JPH04104534A - Radio communication equipment - Google Patents

Abstract

PURPOSE:To obtain a high secrecy with a simple circuit by performing spectrum spread communication after setting a communication line by a prescribed frequency. CONSTITUTION:First, a transmitter performs transmission with a prescribed frequency for a certain short time, and a first local oscillator 37 which is oscillated with a prescribed frequency of a receiver is locked to the received prescribed frequency to set a communication line, and next, the transmitter sets the carrier frequency to an arbitrary frequency lower than a transmission signal and transmits the transmission signal while changing the carrier frequency with the width which is several tens or larger times as wide as the required band width of the transmission signal, and a second oscillator 32 which can be oscillated with the change width of the transmission-side carrier frequency in the receiver follows up the change of the received carrier frequency to change the oscillation frequency, and thereby, the receiver demodulates the transmission signal while receiving the changing transmission frequency. This switching is performed by switch circuits 8, 33, and 36. Thus, radio communication of high secrecy is performed with the simple equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wireless communication device, and more particularly to a wireless communication device for obtaining communication confidentiality.

[Prior Art] Conventionally, wireless communications to obtain communication secrecy have involved dividing the transmission signal into several frequency bands and rearranging the order of the transmission signals, and spreading spectrum communication, which has been used to divide the transmission signal into several frequency bands and rearrange the order of the transmission signals. There are some systems that spread the information over a much wider band than the minimum required for transmitting the information being sent. However, in the former case, a high degree of secrecy cannot be obtained because the number of frequency divisions cannot be made large, and in the latter case, secrecy can be obtained, but the circuit is complicated and the price is high. This results in an increase in the size of the device.

[Problem to be solved by the invention] As described above, in the conventional wireless communication device as described above, if a high degree of confidentiality is to be achieved, the circuit becomes complicated, the price increases, and the device becomes large. There was a problem.

The present invention was made to solve this problem, and an object of the present invention is to obtain a wireless communication device that can perform highly confidential wireless communication with a simple device.

[Means for Solving the Problems] In the wireless communication device according to the present invention, after setting a communication channel using a predetermined frequency, the transmitter sets the carrier frequency to an arbitrary frequency lower than the transmission signal and within the necessary band of the transmission signal. The transmit frequency is changed by a width several ten times or more, and the receiver receives the transmitted frequency by changing its oscillation frequency following the change in the local oscillator or carrier frequency, and the receiver oscillates at a predetermined frequency. It is equipped with a first local oscillator and a second local oscillator that can oscillate within a variation range of the transmission side carrier frequency. It is designed to receive the transmission frequency.

[Operation] In the wireless communication device of the present invention, first, the transmitter transmits at a predetermined frequency for a short fixed period of time, and in the receiver, for example, a first local oscillator that oscillates at a predetermined frequency emits the received predetermined frequency. The transmitter then transmits the transmission signal while changing its carrier frequency to an arbitrary frequency lower than the transmission signal and with a width of several ten times or more than the required bandwidth of the transmission signal. In the receiver, for example, a second local oscillator that can oscillate depending on the change width of the transmitting side carrier frequency changes its oscillation frequency to follow the change in the received carrier frequency, thereby receiving the changing transmission frequency. It demodulates the transmitted signal while

[Examples] Examples of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram of a transmitter showing one embodiment of the present invention, and FIG. 2 is a block diagram of a receiver as well. In the transmitter shown in Fig. 1, (1) is a reference frequency oscillator, (2)
(3> is a frequency divider, (4) is a phase comparator, and (5) is a low-pass filter (LPF), and the above (1) to (5) are
) forms a PLL circuit together with v c O (11), which will be described later. (6) is a function generator that changes the control voltage over time, (7) is a transmission control circuit, (8) is a switch circuit, (9) is a microphone, (10) is a low frequency amplifier circuit, (
11) is a voltage controlled oscillator (VCO), 112) is a buffer amplifier circuit, (13) is a power amplifier circuit, (14) is a low pass filter (LPF), and (15) is a transmitting antenna.

In addition, in the receiver shown in Fig. 2, (21) is the receiving antenna;
(22) is a high frequency amplifier circuit, (23) is a mixing circuit, (2
4) is a bandpass filter (BPF), (25) is an intermediate frequency amplification circuit, (26) is a demodulation circuit, (27) is a low frequency amplification circuit, (28) is a speaker, (29), (35>, (
39) is a frequency divider, (30) and (40) are phase comparator circuits, and (31) and (38) are low-pass filters (L P F
), (32), (37) are voltage controlled oscillators (VC
O), (33), (36) are switch circuits, (34)
) is a reception control circuit.

Here, the VCO (37) is a crystal-controlled VCO that oscillates at a frequency close to a predetermined frequency (for example, 300MHz), and the width of change in the oscillation frequency is controlled by the bandpass filter (24).
(in this example, the bandwidth of the FM-modulated audio signal).

On the other hand, the lock range of the PLL circuit formed by the VCO (32) is wider than the variation range of the transmission frequency of the other transmitter.
In addition, the loop gain is less than 1 for the frequency of the transmission signal (in this example, the audio frequency), but the loop gain is large enough for the frequency at which the transmission frequency changes repeatedly (for example, several tens of Hz). have. V CO (37
) is assumed to be the first VC○, and v c O(32) is assumed to be the second VC○.
It is called VCO.

Next, the operation will be explained. In the transmitter shown in Fig. 1,
Before setting the communication path, the transmission control circuit (7) connects the contacts (a) and (c) of the switch circuit 8), which causes the VCO (11) to adjust the reference frequency and the frequency divider (2). ),
(3) A predetermined frequency determined by the frequency division ratio (for example, 30
0MHz), and this becomes the transmission frequency and is applied to the transmission antenna (15) only for a short fixed period of time.

On the other hand, in the receiver shown in FIG. 2, before the communication path is set, the reception control circuit (34) is connected to the contact (a) of the switch circuit (33).
) and (c) and contacts (a) and (c) of the switch circuit (36>) are connected, and in this state, the receiving antenna (21
) When a signal of the above-mentioned predetermined frequency (for example, 300 MHz) is input, the input is transmitted to the high frequency amplifier circuit (22), the mixing circuit (23), the BPF (25), the intermediate frequency amplifier circuit (25), and the frequency divider. (29), and is further input to the phase comparison circuit (40), where it is compared with the phase of the output of the frequency divider (39), and the PL formed by V CO (37) is
The L circuit is locked to the above-mentioned predetermined frequency after a certain period of time.

The output of the frequency divider (29) is also input to the phase comparator circuit (30), where it is compared with the phase of the output of the frequency divider (35), and the PLL circuit formed by the V CO (32) is is also locked to the above-mentioned predetermined frequency after a certain period of time.

Therefore, in this state, that is, the state in which the communication path is set, the VCO (37) and the VCO (32) are in phase. Thereafter, the oscillation frequency of ■C○ (37) is fixed.

In this way, by using the same method as conventional FM radios to supplement the transmission frequency of the other party in this embodiment, there is no need to supplement the transmission frequency of the other party using a special method, and a special circuit for that purpose is not required. There is. Therefore, if an audio signal is placed on the microphone 9) in this state, the transmission/reception and modulation/demodulation operations of the FM modulation frequency will be the same as in the conventional FM radio.

In this example, after a short fixed period of time has elapsed,
That is, when the communication path is set, in the transmitter, the transmission control circuit <7) energizes the function generator (6) and connects contacts (b) and (c) of the switch circuit (8). , so that V CO (11) is now a function generator (
6) Carrier frequency (transmission frequency) according to the DC control voltage
change.

Figure 3 is a diagram showing an example of how the transmission frequency changes over time. As shown in the figure, the transmission frequency changes over time according to a regulation or randomly, and the width of this change is the transmission signal (in this example, The frequency is ten times or more the minimum bandwidth required by the audio signal (audio signal), and the repetition frequency of this change is sufficiently lower than the frequency of the transmission signal (including a composite wave of two or more waves).

On the other hand, when the receiver of FIG. 2 receives the predetermined frequency and a certain period of time has elapsed, that is, when the communication channel is set, the reception control circuit (34) controls the contacts (b) and (c) of the switch circuit (33). ) and contacts (b) and (c) of the switch circuit (36)
), thereby switching the input to the mixing circuit (23) to the output of the VCO (32), and connecting the frequency divider (3) to the output of the VCO (32).
The input to 5) is switched to the output of the VCO (37). As a result, the phase comparator circuit (30) detects the deviation between the predetermined frequency output by the VCO (37) and the transmission frequency of the other party that is subsequently received.
The loop gain of the PLL circuit formed by Because you have a profit
The oscillation frequency of the V CO (32) will change to follow the change in the transmission frequency of the other party, and as a result, the mixing circuit (
In the output of 23), the frequency change is always only the amount modulated by the transmission signal, and thereafter the audio signal can be demodulated in the same manner as in a normal FM receiver.

In this way, according to the wireless communication device of this embodiment, the first
Since it can be configured with a simple circuit as shown in FIGS. 2 and 2, it is possible to provide a small and inexpensive device.

Regarding the confidentiality of communication, the band during signal transmission is spread to, for example, about 1000 times the minimum band required to transmit this signal, so the S/N deteriorates by about 60 dB. Therefore, the signal cannot be discriminated. In other words, high confidentiality can be obtained.

Furthermore, if an attempt is made to intercept using a device with the same performance, the communication channel is set up instantaneously as described above, so it is actually very difficult to capture the frequency. In addition, the frequency during signal transmission is, for example, about 1000 times the minimum required band of the signal, and the repetition frequency is several tens of times.
Since the signal changes in Hz, the signal passes through the interception receiver, which has a narrow reception band, in a few tens of microseconds, for example.

Therefore, since it is not possible to identify and capture the other party's radio waves within this time, a high degree of confidentiality can be obtained.

[Effects of the Invention] As explained above, the present invention performs spread spectrum communication after setting a communication path using a predetermined frequency, so it is possible to provide a small and inexpensive wireless communication device that can provide a high degree of confidentiality with a simple circuit. There is an effect.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a transmitter showing an embodiment of the present invention, Fig. 2 is a block diagram of a receiver showing an embodiment of the invention, and Fig. 3 shows an example of changes in transmission frequency over time. It is a diagram. In the figure, (1) is the reference frequency oscillator, (2), (
3) is a frequency divider, (4) is a phase comparison circuit, (5) is a low-pass filter (LPF), (6) is a function generator, (7) is a transmission control circuit, and (8) is a switch. circuit, (9) is a microphone,
(10) is a low frequency amplifier circuit, (11) is a voltage controlled oscillator <VCO'), (12) is a buffer amplifier circuit, (13) is a power amplifier circuit, (14) is a low pass filter (LPF) ,
(15) is the transmitting antenna, (21> is the receiving antenna, (22)
) is a high frequency amplifier circuit, (23) is a mixing circuit, (24) is a band pass filter (BPF), (25> is an intermediate frequency amplifier circuit, (26) is a demodulation circuit, (27) is a low frequency amplifier circuit, (
28) is a speaker, (29), (35), (39)
is a frequency divider, (30), (40) are phase comparison circuits, (3
1), (38) are low pass filters (LPF), (
32), (37) are voltage controlled oscillators (VCO), (3
3) and (36) are switch circuits, and (34) is a reception control circuit. −・? - Ding agent Patent attorney Yu Takahashi - All, 1 1.:

Claims (1)

[Claims] A transmitter of a pair of transceivers that performs wireless communication includes a function generator that generates a time function voltage that includes only frequency components sufficiently lower than the lowest frequency component of a signal to be transmitted, and a VCO (voltage A PLL (phase locked loop) that phase-locks a controlled oscillator to a reference frequency, a means for generating a transmission frequency from the output of the VCO, and a means for generating a transmission frequency from the output of the VCO. After the setting, the VCO is frequency-modulated by the output of the function generator, and the switch circuit performs switching so that the frequency bandwidth resulting from the modulation is several tens of times or more the frequency bandwidth necessary for signal transmission, The receiver of the transceiver includes a first VCO with a narrow frequency change range, a second VCO with a wide frequency change range, and a first VCO that receives the transmission frequency of the transmitter and phase-locks the first VCO. a second PLL that receives the transmission frequency of the transmitter and phase-locks the second VCO; and a second PLL that uses the output of the first VCO as a receiving local oscillation frequency when setting a communication channel; The above first and second P
After operating the LL together and setting the communication path, the second PL
A wireless communication device comprising: a switch circuit that operates L and switches the output of the second VCO to be used as a reception local oscillation frequency.