JPH0211071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is capable of transmitting data signals (for example, digitized audio signals corresponding to video signals and general data unrelated to video signals) simultaneously with TV video signals and using the same transmission path. This provides a method for efficiently transmitting signals.

Various applications can be considered for superimposing a data signal on a TV video signal by some means and transmitting it over the same transmission path. For example, systems have been proposed that transmit various types of information only to desired viewers, regardless of the screen. Furthermore, by transmitting the digitized audio signal and the video signal over the same transmission path, the transmission path of a wireless relay system or the like can be used economically.

One of the various methods conventionally used or devised for this purpose is a method in which the data signal is converted into a spread spectrum modulation signal having a spectrum within the video signal band, and the signal is superimposed on the video signal and transmitted. There is. (DCColl and N.
Zervos“The Use of Spread Spectrum
Modulation for the Co−channel
“Transmission of Data and Television”
National Telecommunication Conference,
See 1979, pp15.4.1-15.4.5. ) The present invention relates to an improvement of this method.

In conventional methods, the level of the spread spectrum modulation signal superimposed on the image signal must be kept to a level as low as -40 dB relative to the image signal level so that its adverse effect on the image signal can be ignored. However, there was a drawback that the data signal transmission speed could not be made very high due to the error rate of the data signal.

The purpose of the present invention is to increase the relative level of the spread spectrum modulation signal to the video signal to about -20 dB, thereby increasing the data signal transmission speed to about 100 times compared to the conventional method. For signals, by adding a means to remove superimposed spread spectrum modulation signal components on the receiving side, it is possible to suppress interference to video signals to below an acceptable level. The goal is to provide a transmission method.

Embodiments of the present invention will be described in detail below with reference to the drawings.

A first embodiment of the invention is shown in FIG. On the transmitting side shown in FIG. 1A, a TV video signal is applied to terminal 11. The signal is branched into two, one of which is applied to the sync separation circuit 21, and a horizontal sync signal is taken out. This synchronization signal is transmitted to the bit synchronization generation circuit 22 and the PN (pseudo noise) signal generation circuit 2.
Added to 3. The data signal is applied to the terminal 12 and stored in the buffer memory 24, then read out by the readout circuit 25 using the bit synchronization signal from the bit synchronization generation circuit 22, and then sent to the PN signal generation circuit 23 by the spread spectrum modulation circuit 26.
The resulting signal is modulated using a PN signal of the same type, becomes a spread spectrum modulated signal, is combined with the video signal from the terminal 11 by the adder circuit 27, and is sent out from the output terminal 13 to the transmission line as a composite signal. Various types of transmission lines can be used, such as coaxial transmission lines, microwave FM transmission lines, very high frequency broadcast waves, and laser communication lines.

On the receiving side shown in FIG. 1B, the received composite signal from the transmission line is applied to terminal 14. This signal is 3
Branched out. One is applied to the synchronization separation circuit 31, and a horizontal synchronization signal is taken out. This is done by the bit synchronization generation circuit 32 and the PN signal generation circuit 33.
It is used to generate bit synchronization signals and PN signals for data signal demodulation. The other branch signals of the received signal are applied to a spread spectrum modulation circuit 34, and the signals from 32 and 33 are used to demodulate the original data signal. This demodulated output is taken out from the terminal 16 and is applied to the spread spectrum modulation circuit 35 together with the bit synchronization signal and the PN signal to reproduce a signal with a similar waveform and the same level as the transmitted spread spectrum modulation signal. . However, it is delayed from the original signal by the time required for demodulation and remodulation. The delay circuit 36 accurately delays the received signal by a time equal to the delay time associated with demodulation and remodulation of the spread spectrum signal, and from its output, the reproduced signal from 35 is subtracted in the subtraction circuit 37. As a result, almost only the video signal appears at the output terminal 15.

As is well known, the spread spectrum method has excellent ability to remove interference signals, so even if the signal is mixed and transmitted at a relatively low level compared to video signals,
On the receiving side, it is possible to remove interference caused by the video signal and reproduce the original data signal. However, when the error rate is the same, it is natural that the higher the signal-to-interference power ratio, the faster the transmission speed can be. On the other hand, the mixed spread spectrum modulated data signal interferes with the video signal. Experience has shown that if the power ratio of the video signal to the interfering signal is about 40 dB or more, the effect of the interfering is small. According to the present invention, the data signal component remaining in the video signal can be reduced by 20 dB or more.
The level of the spread spectrum signal in the transmitted signal can be raised to about -20 dB below the video signal level. As a result, the level of the spread spectrum signal can be increased by 20 dB compared to the conventional technology, making it possible to increase the transmission speed by 100 times if the error rate remains the same.

In the embodiment, the bit synchronization signal and PN signal for spread spectrum modulation are created using the horizontal synchronization signal of the TV signal, but this is not always necessary. However, bit synchronization and PN
By associating the signal with a horizontal synchronization signal, there is an advantage that the problem of synchronization reproduction, which is the most troublesome problem in demodulating the spread spectrum system, can be avoided. In spread spectrum demodulation, a certain time delay is unavoidable because the correlation coefficient between the input signal and the PN signal is determined. After accurately delaying the received signal by a time corresponding to this delay time, the spread spectrum modulated signal component is subtracted from the received signal by the regenerated spread spectrum modulated signal so that the time and level exactly match that of the received signal. The key point of the present invention is to effectively remove the . For this purpose, it is necessary to finely adjust the delay time and the level of the reproduced signal. Note that analog delay lines such as delay cables, LC delay circuits, and surface acoustic wave delay lines can also be used as the delay circuit 36, but it is preferable to use a digital delay circuit that performs AD conversion, stores it in digital memory, and then converts it back to DA. For example, there is no change in delay time over time, and stable operation is possible.

In the above embodiment, since the level of the spread spectrum modulation signal included in the received composite signal is known and the time required for demodulating it is also a constant value determined by the circuit system, the delay circuit 36 delays the received composite signal. delay time and subtraction circuit 3
The level of the spread spectrum modulation signal reproduced by 35 added to 7 should be adjusted to the best value at the beginning, but it may change over time in the circuits on both the transmitting side and the receiving side, or Considering the variations in adjustment when a plurality of transmitters and receivers are arbitrarily connected, it is considered desirable to add a means for automatically adjusting them to the best value.

Another aspect of the present invention adds the function of automatically adjusting the delay time and level. In the horizontal blanking period of a TV video signal, there is only a horizontal synchronizing signal, so if this period is extracted from the received composite signal, it is easy to extract the spread spectrum modulation signal component in its pure form, and its level This method takes advantage of the fact that phase and phase can be easily detected. The embodiment shown in FIG. 2 will be described below.

Since the transmitting side is the same as the embodiment shown in FIG. 1A, only the receiving side is shown in FIG. Compared to FIG. 1, a variable delay circuit 38 and a variable level circuit 39 are inserted, making it possible to automatically finely adjust the delay time and level. Electronically controllable variable delay circuits and variable level circuits are well known. Further, as circuits for controlling these, there are a horizontal blanking signal generation circuit 40, a gate circuit 41, a gate circuit 41', a phase difference detection circuit 42, and a level difference detection circuit 43. A gate circuit 41 extracts a signal for only the horizontal blanking period from the composite signal output from the variable delay circuit 38. Further, from the spread spectrum modulation signal reproduced by 35, a signal of the horizontal blanking period is similarly extracted by gate circuit 41'. The output signals of the gate circuits 41 and 41' are applied to a phase difference detection circuit 42 and a level difference detection circuit 43, and their outputs control the variable delay circuit 38 and level variable circuit 39. The spread spectrum modulated signal in the output terminal 15 and the spread spectrum modulated signal reproduced by 35 are very accurately matched and subtracted, so that the residual spread spectrum modulated signal at the output terminal 15 is extremely small.

Next, another embodiment of the present invention shown in FIG. 3 will be described. This is similar to the embodiment shown in FIG. 2, but a level detection circuit 44 detects the magnitude of the component of the residual spread spectrum modulation signal included in the output of the subtraction circuit 37, and A phase difference detection circuit 42 detects the phase difference between the spreading modulation signal and the signal reproduced by 35.
The difference is that the variable delay circuit 38 and the level variable circuit 39 are controlled so that these are detected and reduced. In FIG. 2, the signal before the subtraction circuit 37 is applied to the gate circuits 41 and 41';
In FIG. 3, the signal after the subtraction circuit 37 is applied to the gate circuits 41 and 41', and the second
The difference is that the level difference detection circuit 43 in the figure is replaced by a level detection circuit 44 in FIG. The embodiment shown in Fig. 2 is a feedback type control circuit, whereas the embodiment shown in Fig. 3 is a feedback type control circuit, which has the advantage of less deterioration of characteristics due to changes over time, etc. .

In the embodiments of FIGS. 2 and 3, the variable delay circuit 38 is inserted into the composite signal path;
It is clear that even if it is put into the path of the spread spectrum modulation signal reproduced by No. 5, the operation will be exactly the same, only the control polarity will be different. Further, in the embodiments shown in FIGS. 2 and 3, the delay circuit 36 and the variable delay circuit 38 are provided separately, but it is possible to provide only the variable delay circuit 38 and also have the function of the delay circuit 36. It's okay.

As described above, according to the present invention, a video signal and a data signal (for example, a digitized audio signal corresponding to a video signal or a general data signal unrelated to a video signal) can be efficiently transmitted simultaneously, on the same transmission path, and in the same band. This makes it possible to use transmission lines economically, making it particularly suitable for long-distance transmission such as in sanitary communications.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, where A indicates a transmitting side circuit and B indicates a receiving side circuit. 11 is a video signal input terminal, 12 is a data signal input terminal, 13 is a transmission output terminal to the transmission path, 14 is a reception input terminal from the transmission path, 15 is a video signal output terminal, 16 is a data signal output terminal, 21, 31 is a synchronization separation circuit, 22 and 32 are bit synchronization generation circuits, 23 and 33 are PN signal generation circuits, 24 is a buffer memory, 25 is a readout circuit, 26 and 35 are spread spectrum modulation circuits, 27 is an addition circuit, 3
4 is a spread spectrum demodulation circuit, 36 is a delay circuit, and 37 is a subtraction circuit. FIGS. 2 and 3 are block diagrams showing receiving side circuits of other embodiments of the present invention, respectively. 38 is a variable delay circuit, 39 is a level variable circuit,
40 is a horizontal blanking signal generation circuit, 41, 4
1' is a gate circuit, 42 is a phase difference detection circuit, 43
4 is a level difference detection circuit, and 44 is a level detection circuit.

Claims (1)

[Claims] 1. On the transmitting side, first means (21 to 26) for converting the data signal into a spread spectrum modulation signal having its spectrum within the video signal band; A second means (27) for superimposing the output on the video signal and transmitting it as a composite signal, and on the receiving side, a third means (31 to 34) for reproducing the transmitted data signal from the received composite waveform. and a fourth means of reproducing a signal with a similar waveform and the same level as the transmitted spread spectrum modulation signal using the reproduced data signal (35).
and a fifth means for delaying the received composite waveform so that the spread spectrum modulated signal therein and the signal reproduced by the fourth means coincide in time.
means (36); and sixth means (37) for subtracting the signal reproduced by the fourth means from the received composite waveform delayed by the fifth means and extracting only the video signal. Simultaneous transmission of video and data signals. 2. The transmitting side includes first means (21 to 26) for converting the data signal into a spread spectrum modulation signal having its spectrum within the video signal band, and superimposing the output of the first means on the video signal. and a second means (27) for transmitting the transmitted data signal as a composite signal, and on the receiving side, a third means (31 to 34) for reproducing the transmitted data signal from the received composite waveform, and the reproduced data. A fourth means of reproducing a signal with a similar waveform and the same level as the spread spectrum modulation signal transmitted using a signal (35)
and a fifth means for delaying the received composite waveform so that the spread spectrum modulated signal therein and the signal reproduced by the fourth means coincide in time.
means (36); and sixth means (37) for subtracting the signal reproduced by the fourth means from the received composite waveform delayed by the fifth means and extracting only the video signal.
and extracting a portion of the horizontal blanking period of the received composite waveform applied to the sixth means, and combining the extracted spread spectrum modulation signal in the horizontal blanking period and the signal reproduced by the fourth means. detecting a phase difference and a level difference, and depending on the detected phase difference and level difference, the delay time of the received composite signal added to the sixth means or the delay time of the signal reproduced by the fourth means and the a seventh means (39
~43) A simultaneous transmission system for video and data signals. 3. The transmitting side includes first means (21 to 26) for converting the data signal into a spread spectrum modulation signal having its spectrum within the video signal band, and superimposing the output of the first means on the video signal. and a second means (27) for transmitting the transmitted data signal as a composite signal, and on the receiving side, a third means (31 to 34) for reproducing the transmitted data signal from the received composite waveform, and the reproduced data. A fourth means of reproducing a signal with a similar waveform and the same level as the spread spectrum modulation signal transmitted using a signal (35)
and a fifth means for delaying the received composite waveform so that the spread spectrum modulated signal therein and the signal reproduced by the fourth means coincide in time.
means (36); and sixth means (37) for subtracting the signal reproduced by the fourth means from the received composite waveform delayed by the fifth means and extracting only the video signal.
and extracting a portion of the horizontal blanking period from the video signal output from the sixth means, and combining the residual spread spectrum modulation signal component in the extracted horizontal blanking period and the part reproduced by the fourth means. detecting the phase difference with the signal and the level of the residual spread spectrum modulated signal component, and adding the delay time of the received composite signal to the sixth means or the fourth means according to the detected phase difference and level; Eighth means for automatically fine-tuning the delay time of the signal reproduced by the fourth means and the level of the signal reproduced by the fourth means so that the residual spread spectrum modulation signal component is minimized. (38-42, 44) A video signal data signal simultaneous transmission system.