JPH0691652B2 - TV signal transmission method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal transmission method for multiplex-transmitting another signal to a current television broadcast signal.

Conventional Technology Japan's current NTSC (National Television System Committee)
25 years have passed since color television broadcasting was started in 1960. Meanwhile, various new television systems have been proposed in response to the demand for high-definition screens and the improvement in performance of television receivers. In addition, the contents of the programs to be provided themselves are changing from simple studio programs and relay programs to programs with higher image quality and more realistic images, such as cinema-sized movie broadcasts.

Current broadcasts have specifications of 525 scanning lines, 2: 1 interlaced scanning, luminance signal horizontal bandwidth 4.2MHz, aspect ratio 4: 3 (for example, bibliographic broadcasting technology, bi-color television, edited by Japan Broadcasting Corporation, published by Nippon Broadcasting Corporation). Association, 1961), but under such a background, a television signal composition method has been proposed that is compatible with current broadcasting and expands the amount of transmitted information. An example will be described below.

A carrier wave of the same frequency as the carrier wave of the television signal, which is amplitude-modulated by the video baseband signal and a phase difference of 90 °, is subjected to double-sideband amplitude modulation by a multiplex signal different from the video baseband signal. It is characterized in that a Nyquist filter having a frequency characteristic opposite to the total frequency characteristic up to the video intermediate frequency amplification stage is used to form the residual sideband, and the carrier removed in the blanking period is superimposed.

Next, description will be given with reference to the drawings. FIG. 5 is a spectrum diagram showing a television signal transmission method on the transmitting side. Fifth
FIG. 1A is a spectrum diagram of a television signal that has been subjected to vestigial sideband amplitude modulation in the current television system.
Here, the case where the lower sideband of the image carrier P ₁ is the vestigial sideband is shown. Figure 5 (b) in another multiplex signal from the television signal shown in FIG. 5 (a), the picture carrier P ₁ and the same frequency at and phase 90 ° different carrier P _2, in the blanking period Double sideband amplitude modulation is performed so as to remove the carrier wave P ₂ . FIG. 5 (c) shows that the above-mentioned double sideband amplitude modulation is single sideband amplitude modulation. Fig. 5 (d)
Is a vestigial sideband amplitude modulation instead of the double sideband amplitude modulation described above. The signal of FIG. 5 (d) is shown in FIG. 5 (a).
FIG. 5 (e) shows a television signal to be combined, which is multiplexed with the television signal of FIG. In FIG. 5 (e), the signal to be multiplexed is the signal shown in FIG. 5 (d), but it may be the signal shown in FIGS. 5 (b) and 5 (c). The multiplexed signal is not limited to an analog signal and may be a digital signal.

FIG. 6 is a block diagram showing a television signal transmission method on the transmitting side. 601 is a video baseband signal input terminal, 602
Is an amplitude modulator, 603 is a first filter, 604 is an oscillator, and 605
Is a polyphase device, 606 is a multiple signal input terminal, 607 is a modulator, and 608
Is a second filter, 609 is an adder, and 610 is a composite television signal output terminal. Video baseband signal input terminal 60
An amplitude modulator 602 amplitude-modulates a carrier P ₁ obtained from an oscillator 604 with a video baseband signal input from 1. The obtained amplitude-modulated wave is band-limited by the first filter 603 to form the residual sideband, and then added to the adder 609. Oscillator 604
The carrier P ₁ obtained from the above is phase-shifted by 90 ° by the phase shifter 605 and is referred to as carrier P ₂ . Multiple signal input terminal 606
The carrier wave P ₂ is subjected to double sideband amplitude modulation by the multiplex signal inputted from and carrier removal double sideband amplitude modulation is carried out in the blanking period. The modulated signal is band-limited by the second filter 608 and then added to the adder 609. The output of the adder 609 becomes the composite television signal. That is, the multiplexed signal is superimposed on the video baseband signal to form a composite television signal. It should be noted that due to the frequency characteristic of the second filter 608, the multiplexed signal is the fifth signal.
The signal has a band as shown in FIGS. 5 (b), 5 (c) and 5 (d).

Next, a television signal transmission method on the receiving side will be described.
In the following, the case of terrestrial broadcasting will be taken as an example. FIG. 9 is a block diagram of a current television receiver which performs video synchronous detection. Reference numeral 941 is an antenna, 942 is a tuner, 943 is a video intermediate frequency filter, 944 is a video detector, 945 is a carrier wave reproduction circuit, and 946 is a video baseband signal output terminal. The signal transmitted from the transmission side is received by the antenna 941, frequency-converted to the intermediate frequency band by the tuner 942, and band-limited by the video intermediate frequency filter 943. The band-limited signal is supplied to the video right wave device 944 and the carrier wave reproduction circuit 945. In the carrier recovery circuit 945, the carrier I for synchronous detection is
Play ₁ The band-limited signal is detected by the video detector 944 with the carrier I ₁ and becomes a video baseband signal. Here, the frequency characteristics of the video intermediate frequency filter 943 will be described. The frequency characteristic is shown in FIG. 10 (a). That is, the amplitude at the image carrier I ₁
The Nyquist filter characteristic is such that it is attenuated by 6 dB and has an amplitude characteristic that is almost odd symmetrical with respect to the image carrier I ₁ . On the other hand, as shown in FIG. 5 (d), if the multiplexed signal is band-limited by a filter having a characteristic opposite to the frequency characteristic of the video intermediate frequency filter of the receiver, the shaded area in FIG. 10 (a) is obtained. The multiple signal component of is almost a double sideband. A vector display of this is as shown in FIG. 10 (b). here
I ₁ is a video carrier of the video baseband signal, I ₂ is a carrier of a multiplexed signal, which is a carrier having the same frequency as I ₁ but a phase difference of 90 °. The video baseband signal is a vestigial sideband when the carrier I ₁ is considered as the center, so the upper and lower sidebands become vector a _U and vector a _L , and when decomposed into orthogonal vectors, they become vector a ₁ and vector a _2. . Also, since the multiplexed signal has almost double sidebands, if the upper and lower sidebands are vector b _U and vector b _L , they are the combined vector b ₂
Only the component orthogonal to I ₁ . That is, when the coherent detection is performed on the carrier I ₁ , orthogonal distortion due to the vector a ₂ and vector b ₂ components does not occur, and the interference by the multiple signal to the current television receiver performing the video coherent detection does not occur in principle. When the signal to be multiplexed is a signal as shown in FIG. 5 (b), since it does not become a double sideband when band-limited by the video intermediate frequency filter 943, orthogonal distortion may occur. However, for example, if the level is lowered and multiplexed, the interference given to the current television receiver is reduced. The same applies to the case where the signal to be multiplexed is a signal as shown in FIG. 5 (c), but the degree of interference is further reduced due to the spectrum.

Next, a method of demodulating multiple signals on the receiving side will be described. A signal in the video intermediate frequency band, which is the output of the tuner, is band-limited by a filter so that the video baseband signal becomes a double sideband as shown in FIG. When this is displayed as a vector, it becomes as shown in FIG. 7 (b). Since the multiplexed signal has vestigial sidebands when the carrier I ₂ is considered as the center, the upper and lower sidebands become vectors b _U and b _L , and when decomposed into orthogonal vectors, they become vectors b ₁ and b ₂ . Also, since the video baseband signal becomes almost double sideband due to the filter,
If the upper and lower sidebands are the vector a _U and the vector a _L , they are the combined vector a ₁ and only the component orthogonal to the vector I ₂ . That is, when synchronous detection is performed on carrier I ₂ , the vector
Orthogonal distortion due to the a ₁ and vector b ₁ components does not occur, and only the multiple signal components can be demodulated. FIG. 8 is an example of a block diagram of a television receiver that demodulates multiple signals. 831 is an antenna, 832 is a tuner, 833 is a video intermediate frequency filter, 834 is a video detector, 835 is a carrier reproduction circuit, 836 is a video baseband signal output terminal, 837 is a filter, 838 is a phase shifter, and 839 is a multiplex signal. A detector and 840 are multiple signal output terminals. The signal transmitted from the transmission side is received by the antenna 831, frequency-converted to the intermediate frequency band by the tuner 832, and band-limited by the video intermediate frequency filter 833. The band-limited signal is supplied to the video detector 834 and the carrier wave reproduction circuit 835. The carrier recovery circuit 835 reproduces the carrier I ₁ for synchronous detection. The band-limited signal is
The carrier wave I ₁ is detected by the video detector 834 and becomes a video baseband signal. The output of the tuner 832 is band-limited by the filter 837 as shown in FIG. The carrier I ₁ obtained from carrier recovery circuit 835 in the phase shifter 838 by a carrier I ₂ obtained by 90 degree phase shift, synchronous detection in a multiplex signal detector 839 the band-limited signal. The detection output becomes a multiplexed signal. Even if the multiplexed signal is a signal as shown in FIGS. 5 (b) and 5 (c), it can be demodulated in the same manner. Also, instead of the filter 837, the multiple signal detector 8
After 39, a filter having the same characteristics as the filter 837 in the equivalent low-pass system may be inserted.

As described above, in the current receiver, since the multiplexed signal is almost canceled by the synchronous detection with the image carrier I ₁ , the interference by the multiplexed signal hardly occurs. Also, in the receiver for demodulating multiple signals, not only the video baseband signal but also the filtering and the video carrier as in the above processing.
By performing synchronous detection with I ₂ , multiple signals can be extracted without orthogonal distortion.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above method, when multipath propagation, so-called ghost exists, crosstalk occurs between the current video baseband signal which is the main signal and the multiplex signal which is the sub signal. Occurs and each signal is significantly disturbed.

In view of the above problems, the present invention provides a television signal transmission method capable of transmitting high-quality video signals and multiplex signals even in the presence of a ghost.

Means for Solving the Problems In order to solve the above problems, in the television signal transmission method of the present invention, known reference signals are inserted into the video signal and the multiplexed signal in advance, and the receiving side Passes two demodulated signals, which are separated and demodulated by synchronous detection with two orthogonal detection phases, through two delay lines with taps, and uses the received reference signal to output each delayed signal. An appropriate weight is set and combined. A two-dimensional transversal filter is used.

Effect The present invention uses the above-described two-dimensional transversal filter, and optimizes the tap coefficient of the two-dimensional transversal filter based on the reference signal inserted on the transmission side, thereby performing multipath propagation. By implementing a filter having characteristics opposite to the transmission characteristics of a transmission line in which a so-called ghost exists, high-quality video signals and multiplexed signals can be taken out even in the presence of ghosts, and crosstalk between both signals can be reduced.

Embodiment A television signal transmission method according to an embodiment of the present invention will be described below.
A description will be given with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a transmission device of a television signal transmission method according to an embodiment of the present invention. In FIG.
101 is a video baseband signal input terminal, 102 is a multiple signal input terminal, 103 and 104 are reference signal inserters, 105 is a reference signal generator, 106 is a modulator, 107 is a transmission system, 108 is a demodulator, 1
09 is a ghost elimination device, 1 is a video baseband signal output terminal, and 2 is a multiplex signal output terminal. Hereinafter, the transmission apparatus of the television signal transmission method according to the embodiment of the present invention will be described with reference to FIG.

In the video baseband signal and the multiplexed signal input from the video baseband signal input terminal 101 and the multiplexed signal input terminal 102, the reference signal for ghost removal generated by the reference signal generator 105 is the reference signal inserter. It is added in the vertical blanking interval via 103 or 104. As the reference signal waveform, various waveforms such as pulse waveforms, step waveforms, sinx / x waveforms, and combination waveforms thereof as shown in FIGS. 2 (a) to (d) can be considered. It is necessary to sufficiently include the frequency component within the band. The reference signal waveforms added to the video baseband signal and the multiplexed signal may be the same or different.

The video baseband signal and the multiplexed signal to which the reference signal for removing the ghost is added are orthogonally modulated by the modulator 106. The internal structure of the modulator 106 is the same as that shown in FIG. 6, and the description of the operation is omitted. Transmission system
Consider a high-frequency circuit necessary for various transmissions such as a tuner and an amplifier in 107. In the transmission system 107, so-called linear distortion such as group delay distortion and frequency / amplitude characteristic distortion occurs due to multipath propagation or an intermediate amplifier. In this way, the received signal accompanied by ghost or linear distortion is subjected to quadrature synchronous detection by the demodulator 108, and separated and demodulated into a video baseband signal and a multiplex signal. Demodulator 10
The internal structure of 8 is the same as that shown in FIG. 8, and the description of the operation is omitted.

The video baseband signal and the multiplexed signal which are the output signals of the demodulator 108 include the ghost component and the crosstalk component of each signal. In the ghost elimination device 109, the modulator 106, based on the reference signal inserted on the transmission side,
A filter having the inverse characteristics of the characteristics when the transmission system 107 and the demodulator 108 are regarded as one filter is realized, and the ghost component and the crosstalk component are removed. Modulator 106, transmission system 107,
Since the series of signal processing of the demodulator 108 is a linear operation,
There is a filter having a linear inverse characteristic, and it can be approximately realized by using a two-dimensional transversal filter using a two-line tapped delay line. An example of the internal configuration of the ghost removing device 109 is shown in FIG.

FIG. 3 shows a circuit configuration diagram of the ghost removing device 109. In FIG. 3, 1 is a video baseband signal output terminal, 2 is a multiplex signal output terminal, 3 is a video baseband output input terminal, 4 is a multiplex signal input terminal, 301 is a two-dimensional transversal filter, and 302 is a tap coefficient correction. Arithmetic circuits, 303 and 304 are subtractors, and 305 is a reference signal generator. Two-dimensional transversal filter 301
FIG. 4 shows the internal structure of the.

FIG. 4 shows a circuit configuration diagram of the two-dimensional transversal filter 301. In FIG. 4, 1 is a video baseband signal output terminal, 2 is a multiplex signal output terminal, 3
Is a video baseband signal input terminal, 4 is a multiplex signal input terminal, 401 to 416 are multipliers, 417 to 420 are sign invertors, and 421 to 4
26 is a delay device having a delay time T, 427 to 434 are tap coefficient holders, 435 is a tap coefficient writing terminal, and 436 and 437 are adders.

Hereinafter, the ghost removing device 10 will be described with reference to FIGS. 3 and 4.
The operation of 9 will be described.

As described above, since the modulator 106 is basically a quadrature modulator, while the demodulator 108 is a two-axis coaxial detector that is orthogonal to each other, the modulator 106, the transmission system 107, and the demodulator 108 are connected in series. The signal processing of is a linear operation. That is, the modulator 106 sends out a signal having a complex envelope in which both input signals are the real part and the imaginary part, and the demodulator 108 performs an operation of extracting the complex envelope of the received signal. For example, xn = an + jbn (1) where the sampled value sequences of the reference signals inserted into the video baseband signal and the multiplexed signal, which are the respective input signals of the modulator 106, at each time T are ann and bn, respectively. Defining the complex envelope xn of the modulated wave, modulator 106
Since there is a linear characteristic from to demodulator 108, its impulse response hn is represented by a complex number. Therefore, the output signals of the demodulator 108 corresponding to the reference signals an and bn, that is, the signals at the video baseband signal input terminal 3 and the multiplex signal input terminal 4 in FIG.
Let βn and define a complex signal sequence yn such that yn = αn + jβn (2) Can be expressed as

On the other hand, a two-dimensional transversal filter with yn as input
The output signal of 301, that is, the signals at the video baseband signal output terminal 1 and the multiplex signal output terminal 2 in FIG. 3 or 4 are similarly An and Bn, respectively, and a complex signal zn = An + jBn (4) define the column zn, the tap coefficients c _R i of the two-dimensional transversal filter 301 of FIG. _{4, c I i (i = -N~N} ) a _{ci = c R i + jc I} i ...... (5) becomes a complex tap If defined as the coefficient ci, zn is However, Ct = _{[c - n ...... c O ...... c} N ] Ytn = [yn _{+ N} ...... yn ...... yn _-N] t indicates a transposed matrix.

Can be expressed as On the other hand, from equations (3) and (6), However, The impulse response sequence sn is composed of a modulator 106, a transmission system 107, and a demodulator 10.
8, 2D transversal filter 301 is the overall impulse response. If the number of taps 2N + 1 is infinitely large, The ghost in the transmission system 107 and the linear distortion in the modulator 106 and the demodulator 108 can be completely equalized by the two-dimensional transversal filter 301, and ghost and crosstalk can be eliminated. In reality, the number of taps is finite, and the conditions of Eqs. (9) and (10) are not completely satisfied, but an evaluation function that evaluates the closeness to this condition should be set to minimize it. The complex tap coefficient ci is selected optimally by.

The method for optimizing the complex tap coefficient ci can be roughly classified into a sequential method and a non-sequential method. An example of the former method will be shown. Zero Forcing (Ze
ro Forcing method, Mean Squer
are Error) methods and combinations thereof.
In the following, Mean Square Er
An example of the ror) method will be described.

In the mean square error method, the following evaluation function E is used.

Here, the complex signal sequence rn is the reference signal generator 305 on the receiving side.
It is a signal sequence having a reference signal sequence for the video baseband signal and a reference signal sequence for the multiplex signal generated in 1. in the real part and the imaginary part, respectively. The complex signal sequence rn is matched with the complex signal sequence xn generated by the reference signal generator 105 on the transmission side. Therefore,
Equation (1) represents the sum of squares of the error εn at each sample point, and the squared error E is minimized by the steepest descent method. That is, the tap coefficient after the k-th correction is And complex tap coefficient defined by equation (5) given that, The square error E, which is an evaluation function, is minimized by correcting the tap coefficient successively so that Note that * represents a complex conjugate, Paying attention to the relationship of, the expressions (12) and (13) are combined into one expression, and the expression (11) is used to Equation (14) is obtained. On the other hand, using equations (6) and (11) So in practice You can fix it like this.

In FIG. 3, the tap coefficient correction calculation circuit 302 uses an error signal εn obtained by subtracting the reference signal rn from the output signal zn of the two-dimensional transversal filter 301 using the calculators 303 to 304 and the reference signal generator 305. The input signal yn of the two-dimensional transversal filter 301 is input. The tap coefficient correction operation circuit 302 performs the operation represented by the equation (16) to correct the tap coefficient of the two-dimensional transversal filter 301. By repeating this operation, the tap coefficient c _R i, c _I i is optimized. Converge to values and reduce ghost and crosstalk.

EFFECTS OF THE INVENTION As described above, in the television signal transmission method of the present invention, known reference signals are inserted in advance in the video signal and the multiplexed signal, respectively, and on the receiving side, synchronous detection is performed with orthogonal two-axis detection phases. The two demodulated signals separated and demodulated by the above are passed through two delay lines with taps, and the delayed signals are combined with appropriate weights determined by using the received reference signal. By using a two-dimensional transversal filter, multipath propagation, that is, a filter having a characteristic opposite to the transmission characteristic of a transmission line having a so-called ghost, is realized, two demodulated signals that have been distorted are equalized, and a ghost exists. Also in the lower part, it is possible to take out a good quality video signal and multiplex signal, and it is possible to reduce crosstalk between both signals.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a transmission device of a television signal transmission method in one embodiment of the present invention, and FIGS. 2 (a), (b),
(C) and (d) are waveform diagrams of reference signals generated by the reference signal generator of FIG. 1 and the reference signal generator of FIG. 3, and FIG. 3 is a circuit configuration of an example of the ghost elimination device of FIG. Figure, 4th
The figure is a circuit configuration diagram of an example of the two-dimensional transversal filter of FIG. 3, and FIGS. 5 (a), (b), (c), (d),
(E) and FIG. 6 are respectively a spectrum diagram and a block diagram on the transmitting side in one embodiment of the conventional television signal transmission method, and FIGS. 7 (a), (b) and FIG. 8 are, respectively. Spectrum diagram and block diagram on the receiving side in one embodiment of the conventional television signal transmission method, FIG. 9 and FIG.
(A) and (b) are a block diagram and a spectrum diagram of a current television receiver in a conventional television signal transmission method, respectively. 1 ... video baseband signal output terminal, 2 ... multiplex signal output terminal, 3,101 ... video baseband signal input terminal,
4,102 ...... Multiple signal input terminal, 103,104 …… Reference signal inserter, 105,305 …… Reference signal generator, 106 …… Modulator, 107
...... Transmission system, 108 …… Demodulator, 109 …… Ghost eliminator, 301 …… Two-dimensional transversal filter, 302 ……
Tap coefficient correction arithmetic circuit, 303, 304 ... Subtractor, 401 to 41
6 ... Multiplier, 417-420 ... Sign inverter, 421-426 ...
Delay device, 427 to 434 ... Tap coefficient holder, 435 ... Tap coefficient writing terminal.

Claims (3)

[Claims] 1. A vestigial sideband of a vestigial sideband amplitude-modulated video signal, or a band symmetrical to the vestigial sideband with respect to a frequency of a carrier of the vestigial sideband amplitude modulation, or within both bands. In a television signal transmission system in which a transmission signal is a signal obtained by superimposing a signal obtained by modulating a carrier wave having the same frequency as the carrier wave but having a phase difference of 90 ° with a multiplexed signal different from the video signal, A known reference signal is inserted in each of the multiplexed signals, and on the receiving side, two demodulated signals separated and demodulated by synchronous detection with orthogonal two-axis detection phases are input to two delay lines with taps. Through the baseband signal of the video signal by combining the respective delayed signals with appropriate weights determined by using the received reference signal. TV signal transmission method characterized by retrieving the multiplexed signal. 2. A signal modulated by a multiplex signal is double sideband amplitude modulated by the multiplex signal and attenuated by half at a carrier frequency,
The television signal transmission method according to claim (1), characterized in that the signal has a vestigial sideband by a Nyquist filter having an amplitude characteristic that is oddly symmetrical with respect to the carrier frequency. 3. The television signal transmission method according to claim 1, wherein the signal modulated by the multiplex signal is a signal from which a carrier wave is removed in a blanking period.