JPH0352430A - Information transmission equipment - Google Patents

Abstract

PURPOSE:To improve S/N and to efficiently perform information transmission without imparing the quality of an original signal even when digital code information is added by compressing the component of the original signal by utilizing the correlation of the original signal in which time correlation is intensified in an analog area. CONSTITUTION:The transmission of a pseudo random signal generated from a pseudo noise generator 2 is controlled at a modulator 3 based on the digital code information 1 at a transmission side, and the output of the modulator 3 is converted to an analog signal with a D/A converter 5, and is added on an audio signal or a video signal with an analog adder 7, then, is changed to a transmission signal. A predictive filter 9 for the transmission signal is provided on a reception side, and a prediction error signal can be obtained by performing subtraction between a reception signal and the output of the prediction filter 9, and furthermore, it is decided whether or not a pseudo noise is included in the predictive error signal with a pseudo noise generator 10 which generates the same pseudo random signal as the pseudo random signal at the transmission side and a correlation detector 11. In such a manner, the digital code information can be obtained without impairing the dignity of the audio signal or the video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a technology for transmitting digital information, and more particularly to a technology for transmitting digital code information superimposed on an audio signal, a video signal, or the like.

Conventional technology When interconnecting audio and video equipment, it would be convenient if digital code information could be multiplexed and transmitted on the audio and video signal transmission line, for example, it could be used to transmit equipment control codes. There are many things. Furthermore, the attributes of audio signals and video signals that are being transmitted simultaneously can also be transmitted as code information. For example, if a device number or the like is coded on the transmitting side and multiplexed into the transmitted signal, the source device of the transmitted signal can be identified by the receiving device. Additionally, if it is a problem for the receiving side to be recorded or recorded, the transmitting side can transmit a code that prompts to prohibit recording, and the receiving side can be applied to stop the recording operation based on this code. . Although there are many conveniences in multiplexing and transmitting digital code information on a transmission line for audio and video signals, there is a concern that the quality of the transmitted audio and video signals may be degraded. Therefore, the level of multiplexed code information must be sufficiently lower than the level of the audio signal or video signal. As a technique used in such a case, there is a spread spectrum communication technique.

The outline of the spread spectrum communication method (hereinafter abbreviated as SS method) will be explained below. The basis of the SS system is the law regarding channel capacity proposed by C.E. Shannon. That is, C=communication capacity (bps), W
= Bandwidth (Hz), S = Signal power (Watt), N = Noise power (Watt), then C = WX1og2 (1+S/N)...
・(1) Also, if S/N<(1, C=WX1.44XS/N...(2)
It can be expressed as According to equations (1) and (2), if the noise N is much stronger than the signal S, no matter how bad the S/N ratio is, the desired communication capacity C can be obtained by widening the bandwidth W. . To do this, the original baseband signal is modulated with a pseudorandom signal, converted to a wideband signal, and then transmitted.

FIG. 6 shows an embodiment of the SS system in wireless communication. Further, FIG. 7 shows the signal spectrum at each part of the example of FIG. 6. In FIG. 6, 201 is a carrier wave generator;
2 is a primary modulator, 203 is a spreading modulator, 204 is a pseudo noise generator, 205 and 20B are a transmitting antenna and a receiving antenna, respectively, 207 is a despreading modulator, and 208 is pseudo noise generated by the pseudo noise generator 204. A pseudo noise generator 209 generates the same pseudo noise, and a demodulator demodulates the original signal from the signal modulated by the primary modulator 20.2. In the example of FIG. 6, the original signal having the spectrum as shown in FIG. 7(a) is first modulated by the carrier wave output from the carrier wave generator 201 in the next modulator 202, and the original signal has the spectrum as shown in FIG. 7(b). becomes. Thereafter, it is further modulated in the spreading modulator 203 with pseudo noise generated by the pseudo noise generator 204, but at this point the bandwidth of the transmitted signal is much larger than that of the original signal as shown in FIG. 7(C). It has become wider. Then, it is sent out into the air from the transmitting antenna 205. At this time,
As shown in FIG. 7(C), the transmitted spread signal is buried in noise indicated by diagonal lines. On the receiving side, this is received by the receiving antenna 208, and the despreading modulator 207 performs spreading modulation on the transmitting side using pseudo noise that is exactly the same as the pseudo noise on the transmitting side generated by the pseudo noise generator 208. Figure (b)
The demodulated signal shown in FIG. 7(e) is obtained by demodulating the signal as shown in FIG. 7(e). In FIG. 7(C), the amplitude of the signal buried in noise is increased by adding the diffused signal component h'W4, and the S/N ratio is improved. Modulation in the spreading modulator 203 is performed, for example, by performing balanced modulation with a pseudo-noise signal and performing direct phase modulation. Further, demodulation in the despreading modulator 207 is similarly performed by balanced modulation using a pseudo noise signal. The pseudo-noise signal is a random code sequence having a finite repetition period, such as an M-sequence code.

The despreading modulator 207 demodulates the spread modulation and restores the original bandwidth only when the phase of the spread modulation of the received signal and the phase of the pseudo noise signal output from the pseudo noise generator 208 exactly match.

Now, the feature of the SS system is that it can demodulate the original signal even in a poor noise environment as shown in FIG. 7(C), and can be said to be a communication system with very high noise resistance performance. The communication capacity C is given by equation (1) or equation (2), and has the relationship as shown in FIG.

For example, if the S/N ratio is 16-4 (-40dB),
Approximately 100 KHz of bandwidth is required to obtain a communication capacity of lobps. Therefore, if the original signal of 10 bps is transmitted with a bandwidth approximately 10,000 times wider, the S/N ratio will be -
Even if 40 dBL cannot be secured, demodulation is possible on the receiving side.

Problems to be Solved by the Invention Now, when digital code information is multiplexed and transmitted on an audio signal or a video signal using this SS method,
In order not to degrade the quality of the audio signal or video signal, the level of the superimposed digital code information needs to be sufficiently lower than that of the audio signal or video signal. As an example, consider a case where a communication capacity C of 10 bps is to be obtained. The audio signal band is approximately 20
KHz, so if the digital code information is spread-modulated and superimposed on a 20 KHz bandwidth, from equation (1) or (2), the S/N ratio is 3.5 x 10-4 or more, that is, -35 dB or more. is necessary. Here, S represents a spread-modulated digital code, and N represents an audio signal.

However, when digital coat information spread-modulated with such a large intensity is superimposed, the quality of the audio signal inevitably deteriorates.

Means for Solving the Problems In view of the above problems, the present invention is constructed as follows.

That is, audio signals and video signals are generally signals that have a very strong correlation in temporally close intervals. On the other hand, a pseudorandom signal is not only uncorrelated with audio signals and video signals, but also uncorrelated with adjacent sections. Therefore, only the audio signal or video signal can be suppressed on the receiving side by utilizing the correlation of the received signals. Therefore, in the present invention, in an information transmission device that superimposes digital code information on an analog signal such as an audio signal or a video signal and transmits the same, a pseudo noise generator, a modulator, a DA converter, and an analog adder are provided on the transmitting side. The modulator controls the transmission of the pseudo-random signal generated by the pseudo-noise generator based on digital code information, the output of the modulator is converted into an analog signal by the DA converter, and the analog adder converts the output of the pseudo-random signal into an analog signal. It is added to the signal or video signal to create a transmission signal. A prediction filter for the transmission signal is provided on the receiving side, and a prediction error signal is obtained by subtracting the received signal and the output of the prediction filter.
Furthermore, a pseudo-noise generator that generates the same pseudo-random signal as the pseudo-random signal generated by the pseudo-noise generator on the transmitting side and a correlation detector are provided, and the prediction error signal and the pseudo-random signal are input to the correlation detector. It is determined from the correlation value whether this prediction error signal contains pseudo noise.

Effect By configuring the present invention as described above, only the audio signal or video signal is suppressed while leaving the digital code information in the received signal as it is, so the level of the digital code information superimposed on the transmitting side can be kept sufficiently low. However, demodulation is possible on the receiving side. Therefore, the quality of audio and video signals is not impaired.

Embodiment FIG. 1 shows a block diagram of an information transmission apparatus which is an embodiment of the present invention. In Figure 1, (a) is the sending side, (b)
) is a block diagram of the main parts of the receiving side.

In FIG. 1(a), 1 is a code generator that generates a digital code signal I (n) consisting of a transmitter identification number, etc., and 2 is a code generator M that generates an M-sequence signal M(n) with a code length of L.
The sequence generator 3 is a modulator that controls the transmission of the output M(n) of the M sequence generator 2 with the output I (n) of the code generator 1. 5 is a 1-bit DA converter, which converts the output D(n) of the modulator 3 into an analog signal. The DA converter 5 is
This can be realized with a 1-bit register.

6 is an amplifier that adjusts the amplitude and offset of the output signal of the DA converter 5; 7 is an amplifier that adds the output signal D(1) of the amplifier 6 and the audio signal or video signal X(t) to produce a transmission signal C (t ) is an analog adder.

In FIG. 1(b), 8 is the received transmission signal C(1)
A register 91 delays the output C(n) of the AD converter 8 by one sample;
2 is a subtracter that subtracts the output C (n-1) of the register 91 from the output C (n) of the AD converter 8. and,
This register 91 and subtracter 92 constitute a predictive encoder 9. 10 is an M-sequence generator that generates the same M-sequence as the M-sequence generator in FIG.
12 is the output R of the correlator 11.
This is a code regenerator that regenerates a digital code signal I (n) from (n).

Next, the operation of the embodiment shown in FIG. 1 will be explained.

FIG. 2 shows the output I(
n), waveform examples of the output M(n) of the M-sequence generator 2 and the output D(n) of the modulator 3 are shown. In this example, M(n
) is gated by I (n), resulting in a waveform such as D(n). Here, since I(n) has a value of 1 or 0, D(n) expresses I(n) depending on whether M(n) exists or not in a certain time interval. Modulator 3
can be constructed with a two-person Decido gate.

D(n) is converted into an analog signal by the DA converter 5,
After the amplitude and offset are adjusted by the amplifier 6, it is added to the audio signal X (U) by the analog adder 7 and sent out as C(t).

On the receiving side, the transmission signal C (t) is digitized by an AD converter 8 . The output C (n) of the AD converter 8 is guided to a register 91 and a subtracter 92 . Register 91 is C
(n) is delayed by one sample, and as a result, the output Y(n) of the subtracter 92 is: Y (n) = C (n) - C (n-1)
...-(3). Register 9 acts as a prediction filter that uses the previous sample as a predicted value for the received sample.

Therefore, Y(n) becomes a prediction error signal.

The transmission signal C(t) is: C(t)=X(n)+D(t)
・” (4), which is digitized by the AD converter 8, so that C Cn)=X (n) 10 (n)
= (5). Therefore, the prediction error signal Y (n) that is the output of the subtracter 92 is Y (n): C (n) − C (n-1)
...(6)==X (n) - X
(n-1) 10 (n)-D (n-1)...(7) Here, D(n) and D(n-1) are M-sequence signals, so one period is It is a code word generated from a certain primitive polynomial. Therefore, D (n) − D (n-1
) also have the same M sequence. Therefore, D (n) −
Replace D (n-1) with D(n) and get Y (n) = X (n) - X (n-1) + D
(n) (8) From equation (8), it can be seen that D (n) returns to the prediction error signal Y(n).

Next, the demodulation operation of spread modulation by the correlator 11 will be explained using FIG. This operating principle is the same as the method of extracting periodic signals by cross-correlation, which is well known as the correlation detection method. In FIG. 3, (a) represents the M sequence M'(n) generated by the M sequence generator 11. In FIG. (b) shows the interval included in the time window of length L, which is the target of the correlation calculation, of the spread modulation signal D (n) included in the prediction error signal Y (n), by 'summer' and '0'. Therefore, D (n) that falls in this time window is shifted by one sample time,
D (n-2+k) to () (n+2+k) represent signals delayed by one sample time.

For example, D (n-1+k) is the signal included in the time window one sample time after D (n-2+k).

M'(k) left empty "10110-100" When compared with each signal of D (n-2+k) ~D(n?41+l■, only D(n+k) is "10110~!O"
It can be seen that all the bits corresponding to M'(k) match at "O".The correlation value R (n
) is expressed by the following formula.

k=0 R (n) obtained by calculating equation (8) is expressed as the third
It is shown in figure (c). The correlator 11 executes equation (9) every sample time to obtain the correlation value R (n).

D is the interval in which M(n) is included in D(n).
Since there is a peak in the correlation value R(n) for M'(k) where the phases of both M sequences of (n >M'(n) match), we can use this to Inside D (n
) contains M (n). The code regenerator 12 receives input R(n) as follows:
By determining whether it has a peak, it is possible to identify whether I (n) is "0" or "!".

Next, a second embodiment of the present invention will be described with reference to the drawings. In the first embodiment, the simplest model using the previous sample as the predicted value was realized. Second
In this embodiment, the average of previous and subsequent samples is used as the predicted value to improve the precision of the prediction, and as a result, further improve the S/N ratio of the spread modulation signal included in the prediction error signal.

FIG. 4 is a block diagram of the receiving side of the information transmission apparatus according to the second embodiment. Since the transmitting side is the same as the example shown in FIG. 1, the explanation will be omitted. In the embodiment of FIG. 4, a predictive encoder 9l is provided in place of the predictive encoder 9 of the embodiment of FIG.

Since the other configurations are the same, the same numbers are given to the corresponding components and the description thereof will be omitted.

In the predictive encoder 91 of FIG. 4, 911 to 912 are registers, and 913 is an integrator that multiplies the input by "-2". Further, 9l4 is an adder. Therefore, the output of register 912 is the input C (n) to predictive encoder 91 by 2
The output of the integrator 913 is C
(n) delayed by one sample and multiplied by "-2". Therefore, the output Y (n) of the predictive encoder 91 is Y(n)=C'(n) -2C(n-1)+C(n-2
)...(10). Substituting equation (5) into equation (10), Y (n)” { X (n) −2 X
(n-1)+ X (n-2))+ { D (n)
− 2 D (n-1)+ D (n-2)) −
(11). Here, again due to the properties of the M series (!
The second term on the right side of equation 1) returns to the same M series as D(n).

This is newly expressed as D(n) and Y (n) = ( X (n) - 2 X (n-1)
+ X (n-2)) + D (n)
...(l2) The term { } on the right side of equation (l2) is the average of the samples before and after X(n-1), and the
) is the difference from itself multiplied by twice. In this way,
By processing the transmission signal C (n) with a predictive encoder, the audio signal component can be suppressed and D(n) can be reproduced.

The difference between the embodiment of FIG. 1 and the embodiment of FIG. 4 lies in the configuration of the predictive encoder. Compared to the predictive encoder 9 in FIG. 1 which uses the previous sample as a predicted value, the predictive encoder 91 in FIG.
uses the average value of the previous and subsequent samples, so the prediction error is smaller. In FIG. 5, (a) is the transmission signal C(n)
, (1)) is the prediction error signal Y(n) of the embodiment of FIG.
(c) is the prediction error signal Y(n) in the embodiment of FIG.
are shown respectively.

It is understood from FIG. 5 that the prediction error signal Y(n) in FIG. 4 is smaller than that in FIG. 1, and that the audio signal component is further suppressed.

Effects of the Invention As explained above, according to the present invention, the components of the original signal are compressed by utilizing the correlation of the original signal with strong time correlation, such as an audio signal or a video signal in the analog domain.
This makes it possible to improve the S/N ratio, so even if digital code information is added, the quality of the original signal is not impaired, and very efficient information transmission can be performed.

Furthermore, although the embodiment shown in FIG. 1 and the embodiment shown in FIG. Needless to say, any other configuration that calculates the difference from the sample value can be used.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an information transmission device according to a first embodiment of the present invention, FIG. 6 is a conceptual diagram for explaining a spread spectrum communication method, and FIG. 7 is a spectrum diagram for explaining the method. Figure 8 is a graph showing communication capacity, Figure 2 is a graph showing communication capacity.
FIG. 3 is a diagram showing the correlation of signals to explain the operation of the correlator 11, and FIG. 4 is a waveform diagram for explaining the operation of the correlator 11. FIG. The block diagram and FIG. 5 are waveform diagrams representing prediction error signals in the first and second embodiments of the present invention. l... code generator, 2... M sequence generator, 3...
...Modulator, 5...D/A converter, 7...
Adder, 8.-A/D converter, 9... Predictive encoder 1lO... M sequence generator, 11... Correlator,!
2... Code regenerator.

Claims (3)

[Claims] (1) An information transmission device that superimposes and transmits a second signal whose amplitude is sufficiently smaller than the first signal, and a first pseudo-noise generator that generates pseudo-noise on the transmitting side;
a receiving side, comprising: a modulator that controls transmission of pseudo noise output from the first pseudo noise generator using the second signal; and an adder that superimposes the output of the modulator on the first signal; a predictive encoder that calculates a predicted value from the received signal and calculates a prediction error by calculating the difference between this predicted value and the actual received signal; and a predictive encoder that generates the same pseudo noise as the first pseudo noise generator. and a correlator for determining the strength of correlation between the prediction error output from the predictive encoder and the pseudo noise output from the second pseudo noise generator. information transmission equipment. (2) The information transmission apparatus according to claim 1, wherein the predictive encoder outputs a difference between a sample value and a sample value immediately before the sample value as a prediction error. (3) The information transmission device according to claim 1, wherein the predictive encoder outputs a difference between a sample value and an average value of sample values immediately before and after the sample value as a prediction error.