JPH0378336A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To facilitate the simplification of circuit constitution by removing unnecessary frequency components in an inverse diffusion signal and demodulating a primary modulation wave signal. CONSTITUTION:A modulation part 10 is constituted by connecting an adder 2, a multiplier 3, a frequency conversion circuit (multiplier) 4, LPF(low pass filter) 7, a diffused code generation circuit (PNG) 9 BPF(band pass filter) 14 and a primary modulation circuit 42, etc. A demodulation part 20 is constituted by connecting plural band filters 15-19, an adder 22, two multipliers 5 and 6 and a primary demodulation circuit 23, etc. In the demodulation part 20, the outputs of plural narrow band filters 17-19 are added and the unnecessary frequency components in the inversely diffused signal obtained by inversely diffusing the outputs by a square action are removed and the primary modulation wave signal is demodulated. Thus, a clock recovering circuit, a diffused code generation circuit, a pull-in circuit consisting of a loop and a synchronization holding circuit, all of which are necessary constitution conditions so far in inverse diffusion, are eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a spread spectrum communication system, and in particular, to a reception (
Demodulation) Ill relates to a spread spectrum communication system that eliminates the need for a spreading code signal generation circuit for generating pseudo noise for despreading.

[Technical background]

Spread Spectrum (hereinafter also referred to as "ss") Spread spectrum modulation (SS modulation) used in communications is a method in which a carrier is primary modulated with an information signal, and then the carrier is first modulated with an information signal, and then the carrier is first modulated with a wideband noise-like spreading code. This method modulates the signal and spreads it over a very wide band.

-For boat fishing, direct diffusion (D
S) Method 1 There are frequency hopping (FH) methods, hybrid methods, etc., and the present invention relates to the former DS method.

Such spread spectrum communications include: ■Very high level of confidentiality.

■ Strong against external interference, noise, and intentional interference.

■Can coexist with conventional systems.

■No control station or control channel like an MCA station is required.

■Can be managed using address code.

■With the DS (Direct Diffusion) method, the power density is low, so it appears as if no radio waves exist (transmission is possible with very weak power).

■The number of stations can be increased by allowing a slight decrease in call quality.

(2) Multiplexing within the same frequency band is possible by changing the pseudo-noise code signal.

It has many other features. These features are re-recognized,
Currently, it is being applied not only to the communications field but also to various fields, and is beginning to be applied to consumer equipment.

[Conventional technology]

The basic principle of such spread spectrum communication will be explained with reference to FIGS. 5 and 6. FIG. 5 is a basic configuration diagram of a communication device that implements a spread spectrum communication method using the DS method, and FIGS. 6 (^) to (E) are spectral waveform diagrams of each component.

As shown in FIG. 5, the signal (Fl) as shown in FIG. The spread code signal (Fsa; see (B) in the figure) is secondarily modulated in the spread modulation circuit 43, amplified, and then output from the antenna A as a transmission signal (F + s ). There are no particular restrictions on the type of primary modulation, including frequency modulation (FH) and P S
K (Phase 5-hift Keying) etc. (in this specification, it will be explained that modulation is performed by PSK), and the secondary modulation (spread modulation) is - Pseudo Noi'' Se (PN code) for boat fishing. This PN code must be as random noise-like as possible, and must have a certain period in order to extract the code on the receiver side.

Next, the functions of configuration 1 on the reception (demodulation) side will be explained. At station B, which is the receiving side, the F1s signal obtained from the antenna A2 by a predetermined filter and high-frequency amplifier is despread in a despreading circuit 47 using a spreading code from a spreading code generation circuit 46.

This spreading code generating circuit 46 is the spreading code generating circuit 4 of station A.
4 and the PN code is the same (F ss
). By the way, the radio waves that enter the antenna A2 are not limited to F'ts only, as shown in FIG. 6(C),
There are radio waves (F1a, F313°, . . . ) from other 88 stations and radio waves (Fn) from 41 between the shells.

Therefore, by performing despreading in the despreading circuit 45, the desired radio wave F+3 as shown in FIG. 2(D) is returned to the spectrum as shown in FIG. At step 47, most of the components other than F'is are removed (see (E) in the same figure), and at demodulation circuit 43, the signal is demodulated to the original information signal and output.

In addition, as can be seen from FIG.
Some of the SS waves of n and other stations remain.

The ratio of the residual power which is the sum of these and the power of the target signal is DN
(signal power to interference power ratio), and in order to obtain a large DN ratio, it is advantageous to have a spread band as wide as possible.
It is about 000 times larger.

The basic principles of spread spectrum communication have been explained above, but next we will discuss 1 and 2 when performing spread spectrum communication.
Next, specific operations in each modulation/demodulation will be theoretically explained. Spread spectrum signal 5 in spread spectrum communication (tH F 1a l in Fig. 5 is the information data d
(t) [+1 or -1], spreading code F ss is P (
t) [+1 or -1], l! If the transmitted wave is CO3ωct, it is expressed by the following equation.

S (t) = d (t) P (t)CoSωct
-=-(1) (However, ωc = 2πfc) This spread spectrum signal S (t) is generated by generating a spreading code clock signal from the incoming spread spectrum signal during reception (demodulation), and further converting the spectrum during transmission. d(t) cosωat, which is obtained by multiplying (also called correlation or despreading) with the incoming spread spectrum signal 5(t).
It is converted into a signal in phase PS. Furthermore, the regenerated carrier wave CO
Synchronous detection is performed by multiplying Sωct (actually COSωct), and d (t) (cosωct) 2 = d
(t)(1+CO32ωct)/2 is obtained, and the information data d(t) is demodulated by removing the carrier wave component 2ωat with a filter.

Here, let BD be the bandwidth (main lobe of the spectrum) of the signal d(t)cosωat in the two-phase PS, and let the frequency bandwidth (main lobe of the spectrum) of the spread spectrum signal spread by the spreading code pH) be BD. If Bp, the process gain GP in spread spectrum communication is expressed as GP=BP/BD. This process gain GP has a value of several hundred to several thousand in a normal design value, and since interference signals, noise, etc. are suppressed according to this value, the frequency of the spread spectrum signal with respect to information data d (t) is The wider the band, the greater the improvement effect in anti-jamming properties, anti-noise properties, etc. That is, the improvement effect is almost uniquely determined by the process gain GP.

[Problem to be solved by the invention]

In such conventional spread spectrum communication systems, "despreading"
is the most important, and it is not easy to generate the spreading code necessary for this purpose.Currently, there are despreading methods using an AFC control loop, delay loop, and multiplier, and synchronized loops and multipliers using matched filters. The despreading method is commonly used. Despreading with these configurations is
Both have complex circuit configurations and problems in terms of adjustment and cost, and it is necessary to solve these problems when deploying them to consumer devices.

[Means to solve the problem]

The spread spectrum communication system of the present invention includes, on the modulation side, a means for modulating an information signal with a first carrier wave to generate a primary modulated wave signal, and a means for adding a second carrier wave to this primary modulated wave signal. means for obtaining an added signal using a spreading code; means for obtaining a spread spectrum signal by spreading the added signal using a spreading code; means for outputting a composite spread spectrum signal obtained by adding the code signal equivalently; and on the demodulation side, a bandpass filter means for inputting the composite spread spectrum signal and removing unnecessary noise components; The output of the bandpass filter means is filtered into the second wave by the fourth carrier wave.
Perform frequency conversion.

means for obtaining a frequency-converted composite spread spectrum signal; a plurality of narrowband filtering means each having a different passband for passing a plurality of spectral components included in the composite spread spectrum signal; and these plurality of narrowband filters. an addition means for adding the outputs of the means; a multiplication means for despreading the output of the addition means by a squaring operation; and after removing unnecessary frequency components in the despread signal obtained by the multiplication means, the above-mentioned The above-mentioned problem is solved by providing a demodulation means for demodulating the primary modulated wave signal and communicating.

〔Example〕

Since the spread spectrum communication method of the present invention performs communication with the above configuration, the synchronization pull-in circuit and the synchronization pull-in circuit consisting of a clock recovery circuit, a spreading code generation circuit, and a loop, which have conventionally been essential components in despreading, are required. This eliminates the need for a synchronization holding circuit, etc., and an example of an SS communication device that can realize the system of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of a spread spectrum communication device that implements the spread spectrum communication system of the present invention, in which (A) shows the modulation section (transmission IFI) 10, and (B)
) is the demodulator (reception@) 20.

In these figures, the same components as those in the conventional example shown in FIG. 5 are given the same reference numerals, and detailed explanation thereof will be omitted.

The modulation unit 10 includes an adder 21, a multiplier 31, a frequency conversion circuit (
Multiplier>4. LPF (low-pass P wave filter) 7° Spreading code generation circuit (PNG) 9, BPF” (bandwidth filter) 1
4 and a primary modulation circuit 42, etc., and these are shown in FIG.
) They are connected and configured as shown in the figure. The demodulator 20 also includes a plurality of band P-wave devices 15 to 19 . The adder 22 includes an adder 22, two multipliers 5, 6, a primary demodulation circuit 23, etc., and these are connected as shown in FIG. 1(B). Hereinafter, the specific functions and operations of the modulator 10 and the demodulator 20 will be explained with reference to the spectrum diagrams of FIGS. 3 and 4.

First, when transmitting, the modulating section 10 supplies an information signal d (t) such as data to the primary modulating circuit 42 from the input terminal In+. On the other hand, a carrier wave signal COSω[t having an angular frequency ω1 is input from the input terminal ITL2 to the primary modulation circuit 42.
Here, for convenience of explanation, the primary modulation is assumed to be PSK modulation. As a result, 1 of the waveform like D in FIG. 3(A)
The next modulation signal d (t)cosω[t is generated and output to the adder 2, where it is added to the carrier wave signal COSω2t (P in the same figure (A)) from the input terminal Ins, and d
(t) cosωlt+cO3ω2t, multiplier 3
is output to. Here, the center frequency (carrier wave) of the primary modulation signal is f, (=ω1/2π).

When the frequency of the carrier wave P is f2 (=ω2/2π), the following equation (3) is used between the two: The recarrier signal is selected so that 1/T represents the number of stages of the spreading code, and 1/T represents the tarot rate of the spreading code.

That is, the spreading code generation circuit 9 generates an M-sequence spreading code signal and supplies it to the multiplier 3 via the LPF 7. As a spreading code signal (hereinafter also simply referred to as a "spreading code"), a pseudo-noise code (especially an M-sequence code) is often used, so it is sometimes called a "pseudo-noise code."

The next stage LPF 7 has frequency characteristics that can remove side lobes of the spreading code. Therefore, the addition output signal d(t)CO3ω, t+cosω2t is changed to the multiplier 3 by the spreading code signal pH, which has only the main lobe.
The composite spread spectrum signal S m (t) as shown in FIG. 3TB), that is, p(t)X (d
(t) cosωlt+cO3ω2t l is generated,
It is output to the frequency conversion circuit 4. In addition, in the same figure (B), up to the fifth spectrum is shown, and subsequent spectra are omitted.

Furthermore, the carrier wave signal COSω3t is supplied from the input terminal Ina to the frequency conversion circuit 4, where it is multiplied by the composite spread spectrum signal Sm(t). Therefore, the output of the frequency conversion circuit 4 is +(SM(ω+ω3
)+3M(ω-ω3)).

Among these, +(S14(ω-ω3)) in the low frequency band is blocked from passing by the next stage BPF14, and only +(Ss(ω+ω3)) in the high frequency band is transmitted, and the antenna A1
Sent from

Next, the operation of the demodulator 20 will be explained with reference to FIG. 1(B). Composite spread spectrum signal received by antenna A2 + (SN (ω + ω3)) (Fig. 3 (B)
) is supplied to the frequency conversion circuit (multiplier) 5 after unnecessary frequency components other than the spread spectrum signal are removed by the BPF 15, where it is multiplied by the local oscillation signal wave from the input terminal Ins. A frequency conversion is performed. For convenience, if the same signal COSω3t as the carrier signal is used as the local oscillation signal wave, the composite spread spectrum signal present in the multiplication output can be detected as S m (t). Therefore, the composite spread spectrum signal Sm(t
) A plurality of band-wave transmitters 17 to 19 (B+ to Bn) each tuned to each frequency spectrum of By adding and combining (using the adder 22), we get
The desired composite spread spectrum signal S m (t) can be detected. The composite spread spectrum signal Sm(t), which is the output of the adder 22, is supplied to the multiplier 6 from both input terminals, where it is despread by a squaring operation, and the despread output 5d is
(t) is obtained. The despreading output 5d(t) is 5d(t)=d(cos(ω1−ω2)
t± cos(ω I + ω2) t )
+ m (t) −・−−−−−−−(4)
However, P'(t)=1 m (t) = + + 4z cos2ω2-1:"
+ −Jr d ′(t)+teracos2ω1t. From this despreading output 5d(t), the necessary PSK signal d (only tHcos(ω1-ω2)t is passed through the next stage BPF 16 without detection) is supplied to the primary demodulation circuit 23, Here, the PS is demodulated and the demodulated information signal is output from the output terminal (111t2).

FIG. 2 is a block diagram of a second embodiment of a spread spectrum communication device that implements the spread spectrum communication system of the present invention.
In the figure (A) is the modulation section (transmission side) 30°, and in the figure (B) is the demodulation section (reception side) 40. In these figures, the same components as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted. The main difference between the second embodiment and the first embodiment is that the modulation section 30 includes a multiplier 3 and an LP.
A spectrum correction circuit 21 is inserted and added between F7 and a corrected spread code signal. This is due to the addition of 2,...Kn) to K+. This makes it possible to supplement the power of the composite spread spectrum signal.

That is, the spectrum of a general spread spectrum signal is
It can be represented by the (sinχ/χ)2 curve shown by P in Figure (A). Therefore, if this curve becomes a characteristic similar to that of a straight door indicated by a broken line, it becomes possible to increase the power. If Ha=1, then P is 0.6, so the spectrum is corrected to bring P closer to Ha, resulting in an approximate spectrum P' as shown in FIG. 4B.

In the demodulating section 40, in order to return the spectrum P' to its original value, the gains of the gain adjusters 25 to 27 are set to the characteristics shown in FIG. Therefore, the spectrum of the actual composite spread spectrum signal S m (t) has the characteristics shown in FIG. Further, at the input stage of the despreading (multiplier 6), the spectrum is inversely corrected to the spectrum shown in FIG. This makes it possible to increase the power of the demodulated information signal d
This can contribute to improving the S/N in (t).

In the above explanation, it is assumed that modulation is performed on PS as the primary modulation, but it is not limited to this, and other modulation methods (such as FM modulation) can also be used. It can be realized in a wide range of ways, and can be easily applied to wireless microphones, transceivers, etc. as familiar examples.

〔effect〕

Since the spread spectrum communication system of the present invention communicates in the manner described above, it has the following excellent features.

■Since the clock regeneration circuit, spreading code generation circuit, synchronization pull-in circuit and synchronization holding circuit consisting of loops, etc., which were essential components in the conventional method, are no longer required, the circuit configuration can be considerably simplified and costs can be reduced. A significant reduction has been achieved, making it extremely easy to apply it to consumer devices.

■By eliminating the need for multiple circuits that require advanced technology, such as a synchronization pull-in circuit and a synchronization holding circuit, it is freed from the drawbacks of conventional methods such as the long synchronization pull-in time and problems such as loss of synchronization. It can contribute to stabilizing the operation of spread spectrum communication systems.

■If the spectrum of the spread spectrum signal is corrected, it is possible to further improve the S/N.

Wear.

[Brief explanation of drawings]

FIGS. 1(A) and CB) are block diagrams of the modulator and demodulator of the first embodiment, respectively, which realize the spread spectrum communication system of the present invention, and FIGS. 2(A) and CB) are block diagrams of the spectrum of the present invention. Block diagrams of the modulation section and demodulation section of the second embodiment that realizes the spread communication system, FIGS. 3A and 3B are frequency spectrum diagrams for explaining the operation of the modulation section of both of the above embodiments, and FIG. (A) to (E) are frequency spectrum diagrams for explaining the operation of the main parts of the second embodiment, FIG. 5 is a block configuration diagram showing the basic principle of a communication device realizing the spread spectrum communication system, and
The figure is a spectral waveform diagram of each component of the block diagram shown in Figure 5. 2.22... Adder, 3-6... Multiplier, 7...
LPF (low pass filter), 9... Spreading code generation circuit, 1
0゜30...Modulation section, 14-19...BPF (bandwidth wave device) 20.40...Demodulation section, 21...Spectrum correction circuit, 23...Primary demodulation circuit, 25- 27・
...gain adjuster, 42...primary modulation circuit, In+~
In5...Input terminal, Prefecture2...Output terminal.

Claims (2)

[Claims] (1) On the modulation side, there is a means for modulating the information signal with a first carrier wave to generate a primary modulated wave signal, and a means for adding a second carrier wave to this primary modulated wave signal to obtain an addition signal. and,
A means for obtaining a spread spectrum signal by spreading the added signal using a spreading code, and a means for performing a first frequency conversion on the spread spectrum signal using a third carrier wave to equivalently add the spread spectrum signal and the modulated spread code signal. and a means for outputting the composite spread spectrum signal obtained by the above-described method, and on the demodulating side, a bandpass filter means for inputting the composite spread spectrum signal and removing unnecessary noise components, and a means for outputting the output of the bandpass filter means. means for obtaining a frequency-converted composite spread spectrum signal by performing a second frequency conversion using a carrier wave of 4; a bandpass filtering means, an addition means for adding the outputs of the plurality of narrowband filtering means, a multiplication means for despreading the output of the addition means by a squaring operation, and a despreading means obtained by the multiplication means. 1. A spread spectrum communication system characterized in that communication is carried out by comprising demodulation means for demodulating the primary modulated wave signal after removing unnecessary frequency components from the signal. (2) The modulation side is further provided with a means for performing spreading using a corrected spread code signal that corrects the power spectrum of the spread code signal, and the demodulation side is further provided with an inverse correction means that restores the correction characteristics of the power spectrum to the original state. 2. The spread spectrum communication system according to claim 1, further comprising means for performing despreading after despreading.