JP2001229474A - Receiving circuit and security system using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a security system which can detect a person entering a monitor area by a small number of transmitter receivers and easily monitor a wider range than before while greatly decreasing the number of devices. SOLUTION: A transmitter scatters and radiates a signal modulated into a specific frequency band to space and the radiated radio wave signal reaches a receiver through multiple paths; and the receiver receives the radio wave signal propagated through the multiple paths, a demodulating means demodulates the received signal by the demodulation system corresponding to the modulation system of the transmitting circuit and measures the received power or vector of the demodulated signal, and a comparing circuit compares the received power or vector with specific reference power or a reference vector, thereby judging whether or not there is a trespasser on the signal propagation path of the multiple paths formed between the transmitting circuit and receiving circuit from the comparison result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave receiving apparatus capable of forming a multipath between radio wave transmitting and receiving apparatuses and detecting the presence or absence of an intruder in the multipath based on a signal received by the receiving apparatus. The security system includes:

[0002]

2. Description of the Related Art Hitherto, as a security system for automatically detecting the presence or absence of an intruder in a predetermined area such as indoors, a detection system using an infrared laser has been put to practical use. FIG. 8 shows a configuration example of this system. As shown, in such a system, a plurality of infrared laser transmitters (T
x) and the receiver (Rx) are installed in pairs. As the intruder passes between the paired transmitter and receiver, the laser beam is blocked, during which time the receiver is free of the laser beam. If the receiver detects the interruption of the laser beam, this information is reported to the control center of the security system and the control center takes appropriate action.

[0003]

In the above-mentioned conventional security system, the transmitter and the receiver must be arranged so that the laser beam transmitted from the transmitter can be seen and received. The disadvantage is that the location is subject to certain restrictions. Also, basically,
The area that can be monitored by the receiver and transmitter pair is only the space between the transmitter and the receiver, and when monitoring a wide range of space, it is necessary to install many transceivers to reliably detect intruders Can not do. Furthermore, since the transmitter and the receiver must be installed in pairs, many devices need to be installed, and there is a disadvantage that the system construction is complicated and the cost is high.

The present invention has been made in view of the above circumstances, and an object thereof is to enable a predetermined area to be monitored by a small number of transceivers, to greatly reduce the number of devices to be installed, and to provide a wider area than before. An object of the present invention is to provide a security system that can easily realize range monitoring and can be constructed using only at least one pair of transceivers.

[0005]

In order to achieve the above object, a receiving circuit according to the present invention receives a radio signal which is modulated into a predetermined frequency band in a transmitting circuit, scattered and radiated into space, and receives the signal. A receiving circuit that detects a change in fading that has occurred on a propagation path of the radio signal according to the signal, receives a radio signal propagated via the multipath, and performs frequency conversion on the received signal. Receiving means, a demodulating means for demodulating the received signal obtained by the receiving means by a demodulation method corresponding to a predetermined modulation method, and comparing the signal demodulated by the demodulating means with a predetermined reference signal. Detecting means for determining whether or not a change has occurred on the propagation path of the radio signal in accordance with the result.

[0006] The security system of the present invention comprises:
A transmitting circuit that scatters a signal modulated in a predetermined frequency band and radiates the signal into space, receives a signal transmitted by the transmitting circuit, and invades a propagation path of a radio signal from the transmitting circuit according to a received signal; A receiving circuit for detecting whether or not a user is present, wherein the receiving circuit demodulates a received signal by a demodulation method corresponding to a modulation method performed on the transmission circuit; and Detecting means for comparing the demodulated signal with a predetermined reference signal and determining whether or not an intruder exists on a signal propagation path between the transmitting circuit and the receiving circuit according to the comparison result; .

In the present invention, preferably, the receiving circuit has a receiving power measuring means for measuring a receiving power of the signal demodulated by the demodulating means, and the detecting means is configured to detect the received power by a predetermined value. Power comparing means for comparing with reference power, and judging means for judging whether or not an intruder is present on a signal propagation path between the transmitting circuit and the receiving circuit according to a comparison result of the power comparing means. Having.

Further, in the present invention, preferably, the reference power has a first reference and a second reference power having a value larger than the first reference power, and the comparing means includes: Comparing the power with the first and second reference powers respectively, and when the received power is between the first and second reference powers, It is determined that there is no intruder on the signal propagation path, and the received power is smaller than the first reference power or the second
Is larger than the reference power, it is determined that an intruder exists on the signal propagation path between the transmission circuit and the reception circuit.

In the present invention, preferably, the first and second reference powers are powers determined according to a plurality of received powers received during a predetermined period when the receiving circuit is initialized. .

In the present invention, preferably, the receiving circuit has a vector measuring means for measuring a vector of the signal demodulated by the demodulating means, and the detecting means comprises: Vector comparing means for comparing the vector with the vector, and determining means for determining whether or not an intruder is present on the signal propagation path between the transmitting circuit and the receiving circuit according to the comparison result of the vector comparing means. Have.

In the present invention, preferably, the comparing means includes a vector calculating means for calculating an absolute value of a difference between the measured vector and the reference vector, and the vector difference calculated by the vector calculating means. And a comparison circuit for comparing the absolute value of with a predetermined tolerance.

In the present invention, preferably, the transmission circuit converts the transmission signal into a predetermined pseudo noise code (PN code).
And a spread spectrum circuit that spreads the spectrum by using.

Further, in the present invention, preferably, the receiving circuit has a despreading circuit that performs spectrum despreading using the same pseudo noise code as the transmitting circuit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a circuit diagram showing an embodiment of a security system according to the present invention. As shown, the security system according to the present embodiment includes a transmitter (Tx) 10 and a receiver (R
x) 20-1, 20-2, ..., 20-n, monitor 30
And a security control center. Hereinafter, the configuration and operation of each part of the security system of the present embodiment will be described.

The transmitter 10 scatters a signal modulated in a predetermined high frequency band in a plurality of directions and transmits the scattered signal. Since the transmitted high-frequency signal is transmitted in an unspecified direction in the monitoring area, the transmitter 10 and the receivers 20-1, 20-2,
, 20-n (n is a natural number and n ≧ 2), a multipath is formed, and signals transmitted via the multipath are received by respective receivers.

The receivers 20-1, 20-2,..., 20-n
Receives the signal transmitted via multipath,
The received signal is compared with a preset reference signal, and based on the comparison result, it is determined whether or not an intruder is present in the monitored area. Send. When the monitor 30 receives a detection signal transmitted from any of the receivers 20-1, 20-2,..., 20-n, the monitor 30 determines that there is an intruder in the monitored area, Notify the security control center 40. When the security control center 40 receives the report from the monitor 30, it checks the presence or absence of an intruder in the monitored area based on other information, and takes appropriate measures.

Although a plurality of receivers are provided for the transmitter 10 in the security system shown in FIG. 1, the present invention is not limited to this configuration.
For example, a security system can be configured using only one receiver for one transmitter.

Hereinafter, the principle of the security system according to the present embodiment will be described. In the above-described security system, a transmission signal modulated to a high frequency by the transmitter 10 is transmitted by, for example, an omnidirectional antenna, so that a transmission radio wave is scattered in all directions. For this reason, radio waves arrive from various directions at each receiver,
As a result, each receiver enters a multipath fading (Fading) state. In this case, when the location of the transceiver changes, or when the propagation path of the radio wave between the transceiver changes, the signal power RSSI received by the receiver changes. If the location of the transceiver is fixed, there is no intruder in the monitoring area where multipath is formed,
And under stable conditions with no external radio interference,
The received power RSSI at each receiver becomes almost constant.

When an intruder enters the monitored area, a change occurs in the radio wave propagation path between the transmitter 10 and any one or more receivers. Due to this change, the received power RSSI of one or more receivers fluctuates. The receiver sets in advance the received power obtained under stable conditions as a reference value, compares the power of the signal received at each time thereafter with the set reference value, and calculates the difference between the received power and the reference value. Exceeds a predetermined threshold, it is determined that an intruder is present in the monitored area, and a detection signal is transmitted to the monitor 30.

Hereinafter, two examples of the receiver will be shown, and the configuration and operation of the receiver forming the security system of the present embodiment will be described. First Embodiment of Receiver FIG. 2 is a circuit diagram showing a configuration example of a receiver. As illustrated, the receiver 20a includes an antenna 21, a high-frequency receiving unit (RF receiving unit) 22, a received power measuring unit 23, and a detecting unit 2.
4, the power supply unit 25 and the timer 26.

The high-frequency receiving section 21 amplifies the high-frequency signal received by the antenna 21, and further, if necessary,
The received signal is converted to a predetermined intermediate frequency or baseband by frequency conversion, and the converted intermediate frequency signal or baseband signal is supplied to the received power measuring unit 23.

The received power measuring section 23 is a high-frequency receiving section 22
Measure the power of the signal input from. Here, the measurement of the signal power is performed by a method such as measuring the amplitude and measuring the signal power according to the measured amplitude. Before measuring the reception power, a demodulation process for demodulating a signal may be performed as necessary. For example, when a predetermined signal is modulated in the transmitter 10, the receiver demodulates the received signal according to the modulation method performed by the transmitter, and measures the received power for the demodulated signal. .
Since this demodulation processing is performed on the output signal of the high-frequency receiving unit 21, a demodulation circuit can be provided in the received power measuring unit 23, or a demodulation circuit can be separately provided before the received power measuring unit 23.

The detection unit 24 compares the reception power measured by the reception power measurement unit 23 with a preset reference value.
The presence or absence of an intruder is detected based on the comparison result, and when an intruder is detected, a detection signal _SD is generated and the monitor 30
Send to The detection unit 24 compares the reception power measured by the reception power measurement unit 23 with a reference value input from the outside or a reference value stored in an internal memory in advance to detect an intruder. . The power of the signal received by the receiver changes depending on conditions such as the installation location of the transceiver and the environment of the monitoring area. For this reason, it is preferable to appropriately set the reference value used in the detection unit 24 according to the measurement conditions. For example, the reception power is collected in an initial state when the power is turned on in the receiver, or in a time set in advance by the timer 26, and the reception power is stored in a memory as a reference value. Preferably, noise is removed by a method such as an averaging process from a plurality of received powers continuously collected in a certain time zone, and the obtained received power is stored in a memory as a reference value.

The power supply section 25 supplies a power supply voltage to the high frequency receiving section 22, the received power measuring section 23, the detecting section 24 and the timer 26.

The timer 26 generates a reference timing signal for controlling the overall operation timing of the receiver 20a,
It is supplied to each sub-circuit constituting the receiver. Further, the timer 26 transmits a power control signal S _E to turn on / off the power supply to the power unit 25. Power supply unit 25, in response to the power supply control signal S _E, to turn on / off the supply of power to each part circuit. For example, if a time period in which the monitoring operation is unnecessary is input in advance to the timer 26, the timer 26 transmits a signal for stopping the power supply to the power supply unit 25 when the pause time period starts, and the receiver 20a The supply of power to each of the partial circuits is stopped to reduce power consumption in the standby state. When the pause period ends, the timer 26 transmits a signal for enabling power supply to the power supply unit 25, and starts supplying power to each of the partial circuits of the receiver 20a.

FIG. 3 is a flowchart showing the operation of the receiving circuit 20a of the present embodiment. Hereinafter, the operation of the receiving circuit 20a will be described with reference to FIGS. After the security system is enabled, first, the receiver 20a sets a waiting time to a predetermined time T _S. The timer 26 measures the waiting time T _S , and when the waiting time T _S elapses, transmits a signal to enable the power supply to the power supply unit 25 to supply power to each of the partial circuits of the receiver 20a. Then, the receiver 20a is started (step S1).

After the receiver 20a is activated, a timer 2
At the time set by 6, the receiving operation is performed, the received power is collected, and a reference value is set in the detecting unit 24 based on the received power (step S2). As described above, the reference value is set, for example, based on a plurality of received power values continuously collected in a certain time period, using a value obtained by removing a noise component by an averaging process or the like as a reference value. depending on the received power value, it sets the maximum value TH _H and the minimum value TH _L of the case of detecting the detection unit 24, and stores it in the memory (step S3).

After the above processing is completed, the receiver 20
“a” continuously measures the received power for the time set by the timer 26, and detects the presence or absence of an intruder according to the measurement result. First, in step S4, according to the signal received by the high frequency receiving unit 22, the received power measuring unit 2
3, the signal reception power is measured.

Next, the detection unit 24 compares the reception power measured by the reception power measurement unit 23 with the maximum value TH _H and the minimum value TH _L stored in the memory, respectively.
The presence or absence of an intruder is determined according to the result of the comparison. In step S5, a maximum value TH _H of the measured received power R _E and the reference value are compared, if the measured value is greater than the maximum value _{TH H (R E> TH H} ), determines that the intruder is present, In step S8, a detection signal is transmitted to the monitor. In step S6, the minimum value TH _L of the measured received power R _E and the reference value are compared, the minimum value T measured value
If it is smaller than H _L (R _E <TH _L ), it is determined that an intruder exists, and a detection signal is transmitted to the monitor in step S8.

[0030] That is, if the intruder not, the reception power of the radio wave input to the receiver 20a via a multi-path hardly changes, received power R _E of the signal, the maximum value T
Between H _H and the minimum value TH _L (TH _L < _RE <TH
_H ). Meanwhile provisions, if an intruder is present, multipath changes the received power of the radio wave input to the receiver 20a via the measured received power R _E is the maximum value TH _H and the minimum value TH _L Beyond the specified range (R _E > TH _H
Or R _E <TH _L ).

[0031] whether this manner, by comparing the measured by detector 24 receives power R _E preset maximum value TH _H, the minimum value TH _L, there is an intruder in the monitored area Can be detected.

When one detection process is completed, it is determined whether or not to continue the process. That is, it is determined whether or not the measurement of the received power is completed.
And the above-described processes of steps S4 to S6 are repeatedly performed. When the detection process is completed, for example, a signal for stopping power supply is transmitted to the power supply unit 25. Upon receiving this signal, the power supply unit 25 stops supplying power,
The receiver 20a is kept in a standby state.

The above-described detection process uses the reception power measured by the reception power measurement unit 23 to detect
Determining the presence or absence of the intruder in response to the comparison result between the maximum value TH _H and the minimum value TH _L of the received power and the reference value, but a large momentarily received power due to the influence of noise such as interference changes in May occur. In this case, when the measured value of the received power exceeds the range set by the maximum value TH _H and the minimum value TH _L , the detection unit 24 may erroneously determine that an intruder is present, and may issue a false alarm. In order to prevent this, a method of judging the presence or absence of an intruder by using a value obtained by removing the influence of noise with a smoothing filter or the like on a signal received a plurality of times continuously in a predetermined period is effective. . Note that the received signal smoothing process can be performed using a common processing circuit with the received power averaging process performed to set the reference value at the time of initialization of the receiver. Increase can be minimized.

As described above, the receiver 2 of the present embodiment
According to Oa, the received signal received by the high-frequency receiving unit 22 and further frequency-converted is supplied to the received power measuring unit 24, and the received power _RE is measured. In the detecting unit 24, the received power _RE and the preset maximum value T of the reference value are set.
Is compared with the H _H and the minimum value TH _L, when the reception power R _E is within the range set by the maximum value TH _H and the minimum value TH _L, it is determined that there is no intruder in the monitored area, whereas, when the received power R _E is outside the range set by the maximum value TH _H and the minimum value TH _L, it is determined that an intruder in the monitored zone is present, the detection signal to the monitor 30 are transmitted. It is possible to detect the presence of an intruder in the multipath formation area based on a change in the signal reception level due to fading due to the multipath formed between the transmitter and the receiver. The area can be monitored, and the system can be simplified and the cost can be reduced.

Second Embodiment of Receiver FIG. 4 is a circuit diagram showing another configuration example of the receiver. As illustrated, the receiver 20b includes an antenna 21, a high-frequency receiving unit (RF receiving unit) 22, a received vector measuring unit 23a, a detecting unit 24b, a power supply unit 25, and a timer 26.

The receiver 20b of this embodiment is the same as the first
The received power is measured as compared with the receiver 20a of the embodiment,
Instead of detecting an intruder in response, a vector of the received signal is measured, and an intruder is detected according to a change in the received vector. Hereinafter, the configuration and operation of the receiver 20b of the present embodiment will be described, focusing on the configuration and operation of the reception vector measurement unit 23a and the detection unit 24a in the present embodiment.

The signal received by the high-frequency receiving unit 22 and further subjected to frequency conversion is input to the received vector measuring unit 23a. That is, the signal input to the reception vector measurement unit 23a is an intermediate frequency signal or a baseband signal. The reception vector measurement unit 23a measures a vector of the input signal. Here, it is assumed that the transmitter 10 transmits a signal modulated according to a certain modulation scheme. In the reception vector measurement unit 23a, the input signal is demodulated, the real part and the imaginary part of the demodulated signal are obtained, and the reception vector is obtained. The modulation scheme used for the transmitter 10 is, for example, PSK modulation, QPSK modulation, or the like.

The detection unit 24a includes a reception vector measurement unit 23
The received vector obtained in step a is compared with a preset reference vector, and it is determined whether or not an intruder exists in the monitored area according to the result of the comparison.

Hereinafter, the principle of the receiver 20b of this embodiment will be described. As described above, radio waves scattered in all directions are transmitted by the omnidirectional antenna in the transmitter 10. Thereby, the transmitter 10 and the receiver 20
b, a multipath is formed, and the radio wave transmitted by the transmitter 10 is transmitted to the receiver 20b via the multipath.
To reach. In the receiver 20, the amplitude and phase of the received signal change due to multipath fading.

When the installation location of the transceiver is constant, the reception vector at the receiver 20b is stable under the condition that there is no intruder in the monitoring area where the multipath is formed and there is no radio wave interference from outside. It becomes almost constant. However, when an intruder enters an area where a multipath is formed, a change occurs in a signal transmission path between the transmitter and the receiver. Due to this change, the amplitude or phase of the signal received by the receiver 20b changes. For this reason, in the receiver 20b, the received vector is compared with a preset reference vector, and if the error between these vectors is within a certain error range, there is no large change in the multipath between the transmitter and the receiver.
That is, it can be determined that there is no intruder. On the other hand, when the vector error between the received vector and the reference vector exceeds a certain error range, there is a large change in the multipath between the transmitter and the receiver, and it can be determined that an intruder exists.

FIG. 5 is a diagram showing the principle of detection of the receiver 20b of this embodiment. Here, R _V0 indicates a reference vector, and r indicates an allowable error. As range error range determined by the reference vector R _V0 tolerances and r, the received vector R _V
Is within this error range, there is no significant change in the multipath between the transmitter and the receiver, and it is determined that there is no intruder. Conversely, when the received vector R _V is outside this error range,
A large change occurs in the multipath between the transmitter and the receiver, and it is determined that an intruder exists.

FIG. 6 is a flowchart showing the operation of the receiver 20b of this embodiment. Hereinafter, the operation of the receiver 20b of the present embodiment will be described with reference to FIGS. First, the receiver 20b waits for a predetermined time T _S. The timer 26 measures the waiting time T _S , and when the waiting time T _S elapses, transmits a signal for enabling the power supply to the power supply unit 25 and outputs the signal to the receiver 20.
b to start supplying power to each of the sub-circuits.
b is started (step SS1).

After the receiver 20b is started, a timer 2
At the time set by step 6, the receiving operation is performed, the received vector is measured (step SS2), and the reference vector and the allowable error r are set in the detecting unit 24a based on the received vector (step SS3). As described above, the setting of the reference vector and the permissible error r is, for example, based on a plurality of reception vectors continuously measured in a certain time zone, and removing the noise component by an averaging process or the like from the reference vector R _V0. In addition, an allowable error r when the detection is performed by the detection unit 24a with respect to the reference vector R _V0 according to a deviation of each measured received power vector is set,
It is stored in the memory (step SS3).

After the above processing is completed, the receiver 20
b continuously measures the reception vector R _V for the time set by the timer 26, and detects the presence or absence of an intruder based on the measurement result. First, in step SS4, a signal reception vector is measured by the reception vector measurement unit 23a according to the signal received by the high frequency reception unit 22.

Next, in the detecting section 24a, an error ΔR (ΔR = |) between the received vector measured by the received vector measuring section 23a and the reference vector stored in the memory.
R _V −R _V0 |) is determined, the calculated ΔR is compared with the allowable error r, and the presence or absence of an intruder is determined according to the result of the comparison (step SS5).

When ΔR is larger than the allowable error r (ΔR>
r), it is determined that an intruder exists, and a detection signal is transmitted to the monitor in step SS7. On the other hand, when ΔR is smaller than the allowable error r (ΔR <r), it is determined that there is no intruder, and the process proceeds to the next step SS6.

As described above, the reception vector R _V measured by the detection unit 24a and the preset reference vector R
By comparing with _V0, it can be detected whether or not an intruder exists in the monitored area.

When one detection process is completed, it is determined whether or not to continue the process. That is, it is determined whether or not the process of detecting an intruder ends, and if not, the process returns to step SS4, and the above-described processes of steps SS4 to SS5 are repeatedly performed. When the detection process is completed, for example, a signal for stopping power supply is transmitted to the power supply unit 25. Upon receiving this signal, the power supply unit 25 stops supplying power, and the receiver 20b is kept in a standby state.

The above-described detection processing is performed by using the reception vector measured by the reception vector measurement unit 23a.
The detection unit 24a determines the presence or absence of an intruder based on whether or not the received vector is within a range set by the reference vector and the allowable error r, but the amplitude of the received vector is instantaneously affected by noise such as radio wave interference. Or the phase may change greatly. In this case, the measured value of the received vector may deviate from the range set by the reference vector R _V0 and the permissible error r, and the detection unit 24 may erroneously determine that an intruder is present, and may generate a false alarm. To prevent this, it is effective to determine the presence or absence of an intruder after removing the influence of noise from a signal received a plurality of times continuously during a predetermined period by using a smoothing filter or the like. Note that the received signal smoothing process uses a common processing circuit as the received vector averaging process performed to set the reference vector R _V0 and the allowable error r at the time of initialization of the receiver. Since it can be executed, the increase in the circuit scale is kept to a minimum.

As described above, the receiver 2 of the present embodiment
0b, the received signal received by the high-frequency receiving unit 22 and further frequency-converted is received by the received vector measuring unit 2
4a, and the received vector R _V is measured. An error ΔR between the reception vector R _V and a preset reference vector R _V0 is obtained by the detection unit 24a, and the error ΔR
When R is smaller than the predetermined allowable error r, it is determined that no intruder exists in the monitored area. On the other hand, when the calculated error ΔR is larger than the predetermined error r, the intruder is detected in the monitored area. It is determined that there is, and a detection signal is transmitted to the monitor 30. In this way, it is possible to detect the presence or absence of an intruder in the formation area of the multipath, based on the amplitude and phase change of the reception vector due to fading by the multipath formed between the transmitter and the receiver,
A wide area can be monitored with a simple system configuration, and the system can be simplified and reduced in cost.

In the security system described above, in order to reduce the influence of noise such as radio wave interference, the transmitter 10 spreads the transmission signal using a pseudo noise code (PN code, for example, M sequence).
A signal subjected to so-called secondary modulation is transmitted. The receiver despreads the received signal using the same PN code as the transmitting side, and performs a normal demodulation process and the like. As a result, noise components are dispersed, and erroneous detection due to instantaneous radio wave interference can be prevented.

FIG. 7 is a configuration diagram showing the configuration of the transmission antenna and its reflector in the transmission circuit of the present invention. As described above, in the security system of the present invention,
The transmitter 10 scatters transmission radio waves and radiates them in all directions, thereby forming a multipath between the transmitter and the receiver. FIG. 7 shows a configuration example of a transmission antenna used to scatter transmission radio waves.

As shown in FIG. 7A, the transmission antenna is composed of an antenna element 12 and a reflector 14. The antenna element 12 radiates a high-frequency transmission signal generated by a transmitting unit (not shown) into space. Usually, a reflector used in a radio wave transmitter is used to reflect a transmission radio wave in a certain direction, that is, to converge a radio wave, but in the present invention, in order to form a multipath, a reflection is used. The device 14 is desired to have a so-called omnidirectional radiation characteristic that reflects radio waves emitted by the antenna element 12 in all directions.

FIG. 7B shows an example of the reflector 14. As shown, countless irregularities are formed on the inner wall of the reflector 14. Due to these irregularities, the antenna element 12
The emitted radio waves are scattered, and the reflected waves are emitted in different directions. As a result, the radio waves radiated by the transceiver reach the receiver via a plurality of different paths, respectively, so that a multipath is formed.

[0055]

As described above, according to the security system of the present invention, a predetermined area can be monitored by a small number of transceivers. There is an advantage that it is possible to easily realize monitoring and to realize a security system that can be constructed using only at least one pair of transceivers. In the present invention,
By the transmission circuit constituting the security system, P
The spread spectrum processing is performed on the transmission signal using the N code, and the reception circuit performs spectrum despreading on the reception signal using the same PN code as that of the transmission circuit. Alarms can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a security system according to the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a receiver used in the security system of the present invention.

FIG. 3 is a flowchart showing an operation of the first embodiment of the receiver.

FIG. 4 is a circuit diagram showing a second embodiment of the receiver used in the security system of the present invention.

FIG. 5 is a diagram illustrating an operation principle of a second embodiment of the receiver.

FIG. 6 is a flowchart showing an operation of the second embodiment of the receiver.

FIG. 7 is a diagram illustrating a configuration of a transmission antenna in a transmitter.

FIG. 8 is a diagram illustrating a configuration example of a conventional security system.

[Explanation of symbols]

10, a transmitter, 20, 20a, 20b, 20-1, 20-2, ..., 20
-N: receiver, 21: antenna, 22: high frequency receiver, 23: reception vector measurement unit, 24: detection unit, 25: power supply unit, 26: timer, 30: monitor, 40: security control center.

Claims (17)

[Claims] A transmission circuit receives a radio signal modulated into a predetermined frequency band, scattered and radiated into space, and a change in fading generated on a propagation path of the radio signal in response to the received signal. Receiving a radio signal propagated through the multi-path,
Receiving means for performing frequency conversion on the received signal; demodulating means for demodulating the received signal obtained by the receiving means by a demodulation method corresponding to a predetermined modulation method; and a signal demodulated by the demodulation means and a predetermined reference A receiving circuit that compares the signal with the signal and determines whether or not a change has occurred on the propagation path of the radio signal in accordance with the result of the comparison. 2. A receiving power measuring means for measuring a receiving power of a signal demodulated by the demodulating means, wherein the detecting means comprises a power comparing means for comparing the receiving power with a predetermined reference power; 2. The receiving circuit according to claim 1, further comprising: a determination unit configured to determine whether a change has occurred on the propagation path according to a comparison result of the comparison unit. 3. The reference power has a first reference power and a second reference power having a value larger than the first reference power, and the comparing means compares the reception power with the first and second powers. And the determining means determines that there is no change on the propagation path when the received power is between the first and second reference powers, and the received power is First
3. The receiving circuit according to claim 2, wherein when the reference power is smaller than the second reference power or higher than the second reference power, it is determined that a change has occurred on the propagation path. 4. The receiving circuit according to claim 3, wherein said first and second reference powers are powers determined according to a plurality of received powers received during a predetermined period when the circuit is initialized. 5. A vector measuring means for measuring a vector of a signal demodulated by said demodulating means, said detecting means comprising: vector comparing means for comparing said measured vector with a predetermined reference vector; 2. The receiving circuit according to claim 1, further comprising: a determination unit configured to determine whether a change has occurred on the propagation path according to a comparison result of the units. 6. The vector comparing means for calculating an absolute value of a difference between the measured vector and the reference vector, and an absolute value of the vector difference calculated by the vector calculating means and a predetermined allowable error. 6. The receiving circuit according to claim 5, further comprising: a comparing circuit that compares the signal and 7. The receiving circuit according to claim 5, wherein said reference vector is a vector calculated according to a plurality of received signals received during a predetermined period when the circuit is initialized. 8. A transmission circuit that scatters a signal modulated to a predetermined frequency band and radiates the signal into space, receives a signal transmitted by the transmission circuit, and converts a radio signal from the transmission circuit according to a received signal. A receiving circuit for detecting whether or not an intruder is present on the propagation path, the receiving circuit demodulating means for demodulating a received signal by a demodulation method corresponding to a modulation method performed on the transmission circuit; Comparing a signal demodulated by the demodulation means with a predetermined reference signal, and determining whether an intruder exists on a signal propagation path between the transmission circuit and the reception circuit according to the comparison result. A security system having detection means. 9. The security system according to claim 8, wherein a multipath is formed between said transmission circuit and said reception circuit. 10. The receiving circuit has a receiving power measuring means for measuring a receiving power of a signal demodulated by the demodulating means, and the detecting means comprises a power comparing means for comparing the receiving power with a predetermined reference power. 9. The security according to claim 8, further comprising: means for determining whether an intruder exists on a signal propagation path between the transmission circuit and the reception circuit according to a comparison result of the power comparison means. system. 11. The reference power has a first reference power and a second reference power having a value larger than the first reference power, and the comparing means compares the reception power with the first and second powers. And when the received power is between the first and second reference powers, the intruder is located on a signal propagation path between the transmitting circuit and the receiving circuit. Is determined not to exist, and when the received power is smaller than the first reference power or larger than the second reference power,
The security system according to claim 10, wherein it is determined that an intruder exists on a signal propagation path between the transmission circuit and the reception circuit. 12. The security system according to claim 11, wherein said first and second reference powers are powers determined according to a plurality of received powers received during a predetermined period when said receiving circuit is initialized. 13. The receiving circuit includes vector measuring means for measuring a vector of a signal demodulated by the demodulating means, and the detecting means comprises a vector comparing means for comparing the measured vector with a predetermined reference vector. 9. The security system according to claim 8, further comprising: a determination unit configured to determine whether an intruder exists on a signal propagation path between the transmission circuit and the reception circuit according to a comparison result of the vector comparison unit. . 14. The vector calculating means for calculating an absolute value of a difference between the measured vector and the reference vector, the absolute value of the vector difference calculated by the vector calculating means and a predetermined permissible error. 14. The security system according to claim 13, further comprising: a comparison circuit that compares? 15. The security system according to claim 13, wherein said reference vector is a vector calculated according to a plurality of received signals received during a predetermined period when the receiving circuit is initialized. 16. The security system according to claim 8, wherein said transmission circuit has a spread spectrum circuit for performing spread spectrum on said transmission signal using a predetermined pseudo noise code (PN code). 17. The security system according to claim 16, wherein said receiving circuit has a despreading circuit for performing spectrum despreading using the same pseudo noise code as said transmitting circuit.