has a modulation level of a multiplexed signal lower than 0.1, which is lower than that of a video signal, and is transmitted. For demodulation synchronized with the carrier from the received signal. The signal received by the signal is synchronously detected,
Since a multiplex signal can be reproduced, there is an effect that a digitally encoded PCM audio signal can be received in addition to the video signal and audio signal of the current terrestrial television broadcasting reception.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of a transmitting side for carrying out the present invention, FIG. 3 is a spectrum diagram for explaining the present invention, and FIG. FIG. 5 is a spectrum diagram for explaining the present invention, FIG. 5 is a vector diagram for explaining the present invention, FIG. 6 is a configuration diagram of another embodiment of the present invention, and FIG. 7 is still another embodiment of the present invention. FIG. 8 is a block diagram of another example of the present invention, and FIG. 9 is a block diagram of yet another example of the present invention. 13,57 …… Bandpass filter 14 …… Synchronous detection circuit, 15 …… Carrier recovery circuit 16 …… Data strobe circuit 17 …… Clock recovery circuit 18 …… Digital signal processing circuit 19 …… DAC, 46 …… Mixed circuit 47 …… Local oscillator, 48 …… Synchronous detector 49 …… Reference signal generator, 50 …… Low-pass filter 52 …… Adder, 53 …… Channel selection circuit 54 …… Video synchronous detection circuit, 55,56 ...... Phase shifter 58 …… PLL circuit

Claims (9)

[Claims] 1. A basic signal band in which a video carrier is amplitude-modulated by a vestigial sideband with a video signal, and a quadrature carrier whose phase is different from the video carrier by about 90 degrees has a double sideband in the vestigial sideband. Are present, and the video carrier modulated by the vestigial sideband amplitude modulation and the quadrature carrier modulated by the digitally coded audio signal are modulated by the vestigial sideband amplitude. A multiplexed television signal transmitted by combining the maximum value of the amplitude of the modulated video carrier with the maximum value of the amplitude of the orthogonal carrier modulated by the digitally encoded audio signal at a ratio of 0.1 or less. By receiving, and performing quadrature coherent detection on a signal in a band in which the basic signal band of the signal modulated and transmitted to the quadrature carrier is present to reproduce the digitally encoded voice signal. The multiplexed television signal amplitude-modulated and transmitted in the vestigial sideband is compatible with the current television broadcast, and the service area of the digitally encoded audio signal is about the same as the service area of the current television broadcast. A method of reproducing a transmission signal, characterized by being able to: 2. A video signal is vestigial sideband amplitude modulated by a video signal, and a quadrature carrier whose phase is different from said video carrier by about 90 degrees has a basic signal band within a band having double sidebands within said vestigial sideband. Are present, and the video carrier modulated by the vestigial sideband amplitude modulation and the quadrature carrier modulated by the digital coded signal are vestigial sideband amplitude modulated. The maximum value of the amplitude of the orthogonal carrier modulated by the digitally encoded signal is 0.1 with respect to the maximum value of the amplitude of the video carrier.
A transmission signal reproducing device for reproducing a digitally encoded signal by receiving a multiplexed television signal synthesized and transmitted at the following ratios, the intermediate signal for demodulation receiving the multiplexed television signal: A receiving frequency converting means for converting the frequency, a video signal demodulating means for demodulating a video signal from an output signal of the receiving frequency converting means, and a signal modulated and transmitted to the orthogonal carrier wave of the output signal of the receiving frequency converting means A band pass filter means for passing a band in which the basic signal band exists, and a carrier for reproducing a quadrature detection carrier for detecting a signal modulated and transmitted to the quadrature carrier from an output signal of the band pass filter means. The output signal of the reproduction means and the band pass filter means is synchronously detected by the output signal of the carrier wave reproduction means and modulated into the orthogonal carrier wave. And a synchronous detection means for demodulating a transmitted signal are provided, so that the multiplexed television signal which is vestigial sideband amplitude modulated and transmitted obtains compatibility with the current television broadcasting and the digital signal. A transmission signal reproducing apparatus characterized in that a service area of an encoded audio signal can be made approximately the same as a service area of current television broadcasting. 3. The digitally encoded signal according to claim 2, wherein the digitally encoded signal is converted from a binary digitally encoded signal into a ternary or higher multilevel digitally encoded signal. A transmission signal reproducing device characterized by being a signal. 4. The transmission signal reproducing device according to claim 2, wherein the audio signal is a digitally encoded audio signal as the digitally encoded signal. 5. A basic signal band in a band in which a video carrier is amplitude-modulated by a vestigial sideband with a video signal, and a quadrature carrier whose phase differs from that of the video carrier by about 90 degrees has a double-sideband in the vestigial sideband. Are present, and the video carrier modulated by the vestigial sideband amplitude modulation and the quadrature carrier modulated by the digitally coded audio signal are modulated by the vestigial sideband amplitude. A multiplexed television signal transmitted by combining the maximum value of the amplitude of the modulated video carrier with the maximum value of the amplitude of the orthogonal carrier modulated by the digitally encoded audio signal at a ratio of 0.1 or less. Which is a transmission signal reproducing device for reproducing the digitally encoded audio signal by receiving the reception frequency for receiving the multiplexed television signal and converting it to an intermediate frequency for demodulation. Conversion means, a video signal demodulation means for demodulating a video signal from the output signal of the reception frequency conversion means, and a basic signal band of a signal modulated and transmitted to the orthogonal carrier of the output signal of the reception frequency conversion means exists. Band pass filter means for passing a band, a carrier recovery means for reproducing a carrier wave for quadrature detection for detecting a signal modulated and transmitted to the quadrature carrier wave from the output signal of the band pass filter means, and the band Any of the synchronous detection means for synchronously detecting the output signal of the pass filter means with the output signal of the carrier wave recovery means and demodulating the signal modulated and transmitted to the orthogonal carrier wave; the reception frequency conversion means or the video signal demodulation means By providing a voice demodulation means for extracting and demodulating the frequency-modulated analog voice signal from one of the means, The amplitude-modulated and transmitted multiplexed television signal is compatible with the current television broadcast, and the service area of the digitally encoded audio signal can be made substantially the same as the service area of the current television broadcast. And a transmission signal reproducing device. 6. The digital coded audio signal according to claim 4 or 5, wherein the digitally coded audio signal is multi-valued digitally coded with three or more values from a binary digitally coded audio signal. A transmission signal reproducing device, which is a signal converted into an audio signal. 7. The local oscillating means used for frequency conversion of the receiving frequency converting means according to claim 2, claim 3, claim 4, claim 5 or claim 5, comprising voltage control oscillating means, and the carrier wave. The reproducing means is composed of the phase detecting means and the reference signal oscillating means, and the phase difference between the input signal of the receiving frequency converting means and the reference signal oscillating means is detected by the phase detecting means to cause the voltage control oscillating means. A transmission signal reproducing device characterized by feedback control. 8. The method according to claim 2, claim 3, claim 4, claim 5, or claim 5, wherein the local oscillating means is provided with any one of the plurality of residual sideband amplitude-modulated carriers. A transmission signal reproducing device characterized by being used as a channel selecting means for selecting a carrier wave whose side band is amplitude-modulated. 9. The output signal of the carrier wave reproduction means as a video detection signal for synchronous detection of the video signal demodulation means according to claim 2, claim 3, claim 4, claim 5, or claim 5. A transmission signal reproducing device characterized by being used.