JPH04120827A - Spectrum dispersion modulation/demodulation system - Google Patents

Abstract

PURPOSE:To attain the synchronizing demodulation with a simple circuit constitution by modulating directly the phase of a pseudo noise PN code with an information signal. CONSTITUTION:A clock generator 1 is provided together with a PN code generator 2, variable delay circuit 3, correlator 4, loop filter 5, voltage control oscillator 6, PN code generator 7, and a waveform shaping circuit 8. A modulator consists of only the generator 1, the generator 2, and the circuit 3. Then a PN signal. is inputted to the circuit 3 and the delay time is changed by an information signal. Then the phase modulation is applied to a PN code. Thus the primary demodulation can be omitted and it is possible to attain the synchronizing demodulation that is hitherto difficult to perform in a system where the PN code is turned on and off.

Description

[Detailed description of the invention] Fu11yachu□ The present invention relates to a spectrum spread modulation and demodulation system.

For example, it is applied to wireless communication and confidential communication.

] q (basket conventional, direct spectrum 1 hell spread communication system (SpreadS)
pectrum communication: 5
SC), the mainstream method is to keep the pseudo-yorone (PN) code (spreading code) clock constant and multiply the spreading code by a normal narrowband modulation signal (information signal) to spread the signal.
This method requires two stages of modulation and demodulation, making the circuit configuration complicated. In addition to this, l) O OK (On Off Key), which turns the N code on and off using an information signal.
B) PN code (P
NI) A method of intermittent output, and a CSK (Code Shj, ft.
KeyjnB) method, i.e. 2 depending on the polarity of the data.
Type 11 N code (P N 1 / I) N 2
) has been proposed. For example, there is a literature document titled ``A method of high-speed data transmission in SS modem using rSAW convolver'' (Yoshitaka Uchida and two others, Institute of Electronics, Information and Communication Engineers, Spread Spectrum Technology and Its Application Study Group, June 15, 161990). However, all of these methods change the amplitude of a specific PN code, and it is difficult to perform synchronous tracking using this method because the PN code disappears or is replaced midway. Therefore, it is necessary to perform asynchronous demodulation using an expensive SAW convolver. The disadvantage of this method stems from the fact that the ASK (amplitude shift keying) method is used to modulate the PN code.

On the other hand, a method of encrypting picture and character patterns by changing the phase of the M sequence and creating a two-dimensional array is as follows.
For example, a method has been proposed in Japanese Patent Application Laid-Open No. 152243/1983. That is, on the transmitting side, each pixel position that divides the screen is set in advance according to the basic M arrangement,
Arrange O or 1 signals, invert the O or 1 signals for each bit portion corresponding to a pattern of a picture, character, etc. to be transmitted, and then create an arrangement in which a part is inverted according to the pattern. The present invention relates to an information transmission method using an M array in which a pattern is reproduced by calculating the exclusive OR of the caught array and the original basic M array on the receiving side.

Figures 5(a) and 5(b) show the conventional synchronous direct spec I.
Figure (a) is a block diagram of a spreading modulator and demodulator.
)) is a demodulator. In the figure, 21- is a primary modulation circuit, 2
2 is a clock generator, 23 is a pseudo-noise (PN) code generator, 24 is a multiplier, 25°27 is a correlator, 26 is a first-order demodulation circuit, 28 is a loop filter, 29 is a voltage controlled oscillator, 3o is a pseudo It is a noise (PN) code generator. In the modulator, a signal modulated by a normal modulation method such as FM is multiplied by a signal from a PN code generator 23 in a multiplier 24, and spread modulation is performed. The demodulator is broadly divided into a PN code synchronization circuit (delay locked loop: ■: +r, L) section and a despreading demodulation section.In the DLL section, a correlator 27 performs correlation calculation between the transmitted signal and the receiving side I)N code. The output signal is used as a control signal to control the sleep clock of the PN code generator 30, thereby performing synchronization control. The demodulation section multiplies and combines the synchronized PN code and the received signal, despreads the signal and returns it to a narrow 111'' band signal, and then performs normal demodulation.

The present invention has been made in view of the actual situation as described in 1. By directly modulating the phase of a pseudo-noise (PN) code with an information signal, ? The purpose of this invention is to provide a spectrum spread modulation/demodulation system that is capable of synchronous demodulation with a simple circuit configuration.

Lecture □ In order to achieve the object described in item 1, the present invention includes a clock generator, a pseudo-noise (PN) code generator driven by a clock signal from the clock generator, and a delay time generated by an information signal. a modulator consisting of a variable delay circuit; a pseudo-noise (PN) code generator that is the same as that on the modulation side; a correlator that correlates the output of the pseudo-noise (PN) code generator with the received signal; A demodulator comprising a loop filter that converts the correlation output from the correlator into a control signal, a voltage controlled oscillator whose tarock frequency is variable according to the control signal from the loop filter, and a comparator that extracts a demodulated signal from the output of the loop filter. It is characterized by having the following features. Hereinafter, description will be made based on embodiments of the wooden invention.

FIG. 1 is a block diagram for explaining an embodiment of the spread spectrum modulation and demodulation method according to the present invention. In the figure, 1 is a tarok generator, 2 is a pseudo-noise (PN) code generator, and 3 is a A variable delay circuit, 4 a correlator, 5 a loop filter, 6 a voltage controlled oscillator, 7 a pseudo-noise (PN) code generator, and 8 a waveform shaping circuit.

The modulator consists of only a clock generator 1, a PN code generator 2, and a variable delay circuit 3.The PN signal is input to the variable delay circuit 3, and the delay time is changed using the information signal, thereby applying phase modulation to the PN code. . The demodulator requires a synchronization section similar to conventional ones, but since demodulation is extracted from the synchronization signal,
There is no need for a despreading demodulator like in the past. The synchronization section includes a correlator 4, a loop filter 5, a voltage controlled oscillator 6, and a PN code generator 7, which constitute a synchronization loop in this order.

This section describes the principle of synchronous demodulation. The output of the correlator has characteristics as shown in FIG. 2 with respect to the phase difference of the PN code of the transmitter and receiver (an example where the autocorrelation at two phases separated by a chip is calculated and the difference is calculated). A line segment with a constant slope passing through the origin in the figure (
A, A'), synchronization can be achieved by controlling the correlation output to converge to O. Here, the sending side P
When phase modulation is applied to the N code, the correlation output will also change near the origin in FIG. 2, so the signal can be demodulated by extracting and integrating the correlation output. However, care must be taken because modulation is applied too deeply, extending beyond AA' in FIG. 2 and causing loss of synchronization.

Figure 3 is a block diagram of a spread spectrum modulation/demodulation system suitable for digital signals.
is a pseudo-noise (PN) code generator, 13 is a delay circuit, and 14 is a pseudo-noise (PN) code generator.
is a logic circuit, 15 is a correlator, 16 is a loop filter, 1
7 is a voltage controlled oscillator, 18 is a pseudo-noise (PN) code generator, and 19 is a comparator. The PN signal from the PN code generator 12 is divided into two parts, one of which is passed through a delay circuit 13 with a constant delay time, and phase modulation is performed by switching with the two-way information signal. The demodulator consists of a delay locked loop similar to that shown in FIG. 1(b), but since digital modulation is used, demodulation requires only inputting the loop filter output to the comparator 19 with hysteresis. This will be explained based on FIG. A waveform as shown in b in FIG. 4 is output to the comparator in response to the information signal in a. In other words, an impulse-like signal is generated at the point where the phase changes. Therefore, the signal can be demodulated by determining that a 1 was sent when the signal level exceeded a certain level, and that an O was sent when the signal level fell below a certain signal level. At this time, it is necessary to provide hysteresis characteristics so that the output does not change even if the input is zero or some noise is present.

In the embodiment of the present invention, the PN code is phase modulated, but the drive clock of the PN code generator may be phase modulated.

As is clear from the above explanation, according to the present invention, PN
Since the code itself is modulated, there is no need for a primary modulation/demodulation section as in the prior art. Also, in order to apply phase modulation to the PN code, turn on the PN code.

It is possible to perform synchronous demodulation, which is difficult with the off method.

Furthermore, since the information signal is extracted from the control signal itself in the synchronous circuit, demodulation becomes very simple, which is advantageous in terms of manufacturing and cost.

[Brief Description of the Drawings] Fig. 1 is a block diagram for explaining an embodiment of the spread spectrum modulation/demodulation method according to the present invention, Fig. 2 is a block diagram for explaining the principle of synchronous demodulation, and Fig. 3 is a block diagram for explaining the principle of synchronous demodulation. is a block diagram of a spread spectrum modulation/demodulation method suitable for digital signals, and Figure 4 is a block diagram of a spread spectrum modulation/demodulation method suitable for digital signals.
A diagram showing the signal waveforms of each part of the configuration diagram in Fig. 5.
The figure is a block diagram of a conventional synchronous direct spread spectrum modulator/demodulator. clock generator, 2. Pseudo noise (PN) code generator, 3. Variable delay circuit, 4. Correlator, 5. Loop filter, 6. Voltage controlled oscillator, 7. Pseudo noise ( P
N) Code generator, 8... waveform shaping circuit. Patent Applicant Riko Co., Ltd. Akira Chika Takano (1 idiot) 1st

Claims (1)

[Claims] 1. A modulator consisting of a clock generator, a pseudo noise code generator driven by a clock signal from the clock generator, a delay circuit whose delay time is variable according to an information signal, and a pseudo noise code generator that is the same as the modulation side. a noise code generator; a correlator that correlates the output of the pseudo noise code generator with the received signal;
A demodulator comprising a loop filter that converts the correlation output from the correlator into a control signal, a voltage controlled oscillator whose clock frequency is variable according to the control signal from the loop filter, and a comparator that extracts a demodulated signal from the output of the loop filter. A spread spectrum modulation/demodulation method characterized by comprising: