JPH04336824A - Spread spectrum transmitter-receiver - Google Patents

Abstract

PURPOSE:To enhance the ciphering performance of the spread spectrum communication system. CONSTITUTION:Data signals S1, S2 or a pseudo noise code N3 is fed to FM modulators 2, 8, in which the code is FM-modulated and each FM modulation signal is subjected to polarity modulation by balanced modulators 3, 9 by using pseudo noise codes N1, N2 and obtained spread spectrum modulation signals e1, e2 are synthesized by an adder 11 and a synthesis signal e0 is sent from an antenna 12. The synthesis signal received by an antenna 13 is fed to correlation devices 15, 21 via a high frequency amplifier 14. Moreover, a polarity modulation signal resulting from applying polarity modulation to a carrier signal by using the pseudo noise codes N1, N2 by balanced modulators 16, 22 is fed to the correlation devices. Each amplitude level is detected from the correlation signal from the correlation devices 15, 21 by amplitude detectors 18, 24 respectively and its detection signal is used to allow data decoding circuits 19, 25 to decode a data signal. Thus, since the data signal cannot be decoded even by using a simple square detection circuit at a reception side, the ciphering performance is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum transmitting/receiving apparatus improved to enhance the privacy of transmitted and received data signals.

0002

BACKGROUND OF THE INVENTION In Japanese Patent Application Laid-Open No. 2-69051, the present inventor previously addressed the drawbacks of conventional spread spectrum communication equipment, namely, the use of a SAW convolver as a correlator for despreading a spread spectrum modulated signal. proposed a spread spectrum communication device that improved on the disadvantages of requiring complex elements and circuits to restore the original data, such as the need for identical pseudo-noise code (PN code) generators on the transmitting and receiving sides.

[0003] FIG. 3 shows a transmitting section of the communication device, and FIG. 4 shows a receiving section. In the transmission section, 31 is an input data signal, 32
33 is a multiplication circuit, 34 is a PN (pseudo-noise) code generator, and 35 is a high-frequency transmitter. Further, in the receiving section, 40 and 43 are multiplication circuits;
41 is a fixed oscillator, 42 and 44 are band pass filters, 4
5 represents an FM discriminator, and 46 represents a data output.

[0004] In the above communication device, as described in the above-mentioned publication, a data signal is firstly modulated at two frequencies in a transmitting section, and further modulated secondarily using a PN code, and a spread spectrum signal obtained is transmitted. The receiving section inputs the received spread spectrum signal to the high frequency section, multiplies or squares the output signal to obtain a time series signal, and restores the original data from the time series signal.

[0005]

[Problems to be Solved by the Invention] The receiver does not need to use a SAW convolver or a PN code generator to restore the original data, so it has the advantage of being very simple in configuration. The problem is that it is low. In other words, even if the data signal is spread-modulated and encrypted using a PN code in the transmitter, the data can be easily restored in the receiver using a simple square circuit and an FM discriminator.This point will be discussed below. explain.

FIG. 2(a) shows a data signal S, and as shown in FIG. 2(b), at level 1 of the signal, c
At the level of osω2t, 0, an FM modulated wave of cosω1t is generated. Here, FIG. 2(c) is F of FIG. 2(b).
The time axis expanded waveform of the M modulated wave is shown.

[0007] The above FM modulated wave is polar-modulated with the broadband pseudo-noise code N shown in FIG.
), when N=1, it is modulated to negative polarity (180°) and the same figure (e
) is obtained and this modulated wave is transmitted. On the receiving side, the modulated wave is received and first applied to a squaring circuit. Now, if the polar modulated wave is e,

[0008] When the above e is added to the square circuit, the output e2 is as follows.

The signal component of 2ω(S) is extracted by passing e2 in equation (7) through a band-pass filter, and the signal component of 2ω(S) is either directly FM demodulated or passed through a frequency down-conversion circuit (for example, a flip-flop). The data signal S can be extracted by FM demodulating the signal component. That is, in the above method, since the original data can be restored relatively easily, there is a drawback that the communication lacks confidentiality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spread spectrum modulation transmitting/receiving device with high privacy, in which original data cannot be restored even if a squaring circuit is used on the receiving side.

[0011]

[Means for Solving the Problems] In order to achieve the above object, a spread spectrum transmitting/receiving device according to the present invention obtains a first FM modulated signal by FM modulating a first data signal, and obtains a first FM modulated signal. a first modulator that polar-modulates the signal with a first pseudo-noise code to obtain a first spread spectrum modulated signal; and a second data signal or a third pseudo-noise code that is different from the first data signal. FM modulation and second FM
a second modulating section that obtains a modulated signal and polar modulates the second FM modulated signal with a second pseudo-noise code to obtain a second spread spectrum modulated signal; and the first and second spread spectrum modulated signals. a signal synthesizing section that obtains a synthesized signal by synthesizing the signals, and a spread spectrum transmitting means that transmits the synthesized signal, polarizing the received synthesized signal and a first carrier signal with a first pseudo-noise code. a first correlation processing section that calculates the correlation with the modulated first polarity modulation signal and outputs a first correlation signal; a first data signal restoring unit for restoring a data signal of a second correlation processing section that outputs a second correlation signal; and a second data signal restoration section that detects the amplitude level of the second correlation signal and restores the second data signal based on the detected signal. , and spread spectrum receiving means for restoring the first and second data signals from the received composite signal.

0012

[Operation] In the spread spectrum transmitting means, the first and second data signals, which are different from each other, are FM-modulated, respectively, and the obtained first and second FM-modulated signals are polarity-modulated with the first and second pseudo-noise codes. be done. The first result obtained by this
and a second spread spectrum modulated signal is transmitted.

In the spread spectrum receiving means, the received composite signal and first and second polar modulated signals obtained by polar modulating the first and second carrier signals using first and second pseudo-noise codes, respectively. , to obtain first and second correlation signals. Amplitude levels of the first and second correlation signals are detected, and the first and second data signals are recovered based on the respective detected signals.

[0014]

[Embodiments] Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a spread spectrum transmitter/receiver according to the present invention, where T is a spread spectrum transmitter and R is a spread spectrum receiver.

In the spread spectrum transmitter T, 1
and 5 are input terminals for mutually different data signals S1 and S2, 7 is a switch, 2 and 8 are FM modulators, 3 and 9 are balanced (polarity) modulators, 4 and 10 are pseudo noise codes N1, N
2 is an input terminal, 11 is an adder, 11' is a bandpass filter, and 12 is a transmitting antenna.

In the spread spectrum receiver R, 1
3 is a receiving antenna, 14 is a high frequency amplifier, 15 and 21
is a correlator (e.g. SAW convolver), 16 and 22 are balanced (polarity) modulators, 18 and 24 are amplitude detectors, 19
and 25 are data restoration circuits, 27 and 23 are input terminals for pseudo noise codes N1 and N2, 20 and 26 are output terminals for restored data signals S1 and S2, and 27 and 28 are input terminals for carrier wave signals.

Next, the operation of the above embodiment will be explained. In the spread spectrum transmitter T, the data signal S1 from the input terminal 1 has a waveform as shown in FIG. 2(a), for example, and when applied to the FM modulator 2, cosω1t, At S1=1, cosω2t in Figure 2 (b
) generates the FM modulation signal shown in FIG. This FM modulated signal is AM (polarity) modulated by the balanced modulator 3 using the pseudo noise code N1 shown in FIG. 2(d) from the input terminal 4. however,
Pseudo-noise code N1 is generated using a much higher frequency clock than data signal S1.

Furthermore, the data signal S2 from the input terminal 5 is F
added to the M modulator 8, cosω3t for S2=0,
When S2=1, an FM modulation signal of cosω4t is generated (
ω3=ω1, ω4=ω2). This FM modulated signal is subjected to AM modulation by a balanced modulator 9 using a pseudo noise code N2 from an input terminal 10.

The spread spectrum modulated signals outputted from the balanced modulators 3 and 9 are added by an adder 11, and the resulting composite signal is transmitted from an antenna 12 via a band pass filter 11' for the spread spectrum band. Note that when there is no data signal S2, the switch 7 switches the input terminal 6
, the pseudo noise code N3 is added to the FM modulator 8, and the F
M modulates. However, it is assumed that this N3 is generated at a slower speed than N1 and N2 and at a clock frequency comparable to that of the data signals S1 and S2.

In the spread spectrum receiver R, the received signal from the antenna 13 (the composite signal) is transmitted to the amplifier 1.
4 and applied to one input electrode of the correlator 15. A pseudo-noise code N1 having the same pattern as the pseudo-noise code is applied to the other input electrode of the correlator 15 from an input terminal 17 to a balanced modulator 16, and a carrier signal (cosω1t or cosω2t) from an input terminal 27 is polar-modulated. Add polar modulation signal.

The correlator 15 correlates the received signal with the polar modulation signal and outputs a correlation signal to the amplitude detector 18. The correlation signal has a large amplitude only when the degree of correlation between the received signal and the polar modulation signal is strong, and the amplitude detector 18 detects this large amplitude and adds the detected signal to the data signal restoration circuit. Then, the restored data signal S1 is output to the output terminal 20.

On the other hand, the output signal of the amplifier 14 is transmitted to the correlator 21.
It can also be added to The balanced modulator 22 also has an input terminal 2.
8 (cosω3t or cosω4t
) is added, and a polar modulated signal is output to the correlator 21, which is balanced (polarity) modulated with a pseudo noise code N2 having the same pattern as the pseudo noise code. The correlation signal output from the correlator 21 is applied to the amplitude detector 24, and the data signal restoration circuit 25 restores the data signal S2 from the detected signal and outputs it to the output terminal 26.

Now, on the receiving side, the received signal is
If we perform multiplication detection, the result will be as follows. However, if the output signals (spread spectrum modulation signals) of the balanced modulators 3 and 9 on the transmitting side are e1 and e2,

0024
] It is.

Therefore, the output of the adder 11 is the sum of e1 and e2, and if this is e0, then the square output e02 of e0 is as follows: e02=(e1+e2)2=e12+e22+2e
1e2...(14) Extract the cos2ω(S)t component of e02 using a bandpass filter and let this be [e02]B, then [e02]B=1
/2cos2ω(S1)t+1/2cos2ω(S2t
) +cos[ω(S1)
+ω(S2)]t...(15
).

The first term of the above equation (15) is cos2ω1t
and cos2ω2t, the second term consists of cos2ω3t and cos2ω4t, and the third term consists of ω1+ω3, ω1+
It consists of the components ω4, ω2+ω3, and ω2+ω4. ω1=ω3 ω2=ω4

...Using the condition (15), the first and second terms of equation (15) consist of cos2ω1t and cos2ω2t, and the third term consists of cos2ω1, cos2ω2t, cos
It consists of s(ω1+ω2)t.

Therefore, equation (15) is cos2ω1,co
s2ω2t, cos(ω1+ω2)t, and no matter which frequency component is selected, data signals S1 and S2 cannot be easily separated. When the data signal S2 does not exist, by using the pseudo visual noise code N3 in place of S2, it is possible to improve confidentiality since data signals cannot be separated even by using a square detector. Furthermore, ω1 and ω
3. ω2 and ω4 do not need to be strictly equal, as long as they cannot be separated by a filter or the like.

[0028]

[Effects of the Invention] As explained above, according to the present invention, mutually different data signals or a data signal and a pseudo-noise code are FM-modulated, and each FM-modulated signal is polar-modulated with the pseudo-noise code. Since each spread spectrum modulation signal is combined and transmitted, the data signal cannot be restored on the receiving side even if a simple square detector is used, and the confidentiality of communication can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a spectrogram spread transmitter/receiver according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the above embodiment and the conventional device.

FIG. 3 is a block diagram showing a conventional spread spectrum transmitter.

FIG. 4 is a block diagram showing a conventional spread spectrum transmitter.

[Explanation of symbols]

2,8 FM modulator 3,9 Balanced modulator 11 Adder 15, 21 Correlator 16, 22 Balanced modulator 18, 24 Amplitude detector 19, 25 Data restoration circuit

Claims (1)

[Claims] Claim 1: A spread spectrum transmitter/receiver that transmits and receives an FM-modulated data signal by performing balanced modulation with a pseudo-noise code and performing spread spectrum processing, wherein the first data signal is FM-modulated to generate a first FM-modulated signal. and a first modulation unit that polar-modulates the first FM modulation signal with a first pseudo-noise code to obtain a first spread spectrum modulation signal; FM modulating the signal or a third pseudo-noise code to obtain a second FM-modulated signal, and polar modulating the second FM-modulated signal with a second pseudo-noise code to obtain a second spread spectrum modulation signal. a second modulation section; a signal synthesis section that synthesizes the first and second spread spectrum modulation signals to obtain a composite signal;
and a spread spectrum transmitting means for transmitting the composite signal, and determining the correlation between the received composite signal and a first polar modulated signal obtained by polar modulating a first carrier signal with a first pseudo-noise code. a first correlation processing unit that detects an amplitude level of the first correlation signal and restores a first data signal based on the detected signal;
a data signal restoring unit that correlates the received composite signal with a second polar modulated signal obtained by polar modulating a second carrier signal using a second pseudo-noise code and outputs a second correlation signal. a second correlation processing unit that detects the amplitude level of the second correlation signal, and a second data signal restoration unit that restores the second data signal based on the detected signal; spread spectrum receiving means for restoring the first and second data signals from the synthesized signal.