CN111065096B - Physical layer encryption transmission system and method for wireless communication - Google Patents
Physical layer encryption transmission system and method for wireless communication Download PDFInfo
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- H04L5/00—Arrangements affording multiple use of the transmission path
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Abstract
A physical layer encryption transmission system and a method thereof for wireless communication, comprising a construction module, an estimation module and an encryption module which are operated on a base station of the wireless communication system of the multi-input single-output MISO; the construction module is used for the construction system; the estimation module is used for channel estimation; the encryption module is used for encrypting and sending. The physical layer encryption transmission system for wireless communication further comprises: a recovery module running on the legitimate recipient; the recovery module is used for recovering the data. The method and the device are combined with other structures or methods, so that the defects that the security is not high and the reliability of communication is greatly reduced when the physical layer encryption of the wireless communication system aiming at the multi-input single-output MISO in the prior art is used for resisting the modulation identification and the eavesdropper attack are effectively avoided.
Description
Technical Field
The invention relates to the technical field of information security in wireless communication, also relates to the technical field of framing, in particular to an object layer encryption transmission technology (PLE) in physical layer security technology (PLS), and especially relates to a physical layer encryption transmission system and a method thereof for wireless communication, in particular to a physical layer encryption transmission system and a method thereof based on symbol convolution.
Background
Wireless communication networks are networks that enable interconnection of various communication devices without wiring, and are widely used in civil and military communication systems today, and have become an integral part of life and work. Due to the broadcast nature of wireless channels, dynamic topology of mobile networks and miniaturization of nodes, traditional security policies based on upper layer cryptographic encryption of networks and data processing stacks and their associated protocols face new challenges. The physical layer security uses the non-replicable characteristics of the wireless channel such as randomness, reciprocity, etc. to protect the information security from the physical layer. The security degree is independent of computational complexity, and even if an attacker has strong computational power with the help of coding and signal processing, the information can only be correctly decoded by a legal receiver, and the information can be regarded as the supplement of upper-layer security technology.
In recent years, physical Layer Encryption (PLE) has been attracting more attention, and compared with the upper layer conventional encryption mechanism, the present invention designs the encryption mechanism by utilizing various characteristics of wireless channels and signals, protects the physical layer signals from being interpreted by an eavesdropper, provides signal level security, and is shown in fig. 1 in a block diagram of a PLE-based wireless communication system. The PLE technique has no strict requirement on the number of antennas or channel conditions, so the method can be conveniently applied to various wireless communication systems, and the physical layer encryption PLE scheme before modulation is applied, the encryption mode is that the exclusive-or operation is carried out on the binary bit information after encoding, and the method is a relatively early technical scheme related to PLE, so in the practical application, the safety of the wireless communication system aiming at the multi-input single-output MISO against the modulation recognition and the eavesdropper attack is not high, the improved technical scheme divides the modulation symbol sequence into two paths and then rotates and overlaps the two paths respectively, and the encryption mode has higher communication safety when aiming at the modulation recognition and the eavesdropper attack under the quasi-static channel environment, but leads to the reliability of the communication to be greatly reduced.
Disclosure of Invention
In order to solve the problems, the invention provides a physical layer encryption transmission system and a physical layer encryption transmission method for wireless communication, which effectively avoid the defects of low safety and greatly reduced communication reliability when the physical layer encryption of a wireless communication system for multiple-input single-output MISO is used for resisting modulation identification and eavesdropper attack in the prior art.
In order to overcome the defects in the prior art, the invention provides a physical layer encryption transmission system and a method thereof for wireless communication, which concretely comprises the following steps:
a method of physical layer encrypted transmission for wireless communications, comprising:
aiming at a eavesdropping channel model of a multi-input single-output MISO wireless communication system, firstly, a legal user sends a pilot signal to a base station of the wireless communication system, the base station estimates Channel State Information (CSI) of a legal channel according to a sequence of the pilot signal, and the base station generates a key by using the Channel State Information (CSI); and then carrying out convolution encryption on the key and the symbol sequence modulated by the wireless signal to be forwarded, and transmitting the symbol sequence subjected to convolution encryption and the wireless signal to be transmitted after precoding to a receiver through a channel, wherein the receiver can decrypt the symbol sequence after receiving the symbol sequence subjected to convolution encryption.
The method for encrypting transmission of the physical layer for wireless communication comprises the following specific steps:
step 1: constructing a system;
the building system comprises: base station for a wireless communication system with multiple input single output MISO B The method comprises the steps that a root antenna, a legal receiver and an eavesdropper are all single-antenna wireless communication terminals, the legal receiver and the eavesdropper can both receive wireless signals of a base station of a wireless communication system of the multiple-input single-output MISO, and the structure of the legal receiver and the eavesdropper, which can both receive the wireless signals of the base station of the wireless communication system of the multiple-input single-output MISO, forms an eavesdropping channel model of the wireless communication system of the multiple-input single-output MISO;
the wireless communication system of the multiple-input single-output MISO uses a time division duplex TDD model for communication, wherein N B Is a positive integer greater than 1;
the channel between the base station of the wireless communication system of the multi-input single-output MISO and the legal receiver is mutually independent from the channel between the base station of the wireless communication system of the multi-input single-output MISO and the eavesdropper, and the coherence interval of the channel is Lint;
step 2: channel estimation;
the channel estimation includes: the legal user sends a pilot signal to a base station of the wireless communication system, and the base station estimates Channel State Information (CSI) of a legal channel according to a sequence of the pilot signal;
in addition, h U and hE Channel coefficient vectors between a base station and a legitimate recipient of a wireless communication system of a multiple-input single-output MISO and between a base station and an eavesdropper of a wireless communication system of a multiple-input single-output MISO, respectively, where:
the h is U Is a vector representation of the channel state information CSI of a legitimate channel;
step 3: encrypting and sending;
the encrypted transmission includes: through channel estimation, the base station of the multi-input single-output MISO wireless communication system can acquire channel state information, a method of combining the maximum ratio with the MRC is adopted to pre-code a wireless signal to be forwarded, then the pre-coded wireless signal is modulated, then the modulated wireless signal is subjected to convolution encryption, a signal sequence x after convolution encryption is used as a signal sent by the base station of the multi-input single-output MISO wireless communication system, and a signal received by a legal receiver and a wireless signal received by an eavesdropper are respectively represented as a formula (1) and a formula (2):
in the formula ,nU and nE Noise signals received by legal receivers and by eavesdroppers, n U and nE Respectively conform to
And
as a precoding coefficient
The expression is
H is h U or hE 。
The convolutionally encrypted signal sequence x has an average power limitation, i.e. E (|) |x|| 2 ) And.ltoreq.1, wherein E (#) functions are used to find mathematical expectations.
In the case that the base station of the mimo wireless communication system is a dual antenna base station, the convolutional encryption in step 3 specifically includes the following steps:
step 3-1: generating a secret key;
the key generation includes: the base station of the wireless communication system of the MIMO MISO accurately estimates the channel coefficient vector h between the first antenna and the legal receiver after channel estimation U1 And a second antenna is connected with the legalChannel coefficient vector h between recipients U2, wherein ,
, wherein θU1 and θU2 Representing the phase of the channel between the first antenna and the legal receiver and the phase of the channel between the second antenna and the legal receiver, respectively, the θ U1 and θU2 All obey theta U1 , 
Is a distribution of (3);
will phase theta U1 and θU2 Generating a random key sequence k, wherein
；
Step 3-2: symbol encryption;
the symbol encryption includes: the base station of the wireless communication system of the multiple-input single-output MISO carries out convolution operation on the modulated symbol sequence s and the secret key k to obtain an encrypted symbol sequence x, wherein the encrypted symbol sequence x is shown in a formula (3):
x＝s*k (3)
wherein, represents convolution operation; the register denoted by D is introduced into the convolution operation for storing the current symbol s in the symbol sequence s i Is the previous symbol s of (2) i-1 The method comprises the steps of carrying out a first treatment on the surface of the The initial value in the register D is set to 0, and the encrypted symbol sequence x= [ x ] is obtained from the convolution operation 1 ,x 2 ,…,x N+1 ]X is epsilon phi, wherein phi represents an encrypted symbol x in the encrypted symbol sequence x as an encrypted constellation i Where x is i Representing the ith encrypted symbol in the encrypted symbol sequence x, wherein i and N are positive integers, and the x is the positive integer i As shown in formula (4):
the encryption operation rotates and superimposes two symbols in the symbol sequence s, generating a new encryption constellation; the size of the encrypted constellation space depends on ψ and the length of the key sequence k.
The key sequence k is power normalized, i.e. |k|| 2 ＝1。
After the encryption transmission in step 3, the method for encrypting the transmission system by the physical layer for wireless communication further includes the following steps:
step 4: recovering data;
the data recovery includes: according to the channel reciprocity criterion, legal receivers generate the same secret key k with the base station through the same mechanism; thus, the sequence of symbols y received by the legitimate receiver U The ith symbol y in (b) Ui Is shown in formula (5):
then the legal receiver decrypts the received symbol sequence, the main idea of the decryption adopts Minimum Mean Square Error (MMSE) criterion, and a group of symbols most similar to the received signal are searched for decryption; the decryption criterion is shown in formula (6):
wherein ,
the sign of the prediction is indicated,
the values of the four original constellation points are respectively c 1 ,c 2 ,c 3 ,c 4 And j is a positive integer. The method comprises the following specific steps:
step 4-1: read key sequence k= [ key 1 ,key 2 ]；
Step 4-2: initializing MMSE Cumulant matrix cumulant=zeros (4, n), path matrix
path=zeros (4, n) and optimal path vector opt_path=zeros (1, n);
step 4-3: calculating c using equation (7) k And y is U1 Is the mean square error cumullant (k, 1):
step 4-4: calculating the mean square error accumulation of each state, and storing the arrival path of the minimum accumulation;
step 4-5: searching for an optimal path, the searching for an optimal path comprising: finding a Cumulant matrix
The row number of the minimum value of the last column is marked as m, opt_path (N) =m is set, so that the row number of the minimum value of each column of the Cumulnt matrix is reversely searched one by one from the last column of the Cumulnt matrix, and the row numbers of the minimum values of all columns form a minimum value path Opt_path;
step 4-6: outputting the decrypted symbol sequence
The sequence is the decrypted symbol.
The step 4-4 specifically comprises the following steps:
step 4-4-1: the initial value of j is 2;
step 4-4-2: comparing the values of j and N, if j is greater than N, ending the execution of step 4-4 to step 4-5, and if j is not greater than N, calculating the cumulative mean square error value State (k, i) of the j-th State by using the formula (8):
and (3) obtaining and storing an arrival path (k, j-1) of the minimum cumulative amount Cumulant (k, j) by using the formula (9) and the formula (10):
wherein i, j and k are positive integers;
step 4-4-3: the value of j is incremented by 1 and returned to step 4-4-2 for execution.
Comprising the following steps: a construction module, an estimation module and an encryption module running on a base station of the multiple-input single-output MISO wireless communication system;
the construction module is used for the construction system;
the estimation module is used for channel estimation;
the encryption module is used for encrypting and sending.
The physical layer encryption transmission system for wireless communication further comprises: a recovery module running on the legitimate recipient;
the recovery module is used for recovering the data.
The beneficial effects of the invention are as follows:
1. the randomness and reciprocity of a wireless channel of a wireless communication system of a multiple-input single-output MISO are utilized to generate a key through channel state information thereof, and the wireless signal is encrypted.
2. The modulation mode of the wireless signal is hidden, and the constellation diagram-based reconstruction and the high-order accumulation-based modulation identification can be effectively carried out.
3. Under quasi-static channel conditions, the scheme provided by the invention has better safety performance.
4. The proposal provided by the invention reduces the bit error rate of legal users and has higher communication reliability.
Drawings
Fig. 1 is a schematic diagram of a physical layer encrypted transmission system PLE for wireless communications according to the present invention, wherein Y B is a wireless signal transmitted to a legitimate receiver and Y E is a wireless signal transmitted to an eavesdropper.
Fig. 2 is a block diagram of an eavesdropping channel model of the present invention, in which Base Station represents a Base Station, eavesdropper represents an Eavesdropper, and a User of the Eavesdropper represents a Legitimate receiver.
Fig. 3 is a system configuration diagram of the CONV-EN scheme of the present invention.
Fig. 4 is a diagram showing the comparison of unencrypted and encrypted signal transceiver constellations according to the present invention.
Fig. 5 is a phase distribution histogram of a received signal constellation under the condition of snr=10 dB of the present invention.
Fig. 6 is a graph of modulation recognition success rate of the present invention.
Fig. 7 is a graph of the bit error rate of a normal eavesdropper on a quasi-static channel with snr=10 dB according to the present invention.
Fig. 8 is a graph of bit error rates of legitimate recipients under different PLE schemes of the invention.
Detailed Description
Aiming at the safety communication problem of a wireless communication system of a multi-input single-output MISO, the invention provides a new physical layer encryption PLE scheme, namely CONV-EN scheme for short, which generates a key by using channel state information CSI, can resist modulation identification and eavesdropper attack under the condition of not consuming extra transmission power, ensures safe signal transmission and has higher communication reliability.
The invention will be further described with reference to the drawings and examples.
As shown in fig. 1-8, a method for encrypting a transmission system for a physical layer of wireless communication, comprising:
aiming at a eavesdropping channel model of a multi-input single-output MISO wireless communication system, firstly, a legal user sends a pilot signal to a base station of the wireless communication system, and the base station generates a key by using Channel State Information (CSI) on the assumption that the base station can perfectly estimate the Channel State Information (CSI) of a legal channel according to the sequence of the pilot signal; and then carrying out convolution encryption on the key and the symbol sequence modulated by the wireless signal to be forwarded, and transmitting the symbol sequence subjected to convolution encryption and the wireless signal to be transmitted after precoding to a receiver through a channel, wherein the receiver can decrypt the symbol sequence after receiving the symbol sequence subjected to convolution encryption. According to the channel reciprocity criterion, a legal receiver can estimate Channel State Information (CSI) consistent with a base station, generate a key and decrypt a received signal. Because of the difference of the channels, the channel state information CSI acquired by the eavesdropper is different from both legal parties, namely a legal user and a legal receiver, so that the key cannot be acquired, and the encrypted signal cannot be decrypted. The scheme ensures the safe transmission of wireless signals. The legal user is a wireless communication terminal such as a smart phone, a PDA or a tablet computer of a user who performs wireless communication by using the base station of the wireless communication system of the multiple-input single-output MISO, the eavesdropper is a wireless communication terminal such as a smart phone, a PDA or a tablet computer of a user who performs eavesdropping by using the base station of the wireless communication system of the multiple-input single-output MISO, the receiver is a wireless communication terminal such as a smart phone, a PDA or a tablet computer of a user who performs wireless signal reception by using the base station of the wireless communication system of the multiple-input single-output MISO, and the legal receiver is a wireless communication terminal such as a smart phone, a PDA or a tablet computer of a user who performs wireless signal reception by using the base station of the wireless communication system of the multiple-input single-output MISO.
The method for encrypting the transmission system by the physical layer for wireless communication comprises the following specific steps:
step 1: constructing a system;
the building system comprises: a base station of a wireless communication system of the multi-input single-output MISO is provided with N B antennas, a legal receiver and an eavesdropper are wireless communication terminals of the single antennas, the legal receiver and the eavesdropper can both receive wireless signals of the base station of the wireless communication system of the multi-input single-output MISO, and the structure of the wireless signals of the base station of the wireless communication system of the multi-input single-output MISO can both form an eavesdropping channel model of the wireless communication system of the multi-input single-output MISO;
the wireless communication system of the multiple-input single-output MISO uses a time division duplex TDD model for communication, wherein N B Is a positive integer greater than 1;
assuming that channels between a base station of the wireless communication system of the multiple-input single-output MISO and a legal receiver are mutually independent from channels between the base station of the wireless communication system of the multiple-input single-output MISO and an eavesdropper, wherein the coherence interval of the channels is L int;
step 2: channel estimation;
the channel estimation includes: the legal user sends a pilot signal to a base station of the wireless communication system, and the base station estimates Channel State Information (CSI) of a legal channel according to a sequence of the pilot signal;
in addition, h U and hE Channel coefficient vectors between a base station and a legitimate recipient of a wireless communication system of a multiple-input single-output MISO and between a base station and an eavesdropper of a wireless communication system of a multiple-input single-output MISO, respectively, where:
the h is U Is a vector representation of the channel state information CSI of a legitimate channel;
step 3: encrypting and sending;
the encrypted transmission includes: assuming that through perfect channel estimation, the base station of the multi-input single-output MISO wireless communication system can obtain accurate channel state information, a method of combining the maximum ratio and the MRC is adopted to pre-encode a wireless signal to be forwarded, then the pre-encoded wireless signal is modulated, then the modulated wireless signal is subjected to convolution encryption, the signal sequence x after convolution encryption is used as a signal sent by the base station of the multi-input single-output MISO wireless communication system, and a signal received by a legal receiver and a wireless signal received by an eavesdropper are respectively expressed as a formula (1) and a formula (2):
in the formula ,nU and nE Noise signals received by legal receivers and by eavesdroppers, n U and nE Respectively conform to
And
as a precoding coefficient
The expression is
H is h U or hE 。
The convolutionally encrypted signal sequence x has an average power limitation, i.e. E (|) |x|| 2 ) And.ltoreq.1, wherein E (#) functions are used to find mathematical expectations.
In the design of the CONV-EN scheme, the base station of the wireless communication system of the mimo is considered to be a dual-antenna base station, where the dual antennas are a first antenna and a second antenna, as shown in fig. 3, and the base station as the transmitting end performs the precoding on the bit data Ib of the wireless signal to be transmitted to generate a binary sequence Ic, where the binary sequence Ic is digitally modulated to generate a symbol sequence s= [ s ] with a length N 1 ,...,s 2 ,s N ]As a modulated radio signal, S i Representing the ith symbol and s in the sequence of symbols i E.psij, is the set of symbols in the symbol sequence as the original constellation, i, N are both positive integers.
In the case that the base station of the mimo wireless communication system is a dual antenna base station, the convolutional encryption in step 3 specifically includes the following steps:
step 3-1: generating a secret key;
the key generation includes: assuming that a base station of the mimo wireless communication system is capable of accurately estimating a channel coefficient vector h between the first antenna and a legitimate receiver after channel estimation U1 And a channel coefficient vector h between the second antenna and the legitimate receiver U2, wherein ,
, wherein θU1 and θU2 Representing the phase of the channel between the first antenna and the legal receiver and the phase of the channel between the second antenna and the legal receiver, respectively, the θ U1 and θU2 All obey theta U1 , 
Is a distribution of (3);
will phase theta U1 and θU2 Generating a random key sequence k, wherein
；
Step 3-2: symbol encryption;
the symbol encryption includes: the base station of the wireless communication system of the multiple-input single-output MISO carries out convolution operation on the modulated symbol sequence s and the secret key k to obtain an encrypted symbol sequence x, wherein the encrypted symbol sequence x is shown in a formula (3):
x＝s*k (3)
wherein, represents convolution operation; a register denoted D in fig. 3 is introduced in the convolution operation for storing the current symbol s in the symbol sequence s i Is the previous symbol s of (2) i-1 The method comprises the steps of carrying out a first treatment on the surface of the Setting registerThe initial value in the memory D is 0, and the encrypted symbol sequence x= [ x ] is obtained according to the convolution operation 1 ,x 2 ,…,x N+1 ]X is epsilon phi, wherein phi represents an encrypted symbol x in the encrypted symbol sequence x as an encrypted constellation i Where x is i Representing the ith encrypted symbol in the encrypted symbol sequence x, wherein i and N are positive integers, and the x is the positive integer i As shown in formula (4):
the encryption operation rotates and superimposes two symbols in the symbol sequence s, generating a new encryption constellation; if ψ=2 m, then Φ=22m+2m+1, the encrypted constellation space size depends on ψ and the length of the key sequence k. It is noted that the key changes with the change of the channel, and the encrypted constellation point also changes dynamically, so that a sufficiently chaotic constellation space can be generated.
The key sequence k is power normalized, i.e. |k|| 2 =1, which means that the convolutional encryption operation does not produce additional power consumption.
After the encryption transmission in step 3, the method for encrypting the transmission system by the physical layer for wireless communication further includes the following steps:
step 4: recovering data;
the data recovery includes: according to the channel reciprocity criterion, legal receivers generate the same secret key k with the base station through the same mechanism; thus, the ith symbol y Ui in the symbol sequence y U received by the legitimate receiver is shown in formula (5):
then the legal receiver decrypts the received symbol sequence, the main idea of the decryption adopts Minimum Mean Square Error (MMSE) criterion, and a group of symbols most similar to the received signal are searched for decryption; the decryption criterion is shown in formula (6):
wherein ,
the sign of the prediction is indicated,
the values of the four original constellation points are respectively c 1 ,c 2 ,c 3 ,c 4 And j is a positive integer.
The decryption in the step 4 comprises the following specific steps:
step 4-1: read key sequence k= [ key 1 ,key 2 ]；
Step 4-2: initializing MMSE Cumulant matrix cumulant=zeros (4, n), path matrix
path=zeros (4, n) and optimal path vector opt_path=zeros (1, n);
step 4-3: calculating c using equation (7) k And y is U1 Is the mean square error cumullant (k, 1):
step 4-4: calculating the mean square error accumulation of each state, and storing the arrival path of the minimum accumulation;
step 4-5: searching for an optimal path, the searching for an optimal path comprising: finding a Cumulant matrix
The row number of the minimum value of the last column is marked as m, opt_path (N) =m is set, so that the row number of the minimum value of each column of the Cumulnt matrix is reversely searched one by one from the last column of the Cumulnt matrix, and the row numbers of the minimum values of all columns form a minimum value path Opt_path;
step 4-6: outputting the decrypted symbol sequence
The sequence is the decrypted symbol.
The step 4-4 specifically comprises the following steps:
step 4-4-1: the initial value of j is 2;
step 4-4-2: comparing the values of j and N, if j is greater than N, ending the execution of step 4-4 to step 4-5, and if j is not greater than N, calculating the cumulative mean square error value State (k, i) of the j-th State by using the formula (8):
and (3) obtaining and storing an arrival path (k, j-1) of the minimum cumulative amount Cumulant (k, j) by using the formula (9) and the formula (10):
wherein i, j and k are positive integers;
step 4-4-3: the value of j is incremented by 1 and returned to step 4-4-2 for execution.
The physical layer encryption transmission system for wireless communication comprises: a construction module, an estimation module and an encryption module running on a base station of the multiple-input single-output MISO wireless communication system;
the construction module is used for the construction system;
the estimation module is used for channel estimation;
the encryption module is used for encrypting and sending.
The physical layer encryption transmission system for wireless communication further comprises: a recovery module running on the legitimate recipient;
the recovery module is used for recovering the data.
For the decryption in the step 4, the following is explained:
c k and ci Representative of
And
possible values, c k ,c i E ψ, k, i=1, 2,3,4. Step 4-3 and step 4-4 are calculated according to equation (6)
All possible combinations with y Uj Is recorded with c minimizing the accumulation amount i Step 4 is repeated until all received symbols are calculated. The role of step 5 is to select the path that ultimately yields the smallest MMSE accumulation (i.e., the optimal path). Finally, output
And recovering the original data through demodulation and decoding.
The following experimental simulation is carried out by using the method of the invention:
studies have shown that in a low-speed moving environment, the coherence interval of the channel becomes very large, and can become 15000 symbol periods when the moving speed is 5.4 km/h. The simulation quasi-static channel environment for experimental simulation adopts QPSK modulation mode if not specified, and is specifically as follows:
1. experiment one for simulating anti-modulation recognition performance: from the viewpoint of an eavesdropper, the correct identification of the modulation mode of the signal is an important link for achieving successful eavesdropping. There are two types of modulation recognition that are currently in common use: constellation reconstruction and higher order cumulant based modulation identification. Modulation identification based on constellation reconstruction utilizes a clustering analysis criterion to identify a modulation mode by comparing the similarity degree with a traditional constellation.
Modulation recognition based on high-order cumulant is mature in the field of signal modulation recognition, an eavesdropper can easily acquire modulation information from cyclostationary characteristics, and the influence of phase jitter can be eliminated by using the absolute value of the high-order cumulant; the ratio is used as an identification parameter, and the influence of amplitude on the parameter can be eliminated; the high order cumulants have good anti-fade properties relative to the instantaneous statistics; the modulation recognition algorithm based on the high-order cumulant can inhibit additive noise and provide a high signal-to-noise ratio environment for analysis signals.
After 5 coherence intervals, the signal constellation of the receiving and transmitting end is shown in fig. 4. As can be seen from fig. 4, the signals are encrypted using the CONV-EN system, resulting in a large degree of confusion. The phase distribution of the received signal is shown in fig. 5. As can be seen from fig. 5, the original QPSK constellation phase is concentrated and distributed
The encrypted data basically accords with random distribution in a plane without regularity. On the surface of the simulation result, the encrypted constellation diagram cannot be matched with the constellation template of the existing modulation mode, so that an eavesdropper cannot identify the modulation mode through a constellation diagram reconstruction-based method.
The anti-modulation recognition performance of the COV-EN scheme is evaluated by adopting a modulation recognition algorithm based on high-order cumulants. Under different signal-to-noise ratio conditions, 1000 independent simulations are performed, and the success rate of modulation recognition of the QPSK signal by the modulation recognition algorithm based on the high-order cumulant is shown in fig. 6. As can be seen from FIG. 6, when the signal-to-noise ratio is greater than 5dB, the probability of success in identifying the unencrypted signal reaches over 0.95, which indicates that the algorithm can effectively identify the unencrypted signal. And when the signal-to-noise ratio is greater than 5dB, the success rate of identifying the signals encrypted by the CONV-EN scheme is lower than 0.1, which shows that the PLE scheme provided by the invention has excellent anti-modulation identification performance.
2. The second experiment defines a normal eavesdropper as a passive eavesdropper that is not aware of the original symbol being encrypted and can implement the same demodulation technique as the legitimate receiver. Assuming that the eavesdropper acquires the correct modulation scheme with a very small probability, it tries to demodulate the information.
Fig. 7 shows the bit error rate performance of an ordinary eavesdropper using the Phase Rotation encryption scheme of the prior art and the encryption scheme according to the present invention when the signal-to-noise ratio is 10dB in the quasi-static rayleigh channel. As can be seen from the figure, when the prior art scheme is adopted for encryption, the bit error rate of an eavesdropper can jump to a lower value at a certain momentAt this point it can be considered that an eavesdropper can get part of the correct information by demodulation. This is due to the long coherence interval of the quasi-static channel if the constellation rotation angle is distributed at
The eavesdropper processes the received signal according to the original demodulation standard to obtain partial correct information. However, the CONV-EN scheme provided by the invention can stably maintain the bit error rate of an eavesdropper to be about 0.5, and can eliminate the risk of information leakage. This is because the CONV-EN scheme adopts a block encryption manner to superimpose adjacent symbols together, and the adjacent symbols affect each other, and one constellation point contains information of two symbols. The degree of confidentiality is not only dependent on the key, but the symbol sequence itself is associated.
3. Experiment III the bit error Rate of legal recipients under different PLE systems is formed into a bit error Rate curve as shown in FIG. 8. It can be observed from FIG. 8 that the CONV-EN scheme of the present invention has a bit error Rate of 10 compared with the unencrypted transmission and OSPR scheme -3 Only about 1dB of SNR loss is generated; compared with the scheme in the prior art, the SNR gain of about 3dB is obtained, and the reliability of the wireless communication system of the multi-input single-output MISO is improved. This results from the fact that the scheme adopts the encryption mode of symbol convolution, and legal users obtain interleaving gain during decryption and demodulation.
While the invention has been described by way of examples, it will be understood by those skilled in the art that the present disclosure is not limited to the examples described above, and that various changes, modifications and substitutions may be made without departing from the scope of the invention.
Claims (8)
1. A method for physical layer encrypted transmission for wireless communications, comprising:
aiming at a eavesdropping channel model of a multi-input single-output MISO wireless communication system, firstly, a legal user sends a pilot signal to a base station of the wireless communication system, the base station estimates Channel State Information (CSI) of a legal channel according to a sequence of the pilot signal, and the base station generates a key by using the Channel State Information (CSI); then carrying out convolution encryption on the key and the symbol sequence modulated by the wireless signal to be forwarded, transmitting the symbol sequence subjected to convolution encryption and the wireless signal to be transmitted after precoding to a receiver through a channel, decrypting the symbol sequence after the receiver receives the symbol sequence subjected to convolution encryption,
the method specifically comprises the following specific steps:
step 1: constructing a system;
the building system comprises: base station for a wireless communication system with multiple input single output MISO B The method comprises the steps that a root antenna, a legal receiver and an eavesdropper are all single-antenna wireless communication terminals, the legal receiver and the eavesdropper can both receive wireless signals of a base station of a wireless communication system of the multiple-input single-output MISO, and the structure of the legal receiver and the eavesdropper, which can both receive the wireless signals of the base station of the wireless communication system of the multiple-input single-output MISO, forms an eavesdropping channel model of the wireless communication system of the multiple-input single-output MISO;
the wireless communication system of the multiple-input single-output MISO uses a time division duplex TDD model for communication, wherein N B Is a positive integer greater than 1;
the channel between the base station of the wireless communication system of the multi-input single-output MISO and the legal receiver is mutually independent from the channel between the base station of the wireless communication system of the multi-input single-output MISO and the eavesdropper, and the coherence interval of the channel is Lint;
step 2: channel estimation;
the channel estimation includes: the legal user sends a pilot signal to a base station of the wireless communication system, and the base station estimates Channel State Information (CSI) of a legal channel according to a sequence of the pilot signal;
in addition, h U and hE Channel coefficient vectors between a base station and a legitimate recipient of a wireless communication system of a multiple-input single-output MISO and between a base station and an eavesdropper of a wireless communication system of a multiple-input single-output MISO, respectively, where:
h U ～CN(0,I NB ) I.e. h U Obeying complex gaussian distribution, where I NB Represents N B A row identity matrix;
h E ～CN(0,I NB ) I.e. h E Obeying complex gaussian distribution, where I NB Represents N B A row identity matrix;
the h is U Is a vector representation of the channel state information CSI of a legitimate channel;
step 3: encrypting and sending;
the encrypted transmission includes: through channel estimation, the base station of the multi-input single-output MISO wireless communication system can acquire channel state information, a method of combining the maximum ratio with the MRC is adopted to pre-code a wireless signal to be forwarded, then the pre-coded wireless signal is modulated, then the modulated wireless signal is subjected to convolution encryption, a signal sequence x after convolution encryption is used as a signal sent by the base station of the multi-input single-output MISO wireless communication system, and a signal received by a legal receiver and a wireless signal received by an eavesdropper are respectively represented as a formula (1) and a formula (2):
in the formula ,nU and nE Noise signals received by legal receivers and by eavesdroppers, n U and nE Respectively conform to and
ω as precoding coefficient, expressed as +.>
h is h U or hE 。
2. The method for physical layer encrypted transmissions for wireless communication according to claim 1, the convolutionally encrypted signal sequence x has an average power limitation, i.e. E (|) |x|| 2 ) And.ltoreq.1, wherein E (#) functions are used to find mathematical expectations.
3. The method for physical layer encryption transmission for wireless communication according to claim 2, wherein in the case that the base station of the wireless communication system of the mimo MISO is a dual antenna base station, the convolutional encryption of step 3 specifically comprises the following steps:
step 3-1: generating a secret key;
the key generation includes: the base station of the wireless communication system of the MIMO MISO accurately estimates the channel coefficient vector h between the first antenna and the legal receiver after channel estimation U1 And a channel coefficient vector h between the second antenna and the legitimate receiver U2, wherein ,
wherein θU1 and θU2 Representing the phase of the channel between the first antenna and the legal receiver and the phase of the channel between the second antenna and the legal receiver, respectively, the θ U1 and θU2 All obey theta U1 ,θ U2 Distribution of U (0, 2 pi);
will phase theta U1 and θU2 Generating a random key sequence k, wherein
Step 3-2: symbol encryption;
the symbol encryption includes: the base station of the wireless communication system of the multiple-input single-output MISO carries out convolution operation on the modulated symbol sequence s and the secret key k to obtain an encrypted symbol sequence x, wherein the encrypted symbol sequence x is shown in a formula (3):
x＝s*k(3)
wherein, represents convolution operation; the register denoted by D is introduced into the convolution operation for storing the current symbol s in the symbol sequence s i Is the previous symbol s of (2) i-1 The method comprises the steps of carrying out a first treatment on the surface of the The initial value in the register D is set to 0, and the encrypted symbol sequence x= [ x ] is obtained from the convolution operation 1 ,x 2 ,…,x N+1 ]X is epsilon phi, wherein phi represents an encrypted symbol x in the encrypted symbol sequence x as an encrypted constellation i Where x is i Representing the ith encrypted symbol in the encrypted symbol sequence x, wherein i and N are positive integers, and the x is the positive integer i As shown in formula (4):
the encryption operation rotates and superimposes two symbols in the symbol sequence s, generating a new encryption constellation; the size of the encrypted constellation space depends on ψ and the length of the key sequence k.
4. A method for physical layer encrypted transmission for wireless communication according to claim 3, wherein the key sequence k is power normalized, i.e. k|k| 2 ＝1。
5. The method for physical layer encrypted transmission for wireless communication according to claim 3, wherein after the encrypted transmission in step 3, the method for physical layer encrypted transmission system for wireless communication further comprises the steps of:
step 4: recovering data;
the data recovery includes: according to the channel reciprocity criterion, legal receivers generate the same secret key k with the base station through the same mechanism; thus, the sequence of symbols y received by the legitimate receiver U The ith symbol y in (b) Ui Is shown in formula (5):
then the legal receiver decrypts the received symbol sequence, the main idea of the decryption adopts Minimum Mean Square Error (MMSE) criterion, and a group of symbols most similar to the received signal are searched for decryption; the decryption criterion is shown in formula (6):
wherein ,
the sign of the prediction is indicated,
6. The method for physical layer encrypted transmission for wireless communication according to claim 5, wherein the decrypting in step 4 comprises the specific steps of:
step 4-1: read key sequence k= [ key 1 ,key 2 ]；
Step 4-2: initializing MMSE Cumulant matrix cumulant=zeros (4, n), path matrix
path=zeros (4, n) and optimal path vector opt_path=zeros (1, n);
step 4-3: calculating c using equation (7) k And y is U1 Is the mean square error cumullant (k, 1):
step 4-4: calculating the mean square error accumulation of each state, and storing the arrival path of the minimum accumulation;
step 4-5: searching for an optimal path, the searching for an optimal path comprising: finding a Cumulant matrix
The row number of the minimum value of the last column is marked as m, opt_path (N) =m is set, so that the row number of the minimum value of each column of the Cumulnt matrix is reversely searched one by one from the last column of the Cumulnt matrix, and the row numbers of the minimum values of all columns form a minimum value path Opt_path;
step 4-6: outputting the decrypted symbol sequence
The sequence is the decrypted symbol.
7. The method for physical layer encrypted transmission for wireless communication according to claim 6, wherein the step 4-4 specifically comprises:
step 4-4-1: the initial value of j is 2;
step 4-4-2: comparing the values of j and N, if j is greater than N, ending the execution of step 4-4 to step 4-5, and if j is not greater than N, calculating the cumulative mean square error value State (k, i) of the j-th State by using the formula (8):
and (3) obtaining and storing an arrival path (k, j-1) of the minimum cumulative amount Cumulant (k, j) by using the formula (9) and the formula (10):
Cumulant(k,j)＝min(State(k,i))(9)
wherein i, j and k are positive integers;
step 4-4-3: the value of j is incremented by 1 and returned to step 4-4-2 for execution.
8. A physical layer encrypted transmission system for wireless communication based on the method of any one of claims 1-7, comprising: a construction module, an estimation module and an encryption module running on a base station of a wireless communication system of a multiple-input single-output MISO;
the construction module is used for constructing a system;
the estimation module is used for channel estimation;
the encryption module is used for encrypting and transmitting;
further comprises: a recovery module running on the legitimate recipient; the recovery module is used for recovering data.
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