U.S. patent application number 12/814871 was filed with the patent office on 2010-10-21 for data communication apparatus.
Invention is credited to Satoshi Furusawa, Masaru Fuse, Tsuyoshi Ikushima, Toru Shiozaki.
Application Number | 20100266124 12/814871 |
Document ID | / |
Family ID | 36000076 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100266124 |
Kind Code |
A1 |
Fuse; Masaru ; et
al. |
October 21, 2010 |
DATA COMMUNICATION APPARATUS
Abstract
A data communication apparatus wherein the stealthiness has been
enhanced by significantly increasing the time required for a
wiretapper to decrypt an encrypted text. The data communication
apparatus is constituted by connecting a data transmitting
apparatus and a data receiving apparatus via a transmission path.
The data transmitting apparatus receives a first predetermined
initial value (key information) and information data, generates a
multi-valued signal the level of which varies substantially like a
random number, and converts the multi-valued signal to a modulated
signal of a predetermined modulation format for transmission. The
data receiving apparatus demodulates the modulated signal to output
the multi-valued signal, and then reproduces the information data
from the multi-valued signal and a second predetermined initial
value (key information) that is received.
Inventors: |
Fuse; Masaru; (Osaka,
JP) ; Furusawa; Satoshi; (Osaka, JP) ;
Ikushima; Tsuyoshi; (Nara, JP) ; Shiozaki; Toru;
(Kyoto, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK L.L.P.
1030 15th Street, N.W., Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
36000076 |
Appl. No.: |
12/814871 |
Filed: |
June 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11661313 |
Feb 27, 2007 |
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PCT/JP2005/015860 |
Aug 31, 2005 |
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12814871 |
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Current U.S.
Class: |
380/268 |
Current CPC
Class: |
H04L 2209/08 20130101;
H04L 9/12 20130101; H04L 9/088 20130101 |
Class at
Publication: |
380/268 |
International
Class: |
H04L 9/00 20060101
H04L009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2004 |
JP |
2004-252980 |
Sep 28, 2004 |
JP |
2004-282635 |
Oct 8, 2004 |
JP |
2004-296821 |
Oct 29, 2004 |
JP |
2004-317186 |
Nov 15, 2004 |
JP |
2004-330980 |
Feb 24, 2005 |
JP |
2005-049460 |
Claims
1-98. (canceled)
99. A data transmitting apparatus that performs cipher
communication, comprising: a multi-level code generating part that
generates, from predetermined key information, a multi-level code
sequence a signal level of which varies substantially like a random
number; a first modulating part that generates a first modulated
signal of a predetermined modulation format based on information
data; a second modulating part that generates a second modulated
signal of a predetermined modulation format based on the
multi-level code sequence, wherein by cascading the first
modulating part and the second modulating part, a modulated signal
a modulation condition of which varies substantially like a random
number is generated in correspondence with a combination of signal
levels of the information data and the multi-level code sequence,
and signal points of multiple levels in the modulated signal are
substantially uniformly arranged.
100. A data communication apparatus in which a data transmitting
apparatus and a data receiving apparatus perform cipher
communication, wherein the data transmitting apparatus comprises: a
first multi-level code generating part that generates, from
predetermined key information, a first multi-level code sequence a
signal level of which varies substantially like a random number; a
first modulating part that generates a first modulated signal of a
predetermined modulation format based on information data; a second
modulating part that generates a second modulated signal of a
predetermined modulation format based on the multi-level code
sequence, by cascading the first modulating part and the second
modulating part, a modulated signal a modulation condition of which
varies substantially like a random number is generated in
correspondence with a combination of signal levels of the
information data and the multi-level code sequence, the data
receiving apparatus comprises: a second multi-level code generating
part that generates, from key information equal to the key
information, a second multi-level code sequence a signal level of
which varies substantially like a random number; a demodulating
part that demodulates the modulated signal, and reproduces the
multi-level signal; and a multi-level discriminating part that
discriminates the multi-level signal based on the second
multi-level code sequence according to a predetermined processing,
and reproduces the information data, and signal points of the
multi-level signal are substantially uniformly arranged.
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus that performs
secret communication to prevent illegal wiretapping and
interception by third parties. More particularly, the present
invention relates to an apparatus that selects and sets a specific
encoding and decoding (modulating and demodulating) method to
perform data communication between authorized transmitters and
receivers.
BACKGROUND ART
[0002] Conventionally, to perform communication only among specific
persons, a method is adopted in which key information for encoding
and decoding is shared between the transmitter and the receiver and
an operation or an inverse operation of the information data (plain
text) to be transmitted is mathematically performed based on the
key information to thereby realize secret communication. FIG. 53 is
a block diagram showing the structure of a conventional data
transmitting apparatus based on the method. In FIG. 53, the
conventional data communication apparatus is constituted by
connecting a data transmission apparatus 90001 and a data receiving
apparatus 90002 via a transmission path 913. The data transmission
apparatus 90001 has an encoding part 911 and a modulating part 912.
The data receiving apparatus 90002 has a demodulating part 914 and
a decoding part 915. In the conventional data communication
apparatus, when the encoding part 911 receives information data 90
and first key information 91 and the decoding part 915 receives
second key information 96, the decoding part 915 outputs
information data 98. Hereinafter, the operation of the conventional
data communication apparatus will be explained with reference to
FIG. 53.
[0003] In the data transmission apparatus 90001, the encoding part
911 encodes (encrypts) the information data 90 based on the first
key information 91. The modulating part 912 modulates the
information data encoded by the encoding part 911 in a
predetermined modulation format, and transmits it as a modulated
signal 94 to the data receiving apparatus 90002 via the
transmission path 913. In the data receiving apparatus 90002, the
demodulating part 914 demodulates the modulated signal 94
transmitted via the transmission path 913 in a predetermined
demodulation format, and outputs it as encoded information data.
The decoding part 915 decodes (decrypts) the encoded information
data based on the second key information 96 shared with the
encoding part 911, and reproduces the original information data
98.
[0004] Now, wiretapping by a third party will be explained by using
a wiretapper data receiving apparatus 90003. In FIG. 53, the
wiretapper data receiving apparatus 90003 has a wiretapper
demodulating part 916 and a wiretapper decoding part 917. The
wiretapper demodulating part 916 wiretaps the modulated signal
(information data) transmitted between the data transmitting
apparatus 90001 and the data receiving apparatus 90002, and
demodulates the wiretapped modulated signal by a predetermined
demodulation method. The wiretapper decoding part 917 tries to
decode the signal demodulated by the wiretapper demodulating part
916 based on third key information 99. Here, since the key
information is not shared between the wiretapper decoding part 917
and the encoding part 911, the wiretapper decoding part 917 tries
to decode the signal demodulated by the wiretapper demodulating
part 916 based on the third key information 99 different from the
first key information 91. For this reason, the wiretapper decoding
part 917 cannot correctly decode the signal modulated by the
wiretapper demodulating part 916, and cannot reproduce the original
information data.
[0005] The mathematical encryption (also called computational
encryption or software encryption) technology based on such a
mathematical operation is adaptable, for example, to an access
system as mentioned in a patent document 1. That is, in a PON
(passive optical network) structure in which an optical signal sent
out from one optical transmitter is branched by an optical coupler
and distributed to each of the optical receivers at a plurality of
optical subscriber homes, a signal for other subscribers other than
the desired optical signal is inputted to each optical receiver.
Therefore, by encrypting the information data for each subscriber
by using different pieces of key information, information of each
subscriber is prevented from being leaked and wiretapped, so that
safe data communication can be realized.
The patent document 1: Japanese Laid-Open Patent Publication No.
H09-205420
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0006] However, the conventional data communication apparatus based
on the mathematical encryption technology has the following
problem: Even though the key information is not shared, wiretappers
can perform decryption in theory by trying an operation using all
the possible combinations of key information (brute force attack)
or the application of a special analytical algorithm to the cipher
(modulated signal, or encrypted information data). In particular,
the processing speed of computers has been remarkably improving in
recent years, and if computers based on a new principle such as
quantum computers are realized in the future, it will be possible
to wiretap ciphers within a limited time.
[0007] Accordingly, an object of the present invention is to
provide a high-stealthiness data communication apparatus based on
an astronomical amount of calculations which apparatus
significantly increases the time required for wiretappers to
analyze ciphers.
Solution to the Problems
[0008] The present invention is directed to a data transmitting
apparatus that performs cipher communication. To achieve the above
object, the data transmitting apparatus according to the present
invention is provided with a multi-level encoding part and a
modulating part. The multi-level encoding part receives
predetermined key information and information data, and generates a
multi-level signal the signal level of which varies substantially
like a random number. The modulating part generates a modulated
signal of a predetermined modulation format based on the
multi-level signal. The multi-level encoding part includes: a
multi-level code generating part that generates, from the key
information, a multi-level code sequence the signal level of which
varies substantially like a random number; and a multi-level
processing part that combines the multi-level code sequence and the
information data according to a predetermined processing to thereby
generate a multi-level signal having a level corresponding to a
combination of the signal levels of the multi-level code sequence
and the information data. The multi-level encoding part sets the
inter signal point intervals of the multi-level signal so as to be
substantially uniform.
[0009] Preferably, the inter signal point intervals of the
multi-level signal are smaller than the amplitude of the
information data included in the multi-level signal. The maximum
amplitude of the multi-level signal is equal to or larger than
twice the amplitude of the information data included in the
multi-level signal.
[0010] The data transmitting apparatus may be further provided with
a data inverting part that bit-inverts the information data based
on a predetermined pseudo-random number sequence and outputs the
bit-inverted information data to the multi-level encoding part.
Moreover, the change rates of the multi-level code sequence and the
information data coincide with each other. The information data is
a binary signal.
[0011] Preferably, as the predetermined processing, the multi-level
processing part generates the multi-level signal by adding the
information data to the multi-level code sequence by using the
multi-level code sequence as the reference level. Moreover, as the
predetermined processing, the multi-level processing part may
generate the multi-level signal by level-controlling the
multi-level code sequence according to the information data by
using the multi-level code sequence as the reference level.
[0012] The modulated signal is generated by modulating an
electromagnetic field by the multi-level signal. Moreover, the
modulated signal may be generated by modulating a light wave by the
multi-level signal. At this time, the light wave may be coherent
light.
[0013] Moreover, the data transmitting apparatus may be further
provided with a noise controlling part that is connected between
the multi-level encoding part and the modulating part, combines a
predetermined noise on the multi-level signal, and outputs the
signal to the modulating part as a noise-combined multi-level
signal. At this time, the noise controlling part includes: a noise
generating part that generates the predetermined noise; and a
combining part that combines the noise and the multi-level
signal.
[0014] The multi-level encoding part distributes, in the
noise-combined multi-level signal, the inter signal point intervals
of the multi-level signal so that the signal-to-noise power ratios
calculated between adjoining two signal points are substantially
the same. Moreover, the multi-level encoding part nonuniformly or
nonlinearly distributes, in the noise-combined multi-level signal,
the inter signal point intervals of the multi-level signal so that
the signal-to-noise power ratios calculated between adjoining two
signal points are substantially the same.
[0015] The data transmitting apparatus may be further provided with
an equalizing part that is connected between the multi-level
encoding part and the modulating part and waveform-equalizes the
multi-level signal by predetermined means. Alternatively, the data
transmitting apparatus may be further provided with an equalizing
part that waveform-equalizes the information data by predetermined
means and outputs the waveform-equalized information data to the
multi-level encoding part. Alternatively, in the data transmitting
apparatus, the multi-level encoding part may be further provided
with an equalizing part that is connected between the multi-level
code generating part and the multi-level processing part and
waveform-equalizes the multi-level code sequence by predetermined
means. Alternatively, the data transmitting apparatus may be
further provided with an equalizing part that waveform-equalizes
the modulated signal by predetermined means.
[0016] The equalizing part is a low-pass filter. The low-pass
filter filters a signal component of equal to or lower than half
the signal band of an inputted signal. Alternatively, the
equalizing part may be a high-pass filter that intercepts a
direct-current component included in the signal from an inputted
signal. Alternatively, the equalizing part may be a band-pass
filter that filters a signal component of a predetermined frequency
band from an inputted signal.
[0017] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; a second modulating part that receives the first
modulated signal and information data and generates a second
modulated signal of a predetermined modulation format based on the
information data; and an equalizing part that is connected in the
succeeding stage of the multi-level code generating part and
waveform-equalizes the multi-level code sequence by predetermined
means.
[0018] Alternatively, the data transmitting apparatus may be
provided with: a multi-level code generating part that generates,
from predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that receives information data and generates
a first modulated signal of a predetermined modulation format based
on the information data; a second modulating part that receives the
first modulated signal and the multi-level code sequence and
generates a second modulated signal of a predetermined modulation
format based on the multi-level code sequence; and an equalizing
part that is connected in the succeeding stage of the multi-level
code generating part and waveform-equalizes the multi-level code
sequence by predetermined means.
[0019] Preferably, the data transmitting apparatus may be further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
connected in the preceding stage of the multi-level encoding part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal to the
multi-level encoding part.
[0020] Moreover, the data transmitting apparatus may be further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted between the multi-level encoding part and the modulating
part, amplitude-modulates the multi-level signal based on the
amplitude control signal, and outputs the amplitude-modulated
signal to the modulating part.
[0021] Moreover, the data transmitting apparatus may be further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
connected in the succeeding stage of the modulating part, modulates
the modulated signal in a predetermined modulation format based on
the amplitude control signal, and outputs the modulated signal. At
this time, the amplitude modulating part amplitude-modulates or
intensity-modulates the modulated signal.
[0022] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
level of which varies substantially like a random number; a first
modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; a second modulating part that receives information data
and generates a second modulated signal of a predetermined
modulation format; and a multiplexing part that multiplexes the
first modulated signal and the second modulated signal.
[0023] Preferably, the data transmitting apparatus is further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted in the preceding stage of the second modulating part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal.
[0024] Alternatively, the data transmitting apparatus may be
further provided with: an amplitude control signal generating part
that generates, from predetermined amplitude control key
information, an amplitude control signal the value of which varies
substantially like a random number; and an amplitude modulating
part that is inserted in the preceding stage of the first
modulating part, amplitude-modulates the multi-level code sequence
based on the amplitude control signal, and outputs the
amplitude-modulated signal.
[0025] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; and a second modulating part that receives information
data, modulates the first modulated signal by the information data,
and generates a second modulated signal of a predetermined
modulation format.
[0026] Preferably, the data transmitting apparatus is further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted in the preceding stage of the second modulating part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal.
[0027] Alternatively, the data transmitting apparatus may be
further provided with: an amplitude control signal generating part
that generates, from predetermined amplitude control key
information, an amplitude control signal the value of which varies
substantially like a random number; and an amplitude modulating
part that is inserted in the preceding stage of the first
modulating part, amplitude-modulates the multi-level code sequence
based on the amplitude control signal, and outputs the
amplitude-modulated signal.
[0028] Moreover, the data transmitting apparatus may be further
provided with a base N encoding part that is connected in the
preceding stage of the multi-level encoding part, encodes an
information data group comprising a plurality of pieces of the
information data, into a number in given base system according to a
predetermined processing, and outputs the number to the multi-level
encoding part as a base N encoded signal.
[0029] Preferably, to encode the information data group into the
number in given base system, the base N encoding part varies
multiple levels of the base N encoded signal according to a
combination of logics by the pieces of information data. At this
time, the base N encoding part outputs the base N encoded signal
from the information data group based on the key information.
[0030] Moreover, the base N encoding part may output the base N
encoded signal from the information data group based on key
information different from the above key information. The
multi-level encoding part generates the multi-level signal of any
one of a plurality of predetermined level numbers every
predetermined period.
[0031] Moreover, the data transmitting apparatus may be further
provided with: a synchronous signal generating part that outputs a
predetermined synchronous signal corresponding to the multi-level
signal; and a multi-level processing controlling part that outputs
a multi-level processing control signal that specifies the level
number based on the synchronous signal. The multi-level encoding
part outputs a binary multi-level signal in at least any of the
predetermined periods. In this case, the multi-level encoding part
makes the amplitude of the binary multi-level signal equal to or
larger than the amplitude of the multi-level signal of the maximum
level number of the level numbers, and outputs the binary
multi-level signal. Alternatively, the multi-level encoding part
outputs the information data as the binary multi-level signal.
[0032] Preferably, the data transmitting apparatus changes the
transfer rate of the information data, the multi-level code
sequence or the multi-level signal according to the level number.
Moreover, the data transmitting apparatus increases the transfer
rate of the information data, the multi-level code sequence or the
multi-level signal as the level number decreases.
[0033] Moreover, the present invention is also directed to a data
receiving apparatus that performs cipher communication. To achieve
the above object, the data receiving apparatus according to the
present invention is provided with a demodulating part and a
multi-level decoding part.
The demodulating part demodulates a modulated signal of a
predetermined modulation format, and outputs a multi-level signal.
The multi-level decoding part receives predetermined key
information and the multi-level signal, and outputs information
data. The multi-level decoding part includes: a multi-level code
generating part that generates, from the key information, a
multi-level code sequence the signal level of which varies
substantially like a random number; and a multi-level
discriminating part that discriminates the multi-level signal based
on the multi-level code sequence and outputs the information
data.
[0034] Moreover, the data receiving apparatus may be further
provided with a data inverting part that bit-inverts the
information data outputted from the multi-level decoding part based
on a predetermined pseudo-random number sequence and outputs the
bit-inverted information data.
[0035] Moreover, the multi-level decoding part may further include
an amplitude control signal generating part that generates, from
predetermined amplitude control key information, an amplitude
control signal the value of which varies substantially like a
random number. Moreover, the multi-level discriminating part
discriminates the multi-level signal based on the multi-level code
sequence and the amplitude control signal, and outputs the
information data.
[0036] Preferably, the multi-level discriminating part switches a
threshold value for discriminating the multi-level signal, based on
the level number of the multi-level signal inputted in a
predetermined prescribed period.
[0037] The data receiving apparatus may be further provided with: a
synchronous signal generating part that reproduces a predetermined
synchronous signal corresponding to the multi-level signal; and a
multi-level discrimination controlling part that outputs a
multi-level discrimination control signal that changes the
threshold value at the multi-level discriminating part based on the
synchronous signal. The multi-level decoding part discriminates the
binary multi-level signal at least in any of the predetermined
periods.
[0038] Moreover, the present invention is directed to a data
communication apparatus in which a data transmitting apparatus and
a data receiving apparatus perform cipher communication. To achieve
the above object, in the data communication apparatus according to
the present invention, the data transmitting apparatus is provided
with a multi-level encoding part and a modulating part. The
multi-level encoding part receives predetermined first key
information and information data, and generates a first multi-level
signal the signal level of which varies substantially like a random
number. The modulating part generates a modulated signal of a
predetermined modulation format based on the first multi-level
signal. The multi-level encoding part includes: a first multi-level
code generating part that generates, from the first key
information, a first multi-level code sequence the signal level of
which varies substantially a random number; and a multi-level
processing part that combines the first multi-level code sequence
and the information data according to a predetermined processing so
as to be converted into the first multi-level signal having a level
corresponding to a combination of the signal levels of the first
multi-level code sequence and the information data. The first
multi-level code generating part sets the inter signal point
intervals of the multi-level signal so as to be substantially
uniform.
[0039] Moreover, the data receiving apparatus is provided with a
demodulating part and a multi-level decoding part. The demodulating
part demodulates the modulated signal of the predetermined
modulation format, and outputs a second multi-level signal. The
multi-level decoding part receives predetermined second key
information and the second multi-level signal, and outputs
information data.
[0040] Preferably, the inter signal point intervals of the
multi-level signal are smaller than the amplitude of the
information data included in the multi-level signal. The maximum
amplitude of the multi-level signal is equal to or larger than
twice the amplitude of the information data included in the
multi-level signal.
[0041] The data transmitting apparatus may be further provided with
a data inverting part that bit-inverts the information data based
on a predetermined pseudo-random number sequence and outputs the
bit-inverted information data to the multi-level encoding part.
Moreover, the change rates of the multi-level code sequence and the
information data coincide with each other. The information data is
a binary signal.
[0042] Preferably, as the predetermined processing, the multi-level
processing part generates the multi-level signal by adding the
information data to the multi-level code sequence by using the
multi-level code sequence as the reference level. Moreover, as the
predetermined processing, the multi-level processing part generates
the multi-level signal by level-controlling the multi-level code
sequence according to the information data by using the multi-level
code sequence as the reference level.
[0043] The modulated signal is generated by modulating an
electromagnetic field by the multi-level signal. Moreover, the
modulated signal is generated by modulating a light wave by the
multi-level signal. At this time, the light wave is coherent
light.
[0044] Moreover, the data transmitting apparatus may be further
provided with a noise controlling part that is connected between
the multi-level encoding part and the modulating part, combines a
predetermined noise on the multi-level signal, and outputs the
signal to the modulating part as a noise-combined multi-level
signal. At this time, the noise controlling part includes: a noise
generating part that generates the predetermined noise; and a
combining part that combines the noise and the multi-level
signal.
[0045] The multi-level encoding part distributes, in the
noise-combined multi-level signal, the inter signal point intervals
of the multi-level signal so that the signal-to-noise power ratios
calculated between adjoining two signal points are substantially
the same. Moreover, the multi-level encoding part nonuniformly or
nonlinearly distributes, in the noise-combined multi-level signal,
the inter signal point intervals of the multi-level signal so that
the signal-to-noise power ratios calculated between adjoining two
signal points are substantially the same.
[0046] The data transmitting apparatus may be further provided with
an equalizing part that is connected between the multi-level
encoding part and the modulating part and waveform-equalizes the
multi-level signal by predetermined means. Alternatively, the data
transmitting apparatus may be further provided with an equalizing
part that waveform-equalizes the information data by predetermined
means and outputs the waveform-equalized information data to the
multi-level encoding part. Alternatively, in the data transmitting
apparatus, the multi-level encoding part may be further provided
with an equalizing part that is connected between the multi-level
code generating part and the multi-level processing part and
waveform-equalizes the multi-level code sequence by predetermined
means. Alternatively, the data transmitting apparatus may be
further provided with an equalizing part that waveform-equalizes
the modulated signal by predetermined means.
[0047] The equalizing part is a low-pass filter. The low-pass
filter filters a signal component of equal to or lower than half
the signal band of an inputted signal. Alternatively, the
equalizing part may be a high-pass filter that intercepts a
direct-current component included in the signal from an inputted
signal. Alternatively, the equalizing part may be a band-pass
filter that filters a signal component of a predetermined frequency
band from an inputted signal.
[0048] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; a second modulating part that receives the first
modulated signal and information data and generates a second
modulated signal of a predetermined modulation format based on the
information data; and an equalizing part that is connected in the
succeeding stage of the multi-level code generating part and
waveform-equalizes the multi-level code sequence by predetermined
means.
[0049] Alternatively, the data transmitting apparatus may be
provided with: a multi-level code generating part that generates,
from predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that receives information data and generates
a first modulated signal of a predetermined modulation format based
on the information data; a second modulating part that receives the
first modulated signal and the multi-level code sequence and
generates a second modulated signal of a predetermined modulation
format based on the multi-level code sequence; and an equalizing
part that is connected in the succeeding stage of the multi-level
code generating part and waveform-equalizes the multi-level code
sequence by predetermined means.
[0050] Preferably, the data transmitting apparatus may be further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
connected in the preceding stage of the multi-level encoding part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal to the
multi-level encoding part.
[0051] Moreover, the data transmitting apparatus may be further
provided with an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted between the multi-level encoding part and the modulating
part, amplitude-modulates the multi-level signal based on the
amplitude control signal, and outputs the amplitude-modulated
signal to the modulating part.
[0052] Moreover, the data transmitting apparatus may be further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
connected in the succeeding stage of the modulating part, modulates
the modulated signal in a predetermined modulation format based on
the amplitude control signal, and outputs the modulated signal. At
this time, the amplitude modulating part amplitude-modulates or
intensity-modulates the modulated signal.
[0053] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
level of which varies substantially like a random number; a first
modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; a second modulating part that receives information data
and generates a second modulated signal of a predetermined
modulation format; and a multiplexing part that multiplexes the
first modulated signal and the second modulated signal.
[0054] Preferably, the data transmitting apparatus is further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted in the preceding stage of the second modulating part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal.
[0055] Alternatively, the data transmitting apparatus may be
further provided with: an amplitude control signal generating part
that generates, from predetermined amplitude control key
information, an amplitude control signal the value of which varies
substantially like a random number; and an amplitude modulating
part that is inserted in the preceding stage of the first
modulating part, amplitude-modulates the multi-level code sequence
based on the amplitude control signal, and outputs the
amplitude-modulated signal.
[0056] Moreover, the data transmitting apparatus may be provided
with: a multi-level code generating part that generates, from
predetermined key information, a multi-level code sequence the
signal level of which varies substantially like a random number; a
first modulating part that generates a first modulated signal of a
predetermined modulation format based on the multi-level code
sequence; and a second modulating part that receives information
data, modulates the first modulated signal by the information data,
and generates a second modulated signal of a predetermined
modulation format.
[0057] Preferably, the data transmitting apparatus is further
provided with: an amplitude control signal generating part that
generates, from predetermined amplitude control key information, an
amplitude control signal the value of which varies substantially
like a random number; and an amplitude modulating part that is
inserted in the preceding stage of the second modulating part,
amplitude-modulates the information data based on the amplitude
control signal, and outputs the amplitude-modulated signal.
[0058] Alternatively, the data transmitting apparatus may be
further provided with an amplitude control signal generating part
that generates, from predetermined amplitude control key
information, an amplitude control signal the value of which varies
substantially like a random number; and an amplitude modulating
part that is inserted in the preceding stage of the first
modulating part, amplitude-modulates the multi-level code sequence
based on the amplitude control signal, and outputs the
amplitude-modulated signal.
[0059] Moreover, the data transmitting apparatus may be further
provided with a base N encoding part that is connected in the
preceding stage of the multi-level encoding part, encodes an
information data group comprising a plurality of pieces of the
information data, into a number in given base system according to a
predetermined processing, and outputs the number to the multi-level
encoding part as a base N encoded signal.
[0060] Preferably, to encode the information data group into the
number in given base system, the base N encoding part varies
multiple levels of the base N encoded signal according to a
combination of logics by the pieces of information data. At this
time, the base N encoding part outputs the base N encoded signal
from the information data group based on the key information.
Moreover, the base N encoding part outputs the base N encoded
signal from the information data group based on key information
different from the key information. The multi-level encoding part
generates the multi-level signal of any one of a plurality of
predetermined level numbers every predetermined period.
[0061] Moreover, the data transmitting apparatus may be further
provided with: a synchronous signal generating part that outputs a
predetermined synchronous signal corresponding to the multi-level
signal; and a multi-level processing controlling part that outputs
a multi-level processing control signal that specifies the level
number based on the synchronous signal. The multi-level encoding
part outputs a binary multi-level signal in at least any of the
predetermined periods. In this case, the multi-level encoding part
makes the amplitude of the binary multi-level signal equal to or
larger than the amplitude of the multi-level signal of the maximum
level number of the level numbers, and outputs the binary
multi-level signal. Alternatively, the multi-level encoding part
outputs the information data as the binary multi-level signal.
[0062] Preferably, the data transmitting apparatus changes the
transfer rate of the information data, the multi-level code
sequence or the multi-level signal according to the level number.
Moreover, the data transmitting apparatus increases the transfer
rate of the information data, the multi-level code sequence or the
multi-level signal as the level number decreases.
EFFECT OF THE INVENTION
[0063] The data communication apparatus according to the present
invention encodes and modulates the information data into the
multi-level signal based on the key information, transmits the
multi-level signal, demodulates and decodes the received
multi-level signal based on the same key information, and optimizes
the signal-to-noise power ratios of the multi-level signal to
thereby significantly increase the time required for the analysis
of ciphers, so that a high-stealthiness data communication
apparatus based on an astronomical amount of calculations can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] FIG. 1 is a block diagram showing of the structure of a data
communication apparatus according to a first embodiment of the
present invention.
[0065] FIG. 2 is a schematic view explaining the waveform of a
transmission signal of the data communication apparatus according
to the first embodiment of the present invention.
[0066] FIG. 3 is a schematic view explaining the waveform of a
transmission signal of the data communication apparatus according
to the first embodiment of the present invention.
[0067] FIG. 4 is a schematic view explaining the transmission
signal quality of the data communication apparatus according to the
first embodiment of the present invention.
[0068] FIG. 5 is a block diagram showing the structure of a data
communication apparatus according to a second embodiment of the
present invention.
[0069] FIG. 6 is a block diagram showing of the structure of a data
communication apparatus according to a third embodiment of the
present invention.
[0070] FIG. 7 is a schematic view explaining transmission signal
parameters of a data communication apparatus according to a fourth
embodiment of the present invention.
[0071] FIG. 8 is a view showing an example of the eye pattern of
information data 10.
[0072] FIG. 9 is a view showing an example of the eye pattern of a
multi-level code sequence 12.
[0073] FIG. 10 is a view showing an example of the eye pattern of a
multi-level signal 13.
[0074] FIG. 11 is a view showing an example of a noise signal.
[0075] FIG. 12 is a view showing an example of the eye pattern of a
modulated signal 14 when noise is combined.
[0076] FIG. 13 is a view showing an example of the eye pattern of
the information data 10.
[0077] FIG. 14 is a view showing an example of the eye pattern of
the multi-level code sequence 12.
[0078] FIG. 15 is a view showing an example of the eye pattern of
the multi-level signal 13.
[0079] FIG. 16 is a view showing an example of the noise
signal.
[0080] FIG. 17 is a view showing an example of the eye pattern of
the modulated signal 14 on which the noise signal is combined.
[0081] FIG. 18 is a view showing the relation between a multi-level
signal 15 and the determination threshold value of the multi-level
signal 15.
[0082] FIG. 19 is a view showing an example of the eye pattern of
the multi-level signal 15.
[0083] FIG. 20A is a block diagram showing an example of the
structure of a data communication apparatus according to a sixth
embodiment of the present invention.
[0084] FIG. 20B is a block diagram showing another example of the
structure of the data communication apparatus according to the
sixth embodiment of the present invention.
[0085] FIG. 20C is a block diagram showing another example of the
structure of the data communication apparatus according to the
sixth embodiment of the present invention.
[0086] FIG. 20D is a block diagram showing another example of the
structure of the data communication apparatus according to the
sixth embodiment of the present invention.
[0087] FIG. 21 is a view showing an example of the waveform of an
equalized multi-level signal 24 outputted by an equalizing part
115.
[0088] FIG. 22 is a view explaining the discrimination of an
equalized multi-level signal 25.
[0089] FIG. 23 is a block diagram showing an example of the
structure of a data communication apparatus according to a seventh
embodiment of the present invention.
[0090] FIG. 24 is a block diagram showing another example of the
structure of the data communication apparatus according to the
seventh embodiment of the present invention.
[0091] FIG. 25 is a block diagram showing an example of the
structure of a data communication apparatus according to an eighth
embodiment of the present invention.
[0092] FIG. 26 is a schematic view for explaining the signal
waveforms of parts of the data communication apparatus according to
the eighth embodiment of the present invention.
[0093] FIG. 27 is a schematic view explaining the transmission
signal quality of the data communication apparatus according to the
eighth embodiment of the present invention.
[0094] FIG. 28 is a block diagram showing a second example of the
structure of the data communication apparatus according to the
eighth embodiment of the present invention.
[0095] FIG. 29 is a block diagram showing a third example of the
structure of the data communication apparatus according to the
eighth embodiment of the present invention.
[0096] FIG. 30 is a block diagram showing a fourth example of the
structure of the data communication apparatus according to the
eighth embodiment of the present invention.
[0097] FIG. 31 is a block diagram showing a fifth example of the
structure of the data communication apparatus according to the
eighth embodiment of the present invention.
[0098] FIG. 32A is a block diagram showing an example of the
structure of a data communication apparatus according to a ninth
embodiment of the present invention.
[0099] FIG. 32B is a block diagram showing another example of the
structure of the data communication apparatus according to the
ninth embodiment of the present invention.
[0100] FIG. 33A is a block diagram showing another example of the
structure of the data communication apparatus according to the
ninth embodiment of the present invention.
[0101] FIG. 33B is a block diagram showing another example of the
structure of the data communication apparatus according to the
ninth embodiment of the present invention.
[0102] FIG. 34 is a block diagram showing the structure of a data
communication apparatus according to a tenth embodiment of the
present invention.
[0103] FIG. 35 is a view showing examples of the waveform of
information data group inputted to a base N encoding part 131.
[0104] FIG. 36 is a view showing an example of the waveform of a
base N encoded signal 52 outputted from the base N encoding part
131.
[0105] FIG. 37 is a view showing an example of the waveform of the
multi-level signal 13 outputted from a multi-level processing part
111b.
[0106] FIG. 38 is a view explaining an example of the
discrimination of the multi-level signal 15 by a multi-level
discriminating part 212b.
[0107] FIG. 39 is a view showing the waveform of the multi-level
signal 15 on which noise is combined.
[0108] FIG. 40 is a block diagram showing an example of the
structure of a data communication apparatus according to an
eleventh embodiment of the present invention.
[0109] FIG. 41 is a block diagram showing another example of the
structure of the data communication apparatus according to an
eleventh embodiment of the present invention.
[0110] FIG. 42 is a block diagram showing the structure of a data
communication apparatus according to a twelfth embodiment of the
present invention.
[0111] FIG. 43 is a schematic view for explaining the signal
waveform outputted from a multi-level encoding part 111.
[0112] FIG. 44 is a block diagram showing the structure of a data
communication apparatus according to a thirteenth embodiment of the
present invention.
[0113] FIG. 45 is a schematic view explaining the transmission
signal waveform of the data communication apparatus according to
the thirteenth embodiment of the present invention.
[0114] FIG. 46 is a block diagram showing the structure of a data
communication apparatus according to a fourteenth embodiment of the
present invention.
[0115] FIG. 47 is a block diagram showing the structure of a data
communication apparatus according to a fifteenth embodiment of the
present invention.
[0116] FIG. 48A is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0117] FIG. 48B is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0118] FIG. 48C is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0119] FIG. 49A is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0120] FIG. 49B is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0121] FIG. 49C is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0122] FIG. 50A is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0123] FIG. 50B is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0124] FIG. 50C is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0125] FIG. 51A is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0126] FIG. 51B is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0127] FIG. 51C is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0128] FIG. 52A is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0129] FIG. 52B is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0130] FIG. 52C is a block diagram showing an example of the
structure of a data communication apparatus in which the
characteristics of some of the embodiments of the present invention
are combined.
[0131] FIG. 53 is a block diagram showing the structure of the
conventional data communication apparatus.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0132] 10, 18 information data [0133] 11, 16, 38, 39, 91, 96, 99
key information [0134] 12, 17 multi-level code sequence [0135] 13,
15 multi-level signal [0136] 14, 41, 42, 94 modulated signal [0137]
24, 25 equalized multi-level signal [0138] 27 equalized multi-level
code sequence [0139] 35, 40 amplitude control signal [0140] 36
amplitude-modulated information data [0141] 37 amplitude-modulated
multi-level signal [0142] 110 transmission path [0143] 111
multi-level encoding part [0144] 111a first multi-level code
generating part [0145] 111b multi-level processing part [0146] 112,
122, 123, 912 modulating part [0147] 113 first data inverting part
[0148] 114 noise controlling part [0149] 114a noise generating part
[0150] 114b combining part [0151] 115 equalizing part [0152] 116,
122 first modulating part [0153] 117, 123 second modulating part
[0154] 120 amplitude controlling part [0155] 120a first amplitude
control signal generating part [0156] 120b amplitude modulating
part [0157] 124 multiplexing part [0158] 131, 132 base N encoding
part [0159] 134 synchronous signal generating part [0160] 135
multi-level processing controlling part [0161] 211, 914, 916
demodulating part [0162] 212, 218 multi-level decoding part [0163]
212a second multi-level signal generating part [0164] 212b
multi-level discriminating part [0165] 212c second amplitude
control signal generating part [0166] 213 second data inverting
part [0167] 220, 221 base N decoding part [0168] 233 synchronous
signal reproducing part [0169] 234 multi-level discrimination
controlling part [0170] 236 sub demodulating part [0171] 237
discriminating part [0172] 911 encoding part [0173] 915, 917
decoding part [0174] 10101 to 19108 data transmitting apparatus
[0175] 10201 to 19207 data receiving apparatus
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[0176] FIG. 1 is a block diagram showing the structure of a data
communication apparatus according to a first embodiment of the
present invention. In FIG. 1, the data communication apparatus
according to the first embodiment is constituted by connecting a
data transmitting apparatus 10101 and a data receiving apparatus
10201 via a transmission path 110. The data transmitting apparatus
10101 has a multi-level encoding part 111 and a modulating part
112. The multi-level encoding part 111 includes a first multi-level
code generating part 111a and a multi-level processing part 111b.
The data receiving apparatus 10201 has a demodulating part 211 and
a multi-level decoding part 212. The multi-level decoding part 212
includes a second multi-level code generating part 212a and a
multi-level discriminating part 212b. As the transmission path 110,
a metal line such as a LAN cable or a coaxial cable, or an optical
waveguide such as an optical fiber cable may be used. The
transmission path 110 is not limited to a wired cable such as a LAN
cable, and may be a free space that allows radio signals to
propagate therethrough.
[0177] FIGS. 2 and 3 are schematic views for explaining the
waveforms of the modulated signals outputted from the modulating
part 112. Hereinafter, the operation of the data communication
apparatus according to the first embodiment will be explained by
using FIGS. 1 to 3.
[0178] The first multi-level code generating part 111a generates a
multi-level code sequence 12 (FIG. 2(b)) the signal level of which
varies substantially like a random number, based on predetermined
first key information 11. The multi-level processing part 111b
receives the multi-level code sequence 12 and information data 10
(FIG. 2(a)), and combines these signals by a predetermined
procedure to thereby generate a multi-level signal 13 (FIG. 2(c))
having a level uniquely corresponding to a combination of the
levels of the signals. For example, when the level of the
multi-level code sequence 12 varies like c1, c5, c3 and c4 for the
time slots t1, t2, t3 and t4, with the multi-level code sequence 12
as the bias level, the multi-level processing part 111b adds the
information data 10 to thereby generate the multi-level signal 13
the level of which varies like L1, L8, L6 and L4.
[0179] Here, as shown in FIG. 3, the amplitude of the information
data 10 will be referred to as "information amplitude," the total
amplitude of the multi-level signal 13, as "multi-level signal
amplitude," the level combinations (L1, L4), (L2, L5), (L3, L6),
(L4, L7), and (L5, L8) that the multi-level signal 13 can take in
correspondence with the levels c1, c2, c3, c4, and c5 of the
multi-level code sequence 12, as a first to a fifth "bases," and
the shortest inter signal point interval of the multi-level signal
13, as "step width."
[0180] The modulating part 112 modulates the multi-level signal 13
in a predetermined modulation format, and sends it out to the
transmission path 110 as a modulated signal 14. The demodulating
part 211 demodulates the modulated signal 14 transmitted via the
transmission path 110, and reproduces a multi-level signal 15. The
second multi-level code generating part 212a previously shares
second key information 16 the same as the first key information 11,
and generates a multi-level code sequence 17 corresponding to the
multi-level code sequence 12 based on the second key information
16. The multi-level discriminating part 212b performs the
discrimination (binary determination) of the multi-level signal 15
with the multi-level code sequence 17 as the threshold value, and
reproduces information data 18. Here, the modulated signal 14 of
the predetermined modulation format transmitted and received via
the transmission path 110 by the modulating part 112 and the
demodulating part 211 is obtained by modulating an electromagnetic
wave (electromagnetic field) or a light wave by the multi-level
signal 13.
[0181] The multi-level processing part 111b may generate the
multi-level signal 13 by any method as well as generates the
multi-level signal 13 by the addition of the multi-level code
sequence 12 and the information data 10a as described above. For
example, the multi-level processing part 111b may generate the
multi-level signal 13 by amplitude-modulating the level of the
multi-level code sequence 12 based on the information data 10 or
may generate the multi-level signal 13 by successively reading the
level of the multi-level signal 13 corresponding to the combination
of the information data 10 and the multi-level code sequence 12
from a memory where the levels of the multi-level signal 13 are
prestored.
[0182] While the level of the multi-level signal 13 is represented
in eight steps in FIGS. 2 and 3, the level of the multi-level
signal 13 is not limited to this representation. While the
information amplitude is represented as three times or an integral
multiple of the step width of the multi-level signal 13, the
information amplitude is not limited to this representation. The
information amplitude may be any integral multiple of the step
width of the multi-level signal 13 or is not necessarily an
integral multiple. Further, while in relation thereto, the levels
(bias levels) of the multi-level code sequence 12 are disposed so
as to be substantially at the center of the levels of the
multi-level signal 13 in FIGS. 2 and 3, the disposition of the
levels of the multi-level code sequence 12 are not limited thereto.
The levels of the multi-level code sequence 12 are not necessarily
substantially at the center of the levels of the multi-level signal
13 or may coincide with the levels of the multi-level signal 13.
While it is premised that the change rates of the multi-level code
sequence 12 and the information data 10 are equal to each other and
in synchronization, the present invention is not limited thereto;
the change rates may be such that one is higher (or lower) than the
other or may be asynchronous to each other.
[0183] Next, wiretapping of the modulated signal 14 by a third
party will be explained. It is considered that the third party
decrypts the modulated signal by using a structure corresponding to
the data receiving apparatus 10201 that the authorized user has or
a higher-performance data receiving apparatus (wiretapper data
receiving apparatus). The wiretapper data receiving apparatus
reproduces the multi-level signal by demodulating the modulated
signal 14. However, since the key information is not shared between
the wiretapper data receiving apparatus and the data transmitting
apparatus 10101, the wiretapper data receiving apparatus cannot
generate the multi-level code sequence from the key information
like the data receiving apparatus 10201. For this reason, the
wiretapper data receiving apparatus cannot perform the binary
determination of the multi-level signal with reference to the
multi-level code sequence.
[0184] Wiretapping considered to be performed in such a case
includes simultaneously discriminating all the levels of the
multi-level signal (generally called "brute force attack"). That
is, the wiretapper data receiving apparatus is provided with
threshold values for all the inter signal point intervals that the
multi-level signal can take, performs the simultaneous
determination of the multi-level signal, and analyzes the result of
the determination to thereby try to extract the correct key
information or information data. For example, the wiretapper data
receiving apparatus tries to extract the correct key information or
information data by performing the multi-level determination on the
multi-level signal by using, as the threshold values, the levels
c0, c1, c2, c3, c4, c5 and c6 of the multi-level code sequence 12
shown in FIG. 2.
[0185] However, noise is caused by various factors in actual
transmission systems, and by this noise being combined on the
modulated signal, the level of the multi-level signal fluctuates
with time and momentarily as shown in FIG. 4. In such a case, while
the SN ratio (signal-to-noise intensity ratio) of the signal to be
determined (multi-level signal) determined by the authorized
receiver (data receiving apparatus 10201) depends on the ratio
between the information amplitude and the noise amount of the
multi-level signal, the SN ratio of the signal to be determined
(multi-level signal) determined by the wiretapper data receiving
apparatus depends on the ratio between the step width and the noise
amount of the multi-level signal.
[0186] For this reason, under a condition where the noise level of
the signal to be determined is the same, in the wiretapper
receiving apparatus, the SN ratio of the signal to be determined is
relatively low, so that the transmission characteristic (error
rate) is deteriorated. That is, by using this characteristic, the
data communication apparatus can make wiretapping difficult by
inducing discrimination errors in the third party's brute force
attack using all the threshold values. In particular, in the data
communication apparatus, by setting the step width of the
multi-level signal so as to be on the same order as or lower than
the noise amplitude (the spread of the noise intensity
distribution), the multi-level determination by third parties is
made virtually impossible, so that ideal wiretapping prevention can
be realized.
[0187] As the noise combined on the signal to be determined (the
multi-level signal, or the modulated signal), when an
electromagnetic wave such as a radio signal is used as the
modulated signal, the thermal noise (Gaussian noise) that the
spatial field, an electronic part or the like has may be used, and
when a light wave is used, a photon number fluctuation (quantum
noise) caused when photons are generated may be used in addition to
the thermal noise. In particular, since signal processing such as
recording and duplicating cannot be performed on the signals using
the quantum noise, in the data communication apparatus, by setting
the step width of the multi-level signal with reference to the
noise amount, wiretapping by third parties is made impossible, so
that the absolute safety of the data communication can be
ensured.
[0188] As described above, according to the present embodiment, a
safe data communication apparatus can be provided in which when the
information data to be transmitted is encoded as a multi-level
signal, by appropriately setting the inter signal point intervals
of the multi-level signal with respect to the noise amount, a
decisive deterioration is caused in the reception signal wiretapped
by a third party to thereby make it difficult to decrypt and decode
the reception signal.
Second Embodiment
[0189] FIG. 5 is a block diagram showing the structure of a data
communication apparatus according to a second embodiment of the
present invention. In FIG. 5, in the data communication apparatus
according to the second embodiment, compared with the data
communication apparatus according to the first embodiment (FIG. 1),
a data transmitting apparatus 10102 further has a first data
inverting part 113, and a data receiving apparatus 10202 further
has a second data inverting part 213. Hereinafter, the data
communication apparatus according to the second embodiment will be
explained. Since the structure of the present embodiment
corresponds to that of the first embodiment (FIG. 1), the blocks
performing the same operations are denoted by the same reference
characters, and descriptions thereof are omitted.
[0190] The first data inverting part 113 does not fix the
correspondence between the information of "0" and "1" that the
information data has, and the Low level and the High level, and
changes the correspondence substantially in a random fashion by a
predetermined procedure. For example, like the multi-level encoding
part 111, the first data inverting part 113 performs an exclusive
OR operation with a random number series (pseudo-random number
sequence) generated based on a predetermined initial value, and
outputs the result of the operation to the multi-level encoding
part 111. For the data outputted from the multi-level decoding part
212, the second data inverting part 213 changes the correspondence
between "0" and "1", and "Low and High" in a procedure opposite to
that of the first data inverting part 113. For example, the second
data inverting part 213 shares the same initial value as the
initial value that the first data inverting part 113 has, performs
an exclusive OR operation with the bit-inverted random number
series generated based on this, and reproduces the result as the
information data.
[0191] As described above, according to the present invention, a
safer data communication apparatus can be provided in which by
inverting the information data to be transmitted substantially in a
random fashion, the complexity of the multi-level signal as a
cipher is increased to make the decryption and decoding by third
parties more difficult.
Third Embodiment
[0192] FIG. 6 is a block diagram showing the structure of a data
communication apparatus according to a third embodiment of the
present invention. In FIG. 6, in the data communication apparatus
according to the third embodiment, compared with the data
communication apparatus according to the first embodiment (FIG. 1),
a data communication apparatus 10103 further has a noise
controlling part 114. The noise controlling part 114 includes a
noise generating part 114a and a combining part 114b. Hereinafter,
the data communication apparatus according to the third embodiment
will be explained. Since the structure of the present embodiment
corresponds to that of the first embodiment (FIG. 1), the blocks
performing the same operations are denoted by the same reference
characters, and descriptions thereof are omitted.
[0193] The noise generating part 114a generates a predetermined
noise. The combining part 114b combines the multi-level signal 13
and the noise, and outputs the resultant signal to the modulating
part 112. That is, the level fluctuation of the multi-level signal
13 described in FIG. 4 is deliberately caused, and the SN ratio of
the multi-level signal 13 is controlled to an arbitrary value to
thereby control the SN ratio of the signal to be determined
inputted to the multi-level discriminating part 212b. As mentioned
above, as the noise caused by the noise generating part 114a, the
thermal noise, the quantum noise or the like is used. The
multi-level signal where the noise is combined (superimposed) will
be called a noise-combined multi-level signal.
[0194] As described above, according to the present embodiment, a
safer data communication apparatus can be provided in which by
encoding the information data to be transmitted as the multi-level
signal and arbitrarily controlling the SN ratio thereof, a decisive
deterioration is deliberately caused in the reception signal
quality in wiretapping by third parties to thereby make the
decryption and decoding of the reception signal more difficult.
Fourth Embodiment
[0195] FIG. 7 is a schematic view explaining transmission signal
parameters of a data communication apparatus according to a fourth
embodiment of the present invention. The data communication
apparatus according to the fourth embodiment has a structure
corresponding to the structure of the first embodiment (FIG. 1) or
the third embodiment (FIG. 6). Hereinafter, the data communication
apparatus according to the fourth embodiment of the present
invention will be explained by using FIG. 7.
[0196] Referring to FIG. 1 or FIG. 6, the multi-level encoding part
111 sets the step widths (S1 to S7) of the multi-level signal 13 in
accordance with the fluctuation amount of each level (that is, the
distribution of the intensity of the noise combined on each level)
as shown in FIG. 7. Specifically, the multi-level encoding part 111
distributes the intervals between the two adjoining signal points
of the signal to be determined inputted to the multi-level
discriminating part 212b so that the SN ratios depending on the
inter signal point intervals substantially coincide. When the noise
amounts combined on the levels are the same, the step widths are
set to be the same.
[0197] When an optical intensity modulated signal with a
semiconductor laser (LD) as the light source is assumed as the
modulated signal outputted from the modulating part 112, the
fluctuation width (noise amount) varies depending on the level of
the multi-level signal inputted to the LD. This is attributed to
the fact that the semiconductor laser emits light based on the
principle of stimulated emission with spontaneously emitted light
as the "seed light," and the noise amount thereof is defined by the
relative ratio of the spontaneously emitted light amount to the
stimulatingly emitted light amount. Since the higher the pumping
rate (corresponding to the bias current injected into the LD) is,
the higher the ratio of the stimulatingly emitted light amount is,
the noise amount thereof is small, and conversely, the lower the
pumping rate is, the higher the ratio of the spontaneously emitted
light amount is and the larger the noise amount is. Therefore, by
nonlinearly setting the step widths so as to be large in areas
where the level of the multi-level signal is low and to be small in
areas where the level is high as shown in FIG. 7, the SN ratios of
the intervals between the adjoining signal points of the signal to
be determined are made to coincide.
[0198] Even when an optically modulated signal is used as the
modulated signal, under a condition where the noise due to the
spontaneously emitted light and the thermal noise used for the
optical receiver are sufficiently low, the SN ratio of the
reception signal is determined mainly by shot noise. Under this
condition, since the higher the level of the multi-level signal is,
the larger the noise amount is, by setting the step width so as to
be small in areas where the level of the multi-level signal is low
and to be large in areas where the level is high conversely to the
case of FIG. 7, the SN ratios of the intervals between the
adjoining signal points of the signal to be determined are made to
coincide.
[0199] As described above, according to the present embodiment, a
safer data communication apparatus can be provided in which by
encoding the information data to be transmitted as the multi-level
signal and substantially uniformly disposing the signal points
within the multi-level signal amplitude or substantially uniformly
setting the SN ratios of the intervals between the adjoining signal
points irrespective of the momentary level, the reception signal
quality in wiretapping by third parties is always deteriorated to
make the decryption and decoding of the reception signal more
difficult.
Fifth Embodiment
[0200] In the first embodiment, a data communication apparatus is
explained in which the multi-level signal is generated by combining
the information data to be transmitted and the multi-level code
sequence generated from the information key. In the fifth
embodiment shown below, a case will be explained where a
multi-level signal the binary determination by wiretapping by third
parties of which is significantly difficult is generated.
[0201] First, a problem that arises with the first embodiment will
be described by using FIGS. 1 and 8 to 12. In the explanation that
follows, the "inter signal point interval" refers to the difference
between an arbitrary signal level that the multi-level signal or
the multi-level code sequence can take and the adjoining signal
level. FIG. 8 is a view showing an example of the eye pattern of
the information data 10 the information amplitude of which is "12."
FIG. 9 is a view showing an example of the eye pattern of the
multi-level code sequence 12 outputted form the first multi-level
code generating part 111a. In the multi-level code sequence 12
shown in FIG. 9, the inter signal point intervals are substantially
uniformly disposed. Moreover, the multi-level code sequence 12
shown in FIG. 9 is normalized by the inter signal point intervals,
and the number of levels is "4" and the largest amplitude is
"3."
[0202] The multi-level processing part 111b combines the
information data 10 shown in FIG. 8 and the multi-level code
sequence 12 shown in FIG. 9 by addition, and outputs the
multi-level signal 13 having the eye pattern shown in FIG. 10. In
the multi-level signal 13 shown in FIG. 10, the multi-level signal
amplitude is "15," the information amplitude is "12," and the
number of levels is "8." In the multi-level signal 13 shown in FIG.
10, an inter signal point interval a is larger than the other inter
signal point intervals. That is, a condition occurs where the inter
signal point intervals of the multi-level signal 13 are not
uniform.
[0203] The multi-level signal 13 shown in FIG. 10 is modulated into
the modulated signal 14 by the modulating part 112, and transmitted
to a receiving part 11102. A noise signal such as thermal noise or
quantum noise, for example, as shown in FIG. 11 is combined on the
modulated signal 14. FIG. 12 is a view showing the eye pattern of
the modulated signal 14 when the noise signal shown in FIG. 11 is
combined on the modulated signal 14.
[0204] Wiretapping of the modulated signal 14 by a third party will
be explained. The third party intercepts the modulated signal 14
shown in FIG. 12, and demodulates the modulated signal 14 into a
multi-level signal. The third party tries the binary determination
on the modulated signal 14 shown in FIG. 12. In the modulated
signal 14 shown in FIG. 12, the inter signal point interval a is
larger than the amplitude of the noise signal combined on the
modulated signal 14. Therefore, the third party can obtain an SN
ratio sufficient for the binary determination of the multi-level
signal. Consequently, the third party can easily decode the
information data 10 from the modulated signal 14 without performing
a brute force attack.
[0205] As described above, in the first embodiment, when the inter
signal point intervals of the multi-level signal are not
substantially uniform, wiretapping of the information data is
easily performed by third parties. The fifth embodiment solves this
problem.
[0206] The data communication apparatus according to the fifth
embodiment of the present invention has a similar structure to the
data communication apparatus according to the first embodiment
(FIG. 1). Hereinafter, the data communication apparatus according
to the fifth embodiment of the present invention will be explained
by using FIGS. 1 and 13 to 19. FIG. 13 is a view showing an example
of the eye pattern of the information data 10 the information
amplitude of which is "7." The first multi-level code generating
part 111a performs a conversion from the first key information 11
to the multi-level code sequence 12. The first multi-level code
generating part 111a is constituted by using a random number
generator such as a linear feedback register (LFSR). FIG. 14 is a
view showing an example of the eye pattern of the multi-level code
sequence 12 outputted from the first multi-level code generating
part 111a. In the multi-level code sequence 12 shown in FIG. 14,
the inter signal point intervals are substantially uniformly
disposed. Moreover, the multi-level code sequence 12 shown in FIG.
14 is normalized by the inter signal point intervals, and the
number of levels is "10" and the largest amplitude is "9." At this
time, it is important that the maximum amplitude of the multi-level
code sequence 12 shown in FIG. 14 be larger than the information
amplitude of the information data 10 shown in FIG. 13.
[0207] The information data 10 shown in FIG. 13 and the multi-level
code sequence 12 shown in FIG. 14 are inputted to the multi-level
processing part 111b. The multi-level processing part 111b adds the
amplitudes of the information data 10 and the multi-level code
sequence 12, and outputs the multi-level signal 13. FIG. 15 shows
the eye pattern of the multi-level signal 13 outputted from the
multi-level processing part 111b. The multi-level signal amplitude
of the multi-level signal 13 shown in FIG. 15 is "16." The
multi-level signal amplitude of the multi-level signal 13
corresponds to the sum of the maximum amplitude of the information
data 10 shown in FIG. 13 and the maximum amplitude of the
multi-level code sequence 12 shown in FIG. 14. At this time, since
the multi-level signal amplitude is "16," the amplitude of the
multi-level signal 13 shown in FIG. 15 is equal to or larger than
twice the information amplitude of the information data 10 shown in
FIG. 13. As shown in FIG. 15, all the inter signal point intervals
of the multi-level signal 13 are "1." Consequently, the multi-level
signal 13 shown in FIG. 15 is substantially uniform unlike the
multi-level signal 13 shown in FIG. 13. The inter signal point
intervals of the multi-level signal 13 shown in FIG. 15 are all
smaller than the information amplitude "7" of the multi-level
signal.
[0208] The multi-level signal 13 is modulated by the modulating
part 112, and transferred to the receiving part 11102 via the
transmission path 110. At this time, for example, the noise signal
shown in FIG. 16 is combined on the modulated signal 14. FIG. 17 is
a view showing an example of the eye pattern of the modulated
signal 14 on which the noise signal is combined. Since the
amplitude of the noise signal is larger than the inter signal point
intervals of the modulated signal 14 as shown in FIG. 17, the
modulated signal 14 is in a condition where a signal of an
arbitrary level and the signal of the adjoining level cannot be
distinguished from each other.
[0209] The receiving part 11102 receives the modulated signal 14
via the transmission path 110. The demodulating part 211
demodulates the modulated signal 14 to generate the multi-level
signal 15, and inputs it to the multi-level discriminating part
212b. The second multi-level code generating part 212a generates
the multi-level code sequence 17 by using the second key
information 16, and inputs it to the multi-level discriminating
part 212b. The multi-level code sequence 17 serves as the
discrimination threshold value for the binary determination of the
multi-level signal 15. The multi-level discriminating part 212b
performs the binary determination of the multi-level signal 15 by
using the multi-level code sequence 17. Consequently, the
multi-level signal 15 is decoded into the information data 18 of a
binary signal as shown in FIG. 13. FIG. 18 is a view showing the
relation between the information amplitude of the multi-level
signal 15 inputted to the multi-level discriminating part 212b and
the discrimination threshold value for the decoding by the
multi-level discriminating part 212b. The SN ratio of the modulated
signal 14 to the information amplitude is deteriorated by the noise
signal shown in FIG. 18. However, the amplitude of the noise signal
does not exceed the discrimination threshold value of the
information amplitude of the modulated signal. For this reason, in
the receiving part 11102, the multi-level discriminating part 212b
can perform the discrimination and reproduction of the information
data.
[0210] Next, a case will be considered where as wiretapping, a
third party intercepts the modulated signal 14 shown in FIG. 17,
correctly reproduces the modulated signal 14 into the multi-level
signal 15, and decodes the multi-level signal 15 into the
information data 18. The third party cannot find the discrimination
threshold value for performing the binary determination from the
modulated signal 14 shown in FIG. 17 like the modulated signal 14
shown in FIG. 12. For this reason, the third party tries to decode
the multi-level signal 15 by extracting the key information within
a limited time by performing a round-robin computation using all
the combinations of multi-level code sequence or a special
analysis.
[0211] A threshold value for discriminating the signal levels of
the modulated signal 14 is used as the determination threshold
value. FIG. 19 is a view showing the relation between the modulated
signal 14 and the determination threshold value of the modulated
signal 14. Since the first key information 11 is not shared between
the third party and a transmitting part 11101, the third party
cannot generate the multi-level code sequence 12 based on the first
key information 11. Therefore, it is necessary for the third party
to perform the signal level discrimination of the multi-level
signal by using all the determination threshold values shown in
FIG. 19. However, the inter signal point intervals of the
multi-level signal are smaller than the information amplitude of
the information data. For this reason, it is difficult for the
third party to determine the determination threshold value.
Further, since the discrimination between the signals of the
adjoining signal levels cannot be made because of the noise signal
combined on the modulated signal 14 as shown in FIG. 19, the third
party cannot accurately perform the determination of the inter
signal point intervals of the multi-level signal. Consequently, the
third party cannot avoid a determination error of the level of the
multi-level signal when determining the signal level of the
multi-level signal. Further, since the third party tries the binary
determination on the multi-level signal obtained by the erroneous
determination, the third party cannot decode it into the correct
information data.
[0212] As described above, in the invention according to the
present invention, a multi-level signal is generated that is twice
the information amplitude of the inputted information data and in
which all the inter signal point intervals of the multi-level
signal are substantially uniform. This multi-level signal makes it
difficult for third parties to decode the information signal by the
binary determination of the multi-level signal and accurately
demodulate or determine the modulated signal. Consequently, the
invention according to the present embodiment is capable of
providing a transmitting apparatus that enables the realization of
information transmission with high stealthiness.
[0213] While in the present embodiment, the multi-level signal 13
is generated by the addition of the information data 10 and the
multi-level code sequence 12 by the multi-level processing part
111b, the multi-level signal 13 may be generated by a different
method. For example, a table on the memory may be referred to.
Sixth Embodiment
[0214] FIG. 20A is a block diagram showing the structure of a data
communication apparatus according to a sixth embodiment of the
present invention. In FIG. 20A, the data communication apparatus
according to the sixth embodiment is constituted by connecting a
data transmitting apparatus 12105 and the data receiving apparatus
10201 via the transmission path 110. The data transmitting
apparatus 12105 has the multi-level encoding part 111, the
modulating part 112 and an equalizing part 115. The multi-level
encoding part 111 includes the first multi-level code generating
part 111a and the multi-level processing part 111b. The data
receiving apparatus 10201 has the demodulating part 211 and the
multi-level decoding part 212. The multi-level decoding part 212
includes the second multi-level code generating part 212a and the
multi-level discriminating part 212b. That is, the data
transmitting apparatus 12105 according to the twelfth embodiment is
different from the data transmitting apparatus 10101 according to
the first embodiment (FIG. 1) in that the equalizing part 115 is
further provided.
[0215] Hereinafter, the data communication apparatus according to
the sixth embodiment will be explained with respect mainly to the
equalizing part 115. Since the structure of the present embodiment
corresponds to that of the first embodiment (FIG. 1), the blocks
performing the same operations are denoted by the same reference
characters, and descriptions thereof are omitted.
[0216] In the data transmitting apparatus 12105, the multi-level
signal 13 (see FIG. 2(c)) is inputted to the equalizing part 115.
The equalizing part 115 waveform-equalizes the inputted multi-level
signal 13 by using predetermined means, and outputs an equalized
multi-level signal 24. FIG. 21 is a view showing an example of the
waveform of the equalized multi-level signal 24 outputted by the
equalizing part 115. In FIG. 21, the dotted line represents the
waveform of the multi-level signal 13 inputted to the equalizing
part 115. As the equalizing part 115, a filter such as a low-pass
filter is used. When a low-pass filter is used as the equalizing
part 115 and the high-frequency region of the multi-level signal 13
is bandwidth-shaped, an intersymbol interference occurs because the
response time related to the transition between the multiple levels
of the multi-level signal 13 is limited. In such a case, the
equalized multi-level signal 24 cannot transit to the multiple
levels (L1, L8, L6, L4, L4, and L2) of the multi-level signal 13 at
the predetermined time slots (t1, t2, t3, t4, t5, and t6) as shown
in FIG. 21, and is outputted from the equalizing part 115 as a
signal where a level fluctuation occurs. The equalized multi-level
signal 24 is inputted to the modulating part 112.
[0217] The modulating part 112 converts the equalized multi-level
signal 24 into a signal format suitable for the transmission path
110, and transmits the modulated signal 14 to the transmission path
110. For example, when the transmission path 110 is an optical
transmission line, the modulating part 112 converts the equalized
multi-level signal 24 into an optical signal.
[0218] In the data receiving apparatus 10201, the demodulating part
211 receives the modulated signal 14 via the transmission path 110.
The demodulating part 211 demodulates the modulated signal 14, and
outputs an equalized multi-level signal 25. The equalized
multi-level signal 25 is inputted to the multi-level discriminating
part 212b. The multi-level discriminating part 212b performs the
discrimination of the equalized multi-level signal 25 by using the
multi-level code sequence 17. FIG. 22(a) is a view explaining the
discrimination of the equalized multi-level signal 25 in the
multi-level discriminating part 212b. In FIG. 22(a), the thick
solid line represents an example of the waveform of the equalized
multi-level signal 25, the thin solid line represents an example of
the waveform of the multi-level code sequence 17, and the dotted
line represents an example of the waveform of the multi-level
signal 13.
[0219] Referring to FIG. 22(a), the multi-level discriminating part
212b performs the discrimination (binary determination) of the
equalized multi-level signal 24 with the multi-level code sequence
17 as the threshold value, and reproduces the information data 18.
That is, the multi-level discriminating part 212b can discriminate
the multi-level signal 13, within a range where the deterioration
(the amount of level fluctuation) of the equalized multi-level
signal 25 does not exceed the discrimination level, with the
multi-level code sequence 17 as the discrimination level also when
the multi-level signal 13 where a level fluctuation occurs due to
the intersymbol interference involved in the bandwidth shaping
(that is, the equalized multi-level signal 25) is received.
[0220] Next, wiretapping of the modulated signal 14 by a third
party will be explained. It is considered that like the case
explained in the first embodiment, the third party receives and
decrypts the modulated signal 14 by using a structure corresponding
to the data receiving apparatus 10201 that the authorized user has
or a higher-performance data receiving apparatus (wiretapper data
receiving apparatus). However, since the first key information 11
is not shared between the wiretapper data receiving apparatus and
the data transmitting apparatus 10101, the wiretapper data
receiving apparatus cannot perform the discrimination (binary
determination) of the equalized multi-level signal 25 with
reference to the multi-level code sequence 17 generated from the
key information like the data receiving apparatus 10201.
[0221] In such a case, it is considered that the wiretapper data
receiving apparatus tries to reproduce the correct key information
or the information data 18 by discriminating the equalized
multi-level signal 25 by using a brute force attack. FIG. 22(b) is
a view explaining the discrimination of the equalized multi-level
signal 25 by the wiretapper data receiving apparatus. In FIG.
22(b), the thick solid line represents an example of the waveform
of the equalized multi-level signal 25, the thick dotted line
represents an example of the waveform of the multi-level signal 13,
and the thin dotted lines represent a plurality of discrimination
levels for discriminating the multi-level signal 13.
[0222] When a brute force attack is performed, since the wiretapper
data receiving apparatus does not know the discrimination level of
the equalized multi-level signal 25 based on the multi-level code
sequence 17, it is necessary for it to accurately discriminate and
reproduce the multi-level signal 13 from the equalized multi-level
signal 25 by using the discrimination levels represented by the
thin dotted lines in FIG. 22(b) and then, analyze the correct key
information and the information data 18. However, in the equalized
multi-level signal 25, a level fluctuation occurs due to the
intersymbol interference involved in the bandwidth shaping, for
example, in the circled parts in FIG. 22(b), and a multi-level
transition different from that of the multi-level signal 13 is
exhibited. For this reason, when the equalized multi-level signal
25 is discriminated and reproduced by the wiretapper data receiving
apparatus by using a plurality of discrimination levels, a symbol
error (or a code error) for the multi-level signal 13 is
unavoidable, and further, it is difficult to analyze the correction
key information and the information data 18.
[0223] As described above, according to the present embodiment, a
level fluctuation is caused in the multi-level signal 13 by the
multi-level signal 15, and the equalized multi-level signal 24 is
outputted. Consequently, third parties (wiretapper data receiving
apparatuses) not sharing the key information (the first key
information 11 and the second key information 16) cannot accurately
discriminate and reproduce the multi-level signal 13 from the
equalized multi-level signal 25 which is the modulated signal 14
that is demodulated, so that the decryption by a brute force attack
or the like is difficult. Therefore, the invention according to the
present embodiment is capable of providing a data communication
apparatus that enables information transmission with higher
stealthiness than the data communication apparatus according to the
first embodiment.
[0224] While in the present embodiment, the equalizing part 115 is
connected between the multi-level encoding part 111 and the
modulating part 112, the connection position is not limited
thereto. For example, the equalizing part 115 may be connected to
the input side of the information data 10 of the multi-level
processing part 111b so that the waveform-equalized information
data 10 is outputted to the multi-level processing part 111b (see
FIG. 20B).
[0225] Moreover, the equalizing part 115 may be connected between
the first multi-level code generating part 111a and the multi-level
processing part 111b (see FIG. 20C). In this case, the equalizing
part 115 waveform-equalizes the multi-level code sequence 12, and
outputs the equalized multi-level code sequence to the multi-level
processing part 111b. Moreover, the equalizing part 115 may be
connected to the output side of the modulating part 112 and
waveform-equalize the modulated signal 14 (see FIG. 20D). The data
communication apparatus according to the present embodiment is
capable of performing information transmission with high
stealthiness when the equalizing part 115 is connected to any of
the positions mentioned above.
[0226] It is desirable that the low-pass filter used as the
equalizing part 115 be a low-pass filter that filters signal
components of equal to or lower than half the frequency band of the
inputted signal. For example, when a signal component of equal to
or higher than half the inputted multi-level signal 13 is filtered,
the equalizing part 115 (low-pass filter) outputs the equalized
multi-level signal 24 where the multiple levels are largely
fluctuated due to the intersymbol interference. In this case, it is
difficult for the data receiving apparatus 10201 to discriminate
the equalized multi-level signal 25 demodulated from the modulated
signal 14.
[0227] Moreover, a high-pass filter may be used as the equalizing
part 115. In this case, the data communication apparatus according
to the present embodiment can produce similar effects to those
produced when a low-pass filter is used, by intercepting the
direct-current component or a low-frequency component of the signal
inputted to the equalizing part 115 to thereby cause an intersymbol
interference involved in the drifting of the average value in the
signal outputted from the equalizing part 115.
[0228] Moreover, a band-pass filter may be used as the equalizing
part 115. In this case, the data communication apparatus according
to the present embodiment can produce similar effects to those
produced when a low-pass filter is used, by filtering the signal
component of a predetermined frequency band of the signal inputted
to the equalizing part 115.
Seventh Embodiment
[0229] FIG. 23 is a block diagram showing an example of the
structure of a data communication apparatus according to a seventh
embodiment of the present invention. In FIG. 23, the data
communication apparatus according to the seventh embodiment is
different from that according to the sixth embodiment in the
structure of a data transmitting apparatus 12106. The data
transmitting apparatus 12106 according to the seventh embodiment
has the first multi-level code generating part 111a, the equalizing
part 115, a first modulating part 116, and a second modulating part
117. Since the structure of the present embodiment corresponds to
that of the sixth embodiment (FIG. 20A), the blocks performing the
same operations are denoted by the same reference characters, and
descriptions thereof are omitted.
[0230] In FIG. 23, to the equalizing part 115, the multi-level code
sequence 12 is inputted from the first multi-level code generating
part 111a. The equalizing part 115 waveform-equalizes the
multi-level code sequence 12 by predetermined means, and outputs an
equalized multi-level code sequence 27. The equalized multi-level
code sequence 27 is inputted to the first modulating part 116. The
first modulating part 116 modulates the equalized multi-level code
sequence 27 in a predetermined modulation format, and outputs a
first modulated signal 28. Specifically, the first modulating part
116, for example, amplitude-modulates the equalized multi-level
code sequence 27 to thereby output the first modulated signal
28.
[0231] The first modulated signal 28 is inputted to the second
modulating part 117. Moreover, the information data 10 is inputted
to the second modulating part 117. The second modulating part 117
modulates the first modulated signal 28 and the information data 10
in a predetermined modulation format, and outputs a second
modulated signal 29. For example, the second modulating part 117
adds the first modulated signal 28 and the information data 10 or
amplitude-modulates the level of the first modulated signal 28 by
the information data 10 to output the second modulated signal
29.
[0232] As described above, according to the present embodiment, the
equalizing part 115 causes a level fluctuation in the multi-level
code sequence 12 by the intersymbol interference, and outputs the
equalized multi-level code sequence 27. Then, the first modulating
part 116 outputs the first modulated signal 28 of the predetermined
modulation format based on the equalized multi-level code sequence
27, and the second modulating part 117 modulates the first
modulated signal 28 based on the information data 10 and outputs
the second modulated signal 29 of the predetermined modulation
format. Consequently, it is more difficult for third parties not
sharing the key information (the first key information 11 and the
second key information) to extract the information data 10 from the
equalized multi-level signal 25 which is the equalized multi-level
signal 25 that is demodulated. Thus, the invention according to the
present embodiment is capable of providing a data communication
apparatus that enables information transmission with high
stealthiness like the data transmitting apparatus according to the
fifth embodiment.
[0233] The data communication apparatus according to the seventh
embodiment (FIG. 23) may have a different structure. FIG. 24 is a
block diagram showing another example of the structure of the data
communication apparatus according to the seventh embodiment of the
present invention. In FIG. 24, to the equalizing part 115, the
multi-level code sequence 12 is inputted from the first multi-level
code generating part 111a. The equalizing part 115
waveform-equalizes the multi-level code sequence 12 by
predetermined means, and outputs the equalized multi-level code
sequence 27. The first modulating part 116 modulates the
information data 10, and outputs the first modulated signal 28 of
the predetermined modulation format. The equalized multi-level code
sequence 27 and the first modulated signal 28 are inputted to the
second modulating part 117. The second modulating part 117 outputs
the second modulated signal 29 of the predetermined format based on
the equalized multi-level code sequence 27 and the first modulated
signal 28. Specifically, the second modulating part 117 adds the
equalized multi-level code sequence 27 and the first modulated
signal 28 or amplitude-modulates the level of the first modulated
signal 28 by the equalized multi-level code sequence 27 to output
the second modulated signal 29. In this case, the invention
according to the present embodiment is also capable of providing a
data communication apparatus that enables information transmission
with high stealthiness like the data communication apparatus
according to the sixth embodiment.
[0234] In the data communication apparatus according to the seventh
embodiment (FIGS. 23 and 24), like the sixth embodiment, as long as
a level fluctuation is caused in the equalized multi-level signal
25, the equalizing part 115 may be inserted or connected in any
position of the data transmitting apparatuses 12106 and 12106b. In
FIG. 23, the data transmitting apparatus 12106 may have a structure
such that the equalizing part 115 is connected in the preceding
stage of the second modulating part 117 to cause a predetermined
level fluctuation in the information data 10. Moreover, the data
transmitting apparatus 12106 may have a structure such that the
equalizing part 115 is connected in the succeeding stage of the
first modulating part 116 to cause a predetermined level
fluctuation in the first modulated signal 28. Moreover, in FIG. 24,
the data transmitting apparatus 12106b may have, for example, a
structure such that the equalizing part 115 is connected in the
preceding stage of the first modulating part 116 to cause a
predetermined level fluctuation in the information data 10.
Moreover, the data transmitting apparatus 12106b may have a
structure such that the equalizing part 115 is connected in the
succeeding stage of the second modulating part 117 to cause a
predetermined level fluctuation in the second modulated signal 29.
In any of the structures, the data communication apparatus
according to the seventh embodiment can make it difficult to
discriminate the equalized multi-level signal 25 discriminated by
wiretapper receiving apparatuses.
Eighth Embodiment
[0235] FIG. 25 is a block diagram showing an example of the
structure of a data communication apparatus according to an eighth
embodiment of the present invention. In FIG. 25, the data
communication apparatus according to the eighth embodiment is
different from the data communication apparatus according to the
first embodiment (FIG. 1) in that a data transmitting apparatus
14105 further has an amplitude controlling part 120. The amplitude
controlling part 120 includes a first amplitude control signal
generating part 120a and an amplitude modulating part 120b.
[0236] FIG. 26 is a schematic view for explaining the signal
waveforms of parts of the data communication apparatus according to
the eighth embodiment of the present invention. FIG. 26(a) shows an
example of the waveform of the information data 10. FIG. 26(b)
shows an example of the waveform of amplitude-modulated information
data 36 outputted from the amplitude modulating part 120b. The
dotted line in FIG. 26(b) represents the waveform of the
information data 10 shown in FIG. 26(a). FIG. 26(c) shows an
example of the waveform of the multi-level code sequence 12
outputted from the first multi-level code generating part 111a.
FIG. 26(d) shows an example of the waveform of the multi-level
signal 13 outputted from the multi-level processing part 111b. The
dotted line in FIG. 26(d) represents the waveform of the
multi-level signal 13 shown in FIG. 26(c). The operation of the
data communication apparatus according to the eighth embodiment
will be explained by using FIG. 26. Since the structure of the
present embodiment corresponds to that of the first embodiment
(FIG. 1), the blocks performing the same operations are denoted by
the same reference characters, and descriptions thereof are
omitted.
[0237] In the data transmitting apparatus 14105, the first key
information 11 is inputted to the first amplitude control signal
generating part 120a. Based on the first key information 11, the
first amplitude control signal generating part 120a generates an
amplitude control signal 35 the value of which varies substantially
like a random number. The amplitude control signal 35 is inputted
to the amplitude modulating part 120b. The information data 10
(FIG. 26(a)) is inputted to the amplitude modulating part 120b. The
amplitude modulating part 120b performs a substantially random
amplitude modulation on the information data 10 (FIG. 26(a)) based
on the amplitude control signal 35, and outputs the
amplitude-modulated information data 36 (FIG. 26(b)). As shown in
FIGS. 26(a) and 26(b), by using, as the reference level R, the
amplitude center level of the information data 10 which is the
original signal, the amplitude modulating part 120b performs the
amplitude modulation within a range not changing the polarity.
[0238] The amplitude-modulated information data 36 (FIG. 26(b)) and
the multi-level code sequence 12 (FIG. 26(c)) are inputted to the
multi-level processing part 111b. The multi-level processing part
111b generates the multi-level signal 13 (FIG. 26(d)) by regarding
the level of the multi-level code sequence 12 as the bias level for
the reference level R of the amplitude-modulated information data
36 and adding the multi-level code sequence 12 and the
amplitude-modulated information data 36.
[0239] In the data receiving apparatus 10201, the multi-level
discriminating part 212b receives the multi-level signal 15 from
the demodulating part 211. The multi-level discriminating part 212b
performs the discrimination (binary determination) of the
multi-level signal 15 by using, as the threshold value (reference
level), the multi-level code sequence 17 generated based on the
second key information 16 the same as the first key information 11
(the same as FIG. 26(c)). Here, the amplitude modulating part 120b
does not change the polarity of the original signal (information
data 10) as mentioned above. For this reason, the multi-level
discriminating part 212b can correctly reproduce the information
data 18 by performing the discrimination with reference to the
multi-level code sequence 17 equal to the multi-level code sequence
12.
[0240] Next, wiretapping of the modulated signal by a third party
will be explained. As mentioned above, it is considered that the
third party decrypts the modulated signal by using a structure
corresponding to the data receiving apparatus 10201 or a
higher-performance data receiving apparatus (wiretapper data
receiving apparatus). The wiretapper data receiving apparatus
reproduces the multi-level signal by demodulating the modulated
signal 14. However, since the key information is not shared between
the wiretapper data receiving apparatus and the data transmitting
apparatus 10101, the wiretapper data receiving apparatus cannot
generate the multi-level code sequence from the key information
like the data receiving apparatus 10201. For this reason, the
wiretapper data receiving apparatus cannot perform the binary
determination of the multi-level signal with reference to the
multi-level code sequence.
[0241] Wiretapping considered to be performed in such a case
includes simultaneously discriminating all the levels of the
multi-level signal (generally called "brute force attack"). That
is, the wiretapper data receiving apparatus is provided with
threshold values for all the inter signal point intervals that the
multi-level signal can take, performs the simultaneous
determination of the multi-level signal, and analyzes the result of
the determination to thereby try to extract the correct key
information or information data. For example, the wiretapper data
receiving apparatus tries to extract the correct key information or
information data by performing the multi-level determination on the
multi-level signal by using, as the threshold values, the levels
c0, c1, c2, c3, c4, c5 and c6 of the multi-level code sequence 12
shown in FIG. 2.
[0242] However, as mentioned above, noise is caused by various
factors in actual transmission systems, and since this noise is
combined on the modulated signal, the level of the multi-level
signal fluctuates with time and momentarily as shown in FIG. 4. In
addition, in the present embodiment, the substantially random
amplitude modulation is performed on the multi-level signal based
on the first key information 11 (that is, the amplitude control
signal 35). FIG. 27 is a schematic view explaining the transmission
signal quality of the data communication apparatus according to the
eighth embodiment of the present invention. As shown in FIG. 27,
the level fluctuation width (fluctuation amount) of the multi-level
signal received by the data receiving apparatus 10201 and the
wiretapper data receiving apparatus is larger than that in the
first embodiment.
[0243] Since the SN ratio of the signal to be determined
(multi-level signal) determined by the wiretapper data receiving
apparatus depends on the ratio between the step width and the
fluctuation amount of the multi-level signal, the SN ratio is
further reduced by the effect of the amplitude modulation performed
based on the amplitude control signal 35. Consequently, the data
communication apparatus according to the present embodiment can
make wiretapping difficult by inducing a large number of
discrimination errors in the third party's brute force attack using
all the threshold values. In particular, in the data communication
apparatus, by setting the level fluctuation width by the amplitude
modulation so as to be equal to or larger than the step width of
the multi-level signal, the multi-level determination by third
parties is made virtually impossible to thereby realize ideal
wiretapping prevention, so that absolute safety in data
communication can be ensured.
[0244] The amplitude controlling part 120 may be inserted or
connected in any position different from that of FIG. 25 as long as
a level fluctuation is caused in the multi-level signal 15
determined by the wiretapper data receiving apparatus and the SN
ratio can be controlled. For example, as shown in FIG. 28, the data
communication apparatus may have a structure such that the
amplitude controlling part 120 is inserted between the multi-level
encoding part 111 and the modulating part 112 to cause a
predetermined level fluctuation in the multi-level signal 13.
[0245] Moreover, for example, as shown in FIG. 29, the data
communication apparatus may have a structure such that the
amplitude controlling part 120 is connected in the succeeding stage
of the modulating part 112 to cause a level fluctuation in the
modulated signal 14. In this case, the amplitude modulating part
120b amplitude-modulates or intensity-modulates the modulated
signal 14 according to the kind of the signal transmitted via the
transmission path 110. In any of the structures, the data
communication apparatus according to the eighth embodiment is
capable of controlling the SN ratio of the signal to be determined
(multi-level signal) at the time of the multi-level determination
to a given value.
[0246] While the first amplitude control signal generating part
120a generates the amplitude control signal 35 based on the first
key information 11 inputted to the first multi-level code
generating part 111a in FIG. 25, it may generate the amplitude
control signal 35 based on predetermined first amplitude control
key information 38 different from the first key information 11 as
shown in FIG. 30. Thereby, the correlation between the level change
of the multi-level code sequence 12 and the amplitude modulation by
the amplitude modulating part 120b is suppressed to thereby make
the level change of the multi-level signal 13 more random, so that
more ideal discrimination errors can be induced in the multi-level
determination by the wiretapper data receiving apparatus.
[0247] In actuality, there are cases where the amplitude modulation
by the amplitude modulating part 120b deteriorates the SN ratio of
the signal to be determined the discrimination (binary
determination) of which is performed by the data receiving
apparatus 10201 of the authorized receiver. To suppress such an
effect of the amplitude modulation, the structure of the data
receiving apparatus 10201 may be changed. For example, as shown in
FIG. 31, in a data receiving apparatus 14205d, a multi-level
decoding part 218 may include a second amplitude control signal
generating part 212c in addition to the second multi-level code
generating part 212a and the multi-level discriminating part 212b.
That is, the second amplitude control signal generating part 212c
previously shares second amplitude control key information 39 the
same as the first amplitude control key information 38, and
generates an amplitude control signal 40 corresponding to the
amplitude control signal 35 based on the second amplitude control
key information 39. The multi-level discriminating part 212b
performs the optimum discrimination (binary determination) of the
multi-level signal 15 by using as the threshold value the
multi-level code sequence 17 outputted from the second multi-level
code generating part 212a and while monitoring the momentary level
or the SN ratio of the multi-level signal 15 by the amplitude
control signal 40, thereby reproducing the information data 18.
[0248] As described above, according to the present embodiment, a
safer data communication apparatus can be provided in which by
encoding the information data to be transmitted as the multi-level
signal and arbitrarily controlling the fluctuation level
(fluctuation amount) thereof, a decisive deterioration is
deliberately caused in the reception signal quality in wiretapping
by third parties to thereby make the decryption and decoding of the
reception signal more difficult.
Ninth Embodiment
[0249] FIG. 32A is a block diagram showing an example of the
structure of the data communication apparatus according to a ninth
embodiment of the present invention. The data communication
apparatus according to the present embodiment realizes, by a
different structure, the conversion to the modulated signal 14
based on the multi-level code sequence 12 and the
amplitude-modulated information data 36 which conversion is
performed by the multi-level processing part 111b and the
modulating part 112 (see FIG. 25) in the eighth embodiment. In FIG.
32A, the data communication apparatus according to the ninth
embodiment is constituted by connecting a data transmitting
apparatus 14106 and the data receiving apparatus 10201 via the
transmission path 110. The data transmitting apparatus 14106 has
the first multi-level code generating part 111a, the amplitude
controlling part 120, a first modulating part 122, a second
modulating part 123, and a multiplexing part 124. The amplitude
controlling part 120 includes the first amplitude control signal
generating part 120a and the amplitude modulating part 120b.
[0250] Since the structure of the present embodiment corresponds to
that of the eighth embodiment (FIG. 25), the blocks performing the
same operations are denoted by the same reference characters, and
descriptions thereof are omitted. In FIG. 32A, with the multi-level
code sequence 12 outputted from the first multi-level code
generating part 111a as the original data, the first modulating
part 122 converts it into a predetermined modulation format, and
outputs a first modulated signal 41. With the amplitude-modulated
information data 36 outputted from the amplitude modulating part
120b as the original data, the second modulating part 123 converts
it into a predetermined modulation format, and outputs a second
modulated signal 42. The first modulated signal 41 and the second
modulated signal 42 are inputted to the multiplexing part 124. The
multiplexing part 124 amplitude- or intensity-combines the first
modulated signal 41 and the second modulated signal 42, and
transmits the composite signal to the transmission path 110. That
is, the data communication apparatus according to the ninth
embodiment realizes a circuit structure with high flexibility by
performing the conversion to the modulated signal 14 based on the
multi-level code sequence 12 and the amplitude-modulated
information data 36 which conversion is performed by the
multi-level processing part 111b and the modulating part 112 in
FIG. 25, by the first modulating part 122, the second modulating
part 123 and the multiplexing part 124 at the modulated signal
level.
[0251] While in the data communication apparatus according to the
ninth embodiment (FIG. 32A), the first modulating part 122 and the
second modulating part 123 are placed in parallel and the first
modulated signal 41 and the second modulated signal 42 are
multiplexed, a different structure may be adopted. FIG. 32B is a
block diagram showing another example of the structure of the data
communication apparatus according to the ninth embodiment of the
present invention. As shown in FIG. 32B, the data communication
apparatus according to the present embodiment may have a structure
such that the first modulating part 122 and the second modulating
part 123 are connected in series and the same carrier wave is
modulated by the first modulating part 122 and the second
modulating part 123. The first modulating part 122 modulates the
carrier wave by the multi-level code sequence 12 and outputs the
first modulated signal 41, and the second modulating part 123
modulates the first modulated signal 41 by the amplitude-modulated
information data 36. That is, the data communication apparatus of
this structure performs the conversion to the modulated signal 14
based on the multi-level code sequence 12 and the
amplitude-modulated information data 36 which conversion is
performed by the multi-level processing part 111b and the
modulating part 112 in FIG. 25, by the first modulating part 122
and the second modulating part 123 at the modulated signal
level.
[0252] In the data transmitting apparatus 14106 of FIG. 32A, the
first modulated signal 41 and the second modulated signal 42 are
added together by the multiplexing part 124. On the contrary, in a
data transmitting apparatus 14106b of FIG. 32B, the signals are
integrated together by the first modulating part 122 and the second
modulating part 123. For this reason, although in the data
transmitting apparatus 14106b of FIG. 32B, the waveform of the
generated modulated signal 14 is slightly different from that in
the data transmitting apparatus 14106 of FIG. 32A, a substantially
similar effect can be obtained in that the level that the
amplitude-modulated information data 36 has is combined with
reference to the level of the multi-level code sequence 12.
[0253] Moreover, in the data communication apparatus according to
the ninth embodiment, like the eighth embodiment, as long as a
level fluctuation is caused in the multi-level signal 15 determined
by the wiretapper data receiving apparatus and the SN ratio of the
multi-level signal can be controlled, the amplitude controlling
part 120 may be inserted or connected in any position different
from that in FIG. 32A or 33B. For example, in FIG. 32A or 32B, the
data communication apparatus according to the ninth embodiment may
have a structure such that the amplitude controlling part 120 is
inserted in the preceding stage of the first modulating part 122 to
cause a predetermined level fluctuation in the multi-level code
sequence 12 (see FIGS. 33A and 33B). Moreover, the data
communication apparatus according to the ninth embodiment may have
a structure such that the amplitude controlling part 120 is
connected in the succeeding stage of the first modulating part 122
or the second modulating part 123 or in the succeeding stage of the
multiplexing part 124 to cause a level fluctuation in the first
modulated signal 41 and the second modulated signal 42, or a
composite signal thereof. In any of the structures, the data
communication apparatus according to the ninth embodiment is
capable of controlling the SN ratio of the signal to be determined
(multi-level signal) at the time of the multi-level determination
to a given value.
[0254] Further, in the data communication apparatus according to
the ninth embodiment, the first amplitude control signal generating
part 120a may generate the amplitude control signal based on the
predetermined first amplitude control key information 38 different
from the first key information 11 like FIG. 30. Thereby, in the
data communication apparatus according to the ninth embodiment, the
correlation between the level change of the multi-level code
sequence 12 and the amplitude modulation by the amplitude
modulating part 120b is suppressed to thereby make the level change
of the multi-level signal 15 more random, so that more ideal
discrimination errors can be induced in the multi-level
determination by the wiretapper data receiving apparatus.
[0255] As described above, according to the present embodiment, a
safer data communication apparatus can be provided in which by
encoding the information data to be transmitted as the multi-level
signal and arbitrarily controlling the fluctuation level
(fluctuation amount) thereof and by providing an individual
modulating part for each of the information data and the
multi-level code sequence, a decisive deterioration is deliberately
caused in the reception signal quality in wiretapping by third
parties with a more flexible structure to thereby make the
decryption and decoding of the reception signal more difficult.
Tenth Embodiment
[0256] FIG. 34 is a block diagram showing the structure of a data
communication apparatus according to a tenth embodiment of the
present invention. In FIG. 34, the data communication apparatus
according to the tenth embodiment is different from the data
communication apparatus according to the first embodiment (FIG. 1)
in that a data transmitting apparatus 16105 further has a base N
encoding part 131 and a data receiving apparatus 106205 further has
a base N decoding part 220.
[0257] Hereinafter, the data communication apparatus according to
the tenth embodiment will be explained with respect mainly to the
base N encoding part 131 and the base N decoding part 220. Since
the structure of the present embodiment corresponds to that of the
first embodiment (FIG. 1), the blocks performing the same
operations are denoted by the same reference characters, and
descriptions thereof are omitted.
[0258] In the data transmitting apparatus 16105, an information
data group including a plurality of pieces of information data is
inputted to the base N encoding part 131. It is assumed that first
information data 50 and second information data 51 are inputted as
the information data group. FIG. 35 is a view showing examples of
the waveform of the information data group inputted to the base N
encoding part 131. FIG. 35(a) shows the first information data 50
inputted to the base N encoding part 131. FIG. 35(b) shows the
second information data 51 inputted to the base N encoding part
131.
[0259] The base N encoding part 131 encodes the first information
data 50 and the second information data 51 into a base N (in this
example, N=4) number to thereby output them as a base N encoded
signal 52 having predetermined multiple levels. N is an arbitrary
natural number. Thereby, the base N encoding part 131 can increase,
by log 2N times, the amount of information that can be transmitted
per time slot. FIG. 36 is a view showing an example of the waveform
of the base N encoded signal 52 outputted from the base N encoding
part 131. Referring to FIG. 36, for example, the base N encoding
part 131 can output the base N encoded signal 52 having multiple
levels of four steps by assigning a multiple level 00 when the
combination of logics in the first information data 50 and the
second information data 51 is {L, L}, a multiple level 01 when the
combination is {L, H}, a multiple level 10 when the combination is
{H, L}, and a multiple level 11 when the combination is {H, H}. The
base N encoded signal 52 outputted from the base N encoding part
131 and the multi-level code sequence 12 outputted from the first
multi-level code generating part 111a (see FIG. 2(b)) are inputted
to the multi-level processing part 111b.
[0260] The multi-level processing part 111b combines the base N
encoded signal 52 and the multi-level code sequence 12 by a
predetermined procedure, and outputs the composite signal as the
multi-level signal 13. For example, the multi-level processing part
111b generates the multi-level signal 13 by adding the base N
encoded signal 52 with the level of the multi-level code sequence
12 as the bias level. Alternatively, the multi-level processing
part 111b may generate the multi-level signal 13 by
amplitude-modulating the multi-level code sequence 12 by the base N
encoded signal 52. FIG. 37 is a view showing an example of the
waveform of the multi-level signal 13 outputted from the
multi-level processing part 111b. In FIG. 37, the multiple levels
of the multi-level signal 13 fluctuate in four steps at
predetermined level intervals (in this case, intervals of three
levels). The dotted lines show the ranges where the multiple levels
of the multi-level signal 13 fluctuate, with reference to the bias
level (multi-level code sequence 12).
[0261] The multi-level signal 13 outputted from the multi-level
processing part 111b is inputted to the modulating part 112. The
modulating part 112 modulates the multi-level signal 13 into a
signal format suitable for the transmission path 110, and transmits
the modulated signal to the transmission path 110 as the modulated
signal 14. For example, when the transmission path 110 is an
optical transmission line, the modulating part 12 converts the
multi-level signal 13 into an optical signal.
[0262] In a data receiving apparatus 16205, the demodulating part
211 receives the modulated signal 14 via the transmission path 110.
The demodulating part 211 demodulates the modulated signal 14, and
outputs the multi-level signal 15. The multi-level signal 15 is
inputted to the multi-level discriminating part 212b. The
multi-level discriminating part 212b discriminates the multi-level
signal 15 by use of the multi-level code sequence 17 outputted from
the second multi-level code generating part 212a to thereby output
a base N encoded signal 53. FIG. 38 is a view explaining an example
of the discrimination of the multi-level signal 15 by the
multi-level discriminating part 212b. In FIG. 38, the thick solid
line represent the waveform of the multi-level signal 15, and the
thin solid line and the dotted lines represent the determination
waveforms for discriminating the multi-level signal 15. The thin
solid line (determination waveform 2) is the waveform of the
multi-level code sequence 17.
[0263] Referring to FIG. 38, the multi-level discriminating part
212b generates a waveform (determination waveform 1) which is the
multi-level code sequence 17 that is shifted upward by a
predetermined level interval with the multi-level code sequence
(determination waveform 2) as the center and a waveform
(determination waveform 3) which is the multi-level code sequence
17 that is shifted downward by the predetermined level interval
with the multi-level code sequence 17 as the center. The
predetermined level interval is predetermined between the
multi-level discriminating part 212b and the multi-level processing
part 111b in the data transmitting apparatus 16105, and in this
example, it is an interval of three levels. The multi-level
discriminating part 212b discriminates the multi-level signal 151
by using the determination waveforms 1 to 3.
[0264] At the time slot t1, the multi-level discriminating part
212b compares the determination waveform 1 and the multi-level
signal 15, and determines that the multi-level signal 15 is lower
in level than the determination waveform 1. Moreover, the
multi-level discriminating part 212b compares the determination
waveform 2 and the multi-level signal 15, and determines that the
multi-level signal 15 is lower in level than the determination
waveform 2. Moreover, the multi-level discriminating part 212b
compares the determination waveform 3 and the multi-level signal
15, and determines that the multi-level signal 15 is higher in
level than the determination waveform 3. That is, the multi-level
discriminating part 212b determines that the multi-level signal 15
is {Low, Low, High} at the time slot t1. Likewise, at the time slot
t2, the multi-level discriminating part 212b determines that the
multi-level signal 15 is {Low, High, High} at the time slot t2, and
determines that the multi-level signal 15 is {Low, Low, Low} at the
time slot t3. Although omitted, the operations at the time slot t4
and subsequent time slots are similar.
[0265] Then, the multi-level discriminating part 212b associates
the numbers of Low's and High's in the determination with the
multiple levels of the base N encoded signal 52 to thereby
reproduce the base N encoded signal 52. For example, by associating
{Low, Low, Low} with the multiple level 00, {Low, Low, High} with
the multiple level 01, {Low, High, High} with the multiple level
10, and {High, High, High} with the multiple level 11, the
multi-level discriminating part 212b can reproduce the base N
encoded signal 53. The base N encoded signal 53 reproduced by the
multi-level discriminating part 212b is inputted to the base N
decoding part 220.
[0266] The base N decoding part 220 decodes the base N encoded
signal 52, and outputs it as the information data group.
Specifically, the base N decoding part 220 performs an operation
opposite to that performed by the base N encoding part 131 to
thereby output first information data 54 and second information
data 55 from the base N encoded signal 52.
[0267] Next, wiretapping of the modulated signal 14 by a third
party will be explained. Since the first key information 11 is not
shared between the third party and the data transmitting apparatus
16105 like the case described in the first embodiment, the third
party cannot reproduce the first information data 54 and the second
information data 55 from the wiretapped modulated signal 14. In
actual transmission systems, noise is caused by various factors,
and this noise is combined on the modulated signal 14. That is,
noise is combined also on the multi-level signal 15 which is the
modulated signal 14 that is demodulated. FIG. 39 is a view showing
the waveform of the multi-level signal 15 on which noise is
combined. Referring to FIG. 39, the data communication apparatus
according to the tenth embodiment can make wiretapping more
difficult by inducing discrimination errors in the third party's
brute force attack using all the threshold values because of the
noise combined on the multi-level signal 15 like the case described
in the first embodiment.
[0268] As described above, according to the present invention, the
base N encoding part 131 converts the information data group all
together into the base N encoded signal 52, and the base N decoding
part 220 reproduces the information data group all together from
the base N encoded signal 53. Thereby, in the data communication
apparatus according to the present embodiment, the amount of
information that can be transmitted per time slot can be made
larger than in the data communication apparatus according to the
first embodiment. Moreover, by converting the information data
group into the base N encoded signal 52, data transmission with
higher stealthiness can be realized.
Eleventh Embodiment
[0269] FIG. 40 is a block diagram showing an example of the
structure of a data communication apparatus according to an
eleventh embodiment of the present invention. In FIG. 40, the data
communication apparatus according to the eleventh embodiment is
different from that of the tenth embodiment (FIG. 34) in the
operations of the base N encoding part 132 and the base N decoding
part 221. In the eleventh embodiment, the base N encoding part 132
generates the base N encoded signal 52 from the information data
group based on the first key information 11. Moreover, the base N
decoding part 221 generates the information data group from the
base N encoded signal 53 based on the second key information 16.
Hereinafter, the data communication apparatus according to the
eleventh embodiment will be explained with respect mainly to the
base N encoding part 132 and the base N decoding part 221. Since
the structure of the present embodiment corresponds to that of the
tenth embodiment (FIG. 34), the blocks performing the same
operations are denoted by the same reference characters, and
descriptions thereof are omitted.
[0270] In a data transmitting apparatus 16106, the first key
information 11 is inputted to the base N encoding part 132. The
base N encoding part 132 generates the base N encoded signal 52
from the information data group based on the first key information
11. For example, the base N encoding part 132 changes the
correspondence between the combination of logics in the first
information data 50 and the second information data 51 and the
multiple levels of the base N encoded signal 52 by the first key
information 11. The base N encoded signal 52 outputted from the
base N encoding part 132 is inputted to the multi-level processing
part 111b.
[0271] In a data receiving apparatus 16206, the base N encoded
signal 53 outputted from the multi-level discriminating part 212b
is inputted to the base N decoding part 221. Moreover, the second
key information 16 is inputted to the base N decoding part 221. The
base N decoding part 221 outputs the information data group from
the base N encoded signal 53 based on the second key information
16. Specifically, the base N decoding part 221 performs an
operation opposite to that performed by the base N encoding part
132 to thereby output the first information data 54 and the second
information data 55 from the base N encoded signal 53.
[0272] As described above, according to the present embodiment, the
base N encoding part 132 generates the base N encoded signal 52
from the information data group based on the first key information
11, and the base N decoding part 221 reproduces the information
data group from the base N encoded signal 53 based on the second
key information 16 by the operation opposite to that performed by
the base N encoding part 132. Thereby, the data communication
apparatus according to the present embodiment can realize data
communication the wiretapping of which is more difficult than in
the data communication apparatus according to the tenth
embodiment.
[0273] In the data communication apparatus according to the
eleventh embodiment, the base N encoding part 132 may generate the
base N encoded signal 52 from the information data group by using
third key information 56 different from the first key information
11. Likewise, the base N decoding part 221 may reproduce the
information data group from the base N encoded signal 53 by using
fourth key information 57 different from the second key information
16 (see FIG. 41). Here, the third key information 56 and the fourth
key information 57 are the same key information. Thereby, in the
data communication apparatus according to the present embodiment,
the key information used by the multi-level processing part 111b
and the key information used by the base N encoding part 132 can be
made separate, so that data communication the wiretapping of which
is more difficult can be realized.
Twelfth Embodiment
[0274] FIG. 42 is a block diagram showing the structure of a data
communication apparatus according to a twelfth embodiment of the
present invention. In FIG. 42, the data communication apparatus
according to the twelfth embodiment is different from that of the
first embodiment (FIG. 1) in that a data transmitting apparatus
19105 further has a synchronous signal generating part 134 and a
multi-level processing controlling part 135 and a data receiving
apparatus 19205 further has a synchronous signal reproducing part
233 and a multi-level discrimination controlling part 234.
[0275] FIG. 43 is a schematic view for explaining the signal
waveform outputted from the multi-level encoding part 111.
Hereinafter, the data communication apparatus according to the
fifth embodiment will be explained by using FIGS. 42 and 43. Since
the structure of the present embodiment corresponds to that of the
first embodiment (FIG. 1), the blocks performing the same
operations are denoted by the same reference characters, and
descriptions thereof are omitted.
[0276] In FIG. 42, the synchronous signal generating part 134
generates a synchronous signal 64 of a predetermined period, and
outputs it to the multi-level processing controlling part 135. The
multi-level processing controlling part 135 generates a multi-level
processing control signal 65 based on the synchronous signal 64,
and outputs it to the multi-level processing part 111b. The
multi-level processing control signal 65 is a signal that specifies
the number of levels (hereinafter, referred to as level number) of
the multi-level signal 13 outputted by the multi-level processing
part 111b. The multi-level processing part 111b generates a
multi-level signal from the information data 10 based on the
multi-level processing control signal 65 and the multi-level code
sequence 12, and outputs, as the multi-level signal 13, a signal
which is the generated multi-level signal the level number of which
has been switched. For example, as shown in FIG. 43, the
multi-level processing part 111b outputs a multi-level signal of
the level number "8" in the periods A and C, and outputs a signal
of a level number "2" in the period B. More specifically, the
multi-level processing part 111b may output a composite signal of
the information data 10 and the multi-level code sequence 12 in the
periods A and C and output the information data 10 as it is in the
period B.
[0277] The synchronous signal reproducing part 233 reproduces a
synchronous signal 66 corresponding to the synchronous signal 64,
and outputs it to the multi-level discrimination controlling part
234. The multi-level discrimination controlling part 234 generates
a multi-level discrimination control signal 67 based on the
synchronous signal 66, and outputs it to the multi-level
discriminating part 212b. The multi-level discriminating part 212b
performs discrimination based on the multi-level discrimination
control signal 67 while switching the threshold value (multi-level
code sequence 17) for the multi-level signal 15 outputted from the
demodulating part 211, and reproduces the information data 18. For
example, as shown in FIG. 43, the multi-level discriminating part
212b discriminates the multi-level signal of the level number "8"
in the periods A and C by using, as the threshold value, the
multi-level code sequence 17 the level of which successively
changes, and discriminates the binary signal based on a
predetermined fixed threshold value in the period B.
[0278] While in FIG. 43, the threshold value (average level) for
the binary signal in the period B coincides with the average level
(C3) of the multi-level signals in the periods A and C, the present
invention is not limited thereto; it may be set to any level. While
in FIG. 43, the amplitude of the binary signal in the period B
coincides with the amplitude (information amplitude) of the
information data 10, the present invention is not limited thereto;
it may be set to any amplitude as long as it has a magnitude that
can be discriminated by a fixed threshold value by the multi-level
discriminating part 212b. While in FIG. 43, the transfer rates in
the periods A and C and in the period B are the same, the present
invention is not limited thereto; they may be different transfer
rates. In particular, it is preferable that the smaller the level
number is, the higher the transfer rate is.
[0279] Moreover, in FIG. 43, the multi-level processing part 111b
outputs the multi-level signal 13 where switching is made between
the multi-level signal of the level number "8" and the binary
signal. However, the combination of level numbers of the
multi-level signal 13 is not limited thereto; it may be any
combination of level numbers. For example, the multi-level
processing part 111b may output the multi-level signal 13 where
switching is made between the multi-level signal of the level
number "8" and a multi-level signal of the level number "4."
Further, in the data communication apparatus shown in FIG. 42, the
transfer rates of the pieces of information data 10 and 18, the
multi-level code sequences 12 and 17, and the multi-level signals
13 and 15 may be changed according to the value of the level
number.
[0280] As described above, according to the present embodiment, by
causing a decisive deterioration in the reception signal quality in
wiretapping by third parties by encoding the information data to be
transmitted as a multi-level signal, a safe communication channel
only for specific receivers is ensured, and by reducing the level
number as appropriate, communication not requiring safety is
selectively realized. Thereby, a stealth communication service and
a general communication service are mixedly provided by using the
same modulating and demodulating systems and transmitting system,
and an efficient communication apparatus can be provided.
Thirteenth Embodiment
[0281] FIG. 44 is a block diagram showing the structure of a data
communication apparatus according to a thirteenth embodiment of the
present invention. In FIG. 44, the data communication apparatus
according to the thirteenth embodiment is different from that of
the twelfth embodiment (FIG. 42) in that the data receiving
apparatus 10201 does not have the synchronous signal reproducing
part 233 and the multi-level discrimination controlling part
234.
[0282] FIG. 45 is a schematic view for explaining the signal
waveform outputted from the multi-level encoding part 111.
Hereinafter, the data communication apparatus according to the
thirteenth embodiment will be explained by using FIGS. 44 and 45.
Since the structure of the present embodiment corresponds to that
of the twelfth embodiment (FIG. 42), the blocks performing the same
operations are denoted by the same reference characters, and
descriptions thereof are omitted.
[0283] In FIG. 44, the multi-level processing part 111b outputs the
multi-level signal 13 which is the output signal while switching
the level number thereof, based on the multi-level processing
control signal 65, and when the level number of the multi-level
signal 13 is decreased, sets the amplitude of the multi-level
signal so as to be large. For example, as shown in FIG. 45, while
the level number is "8" in the periods A and C, in the period B,
the level number is "2," and the amplitude is made sufficiently
large. More specifically, the multi-level processing part 111b
outputs the multi-level signal 13 while setting the amplitude of
the binary signal in the period B so as to be equal to or larger
than that of the multi-level signals in the period A and C.
[0284] The multi-level discriminating part 212b performs the
discrimination (binary determination) of the multi-level signal 15
outputted from the demodulating part 211 by using the multi-level
code sequence 17 as the threshold value irrespective of the level
number, and reproduces the information data. For example, as shown
in FIG. 45, in the periods A and C, the multi-level signal of the
total level number "8" is discriminated by using, as the threshold
value, the multi-level code sequence 17 the level of which
successively changes, and in the period B, the binary signal is
discriminated based on the multi-level code sequence 17.
[0285] As described above, according to the present embodiment, by
causing a decisive deterioration in the reception signal quality in
wiretapping by third parties by encoding the information data to be
transmitted as the multi-level signal, a safe communication channel
only for specific receivers is ensured, and by reducing the level
number as appropriate and increasing the amplitude, the threshold
value control at the time of reception of the multi-level signal is
facilitated to thereby selectively realize communication not
requiring safety with a simpler structure. Thereby, a stealth
communication service and a general communication service are
mixedly provided by using the same modulating and demodulating
systems and transmitting system, and an efficient and economical
communication apparatus can be provided.
Fourteenth Embodiment
[0286] FIG. 46 is a block diagram showing the structure of a data
communication apparatus according to a fourteenth embodiment of the
present invention. In FIG. 46, the data communication apparatus
according to the fourteenth embodiment is constituted by connecting
a data transmitting apparatus 19105, the data receiving apparatus
10201 and a sub data receiving apparatus 19207 via the transmission
path 110 and a branching part 235. The data communication apparatus
according to the fourteenth embodiment is different from that of
the thirteenth embodiment (FIG. 44) in that the branching part 235
and the sub data receiving apparatus 19207 are further provided.
Although omitted in FIG. 46, the multi-level decoding part 212
includes the second multi-level code generating part 212a and the
multi-level discriminating part 212b. Hereinafter, the data
communication apparatus according to the fourteenth embodiment will
be explained. Since the structure of the present embodiment
corresponds to that of the thirteenth embodiment (FIG. 44), the
blocks performing the same operations are denoted by the same
reference characters, and descriptions thereof are omitted.
[0287] In FIG. 46, the data transmitting apparatus 19105 transmits
the modulated signal 14 which is the multi-level signal shown in
FIG. 45 that is modulated. The branching part 235 branches the
modulated signal 14 transmitted via the transmission path 110 into
a plural number m (m is an integer equal to or higher than 2; in
FIG. 24, m=2), and outputs the branch signals. The data receiving
apparatus 10201 is provided so as to correspond to a number n (n is
an integer equal to or lower than m; in FIG. 46, n=1) of modulated
signals among the number m of modulated signals outputted from the
branching part 235. In the periods A and C, the data receiving
apparatus 10201 demodulates and decodes the modulated signal based
on the second key information 16 shared as the same key as the
first key information 11, thereby reproducing the information data
18. The data receiving apparatus 10201 may discriminate the binary
signal in the period B.
[0288] The sub data receiving apparatus 19207 is provided so as to
correspond to a number m-n (in FIG. 46, m-n=2-1=1) among the number
m of modulated signals outputted from the branching part 235. A sub
demodulating part 236 demodulates the modulated signal, and
reproduces the multi-level signal 15. An discriminating part 237
discriminates the multi-level signal 15 outputted from the
corresponding sub demodulating part 236 based on a predetermined
fixed threshold value, and reproduces the information data (partial
information data 68) only in the period B shown in FIG. 45.
[0289] While in FIG. 46, the branch number m at the branching part
235 is 2, the data receiving apparatus 10201 is provided so as to
correspond to a number n-1 of modulated signals among the number m
of signals and the sub data receiving apparatus 19207 is provided
so as to correspond to a number m-n=1 of modulated signals, the
present invention is not limited thereto; the numbers may be set to
any values as long as m.gtoreq.n, and the corresponding number of
data receiving apparatuses and sub data receiving apparatuses are
provided.
[0290] As described above, according to the present embodiment, by
causing a decisive deterioration in the reception signal quality in
wiretapping by third parties by encoding the information data to be
transmitted as the multi-level signal, a safe communication channel
only for specific receivers is ensured and by reducing the level
number as appropriate, a broadcast communication to an indefinite
number of receivers is selectively realized. Thereby, a stealth
communication service and a communication service such as a
broadcast communication and a broadcast are mixedly provided by
using the same modulating and demodulating systems and transmitting
system, and an efficient communication apparatus can be
provided.
Fifteenth Embodiment
[0291] FIG. 47 is a block diagram showing the structure of a data
communication apparatus according to a fifteenth embodiment of the
present invention. In FIG. 47, the data communication apparatus
according to the fifteenth embodiment is constituted by connecting
a data transmitting apparatus 19108, a plurality of data receiving
apparatuses 10201a and 10201b, and a sub data receiving apparatus
19207 via the transmission path 110 and the branching part 235. The
data transmitting apparatus 19108 further has a key information
selecting part 136 compared with the fourteenth embodiment (FIG.
46). Although omitted in FIG. 47, the multi-level decoding part 212
includes the second multi-level code generating part 212a and the
multi-level discriminating part 212b. Hereinafter, the data
communication apparatus according to the fifteenth embodiment will
be explained. Since the structure of the present embodiment
corresponds to that of the fourteenth embodiment (FIG. 46), the
blocks performing the same operations are denoted by the same
reference characters, and descriptions thereof are omitted.
[0292] In FIG. 47, the key information selecting part 136 selects
one from among a plural number n of pieces of predetermined key
information (in FIG. 47, n=2; first key information 11a and third
key information 11b). The multi-level encoding part 111 generates
the multi-level signal 13 as shown in FIG. 45 based on the selected
key information. A number n of data receiving apparatuses (10201a
and 10201b) are provided so as to correspond to the number n of
modulated signals among a number m (in FIG. 47, m=3) of modulated
signals branched and outputted by the branching part 235, and
demodulate and decode the modulated signals based on second key
information 16a and fourth key information 16b shared as the same
key as the corresponding first key information 11a and third key
information 11b, thereby reproducing the corresponding pieces of
information data (18a and 18b).
[0293] Specifically, in FIG. 45, when the data transmitting
apparatus 19108 generates the multi-level signal 13 by using the
first key information 11a in the period A, the data receiving
apparatus 10201a demodulates the modulated signal inputted in the
period A, and reproduces the information data 18a by using the
second key information 16a. When the data transmitting apparatus
19108 generates the multi-level signal 13 by using the third key
information 11b in the period C, the data receiving apparatus
10201b demodulates the modulated signal inputted in the period C,
and reproduces the information data 18b by using the fourth key
information 16b. The data receiving apparatuses 10201a and 10201b
may demodulate the modulated signal inputted in the period B to
reproduce partial information data 58.
[0294] The sub data receiving apparatus 19207 is provided so as to
correspond to a number m-n (in FIG. 47, m-n=3-2=1) of modulated
signals among a number m of modulated signals outputted from the
branching part 235, demodulates the modulated signals,
discriminates them based on a predetermined fixed threshold value,
and reproduces the information data (partial information data 58)
only in the period B shown in FIG. 45.
[0295] While in FIG. 47, the branch number m at the branching part
235 is 3, the data receiving apparatus 10201 is provided so as to
correspond to a number n-2 of modulated signals among the number m
of signals and the sub data receiving apparatus 19207 is provided
so as to correspond to a number m-n=1 of modulated signals, the
present invention is not limited thereto; the numbers may be set to
any values as long as m.gtoreq.n, and the corresponding number of
data receiving apparatuses and sub data receiving apparatuses are
provided.
[0296] As described above, according to the present embodiment, by
causing a decisive deterioration in the reception signal quality in
wiretapping by third parties by encoding the information data to be
transmitted as the multi-level signal, and by providing a plurality
of pieces of key information and making switching thereamong for
use, a safe communication channel only for specific receivers is
ensured, and by reducing the level number as appropriate, a
broadcast communication to an indefinite number of receivers is
selectively realized. Thereby, a stealth communication service and
a communication service such as a broadcast communication and a
broadcast are mixedly provided by using the same modulating and
demodulating systems and transmitting system, and an efficient
communication apparatus can be provided.
[0297] The data communication apparatuses according to the second
to fifteenth embodiments may have the characteristics of some of
the embodiments in combination. For example, the data communication
apparatuses according to the second to the seventh and the ninth to
the fifteenth embodiments may have the characteristic of the eighth
embodiment (for example, see FIGS. 48A to 48C). For example, the
data communication apparatuses according to the second to the ninth
and the eleventh to the fifteenth embodiments may have the
characteristic of the tenth embodiment (for example, see FIGS. 49A
to 49C). For example, the data communication apparatuses according
to the second to the eleventh and the thirteenth to the fifteenth
embodiments may have the characteristic of the twelfth embodiment
(for example, see FIGS. 50A to 50C). For example, the data
communication apparatuses according to the second to the seventh
and the ninth to the fifteenth embodiments may have the
characteristics of the eighth and the twelfth embodiments (for
example, see FIGS. 51A to 51C). For example, the data communication
apparatuses according to the second to the ninth and the eleventh
to the fifteenth embodiments may have the characteristics of the
tenth and the twelfth embodiments (for example, see FIGS. 52A to
52C).
[0298] The processings performed by the data transmitting
apparatuses, the data receiving apparatuses and the data
communication apparatuses according to the first to the fifteenth
embodiments may be grasped as data transmitting methods, data
receiving methods and data communication methods having a series of
processing procedures.
[0299] The data transmitting methods, the data receiving methods,
and the data communication methods are realized by a CPU
interpreting and executing predetermined program data capable of
executing the processing procedures stored in a storage device (a
ROM, a RAM, a hard disk, etc.). In this case, the program data may
be installed into the storage device via a storage medium, or may
be directly executed on the storage medium. The storage medium
includes semiconductor memories such as ROMs, RAMs and flash
memories, magnetic disk memories such as flexible disks and hard
disks, optical disk memories such as CD-ROMs, DVDs, and BDs, and
memory cards. The storage medium is a general idea including
communication media such as the telephone line and carrying
paths.
INDUSTRIAL APPLICABILITY
[0300] The data communication apparatus according to the present
embodiment is useful as a safe secret communication apparatus that
is never wiretapper nor intercepted.
* * * * *