JPH07105941B2 - Transmission signal transmission method and transmission signal transmission device - 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 transmission signal transmission method and a transmission signal transmission device which are 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, regarding the possibility of multiplex transmission to the current terrestrial television broadcasting, the broadcast technology sosho 2 “broadcast system” edited by the Japan Broadcasting Corporation in January 1983 is published by the Japan Broadcasting Corporation.
Although described on pages 205 to 208, there is no description about a system capable of ensuring a transmission capacity of about 1 megabit / second 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 transmission method and a transmission apparatus for multiplex-transmitting another signal to an amplitude-modulated signal, and in particular, it is possible to multiplex high-quality digitally encoded PCM audio signals into current television broadcasting. It is an object of the present invention to provide a transmission signal transmission method and a transmission device thereof, which are effective for generating a signal of a transmission system for multiplex transmission of signals.

[Means for solving problems]

The above object is achieved by modulating the quadrature component of an amplitude-modulated carrier with another multiplexed signal. In particular, in the case of a video signal with vestigial sideband amplitude modulation, an orthogonal relationship with the video signal of the carrier wave is provided by a multiplex signal such as PCM digitally encoded within the band in which both sidebands of the carrier wave are transmitted. It is achieved by modulating and transmitting.

[Action]

Residual sideband Amplitude-modulated video signal Carrier has a double-sided band and is limited to the general amplitude-modulated band (DSB) so that the carrier has an orthogonal relationship between the video signal and the multiplexed signal. Since it is modulated by the modulation, the influence of the multiplexed signal on the reproduced video signal can be reduced. Modulation level of multiplex signal 0.1
By making the value lower than the video signal, it is possible to reduce the influence of the multiplexed signal on the video signal reproduced by the envelope detection. Further, since the multiplexed signal is synchronously detected and reproduced, the orthogonally modulated video signal is not demodulated and the influence is reduced.

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. 2 channels (eg 12 bits x 2
Channel × 32K sampling × 1.3 redundancy ≈ 1Mbps) can be transmitted.

Moreover, since the frequency and the modulation method are different from the current FM audio signal, simultaneous transmission is possible without affecting each other.

〔Example〕

FIG. 1 shows an example of a transmitter for multiplex transmission of digitally encoded PCM audio signals to a current terrestrial transmission television as an embodiment of the present invention. 1 is a video signal processing circuit, 2 to 4 are video signal input terminals, 5 is a carrier wave oscillator,
6 is an AM modulation circuit, 7 is a PCM audio input terminal, 8 is an analog-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, and 12 is digital. A modulator circuit, 13 is an adder, 14 is a VSB filter for vestigial sideband amplitude modulation, and 15 is an antenna.

The R, G, B video signals input from the video input terminals 2, 3 and 4 are processed by the video signal processing circuit 1 such as brightness signal processing and color difference signal processing, and are processed by AM modulation as video transmission signals by adding synchronization signals. Input to the circuit 6. In the AM modulation circuit 6, the output of the carrier oscillator 5 is AM-modulated by the video transmission signal, and the VSB filter 1
The band is limited to the television broadcasting band by 4 and transmitted from the antenna 15. The above is the same as the conventional terrestrial television broadcasting. Next, the signal applied to the adder 13 will be described below.

The multiplexed PCM voice signal is added to the PCM voice input terminal 7 and converted into a digital signal by the ADC 8. Next, in addition to the digital signal processing circuit 9, processing such as code addition and interleaving for detecting and correcting an error occurring during transmission is performed. Subsequently, unnecessary high-pass components are removed via the low-pass filter 10 suitable for the transmission rate of the digital code. The digitally encoded voice is modulated by a digital modulation circuit 12 on a video signal carrier that is phase-shifted by about 90 degrees via a phase shifter 11. The output is added to the adder 13 and added to the carrier wave modulated by the video transmission signal. As a result, the video carrier wave is modulated in the orthogonal relationship between the video transmission signal and the PCM audio signal.

FIG. 2 shows an embodiment in which the conventional FM audio signal is multiplexed in addition to the above PCM audio signal multiplexing and compatibility with the conventional technology is taken into consideration. The same symbols as those in FIG. 1 have the same functions. In the video signal processing circuit 1, 16 is a matrix circuit, 17 is a luminance signal processing circuit, 18 is a color difference signal processing circuit, and 19 is an NTSC signal format generation circuit. 20 is an adder, 21 is an audio signal input terminal for FM modulation, 22 is a carrier oscillator for audio signals, and 23 is an FM
It is a modulation circuit.

In FIG. 2, the signal processing of the PCM audio signal and the signal processing of the video signal are the same as in FIG. In the video signal processing circuit 1, the matrix circuit 16 receives the input R, G, B primary color signals.
The luminance signal and the color difference signal are separated by and processed by the luminance signal processing circuit 17 and the color difference signal processing circuit 18, respectively, and then converted into a video transmission signal by the NTSC generation circuit 19. Now, the audio signal of the audio signal input terminal 21 newly added in this circuit is the FM modulation circuit 23.
Then, the carrier wave of the audio carrier wave circuit 22 is FM-modulated, and the output signal is added to the adder 20. In the adder 20, the V including the AM-modulated video signal and the digitally-modulated PCM audio signal is added.
The output signal of the SB filter 14 and the FM-modulated audio signal are added, and the output is transmitted by the antenna 15.

The modulated signal spectrum is shown in FIG. The figure (a) is the output of the video signal processing circuit 1, and the NTSC transmission format is the spectrum of the processed video transmission signal.
There is a 25MHz band. Next, the spectrum of the output obtained by AM-modulating the video carrier f _c is that shown in FIG. 7B, which is a double sideband amplitude modulation (DSB) signal. On the other hand, in the same figure (c), the digital modulation circuit 12
The output spectrum of is shown. Here, the spectrum of the PCM audio signal shows the spectrum when the carrier wave is modulated by a signal with a roll-off of 0.5 at a transmission rate of 1 Mbit / sec. FIG. 3D shows a spectrum in which an AM-modulated video transmission signal and a digitally-modulated PCM audio signal are added. The figure (e) shows the spectrum of the FM modulated audio signal, and the audio carrier f _s is 4.5 MHz from the video carrier f _c.
It's far away. FIG. 6F shows the spectrum of the output signal of the adder 20. The video transmission signal is attenuated from −0.75MHz point by the VSB filter from the video carrier. What is shown by the dotted line is a PCM with a 90 degree phase shift from the video carrier
It is a digital modulation spectrum of a signal carrier. Also, in the vicinity of 4.5MHz above the video transmission signal band of 4.25MHz, there is a spectrum in which the audio carrier is FM-modulated. Since both sidebands are transmitted at ± 0.75MHz with respect to the image carrier, it can be considered as general amplitude modulation (DSB).

FIG. 4 is a vector representation of the relationship between the video carrier and the PCM signal. As shown in FIG. 3 (c), a signal within ± 0.75 MHz which is orthogonal to a carrier wave having a double sideband is modulated with amplitudes A and −A by making it correspond to digital codes 1 and 0. When the video carrier amplitude V _c is 1 in the vector, the modulated signal V _cp is V _cp = cos ω _ct ± A sin ω _ct (1). Where ω _c is the angular frequency of the carrier. (1)
When you expand the expression, Is.

Further, in general, when the video carrier V _c cos ω _ct is modulated with the signal of V m cos ω _mt , the modulated signal V _c in the DSB area is Then, the carrier amplitude V _c = 1 and the orthogonal modulation component by the PCM signal is added to this V _c , and the signal V _cp becomes Is. The vector is shown in FIG.

Hereinafter, it will be described that the modulation level A of the PCM audio signal affects the interference between the video signal and the PCM audio signal.

First, with the video signal when this transmission signal is received by the receiver
Consider a receiver for PCM audio signals. FIG. 6 shows an example of a receiver. 101 is an antenna, 102 is a high frequency amplification circuit, 103 is a frequency conversion circuit, 104 is an intermediate frequency amplification circuit, 105 is a video signal detection circuit, 106 is a video signal amplification circuit, 107 is a color difference signal demodulation circuit, and 108 is a primary color signal demodulation circuit. , 109 is a cathode ray tube, 11
0 is an audio intermediate wave amplification circuit, 111 is an audio FM detection circuit, 112 is an audio signal output terminal, 113 is a band pass filter, 114 is a synchronous detection circuit, 115 is a carrier wave reproduction circuit, 116 is a code identification circuit,
Reference numeral 117 is a clock reproduction circuit, 118 is a digital signal processing circuit, 119 is a digital / analog conversion circuit (hereinafter referred to as a DAC), and 120 is an output terminal for multiplex-transmitted PCM audio signals.

A television signal input from the antenna 101 is amplified by a high frequency amplifier circuit 102, frequency converted to an intermediate frequency for demodulation by a frequency conversion circuit 103, and amplified by an intermediate frequency amplifier circuit 104. The tuning is performed by changing the local oscillation frequency of the frequency conversion circuit 103. Regarding the video signal band from the signal amplified by the intermediate frequency amplifier circuit 104, the video signal detection circuit
The primary color signal demodulation circuit 108 detects the three primary colors of R, G, B from the luminance signal output from the video signal amplification circuit 106 and the color difference signal output from the color difference signal demodulation circuit 107, and the CRT 9
Projected on. On the other hand, the voice band is amplified by the voice intermediate frequency amplifier circuit 110, detected and demodulated by the voice FM detection circuit 111, and a voice signal is obtained at the voice signal output terminal 112. The above is the same as the conventional television receiver.

In addition to the above, in order to demodulate the PCM audio signal that is digitally modulated and multiplexed and transmitted, the PCM audio signal band that is multiplexed and transmitted by the bandpass filter 113 is selected from the output of the frequency conversion circuit 103, amplified, and subjected to synchronous detection. In the circuit 114, the signal synchronized with the carrier regenerated by the carrier regenerator 115 is used to detect and demodulate the signal modulated with the component orthogonal to the amplitude modulation component of the carrier. The signal obtained as a result is converted into a digital code at a point having a small error rate by using the code identification circuit 116, and an error occurring during transmission in the digital signal processing circuit 118 is detected and corrected using an error detection / correction code. . The clock recovery circuit 117 is a circuit for extracting a transmission clock from the signal output from the synchronous detection circuit 114.
It is necessary for digital encoding at the point where the error rate of the output signal of 4 is small (so-called maximum opening of eye pattern). The output of the digital signal processing circuit 118, which has completed signal processing such as error detection and correction, is converted into an analog signal by the DAC 119 and returned to an audio signal, and is obtained as the original audio signal at the output terminal 102 of the multiplex-transmitted PCM audio signal. .

Now, the interference of the PCM audio signal with the video signal in the receiver will be described below. Not a disturbance is reproduced only coefficients of cos omega _ct, regardless of the value of A (see equation (1)) (i.e. the video signal only) is about what is synchronously detected by the video signal detection circuit cos omega _ct . In the case where the video signal detection circuit performs envelope detection, lowering the value of A from 1 can reduce interference. For example, A is 0.1
Then, Therefore, a signal of 0.005 (about -46 dB) is affected compared to 1, but I think that it will not be a 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, from the video signal
The interference of the PCM voice signal to the detection circuit can be eliminated by demodulating only the component orthogonal to the carrier wave in the synchronous detection circuit 114 as shown in FIG. Signal level to noise ratio (hereinafter SN
Ratio), assuming that the SN ratio of the video signal is 40 dB and the practical level, the bandwidth is about 4 times that of the transmission bandwidth of 1 MHz of the PCM audio signal, so the SN ratio of PCM audio is 46 dB.
However, if the modulation level A of the PCM audio signal is 0.1, SN
The 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 with a general binary signal, the SN ratio is 17.4 dB and the bit error rate is 1 × 10 ⁻⁴ (general theoretical value). If the SN ratio of the video signal is 40 dB, even if A is set to 0.1, P
The SN ratio of a CM voice signal is 26 dB, which is a practically sufficient value for digital signal transmission, and even if A is 0.1, there is a margin of about 10 dB in the SN ratio for a bit error rate of 1 × 10 ^-4 . It can be seen that it is practically sufficient even if A is 0.1 or less.

As described above, the transmission signal generator of the present invention can be realized by the embodiments of FIGS. 1 and 2, and the receiver shown in FIG. 6 is taken as an example to digitize the PCM to about 1 Mbit / sec.
Audio signals can be transmitted without interfering with conventional television video and audio signals.

FIG. 7 shows another embodiment of the present invention. This circuit is based on the circuit of FIG. 2, and the same numbers have the same functions. It is a new addition, 30 is a crystal oscillator, 31 is an oscillation circuit, 32
Is a multiplying circuit, 34 and 41 are high frequency amplifying circuits, and 35 is a diplexer. The image carrier is a crystal oscillator 30 and an oscillation circuit 31.
It is obtained by multiplying the original oscillation frequency generated in (1) by the multiplication circuit 32.
This carrier is used for AM modulation of the image, and the phase is shifted by π / 2 to be a carrier for digital modulation. Further, the signal obtained by amplifying the FM-modulated audio carrier by the high frequency amplifier circuit 41 and the video carrier signal amplified by the high frequency amplifier circuit 34 via the VSB filter 14 are combined by the diplexer 35 and emitted by the antenna 15. Also in the present invention, the transmission signal of the present invention is obtained, and the spectrum of the radio wave emitted from the antenna 15 is the same as that in FIG. 3 (f).

FIG. 8 shows another embodiment of the present invention. 24 and 30 are crystal oscillators, 25 and 31 are oscillation circuits, 26 is a video input terminal, 27 is an AM modulation circuit, 28 is a high frequency amplification circuit, 29 and 40 are frequency conversion circuits, 32 and 39 are frequency multiplication circuits, 33 Is a signal synthesis circuit, 34, 41
Is a high frequency amplifier circuit, 35 is a diplexer, 36 is a transmitting antenna, 37 is a voice input terminal, 38 is an FM modulation circuit, 42 is an ADC, 43
Is a digital signal processing circuit, 44 is a low-pass filter, 45
Is a phase shifter, and 46 is a digital modulation circuit. The video signal input from the video input terminal 26 is AM-modulated by the AM modulation circuit 27 at the intermediate frequency obtained by the crystal oscillator 24 and the oscillation circuit 25. This signal is combined with the digitally modulated wave by the combining circuit 33 and amplified by the high frequency amplifier circuit 28. Further, the signal generated by the crystal oscillator 30 and the oscillation circuit 31 is multiplied by the multiplication circuit 32, and the obtained signal and the output signal of the high frequency amplification circuit 28 are combined by the frequency conversion circuit 29. The output of the frequency conversion circuit 29 is the carrier wave of the image, which is again amplified by the high frequency amplification circuit 34, band-limited by the VSB filter 14, and then input to the diplexer 35.

On the other hand, a voice signal is input from the voice signal input terminal 37 and branched into two systems, a conventional FM modulation system and a new digital modulation system. Audio signal (analog) input to FM modulation circuit 38
Is a frequency conversion circuit that FM-modulates the built-in reference frequency.
In 40, it is converted into the voice carrier frequency inputted from the multiplication circuit 39, and inputted into the diplexer 35 via the high frequency amplifier circuit 41. The audio signal input to the ADC 42 is converted into a digital signal by the ADC 42, processed by the digital signal processing circuit 43, and then processed by the low-pass filter 44. Frequency) is phase-shifted by the phase shifter 45 by about 90 degrees, and the image intermediate frequency is digitally modulated. The output of the digital modulation circuit is input to the signal synthesis circuit 33. The carrier wave synthesized by the diplexer 35 is emitted from the antenna 36 as a transmission radio wave. The spectrum of the output radio wave is shown in FIG. 3 (f), which enables multiplex transmission of the PCM audio signal of the present invention.

Next, FIG. 9 shows still another embodiment. This circuit is a modification of the embodiment shown in FIG. The same numbers in the figures indicate the same functions. The feature of this circuit is that the carrier of digital modulation is reproduced from the carrier after the video AM modulation. Since image AM modulation does not have a modulation degree of 100%, the output of the frequency conversion circuit 29 is guided to the carrier wave reproduction circuit 47, and a limiter is applied here to extract the fundamental wave. The carrier wave obtained here is phase-shifted by about 90 ° by the phase shifter 45, and this is modulated with a digital signal. The modulated signal is the frequency conversion circuit.
Composite with 29 outputs. After that, radio waves are emitted through the high frequency amplifier circuit 34, the VSB filter 14, and the diplexer 35. Also in this embodiment, the spectrum of the transmission signal has the format shown in FIG. 3 (f), and the multiplex transmission of the PCM voice signal can be achieved.

As a digital modulation method, quadrature component amplitudes A and -A
If quadrature modulation corresponding to the input digital signals 1 and 0 is performed, 1 Mbit / sec data can be transmitted in the band of the above-described embodiment. If the quadrature amplitude is O, A or O,
It may be transmitted in a binary value of −A or in a multivalued value of three or more values. The sideband component of the digital modulation is described in the double sideband region of the residual sideband amplitude modulation.However, if a small deterioration of the error rate in digital transmission is allowed, transmission outside the band is possible. is there.

Regarding the transmission power of the transmitting station, the increase in the carrier amplitude due to PCM audio signal multiplexing results in a voltage as shown in equation (1). When A = 0.1, the increase in power is 1.01 times, which is a slight increase.

〔The invention's effect〕

According to the present invention, to the carrier wave to be amplitude-modulated, to the quadrature component of the carrier wave, by transmitting the modulation level of the multiplex signal lower than 0.1 and the modulation level of the amplitude modulation,
In addition to the video and audio signals that can be transmitted by the current terrestrial television broadcasting, it has the effect of transmitting digitally encoded PCM audio signals.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the present invention, FIG. 3 is a spectrum diagram of a signal obtained in the embodiment of the present invention, and FIG. And FIG. 5 are vector diagrams of signals, FIG. 6 is a block diagram of an example of a receiver for receiving a transmission signal of the present invention, and FIG. 7 is a block diagram of another embodiment of the present invention,
FIG. 8 is a block diagram of another embodiment of the present invention, and FIG. 9 is a block diagram of yet another embodiment of the present invention. 1 ... Video signal processing circuit, 6 ... AM modulation circuit, 5 ... Carrier oscillator, 11 ... 90 degree phase shifter, 12 ... Digital modulation circuit, 13 ... Adder, 14 ... VSB filter, 23 …… FM modulator, 32,39 …… Multiplication circuit, 29,40 …… Frequency conversion circuit,
35 …… diplexer, 15, 36 …… antenna.

Claims (6)

[Claims] 1. A first carrier is vestigial sideband amplitude modulated with a video signal and a second carrier having a phase difference of approximately 90 degrees from the first carrier has double sidebands within the vestigial sideband. The first carrier wave, which is modulated with a binary or more digitally encoded voice signal so that a basic signal band exists within the band, and is vestigial sideband amplitude modulated, and the binary or more digitally encoded voice signal. The second carrier wave modulated with a signal is modulated with the digitally encoded audio signal of two or more values with respect to the maximum value of the amplitude of the first carrier wave subjected to the vestigial sideband amplitude modulation. The maximum value of the amplitude of the second carrier is
Current television broadcasting by synthesizing and transmitting the first carrier wave and the second carrier wave that are different in frequency from the second carrier wave that is frequency-modulated with the audio signal And a service area of the digitally encoded audio signal can be made comparable to a service area of current television broadcasting. 2. A first carrier wave generating means for generating a carrier wave, a video modulating means for amplitude-modulating the output carrier wave of the first carrier wave generating means with a video signal by a vestigial sideband amplitude, and a phase of the carrier wave is approximately 90 degrees. Second carrier generating means for generating orthogonal carrier waves having different degrees, digital modulating means for digitally amplitude-modulating the output carrier of the second carrier generating means with a digitally encoded audio signal, and output of the video signal modulating means Mixing means for synthesizing the signal and the output signal of the digital modulation means with a ratio of the maximum amplitude of the output signal of the video signal modulation means to the maximum amplitude of the output signal of the digital modulation means is 0.1 or less. , The compatibility with the current television broadcasting is obtained and the service area of the digitally encoded audio signal is supported by the current television broadcasting. The signal transfer device, characterized in that it about the same as the Bisueria. 3. The transmission signal transmission device according to claim 2, wherein the modulation signal by the digital modulation means is a multi-valued digitally encoded audio signal of three or more values. 4. A first carrier wave generating means for generating a carrier wave, a video modulating means for amplitude-modulating the output carrier wave of the first carrier wave generating means with a video signal by a vestigial sideband, and a phase of the carrier wave is approximately 90 degrees. Second carrier generating means for generating orthogonal carrier waves having different degrees, digital modulating means for digitally amplitude-modulating the output carrier of the second carrier generating means with a digitally encoded audio signal, and output of the video signal modulating means Mixing means for synthesizing the signal and the output signal of the digital modulation means with a ratio of the maximum amplitude of the output signal of the video signal modulation means to the maximum amplitude of the output signal of the digital modulation means is 0.1 or less. , And a signal synthesizing unit for synthesizing an audio carrier frequency-modulated by an audio signal to the output signal of the mixing unit, thereby achieving compatibility with current television broadcasting. In addition, the transmission signal transmission device is characterized in that the service area of the digitally encoded audio signal can be made approximately the same as the service area of current television broadcasting. 5. A transmission signal transmission device according to claim 4, wherein the modulation signal in said digital modulation means is a multi-valued digitally encoded audio signal of three or more values. 6. The claim 5 according to claim 5, wherein the multi-valued digitally encoded audio signal of three or more values and the audio signal frequency-modulating the audio carrier are the same audio signal. And a transmission signal transmission device.