JPH0642655B2 - Asynchronous spread spectrum communication method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spread spectrum communication method which is one form of a wireless transmission method, and in particular, synchronization acquisition and synchronization, which are considered to be the most difficult part in execution of spread spectrum communication. The present invention relates to a completely asynchronous spread spectrum communication method which requires no maintenance circuit.

[Prior Art] A spread spectrum communication method is a direct sequence method according to a spread method.
They are roughly classified into frequency hopping methods and each have their own unique characteristics, but the common point is that they are more resistant to interference and interference and superior in confidentiality than the conventional general communication methods. It is a communication method that has been widely spread and developed mainly in the field of military communication. Although there are differences in the means, the basic configuration is that the distribution width of the transmission power is expanded to the extent that it cannot be compared with the conventional communication method using the PN code, and the average power density when evaluated in a narrow band is significantly reduced. Excuse me. Therefore, when the signal is received by the conventional communication method, the noise level is merely increased. In order to receive and demodulate the signal, a coherent (continuous) signal including information to be transmitted is obtained by despreading using a PN code that is exactly the same as the PN code at the time of transmission and has the same phase. Is converged and then demodulated. In this process, the reference signal of the receiving device must be accurately synchronized with the received PN code in terms of both the position of the code pattern and the code rate. The synchronization technology for this purpose, that is, the synchronization acquisition technology and the synchronization maintenance technology, dominates the effectiveness of spread spectrum communication, and the greatest amount of development power has been invested, and various synchronization methods have been devised.

[Problems to be Solved by the Invention] As described above, the synchronization technology in the spread spectrum communication technology is the greatest research subject, and spread spectrum communication cannot be established without the synchronization technology.

Furthermore, the circuit for synchronization is usually composed mainly of a logic circuit that operates according to a series of algorithms, and since it occupies the main part of the device, it is necessary to reduce the size and cost of the device at present. Technology is difficult.

[Means for Solving Problems] The present invention originates from development for simplifying synchronization,
As a result, among the features of spread spectrum communication,
Although the processing gain effect is reduced, it has the basic features of low interference with other communications, low interference, and strong concealment with respect to ordinary communication methods, and requires no synchronization circuit. It is possible to provide a completely asynchronous spread spectrum communication method.

The method includes a spread spectrum signal that does not include information to be transmitted in a first frequency band and a first frequency band in any second frequency band other than a frequency band having a harmonic frequency relationship with the first frequency band. A second spread spectrum signal that has a specific correlation with the spread spectrum signal and that contains information to be transmitted, is synthesized by using an inactive element, and is transmitted at the same time; Wave spread spectrum signal is received at the same time, after being multiplied by the multiplier, the output is further squared, and among the multiple frequency components generated, it is located in the middle of the first and second spread spectrum signal frequencies. A completely asynchronous spectrum equipped with a receiver capable of extracting twice the calculated frequency (coherent signal is obtained in the process) and demodulating this. It is a non-diffusion communication method.

[Operation] The operation principle of this method will be described using mathematical expressions.

In the transmitter, as a means for obtaining the _first spread spectrum signal f ₁ , first the first carrier wave f _c1 (f _c1 = Ec · cos ω
₁ t However, Ec is the amplitude of the carrier, ω ₁ is the angular frequency of the carrier, and PN code fp (fp = Ep · cos pt where Ep is PN
When the amplitude of the code, p is the instantaneous angular frequency of the PN code) is amplitude-modulated, the output e ₁ is shown below.

e ₁ = (Ec + Ep ・ cos pt) ・ cos ω ₁ t = Ec ・ cos ω ₁ t + Ep ・ cos pt ・ cos ω ₁ t = Ec ・ cos ω ₁ t + (Ep / 2) ・ cos (ω ₁ + p) t + (Ep / 2) ・ cos (ω ₁ -p) t …… Extracts the second term component of the equation with a bandpass filter,
This is the first spread spectrum signal f ₁ . That is, f ₁ = E ・ cos (ω ₁ + p) t, where E = Ep / 2 …… As a means to obtain the _second spread spectrum signal f ₂ , the second carrier f _c2 (f _c2 = Ec ・ cos ( ω ₂ + Δf) t where Ec is the amplitude of the carrier and is equal to the amplitude of f _c1 , ω ₂ is the angular frequency of the carrier, Δf is the instantaneous angular frequency of the information to be transmitted), and the PN code fp With amplitude modulation, the output e ₂ is shown below.

e ₂ = (Ec + Ep ・ cos pt) ・ cos (ω ₂ + Δf) t = Ec ・ cos (ω ₂ + Δf) t + Ep ・ cos pt ・ cos (ω ₂ + Δf) t = Ec ・ cos ( ω ₂ + Δf) t + (Ep / 2) cos (ω ₂ + Δf + p) t + (Ep / 2) cos (ω ₂ + Δf) -p) t …… The band-pass filter for the third term component of the equation Take out with
This is the second spread spectrum signal f ₂ . That is, f ₂ = E ・ cos ((ω ₂ + Δf) -p) t, where E = Ep / 2 ...... f ₁ and f ₂ obtained by the above means are independently amplified to a predetermined power. Then, after being combined by a power combiner composed of non-active elements, it is radiated into space from an appropriate antenna. Here, it should be noted that the power combiner should not use active elements. Because there is practically no active element having perfect linearity and has some non-linear area, if f ₁ and f ₂ pass through this non-linear area at the same time, the explanation will be given in the later-described receiver. This is because the coherent component of 1 may be generated, and the confidentiality, which is one of the characteristics of the present method, is considerably deteriorated.

The receiving device amplifies f ₁ and f ₂ to a predetermined amplitude by independent selection amplifiers, multiplies them, and then squares them. This multiplication and squaring process is performed by a high frequency analog multiplier (hereinafter referred to as a high frequency multiplier at the end) within a complete real time. The process will be described below using mathematical expressions.

The change that f ₁ and f ₂ undergo in the high frequency multiplier is shown by the following equation.

(f ₁ × f ₂ ) ² …… Expands expressions by substituting them into the equation.

(f ₁ × f ₂ ) ² = E ²・ cos ² (ω ₁ + p) t ・ E ²・ cos ² ((ω ² ₊ Δf) -p) t = E ⁴・ (1/2) ・ (1 _{+ cos2 (ω 1 + p)} t × (1/2) · (1+ · cos2 ((ω 2 + Δf) -p) t) = (E 4/4) · {1 + cos2 (ω 1 + p _{) t + cos2 ((ω 2} + Δf) -p) t) cos2 (ω 1 + p) t + cos2 ((ω 2 + Δf) -p) t} = (E 4/4) · {1 + cos2 (ω ₁ + p) t + cos2 ((ω ₂ + Δf) -p) t + (1/2) ・ cos2 ((ω ₂ + Δf) + ω ₁ ) t + (1/2) ・ cos2 ((ω ₂ + Δf) -ω ₁ -2p) t} = E ⁴・ (1/4) + E ⁴・ (1/4) cos2 (ω ₁ + p) t + E ⁴・ (1/4) cos2 ((ω ₂ + Δf) -p) t + E ⁴・ (1/8) cos2 ((ω ₂ + Δf) + ω ₁ ) t + E ⁴・ (1/8) cos2 ((ω ₂ + Δf) -ω ₁ -2p) t ...... In the equation, the first term is the direct current component, the second term is the frequency component twice f ₁ , the third term is the frequency component twice f ₂ , and the fourth term is the first carrier wave and the second carrier wave. A coherent component that is twice the sum and does not include the instantaneous angular frequency p of the PN code. The fifth term is twice the difference between the first and second carrier waves minus the instantaneous angular frequency of the PN code. Is a component of.

That is, the first term is coherent in the direct current component but has no information to be transmitted, and the second, third and fifth terms are all so-called spread spectrum signals including the instantaneous angular frequency p of the PN code. They are synonymous. Only the fourth term is a coherent wave that does not include the instantaneous angular frequency p of the PN code and is determined only by the first and second carriers.
This coherent wave has the information Δf contained in the second carrier to be transmitted. If the component of the fourth term is selected and extracted by the filter, the subsequent processing is performed by the general receiver configuration. The method can be used to easily demodulate the information Δf to be transmitted.

In the explanation of the operation, it is obvious that the power combiner is not required under the environment where independent antennas can be used for the first and second spread spectrum signals, respectively. Each of the second spread spectrum signals can be efficiently radiated. It should be noted that when using an integral antenna, it is necessary to use a power combiner composed of inactive elements.

[Embodiment] Here, in order to avoid complexity, only one embodiment will be described. However, as described in the above-mentioned operation, the present invention has a wide variety of implementation methods by using the operation principle. It doesn't wait to exist over the world.

Based on the operation principle of the present invention, the information to be transmitted is voice, and the method of performing primary modulation on the second carrier wave is the FM method,
The FH method is used as the method of spreading with a PN code. A block diagram of the transmitter is shown in FIG. 1, a frequency spectrum in each part of the transmitter is shown in FIG. 2, and a frequency spectrum in each part of the transmitter is shown in FIG.

The configuration and operation of the transmitter will be described with reference to FIG.

The input voice is amplified by the amplifier 1 and then the normal FM
Similarly to the transmission, the frequency conversion circuit 2 FM-modulates the second carrier wave (fc2) from the second carrier generation circuit 3.

White noise is generated by the PN code generation circuit 4, and the third carrier wave from the third carrier wave generation circuit 5 is F by the FH signal generation circuit 6.
M-modulate. At this point, a PN code equivalent to the FH code is obtained, and the spreading band is uniquely determined by the white noise and the FM modulation degree. The PN code (fc3) is distributed by the distributor 7, and is guided to the balanced modulation circuit 8 of the voice input circuit and the balanced modulation circuit 10 for the first carrier.

When the second carrier wave (fc2) is balanced-modulated by the PN code (fc3) in the balanced modulation circuit 8, the spectrum shown in FIG. 3 (a) is obtained, so that only the lower sideband (f2) is generated by the bandpass wave circuit 11. Are taken out (see FIG. 3 (b)).

When the first carrier (fc3) that is not modulated from the first carrier is balanced-modulated by the PN code (fc3) in the balanced modulator 10, the spectrum shown in FIG. To take out only the lower sideband (f1) (see FIG. 3 (d)).

f1 and f2 are amplified by the power amplifier circuits 13 and 14, respectively, and unnecessary harmonics are removed by the low-pass wave circuits 15 and 16 and then combined by the power combiner circuit 17 (FIG. 3 (e)).
), Emitted from the transmitting antenna.

Next, the configuration and operation of the receiving device for receiving this signal will be described with reference to FIG.

The signal input from the reception antenna is f1 by the distributor 20.
, F2 and band-pass wave circuits 21, 22 respectively
And is amplified by the high frequency amplifier circuits 23 and 24, and then calculated in real time by the high frequency multiplier 25. When the band-pass wave circuit 26 that passes only the (f1 + f2) ² component of the plurality of frequency components thus obtained is passed, the coherent wave already described is obtained (see FIG. 3 (f)).

Hereinafter, it is possible to demodulate the voice, which is information to be transmitted by a normal FM receiving device, such as demodulation by the frequency conversion circuit 27 using the local oscillation signal from the local oscillation circuit 28 and amplification by the amplification circuit 29. .

[Effects of the Invention] As described above, according to the method of the present invention, the method of performing the primary modulation of the information to be transmitted on the second carrier wave is not limited to AM, FM, FSK and other modulation formats. Also, both the PN code spreading method, the DS method and the FH method are possible, and the structure of the transmitter and the receiver can be constructed by the conventional technique, and special elements (convolver, matched filter, etc.) and complicated Since a synchronizer is not required at all, it is possible to provide a spread spectrum method that is extremely practical and versatile.

[Brief description of drawings]

FIG. 1 is a block diagram of a transmitter in an embodiment for carrying out the method of the present invention, FIG. 2 is a block diagram of a receiver in an embodiment for carrying out the method of the present invention, and FIG. 3A and 3B show signal waveforms at predetermined locations of the receiver.

Claims (3)

[Claims] 1. A first spread spectrum signal that does not contain information to be transmitted and is modulated at a specific frequency, and a second spread spectrum signal that contains information to be transmitted and is modulated at the specific frequency. It can be obtained by receiving the first and second spread spectrum signals at the same time as they are at the same time or by combining them using inactive elements and transmitting at the same time, and then multiplying by the multiplier and squaring the output. A receiver capable of obtaining information to be transmitted by extracting and demodulating a frequency twice as high as a frequency located between the first spread spectrum signal and the second spread spectrum signal from a plurality of frequency components A non-synchronous spread spectrum communication method that does not require a circuit for synchronization acquisition and synchronization maintenance. 2. The first spread spectrum signal is the first carrier frequency having a single spectrum modulated by a first PN (pseudo noise) code, and the second spread spectrum signal is The asynchronous spread spectrum communication method according to claim 1, wherein the second carrier frequency, which has undergone primary modulation with information to be transmitted, is modulated with a second PN code. 3. The first PN code and the second PN code are the same, but the first spread spectrum signal and the second spectrum are in the state of being converted into the first and second spread spectrum signals. The asynchronous spread spectrum communication according to claim 2, wherein the asynchronous frequencies are distributed symmetrically with respect to the origin of a calculated frequency located in the middle of the spread signal and symmetrically shifted instantaneously. Method.