JPH05191379A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To constitute the system so that an output signal obtains an output whose envelope is constant by providing a receiving signal and plural reverse spread codes, and demodulating an information signal by a mutual correlation value of the receiving signal and the reverse spread code. CONSTITUTION:On a transmitting side 1, a PN signal generator 4 generates a spread code P at a timing of a clock of a clock generator 6, and it is used for a pseudo random number code. A PN signal generator 9 of a receiving side 2 generates a reverse spread code of the same sequence as the diffusion code of the transmitting side, and a PN converter 11 is a circuit for inverting the reverse code of the generator 9 every second code. In such a state, a correlator A takes a mutual correlation of the signal of the generator 9 and the receiving signal, and a correlator B takes a mutual correlation of the reverse spread signal converted by the reverse spread code converting circuit 11 and the receiving signal. Subsequently, a discriminating/reproducing circuit 10 decides output levels by outputs of the correlators A, B, and reproduces information signals d1, d2. As a result, since a quadruple modulation is executed by the spread signal, an output signal can obtain an output whose envelope is constant, and the output signal of a final amplification stage of a transmitting side equipment becomes a constant envelope, and becomes simple.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spread spectrum communication system. For example, it is applied to optical communication, wireless communication, and power line carrier.

[0002]

2. Description of the Related Art As a publicly known document describing the prior art of the present invention, "Spread spectrum communication" (Mitsuo Yokoyama, Science and Technology Publishing Company 1988. p.10-13, p.290-293, p.324-325) )
There is. In spread spectrum communication, in order to demodulate information spread by a spread code, the same code as the spread code must be multiplied by the spread information. A circuit for that purpose is a correlator, and there are a matched filter having the same configuration as in FIG. 8 and a convolver having the configuration in FIG. However, in FIG. 10, 41 (1) to 41 (2
N) is a delay circuit, 42 (1) to 42 (N) are mixers, 4
Reference numeral 3 is a circuit for obtaining the total sum. In both circuits, when the input signal is the same as the despreading code, a positive sharp correlation output is periodically output, and when the input signal is a code obtained by inverting the spreading code, a negative correlation output is periodically output. .. Also, if there is no correlation between the input signal and the despread signal, no output signal is output.

In a conventional spread spectrum communication system using a correlator, a pseudo random number code (P
One information signal had to be assigned to one cycle of (N codes). Further, in the conventional spread spectrum communication, since the information signal is transmitted bit by bit, there is a drawback that it is weak against fading. Further, in the conventional modulation method such as the four-phase modulation method, it is difficult to obtain an output with a constant envelope when adding two modulated carrier waves.

Further, in the conventional spread spectrum communication, it is necessary for the receiving side to take the phase period of the despreading code and the received signal. For this purpose, a synchronous circuit using a delay locked loop (hereinafter, DLL) is usually used. This is P, which is several chip times earlier than the PN generator in the DLL.
Correlation between N signal and received signal, and P that is several chip times late
A phase difference signal for synchronization control is obtained by two of the correlation between the N signal and the received signal. However, this DLL is
If the gains of the two correlators are out of balance, the tracking characteristic is adversely affected.

[0005]

The present invention has been made in view of the above-mentioned circumstances, and it is possible to allocate two pieces of information to one period of a pseudo noise code used for a spread code,
Further, if the transmission rate is the same, the time during which 1-bit information is transmitted becomes long, so that it should be strong against fading, and 4-level modulation should be performed using a spread signal instead of a carrier wave. Therefore, the output signal can obtain an output with a constant envelope, and the final amplification stage of the transmitter can easily be operated because the output signal is a constant envelope, and the first despreading code and the second despreading code can be used. By selecting a code that inverts the despreading code of the so that it is as orthogonal as possible, and adjusting the signal switching method on the transmission side to this, it is possible to increase orthogonality, facilitate identification of information signals, and perform coefficient multiplication. By preparing the despreading code for the coefficient of the converter beforehand, the clock generation circuit and the despreading code generation circuit become unnecessary, and the need for clock synchronization is eliminated. (2) By constructing a synchronous loop using a correlator for a (NRZ) code and a correlator for a Manchester code, the circuit becomes simple and it is not necessary for the two correlators to be in parallel. The purpose of the invention is to provide a spread spectrum communication system.

[0006]

In order to achieve the above object, the present invention provides (1)
The transmitting side is provided with a spectrum spreading means for modulating a signal obtained by alternately switching two information signals at the modulation rate of the spreading code and then transmitting the modulated signal, and the receiving side is the same as the spreading code used on the transmitting side. A first despreading code which is a code,
A second despreading code, which is a code in which every other code of the spreading code is replaced by an opposite code, and a cross-correlation value between the received signal and the first despreading code, and the received signal and the second despreading code. 2 sent from the sender depending on the cross-correlation value with the despread code
Demodulating one information signal, or (2) the transmitting side is provided with a spectrum spreading means for modulating a signal obtained by arbitrarily switching the two information signals at the modulation rate of the spreading code and transmitting the modulated signal. On the receiving side, a first despreading code, which is the same code as the spreading code used on the transmitting side, and a code of the spreading code, in which the information signal on the transmitting side is replaced with an opposite code in the same pattern as the switching pattern. A second despreading code is provided, and two of the two signals sent from the transmitting side are transmitted according to the cross-correlation value between the received signal and the first de-spreading code and the cross-correlation value between the received signal and the second de-spreading code. Demodulating the information signal, and (3) inputting the first despread code and the received signal to the two correlators for obtaining the cross-correlation value, and inputting the cross-correlation value to the first correlator. The second despreading code is obtained in the second correlator. It has a correlator for inputting a received signal to obtain a cross-correlation value, and (4) N correlators for connecting the delay circuits in cascade as two correlators for obtaining the cross-correlation value. (N is a natural number) coefficient multipliers are connected, and two correlators for obtaining the sum of the outputs of the coefficient multipliers are provided, and the coefficient of the coefficient multiplier of the first correlator is the first despreading code. Using a code string in which the second despreading code is reversely rearranged is used as a coefficient of the coefficient multiplier of the second correlator. (5) In (2), the two correlators that obtain the cross-correlation value are input to the first correlator and the first despread code and the received signal are input to obtain the cross-correlation value, The second correlator has a correlator that inputs the second despread code and the received signal to obtain a cross-correlation value, N, the (6) above (2), as two correlators for obtaining the cross-correlation value, to the connection point of the delay circuits connected in cascade to the delay circuit
Number (N is a natural number) of coefficient multipliers are connected to each other, and two correlators for obtaining the sum of outputs of the coefficient multipliers are provided, and the coefficient of the coefficient multiplier of the first correlator has the first despreading. Using a code sequence in which the codes are reversed, and having a correlator using a code sequence in which the second despreading code is reversed in the coefficient multiplier coefficient of the second correlator; Alternatively, (7) the transmitting side is provided with a spectrum spreading means for modulating a signal obtained by alternately switching two information signals at the timing of a clock for generating a spreading code by the spreading code and then transmitting the signal, and on the receiving side,
A correlation value between a non-return toe zero (NRZ) despreading code of the same sequence as the transmission side spreading code and the received signal, and a Manchester-coded despreading code and reception signal of the same sequence as the transmitting side spreading code. Demodulating the two information signals sent from the transmission side by the correlation value of
(8) In (7), in order to synchronize the despreading code on the receiving side, the first correlator obtains a cross-correlation value between the non-return to zero (NRZ) despreading code and the received signal. , The second correlator takes a cross-correlation value between the Manchester-despread code and the received signal, and multiplies the output of the first correlator by the output of the second correlator, A synchronization holding method for holding the phase of the despreading code by using the control signal of the circuit that shifts the phase of the despreading code is provided. Further, (9) In (7), the spreading code is spread by the spreading code. In order to demodulate the two information signals thus demultiplexed, the received signal is despread by the despreading code, and the despread signal is distributed to the two signals at the timing of the clock for generating the despreading code. Is it the sender A demodulation system for demodulating two transmitted information signals is further provided. Further, (10) in (8), the first information is demodulated to demodulate the two information signals spread by the spreading code. A demodulation method for demodulating two information signals by the output of the correlator and the output of the second correlator, or (11) in the spread spectrum communication in the base band, Despread with a first correlation signal obtained by despreading a signal which is spread and transmitted with a pseudo random number signal of Return to zero code with a pseudo random number code of NRZ code and a pseudo random number code of Manchester code Pseudo-random number signal obtained by respectively obtaining a cross-correlation output with the second correlation signal obtained by (12) In (12), the signal spread by the pseudo random number signal of the NRZ code on the transmission side in (12) is a pseudo random number signal obtained by the pseudo random number signal sync lock loop. Using a receiver to demodulate the information signal by despreading, and
(13) Reception of demodulating an information signal by extracting the first correlation signal in the pseudo random number signal synchronization lock loop from the signal spread by the pseudo random number signal of the NRZ code on the transmission side in (11) above It is characterized by having a machine. Hereinafter, description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining an embodiment (claims 1 and 3) of a spread spectrum communication system according to the present invention. In the figure, 1 is a transmitter, 2 is a receiver, and 3 is a signal. Switcher 4, PN (pseudo noise) generator, 5 mixer, 6 clock generator, 7 correlator A, 8 correlator B, 9 PN
A signal generator, 10 is an identification reproduction circuit, and 11 is a PN (pseudo noise) converter. Here, for simplification, the case of transmitting all in the base band will be described, but the present invention can be applied to the case of transmitting in the carrier band.

First, the operation of each unit on the transmitting side will be described. The spread code P is generated in the PN signal generator 4 at the timing of the clock of the clock generator 6. The spreading code generated by this circuit is usually a pseudo-random number (noise)
A code (PN code) is used. In the present invention, it is desirable to use a sequence in which the occurrence probabilities of the logical value 1 and the logical value -1 are almost equal, for example, a pseudo random number sequence of M series. The time width of one code (the time width of one chip) of this spread code generating circuit is Tt. The signal switch 3 receives the input information signal d1.
And d2 are alternately switched at the same intervals as the code time width Tt of the spread code and are passed to the mixer 5 in the next stage. A concrete example of the signal switch 3 is shown in FIG. 12a, 12b in the figure
Is an AND circuit, 13 is an inverter, 14 is an OR circuit, 1
Reference numeral 5 is a frequency divider. The frequency divider 15 is provided to generate the time width Tt of the spread code from the signal of the clock 6. In this way, the mixer 5 multiplies the signal from the signal switcher by the spread code and transmits the result to the transmission path.

Next, the operation of each unit on the receiving side will be described. The PN signal generator 9 is a despreading code generation circuit that generates a despreading code of the same sequence as the spreading code on the transmission side. P
The N converter 11 is a circuit for inverting the despreading code of the PN signal generator 9 every other code, specifically, a circuit as shown in FIG. 3, in which 16 is an EX-OR circuit and 17 is a division circuit. It is a circulator. The frequency divider 17 is also provided to create the time width Tt of the despreading code from the clock, like the frequency divider of FIG. The correlator A takes a cross-correlation between the signal of the despreading code generating circuit 9 and the received signal. The correlator B takes the cross-correlation between the despread signal converted by the spread code conversion circuit 11 and the received signal. The discriminating / reproducing circuit 10 is a circuit for judging the output level from the outputs of the correlators A and B and reproducing the information signals d1 and d2.

FIGS. 5A to 5F are time charts of the signals of the respective parts on the transmission side. FIG. 4 shows the signals of the respective parts in the configuration of FIG. The information signals d1 and d2 to be transmitted are shown in FIGS. In the example of FIGS. (A) and (b), the information-acquisition state (d1,
d2) = (0,0), (0,1), (1,0), (1,1). FIG. 6C shows the clock 6 in FIG. 4, and the information signals d1 and d2 are alternately switched at the timing of dividing this clock by 2, and as shown in FIG. To be converted. Further, the mixer 5 further multiplies the spread signal generated by the spread signal generator 4 (FIG. (E)), converts into a transmission signal S (t) shown in FIG. .. The signal spread on the transmitting side is despread as shown below and demodulated into two signals.

The received signal is S '(t). The received signal S '(t) is input to two correlators A and B. Here, the despreading code that is multiplied by the received signal S ′ (t) by the correlator A is PA (t), and the despreading code that is multiplied by the received signal S ′ (t) by the correlator B is PB (t). ). The despreading code PA is a code in the same sequence as the spreading code P on the transmitting side. Here, the arrangement of the spreading code and the despreading code PA is expressed as follows.

[0012]

[Equation 1]

However, here, P ₁ , P ₂ , P ₃ , ... P _N-1 ,
P _N represents each code. Then, one of the despreading codes PB is a code in which every other spreading code P is inverted, and thus can be expressed as follows.

[0014]

[Equation 2]

The correlator generates a signal having a positive sharp peak when the received signal is input with the same code sequence as the despread code, and is also input with the code sequence in which the despread code is inverted. It is known that at times, a signal with a negative sharp peak is generated, and for signals that are uncorrelated with the despreading code, the signal level is kept near zero. Use this. First, the information signal (d1, d2) =
Consider the case where (0,0) is transmitted. At this time, all the transmitted signals S to be transmitted are transmitted with the spread code P inverted, so that the received signal S'is received as follows.

[0016]

[Equation 3]

Therefore, a negative signal is generated in the correlator A on the receiving side. Further, in the correlator B, since there is no correlation between the despread code PB and the received signal S ', no signal is generated. Next, consider a case where the transmitting side transmits the information signal (d1, d2) = (1, 1). Since the transmitted code S is transmitted with the spread code P as it is, the received signal S'is received as follows.

[0018]

[Equation 4]

Therefore, a positive signal is generated in the correlator A on the receiving side. Further, in the correlator B, since there is no correlation, no signal is generated. Next, on the transmitting side, the information signals (d1, d
Consider the case where 2) = (0,1) is transmitted. Since the spread signal P is inverted when the information signal d1 is sent and is sent as it is when the information signal d2 is sent, the send signal S sent is as follows. Be received.

[0020]

[Equation 5]

Therefore, the correlator B produces a negative signal. Further, since there is no correlation in the correlator A, no signal is generated. Next, on the transmission side, the information signal (d1, d2) = (1,
Consider the case where 0) is transmitted. Transmission signal S sent
When the information signal d1 is sent, the spread code P is sent as it is, and when the information signal d2 is sent, it is sent inverted, so that the received signal S'is received as follows.

[0022]

[Equation 6]

Therefore, S '= PB, and a positive signal is generated in the correlator B on the receiving side. In the correlator A,
No signal is generated because there is no correlation. The relationship between the following transmission signal and correlator output is summarized in FIG. In this way, the received signal S'is separated into two signals and demodulated into the information signals d1 and d2 by the identification / reproduction section 10 by the outputs of the two correlators.

Next, claim 2 and claim 5 will be described. In claim 1, the orthogonality of the first despread code sequence and the second despread code sequence obtained by converting the first despread code may be low. However, in this method, a code that inverts the first despreading code and the second despreading code so as to be orthogonal to each other is selected as much as possible, and the signal switching method on the transmission side is adapted to this to enhance orthogonality. Therefore, the information signal can be easily identified. Further, in the description of claim 1, the switching of the information signals d1 and d2 is performed alternately, but it is not always necessary to perform the switching alternately, and the information signals d1 and d2 are not necessarily required.
Need not be the same during the 1-bit time width of the information signal. When the switching of the information signal is changed by another rule or arbitrarily, the same effect can be obtained by inverting the corresponding code of the despread code input to the correlator B according to the switching. For example, the signal D produced by the signal switcher converts the information signals d1 and d2

[0025]

[Equation 7]

If the data is transmitted in the order of, the despread code string PB 'may be as follows.

[0027]

[Equation 8]

Next, claim 4 will be described. Claim 1
In the correlator used in (1), it is necessary to use a clock generation circuit and a despreading code generation circuit, and there is a problem of clock synchronization. However, according to the present method, these circuits are unnecessary, and clock synchronization is not necessary. 8 and 9 are diagrams showing a correlator A and a correlator B for obtaining other cross-correlation values, in which 31a (1) to 31a in FIG.
a (N-1), 31b (1) to 31b (N-1) are delay elements, 32a (1) to 32a (N), 32b (1) to 3
2b (N) is a coefficient multiplier, and 33a and 33b are accumulators. 8 and 9 are different only in the coefficient of the coefficient multiplier, the configuration will be described with reference to FIG. 8 for FIG.
Elements that are the same as are designated by the same numbers, and the numbers are followed by'a 'in FIG. 8 and'b' in FIG.

FIG. 8 is the same as the correlator used in the conventional spread spectrum communication, and includes 31a (1) to 31a.
(N-1) is a delay element, and each delay element has a characteristic of delaying the signal by the code time width of the spread code. Also, 3
2a (1) to 32a (N) are coefficient multipliers, and each coefficient is set with a coefficient in which the spreading code sequence P on the transmission side is reversed from C1 to CN. 33a is a circuit for obtaining the sum of all coefficient multipliers. When the spread code P is input to this correlator, a correlation output having a positive peak for each cycle of the spread code sequence is obtained. Further, when a code string in which the code of the spread code P is inverted is input, a correlation output having a negative peak for each code of the spread code sequence is obtained. Therefore, it can be seen that this can achieve the same function as the correlator A in FIG.

In the correlator shown in FIG. 9, despreading codes PB having another coefficient are arranged in reverse order from C1 to CN. Therefore, this correlator is the correlator B in FIG.
You can see that it works the same as. By using the above two correlators on the receiving side as shown in FIG. 7, two information signals can be obtained from the received signal S '.

Next, claim 6 will be described. Claim 4
In addition to the reason for the above claim 1, there is a problem that the conversion circuit from the first despreading code to the second despreading code used in claim 2 becomes complicated, but the coefficient of the coefficient multiplier is By preparing the second despreading code in advance, it is possible to easily realize the second correlator. That is, when demodulating the signal modulated as in claim 2, the coefficient of the coefficient multiplier of the correlator B in FIG.
It is sufficient to use the one in which the expressions are arranged in reverse order.

Next, another embodiment of the spread spectrum communication system according to the present invention will be described. The structure of the transmitter in this embodiment is the same as the structure of the transmitter shown in FIG. A specific example of the signal switch is as shown in FIG.
The configuration is obtained by removing the frequency divider 15 in the signal switcher shown in FIG.

FIG. 12 is a block diagram of the receiving side using the synchronization holding method of claim 8 and the demodulating method of claim 9, wherein:
Reference numeral 50 is a synchronization holding circuit, 51 and 52 are multipliers, 53 is an integrator, 54a and 54b are low-pass filters (LPFs), 5
5 is an EX-OR circuit, 56 is a voltage control clock, 57 is a despreading signal generator, 58 is a multiplier, and 59 is an identification reproduction circuit. The despread signal generator 57 is for generating the same PN code sequence as on the transmitting side. The clock frequency of the voltage control clock 56 changes according to the control signal. The exclusive OR circuit (EX-OR circuit) 55 takes an exclusive logical OR of the despread signal and the clock,
It has a function to convert the pseudo spread signal into Manchester. The combination of the multiplier 51 and the low-pass filter 54a and the combination of the multiplier 52 and the low-pass filter 54b obtain the cross-correlation value between the despread signal and the received signal, respectively.
The combination of the multiplier 51 and the low-pass filter 54a is called a correlator A, and the combination of the multiplier 52 and the low-pass filter 54b is called a correlator B.

The correlator A outputs the cross-correlation value between the received signal and the non-return toe zero (NRZ) PN signal, and the correlator B outputs the cross-correlation value between the received signal and the Manchesterized PN signal. Output. The integrator 53 outputs the product of the correlation output of the correlator A and the correlation output of the correlator B. The voltage control clock is controlled by the signal from the integrator 53. The multiplier 58 multiplies the synchronized PN signal from the synchronization holding unit 50 by the received signal, and despreads the received signal. The identification reproduction circuit 59 demodulates the reception signal despread by the multiplier 58 into two information signals by the clock of the voltage control clock 56.

FIG. 14 is a block diagram of the receiving side using the synchronous holding system of claim 8 and the demodulating system of claim 10. In the figure, 70 is a synchronous holding circuit, 71 and 72 are low-pass filters (LPF), Reference numeral 73 is an identification reproducing circuit, and other parts having the same operations as those in FIG. 12 are denoted by the same reference numerals. The low pass filters 71 and 72 are the low pass filters 5 of FIG.
It has the same function as 4a and 54b, and also has the function of cutting off the high frequency components of the signal output to the identification reproduction circuit 53. The code of non-return toe zero (NRZ) is shown in FIG.
As shown in (a), it is a code format that gives a certain value to the logical value 0 and the logical value 1. In addition, the Manchester code has a logical value of 0 as shown in FIG.
The state change from negative to positive is assigned, and the state change from positive to negative is assigned to the logical value 1. In the case of a PN code sequence, its autocorrelation function is
It is known to have the characteristics shown in FIG. Further, when the Manchester code is used, FIG.
It is known to have the characteristics shown in (b). On the other hand, the cross-correlation values of the same PN code sequence using the NRZ code and those using the Manchester code are shown in FIG.
It is known to have the characteristics given in (c).

FIGS. 16 (a) to 16 (f) are diagrams showing time charts of signals of respective parts on the transmission side. Information signal (d
2, d1) is (0,0) → (0,1) → (1,0) → (1,
It shows the case where the transmission is changed to 1). The diagrams (a) and (b) represent the information signal d1 and the information signal d2, respectively. FIG. 6C shows the output signal of the clock 6 in FIG.
4D shows an output signal of the signal switcher shown in FIG. 4. When the clock signal has a logical value 0, the information signal d1 is output by the clock signal shown in FIG. 4C, and when the clock signal has a logical value 1, d2 is output. Figure (e) shows P generated by the spread signal generator 4 of Figure 4.
N signal. The output signal from the signal switcher of FIG. 6D is multiplied by the PN signal of FIG. 6E and modulated like the transmission signal of FIG. Here, in order for the correlation output to have the characteristic of FIG. 18, it is desirable that the 1-bit time width Tb of the PN signal of the information signal be one cycle of the spread signal or an integral multiple thereof. In this way, the modulated information signal is (d2, d1) = (0,0) and (d2, d1)
== (1,1), the transmission signal becomes an NRZ PN signal. When the information signal is (d2, d1) = (0, 1) and (d2, d1) = (1, 0), the transmission signal is a Manchester code PN signal.

Next, the synchronization holding unit on the receiving side will be described with reference to FIG. The information signal from the transmitting side is (d
2, d1) = (1,1), the PN signal of the received signal is the NRZ code. Therefore, the correlator A takes the cross-correlation between the NRZ despread signal and the NRZ received signal. Therefore, when the cross-correlation value of the received signal and the despread signal is taken, the correlation output takes the output value given in the form of FIG. 19 (g) with respect to the phase difference. on the other hand,
In the correlator B, the Manchester-despread signal and the NR
Since the cross-correlation value of the Z received signal is obtained, the correlation output takes the output value given in FIG. 19 (h) for the phase difference.

When the information signal is sent at (d2, d1) = (0, 0), the received signal is a PN signal with the NRZ code inverted, and therefore the correlator A produces a correlation output due to the phase difference. The output value in FIG. 19A and the correlation value B are shown in FIG.
The output value is 9 (b). The information signal is (d2, d1) =
If the received signal is (1, 0), the received signal is a Manchester-coded PN signal, so the correlator A uses NRZ.
The despread signal of 1 and the received signal of the Manchester code are correlated. Therefore, the correlation output of the correlator A takes the output value shown in FIG. 19E with respect to the phase difference. On the other hand, the correlator B takes the cross-correlation value between the Manchester-despread signal and the Manchester-coded PN signal, and therefore the correlation output takes the output value given by (f).

When the information signal is sent at (d2, d1) = (0, 1), the received signal is the PN signal with the Manchester code inverted, so that the correlator A produces a correlation output due to the phase difference. The output of the correlator B is shown in FIG.
It becomes (d). The multiplier 53 multiplies the output of the correlator A and the output of the correlator B. The output of the multiplier 53 is (a) × (b), (c) × in FIG.
(D), (e) × (f), and (g) × (h) will be output. Therefore, as shown in FIG. 20, the output of the multiplier 53 is the output value for damping the phase difference in the case of (a) × (b) in FIG. 19 and (g) × (h) in FIG. It becomes the output characteristic of a). Further, in the case of (c) × (d) in FIG. 19 and (e) × (f) in FIG. 19, the output characteristics are shown in FIG. 20 (b). Therefore, in either case, a feedback control loop can be formed by inputting this output to the voltage control clock 56 from the loop filter 54. This allows the despread signals to be synchronized.

The demodulation on the receiving side in FIG. 12 is performed as follows. The despread signal from the sync hold circuit 56 and the received signal are multiplied by the multiplier 58 to despread the received signal. In the despread reception signal, the information signal d1 exists when the clock has the logical value 0,
Since the information signal d2 exists when the clock has the logical value 1, the information can be restored by distributing the two signals according to the logical value of the clock signal from the voltage control clock 56 of the synchronous holding circuit 56. The circuit of this specific example is shown in FIG. The despread signal from the transcoder 58 is distributed to two signals by the switch circuits 61 and 62 which are rendered conductive when the logical value of the clock signal from the voltage control clock 56 is 0. The low pass filter 63 smoothes the output of the sweep circuit 61 and restores the information signal d1. Further, the low-pass filter 64 smoothes the output of the switch circuit 62 and restores the information signal d2.

As another demodulation method, the circuit configuration of FIG. 14 can be considered. The synchronization holding circuit 70 of FIG.
The same operation as that of the second synchronization holding circuit 50 is shown. When the output of the correlator A and the output of the correlator B of the synchronization holding circuit 70 are synchronized, the output value shown in FIG. 15 is taken, so that the information signal can be demodulated. ..
Both the output of the correlator A and the output of the correlator B are sent to the identification / reproduction circuit 73, and are restored to the information signal d1 and the information signal d2.

In the invention described above with reference to FIGS. 1 to 20, since two information signals are switched alternately, there are two types of transmission signals, NRZ code and Manchester code. Therefore, on the receiving side, the roles of the correlation output of the NRZ code correlator and the Manchester code correlator are switched depending on whether the transmission signal is the NRZ code or the Manchester code. As described above, in the spread spectrum communication system by the direct sequence (Derect Sequence; DS) system up to now, a delay locked loop (DLL) has been mainly used in order to obtain synchronization of the pseudo random number signal.
However, in the delay lock loop, it is difficult to balance the gains of the two correlators, and if the balance is lost, there is a drawback that the synchronization tracking characteristic deteriorates. The embodiments described below are configured by two correlators that do not require a balance, and thus a phase lock loop and a spectrum using the phase lock loop, which does not require adjustment and has good tracking characteristics, with a simple structure. It describes a spreading receiver.

FIG. 21 is a block diagram of a phase locked loop. In the figure, 81a and 81b are mixers, 82a and 82b are integrators, 83 is a multiplier, 84 is an EX-OR circuit, 85 is a PN signal generator, 86 is a voltage control clock (VCC: Vo
ltage Controlled Clock). Voltage control clock 8
An NRZ code PN signal is generated from the PN signal generator 85 by a clock signal from the PN signal generator 6. PN signal is usually M
A series of PN code signals is used. PN signal generator 85
The PN signal generated by the
And the EX-OR circuit 84 perform an exclusive logical OR. This makes the PN signal NR
The Z code is converted to Manchester code.

N generated by the PN signal generator 85
The RZ code PN signal and the Manchester-encoded PN signal by the EX-OR circuit 84 are multiplied by the received signal S ′ (t) by the respective mixers 81a and 81b. The outputs of the mixers 81a and 81b are input to the integrators 82a and 82b, respectively. The mixer 81a and the integrator 82a provide a cross-correlation output of the received signal S '(t) and the NRZ code PN signal. Also, the mixer 8
The cross-correlation between the received signal S '(t) and the PN signal of Manchester code is obtained by 1b and the integrator 82b. The cross-correlation output signal from the integrator 82a and the cross-correlation output signal from the integrator 82b are multiplied by the multiplier 83, and this output signal is input to the voltage control clock 86 as a control signal.

Next, the operation of the phase locked loop shown in FIG. 21 will be described. It is known that the autocorrelation function of the M-sequence PN signal of the NRZ code is given in FIG. The cross-correlation function between the NRZ code PN signal and the Manchester code PN signal is shown in FIG.
8 (c) is known. Therefore, by obtaining the cross-correlation value of the NRZ PN signal included in the received signal S ′ (t) and the Manchester code PN signal from FIG. 18C, the PN signal in the received signal and the PN signal An output signal corresponding to the phase difference from the PN signal generated by the signal generator can be obtained. Therefore, by feeding back this output signal as a control signal of the voltage control clock 86, a phase locked loop of the PN signal can be formed.

However, on the transmitting side, the information signal d (t)
And the PN signal P (t)
(T) is transmitted to the transmission line. Therefore, the transmission signal S (t) is PN when the information signal d (t) is "1".
The signal P (t) is output as it is, but when the information signal is "0", the phase of the PN signal P (t) is inverted and output. Therefore, when the information signal is "0", the cross-correlation value between the received signal S '(t) and the NRZ PN signal and the cross-correlation value between the received signal S' (t) and the Manchester code PN signal are Both 18 (a) and 18 (c) have a form in which the positive / negative of the correlation output R is inverted. For this reason, it becomes impossible to perform synchronous tracking using the cross-correlation characteristic of FIG.

Therefore, the information signal is obtained by multiplying the cross-correlation value of the reception signal S '(t) and the PN signal of the NRZ code by the cross-correlation value of the reception signal S' (t) and the PN signal of the Manchester code. Irrespective of "0" or "1", it is possible to always obtain an output signal that reduces the phase difference.
The output characteristic of the product of these two correlation outputs is shown in FIG. At this time, the received signal S '(t) and the PN of the NRZ code
As for the cross-correlation value of the signal, the cross-correlation value of the received signal S '(t) and the PN signal of the Manchester code is only inverted according to the information signal, so that it is not necessary to balance the two correlation outputs.

FIG. 22 is a block diagram of a spread spectrum receiver using a phase locked loop. In the figure, 87 is a phase locked loop, 91 is a mixer, 92 is an integrator, 93 is a comparator, and others, and FIG. Portions having the same function are designated by the same reference numerals. The synchronized PN signal from the phase locked loop 87 and the received signal are multiplied by the mixer 91, the output thereof is integrated by the integrator 92, and the received signal is despread. The output from the integrator 92 can be judged by the comparator 93, and information "1" or "0" can be obtained. At this time, since the despreading of the received signal is performed independently of the phase lock loop, the time constant of the integrator 93 can be set separately from the integrators 82a and 82b in the phase lock loop.

FIG. 23 is a block diagram showing another embodiment of the spread spectrum receiver. In the figure, reference numeral 94 is a comparator, and other parts having the same functions as those in FIG. 21 are designated by the same reference numerals. The information signal can also be demodulated by taking out the cross-correlation output of the PN signal of the NRZ code and the reception signal as it is as a demodulation signal and judging the output by the comparator 94.

[0050]

As is apparent from the above description, the present invention has the following effects. (1) Effects on Claims 1 and 3: In the spread spectrum communication system using the conventional correlator, one information signal must be assigned to one period of the pseudo random number code (PN code). However, according to this method, two pieces of information can be assigned to one cycle. Further, in the conventional spread spectrum communication, since the information signal is transmitted bit by bit, it has a drawback that it is weak against fading. However, according to this method, if the transmission rate is the same as the conventional one, the information of 1 bit is transmitted. Is transmitted for a longer period of time, which makes it more resistant to fading. Further, according to the present invention, since the spread signal is used to perform four-level modulation, it is possible to obtain an output signal having a constant envelope. Therefore, the final amplification stage of the transmitter is simple because the output signal is a constant envelope. (2) Effects on Claims 2 and 5: A code that inverts the first despreading code and the second despreading code so as to be as orthogonal as possible can be selected, and the signal switching method on the transmission side can be selected accordingly. By combining them, orthogonality can be increased,
The information signal can be easily identified. (3) Effect on Claim 4: By preparing the despreading code inside the correlator in advance, the clock generation circuit and the despreading code generation circuit are unnecessary, which is advantageous in terms of cost and circuit size. become. Also, there is no need for clock synchronization. (4) Effect on claim 6: In addition to the effect on claim 1 of claim 4, the coefficient of the coefficient multiplier is set to the second value in advance.
Since the despreading code can be prepared in advance, the conversion circuit for converting the first despreading code into the second despreading code is unnecessary, which is advantageous in terms of cost and circuit size. (5) Effect on claim 7: Since two information signals are transmitted at the same time, there is an advantage that fading is stronger than in the case of transmitting bit by bit.
Further, in the conventional modulation method such as the four-phase modulation method, it is difficult to obtain an output with a constant envelope when adding two modulated carrier waves. However, according to the present invention, since two pieces of information are four-valued modulated by a code, it is possible to obtain an output whose output signal has a constant envelope. For this reason, the final amplification stage of the transmitter is also easy because the output signal is a constant envelope. Furthermore, by switching the information signal by the clock,
Since the two information signals are modulated, the PN signal can be transmitted by the combination of the NRZ code and the Manchester code without adding any special circuit. (6) Effect on claim 8: In the conventional PN signal synchronization holding circuit, the synchronization is held mainly by the delay locked loop (DLL). However, it is difficult to balance two correlation outputs. It was However, in the synchronization holding circuit of the present invention, the synchronization loop is configured by using a non-return to zero (NRZ) code correlator with a correlation value and a Manchester coded correlator. Is simple, and the two correlators need not be in agreement. (7) Effect on claim 9: As a method of demodulating a received signal, the received signal and the despread signal are multiplied, and thereafter, the received signal is restored to two information signals by the clock signal, so that the identification reproduction is performed. It has the advantage of simplifying the circuit. (8) Effect on Claim 10: As a method for demodulating a received signal, the information signal is demodulated by obtaining a correlation output from two correlators in the synchronous loop, so that the multiplier is not necessary. Has the advantage of. (9) Effect on claim 11: A signal obtained by multiplying the cross-correlation output of the received signal and the PN signal of the NRZ code and the correlation output of the received signal and the PN signal of the Manchester code with the control signal of the voltage control clock. Therefore, synchronization tracking can be performed regardless of the information signal. Also,
The adjustment of the phase-locked loop becomes unnecessary because it no longer requires the balancing of the two correlators required in a conventional delay-locked loop. Therefore, it is advantageous in terms of manufacturing cost. (10) Effect on claim 12: Since only the PN signal is taken out from the phase locked loop to despread the received signal, the time constant of the integrator used for despreading is independently determined. You can (11) Effect on claim 13: Since the output from the correlator that takes the received signal of the phase-locked loop and the PN signal of the NRZ code in claim 11 is taken out as it is as a demodulation signal, the number of parts is small and therefore the spectrum is low in cost. A spreading receiver can be configured.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a spread spectrum communication system according to the present invention.

FIG. 2 is a diagram showing an example of a signal switch.

FIG. 3 is a diagram showing an example of a PN converter.

FIG. 4 is a block diagram of a transmitting side.

FIG. 5 is a diagram showing a time chart of signals of various parts on the transmission side.

6 is a diagram showing the outputs of correlators A and B. FIG.

FIG. 7 is a diagram showing a correlation circuit.

8 is a diagram showing a correlator A. FIG.

9 is a diagram showing a correlator B. FIG.

FIG. 10 is a diagram showing a convolver.

FIG. 11 is a diagram showing another example of the signal switch.

FIG. 12 is a block diagram of a receiving side.

FIG. 13 is a diagram showing an identification reproduction circuit.

FIG. 14 is another block diagram of the receiving side.

FIG. 15 is a diagram showing a correlator output.

FIG. 16 is a diagram showing a time chart of signals of various parts on the transmission side.

FIG. 17 is a diagram showing a baseband code.

FIG. 18 is a diagram showing a correlation function.

FIG. 19 is a diagram showing a correlator output.

FIG. 20 is a diagram showing an output of a product of a correlator.

FIG. 21 is a block diagram of a phase locked loop.

FIG. 22 is a block diagram of a spread spectrum receiver using a phase locked loop.

FIG. 23 is a block diagram showing another embodiment of the spread spectrum receiver.

[Explanation of symbols]

1 ... Transmitter, 2 ... Receiver, 3 ... Signal switcher, 4 ... PN signal generator, 5 ... Mixer, 6 ... Clock generator, 7 ... Correlator A, 8 ... Correlator B, 9 ... PN signal generation Device, 10 ... identification reproduction circuit, 11 ... PN converter.

Claims (13)

[Claims] 1. A transmitting side is provided with a spread spectrum means for modulating a signal obtained by alternately switching two information signals at a modulation rate of a spreading code and then transmitting the modulated signal, and a receiving side is used at the transmitting side. The same code as the spread code
And a second despreading code, which is a code in which every other code of the spreading code is replaced with an opposite code, the cross-correlation value between the received signal and the first despreading code, and A spread spectrum communication system characterized by demodulating two information signals sent from a transmitting side by a cross-correlation value between a received signal and a second despread code. 2. The transmitting side is provided with a spread spectrum means for modulating a signal obtained by arbitrarily switching two information signals at the modulation rate of the spreading code and then transmitting the modulated signal, and the receiving side is used at the transmitting side. The same code as the spread code
And a second despreading code, which is a code in which the code of the spreading code is replaced with an opposite code in the same pattern as the switching pattern of the information code on the transmitting side, and the received signal and the first signal
2. A spread spectrum communication system characterized by demodulating two information signals sent from a transmitting side by a cross-correlation value with the despreading code and the cross-correlation value between the received signal and the second despreading code. 3. Two correlators for obtaining the cross-correlation value,
The first despread code and the received signal are input to the first correlator to obtain a cross-correlation value, and the second despread code and the received signal are input to the second correlator. The spread spectrum communication system according to claim 1, further comprising a correlator that obtains a value. 4. As two correlators for obtaining the cross-correlation value, N (N is a natural number) coefficient multipliers are connected to the connection points of each delay circuit in which delay circuits are cascade-connected, and Two correlators for obtaining the sum of outputs are provided, and the code sequence in which the first despreading code is reversed is used as the coefficient of the coefficient multiplier of the first correlator, and the correlator of the second correlator is used. 2. The spread spectrum communication system according to claim 1, wherein the coefficient multiplier has a correlator that uses a code sequence in which the second despreading code is reversed. 5. Two correlators for obtaining the cross-correlation value,
The first despread code and the received signal are input to the first correlator to obtain a cross-correlation value, and the second despread code and the received signal are input to the second correlator. The spread spectrum communication system according to claim 2, further comprising a correlator that obtains a value. 6. As two correlators for obtaining the cross-correlation value, N (N is a natural number) coefficient multipliers are connected to connection points of each delay circuit in which delay circuits are connected in cascade, and Two correlators for obtaining the sum of outputs are provided, and the code sequence in which the first despreading code is reversed is used as the coefficient of the coefficient multiplier of the first correlator, and the correlator of the second correlator is used. The spread spectrum communication system according to claim 2, wherein the coefficient of the coefficient multiplier has a correlator that uses a code sequence in which the second despreading code is reversed. 7. The transmitting side is provided with a spread spectrum means for modulating a signal obtained by alternately switching two information signals at a clock timing for generating a spreading code and then transmitting the modulated signal, and the receiving side is provided with a transmitting device. Of the non-return toe zero (NRZ) despreading code in the same sequence as the spreading code on the side and the received signal, and the Manchester-coded despreading code and the received signal in the same sequence as the spreading code on the transmitting side. A spread spectrum communication system characterized by demodulating two information signals sent from a transmitting side by a correlation value. 8. A non-return to zero (NR) is used in the first correlator to synchronize the despread code on the receiving side.
Z), the cross-correlation value between the despread code and the received signal is taken, and the second correlator takes the cross-correlation value between the Manchester despread code and the received signal, and the output of the first correlator is obtained. , A synchronization holding method for holding the phase of the despreading code by using a signal obtained by multiplying the output of the second correlator as a control signal of a circuit for shifting the phase of the despreading code. The spread spectrum communication system according to claim 7. 9. In order to demodulate the two information signals spread by the spreading code, the received signal is despread by the despreading code, and the despread signal is generated at the timing of the clock for generating the despreading code. 8. The spread spectrum communication system according to claim 7, further comprising a demodulation system for demodulating two information signals sent from the transmitting side by distributing the two information signals. 10. A demodulation for demodulating two information signals by the output of the first correlator and the output of the second correlator in order to demodulate the two information signals spread by the spreading code. The spread spectrum communication system according to claim 9, further comprising a system. 11. In a spread spectrum communication in a base band, a signal transmitted by spreading an information signal with a pseudo random number signal of NRZ (non-return to zero) code,
A first correlation signal obtained by despreading with a pseudo random number code of NRZ code and a second correlation signal obtained by despreading with a pseudo random number code of Manchester code respectively obtain cross-correlation outputs, A spread spectrum communication system characterized by having a pseudo random number signal synchronous lock loop using a signal obtained by multiplying each cross correlation output as a damping signal of a phase locked loop circuit. 12. The information signal is demodulated by despreading the signal spread by the pseudo random number signal of the NRZ code on the transmission side using the pseudo random number signal obtained by the pseudo random number signal synchronization lock loop. The spread spectrum communication system according to claim 11, further comprising a receiver. 13. A receiver for demodulating an information signal by extracting a first correlation signal in the pseudo random number signal synchronization lock loop from a signal spread by a pseudo random number signal of an NRZ code on the transmission side. 11. The method according to claim 11,
The spread spectrum communication system described.