JP2715407B2 - Television signal processing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal processing method for multiplexing and transmitting another digital signal to an existing television broadcast signal. Conventional technology The current NTSC [National Television System Committee of Japan]
mittee)] Color television broadcasting by the system
More than 25 years have passed since the year began. In the meantime, various new television schemes have been proposed along with the demand for high-definition screens and the improvement in performance of television receivers. Also, the content of the service program itself is not only a studio program or a relay program, but also a program having a higher quality and more realistic image such as a cinema-size movie broadcast, or more information such as a text multiplex broadcast. Is changing to a program that conveys The current broadcast has various specifications such as 252 scanning lines, 2: 1 interlaced scanning, luminance signal horizontal bandwidth of 4.2 MHz, and a spectral ratio of 4: 3 (for example, Sentence Broadcasting Technology Multi-Colored Television)
Japan Broadcasting Corporation, Japan Broadcasting Publishing Association, 1961), but in such a background, it is necessary to transmit more information while maintaining compatibility with current broadcasting. Television signal construction methods have been proposed. For example,
The character multiplexing method multiplexes and transmits a digital signal to a vertical blanking engine of an NTSC signal. The example described below is a television signal configuration method for multiplexing a high frequency component of a luminance signal with an analog signal in order to improve horizontal resolution. NTSC
System television signal with time frequency ₁ and vertical frequency
To illustrate in _{two-dimensional} plane is shown in Figure 5. The color signal C exists in the second and fourth quadrants from the phase relationship of the color subcarrier _SC . Here, the high-frequency components of the luminance signal are multiplexed in the first and third vacant quadrants, and the receiving side separates the chrominance signal and the multiplexed high-frequency component by field operation to improve the horizontal resolution. (Japanese Patent Laid-Open No. 59-1713
Problems to be Solved by the Invention As described above, in the current television broadcasting, the signal band is limited by the standard, and it is not easy to add some multiplexed information. For example, a method for improving the horizontal resolution has been proposed, but there remains a problem in terms of compatibility with the current television broadcast and deterioration of the high-frequency component demodulation characteristics at the time of a moving image. Also, a large amount of digital signals cannot be multiplexed within a limited vertical flyback period as in the case of teletext broadcasting. Further, from the viewpoint of effective use of radio wave resources, it is impossible to extend the transmission band. The present invention has been made in view of the above problems, and provides a television signal processing method that is compatible with the current television system and that can multiplex and transmit a large amount of digital information within a band defined by a standard. With the goal. Means for Solving the Problems To solve the above problems, a television signal processing method of the present invention is a multiplexed signal obtained by modulating a subcarrier with a digital signal, and has the same frequency as the video carrier and a phase of 90 degrees. A different carrier is amplitude-modulated in both sidebands, attenuated by half at the frequency of the video carrier, and a signal converted into a residual sideband by a Nyquist filter having an oddly symmetrical amplitude characteristic with respect to the frequency of the video carrier. A television signal processing method for receiving a signal superimposed in the band of the television signal subjected to vestigial sideband amplitude modulation, the received signal, band-limited by a band-pass filter, the reproduced video carrier and Synchronous detection of the output signal of the filter is performed with a carrier having a phase difference of 90 degrees, a subcarrier is recovered from the detected signal, and digital demodulation is performed. It is characterized in demodulating the signal. Effect of the Invention The present invention generates a television signal which enables multiplex transmission of a large amount of digital information within the band of the current television broadcasting standard by the above-mentioned method, so that a dedicated receiver receives the conventional television broadcasting. Not only video but also a large amount of multiplexed digital information can be obtained, and a current television receiver can receive conventional television broadcast video almost without any trouble. Embodiment Hereinafter, a television signal processing method according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a spectrum diagram showing a television signal processing method on the transmission side according to one embodiment of the present invention. FIG. 1A is a spectrum diagram of a television signal subjected to vestigial sideband amplitude modulation in the current television system. It is shown here when the lower sideband of the video carrier P ₁ is a vestigial sideband. Figure 1 (b) is a subcarrier P _3, is a spectrum diagram of a multi-signal phase-shift keying (PSK) modulated with digital signals band-limited by the pre-roll-off filter. In Figure 1 (c) is the multiplexed signal band-limited, which picture carrier P ₁ and the same frequency at and phase of ± 90 degrees from the carrier P _2, and double sideband amplitude-modulated so as to remove the carrier P ₂ It is. FIG. 1 (d) shows a case where the double sideband amplitude modulation in the above is changed to single sideband amplitude modulation. FIG. 1 (e) shows a case where the above-mentioned double sideband amplitude modulation is replaced with a residual sideband amplitude modulation. For example, the first
FIG. 1 (f) is a signal obtained by multiplexing the signal of FIG. 1 (e) with the television signal of FIG. 1 (a), which is an example of a television signal synthesized according to the present invention. FIG. 1 (b)
Shows the case of phase shout keying (PSK) modulation, but the amplitude shift keying (ASK)
Modulation or frequency shift keying (FSK) modulation may be used. Further, the phase shift keying modulation may be two-phase shift keying (BPSK) modulation or multi-phase shift keying modulation such as four-phase phase shift keying (QPSK) modulation. Similarly, amplitude shift keying modulation may be of two levels or of multiple levels. Similarly, the frequency shift keying modulation may be of two frequencies or of multiple frequencies. In FIG. 1 (f), the signal to be multiplexed is the signal of FIG. 1 (e), but may be the signal of FIG. 1 (c) or FIG. 1 (d). FIG. 2 is a block diagram showing a television signal processing method on the transmitting side according to one embodiment of the present invention. 1 is a video baseband signal input terminal, 2 is an amplitude modulator, 3 is a first filter, 4 is a first oscillator, 5 is a transporter, 6 is a digital signal input terminal, 7 is a modulator, 8 is a second filter, 9
Is an adder, 10 is a composite television signal output terminal, 11 is a second oscillator, and 12 is a four-phase modulator. A video baseband signal input from a video baseband signal input terminal 1 is used to convert a carrier P ₁ obtained from a first oscillator 4 into an amplitude modulator 2.
Amplitude modulation. The obtained amplitude-modulated wave is band-limited by the first filter 3 to be a residual sideband, and then added to the adder 9. Those obtained by 90 degree phase shift by the transfer device 5 to the carrier P ₁ obtained from the first oscillator 4 and the carrier P _2. The digital signal input from the digital signal input terminal 6 is
Subcarriers P ₃ obtained from the second oscillator 11, a quadrature phase shift keying modulated multiplexed signal in 4-phase modulator 12. Note that the four-phase modulator 12 may be another polyphase modulator, frequency modulator, or amplitude modulator. The multiplexed signal is supplied to the modulator 7 and the carrier removed double sideband amplitude modulation with the carrier P ₂ a double sideband amplitude modulation retrace period. In addition,
Although the phase shift direction of the transfer device 5 may be fixed, the phase shift direction may be changed, for example, every horizontal scanning period. The phase shift amount of the transfer unit 5 is set so that when combined by the adder 9, the phase difference between the carrier of the video system and the carrier of the multiplexed signal system which is removed is ± 90 degrees. . The modulated signal is added to the adder 9 after band limitation by the second filter 8. The output of the adder 9 is a composite television signal. That is, the multiplexed signal is superimposed on the video baseband signal to form a composite television signal.
Due to the frequency characteristic of the second filter 8, the multiplexed signal is a signal having a band as shown in FIGS. 1 (c), 1 (d) and 1 (e). Next, the effect of the present invention when a composite television signal is received by a current television receiver according to an embodiment of the present invention will be described. In the following, the case of terrestrial broadcasting is taken as an example. FIG. 4A is a block diagram of a current television receiver that performs video synchronous detection. 41 is an antenna, 42
Is a tuner, 43 is a video intermediate frequency filter, 44 is a video detector, 45 is a carrier reproduction circuit, and 46 is a video baseband signal output terminal. The signal transmitted from the transmitting side is
, Is frequency-converted to an intermediate frequency band by the tuner 42, and band-limited by the video intermediate frequency filter 43. The band-limited signal is supplied to a video detector 44 and a carrier recovery circuit 45. In the carrier recovery circuit 45, the carrier wave for synchronous detection is used.
Play I ₁ . Band-limited signal is detected in the video detector 44 in carrier I _1, the video baseband signal. Here, the frequency characteristics of the video intermediate frequency filter 43 will be described. FIG. 4 (b) shows the frequency characteristics.
It is. That amplitude is 6dB attenuation at the picture carrier I _1, and has a Nyquist filter characteristic having a substantially odd symmetrical amplitude characteristic with respect to the picture carrier I _1. On the other hand, as shown in FIG. 1 (e), if the multiplexed signal is band-limited by a filter having characteristics opposite to the frequency characteristics of the video intermediate frequency filter of the receiver, the hatched portion in FIG. 4 (b) Are almost double-sided wavebands. FIG. 4 (c) shows a vector representation of this. Where I ₁ is the video carrier of the video baseband signal and I ₂ is the carrier of the multiplexed signal.
I ₁ with the same frequency as a and the phase is 90 degrees different carriers.
Since the video baseband signal has to think about the carrier I ₁ and vestigial sideband, vector a ₁ vertical sideband vector a _U, it is decomposed next orthogonal vectors vector a _L,
A vector a _2. Further, since the multiplexed signal has almost both sidebands, if the upper and lower sidebands are a vector b _U and a vector b _L , their combined vector is b ₂ , which is only a component orthogonal to the vector I ₁ . That vector a ₂ When synchronous detection at the carrier I _1, not generated distortion orthogonal by vector b ₂ components, interference due to multipath signals for the current television receiver doing the video synchronous detection does not occur in principle. If the signal to be multiplexed is a signal as shown in FIG. 1 (c), the band is not double-sideband when the band is limited by the video intermediate frequency filter 43, so that orthogonal distortion may occur. However, multiplexing at lower levels, for example, reduces the interference to current television receivers. The same applies to the case where the signal to be multiplexed is a signal as shown in FIG. 1 (d). However, since the attenuation of the video intermediate frequency filter 43 is large, the degree of interference is further reduced. Next, a multiplexed signal demodulation method on the receiving side according to one embodiment of the present invention will be described. The signal of the video intermediate frequency band, which is the output of the tuner, is band-limited by a filter so that the video baseband signal is in both sidebands as shown in FIG. FIG. 3B shows a vector representation of this. Since multiplex signal has to think about the carrier I ₂ and vestigial sideband, upper and lower sideband vector b _U, vector b _L
When decomposed into orthogonal vectors, vector b ₁ , vector b
It becomes ₂ . In addition, since the video baseband signal is almost double-sideband by the filter, if the upper and lower sidebands are vector a _U and vector a _L , their composite vector is a ₁ , which is only a component orthogonal to the vector I ₂ . That is, carrier I ₂
When the synchronous detection is performed on the axis, the orthogonal distortion due to the components of the vector a ₁ and the vector b ₂ does not occur, and only the multiplex signal component can be demodulated. FIG. 3 (c) is an example of a block diagram of a television receiver for demodulating a multiplex signal. 31 is an antenna, 32 is a tuner, 33 is a video intermediate frequency filter, 34 is a video detector, 35 is a carrier recovery circuit, 36 is a video baseband signal output terminal, 37 is a filter, 38 is a transporter, and 39 is multiplex signal detection. , 20 is a four-phase transfer demodulator, 21 is a subcarrier recovery circuit, and 22 is a digital signal output terminal. The signal transmitted from the transmitting side is received by the antenna 31, frequency-converted to an intermediate frequency band by the tuner 32,
Is limited. The band-limited signal is sent to a video detector.
34, supplied to the carrier recovery circuit 35. Carrier recovery circuit 35
In reproduces the carrier I ₁ for synchronous detection. Band-limited signal is detected in the video detector 34 in carrier I _1,
It becomes a video baseband signal. The output of the tuner 32 is band-limited by the filter 37 as shown in FIG. The carrier I ₁ obtained from the carrier recovery circuit 35 is ±
Carrier wave I ₂ obtained by 90 degree phase shift, to synchronous detection of band-limited signals in the multiplexed signal detector 39. The detection output becomes a multiplex signal. Even if the multiplex signal is a signal as shown in FIGS. 1 (c) and 1 (d), it can be similarly demodulated. Subcarrier I obtained from subcarrier recovery circuit 21
_{In step 3} , the demodulated multiplex signal is subjected to four-phase phase shift keying demodulation in a four-phase demodulator 20. The four-phase demodulator 20 may be another polyphase demodulator, frequency demodulator, or amplitude demodulator according to the transmitting side. The demodulated output becomes a digital signal and is output from the digital signal output terminal 22. In the above current receiver as mentioned, by synchronous detection by the video carrier I _1, since multiple signals are substantially canceled, interference due to multipath signal is hardly generated. In the receiver for multiplexed signal demodulation, not only the video baseband signal but also the filter operation and the video carrier
By synchronous detection by I _2, multiplexed signals can also be taken out without strain orthogonal. As is apparent from the above description, the television signal processing method of the present invention is a multiplexed signal obtained by modulating a subcarrier with a digital signal, and has the same frequency as the video carrier and a phase of 90%.
A carrier signal having different sidebands is amplitude-modulated in both sidebands, attenuated by half at the frequency of the video carrier, and converted into a residual sideband by a Nyquist filter having an odd-symmetrical amplitude characteristic with respect to the frequency of the video carrier. A large amount of digital signals can be multiplexed in the band of the current television system by superimposing the carrier wave in the band of the television signal subjected to the vestigial sideband amplitude modulation and transmitting and receiving. And, even when the signal is received by the current television receiver, there is almost no interference and there is compatibility. A dedicated receiver can extract a large amount of multiplexed digital signals,
It is very effective from the viewpoint of effective use of radio wave resources.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (a) is a spectrum diagram of a vestigial sideband amplitude-modulated television signal in a current television system according to an embodiment of the present invention, and FIG. 1 (b) is a subcarrier. FIG. 1 (c), FIG. 1 (d), and FIG. 1 (e) show a carrier wave having a phase different from that of a video carrier by ± 90 degrees by the multiplex signal. FIG. 1 (f) is a spectrum diagram in which the signal shown in FIG. 1 (e) is multiplexed with the signal shown in FIG. 1 (a), and FIG. 2 is an embodiment of the present invention. Block diagram showing a television signal processing method on the transmitting side in FIG.
3A and 3B are a spectrum diagram and a vector diagram at the time of demodulation of a multiplex signal, and FIG. 3C is a block diagram of a television receiver for demodulating a multiplex signal according to an embodiment of the present invention. FIG. 4 (a) is a block diagram of a current television receiver performing video synchronous detection, and FIGS. 4 (b) and 4 (c) are spectra of the current television receiver at the time of synchronous detection. Figure and vector diagram, Figure 5 is NT
FIG. 3 is a spectrum diagram showing an SC television signal on a two-dimensional plane of time frequency ₁ and vertical frequency ₂ . 5,38… Transfer device, 33,43… Video intermediate frequency filter, 8
... Second filter, 37 filter, 12 four-phase modulator, 20 four-phase demodulator.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hideshi Inoue               1006 Kadoma Kadoma Matsushita Electric Industrial               Inside the corporation (72) Inventor Hitoshi Takai               1006 Kadoma Kadoma Matsushita Electric Industrial               Inside the corporation (72) Inventor Koji Aono               2-10, Kotobukicho, Takamatsu               Industrial Co., Ltd.                (56) References JP-A-62-221286 (JP, A)

Claims (1)

(57) [Claims] A multiplexed signal obtained by modulating a subcarrier with a digital signal.
A carrier having the same frequency as the video carrier and a phase different by 90 degrees is amplitude modulated on both sides of the band, attenuated by half at the frequency of the video carrier, and retained by a Nyquist filter having an oddly symmetric amplitude characteristic with respect to the frequency of the video carrier. A television signal processing method for receiving a signal in which a signal in a sideband is superimposed in a band of a television signal obtained by modulating the video carrier with a residual sideband amplitude, comprising: The band is limited, and the output signal of the filter is synchronously detected with a carrier having a phase different from that of the reproduced video carrier by 90 degrees, the subcarrier is reproduced from the detected signal, and the digital signal is demodulated by digital demodulation. Characteristic television signal processing method.