CN111683033A - Encryption and Transmission Method Based on Constellation Rotation in TR_OFDM System - Google Patents

Abstract

The invention relates to the technical field of wireless communication, and relates to an encryption and transmission method based on constellation rotation in a TR_OFDM system; the encryption method comprises that a transmitting end and a receiving end respectively quantize the estimated channel, and determine that a quaternion is used as a secret key; The transmitting end converts the transmitted signal to constellation mapping after serial-to-parallel conversion, and maps it to three-dimensional constellation points, and uses quaternion to rotate and encrypt the modulated QPSK signal; and modulates by OFDM; Time inversion to obtain a time inversion mirror; the modulated OFDM symbols are subjected to parallel-to-serial conversion and then passed through a time inversion mirror, and then transmitted by the channel. For the transmission method, the receiver receives the encrypted constellation points; The corresponding quaternion is decrypted, and the channel between the eavesdropper and the sender is different, so the corresponding quaternion cannot be obtained for decryption, thereby ensuring the security of the TR_OFDM system.

Description

Encryption and Transmission Method Based on Constellation Rotation in TR_OFDM System

technical field

The present invention relates to the technical field of wireless communication, in particular to an encryption and transmission method based on constellation rotation in a TR_OFDM (Time Reversal_Orthogonal Frequency Division Multiplexing) system.

Background technique

With the rapid development of wireless communication technology, people's work and life have become more and more convenient, and mobile terminals such as mobile phones and notebook computers are gradually changing people's way of life. Especially with the emergence of technologies such as mobile payment, Internet of Things, and autonomous driving, ensuring the security of communication has become more and more critical. The traditional encryption scheme mainly encrypts data through a secret key encryption system. Using the high complexity of the encryption algorithm, it is assumed that the eavesdropper's equipment cannot be attacked and cracked for a long time. With the continuous development of computer technology, these will not be possible. Then there is the problem, especially the emergence of quantum computers, which poses a huge challenge to the security of wireless communication.

At present, the commonly used security encryption mechanism is relatively independent from the physical layer in design. In the upper layer of the wireless communication system, the security technology based on traditional cryptography is used to ensure the security of the communication system, and the characteristics of the physical layer are not fully utilized. In recent years, the emergence of physical layer security technology based on the security principle of information theory has attracted widespread attention, providing a new idea for wireless communication security research. Compared with traditional encryption mechanisms, this is a theoretically proven method. Based on the strong security strategy, the wireless communication security strategy is designed from the perspective of the physical layer, as the improvement and supplement to the traditional encryption algorithm.

Time Reversal Technology (Time Reversal, TR) was first proposed by M. Fink in 1992. Whether in a homogeneous media environment or a non-homogeneous media environment, the signal processed by time inversion technology has temporal focus and spatial focus. Time focus means that the signal energy of each path will focus at the same moment. Spatial focusing means that the electromagnetic energy will be focused at the target point in space, while at other positions of the target point, the electromagnetic energy is very low or even negligible. The so-called time inversion is the inversion of the received signal in the time domain, which is equivalent to the phase conjugation in the frequency domain. In a communication system, the receiver first sends a very short detection pulse in the time domain, which undergoes reflection, scattering, and diffraction in the channel, and is finally received by the transmitter. The transmitting end performs a time inversion operation on the received signal. In a complex multipath environment, after the signal processed by time inversion is re-transmitted, the time-space focusing of time inversion technology will appear at the target point. characteristic. At the same time, it should be pointed out that this space-time focusing characteristic is adaptive to the environment. The more complex the environment is, the more obvious the space-time focusing effect will be. This focusing effect is applied in the field of communication, which can improve the performance of the communication system and ensure the safe transmission of information.

Orthogonal Frequency Division Multiplexing (OFDM) technology decomposes a wideband channel into many parallel narrow subchannels, so that the bandwidth of each subchannel is smaller than the coherence bandwidth of the channel, so that the fading experienced by each channel is approximately Flatness fading. Therefore, the inter-symbol interference caused by the time dispersion of the wireless channel can be effectively suppressed, and the complexity of equalization in the receiver can be reduced.

The TR_OFDM system can reduce inter-symbol interference and inter-carrier interference, shorten the cyclic prefix length, and improve spectral efficiency. Stable, high-speed, green communication can be achieved in complex multipath environment, but if there is an eavesdropper in the TR_OFDM system, the security of the system cannot be guaranteed.

SUMMARY OF THE INVENTION

Based on the problems existing in the prior art, the present invention aims at the problem that information cannot be safely transmitted if there is an eavesdropper in the TR_OFDM system. The problem to be solved by the present invention is the physical layer security of the TR_OFDM system. The present invention designs a constellation encryption mechanism, The constellation mapped by TR_OFDM is encrypted, and the receiving end performs corresponding decryption, so as to ensure that eavesdroppers cannot obtain the information before encryption.

The present invention solves the above technical problem by adopting a scheme of encryption and transmission method based on constellation rotation in the TR_OFDM system.

In the first aspect of the present invention, the present invention proposes an encryption method based on constellation rotation in the TR_OFDM system. The encryption method is based on the TR_OFDM system and adopts constellation encryption. The encryption method includes:

The sending end and the receiving end quantize the estimated channel respectively, determine a quaternion, and use this quaternion as the secret key for encryption and decryption of both parties;

The transmitting end performs constellation mapping after parallel conversion of the transmitted signal string; performs constellation rotation encryption on the mapped transmitted signal with the secret key, and modulates by OFDM;

The sender performs time inversion on the estimated channel state information to obtain a time inversion mirror;

The modulated OFDM symbols are converted from parallel to serial and then passed through a time inversion mirror and transmitted through the channel, and the receiver receives the encrypted constellation points.

Further, the process of estimating the channel includes using a Rayleigh channel, the transmitter and the receiver perform channel estimation with each other, and the transmitter and receiver send sounding signals to each other to perform channel estimation with the sounding signals.

Further, the judgment method includes that the receiving end uses the minimum distance for demodulation, that is, the receiving end decrypts the fast Fourier transformed signal and then compares it with the original mapping point, and judges the point closest to the original mapping point as its corresponding point. quaternary signal.

Further, before performing parallel-serial conversion, the transmitting end performs inverse fast Fourier transform on the transmitted signal after constellation rotation, and adds a cyclic prefix.

In a second aspect of the present invention, the present invention further provides a constellation rotation-based secure transmission method in a TR_OFDM system, the secure transmission method comprising:

Before quantizing the estimated signal, the transmitting end and the receiving end perform channel estimation with each other, and the eavesdropping end passively detects the detection channel;

The sending end and the receiving end quantize the estimated channel respectively, and determine a quaternion as the secret key for both encryption and decryption;

The transmitting end performs constellation mapping after parallel conversion of the transmitted signal strings; the mapping into three-dimensional constellation points performs constellation rotation encryption on the mapped transmitted signals at the angle of the secret key, and modulates by OFDM;

The sender performs time inversion on the estimated channel state information to obtain a time inversion mirror;

The modulated OFDM symbols are converted from parallel to serial and then passed through a time reversal mirror, and transmitted through the channel;

After the receiving end and the eavesdropping end perform serial-to-parallel conversion on the received OFDM symbols, the encrypted constellation points are obtained;

The receiving end uses the secret key to decrypt the encrypted constellation point, but the eavesdropping end cannot decrypt the constellation point.

Further, perform inverse fast Fourier transform and add cyclic prefix on the transmitted signal after the constellation rotation; perform corresponding fast Fourier transform and remove the cyclic prefix on the transmitted signal before the constellation inverse rotation.

Further, using the secret key to decrypt the encrypted constellation points at the receiving end includes performing fast Fourier transform on the encrypted constellation points, and using the secret key to perform inverse constellation rotation; After the string conversion, the receiver decodes the original transmitted signal.

Beneficial effects of the present invention:

The present invention generates a secret key for constellation encryption by using the channel for both nodes Alice and Bob of legal communication, the transmitting end Alice uses the secret key to encrypt the constellation point corresponding to the modulated signal, and the legal receiving end Bob uses the secret key pair to generate constellation points for decryption. The eavesdropping node Eve does not know the encrypted secret key, so it cannot decrypt the encrypted constellation points, thereby ensuring the security of the system.

Description of drawings

Fig. 1 is a scene diagram based on the TR-OFDM system provided by the present invention;

2 is a flowchart of an encryption method based on constellation rotation in the TR_OFDM system of the present invention;

FIG. 3 is a flowchart of a secure transmission method based on constellation rotation in the TR_OFDM system of the present invention;

FIG. 4 is a block diagram of a preferred secure transmission method based on constellation rotation in a TR_OFDM system provided by the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Figure 1 is a scene diagram based on the TR-OFDM system provided by the present invention. As shown in Figure 1, it is assumed that there are three nodes, the sending node Alice, the receiving node Bob, and the eavesdropping node Eve (passive eavesdropping); Alice and Bob are legitimate communication nodes , have 1 transmitting antenna and 1 receiving antenna respectively. Eve is an eavesdropping node (passive eavesdropping) with 1 receiving antenna and the distance between Alice and Bob is greater than half a wavelength.

In the actual scene, due to the time-varying channel (due to the influence of the positional changes of the two communicating parties and reflectors in the wireless communication environment, the fading characteristics of the channel will change at any time, and the channel will change at more than 2 time points when the interval exceeds the channel coherence time length). are different), reciprocity (during the channel coherence time, when users at both ends of the same communication link exchange information, the channel fading characteristics experienced by the two receiving signals are the same) and difference (in the rich multi- In the radial scattering environment, when the information from the same signal sender is received, when the two signal receivers are separated by more than half a wavelength, the channels experienced by the signals received by the two are irrelevant).

Based on the above scenario, as shown in Figure 2, the present invention proposes an encryption method based on constellation rotation in the TR_OFDM system, including:

101. The transmitting end and the receiving end respectively quantize the estimated channel, and determine that a quaternion is used as the secret key for encryption and decryption of both parties;

Since the transmitting end and the receiving end send probing channels to each other, it can be assumed that the channel estimation is ideal, that is, it is assumed that the results of quantizing the same channel by the two are consistent.

The role of channel estimation is to generate the secret key for constellation encryption and to generate the subsequent time-reversal mirror.

Alice and Bob send probe signals respectively, and the channel impulse response between the sender Alice and the receiver Bob is expressed as:

Suppose the channel impulse response between Alice's and Eve is h _ij ^e [k]:

It can be seen that for the sender, the channel impulse response is the same at the receiver and the eavesdropper.

At the same time, Alice and Bob quantize h ^r [k], and decide it as a quaternion q, which is used as the secret key for encryption and decryption of both parties.

For the judgment method, the embodiment of the present invention adopts the minimum distance judgment method, that is, the receiving end uses the minimum distance for demodulation, that is, the receiving end decrypts the fast Fourier transformed signal and then compares it with the original mapping point. The point closest to the mapping point is determined as its corresponding quaternary signal.

The mapping result table shown in Table 1 can be used to make a decision:

Table 1 Mapping result table

1 2 3 4 5 6 7 8 9 10 1 1.4142 2.0004 1.4134 1.4119 1.4180 1.4122 1.4205 2.0021 1.4114 1.9997 2 2.0000 1.4154 2.0006 1.9988 0.0050 2.0000 0.0090 1.4235 2.0024 1.4212 3 1.4143 0.0014 1.4158 1.4148 1.4108 1.4161 1.4078 0.0112 1.4204 0.0101 4 4.0029 1.4135 0.0017 0.0023 2.0003 0.0027 1.9999 1.4078 0.0068 1.4068

Assuming that the mapping table mapping=[1+1i, -1+1i, -1-1i, 1-1i].*(1/sqrt(2)), the quaternary signal 0 in the mapping table corresponds to 1+1i, 1 Corresponds to -1+1i, 2 corresponds to -1-1i, 3 corresponds to 1-1i; the first line is the distance from the received signal to the first quaternary signal, the second line to the fourth line and so on; take The minimum distance is the corresponding quaternary number. For example, the minimum value in the first column is 1.4142e-16, indicating that the first received symbol is the closest to the first mapping point, so the received signal is judged as a quaternary signal of 0.

The quaternion used in the present invention will be specifically introduced below:

q=[w,x,y,z]=w+xi+yj+zk

Among them, [w, x, y, z] are respectively represented as a set of quaternions; these four numbers can be obtained in a random way; where i, j, k are imaginary numbers and satisfy:

i ² =j ² =k ² =-1;

ij=-ji=k;

jk=-kj=i

ki=-ik=j

For the conjugation of quaternions, it is expressed as:

For the modulus length of the quaternion, its calculation formula is expressed as:

且满足，qq^-1＝1；For the inverse of this set of quaternions, it can be expressed as:

And satisfy, qq ^-1 =1;

102. The transmitting end performs constellation mapping after serial-to-parallel conversion of the transmitted signal; the mapping is performed as a three-dimensional constellation point s(n).

四个点，四个点正好可以构成一个正四面体。Assume that the three-dimensional constellation points corresponding to the QPSK signal s(n) are:

Four points, four points can just form a regular tetrahedron.

Perform constellation rotation encryption on the mapped transmitted signal s(n) with the secret key, and modulate by OFDM;

Constellation rotation is performed on the mapped three-dimensional constellation point s(n), and the rotated encrypted signal s'(n) is expressed as s'(n)=qs(n)q ^-1

s'(n)=qs(n)q ^-1 : The meaning is: the three-dimensional constellation point s(n) is rotated by the angle θ around the axis l;

θ＝2arccos(w)；in:

θ=2arccos(w);

Then perform inverse discrete Fourier transform to generate OFDM symbols:

103. The transmitting end performs time inversion on the estimated channel state information to obtain a time inversion mirror TRM (TimeReversal Mirror);

The time-reversal mirror is expressed as

104. After parallel-serial conversion, the modulated OFDM symbols are passed through a time inversion mirror and transmitted through a channel, and the receiving end receives the encrypted constellation points.

Alice adds a cyclic prefix to the generated OFDM symbol, and then passes through the time inversion mirror after parallel-to-serial conversion; at this time, the signal received by the receiver is expressed as:

Among them, the above process can be equivalent to that there is an equivalent channel between Alice and Bob, which is an autocorrelation function, and there is a peak when K=L-1; the equivalent channel is expressed as:

Based on the above embodiment, as shown in FIG. 3 , the present invention also provides a constellation rotation-based secure transmission method in a TR_OFDM system, and the secure transmission method includes:

201. The transmitting end and the receiving end send a probe signal to each other to perform channel estimation with the probe signal, and before quantizing the estimated signal, the eavesdropping end passively probes the probe channel;

Alice and Bob send probe signals to each other, assuming that the channel state information estimated by Alice and Bob is ideal.

202. Alice at the sending end and Bob at the receiving end respectively quantize ^hr [k], and determine a quaternion q, which is used as a secret key for encryption and decryption by both parties.

203. The transmitting end performs constellation mapping after converting the transmitted signal string into parallel; performs constellation rotation encryption on the mapped transmitted signal with the secret key, and modulates in an OFDM manner;

In this embodiment, the transmitted signal is a binary signal, and the binary signal is subjected to serial-to-parallel transformation, and then constellation mapping is performed; it is mapped to a three-dimensional coordinate point, and the mapped signal s'(n) is encrypted by constellation rotation using the previously generated secret key. , expressed as s'(n)=qs(n)q ^-1 . Then perform IFFT, add a cyclic prefix, and perform parallel-to-serial transformation.

Among them, S'(n) is the rotated encrypted signal; x(k) is the modulated OFDM symbol, which is expressed as:

204. The transmitting end performs time inversion on the estimated channel state information to obtain a time inversion mirror;

In this embodiment, Alice at the transmitting end performs time inversion on the estimated channel state information H _r (k) to obtain a time inversion mirror. The OFDM symbols x(k) are passed through the time reversal mirror and transmitted through the channel.

205. After parallel-serial conversion, the modulated OFDM symbols pass through a time inversion mirror, and are transmitted through a channel;

206. After the receiving end and the eavesdropping end perform serial-to-parallel conversion on the received OFDM symbols, the encrypted constellation points are obtained;

For the receiving end, refer to the above-mentioned embodiment, and for the eavesdropping end:

The signal received by the eavesdropping terminal Eve is:

Among them, the above process can be equivalent to that there is an equivalent channel between Alice and Eve, which is a cross-correlation function, which is much smaller than _hrq [k]. The equivalent channel is expressed as:

207. The receiving end uses the secret key to decrypt the encrypted constellation point, but the eavesdropping end cannot decrypt the constellation point.

The receiving end performs inverse fast Fourier transform on the received signal, and the parallel-to-serial transformed symbol s'(n)=qs(n)q ^-1 performs constellation inverse rotation, which is expressed as: s(n)=q ^-1 ( qs(n)q ^-1 )q.

The eavesdropping end performs inverse fast Fourier transform on the received signal, and the parallel-to-serial transformed symbol s(n)=q ^-1 (qs(n)q ^-1 )q, because Eve cannot obtain the data between Alice and Bob The corresponding quaternion cannot be generated without the channel state information, so the constellation inverse rotation cannot be performed on the received signal. This ensures the security of communication between Alice and Eve.

It can be understood that, for the explanation of the parameters expressed by the formulas such as signals and channels in the embodiments of the present invention, reference may be made to the prior art, for example, related papers and patents on the transmission method of time inversion, for example, refer to patents such as CN107911191A; The point is not here, the core of which is to use the quaternion as the secret key of the constellation encryption process. Therefore, the present invention does not provide a more specific explanation for these parameters.

Figure 4 shows a preferred secure transmission method based on constellation rotation in the TR_OFDM system. Under this method, the entire transmission process is a mirroring process, including the encryption process and the decryption process, and the corresponding encryption process needs to be performed before the constellation mapping. Serial-parallel exchange, then constellation rotation, IFFT and cyclic prefix are used for modulation processing, and then parallel-serial conversion is performed after processing, and the result of parallel-serial conversion is transmitted through the time inversion mirror to the receiving end through the multipath channel; , the receiving end will perform the decryption process, including serial-to-parallel conversion; the demodulation process of removing the cyclic prefix and FFT; after the demodulation is completed, the constellation inverse rotation is performed, and the constellation inversely mapped signal is output through the parallel-serial conversion.

The node referred to in the embodiments of the present invention can be understood as an abstract machine that responds to specific external trigger conditions and performs state transitions according to certain rules, which can be mobile phones, tablet computers, handheld computers, personal PC computers, servers, etc., which can install applications Software and equipment capable of networking; it can also be understood as a physical machine capable of data communication, such as modems, repeaters, routers, gateways, and so on.

In the description of the present invention, it should be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top" "," "inside", "outside", "front", "center", "both ends", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, only for the convenience of describing the present invention and The description is simplified rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as limiting the invention.

In the present invention, unless otherwise expressly specified and limited, terms such as "installation", "arrangement", "connection", "fixation" and "rotation" should be understood in a broad sense, for example, it may be a fixed connection or a It can be a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between the two elements, Unless otherwise clearly defined, those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (7)

1. An encryption method based on constellation rotation in a TR _ OFDM system, the method comprising:

the sending end and the receiving end respectively quantize the estimated channel and judge the channel into a quaternion which is used as a secret key for encryption and decryption of both parties;

the sending end carries out constellation mapping after carrying out serial-parallel conversion on the sent quaternary signal; mapping into a three-dimensional coordinate point, performing constellation rotation encryption on the mapped transmission signal by using the secret key, and modulating by adopting an OFDM (orthogonal frequency division multiplexing) mode;

the sending end carries out time reversal on the estimated channel state information to obtain a time reversal mirror;

and after parallel-serial conversion, the modulated OFDM symbols pass through a time reversal mirror and are transmitted through a channel, and a receiving end receives the encrypted constellation points.

2. The encryption method based on constellation rotation in TR _ OFDM system as claimed in claim 1, wherein the estimating of the channel comprises using a rayleigh channel, and the transmitting end and the receiving end transmit a sounding signal to each other to perform channel estimation on the sounding signal.

3. The encryption method based on constellation rotation in TR _ OFDM system according to claim 1, wherein the decision manner includes that the receiving end performs demodulation with minimum distance, that is, the receiving end decrypts the signal after fast fourier transform and then compares it with the original mapping point, and decides the closest point of the original mapping point as its corresponding quaternary signal.

4. The encryption method based on constellation rotation in the TR _ OFDM system according to claim 1, wherein before the parallel-to-serial conversion, the transmitting end performs inverse fast fourier transform on the transmission signal after the constellation rotation and adds a cyclic prefix.

5. A safe transmission method based on constellation rotation in a TR _ OFDM system is characterized in that the safe transmission method comprises the following steps:

the transmitting end and the receiving end mutually transmit detection signals to perform channel estimation on the detection signals, and the eavesdropping end performs passive detection on the detection channels;

the sending end and the receiving end respectively quantize the estimated channel and judge the channel into a quaternion which is used as a secret key for encryption and decryption of both parties;

the sending end carries out constellation mapping after carrying out serial-parallel conversion on the sending signal; carrying out constellation rotation encryption on the mapped sending signal by using the angle of the secret key, and modulating by adopting an OFDM (orthogonal frequency division multiplexing) mode;

the sending end carries out time reversal on the estimated channel state information to obtain a time reversal mirror;

the modulated OFDM symbols are subjected to parallel-serial conversion, pass through a time reversal mirror and are transmitted through a channel;

modulating the received OFDM symbols by a receiving end and an eavesdropping end, and then carrying out serial-to-parallel conversion to obtain encrypted constellation points;

the receiving end decrypts the encrypted constellation point by using the secret key, and the eavesdropping end cannot decrypt the constellation point.

6. The safe transmission method based on constellation rotation in TR _ OFDM system according to claim 5, wherein said transmitted signal after constellation rotation is inverse fast Fourier transformed and added with cyclic prefix; and carrying out corresponding fast Fourier transform and cyclic prefix removal on the transmitted signal before constellation reverse rotation.

7. The method according to claim 5, wherein the decrypting the encrypted constellation points by the receiving end using the key comprises performing fast fourier transform on the encrypted constellation points, performing constellation inverse rotation using the key, and performing constellation inverse mapping on the encrypted signals using the key; after the constellation inverse mapping result is converted in parallel and serial, the receiving end resolves the initial sending signal.

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