JPH0373185B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention scrambles the spectrum of a signal source in the frequency range and further applies emphasis in order to improve the confidentiality of communications or provide protection against leakage due to frequency interference in communications. The present invention relates to a reception method for modulated transmission waves, which provides high communication secrecy and which can prevent deterioration of speech quality due to fading noise generated in PM transmission paths. (Prior Art) FIG. 11 is a functional block diagram showing a conventional confidential reception system, in which 1 is a receiving antenna, 2 is a PM demodulator, 3 is a spectrum descrambler, and 4 is an output terminal. , b indicate observation points. Figure 2 is a diagram schematically representing the spectrum of each part of the conventional reception system when simple spectrum inversion is used as the spectrum descrambling part, and a and b correspond to observation points a and b in Figure 11, respectively. are doing. Figure 3 is a block diagram showing an example of a transmission system, where 5 is an input terminal, 6 is a spectrum scrambling section, 7 is a PM transmitting section, 8 is a transmitting antenna, and c and d indicate observation points. There is. FIG. 4 is a diagram schematically showing the spectrum of each part of the transmission system, and c and d correspond to observation points c and d in FIG. 3, respectively. This type of conventional reception system uses a configuration in which a spectrum descrambler 3 is cascaded to a PM demodulator 2 as shown in FIG. The demodulated signal obtained by PM demodulation was subjected to spectrum descrambling (in particular, simple spectrum inversion is considered here), and the confidential signal was decoded and reproduced. The period from when a phase-modulated signal is emitted until it is received by a receiving antenna is called a PM transmission path.If the PM transmission path forms a standing wave electric field and fading noise is mixed into the received demodulated signal, This is called a fading PM transmission line. Mobile communications such as car telephones are mostly affected by fading noise. FIG. 5 shows the average power spectrum of noise in such a fading PM transmission path. The reception level of 10 dBμ in Figure 5 represents the electric field at the edge of the car phone service area.
22 dBμ indicates the electric field at the center of the area, and exhibits an integral characteristic with a slope of -20 dB/decade over the entire area. Therefore, we have decided to show it schematically as shown in the shaded area in Figure 2a. Hereinafter, the spectrum having the shape of this diagonal line will be referred to as an inverted triangle. Since the demodulated signal contains fading noise as shown in the shaded area in Figure 2a, the spectrum inverter 3 converts the inverted triangular noise into triangular noise as shown in Figure 2b. be done. When the FM demodulation function is used instead of the PM demodulation function, fading noise having a flat spectrum is mixed in as shown in FIG. Figure 6 shows when demodulating PM,
Furthermore, the fading noise when simple spectrum inversion is performed after PM demodulation is also shown. These three patterns show typical noise power spectra, and Table 1 shows the values of their auditory levels determined by analysis using the Zwicker method and experimentally. As shown in Table 1, even if the noise power is kept equal for the three patterns, the inverted triangle has the lowest auditory level, the flat type is approximately 4 dB higher than the inverted triangle, and the triangular type has the highest level compared to the inverted triangle. The sound is heard approximately 10dB higher. From this fact, it can be seen that when the confidential message receiver shown in FIG. 11 is used, the speech quality deteriorates by 10 dB (power) compared to the SNR of the PM receiver that does not use the confidential message.

[Table] As a method to prevent this reception SNR deterioration,
As shown in FIG. 7, the applicant has disclosed a method using a secret receiver in which a differential function section is added to the front end of the spectrum descrambling section and an integral function section is added to the rear end (Japanese Patent Application No. 58−179395). This method is used to receive a PM modulated wave emitted using a confidential message transmitter shown in FIG. 8 or 18 and to decode the confidential message. In FIG. 7, 9 is a receiving antenna, 10 is a PM demodulator, 1
1 is a differential function section, 12 is a spectrum descrambling section, 13 is an integration function section, and e to h are observation points. In Fig. 8, 15 is an input terminal;
6 is a differential function section, 17 is a spectrum scramble section, 18 is an integration function section, 19 is a PM transmission section, and i to l are observation points. In Figure 18,
61 is an input terminal, 62 is a differential function section, 63 is a spectrum scramble section, 64 is an FM transmission section, 6
5 is an antenna. FIG. 9 shows the spectrum at each observation point in FIG. 7, and e to h correspond to observation points e to h. FIG. 10 shows the spectrum at each observation point in FIG. 8, and i to l correspond to observation points i to l, respectively. The spectra in Figures 9 and 10 are shown schematically, and now the 10th input terminal is connected to the 15th input terminal in Figure 8.
Assume that a signal having the spectrum shown in Figure i is input. The input signal is differentiated by 16 to become as shown in FIG. 10j, and then encrypted by a spectrum scrambler 17 and scrambled on the frequency range as shown in FIG. 10k. The scrambled signal is then integrated at 18, spectrumd as in Figure 10l, PM modulated at 19, and 2
It is emitted from the 0 antenna. Fading PM
The transmitted radio waves are received by 9 antennas and 1
0 PM demodulator. The case where FIG. 8 is used as the transmission method has been explained above, but the same conclusion can be reached even when FIG. 18 is used. This is clear from the well-known fact that the function is equivalent to that of the FM transmitter 64 shown in FIG. The spectrum of PM demodulation, as shown in FIG. 9e, has the same shape as that in FIG. 10l, except for the inclusion of fading noise shown by diagonal lines. The demodulated output of 10 is differentiated by 11 and the spectrum is corrected as shown in FIG. 9f. Please note that the noise component is flat as a characteristic of the spectrum of f.
Because of the noise characteristics of f, the noise characteristics can be kept unchanged no matter how much spectrum descrambling is performed by 10. On the other hand, the signal components are affected by spectrum descrambling and become as shown in FIG. 9g. The signal subjected to spectrum descrambling is 13 in Figure 7.
is integrated, and has a spectrum as shown in Fig. 9h. It becomes clear that the spectra of the input signal in FIG. 10i and the signal component in FIG. 9h are equal to each other, and that the noise in FIG. 9h forms an inverted triangular spectrum in FIG. If the 12 spectrum descramblers in Figure 7 and the 17 spectrum scramblers in Figure 8 have opposite characteristics of the spectrum scramblers, such as S (*) and S ^-1 (*), then The above relationship in FIG. 9h holds. As mentioned above, a method for solving the drawbacks of the conventional method has already been disclosed by the applicant. In addition to the essential function of receiving function 10, additional functions such as differential function 11 and integral function 13 are required, and when realized by a circuit, the circuit has the disadvantage of being complicated and economically expensive. . (Problems to be Solved by the Invention) As described above, the conventional PM demodulation method has the drawbacks that the noise characteristics are affected by spectrum scrambling and the circuit configuration is complicated. (Means for Solving the Problems) The present invention is characterized in that, in a method of receiving spectrum-scrambled and phase-modulated transmitted waves, an FM receiving means for frequency demodulating the received waves;
This is a PM signal reception system that includes a spectrum scrambling means connected to the output thereof, and an integrating means connected to the output thereof. (Function) According to the above configuration, the noise spectrum of the output of the FM receiving means is flat, and therefore the noise spectrum is not affected by spectrum scrambling.
Further, the noise spectrum at the output of the integrating means has a so-called inverted triangle shape, so that hearing level noise can be minimized. (Example) It is well known to those skilled in the art that PM signals can be demodulated using an FM demodulator and an integrating means.
(written by Masanobu Watanabe) on page 51. The present invention advances this technology. FIG. 1 is a functional block diagram showing one embodiment of the present invention, in which 21 is a receiving antenna, 22 is an FM
demodulation section, 23 is a spectrum descrambling section;
24 represents an integrating section, 25 represents an output terminal section, and m, n, and o each represent an observation point.
FIG. 12 is a diagram schematically representing the spectrum of each observation point in the embodiment of the present invention, (m),
(n) and (o) correspond to points m, n, and o in FIG. In FIG. 1, an FA receiving section 22, a spectrum descrambling section 23, and an integrating section 24 are connected in cascade to form a processing function. When receiving the PM modulated wave emitted by the already disclosed spectrum scramble transmitter shown in FIG. 8 using such a processing function, the spectrum shown in FIG. 12 is generated at each point in FIG. 1st as shown in figure o
It can be seen that the spectrum of the input signal shown in Figure 0i is correctly received, the fading noise forms the inverted triangle shown in Figure 6, and the speech quality is not degraded compared to when receiving PM without using secret speech. here
It will be explained that the FM demodulated output signal has a spectrum as shown in Fig. 12m. FIG. 13 is a diagram showing a detailed configuration example of the PM demodulation section. In the figure, 26 is the input terminal of the PM demodulator, 27 is the FM demodulator, 28 is the integral filter,
29 is an output terminal of the PM demodulator. This configuration is an example of a configuration of a PM demodulator that uses an FM demodulator, focusing on the excellent operational stability of the FM demodulator. The conventional spectrum scrambling reception system disclosed by the applicant (Japanese Patent Application No. 1983-1999) shown in FIG.
When the PM demodulation means having the configuration shown in FIG. 13 is applied to the 10 PM demodulation means of 179395), a spectrum scrambling reception system having the configuration shown in FIG. 15 is obtained. In FIG. 15, 30 is a receiving antenna, 31
3 is an FM demodulating means, 32 is an integrating means, 33 is a differentiating means, 34 is a spectrum descrambling means, 3
5 is an integrating means, 36 is an output terminal, r, s,
t indicates an observation point. In the figure, 33 differentiation and 35 integration are additional means, 31 FM demodulation,
Integration at 32 and spectrum descrambling at 34 are essential means. FIG. 16 shows an implementation example of the spectrum scrambler means. In Fig. 16, 40 is an input terminal, 41 is a mixer, 42 is a local oscillator, 43 is a low-pass filter, 44-46 are switches, 47-
49 is a band pass filter, 50-52 is a mixer, 5355 is a variable frequency local oscillator, 56-5
8 is a low-pass filter whose cut-off frequency is adjustable, 59 is an adder, 60 is an output terminal,
EA, EB, ..., EP are observation points. The spectrum appearing at each of these points is shown in Figure 17 EA~
Shown in EM. In Figure 17, EA~EM is the point EA
~Each corresponds to EM. The frequency of the local oscillator 42 is fixed at ₁ + ₂ (= ₀ ), the cutoff frequency of the low pass 43 is fixed at ₂ , and the frequency of the band pass filter 4 is fixed at 2.
The passband bands of 7 to 49 are [ ₁ , ₁ +w], [ ₁ +
w, ₁ + 2w] and [ ₂ −w, ₂ ], respectively. Here, w=( _2-1 )/ _m , which is determined by the number m of band divisions of the input signal and the input bandwidth ( _{2-1 )} . Here, the case where the number of band divisions m is 3 will be explained, but the explanation will be omitted since the analogy can be easily made even when m is other than 3. The oscillation frequency of the variable local oscillator is set to 2( ₁ +w) for 53 and 2( ₁ +w) for 54, respectively.
w), 55 is 2 ₂ −w, and the cutoff frequency of the variable cutoff low pass filter is set to _1.
Set +2w, 57 to ₁ +w, 58 to ₂ , switch 44 to EA side, 45 to EB side, 46 to EA
Set on the side. When a signal having the spectrum schematically shown in FIG. 17EA is input to the input terminal 40, a signal whose spectrum is simply inverted as shown in (EB) appears at point EB. (EA) and (EB) are filter banks formed by bandpass filters 47 to 49, and (EM) and (EB) are divided into m bands as shown by dotted lines. 1, 2, in the figure
3 means a signal component existing in the input signal band, and 1', 2', and 3' indicate that each component is inverted, as in (EB). 44 and 47 are (EA) 1
The spectrum of (EC) appears at point EC. The mixer 50 outputs the product of the output of 53 and the output of 47, and the spectrum of the output signal becomes a double-sided wave as shown in FIG. 17 (ED). If only the lower side of these both-side waves is extracted at 56, a spectrum (EE) will appear at point EE. With this operation, component 1 is inverted and the frequency
Only w is deflected. Due to the action of 45 and 48,
After the spectrum (EF) is extracted, mixer 5
1 modulates with the output signal of the local oscillator 54 and extracts the lower band of the modulated wave at 57 to obtain the spectrum (EH). During this time, component 2 has a frequency _w
is deflected downward. The third signal component 3 is extracted at 46 and 49 and then modulated by the output of the local oscillator at mixer 52,
The lower sideband of the modulated wave is extracted and subjected to spectrum inversion in the same frequency range. 3 points
If the sum of the three signals at EE, EH, and EL is calculated using 59 adders, a spectrum (EM) appears at point EM. As can be clearly seen by comparing the spectra (EA) and (EM), each component varies depending on the state of switches 44 to 46 and the frequency of local oscillators 53 to 55.
^M・m! Now, if we take the pattern shown by (EM) as the scramble output, the descrambling is as follows:
You can do the opposite of this operation. That is, (EM)
The spectrum (EA) of the source signal can be found by shifting component 1 upwards w, inverting component 2, shifting only w downward, and inverting component 3. This spectrum descrambling means sets 44 on the EB side, 45 on the EA side, and 46 on the EB side in _FIG . ( ₁ + w),
Set 55 to 2 ( ₁ + 2w), set the cutoff frequency of each of the low-pass filters 56 to 58, and set 56 to 2 (1 + 2w).
This can be achieved by setting ₂ , 57 to ₁ +w, and 58 to ₁ +2w. By the way, the differentiating means converts the input signal G(f) into f ² G(f)
The integrating means has a function of converting the input signal F(f) into a spectrum of f ^-2 F(f). The frequency is shown here. In FIG. 15, the fact that the spectrum at observation point t is equal to the spectrum at observation point r can be understood from the fact that the integral of 32 and the differential of 33 cancel each other out (f ^-2 ·f ² =1). In other words, even if the 31 FM demodulation output is directly spectrum descrambled, the PM demodulation output (corresponding to point S in Figure 15) will be as shown in Figure 7.
Even if the spectra are descrambled after differentiating, they will match correctly if the characteristics of the descramblers are equal. Therefore, it can be seen that the spectrum at point m in the embodiment of the present invention is as shown in FIG. 12m. Returning the discussion to Figure 15. The present invention is a configuration obtained when the integral of 32 and the differential of 33 are canceled out in advance so that the output of 31 is guided to the descrambler of 34. In FIG. 1, which is an embodiment of the present invention, 22
The FM demodulating means and the integrating means 24 are each part of the PM demodulating means. It is clear that FIG. 1 actually has a structure in which a spectral lamb descrambler 23 is inserted at point P of the PM demodulator shown in FIG. 13, and does not include any additional means. As explained above, according to the method of the present invention,
By using the FM demodulation means, the spectrum descrambling means, and the integration means in tandem, the first advantage is that the confidentiality of communication can be increased. The second advantage is that deterioration in speech quality can be completely prevented, and the third advantage is that the manufacturing cost of the circuit does not increase at all when applying the present invention because no additional means are used. It will be done. The above explanation has focused mainly on the auditory noise level, with emphasis on preventing deterioration of call quality and disclosing technology for realizing it economically. The following describes the degree of secrecy in the PM transmission path when the spectrum scramble reception method disclosed in the present invention is combined with the spectrum scramble transmission method shown in FIG. This shows that a new effect that improves interference resistance is generated. A signal called power G(f) is input to the input terminal of FIG. 815. 16 differential, 17 scrambler, 18
A signal with power T(f) is obtained at point l by the integrating means. That is, T(f) is T(f)=f ^-2 S[f ² G(f)] (1) Here, S[*] indicates spectrum scrambling, and the signal * is scrambled to find S[*] . When T(f) in Equation 1 is PM modulated and emitted, and FM demodulated at 22 in FIG. 1, which is an embodiment of the method of the present invention, if the PM transmission path is ideal, the demodulation power R(f)
is given as the differential form of T(f), ie, f ² T(f). Therefore, R(f)=f ² T(f)=S[f ² G(f)] (2) In the method of the present invention, after FM demodulation, the spectrum is immediately descrambled, integrated at 24, and output. Ru. If the power of the output signal is O(f), it is given as follows. O(f)=f ^-2 S ^-1 [R(f)] (3) Here, S ^-1 [*] represents the spectrum descrambling function and satisfies the following relationship. S ^-1 [*]=SS ^-1 [*]=* Substituting equation 2 into equation 3, O(f)=f ^-2 S ^-1 [S[f ² G(f)]] = f ^-2 S ^-1 S [f ² G(f)] = G(f) (4) If the PM transmission path satisfies the noise-free and distortion-free conditions, the transmitted input signal G(f) will be correctly reproduced on the receiving side. I know what will happen. Therefore, it becomes clear that the present invention has a fourth advantage. (Effect of the invention) As described above, according to the present invention, with a simple configuration,
A PM reception system with noise characteristics that is not affected by spectrum scrambling can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a diagram schematically representing the spectrum of each part of a conventional reception system, Figure 3 is a block diagram showing an example of a transmission system, and Figure 4 is a transmission system. A diagram schematically representing the spectrum of each part of the system. Figure 5 shows a long-term average spectrum of fading noise power mixed in during PM demodulation. Figure 6 shows a typical power spectrum pattern of fading noise. FIG. 7 is a block diagram showing another example of the conventional receiving system.
Figure 8 is a block diagram showing another example of a conventional transmission system, Figure 9 is a diagram schematically representing the spectrum of each part of the reception system, and Figure 10 is a diagram schematically representing the spectrum of each part of the transmission system. 11 is a block diagram showing the conventional receiving system, FIG. 12 is a diagram schematically representing the spectrum of each part of the embodiment of the present invention, and FIG. 13 is a block diagram showing the detailed configuration of PM demodulation means. , FIG. 14 is a diagram schematically representing the spectrum of each part of the PM demodulation means, and FIG.
FIG. 16 is a block diagram showing the configuration of a confidential reception system using FM demodulation means, and FIG. 17 is a diagram schematically showing the spectrum of each part of FIG. 16. 18th
The figure is a block diagram showing another example of the transmission method. 1, 9, 21, 30...Receiving antenna, 2, 1
0...PM demodulation section, 3, 12, 23... Spectrum descrambling section, 6, 17, 34... Spectrum scrambling section, 7, 19... PM modulation (transmission) section, 8, 20... Transmission antenna, 11,
16, 33... Differential part, 13, 18, 24, 2
8, 32, 35... Integral part, 22, 27, 31...
...FM demodulation section, 40...Input terminal, 41, 50~
52...Mixer, 42, 53-55...Local oscillator, 43, 56-58...Low pass filter, 4
4 to 46...Switch, 47, 49...Band pass filter, 59...Adder, 60...Output terminal. 61...Input terminal, 62...Differential part, 63...
...Spectrum scrambling section, 64...FM modulation (transmission) section, 65...Antenna.

Claims (1)

[Claims] 1 Differentiating means and spectrum scrambling means
In a method of receiving a transmission wave that is generated by a transmitter provided with FM transmission means in this order, spectrum scrambled, and phase shift modulated, at least an FM reception means for frequency demodulating the received wave, and a demodulation of the FM reception means. A spectrum scrambling reception method is provided with means for spectrum descrambling an output signal and means for integrating the descrambled output, and receiving the spectrum scrambled signal on a phase shift modulation (PM) wireless transmission path.