JPH0652892B2 - Spread spectrum communication system - Google Patents

Description

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

[Technical background]

Spread spectrum (SS) communication method is approx.
Developed 50 years ago in Europe, 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 small-sized and low-priced devices, and such a communication system is regaining attention. The spread spectrum communication system is a system in which a carrier is first-modulated by an information signal and secondarily modulated by a broadband noise-like spread code to spread it in a very wide band. Generally, there are a direct spread (DS) system, a frequency hopping (FH) system, a hybrid system, etc. depending on the difference in the secondary modulation system, and the present invention system is related to the former DS system.

Such spread spectrum communication has very high confidentiality (confidentiality), is strong against external interference, noise, and intentional interference,
Can coexist with conventional systems, does not require a control station such as MCA station or control channel, can manage by address code, DS (Direct Spread) method has low power density, so radio waves do not exist Visible (transmittable with weak power), the number of stations can be increased by allowing a slight decrease in call quality, it is possible to multiplex in the same frequency band by changing the pseudo-noise code signal, and so on. There is a feature of. These features have been re-recognized, and now they are being applied not only in the telecommunications field but also in other fields, and are beginning to be applied to consumer equipment.

[Conventional technology]

The basic principle of spread spectrum communication will be described with reference to FIGS. 5 and 6. FIG. 5 is a basic configuration diagram of a communication device that realizes a conventional spread spectrum communication system by the DS system, and FIG. 6 is a spectrum waveform diagram in each component. As shown in FIG. 5, 1 of station A, which is the transmitting side,
The signal (F ₁ ) as shown in FIG. 6 (a) which is primary-modulated by the secondary modulator 31 is spread by the spread code signal (F _SS ; see FIG. 2 (b)) from the spread code generation circuit 39. After being secondarily modulated by the modulation circuit 36 and amplified, it is output from the antenna A _{1 as} a transmission signal (F _1S ). The type of primary modulation is not particularly limited, and frequency modulation (FM) or PSK (Phase Shift Keyin)
g) or the like (which is described as performing modulation by PSK in this specification), the secondary modulation (spread modulation) is generally spread modulation by a pseudo noise code (Pseudo Noise: PN code). This PN code needs to be as random noise as possible and has a constant period for the receiver to extract the code.

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 by the predetermined filter and the high frequency amplifier from the antenna A ₂ is _fed to the despreading circuit 4
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 coming into the antenna A ₂ are not limited to F _1S, but as shown in FIG. 6 (c), radio waves from other SS stations (F _2S , F _3S , ...) Radio wave (F _n ) exists. Therefore, by performing despreading by the despreading circuit 47, the desired radio wave F _1S as shown in FIG. 3D is returned to the spectrum as shown in FIG. 2A and the filter (preferably a narrow band wave filter) 41 Most of the components other than F _1S are removed at (see (e) in the same figure), and the demodulation circuit 43 demodulates and outputs the original information signal. The figure
As can be seen from (e), in the output signal of the filter 41, F _n 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 the primary and secondary modulation / demodulation in the case of performing spread spectrum communication will be theoretically described. The spread spectrum signal S (t) {F _1S } in FIG. 5 in spread spectrum communication has information data of d (t) [+ 1 or -1] and spreading code F _SS of P (t) [+ 1 or- 1],
When the carrier wave and cos .omega _c t, it is 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) in the receiving (or demodulation), and incoming A spread code clock signal is generated from the spread spectrum signal, and the spread code P (t) (actually with a slight delay) synchronized with the spread code in the spread spectrum signal at the time of transmission. Is obtained, and multiplication (also called correlation or despreading) is performed on the incoming spread spectrum signal S (t), and 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.

[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 problems in terms of adjustment and cost, and it is necessary to solve these problems when deploying to consumer equipment.

[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, first, on the modulation side (10), the PSK modulation means for multiplying the information signal and the first carrier wave to generate the two-phase PSK signal as the primary modulated wave signal, and the obtained two-phase PSK signal Second
Means for adding the two carrier waves to obtain an added two-phase PSK signal, a spread code generation means for inputting a clock signal and generating a spread code signal based on the clock signal, and the added two-phase PSK signal and the spread code signal And a spread means for obtaining a spread spectrum signal by performing spread by multiplication.

Further, the demodulation side (20) is provided with a separating means for inputting the spread spectrum signal and separating and outputting the first and second spread signals having different frequency spectrum components according to the first and second carrier waves. , The separated first spread signal and the second
First multiplying means for obtaining a multiplication output signal by multiplying the spread signal of No. 1, and the obtained multiplication output signal are separated into two signals corresponding to the difference between the frequencies of the first and second carrier waves and the sum frequency. And after separating the obtained two squared output signals from the second multiplication means for multiplying both to obtain two squared output signals having twice the frequency of the first and second carriers. First and second carrier wave reproducing means for respectively dividing the frequency to obtain first and second reproduced carrier waves, and inputting the obtained second reproduced carrier wave and second spread signal and reproducing them by multiplication of both Spreading code signal reproducing means for generating a spreading code signal, despreading signal generating means for generating a despreading signal by inputting the reproduced spreading code signal and the first reproduced carrier wave, and despreading signal And the first spread signal are input to perform despreading by multiplying them. It is constituted by a despreading means for obtaining an information signal by demodulating the first modulation wave signal.

The frequency interval between the first carrier wave and the second carrier wave is (2
With N-1) / {2 ( 2 n -1) T 0}, in the presence of a spectrum of the second spread signal between sideband of the first spread signal, and to perform the communication.

〔Example〕

Since the spread spectrum communication system of the present invention performs communication with the above-described configuration, a clock recovery circuit, a spread code generation circuit, which has been essential in the conventional despreading configuration,
A sync pull-in circuit and a sync holding circuit formed of loops are unnecessary, and one 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 diagram of an embodiment of a spread spectrum communication apparatus that can realize the spectrum spread communication system of the present invention. FIG. 1 (A) shows a modulation unit (transmission side) 10 and FIG. The demodulation unit (reception side) 20. In these figures, a part of the configuration of the antenna and the like is omitted.

The modulation unit 10 includes an LPF (low pass filter) 11, an arithmetic circuit (adder) 1, two multipliers 3 and 4; a spread code generation circuit.
A (PNG) 2 and a BPF (band pass filter) 14 are provided, and these are connected as shown in FIG. 1 (A). The demodulation unit 20 includes five BPFs 15 to 19 and two LPFs.
12, 13; delay circuit (DL) 21, adder 22, subtractor 23, two 1/2 frequency dividers 25, 26 and five multipliers 5
9 to 9 and the like, which are connected as shown in FIG. 1 (B). The delay circuit 21, the adder 22 and the subtractor 23 constitute a comb-tooth filter 24 having two types of transmission characteristics, and the transmission characteristics thereof are shown in FIGS. 2 (A) and (B).
Are shown as addition characteristics and subtraction characteristics, respectively. Hereinafter, specific functions and operations will be described with reference to the frequency spectrum diagrams of FIGS. 3 and 4.

First, when transmitting, in the modulator 10, the input terminal In
_{From 1 the} information signal d (t) (in this case, data) is LPF
It is supplied to the multiplier 3 via 11. On the other hand, input terminal In ₂
Then, the carrier signal cosω _c1 t is supplied to the multiplier 3 to perform multiplication with the information signal d (t), and the primary modulation signal d (t) cosω _c1 t as shown in (a) of FIG. 3 (A). (Here, it is assumed to be a two-phase PSK modulated signal) and outputs it to the arithmetic circuit 1. In addition, the carrier signal cos ω _c2 t from the input terminal In ₃ (see FIG.
Since (B) of (A) is supplied to the arithmetic circuit 1, it is added to the above two-phase PSK signal d (t) cosω _c1 t, and d
(t) cosω _c1 t + cosω _c2 t, which is output to the multiplier 4. Further, the clock signal S _c (t) is supplied from the input terminal In ₄ to the spread code generating circuit 2, and the spread code signal P (t) is generated based on this. As the spreading code, a pseudo-noise code is usually used often (among other things, an M-sequence code is often used), and thus is sometimes called a "pseudo-noise code". The spread code P (t) generated by the spread code generation circuit 2 is supplied to the multiplier 4, where the 2
The phase PSK signal d (t) cosω _c1 t + cosω _c2 t is multiplied (spread spectrum), and the spread spectrum signal P (t) {d
_{(t) cosω c1 t + cosω} c2 t} ( hereinafter referred to as "S _M (t)") and (FIG. 3 (B) refer), only the main lobe of the spectrum spread signal is passed by BPF 14, it is transmitted hand,
Output from output terminal Out ₁ .

Here, the principle of spread spectrum will be described. As for the interval between the angular frequencies ω _c1 and ω _c2 in FIG. 3 (A), the one-bit time length of the clock signal is T ₀ , the M code is used in the spreading code generating circuit 2, and the M series code generating circuit ( When a shift register is used in (not shown), the interval is given by {2 (2 ⁿ −1) T ₀ } ^−1, where n is the number of stages. In the frequency spectrum of the spread spectrum signal shown in Fig. 6 (B), the frequency interval between sidebands + Sa ₁ and + Sa ₂ and the frequency interval between + Sb ₁ and + Sb ₂ are {(2 ⁿ −1)
The spacing is given by T ₀ } ⁻¹ and sideband + Sa ₁
~ + Sa _n, and -Sa ₁ ~-Sa _n, sideband + Sb ₁ ~ + Sb _n,
−Sb ₁ to −Sb _n are alternately arranged at equal intervals.
Note that 2 ⁿ -1 is the spread code length.

FIG. 4 shows the frequency band of the spread spectrum signal together with the angular frequencies ω _c1 and ω _{c2 of} both carriers, and the portion of the solid line (c) (between (a) and (b) in the figure). Indicates the main lobe.

In the method of the present invention, the selection of frequency is an important point,
The spectrum of the second spread signal S ₂ (t), which will be described later, is selected to exist between the sidebands in the frequency spectrum of the first spread signal S ₁ (t), which will be described later. In other words Figure 3, a primary modulation (2-phase PSK modulation) signal d (t) cos .omega _c1 t carrier angular frequency omega _c1 of the frequency interval between the carrier angular frequency omega _c2 of the carrier signal cos .omega _c2 t 1 / { 2 (2 ⁿ −1) T ₀ }. However, the interval is not limited to this, and the interval may be logically determined by (2N −) / {2 (2 ⁿ −1) T ₀ }. Note that N is a positive integer, and in FIG. 3, N =
The case of 1 is shown. By thus determining the frequency interval, the spectra of both spread signals S ₁ (t) and S ₂ (t), which will be described later, are arranged alternately without overlapping.

Next, the function of the demodulation unit 20 will be described with reference to FIG. The spread spectrum signal S _M (t) (see FIG. 3 (B)) input to the input terminal In ₅ is subjected to removal of frequency components other than the spread spectrum signal by the BPF 15, and the delay circuit 21, the adder 22, And the positive input terminal of the subtractor 23 at the same time.

Since the output of the delay circuit 21 is supplied to the negative input terminals of the adder 22 and the subtractor 23, the delay circuit 21, the adder 22 and the subtractor 23 add the addition characteristic and the subtraction characteristic (respectively, respectively). A comb-tooth filter 24 having a structure shown in FIGS. 2A and 2B is formed. Now, assuming that the delay time in the delay circuit 21 is T (= 1 / F), in the case of addition, as shown in FIG. 2 (A), 1 / T, 2 / T, 3 / T,
The gain doubles at the frequency of N / T (N is a natural number), and the output becomes 0 at each intermediate frequency, and a steep dip can be made. 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. The gain is doubled at the frequency of. Therefore, by setting the delay time to T = (2 ⁿ −1) T _0, and matching the frequency of the crests or troughs of the comb-teeth filter 24 with the sideband frequency of the spread spectrum signal,
The first spread signal P in the spread spectrum signal S _M (t)
(t) d (t) cosω _c1 t (hereinafter also referred to as “S ₁ (t)”) and the second spread signal P (t) cosω _c2 t (hereinafter also referred to as “S ₂ (t)”) Separate detection is possible. As a result, the output signal of the adder 22 is S ₁ (t) (see FIG. 3 (C)).
And the output signal of the subtractor 23 becomes S ₂ (t) (see FIG. 3D). The specific separating operation of the comb-tooth filter 24 is as follows. Here, the delay circuit 2 is used.
The representation of the delay of the spread spectrum signal S _M (t) by 1 is
It 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 24 and the like) will be described. The spread spectrum signal S _M (tT) output from the delay circuit 21 of FIG. 1 (B) is S _M (tT) = P (tT) {d (tT) cosω _c1 (tT) + cosω _c2 (tT) } (2) Here, as a precondition, the period of P (t) and the delay time T are made equal, and cosω _c1 t is in phase with the period of P (t),
If a continuous wave that repeats at the same level, cos ω _c2 t has a reverse phase at a period of P (t), and a continuous wave that repeats at the same level, S _M (tT) is S _M (tT) = P (t) {d ( tT) cosω _c1 t − cosω _c2 t} (3) Therefore, the addition output S _M (t) + S _M (tT) {= S
₁ (t)} becomes S _M (t) + S _M (tT) = {d (t) + d (tT)} P (t) cosω _c1 t (4). On the other hand, the subtraction output S ₂ (t) is S ₂ (t) = S _M (t) −S _M (tT) = 2P (t) cosω _c2 t + {d (t) -d (tT)} P ( t) cosω _c1 t (5)

Next, the despreading operation will be specifically described according to the configuration of FIG. The output of the multiplier 16 is demodulated 2-phase PSK
The signal Sp (t) is obtained. That is, Sp (t) = S ₁ (t) × S ₂ (t) = {d (t) + d (tT)} cos (ω _c1 −ω _c2 ) t + {d (t) + d (tT) } Cos (ω _c1 + ω _c2 ) t ... (6) If the delay time T is sufficiently shorter than the 1-bit time length of the information data d (t), d (tT) is d
It can be approximated as (t). Therefore, demodulation 2-phase PSK signal Sp
(t) becomes Sp (t) = d (t) cos (ω _c1 −ω _c2 ) t + d (t) cos (ω _c1 + ω _c2 ) t …… (7) Was also confirmed to be valid. Note that the minute crosstalk component is omitted for convenience of explanation.

The addition output signal S separated and detected by the above principle
₁ (t) is supplied to the multipliers 5 and 6, and the subtraction output signal S ₂ (t)
Are supplied to multipliers 6 and 7. Therefore, in the multiplier 6, despreading is performed by multiplication of both signals, and the spread code signal P (t) becomes DC by multiplication, and a demodulation two-phase PSK signal (multiplication output signal) d ( t) {cos (ω _c1 −ω
_c2 ) t + cos ( _ωc1 + _ωc2 ) t} is obtained. This output signal is two two-phase PSK signals d (t) cos (ω _c1 −ω _c2 ) t and d
(t) cos (ω _c1 + ω _c2 ) t {(d) and (e) of FIG. 3 (E), respectively. It is the sum of and, and it is possible to separate and detect with a band pass filter whose pass frequency band is appropriately selected. So, two-phase PSK
The signals d (t) cos (ω _c1 −ω _c2 ) t and d (t) cos (ω _c1 + ω
_c2 ) t is separated by the BPFs 16 and 17, respectively, and then both are supplied to the multiplier 9 for multiplication to obtain two squared output signals cos2ω _c1 t and cos2ω _c2 t. This signal c
Set os2ω _c1 t and cos2 ω _c2 t to the next-stage BPFs 18 and 19
After being separated by, the 1/2 dividers 25 and 26 respectively perform 1/2 division processing to obtain signals of the first and second reproduced carrier waves cosω _c1 t and cosω _c2 t, and the multiplier 7 respectively. And 8. As a result, in the multiplier 7, the subtractor 23
Is multiplied by the subtraction output signal S ₂ (t) to generate a reproduction spread code signal P (t) and a cos 2ω _c2 t component. Out of this co
The s2ω _c2 t component is removed by the LPF 12 in the next stage, and only the spread code signal P (t) is output to the multiplier 8. The multiplier 8 outputs the divided output signal cosω from the 1/2 divider 25.
_{Since c1} t is supplied, the despreading signal P (t) cosω _c1 t is generated by the multiplication of the two and is output to the multiplier 5. By the way, since the addition output signal S ₁ (t) from the adder 22 is supplied to the multiplier 5, the addition output signal S ₁ (t) is despread and the two-phase PSK signal by the multiplication of both. Is simultaneously detected, and the information signal d (t) and the carrier component cos2ω _c1 t are detected. Of these, cos 2 ω _c1 t is removed by the LPF 13 in the next stage, so that only the demodulated information signal d (t) can be obtained from the output terminal Out ₂ .

〔effect〕

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

The despreading by the AFC control loop, the delay locked loop and the multiplier, which are indispensable constituent elements in the conventional method, is specifically a clock recovery circuit, a spread code generation circuit, a sync pull-in circuit and a sync hold circuit composed of a loop. Since these are mainly used, these circuits are no longer needed, so the circuit configuration can be considerably simplified and the cost can be significantly reduced.
Deployment to consumer equipment has become extremely easy.

Since multiple circuits that require advanced technology, such as the sync pull-in circuit and sync hold circuit, are no longer required, there is the problem that the sync pull-in time in the conventional method is long, and there is a possibility of loss of sync. Can contribute to stabilizing the operation of the spread spectrum communication system.

[Brief description of drawings]

FIGS. 1 (A) and 1 (B) are block diagrams showing a modulation section and a demodulation section of an embodiment of the apparatus capable of realizing the spread spectrum communication system of the present invention, and FIG. 2 is a frequency characteristic diagram of a comb-shaped filter, 3 is a frequency spectrum diagram for explaining the operation of each component of the apparatus of FIG. 1, FIG. 4 is a frequency spectrum diagram showing the frequency band of the spread spectrum signal together with the angular frequencies ω _c1 and ω _c2 of each carrier, and FIG. FIG. 6 is a schematic block diagram showing the basic configuration of a spread spectrum communication device conventionally used, and FIG. 6 is a spectrum waveform diagram in each component of the block diagram shown in FIG. 1, 22 ... Operation circuit (adder), 2 ... Spread code generation circuit, 3-9 ... Multiplier, 10 ... Modulation section, 11-13
...... LP (low pass wave filter), 14 to 19 ...... BPF (band pass filter), 20 ...... demodulation section, 21 ...... delay circuit, 23 ...
… Subtractor, 24 …… Comb filter, 25, 26 …… 1 /
Divider by 2, In _{1 to} In ₅ …… Input terminal, Out _{1 to} Out ₂ ……
Output terminal.

Claims (1)

[Claims] 1. A PSK modulating means for multiplying an information signal and a first carrier wave to generate a two-phase PSK signal as a primary modulated wave signal, and a two-phase PSK signal obtained on the modulating side. Adding means for adding two carrier waves to obtain an added two-phase PSK signal, spreading code generating means for inputting a clock signal and generating a spread code signal based on the clock signal, the added two-phase PSK signal and the spread code And a spreading means for obtaining a spread spectrum signal by performing spread by multiplication by inputting a signal, and the demodulation side inputs the spread spectrum signal and has different frequency spectra corresponding to the first and second carrier waves. Separating means for separating and outputting the first and second spread signals having components, and first multiplying means for multiplying the separated first spread signal and second separated signal to obtain a multiplication output signal. ,
The obtained multiplication output signal is separated into two signals corresponding to the difference between the frequencies of the first and second carriers and the sum frequency, and the two signals are multiplied to obtain the two signals of the first and second carriers. A second multiplication means for obtaining two squared output signals having a doubled frequency; and a second multiplication means for separating the obtained two squared output signals and then dividing them respectively to obtain first and second reproduced carriers. First and second carrier wave reproducing means, spread code signal reproducing means for inputting the obtained second reproduced carrier wave and the second spread signal, and generating a reproduced spread code signal by multiplying them, and the reproducing means. A despread signal generating means for inputting a spread code signal and the first reproduced carrier wave to generate a despread signal by multiplying the both, and inputting the despread signal and the first spread signal The primary modulated wave signal is demodulated by performing despreading by multiplication of both. A despreading means for obtaining a broadcast signal, a frequency interval of the first carrier and the second carrier, (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 a 1-bit time length of the clock signal) The first
A spread spectrum communication system characterized in that the spectrum of the second spread signal is allowed to exist between the sidebands of the spread signal of 1.