DESCRIPTION
Title of Invention
HIGHLY-SECURE WIRELESS COMMUNICATION SYSTEM
5
Technical Field
[0001]
The present invention relates to provision of a
wireless unit that achieves highly secure wireless
10 communication. More particularly, the present invention is
concerned with a technology for realizing a wireless
communication system that can detect or eliminate
concealment of information to be transmitted and external
interference on the information by employing a multipath
15 wave which is derived from obstacles, which reflect or
scatter a radio wave, in an environment in which the
wireless unit is placed.
Background Art
20 [0002]
For fostering an industry that can continuously grow,
implementation of a new energy generation/distribution
system that can achieve both highly efficient energy
consumption and reduction of industrial wastes has been
25 socially demanded. Construction of a new energy and
3
communication fusing network intended to generate or
distribute energy is in progress in various places in the
world. The energy and communication fusing network aims to
link various pieces of equipment that are engaged in
5 generation, distribution, and consumption of energy, share
pieces of information concerning the operating situations
of the pieces of equipment and an ambient environment among
all the pieces of equipment or specific pieces of equipment,
control the operating states of the pieces of equipment,
10 which are linked over the network, using the pieces of
information, and optimize the performances, which all the
pieces of equipment linked over the network should attain,
as an entire system. For implementation of the network,
since the number of pieces of equipment to be linked is
15 very large, use of a wireless network is expected in order
to reduce a cost of introduction of the network and a cost
of maintenance of the network.
[0003]
The wireless network is expected to reduce the costs
20 of introduction and maintenance but is confronted with such
issues that it is easy to intercept or alter data, which
flows over the network, because of a physical nature of an
electromagnetic wave serving as a communication medium for
wireless communication, and that it is difficult to control
25 the pieces of equipment using the data or sustain the
4
security of monitoring information. In particular, if the
pieces of equipment linked over the energy and
communication fusing network generate or distribute a
resource, which is directly connected to civilian lives,
5 such as electric power, tap water, or gas, malicious
interception or alteration of the data would give a severe
blow to the civilian lives. The issue that it is difficult
to control the pieces of equipment or sustain the security
of monitoring information has to be resolved without fail
10 in order to implement the energy and communication fusing
network with a wireless technology.
[0004]
Wireless communication is achieved along plural
different paths that extend from a transmitting point to a
15 receiving point, that is, plural multipath reflection
propagation paths derived from reflections caused by pieces
of equipment because the pieces of equipment existent
between the transmitting point and receiving point of
communication act as electromagnetic wave scattering bodies.
20 The plural paths derived from multipath reflections are
intrinsic to the transmitting point and receiving point.
At any spatial point other than the transmitting and
receiving points, a signal sent from the transmitting point
reaches another spatial point along paths different from
25 the paths extending from the transmitting point to the
5
receiving point. A signal generated at any spatial point
reaches the receiving point along paths different from the
paths extending from the transmitting point to the
receiving point. This brings about a possibility that
5 information which cannot be obtained at any spatial point
may be transferred between the transmitting and receiving
points by selecting or combining plural paths extending
from the transmitting point to the receiving point. As a
technology employing this principle, Patent Literature 1 is
10 cited. A frequency spectrum of a receiving signal is used
as a key to encrypt information that should be transmitted,
and the information is transmitted from the transmitting
point. At the receiving point, the receiving signal is
decrypted using the frequency spectrum. Patent Literature 2
15 describes that the behavior of receiving electric power
which temporally fluctuates and is called a delay spread in
mobile communication is used as a key to encrypt
information that should be transmitted, and the information
is transmitted from the transmitting point. At the
20 receiving point, the receiving signal is decrypted using
the delay spread. Further, Patent Literature 3 describes
that a transmitter transmits an impulse train, an impulse
response intrinsic to the receiving point is used as a key
to encrypt information that should be transmitted, and the
25 information is transmitted from the transmitting point. At
6
the receiving point, the receiving signal is decrypted
using the impulse response. Due to the reversibility of an
electromagnetic wave and the symmetry of transmitting and
receiving in communication, whether a signal wave on the
5 same time base is transmitted from the transmitting point
to the receiving point or from the receiving point to the
transmitting point, the signal wave of the receiving signal
is held unchanged. The signal wave stems from interference
of an electromagnetic wave that is transmitted over plural
10 transmission lines derived from intrinsic multipath
reflections and formed between the transmitting and
receiving points. Therefore, it is very difficult to
acquire the signal wave at any spatial point other than the
transmitting and receiving points.
15
Citation List
Patent literature
[0005]
PTL 1: Japanese Patent Application Laid-Open No. 2008-
20 199263
PTL 2: Japanese Patent Application Laid-Open No. 2013-
066078
PTL 3: Japanese Patent Application Laid-Open No. 2005-
130127
25
7
Summary of Invention
Technical Problem
[0006]
In the aforesaid technologies, an irregular change in
5 a signal wave on a time base of a receiving signal in
mobile communication is used as a cipher key to conceal a
signal that should be transmitted. In consideration of
application to point-to-point communication, since the
change in the signal wave is so feeble that it is difficult
10 to make the key, which is used to conceal the signal,
complex, the degree of concealment cannot be raised. The
technologies will be described below. As for Patent
Literature 1, since many frequencies in a wide frequency
band have to be used to obtain the complex frequency
15 spectrum through point-to-point communication, the
frequency use efficiency may be degraded. As for Patent
Literature 2, a temporal change in a received signal
strength indicator (RSSI) is not manifested through pointto-
point communication. In order to forcibly induce a
20 signal change, plural antennas have to be used to change
the radiation pattern for a transmission signal. In order
to largely change the radiation pattern, the number of
antennas has to be increased. This brings about an
increase in the size of equipment and a rise in a cost of
25 equipment. As for Patent Literature 3, since a pulsating
8
wave is used as a transmission wave, many frequency
components are needed to produce the pulsating wave.
Similarly to Patent Literature 1, the frequency use
efficient may be degraded. Further, the technologies can
5 conceal information, which should be transmitted, through
encryption, and can therefore exert an effect of preventing
tapping of the signal. However, the technologies do not
take account of blocking of a signal by an external
intruder or alteration of the signal through “identity
10 fraud.”
[0007]
An object of the present invention is to detect
alteration of a signal, which is transferred between a
transmitter and receiver, in an electromagnetic environment
15 in which plural scattering bodies that scatter an
electromagnetic wave exist between the transmitter and
receiver, an electromagnetic wave radiated from the
transmitter is reflected from the scattering bodies along
multiple paths, and the reflected waves interfere with one
20 another and reach the receiver.
Solution to Problem
[0008]
A highly secure wireless communication system to be
25 disclosed includes a transmitter that transmits one piece
9
of information at predetermined different angles of
polarization of a circularly polarized wave with which a
carrier is circularly polarized, and a receiver that
restores receiving information in relation to the
5 predetermined angles of polarization and compares the
results of restoration, which relate to the predetermined
angles of polarization, with one another.
Advantageous Effects of Invention
10 [0009]
According to the present invention, alteration of a
signal that is transferred between a transmitter and
receiver can be detected in an electromagnetic environment
in which plural scattering bodies that scatter an
15 electromagnetic wave exist between the transmitter and
receiver, an electromagnetic wave radiated from the
transmitter is reflected from the scattering bodies along
multiple paths, and the reflected waves interfere with one
another and reach the receiver.
20
Brief Description of Drawings
Fig. 1 is a diagram showing an example of
configurations of a transmitter and receiver constituting a
highly secure wireless communication system.
25 Fig. 2 is an explanatory diagram concerning the
10
operating principle of the highly secure wireless
communication system.
Fig. 3 is a diagram showing another example of
configurations of a transmitter and receiver constituting a
highly 5 secure wireless communication system.
Fig. 4 is a diagram showing still another example of
configurations of a transmitter and receiver constituting a
highly secure wireless communication system.
Fig. 5 is a diagram showing still another example of
10 configurations of a transmitter and receiver constituting a
highly secure wireless communication system.
Fig. 6 is a diagram showing the principles of
production under which a circularly polarized wave is
produced by a transmitter included in a highly secure
15 wireless communication system.
Fig. 7 is a diagram showing still another example of
configurations of a transmitter and receiver constituting a
highly secure wireless communication system.
Fig. 8 is a diagram showing an example of an operating
20 algorithm for a transmitter and receiver constituting a
highly secure wireless communication system.
Fig. 9 is a diagram showing still another example of
configurations of a transmitter and receiver constituting a
highly secure wireless communication system.
25 Fig. 10 is a diagram showing still another example of
11
configurations of a transmitter included in a highly secure
wireless communication system.
Fig. 11 is a diagram showing an example of a
configuration of an elevator system to which a highly
secure wireless communication system is adapted5 .
Fig. 12 is a diagram showing an example of a
configuration of a transforming facility monitoring system
to which a highly secure wireless communication system is
adapted.
10
Description of Embodiments
[0011]
An example of an embodiment uses two transmitting
antennas to produce a transmission wave, the direction of
15 polarization of which is varied at a first frequency, by
recomposing an information signal at sampling timings
exhibiting a frequency higher than the first frequency,
weighting the recomposed signal, and convoluting the
weighted signal to a carrier. A receiver reconstructs the
20 information signal using the weight according to the
sampling timings.
[0012]
In another example of the embodiment, the number of
different sampling points within a first cycle of a
25 transmission wave, with which an original information
12
signal is circularly polarized at the first frequency, and
plural values allocated to the respective points are
rearranged during the same number of repetitive cycles as
the number of sampling points. Plural values obtained
5 during the cycles can be discriminated from one another.
[0013]
In still another example of the embodiment, an
information signal weighted with an arbitrary weight is
transmitted from a first transmitting or receiving point to
10 a second transmitting or receiving point. At the second
transmitting or receiving point, the signal is demodulated
in order to reproduce the weight. A new information signal
weighted with the reproduced weight is transmitted to the
first transmitting or receiving point. At the first
15 transmitting or receiving point, the receiving signal is
demodulated in order to reproduce the new information
signal that is transmitted from the second transmitting or
receiving point while being weighted with the weight used
for the initial weighting. Thereafter, the information
20 signal weighted with the same weight is transmitted from
the first transmitting or receiving point to the second
transmitting or receiving point. At the second
transmitting or receiving point, the signal is demodulated
in order to reproduce the information signal using the
25 weight with which the information signal has previously
13
been weighted. The weight obtained by demodulating the
receiving signal is used to transmit the new information
signal to the first transmitting or receiving point.
[0014]
5 In still another example of the embodiment, at a first
transmitting or receiving point and second transmitting or
receiving point, if a weight used to weight a previous
information signal to be transmitted, and a weight obtained
by demodulating a receiving signal are inconsistent with
10 each other at any of different sampling points within a
first cycle, appearance of an external intruder is
recognized. An information signal component associated
with the sampling point at which the inconsistency occurs
is discarded, and a new information signal component is
15 transmitted. In this case, the information signal
component that is associated with the sampling point at
which the inconsistency occurs and is transmitted is
replaced with a dummy signal that has nothing to do with
monitoring or control of equipment.
20 [0015]
Referring to Fig. 2, the principles of the embodiment
will be described below. A fixture 371 that is an
electromagnetic wave scattering body exists between a
transmitting antenna 370 included in a transmitter 375 and
25 a receiving antenna 380 included in a receiver 385. There
14
is no path along which an electromagnetic wave directly
reaches the receiving antenna 380 from the transmitting
antenna 380. An electromagnetic wave radiated from the
transmitting antenna 370 is repeatedly reflected from
5 plural electromagnetic wave reflecting objects 372 that are
distributed around the transmitter 375 and receiver 385,
and reaches the receiving antenna 380. A transmission wave
391 transmitted from the transmitter 375 in a first
direction of polarization using the transmitting antenna
10 370 that varies a direction of polarization reaches the
receiver 385 in a third direction of polarization as a
receiving wave 392 that is a synthetic wave of a reflected
wave 393a of a path length L1a and a reflected wave 393b of
a path length L1b. Further, a transmission wave 395
15 transmitted from the transmitter 375 in a second direction
of polarization according to another timing by varying the
direction of polarization reaches the receiver 385 in a
fourth direction of polarization as a receiving wave 396
that is a synthetic wave of a reflected wave 397a of a path
20 length L2a and a reflected wave 397b of a path length L2b.
In the example of Fig. 2, the waves 393a and 393b are
canceled out by the receiving antenna 380, the
polarizations of which are fixed, at points P4 and P8
because of the angles of a polarized transmission
25 electromagnetic wave. The electric powers received by the
15
receiving antenna 380 from the waves 397a and 397b are
varied depending on the angles of the polarized
transmission electromagnetic wave. However, the receiving
electric powers will not be zeros irrespective of an angle
of 5 polarization. A combination of paths along which
electric powers propagate to be canceled out at a receiving
point is determined with a relationship between a path
length and a rotational frequency of a polarized wave.
Changing the combination of paths can be achieved by
10 changing a frequency difference between carriers used to
generate a circularly polarized wave.
[0016]
A communication procedure will be described below.
Fixed information is given to a transmitter and receiver in
15 advance. The fixed information is used to exchange the
capabilities of the transmitter and receiver, and is
transmitted or received by the transmitter and receiver.
The transmitter and receiver can obtain the same receiving
wave shown in Fig. 2. The receiving wave is used as a key
20 to transmit an information signal from the transmitter to
the receiver by varying an angle of polarization and
applying different weights in relation to different angles
of polarization. The receiver stores the receiving wave,
restores the weights in relation to the sampling points
25 associated with the different angles of polarization,
16
extracts the converted information signal from the
receiving signal using the key according to the weights,
and reproduces the information signal from the receiving
signal demodulated using the receiving wave, which is
preserved 5 in advance, as the key. The cycle of the
information signal is much longer than the rotation cycle
of the polarized wave. Therefore, while the sampling
points needed to reproduce the weights are obtained, a
change in the information signal converted using the
10 receiving signal wave as the key can be ignored. The cycle
of the information signal has to be four times or more to
one hundred times or less longer than the rotation cycle of
a polarized wave in terms of the current situation of
devices employed in digital signal processing for detecting
15 an information signal independently (as for a frequency, a
one tenth or more or one fourth or less). Preferably, a
difference of a multiple of about ten (one digit) is needed.
Therefore, the frequency of a circularly polarized wave is
ten times or more higher than the upper-limit frequency of
20 an information signal and ten times or more lower than the
frequency of a carrier.
[0017]
Next, the receiver uses the capability of the
transmitter to convert an information signal using a newly
25 received receiving wave as a key, uses restored weights to
17
weight the information signal in relation to angles of
polarization, and returns the information signal to the
transmitter using a circularly polarized wave, and thus
updates the receiving wave. For a better understanding,
5 Fig. 2 shows only components of the transmitter and
receiver that are concerned with transmitting or receiving.
In reality, the transmitter 375 and receiver 380 have a
transmitting or receiving capability. The transmitting
antenna 370 and receiving antenna 380 can cope with fixed
10 polarization and circular polarization. Using the
communication procedure, an information signal to be
transferred between transmitting and receiving points is
converted using an intrinsic receiving wave, which can be
obtained at the transmitting and receiving points alone, as
15 a key, and radiated to a free space. This exerts an effect
of concealing the information signal from an outsider who
exists at another spatial point at which the intrinsic
receiving wave cannot be acquired. Assume that the same
information signal is transmitted in directions of
20 polarization Pi with different weights. If an external
intruder exists on a path 393a or 393b and alters a signal
on the path, an effect of alteration on a receiving signal
is not obtained at sampling points associated with angles
of polarization P4 and P8. When the capabilities of the
25 transmitter 375 and receiver 385 are exchanged and
18
alternately perform communication, if the same information
is transferred over one reciprocation, the fact that the
external intruder has altered the signal at the sampling
points associated with the angles of polarization P4 and P8
5 can be recognized, and the external intruder can be
detected. After the external intruder is detected, the
altered signal can be repaired by discarding data items
received at the sampling points associated with the angles
of polarization P4 and P8. Further, the data item sent
10 from the sampling points are replaced with dummy data items,
whereby the external intruder can be provided with
intentionally ineffective information.
[0018]
Examples will be described below in conjunction with
15 the drawings.
Example 1
[0019]
Fig. 1 is a diagram showing an example of
20 configurations of a transmitter and receiver constituting a
wireless system of the present example. In the transmitter,
a band limiting filter 2 determines the upper limit of
frequencies contained in a signal that falls within a
frequency band (f1) and is produced by an information
25 signal production circuit 1. A modulation circuit 3
19
convolutes a circularly polarized wave frequency carrier
(fr) 4 to the signal. A harmonic mixer 5 convolutes a
transmission carrier frequency carrier (fc) 6 to the signal.
A spurious removing filter 7 removes an unnecessary
harmonic 5 component from the signal. A cosine weighting
circuit 12 controls the amplitude of the signal. The
signal is then radiated from a transmitting vertical
antenna 11. At the same time, the signal whose amplitude
is controlled by a sine weighting circuit 14 is radiated to
10 the space from a transmitting horizontal antenna 13. Thus,
a circularly polarized electromagnetic wave 10 that
propagates while varying the angle of polarization is
formed. The cosine weighting circuit 12 and sine weighting
circuit 14 weight the amplitudes of signals, which are
15 radiated from the vertical antenna 11 and horizontal
antenna 13 respectively, at the same frequency as that of
the transmission circularly polarized frequency carrier
(fr) 4 so that the signals have a phase difference of 90.
Therefore, the rotational frequency of a circularly
20 polarized electromagnetic wave is identical to that of the
rotational frequency carrier (fr) 4.
[0020]
The receiver includes a receiving vertical antenna 31
that radiates a signal whose amplitude is controlled by a
25 cosine weighting circuit 32, and a receiving horizontal
20
antenna 33 that radiates a signal whose amplitude is
controlled by a sine weighting circuit 34. Signals
inputted through the antennas are added up, and convoluted
to a receiving carrier frequency carrier (fc) 28 by a
harmonic 5 mixer 27. The resultant signal is passed through
a low pass filer 26 and a retarder 22 that cascades a
frequency component of a circularly polarized wave and a
frequency component of an information signal. An integral
number of signal components is multiplied by a receiving
10 circularly polarized wave frequency carrier (fr) 21 by a
demodulator 23 while being provided with a phase different
that is equivalent to a quotient obtained by dividing the
cycle of the circularly polarized wave by an integer. The
integral number of signal components is then stored in an
15 integral number of registers 24.
[0021]
The vertical antenna 11 and horizontal antenna 13 of
the transmitter are formed with two linear polarization
antennas that are spatially orthogonal to each other.
20 Likewise, the vertical antenna 31 and horizontal antenna 33
of the receiver are formed with two linear polarization
antennas that are spatial orthogonal to each other.
[0022]
The frequency of an information signal produced by the
25 information signal generation circuit 1 is much lower than
21
the frequency of a circularly polarized wave, and is
therefore thought to remain constant during the cycle of
the circularly polarized wave. Data items stored in the
respective registers 24 are held intact unless the
5 circularly polarized electromagnetic wave 10 is
intentionally and externally altered in the course of
propagation from the transmitter to receiver. A baseband
circuit 25 compares the contents of the registers 24 with
one another to check if the contents are identical to one
10 another. If the contents of any of the registers are
different from those of the others, presence of externally
intentional alteration is recognized. By discarding the
contents of the register which are different from the
contents of the other registers, an information signal sent
15 from a transmission unit can be isolated from an adverse
effect of an externally intentional alteration activity.
[0023]
According to the present example, not only presence of
an externally intentional alteration activity can be
20 detected but also alteration of an information signal,
which should be transmitted, by the alteration activity can
be inhibited. This exerts an effect of achieving highly
secure transmission of the information signal.
25 Example 2
22
[0024]
Fig. 3 is a diagram showing another example of
configurations of a transmitter and receiver constituting
the wireless communication system of the present example.
A difference from the example 5 shown in Fig. 1 is that the
receiver further includes a dummy signal generation circuit
15. The dummy signal generation circuit 15 generates a
dummy signal that has nothing to do with an information
signal, which should be sent from the transmitter, during a
10 period equivalent to a value (Tr/N) obtained by dividing
the cycle (Tr) of a circularly polarized wave by an integer.
In the present example, an adaptive phase shifter (Txi) 16
and adder 17 are newly included. The adaptive phase
shifter (TXi) 16 is adjusted so that the dummy signal
15 generated by the dummy signal generation circuit 15 can be
transmitted at an angle of polarization equivalent to a
period during which an externally intentional alteration
activity detected by the baseband circuit 25 takes place.
The angle of polarization of an electromagnetic wave to be
20 radiated from the transmitting antennas 11 and 13 during
transmission is not always consistent with the angle of
polarization of a receiving electromagnetic wave relating
to presence of the externally intentional alteration
activity detected by the receiver at the same time. When
25 information is transmitted by dividing the cycle (Tr) of a
23
circularly polarized wave, the angle of polarization at the
time when the electromagnetic wave is radiated from the
transmitter can be identified by convoluting different
codes in relation to the divisions of the cycle.
5 [0025]
According to the present example, not only an adverse
effect of an externally intentional alteration activity on
a receiving signal can be eliminated but also data that may
persuade a person, who is concerned with the alteration
10 activity, to keep from transmitting data devoid of
information or to keep from performing the alteration
activity can be transmitted. This exerts an effect of
generating a force of inhibiting the externally intentional
alteration activity.
15
Example 3
[0026]
Fig. 4 is a diagram showing another example of
configurations of a transmitter and receiver constituting a
20 wireless system of the present example. A difference from
the transmitter in the example shown in Fig. 1 is that a
block code production circuit 19 that produces a different
block code during each of division periods into which the
cycle of a rotational frequency is divided by an integer is
25 substituted for the circularly polarized wave frequency
24
carrier (fr) 4, and a multiplier 18 is substituted for the
modulation circuit 3 in order to convolute the block codes,
which are produced by the block code production circuit 19,
to an information signal. A difference from the receiver
in 5 the example shown in Fig. 1 is that an integral number
of signal components is stored in the respective registers
24 as they are via the retarder 22, which cascades a
frequency component of the circularly polarized wave and a
frequency component of the information signal, while being
10 provided with a phase difference equivalent to a quotient
obtained by dividing the cycle of a circularly polarized
wave by an integer. The contents of each of the registers
24 are multiplied by any of different block codes, which
are produced by the block code production circuit 19, by
15 the multiplier 37, and the contents of the registers are
then stored in second registers 38.
[0027]
According to the present example, by checking the
contents of the second registers 38, signal components
20 relating to angles of polarization of a received
electromagnetic wave can be associated with angles of
polarization of an electromagnetic wave radiated from the
transmitter using the block codes. The effect of Example 2
can be exerted. That is, data devoid of information or
25 data that may deter an alteration activity can be
25
transmitted to a person concerned with the externally
intentional alteration activity.
Example 4
5 [0028]
Fig. 5 is a diagram showing another example of
configurations of a transmitter and receiver constituting a
wireless system of the present example.

We Claim:
1. A highly secure wireless communication system
comprising:
5 a transmitter that transmits one piece of information
at predetermined different angles of polarization of a
circularly polarized wave with which a carrier is
circularly polarized; and
a receiver that restores receiving information in
10 relation to the predetermined angles of polarization, and
compares the results of restoration, which relate to the
predetermined angles of polarization, with one another.
2. The highly secure wireless communication system
15 according to claim 1, wherein:
the transmitter divides the rotational frequency of a
circularly polarized wave which is higher than the
frequency of the information, allocates different codes to
the divisions of the rotational frequency, convolutes the
20 codes to the information, and transmits the information as
a transmission signal; and
the receiver compares the results of restoration of
codes, which are contained in a receiving signal, with one
another.
25
46
3. The highly secure wireless communication system
according to claim 2, wherein;
the transmitter generates dummy information in
relation to a specific angle of polarization of a
5 transmission polarized wave; and
the receiver decodes the codes, which are contained in
the receiving signal, in relation to the predetermined
angles of polarization, identifies the code with which an
external intruder adversely affects the information, adds
10 the dummy information to the information in relation to an
angle of polarization at which the identified code is
transmitted, and transmits the information.
4. The highly secure wireless communication system
15 according to claim 2, wherein:
the transmitter generates dummy information in
relation to a specific angle of polarization of a
transmission polarized wave; and
the receiver decodes the codes, which are contained in
20 the receiving signal, in relation to the predetermined
angles of polarization, identifies the code with which an
external intruder adversely affects the information,
replaces the information with the dummy information in
relation to the angle of polarization at which the code is
25 transmitted, and transmits the information.
47
5. The highly secure wireless communication system
according to any of claims 2 to 4, wherein the codes have a
circulatory property.
5
6. The highly secure wireless communication system
according to any of claims 1 to 5, wherein wireless units
each including the transmitter and receiver transmit or
receive information using stereotyped information which the
10 wireless units retain in common, and the transmission
timing of the information is recognized based on
transmitting or receiving of the stereotyped information.
7. The highly secure wireless communication system
15 according to claim 6, wherein the wireless unit transmits
the stereotyped information in response to acknowledgement
of the stereotyped information received, and transmits the
stereotyped information before transmitting the information.
20 8. A highly secure wireless communication system
comprising:
a transmitter that transmits one piece of information
at predetermined different angles of polarization of a
circularly polarized wave with which a carrier is
25 circularly polarized, acquires propagation information
48
transferred between the transmitter and a receiver, and
uses the propagation information as a key to encrypt the
information; and
a receiver that receives the encrypted information.
5
9. The highly secure wireless communication system
according to claim 8, wherein the propagation information
is a time base profile of a receiving electric field.
10 10. The highly secure wireless communication system
according to claim 9, wherein the propagation information
is a code string obtained by digitizing the results of
detection of an envelope of receiving electric power using
a specific threshold.
15
11. The highly secure wireless communication system
according to claim 10, wherein the frequency of the code
string resulting from digitization is a one hundredth or
more or one fourth or less of the rotational frequency of a
20 polarized wave.
12. The highly secure wireless communication system
according to any of claims 1 to 11, wherein the circularly
polarized wave is produced with a wave obtained by adding
25 up two carriers having different frequencies.
49
13. The highly secure wireless communication system
according to any of claims 1 to 12, wherein a signal to
which the information is convoluted is digitally converted
5 into a signal having a highly carrier frequency by a delta
sigma circuit.
14. The highly secure wireless communication system
according to any of claims 1 to 12, wherein a receiving
10 wave having a carrier frequency is digitally converted to a
wave, which falls within a lower frequency band of the
circularly polarized wave, by a delta sigma circuit.
15. The highly secure wireless system according to
15 claims 1 to 14, wherein two antennas whose polarizations
are orthogonal to each other are used to produce the
circularly polarized wave.
16. The highly secure wireless system according to
20 claim 15, wherein two antennas whose polarizations are
orthogonal to each other are two linear polarization
antennas that are spatially orthogonal to each other.
17. The highly secure wireless communication system
25 according to claims 1 to 16, wherein the frequency of the
50
circularly polarized wave is ten times or more higher than
the upper-limit frequency of the information and ten times
or more lower than the frequency of a carrier.
18. 5 An elevator control system wherein a wireless unit
including a transmitter, which transmits one piece of
information at predetermined different angles of
polarization of a circularly polarized wave with which a
carrier is circularly polarized, and a receiver, which
10 restores receiving information in relation to the
predetermined angles of polarization and compares the
results of restoration, which relate to the predetermined
angles of polarization, with one another is disposed at
each of an elevator and a building in which the elevator is
15 installed.
19. A transforming facility monitoring system wherein a
wireless unit including a transmitter, which transmits one
piece of information at predetermined different angles of
20 polarization of a circularly polarized wave with which a
carrier is circularly polarized, and a receiver, which
restores receiving information in relation to the
predetermined angles of polarization and compares the
results of restoration, which relate to the predetermined
25 angles of polarization, with one another is disposed at
51
each of transforming apparatuses and base stations located
in the vicinity of the transforming apparatuses.