An Image Secure Transmission Method Based on ACO-OFDM Visible Light Communication

Abstract

The present invention discloses an image secure transmission method based on ACO-OFDM visible light communication, which is characterized in that: joint encryption is performed between the upper layer and the physical layer of the ACO-OFDM system. The specific process is as follows: at the upper layer of the ACO-OFDM system, the original image is encrypted based on Fresnel diffraction double random phase encryption technology and encoded into a computer-generated hologram; then, the initial values of two two-dimensional hyperchaotic systems are determined by mixing the SHA-256 value of the original image and an external key, four chaotic sequences are generated, two of the sequences are used to perform bitwise exclusive OR on the odd and even bits of the transmitted binary bit stream, and the other two sequences are used to perform chaotic scrambling on the real and imaginary parts of the QAM symbol stream to achieve encryption at the physical layer. The present invention adopts joint encryption between the upper layer and the physical layer of the ACO-OFDM system, further enhancing the security of image transmission. In addition, the upper layer encrypts the original image into a binary real-valued computer-generated hologram, improving the anti-noise performance of the ACO-OFDM system. The present invention is applicable to the secure transmission of image data between visible light transceiver devices.

Description

Technical Field

[0001] The present invention relates to the fields of visible light communication and image transmission. Specifically, it particularly relates to an image secure transmission method based on ACO-OFDM visible light communication. Background Art

[0002] Currently, information transmission in wireless networks is accomplished through 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 is used according to the type of application. However, with the rise of the Internet of Things (IoT) and Industry 4.0, the number of applications and devices connected to the network increases every day. Therefore, the requirements for wireless access, capacity, and security have increased exponentially, and a large amount of information requires new technologies to support broadband services and adapt to the existing traffic.

[0003] 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 advantages such as rich spectrum resources, no electromagnetic pollution, and high security. In addition, visible light communication uses the currently most widely used LED as the emission source, combining lighting and communication, which makes it considered a technology with great potential for future communication.

[0004] To ensure high data rate transmission and reduce implementation complexity, VLC can draw on the orthogonal frequency division multiplexing (OFDM) multi-carrier modulation scheme of radio frequency. The remarkable feature of OFDM is to use computationally efficient and simple one-dimensional frequency domain equalization technology to transform the frequency selective fading of the communication channel into a flat fading channel. In addition, OFDM can effectively utilize spectrum resources while ensuring high data rate communication. The OFDM multi-carrier modulation format modulates the amplitude and phase information of the carrier signal in the case of radio frequency-based wireless communication. The visible light communication link is implemented using LEDs, and the fact that LEDs generate incoherent light enables the OFDM time-domain signal to modulate the intensity of the light source, which is imperceptible to the human eye. Therefore, VLC usually adopts the 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 (i.e., positive) in nature. Therefore, in order to obtain a real-valued signal, the input frame structure of the IFFT module is constrained by Hermitian symmetry to ensure the real-valued nature of the time-domain signal output by the IFFT. In order to generate a positive signal, various optical OFDM technologies have been proposed, such as direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), flipped OFDM (Flip-OFDM), and so on. Each variant of OFDM has certain trade-offs in terms of spectral efficiency, power efficiency, computational complexity, and bit error rate performance. VLC based on ACO-OFDM is a potential candidate solution for VLC applications. Without loss of generality, the present invention is based on the ACO-OFDM VLC system.

[0005] With the advent of the big data era, images play an increasingly important role in data transmission. However, in the process of image transmission, ensuring the security of images is also particularly important. During the image transmission process, without good security measures, hackers or malicious attackers can easily obtain important information in the images, 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.

[0006] In summary, it is necessary to protect the image transmission of the visible light communication system based on ACO-OFDM to ensure information security. Summary of the Invention

[0007] The object of the present invention is to provide an image secure transmission method based on ACO-OFDM visible light communication.

[0008] The present invention is an image secure transmission method based on ACO-OFDM visible light communication, comprising the following steps:

[0009] Transmitter:

[0010] 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 computer-generated hologram;

[0011] Step (2): Determine the initial values of two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image and an external key, and generate four chaotic sequences for encrypting the binary bit stream and the QAM symbol stream;

[0012] Step (3): Serial-to-parallel convert the binary real-valued computer-generated hologram into a binary bit stream, and perform bitwise exclusive OR on the odd bits and even bits of the binary bit stream respectively by using two of the four chaotic sequences to obtain an encrypted binary bit stream;

[0013] Step (4): Perform m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream, and perform 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 an encrypted QAM symbol stream;

[0014] 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 IFFT on the ACO-OFDM signal matrix to generate a real-valued time-domain ACO-OFDM signal;

[0015] Step (6): Add a cyclic prefix CP, perform serial-to-parallel conversion, and perform clipping and negative wave clipping processing on the time-domain ACO-OFDM signal in sequence, and then load it onto the LED through digital-to-analog conversion and send it through visible light. The emitted visible light signal propagates through the space channel to the receiver;

[0016] Receiver:

[0017] Step (1): The photodetector PD at the receiver converts the received optical signal into an electrical signal, and then performs analog-to-digital conversion, serial-to-parallel conversion, and removes the cyclic prefix CP in sequence to obtain the received time-domain ACO-OFDM signal;

[0018] Step (2): Perform fast Fourier transform FFT, inverse Hermitian symmetry transform, and serial-to-parallel conversion on the received time-domain ACO-OFDM signal in sequence to obtain an encrypted QAM symbol stream;

[0019] Step (3): Decrypt the received encrypted QAM symbol stream by using the same chaotic sequence key as that at the transmitter;

[0020] Step (4) demodulates the decrypted QAM symbol stream to obtain an encrypted binary bit stream, and then decrypts it using the same chaotic sequence key as that at the transmitting end. After that, it is converted from serial to parallel to obtain an encrypted binary real-valued computer-generated hologram.

[0021] Step (5) decrypts the encrypted binary real-valued computer-generated hologram based on the Fresnel diffraction system double random phase decryption technology to obtain the original image.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The present invention proposes an image secure transmission method based on joint encryption of the upper layer and the physical layer of an ACO-OFDM visible light communication system, realizing multi-level encryption at the image level, bit level, and symbol level, and improving the security of image information transmission.

[0024] The present invention encrypts the original image using the Fresnel diffraction double random phase encryption technology and encodes it into a binary real-valued computer-generated hologram, improving the anti-noise performance of the system.

[0025] Among various types of chaotic systems, the two-dimensional hyperchaotic system has advantages such as fast iteration speed and strong robustness. The present invention applies 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 key cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a system structure block diagram of the present invention;

[0027] Figure 2 is a schematic diagram of image encryption based on Fresnel diffraction double random phase encryption and holographic coding;

[0028] Figure 3 is a schematic diagram of image decryption based on Fresnel diffraction double random phase encryption and holographic coding. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] As Figure 1 shown, an image secure transmission method based on ACO-OFDM visible light communication of the present invention includes the following steps:

[0031] Transmitting end:

[0032] 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 computer-generated hologram;

[0033] Step (2): Determine the initial values of two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image with an external key, and generate four chaotic sequences for encrypting the binary bit stream and the QAM symbol stream;

[0034] Step (3): Serial-to-parallel convert the binary real-valued computer-generated hologram into a binary bit stream, and apply two of the four chaotic sequences to perform bitwise exclusive OR on the odd and even bits of the binary bit stream respectively to obtain an encrypted binary bit stream;

[0035] Step (4): Perform m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream, and apply the other two of the four chaotic sequences to perform chaotic scrambling on the real and imaginary parts of the QAM symbol stream respectively to obtain an encrypted QAM symbol stream;

[0036] Step (5): Perform serial-to-parallel conversion and Hermitian mapping on the encrypted QAM symbol stream, construct an ACO-OFDM signal matrix according to the ACO-OFDM data characteristic requirements, and then perform inverse fast Fourier transform IFFT on the ACO-OFDM signal matrix to generate a real-valued time-domain ACO-OFDM signal;

[0037] Step (6): Add a cyclic prefix CP, perform serial-to-parallel conversion, and perform clipping and negative peak clipping processing on the time-domain ACO-OFDM signal in sequence, then load it onto the LED through digital-to-analog conversion and send it through visible light. The emitted visible light signal propagates through the space channel to the receiving end;

[0038] Receiving end:

[0039] Step (1): The photodetector PD at the receiving end converts the received optical signal into an electrical signal, and then performs analog-to-digital conversion, serial-to-parallel conversion, and removes the cyclic prefix CP in sequence to obtain the received time-domain ACO-OFDM signal;

[0040] Step (2): Perform fast Fourier transform FFT, inverse Hermitian symmetry transform, and serial-to-parallel conversion on the received time-domain ACO-OFDM signal in sequence to obtain an encrypted QAM symbol stream;

[0041] Step (3): Decrypt the received encrypted QAM symbol stream using the same chaotic sequence key as the sending end;

[0042] Step (4): Demodulate the decrypted QAM symbol stream to obtain an encrypted binary bit stream, and then decrypt it using the same chaotic sequence key as the sending end, and then perform serial-to-parallel conversion to obtain an encrypted binary real-valued computer-generated hologram;

[0043] Step (5) decrypts the encrypted binary real-valued computer-generated hologram based on the double random phase decryption technology of the Fresnel diffraction system to obtain the original image.

[0044] For the method described above, in step (1) of the sender, the original image is encrypted based on the double random phase encryption technology of the Fresnel diffraction system and encoded into a binary real-valued computer-generated hologram. The schematic diagram is as Figure 2 shown, and specifically includes the following steps:

[0045] (1.1) Encrypt the original image. Place the original image I(x, y) on the object plane Σ. Place a white noise random phase plate p1(x, y) = exp(j2πα(x, y)) closely on the object plane Σ. Place the second white noise random phase plate p2(x, y) = exp(j2πβ(ξ, η)) on the spectral plane Σ1, where α, β ∈ [0, 1]; z1 and z2 are the distances of the two Fresnel diffractions respectively. Assume that a plane light wave with wavelength λ is vertically incident on the object plane Σ. After being modulated by the first random phase plate p1 and undergoing Fresnel diffraction at a distance of z1, the original image reaches the second random phase plate p2. Under the condition of Fresnel approximation, the complex amplitude distribution at the second random phase plate is:

[0046] q(ξ, η) = F F {I(x, y)exp[j2πα(x, y)]; z1}

[0047] where F F represents the Fresnel transform, and then undergoes Fresnel diffraction at a distance of z2 to reach the output plane Σ2. The complex amplitude distribution of the encrypted image obtained is:

[0048] E(x, y) = F F {q(ξ, η)exp[j2πβ(ξ, η)]; z2}

[0049] (1.2) Record the encrypted image using the Lohmann encoding method, and convert the encrypted image E(x, y) into a binary real-valued computer-generated hologram E(m, n).

[0050] For the method described above, in step (2) of the sender, the initial values of two two-dimensional hyperchaotic systems are determined by mixing the SHA-256 value of the original image and an external key, and four chaotic sequences are generated for encrypting the binary bit stream and the QAM symbol stream;

[0051] One of the chaotic models adopted in the present invention is the Cross two dimensional hyperchaotic system (CTDHCS) model, and its iterative formula is as follows:

[0052]

[0053] Among them, α and β are two control parameters of CTDHCS. When α = 2 and β = 1, CTDHCS exhibits hyperchaotic properties;

[0054] Another chaotic model is the Gao's two dimensional hyperchaotic system (GTDHCS) model, and its iterative formula is as follows:

[0055]

[0056] Among them, μ and γ are two control parameters of GTDHCS. When μ = 5 and γ = 5, GTDHCS exhibits hyperchaotic properties;

[0057] The specific steps to generate four chaotic sequences are as follows:

[0058] (2.1) Input the original image into the SHA-256 function to generate its hash value H, that is, a hexadecimal sequence with a length of 64;

[0059] (2.2) Use SK = bitxor(H, EK) to mix the hash value H with the external key EK (which consists of 64 real random hexadecimal numbers) to obtain the session key SK, further enhancing confidentiality, where bitxor(a, b) represents the bitwise exclusive OR operation of a and b;

[0060] (2.3) Extract the initial values of the chaotic system from the session key SK, which are expressed as follows:

[0061]

[0062] Among them, the hex2dec operation can convert the string of hexadecimal numbers into a decimal integer. A(1) and B(1) are the extracted initial values of CTDHCS, and U(1) and V(1) are the extracted initial values of GTDHCS;

[0063] (2.4) Iterate according to the extracted initial values to obtain four chaotic sequences A, B, U, and V based on two two-dimensional hyperchaotic systems; First, use the iterative formulas of the two two-dimensional hyperchaotic systems to iterate the initial values (n + l) times, so as to generate 4 sequences with a length of (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 brought by the transient process of the chaotic system; Then apply the chaotic sequences A and B to the encryption of the binary bit stream, and apply the chaotic sequences U and V to the encryption of the QAM symbol stream.

[0064] For the method described above, in step (3) of the sender, the binary real-valued computer-generated hologram is converted from serial to parallel to a binary bit stream, and two of the four chaotic sequences are used to perform bitwise exclusive OR on the odd and even bits of the binary bit stream respectively to obtain an encrypted binary bit stream, which specifically includes the following steps:

[0065] (3.1) Convert the binary real-valued computer-generated hologram from serial to parallel to a binary bit stream;

[0066] (3.2) Preprocess the chaotic sequences A and B as follows:

[0067]

[0068] where 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 a divided by b, and the processed chaotic sequences only contain 0 and 1, that is, a(i), b(i) ∈ {0, 1};

[0069] (3.3) Perform bitwise exclusive OR on the odd and even bits of the chaotic sequences a(i) and b(i) obtained after preprocessing and the binary bit stream x after serial-to-parallel conversion respectively to obtain an encrypted binary bit stream It is expressed as follows:

[0070]

[0071] where bitxor(a, b) represents the bitwise exclusive OR operation of a and b.

[0072] For the method described above, in step (4) of the sender, the encrypted binary bit stream is subjected to m-QAM quadrature amplitude modulation to obtain a QAM symbol stream, and the other two of the four chaotic sequences are used to perform chaotic scrambling on the real and imaginary parts of the QAM symbol stream respectively to obtain an encrypted QAM symbol stream, which specifically includes the following steps:

[0073] (4.1) Perform m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream;

[0074] (4.2) Preprocess the chaotic sequences U and V as follows:

[0075]

[0076] where 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 a divided by b, and the processed chaotic sequences only contain -1 and 1, that is, u(i), v(i) ∈ {-1, 1};

[0077] (4.3) The QAM symbol stream is represented by S = [S1, S2,..., S l T where [] T denotes matrix transpose, l denotes the length of the QAM symbol stream; the preprocessed chaotic sequences 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 is represented as:

[0078]

[0079] where real(a) returns the real part of a, and imag(a) returns the imaginary part of a.

[0080] For the method described above, steps (5) and (6) at the transmitter and steps (1) and (2) at the receiver realize the generation, transmission and reception of the ACO-OFDM signal;

[0081] Step (5) at the transmitter performs serial-to-parallel conversion on the encrypted QAM symbol stream to obtain the effective data matrix of the ACO-OFDM signal, which is represented as:

[0082]

[0083] where Q and M are the number of OFDM effective data subcarriers and the total number of OFDM symbols respectively. In the ACO-OFDM visible light communication system of the present invention, only odd subcarriers are modulated and assigned Hermitian symmetry, while even subcarriers are assigned zero. Therefore, Q is one-fourth of the number of OFDM subcarriers N, that is, Q = N / 4; perform Hermitian mapping on the effective data matrix of the ACO-OFDM signal. According to the ACO-OFDM data characteristic requirements, that is, modulate odd subcarriers and assign Hermitian symmetry, and set even subcarriers to zero, to form the ACO-OFDM signal matrix which is represented as:

[0084]

[0085] Perform inverse fast Fourier transform IFFT on the ACO-OFDM signal matrix to generate a real-valued time-domain ACO-OFDM signal;

[0086] Step (6) at the transmitter sequentially performs adding cyclic prefix CP, parallel-to-serial conversion, and clipping and limiting to remove negative waves on the time-domain ACO-OFDM signal, and then loads it onto the LED through digital-to-analog conversion and transmits it through visible light. The emitted visible light signal propagates through the space channel to the receiver;

[0087] ​At the receiving end, step (1): The optical detector PD at the receiving end converts the received optical signal into an electrical signal, and then performs analog-to-digital conversion, serial-to-parallel conversion, and removal of the cyclic prefix CP in sequence to obtain the received time-domain ACO-OFDM signal;

[0088] At the receiving end, step (2): Perform fast Fourier transform FFT, inverse Hermitian symmetry transform, and parallel-to-serial conversion on the received time-domain ACO-OFDM signal in sequence to obtain an encrypted QAM symbol stream;

[0089] For the method described above, the decryption method corresponding to the receiving end specifically includes:

[0090] The receiving end step (3) corresponds to the decryption of the encrypted QAM symbol stream in the sending end step (4), and uses the same chaotic sequence key as in the sending end step (4) to decrypt the received encrypted QAM symbol stream;

[0091] The receiving end step (4) corresponds to the decryption of the encrypted binary bit stream in the sending end step (3), and uses the same chaotic sequence key as in the sending end step (3) to decrypt the received encrypted binary bit stream;

[0092] The receiving end step (5) corresponds to the decryption of the encrypted image in the sending end step (1). The schematic diagram of image decryption is as Figure 3 shown. During the decryption process, the received binary real-valued computer-generated hologram E'(m,n) is placed on the input plane, irradiated by a monochromatic vertically incident light, and then a standard Fourier transform is performed. The computer-generated hologram is reproduced to obtain the encrypted image E'(x,y) and its conjugate; the conjugate of the encrypted image E'(x,y) is taken to achieve decryption. The -1st order reproduced conjugate image is introduced into the Fresnel diffraction double random phase decryption system, and after passing through two Fresnel diffractions with distances z3 and z4 and the modulations of two random phase plates p3 and p4 respectively, the decrypted original image I'(x,y) is obtained on the output plane Σ':

[0093] I'(x,y)exp[-j2πα(ξ,η)] = F F {F F [E'*(x,y); z3]exp[j2πβ(ξ,η)]; z4}

[0094] where * represents the conjugate, z3 = z2, z4 = z1, p3 = p2, p4 = p1.

[0095] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An image secure transmission method based on ACO-OFDM visible light communication, characterized in that Including the following steps: Transmitter: 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 computer-generated hologram; Step (2) Determine the initial values of two two-dimensional hyperchaotic systems by mixing the SHA-256 value of the original image with an external key, and generate four chaotic sequences for encrypting the binary bit stream and the QAM symbol stream; Step (3) Serial-to-parallel convert the binary real-valued computer-generated hologram into a binary bit stream, and apply two of the four chaotic sequences to perform bitwise exclusive OR on the odd and even bits of the binary bit stream respectively to obtain an encrypted binary bit stream; Step (4) Perform m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream, and apply the other two of the four chaotic sequences to perform chaotic scrambling on the real and imaginary parts of the QAM symbol stream respectively to obtain an encrypted QAM symbol stream; Step (5) Perform serial-to-parallel conversion and Hermitian mapping on the encrypted QAM symbol stream, construct an ACO-OFDM signal matrix according to the ACO-OFDM data characteristic requirements, and then perform inverse fast Fourier transform IFFT on the ACO-OFDM signal matrix to generate a real-valued time-domain ACO-OFDM signal; Step (6) After successively adding a cyclic prefix CP, serial-to-parallel conversion, and clipping and limiting to remove negative waves to the time-domain ACO-OFDM signal, load it onto the LED through digital-to-analog conversion, and send it through visible light. The emitted visible light signal propagates through the spatial channel to the receiver; Receiver: Step (1) The photodetector PD at the receiver converts the received optical signal into an electrical signal, and then successively 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) Perform fast Fourier transform FFT, inverse Hermitian symmetry transform, and serial-to-parallel conversion on the received time-domain ACO-OFDM signal successively to obtain an encrypted QAM symbol stream; Step (3) Decrypt the received encrypted QAM symbol stream using the same chaotic sequence key as the transmitter; Step (4) Demodulate the decrypted QAM symbol stream to obtain an encrypted binary bit stream, and then decrypt it using the same chaotic sequence key as the transmitter. After that, perform serial-to-parallel conversion to obtain an encrypted binary real-valued computer-generated hologram; Step (5) Decrypt the encrypted binary real-valued computer-generated hologram based on the double random phase decryption technology of the Fresnel diffraction system to obtain the original image.

2. The image secure transmission method based on ACO-OFDM visible light communication according to claim 1, wherein The specific content of step (1) of the transmitter includes: (1.1) Encrypt the original image. The original image is encrypted through two Fresnel diffractions and the modulation of two random phase plates to obtain an encrypted image, and then perform a standard Fourier transform on the encrypted image; (1.2) Record the encrypted image using the Lohmann coding method, and convert the encrypted image into a binary real-valued computer-generated hologram.

3. The image secure transmission method based on ACO-OFDM visible light communication according to claim 1, wherein The specific content of step (2) of the transmitter includes: (2.1) Input the original image into the SHA-256 function to generate its hash value H, that 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, where the external key EK consists of 64 truly random hexadecimal numbers, to obtain the session key SK, further enhancing confidentiality, where bitxor(a, b) represents the bitwise exclusive OR operation of a and b; (2.3) Extract the initial value of the chaotic system from the session key SK; (2.4) Iterate according to the extracted initial value to obtain four chaotic sequences based on two two-dimensional hyperchaotic systems.

4. The image secure transmission method based on ACO-OFDM visible light communication according to claim 1, wherein The specific steps of the sender in step (3) include: (3.1) Serial-to-parallel convert the binary real-valued computer-generated hologram into a binary bit stream; (3.2) Preprocess two of the four chaotic sequences, and the processed chaotic sequences only contain 0 and 1; (3.3) Perform bitwise exclusive OR on the odd and even bits of the preprocessed chaotic sequences and the serial-to-parallel converted binary bit stream respectively to obtain the encrypted binary bit stream.

5. The image secure transmission method based on ACO-OFDM visible light communication according to claim 1, wherein The specific steps of the sender in step (4) include: (4.1) Perform m-QAM quadrature amplitude modulation on the encrypted binary bit stream to obtain a QAM symbol stream; (4.2) Preprocess the other two of the four chaotic sequences, and the processed chaotic sequences only contain -1 and 1; (4.3) Multiply the preprocessed chaotic sequences with the real and imaginary parts of the QAM symbol stream respectively.

6. The image secure transmission method based on ACO-OFDM visible light communication according to any one of claims 1-5, characterized in that, The corresponding decryption method of the receiver specifically includes: The step (3) of the receiver corresponds to the decryption of the encrypted QAM symbol stream in step (4) of the sender, and uses the same chaotic sequence key as in step (4) of the sender to decrypt the received encrypted QAM symbol stream; The step (4) of the receiver corresponds to the decryption of the encrypted binary bit stream in step (3) of the sender, and uses the same chaotic sequence key as in step (3) of the sender to decrypt the received encrypted binary bit stream; The step (5) of the receiver corresponds to the decryption of the encrypted image in step (1) of the sender. The received binary real-valued computer-generated hologram undergoes a standard Fourier transform to obtain the encrypted image and its conjugate. The -1st order reconstructed conjugate image undergoes two Fresnel diffractions and the modulation and decryption of two random phase plates to restore the original image.

Images