JPH07107005A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To provide a communication system for performing pseudo spread spectrum communication with simple circuit constitution by multiplying and transmitting intermediate frequency signals and spread signals and performing detection by using the same spread signals on a reception side. CONSTITUTION:A transmitter 110 multiplies the intermediate frequency signals obtained in a modulation means 111 and the spread signals obtained in a spread signal generation means 112 in a balanced modulator 113. Then, corresponding to the respective spread signals, target signal components separated for the frequency of a carrier wave on an upper side and a lower side are generated and the target signal components are transmitted. Also, a receiver 120 multiplies the spread signals obtained in the spread signal generation means 121 and the target signal components, restores the intermediate frequency signals and obtains original signals by a demodulation means 123. Thus, an intermediate frequency component is spread into 2n pieces of the target signal components and transmitted corresponding to the number (n) of the spread signals, the original intermediate frequency component can be synthesized from the target signal components and the simple spread spectrum communication can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system used for wireless transmission of information.

[0002] In recent years, mobile communications such as car telephones have spread rapidly along with satellite communications, so that the method of allocating different frequencies to individual communications has run out of frequency space.

In order to solve such a problem, a spread spectrum communication system has been proposed as a method for multiple use of a frequency space in a plurality of communication channels, and has been put to practical use in the field of satellite communication and the like.

The spread spectrum communication system is a communication system in which a carrier of the same frequency which is spread spectrum by a spread code corresponding to each communication channel is transmitted, and the receiving side demodulates using the same spread code to obtain information. is there.

[0005]

2. Description of the Related Art The principle configuration of a conventional spread spectrum communication system is shown in FIG. In the transmitting section shown in FIG. 4, the carrier wave is digitally modulated by the primary modulator 411 with the baseband signal and sent to the spread spectrum section 412. In the spread spectrum unit 412, the digital modulated wave and the spread signal generated by the spread spectrum signal generator 413 are multiplied by the multiplier 414, and the spread spectrum carrier (hereinafter referred to as spread spectrum wave) is transmitted by the transmitter. 415.

However, in an actual communication system, it is often the case that the carrier wave is not directly modulated by the baseband signal but the information is embedded in the spreading signal. On the other hand, in the receiving unit, the spread spectrum wave received by the receiver 421 is sent to the spread demodulation unit 422, and is multiplied by the spread demodulation signal generated by the spread demodulation signal generator 424 by the multiplier 423 to obtain the band. It is sent to the primary demodulator 426 via the filter 425, and demodulated into a digital signal by the primary demodulator 426.

If the spread spectrum wave received by the receiver 421 is of a target channel, the spread signal used for this spread spectrum wave and the spread demodulation signal generated by the spread demodulation signal generator 424 described above. Both the code sequence and the phase of the signal match. In this case, if the correlation is obtained by the multiplier 423, the digital modulated wave before the spread spectrum processing is obtained, and the primary demodulator 426
Is demodulated to the original digital signal. On the other hand, the spread spectrum waves of the other channels become noise-like components due to the above-described correlation processing.

The code sequences of the spreading signal and the spreading demodulation signal described above have steep autocorrelation characteristics and there are many code sequences with small cross-correlation. It is necessary that the parts also have the same statistical properties, and the maximum length sequence (M sequence) and Gold
Series etc. are used.

In the spread spectrum communication system, when the power density of the spread spectrum wave transmitted from the transmission side is spread over a wide frequency band and demodulated using the same code sequence as that used for spread spectrum Since only the original digital signal is demodulated, it is highly resistant to frequency selective fading and interference and highly confidential.

[0010]

In the above-described conventional spread spectrum communication system, it is necessary for both the transmitting side and the receiving side to have a mechanism for generating a complicated code sequence as a spreading signal. , Both the receiving side and the device side are large and expensive. Therefore, the applicable range of this communication method has been limited to a large-scale communication system such as a satellite communication system.

By the way, since the transceiver and the cordless telephone are used for personal communication in a short distance, the high confidentiality provided by the above-mentioned spread spectrum communication method is not necessary, and conversely, the device can be downsized. It is important to reduce the price.

It is an object of the present invention to provide a spread spectrum communication system for performing pseudo spread spectrum communication using a simple circuit configuration.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. The invention of claim 1 provides a transmitting device 110.
Is a modulation means 111 for transmitting an intermediate frequency signal obtained by modulating a carrier wave with an input signal, and a spread signal generation means for generating at least one spread signal different from the intermediate frequency signal and having frequencies different from each other. 11
2 and a balanced modulator 113 that multiplies the intermediate frequency signal and at least one spread signal and transmits the multiplication result. The receiving device 120 spreads the spread signal to generate at least one spread signal. Generating means 121, detecting means 122 for multiplying the received signal by at least one spread signal, and demodulating means 1 for demodulating the output of the detecting means 122.
23 is provided.

According to a second aspect of the present invention, in the spread spectrum communication system according to the first aspect, the spread signal generating means 112 of the transmitting device 110 has a phase of the spread original signal and the spread signal having a frequency which is the basis of the spread signal frequency. An oscillating means 114 for generating a sync signal serving as a synchronization reference and sending this sync signal to the modulating means 111, and a synthesizing means 115 for synthesizing at least one spread signal based on the spread original signal and the sync signal. The modulation means 111 is configured to superimpose the synchronization signal and the intermediate frequency signal and send the superimposed signal to the balanced modulator 113, and the spread signal generation means 121 of the reception device 120 is
Extraction means 124 for extracting a synchronization signal from the output of the detection means 122, a spread source signal is generated based on the synchronization signal, and at least one spread signal is synthesized based on the spread source signal and the synchronization signal. It is characterized in that it is configured to include a synthesizing means 125.

[0015]

According to the invention of claim 1, in the transmitter 110,
The intermediate frequency signal obtained by the modulation means 111 and the spread signal obtained by the spread signal generation means 112 are balanced modulator 113.
Is multiplied to generate target signal components corresponding to each spread signal, the target signal components being separated from each other by the carrier frequency, and these target signal components are transmitted. Also,
In the reception device 120, the detection means 122 restores the intermediate frequency signal by multiplying the spread signal obtained by the spread signal generation means 121 and the above-mentioned target signal component, and the demodulation means 123 obtains the original signal. .

As described above, the transmitter 110 and the receiver 1
If the same spread signal is used for both 20 and 20, the intermediate frequency component is spread and transmitted to 2n target signal signals according to the number n of spread signals, and at the receiving side, the original intermediate frequency from these target signal components is transmitted. The components can be combined, and simple spread spectrum communication can be realized.

According to a second aspect of the invention, the synthesizing means 11 is based on the spread original signal and the synchronizing signal obtained by the oscillating means 114.
5, the spread signals are combined, and the spread frequency signals are used to balance-modulate the intermediate frequency signal on which the synchronization signal is superimposed. In the receiving device 120, the extraction unit 124 extracts the synchronization signal from the output of the detection unit 122,
Based on this synchronization signal, the synthesizing means 125 synthesizes the spread signals and inputs them to the detecting means 122.

In this case, the spreading signal generating means 121 of the receiving device 120 causes the transmitting device 1 to send the signal based on the synchronization signal.
It is possible to reliably combine the same spread signal as the spread signal in 10.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a block diagram of an embodiment of a communication system to which the spread spectrum communication system of the present invention is applied.
Further, FIG. 3 shows a diagram for explaining the spread spectrum action according to the present invention.

In FIG. 2, the modulation circuit 211 and the carrier wave oscillation circuit 212 correspond to the modulation means 111. The modulation circuit 211 superimposes a pilot signal for phase synchronization on the input signal Si to generate a carrier wave oscillation circuit. Enter in 212. The carrier wave oscillating circuit 212 modulates a carrier wave having a frequency fi (for example, 455 kHz) according to the above-mentioned input signal to generate an intermediate frequency signal, and sends it to the balanced modulator 113.

Here, as the above-mentioned pilot signal, for example, a 10 kHz sine wave signal is supplied from an oscillation circuit 214 described later, and this signal may be used. If the input signal is a digital signal, the modulation circuit 2
Reference numeral 11 may convert the input digital signal into a Manchester code of 10 kbps and send it to the carrier wave oscillation circuit 212.
In this case, this Manchester code can be used to synchronize the phase of the spread signal.

The oscillator circuit 214 and the frequency synthesizer 215 correspond to the spread signal generating means 112. The oscillating circuit 214 corresponds to the oscillating means 114, generates the pilot signal described above and sends it to the modulating circuit 211, and also generates the spread original signal of the frequency fs and the signal of the frequency d and corresponds to the synthesizing means 115. It is sent to the frequency synthesizer 215. Based on this spread source signal,
The number of frequency synthesizers 215 is n (for example, 10)
The spread signals of are combined and sent to the balanced modulator 113.

Here, the oscillating circuit 214 generates, for example, a signal having a frequency fs higher than the frequency fi of the carrier wave as a spread original signal, and multiplies the pilot signal by frequency d.
Should generate the signal. In addition, the frequency synthesizer 2
15 is the frequency of the spread original signal and the signal of frequency d.
It is only necessary to synthesize n spread signals having a spectrum arranged at intervals of fHz to dHz (for example, 40 Hz).

These spread signals and the intermediate frequency signal obtained by the carrier oscillation circuit 212 described above are balanced modulator 1
Multiply by 13 to obtain n pairs of target signal components that are in a mirror image relationship with each other, as shown in FIG. The frequency of the target signal component corresponding to each spread signal is separated by the intermediate frequency fi between the upper side and the lower side of the frequency of the corresponding spread signal.

These target signal components are filtered by the filter 216.
Is input to the amplifier 217 via the amplifier, amplified by the amplifier 217, and then transmitted. This filter 216
May suppress the intermediate frequency component leaked to the output of the balanced modulator 113.

In this way, the intermediate frequency component of the frequency fi can be spread into 2n target signal components and transmitted. On the other hand, in FIG. 2, the amplifier 221 and the detection circuit 2
Reference numeral 22 corresponds to the detection means 122, and the amplifier 221 amplifies the received signal and inputs it to the detection circuit 222. The detection circuit 222 multiplies the spread signal generated by the spread signal generation means 121 by the received signal, and sends the obtained signal to the demodulation circuit 224 corresponding to the demodulation means 123 via the demultiplexing circuit 223.

Here, if the spread signal used on the reception side and the spread signal used on the transmission side match, the detection circuit 222 vectorically combines the components corresponding to the 2n target signal components. Then, the energy of the original intermediate frequency component is regenerated. In other words, even if the power of each target signal component to be transmitted is weak,
It is possible to reproduce the intermediate frequency component having n times the power. Therefore, the demodulation circuit 224 may demodulate the intermediate frequency component according to the modulation method (for example, FM method) used on the transmitting side to obtain the original signal.

A method for generating the same spread signal as the spread signal used on the transmitting side on the receiving side will be described below. In FIG. 2, the demultiplexing circuit 223 and the waveform shaping circuit 2
25, the PLL circuit 226, the reference crystal oscillator 227, and the multiplication circuit 228 correspond to the extraction means 124.
In the extracting means 124, the demultiplexing circuit 223 demultiplexes the pilot signal component from the above-mentioned intermediate frequency component,
It is sent to the PLL circuit 226 via the waveform shaping circuit 225. This PLL circuit 226 is set to 1 based on the output of the reference crystal oscillator 227 and the signal from the waveform shaping circuit 225.
A clock signal of 0 kHz is generated, a frequency multiplication circuit 227 multiplies the frequency of this clock signal to generate a signal of 40 kHz, and the frequency synthesizer 231 and the oscillation circuit 232.
Send to.

In the case of digital signal communication, a 10 kbps Manchester signal is obtained from the demultiplexing circuit 223, and the original information is obtained by demodulating the digital signal obtained by the PLL circuit 226 based on this Manchester signal. Restored.

In FIG. 2, the frequency synthesizer 231
The oscillating circuit 232 and the oscillating circuit 232 correspond to the synthesizing means 125, and constitute the spread signal generating means 121 together with the extracting means 124 described above.

In the synthesizing means 125, the oscillator circuit 2
32 is the frequency fs based on the 40 kHz signal described above.
The original spread signal is generated and sent to the frequency synthesizer 231. In addition, the frequency synthesizer 2
Similar to the transmitting side, 31 is configured to synthesize n spread signals based on the spread original signal and the 40 kHz signal.

Here, 10 obtained by the PLL circuit 226.
Since the phase of the kHz clock signal is synchronized with the phase of the pilot signal superimposed on the transmission side, the oscillator circuit 232 and the frequency synthesizer 2 are based on this clock signal.
By operating 31 and 31, the same spread signal as the transmitting side can be reproduced.

Therefore, this frequency synthesizer 23
If the spread signal obtained in 1 is sent to the detection circuit 222,
The detection circuit 222 reproduces the original intermediate frequency component.

As described above, it is possible to realize a pseudo spread spectrum communication by generating a spread signal using a relatively simple circuit such as an oscillation circuit or a frequency synthesizer.

Therefore, the present invention can be applied to applications requiring downsizing and cost reduction, such as cordless telephones and transceivers, and a communication system effective in these fields can be provided.

Further, in the present invention, by detecting each target signal component using the spread signal on the receiving side, the intermediate frequency component is vector-wise added and amplified, whereas the noise component is They cancel each other out because of the random phase. Therefore, the application of the present invention also has the effect of improving the S / N ratio of the received signal.

Since the effect of improving the S / N ratio is proportional to the number n of spread signals, a larger effect can be expected by using a large number of spread signals. For example, if the intermediate frequency is set to a high frequency, a wider range can be set as the band of the spread signal, so that the number of spread signals can be easily increased and a high S / N ratio can be easily realized. .

[0038]

As described above, the present invention utilizes the property of the balanced modulator to generate 2n target signal components corresponding to n spread signals on the transmitting side, and the same on the receiving side. By detecting using the spread signal of, the intermediate frequency component dispersed in the 2n target signal components can be restored. The above-mentioned spread signal generating means for generating n spread signals can be realized by a relatively simple circuit. Therefore, by applying the present invention, pseudo spectrum spread can be performed using a simple circuit. A communication method can be realized. As a result, it is possible to provide an effective communication system in the fields of cordless telephones, transceivers, and the like, and promote the spread of these devices.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment of a communication system to which the system of the present invention is applied.

FIG. 3 is a diagram illustrating a spread spectrum effect according to the present invention.

FIG. 4 is a principle configuration diagram of a conventional spread spectrum communication system.

[Explanation of symbols]

 110 Transmitter 111 Modulating means 112, 121 Spreading signal generating means 113 Balanced modulator 114 Oscillating means 115, 125 Combining means 122 Detection means 123 Demodulating means 124 Extracting means 211 Modulating circuit 212 Carrier wave oscillating circuit 214, 232 Oscillating circuit 215, 231 Frequency Synthesizer 216 Filter 217, 22 1 Amplifier 222 Detection circuit 223 Demultiplexing circuit 224 Demodulation circuit 225 Waveform shaping circuit 226 PLL circuit 227 Reference crystal oscillator 228 Multiplication circuit 411 Primary modulator 412 Spread spectrum unit 413 Spread spectrum signal generator 414, 423 Multiplication Device 415 Transmitter 421 Receiver 424 Spreading demodulation signal generator 425 Bandpass filter 426 Primary demodulator

Claims (2)

[Claims] 1. A transmitter (110) for transmitting an intermediate frequency signal obtained by modulating a carrier wave by an input signal, and a modulating means (111), and a frequency different from the intermediate frequency signal and different from each other. A spread signal generating means (112) for generating at least one spread signal, and a balanced modulator (11) for multiplying the intermediate frequency signal by the at least one spread signal and transmitting the multiplication result.
3), wherein the receiving device (120) multiplies the spread signal generation means (121) for generating the at least one spread signal and the detection signal for multiplying the received signal by the at least one spread signal. (122) and demodulation means (1) for demodulating the output of the detection means (122).
23), and a spread spectrum communication system. 2. The spread spectrum communication system according to claim 1, wherein the spread signal generating means (112) of the transmission device (110) synchronizes the phase of the spread original signal and the spread signal having a frequency which is the basis of the frequency of the spread signal. And a synchronization signal serving as a reference of the above, and at least one spread signal is synthesized on the basis of the oscillating means (114) for sending this sync signal to the modulating means (111) and the spread original signal and the sync signal. And a synthesizing means (115) for modulating the synchronization signal and the intermediate frequency signal, and the modulating means (111) superimposes the synchronization signal and the intermediate frequency signal on the balance modulator (113). The generating means (121) extracts the synchronizing signal from the output of the detecting means (122), and generates a spread original signal based on the synchronizing signal. Based on the Tijara signal and a synchronization signal, the spread spectrum communication system, characterized in that a configuration in which a synthesizing means for synthesizing at least one spreading signal (125).