High spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing and power superimposed code.

In this paper, we propose a high spectral efficiency modulation scheme based on joint interaction of orthogonal compressed chirp division multiplexing (OCCDM) and power superimposed code (PSC) under the intensity modulation and direct detection (IM/DD) system. OCCDM is a novel orthogonal chirp division multiplexing technology featuring spectral compression through the implementation of processing similar to a discrete Fourier transform, enhancing the spectral efficiency (SE) through bandwidth savings without loss of orthogonality of each chirp. Meanwhile, PSC technology enables multiple code words being transmitted superimposed on the same chirp. This technique involves allocating varying power levels to different users, thereby distinguishing them, increasing the transmission's net bit rate and substantially boosting the SE. The transmission has been performed experimentally using a 2 km 7-core fiber span. The impact of the above-mentioned technologies on the bit error rate (BER) performance is assessed in the power, frequency, and joint domain. The BER and enhancements in the SE can be balanced when the spectral bandwidth compression factor (α) and power distribution ratio are equal to 0.9 and 4, respectively. The observed outcome leads to the transmission's SE increase to more than double the baseline value, at 2.22 times. Based on the above analysis, we believe this structure is expected to become a potential for developing next-generation PON.

Sliced chaotic encrypted transmission scheme based on key masked distribution in a W-band millimeter-wave system.

In order to guarantee the information of the W-band wireless communication system from the physical layer, this paper proposes the sliced chaotic encrypted (SCE) transmission scheme based on key masked distribution (KMD). The scheme improves the security of free space communication in the W-band millimeter-wave wireless data transmission system. In this scheme, the key information is embedded into the random position of the ciphertext information, and then the ciphertext carrying the key information is encrypted by multi-dimensional chaos. Chaotic system 1 constructs a three-dimensional discrete chaotic map for implementing KMD. Chaotic system 2 constructs complex nonlinear dynamic behavior through the coupling of two neurons, and the masking factor generated is used to realize SCE. In this paper, the transmission of 16QAM signals in a 4.5 m W-band millimeter-wave wireless communication system with a rate of 40 Gb/s is proved by experiments, and the performance of the system is analyzed. When the input optical power is 5 dBm, the bit error rate (BER) of the legitimate encrypted receiver is 1.23 × 10-3. When the offset of chaotic sequence x and chaotic sequence y is 100, their BERs are more than 0.21. The key space of the chaotic system reaches 10192, which can effectively prevent illegal attacks and improve the security performance of the system. The experimental results show that the scheme can effectively distribute the keys and improve the security of the system. It has great application potential in the future of W-band millimeter-wave wireless secure communication.

Secure high-density constellation mapping OTFS modulation scheme with low PAPR.

In this paper, a secure orthogonal time-frequency space (OTFS) modulation transmission system based on 3D dense constellation mapping (DCM) geometric shaping is proposed, and a selective reduction amplitude algorithm (SRA) for DCM to reduce peak average power ratio (PAPR) is presented. The DCM is based on regular tetrahedron construction to improve its space utilization efficiency. The proposed SRA involves reducing high PAPRs transmitter and restoring them at the receiving end, which only requires an additional 0.57% of the total transmission capacity. The algorithm reduces PAPR while ensuring the bit error rate performance of the system, so it is suitable for systems that need to process large amounts of transmitted data quickly. By verifying the actual transmission performance on a 2 km of 7-core optical fiber transmission system, the optical transmission with a bit rate of 33.93Gb/s is achieved. The experimental results show that when the bit error rate (BER) reaches the 3.8×10-3 threshold, the OTFS system using DCM and SRA could improve the receiver sensitivity by 3.7 dB compared with the OTFS system using concentric cube mapping and SRA, and 2.7 dB compared with the OFDM system using DCM. After adding the SRA, the PAPR of the OTFS system is reduced by more than 2.2 dB. When the received optical power reaches near the bit error rate threshold, the SRA valid data can be fully recovered by optimizing the SRA.

Physical layer security scheme for key concealment and distribution based on carrier scrambling.

The purpose of this study is to present a physical layer security scheme for key concealment and distribution based on carrier scrambling. The three-dimensional (3D) Lorenz system is used to generate independent chaotic sequences that encrypt the information with bit, constellation and subcarrier. In order to realize the flexible distribution of the key and ensure its security, the key information is loaded into a specific subcarrier. While key subcarrier and the ciphertext subcarrier are scrambled simultaneously. The encrypted key position information is processed and transmitted in conjunction with the training sequence (TS) to facilitate demodulation by the legitimate receiver. The processed TS can accommodate up to 10 key position information, thereby demonstrating the scheme's exceptional scalability. Experimental results show that the proposed scheme can safely transmit 131.80 Gb/s Orthogonal frequency division multiplexing (OFDM) signals across 2 km 7-core fiber. Meanwhile, the scheme enables simultaneous flexible distribution and concealment of the key, thereby offering a promising solution for physical layer security.

Chaos key enhanced physical layer secure transmission method based on the convolutional long short-term memory neural network.

In this paper, we propose a method for training a key-enhanced chaotic sequence using the convolutional long short term memory neural network (CLSTM-NN) for secure transmission. This method can cope with the potential security risk posed by the degradation of chaotic dynamics when using chaotic model encryption in traditional secure transmissions. The simulation results show that the proposed method improves the key space by 1036 compared to traditional chaotic models, reaching 10241. The method was applied to orthogonal chirp division multiplexing (OCDM). To demonstrate the feasibility of the proposed scheme, we conducted transmission experiments of encrypted 16 quadrature amplitude modulation (QAM) OCDM signals at a speed of 53.25 Gb/s over a 2 km length of 7-core optical fiber and test different encryption schemes. After key enhancements, the overall number of keys in the system can increase from 18 to 105.The results show that there is no significant difference between the bit error rate (BER) performance of the encryption method proposed in this paper and the traditional encryption method. The maximum performance difference between the different systems does not exceed 1 dBm. This fact proves the feasibility of the proposed scheme and provides new ideas for the next generation of secure transmission.

Highly secure non-orthogonal multiple access based on key accompanying transmission in training sequence.

This paper proposes a high-security chaotic encrypted power sparse coding division (CE-PSCD) scheme for 7-core fiber based on non-orthogonal multiple access (NOMA) technology. The method utilizes power multiplexing to realize parallel transmission of two signals. Joint encryption of the four-dimensional region is realized using constellation mapping encryption, carrier frequency encryption, symbol scrambling, and sparse code scrambling. What we believe to be a new dimension for encryption of autonomously designed sparse codes is proposed. Meanwhile, we hide the chaotic key in training sequence (TS) to realize the co-transmission of the key and the message. A 70 Gb/s CE-PSCD signal transmission over 2 km of 7-core fiber is demonstrated experimentally. At the limit of forward error correction (FEC) ∼3.8 × 10-3, the difference in the encrypted sensitivity among different users at the equal power level is 0.36 dB, which means that the fairness of users will not be destroyed. The key space can reach 10134, with a bit error rate (BER) of about 0.5 for brute-force cracking at illegal receivers. As long as the key bits in the hidden TS are wrong by one bit, the BER stays around 0.5. The results show no significant attenuation of the signal before and after encryption at either high or low power, verifying the high-security performance of our proposed scheme.

High-security multidimensional data protection system based on the Hartley algorithm-driven chaotic scheme.

This paper proposes a high-security multidimensional data protection system based on the Hartley algorithm-driven chaotic scheme. We utilize the fast Hartley algorithm instead of the fast fourier computation, and we employ chaotic sequences generated by the multi-winged chaotic system to achieve chaos-driven 3D constellation mapping, effectively integrating the chaotic system with the stochastic amplitude modulator. We reduce the signal's peak-to-average power ratio (PAPR) by deploying a random amplitude modulator. Simultaneously, this approach enhances the security of the physical layer of the signal. The PAPR reduction can reach up to 2.6 dB, while the most robust and stable modulator scheme can gain 2 dB. Finally, in the Hartley frequency domain, the signal's frequency is disrupted, providing the entire system with a key space of 10131 to resist violent cracking and thus improving the system's overall security. To validate the feasibility of our scheme in comparison to conventional IFFT-based encrypted 3D orthogonal frequency division multiplexing, We achieved a transmission rate of 27.94 Gb/s over a 2 km multicore fiber. Experimental results show that since the random amplitude generator effectively reduces PAPR, our proposed encryption scheme increases the forward error correction threshold range by 1.1 dB, verifying that our proposed scheme has highly reliable security performance.

High-security space division multiplexing optical transmission scheme based on constellation grid selective twisting.

In this paper, we propose a high-security space division multiplexing optical transmission scheme based on constellation grid selective twisting, which adopts the Rossler chaos model for encrypting PDM-16QAM signals, being applied to a multicore, few-mode multiplexing system. The bitstream of the program is passed through XOR function before performing constellation grid selective twisting and rotation of the constellation map to improve the security of the system. The proposed system is verified experimentally by using 80-wave and 4-mode multiplexing in one of the 19-core 4-mode fibers. Based on the proposed encryption method, a net transmission rate of 34.13 Tbit/s, a transmission distance of 6000 km, and a capacity distance product of 204.8 Pb/s × km is achieved under encrypted PDM-QPSK modulation. Likewise, a net transmission rate of 68.27 Tbit/s, a transmission distance of 1000 km, and a capacity distance product of 68.27 Pb/s × km is achieved based on encrypted PDM-16QAM modulation. It is experimentally verified that the sensitivity of the initial value in Rossler's chaotic model is in the range of 10-16∼10-17. Meanwhile, the proposed encryption scheme achieves a large key space of 10101, which is compatible with the high-capacity distance product multicore and few-mode multiplexing system. It is a promising candidate for the next-generation highly-secured high-capacity transmission system.

Ultrahigh-order QAM secure transmission based on delta-sigma modulation using discrete memristive-enhanced chaos.

This Letter proposes a high-security and high-order signal transmission method that is based on delta-sigma modulation (DSM) and discrete memristive-enhanced chaos (DMEC). We employ the DMEC for the encryption of DSM signals to achieve a key space of 1098 in size. Moreover, we demonstrated a high-security transmission of 16384QAM signals using the DSM over a 25 km single-mode fiber in the intensity-modulated direct detection (IMDD) system. The experimental results show that the proposed ultrahigh-order transmission scheme based on DMEC and DSM guarantees high signal transmission performances with improved security and a key sensitivity level of 10-17.

Enhancing secure transmission and key distribution for ultrahigh-order QAM via delta-sigma modulation and discrete memristive-enhanced chaos.

In this Letter, we propose a method for ultrahigh-order QAM secure transmission and key distribution based on delta-sigma modulation (DSM) and discrete memristive-enhanced chaos (DMEC). The disturbance vectors generated by the DMEC scramble the DSM signals in both frequency and time domains, resulting in highly secure DSM signals. Through the key modulation and power adjustment and then superimposing them on the encrypted signals, the method achieves simultaneous transmission of keys and signals without the need for additional spectral resources. This approach allows for secure communication with continuous key iteration and updates, offering an effective solution for implementing "one-time pad" encryption. In the experimental demonstration, we achieved a secure transmission and key distribution of a 16384QAM signal at a rate of 17.09 Gb/s over 25 km in an intensity-modulated direct detection (IMDD) system, based on DSM.

Dynamic updated key distribution encryption scheme with the wireless rate of 102†Gb/s based on a syncretic W band-PON transmission system.

In this paper, a dynamic updated key distribution encryption scheme based on syncretic W band-passive optical network (PON) is proposed. The 102 Gb/s encrypted data rate using 64QAM is successfully transmitted over the 50 m wireless distance under 15% soft-decision forward error correction (SD-FEC) for a pre-FEC bit error rate (BER) threshold of 1.56 × 10-2. The scheme can realize an error-free public key transmission and public key updates up to 1014 times. In the encryption transmission system, there is a small deviation of the private key, and the received BER is more than 0.45. As far as we know, this is the first time to complete a dynamic key distribution based on a syncretic W band-PON system.

Concurrent performance and security enhancement of ultrahigh-order DSM signals via null subcarriers.

In this paper, we propose leveraging null subcarriers in discrete multi-tone modulation (DMT) to process the DMT signal in both time and frequency domains. Additionally, we employ discrete memory enhanced chaos (DMEC) to scramble the signal in the frequency domain, thereby achieving physical layer signal encryption while ensuring a more uniform power distribution in the time-domain waveform. In our experimental demonstration, we achieved high-security transmission of a DSM-based 65536-QAM signal at a data rate of 16.01 Gb/s over a 25 km single-mode fiber (SMF) in an intensity-modulation direct-detection (IMDD) system. Additionally, in the transmission experiments for 13684-QAM and 65536-QAM signals, the proposed method demonstrated a receiver sensitivity gain of over 0.5 dB compared to the traditional DSM-based ultrahigh-order transmission.

Joint constellation shaping optical modulation scheme based on a pair of common-bottomed trigonal cones.

A joint constellation shaping (JCS) three-dimensional (3D) 16-ary modulation scheme constructed with a pair of common-bottomed trigonal cones (CBTC) as primitives is proposed. Compared to the 3D traditional constellation (TC) and the 3D geometric constellation shaping (GS) structure previously proposed by our group (GGS), the constellation figure of merit (CFM) is improved by 0.3906 and 0.0097, respectively. Meanwhile, probabilistic shaping (PS) is employed to optimize the 3D-CBTC-16CAP constellation structure for the second time to enhance the CFM of the constellation further. Compared to the 3D-CBTC-16CAP, after PS the 3D-JCS-16CAP has a CFM improvement of 0.5014. Experiments are carried out to transmit the signals across a 2 km seven-core fiber. At the bit error rate (BER) threshold ∼3.8 × 10-3, the 3D-CBTC-16CAP scheme demonstrates an improvement in the receiver sensitivity by 0.76 and 0.39 dB compared with 3D-TC-16CAP and 3D-GGS-16CAP. In addition, the transmission effect of the signals after joint PS is verified. Experiments show that the proposed 3D-JCS-16CAP scheme has the most significant enhancement effect when used in conjunction with PS, and the receiver sensitivity is improved by about 0.97 and 0.34 dB compared with the 3D-JTC-16CAP (3D-TC-16CAP signal after joint PS) and 3D-JGGS-16CAP (3D-GGS-16CAP signal after the joint PS).

Optimized intensity-modulated type PTS-based PAPR reduction scheme for intensity-modulated direct-detection optical OFDM systems.

High peak-to-average power ratio (PAPR) of the signal is a major drawback in optical orthogonal frequency division multiplexing (OFDM) system. In this paper, an intensity-modulated type Partial Transmit Sequences (PTS) based scheme is proposed and applied to the intensity-modulated OFDM (IMDD-OFDM) system. The proposed intensity-modulated type PTS (IM-PTS) scheme ensures that the time-domain signal output by the algorithm is real value. What's more, the complexity of the IM-PTS scheme has been reduced without much performance penalty. A simulation is performed to compare the PAPR of different signal. In the simulation, the PAPR of OFDM signal is reduced from 14.5 dB to 9.4 dB at 10-4 probability. We also compare the simulation results with another algorithm based on the PTS principle. A transmission experiment is conducted in a seven-core fiber IMDD-OFDM system at a rate of 100.8Gbit/s. The Error Vector Magnitude (EVM) of received signal is reduced from 9 to 8 at -9.4dBm received optical power. Furthermore, the experiment result shows that the reduction of complexity has little performance impact. The optimized intensity-modulated type PTS (O-IM-PTS) scheme effectively increases the tolerance of the nonlinear effect of the optical fiber and reduces the requirement for linear operating range of optical device in the transmission system. During the upgrade process of the access network, there is no need to replace the optical device in the communication system. What's more, the complexity of PTS algorithm has been reduced, which lower data processing performance requirements of the devices such as ONU and OLT. As a result, the cost of network upgrades is reduced a lot.

4-D constellation construction and encryption scheme based on bit-level dimension dissecting and reorganization.

A 4-dimensional (4-D) constellation construction and encryption scheme of dimension dissecting reorganization are proposed in this paper. In this scheme, the high-dimensional constellation is constructed by gradually decomposing and superimposing the low-dimensional constellation, and the mapping dimension, phase, and arrangement order of signals are scrambled to realize the encryption. This scheme uses the evolution from low dimension to high dimension to reduce the difficulty of constructing a high-dimensional constellation, and the confusion between dimensions facilitates the encryption of high-dimensional information. To verify the performance, an experiment to demonstrate the transmission of 46.7 Gb/s 4-D constellation mapping the intensity modulation/direct detection carrierless amplitude and phase on 2 km 7-core optical fiber has been successfully carried out.

High-security optical transmission system with multi-dimensional multiplexing based on quaternion chaotic encryption.

In this paper, we propose a multi-dimensional multiplexing scheme for space division multiplexing optical transmission systems based on quaternion chaotic encryption. A constellation compression shaping mapping method is designed to replace the traditional 2n mapping scheme, which leads to flexible encoding modulation. In order to achieve orthogonality between data symbols and effectively suppress crosstalk, the spectrally superposed transmission of three-dimensional (3D) constellation data is carried out by code division multiplexing and 4D carrier-less amplitude phase joint modulation techniques based on orthogonal basis. The Chen's chaotic model is utilized to generate the rotation angle of the constellation points, which enables data encryption without changing the transmitted power, enhancing system's security. The feasibility and superiority of the proposed scheme are successfully verified by constructing an experimental platform for a seven-core fiber transmission system.

116.66-Tb/s WDM transmission over 16†Km field deployed 7-core fiber based on sub-constellations overlap constellation shaping.

Constellation shaping (CS) has always been a popular research hotspot in optical communication. Recently, most researchers have focussed on using constellation-shaping technology to improve the system's performance, ignoring the additional penalty it brings to the coherent system. This paper proposes a method of constellation truncation using sub-constellation overlap to perform CS on quadrature amplitude modulation (QAM). The experimental results show that compared with the traditional probabilistic shaping 16QAM, the proposed scheme can effectively avoid the extra penalty brought by CS and achieve a gain from 0.5 to 1.5 dB in optical signal-to-noise ratio. To practically verify the proposed scheme's performance, 7-core 16 km fiber span is deployed in the field to experimentally perform space division multiplexed coherent transmission. The wavelength division multiplexing (WDM) of 93 carriers was used to achieve coherent transmission at a net rate of 116.66-Tb/s.

16QAM OFDM-PON based on polar code and CCDM joint chaotic encryption.

A new optical transmitting scheme based on chaotic constant component distribution matcher (CCDM) and Polar coding was proposed. The data is first encrypted by Polar coding using a five-dimensional chaotic sequence. Then the encrypted data is divided into two paths to perform chaotic CCDM encryption operations with different schemes. Finally, the two channels are merged, and the subcarriers are scrambled. The transmission experiment of 16QAM-OFDM signal on 2 km seven-core fiber is conducted to verify the scheme's feasibility. The experimental results show that the received optical power of all ONUs is less than -15dBm when the BER of all ONUs is reduced to less than 10-3. In addition, the key space of the proposed system reaches 1085, and the security performance is further enhanced. The advantages of BER and safety performance make this two-path chaotic encrypted OFDM-PON with an optimistic application prospect in the current optical transmission systems.

High security optical OFDM transmission scheme with four-dimensional region joint encryption based on power division multiplexing.

In this paper, a high security chaotic encryption scheme for orthogonal frequency division multiplexing (OFDM) transmission system is proposed by using power division multiplexing (PDM) technology and four-dimensional region joint encryption. The scheme uses PDM to realize simultaneous transmission of multiple user information, which can achieve a good compromise among system capacity, spectral efficiency and user fairness. In addition, bit cycle encryption, constellation rotation disturbance (CRD) and region joint constellation disturbance (RJCD) are used to realize four-dimensional region joint encryption, effectively improving the physical layer security. The masking factor is generated by the mapping of two-level chaotic systems, which can enhance the nonlinear dynamics and improve the sensitivity of encrypted system. A 11.76 Gb/s OFDM signal transmission over 25 km standard single-mode fiber (SSMF) is experimentally demonstrated. At the forward-error correction (FEC) bit error rate (BER) limit -3.8×10-3, the proposed receiver optical power based on quadrature phase shift keying (QPSK) without encryption, QPSK with encryption, variant-8quadrature amplitude modulation (V-8QAM) without encryption and V-8QAM with encryption are about -13.5dBm, -13.6dBm, -12.2dBm, and -12.1dBm. The key space is up to 10128. The results show that this scheme not only improves the security of the system and the ability to resist attackers, but also improves the system capacity and has the potential to serve more users. It has a good application prospect in the future optical network.

High-security 3D CAP modulation scheme based on a pyramid constellation design for 7-core fiber.

This paper proposes a 3-dimensional (3D) carrier-less amplitude and phase modulation (CAP) based on a pyramid constellation design encryption scheme for 7-core fiber in passive optical network (PON). The chaos sequences generated by the 4D hyperchaotic system are applied to produce the masking factor, and the pyramid Rubik's cube rotation rules are used to flip and rotate the constellation points. To verify the performance of the proposed 3D CAP-PON system, 25.5Gb/s encrypted Pyraminx-3D-CAP-16 signal transmission over 2 km 7-core fiber is experimentally demonstrated. Compared with the traditional 3D-CAP-16 signal, the proposed Pyraminx-3D-CAP-16 signal achieves a sensitivity gain of 0.5 dB under the limit of hard decision forward error correction (HD-FEC) 3.8 × 10-3. Compared with the Pyraminx-3D-CAP-16 signal, the encrypted Pyraminx-3D-CAP-16 signal has little difference from that before encryption, which has a great application prospect in the physical layer security enhancement of the 3D-CAP-PON system.