CN114189309B - Self-adaptive safe communication device and method based on vortex electromagnetic waves - Google Patents
Self-adaptive safe communication device and method based on vortex electromagnetic waves Download PDFInfo
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Abstract
A self-adaptive safe communication device and method based on vortex electromagnetic waves relate to the technical field of wireless communication. Generating a direction radiation coefficient table of the N-array element uniform circular antenna array under a given carrier frequency; adaptively selecting an orbit angular momentum mode for sending artificial noise; transmitting signals and modulating the orbital angular momentum of artificial noise; orbital angular momentum coaxial multimode multiplex transmission. The invention can realize safe wireless communication by using only one uniform circular antenna array. The artificial noise is multiplexed in a non-0 mode, interference to legal users is avoided, the channel capacity of an eavesdropper is reduced, and high-capacity secret communication is achieved. Meanwhile, the optimal mode of artificial noise is selected in a self-adaptive mode according to the direction angle information of the eavesdropper, so that the eavesdropper is shielded to the maximum extent, and the confidentiality of the system is improved. When the eavesdropper direction is unknown, a mode of artificial noise modal random jumping is adopted, potential eavesdroppers in all directions are shielded, and the system secrecy capacity is improved.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to the technical field of a self-adaptive safe communication method based on vortex electromagnetic waves.
Background
Currently, security of wireless communications faces increasingly serious challenges. First, security measures based on computational theory are becoming increasingly vulnerable. For a long time, the security of wireless communication is mainly guaranteed at the high level of a communication protocol stack by means of authentication and encryption technologies. However, as some widely used encryption algorithms, such as KASUMI, AES128/256, MD5, etc., are broken in recent years, the vulnerability of the passive defense system is exposed. The rapid advancement of quantum computing has also made security approaches based on computational theory face serious challenges. Second, wireless communication is naturally open and broadcast, and is more susceptible to interception and eavesdropping by third parties. Third, the physical layer at the bottom of the protocol stack lacks the necessary security measures to take. This results in the eavesdropper being "able to obtain" the secret data (even the key) but "unable to understand" its contents; when the eavesdropper steals the complete key or has strong computing power, the eavesdropper can decrypt the ciphertext completely.
In order to meet these challenges, a new security technology needs to be found by breaking through the traditional cryptography-based security policy. The physical layer secure communication technology, which is developed to meet this requirement, is a key means for implementing security and communication integration. The technology is mainly based on Shannon 'unconditional security theory' and Wyner 'eavesdropping channel model', starts with diversity, uniqueness and non-falsification of a wireless channel, makes full use of the difference between a legal receiver and an eavesdropper physical channel, carries out targeted processing on received and sent signals, and realizes the advantage situation that 'the legal receiver signals are strong and stable, and the eavesdropper signals are weak and random', thereby realizing information blocking on the eavesdropper on a physical layer, improving the security of wireless communication essentially, and having wide potential application prospect in the field of wireless communication.
In recent years, with the rapid development of multi-antenna technology in wireless communication, various Beamforming methods proposed in the early days are discovered by academia, and the technology is a technology for effectively establishing a dominant channel of a legal communicator; it is possible to realize unconditional safe communication by using the randomness and uniqueness of a wireless channel under the guidance of the existing physical layer safe communication theory. The specific scheme is as follows: a null space artificial noise method, a beam forming method, a regulation and control communication method and the like.
The Artificial Noise (AN) method is to add appropriate Artificial Noise to the transmitting end, so that the channel quality gap between AN eavesdropper and a legal receiver can be artificially increased at the expense of partial transmitting power. Thus, even if the channel noise of the legitimate receiver is stronger than that of the eavesdropper, secure transmission is possible. Under the condition that the Channel State Information (CSI) of the receiving end is known, the AN projects on the null space of the receiving end, so that the AN has no influence on the received signal of the receiving end, and can generate strong interference on the signal of the eavesdropping end. However, the method is implemented on the premise that the CSI of the receiving end is accurately obtained, which is often difficult to implement in practice. The transmitting side uses the antenna array redundancy to send artificial noise in the null space of the legal channel and send secret signals in other spaces of the legal channel. When the signal reaches the legal receiver, the artificial noise in the null space can be naturally eliminated in the wireless channel, and the secret signal is normally and stably received, so that the artificial noise does not influence the legal receiver. Because the wireless channels have difference, the artificial noise sent by the legal transmitter can not be naturally eliminated after the artificial noise passes through the wiretapping channel, so that the signal-to-noise ratio of the signal received by the wiretapping person is reduced, and the low interception probability of the confidential information in wireless transmission is further ensured. However, the application scenarios of the above methods are limited, reducing the system user capacity.
The beamforming method is introduced in the physical layer security field along with the wide application of the MIMO technology in wireless communication. The wireless communication equipment with multi-antenna transmission capability can utilize the spatial degree of freedom to carry out beam forming so that signals of a legal transmitter are effectively received by a legal receiver only in a specific direction, and therefore the signals are reduced and even completely prevented from being received by an eavesdropping end, and further the safety transmission performance is improved. In addition, the safe transmission performance can be improved by utilizing the combined design of beam forming and artificial noise based on the multi-antenna technology. To give an analytical form of the secret Capacity in MIMO communication scenarios, t.liu and s.shamai.anote on secret Capacity Channel J. IEEE trans. on Information Theory,2009,55(6):2547-2553 discloses converting the MIMO Channel into a degraded version by introducing the concept of Channel enhancement, but still does not give an analytical representation of the secret Capacity (the maximum transmission rate of the sender when an eavesdropper cannot intercept Information) and the optimal input distribution. S. Shafiee and S.Ulukus. Achievable Rates In Gaussian MISO Channel with secret Constraints [ C ]. In Proceedings ofhe IEEE int. Symp. information. theory, Nice, France,2007: 2466. 2470. configuring dual antennas for Alice (the legitimate sender) and Bob (the legitimate receiver) and Eve (the eavesdropper) configuring a specific configuration of a single antenna gives a closed representation of the privacy capacity and further analyzes the impact on system security In the presence of multiple eavesdroppers.
In summary, although a complete theory and technical system have been developed for the research of the physical layer secure communication technology, the technology is not widely applied in the application scenarios with complex environment and diverse services. The reason is mainly that: poor environmental adaptability, narrow application range and many preconditions. In order to make the physical layer secure communication technology practically widely used, the above bottleneck problem must be solved.
Based on the orthogonal physics principle among the vortex electromagnetic wave OAM modes, the technical characteristics of simultaneous same-frequency common-beam parallel transmission of multi-channel information on a plurality of OAM modes are taken as the core advantages and values: 1) ultra-high spectral efficiency; 2) extremely low probability of interception; 3) and (3) super-strong anti-interference capability.
The multiplexing of a plurality of intrinsic modes of vortex electromagnetic waves is generally realized by adopting a coaxial transmission mode of a large ring and a small ring at present. As shown in fig. 1, the transmitter antenna array uses 4 coplanar coaxial uniform circular array antennas (UCAs). The radius of UCA of the outer ring is a 0 Emitting electromagnetic waves of OAM mode 0 (namely conventional non-vortex plane waves or spherical waves), wherein the radius of UCA at the innermost ring is a 3 The electromagnetic wave of the OAM mode 3 is emitted, and so on.
The method does not fully exert the OAM multi-mode multiplexing communication technology, has a complex transmitting antenna structure and larger redundancy, and is not beneficial to the practicability of the technology.
Disclosure of Invention
The invention provides a vortex electromagnetic wave-based self-adaptive safe communication method, which realizes safe wireless communication and improves the safety of a wireless communication system.
An adaptive security communication device based on vortex electromagnetic waves, comprising:
a legal sender module, which is used for transmitting the expected sending signal of the legal sender in the form of plane wave by adopting a conventional beam forming method in a mode 0; after the signal is multiplexed with the artificial noise of mode self-adaption in the step of coaxial multimode multiplexing transmission, the signal is transmitted to a legal receiver module;
the mode self-adapting module is used for selecting an optimal mode for the artificial noise to be transmitted;
the mode mapping module modulates the artificial noise to a specified orbital angular momentum mode according to the determined transmission mode of the artificial noise;
the coaxial multimode multiplexing transmission module is used for multiplexing the expected signal and the artificial noise modulated in the orbital angular momentum mode and sending the signals out through an antenna;
and the legal receiver module is used for receiving the signal of the legal sender in the mode 0.
A self-adaptive safe communication method based on vortex electromagnetic waves comprises the following steps:
step S1, generating a directional radiation coefficient table of the N-array element uniform circular antenna array under a given carrier frequency;
step S2, adaptively selecting an orbit angular momentum mode for sending artificial noise;
step S3, transmitting signals and modulating the orbital angular momentum of artificial noise;
and step S4, the orbital angular momentum coaxial multimode multiplexing transmission.
Preferably, in step S1 of the present invention, a directional radiation coefficient table of the N-element UCA antenna at a given carrier frequency is generated, which specifically includes the following steps:
according to the orbital angular momentum communication theory, the electromagnetic radiation of a uniform circular antenna array with N array elements at a point with an orbital angular momentum mode l, a direction angle theta and an azimuth angle phi is described by the following formula:
wherein N is the number of elements of the uniform circular antenna array, j is the unit of imaginary number, j 2 K is the carrier wave number, k is 2 pi/lambda, lambda is the carrier wavelength, phi n Is the azimuth angle of the nth antenna element, J l Is a first class I order Bessel function, and R is the radius of the uniform circular antenna array; j is a function of l 、e jlφ Is a mathematical index expression;
as can be seen from the above equation, given an antenna structure defined by N and R and a carrier wavelength λ, the radiation energy amplitude and phase are related to Φ, θ, and l; obtaining an amplitude value of the electromagnetic radiation A and normalizing to obtain a radiation pattern of orbital angular momentum, and finding that the amplitude value is irrelevant to phi and only relevant to l and theta;
the antenna radiation pattern grid is designed into a two-dimensional grid with N rows and M columns, wherein N represents the number of antenna array elements and is equal to the number of modes which can be realized by the uniform circular antenna array, and M represents the number of discretized direction angles in the antenna radiation pattern; each row corresponds to one orbital angular momentum mode, from mode 0 to mode N-1, containing radiation values at M angles.
Preferably, in step S2 of the present invention, the OAM mode for sending the artificial noise is adaptively selected, which specifically includes the following steps:
setting x as [ x ] to be sent by legal sender 1 ,x 2 ,…,x N ] T Both the legal receiver and the eavesdropper are receiving by a single antenna; by using h l ＝[h l,1 ,h l,2 ,…,h l,N ] T Representing the channel from the N array element antenna of the transmitting party to the receiving antenna in the orbital angular momentum mode I, and the channel gain between the antenna array elements is defined as
Wherein r represents the distance between the transmitting and receiving antenna elements, c 0 Is a constant characterizing the antenna configuration, e -jkr 、
Is a mathematical exponential expression;
the legitimate sender sends a signal x in mode 0, and the channel matrix for mode 0 between the legitimate sender and the legitimate receiver is denoted h 0,b The channel matrix of mode 0 between the legitimate sender and the eavesdropper is denoted h 0,e (ii) a The legitimate sender sends an artifact w in a mode l, the channel matrix of the mode l between the legitimate sender and the legitimate receiver is denoted h l,b The channel matrix of the mode l between the legitimate sender and the eavesdropper is denoted h l,e (ii) a The artificial noise is expressed as w ═ w 1 ,w 2 ,…,w N ] T Is a zero mean Gaussian signal with power set to
The received signal y of the legitimate receiver b And a received signal y of an eavesdropper e Are respectively represented as
Wherein n is b And n e Respectively representing additive Gaussian noise at a legal receiver and at an eavesdropper, with noise power of
And
transmission signal x, artificial noise w, additive gaussian noise n b And n e Are all independent of each other;
legal sender is located in axial direction, h l,b 0 at the legal receiver, where l ≠ 0, which is not affected by artificial noise, then the signal-to-interference-plus-noise ratio γ of the legal receiver b For a signal-to-noise ratio gamma with an eavesdropper e Are respectively as
Accordingly, the channel capacities of the legitimate receiver and the eavesdropper are C, respectively b ＝log(1+γ b ) And C e ＝log(1+γ e ) The secret capacity is:
C＝C b -C e
search for the best OAM mode l of the artificial noise transmission 0 To maximize the security capacity
Preferably, in step S2, the method adaptively selects an OAM mode for sending the artificial noise, further including the following steps:
adaptive selection of OAM modalities when the orientation of an eavesdropper is known
At a known direction angle theta of an eavesdropper e In the process, an 'antenna radiation pattern table' is used for searching the optimal OAM mode for sending the artificial noise,
step S2.1.1, determining the quantified value of the eavesdropper heading angle: determining the angle theta to the direction in the antenna radiation diagram table e Closest angle of orientation, noted
Step S2.1.2, calculate the signal power received at the eavesdropper: the first row in the "antenna radiation diagram table" is the radiation coefficient of mode 0, so as to
For indexing, the radiation coefficient of the desired signal in the direction is obtained
Combining transmit signal power
Obtaining the signal power of an eavesdropper;
step S2.1.3, calculating the noise power of each mode i at the eavesdropper: the radiation coefficients of the modes are respectively extracted from an antenna radiation diagram table
Incorporating artificial noise power
And additive Gaussian noise power at eavesdropper
The noise power of each mode can be obtained;
step S2.1.4, calculating the signal interference noise ratio of each mode i at the eavesdropper according to the signal power and the noise power obtained in the above steps:
step S2.1.5, finding the mode with the largest signal interference noise ratio, that is, the solved OAM mode capable of minimizing the channel capacity of the eavesdropper, and using the mode as the OAM mode for sending artificial noise;
and when a plurality of eavesdroppers with known direction angles exist, selecting the directions of K eavesdroppers, wherein K is less than N, repeating the steps, and searching the OAM mode optimal to each eavesdropper.
Preferably, in step S2, the method adaptively selects an OAM mode for sending the artificial noise, further including the following steps:
when the orientation of the eavesdropper is unknown, the OAM mode jumps:
when the orientation of an eavesdropper is unknown, the OAM mode of artificial noise is determined by randomly selecting an OAM mode:
step S2.2.1, according to the antenna structure, determining a candidate mode set:
after the antenna structure is determined, the radiation pattern of the mode 0 for sending legal user data is determined, user data leakage occurs in the side lobe direction of the mode 0, and in other directions, the user data leakage amplitude is relatively small;
searching candidate OAM modes by using the antenna radiation pattern table in the step S1; sequentially checking the mode with the strongest amplitude in the direction of the side lobe from the first side lobe of the mode 0, and adding the mode into the candidate mode set until the previous stronger side lobes are processed;
step S2.2.2, determining the frequency of modal hopping:
setting a mode hopping frequency to select between a symbol rate and a frame rate, namely, the duration of one mode is more than or equal to one symbol duration and less than or equal to the duration of one data frame;
at step S2.2.3, a modality is randomly selected from the set of candidate modalities.
Preferably, the OAM modulation of the transmission signal and the artificial noise in step S3 of the present invention includes the following steps:
the transmission signal x, denoted x, is modulated with mode 0, respectively 0 (ii) a Using OAM modality l determined in step 2 0 Modulated artifacts w, noted as w l0 (ii) a And when a plurality of artificial noises are required to carry out OAM modulation, the plurality of artificial noises are modulated according to the determined modes respectively.
Preferably, in step S4 of the present invention, the OAM coaxial multimode multiplexing transmission includes the following processes:
transmitting signal x obtained by OAM modulation 0 And artificial noise w l0 After multiplexing, transmitting through a uniform circular antenna array; and when a plurality of artificial noises modulated by OAM exist, superposition multiplexing is directly carried out.
Compared with the prior art, the technical scheme of the invention has the following advantages:
1) the security capacity is large. The invention uses the useful signal to obtain the maximum channel capacity in the axial direction, and the eavesdropper is shielded by the artificial noise of the OAM mode self-adaptive modulation, and the channel capacity is very limited, thereby obtaining the large secret capacity.
2) The probability of interception is low. By means of OAM multi-mode multiplexing communication, the security technology is expanded from a time-frequency plane of traditional frequency hopping communication to a time-frequency-state high-dimensional space, and the interception resistance of wireless communication is greatly improved.
3) The self-adaptive mode method of the invention adopts the method of looking up the table by the antenna directional diagram, greatly simplifies the calculation amount of the algorithm, and has simple, convenient and efficient realization and strong practicability.
4) The invention realizes the safe wireless communication by using only one uniform circular antenna array by utilizing the OAM multi-mode multiplexing technology.
5) The invention utilizes the characteristic that the OAM non-0 mode does not have radiation in the axial direction, and reuses artificial noise in the non-0 mode, thereby not generating interference to legal users, reducing the channel capacity of an eavesdropper and realizing large-capacity secret communication.
6) The invention adaptively selects the optimal mode of the artificial noise according to the direction angle information of the eavesdropper, shields the eavesdropper to the maximum extent and improves the security performance of the system.
7) When the direction of an eavesdropper is unknown, the method shields potential eavesdroppers in all directions by adopting a mode of random jump of an artificial noise mode, and improves the secrecy capacity of the system.
Drawings
Fig. 1 is a schematic diagram of a multimode coaxial transmission mode of a large-circle sleeve and a small-circle sleeve in the prior art.
Fig. 2 is a schematic structural diagram of an adaptive security communication apparatus based on an OAM modality.
Fig. 3 is a flowchart of a secure communication method based on OAM multimodal adaptation.
FIG. 4 is a schematic view of the modal adaptation process of the present invention.
Fig. 5 is a schematic diagram illustrating a modal random hopping process according to the present invention.
Fig. 6 is a schematic diagram of the basic principle of the present invention.
Fig. 7 is a two-dimensional radiation pattern of different OAM modes.
Fig. 8 is a multi-dimensional security communication flow diagram for hopping from a traditional "time-frequency" to a "time-frequency state".
Detailed Description
The technical scheme of the invention is explained in detail by combining the drawings as follows:
as shown in fig. 2, an adaptive security communication apparatus based on vortex electromagnetic waves includes:
the legitimate sender, in the mode 0, adopts the conventional beamforming method to transmit its own desired transmission signal in the form of plane wave. The signal is multiplexed with the mode self-adaptive artificial noise in the step of coaxial multimode multiplexing transmission and then transmitted to a legal receiver.
And (4) mode self-adaptation, namely selecting the optimal mode for the artificial noise to be transmitted according to a certain method.
And mode mapping, namely modulating the artificial noise to a specified OAM mode according to the determined transmission mode of the artificial noise.
And the coaxial multimode multiplexing transmission is used for multiplexing the expected signal and the artificial noise modulated in the OAM mode and sending the signals through an antenna.
The legitimate receiver, in mode 0, receives the signal of the legitimate sender.
The artificial noise modulated by the OAM mode points to a potential eavesdropper, the signal-to-noise ratio is degraded, and the eavesdropper cannot eavesdrop the data of a legal sender to realize safe transmission.
As shown in fig. 3, an adaptive secure communication method based on vortex electromagnetic waves includes the following steps:
step S1, generating a directional radiation coefficient table of the N-array element uniform circular antenna array under a given carrier frequency;
step S2, adaptively selecting an orbit angular momentum mode for sending artificial noise;
step S3, transmitting signals and modulating the orbital angular momentum of artificial noise;
and step S4, the orbital angular momentum coaxial multimode multiplexing transmission.
The specific process is as follows:
step S1, generating a directional radiation coefficient table of the N-element UCA antenna at a given carrier frequency:
according to the OAM communication theory, the electromagnetic radiation of UCA of N array elements at a point with mode l, direction angle theta and azimuth angle phi can be described by the following formula
Wherein N is UCA antenna array element number, j is imaginary number unit (j) 2 K is the carrier wave number (k is 2 pi/lambda, lambda is the carrier wavelength), phi, 1 n Is the n-thAzimuth angle of the antenna element, J l Is a first class I Bessel function, R is UCA radius, and l is OAM mode; j is a function of l 、e jlφ Is a mathematical exponential expression. From the above equation, given an antenna configuration (determined by N and R) and a carrier frequency (determined by carrier wavelength λ), the radiated energy amplitude and phase are related to Φ, θ, and l. And (3) obtaining the amplitude value of A and normalizing to obtain the radiation pattern of the OAM, wherein the amplitude value is irrelevant to phi and only relevant to l and theta.
For UCA with a given array element number N, the directional radiation pattern is determined under a given carrier frequency, and the UCA can be pre-calculated and stored as a table of the radiation pattern, so that the calculation amount of real-time calculation is saved, and the algorithm execution is simplified.
The antenna radiation pattern grid is designed as a two-dimensional table with N rows and M columns, wherein N represents the number of antenna elements and is also equal to the number of modes which can be realized by UCA (because UCA has N OAM modes at most), and M represents the number of discretized direction angles in the antenna radiation pattern. Each row corresponds to one OAM mode, comprising M angular radiation values from mode 0 to mode N-1. For example, a direction angle interval of 1 ° from-90 ° to 90 ° may be taken, totaling 181 values, i.e., M ═ 181. The following is an example of a 1 ° spaced radiation pattern table for an 8-element UCA, where | a (n, m) | represents the radiation amplitude coefficient for mode n at angle m.
Step S2, adaptively selecting an OAM mode for sending the artificial noise:
setting x as [ x ] for data to be sent by legal sender Alice 1 ,x 2 ,…,x N ] T Both the legal receiver Bob and the eavesdropper Eva receive with a single antenna. By using h l ＝[h l,1 ,h l,2 ,…,h l,N ] T When the OAM mode is I, the channel from the N array element antenna of the sending party to the receiving antenna is expressed, and the channel gain between the antenna array elements can be defined as
Wherein r represents the distance between the transmitting and receiving antenna elements, c 0 Is a constant characterizing the antenna configuration, e -jkr 、
Is a mathematical exponential expression;
a legal sender Alice sends a signal x in a mode 0, and a channel matrix of the mode 0 between the legal sender Alice and a legal receiver Bob is represented as h 0,b The channel matrix of mode 0 between the legal sender Alice and the eavesdropper Eva is denoted as h 0,e (ii) a A legal sender Alice sends artificial noise w in a mode l, and a channel matrix of the mode l between the legal sender Alice and a legal receiver Bob is represented as h l,b The channel matrix of the mode l between the legal sender Alice and the eavesdropper Eva is denoted as h l,e . The artificial noise is expressed as w ═ w 1 ,w 2 ,…,w N ] T Is a zero mean Gaussian signal with power set to
The received signal y of the legitimate receiver Bob b And the received signal y of the eavesdropper Eva e Are respectively represented as
Wherein n is b And n e Respectively represent additive Gaussian noise at a legal receiver Bob and an eavesdropper Eva, and the noise power is
And
transmission signal x, artificial noise w, additive gaussian noise n b And n e Are all independent of each other.
H since the legal receiver Bob is located in the axial direction l,b (l ≠ 0) is 0 at the legitimate receiver Bob and therefore is not affected by artifacts. The signal to interference plus noise ratio y of the legitimate receiver Bob b Signal to noise ratio γ of sum Eva e Are respectively as
Accordingly, the channel capacities of the legitimate receiver Bob and the eavesdropper Eva are respectively C b ＝log(1+γ b ) And C e ＝log(1+γ e ). According to the wireless communication safety theory, the secret capacity of the scheme is
C＝C b -C e 。
The purpose of OAM mode adaptation is to find the optimum OAM mode l for artificial noise transmission 0 To maximize the security capacity
Since the signal-to-noise ratio of Bob is not affected by the orientation of the eavesdropper, the direction and the power of the artificial noise, and the channel capacity does not change along with the OAM mode of the artificial noise, the problem is equivalent to minimizing the channel capacity of Eva and also equivalent to minimizing the signal-to-interference-and-noise ratio of the eavesdropper, namely gamma e 。
Specifically, two cases can be classified: the OAM mode is selected in a self-adaptive mode when the orientation of the eavesdropper Eva is known, and the OAM mode randomly jumps when the orientation of the eavesdropper Eva is unknown.
(1) Step S2.1, when the orientation of the eavesdropper Eva is known, the OAM mode is selected in a self-adaptive mode:
at the known Eva Direction Angle θ e Then, using the "antenna radiation pattern table" in step S1, the optimum OAM mode (denoted by l) for transmitting the artificial noise is searched for 0 )。
The specific process is shown in fig. 4:
at step S2.1.1, a quantified value of the eavesdropper heading angle is determined. Determining the angle theta to the direction in an antenna radiation diagram table e Closest angle of direction, noted
For example, if the directional angles in the "antenna radiation pattern table" are spaced at 1 °, the pair θ is e Is subjected to rounding to obtain
At step S2.1.2, the power of the signal received at Eva by the eavesdropper is calculated. The first row in the "antenna radiation diagram table" is the radiation coefficient of mode 0, so as to
For indexing, the radiation coefficient of the desired signal in the direction is obtained
Combining transmit signal power
The signal power at Eva of the eavesdropper can be obtained.
Step S2.1.3, calculating the noise power of each mode l (l is more than or equal to 1 and less than N) at the evap of the eavesdropper. The radiation coefficients of the modes are respectively extracted from an antenna radiation diagram table
Incorporating artificial noise power
And additive Gaussian noise Power at Eva
The noise power of each mode can be obtained.
And S2.1.4, calculating the signal interference noise ratio of each mode l (1 is more than or equal to l and less than N) at the position of the eavesdropper Eva according to the signal power and the noise power obtained in the step.
At step S2.1.5, the mode with the largest signal-to-interference-and-noise ratio (denoted as l) is found 0 ) That is, the OAM mode solved to minimize the eavesdropper Eva channel capacity is used as the OAM mode for transmitting the artificial noise.
When there are a plurality of eavesdroppers with known direction angles, the directions of K (K < N) eavesdroppers can be selected, the steps are repeated, and an OAM mode optimal for each eavesdropper is found, so that superposition can be carried out in the subsequent steps. The superposition of artificial noises of a plurality of modes does not deteriorate the security effect of the method, but enhances the security effect of the method.
(2) Step S2.2, when the orientation of the eavesdropper Eva is unknown, the OAM mode jumps
When the orientation of the eavesdropper Eva is unknown, the OAM mode of the artificial noise is determined by randomly selecting the OAM mode (marked as l) 0 )。
The specific process is shown in fig. 5:
at step S2.2.1, a set of candidate modalities is determined based on the antenna structure.
After the antenna structure is determined, the radiation pattern of mode 0 transmitting legitimate user data is determined (as shown in fig. 7). It can be seen that the user data leakage occurs mainly in the side lobe direction of mode 0, while in other directions the user data leakage magnitude is relatively small. In order to achieve a good shielding effect, the artifacts should be transmitted as much as possible in the direction of the stronger side lobe of mode 0.
Based on this, candidate OAM modalities are searched using the "antenna radiation pattern table" in step S1. And (4) sequentially checking the mode with the strongest amplitude in the direction of the side lobe from the first side lobe of the mode 0, and adding the mode into the candidate mode set until the previous strong side lobes are processed.
Take the 8-antenna UCA array shown in fig. 7 as an example: the first minor lobe is located in a range of about 7 degrees to 11 degrees, and the mode 3 has the strongest amplitude in the direction, so the mode 3 is added into the candidate mode set; the second sub-lobe is located in the range of about 14 degrees to 17 degrees, and the mode 2 has the strongest amplitude in the direction, so that the mode 2 is added into the candidate mode set; and so on.
At step S2.2.2, the frequency of modal hopping is determined.
The frequency (jump speed) of modal jump directly affects the safety performance of the system, generally speaking, the higher the frequency, the better the confidentiality, but the higher the frequency, the higher the requirements on the performance of devices such as a frequency synthesizer, a power amplifier and the like are put forward.
The patent sets the mode hopping frequency to be selected between a symbol rate and a frame rate, i.e., a mode duration is not shorter than a symbol duration but not longer than a duration of a data frame.
At step S2.2.3, a modality is randomly selected from the set of candidate modalities.
Unlike the pseudo-random frequency hopping mode of frequency hopping communications, the mode hopping of the scheme can be random and does not need to be agreed with any receiver.
Step S3, OAM modulation of the transmission signal and the artificial noise:
the transmission signal x, denoted x, is modulated with mode 0, respectively 0 . Using OAM modality l determined in step 2 0 Modulated artifacts w, noted as w l0 . And when a plurality of artificial noises are required to carry out OAM modulation, the plurality of artificial noises are modulated according to the determined modes respectively.
Step S4, OAM coaxial multimode multiplexing transmission:
transmitting signal x obtained by OAM modulation in the last step 0 And artificial noise w l0 And after multiplexing, transmitting through UCA antenna. And when a plurality of artificial noises modulated by OAM exist, superposition multiplexing is directly carried out.
As shown in fig. 6, the present invention provides an adaptive secure communication method based on vortex electromagnetic waves. When a plurality of eavesdroppers exist, the OAM mode of artificial noise is preferably sent, so that stronger artificial noise exists in a plurality of directions, and the purpose of shielding the eavesdroppers is achieved. The basic principle of the method is summarized as follows:
(1) the legal sender uses mode 0 (namely plane wave) to send own data; because the beam has low radiation in the non-axial direction, useful signals which can be intercepted by a potential eavesdropper are very weak;
(2) meanwhile, an optimal OAM mode is selected in a self-adaptive mode to send artificial noise, potential eavesdroppers in a specific direction or an unspecific direction are interfered, and data of a legal user are prevented from being eavesdropped by the potential eavesdroppers;
(3) the legal receiver is in the axial direction, the data of the legal sender is received by using the mode 0, and the legal receiver is not influenced by artificial noise because the artificial noise mode does not radiate in the axial direction.
The core innovation of the self-adaptive safe communication method is mainly embodied in the second point. When the sender knows the orientation of the eavesdropper, one or more OAM modalities may be adaptively selected, the selected modality having stronger radiation in the direction in which the eavesdropper is located. The legal sender sends artificial noise with certain power to shield the eavesdropper. For example, if the transmitting party knows that the eavesdropper angle of 20 ° is in the direction, it can be seen from fig. 7 that the signal amplitude of mode 0 is low, while mode 1 and mode 3 have stronger radiation in this direction (the area indicated by the arrows). It is possible to choose to transmit the artifact in either modality 1 or modality 3, or both modality 1 and modality 3, to mask the eavesdropper.
When the transmitter does not know the position of the eavesdropper, the mode of sending the artificial noise can be randomly selected in a certain mode in a mode similar to frequency hopping communication, namely, the artificial noise is sent by using a certain mode in a certain time period, the artificial noise is sent by using another mode in the next time period, and the steps are repeated so as to achieve the purpose of shielding the eavesdropper in all directions.
Fig. 7 shows a two-dimensional radiation pattern of 4 OAM modes, i.e., mode 0, mode 1, mode 2, and mode 3, generated by an 8-array element UCA. It can be seen that the radiation pattern of mode 0 has the strongest normalized gain in the main lobe of the axial direction (direction angle of 0 °); the normalized gain of the mode 1, the mode 2 and the mode 3 in the axial direction is 0, and the main lobes of the mode 1, the mode 2 and the mode 3 are separated into lobes which are symmetrical on two sides in the axial direction and have smaller amplitude, which means that the OAM vortex wave of the non-0 mode can radiate energy to a specific direction.
As shown in fig. 8, in order to further improve the security of wireless communication, the present invention introduces a technique of OAM modal adaptive hopping. Frequency hopping communication is also a conventional technique for effectively enhancing the security of wireless communication. In frequency hopping communication, carrier frequencies of a transmitting party and a receiving party jump pseudo-randomly according to a preset rule, only one main parameter of the frequency changes along with time, and the randomness of a wireless signal is limited in a two-dimensional space. After an OAM multi-mode multiplexing communication concept is introduced, wireless signals can hop OAM quantum states while hopping frequency, and the randomness of the signals is expanded to a high-dimensional space of time-frequency-state. In other words, the anti-interception capability of the secure communication is significantly improved in a dimension expansion mode by randomly transmitting the traditional frequency hopping signal among different OAM modes.
Claims (8)
1. An adaptive security communication device based on vortex electromagnetic waves, comprising:
a legal sender module, which is used for transmitting the expected sending signal of the sender in the form of plane wave by adopting a conventional beam forming method in the mode 0; the signal is transmitted to a legal receiver module after the modal adaptive module and the artificial noise of the modal adaptive module are multiplexed;
the mode self-adaption module is used for selecting an optimal mode for the artificial noise to be sent by the legal sender module;
the mode mapping module modulates the sending signal and the artificial noise to a specified orbital angular momentum mode according to the transmission mode of the artificial noise determined by the mode self-adapting module;
the coaxial multi-mode multiplexing transmission module is used for multiplexing the transmission signal modulated by the mode mapping module and the artificial noise and transmitting the signals through an antenna;
and the legal receiver module is used for receiving the signal sent by the coaxial multimode multiplexing transmission module in the mode 0.
2. A self-adaptive safe communication method based on vortex electromagnetic waves is characterized by comprising the following steps:
step S1, generating an antenna radiation pattern table of the N-array element uniform circular antenna array under a given carrier frequency;
step S2, an antenna radiation diagram table is used for self-adaptively selecting an orbital angular momentum mode for sending artificial noise;
step S3, carrying out orbital angular momentum modulation on the transmission signal and the artificial noise by using an orbital angular momentum mode;
and step S4, performing orbital angular momentum coaxial multimode multiplexing transmission on the transmitting signal obtained by the orbital angular momentum modulation and the artificial noise.
3. The adaptive secure communication method according to claim 2, wherein the step S1 is to generate an antenna radiation pattern table of the N-element UCA antenna at a given carrier frequency, and the specific process is as follows:
according to the orbital angular momentum communication theory, the electromagnetic radiation of a uniform circular antenna array with N array elements at a point with an orbital angular momentum mode l, a direction angle theta and an azimuth angle phi is described by the following formula:
wherein N is the number of elements of the uniform circular antenna array, j is the unit of imaginary number, j 2 K is the carrier wave number, k is 2 pi/lambda, lambda is the carrier wavelength, phi n Is the azimuth angle of the nth antenna element, J l Is a first class I Bessel function, R is the radius of the uniform circular antenna array；j l 、e jlφ Is a mathematical exponential expression;
as can be seen from the above equation, given an antenna structure defined by N and R and a carrier wavelength λ, the radiation energy amplitude and phase are related to Φ, θ, and l; obtaining an amplitude value of the electromagnetic radiation A and normalizing to obtain a radiation pattern of orbital angular momentum, and finding that the amplitude value is irrelevant to phi and only relevant to l and theta;
the antenna radiation diagram grid is designed into a two-dimensional table with N rows and M columns, wherein N represents the number of antenna array elements and is equal to the number of modes which can be realized by the uniform circular-ring antenna array, and M represents the number of discretized direction angles in the antenna radiation diagram; each row corresponds to one orbital angular momentum mode, from mode 0 to mode N-1, containing radiation values at M angles.
4. The adaptive secure communication method according to claim 3, wherein in step S2, the OAM mode for sending the artificial noise is adaptively selected by using an antenna radiation pattern table, which specifically includes the following steps:
setting x as [ x ] to be sent by legal sender 1 ,x 2 ,…,x N ] T Both the legal receiver and the eavesdropper are receiving by a single antenna; by using h l ＝[h l,1 ,h l,2 ,…,h l,N ] T When the orbital angular momentum mode l is represented, the channel from the N array element antenna of the sending party to the receiving antenna is defined as the channel gain between the N antenna array element and the single antenna of the receiving party
Wherein r represents the distance between the transmitting and receiving antenna elements, c 0 Is a constant characterizing the antenna configuration, e -jkr 、
Is a mathematical exponential expression;
legitimate sender sends signal x in mode 0, legitimate sender and legitimateThe channel matrix for inter-receiver mode 0 is denoted h 0,b The channel matrix of mode 0 between the legitimate sender and the eavesdropper is denoted h 0,e (ii) a The legitimate sender sends an artificial noise w in a mode l, and the channel matrix of the mode l between the legitimate sender and the legitimate receiver is denoted h l,b The channel matrix of the mode l between the legitimate sender and the eavesdropper is denoted h l,e (ii) a The artificial noise is expressed as w ═ w 1 ,w 2 ,…,w N ] T Is a zero mean Gaussian signal with power set to
The received signal y of the legitimate receiver b And a received signal y of an eavesdropper e Are respectively represented as
Wherein n is b And n e Respectively representing additive Gaussian noise at a legal receiver and at an eavesdropper, with noise power of
And
transmission signal x, artificial noise w, additive gaussian noise n b And n e Are all independent of each other;
legal sender is located in axial direction, h l,b 0 at the legal receiver, where l ≠ 0, which is not affected by artificial noise, then the signal-to-interference-plus-noise ratio γ of the legal receiver b For a signal-to-noise ratio gamma with an eavesdropper e Are respectively as
Accordingly, the channel capacities of the legitimate receiver and the eavesdropper are C, respectively b ＝log(1+γ b ) And C e ＝log(1+γ e ) The secret capacity is:
C＝C b -C e
search for the best OAM mode l of the artificial noise transmission 0 To maximize the security capacity
5. The adaptive security communication method according to claim 3, wherein the step S2 uses an antenna radiation pattern table to adaptively select the OAM mode for transmitting the artificial noise, further comprising the following steps:
when the position of the eavesdropper is known, the OAM mode is selected adaptively:
at a known direction angle theta of an eavesdropper e In the process, an 'antenna radiation pattern table' is used for searching the optimal OAM mode for sending the artificial noise,
step S2.1.1, determining the quantified value of the eavesdropper heading angle: determining the angle theta to the direction in the antenna radiation diagram table e Closest angle of direction, noted
Step S2.1.2, calculate the signal power received at the eavesdropper: the first row in the "antenna radiation diagram table" is the radiation coefficient of mode 0, so as to
For indexing, the radiation coefficient of the desired signal in the direction is obtained
Combining transmit signal power
Obtaining the signal power of an eavesdropper;
step S2.1.3, calculating the noise power of each mode i at the eavesdropper: the radiation coefficients of the modes are respectively extracted from an antenna radiation diagram table
Incorporating artificial noise power
And additive Gaussian noise power at eavesdropper
The noise power of each mode can be obtained;
step S2.1.4, calculating the signal interference noise ratio of each mode i at the eavesdropper according to the signal power and the noise power obtained in the above steps:
step S2.1.5, finding the mode with the largest signal interference noise ratio, that is, the solved OAM mode capable of minimizing the channel capacity of the eavesdropper, and using the mode as the OAM mode for sending artificial noise;
and when a plurality of eavesdroppers with known direction angles exist, selecting the directions of K eavesdroppers, wherein K is less than N, repeating the steps, and searching the OAM mode optimal to each eavesdropper.
6. The adaptive secure communication method according to claim 3, wherein the adaptively selecting the OAM mode for transmitting the artificial noise in step S2 further comprises the following steps:
when the orientation of the eavesdropper is unknown, the OAM mode jumps:
when the orientation of an eavesdropper is unknown, the OAM mode of artificial noise is determined by randomly selecting an OAM mode:
step S2.2.1, according to the antenna structure, determining a candidate mode set:
after the antenna structure is determined, the radiation pattern of the mode 0 for sending legal user data is determined, user data leakage occurs in the side lobe direction of the mode 0, and in other directions, the user data leakage amplitude is relatively small;
searching candidate OAM modes by using the antenna radiation pattern table in the step S1; sequentially checking the mode with the strongest amplitude in the direction of the side lobe from the first side lobe of the mode 0, and adding the mode into the candidate mode set until the previous stronger side lobes are processed;
step S2.2.2, determining the frequency of modal hopping:
setting a mode hopping frequency to select between a symbol rate and a frame rate, namely, the duration of one mode is more than or equal to one symbol duration and less than or equal to the duration of one data frame;
at step S2.2.3, a modality is randomly selected from the set of candidate modalities.
7. The adaptive secure communication method according to claim 5 or 6, wherein the OAM modulation is performed on the transmission signal and the artificial noise by using an orbital angular momentum mode in the step S3, which includes the following steps:
the transmission signal x, denoted x, is modulated with mode 0, respectively 0 (ii) a Using OAM modality l determined in step 2 0 Modulated artifacts w, noted as w l0 (ii) a When a plurality of manual works are requiredAnd when OAM modulation is carried out on the noise, the plurality of artificial noises are modulated according to the determined modes respectively.
8. The adaptive security communication method according to claim 7, wherein the OAM coaxial multimode multiplexing transmission of the transmitting signal and the artificial noise obtained by the orbital angular momentum modulation in the step S4 includes the following steps:
transmitting signal x obtained by OAM modulation 0 And artificial noise w l0 After multiplexing, transmitting through a uniform circular antenna array; and when a plurality of artificial noises modulated by OAM exist, superposition multiplexing is directly carried out.
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