JPH0652891B2 - Spread spectrum communication system - Google Patents

Description

The present invention relates to a spread spectrum communication system, and in particular, a spread code generation circuit for generating pseudo noise for despreading is unnecessary on the receiving (demodulating) side. And spread spectrum communication system.

[Technical background]

The recent development of communication technology and diversification of system technology in Japan is remarkable. One of them is multiplex communication represented by optical communication technology, and in communication technology using radio waves, multi-channel access (MCA) has become mainstream in order to effectively use the electric waves of the analog modulation method.
However, this MCA has the advantage that a specific person cannot occupy the same frequency, but of course the number of channels is limited, so that calls over more than one channel cannot be performed simultaneously.
For this reason, it is routinely necessary to wait for a call in a large city, which is frequently used. This is because frequency resources, which are finite resources, are used by simply dividing the bandwidth, and considering the quality, emotion, and immediacy of information, it seems that such a technology has reached its limit. Be done.

Therefore, research and development of even more efficient communication methods
It has been made by many researchers for a long time, and one of them is a spread spectrum communication system. This spread spectrum
The (Spread Spectrum: SS) communication method was developed in Europe about 50 years ago, and the basic idea was established in the 1950s. In the 1960s, a pseudo-noise code generation circuit was created with 100 transistors, but the early technology was immature, and the development of active elements and manufacturing technology that compose them was long awaited. In recent years, due to the development of high-density IC technology and the cost reduction of ICs, it has become possible to manufacture a small-sized and low-priced device, and such a communication system has been regained attention.

A spread spectrum communication system is a system in which a carrier is first-order-modulated with an information signal and then spread by a broadband noise-like spread code.
This is a method of performing next modulation and spreading over a very wide frequency band. Generally, there are a direct spread (DS) system, a frequency hopping (FH) system, a hybrid system, etc., depending on the difference of the secondary modulation system.
Regarding the scheme. Such spread spectrum communication has extremely high confidentiality (confidentiality), is resistant to external interference, noise and intentional interference, can coexist with conventional systems, and does not require a control station or control channel such as an MCA station. Since the power density is low in the DS (Direct Spread) method that can be managed by the address code, it seems that there is no radio wave (sending with weak power is possible). Can be increased, and it is possible to multiplex by changing the pseudo-noise code signal in the same band, etc. These are recognized, and these are now recognized not only in the communication field but also in various fields. Is progressing, and deployment to consumer equipment has also begun.

[Conventional technology]

A conventional spread spectrum communication system will be described with reference to FIGS. 9 and 10. FIG. 9 is a basic block configuration diagram for realizing a spread spectrum communication system by the DS system, and FIG. 10 is a spectrum waveform diagram in each component. As shown in FIG. 9, the signal (F ₁ ) as shown in FIG. 10 (a), which is primary-modulated by the primary modulator 31 of the station A on the transmission side, is spread by the spreading modulation circuit 36. The signal (F _SS ; see FIG. 2B) from the code generation circuit 39 is secondarily modulated, power-amplified and output from the antenna A _{1 as} a transmission signal (F _1S ). The primary modulation is not particularly limited, and frequency modulation (FM) or PSK (Phase Shift Key)
ing) or the like (in the present specification, description will be made assuming that modulation is performed by this PSK), and secondary modulation (spread modulation) is
Generally, spread modulation is performed using a pseudo noise code (PN code). This PN code needs to be as random noise as possible and has a constant period in order to extract the code on the receiver side.

Next, the configuration and functions of the receiving side will be described. In the B station on the receiving side, the F _1S signal obtained from the antenna A ₂ by the predetermined filter and the high frequency amplifier is _fed to the despreading circuit 3
In step 7, despreading is performed by the spreading code from the spreading code generation circuit 49. The spread code generation circuit 49 is synchronized with the spread code generation circuit 39 of the A station, and the PN code is also equivalent (F _SS ). By the way, the radio waves entering the antenna A ₂ are not limited to F _1S, and as shown in FIG. 10 (c),
There are radio waves ( _F2S , _F3S , ...) From other SS stations and general radio waves ( _Fn ). Therefore, by performing despreading in the despreading circuit 37, the desired radio wave F _1F as shown in FIG. 3D is returned to the spectrum as shown in FIG. 2A, and the filter 41 is preferably a narrow band wave filter. Most of the components other than F _1S are removed (see (e) in the figure), and the demodulation circuit 43 demodulates and outputs the original information signal. As can be seen from FIG. 6E, in the output signal of the filter 41, Fn of the interference wave and a part of the SS wave of the multi-station remain in addition to F _1S . The ratio of this residual power to the power of the target signal is called the DN ratio (signal power to interference power ratio), and in order to obtain a large DN ratio, it is advantageous that the spreading band is as wide as possible. It is in the range of 100 to 1000 times the frequency band of the information signal.

The basic principle of spread spectrum communication has been described above.
Next, a specific operation in each modulation / demodulation will be theoretically explained. A spread spectrum signal S (t) {F _1S } in FIG. 9 in spread spectrum communication has information data of d (t) [+ 1 or -1] and spreading code F _SS of P (t) [+ 1 or- 1], carrier wave cosω
_{Let c} t be expressed by the following equation.

S (t) = d (t ) P (t) cosω c t ...... (1) ( where, ω _{c =} 2πf _c) the spread spectrum signal S (t) at the reception (demodulation), spectra incoming A spread code clock signal is generated from the spread signal, and the spread code P (t) synchronized with the spread code in the spread spectrum signal at the time of transmission (actually with some delay) Is obtained and is multiplied by the incoming spread spectrum signal S (t) (also called correlation or despreading) to obtain d (t) cosω
It is converted into _c t becomes two-phase PSK signal. Furthermore, the carrier cos .omega _c t reproduced And performs synchronous detection by _{multiplying, d (t) (cosω c} t) 2 = d (t) (1 + cos2ω c t) / 2 was obtained, and the information data by removing the carrier component 2 [omega _c t by the filter d (t) is demodulated.

Here, the bandwidth of the two-phase PSK signal d (t) cosω _c t (referred to as spectral main lobe of) the B _D, spread code P (t)
Assuming that the bandwidth of the spread spectrum signal spread by (is the main lobe of the spectrum) is B _p , the process gain G _p in spread spectrum communication is expressed by G _p = B _p / B _D (2) Be done. The process gain G _p is a value of several hundreds to several thousands in a normal design value, and the interference signal, noise, etc. are suppressed according to this value, so that the information data d (t)
On the other hand, the wider the frequency band of the spread spectrum signal, the higher the effect of improvement in interference resistance and noise resistance. That is,
The improvement effect is almost uniquely determined by the process gain G _p .

[Problems to be Solved by the Invention]

In such a spread spectrum communication system, "despreading" is the most important, and it is not easy to generate a spreading code necessary for doing so. At present, the despreading method using an AFC control loop, a delay lock loop and a multiplier is used. , The despreading method with a synchronous loop using a matched filter and a multiplier is generally used. The despreading by these configurations has a complicated circuit configuration, and there are also problems in terms of adjustment and cost, and these problems need to be solved when applied to consumer equipment. Moreover, since a very wide frequency band is required, there is a problem in effective use of the frequency band (or radio waves), and the usable frequency band is actually limited, making it difficult to design as desired. There are drawbacks such as.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the spread spectrum communication system of the present invention is equipped with the following means for communication. That is, on the modulation side (10), PSK modulating means for PSK modulating the information signal with the first carrier wave to obtain a PSK modulated signal,
Spreading code generating means for inputting a clock signal to generate a spreading code signal, and first spreading means for obtaining a first spread spectrum signal by spreading by multiplying the obtained spread code signal by a PSK modulation signal. And a sum conversion means for inputting a spread code signal and a clock signal to obtain a sum conversion output signal, and a second carrier to multiply the obtained sum conversion output signal to obtain a second spread spectrum signal. A second diffusion means,
It is provided with an addition unit or the like that adds the second spread spectrum signal and the first spread spectrum signal and outputs the added spread spectrum signal.

In addition, the demodulator (20) receives the added spread spectrum signal as the first signal.
Means for separating and detecting the spread spectrum signal and the second spread spectrum signal, a delay circuit for delaying the separated and detected second spread spectrum signal by one time slot, and a delay circuit of this delay circuit. Multiplying means for multiplying the output and the second spread spectrum signal to obtain a demodulated spread code signal; and multiplying the obtained demodulated spread code signal by the first spread spectrum signal to despread it and demodulate P
Equipped with despread demodulation means to obtain SK signal.

Note that the frequency interval between the first carrier wave and the second carrier wave is (2
N-1) / {2 (2 ⁿ -1) T ₀ } (where N is a positive integer, n is the number of shift register stages in the spread code generating means, and T ₀ is a 1-bit time length of the clock signal) Thus, the spectrum of the second spread spectrum signal is allowed to exist between the sidebands of the first spread spectrum signal for communication.

〔Example〕

In the spread spectrum communication system of the present invention, since the communication is performed by the above-mentioned configuration, the synchronization composed of the clock recovery circuit, the spread code generation circuit, and the loop, which have been indispensable constituent elements in the past in the despreading. A pull-in circuit and a synchronization holding circuit are unnecessary, and a specific example of a device that can realize the method of the present invention will be described below with reference to the drawings.

FIG. 1 is a block configuration diagram of a first embodiment of a spread spectrum communication apparatus capable of realizing a spread spectrum communication system of the present invention, in which FIG. 1 (A) is a modulator (transmitting side) 10 and FIG. 1 (B). Is a demodulation unit (reception side) 20. A part of the configuration of the antenna and the like is omitted.

As shown in FIG. 1 (A), the modulator 10 includes two multipliers 2 and 3; an arithmetic circuit (adder) 6, a sum conversion circuit 8, a spread code generation circuit (PNG) 9 and a BPF (band wave). 11) and the like, which are connected as shown in FIG. 1 (A). The sum conversion circuit 8 is, for example, an EX-OR gate 25 and a D
It is realized by connecting a flip-flop circuit (hereinafter also referred to as “DFF”) 26 as shown in the figure. The demodulation unit 20 has two BPFs 13 and 15; two delay circuits (DL).
16, 17; two multipliers 4, 5; an adder 18, a subtractor 22, and an LPF (band pass filter) 24 are connected as shown in FIG. 1 (B). The delay circuit 16, the adder 18, and the subtractor 22 form a comb-shaped filter 19 having two types of transmission characteristics, and the transmission characteristics are added to FIGS. 5 (A) and 5 (B), respectively. This is as shown as the characteristics and the subtraction characteristics. Hereinafter, regarding 20 specific functions and operations of the modulator 10 and the demodulator, the frequency spectrum diagrams of FIGS. 2 and 3 and the timing chart (signal waveform diagram) of FIG. 4 will be described.
Will be described with reference to.

When transmitting, first, in the modulator 10, the information signal d (t) is modulated by the first carrier ω _{c1 by the} primary modulator (not shown), and the waveform ((A) in FIG. The primary modulation signal d (t) cosω _c1 t (here, a two-phase PSK modulation signal) as shown in (a) is supplied to the multiplier 2 via the input terminal In ₁ . On the other hand, the clock signal S from the input terminal In _2
c (t) is supplied to the spread code generation circuit 9, and the spread code signal P (t) is generated based on this signal. A pseudo-noise code is generally used as the spreading code, and an M-sequence code is often used among them, so it is also called a "pseudo-noise code". Spread code P generated by spread code generation circuit 9
(t) is supplied to the multiplier 2, where the two-phase PSK signal d
(t) cosω _c1 t Spread spectrum is performed by multiplication,
Spread spectrum signal P (t) d (t) cos ω _c1 t (hereinafter “S
₁ (t) ”(see Fig. 2 (c)). The spread code signal P (t) and the clock signal S _c (t) are also respectively supplied to the EX-OR gate 25 of the sum conversion circuit 8 and the _{T of the} DFF 26.
It is supplied to the (clock) terminal. This sum conversion circuit 8 is Modu
lo2, that is, modulo 2, is added, and the spread code signal P
Figure 1 is a (t) binary input signals of the point (a) (A) and a _i, a sum converted output signal Ps (t) the signal of points (b) b
_{If i} , It is represented by. The relationship between a _i and b _i is as shown in FIGS. 4 (A) and 4 (B), respectively. _{That, b 1 = a 1 + b} 0 = 1, b 2 = a 2 + b 1 = 1, b 3 = a 3 + b 2 = 1, b 4 = a 4 + b 3 = 0, which is ... a.

On the other hand, the carrier signal cos ω _c2 t as shown in (b) of FIG. 2 (B) is supplied to the multiplier ₃ from the input terminal In ₃ , where the output signal Ps (t) from the summation conversion circuit 8 is supplied. Spreading is performed by multiplication, and the spread spectrum signal S ₂ (t) = P as shown in FIG.
s (t) cos ω _c2 t is output and supplied to the adder 6. Therefore, the addition with the spread spectrum signal S ₁ (t) is performed here (see FIG. 8E), and the addition signal output is the BP of the next stage.
In F11, only the main lobe of the spread spectrum signal is transmitted and transmitted, and output from the output terminal Out ₁ . This addition spectrum addition signal S ₁ (t) + S ₂ (t) is expressed by the following equation.

S ₁ (t) + S ₂ (t) = P (t) d (t) cosω _c1 t + Ps (t) cosω _c2 t (4) Here, the frequency spectrum of the spread spectrum signal will be described. Sidebands Sa ₁ and Sa in Figures (C) and (D)
The interval between _{2 and} the interval between Sb ₁ and Sb ₂ is the clock signal Sc (t)
If the 1-bit time length of is equal to T ₀ , the M-sequence code in the spreading code generation circuit 9 is used, and the number of stages is n when a shift register is used in the M-sequence code generation circuit (not shown), {( 2 ⁿ −1) T ₀ } ⁻¹ , and
Two sideband + Sa ₁ ~ + Sa _n, and -Sa ₁ ~-Sa _n, sideband + Sb ₁ ~ + Sb _n, the -Sb ₁ ~-Sb _n, respectively alternately as shown in FIG. (E) Are evenly spaced. Therefore,
The frequency spacing between the double sideband Sa ₁ and Sb columns is (2 (2 ⁿ −1)
It is given by T ₀ } ^-1 . FIG. 3 is a frequency characteristic diagram of the spread spectrum signal, and the solid line portion (between (a) and (b) in the figure) shows the main lobe. Note that 2 ⁿ -1 is the spread code length.

In the method of the present invention, the selection of frequency is an important point,
The spectrum of the spread spectrum signal S ₂ (t) is selected to exist between the sidebands in the frequency spectrum of the spread spectrum signal S ₁ (t). That is, in FIG.
A carrier angular frequency omega _c1 follows modulation (2-phase PSK modulation) signal d (t) cosω _c1 t, the frequency interval of the carrier wave angular frequency omega _c2 of the carrier signal _{cosω c2 t 1 / {2 (} 2 n -1) T ₀ }. It is not limited to this, in theory may be a gap determined by (2N-1) / {2 (2 n -1) T 0}. However, N is a positive integer, and FIG. 2 shows the case where N = 1. By thus defining the frequency interval, the spectra of both spread spectrum signals S ₁ (t) and S ₂ (t) are arranged alternately without overlapping.

Next, referring to FIG. 1 (B), the function of the demodulation unit 20 will be described with reference to FIG. Spread spectrum signal S _M (t) {= S ₁ (t) + S ₂ (t)} that has entered the input terminal In ₄ .
The frequency component other than the spread spectrum signal is removed by the BPF 13 (see FIG. 2 (E)), and the result is supplied to the positive input terminals of the delay circuit 16, the adder 18, and the subtractor 22.
In addition, the output of the delay circuit 16 is added to the adder 18 and the subtractor 2
The delay circuit 16, the adder 18, and the subtractor 22 have the addition characteristic and the subtraction characteristic (see FIGS. 5A and 5B, respectively) by the configuration in which they are supplied to the negative input terminal of 2. The tooth profile filter 19 is formed. Delay circuit 1
Assuming that the delay time in 6 is T (= 1 / F), 1 / T, 2 / T, 3 / T, ..., In the case of addition, as shown in FIG.
The gain is doubled at the frequency of N / T (N is a natural number),
At each of these intermediate frequencies, the output is 0 and a steep dip is possible. In the case of subtraction, conversely, as shown in Fig. 7B, there is a valley (gain 0) at the frequencies of 1 / T, 2 / T, 3 / T, ..., N / T, and the middle of them. Gain at frequency of 2
Doubled. Therefore, if the delay time is set to T = (2 ⁿ −1) T ₀ and the frequency of the peaks or troughs of the comb-shaped filter 19 is matched with the sideband frequency of the spread spectrum signal, the spread spectrum signal S ₁ (t) And S ₂ (t) can be detected separately. Therefore, the spread spectrum signal S ₁ (t) (see FIG. 2 (C)) is output from the adder 18, and the spread spectrum signal S ₂ (t) (see FIG. 2D) is output from the subtractor 22. ) Are obtained separately.

The delay circuit 17 is configured to add a delay of one time slot of the sum conversion output signal Ps (t). Therefore, the input side and the output side of the delay circuit 17 are shown in FIG.
The waveforms are as shown in (D). These two signals are multiplied by the multiplier 5 and the carrier component is removed by the LPF 24, whereby the spread code signal P (t) equivalent to that at the time of modulation is detected as shown in FIG. . (However, the extreme positive is the opposite). This spread code signal P (t) is supplied to the multiplier 4,
Despreading is performed by multiplication with the spread spectrum signal S ₁ (t) from the adder 18. Therefore, a signal obtained by demodulating the spread spectrum signal S ₁ (t) is obtained from the multiplier 4, and the BPF is obtained.
Unwanted frequency components are removed at 11 and output terminal Out
_{The 2-} phase two-phase PSK signal d (t) cosω _c1 t is output. The expression of the delay of the spread spectrum signal S _M (t) by the delay circuit 16 is omitted for convenience of explanation.

Here, the separation detection operation of the spread spectrum signal S _M (t) (the operating principle of the comb-shaped filter 19 and the like) will be described. The spread spectrum signal S _M (tT) output from the delay circuit 16 shown in FIG. 1 (B) is S _M (tT) = S ₁ (tT) + S ₂ (tT) = P (tT) d (tT ) cosω _c1 (tT) + Ps (tT) cosω _c2 (tT) (5) Here, as a precondition, P (t) {or Ps
(t)} is equal to the delay time T, and cosω _c1 t is in-phase at the period of P (t), continuous wave repeated at the same level, cosω
Assuming that _c2 t is a continuous wave having a phase opposite to that of P (t) and repeating at the same level, S _M (tT) is S _M (tT) = P (t) d (tT) cosω _c1 t −Ps ( t) cosω _c2 t (6) Therefore, the addition output S _M (t) + S _M (tT) {= S ₁
(t)} is S ₁ (t) = S _M (t) + S _M (tT) = {d (t) + d (tT)} P (t) cosω _c1 t (7) On the other hand, the subtraction output S _M (t) + S _M (tT) {= S ₂ (t)}
Is S ₂ (t) = S _M (t) -S _M (tT) = 2Ps (t) cosω _c2 t + d (t) -d (tT)} P (t) cosω _c1 t ...... (8) Become. Here, {d (t) −d (t-
T)} P (t) cosω _c1 t is a crosstalk component that cannot be separated by the comb-tooth filter 19, but the delay time is longer than the one-chip time length (= 1 bit time length) of the information data d (t). Since it is chosen very short, it can be omitted approximately. Therefore, the subtraction output S ₂ (t) becomes S ₂ (t) ≈2Ps (t) cosω _c2 t (9).

Next, the despreading operation will be specifically described according to the configuration of FIG. First, the operation of generating the spread code signal P (t) will be described. The subtraction output S ₂ (t) is used in the multiplier 5 and the delay circuit 1 for generating the spread code signal P (t).
7 is supplied. The delay circuit 17 outputs the sum conversion output signal Ps.
This is for delaying (t) by one chip time length (one time slot). When the delay time is τ, the delayed subtraction output is S ₂ (t-τ). Therefore, the delayed subtraction output S ₂ (t-
τ) is multiplied by 2 ₂ (t) to obtain the spread code signal P
converted to (t). Since this method is “delayed detection” that has been conventionally performed, a detailed explanation of its principle is omitted.

Next, the demodulation operation will be described. Since unnecessary frequency components in the output signal of the multiplier 5 are removed by the LPF 24,
A signal equivalent to the spread code signal P (t) at the time of modulation is output from the LPF 24 and supplied to the multiplier 4. Since the addition output S ₁ (t) is also supplied to the multiplier 4, both signals are multiplied here to convert P (t) into a direct current, and the demodulated two-phase PSK signal {d (t) + d Only (tT)} cosω _c1 t is output. The demodulated two-phase PSK signal is output from the output terminal Out ₂ after removing unnecessary noise components in the BPF 15.

Next, a second embodiment of a communication device capable of realizing the communication system of the present invention will be described with reference to the circuit block diagram of FIG. 6, the frequency spectrum of FIG. 7 and the timing chart of FIG. FIG. 6 (A) is a block configuration diagram of the modulation section, and FIG. 6 (B) is a block configuration diagram of the demodulation section. In these figures, the same components as those of the first embodiment shown in FIG. A number is given and detailed description thereof is omitted.

The modulator 30 has a higher BP than the modulator 10 of the first embodiment.
The difference is that an F (bandpass filter) 11 is inserted between the multiplier 2 and the arithmetic circuit 6, and another BPF 12 is added and inserted between the multiplier 3 and the arithmetic circuit 6, There are no changes to other components. This BPF 11 is a spread spectrum signal S ₁ (t) {= P (t) d (t) co from the multiplier 2.
Only the main lobe of the frequency spectrum of sω _c1 t} is passed and supplied to the arithmetic circuit 6.
Is the spread spectrum signal S ₂ (t) {= Ps from the multiplier 3.
Only the main lobe of the frequency spectrum of (t) cos ω _c2 t} is passed and supplied to the arithmetic circuit 6. As a result, the addition spread spectrum signal S ₁ (t) + S ₂ (t) {= having the frequency spectrum as shown in FIG.
S _M (t), refer to the equation (3)} is output from the output terminal Out _{1 as in} the first embodiment. Further, the explanation of the operation of the sum conversion circuit 8 and the explanation of the signal waveforms of FIGS. 8 (A) and 8 (B) are the same as those of the modulation section 10 of the first embodiment. The explanation of the functions and operating principles is omitted.

As shown in FIG. 7, the frequencies of the two carrier waves ω _c1 and ω _c2 are selected so as to be sufficiently separated from each other, and the BPFs 11 and 1 are selected.
The two passbands (the bands of the main lobes I and II of the frequency spectrum of the spread spectrum signals S ₁ (t) and S ₂ (t)) do not overlap each other (that is, the spread code length 2 ⁿ −1 is N. By setting the condition of> 2 ⁿ −1}, the configuration of the demodulation unit 40 can be further simplified as compared with the demodulation unit 20 as described later. However, the frequency band used is doubled as compared with the configuration of the first embodiment.

Next, with reference to FIG. 6 (B), the configuration and function of the demodulation unit 40 will be described with reference to the frequency spectrum diagram of FIG. 7 and the timing chart of FIG. As is clear from comparison between FIG. 6 (B) and FIG. 1 (B), the demodulation unit 40 has a simpler structure than the demodulation unit 20, and the comb-teeth filter 19 is omitted. ing. Instead, a BPF 14 is added and inserted between the input terminal In ₄ and the multiplier 5 and the delay circuit 17. In such a configuration, the addition spread spectrum signal S _M (t) {= S ₁ (t) + S ₂ (t) = P (t) d (t) c as shown in FIG. 7 is input from the input terminal In ₄ .
osω _c1 t + Ps (t) cosω _c2 t} is supplied to the BPFs 13 and 14. The BPF 13 passes only the spread spectrum signal S ₁ (t) and supplies it to the multiplier 4. On the other hand, BPF14
Is only the spread spectrum signal S ₁ (t) and the multiplier 5
And to the delay circuit 17. That is, both BPFs 13, 1
4, the spread spectrum signals S ₁ (t) and S ₂ (t) are separately obtained.

The delay circuit 17 gives a delay of one time slot of the sum conversion output signal Ps (t). Therefore, the input side and the output side of the delay circuit 17 have the waveforms shown in FIGS. 8 (C) and 8 (D), respectively. These two signals are multiplied by the multiplier 5 and the carrier component is removed by the LPF 24, so that a spread code signal P ((the polarity is opposite) equivalent to that at the time of modulation as shown in FIG. t) is detected. The spread code signal P (t) is supplied to the multiplier 4 and is subjected to despreading by multiplication with the spread spectrum signal S ₁ (t) from the BPF 13. Therefore, the spread spectrum signal S ₁ (t) is output from the multiplier 4.
Is obtained, the unnecessary frequency component is removed by the BPF 11, and the two-phase PSK signal d (t) cosω _c1 t is output from the output terminal Out ₂ .

[Effect]

As is clear from the above description, the spread spectrum communication system of the present invention has various excellent features as follows.

Since the clock recovery circuit, spreading code generation circuit, synchronization pull-in circuit and synchronization holding circuit that are loops, which were indispensable in the conventional method, are no longer required, the circuit configuration can be greatly simplified and the cost can be reduced. Because it can contribute to the reduction
Deployment to consumer equipment has become extremely easy.

Since the circuits for synchronizing such as the sync pull-in circuit and the sync hold circuit, which require high technology, are not required, it takes a long time to pull in the sync in the conventional method, and there is a problem that the sync is lost. It is released and can contribute to stabilization of the operation of the spread spectrum communication system.

[Brief description of drawings]

FIGS. 1 (A) and 1 (B) are block configuration diagrams of a modulator and a demodulator of the first embodiment capable of realizing the spread spectrum communication system of the present invention, and FIGS. 2 (A) to 2 (E) are A frequency spectrum diagram for explaining the operation of each component of the first embodiment, FIGS. 3 and 7 are frequency spectrum diagrams of spread spectrum signals in the first and second embodiments, respectively, and FIGS. 4 and 8 are respectively. Timing chart for explaining operation of main components of the first and second embodiments, fifth
Figures (A) and (B) are characteristic diagrams of comb-shaped filters, and Figures 6 (A) and (B)
Is a block configuration diagram of a modulation section and a demodulation section of the second embodiment for realizing the system of the present invention, FIG. 9 is a schematic block diagram showing a basic configuration of a spread spectrum communication device conventionally used, and FIG. FIG. 6 is a spectrum diagram for explaining the operation of the illustrated apparatus. 2-5 ... Multiplier, 6, 18 ... Adder, 8 ... Sum conversion circuit, 9 ... Spread code generation circuit, 11-15 ... BP
F (band pass filter), 10, 30 ... Modulator, 16, 17 ...
... Delay circuit, 19 ... Comb-shaped filter, 20, 40 ...
Demodulation unit, 22 ... Subtractor, In _{1 to} In _4, ... Input terminal, Ou
t _{1 to} Out ₂ ... Output terminal.

Claims (1)

[Claims] 1. A modulation side is provided with an information signal P on a first carrier.
PSK modulation means for performing SK modulation to obtain a PSK modulation signal, spreading code generation means for inputting a clock signal to generate a spread code signal, and spreading by multiplying the obtained spread code signal by the PSK modulation signal. A first spread means for obtaining a first spread spectrum signal, a sum conversion means for receiving the spread code signal and the clock signal to obtain a sum conversion output signal, and the obtained sum conversion output signal. Second spreading means for multiplying the second carrier to obtain a second spread spectrum signal;
The adding means for adding the second spread spectrum signal and the first spread spectrum signal to output the added spread spectrum signal is provided, and the added spread spectrum signal is added to the first spread spectrum signal on the demodulation side. Separation detecting means for separating and detecting the second spread spectrum signal, a delay circuit for delaying the separated and detected second spread spectrum signal by one time slot, an output of the delay circuit and a second Multiplication means for obtaining a demodulated spread code signal by multiplying the spread spectrum signal of
Despread demodulation means for despreading the first spread spectrum signal by multiplying the obtained demodulated spread code signal by the first spread spectrum signal to obtain a demodulated PSK signal, wherein the first carrier wave And the frequency interval of the second carrier is (2N-
1) / {2 (2 ⁿ −1) T ₀ } (where N is a positive integer, n is the number of shift register stages in the spread code generating means, and T ₀ is the 1-bit time length of the clock signal) A spread spectrum communication system, characterized in that the spectrum of the second spread spectrum signal is allowed to exist between the sidebands of the first spread spectrum signal for communication.