JPH0993161A - Modulation demodulation system for spread spectrum communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a modulation demodulation system for spread spectrum communication in which a PN code generator at receiver side is omitted. SOLUTION: The modulation demodulation system for spread spectrum communication is provided with a frequency converter 21 converting a signal frequency, a surface acoustic wave convolver element 22 outputting an autocorrelation signal, a detector 23 detecting the autocorrelation signal, and a data demodulation circuit 24 demodulating. Then two kinds of PN code in timewise inverting relation are multiplied by binary digital data signals to apply CSK modulation and the autocorrelation signal of the PN code is detected by using the surface acoustic wave convolver element 22 and the detector 23 and the same code or different code are judged for consecutive data to demodulate the signal depending on the presence of the autocorrelation signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation / demodulation system for spread spectrum communication using a surface acoustic wave convolver element.

[0002]

2. Description of the Related Art In a spread spectrum communication in which a PN code (pseudo noise code) is applied to a digital data signal to spread and modulate a frequency spectrum, and the same PN code is despread to demodulate a data signal, a surface acoustic wave is used. Examples of synchronization detection of received signals and demodulation of data signals using a convolver element have been reported.

For example, CSK using PN code for primary modulation
(Code shift keying) Modulation and demodulation method of spread spectrum communication (spread spectrum communication modem) which is directly spread by modulation is described in the Technical Report SST92-94, pages 19 to 24, and FSK (frequency shift keying) is used for primary modulation. ) A modulation / demodulation method of spread spectrum communication in which direct modulation is adopted by using PN code as a secondary modulation and PN code is disclosed on pages 1 to 6 of SIST 92-60.

[0004]

However, in the conventional modulation / demodulation system of spread spectrum communication, the receiver side has P
Since the N code generator is required, there has been a problem that the circuit scale increases and the cost also increases.

The present invention solves the above problems and provides a simple and inexpensive modulation / demodulation system for spread spectrum communication by omitting the PN code generator for the reference signal, which was essential on the receiving side. With the goal.

[0006]

In order to solve the above problems, a modulation / demodulation system for spread spectrum communication according to the present invention is
Frequency conversion means for converting the frequency of the signal, demultiplexing means for demultiplexing the frequency-converted signal, delay means for delaying the signal, surface acoustic wave convolver element for outputting the autocorrelation signal, and the autocorrelation signal A spread spectrum communication device comprising a detecting means for detecting and a data demodulating means for demodulating a signal, wherein two kinds of PN codes in a time-reversal relationship are applied to each of binary values of a signal of digital data. CSK-modulated signal is split into two, the PN code of one signal is time-inverted and the phase of the other signal is shifted by 1 bit from each other, and the autocorrelation signal of the PN code is converted into a surface acoustic wave convolver element. The signal is demodulated by detecting the same sign or different sign of continuous data depending on the presence or absence of the autocorrelation signal.

[0007]

With this configuration, since the PN code generator is not required on the receiver side, the spread spectrum signal can be demodulated with a simple and inexpensive circuit configuration.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a modulation / demodulation system of spread spectrum communication in a first embodiment of the present invention.

On the transmitter side, the digital data generated by the data generator 1 is sent to the PN code generator 2,
The code generator 2 generates two different PN codes that are time-reversed with each other for binary 1/0 of digital data. Then, the modulator 3 receives the PN code signal, multiplies it by the carrier frequency signal, and transmits it from the antenna 4.

On the other hand, when a signal is received by the antenna 5 on the receiver side, the received signal is frequency-converted by the frequency converter 6 as frequency conversion means. Then, the demultiplexer 7 as demultiplexing means demultiplexes the frequency-converted reception signal into two waves and supplies the two signals to the two paths.

The one path is directly input to one input terminal of the surface acoustic wave convolver element 9. In another path, the delay element 8 serving as a delay unit delays the received signal, and then the signal is input to another input terminal of the surface acoustic wave convolver element 9. The surface acoustic wave convolver element 9 generates signals of the above two waves, and generates an autocorrelation signal (convolution signal) at the output electrode 15 (see FIG. 2). And
The presence or absence of the autocorrelation signal on the output electrode 15 is detected by the detector 10 as the detection means, and demodulated into digital data by the data demodulation circuit 11 as the data demodulation means.

FIG. 2 is an external perspective view of a surface acoustic wave convolver element used in the modulation / demodulation system of spread spectrum communication in the first embodiment of the present invention. In FIG. 2, the piezoelectric substrate 12 is made of, for example, a LiNbO ₃ single crystal, and the IDT electrode 1 having a interdigital shape is formed on both ends of the upper surface thereof.
Reference numerals 3 and 14 are formed as input terminals for signals from the demultiplexer 7 and the delay element 8, respectively. Further, the piezoelectric substrate 1
2 center portion of the upper surface (that is, the IDT electrodes 13 and 14 at both ends).
An output electrode 15 for detecting an autocorrelation signal is formed in the middle).

At this time, the length L of the output electrode 15 is K ≦ L ≦ 1.3K where K = Vs × Td Vs: surface acoustic wave velocity of the piezoelectric substrate 12 (m / sec) Td: bit length of data ( Seconds).

As a result, the PN for one bit of data is efficiently included including the signal delayed by the multipath fading.
The code correlation can be detected.

If L is less than K, the autocorrelation signal becomes small and the S / N ratio is significantly lowered. Further, if L exceeds 1.3K, the autocorrelation signal is mixed from the data before and after the data to be detected, and the S / N ratio is lowered. Therefore, in order to detect an autocorrelation signal with a good S / N ratio, it is desirable to satisfy the above conditions.

FIG. 3 is a waveform diagram of an autocorrelation signal detected by a detector used in the modulation / demodulation system of spread spectrum communication in the first embodiment of the present invention. In the case of this embodiment,
Data included in the frequency-converted received signal, for example, [10110101001] is correlated with 1-bit delayed data [0110101001-]. In this embodiment, since an autocorrelation signal is generated in the case of a different code, if the presence or absence of a peak of the autocorrelation signal is represented by 1,0, [1101111101-] can be obtained from the above two data. In the actual modulation / demodulation operation, it was confirmed that the peak of the autocorrelation signal shown in FIG. 3 appears at [1101111101-].

(Embodiment 2) FIG. 4 is a block diagram showing a modulation / demodulation system of spread spectrum communication in a second embodiment of the present invention.

On the transmitter side, the digital data generated by the data generator 16 is sent to the PN code generator 17, and the PN code generator 17 outputs 2 of 1/0 of the digital data.
Two different Ps that are time-reversed with each other
Generate N codes. Then, the modulator 18 receives the signal of the PN code, multiplies it by the signal of the carrier frequency, and transmits it from the antenna 19.

On the other hand, on the receiver side, when a signal is received by the antenna 20, the received signal is frequency-converted by the frequency converter 21 as frequency conversion means and input to the surface acoustic wave convolver element 22. The surface acoustic wave convolver element 22 generates an autocorrelation signal at the output electrode 27 (see FIG. 5) according to the received signal. Then, the presence or absence of the autocorrelation signal on the output electrode 27 is detected by the wave detector 23 as the wave detecting means, and demodulated into digital data by the data demodulating circuit 24 as the data demodulating means.

FIG. 5 is an external perspective view of a surface acoustic wave convolver element used in a modulation / demodulation system of spread spectrum communication according to a second embodiment of the present invention. In FIG. 5, the piezoelectric substrate 25 is made of, for example, a single crystal of LiNbO ₃ , and one end of the upper surface thereof has the IDT electrode 2 having a interdigital shape.
6. A grating 28 for reflecting surface acoustic waves is formed at the other end. Further, an output electrode 27 for detecting an autocorrelation signal is formed in the central portion of the upper surface of the piezoelectric substrate 25 (that is, between the IDT electrode 26 and the grating 28).

The surface acoustic wave generated in the other end direction by the signal supplied to the IDT electrode 26 is reflected by the grating 28, and the self-correlation between the generated surface acoustic wave and the reflected surface acoustic wave delayed by 1 bit. A signal is obtained from the output electrode 27. It should be noted that the present embodiment uses the reflected signal (reflected surface acoustic wave), and thus has the excellent feature that the demultiplexer and the delay element used in (Example 1) are not required.

At this time, similarly to (Example 1), the length L of the output electrode 27 is K ≦ L ≦ 1.3K where K = Vs × Td Vs: surface acoustic wave velocity (m / m) of the piezoelectric substrate 25. Seconds) Td: Set as the data bit length (seconds).

If L is less than K, the autocorrelation signal becomes small and the S / N ratio is remarkably lowered. Further, if L exceeds 1.3K, the autocorrelation signal is mixed from the data before and after the data to be detected, and the S / N ratio is lowered. Therefore, in order to detect an autocorrelation signal with a good S / N ratio, it is desirable to satisfy the above conditions.

The waveform diagram of the autocorrelation signal detected by the detector 23 of this embodiment is the same as that described in (Embodiment 1) shown in FIG.

The signals used in (Example 1) and (Example 2) of the present invention are set to the following values. That is, the PN code is a 127-chip M-sequence code and its time-reversed code, the chip rate is 13 MHz, and the data transfer rate is 205 kbps.

The carrier frequency is set to 200 MHz in consideration of the frequency characteristic of the convolution effect of the surface acoustic wave convolver elements 9 and 22.

Furthermore, in (Embodiment 1) and (Embodiment 2), as a result of measurement of BER (bit error rate) in the presence of thermal noise, it was confirmed that a value close to the theoretical value was obtained. In addition, as a result of examining the anti-interference property with respect to the interference signal due to the CW signal and other spread spectrum signals,
It was also confirmed that there was no problem in practical use.

As described above, it was confirmed that all of the examples have excellent characteristics as a demodulation system for spread spectrum signals.

[0030]

According to the modulation / demodulation system of spread spectrum communication of the present invention, the frequency conversion means for converting the frequency of the signal, the demultiplexing means for demultiplexing the frequency-converted signal, the delay means for delaying the signal, A surface acoustic wave convolver element that outputs a correlation signal, and detection means that detects an autocorrelation signal,
A spread spectrum communication device comprising data demodulation means for demodulating a signal, wherein two types of PNs are in time-reversed relationship with each other for each of the two values of the digital data signal.
A CSK-modulated signal is demultiplexed into two, the PN code of one signal is time-inverted, and the phase of the other signal is shifted by one bit from each other, and the autocorrelation signal of the PN code is a surface acoustic wave. A method is adopted in which detection is performed using a convolver element and detection means, and the same code or different code of continuous data is determined depending on the presence or absence of an autocorrelation signal to demodulate the signal.

With this configuration, the PN code generator is not required on the receiver side, so that the spread spectrum signal can be demodulated with a simple and inexpensive circuit configuration. Therefore, by using the present invention, various wireless data transmission devices such as a wireless LAN modem, a distance measuring device, and a wireless game machine can be provided at a small size and at a low price.

[Brief description of drawings]

FIG. 1 is a block diagram showing a modulation / demodulation system for spread spectrum communication according to a first embodiment of the present invention.

FIG. 2 is an external perspective view of a surface acoustic wave convolver element used in a modulation / demodulation system of spread spectrum communication according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram of an autocorrelation signal detected by a detector used in the modulation / demodulation method of spread spectrum communication according to the first embodiment of the present invention.

FIG. 4 is a block diagram showing a modulation / demodulation system for spread spectrum communication according to a second embodiment of the present invention.

FIG. 5 is an external perspective view of a surface acoustic wave convolver element used in a modulation / demodulation method of spread spectrum communication according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Data Generator 2 PN Code Generator 3 Modulator 4 Antenna 5 Antenna 6 Frequency Converter 7 Demultiplexer 8 Delay Element 9 Surface Acoustic Wave Convolver Element 10 Detector 11 Data Demodulation Circuit 12 Piezoelectric Substrate 13 IDT Electrode 14 IDT Electrode 15 Output electrode 16 Data generator 17 PN code generator 18 Modulator 19 Antenna 20 Antenna 21 Frequency converter 22 Surface acoustic wave convolver element 23 Detector 24 Data demodulation circuit 25 Piezoelectric substrate 26 IDT electrode 27 Output electrode 28 Grating

Claims (4)

[Claims] 1. A frequency conversion means for converting the frequency of a signal, a demultiplexing means for demultiplexing the frequency-converted signal, a delay means for delaying the signal, and a surface acoustic wave convolver element for outputting an autocorrelation signal. A spread spectrum communication device comprising a detection means for detecting an autocorrelation signal and a data demodulation means for demodulating a signal, the two types being in a time reversal relationship with respect to each of the two values of the digital data signal. The CSK-modulated signal is demultiplexed into two by applying the PN code of No. 1, the PN code of one signal is time-inverted, and the phase of the other signal is shifted by 1 bit from each other, and the autocorrelation signal of the PN code is elastic A spectrum characterized by detecting using a surface wave convolver element and a detecting means, judging the same sign or different sign of continuous data depending on the presence or absence of an autocorrelation signal, and demodulating the signal. Modulation and demodulation system of diffusion communication. 2. A piezoelectric substrate having two IDT electrodes for exciting surface acoustic waves at both ends thereof, and an output electrode for detecting an autocorrelation signal at a central portion of the piezoelectric substrate and an intermediate portion of the two IDT electrodes. 2. A modulation / demodulation system for spread spectrum communication according to claim 1, wherein a surface acoustic wave convolver element is used to input two demultiplexed signals to each IDT electrode to generate an autocorrelation signal and take out from the output electrode. . 3. A frequency conversion means for converting the frequency of the signal, a surface acoustic wave convolver element for outputting the autocorrelation signal, a detection means for detecting the autocorrelation signal, and a data demodulation means for demodulating the signal. A spread spectrum communication device, wherein CSK modulation is performed by applying two types of PN codes having a time-reversal relationship to each of binary values of a digital data signal, and an autocorrelation signal of the PN code is a surface acoustic wave convolver element. A modulation / demodulation method for spread spectrum communication, characterized by detecting the same sign or different sign of continuous data depending on the presence or absence of an autocorrelation signal, and demodulating the signal. 4. An IDT electrode for exciting a surface acoustic wave on one end of the piezoelectric substrate, a grating for reflecting the surface acoustic wave on the other end of the piezoelectric substrate, and a central portion of the piezoelectric substrate and I.
Using a surface acoustic wave convolver element having an output electrode for detecting an autocorrelation signal in an intermediate portion between the DT electrode and the grating, the surface acoustic wave generated in the grating direction from the IDT electrode and the surface acoustic wave reflected by the grating are used. 4. The modulation / demodulation system for spread spectrum communication according to claim 3, wherein the autocorrelation signal is extracted from the output electrode.