CN116389651A - A secure image transmission method based on ACO-OFDM visible light communication - Google Patents

Abstract

The invention discloses an ACO-OFDM visible light communication-based image safety transmission method, which is characterized by comprising the following steps of: the encryption is combined with the physical layer at the upper layer of the ACO-OFDM system. The specific process is as follows: encrypting an original image on the upper layer of the ACO-OFDM system based on a Fresnel diffraction double random phase encryption technology, and performing code conversion to obtain a calculation hologram; and then, mixing the SHA-256 values of the original image with an external key to determine initial values of two-dimensional hyperchaotic systems, generating four chaotic sequences, carrying out bit exclusive OR on odd bits and even bits of the transmitted binary bit stream by using the two sequences, carrying out chaotic scrambling on real parts and imaginary parts of the QAM symbol stream by using the other two sequences, and realizing encryption of a physical layer. The invention adopts the upper layer and physical layer of ACO-OFDM system to encrypt, further enhances the security of image transmission. In addition, the upper layer encrypts and converts the original image into a binary real-value calculation hologram, so that the anti-noise performance of the ACO-OFDM system is improved. The invention is suitable for the safe transmission of the image data between the visible light receiving and transmitting devices.

Description

A secure image transmission method based on ACO-OFDM visible light communication

technical field

The present invention relates to the field of visible light communication and image transmission, in particular, to an image security transmission method based on ACO-OFDM visible light communication.

Background technique

Information transmission in current wireless networks is done by technologies operating in the radio frequency band, such as: Wi-Fi, Bluetooth, NFC, cellular networks, satellite networks, etc., each of these technologies has its own performance characteristics, and Use according to application type. However, with the rise of the Internet of Things (IoT) and Industry 4.0, the number of applications and devices connected to the network is increasing every day, so the requirements for wireless access, capacity and security are increasing exponentially, and large amounts of information New technologies are needed to support broadband services and accommodate existing traffic.

In order to solve the above problems and the severe congestion of the radio spectrum, researchers have developed a new technology called Visible Light Communication (VLC), which uses the visible light band for data transmission, and has the advantages of rich spectrum resources, no electromagnetic pollution, and safe Advantages of high sex. In addition, visible light communication uses the most widely used LED as the emission source, which combines lighting and communication, which makes it considered a technology with great potential for future communication.

In order to ensure high data rate transmission and reduce implementation complexity, VLC can learn from the Orthogonal Frequency Division Multiplexing (OFDM) multi-carrier modulation scheme of radio frequency. The salient feature of OFDM is to convert the frequency-selective fading of the communication channel into a flat fading channel by using a computationally efficient and simple one-dimensional frequency domain equalization technique. In addition, OFDM can effectively utilize spectrum resources while ensuring high data rate communication. The OFDM multicarrier modulation format modulates the amplitude and phase information of a carrier signal in the case of radio frequency based wireless communications. Visible light communication links are implemented using LEDs, and the fact that LEDs produce incoherent light allows OFDM time-domain signals to modulate the intensity of the light source without being perceived by the human eye. Therefore, VLC usually adopts a special modulation and demodulation format of intensity modulation/direct detection (IM/DD), which forces the OFDM time-domain signal to be both real-valued and unipolar in nature (i.e., positive). Therefore, in order to obtain a real-valued signal, the Hermitian symmetry constraint is imposed on the input frame structure of the IFFT module, so that the time-domain signal output by the IFFT can guarantee its real-valued property. In order to generate positive signals, various optical OFDM technologies have been proposed, such as DC offset optical OFDM (DCO-OFDM), asymmetrically limited optical OFDM (ACO-OFDM), flipped OFDM (Flip-OFDM) and so on. Each variant of OFDM has certain tradeoffs in terms of spectral efficiency, power efficiency, computational complexity, and bit error rate performance. The VLC based on ACO-OFDM is a potential candidate solution for VLC application. On the premise of not losing the generality, the present invention provides the VLC system based on ACO-OFDM.

With the advent of the era of big data, images play an increasingly important role in data transmission. However, in the image transmission process, it is particularly important to ensure the security of the image. In the process of image transmission, if there are no good security measures, hackers or malicious attackers can easily obtain important information in the image, resulting in data leakage. This will not only cause losses to the interests of enterprises or individuals, but also affect the image and reputation of enterprises or individuals in the market.

To sum up, it is necessary to protect the image transmission based on the ACO-OFDM visible light communication system to ensure information security.

Contents of the invention

The purpose of the present invention is to provide an image security transmission method based on ACO-OFDM visible light communication.

The present invention is an image security transmission method based on ACO-OFDM visible light communication, comprising the following steps:

sender:

Step (1) Encrypt the original image based on the double random phase encryption technology of the Fresnel diffraction system, and encode and convert it into a binary real-valued computational hologram;

Step (2) determines the initial value of two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image with the external key, produces four chaotic sequences, and is used for the encryption of the binary bit stream and the QAM symbol stream;

Step (3) The binary real-valued calculation hologram is converted into a binary bit stream in parallel, and two of the four chaotic sequences are used to perform bit XOR on the odd and even bits of the binary bit stream to obtain encrypted binary bits flow;

Step (4) Carry out m-QAM quadrature amplitude modulation to the encrypted binary bit stream to obtain the QAM symbol stream, apply the other two of the four chaotic sequences to chaotically scramble the real and imaginary parts of the QAM symbol stream respectively, and obtain the encrypted The QAM symbol stream;

Step (5) Perform serial-to-parallel conversion and Hermitian mapping on the encrypted QAM symbol stream, form an ACO-OFDM signal matrix according to the ACO-OFDM data characteristic requirements, and then perform inverse fast Fourier transform on the ACO-OFDM signal matrix IFFT, generating real-valued time-domain ACO-OFDM signals;

Step (6) The time-domain ACO-OFDM signal is sequentially processed by adding cyclic prefix CP, parallel-to-serial conversion, clipping, clipping and clipping, and loading it on the LED through digital-to-analog conversion, and sending it through visible light. Propagate to the receiving end through the spatial channel;

Receiving end:

Step (1) The photodetector PD at the receiving end converts the received optical signal into an electrical signal, and then sequentially performs analog-to-digital conversion, serial-to-parallel conversion, and removes the cyclic prefix CP to obtain the received time-domain ACO-OFDM signal;

Step (2) performing fast Fourier transform FFT, anti-Hermitian symmetric transform, and parallel-serial conversion to the received time-domain ACO-OFDM signal successively to obtain an encrypted QAM symbol stream;

Step (3) adopts the same chaotic sequence key of the sending end to decrypt the encrypted QAM symbol stream received;

Step (4) Demodulate the decrypted QAM symbol stream to obtain an encrypted binary bit stream, then use the same chaotic sequence key as the sender to decrypt, and then serially convert it into an encrypted binary real-valued calculation hologram;

Step (5) Decrypt the encrypted binary real-valued calculation hologram based on the double random phase decryption technology of the Fresnel diffraction system to obtain the original image.

Compared with the prior art, the present invention has the following advantages:

The present invention proposes an image security transmission method based on joint encryption of the upper layer and the physical layer of the ACO-OFDM visible light communication system, which realizes image-level, bit-level, and symbol-level multi-level encryption, and improves the security of image information transmission.

The invention utilizes the Fresnel diffraction double random phase encryption technology to encrypt the original image, and encodes and converts it into a binary real value calculation hologram, thereby improving the anti-noise performance of the system.

Among various types of chaotic systems, the two-dimensional hyperchaotic system has the advantages of fast iteration speed and strong robustness. The invention uses the chaotic sequences generated by two two-dimensional hyperchaotic systems to perform chaotic scrambling on the binary bit stream and the QAM symbol stream, and utilizes the sensitivity of the chaotic key to the initial value to increase the difficulty of deciphering the key.

Description of drawings

Fig. 1 is a system structure block diagram of the present invention;

Figure 2 is a schematic diagram of image encryption based on Fresnel diffraction double random phase encryption and holographic encoding;

Fig. 3 is a schematic diagram of image decryption based on Fresnel diffraction double random phase encryption and holographic encoding.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, the present invention is an image security transmission method based on ACO-OFDM visible light communication, which includes the following steps:

sender:

Step (1) Encrypt the original image based on the double random phase encryption technology of the Fresnel diffraction system, and encode and convert it into a binary real-valued computational hologram;

Step (2) determines the initial value of two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image with the external key, produces four chaotic sequences, and is used for the encryption of the binary bit stream and the QAM symbol stream;

Step (3) The binary real-valued calculation hologram is converted into a binary bit stream in parallel, and two of the four chaotic sequences are used to perform bit XOR on the odd and even bits of the binary bit stream to obtain encrypted binary bits flow;

Step (4) Carry out m-QAM quadrature amplitude modulation to the encrypted binary bit stream to obtain the QAM symbol stream, apply the other two of the four chaotic sequences to chaotically scramble the real and imaginary parts of the QAM symbol stream respectively, and obtain the encrypted The QAM symbol stream;

Step (5) Perform serial-to-parallel conversion and Hermitian mapping on the encrypted QAM symbol stream, form an ACO-OFDM signal matrix according to the ACO-OFDM data characteristic requirements, and then perform inverse fast Fourier transform on the ACO-OFDM signal matrix IFFT, generating real-valued time-domain ACO-OFDM signals;

Step (6) The time-domain ACO-OFDM signal is sequentially processed by adding cyclic prefix CP, parallel-to-serial conversion, clipping, clipping and clipping, and loading it on the LED through digital-to-analog conversion, and sending it through visible light. Propagate to the receiving end through the spatial channel;

Receiving end:

Step (1) The photodetector PD at the receiving end converts the received optical signal into an electrical signal, and then sequentially performs analog-to-digital conversion, serial-to-parallel conversion, and removes the cyclic prefix CP to obtain the received time-domain ACO-OFDM signal;

Step (2) performing fast Fourier transform FFT, anti-Hermitian symmetric transform, and parallel-serial conversion to the received time-domain ACO-OFDM signal successively to obtain an encrypted QAM symbol stream;

Step (3) adopts the same chaotic sequence key of the sending end to decrypt the encrypted QAM symbol stream received;

Step (4) Demodulate the decrypted QAM symbol stream to obtain an encrypted binary bit stream, then use the same chaotic sequence key as the sender to decrypt, and then serially convert it into an encrypted binary real-valued calculation hologram;

Step (5) Decrypt the encrypted binary real-valued calculation hologram based on the double random phase decryption technology of the Fresnel diffraction system to obtain the original image.

In the method described above, the sending end step (1) encrypts the original image based on the double random phase encryption technology of the Fresnel diffraction system, and encodes and converts it into a binary real-valued calculation hologram. The schematic diagram is shown in Figure 2. Specifically include the following steps:

(1.1) Encrypt the original image, place the original image I(x, y) on the object plane Σ, and place a white noise random phase plate p ₁ (x, y)=exp( j2πα(x,y)), place a second white noise random phase plate p ₂ (x,y)=exp(j2πβ(ξ,η)) on the spectral plane Σ ₁ , where α,β∈[0,1 ]; z ₁ and z ₂ are the distances of two Fresnel diffractions respectively; assuming that the plane light wave with wavelength λ illuminates the object plane Σ vertically, the original image is modulated by the first random phase plate p ₁ and the distance is z ₁ After Fresnel diffraction, it reaches the second random phase plate p ₂ ; under the condition of Fresnel approximation, the complex amplitude distribution at the second random phase plate is:

q(ξ,η)=F _F {I(x,y)exp[j2πα(x,y)]; z ₁ }

Where _FF represents the Fresnel transformation, and then reaches the output plane Σ ₂ through Fresnel diffraction at a distance z ₂ , and the complex amplitude distribution of the obtained encrypted image is:

E(x,y)=F _F {q(ξ,η)exp[j2πβ(ξ,η)]; z ₂ }

(1.2) Record the encrypted image by means of Roman encoding, and convert the encrypted image E(x,y) into a binary real-valued computational hologram E(m,n).

In the method described above, the sender step (2) determines the initial values of the two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image with the external key, and generates four chaotic sequences for binary bit streams and Encryption of QAM symbol streams;

One of the chaotic models adopted in the present invention is a cross two-dimensional hyperchaotic system (Cross two dimensional hyperchaotic system, CTDHCS) model, and its iteration formula is as follows:

Among them, α and β are two control parameters of CTDHCS. When α=2 and β=1, CTDHCS exhibits hyperchaotic properties;

Another chaotic model is Gao’s two dimensional hyperchaotic system (GTDHCS) model, and its iteration formula is as follows:

Among them, μ and γ are two control parameters of GTDHCS. When μ=5 and γ=5, GTDHCS exhibits hyperchaotic properties;

The specific steps to generate four chaotic sequences are as follows:

(2.1) Input the original image into the SHA-256 function to generate its hash value H, which is a hexadecimal sequence with a length of 64;

(2.2) Use SK=bitxor(H,EK) to mix the hash value H with the external key EK (which consists of 64 truly random hexadecimal numbers) to obtain the session key SK to further improve confidentiality , where bitxor(a,b) represents the bitwise XOR operation of a and b;

(2.3) Extract the initial value of the chaotic system from the session key SK, expressed as follows:

Among them, the hex2dec operation can convert the string of hexadecimal numbers into decimal integers, A(1) and B(1) are the initial values of the extracted CTDHCS, U(1) and V(1) are the extracted GTDHCS initial value;

(2.4) Obtain four chaotic sequences of A, B, U, and V according to the two-dimensional hyperchaotic system iteration according to the extracted initial value; first, use the two-dimensional hyperchaotic system iteration formula to iterate the initial value (n+l ) times, resulting in 4 sequences of length (n+l): A(i), B(i), U(i), V(i), i=1, 2,...,n+l, where l is the pre-iteration time to eliminate the negative impact of the transient process of the chaotic system; then the chaotic sequences A and B are applied to the encryption of the binary bit stream, and the chaotic sequences U and V are applied to the encryption of the QAM symbol stream.

In the method described above, step (3) at the sending end converts the binary real-valued calculation hologram into a binary bit stream in parallel, and applies two of the four chaotic sequences to the odd bits and even bits of the binary bit stream respectively. Bit XOR to obtain an encrypted binary bit stream, which specifically includes the following steps:

(3.1) Parallel-serial conversion of binary real-valued computing holograms into binary bit streams;

(3.2) Preprocess the chaotic sequence A and B, as follows:

Among them, the floor function returns the largest integer not greater than the given value, the abs function returns the absolute value of the given value, mod(a,b) returns the remainder of dividing a by b, and the processed chaotic sequence only contains 0 and 1, that is a(i), b(i)∈{0,1};

表示如下：(3.3) Exclusively OR the chaotic sequences a(i) and b(i) obtained after preprocessing with the odd and even bits of the binary bit stream x after the parallel-serial conversion to obtain the encrypted binary bit stream

Expressed as follows:

Where bitxor(a,b) represents the bitwise XOR operation of a and b.

In the method described above, the sending end step (4) carries out m-QAM quadrature amplitude modulation to the encrypted binary bit stream to obtain the QAM symbol stream, and uses the other two of the four chaotic sequences to the real part of the QAM symbol stream and The imaginary part is chaotically scrambled respectively to obtain the encrypted QAM symbol stream, which specifically includes the following steps:

(4.1) m-QAM quadrature amplitude modulation is carried out to the encrypted binary bit stream to obtain the QAM symbol stream;

(4.2) Preprocess the chaotic sequences U and V as follows:

Among them, the floor function returns the largest integer not greater than the given value, the abs function returns the absolute value of the given value, mod(a,b) returns the remainder of dividing a by b, and the processed chaotic sequence only contains -1 and 1, That is, u(i), v(i)∈{-1,1};

表示为：(4.3) The QAM symbol flow is represented by S=[S ₁ , S ₂ ,...,S _l ] ^T , where [] ^T refers to the matrix transposition, and l refers to the length of the QAM symbol flow; the preprocessed chaotic sequence u(i) and v(i) are multiplied with the real and imaginary parts of the QAM symbol stream S respectively, and the encrypted QAM symbol stream

Expressed as:

Where real(a) returns the real part of a, and imag(a) returns the imaginary part of a.

The method described above, the sending end steps (5) and (6) and the receiving end steps (1) and (2), realize the generation and sending and receiving of the ACO-OFDM signal;

进行串并转换，得到ACO-OFDM信号的有效数据矩阵，表示为：Step (5) at the sending end sends the encrypted QAM symbol stream

Perform serial-to-parallel conversion to obtain the effective data matrix of the ACO-OFDM signal, expressed as:

表示为：Where Q and M are the number of effective data subcarriers of OFDM and the total number of OFDM symbols respectively, the present invention is based on the ACO-OFDM visible light communication system, only odd subcarriers are modulated and assigned Hermitian symmetry, while even subcarriers are assigned zero , so Q is a quarter of the number N of OFDM subcarriers, that is, Q=N/4; Hermitian mapping is performed on the effective data matrix of the ACO-OFDM signal. Carriers are assigned Hermitian symmetry, and even subcarriers are set to zero to form an ACO-OFDM signal matrix

Expressed as:

进行逆快速傅里叶变换IFFT，生成实值的时域ACO-OFDM信号；For ACO-OFDM signal matrix

Perform inverse fast Fourier transform IFFT to generate real-valued time-domain ACO-OFDM signals;

Step (6) at the sending end adds the cyclic prefix CP to the ACO-OFDM signal in the time domain, parallel-to-serial conversion, clipping, limiting, and negative wave processing, and then loads it on the LED through digital-to-analog conversion, and sends it through visible light. The visible light signal propagates to the receiving end through the spatial channel;

Step at the receiving end (1) The photodetector PD at the receiving end converts the received optical signal into an electrical signal, and then sequentially performs analog-to-digital conversion, serial-to-parallel conversion, and removes the cyclic prefix CP to obtain the received time-domain ACO-OFDM signal;

The receiving end step (2) performs fast Fourier transform FFT, anti-Hermitian symmetric transform, and parallel-serial conversion on the received time-domain ACO-OFDM signal in sequence to obtain an encrypted QAM symbol stream;

For the method described above, the decryption method corresponding to the receiving end specifically includes:

The receiver step (3) corresponds to the decryption of the transmitter step (4) encrypted QAM symbol flow, and adopts the same chaotic sequence key of the transmitter step (4) to decrypt the received encrypted QAM symbol stream;

The receiving end step (4) corresponds to the decryption of the sending end step (3) encrypted binary bit stream, and adopts the same chaotic sequence key of the sending end step (3) to decrypt the received encrypted binary bit stream;

The receiving end step (5) corresponds to the decryption of the encrypted image in the sending end step (1), and the image decryption principle diagram is shown in Figure 3. During the decryption process, the received binary real value calculation hologram E'(m ,n) Placed on the input plane, irradiated with monochromatic vertical incident light, and then do a standard Fourier transform, calculate the hologram reproduction to obtain the encrypted image E'(x,y) and its conjugate; take the encrypted image E'(x , y) to achieve decryption, the -1-level reconstructed conjugate image is introduced into the Fresnel diffraction double random phase decryption system, and it undergoes two Fresnel diffractions with distances of z ₃ and z ₄ and two random phases respectively The modulation decryption of plates p ₃ and p ₄ obtains the decrypted original image I'(x,y) at the output plane Σ':

I'(x,y)exp[-j2πα(ξ,η)]=F _F {F _F [E'*(x,y); z ₃ ] exp[j2πβ(ξ,η)]; z ₄ }

Wherein * represents conjugation, z ₃ =z ₂ , z ₄ =z ₁ , p ₃ =p ₂ , p ₄ =p ₁ .

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (6)

1. An ACO-OFDM visible light communication-based image security transmission method is characterized by comprising the following steps:

and the transmitting end:

encrypting an original image based on a double random phase encryption technology of a Fresnel diffraction system, and performing code conversion to obtain a binary real value calculation hologram;

step (2) mixing SHA-256 values of an original image with an external key to determine initial values of two-dimensional hyperchaotic systems, and generating four chaotic sequences for encrypting binary bit streams and QAM symbol streams;

converting binary real value calculation holograms into binary bit streams in parallel and serial, and performing bit exclusive OR on odd bits and even bits of the binary bit streams respectively by using two of four chaotic sequences to obtain encrypted binary bit streams;

performing m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream, and performing chaotic scrambling on the real part and the imaginary part of the QAM symbol stream respectively by using the other two of the four chaotic sequences to obtain the encrypted QAM symbol stream;

step (5) serial-parallel conversion and hermitian mapping are carried out on the encrypted QAM symbol stream, an ACO-OFDM signal matrix is formed according to the ACO-OFDM data characteristic requirement, inverse Fast Fourier Transform (IFFT) is carried out on the ACO-OFDM signal matrix, and a real-valued time domain ACO-OFDM signal is generated;

sequentially adding a cyclic prefix CP, parallel-to-serial converting, clipping and negating wave treatment to the time domain ACO-OFDM signal, loading the time domain ACO-OFDM signal onto an LED through digital-to-analog conversion, transmitting the time domain ACO-OFDM signal through visible light, and transmitting the transmitted visible light signal to a receiving end through a spatial channel;

the receiving end:

the photoelectric detector PD at the receiving end converts the received optical signal into an electric signal, and then sequentially performs analog-digital conversion, serial-parallel conversion and cyclic prefix CP removal to obtain a received time domain ACO-OFDM signal;

step (2) carrying out fast Fourier transform FFT, inverse hermitian symmetric transform and parallel-serial conversion on the received time domain ACO-OFDM signal in sequence to obtain an encrypted QAM symbol stream;

step (3) adopting the same chaotic sequence key of the transmitting end to decrypt the received encrypted QAM symbol stream;

demodulating the decrypted QAM symbol stream to obtain an encrypted binary bit stream, decrypting by adopting a chaotic sequence key which is the same as that of a transmitting end, and then converting the encrypted binary real value into a binary real value calculation hologram in a serial-parallel manner;

and (5) decrypting the encrypted binary real value calculation hologram based on the double random phase decryption technology of the Fresnel diffraction system to obtain an original image.

2. The method for safely transmitting an image based on ACO-OFDM visible light communication according to claim 1, wherein the transmitting-side step (1) specifically comprises:

the method comprises the steps of (1.1) encrypting an original image, obtaining an encrypted image after the original image is modulated and encrypted by two Fresnel diffractions and two random phase plates, and performing standard Fourier transform on the encrypted image;

(1.2) recording the encrypted image by using a Roman coding mode, and converting the encrypted image into a binary real-valued calculation hologram.

3. The method for safely transmitting an image based on ACO-OFDM visible light communication according to claim 1, wherein the transmitting-side step (2) specifically comprises:

(2.1) inputting the original image into an SHA-256 function to generate a hash value H, namely a hexadecimal sequence with the length of 64;

(2.2) mixing the hash value H with an external key EK (which consists of 64 truly random hexadecimal numbers) using sk=bitxor (H, EK), where bitxor (a, b) represents a bitwise exclusive-or operation of a and b, to obtain the session key SK, further improving confidentiality;

(2.3) extracting an initial value of the chaotic system from the session key SK;

and (2.4) iterating according to the extracted initial values according to the two-dimensional hyper-chaotic systems to obtain four chaotic sequences.

4. The method for safely transmitting an image based on ACO-OFDM visible light communication according to claim 1, wherein the transmitting-side step (3) specifically comprises:

(3.1) binary real-valued computed holograms are converted into binary bit streams in parallel-serial;

(3.2) preprocessing two of the four chaotic sequences, wherein the processed chaotic sequences only comprise 0 and 1;

and (3.3) respectively carrying out bit exclusive OR on the preprocessed chaotic sequence and the odd-numbered bits and the even-numbered bits of the binary bit stream subjected to parallel-serial conversion to obtain an encrypted binary bit stream.

5. The method for safely transmitting an image based on ACO-OFDM visible light communication according to claim 1, wherein the transmitting-side step (4) specifically comprises:

(4.1) performing m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream;

(4.2) preprocessing the other two of the four chaotic sequences, wherein the processed chaotic sequences only comprise-1 and-1;

and (4.3) multiplying the preprocessed chaotic sequence by the real part and the imaginary part of the QAM symbol stream respectively.

6. The image security transmission method based on ACO-OFDM visible light communication according to claims 1 to 5, wherein the decryption method corresponding to the receiving end specifically comprises:

the receiving end step (3) corresponds to the decryption of the encrypted QAM symbol stream in the transmitting end step (4), and the same chaotic sequence key in the transmitting end step (4) is adopted to decrypt the received encrypted QAM symbol stream;

the step (4) of the receiving end corresponds to the step (3) of decrypting the encrypted binary bit stream of the transmitting end, and the same chaotic sequence key of the step (3) of the transmitting end is adopted to decrypt the received encrypted binary bit stream;

the receiving end step (5) corresponds to the decryption of the encrypted image in the transmitting end step (1), the received binary real value calculation hologram is subjected to primary standard Fourier transform to obtain the encrypted image and conjugate thereof, and the-1-level reproduction conjugate image is subjected to two Fresnel diffraction and modulation decryption of two random phase plates to recover the original image.

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