JP2001007731A - Spread spectrum transmitter and receiver thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify constitution and to enhance confidentiality. SOLUTION: A voice signal obtained by a microphone 1 is amplified by a voice amplifier circuit 2, and an additional signal outputted by an oscillating means 3 of frequencies in a band other than a required voice band is superimposed on the voice signal, and carrier waves are frequency-modulated by a modulating means 4 as a modulated signal. The modulated signal is spread by a spreading means 6, and transmitted via a transmitting circuit 7. This spread spectrum receive is provided with a filter for removing the additional signal after inverse spread and demodulation. Thus, the band of the signal before spreading can be increased, regardless of the voice signal by superimposing the additional signal, and a spectrum before spreading is overlapped on a transmission spectrum so that confidentiality is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum transmitter and a spread spectrum receiver mainly used for wireless transmission of signals such as voice.

[0002]

2. Description of the Related Art Spread spectrum communication has been mainly applied to military communication equipment. However, in recent years, it has been applied to mobile communication by a code division multiple access (CDMA) system and consumer equipment such as a cordless telephone. In particular, wireless local area networks (hereinafter referred to as “wireless LANs”)
And various wireless systems with relatively low power, 2.
Although operating in a frequency band called the ISM band such as the 4 GHz band, it is specified that many of these wireless systems transmit by a spread spectrum system. For example, even in Japan, the standard for wireless LAN is "Low power data communication system / wireless LAN system standard RCR STD
-33 ", established by the Association of Radio Industries and Businesses, and stipulates transmission using the spread spectrum method. The spread spectrum method includes a direct spread method and a frequency hopping method. Of these, the direct spreading method uses a relatively long-period pseudo-random binary sequence such as an M sequence as a spreading sequence,
The frequency is spread by multiplying the normal transmission signal modulated with an information signal such as voice by the spreading sequence. Then, the receiving side despreads by multiplying the received signal in synchronism with the transmitting side by synchronizing the same spreading sequence with the transmitting side to return to the signal before spreading, and then performs normal detection and demodulation. These signal processings are described in detail in the literature (Marubayashi, Nakagawa, Kono, Spread Spectrum Communication and Its Applications, published by the Institute of Electronics, Information and Communication Engineers, 1998). Therefore, in order to correctly demodulate the transmission signal by the direct spreading method, it is necessary to prepare the same spreading sequence as that of the transmission in the receiver. Therefore, when the same spreading sequence is different in transmission and reception, or when received by a normal receiver that does not perform despreading, the demodulated waveform is significantly distorted and cannot be read, or it is difficult to confirm even the presence of a signal (radio wave). . Therefore, by keeping the same series private to third parties, the confidentiality of communication is enhanced.

Hereinafter, a conventional spread spectrum transmitter and receiver will be described. FIG. 11 is a block diagram of a conventional spread spectrum transmitter, and FIG. 12 is a block diagram of a conventional spread spectrum receiver. In FIG. 11, 1
Is a microphone that outputs an audio signal as an information signal to be transmitted from a sound wave, 2 is an audio amplifier circuit, 4 is a modulation unit that generates a carrier wave and modulates the carrier wave with a modulation signal, and has a modulation input terminal 41. For example, in the case of frequency modulation, the modulation means 4 often uses an oscillation circuit based on a phase locked loop (PLL), and a modulation input terminal is connected to a frequency control input of a voltage variable frequency oscillator (VCO). Numeral 5 is a spreading sequence generating means for generating a spreading sequence, and 6 is a spreading means for multiplying the output of the modulating means 4 by multiplying the spreading sequence by frequency, and for example, a balanced modulator or a multiplier is used. A transmission circuit 7 amplifies the transmission signal frequency-spread by the spreading means 6, converts the frequency if necessary, and transmits the signal from the antenna. In FIG. 12, reference numeral 10 denotes a receiving circuit that amplifies a high-frequency signal received by an antenna, converts the signal into an intermediate frequency signal or a baseband signal, and amplifies the signal to a required level. Are generated in synchronism with the transmitting side, 12 is a despreading means for multiplying the output of the despreading sequence generating means 11 by the output of the receiving circuit 10 and despreading, and 13 is a despreading means. It is a demodulation means for detecting a signal and demodulating a modulated signal, that is, an audio signal as an information signal. As the despreading means 12, a balanced modulator or a multiplier is used similarly to the spreading means. As the demodulation means 13, a means according to the modulation format in the transmitter is used. For example, in the case of frequency modulation, a frequency discriminator is used. Reference numeral 15 denotes an audio amplifier circuit, and reference numeral 16 denotes a speaker, which amplifies a demodulated audio signal to a required level and converts the signal into a sound wave.

The operation of the spread spectrum transmitter and the receiver configured as described above will be described below.
The information signal obtained by the microphone 1 and the audio amplification circuit 2 is input to the modulating means 4 and modulates a carrier to obtain a normal transmission signal. Then, the transmission signal frequency-spread by the spreading means 6 is amplified by the transmission circuit 7, frequency-converted as necessary, and transmitted from the antenna. In the receiver, the transmission signal received by the antenna is
After being amplified by the despreading means 12 and despread by the despreading means 12, it is demodulated by the demodulation means 13 to reproduce an audio signal as an information signal. The audio signal is amplified by the audio amplification circuit 15 and causes the speaker to sound. The above-described conventional spread spectrum transmitter and receiver transmit an analog audio signal. Instead of the audio signal, a binary digital signal or a baseband signal in which the digital signal is band-limited by an appropriate filter. Is an information signal, a configuration of a digital spread spectrum spread transmitter and a spread spectrum receiver is obtained.

[0005]

However, in the conventional spread spectrum transmitter and spread spectrum receiver, a signal based on the spread spectrum method is converted into a signal by a receiver compatible with a normal radio wave format which is not compatible with the spread spectrum method. When three parties intercept, confidentiality may deteriorate. For example, when the period of the spreading sequence is Ts, for example, as shown in FIG. 13, the spectrum of the spreading sequence generally has line spectra arranged at intervals of fs = 1 / (Ts). And modulating means 4
When the spectrum of the output signal is relatively narrow as shown in FIG. 14, the output of the spreading means 6, that is, the spectrum of the frequency-spread transmission signal is as shown in FIG. In the figure, fo indicates a carrier frequency. For example,
When the audio signal level is low when the modulation means 4 is frequency modulation or when a low tone is transmitted when the modulation means 4 is amplitude modulation, the spectrum of the output signal of the modulation means 4 is narrow band signal as shown in FIG. , And the spectrums of the ordinary frequency-modulated or amplitude-modulated signals are arranged at intervals of fs = 1 / (Ts). Therefore, when intercepting with a receiver compatible with a normal radio wave format, if the receiver has a band-pass filter with a pass bandwidth of about fs and the reception frequency is tuned to fo ± nfs (n is an integer), Has a problem that demodulation can be performed and confidentiality is deteriorated.

An object of the present invention is to solve the above problems and to provide a spread spectrum transmitter and a spread spectrum receiver which can transmit with high confidentiality with a simple configuration.

[0007]

According to the present invention, in order to achieve the above object, in a transmitter, a modulating means for modulating a carrier wave by an information signal, and a signal generated by the modulating means are frequency-spread by a direct spreading method. Spreading means for modulating, a transmission circuit for supplying the output of the frequency spreading means to the antenna as a transmission signal, and an oscillation means for generating an additional signal of a frequency outside the required band of the information signal, in the receiver, A receiving circuit that receives a signal that has been frequency-spread and transmitted by a direct spreading method, and that outputs a modulated signal by despreading and demodulating, and from an information signal and an additional signal included in the modulated signal, for removing the additional signal. With the provision of the filter means, it is possible to provide a spread-spectrum transmitter and a spread-spectrum receiver that are simple in configuration and capable of highly confidential transmission. Was Tsu.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a modulating means for modulating a carrier wave by an information signal, and a spreading means for frequency-spread modulating a signal generated by the modulating means by a direct spreading method. A transmitting circuit that supplies an output of the frequency spreading unit to the antenna as a transmission signal, and an oscillating unit that generates an additional signal having a frequency outside a required transmission band of the information signal, wherein the modulation unit applies the information signal to the information signal. A signal in which the additional signal is superimposed is modulated as a modulation signal, and the additional signal expands the band of the output signal of the modulating means, and the reciprocal of the period of the spreading sequence (Ts) fs = 1 / (Ts). Since the spectrums of the signals overlap each other, an effect of improving the confidentiality is obtained.

According to a third aspect of the present invention, there is provided a spreading means for generating a signal which is frequency-spread modulated by a direct spreading method, a modulating means for modulating an output signal of the spreading means with an information signal, and A transmitting circuit for supplying a signal generated by the means to the antenna as a transmission signal; and an oscillating means for generating an additional signal having a frequency outside a required transmission band of the information signal, wherein the modulation means adds the signal to the information signal. A signal in which the signal is superimposed is modulated as a modulation signal.The additional signal broadens the band of the output signal of the modulation means, and the reciprocal of the period (Ts) of the spreading sequence fs = 1 / (Ts) Are overlapped with each other, and an effect of improving confidentiality is obtained.

According to a fifth aspect of the present invention, in the first or third aspect of the present invention, the modulating means performs frequency modulation, and modulates with an additional signal even when the amplitude of the information signal is small. Since the band of the output signal of the means is widened and the spectrums of the transmission signals arranged at intervals of the reciprocal fs = 1 / (Ts) of the period (Ts) of the spreading sequence overlap each other, the effect of improving the secrecy is obtained.

According to a sixth aspect of the present invention, in the first aspect of the invention, the maximum value of the amplitude of the additional signal is such that the frequency shift when the amplitude of the information signal is zero is equal to that of the direct spread. It is configured to be greater than half the reciprocal of the spread signal period, and even when the amplitude of the information signal becomes zero, the reciprocal of the period (Ts) of the spread sequence by superposition of the additional signal fs = 1 Since the spectra of transmission signals arranged at intervals of / (Ts) overlap with each other, an effect of improving confidentiality is obtained.

According to a seventh aspect of the present invention, in the first or third aspect of the invention, the modulating means performs amplitude modulation, and a frequency component of the information signal has a low frequency range.
Even in the case of bass only, the additional signal widens the band of the output signal of the modulation means, and the reciprocal fs of the period (Ts) of the spreading sequence
Since the spectra of the transmission signals arranged at intervals of 1 / (Ts) overlap each other, an effect of improving the confidentiality is obtained.

[0013] The invention according to claim 8 of the present invention receives a signal spread and transmitted by a direct spreading method,
2. A receiving and demodulating circuit for outputting a modulated signal by despreading and demodulating, and a filter means for removing the additional signal from an information signal and an additional signal included in the modulated signal. When a signal transmitted by the transmitter according to the fifth aspect is received, an additional signal for confidential speech is removed, and an effect that an information signal is reproduced well is obtained.

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

(Embodiment 1) FIG. 1 is a block diagram of a spread spectrum transmitter according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a microphone that outputs an audio signal as an information signal to be transmitted from a sound wave, and 2 denotes an audio amplifier circuit that amplifies the audio signal. Reference numeral 3 denotes an oscillating means for generating an additional signal having a frequency outside the required band of the voice signal.
Since it is z, for example, a 60 Hz rectangular wave signal is supplied from a digital circuit (not shown) for controlling other circuits and the like,
It is composed of a band-pass filter or a low-pass filter for shaping the waveform into a sine wave.

Reference numeral 30 denotes an adder circuit, which superimposes the additional signal on the output of the audio amplifier circuit 2 and outputs it as a modulation signal. 4
Is a modulation means for generating a carrier wave and frequency-modulating the carrier wave with a modulation signal, and has a modulation input terminal 41. The modulating means 4 may be, for example, an oscillation circuit having a phase locked loop as shown in the figure, and the modulation input terminal 41 is connected to a modulation input or a frequency control input of a voltage variable frequency oscillator (VCO) in the phase locked loop.

Reference numeral 5 denotes a spreading sequence generating means for generating a spreading sequence, which generates a pseudo-random binary sequence having a period Ts, such as an M sequence, similarly to a conventional spread spectrum transmitter. Numeral 6 denotes spreading means for multiplying the output of the modulating means 4 with the spreading sequence and spreading the frequency, and comprises a balanced modulator or a multiplier. Reference numeral 7 denotes a transmission circuit which amplifies a transmission signal frequency-spread by the spreading means 6, converts the frequency if necessary, and transmits the signal from an antenna. Note that the oscillation means 3
The amplitude of the additional signal output from the audio signal is such that the amplitude of the audio signal is zero, that is, the frequency shift of the modulating means 4 when there is no sound is ± fs.
/ 2 (= 1 / (2Ts)) or more.

The operation of the spread spectrum transmitter configured as described above will be described below. An audio signal as an information signal obtained by the microphone 1 and the audio amplification circuit 2 is superimposed with an additional signal from the oscillating unit 3 and input to the modulation unit 4 to frequency-modulate the carrier.
The output of the modulating means 4 is frequency-spread by the spreading means 6, amplified by the transmission circuit 7, frequency-converted as necessary, and transmitted from the antenna. At this time, since the 60 Hz sine wave is superimposed on the normal audio signal which is the modulation signal in the modulating means 4, ± fs is always applied regardless of the information signal.
/ 2 or more frequency shift.

Therefore, even if the user speaks to the microphone 1 in a low voice, the spectrum of the output signal of the modulating means 4 has a spread of ± fs / 2 or more, for example, as shown in FIG. Becomes Since the output signal is frequency-spread by the spreading means 6, the spectrum of the transmission signal in the transmission circuit 7 is similar to that of the conventional spread-spectrum transmitter in that the spectrum of FIG.
Line up everywhere. That is, as shown in FIG. 3, the spectrums of FIG. 2 are arranged side by side while overlapping each other.

Such a transmission signal is converted into a normal radio wave format (frequency modulation, F
M), if a receiver is equipped with a band-pass filter with a pass bandwidth of about fs and the reception frequency is tuned to fo ± nfs (n is an integer), The spectra overlap, and the output signal of the modulating means 4 shown in FIG. 2 cannot be reproduced. Specifically, the demodulated audio signal is significantly distorted and becomes unreadable. Therefore, good confidentiality can be secured.

In the present embodiment, an additional signal of 60
Although a sine wave of Hz is used, any signal may be used as long as the signal is generally band-limited outside the required transmission band of the information signal. For example, if the information signal is a telephone voice signal as in the present embodiment, 3 kHz
A distorted waveform such as a rectangular wave having a fundamental frequency of z or more may be used. In this case, since the oscillating means 3 does not need to shape the waveform into a sine wave, no filter is required, and the circuit or the signal processing in the means is simplified. It is also suitable when the required transmission band of the information signal requires a low frequency. The larger the amplitude of the additional signal, the higher the confidentiality. However, since the signal after despreading in the receiver has a wide band, it is desirable to minimize the additional signal. According to the experiments by the inventors, it is desirable to set the range so as not to exceed the maximum amplitude of the information signal (audio signal).

Further, in this embodiment, an example is shown in which an audio signal (analog signal) is transmitted as an information signal. However, the information signal may be band-limited, and may be standardized in, for example, mobile phones in Japan and Europe. Such a digital signal may be a signal whose band is limited by a cosine roll-off filter, a Gaussian filter, or the like.

(Embodiment 2) FIG. 4 is a block diagram of a spread spectrum receiver according to Embodiment 2 of the present invention. In FIG. 4, reference numeral 10 denotes a receiving circuit which amplifies a high-frequency signal received by an antenna, converts the signal into an intermediate frequency signal or a baseband signal, and amplifies the signal to a required level. Are generated in synchronism with the transmitting side, 12 is a despreading means for multiplying the output of the despreading sequence generating means 11 by the output of the receiving circuit 10 and despreading, and 13 is a despreading means. It is a demodulation means for detecting a signal and demodulating a modulated signal, that is, an audio signal as an information signal.

As the despreading means 12, a balanced modulator or a multiplier is used similarly to the spreading means. As the demodulation means 13, a means according to the modulation format in the transmitter is used. For example, in the case of frequency modulation, a frequency discriminator is used. Reference numeral 14 denotes a high-pass filter as filter means for removing a component having a frequency lower than the band of the information signal required for transmission. For example, in the case of telephone voice, a cut-off frequency of about 300 Hz is used. Reference numeral 15 denotes an audio amplifier circuit, and reference numeral 16 denotes a speaker, which amplifies a demodulated audio signal to a required level and converts the signal into a sound wave.

The operation of the spread spectrum receiver configured as described above will be described below. The signal received by the antenna is frequency-converted and amplified by the receiving circuit 10, despread by the despreading unit 12, and then demodulated by the demodulation unit 13, as in the conventional spread spectrum receiver. Demodulation means 13 generally reproduces a modulated signal from the transmitter, and when receiving a signal from the spread spectrum transmitter described in (Embodiment 1),
A demodulated signal in which an additional signal is superimposed on an audio signal as an information signal is reproduced.

Since the additional signal has a lower frequency than the band of the information signal, the demodulated signal is filtered by the high-pass filter 14 to remove the additional signal. Therefore, only an audio signal appears at the output of the high-pass filter 14, and the audio signal is amplified by the audio amplifier circuit 15 to sound the speaker.

In this embodiment, the additional signal is 60
Although the example where the sine wave of Hz is superimposed was explained,
As described in (Embodiment 1), the additional signal may be a signal whose band is limited outside the required transmission band of the information signal. For example, when the additional signal is a rectangular wave of 10 kHz, a low-pass filter having a cutoff frequency of about 3 kHz may be used as a filter instead of the high-pass filter 14. In this case, since the cutoff frequency of the filter means is increased, the size of the capacitor and the like can be reduced when the filter means is constituted by an analog circuit. It is also suitable when the required transmission band of the information signal requires a low frequency.

In this embodiment, an example is shown in which an audio signal (analog signal) is transmitted as an information signal. However, the information signal may be band-limited, and may be standardized in, for example, mobile phones in Japan and Europe. Such a digital signal may be a signal whose band is limited by a cosine roll-off filter, a Gaussian filter, or the like. In this case, instead of the audio amplification circuit 15, a data determination unit for converting a demodulated signal to a digital signal and a circuit for processing digital data are provided.

(Embodiment 3) FIG. 5 is a block diagram of a spread spectrum transmitter according to Embodiment 3 of the present invention. In FIG. 5, reference numeral 1 denotes a microphone, 2 denotes an audio amplification circuit, 5 denotes a spreading sequence generating means, 6 denotes a spreading means, and 30 denotes an addition circuit, which are the same as those described in the first embodiment. Reference numeral 3 denotes an oscillating means for generating an additional signal having only a frequency component equal to or higher than the upper limit frequency of the required band of the audio signal. For example, a rectangular wave signal is supplied from a digital circuit (not shown) for controlling other circuits. And a band-pass filter or a low-pass filter for shaping the waveform as necessary. 8 is a local oscillator for generating a carrier wave.

Numeral 40 designates a modulating means for modulating the amplitude of the carrier wave spread by the spreading means 6 with a modulation signal outputted from the adding circuit 30 and outputting the modulated wave. For example, a multiplying circuit or a balanced modulation circuit is used. A transmission circuit 7 amplifies the signal modulated by the modulating means 40, converts the frequency as necessary, and transmits the signal as a transmission signal from the antenna.

If the frequency of the additional signal output from the oscillating means 3 is denoted by fa, the frequency of the additional signal is set so that fs-fa is within the band of the information signal, for example, 300 Hz to 3 kHz for telephone voice. Select.

The operation of the spread spectrum transmitter configured as described above will be described below. A sound signal as an information signal obtained by the microphone 1 and the sound amplification circuit 2 is superimposed with an additional signal from the oscillating means 3 and input to the modulating means 40 as a modulation signal. On the other hand, the carrier signal output from the local oscillator 8 is spread in frequency by the spreading means 6 to have a spectrum similar to that shown in FIG. The modulating means 40 amplitude-modulates the carrier signal frequency-spread by the modulation signal, and outputs a frequency-spread amplitude-modulated signal. The signal is amplified by the transmission circuit 7, frequency-converted as necessary, and transmitted from the antenna. If the additional signal, that is, the output of the oscillating means 3 is a sine wave, the sine wave of the frequency fa is superimposed on the information signal in the modulated signal of the modulating means 4, so as shown in FIG. It has a line spectrum.

The modulating means 40 amplitude-modulates the spread carrier signal having the spectrum shown in FIG. 13 with the modulated signal, so that the output spectrum is as shown in FIG. Therefore, even when the audio signal as the information signal is only a low tone, the spectrum of the output signal of the modulating means 40 and the spectrum of the transmission signal in the transmission circuit 7 are such that the line spectrum by the additional signal overlaps with the spectrum of the information signal. Become.

Such a transmission signal is converted into a normal radio wave format (amplitude modulation, AM) which is not compatible with the spread spectrum system.
And the receiver has a pass bandwidth of fs
With a band pass filter of about fo ±
Even when tuning to nfs (n is an integer), the spectrum of the additional signal overlaps, and the modulated signal or information signal shown in FIG. 6 cannot be reproduced. Specifically, the demodulated signal has a spectrum as shown in FIG.
(fs-fa) and is superimposed on the demodulated audio signal, making it difficult to read. Therefore, good confidentiality can be secured.

In the above embodiment, an example in which a sine wave is used as an additional signal has been described. However, in general, any signal may be used as long as the signal is band-limited to a higher band than a required transmission band of the information signal. For example, if the information signal is a telephone voice signal as in the present embodiment, a distortion waveform such as a rectangular wave having a fundamental frequency of 3 kHz or more may be used. In this case, since the oscillating means 3 does not need to shape the waveform into a sine wave, no filter is required, and the circuit or the signal processing in the means is simplified. Alternatively, a spectrum having an appropriate spread between the frequencies fa1 and fa2 and fs-fa1 near the upper limit of the required transmission band of the information signal may be used. In this case, the modulated signal has a spectrum as shown in FIG. 9, and the additional signal has a frequency of fs-fa2 to fs-fa2 when received by the ordinary receiver.
Converted between s-fa1. Therefore, the signal is superimposed on a large part of the band of the demodulated audio signal, which makes it even more difficult to read.

In this embodiment, an example in which an audio signal (analog signal) is transmitted as an information signal has been described. However, as in the first embodiment, a digital signal is band-passed by a cosine roll-off filter, a Gaussian filter, or the like. A restricted signal may be used.

In order to receive a transmission signal from the spread spectrum transmitter according to the present embodiment, in the spread spectrum receiver described in (Embodiment 2), the demodulation means 13 performs amplitude detection such as synchronous detection or linear detection. A detection circuit for modulation may be used, and a low-pass filter may be used instead of the high-pass filter 14. In this case, the cutoff frequency of the low-pass filter may be set near the upper limit of the required transmission band of the information signal.

(Embodiment 4) FIG. 10 is a block diagram showing another configuration of a spread spectrum transmitter according to Embodiment 4 of the present invention. In FIG. 10, 1 is a microphone, 2 is an audio amplifying circuit, 3 is an oscillating means, 5 is a spreading sequence generating means, 6 is a spreading means, 8 is a local oscillator, 30 is an adding circuit, 40 is a modulating means, and 7 is a transmitting circuit. These are the same as those described in (Embodiment 3). As is clear from the figure, the present embodiment is different from the configuration of the third embodiment only in that the order of the spreading means 6 and the modulating means 40 is reversed. The processing in the spreading means 6 and the modulating means 40 is a signal processing by multiplication as described in the above embodiment, so that even if the order is changed (Embodiment 3).
It operates in exactly the same way and has the same confidential effect.

[0039]

As described above, according to the present invention, the transmitter transmits an additional signal having a spectrum outside the required transmission band of the information signal to be transmitted by superimposing the additional signal on the information signal. The spectrum spreads, and the spectrum after the frequency spread is in a state where the spectrum before the spread is overlapped. Therefore, when a third party intercepts with a normal receiver that does not support the spread spectrum method having a narrow-band filter, the waveform of the demodulated signal is distorted, making it difficult to read, and the confidentiality is improved. In addition, in the receiver according to the present invention, the information signal is satisfactorily received by providing the filter means for removing the additional signal after demodulation. As described above, in the transmitter, an excellent spread-spectrum transmitter having the effect of increasing the confidentiality only by adding an extremely simple circuit, that is, adding a filter in the receiver, and adding a filter such as a sine wave to the receiver, and A spread spectrum receiver can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a spread spectrum transmitter according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing an example of a spectrum of an output of a modulating means of the spread spectrum transmitter according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of a spectrum of a transmission signal of a spread spectrum transmitter according to Embodiment 1 of the present invention.

FIG. 4 is a block diagram of a spread spectrum receiver according to Embodiment 2 of the present invention.

FIG. 5 is a block diagram of a spread spectrum transmitter according to Embodiment 3 of the present invention.

FIG. 6 is a diagram illustrating an example of a spectrum of a modulated signal of a spread spectrum transmitter according to Embodiment 3 of the present invention.

FIG. 7 is a diagram showing an example of a spectrum of a transmission signal of a spread spectrum transmitter according to Embodiment 3 of the present invention.

FIG. 8 is a diagram illustrating an example of a spectrum of a demodulated signal received by a normal receiver as a transmission signal of a spread spectrum transmitter according to Embodiment 3 of the present invention.

FIG. 9 is a diagram showing an example of a spectrum of a modulated signal of the spread spectrum transmitter according to the first or third embodiment of the present invention.

FIG. 10 is a block diagram showing another configuration of a spread spectrum transmitter according to Embodiment 4 of the present invention.

FIG. 11 is a block diagram of a conventional spread spectrum transmitter.

FIG. 12 is a block diagram of a conventional spread spectrum receiver.

FIG. 13 is a diagram showing an example of a spectrum of a transmission signal of a conventional spread spectrum transmitter when no modulation is performed.

FIG. 14 is a diagram showing an example of a spectrum of an output signal of a modulating means of a conventional spread spectrum transmitter.

FIG. 15 is a diagram showing an example of a spectrum of a transmission signal of a conventional spread spectrum transmitter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microphone 2 Audio amplification circuit 3 Oscillation means 4 Modulation means 5 Spreading sequence generation means 6 Spreading means 7 Transmission circuit 8 Local oscillator 10 Receiving circuit 11 Despreading sequence generation means 12 Despreading means 13 Demodulation means 14 High-pass filter 15 Audio amplification circuit 30 Adder circuit 40 Modulation means

Claims (8)

[Claims] 1. A modulating means for modulating a carrier wave by an information signal, a spreading means for frequency-spread modulating a signal generated by the modulating means by a direct spreading method, and an output of the frequency spreading means is supplied to an antenna as a transmission signal. And a oscillating means for generating an additional signal having a frequency outside the required transmission band of the information signal, wherein the modulation means modulates a signal obtained by superimposing the additional signal on the information signal as a modulation signal. Spreading transmitter. 2. The spread spectrum transmitter according to claim 1, wherein said oscillating means generates an additional signal having a frequency lower than a required transmission band of the information signal. 3. A spreading means for generating a signal which is frequency-spread modulated by a direct spreading method, a modulation means for modulating an output signal of the spreading means with an information signal, and a signal generated by the modulation means as a transmission signal. A transmitting circuit for supplying to the antenna, and oscillating means for generating an additional signal having a frequency outside the required transmission band of the information signal, wherein the modulation means superimposes the additional signal on the information signal as a modulation signal. A spread spectrum transmitter that modulates. 4. The spread spectrum transmitter according to claim 3, wherein said oscillating means generates an additional signal having a frequency lower than a required transmission band of the information signal. 5. The spread spectrum transmitter according to claim 1, wherein said modulating means performs frequency modulation. 6. The maximum value of the amplitude of the additional signal is such that the frequency shift when the amplitude of the information signal is zero is greater than half the reciprocal of the spread signal period in direct spreading. 5. The spread spectrum transmitter according to 5. 7. The spread spectrum transmitter according to claim 1, wherein said modulation means performs amplitude modulation. 8. A receiving and demodulating circuit for receiving a signal spread and transmitted by a direct spreading method, despreading and demodulating the signal, and outputting a modulated signal; A spread spectrum receiver comprising: a filter for removing a signal.