JPH0722387B2 - Signal multiplexing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a signal multiplexing method in a video transmission system that employs a vestigial sideband transmission method.

2. Description of the Related Art In recent years, it has become popular to multiplex various kinds of information on a television signal or the like to provide more advanced services. Text-multiplexed broadcasting is one example, but it is necessary to multiplex various signals with television signals even in urban CATV and the like.

There are roughly two types of conventional multiplexing methods.
There are a time multiplex system such as a character multiplex broadcast in which information is superimposed on a synchronization signal section, or a frequency multiplex system widely used in CATV and the like.

FIG. 9 shows a circuit configuration diagram of character multiplex broadcasting as an example of the time multiplex system. 2 is a video signal input terminal,
91 is a character signal superimposing device, 92 is a waveform shaping filter, 93 is a character signal (sub signal) input terminal, 1 is a carrier wave input terminal, 3 is an amplitude modulator, and 11 is a vestigial sideband filter.
98 is configured, and 12 is a transmission line. A demodulation system 99 is composed of a wave detector 95, a video signal output terminal 17, a sync separator 95, a character signal extractor 96, and a character signal (sub-signal) output terminal 97. In the transmission system 98, the sub-signal is burst-multiplexed in the vertical blanking interval by the character signal superposer 91. In the demodulation system 99, after being detected by the wave detector 94, the sync signal is separated by the sync separator 95, and the sub-signal is separated by the character signal extractor 96 based on this sync signal (for example, "Broadcasting Technology" VOL. 36.No.10.PP.105 ~ PP.111).

Frequency multiplexing is often used in urban CATV, but a data transmission band is provided separately from the video signal band (for example, National Technical Report VOL.30.No.1.P.
P.61 ~ PP.70).

In addition, for the purpose of scrambling, a descramble pulse may be amplitude-modulated and superimposed on a voice carrier. FIG. 10 is a waveform diagram explaining this method. In FIG. 10, the scrambled video signal raises the level of the sync signal portion, and the sync signal is embedded in the video signal level, whereby the sync concealment is performed. At the time of descrambling, the envelope of the audio carrier wave is detected, a certain offset (time delay) is given, and then the video signal level is lowered to recover the synchronization signal. The confidentiality is improved by changing the offset amount from time to time (for example, IEEE Trans.VOL.CE-30.No.3.Aug.
1984 PP.499 to PP.500).

Problems to be Solved by the Invention All of the conventional methods have complicated configurations (especially demodulation systems), and in the case of the frequency multiplexing method, extra spectrum is consumed, which is not preferable in terms of spectrum utilization efficiency. Also, when amplitude modulation is applied to the audio carrier wave and superimposed, crosstalk with the video signal, and when the audio signal is already multiplexed such as stereo broadcasting, interference is caused by amplitude-phase conversion (AM-PM conversion). Sometimes.

In view of the above problems, the present invention provides a signal multiplexing method that is simple in structure, increases the occupied spectrum, and multiplexes sub-signals without degrading video signals and audio signals. .

Means for Solving the Problems In order to solve the above problems, in the transmitting side, in the vestigial sideband band of the vestigial sideband amplitude modulated television signal, and the carrier of the vestigial sideband amplitude modulation In a band symmetrical to the vestigial sideband band with respect to the frequency of, the same frequency as the carrier of the vestigial sideband amplitude modulation and phase 90
° Using different signals as sub-carriers, superimposing a double sideband signal obtained by subjecting the sub-carriers to spread-amplitude modulation of the sub-carriers with a sub-signal that has been spectrum spread by pseudo noise
On the receiving side, the frequency spectrum of the double sideband signal is held symmetrically with respect to the frequency of the carrier of the vestigial sideband amplitude modulation, and the carrier wave of the vestigial sideband amplitude modulation is used for quadrature using the regenerated carrier. It is characterized in that the spectrum-spread sub-signal is separated by performing detection.

Action The present invention does not increase the occupied spectrum because the video and sub-signals are multiplexed on the orthogonal modulation axes as described above. Further, by using the synchronous detection, the signals can be easily separated and the configuration is simplified.

However, in general, when such a quadrature modulation method is applied to the vestigial sideband transmission method, the vestigial sideband filter restricts the sidebands asymmetrically, resulting in so-called quadrature distortion, which causes interference between both signals. Cause

Therefore, in the present invention, the cross-talk between the sub-signal and the video signal is reduced by inserting a spread spectrum sub-signal having a narrow spectrum such that both sidebands are symmetrically transmitted at a low level. . Furthermore, in principle, it is possible to completely separate the video signal and the spread spectrum sub-signal by performing quadrature synchronous detection on the receiving side without using the Nyquist filter.

This is because if the vestigial sideband filter removes the frequency component above the frequency fc on one side, the frequency component of the spectrum-spread sub-signal has only the component below fc. Therefore, the spectrum-spread sub-signal is input to the quadrature synchronous detector without any band limitation on both sidebands, so if the carrier is completely reproduced on the receiving side, the sub-signal Does not interfere with the video signal. In addition, the video signal after the vestigial sideband amplitude modulation is
The vestigial sideband filter asymmetrically limits the band, which causes so-called orthogonal distortion and gives a disturbing component on the modulation axis of the orthogonal sub-signal.This disturbing component is a frequency component of fc or higher, and After detection, the sub-signal filter (low-pass filter) extracts only the frequency component of fc or less, so that only the sub-signal can be completely extracted.

Regeneration of the carrier wave on the receiving side is performed with reference to the high-level carrier wave for the video signal (this carrier wave is transmitted without being suppressed), and further, the sub-signal is spectrum-spread and carrier-removing amplitude modulation is performed. Since the DC component of the quadrature modulation axis is reduced by, it is extremely easy. if,
Even if the detection phase is slightly deviated, the spectrum-spread sub-signal has a low power density, so there is little interference with the video signal, and conversely, interference from the video signal to the sub-signal occurs during the despreading process. Effectively eliminated. There are other advantages to using spread spectrum techniques. It is possible to perform code multiplexing by maintaining confidentiality and using multiple pseudo-noises that have small correlation with each other for the pseudo-noise used for spreading, and by utilizing the sharp time separation characteristic, it is possible to propagate multiple waves and echo. On the other hand, it is possible to obtain good characteristics.

Example Hereinafter, a signal multiplexing method according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a transmission device to which the signal multiplexing method according to the first embodiment of the present invention is applied. First
In the figure, 1 is a carrier wave input terminal, 2 is a video signal input terminal, 3 is an amplitude modulator, 4 is a 90 ° phase shifter, 5 and 109 are multipliers, 6 is a sub-signal band limiting filter, and 7 is pseudo noise generation. , 8 is a sub-signal input terminal, 10 is a multiplexer, and 11 is a vestigial sideband filter, which constitute the transmission system 100. 1
2 is a transmission line. 13, 18 and 22 are multipliers, 14 is a video signal filter, 15 is a 90 ° phase shifter, 16 is a reproduction carrier input terminal,
17 is a video signal output terminal, 19 is a sub-signal filter, 23 is a reproduction pseudo noise generator, and 24 is a low-pass filter (LPF in the figure).
, 123 is a sub-signal output terminal, and these constitute the demodulation system 101.

Regarding the transmission device configured as described above, the second
The operation will be described with reference to FIGS. 3, 3 and 4.

In the transmission system 100, the carrier wave is first divided into two systems,
The phase of one of them is shifted by 90 ° by the phase shifter 4. The two orthogonal carrier waves undergo amplitude modulation by the amplitude modulator 3 and the multiplier 5 by the video signal and the spectrum-spread sub-signal, respectively, and are combined by the multiplexer 10. The quadrature-modulated wave is transmitted by removing a part of the sideband by the residual sideband filter 11.

The pseudo noise generator 7 is a pseudo noise generator for spectrum-spreading the sub-signal, but in other words, it is a generator of a certain code sequence. As the code sequence, various types such as the longest linear code (m sequence) and the Gold code have been proposed, and as an example of the pseudo noise generator 7 in FIG.
An example of a circuit configuration diagram of 7-stage m-series is shown. In FIG. 2, 201 to 207 are shift registers (abbreviated as SR in the figure),
Reference numeral 208 is an exclusive OR, 209 is a shift register driving clock input terminal, and 210 is a pseudo noise output terminal. The pseudo noise band is selected to be much wider than that of the side signal.

FIG. 3 shows a frequency characteristic diagram of the vestigial sideband filter 11, and FIG. 4 shows a spectrum diagram when a carrier is modulated by a sub-signal which has been spectrally spread and further has passed through a band limiting filter. However, _O is a carrier frequency. In this way, the spectrum of the sub-signal system is band-limited so that both side bands pass, thereby reducing crosstalk between the sub-signal and the video signal.

In the demodulation system 101 of FIG. 1, the phase-locked regenerated carrier wave that is phase-locked with the modulation axis of the sub-signal is phase-shifted by the phase shifter 15 and the multiplier 13,
If the video signal filter 14 performs synchronous detection, the video signal is demodulated. The demodulation of the sub-signal may be performed in the reverse procedure of the transmission process. First, the multiplier 18 and the sub-signal filter 19 are used by using the reproduced carrier wave that is phase-locked to the sub-signal.
If the synchronous detection is performed with, the spread spectrum sub-signal is separated and detected. Further, the pseudo noise having the same code sequence as that of the transmission system and having the same phase is reproduced by the reproduction pseudo noise generator 23, and the multiplier 22 and the low-pass filter 24 perform correlation detection to demodulate the sub-signal. Note that the carrier is not suppressed in the video signal modulation, but is suppressed in the sub-signal modulation, so it is easy to configure it by configuring a phase-locked loop (PLL) that locks to the phase of the former carrier. A reproduced carrier wave can be obtained. In addition, to reproduce pseudo noise, a kind of phase locked loop such as tau dither loop and delay locked loop (DL
L) etc. can be used (For a series of spread spectrum technology, see "CD Spread Communication System" by RCDixon).

FIG. 5 is a block diagram of a transmission device to which the signal multiplexing method according to the second embodiment of the present invention is applied. In this embodiment, the video signal is not provided with the synchronization information, but the sub-signal is provided with the information, so that the scrambling effect is provided.

In the figure, 1 is a carrier input terminal, 3 is an amplitude modulator,
4 is a 90 ° phase shifter, 5 is a multiplier, 10 is a multiplexer, 11 is a vestigial sideband filter, 6 is a sub-signal band limiting filter, 7 is a pseudo noise generator, and the above is the transmission of FIG. It is similar to system 100. In the transmission system 500 of FIG. 5, the difference from that of FIG. 1 is that 2 is a video signal input terminal having no synchronization information, 58 is a vertical synchronization signal input terminal as a sub signal, and a multiplier. Instead of, 25 exclusive OR circuits are used, and 26 drive clock input terminals are added.
The transmission system 500 is configured as described above. The 12 transmission lines are the same as those in FIG.

Further, the multipliers 13 and 18, the 90 ° phase shifter 15, the video signal filter 14 and the sub-signal filter 16 at the reproduction carrier input terminal 19 are the same as those of the demodulation system 101 in FIG. . The demodulation system of FIG. 5 differs from that of FIG. 1 in that 17 is a video signal output terminal having no synchronization information, a delay line matched filter 20 is used for demodulating a spread spectrum side signal, and 21 is a synchronization signal. It is a signal output terminal. The demodulation system 501 is configured as described above.

In the transmission system 500 of FIG. 5, the vertical synchronization signal is spectrum-spread by the pseudo noise generated by the pseudo noise generator 7. On the other hand, the horizontal synchronization information is superimposed on the period of pseudo noise. That is, although pseudo noise is a code sequence, if the code length is n and the horizontal synchronization frequency is _H , the pseudo noise generator driving clock frequency is selected to be _H × n, and the pseudo noise period and horizontal The synchronization cycle matches.

In the demodulation system 501 of FIG. 5, as in the first embodiment, the spread carrier sync signal is separated by performing synchronous detection by the reproduced carrier wave, the multiplier 18, and the auxiliary signal filter 19. Then, the synchronization signal is extracted by using the delay line matched filter 20 that matches the transmission pseudo noise.

The delay line matched filter 20 is constructed, for example, as shown in FIG. 601 to 607 are delay elements (abbreviated as T in the figure)
The signal propagates from left to right. 608 and 609 are adders (abbreviated as Σ in the figure), 610 are subtractors (abbreviated as − in the figure), 6
11 is an input terminal and 612 is an output terminal. The delay line matched filter is configured to identify code sequences, and also only certain code sequences. Assuming that the delay time of each delay element is equal to the clock period of the target code, the second bit is 60 when the first bit of the code is 607.
The sixth and third bits are at 605 and so on. If [0100111], which is a code string matching this filter, is input, the polarities of all the codes are matched and added, so that the maximum output is obtained. FIG. 7 is a waveform diagram of input and output of this filter.

As in the above example, a sharp pulse appears at the synchronizing signal output terminal 21 in FIG. 5 at every horizontal synchronizing cycle. Further, in the vertical blanking interval, the code sequence is inverted by the exclusive OR circuit 25, so that the pulse appears in the opposite direction. In this way, on the receiving side, the horizontal sync signal is reproduced by this pulse, and the vertical sync signal is reproduced by the polarity of the pulse. It should be noted that the scramble effect can be enhanced by changing the pseudo noise sequence as needed or changing the offset (offset) between the demodulation pulse position and the horizontal sync pulse position to be reproduced. It should be noted that, as in the first embodiment, a delay locked loop or the like can be used to reproduce the sync signal.

FIG. 8 is a circuit configuration diagram of a transmission device to which the signal multiplexing method according to the third embodiment of the present invention is applied. 1 is a carrier wave input terminal, 2 is a video signal input terminal without synchronization information, 3 is an amplitude modulator, 4 and 15 are 90 ° phase shifters, 5 and 13 and 18 are multipliers, 10 is a multiplexer, 11 Is a residual sideband filter, 6 is a sub-signal band limiting filter, 25 is an exclusive OR circuit, 58 is a vertical sync signal input terminal, 7 is a pseudo noise generator, 26 is a drive clock input terminal, and 12 is a transmission line. , 14 are video signal filters,
Reference numeral 17 is a video signal output terminal without synchronization information, 16 is a reproduction carrier input terminal, 19 is a sub signal filter, 20 is a delay line matching filter, 21 is a synchronization signal output terminal, and the above is the same as the configuration of FIG. belongs to. The difference from the configuration of FIG. 5 is that a pseudo noise generator 84 of a series different from that of the pseudo noise generator 7 is provided and the control signals are code-multiplexed. Accordingly, the exclusive OR circuit of 83, the sub-signal band limiting filter of 82, the multiplexer of 81, the control signal input terminal of 85, the multiplier of 22, the reproduced pseudo noise generator of 23, the low-pass filter of 24 ( (Abbreviated as LPF in the figure), 86 control signal output terminals are added. The pseudo noise sequence generated by the pseudo noise generator 7 matches the delay line matching filter 20, and the pseudo noise generators 84 and 23 generate pseudo noise having the same code sequence.

Code multiplexing can be performed in this manner by selecting a code string so that the cross-correlation of the code sequences generated by the pseudo noise generators 7 and 84 becomes small. In this embodiment, an example of multiplexing two sub-signals is shown, but it is also possible to multiplex more sub-signals by preparing more pseudo noise. Also, a method using a delay line matched filter for demodulating the synchronizing signal and a method for reproducing the pseudo noise and despreading using a delay locked loop for demodulating the control signal are illustrated, but either one is the same method. Alternatively, the demodulation may be performed using the opposite methods. Note that it is conceivable to carry more advanced information on the control signal in addition to the pseudo noise change, the offset, etc. as described in the second embodiment.

In any of the first, second and third embodiments, the phase shifter 4 may be placed after the multiplier 5 or before or after the amplitude modulator 3, or At the same time, it may be provided in a plurality of places, and as a result, they may be combined by the multiplexer 10 with a 90 ° phase difference. However, accordingly, the phase shift amount of the phase shifter and the phase of the reproduced carrier wave added to the multiplier 13 or the multiplier 18 must be selected optimally.

EFFECTS OF THE INVENTION As described above, the signal multiplexing method according to the present invention is applied to the vestigial side with respect to the vestigial sideband band of a vestigial sideband amplitude-modulated television signal and the carrier frequency of the vestigial sideband amplitude modulation. A subcarrier of a signal having the same frequency as the carrier of the vestigial sideband amplitude modulation and having a phase difference of 90 ° in a band symmetrical to the waveband, and the subcarrier is spread by a subsignal spread by pseudo noise. By superimposing the double sideband signals obtained by carrier removal amplitude modulation, the configuration is simple without increasing the occupied spectrum, there is no crosstalk between the video signal and the sub signal, or the crosstalk characteristics are good. Various signal multiplexing becomes possible.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a transmission device to which the signal multiplexing method according to the first embodiment of the present invention is applied, FIG. 2 is a circuit configuration diagram of an example of the pseudo noise generator 7 of FIG. 1, and FIG. FIG. 4 is a frequency characteristic diagram of the vestigial sideband filter 11, FIG. 4 is a spectrum diagram when an orthogonal carrier wave is modulated by a sub signal, and FIG. 5 is a transmission device to which the signal multiplexing method according to the second embodiment of the present invention is applied. 6 is a circuit configuration diagram of an example of the delay line matching filter 20 of FIG. 5 and an input / output waveform diagram, and FIG. 8 is a signal diagram of a third embodiment of the present invention. FIG. 9 is a circuit configuration diagram of a character multiplex broadcasting as an example of a conventional signal multiplexing method, and FIG. 10 is a scramble waveform diagram as an example of a conventional signal multiplexing method. Is. 1 ... Carrier wave input terminal, 2 ... Video signal input terminal, 3 ...
… Amplitude modulator, 4,15… 90 ° phase shifter, 5,13,18,22,109…
… Multiplier, 10, 81 …… Adder, 11 …… Remaining sideband filter, 6, 82 …… Sub signal band limiting filter, 8 …… Sub signal input terminal, 58 …… Vertical sync signal input terminal, 7 , 84 ... Pseudo noise generator, 25, 83 ... Exclusive OR circuit, 12 ... Transmission line, 85 ... Control signal input terminal, 14 ... Video signal filter, 17 ... Video signal output terminal, 19 ... Sub signal filter, 20 ... Delay line matching filter, 21 ... Synchronous signal output terminal, 23 ... Reproduction pseudo noise generator, 24 ... Low pass filter (LPF), 86 ... Control signal output terminal, 123 …… Sub signal output terminal.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 7/081 7/167 7251-5C H04N 7/167

Claims (3)

[Claims] 1. A transmitting side is symmetrical with respect to the vestigial sideband band in the vestigial sideband band of a vestigial sideband amplitude-modulated television signal and with respect to the frequency of a carrier wave of the vestigial sideband amplitude modulation. Within the band, a signal having the same frequency as the carrier of the vestigial sideband amplitude modulation and having a phase difference of 90 ° is used as the subcarrier, and the subcarrier is amplitude-modulated by removing the carrier with the subsignal spectrally spread by pseudo noise. By superimposing the double sideband signal obtained by
By holding the frequency spectrum of the double sideband signal symmetrically with respect to the frequency of the carrier of the vestigial sideband amplitude modulation, by performing quadrature detection using the regenerated carrier phase-locked to the carrier of the vestigial sideband amplitude modulation. A signal multiplexing method, wherein the spread spectrum sub-signal is separated. 2. The signal multiplexing method according to claim 1, wherein one or a plurality of sub-signals are spread by the pseudo noise. 3. The signal multiplexing method according to claim 1, wherein the television signal is a video signal having no synchronization information, and the sub-signal has synchronization information.