JPH05292062A - Spread spectrum correlation method and synchronization method - Google Patents

Abstract

(57) [Abstract] [Purpose] A single correlator is used to obtain the correlation characteristics required for synchronization and demodulation even for non-coherent pulsed light. The output from the pulsed PN code generator 1 and the output from the Manchesterized PN code generator 12 are multiplied by a multiplier 2
And a correlator consisting of an integrator 4 to obtain the cross-correlation between them. Synchronization control and the like are performed using this correlation output. That is, a pseudo noise (PN) code sequence (sequence A) is Manchester-coded on one side of the transmission side or the reception side, and a pulsed sequence of each chip of the sequence A is used on the other side. Cross-correlation calculation of series is performed. By dividing Manchester encoding and pulse encoding into the transmitting side and the receiving side, it becomes possible to perform synchronous control with a single correlator even for noncoherent optical pulses.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spread spectrum correlation method and a synchronization method, and more particularly to a correlation method and a synchronization method in spread spectrum communication. For example, it is applied to spread spectrum (SS) communication, optical communication, wireless communication, and the like.

[0002]

2. Description of the Related Art Generally, direct sequence (D)
In the S) system spread spectrum communication device, the received signal and the spread code (pseudo noise code = PN code) are correlated for synchronization of the spread code between the transmission and reception devices, and the correlation value is used as a control signal for the PN code. It is common to control the frequency of the clock for use. An example of such a code synchronization circuit is disclosed in Japanese Patent Laid-Open No. 1-228338. This is a so-called delay lock loop method, in which two adjacent points in the receiving side code sequence are correlated with the received signal, and the difference signal between the two is used as a control signal to control the frequency of the code clock generator to synchronize. Is to take.

Conventionally, in the direct spread type spread spectrum (SS) communication system, positive and negative binary sequences are mostly handled as pseudo noise codes used for spreading. However, it is not necessary to limit to binary if the required correlation characteristic is obtained. For example, “Characteristics and applications of DS-SS system by RZ code” (Fukuyama Sogai, SICE 89-16, P.33-37, 198)
9.8., 4-5), each chip of the PN code is returned to zero (RZ), and the autocorrelation characteristics in the case of using the pulsed PN code are reported. Since the PN code itself can take positive and negative values, it takes three values as a whole including zero, but the pseudo noise (PN) 1 code takes only two values. In this document, the correlation characteristic and spectrum characteristic of the RZ code are shown.

In the "simple coherent code tracking system in spread spectrum communication" (IEICE, RCS88-4), a PN code and a PN code orthogonal thereto (OPN code) are used. A synchronization method using cross-correlation of the Manchesterized PN code in (1) has been proposed. Furthermore, the “spread spectrum correlation method and the synchronization method and the modulation / demodulation method” of Japanese Patent Application No. 3-44284 previously proposed is a PN code sequence,
The present invention relates to a spread spectrum correlation method and a synchronization / modulation / demodulation method that use the cross-correlation of a code sequence obtained by subjecting this code sequence to Manchester coding and pulse coding, and non-coherent pulsed light cannot be used as a transmission medium. This is because non-coherent light cannot generate a negative pulse.

[0005]

[Object] The present invention has been made in view of the above circumstances, and spread spectrum correlation that can obtain the correlation characteristics required for synchronization and demodulation with a single correlator even for non-coherent pulsed light. The purpose is to provide a method and a synchronization method.

[0006]

In order to achieve the above object, the present invention provides (1)
In a correlation method in spread spectrum communication, a pseudo-noise (PN) code sequence (sequence A) is Manchester-coded on one of the transmitting side and the receiving side, and a pulsed sequence of each chip of sequence A is used on the other side. , Performing a cross-correlation operation on both code sequences in the correlation unit, or
(2) In the correlation method in spread spectrum communication,
Which of the output of sequence A is 0 or 1 after Manchester-encoding a pseudo noise (PN) code sequence (sequence A) is used on one of the transmitting side and the receiving side and each chip of sequence A is pulsed on the other side A cross-correlation operation of both code sequences is performed in the correlating unit by using a sequence whose output is 0 in either one of the states, or (3) in the correlation method in spread spectrum communication, either the transmitting side or the receiving side A pseudo-noise (PN) code sequence (sequence A) is used as a Manchester-encoded sequence, and after pulsing each chip of the sequence A to the other, a pulse within one cycle of the pseudo-noise (PN) code among positive and negative pulses A cross-correlation operation of both code sequences is performed in the correlator using a sequence in which the pulse output having a polarity whose number becomes an odd number is 0. Further, in (4) above (1), (2) or (3) ,Previous The duty ratio of the series of pulsed it was about 50%, or (5) above (1) to
In the spread spectrum correlation method described in any one of (4), pulse light that is turned on / off by a pseudo noise (PN) code is transmitted on the transmitting side, and Manchester encoding pseudo noise (PN) code is used on the receiving side. The cross-correlation with the received light is obtained by the correlating unit and used as the synchronization control signal. Hereinafter, description will be given based on examples of the present invention.

First, FIG. 6 shows the cross-correlation characteristics of the Manchesterized PN code and the pulsed PN code according to the present invention.
A description will be given using (a) to (d). The figure (a) is the original PN code, and the figure obtained by Manchester encoding this is the figure (b). In addition, a pulsed PN code in which the duty ratio X is pulsed for each chip is shown in FIG. Furthermore, a pulsed PN code in which the output of one polarity of the positive and negative pulses is zero is shown in FIG.

Next, FIGS. 7A to 7D show the cross-correlation characteristics of the Manchesterized PN code and the pulsed PN code.
The correlation calculation is performed by multiplying two code sequences and integrating them for a certain period of time. FIG. 1 which will be described later when shown in the figure
This is the part consisting of the multiplier and the integrator. In an actual circuit, a double balanced mixer is used as a multiplier,
As the integrator, a low pass filter may be used, a method using a SAW convolver that performs multiplication and integration at the same time, a method of digitally calculating a correlation value after A / D conversion of a received signal, and the like can be considered. 6 (b) and 6 (c), the pulsed duty ratio X is 1.0, 0.75,
FIG. 7 shows the result of calculation of the cross-correlation characteristics for the cases of 0.5 and 0.25. Figure (a) corresponds to the unpulsed case and was inserted for comparison. From this figure, it can be seen that an S-shaped special treatment symmetrical with respect to the origin can be obtained regardless of the duty ratio X. Therefore, this can be used as it is as a control signal of the code synchronization circuit. When the duty ratio X is 1.0 to 0.5, the correlation peak value hardly decreases. Further, when the duty ratio X is 0.5, the origin-symmetrical correlation characteristic having a double slope as compared with the case of not pulsing in the range of ± T / 4 is obtained. When the duty ratio X is less than 0.5, the correlation peak portion is scraped and flattened, resulting in a trapezoidal characteristic. In the range where the delay time exceeds ± T, a minute triangular wave-shaped correlation output is generated with pulse encoding. The above corresponds to claim 1 of the present invention.

Next, FIGS. 8 (a)-(d) and 9 (a)-
The cross-correlation characteristics between the Manchesterized PN code of FIG. 6B and the pulsed PN code in which one of FIG. 6D is zero will be described with reference to FIG. When the M sequence is used for the PN code, an odd number of pulses are included in one cycle of the PN code. Since the number of positive pulses and the number of negative pulses are different by one, if there are an even number of positive pulses, then there will be an odd number of negative pulses. FIG. 8 shows the correlation characteristics when a signal having a polarity (+ or −) having an odd number of pulses is left in one cycle of the PN code, and FIG. 9 is a polarity characteristic having an even number of pulses in one cycle of the PN code ( It is the correlation characteristic when the signal of − or +) is left. Within the range of the delay time of about ± T, the characteristics shown in FIG. 7 are halved in the vertical direction regardless of the value of the duty ratio X. However, in the range where the delay time exceeds ± T, when the number of pulses in one cycle is an odd number, the same characteristic as in the case of FIG. 7 appears, whereas when the number of pulses in one cycle is an even number, the correlation The output is cleanly zero. It is preferable that the correlation characteristics of FIGS. 8 and 9 are used.
Then, it is the third aspect that uses the characteristics of FIG. Claim 4
7 corresponds to setting the duty ratio X to 0.5 in FIGS. 7 to 9, and as can be seen from the figures, shows a correlation characteristic most suitable for synchronous control when it is just 0.5.

FIG. 1 is a block diagram for explaining an embodiment of a spread spectrum correlation system according to the present invention. In the figure, 1 is a pulsed PN code generator, 2 is a multiplier, and 3 is a Manchesterized PN code. The generator 4 is an integrator. Pulsed PN
The output from the code generator 1 and the output from the Manchesterized PN code generator 3 are input to a correlator consisting of a multiplier 2 and an integrator 4, and the cross-correlation between them is obtained. This correlation output is used to perform synchronization control and the like described later.

FIG. 2 is a block diagram of the pulsed PN code (waveform of FIG. 6C) generator shown in FIG. 1. In the figure, 5 is a clock generator, 6 is a PN code generator, and 7 is a monostable. The multivibrator, 8 is a 3-state buffer. The clock generator 5 drives the PN code generator 6 and the monostable multivibrator 7 which is triggered by a negative edge, and the output of the PN code generator 6 is passed through a 3-state buffer 8 to be turned ON / OFF by the output of the monostable multivibrator. OFF control is performed to generate a pulsed PN code sequence. In order to stabilize the output when turned off, the output line is connected to a voltage source that is half the power supply voltage via a resistor.

FIG. 3 is a Manchesterized P in FIG.
It is a figure which shows the block diagram of an N code generator, and the example of the code synchronizing circuit which used the correlation system. In the figure, 9 is a correlator, 10 is a loop filter, 11 is a voltage controlled oscillator, 12 is a PN code generator, and 13 is an EX-OR (exclusive OR) circuit.
Using the output signal of FIG. 2 as a received signal, a Manchester-ized PN code is generated on the receiving side, and a correlation calculation between this and the received signal is performed. The output of the voltage controlled oscillator 11 is used as a clock signal to drive the PN code generator 12, and the output and the clock signal are input to the exclusive OR circuit 13 to obtain the Manchesterized PN code. The code and the received signal are input to a correlator, the correlation output is passed through a loop filter to control the voltage controlled oscillator 11, and the code is synchronized.

FIG. 4 is a block diagram of the pulsed PN code (waveform shown in FIG. 6D) generator shown in FIG. 1. In the figure, 14 is an AND circuit, and other parts that have the same function as those in FIG. The same reference numerals are attached. P by the output of the clock generator
The N code generator 6 and the monostable multivibrator 7 which is triggered by a negative edge are driven, the output signals of both are passed through the AND circuit 14, the transistors are driven, and the light emitting diode is turned ON / OFF. The unipolar pulsed PN code sequence of (d) is generated and pulsed light is emitted.

FIG. 5 is a diagram showing the code synchronization circuit in FIG. 4, in which reference numeral 15 is a preamplifier, and other parts having the same operation as in FIG. The received light is detected by the photodiode and amplified by the preamplifier 15 and then
Code synchronization is measured by the same code synchronization circuit as in the case. Since a unipolar pulse is used on the transmission side, this is an example for claim 2. Further, since an optical pulse is used for transmission, it is also an example for claim 5. With respect to claim 3, in the embodiments of claims 2 and 5, the polarity of the output of the PN code generator may be inverted by an inverter so that the number of pulses in one cycle of the PN code is even. Finally,
Regarding claim 4, the monostable multivibrator is turned on.
The time constant may be adjusted so that the time between states is half the time of one chip of the PN code.

[0015]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: In the spread spectrum correlation method according to claim 1, one of the input PN code sequences of the correlator is Manchester-coded and the other is pulse-coded. Synchronous control is possible with one correlator, and one signal power can be reduced to X times when the pulse duty ratio is X, and conversely, peak power can be increased to 1 / X times. Can be done. Therefore,
The former leads to cost reduction and the latter saves energy. On the contrary, by increasing the peak power, the transmission distance can be extended. (2) Effect corresponding to claim 2: In the spread spectrum correlation method of claim 2, in addition to the effect of claim 1, since only a pulse of one polarity is used in pulse encoding, The circuit for obtaining the coded PN code is simpler than in the case of claim 1 and leads to cost reduction. Furthermore, since the pulsed PN code takes only binary values of 1 or 0, it can be realized as a pulse signal of non-coherent light. (3) Effect corresponding to claim 3: In the spread spectrum correlation method of claim 3, in addition to the effects of claims 1 and 2, only pulses of an even-numbered polarity are used in pulse encoding. Since the correlation output is strictly zero in the region where the delay time exceeds ± 1 chip time, there is no fear of false synchronization. (4) Effect corresponding to claim 4: In the spread spectrum correlation method of claim 4, in addition to the effects of claims 1 to 3, the duty ratio at the time of pulse coding is set to 50%, so the input signal Despite the energy being halved, the correlation peak value does not change, and the slope of the synchronous control region shown by the straight line passing through the origin is doubled, improving the synchronous tracking characteristic. (5) Effect corresponding to claim 5: In the spread spectrum correlation method according to claim 5, in addition to the effects of claims 1 to 4, by performing pulse generation on the transmission side, non-coherent pulsed light can be obtained. Communication is possible.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a pulsed PN code generator in FIG.

FIG. 3 is a diagram showing a code synchronization circuit for FIG.

4 is another configuration diagram of the pulsed PN code generator in FIG. 1. FIG.

5 is a diagram showing a code synchronization circuit for FIG. 4;

FIG. 6 is a diagram for explaining cross-correlation characteristics of a Manchesterized PN code and a pulsed PN code according to the present invention.

FIG. 7 is a diagram for explaining cross-correlation between FIG. 6 (b) and FIG. 6 (c).

FIG. 8 is a diagram for explaining cross-correlation between FIG. 6 (b) and FIG. 6 (c).

9 is a diagram for explaining cross-correlation between FIG. 6 (b) and FIG. 6 (c).

[Explanation of symbols]

1 ... Pulsed PN code generator, 2 ... Multiplier, 3 ... Manchesterized PN code generator, 4 ... Integrator.

Claims (5)

[Claims] 1. In a correlation method in spread spectrum communication, a pseudo-noise code sequence (sequence A) is Manchester-encoded on one of the transmitting side and the receiving side, and each chip of sequence A is pulsed on the other side. A spread spectrum correlation method characterized by performing cross-correlation calculation of both code sequences in a correlation unit using. 2. In a correlation method in spread spectrum communication, a pseudo-noise code sequence (sequence A) is Manchester-coded on one of the transmitting side and the receiving side, and each chip of the sequence A is pulsed on the other side. A spread spectrum correlation method characterized by using a sequence whose output is 0 when the output of the sequence A is either 0 or 1 and performing a cross-correlation operation of both code sequences in the correlation unit. 3. In a correlation system in spread spectrum communication, a pseudo-noise code sequence (sequence A) is Manchester-encoded on one of the transmitting side and the receiving side, and after each chip of the sequence A is pulsed on the other side. , A spectrum characterized by performing a cross-correlation operation of both code sequences in the correlation unit by using a sequence in which the pulse output of the polarity in which the number of positive and negative pulses in one cycle of the pseudo-noise code is odd is 0 is used. Diffusion correlation method. 4. The duty ratio of the sequence to be pulsed is set to about 50%.
The spread spectrum correlation method described. 5. The spread spectrum correlation method according to claim 1, wherein the transmitting side transmits pulsed light that is turned on / off by a pseudo noise code, and the receiving side transmits a Manchester coded pseudo noise code. A spread spectrum synchronization method characterized in that a correlation control signal is obtained by using a correlation unit to obtain a cross correlation with the received light.