Coherent Optical OFDM Research Articles

A physical layer security enhancement scheme for CO-OFDM systems based on 3D Brownian motion and TZBN Joint Scramble

In this paper, we propose a scheme for enhancing the physical layer security and transmission performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The scheme for OFDM data first after 3-dimensional (3D) Brownian motion rotational permutation, and then according to the time zone and band number (TZBN) scrambling to achieve the effect of further data perturbation, which through the SHA-256 algorithm and 6-dimensional (6D) hyperchaotic processing to obtain the chaotic keys to enhance the security. After simulation experiment of 16QAM CO-OFDM security system transmitting over 80 km standard single-mode fiber (SSMF) at the symbol rate of 30 Gbaud, it is shown that the encryption scheme can guarantee that the authorized user receives valid data and the eavesdropper obtains the information with the BER of about 0.5. The key space of the scheme is about 2.88×10194, which can effectively resist attacks such as violent attacks and chosen plaintext attacks. And the peak-to-average power ratio (PAPR) can be reduced by about 1.09 dB while the encryption process.

Physical layer security enhanced scheme based on joint encryption of DNA and RNA data perturbation in CO-OFDM system

—In the work, we propose a new chaotic encryption algorithm for optical physical layer security enhanced in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The proposed algorithm adopts the six-dimensional (6D) hyperchaotic to achieve the generation of key sequences, which can effectively improve the unpredictability and security of the system. The encryption scheme includes two steps, first, the binary sequence is disturbed by DNA and RNA two-stage encoding and RNA mutation, and then the initial encrypted data is injected into the algorithm module with two-dimensional continuous chaotic mapping (2D-SCL) and Brownian motion to scramble successively. Simulations in a 16QAM CO-OFDM system at a symbol rate of 30 Gbaud over 80 km of standard single-mode fiber (SSMF) show that a legitimate user is able to successfully decrypt the received signals, and an illegal eavesdropper obtains a useless signal with a bit error rate (BER) of about 0.5. The scheme can tolerate very small deviations and has a key space of approximately 10294, which can effectively withstand illegal attacks. And the peak-to-average power ratio (PAPR) can be reduced by about 1.01 dB.

Physical Layer Encryption for CO-OFDM Systems Enabled by Camera Projection Scrambler

In this paper, we propose a camera projection approach to enhance the physical layer security of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The data are converted to the new location by the camera projection module in the encryption system, where the 5D hyperchaotic system provides the keys for the camera projection module. The simulated 16QAM CO-OFDM security system over 80 km SSMF is shown to provide a key space of about 9 × 1090 through the five-dimensional (5D) hyperchaotic system, making it impossible for eavesdroppers to obtain valid information, and the peak-to-average power ratio (PAPR) is reduced by about 0.8 dB.

Gaussian wavelet basis expansion based phase noise suppression method for coherent optical OFDM systems

In this paper, we developed a phase noise suppression method based on Gaussian wavelet basis expansion (GWBE) for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with traditional phase noise suppression methods, the GWBE method significantly enhances the system’s robustness to laser phase noise, providing improved phase noise suppression, especially in scenarios with high linewidth. Additionally, the method demonstrates excellent performance in 32-QAM and 64-QAM. By employing the proposed GWBE method, the impact of laser phase noise on CO-OFDM can be effectively mitigated.

A novel PAPR reduction scheme based on time-delay neural network for CO-OFDM systems

In this paper, we propose a low-complexity peak-to-average power ratio (PAPR) reduction scheme based on time-delay neural network (TDNN) for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems to reduce the limitation of PAPR on the total power of laser diodes and the impact of fiber nonlinear effects. The proposed scheme is jointly trained on traditional iterative clipping and filtering (ICF) scheme and simplified clipping and filtering (SCF) scheme, and changes the objective function by adjusting the given training weight α. Compared to the original orthogonal frequency division multiplexing (OFDM) signal of existing system, our method achieves an adjustable PAPR reduction of 5.31 dB to 6.12 dB for 10−4 complementary cumulative distribution function (CCDF). When bit error rate (BER) Pe=10−3, the proposed scheme (α=0.5) achieves additional transmission distances of 220 km, 55 km, 105 km, and 100 km, compared to the original OFDM signal, partial transmission sequence (PTS) scheme, ICF scheme, and feedforward neural network (FNN)-based ICF scheme, respectively. Besides, our method achieves 86.3% and 80.0% floating-point operations (FLOPs) reductions, compared with PTS scheme and ICF scheme, respectively, which effectively reduces the complexity of PAPR reduction module, saving the system computational time.

Efficient Chromatic and Residual Dispersion Post compensation for Coherent Optical OFDM

Efficient Chromatic and Residual Dispersion Post compensation for Coherent Optical OFDM

Enhanced Physical Layer Security and PAPR Performance Based on Disturbance of Data Cluster Under Chaotic Sequence Color Seeking Mechanism in CO- OFDM System

This study proposes a physical layer encryption scheme based on disturbance of data cluster under color seeking mechanism of chaotic sequence which is generated by Brownian motion determined by keys aiming to improve security of coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Chaotic sequences with good randomness and unpredictability are endowed with a unique color composed of two primary colors and go through order transformation by sorting and seeking, which forms the chaotic sequence color seeking mechanism. The disturbance of transmitted data is realized according to chaotic sequence color seeking mechanism and PAPR performance is optimized simultaneously. The security of system is enhanced due to a key space of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> and PAPR can be reduced by 0.5 dB. An experiment conducted in a 40 GHz 16QAM CO-OFDM system over an 80 km standard single mode fiber (SSMF) shows that the authorized user can successfully decrypt the received signal, while the eavesdroppers cannot derive valid information with bit error rate (BER) at approximately 0.5. Analyses of peak to average power ratio (PAPR) performance and time complexity of the scheme are further carried out under different cluster forming methods to derive the optimized configuration which is critical in encryption.

A novel PAPR reduction scheme based on nonlinear real-valued support vector regression for CO-OFDM systems

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems suffer from the high peak-to-average ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals, which leads to the back-off of laser power and fiber nonlinear effects, thereby deteriorating the bit error rate (BER) performance and limiting the transmission distance. Iterative clipping and filtering (ICF) scheme, as a direct, simple and effective PAPR reduction scheme that only processes signals at the transmitter, but requires multiple fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT), resulting in high computational complexity. We propose a novel scheme using the machine learning (ML) technique, which is based on nonlinear real-valued support vector regression (NRSVR) and trained on ICF scheme. The simulation results show that compared with ICF scheme, the proposed scheme has a similar PAPR0 for 10−4 complementary cumulative distribution function (CCDF), an additional 15 km of single mode fiber (SMF) transmission for 16 dB optical signal-to-noise ratio (OSNR) and 10−3BER, and a significant time complexity reduction. Compared with other ML-based schemes, the proposed scheme also achieves better performance and lower computational complexity.

Free space optical communication in Indian cities; channel characteristics and link performance

Abstract Free Space Optical (FSO) communication systems, offering high-speed and high-bandwidth transmission, have emerged as a possible substitute for conventional wired and wireless communication systems. However, FSO links are susceptible to atmospheric deficiencies including attenuation, scintillation, and turbulence, which may severely impact the performance of the communication link. In this research paper, we propose and analyze the performance of a 25 Gbps dual-polarization quadrature phase shift keying (DP-QPSK) coherent optical orthogonal frequency division multiplexing (CO-OFDM)-based FSO communication link with spatial diversity technique under various climatic conditions in four different geographical locations of India, i.e., Delhi, Ahmedabad, Kolkata, and Chennai in the year 2021. The proposed FSO communication system is evaluated through performance analysis and parametric evaluation under various weather conditions such as clear sky, fog, haze, rain, cloud, and thermal gradient. Key performance metrics such as bit error rate (BER), Q-factor, signal-to-noise ratio (SNR), received power, communication range, and reliability are analyzed based on the simulation results. The proposed FSO communication system provides high data rates, improved power efficiency, better resilience to atmospheric impairments, reliable communication links under different weather conditions, and a practical solution for high-speed and high-bandwidth communication in various applications.

A Novel PAPR Reduction Scheme Based on Joint Traditional Algorithm and Machine Learning for CO-OFDM Systems

The high peak-to-average power ratio (PAPR) deteriorates the performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Machine learning (ML) has evolved into a powerful technology to reduce PAPR with its flexible learning ability. We propose a joint scheme which adopts iterative partial transmission sequence (IPTS) scheme cascading a feedforward neural network (FNN) trained on iterative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pmb {\mu }$ </tex-math></inline-formula> -law companding and filtering (IMCF) algorithm. The proposed scheme greatly reduces the complexity of partial transmission sequence (PTS) scheme, which has excellent PAPR reduction effect and BER performance. Our method achieves a 5.03 dB PAPR reduction for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\pmb {^{-4}}\,\,\pmb {CCDF}$ </tex-math></inline-formula> and an additional transmission distance of 200 km SMF for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\pmb {^{-3}}\,\,\pmb {BER}$ </tex-math></inline-formula> , compared with the original OFDM signal. Meanwhile, the computational complexity of proposed scheme is reduced by 32.4%, compared with IPTS cascading IMCF (IPTS-IMCF) scheme.

Research on alleviating nonlinear problem by data feature extraction and fusion based on DFT-spread

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system is susceptible to nonlinear effects because of its intrinsic high peak-to-average ratio (PAPR). In this paper, two methods based on discrete Fourier transform spread (DFT-S) are introduced to improve the nonlinear tolerance of CO-OFDM system by extracting and fusing data features, which extract the features of communication data and perform feature fusion to get the important significance of the data. The first one is based on the 2-ary amplitude shift keying (2-ASK) modulation and the Hermitian symmetry of DFT, and the other one is based on the advantages of selective mapping algorithm and characteristics of data subcarrier mapping mode which has a significant impact on PAPR. Simulation results show that compared with the traditional CO-OFDM and DFT-S CO-OFDM systems, the improved methods have better performance in terms of PAPR and BER.

Low complexity partition-recombined SLM scheme for reducing PAPR in coherent optical OFDM systems

High peak-to-average power ratio (PAPR) remains the main challenge of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Selective mapping (SLM) is a well-known effective PAPR reduction technique, but it suffers from high computational complexity. To reduce the PAPR of OFDM signals, a low-complexity, partition-recombined SLM (PRSLM) scheme is proposed. The PRSLM scheme can generate more candidate signals than that of the conventional-original SLM (COSLM) scheme. The real and imaginary components of time-domain symbols are first partitioned, and then recombined to generate new candidate signals, which reduces computational complexity significantly. A 40-GBaud single-polarization CO-OFDM transmission system is set up to evaluate the performance of the PRSLM scheme. Simulation results show that the proposed scheme achieves 61.9% reduction in complex multiplication complexity, and 60.3% reduction in addition complexity compared with the COSLM scheme when the FFT size is 128. Furthermore, the proposed scheme achieves a similar PAPR reduction performance to the COSLM scheme without bit error rate degradation. In a nutshell, the PRSLM scheme improves noise tolerance and implementation efficiency of high-speed optical communication as well as alleviates nonlinear impairments.

QCOB: a novel QPSK coherent optical OFDM modulation technique for mitigation of fiber impairments

Abstract Modern optical communication heavily relies on coherent optical orthogonal frequency division multiplexing (CO-OFDM) modulation. But the usage of optical OFDM for fiber optic communication is still constrained in comparison to other modes of communication like visible light communication (VLC) and wireless communication due to a number of issues such as various sorts of fiber impairments including dispersion and attenuation. In this research paper, a novel optical OFDM modulation technique has been proposed. It is quadrature phase shift keying (QPSK) CO-OFDM modulation with Bessel optical filter in fiber optical link and is named as QCOB. This modulation technique works for optical fiber transmission. Its testing has been carried out for parameters like bit error rate (BER) and quality-factor (Q-factor) over a range of fiber length, fiber dispersion coefficient and input power. This modulation employs coherent optical OFDM with QPSK for subcarrier modulation. The optical link utilizes a Bessel optical filter. Improved results have been achieved over conventional QPSK CO-OFDM (QCO). The obtained results demonstrate the superiority of the QCOB technique in terms of performance enhancement and fiber impairment reduction. In comparison to the QCO technique, the BER performance (reduction in BER) of the QCOB technique shows an improvement of around 7.4, 100, 14.4, 46.4 and 3.4% for dispersion coefficient values of 10, 20, 30, 50 and 100 (in ps/nm-km), respectively.

Mitigation of fiber impairments by developing a novel coherent optical 16-QAM OFDM modulation technique

Mitigation of fiber impairments by developing a novel coherent optical 16-QAM OFDM modulation technique

Performance Evaluation of Dispersion Compensation Fiber-based Coherent Optical OFDM-WDM for Long Haul RoF

Demanding extra Bandwidth and high data rates has been meet by the integration both of wired and wireless communication systems. For that the Radio over Fiber (RoF) technology has gained a traction. In this article a Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) is proposed as the main wired system for transmitting data at high rates suffers from the polarization mode dispersion and chromatic dispersion of the optical channel which mitigates the data rates. Thus, to combat these limitations a Desperation Compensation Fiber (DCF) which adds negative attenuation to the optical signals transmitted in optical fiber is suggested. Moreover, the addition of Wavelength- Division- Multiplexing (WDM) to the system of transmission provides better bandwidth saving, high data rates, and better spectral efficiency, and power utilization. The efficiency of high data rate CO-OFDM integrated with RoF for long haul transmission between 100km and 450km with data rates up to 10 Gbps have been investigated in this article with SMF-DCF with 16 DPSK and 16-QAM modulations schemes respectively. The simulation results showed that the proposed system can achieve a high data rate up to 55 Gbps but when integrated with WDM, with a fiber link length can be increased to up to 6600 kilometers, with highest data rate up to 1.65 Tbps.

Performance investigation of various modulation techniques in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system

Abstract One of the essential aspects of life is communication and in all communication systems, modulation and demodulation perform a crucial role in the transmission of transmitter-to-receiver data. Using various multiplexing techniques such as FDMA, CDMA and TDMA to work with the communication system, faced various problems such as low bit rate, multi-path fading, ISI and time dispersion. The incorporation of the OFDM approach gives an attractive solution to the aforementioned issues. OFDM transmitters and OFDM receivers with different modulation techniques are included in the OFDM-based different communication system. CO-OFDM was recently suggested and its extreme robustness against polarisation mode dispersion and chromatic dispersion was demonstrated in proof-of-concept transmission experiments. Optical fiber-based wired networks and also free space wireless networks require a premier technique for multiplexing i.e. CO-OFDM. In this paper, we investigated the performance of various modulation techniques which highlights several benefits such as channel robustness and greater efficiency of the available spectrum where multicarrier is used as high data rate bit streams from a single source are divided into the number of small subcarriers. OFDM is commonly regarded as discrete multitone (DMT) in this case. So in this review article, OFDM systems are also incorporated with their advantages and applications.

Estimation of channel distortion in orthogonal frequency division multiplexing system using pilot technique

Orthogonal frequency-division multiplexing (OFDM) is resistant to frequency selective fading due to the longer symbol duration. However, mobile applications channel timing fluctuations in one OFDM signal cause intercarrier-interference (ICI), which reduces performance. This research presented the support vector regression (SVR) model-based channel estimation technique for coherent optical communication systems. Due to the coherent optical orthogonal frequency-division-multiplexed (COOFDM) system, a channel model is developed that includes linear fibre dispersion effects, noise from optical amplifiers, and inter-carrier interference generated by laser phase noise. As a result, for such a system, an accurate channel estimate is essential. Based on this concept, derivation of channel estimation and phase estimation for the system of CO-OFDM. The proposed method is tested and evaluated using MATLAB software. Computer simulation results for several standard methods such as extreme learning machines (ELM) and artificial neural networks (ANN) validate the feasibility of the suggested methodology. The CO-OFDM system’s transmission experiments and computer simulations prove that the support vector machine-based model following pilot-assisted phase estimation gives the optimal performance. Therefore, results depicted that the channel estimation utilizing the SVR model gives good performance than the other methods, thus the proposed model gives an accurate CE process, respectively.

Iterative detection of CO‐OFDM signals with phase errors using circular random variables

SummaryWe propose a low‐complexity graph‐based iterative algorithm for the detection of coherent optical OFDM signals in the presence of residual carrier frequency offset and phase noise. We exploit the circular properties of the frequency offset and phase noise and derive graphical messages using the Gaussian probability density function. The proposed algorithm shows similar error rate performance as the existing algorithm at a much lower implementation complexity.

Security Enhancement in Coherent OFDM Optical Transmission With Chaotic Three-Dimensional Constellation Scrambling

In this paper, we propose and experimentally demonstrate a novel hybrid chaos-based three-dimensional (3-D) constellation scrambling scheme to simultaneously improve the physical layer security and transmission performance of the coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. A 3-D regular hexahedron signal constellation is constructed by the constellation figure of merit principle, which not only expands the encryption dimension but improves the error performance. The dynamic parameters for constellation scrambling are generated by the 5-D hybrid chaotic scheme based on the combination of a 3-D hyperchaotic Hénon mapping and two independent 1-D Logistic mappings, as such a key space of ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> is introduced to enhance the security level of OFDM data encryption during transmission. Furthermore, a transmission experiment for encryption of 144 Gbps 16-quadrature-amplitude-modulation OFDM data over a 100 km standard single-mode fiber in a CO-OFDM system is demonstrated. Compared with the case of using the 3-D rectangular constellation, a 2 dB bit error rate performance improvement is achieved. The results show that the proposed scheme could effectively enhance the system security and transmission performance, which suggests a scalable strategy for future physically secured CO-OFDM systems.

A Physical Layer Security-Enhanced Scheme in CO-OFDM System Based on CIJS Encryption and 3D-LSCM Chaos

In this paper, a security enhanced physical layer encryption scheme is proposed for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. This scheme is based on a concatenated inter-domain joint scrambling (CIJS) method, while adopting the three-dimension logistic sine cascading mapping (3D-LSCM) as a chaos key system to improve the security. Thrice inter-domain cat mappings are implemented, which fully exploits the characteristic domains of OFDM data and greatly increases the possible permutations. An experiment of the encryption scheme is realized successfully in a 16QAM CO-OFDM system at a symbol rate of 40 Gbaud over an 80 km standard single mode fiber. The experiment shows that no bit error rate (BER) and peak to average power ratio (PAPR) penalties are introduced in this scheme. The proposed 3D-LSCM chaos system shows superior properties of high sensitivity to initial values and improved uniform distribution, which guarantees the large entropy and further the system's security. This scheme can effectively prevent against a chosen-text attack which is the most effective attack method due to the extremely small tolerabledeviation and the large key space of 1.12 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">207</sup> .