CN113114407A - Secret communication method and system - Google Patents

Secret communication method and system Download PDF

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CN113114407A
CN113114407A CN202110367461.2A CN202110367461A CN113114407A CN 113114407 A CN113114407 A CN 113114407A CN 202110367461 A CN202110367461 A CN 202110367461A CN 113114407 A CN113114407 A CN 113114407A
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frequency hopping
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artificial noise
frequency
sequence
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CN113114407B (en
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宋长庆
赵梦韵
秦俪之
赵宏志
邵士海
唐友喜
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University of Electronic Science and Technology of China
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/713—Spread spectrum techniques using frequency hopping
    • H04B1/7136—Arrangements for generation of hop frequencies, e.g. using a bank of frequency sources, using continuous tuning or using a transform
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/713—Spread spectrum techniques using frequency hopping
    • H04B1/7156—Arrangements for sequence synchronisation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a secret communication method and a system, comprising the following steps: s1, a secret communication frequency hopping transmitter generates a secret information sequence s (n) and an artificial noise sequence c (n), and a sum signal of the secret information sequence s (n) and the artificial noise sequence c (n) is transmitted after frequency hopping modulation and radio frequency modulation; s2, the authorized frequency hopping receiver performs frequency hopping synchronization by using the synchronization hopping information to obtain a propagation delay estimated value, and removes frequency hopping of the received signal; s3, carrying out frequency offset and channel attenuation estimation on the received signal by using the synchronous hopping information, and compensating a local reference artificial noise sequence of the receiver by using the obtained estimation value; s4, subtracting the compensated local reference artificial noise sequence from the digital baseband receiving signal to suppress artificial noise components in the baseband receiving signal; and S5, demodulating the baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter. The invention effectively improves the secrecy performance of the communication system and ensures the suppression effect of artificial noise at the authorized frequency hopping receiver.

Description

Secret communication method and system
Technical Field
The present invention relates to the field of communications, and in particular, to a secret communication method and system under artificial noise suppression.
Background
With the gradual advance of 5G commercialization, the security and confidentiality of communication will still be the core metrics of future communication systems. In a complex modern electromagnetic environment, however, ubiquitous interference and eavesdropping seriously threaten the security of wireless communications. In order to improve the security performance of the communication system, frequency hopping is widely used for interference resistance and reconnaissance. But under long-term strong interception, the frequency hopping parameters of the communication frequency hopping transmitter of the party I can be accurately estimated by the enemy. Once this occurs, the secret information in existing frequency hopping communication systems will be continuously eavesdropped by the adversary.
The artificial noise technology can reduce the channel quality at the position of the eavesdropper, and simultaneously ensure the normal communication of the own receiver, thereby effectively resisting the eavesdropping of an enemy. However, the existing artificial noise technology is mainly applied to a fixed-frequency communication system, and once the system is actively interfered by an eavesdropper, the communication system of the party faces the risk of paralysis.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a secret communication method and a secret communication system, which realize the advantage complementation of a frequency hopping technology and artificial noise, effectively improve the secret performance of a communication system and ensure the suppression effect of the artificial noise at an authorized frequency hopping receiver.
The purpose of the invention is realized by the following technical scheme: a secure communication method comprising the steps of:
s1, a secret communication frequency hopping transmitter generates a secret information sequence s (n) and an artificial noise sequence c (n), and a sum signal of the secret information sequence s (n) and the artificial noise sequence c (n) is transmitted after frequency hopping modulation and radio frequency modulation;
s2, the authorized frequency hopping receiver performs frequency hopping synchronization by using the synchronization hopping information to obtain a propagation delay estimated value, and removes frequency hopping of the received signal;
s3, carrying out frequency offset and channel attenuation estimation on the received signal by using the synchronous hopping information, and compensating a local reference artificial noise sequence of the receiver by using the obtained estimation value;
s4, subtracting the compensated local reference artificial noise sequence from the digital baseband receiving signal to suppress artificial noise components in the baseband receiving signal;
and S5, demodulating the baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
Further, the step S1 includes the following sub-steps:
s101, at a secret communication frequency hopping transmitter, an artificial noise sequence c (n) obeys Gaussian distribution with the mean value of 0 and is not related to secret information s (n); the sum signal of the two signals is transmitted after frequency hopping modulation and radio frequency modulation, the frequency hopping pattern and artificial noise information of the transmitter are known to the authorized frequency hopping receiver, and the frequency hopping transmission signal at the communication frequency hopping transmitter is represented as:
Figure BDA0003007789790000021
wherein s (t), c (t) represent continuous time signal forms of the base band secret information sequence s (n) and the artificial noise sequence c (n), respectively, fc、fiRespectively representing the center frequencies of the radio frequency modulation and the frequency hopping modulation,
Figure BDA0003007789790000022
representing the phase of the transmitted signal, i being a non-negative integer, T representing the period of each hop of the signal, g (T) being a rectangular window function, at T ∈ (0, T)]The value in the time interval is 1, otherwise, the value is 0, namely:
Figure BDA0003007789790000023
s102, at a secret communication frequency hopping transmitter, a transmitted frequency hopping signal comprises a synchronous hop and an information hop, wherein the synchronous hop comprises synchronous sequence information, and the synchronous sequence is known to an authorized frequency hopping receiver.
Further, the step S2 includes the following sub-steps:
s201, representing a received frequency hopping signal at an authorized frequency hopping receiver as:
Figure BDA0003007789790000024
wherein the content of the first and second substances,
Figure BDA0003007789790000025
tau respectively represents complex channel fading and propagation delay between the secret communication frequency hopping transmitter and the authorized frequency hopping receiver; w (t) represents a thermal noise signal at the licensed frequency hopping receiver, and
Figure BDA0003007789790000026
not related;
recording the sampling period of the authorized frequency hopping receiver as TsThen the discrete form of the frequency hopping signal received at the authorized frequency hopping receiver is expressed as:
Figure BDA0003007789790000027
wherein D is tau/TsDenotes the normalized propagation delay, Fc＝fcTs、Fi＝fiTsRepresenting the normalized radio frequency and the normalized frequency hopping at the communication frequency hopping transmitter, g (N-D-iN) and w (N) are discrete versions of g (T- τ -iT) and w (T), respectively, N ═ T/TsRepresenting the number of symbols contained in each hop signal;
s202, authorizing a frequency hopping receiver to generate a fixed-frequency carrier signal, wherein the frequency of the fixed-frequency carrier signal is the same as that of a synchronous hop, conjugate multiplying the carrier signal by a received signal, and low-pass filtering the product signal, wherein after the low-pass filtering, only the synchronous hop part in the received signal is successfully converted into a baseband by down conversion, and other hop information is filtered by a filter;
s203, performing correlation operation by using the signal after low-pass filtering and a synchronization sequence contained in the synchronization jump to obtain a normalized propagation delay estimation value, and recording the normalized propagation delay estimation value as a normalized propagation delay estimation value
Figure BDA0003007789790000028
Assuming that the time synchronization operation is performed perfectly, i.e.
Figure BDA0003007789790000029
S204, using the time delay estimated value of synchronous jump synchronous operation, authorizing the frequency hopping receiver to generate a frequency hopping carrier signal with the same frequency hopping rule as the received signal in the local frequency synthesizer, wherein the signal is represented as:
Figure BDA0003007789790000031
wherein, Fi＝fiTsAnd
Figure BDA0003007789790000032
respectively representing the normalized hopping frequency and phase of the local hopping carrier at the receiver, g (n-D-iN) being a discrete form of a rectangular window function g (t- τ -iT);
s205, conjugate multiplication is carried out on m (n) and the received frequency hopping signal to obtain
Figure BDA0003007789790000033
Wherein m is*(n) represents a conjugate of m (n),
Figure BDA0003007789790000034
indicating the phase of the radio frequency carrier at the authorized frequency hopping receiver,
Figure BDA0003007789790000035
denotes the equivalent phase shift, w, of r (n)r(n) indicates reception after frequency hopping is releasedDiscrete forms of the thermal noise portion in the signal;
s206, after r (n) is obtained, low-pass filtering is carried out on the r (n) to filter out signals and thermal noise outside the signal bandwidth, and the obtained signals are represented as follows:
rLPF(n)＝rs(n)+rc(n)+wLPF(n)，
wherein the content of the first and second substances,
Figure BDA0003007789790000036
Figure BDA0003007789790000037
rs(n)、rc(n) and wLPF(n) respectively representing a secret information part, an artificial noise part and a thermal noise part in the low-pass filtered received signal,
Figure BDA0003007789790000038
representing the low-pass filtered equivalent complex channel fading, g (n) is a discrete form of a rectangular window function g (t).
Further, the step S3 includes the following sub-steps:
s301, in secret communication system, the sending sequence of synchronous jump is known, the received synchronous jump signal is used to make frequency deviation estimation to the received signal, r is firstLPF(n) processing to obtain a normalized frequency offset estimate of the digital baseband received signal of
Figure BDA0003007789790000039
Wherein arg [. C]Representing the argument of a plurality [ ·]*Represents a conjugate of a complex number;
the received synchronous jump signal is used to carry out channel attenuation estimation to the received signal, and the maximum likelihood estimation method is adopted to obtain the channel gain estimation value of
Figure BDA0003007789790000041
S302, in the frequency hopping synchronization operation, the time delay information of the received signal is obtained, and the information is used for the reference artificial noise sequence c generated locallyref(n) compensating to obtain a time delay compensated sequence represented as
ct(n)＝cref(n-D)；
Then, using the frequency offset estimation value
Figure BDA0003007789790000042
Performing frequency offset compensation to obtain
Figure BDA0003007789790000043
Finally, using the channel attenuation estimate
Figure BDA0003007789790000044
Performing channel attenuation compensation to obtain
Figure BDA0003007789790000045
Therefore, the time delay, the frequency offset and the channel attenuation compensation of the local reference artificial noise signal are completed.
Further, the step S4 includes the following sub-steps:
s401, subtracting the local reference artificial noise signal after time delay, frequency offset and channel attenuation compensation from the digital baseband receiving signal to realize artificial noise suppression of the receiving signal, wherein the digital baseband receiving signal after artificial noise suppression is represented as:
Figure BDA0003007789790000046
wherein the content of the first and second substances,
Figure BDA0003007789790000047
representing the residual artificial noise part after the artificial noise suppression, so that the artificial noise suppression of the received signal is completed, and the obtained residual received signal can be further demodulated to extract the secret information;
s402, measuring the artificial noise suppression performance of the secret communication system, wherein the adopted index is the artificial noise suppression ratio which represents the ratio of the power of the artificial noise and the thermal noise in the received signal before the artificial noise suppression operation to the power after the suppression operation, namely
Figure BDA0003007789790000048
Wherein, P {. is to calculate the signal power, and the higher the artificial noise suppression ratio, the more thorough the artificial noise component in the received signal is suppressed, that is, the better the artificial noise suppression performance is.
A secure communication system comprising:
the secret communication frequency hopping transmitter is used for generating a sum signal of a secret signal and artificial noise and transmitting the sum signal in an information hopping time slot; periodically sending a synchronization hop containing a synchronization sequence between the information hop time slots;
the authorized frequency hopping receiver is used for receiving the confidential frequency hopping signal transmitted by the confidential communication frequency hopping transmitter, and firstly, the frequency hopping removing operation is carried out on the received frequency hopping signal to obtain a digital baseband receiving signal; then, carrying out frequency offset and channel attenuation estimation on the obtained digital baseband receiving signal, and compensating a locally generated reference artificial noise sequence by using the obtained estimation value; then, the compensated artificial noise sequence is used for carrying out artificial noise component suppression on the digital baseband receiving signal; and finally, demodulating the digital baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
Further, the licensed frequency hopping receiver comprises:
the frequency hopping carrier unit is used for generating a receiving synchronous carrier and generating a local frequency hopping carrier required by the debounce operation;
the frequency hopping synchronization unit is used for realizing frequency hopping synchronization, removing frequency hopping from the received signal and obtaining a propagation delay value of the received signal;
a baseband parameter estimation unit, configured to estimate frequency offset and channel attenuation of a received signal on a digital baseband;
the artificial noise compensation unit is used for compensating the local reference artificial noise signal from four dimensions of time delay, frequency, amplitude and phase on a digital baseband;
an artificial noise suppression unit for suppressing an artificial noise component in the digital baseband reception signal;
and the demodulation recovery unit is used for demodulating the digital baseband receiving signal after the artificial noise suppression and recovering the confidential information sent by the frequency hopping communication frequency hopping transmitter.
The invention has the beneficial effects that: the method and the device estimate and compensate the time delay, the frequency offset and the channel attenuation of the received signal with high precision, effectively improve the confidentiality of a communication system and ensure the suppression effect of artificial noise at an authorized frequency hopping receiver; the advantages of the frequency hopping technology and the artificial noise are complemented, the secrecy performance of a communication system is effectively improved, and the suppression effect of the artificial noise at the authorized frequency hopping receiver is ensured;
drawings
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a schematic diagram of a secure communication architecture in an embodiment;
FIG. 3 is a diagram illustrating a simulation of the performance of the secure communication system in an embodiment.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
As shown in fig. 1, a secure communication method includes the steps of:
s1, a secret communication frequency hopping transmitter generates a secret information sequence s (n) and an artificial noise sequence c (n), and a sum signal of the secret information sequence s (n) and the artificial noise sequence c (n) is transmitted after frequency hopping modulation and radio frequency modulation:
s101, at a secret communication frequency hopping transmitter, an artificial noise sequence c (n) obeys Gaussian distribution with the mean value of 0 and is not related to secret information s (n); the sum signal of the two signals is transmitted after frequency hopping modulation and radio frequency modulation, the frequency hopping pattern and artificial noise information of the transmitter are known to the authorized frequency hopping receiver, and the frequency hopping transmission signal at the communication frequency hopping transmitter is represented as:
Figure BDA0003007789790000061
wherein s (t), c (t) represent continuous time signal forms of the base band secret information sequence s (n) and the artificial noise sequence c (n), respectively, fc、fiRespectively representing the center frequencies of the radio frequency modulation and the frequency hopping modulation,
Figure BDA0003007789790000062
representing the phase of the transmitted signal, i being a non-negative integer, T representing the period of each hop of the signal, g (T) being a rectangular window function, at T ∈ (0, T)]The value in the time interval is 1, otherwise, the value is 0, namely:
Figure BDA0003007789790000063
s102, at a secret communication frequency hopping transmitter, a transmitted frequency hopping signal comprises a synchronous hop and an information hop, wherein the synchronous hop comprises synchronous sequence information, and the synchronous sequence is known to an authorized frequency hopping receiver.
S2, the authorized frequency hopping receiver performs frequency hopping synchronization by using the synchronization hopping information to obtain a propagation delay estimated value, and removes frequency hopping of the received signal:
s201, representing a received frequency hopping signal at an authorized frequency hopping receiver as:
Figure BDA0003007789790000064
wherein the content of the first and second substances,
Figure BDA0003007789790000065
tau respectively represents complex channel fading and propagation delay between the secret communication frequency hopping transmitter and the authorized frequency hopping receiver; w (t) represents a thermal noise signal at the licensed frequency hopping receiver, and
Figure BDA0003007789790000066
not related;
recording the sampling period of the authorized frequency hopping receiver as TsThen the discrete form of the frequency hopping signal received at the authorized frequency hopping receiver is expressed as:
Figure BDA0003007789790000067
wherein D is tau/TsDenotes the normalized propagation delay, Fc＝fcTs、Fi＝fiTsRepresenting the normalized radio frequency and the normalized frequency hopping at the communication frequency hopping transmitter, g (N-D-iN) and w (N) are discrete versions of g (T- τ -iT) and w (T), respectively, N ═ T/TsRepresenting the number of symbols contained in each hop signal;
s202, authorizing a frequency hopping receiver to generate a fixed-frequency carrier signal, wherein the frequency of the fixed-frequency carrier signal is the same as that of a synchronous hop, conjugate multiplying the carrier signal by a received signal, and low-pass filtering the product signal, wherein after the low-pass filtering, only the synchronous hop part in the received signal is successfully converted into a baseband by down conversion, and other hop information is filtered by a filter;
s203, performing correlation operation by using the signal after low-pass filtering and a synchronization sequence contained in the synchronization jump to obtain a normalized propagation delay estimation value, and recording the normalized propagation delay estimation value as a normalized propagation delay estimation value
Figure BDA0003007789790000071
Assuming that the time synchronization operation is performed perfectly, i.e.
Figure BDA0003007789790000072
S204, using the time delay estimated value of synchronous jump synchronous operation, authorizing the frequency hopping receiver to generate a frequency hopping carrier signal with the same frequency hopping rule as the received signal in the local frequency synthesizer, wherein the signal is represented as:
Figure BDA0003007789790000073
wherein, Fi＝fiTsAnd
Figure BDA0003007789790000074
respectively representing the normalized hopping frequency and phase of the local hopping carrier at the receiver, g (n-D-iN) being a discrete form of a rectangular window function g (t- τ -iT);
s205, conjugate multiplication is carried out on m (n) and the received frequency hopping signal to obtain
Figure BDA0003007789790000075
Wherein m is*(n) represents a conjugate of m (n),
Figure BDA0003007789790000076
indicating the phase of the radio frequency carrier at the authorized frequency hopping receiver,
Figure BDA0003007789790000077
denotes the equivalent phase shift, w, of r (n)r(n) represents a discrete form of a thermal noise portion in the received signal after frequency hopping is released;
s206, after r (n) is obtained, low-pass filtering is carried out on the r (n) to filter out signals and thermal noise outside the signal bandwidth, and the obtained signals are represented as follows:
rLPF(n)＝rs(n)+rc(n)+wLPF(n)，
wherein the content of the first and second substances,
Figure BDA0003007789790000078
Figure BDA0003007789790000079
rs(n)、rc(n) and wLPF(n) respectively representing a secret information part, an artificial noise part and a thermal noise part in the low-pass filtered received signal,
Figure BDA00030077897900000710
representing the low-pass filtered equivalent complex channel fading, g (n) is a discrete form of a rectangular window function g (t).
S3, carrying out frequency offset and channel attenuation estimation on the received signal by using the synchronous hopping information, and compensating a local reference artificial noise sequence of the receiver by using the obtained estimation value:
s301, in secret communication system, the sending sequence of synchronous jump is known, the received synchronous jump signal is used to make frequency deviation estimation to the received signal, r is firstLPF(n) processing to obtain a normalized frequency offset estimate of the digital baseband received signal of
Figure BDA0003007789790000081
Wherein arg [. C]Representing the argument of a plurality [ ·]*Represents a conjugate of a complex number;
the received synchronous jump signal is used to carry out channel attenuation estimation to the received signal, and the maximum likelihood estimation method is adopted to obtain the channel gain estimation value of
Figure BDA0003007789790000082
S302, in the frequency hopping synchronization operation, the time delay information of the received signal is obtained, and the information is used for the reference artificial noise sequence c generated locallyref(n) compensating to obtain a time delay compensated sequence represented as
ct(n)＝cref(n-D)；
Then, using the frequency offset estimation value
Figure BDA0003007789790000083
Performing frequency offset compensation to obtain
Figure BDA0003007789790000084
Finally, using the channel attenuation estimate
Figure BDA0003007789790000085
Performing channel attenuation compensation to obtain
Figure BDA0003007789790000086
Therefore, the time delay, the frequency offset and the channel attenuation compensation of the local reference artificial noise signal are completed.
S4, subtracting the compensated local reference artificial noise sequence from the digital baseband receiving signal to suppress artificial noise components in the baseband receiving signal;
s401, subtracting the local reference artificial noise signal after time delay, frequency offset and channel attenuation compensation from the digital baseband receiving signal to realize artificial noise suppression of the receiving signal, wherein the digital baseband receiving signal after artificial noise suppression is represented as:
Figure BDA0003007789790000087
wherein the content of the first and second substances,
Figure BDA0003007789790000088
representing the residual artificial noise part after the artificial noise suppression, so that the artificial noise suppression of the received signal is completed, and the obtained residual received signal can be further demodulated to extract the secret information;
s402, measuring the artificial noise suppression performance of the secret communication system, wherein the adopted index is the artificial noise suppression ratio which represents the ratio of the power of the artificial noise and the thermal noise in the received signal before the artificial noise suppression operation to the power after the suppression operation, namely
Figure BDA0003007789790000089
Wherein, P {. is to calculate the signal power, and the higher the artificial noise suppression ratio, the more thorough the artificial noise component in the received signal is suppressed, that is, the better the artificial noise suppression performance is.
And S5, demodulating the baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
A secure communication system comprising:
the secret communication frequency hopping transmitter is used for generating a sum signal of a secret signal and artificial noise and transmitting the sum signal in an information hopping time slot; periodically sending a synchronization hop containing a synchronization sequence between the information hop time slots;
the authorized frequency hopping receiver is used for receiving the confidential frequency hopping signal transmitted by the confidential communication frequency hopping transmitter, and firstly, the frequency hopping removing operation is carried out on the received frequency hopping signal to obtain a digital baseband receiving signal; then, carrying out frequency offset and channel attenuation estimation on the obtained digital baseband receiving signal, and compensating a locally generated reference artificial noise sequence by using the obtained estimation value; then, the compensated artificial noise sequence is used for carrying out artificial noise component suppression on the digital baseband receiving signal; and finally, demodulating the digital baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
Further, the licensed frequency hopping receiver comprises:
the frequency hopping carrier unit is used for generating a receiving synchronous carrier and generating a local frequency hopping carrier required by the debounce operation;
the frequency hopping synchronization unit is used for realizing frequency hopping synchronization, removing frequency hopping from the received signal and obtaining a propagation delay value of the received signal;
a baseband parameter estimation unit, configured to estimate frequency offset and channel attenuation of a received signal on a digital baseband;
the artificial noise compensation unit is used for compensating the local reference artificial noise signal from four dimensions of time delay, frequency, amplitude and phase on a digital baseband;
an artificial noise suppression unit for suppressing an artificial noise component in the digital baseband reception signal;
and the demodulation recovery unit is used for demodulating the digital baseband receiving signal after the artificial noise suppression and recovering the confidential information sent by the frequency hopping communication frequency hopping transmitter.
In an example of the present application, a practical system architecture constructed in accordance with the present application is shown in fig. 2, where the secret information and the artificial noise sequence are transmitted together at a communication hopping transmitter and the artificial noise suppression operation is performed after the frequency hopping is released at an authorized hopping receiver. The MATLAB tool is utilized to simulate and verify the secret communication performance provided by the invention under the condition of time synchronization error, and the simulation parameters are set as follows:
Figure BDA0003007789790000091
Figure BDA0003007789790000101
fig. 3 simulates the variation trend of the artificial noise suppression performance of the security system along with the synchronization error, wherein gamma represents the power ratio of artificial noise to thermal noise at the authorized frequency hopping receiver, and N represents the length of each hop signal. It can be seen that as the synchronization error increases, the artificial noise suppression ratio is continuously reduced, indicating that the presence of the synchronization error may reduce the suppression performance of the artificial noise. In addition, when the length and the synchronization error of each hop signal are fixed, the artificial noise suppression ratio is increased along with the increase of the power ratio of the artificial noise to the thermal noise, but the power of the residual artificial noise is also increased, which indicates that the blind increase of the artificial noise power can raise the bottom noise level at the authorized frequency hopping receiver instead, thereby reducing the performance of the communication system; when the power ratio of the synchronization error and the artificial noise to the thermal noise is fixed, the artificial noise suppression ratio is increased along with the reduction of the length of each hop of signal, which shows that the reduction of the length of each hop of signal can effectively improve the artificial noise suppression performance of the security system and the robustness of the system to the synchronization error.
In summary, in view of the security problem in the wireless communication system, in the transmission scenario of the frequency hopping system, in the wireless channel, a brand-new secret communication system and method are provided herein to improve the secret performance of the system, achieve the advantage complementation of the frequency hopping technology and the artificial noise, effectively improve the secret performance of the communication system, and ensure the suppression effect of the artificial noise at the authorized frequency hopping receiver. The simulation result preliminarily verifies the effectiveness and feasibility of the method.
The present invention has been described herein in detail with respect to specific embodiments thereof, which are provided to enable those skilled in the art to make or use the invention, and various modifications thereof will be apparent to those skilled in the art. The present invention is not limited to these examples, or to certain aspects thereof. The scope of the invention is specified by the appended claims.
While the foregoing description shows and describes a preferred embodiment of the invention, it is to be understood, as noted above, that the invention is not limited to the form disclosed herein, but is not intended to be exhaustive or to exclude other embodiments and may be used in various other combinations, modifications, and environments and may be modified within the scope of the inventive concept described herein by the above teachings or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. A secure communication method, characterized by: the method comprises the following steps:
s1, a secret communication frequency hopping transmitter generates a secret information sequence s (n) and an artificial noise sequence c (n), and a sum signal of the secret information sequence s (n) and the artificial noise sequence c (n) is transmitted after frequency hopping modulation and radio frequency modulation;
s2, the authorized frequency hopping receiver performs frequency hopping synchronization by using the synchronization hopping information to obtain a propagation delay estimated value, and removes frequency hopping of the received signal;
s3, carrying out frequency offset and channel attenuation estimation on the received signal by using the synchronous hopping information, and compensating a local reference artificial noise sequence of the receiver by using the obtained estimation value;
s4, subtracting the compensated local reference artificial noise sequence from the digital baseband receiving signal to suppress artificial noise components in the baseband receiving signal;
and S5, demodulating the baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
2. A secure communication method according to claim 1, characterized in that: the step S1 includes the following sub-steps: the step S1 includes the following sub-steps:
s101, at a secret communication frequency hopping transmitter, an artificial noise sequence c (n) obeys Gaussian distribution with the mean value of 0 and is not related to secret information s (n); the sum signal of the two signals is transmitted after frequency hopping modulation and radio frequency modulation, the frequency hopping pattern and artificial noise information of the transmitter are known to the authorized frequency hopping receiver, and the frequency hopping transmission signal at the communication frequency hopping transmitter is represented as:
Figure FDA0003007789780000011
wherein s (t), c (t) represent continuous time signal forms of the base band secret information sequence s (n) and the artificial noise sequence c (n), respectively, fc、fiRespectively representing the center frequencies of the radio frequency modulation and the frequency hopping modulation,
Figure FDA0003007789780000012
representing the phase of the transmitted signal, i being a non-negative integer, T representing the period of each hop of the signal, g (T) being a rectangular window function, at T ∈ (0, T)]The value in the time interval is 1, otherwise, the value is 0, namely:
Figure FDA0003007789780000013
s102, at a secret communication frequency hopping transmitter, a transmitted frequency hopping signal comprises a synchronous hop and an information hop, wherein the synchronous hop comprises synchronous sequence information, and the synchronous sequence is known to an authorized frequency hopping receiver.
3. A secure communication method according to claim 1, characterized in that: the step S2 includes the following sub-steps:
s201, representing a received frequency hopping signal at an authorized frequency hopping receiver as:
Figure FDA0003007789780000021
wherein the content of the first and second substances,
Figure FDA0003007789780000022
tau respectively represents complex channel fading and propagation delay between the secret communication frequency hopping transmitter and the authorized frequency hopping receiver; w (t) represents a thermal noise signal at the licensed frequency hopping receiver, and
Figure FDA0003007789780000023
not related;
recording the sampling period of the authorized frequency hopping receiver as TsThen the discrete form of the frequency hopping signal received at the authorized frequency hopping receiver is expressed as:
Figure FDA0003007789780000024
wherein D is tau/TsDenotes the normalized propagation delay, Fc＝fcTs、Fi＝fiTsRepresenting the normalized radio frequency and the normalized frequency hopping at the communication frequency hopping transmitter, g (N-D-iN) and w (N) are discrete versions of g (T- τ -iT) and w (T), respectively, N ═ T/TsRepresenting the number of symbols contained in each hop signal;
s202, authorizing a frequency hopping receiver to generate a fixed-frequency carrier signal, wherein the frequency of the fixed-frequency carrier signal is the same as that of a synchronous hop, conjugate multiplying the carrier signal by a received signal, and low-pass filtering the product signal, wherein after the low-pass filtering, only the synchronous hop part in the received signal is successfully converted into a baseband by down conversion, and other hop information is filtered by a filter;
s203, performing correlation operation by using the signal after low-pass filtering and a synchronization sequence contained in the synchronization jump to obtain a normalized propagation delay estimation value, and recording the normalized propagation delay estimation value as a normalized propagation delay estimation value
Figure FDA0003007789780000025
Assuming that the time synchronization operation is performed perfectly, i.e.
Figure FDA0003007789780000026
S204, using the time delay estimated value of synchronous jump synchronous operation, authorizing the frequency hopping receiver to generate a frequency hopping carrier signal with the same frequency hopping rule as the received signal in the local frequency synthesizer, wherein the signal is represented as:
Figure FDA0003007789780000027
wherein, Fi＝fiTsAnd
Figure FDA0003007789780000028
respectively representing the normalized hopping frequency and phase of the local hopping carrier at the receiver, g (n-D-iN) being a discrete form of a rectangular window function g (t- τ -iT);
s205, conjugate multiplication is carried out on m (n) and the received frequency hopping signal to obtain
Figure FDA0003007789780000029
Wherein m is*(n) represents a conjugate of m (n),
Figure FDA00030077897800000210
indicating the phase of the radio frequency carrier at the authorized frequency hopping receiver,
Figure FDA00030077897800000211
denotes the equivalent phase shift, w, of r (n)r(n) represents a discrete form of a thermal noise portion in the received signal after frequency hopping is released;
s206, after r (n) is obtained, low-pass filtering is carried out on the r (n) to filter out signals and thermal noise outside the signal bandwidth, and the obtained signals are represented as follows:
rLPF(n)＝rs(n)+rc(n)+wLPF(n)，
wherein the content of the first and second substances,
Figure FDA0003007789780000031
Figure FDA0003007789780000032
rs(n)、rc(n) and wLPF(n) respectively representing a secret information part, an artificial noise part and a thermal noise part in the low-pass filtered received signal,
Figure FDA0003007789780000033
representing the low-pass filtered equivalent complex channel fading, g (n) is a discrete form of a rectangular window function g (t).
4. A secure communication method according to claim 1, characterized in that: the step S3 includes the following sub-steps:
s301, in secret communication system, the sending sequence of synchronous jump is known, the received synchronous jump signal is used to make frequency deviation estimation to the received signal, r is firstLPF(n) processing to obtain a normalized frequency offset estimate of the digital baseband received signal of
Figure FDA0003007789780000034
Wherein arg [. C]Representing the argument of a plurality [ ·]*Represents a conjugate of a complex number;
the received synchronous jump signal is used to carry out channel attenuation estimation to the received signal, and the maximum likelihood estimation method is adopted to obtain the channel gain estimation value of
Figure FDA0003007789780000035
S302, in the frequency hopping synchronization operation, the time delay information of the received signal is obtained, and the information is used for the reference artificial noise sequence c generated locallyref(n) compensating to obtain a time delay compensated sequence represented as
ct(n)＝cref(n-D)；
Then, using the frequency offset estimation value
Figure FDA0003007789780000036
Performing frequency offset compensation to obtain
Figure FDA0003007789780000037
Finally, using the channel attenuation estimate
Figure FDA0003007789780000038
Performing channel attenuation compensation to obtain
Figure FDA0003007789780000041
Therefore, the time delay, the frequency offset and the channel attenuation compensation of the local reference artificial noise signal are completed.
5. A secure communication method according to claim 1, characterized in that: the step S4 includes the following sub-steps:
s401, subtracting the local reference artificial noise signal after time delay, frequency offset and channel attenuation compensation from the digital baseband receiving signal to realize artificial noise suppression of the receiving signal, wherein the digital baseband receiving signal after artificial noise suppression is represented as:
Figure FDA0003007789780000042
wherein the content of the first and second substances,
Figure FDA0003007789780000043
representing the residual artificial noise part after the artificial noise suppression, so that the artificial noise suppression of the received signal is completed, and the obtained residual received signal can be further demodulated to extract the secret information;
s402, measuring the artificial noise suppression performance of the secret communication system, wherein the adopted index is the artificial noise suppression ratio which represents the ratio of the power of the artificial noise and the thermal noise in the received signal before the artificial noise suppression operation to the power after the suppression operation, namely
Figure FDA0003007789780000044
Wherein, P {. is to calculate the signal power, and the higher the artificial noise suppression ratio, the more thorough the artificial noise component in the received signal is suppressed, that is, the better the artificial noise suppression performance is.
6. A secure communication system based on the method of any one of claims 1 to 5, characterized in that: the method comprises the following steps:
the secret communication frequency hopping transmitter is used for generating a sum signal of a secret signal and artificial noise and transmitting the sum signal in an information hopping time slot; periodically sending a synchronization hop containing a synchronization sequence between the information hop time slots;
the authorized frequency hopping receiver is used for receiving the confidential frequency hopping signal transmitted by the confidential communication frequency hopping transmitter, and firstly, the frequency hopping removing operation is carried out on the received frequency hopping signal to obtain a digital baseband receiving signal; then, carrying out frequency offset and channel attenuation estimation on the obtained digital baseband receiving signal, and compensating a locally generated reference artificial noise sequence by using the obtained estimation value; then, the compensated artificial noise sequence is used for carrying out artificial noise component suppression on the digital baseband receiving signal; and finally, demodulating the digital baseband receiving signal after the artificial noise suppression to recover the secret information sent by the secret communication frequency hopping transmitter.
7. A secure communications system according to claim 6, characterized in that: the licensed frequency hopping receiver comprises:
the frequency hopping carrier unit is used for generating a receiving synchronous carrier and generating a local frequency hopping carrier required by the debounce operation;
the frequency hopping synchronization unit is used for realizing frequency hopping synchronization, removing frequency hopping from the received signal and obtaining a propagation delay value of the received signal;
a baseband parameter estimation unit, configured to estimate frequency offset and channel attenuation of a received signal on a digital baseband;
the artificial noise compensation unit is used for compensating the local reference artificial noise signal from four dimensions of time delay, frequency, amplitude and phase on a digital baseband;
an artificial noise suppression unit for suppressing an artificial noise component in the digital baseband reception signal;
and the demodulation recovery unit is used for demodulating the digital baseband receiving signal after the artificial noise suppression and recovering the confidential information sent by the frequency hopping communication frequency hopping transmitter.
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