JPH02272928A - Multi-channel type spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To simplify circuit configuration by using a matched filter for inversely spreading a signal being applied with spread spectrum modulation, switching the carrier frequency being FSK(frequency shift keying)-modulated to form a multi-channel. CONSTITUTION:In a transmitter side, (PPM) pulse position or pulse phase modulation(PPM) is executed to an input signal in a V-F(voltage-frequency) converter 7 and on the other hand, in an FSK modulation part, the modulation is executed by a carrier corresponding to the set of channel changeover switches 11 and 17. The spectrum diffusion modulation is executed to the signal, for which the FSK modulation is executed in such a way, and the signal is transmitted. On the other hand, in a receiver a matched filter 53 is used and, the signal being applied with spread spectrum modulation is inversely spreaded on the transmitter side. Thus, a multi-channel type spread spectrum communication equipment having the simple circuit configuration can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-channel spread spectrum communication device, and in particular uses a so-called matched filter to despread a spread spectrum modulated signal to simplify the circuit configuration. The present invention relates to a communication device that enables multi-channel communication through frequency division.

[Prior Art] Conventionally, in spread spectrum (SS) communication devices, in order to multiplex or make communication channels multi-channel, PN (pseudo-noise) that has no or very little correlation with each other is used for each channel. A so-called code division multiplex communication system is used in which transmission and reception are performed using codes. In such a multi-channel SS communication device, the transmitter side is provided with means for generating a PN code corresponding to each channel, and the receiver side is provided with a so-called image code corresponding to the PN code used for each transmission channel. and a means such as a 5AW (surface acoustic wave) convolver for despreading the spread spectrum modulated signal using each image PN code.

[Problems to be Solved by the Invention] However, in such a conventional multi-channel SS communication device, a means for generating mutually uncorrelated PN codes corresponding to each channel is required on the transmitter side, and In particular, it is necessary to provide a means for generating an image PN code corresponding to each channel, a SAW convolver, and a complicated circuit on the receiver side, which has the disadvantage of increasing the size of the transceiver and increasing the cost. Furthermore, as a result of the circuit becoming more complex, reliability is lowered and advanced circuit technology is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multichannel SS communication device having a simple circuit configuration in view of the problems with the conventional devices described above.

Another object of the present invention is to reduce the size, cost, and reliability of SS communication devices.

Still another object of the present invention is to provide SS with a simple circuit configuration.
The objective is to further enhance the privacy of communication devices.

[Means for Solving the Problems] In order to achieve the above-mentioned object, a multi-channel spread spectrum communication device according to the present invention includes a PPM modulating means for pulse position modulating an input signal, and a PPM modulating means for modulating the PPM using a hair adjustment stage. FSK modulation means for frequency shift modulating the signal modulated by the FSK modulation means, channel switching means for switching the carrier frequency of modulation by the FSK modulation means, and SS modulation means for spread spectrum modulation of the signal modulated by the FSK modulation means. includes a transmitter having a In addition, a receiver used in combination with such a transmitter includes a frequency converting means into which a received signal is input, and a local oscillator signal of a frequency switched corresponding to each transmission channel is supplied to this frequency converting means. a despreading means for performing correlation detection on the signal frequency-converted by the frequency conversion means using a matched filter;
The apparatus includes FSK demodulation means for demodulating, and PPM demodulation means for PPM demodulating the output of the FSK demodulation means.

[Operation] In a multi-channel spread spectrum communication device having the above-described configuration, an input signal is first PPM-modulated and then FSK-modulated on the transmitter side. When performing this FSK modulation, modulation is performed using a carrier wave corresponding to the channel set by the channel switching means. The FSK modulated signal is then spread spectrum modulated and transmitted.

On the other hand, the receiver receives the signal transmitted from the transmitter and converts the frequency of the signal to obtain a predetermined intermediate frequency signal. In this case, as the local signal supplied to the frequency converting means, a signal with a frequency switched in accordance with the transmission channel of the transmitter is used. As a result, a signal having, for example, a constant frequency can be obtained as an intermediate frequency signal regardless of the channel. Therefore, such an intermediate frequency signal can be despread using a matched filter,
The despread signal is sequentially subjected to FSK demodulation and PPM demodulation to obtain a received signal.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIGS. 1(a) and 1(b) show configuration examples of a transmitter and a receiver, respectively, of a multichannel spread spectrum communication device according to an embodiment of the present invention.

The transmitter shown in FIG. 1(a) includes a microphone 1 for transmission, a microphone amplifier 3, a low-pass filter 5, and a V-F
(voltage-frequency) PPM modulation section having a converter 7, a crystal oscillator 9 corresponding to each channel, a channel changeover switch 11, an oscillation circuit 13, another crystal oscillator 15 corresponding to each channel, a channel changeover switch 17, An oscillation circuit 19, an FSK modulation section having a high frequency electronic switch 21, a multiplier 23, and a double balanced modulator (DBM) 25
and an SS modulation section having a PN code generator 27, a low-pass filter 29, and a transmitting antenna 31. Note that the crystal oscillator 9 and channel selection switch 11 in the FSK modulation section. The other crystal oscillator 15, channel changeover switch 17, etc. can also be realized by a so-called synthesizer circuit. Further, when the transmission signal is a signal other than an audio signal, for example, a data signal or the like, appropriate input circuits are used in place of the microphone 1 and the microphone amplifier 3, respectively. In addition, the channel changeover switch 11
and 17 are normally used that operate in conjunction with each other.

In addition, as shown in FIG. 1(b), the receiver includes a receiving section including a receiving antenna 33, a bandpass filter 35, and a receiving amplifier 37, a mixer 39 composed of a double-balanced modulator, etc., and a mixer 39 for each channel. A frequency converter having a corresponding crystal oscillator 41, a channel changeover switch 43, an oscillation/multiplier 45, and a bandpass filter 47, and an amplifier 4.
9, bandpass filter 51, matched filter 53, amplifier 55. A demodulation section including a demodulator 57, an AGC amplifier 59, an amplifier 61, a converter rotor 3, and an F-V (frequency-
The PPM demodulator includes a voltage) converter 65 and a low-pass filter 67, a power amplifier 69, and a speaker 71. The crystal oscillator 41, channel changeover switch 43, etc. can also be realized by a synthesizer circuit as in the case of a transmitter. The matched filter 55 is realized by, for example, a surface acoustic wave (SAW) element, has a simple structure, has its own unique code sequence, and is capable of despreading a signal SS-modulated by a specific PN code. It is possible. Therefore, when using a matched filter, there is no need to connect an external PN code generator like a SAW convolver. The demodulator 57 includes, for example, a diode and a capacitor, and performs envelope detection of the signal despread by the matched filter.

Next, the operation of the multi-channel spread spectrum communication device having the above configuration will be explained.

First, in the transmitter of FIG. 1(a), microphone 1
The audio signal input from the microphone amplifier 3 is amplified by the microphone amplifier 3, limited to a predetermined frequency band by the low-pass filter 5, and then PPM (pulse position or pulse phase) modulated by the V-F converter 7. On the other hand, in the FSK modulation section, predetermined ones of the corresponding crystal oscillators 9 and 15 are connected to the oscillation circuits 13 and 19 depending on the settings of the channel changeover switches 11 and 17, respectively. Furthermore, the high frequency switch 21 is turned on and off by the output of the V-F converter 7, and FSK (frequency shift keying) modulation is performed. For example, V-F converter 7
When the digital output of is high level, high frequency switch 2
1 is connected to the oscillation circuit 13 side, and conversely, when the level is low, it is connected to the oscillation circuit 19 side. As a result, depending on the output of the V-F converter 7, for example, 5°7 Mllz and 5°
．． 72M1lz signals are sequentially output as FSK modulated signals.

Such an FSK modulated signal is then applied to a multiplier 23, where the frequency is multiplied by a factor of 50, for example, and then applied to one input of a double-balanced modulator 25. Double balanced modulator 25
A predetermined PN from the PN code generator 27 is input to the other input of
A code signal is applied. As a result, the output signal of the multiplier 23 is spread spectrum (SS) modulated, and after unnecessary band components are removed by the low-pass filter 29, it is transmitted from the transmitting antenna 31. In this case, the carrier frequency of the transmission signal is 285 MHz and 286 MHz, for example.
MHz.

Next, in the receiver shown in FIG. 1(b), the thus transmitted signal is received by the receiving antenna 33, selectively amplified via the bandpass filter 35 and the receiving amplifier 37, and then sent to the mixer 39. Input to one terminal.

In addition, the channel changeover switch 43 allows the crystal oscillator 41
A predetermined one of them is connected to an oscillator and multiplier 45, whereby a local oscillator signal corresponding to the transmission channel is generated and applied to the other input of mixer 39. For example, if the frequency of the local oscillation signal is 141 MHz, the frequency is 285 Mll.
z and 288 Mt (received signal of z is 144
MHz and 145 MHz intermediate frequency signals. Such an intermediate frequency signal is passed through a bandpass filter 4.
7, intermediate frequency amplifier 49, and other bandpass filters 51
After amplification and removal of unnecessary band components, the signal is input to a matched filter 53. The matched filter 53 has a center frequency f, for example. -144 MHz, and is configured to despread a signal subjected to spread spectrum modulation by the PN code generator 27 on the transmitter side. In this case, the matched filter 53 also has the function of a bandpass filter, so that the 145 MHz signal among the intermediate frequency signals is not passed through or is greatly attenuated. This allows the matched filter 53 to also perform FSK demodulation. In this way, the signal that has been subjected to correlation detection and FSK demodulation by the matched filter 53 is amplified by the amplifier 55 and then subjected to envelope detection in the demodulator 57. The output of the demodulator 57 is amplified by an amplifier 61 and then compared with a predetermined threshold value by a comparator 63 to generate a waveform-shaped signal. After this waveform-shaped signal is PPM demodulated in the F-V converter 65,
The original audio signal is extracted via a low-pass filter 67. This audio signal is output as audio by the power amplifier 69 and the speaker. Note that the output of the demodulator 57 is amplified to a predetermined level in an AGC amplifier 59 and controls a variable attenuator (not shown) inserted after the receiving amplifier 37 and after the bandpass filter 47, for example. As a result, an AGC operation is performed to keep the level of the received signal constant.

Note that in the above explanation, a communication device that transmits and receives one transmission signal via multiple channels has been described;
It is clear that the present invention can also be applied, for example, to cases where a plurality of transmission signals are frequency-divided and multiplexed transmission and reception are performed.

[Effects of the Invention] As described above, according to the present invention, a matched filter is used for despreading a signal subjected to spread spectrum modulation, and multi-channeling is achieved by switching the carrier wave frequency of FSK modulation. The circuit configuration is simplified compared to a device that switches the PN code for each channel using, for example, a transmitter/receiver that is smaller in size, lower in price, and higher in reliability. This means that A/D
It is also aided by the use of V-F converters and F/V converters instead of converters and D/A converters and the like. Furthermore, the present invention has the advantage of extremely high confidentiality because the input signal is transmitted after being modulated in three stages, for example, PPM modulation, FSK modulation, and spread spectrum modulation.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are block circuit diagrams respectively showing configuration examples of a transmitter and a receiver used in a multi-channel spread spectrum communication device according to an embodiment of the present invention. 1; Microphone, 3; Microphone amplifier, 5, 29
．． 67; Low-pass filter, 7. V-F converter, 9, 15.41; Crystal resonator, 11.17, 43; Channel selection switch, 13.19
oscillation circuit, 21; high frequency switch, 23; multiplier, 25; double balanced modulator, 27, PN Coco generator, 31; transmitting antenna, 33; receiving antenna, 3
5, 47.51, bandpass filter, 37; receiving amplifier,
39; Mixer, 45; Oscillator and multiplier, 49.55.81; Amplifier, 53; Matched filter, 57; Demodulator, 59, A
GC amplifier, 63; Comparator, 85, F-V converter, 69; Power amplifier, 71, Speaker. Patent applicant Mitsui Metal Mining Co., Ltd.

Claims (1)

[Claims] PPM modulation means for pulse position modulating an input signal;
FSK modulation means for frequency shift modulating the signal modulated by the PM modulation means; channel switching means for switching the carrier frequency of modulation by the FSK modulation means;
a transmitter having SS modulation means for spread spectrum modulating a signal modulated by the SK modulation means; a frequency conversion means to which a signal received from the transmitter is input; a local oscillation means capable of supplying a local oscillation signal with a frequency switched in accordance with the carrier frequency; a despreading means for correlation detection of the signal frequency-converted by the frequency conversion means using a matched filter; 1. A multichannel spread spectrum communication device comprising: a receiver having FSK demodulation means for FSK demodulating a signal obtained by FSK demodulation; and PPM demodulation means for PPM demodulating the output of the FSK demodulation means.