Nonlinear Distortion Mitigation Research Articles

Joint PAPR and Non-linear Distortion Mitigation in OQAM-FBMC Based Visible Light Communication System

Joint PAPR and Non-linear Distortion Mitigation in OQAM-FBMC Based Visible Light Communication System

Low-complexity fiber nonlinear distortion mitigation for long-haul optical transmission based on transformer and triplets

Low-complexity fiber nonlinear distortion mitigation for long-haul optical transmission based on transformer and triplets

RF classification-based nonlinear distortion mitigation for 120 Gbit/s PAM8-modulated optical interconnects in IM/DD

RF classification-based nonlinear distortion mitigation for 120 Gbit/s PAM8-modulated optical interconnects in IM/DD

Joint Tx and Rx Look-Up-Table Based Nonlinear Distortion Mitigation in Reduced State MLSE for 180 Gbit/s PAM-8 IM-DD System

Joint Tx and Rx Look-Up-Table Based Nonlinear Distortion Mitigation in Reduced State MLSE for 180 Gbit/s PAM-8 IM-DD System

Behavioral Modeling of Direct-Conversion Receivers for Nonlinear Distortion Mitigation

Behavioral Modeling of Direct-Conversion Receivers for Nonlinear Distortion Mitigation

Nonlinear distortion mitigation of DML-based OFDM optical systems with non-orthogonal DFT-precoding.

We propose a non-orthogonal discrete Fourier transform (DFT) matrix precoding scheme for the mitigation of nonlinear distortion induced by the interaction between laser chirp and fiber dispersion in a directly modulated laser (DML)-based orthogonal frequency division multiplexing (OFDM) transmission system. Compared with conventional OFDM, the proposed method can decrease the peak-to-average power ratio (PAPR) and significantly reduce the nonlinear distortion without sacrificing spectral efficiency (SE). The cascaded binary-phase-shift-keying iterative detection (CBID) algorithm is used to eliminate the inter-carrier interference (ICI) that is purposely induced by the non-orthogonal precoding. The performance of the proposed scheme is experimentally evaluated, achieving ∼0.4-dB sensitivity improvement at the KP4-forward error correction (FEC) threshold over the T/2-spaced third-order Volterra nonlinear equalizer (VNLE). Meanwhile, compared to the VNLE, the reduction in computational complexity of one OFDM frame is 90% for multiplication and 88.32% for addition in this work.

Predistorter for Nonlinear Distortion Mitigation in GFDM Systems

Next-generation wireless systems use the non-orthogonal modulation technique known as generalized frequency division multiplexing (GFDM). The nonlinearity of the high-power amplifier (HPA) greatly affects the performance of the wireless system. Without phase distortion and only amplitude distortion in the GFDM system using HPA Model Rapp. The effects of nonlinear distortion that occur involve distortion of the amplitude, signal constellation distribution, and spectral distribution. There are two contributions to this paper. First, the impact of HPA Model Rapp's nonlinear distortion on the GFDM system in the AWGN (additive white Gaussian noise) and Rayleigh channels was investigated. The simplicity of this model is the reason it was picked and has an AM/AM (amplitude modulation/amplitude modulation) curve. Second, the linearization of HPA with the use of a predistorter method in GFDM systems has been proposed. The nonlinear distortion impact of HPA can be mitigated by this predistorter. This technique is implemented in the transmitter section. The system performance investigated is determined by a bit error rate (BER) analysis, a constellation diagram, and a spectrum analysis. HPA generates a 55 dB rise in out-of-band (OOB) in the signal spectrum. The HPA effect was successfully compensated for by a 55 dB decrease in the OOB value of the predistorter system.

Purely nonlinear amplified ultralow-noise transmission using hybrid second-order DRA and PPLN-based PSA.

We report ultralow-noise transmission over a 102-km single-mode fiber using a purely nonlinear amplification scheme consisting of a second-order distributed Raman amplifier (DRA) and a phase-sensitive amplifier (PSA) based on periodically poled LiNbO3 waveguides. The hybrid DRA/PSA features a broadband gain over the C and L bands and an ultralow-noise advantage, with a less than -6.3 dB effective noise figure in the DRA stage and a 1.6 dB optical signal-to-noise ratio (OSNR) improvement in the PSA stage. Compared with the unamplified link, the OSNR is improved by 10.2 dB for a 20-Gbaud 16QAM signal in the C band, resulting in error-free detection (a bit-error rate of less than 3.8 × 10-3) for the signal with a low link input power of -25 dBm. Mitigation of nonlinear distortion is also achieved by the proposed nonlinear amplified system due to the subsequent PSA.

High-Efficiency Mitigation of Nonlinear Distortion in Microwave Photonics Link Assisted by Artificial Neural Network

A microwave photonics radio over fiber link can deliver the radio frequency (RF) signal to realize the antenna remote. When the signal is a broadband and multicarrier RF signal, there are some linear distortions in the link, such as the crossmodulation distortion (XMD) and third-order intermodulation distortion (IMD3). It will destroy the wide-bandwidth performance of the link. Traditional postdigital compensation methods for XMD and IMD3 mitigation extract the baseband signal and reconstruct the compensation signal with calculated compensation factor. Here, a kind of artificial neural network genetic algorithm (ANN-GA) distortion compensation technique is proposed to seek the compensation factor instead of calculations. The neural network algorithm is used to fit the mapping function between the compensation factor and the distortion and give a set of predicted data as the original individual fitness value for the genetic algorithm. Based on the original value, the minimal distortion, the corresponding optimal compensation factors γ and α are found with optimization iterations. Taking advantage of the optimal compensation factors, based on the traditional postdigital compensation method, the distortion is mitigated with a suppression ratio of -84.4 dB. In our paper, the mitigation technology of the XMD and IMD3 can be applied for any kinds of link instead of mathematically modelling the link and calculating the compensation factor. The technology can improve the intelligence and flexibility of microwave photonic link linearization design.

Nonlinear Distortion Mitigation in Multi-IF over Fiber Transmission Using Modulation-Based Adaptive Power Allocation

We propose a modulation-based adaptive power allocation (MBAPA) technique for nonlinear distortion mitigation in intermediate frequency over fiber (IFoF) systems. The technique allocates the spectral power of each IF band according to the required signal-to-noise power ratio (SNR) of the modulation format. To demonstrate the performance of the technique, transmission experiments were performed in 10 km and 20 km with 24-IF bands using OFDM signals. The feasibility of the proposed MBAPA technique was experimentally verified by reducing inter-modulation distortion (IMD) power and enhancing channel linearity.

Mitigation of Nonlinear Distortions for a 100 Gb/s Radio-Over-Fiber-Based WDM Network

Next-generation cloud radio access networks (C-RANs) are anticipated to provide multi-Gbps data rate transmission and ultra-high bandwidth capacity, which is one of the key performance indicators for future mobile networks. The integral layout of fiber optics and radio network manages the capabilities of the C-RAN, but needs to be optimized in terms of cost, reliability and further scalibility. For C-RAN architectures, Radio over Fiber (RoF) transport-based fronthaul is a promising candidate but the associated issues of distortions due to nonlinear impairments (NLIs) from power amplifier, linear distortions (LDs) due to modulating lasers and high peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals need to be addressed. This work investigates these performance limiting factors and presents a DSP receiver-based solution to mitigate the effects of NLIs, LDs and high PAPR. Simulations are performed by applying a various range of transmission input powers, different quadrature amplitude modulation (QAM) formats for the OFDM signal, optimized filtering at the receiver end and varying channel spacing among the optical WDM channels to analyze the performance of the proposed receiver under different conditions. The simulations and theoretical model of the proposed case studies verify that the presented solution for the RoF transport utilize less power, performs better for longer transmission distances, supports higher modulation formats and transports large number of WDM channels in the presence of NLIs and DLs as compared to the conventional RoF approach. With compensation of NLIs and LDs, transmission distance up to 10 km is investigated using 16 WDM channels with aggregate data rate of 100 Gb/s which shows that the proposed receiver can be used for future C-RAN fronthaul networks.

Modulation nonlinearity characterization for rate-equation-based diode lasers using cross-correlation-calculation-enabled behavioral modeling.

In this Letter, we investigate and analyze the performance of cross-correlation-enabled behavioral modeling in characterizing the modulation nonlinearity for rate-equation-based diode lasers. The Volterra series is utilized for nonlinearity characterization, and kernels are calculated using the cross-correlation method. The effectiveness of behavioral modeling for nonlinearity characterization is validated by both simulation and experiment. A large-signal response for 100-Gb/s PAM-4 signals is fitted to the measured one successfully in the simulation and 50-Gb/s PAM-4 in the experiment. It is found that the eye skew and amplitude nonlinearity can be emulated as second-order nonlinear distortion. The results can provide guidance for nonlinear distortion mitigation in high-speed optical interconnects.

Fast remodeling for nonlinear distortion mitigation based on transfer learning.

We have proposed and demonstrated a transfer learning (TL)-assisted deep learning network (DNN) for nonlinear distortion compensation in optical side-band PAM-4 modulation and direct-detection transmission. Since there exists partial correlation of nonlinear distortions, we can transfer the parameters of the trained DNN to the target model to speed up remodeling and reduce complexity. We conduct experiments to demonstrate the effectiveness of the proposed scheme in Nyquist PAM-4 transmissions. The required iterations or train size with TL can be less than half of that with retraining without any performance degradation in single-channel transmission. We also extend the proposed scheme into multi-channel transmissions. Since all channels co-propagate on the same fiber, the correlation of nonlinear distortions enables TL to share the parameters among different channels and realize fast remodeling with a better starting rather than a stochastic beginning. The experimental results show that the iterations of TL are one-fourth that of retraining without performance penalty in five-channel transmission.

Raman-enhanced optical phase conjugator in WDM transmission systems.

Optical phase conjugation (OPC) can be applied to boost the performance of long-haul transmission by mitigating the impairments from fiber nonlinearity. Unfortunately, noticeable nonlinear noise in the conjugator for optical orthogonal frequency division multiplexing (OFDM) systems often degrades the signal quality. In this paper, we demonstrate nonlinear distortion mitigation in OPC by introducing backward Raman amplification to the conjugator. Raman amplification allows a lower input signal power, thus suppressing the OPC distortion while maintaining the conjugated output power. We investigate the performances of Raman-enhanced OPC in both back-to-back (BTB) and transmission systems with 3 × 25 Gbaud optical OFDM signals. In the BTB OPC system, Raman amplification boosts the tolerance to system nonlinearity, achieving a 3-dB improvement in the output power, a 2.4-dB improvement in the Q factor, and a 6-dB improvement in the input dynamic range. In the transmission system with Raman-enhanced OPC, the optimum launched power is increased by 2 dB and the maximum Q factor is increased by 0.4 dB compared to direct transmission. Similar performances are observed in all the wavelengths, indicating that our scheme works well with WDM transmission systems.

Nonlinear Distortion Mitigation by Machine Learning of SVM Classification for PAM-4 and PAM-8 Modulated Optical Interconnection

We demonstrated a support vector machine (SVM) based machine learning method to mitigate modulation nonlinearity distortion for PAM-4 and PAM-8 vertical cavity surface emitter laser multi-mode fiber (VCSEL-MMF) optical link. Simulations at 100 Gb/s data rate and experimental work at 60 Gb/s data rate were carried out. We achieved a significant improvement in bit error rate (BER) when complete binary tree SVMs (CBT-SVMs) are applied for both PAM-4 and PAM-8 signals. Quantitative analysis of the sensitivity gain versus modulation nonlinearity distortion is presented with experimentally verification. The results indicate that CBT-SVMs have better performance for PAM-8 compared to PAM-4. The sensitivity gain increases almost linearly with the increase of eye-linearity (increase of modulation nonlinearity distortion). Up to 2.5-dB sensitivity improvement is achieved by the proposed CBT-SVMs at eye-linearity of 1.72 for PAM-4.

Predistorter for MIMO System with Nonlinear Power Amplifiers

A multiple input multiple output (MIMO) system with nonlinear power amplifiers (PAs) is considered. The nonlinear PAs distort the transmitted signal causing performance degradation. The common approach for the mitigation of nonlinear distortions is the linearization of each one of the PAs in the MIMO system separately. We propose to apply a more generic approach in the form of a global linearization of the entire nonlinear MIMO channel . The aim of the global linearization is to reduce the nonlinear distortions seen at the receiver. An iterative technique is proposed for the implementation of such a linearization. The proposed technique improves the system performance, including: 1) power efficiency of the PAs, 2) quality of the received signal, measured in terms of symbol error rate, and 3) spectral purity of the transmitted signals.

Volterra series based blind equalization for nonlinear distortions in short reach optical CAP system

In this paper, we propose a blind Volterra series based nonlinear equalization (VNLE) with low complexity for the nonlinear distortion mitigation in short reach optical carrierless amplitude and phase (CAP) modulation system. The principle of the blind VNLE is presented and the performance of its blind adaptive algorithms including the modified cascaded multi-mode algorithm (MCMMA) and direct detection LMS (DD-LMS) are investigated experimentally. Compared to the conventional VNLE using training symbols before demodulation, it is performed after matched filtering and downsampling, so shorter memory length is required but similar performance improvement is observed. About 1dB improvement is observed at BER of 3.8×10−3 for 40Gb/s CAP32 signal over 40km standard single mode fiber.

Mitigation of nonlinear distortion in hybrid Raman/phase-sensitive amplifier links.

Hybrid systems combining distributed Raman amplification and phase-sensitive amplifiers (PSAs) are investigated in numerical simulations. We focus on the mitigation of fiber nonlinearities and the impact of the span power map which is also important in systems employing optical phase conjugation or phase-conjugated twin waves. We simulate multi-span PSA links with and without distributed Raman amplification and show that by including distributed Raman amplification, the transmission distance increases more at optimum launch power than in the linear regime. For a 5-channel WDM QPSK PSA-amplified system, we observe a transmission reach increase by a factor of 8.1 by including ideal distributed Raman amplification.

Multiple‐input multiple‐output symbol rate signal digital predistorter for non‐linear multi‐carrier satellite channels

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD has lower digital processing rate reducing the required hardware cost of the predistorter. The proposed DPD outperforms, in total degradation, both data and signal DPD schemes. Further, it performs closest to a channel bound described by an ideally mitigated channel with limited maximum output power.

Nonlinear distortion mitigation in visible light communications

Many physical devices used in VLC systems exhibit nonlinear effects, which can significantly degrade the overall system performance. For example, the LED is the major source of nonlinearity. The forward current is zero unless the forward voltage exceeds a turn-on value. The forward current is also limited with a maximum permissible value. In addition, the electrical-tooptical conversion is also nonlinear. In this article, we provide an overview of techniques related to modeling and distortion mitigation techniques of the nonlinearity in VLC systems. Appropriate models and robust nonlinearity mitigation techniques are crucial to support high-speed transmissions in practical VLC systems.