JPH0761147B2 - Transmission signal reproduction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex transmission system, and more particularly to receiving a signal of a transmission system that multiplexes and transmits a digitally encoded audio signal and the like to a video signal. The present invention relates to an effective transmission signal reproducing device.

[Conventional technology]

For the method of multiplexing digitally encoded audio signals and video signals, report in "Satellite Broadcast Receiver", Part 1 of the Satellite Broadcasting Receiving Technology Study Group Report, issued by the Institute of Radio Engineers of Japan, published in June 1983. However, since the current NTSC video signal is multiplexed with the audio signal digitally encoded using the 5.7272MHz subcarrier, the current terrestrial television broadcasting band is not satisfied and the terrestrial television broadcasting is not satisfied. Is difficult to use.

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 audio.

[Problems to be Solved by the Invention]

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

It is an object of the present invention to provide a reproducing device for stably receiving and reproducing those signals when other signals are multiplexed and transmitted on the amplitude-modulated signal, and particularly high quality is applied to current terrestrial television broadcasting. Another object of the present invention is to provide a transmission signal reproducing apparatus which is effective in stably receiving and reproducing a transmission method in which a digitally encoded audio signal or the like is multiplexed and transmitted as a multiplex signal.

[Means for Solving the Problems]

The above object is to provide a comb-shaped filter for efficiently attenuating the amplitude-modulated signal in a receiver that demodulates another signal that is modulated and modulated by having a phase relationship orthogonal to the amplitude-modulated carrier wave. To be achieved.

[Action]

The comb filter has less attenuation of the spectrum of the multiplex-transmitted multiplex signal and more attenuation of the spectrum of the video signal, so that interference from the video signal to the multiplex signal can be reduced and the multiplex signal of the multiplex transmission can be stabilized. Can receive and play.

〔Example〕

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

In the figure, 1 is an antenna, 2 is a high frequency amplifier 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, and 10 is an audio intermediate frequency amplification circuit. Circuit, 11 voice FM detection circuit, 12 voice signal output terminal, 13 comb filter, 14 synchronous detection circuit,
Reference numeral 15 is a carrier wave reproduction circuit, 16 is a code identification circuit, 17 is a clock reproduction circuit, 18 is a digital signal processing circuit, 19 is a digital-analog conversion circuit (hereinafter abbreviated as DAC), and 20 is digitally encoded and multiplex-transmitted. 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 a digitally encoded voice signal, a comb filter is used from the output of the frequency conversion circuit 3.
A digitally encoded voice signal band multiplexed and transmitted by 13 is selected and amplified, and in the synchronous detection circuit 14, a signal synchronized with the carrier reproduced by the carrier reproduction circuit 15 is used to generate an amplitude modulation component of the carrier. A signal (voice signal) modulated with orthogonal components is detected and demodulated. The resulting signal (speech signal) is converted into a digital code by the code identification circuit 16 at a point where the error rate is small, and the error generated during transmission in the digital signal processing circuit 18 is detected and corrected using the error detection and correction code. To do.

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 by the digital signal processing circuit 18 is converted into an analog signal by the DAC 19 to be returned as an audio signal, and the digitally encoded and multiplexed audio signal is obtained at the output terminal 20.

An example of a transmitter that generates the signal transmitted in the above embodiment is shown in FIG. In the figure, 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 Modulator, 32 is a video signal carrier generator, 33 is an input terminal for audio signals that are digitally encoded and multiplexed, and 34
Is an analog-to-digital converter (hereinafter abbreviated as ADC), 35
Is a digital signal processing circuit, 36 is a spectrum processing circuit,
37 is a phase shifter, 38 is a modulator for digitally encoded voice signal, 39 is an adder, 40 is VSB for vestigial sideband amplitude modulation
A filter, 41 is an adder, and 42 is an antenna.

The audio signal from the audio signal input terminal 21 is used as an audio carrier from the audio signal carrier generator 23 in the FM modulator 22.
Modulate. The RGB primary color signals input to the video signal input terminals 24-26 are separated into a luminance signal and a color difference signal by the matrix circuit 27, processed by the luminance signal processing circuit 28 and the color difference signal processing circuit 29, respectively, and then added by the adder 30. To do. With the signal after addition, the carrier wave from the video signal carrier wave generator 32 is transferred to the video modulator 31.
Is modulated using the VSB filter 40, the VSB filter 40 band-limits it to the television broadcast band, the adder 41 adds it to the audio signal, and the signal is transmitted from the antenna 42.

The above is the same as the conventional terrestrial television broadcasting. The following is added in order to multiplex and transmit high-quality voice signals to the above signals.

A voice signal to be multiplex-transmitted is added to the input terminal 33, the voice signal is converted into a digital signal by the ADC 34, and a code for detecting and correcting an error occurring during transmission is added by the digital signal processing circuit 35, or interleave processing is performed. Etc.,
It is passed through a spectrum processing circuit 36 suitable for reducing interference with the video signal at the receiver. With this digitally encoded audio signal, a video signal carrier whose phase is shifted by 90 degrees via a phase shifter 37 is used as a modulator for the digitally encoded audio signal.
The signal is modulated by 38, and the adder 39 adds the carrier wave modulated by the video signal. As a result, the carrier wave for the video signal is modulated by the video signal and the digitally encoded audio signal which are in a mutually orthogonal phase relationship.

The frequency spectrum of the modulated signal is shown in FIG. 3, and the vector diagram of the modulation state of the video signal of the video signal carrier and the digitally encoded audio signal is shown in FIG. 43 in FIG. 3 is a frequency spectrum of the video signal after the VSB filter, 44 is a frequency spectrum of the FM-modulated audio signal, and 45.
Indicates the frequency spectrum of a voice signal which is digitally encoded and multiplexed. Here, the spectrum of the digitally encoded voice signal shows the spectrum in the case where the carrier wave of the signal having the roll-off rate of 0.5 at the transmission rate of 1 Mbit / sec is modulated.

In FIG. 3, the carrier frequency of the video signal is shown as 0 Hz. The spectrum below -0.75MHz with respect to the video signal carrier is attenuated by the VSB filter that uses vestigial sideband amplitude modulation. The spectrum of the video signal exists up to 4.2MHz, and the audio signal carrier is FM near 4.5MHz.
A modulated spectrum is present. Since both sidebands are transmitted at ± 0.75 MHz with respect to the video signal carrier, it can be considered as general amplitude modulation (DSB). ± 0.75MHz orthogonal to the video signal carrier that has both sidebands
When the signals within are corresponding to digital codes 1 and 0 and carrier-amplitude-modulated with amplitudes A and −A, the vector of the video signal carrier is cos ωct ± A sin ωct (1 when the video signal is 1). ). Where ωc is the angular frequency of the carrier.

Expanding equation (1) above Is.

Consider now the disturbance from a digitally encoded audio signal to the received video signal. Video signal detection circuit is cos
In the case of synchronous detection with ωct, regardless of the value of A, only the coefficient of cos ωct (that is, only the video signal) is reproduced and does not interfere. In the case where the video signal detection circuit performs envelope detection, lowering the value of A from 1 can reduce the interference. For example, if A is 0.1, Therefore, a signal of 0.005 (about -40 dB) is affected compared to 1, but it is considered that there is no practical problem if the signal level to noise ratio of the video signal (hereinafter referred to as SN ratio) 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, regarding the interference of the digitally encoded audio signal from the video signal to the demodulation circuit, FIG. 5 in which the vicinity of the video signal carrier frequency of FIG. 3 is enlarged and FIG. 6 showing the reception comb filter characteristic are used. explain. 5A shows a curve showing a spectrum of a digitally encoded audio signal to be multiplexed and transmitted, 47 shown in FIG. 5B shows a curve of a video signal, and 48 in FIG. 6 shows a receiver. It is a characteristic curve of a comb filter.

Since the spectrum of the video signal has a strong correlation with the horizontal synchronizing frequency f _H , the spectrum is concentrated at the frequency of f _H , so that the curve 47 is obtained. Also, the digitally encoded voice signal also becomes as shown by the curve 46 by the operation of providing the horizontal synchronization frequency f _H with the inverse correlation. In this relationship, the orthogonally multiplexed signal is taken out by the comb filter of the receiver shown in the characteristic curve 48 to reduce the interference from the video signal, and further, as shown in FIG. It can be eliminated by demodulating only the component.

Regarding the comb filter characteristics, it is better to let the video signal carrier wave pass for reproducing the carrier wave. Considering the SN ratio, assuming that the SN ratio of the video signal is at a practical level of 40 dB, the transmission bandwidth of the digitally encoded audio signal is 1 MHz.
Since it is about 4 times as high as that of the above, the SN ratio of the digitally encoded voice signal is 46 dB, but when the modulation level A of the digitally encoded voice signal is 0.1, the SN ratio is about 26 dB.

As described above, according to this embodiment, since the video signal spectrum can be efficiently reduced, there is an effect that the audio signal digitally encoded into the video signal and multiplexed and transmitted can be stably received and reproduced.

As an example of the spectrum processing circuit 36, a means for concentrating the spectrum of a digitally encoded voice signal at a certain frequency interval will be described with reference to FIGS. 7, 8 and 9. 61 is an input terminal, 62 is a time axis compression circuit, 63 is a timing generation circuit, 64 is a delay circuit, 65 is a changeover switch, 66 is an output terminal, 67 is a data string of the input terminal 61, and 68 is a time axis compression circuit 62. An output data sequence, 69 is an output data sequence of the delay circuit 64, 70 is an output data sequence of the changeover switch 65, 71 is an output data sequence of the changeover switch 65 when the output of the delay circuit 64 is inverted, and 72 is a data sequence 70. Spectrum, 73 is data string
71 spectra.

The data sequence 67 applied to the input terminal 61 is time-axis compressed by the time axis compression circuit 62 at the timing of the timing generation circuit 63 to form an intermittent data sequence shown in the data sequence 68. When this intermittent data sequence is delayed by the delay circuit 64 for the delay time τ, that is, in the example of FIG. 8, the data sequence 69 obtained by delaying by 5 data and the intermittent data sequence 68 are added by the changeover switch 65, It becomes as shown in the data column 70. This data string
In the data 70, the data delayed in the period without the data string of the data string 68 is inserted, and the data has a correlation with the delay time τ. As a result, the spectrum shown by the curve 72 in FIG. 9 is obtained.

On the other hand, when the output of the delay circuit 64 is inverted, the result is as shown in the data string 71, and there is an inverse correlation at the delay time τ. As a result, as shown by the curve 73 in FIG. 9, 0,1 /
The spectrum has a dip at τ, 2 / τ, 3 / τ, .... When this spectrum is modulated using a carrier wave, a curve 46 shown in FIG. 5 (a) is obtained. As described above, if the same data is transmitted between the intermittent data, the data transmission rate is increased. Therefore, in order to reduce the increase in the transmission rate and to have a spectrum dip, 5 data of a _{0 to} a ₄ It is also conceivable to insert two or three pieces of data between them for transmission. In this case, the increase in the data transmission rate can be reduced, but the dip amount cannot be expected as shown by the curves 72 and 73, but the dip frequency of the spectrum is the same as the curves 72 and 73 because it is determined by the delay time τ.

Next, an example of a demodulation circuit for demodulating the data strings 70 and 71 will be described with reference to FIGS. 10 and 11. 74 is an input terminal,
75 is a timing demodulation circuit, 76 is a changeover switch, 77 is a time axis expansion circuit, 78 is an output terminal, 79 is a changeover switch, 80 is a delay circuit, 81 is a coincidence detection circuit, and 82 is a coincidence detection output.

The data of the data train 68 or 69 is obtained by switching the changeover switch 76 at the timing when the data trains 70 and 71 of FIG.
Thus, the data string 67 can be demodulated. In FIG. 11, since the data strings 68 and 69 are obtained by the changeover switch 79, the delay circuit 80 and the coincidence detection circuit 81 detect coincidence and the coincidence detection output 82.
To get The data strings 68 and 69 are matched if no error occurs during signal transmission, but if an error occurs during transmission, the data is detected by the match detection circuit 81 as a mismatch, and an output is obtained at the match detection output 82. . Match detection circuit is generally EOR
It can be configured with a gate and the like, and the output can be used for digital signal processing such as error detection.

In the case where the relationship between the delay time τ and the data transmission rate associated with the dip frequency of the spectrum is not synchronized, a ₄ and a ₀ or between data strings 71 of a ₄ and a ₀ of the data string 70 This can be absorbed by providing a space between the data and the like where data is not transmitted.

Another embodiment of the present invention is shown in FIG. 90 is a filter, 91
Is a frequency conversion circuit, and the same reference numerals as those in FIG. 1 indicate the same functions. The difference from FIG. 1 is that a filter 90 and a frequency conversion circuit 91 are provided in order to lower the frequency for demodulating a digitally encoded and multiplex-transmitted audio signal below the frequency for video signal demodulation.

According to this embodiment, the video signal is demodulated at the intermediate frequency of the output of the frequency conversion circuit 3 (58.75 MHz is generally used in Japanese terrestrial broadcasting television), and the output of the frequency conversion circuit 91 is further demodulated. Since the audio signal digitally encoded and multiplexed and transmitted at a low intermediate frequency (for example, about 5 MHz) is demodulated, the circuit delay time of the carrier wave reproduced by the carrier wave reproduction circuit 15 used in the synchronous detection circuit 14 A phase error due to the above is reduced by lowering the frequency, and there is an effect that a voice signal stably digitally encoded and multiplexed and transmitted can be demodulated.

Yet 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 FIGS. 1 and 12 indicate the same functions. 91 is a frequency conversion circuit, 93
Is a mixing circuit, 94 is a voltage-controlled local oscillator, 95 is a reference signal generator, 96 is a low-pass filter, and the frequency conversion circuit 91 of FIG. 12 is composed of a mixing circuit 93 and a voltage-controlled local oscillator 94. .

The difference from FIG. 12 is that in FIG.
Then, reproduce the orthogonal carrier that is orthogonal to the video signal carrier,
Compared to the case where the synchronous detection circuit 14 detects the digitally encoded audio signal multiplexed and transmitted on the orthogonal carrier orthogonal to the video signal carrier, in FIG. 13, the modulation and the image by the digitally encoded audio signal are detected. The reference signal generator uses the fact that the modulation by the signal is orthogonal and the DC component of the modulation by the digitally encoded audio signal is small.
The phase difference between 95 and the intermediate frequency signal containing the carrier wave is detected by the synchronous detection circuit 14 and the low-pass filter 96, and is fed back to the voltage-controlled local oscillator 94, so that the carrier wave of the intermediate frequency wave is generated by the reference signal generator 95. That is, the output of the synchronous detection circuit 14 is used as a detection output in synchronization with the output of.

According to the present embodiment, since the intermediate frequency for demodulation coincides with the frequency of the reference frequency 95, the frequency deviation of the comb filter 13 due to the frequency drift of the frequency conversion circuit 3 or the like and the demodulation frequency drift occur. Less than 12th
There is an effect that demodulation can be performed more stably than the embodiment shown in the figure.

FIG. 14 is a block diagram of an example of a transmitter for further effectively reducing the interference from a video signal in a receiver having a comb filter of the present invention to a digitally encoded and multiplex-transmitted audio signal. . Reference numeral 97 is an inverse characteristic filter of the comb filter characteristic of the receiver, and the same reference numerals as those in FIG. 2 indicate the same functions. Based on the comb filter characteristics shown in FIG. 6, the receiver extracts the digitally encoded and multiplex-transmitted voice signal spectrum shown in FIG. 5 (a) and demodulates it with the synchronous detection circuit 14 (FIG. 13). To do. At that time, due to the attenuation near the dip of the comb filter characteristic shown in FIG.
There is a possibility that the spectrum in the vicinity of the dip in the spectrum shown in FIG. 5 (a) (the dip point is not necessary but in the vicinity thereof) may be attenuated, and the error rate of the digital signal generated by the transmission may be deteriorated.

In order to reduce the deterioration, the output of the modulator 38 (Fig. 14) having the spectrum shown in Fig. 5 (a) has an inverse characteristic having an inverse characteristic of the comb filter characteristic on the receiver side shown in Fig. 6. The inverse characteristic filter 97 can be transmitted by transmitting it through the filter 97.
And the transmission path characteristics of a digitally encoded and multiplex-transmitted audio signal that passes through both the filter and the comb filter of the receiver are substantially flat in frequency.

According to this example, there is an effect that the deterioration of the characteristics due to the reception comb filter can be reduced, and the interference from the video signal to the audio signal that has been digitally encoded and multiplexed and transmitted can be reduced. In the receiver of the embodiment of the present invention, the comb filter is described as the intermediate frequency band comb filter inserted in the preceding stage of the synchronous detection circuit 14, but in the present invention, the synchronous detection circuit 14 performs synchronous detection. Since it is only necessary to add the characteristic of the comb filter to the signal to be generated, the comb filter is not limited to the intermediate frequency band, and for example, the same effect can be obtained by adding the output signal of the synchronous detection circuit 14 to the comb filter. .

〔The invention's effect〕

According to the present invention, since the spectrum of the video signal can be effectively reduced by the comb filter, there is an effect that a multiplexed signal such as an audio signal multiplexed and transmitted by orthogonal multiplexing can be stably received.

[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 example of a transmitter for carrying out the present invention, FIG. 3 is a frequency spectrum diagram of a signal relating to the present invention, and FIG. FIG. 5 is a vector diagram of a signal related to the present invention, FIG. 5 is an enlarged view of a spectrum of a signal related to the present invention, FIG. 6 is a characteristic example diagram of a comb filter used in the present invention, and FIG. 8 is a diagram showing a configuration example for concentrating the spectrum of a signal related to the signal, FIG. 8 is an operation explanatory diagram of the configuration example of FIG. 7, FIG. 9 is a spectrum diagram for explaining the configuration example of FIG. 7, and FIG. Is an example diagram of a circuit for demodulating a spectrum-concentrated and transmitted signal according to the present invention, FIG. 11 is another example diagram of a circuit for demodulating a spectrum-concentrated and transmitted signal according to the present invention, and FIG. 12 is a book FIG. 13 is a block diagram of another embodiment of the invention, FIG. 13 is a block diagram of yet another embodiment of the present invention, and FIG. It is a block diagram of the other example of the transmitter used when implementing this invention. Symbol description 1 ... Antenna, 3 ... Frequency conversion circuit, 13 ... Comb filter, 14 ... Synchronous detection circuit, 15 ... Carrier recovery circuit, 18 ... Digital signal processing circuit, 36 ... Spectrum processing circuit, 91 …… Frequency conversion circuit, 93 …… Mixed circuit, 94
...... Local oscillator, 95 …… Reference signal generator, 96 …… Low pass filter, 97 …… Inverse characteristic filter

Claims (2)

[Claims] 1. A video signal carrier is vestigial sideband amplitude modulated with a video signal, and a quadrature carrier having a phase difference of 90 degrees from the video signal carrier is within a band having double sidebands within the vestigial sideband. A basic signal band exists and is modulated by a digitally encoded signal to be multiplexed (hereinafter referred to as a multiplexed signal), and the residual sideband amplitude modulation signal spectrum of the video signal is determined every horizontal scanning period of the video signal. Has a peak level and has a comb-shaped frequency spectrum characteristic so as to have a valley portion in the frequency range between the peak level and the peak level, and the signal spectrum of the multiplex signal is the comb-shaped frequency spectrum characteristic. At the frequency position where the frequency relationship shifts and the peak level is obtained in the comb-shaped spectrum characteristic, the frequency becomes the valley bottom and the frequency in the comb-shaped spectral characteristic becomes the valley part. The signal processing is performed so that the signal spectrum has a peak level at the position, and the quadrature signal modulated with the digital signal multiplex signal and the vestigial sideband amplitude-modulated video signal carrier wave. The carrier wave receives the multiplexed television signals transmitted and synthesized with each other at a ratio such that the ratio of the maximum value of the latter to the maximum value of the latter is 0.1 or less, and is digitally encoded from there. In the transmission signal reproducing device for reproducing the multiplexed signal, carrier wave reproducing means for reproducing a quadrature detection carrier wave for receiving the multiplexed television signal for synchronous detection, and the received multiplexed television signal, Synchronous detection is performed using the quadrature detection carrier regenerated by the carrier regenerating means, and digitally encoded used for the modulation of the quadrature carrier. Synchronous detection means for demodulating the multiplexed signal, be located upstream or downstream of the synchronous detection means,
A comb-shaped filter having a comb-shaped characteristic as a reception comb-shaped characteristic that can suppress the signal spectrum of the video signal, which has a peak level for each horizontal scanning frequency, to reduce interference with the reproduced multiplexed signal from the video signal. A transmission signal reproducing apparatus comprising: 2. The transmission signal reproducing device according to claim 1, wherein the digitally encoded multiplexed signal is an audio signal.