JP2715125B2 - Spread spectrum communication equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication apparatus, and more particularly to a communication apparatus that performs modulation by switching a plurality of PN (pseudo noise) codes according to the state value of a transmission signal. About.

[Prior Art] Conventionally, as a spread spectrum communication system, for example, DS-FSK (Direct Sequence-Frequency Shift Keyin) has been used.
g) The method using the method is known (IEICE, Spread Spectrum Communication Research Group, April 1-2, 1988)
(See “Asynchronous SSC Transceiver Using SAW Convolver” in Tsubouchi). In such a communication system, input data is input to a voltage controlled oscillator (VCO), so-called FSK modulation for changing a frequency according to a state value of the input data is performed, and this FSK-modulated signal is converted into a single signal. A transmission signal is obtained by performing spread modulation using a PN code. Such a system has an advantage that a relatively long distance communication can be performed even by using a weak radio wave having an extremely low electric field strength.

[Problems to be Solved by the Invention] However, in the above-described conventional communication system,
Since a VCO or the like is used for FSK modulation, there is a disadvantage that the frequency of the transmission signal is adversely affected by a change in the surrounding environment or noise and becomes unstable. Further, since at least two types of transmission carrier frequencies are required, there is a problem in effective use of the frequency band.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spread spectrum communication apparatus which has excellent transmission frequency stability and enables effective use of a frequency band in view of the above-described problems in the conventional communication system.

[Means for Solving the Problems] In order to achieve the above object, a spread spectrum communication apparatus according to the present invention includes a PN code generating means for generating a plurality of types of PN codes having little inter-code interference as a transmitter; Selecting means for selecting and outputting one of the plurality of types of PN codes in accordance with each state value of the input data; and transmitting a transmission signal generated by modulating a carrier having a constant frequency based on the output of the selecting means. And a transmission means for performing the transmission. As a receiver, receiving means for receiving the transmission signal, and a SAW convolver, configured to use a SAW convolver to determine the correlation between the output signal of the receiving means and a PN code excluding at least one of the plurality of types of PN codes. The one having the correlation detecting means to be obtained is used.

[Operation] In the apparatus having the above-described configuration, a PN code with little intersymbol interference with each other corresponding to each state value of input data, for example, data “1” or “0”, is selected on the transmitter side. Is selected and output. Then, the transmission signal generated based on the output of the selection means is transmitted from the transmission means having, for example, a transmission amplifier. On the receiver side,
The transmission signal transmitted in this manner is received, and the frequency band of the reception signal is despread by a correlator such as a convolver using surface acoustic waves (SAW) to demodulate data. In this case, as the despreading PN code input to the correlator, an image PN code for any one of the plurality of types of PN codes can be used.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a transmitter in a spread spectrum communication apparatus according to one embodiment of the present invention. The transmitter in FIG.
Oscillator 1 generating a 250 MHz signal, balanced modulator 3, first
A PN code generator 5 for generating a PN code of the type (PN code A), a PN code generator 7 for generating a PN code of the second type (PN code B), and a data input circuit 9 are schematically shown. It has changeover switches 11 and 13 such as data selectors / multiplexers, low-pass filters 15 and 19, a transmission amplifier 17, and a transmission antenna 21. The data input circuit 9
For example, it is constituted by a microprocessor for providing binary digital data. The changeover switches 11 and 13 are actually set to PN according to the state value of the transmission data from the data input circuit 9.
It is composed of an electronic circuit for selectively outputting either the code A or the PN code B.

FIG. 2 shows a schematic of a receiver used with the transmitter of FIG. The receiver shown in the figure is composed of an oscillator 23 for generating a signal of, for example, 250 MHz, and a PN code A 'having an image relationship with the PN code A generated from the PN code generator 5 in FIG.
A PN code generator 25, a balanced modulator 27, a low-pass filter 29, and a correlator 31 such as a SAW convolver to which an output of the low-pass filter 29 is applied to one input. ing. The receiver of FIG.
, A bandpass filter 35, a receiving amplifier 37, and a logarithmic amplifier 39
And a low-pass filter 41. The output of the receiving circuit constituted by these components is connected to the other input of the correlator 31. Further, the output of the correlator 31 includes, for example, an amplifier 43 for amplifying a signal having a frequency of 500 MHz, a high-pass filter 45, a detection circuit 47, an amplifier 49, and a comparator for comparing the output of the amplifier 49 with a predetermined signal. 51 and the data output circuit 53 are connected.

The operation of the spread spectrum communication apparatus having the above configuration will be described with reference to FIG. In the transmitter shown in FIG. 1, it is assumed that the data input circuit 9 outputs a data input signal as shown in FIG. 3 (a), for example. This data input signal is digital data "1"
Corresponds to a high level, for example, and data “0” corresponds to a low level. Then, the changeover switches 11 and 13 are switched according to the data value of such a data input signal. When the data input signal is at a high level, that is, when the data is "1", the switches 11 and 13 are connected to the side of the PN code generator 5, from which the first type PN code A is output. The output is input to the balanced modulator 3. On the other hand, when the data input signal is low level, that is, when the data is "0", the switches 11 and 13 are connected to the PN code generator 7 side and the second type PN code B is connected to the balanced modulator. 3 is input. Preferably, the PN code generators 5 and 7 can generate PN codes with little intersymbol interference, for example. In this way, different types of PN codes are input to one input of the balanced modulator 3 according to the state value of the data input as shown in FIG. 3 (d).

A signal of 250 MHz is input from the oscillator 1 to the other input of the balanced modulator 3, and this signal is mixed with the output of the composite PN code to generate a transmission signal. This transmission signal is transmitted from the antenna 21 after being amplified through the low-pass filter 15, the transmission power amplifier 17, and the low-pass filter 19 at the final stage, and after unnecessary band components are removed.

The transmission radio wave transmitted from the transmitter in this way is
The signal is received by an antenna 33 of the receiver shown in the figure, is selectively amplified through a bandpass filter 35, an amplifier 37, a logarithmic amplifier 39, and a low-pass filter 41, and is then applied to one input of a correlator 31. Further, it has an image relationship with the PN code A output from the PN code generator 5 on the transmitter side.
A PN code A 'is generated from a PN code generator 25 and applied to one input of a balanced modulator 27. A signal of 250 MHz is applied from the oscillator 23 to the other input of the balanced modulator 27, whereby a PN code frequency-converted to a center frequency of 250 MHz is applied to the other input of the correlator 31 via the low-pass filter 29. Is done. Thus, the correlator 31, for example a SAW convolver,
A signal as shown in FIG.
That is, the output of the correlator 31 is data “1”, that is, PN
A convolution waveform is output to a portion corresponding to code A. Such a signal is supplied to an amplifier 43 and a high-pass filter 45.
(F) of FIG. 3 by detecting with the detector 47 through
The detection output shown in FIG. This detection output is compared with a predetermined threshold value in a comparator 51, and further a data output circuit
By performing amplification, pulse width extension, waveform shaping, and the like in 53, a data output as shown in FIG. 3 (g) is obtained.

In the configuration described above, two PN code generators 5 and 7 are provided in the transmitter and are switched and output by switching means 11 and 13 such as a data selector / multiplexer. As a means for obtaining a different PN code according to the state value of the data input, a Gold code generator can be used.

[Effect of the Invention] As described above, according to the present invention, for example, a weak radio can be realized without using a circuit whose frequency such as a VCO is easily affected by changes in the surrounding environment, noise, and the like, and with a very simple configuration. A spread spectrum communication device suitable for the device can be realized. Further, since the carrier frequency is a single frequency, the frequency band can be effectively used.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram schematically showing a transmitter in a spread spectrum communication apparatus according to one embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a receiver used in combination with the transmitter of FIG. FIG. 3 is a circuit diagram, and FIG. 3 is a waveform diagram for explaining the operation of the device shown in FIG. 1 and FIG. 1; Oscillator, 3; Balanced modulator, 5, 7; PN code generator, 9; Data input circuit, 11, 13; Switching circuit, 15, 19; Low-pass filter, 1
7; transmit amplifier, 21; transmit antenna, 23; oscillator, 25; PN code generator, 27; balanced modulator, 29, 41; low-pass filter, 31;
Correlator, 33; receive antenna, 35; bandpass filter, 37, 43, 4
9; amplifier, 39; logarithmic amplifier, 45; high-pass filter, 47; detector, 51; comparator, 53; data output circuit.

Claims (1)

(57) [Claims] 1. A carrier generating means for generating a carrier having a constant frequency, a PN code generating means for generating a plurality of types of PN codes having little intersymbol interference, and the plurality of types corresponding to each state value of input data. Selecting means for selecting and outputting one of the PN codes, generating a transmission signal by modulating the carrier with the output of the selection means, transmitting means for transmitting the generated transmission signal, Receiving means for receiving, and a correlation detecting means for obtaining a correlation with respect to an output signal of the receiving means using a SAW convolver to a PN code excluding at least one of the plurality of types of PN codes. Spread spectrum communication equipment.