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Radio over Fiber systems based on 850nm Vertical Cavity Surface Emitting Lasers constitute an attractive solution to realize cost-and-consumption-efficient 4G/5G Front Hauls while reusing the existing in-building G.652 fiber infrastructures. In view of such application, the mitigation of the nonlinearities of these systems through an effective local predistortion loop is demonstrated for a transmission distance of 2Km.

This letter presents a comparative evaluation between three different behavioral models to perform digital predistortion (DPD) that enhances the linearity of radio-over-fiber (RoF)-based front haul links for the mobile network. In particular, the intention is to jump out of the volterra box and propose models based on segmentation approach. Especially the decomposed vector rotation (DVR) model is compared to volterra polynomials such as memory and generalized memory polynomial (GMP) architectures. DPD is employed to RoF links that are based on distributed feedback laser emitting at 1310 nm, and standard single-mode fiber for long-term evolution 20-MHz signal with 256-QAM modulation format. The effectiveness of the digital predistortion methodology is investigated for varying input powers in terms of normalized mean square error, adjacent channel power ratio, and error vector magnitude. The experimental results demonstrate that DVR achieves elevated linearization when compared to memory polynomial and GMP models.

In recent years, the demand of efficient and broadband wireless access has escalated, for which Radio over Fiber (RoF) is considered as an appropriate solution. In this paper, we present a Digitized Transmission of 20 MHz LTE signal having 64 quadrature amplitude modulation over 70 Km of Standard Single Mode Fiber (SSMF) for broadband wireless signal transportation and distribution applications. The performance analysis has been evaluated for conventional Analog Radio over Fiber (A-RoF) and proposed Digital Radio over Fiber (D-RoF). The bandpass sampling technique is discussed and employed for digitizing the RF signal. As a figure of merit, the performance evaluation of two architectures is reported by analyzing the Error Vector Magnitude (EVM), Signal to Noise Ratio and Eye-Opening Penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 70 Km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog to digital converter (ADC) resolution bits. An experimental validation of the proposed analytical D-RoF model is done for 30 Km of SSMF, whose experimental results are in line with the analytical ones. The evaluated parameters are within the LTE specifications, proving this is a cost and power effective solution for next generation wireless networks.

Sigma delta radio over fiber (ΣΔ-RoF) link as an optical front haul find its application in 5G cloud/centralized radio access network (C-RAN). The presence of 1-bit sigma delta (ΣΔ) modulation results in high quantization error that can be reduced by addition of band pass filter (BPF) at the receiver side. However, this BPF leads to an additional unwanted magnitude and phase noise that severely affects the signal integrity. In order to reduce the effects of conventional BPF, a Pre-BPF is proposed which is inserted before ΣΔ modulator to counteract the magnitude and phase response of conventional BPF. The proposed system is practically validated for 5G new radio (NR) 100-MHz signal with 256 quadrature amplitude modulation centered at 3 GHz with 5 km of link length. The experimental realization compares analog radio over fiber (A-RoF), conventional ΣΔ-RoF and Pre-BPF-ΣΔ-RoF. The experimental results suggest a significant reduction of error vector magnitude and adjacent channel leakage ratio for Pre-BPF-ΣΔ-RoF as compared to conventional A-RoF and ΣΔ-RoF system.

In this paper machine-learning (ML) dependent digital-predistortion (DPD) methodology is presented that overcomes the impairments of signal and non-linearities in Optical Front-hauls with the use of Radio over Fiber (RoF) systems. Volterra methods have been realized in the past for this purpose, however, they are not straight forward while classical artificial networks necessitate the optimum arrangement. The proffered support vector regression (SVR) method using grid search lessens the issues in Volterra based DPD and traditional artificial neural networks techniques In this work, the experimental evaluation for Long Term Evolution 20 MHz, 256 quadrature amplitude modulated signal using 850 nm Multi Mode Vertical cavity surface emitting lasers and Multi-Mode Fiber is linearized using SVR based DPD. The experimental analysis finds that SVR-DPD gathers the RoF non-linearities hence proving to be extraordinarily robust.

This letter presents a novel neural network (NN) based digital predistortion (DPD) technique to obliterate the signal impairments and nonlinearities in radio over fiber (RoF) systems. DPD is generally performed with volterra based procedures that utilizes indirect learning architecture (ILA) that can become complex and expensive computationally. The proposed method using NNs evades issues associated with ILA and utilizes a NN to first model the RoF link and then training a NN based predistorter by backpropagating through the RoF NN model. Furthermore, the experimental evaluation is carried out for long term evolution 20-MHz 256-QAM modulation signal using 1310 nm distributed feedback laser, and standard single-mode fiber to establish a comparison between NN based RoF link and volterra based generalized memory polynomial using ILA. The efficacy of the DPD is examined by reporting adjacent channel power ratio, mean square error, and error vector magnitude. The experimental findings imply that NN-DPD convincingly learns the RoF nonlinearities which may not suit a volterra based model, and hence may offer a favorable trade-off in terms of computational overhead and DPD performance.

This paper introduces the realization and evaluation of multi input multi output (MIMO) wireless system and fiber based sigma delta Radio-over-Fiber (Δ-RoF)based optical link as a front haul using fifth generation (5G) new radio (NR) multiband signals. The proposed 5G NR signals comprise of 3 GHz flexible waveforms and 23 GHz-400 MHz bandwidth. The Δ-RoF has been demonstrated by using 2nd order Sigma-Delta Modulation (SDM) with 5 km of Standard Single Mode Fiber. The EVM performance for the system meets the 3GPP Release 16. Furthermore, EVM performance for received optical power is evaluated up to 400 MHz bandwidth. It can be concluded that Δ-RoF-MIMO system suits the required range of the 5G C-RAN fronthaul networks and can be a propitious candidate for future mobile haul applications.

Sigma-delta radio over fiber (ΣΔ-RoF) is an expedient technology for next-generation networks including 5G cloud/centralized radio access networks (C-RAN). In this article, we demonstrate a realistic experimental scenario for ΣΔ-RoF link targeting C-RAN fronthaul applications, by using baseband second-order 1-bit sigma-delta modulation (ΣΔ-M). The experimental set-up validates the LTE 20 MHz signals having modulation order of 256-quadrature amplitude modulation for a carrier frequency of 3 GHz, up to 10 km of standard single mode fiber. A detailed analysis of the ΣΔ-RoF system performance is reported by adjacent channel leakage ratio and error vector magnitude. Furthermore, an experimental study is evaluated where ΣΔ-RoF is compared with its counterparts. It is deduced that ΣΔ-RoF corroborates the present range of C-RAN fronthaul networks and can be a promising candidate for future mobile haul applications.

The Radio access network in fifth generation (5G) of mobile networks requires streamlining in order to absorb the enormous incoming wireless data traffic. In this context, this paper presents the realization and evaluation of 5G new radio (NR) fiber wireless (FiWi) multi input multi output (MIMO) wireless system for enhanced mobile broadband (eMBB) scenario utilizing digital predistortion (DPD). The optical fronthaul (OFH) has been realized with analog radio over fiber (A-RoF) technology. As a proof of concept, the proposed 5G NR signals encompasses the supercell in a long reach scenario at a wireless distance of 5 km while femto cell scenario is realized at a 10 meters distance with 20 GHz band. Additionally, a traditional volterra based DPD is applied for performance enhancement. The EVM (error vector magnitude) performance is estimated for 5G NR bands which meets the requirements set by third Generation Partnership Project (3GPP). It can be concluded that MIMO enabled 5G-NR FiWi system using OFH can be a buoyant contender for future fronthaul applications.

This paper reports the performance evaluation and realization of fifth generation (5G) new radio (NR) multiband signals employing Analog Radio-over-Fiber based optical link as a front haul. The proposed 5G NR signals comprise of 3 GHz flexible waveforms and 23 GHz–400 MHz bandwidth. The EVM performance for the system meets the 3GPP Release 16. Furthermore, EVM performance for received optical power is evaluated up to 400 MHz bandwidth. Besides, we perform an evaluation for coexisting 5G and 4G systems with cleaner and lower EVM in limits for offset greater than 15 MHz.

Radio over fiber (RoF) is a promising solution for the next-generation wireless networks including fifth-generation Cloud/Centralized Radio Access Network (C-RAN). There exists a possibility to use Sigma Delta Modulated RoF (S-DRoF) that combines the advantages of analog RoF and digital RoF by means of sigma delta modulation (SDM) at the transmitter side subsequently replacing the employment of expensive and high-speed digital-to-analog converters. In this paper, we demonstrate the usage of second-order SDM for LTE 20 MHz signal having 64 QAM modulation on a central carrier frequency of 1.14 GHz for the implementation of S-DRoF for 20 km of standard single mode fiber with baud rate from 25 to 100 Mbaud. Furthermore, a comprehensive analysis of the design of SDM is explained followed by the experimental setup. The performance is reported in terms of error vector magnitude, constellations and adjacent channel power ratio. The results show that the proposed architecture performance is in with accordance to the limitations set by the 3GPP (Third Generation Partnership Project) standards and is a reasonable choice either for upgrading installed systems as well as for the new deployments.

International audience; The article demonstrates a novel Digital Predistortion (DPD) architecture for Mobile Front Haul links for the advanced Long-Term Evolution (LTE) and upcoming 5G networks. Precisely, the use of a feedback approximation method has been proposed and experimentally demonstrated herein that simplifies the complexities in realizing the practical DPD technique for Multi-Mode VCSELs and Multi-Mode Fibers based Radio over Fiber systems. As a figure of merit, linearization efficiency is provided in terms of Adjacent Channel Power Ratio, Normalized Mean Square Error and Error Vector Magnitude referring to a complete LTE frame occupying 10 MHz with 256-QAM modulation format.

Radio over Fiber is a promising technology for the 5G Cloud Radio Access Network. We demonstrate experimentally Sigma Delta Radio over Fiber by means of Sigma Delta Modulator (SDM) subsequently replacing expensive digital to analog converters. A second order SDM is proposed for LTE 20 MHz signal having 256 QAM modulation on a carrier frequency of 3.5 GHz for 10 Km of fiber length. The performance is reported in terms of error vector magnitude, adjacent channel leakage ratio and eye-opening penalty. The results show that the proposed architecture performance is cost and power efficient solution for next-generation wireless networks. Keywords: Radio over fiber, Sigma delta modulation, 5G C-RAN, EVM, ACPR

Machine learning (ML) methodologies gave an innovative and realistic direction to cope up with nonlinearity issues in fiber optics communication. In this paper, a 40-Gb/s 128-quadrature amplitude modulation (QAM) signal based Radio over Fiber (RoF) system is experimentally evaluated for 70 km of standard single mode fiber length which utilizes support vector machine (SVM) decision method to indicate an effective nonlinearity mitigation. The influence of different impairments in the system is evaluated that includes the influences of Mach-Zehnder Modulator nonlinearities, in-phase and quadrature phase skew of the modulator, input signal power and noise due to amplified spontaneous emission. By employing SVM, the results demonstrated in terms of bit error rate and eye linearity suggest that impairments are significantly reduced and licit input signal power span of 5dBs is enlarged to 15 dBs.

Use of Machine Learning (ML) methodologies in optical communications has paved a new pathway. In this paper, firstly, we discuss the use of ML methodologies for reducing optical fiber nonlinearities, nonlinearity compensation, fault detection and optical performance monitoring. Then we present our recent work where we compare RL-SARSA and SVM based method with conventional method. The results show that RL-SARSA and SVM methods are successful candidates in mitigating the nonlinearities in proposed system as compared to conventional optical communication system.

We propose a 10-Gb/s 64-quadrature amplitude modulation (QAM) signal-based Radio over Fiber (RoF) system for 50 km of standard single mode fiber length which utilizes Reinforcement Learning (RL) SARSA based decision method to indicate an effective decision which mitigates nonlinearity. By utilizing RL-SARSA algorithm, the results demonstrate that significant reduction can be obtained in terms of bit error rate.

Machine learning (ML) methodologies have been looked upon recently as a potential candidate for mitigating nonlinearity issues in optical communications. In this paper, we experimentally demonstrate a 40-Gb/s 256-quadrature amplitude modulation (QAM) signal-based Radio over Fiber (RoF) system for 50 km of standard single mode fiber length which utilizes support vector machine (SVM) decision method to indicate an effective nonlinearity mitigation. The influence of different impairments in the system is evaluated that includes the influences of Mach-Zehnder Modulator nonlinearities, in-phase and quadrature phase skew of the modulator. By utilizing SVM, the results demonstrated in terms of bit error rate and eye linearity suggest that impairments are significantly reduced and licit input signal power span of 5dBs is enlarged to 15 dBs.

Analog Radio-over-Fiber (A-RoF) communication technology constitutes a promising technique for next generation radio access networks thanks to its relatively low bandwidth requirements. Within this context, an efficient predistortion technique is proposed, which can be applied to reduce the impairments of A-RoF systems due to the combined effects of frequency chirp of the laser source and chromatic dispersion of the optical channel. The radio frequency signal is firstly put in digital form through an analog to digital converter, then the predistortion operation is realized, and finally the resulting signal is put again into analog form. A comprehensive analysis on the theoretical basis of the proposed approach is presented, together with the approximations introduced, which makes it practically realizable. The improvements on the quality of the received signal due to the proposed solution are illustrated with reference to scenarios of applicative interest. The performance of proposed technique is evaluated in terms of adjacent channel leakage ratio and error vector magnitude when long term evolution signal is applied at the input.

Radio over fiber (RoF) is an empowering technology for the next-generation wireless networks including fifth generation cloud radio access networks. In this paper, we propose a new fronthaul interface which has been demonstrated for a 20-MHz LTE signal having 64-Quadrature amplitude modulation (QAM) modulation over 50 km of standard single-mode fiber. The proposed methodology potentially reduces the overall bandwidth requirement of the link. The performance analysis has been demonstrated for conventional analog RoF (A-RoF) and proposed digital RoF (D-RoF). As a figure of merit, the performance evaluation of the two architectures is reported by analyzing error vector magnitude (EVM), signal-to-noise ratio and eye-opening penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 50 km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog-to–digital-converter resolution bits. For the D-RoF link, the EVM was measured to be less than 2 % at 50 km. This is within the LTE specifications, proving it as a cost and power effective solution for next-generation wireless networks.

The article proposes a Digital Predistortion (DPD) methodology that substantially meliorates the linearity of limited range Mobile Front Haul links for the extant Long-Term Evolution (LTE) and future (5G) networks. Specifically, the DPD is employed to Radio over Fiber links that contrive of Vertical Cavity Surface Emitting Lasers (VCSELs) working at 850 nm. Both, Memory and Generalized Memory Polynomial models are implied to Single Mode (SM) and Multi-Mode (MM) VCSELs respectively. The effectiveness of the proposed DPD methodology is analyzed in terms of Normalized Mean Square Error, Normalized Magnitude, Normalized phase and Adjacent Channel Power Ratio. The demonstration has been carried out with a complete (Long Term Evolution) LTE frame of 10 ms having 5 MHz bandwidth with 64-QAM modulation configuration. Additionally, the effectuality of the proposed DPD technique is evaluated for varying levels of input power and link lengths. The experimental outcomes signify the novel capability of the implied DPD methodology for different link lengths to achieve higher system linearization.

Sigma Delta Radio over Fiber (S-DRoF) systems are looked upon as an enabling technology due to their advantages that comes due to combination of analog and digital radio over fiber (RoF) systems. In this paper, we have proposed and experimentally demonstrated a Multi-stAge-noise-SHaping (MASH) based Sigma Delta Modulated RoF system targeting 5G C-RAN (cloud/centralized radio access network) fronthaul applications. The evaluation has been done for LTE 20 MHz signal having 256 quadrature amplitude modulation with a carrier frequency of 3.5 GHz up to 5 Km of Standard Single Mode Fiber (SSMF). Furthermore, a comprehensive analysis of the design is explained followed by the experimental setup. The performance is reported in terms of error vector magnitude (EVM) and adjacent channel leakage ratio. It is concluded that S-DRoF substantiates the desired range of the 5G C-RAN fronthaul networks.

This letter unfolds a digital predistortion (DPD) technique that improves the linearity of limited range mobile front haul links for the contemporary long-term evolution (LTE) and future (5G) networks. In particular, the proposed technique is applied to radio-over-fiber links based on single-mode (SM) vertical cavity surface emitting lasers emitting at 850 nm and standard SM fibers. Both the memory and generalized memory polynomial models are exploited for the predistorter and identified by utilizing indirect learning architecture. The impact of the DPD technique is observed by the link performance improvement in terms of normalized mean square error and adjacent channel power ratio, referring to complete LTE frames of 10 ms occupying 5-MHz bandwidth and having 64-quadrature amplitude modulation format. Furthermore, the effectiveness of the DPD approach, when varying input power levels, is investigated. The experimental results demonstrate the capability of the proposed DPD technique to achieve promising linearization performance.

Due to their inherent capillary distribution properties, Radio over Fiber (RoF) systems are expected to play a major role within future fifth generation wireless networks. However, significant bounds on the technology usability are set by the nonlinear generation of spurious frequencies, which, in the case of RoF links exploiting Directly Modulated Lasers (DML), has the combined effect of laser chirp and optical fiber dispersion among its prevailing causes. In this paper, a signal digital predistortion system, which can lower these detrimental effects, is proposed in two different versions. A detailed description of its functional model is given, and its attractive features in terms of quality improvement of the received signal is illustrated.