Search

We propose a novel design of orthogonal frequency division multiplexing-mode division multiplexing (OFDM-MDM) based radio over free space optical (RoFSO) transceiver under the dust effect. Two separate 20 Gbps-40 GHz 4-QAM data bearing optical beams are transported over two distinctive Hermite-Gaussian modes; HG00 and HG01, of a single-frequency laser to realize a single-channel 40 Gbps-80 GHz 5G communication link. The link performance and availability are investigated under the impact of clear climate and under varied dust conditions, including very light dust, light dust, moderate dust, and dense dust using signal-to-noise ratio (SNR) and total power as the key evaluation parameters. Further, we have determined the maximum reachable link distance within acceptable performance criteria, i.e., SNR 20 dB for each desert weather conditions. A higher data rate with tolerable SNR and power requirements for 5G applications has been verified.

Optical wireless communications (OWC) has emerged as a strong candidate for wireless communications, due to the capacity limitation in the radio frequency (RF) spectrum. Especially visible light communication (VLC) has great potential for short-range outdoor vehicular communications, as vehicle LED lights also transmit data. However, outdoor VLC channels vary fast and, experience multipath scattering and reflection resulting in time domain dispersion. Outdoor VLC links are also subjected to high levels of ambient noise, especially from the sun. Orthogonal frequency-division multiplexing (OFDM), which has proven robustness to multi path fading and noise effects in RF links can also be deployed in VLC links. In this paper, optical OFDM (O-OFDM) along with adaptive modulation scheme is investigated in VLC for vehicle to vehicle (V2V) communications. A (2 x 2) multiple input multiple output (MIMO) channel, with multiple polarimetric bidirectional reflections and realistic sunlight interference is considered. Two schemes of O-OFDM; direct current biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are investigated. Simulation results of the proposed model show increase in data rates up to 50 Mbps along with reduced bit error rate (BER) under both line of sight (LOS) and non-LOS and high noise conditions.

In this article, the performance of a new time domain signal pre-equalization method for use with optical orthogonal frequency division multiplexing (OFDM) and a silicon photomultiplier (SiPM) based receiver is studied. A SiPM contains a large array of microcells and each microcell is able to detect single photons. Therefore, a SiPM can be used to create arguably the most sensitive optical receiver, which can detect light intensity signals by counting the number of arriving photons within each signal sampling period. However, each photon detection triggers an avalanche-and-quenching process and the related microcell becomes inactive for a recovery time of several nanoseconds. Consequently, any photons arriving during this period cannot be detected. This effect can cause a non-linear distortion of the received signal and, when the OFDM sampling period is short, also introduces interference between signal samples. In this article, a new signal pre-equalization method is specifically designed to compensate for the impact of the finite recovery time. In this method, the number of active microcells during the transmission of each OFDM signal sample is first estimated. Then, the amplitude of the time domain signal sample is pre-adjusted based on the predicted fraction of microcells that are active. Using this approach, the negative impacts of the recovery time of the microcells are significantly reduced. The results that are presented show that when this new form of pre-equalization is used the bit error rate (BER) performance of the system is improved for a wide range of irradiance levels.

To improve the performance of optical fiber transmission and to compensate the fiber chromatic dispersion (CD), we propose to use fiber Bragg grating (FBG) in intensity modulator/direct detection IM/DD optical orthogonal frequency division multiplexing (OOFDM) system, and experimentally demonstrate 2.5-Gbit/s QPSK-OFDM transmission over 200 km SMF-28. FBG used before the detection as a chromatic dispersion compensation module, reducing the beating noise between ASE noise and OFDM signal. By using the FBG in IM/DD OOFDM system, our experimental results show that the receiver sensitivity was improved about 2 dB at a bit error rate (BER) of $1 \times {10^{ - 3}}$ for 2.5 Gbit/s QPSK-OFDM signals after 200 km SMF-transmission compared to regular system without FBG.

Instability of the local oscillator causes phase noise – a phenomenon that is a disadvantage and is considered to be a major obstacle in the functioning of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An attempt has been made in this paper to reduce the effects of common phase errors generated by phase noise. In this paper, a least mean square (LMS) based algorithm is proposed for estimation of phase noise. Using this proposed algorithm, the major problem of phase ambiguity caused by cycle slip is avoided and the bit error rate is greatly improved. Further, there is no requirement for modifying the frame structure of OFDM using this algorithm. A CO-OFDM system with the 8-PSK technique is used to implement the algorithm concerned. Furthermore, the algorithm, using the 8-PSK modulation technique, is analyzed and compared with the existing QPSK technique and with other algorithms. The investigations reveal that 8-PSK outperforms existing LMS algorithms using other techniques and significantly reduces the bit error rate.

Orthogonal frequency division multiplexing (OFDM) is a candidate modulation technique to achieve high-speed data transmission in visible light communication systems that provide both illumination and downlink data transmission. This paper proposes a method called polarity-header optical OFDM (PHO-OFDM) specially designed to account for the nonlinear response of the LED transmitters. To make the transmitted signal positive, as required for intensity modulation and direct detection systems, a signal header containing the sign information of the bipolar OFDM signal is transmitted followed by the amplitude of the signal. The binary sign information can be encoded and transmitted via a few samples using $M$ -ary pulse-amplitude modulation. The amplitude of the OFDM signal that is larger than the maximum LED power is sent in a subsequent frame to reduce the nonlinear distortion due to peak-power clipping. Furthermore, illumination requirements are taken into account, and their effects on the system performance are discussed. This paper also considers the overhead cost of adding a cyclic prefix to minimize intersymbol interference in dispersive channels. Compared with state-of-the-art optical OFDM techniques, the proposed PHO-OFDM achieves a better BER performance and higher data throughput, and provides a larger illumination flexibility.

In this letter, we developed a novel phase offset (PHO)-based channel estimation method for optical orthogonal frequency division multiplexing (OFDM)/offset quadrature amplitude modulation (OQAM). In this approach, the suppression of intrinsic imaginary interference (IMI) induced by both the linear and nonlinear impairment could be improved by increasing the pseudo pilot power with the using of PHO. As demonstrated in the numerous Montel Carlo simulation results, PHO outperforms the interference approximation methods (IAMs) for both the suppressing IMI and combating the fiber nonlinearity induced interference.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the popular techniques used for 4 G, 5 G and backbone optical communication networks to meet the large data transfer requirement applications. Optical Communication model based on Coherent Optical OFDM (CO-OFDM) using 4-Quadrature Amplitude Modulation (QAM), 16-QAM and 64-QAM has been evaluated by different researchers. To understand and evaluate the effects of polarization, we have proposed an Optical Communication model with Polarization Division Multiplexing (PDM). The proposed CO-OFDM PDM system has been evaluated for different link lengths of 50, 100 and 150 km at varying data rates of 10, 20 and 30 Gbps. The performance of the designed link has been evaluated in terms of Q-factor, Bit Error Rate (BER), Optical Spectrum and constellation diagram. The results clearly exhibit that the Q-factor, BER and constellations are superior when PDM is incorporated with the CO-OFDM link using X-QAM.

Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms.

The orthogonal frequency division multiplexing (OFDM) waveform is a well-known implementation for light fidelity but quite a novel implementation for optical camera communication (OCC). This paper proposes the two-dimensional OFDM (2D-OFDM) OCC system, namely screen OCC, which implements a single screen luminaire, composed of multiple cells so that a data rate of up to 50 kb/s can be achieved with the 2D-OFDM waveform. This paper includes a mature system design based on theoretical analysis and implementation validation. The various technical details described include system architectures, theoretical analyses of the link budget, and detailed implemental guidance for the proposed Screen OFDM system. The reliability of the proposed system was verified through numerical performance measurements, as recorded that the overall BER of 10-5 is achievable within the communication distance of 4.5 m and the viewing angle of 30°. The overall performance of the screen OFDM is also compared with a single-carrier modulation approach, asynchronous-quick-link code within the ongoing IEEE 802.15.7m standard, to demonstrate the reliable performance of the proposing system.

In this paper and as a first time, we have designed and simulated 100 Gbps long haul intensity modulation and direct detection (IM/DD) optical orthogonal frequency division multiplexing (OFDM) system with high order modulation techniques by using optisystem software QAM IM/DD OFDM system was analyzed and simulated to provide high data rate for downstream signal by using dispersion compensation fiber (DCF) inside fiber link. 4-QAM OFDM system demonstrated the best BER performance compared to other simulated systems for long haul transmission distance. For comparison and investigation, important results as eye diagram, Q factor, Eb/No and BER are explained against propagation length for every simulated system.

openaire: EC/H2020/777222/EU//ATTRACT This paper studies a novel way to estimate the position of an object in an indoor environment, using the Channel State Information (CSI) that a Visible Light Communication (VLC) system collects to maintain the link-level connectivity. First, supervised learning is applied to characterize, the effect that an object in variable but known positions has on the received optical wireless signal. Second, the trained classifier is used to estimate the new unknown positions that the object may take, making use of the instantaneous CSI that is used to equalize the data-carrying signal samples in reception. The practical validation of the proposed positioning approach was done with the aid of a software-defined VLC link based on OFDM, in which a copy of the intensity modulated signal coming from a Phosphor-converted LED is captured by Photodetectors (PDs) in different room locations. Then, the CSI of the VLC receiver is used to train a Random Forest classifier, which will predict the position of the object during the assessment phase. The performance evaluation of our experimental setting shows that the proposed VLC-based positioning approach can reach a few centimeter accuracy, provided that a proper training is executed, without the necessity of deploying a large number of PDs in the room, or adding a VLC receiver on the object to be tracked.

In both optical wireless and optical fiber communication, orthogonal frequency division multiplexing (OFDM) plays an important role in data transmission. In the similar context, DC-coupled optical (DCO) OFDM and asymmetrically clipped optical (ACO) OFDM are discussed. DCO-OFDM has better peak to average power ratio (PAPR) but bit error rate (BER) performance is poor; however, in case of ACO-OFDM, PAPR is poor but BER performance is good. Moreover, DCO-OFDM is more power hungry; therefore, ACO-OFDM is considered as a preferred choice. Recently, asymmetrically clipped DC-biased optical (ADO)-OFDM is proposed, which shows good PAPR and BER performance. Clipping and µ-law companding techniques are discussed for PAPR reduction. The mathematical model is developed for all the three methods for received signal while considering clipping and companding noises along with channel noise. It is found that ADO-OFDM is better choice in comparison to DCO and ACO-OFDM. However, in case of ADO-OFDM, receiver structure is more complex.

This paper presents empirical results about visible light communication, which is employed to monitor particulate matter data (PM). We used three nodes that transfer data using OFDM to the monitor node which displays the PM data. We achieved 36 m in three hops.

Orthogonal frequency division multiplexing (OFDM/OQAM) offset orthogonal amplitude modulation (OFDM/OQAM) systems have attracted wide attention due to their high spectral efficiency and low out-of-band power radiation. However, the OFDM/OQAM system has inherent virtual interference (IMI) and nonlinear interference (NI) in the face of multipath fading channel. Therefore, the development of effective channel estimation methods and pseudo-pilots to suppress IMI and NI effects is very important to maintain the performance of OFDM/OQAM systems. In order to reduce the interference caused by the correlation characteristics, the interference approximate expansion method (IAM-E) is proposed in this paper. The time-frequency localization (TFL) properties of IOTA filters in O-OFDM/OQAM systems are analyzed, and the least squares estimation of the channel transmission matrix in frequency domain is carried out. Theoretical analysis and simulation results show that IAM-E is an effective interference suppression method.

Orthogonal frequency-division multiplexing offsetquadrature amplitude modulation (OFDM/OQAM) system relaxes the orthogonal condition of the sub-carriers from the complexed domain to the real field. With the improve of transmission efficiency, it also greatly increases the interference of nonlinear effect. In this paper, we design the Pseudo Pilot according to the nonlinear transmission model established before, which can immensely promote the tolerance of optical OFDM/OQAM system to nonlinear interference.

ABDULKAFI, Ayad Atiyah/0000-0002-1160-6011 WOS:000429305800022 Achieving high spectral efficiency is the key requirement of 5G and optical wireless communication systems and has recently attracted much attention, aiming to satisfy the ever increasing demand for high data rates in communications systems. In this paper, we propose a new precoding/decoding algorithm for spectral efficient optical orthogonal frequency division multiplexing (OFDM) scheme based visible light communication (VLC) systems. The proposed coded modulated optical (CMO) based OFDM system can be applied for both single input single output (SISO) and multiple input multiple-output (MIMO) architectures. Firstly, the real OFDM time domain signal is obtained through invoking the precoding/decoding algorithm without the Hermitian symmetry. After that, the positive signal is achieved either by adding a DC-bias or by using the spatial multiplexing technique. The proposed CMO-OFDM scheme efficiently improves the spectral efficiency of the VLC system as it does not require the Hermitian symmetry constraint to yield real signals. A comparison of the performance improvement of the proposed scheme with other OFDM approaches is also presented in this work. Simulation results show that the proposed CMO-OFDM scheme can not only enhance the spectral efficiency of OFDM-based VLC systems but also improve bit error rate (BER) performance compared with other optical OFDM schemes.

The need for multiple transmit chains poses a major challenge in optical orthogonal frequency division multiplexing (OFDM) system utilising grouped light emitting diodes (LEDs) for the purpose of peak-to-average power ratio (PAPR) reduction. Thus, recent study propose the use of pilot-assisted (PA) electrical PAPR reduction technique to further reduce PAPR and limit the number of transmit chains in the system. This paper presents the application of order statistics to derive the analytical solutions of PAPR distributions in the PA optical OFDM system utilising grouped LEDs. It is shown that the results obtained via analysis are in good agreement with that of computer simulations.

Laser phase noise tolerance in direct detection optical orthogonal frequency division multiplexing (OFDM) transmission system is experimentally demonstrated using laser linewidth emulator. With this linewidth emulator, the linewidth of the laser can be broadened independently without inducing other laser's noise characteristics such as relative intensity noise and chirping. The results show the effect of phase-to-intensity noise conversion due to the laser's phase noise and chromatic dispersion. This induces noise pedestals not only onto the optical carrier, but also to each of the subcarriers, and thus produces intersubcarriers interference. Measurements show 6 dB Q-degradation is suffered by the system when 10 MHz linewidth is used as compared to using narrowest emulator linewidth of 256 kHz. Transmission with the linewidth emulator set to 20 MHz is also shown where it can still be tolerated by 400 km of fiber at the Q of 9.606 dB with respect to $1.6\,\times \,10^{{\rm - 3}}$ bit error rate. Simulation of 16 quadratic-amplitude modulation (QAM) (∼128 Gb/s) and 4 QAM (∼100 Gb/s) using VPItransmissionMaker are also presented to demonstrate the effect of carrier's phase-to-intensity noise conversion when a high data rate and wide OFDM signal bandwidth are used with the linewidth emulator as the system's laser source. The results show that a phase rotation term is insignificant for lower M-size QAM with fiber length less than 500 km. This presents the high effectiveness and reliability of the laser linewidth emulator to discretely determine an independent phase noise tolerance from the other laser's noise characteristics in the optical OFDM transmission system.

Due to the unique phase noise (PN) characteristics in direct-detection optical OFDM (DDO-OFDM) systems, the design of PN compensator is considered as a difficult task. In this paper, a laser PN suppression scheme with low complexity for DDO-OFDM based on coherent superposition of data carrying subcarriers and their phase conjugates is proposed. Through theoretical derivation, the obvious PN suppression is observed. The effectiveness of this technique is demonstrated by simulation of a 4-QAM DDO-OFDM system over 1000 km transmission length at different laser line-width and subcarrier frequency spacing. The results show that the proposed scheme can significantly suppress both varied phase rotation term (PTR) and inter-carrier interference (ICI), and the laser line-width can be relaxed with up to 9 dB OSNR saving or even breakthrough of performance floor.

Optical wireless communication (OWC) has recently gained much attention for addressing the increasing demand in the global broadband access market. Flip-orthogonal frequency division multiplexing (Flip-OFDM) is a type of OFDM that can be implemented in indoor OWC. Due to the ability of Flip-OFDM to keep the same bit error rate performance in asymmetrically clipped optical OFDM (ACO-OFDM) while saving 50% of the receiver hardware complexity, it can be used as an alternative to ACO-OFDM. However, the main drawback that can reduce the performance of the Flip-OFDM is the high peak-to-average power ratio (PAPR). So, in this article, partial transmit sequence (PTS) is applied to reduce the PAPR of Flip-OFDM over ceiling bounce model. Simulation results show that the proposed PTS-based Flip-OFDM achieves significantly lower PAPR values compared to Flip-OFDM.

usc Refereed/Peer-reviewed To improve flexibility, energy efficiency, and speed of elastic optical orthogonal frequency division multiplexing systems, a reconfigurable multi-precision fast Fourier transform (FFT) is presented. The minimum required FFT word length for different criteria-namely, the bit error rate (BER), FFT size, modulation format, and optical signal-to-noise ratio-is determined using simulations. At run time, system performance is improved significantly by using a reconfigurable multi-precision FFT, while the target BER is satisfied. The proposed design is synthesized on an FPGA, and the results show that both energy efficiency and processing speed are improved about 79% and 78%, respectively, compared with the conventional design.

Real-time optical OFDM transmissions based on FPGA with 6.93 bit/s/Hz spectral efficiency by using simple directly modulated DFB laser and DAC/ADC with sampling rate as low as 2GS/s without inline amplifier are experimentally demonstrated. 7.09-Gb/s OFDM signals with subcarrier modulation format up to 512-QAM can be successfully transmitted over 50-km SSMF with adopted HD-FEC (3.8×10 −3 ). The robustness of system performance is also extensively explored to determine the tolerance to DAC/ADC resolution mismatch. It is shown that aggregate system capacity can be maintained almost constant for DAC/ADC resolution mismatch as large as 3bits due to the utilization of adaptive bit and power loading scheme. On the other hand, for a certain system configuration and an expected signal line rate, it also gives a reference minimum DAC/ADC boundary for practical deployment.

This letter describes a new non-linear algorithm for clipping noise mitigation in intensity modulation/direct detection dc biased optical orthogonal frequency division multiplexing (DCO-OFDM) systems. Clipping noise is often the major limitation in DCO-OFDM. In this letter, we show that extra information about the clipped signal can be extracted using a non-linear process and then used to mitigate the clipping noise. The effectiveness of the new algorithm is demonstrated by simulation and in an optical wireless experiment.

In recent years, with the improvement of computing performance, the application of neural networks in communication field has been widely studied. In this paper, we propose and apply neural networks (NNs) to improve the transmission performance of optical orthogonal frequency division multiplexed (O-OFDM) signals. A pair of NNs is added in transmitter and receiver respectively, to modify and restore the QAM constellation. The main target for NNs is to reduce the peak to average power ratio (PAPR) of the O-OFDM signals and the bit error rate (BER) of the received signals. The proposed scheme is verified by the simulations. And a transmission of 18.8 Gb/s, 16-QAM optical OFDM signals is successfully demonstrated and analyzed for the cases with and without NNs. The experimental results show that, the PAPR and BER can be improved significantly (~4 dB for BER) after using NNs, since PAPR is reduced and more importantly the channel distortion and noises are effectively compensated by NNs via learning procedure.

For adaptive optical OFDM system with various modulation signals, we propose a noise-robust modulation format identification based on peak-density clustering algorithm for effective symbol decision. The proposed method has been experimentally evaluated for M-QAM signals.

We report a tunable OFDM demultiplexer whose major element is a star coupler-based optical DFT circuit. Variable channel number 20 to 100 Gsymbol/s OFDM signals were demultiplexed by selecting delay lines into the star coupler.

Enhanced power loading based on machine learned subcarrier interactions and nonlinear SNR progression is proposed to improve BER performance in optical coherent OFDM systems, achieving a gain of 0.5 dB in OSNR vs. classical schemes.

We experimentally demonstrate the feasibility of implementing a cost effective all-optical fractional orthogonal frequency division multiplexing (AO-FrOFDM) receiver using an arrayed waveguide grating (AWG). The all-optical fractional Fourier transform at the receiver is implemented by modifying the second slab coupler from a conventional all-optical discrete Fourier transform AWG. The open eye diagrams obtained from the experimental results indicate that 12 × 10 Gbit/s DBPSK AO-FrOFDM signals were successfully demultiplexed.

A CO-OFDM system combines the advantages of both coherent detection and OFDM modulation for future high speed fiber transmission. In this paper, we propose an I/Q modulation technique using dual-drive MZMs for high rate 10 Gb/s CO-OFDM system. The proposed modulator provides 10.63 dBm improved optical spectra compared to a single dual-drive MZM. The simulation results in terms of BER and Q factor are quite satisfactory upto a transmission reach of 3,000 km and that to without making use of any dispersion compensation. A BER of about 8.03×10−10 and 15.06 dB Q factor have been achieved at −10.43 dBm received optical power.

We present an approximate analytical method to evaluate the performance measurements in optical orthogonal frequency-division multiplexing networks. Our approach divides the network into layers, and the equivalent path technique is used to model each path as an equivalent single-link system. The analysis of the performance measurements for an equivalent single-link system is based on a superposition concept using the Kaufman/Delbrouck recursion model. We assume static routing with a first-fit spectrum allocation. The simulation results indicating the accuracy of our method are presented.

We mathematically and experimentally demonstrate the nonlinearity suppression of optical transmitter in multiband orthogonal frequency division multiplexing based radio over fiber system (multiband OFDM-RoF) by feed-forward technique. The proposed method is a simple technique that can decrease static and dynamic nonlinear transfer characteristics. Nonlinearity of multiband OFDM-RoF has been experimentally evaluated by transmitting nine optical OFDM channels. Experimental results show that nonlinear components from optical transmitter are suppressed and EVM is improved by 7.3% in multiband OFDM signal by using the proposed technique. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1236–1240, 2016

본 논문에서는 무선 및 이동통신을 위한 클라우드 무선 가입자 네트워크를 지원하는 프론트홀에서 무선 라디오파의 광섬유 전송망의 기술을 제안하고 구현한다. 하향 링크는 OFMD (orthogonal frequency division multiplexing) (O기법을 사용하였고 상향방향의 전송은 SC-FDMA (single carrier-frequency multiple access) 방식으로 구현하였다. 64, QAM, 16QAM, QPSK 등 다양한 변조 방식에 대해 시스템 파라메터를 도출하고 측정치를 기반으로 성능을 분석하였다.

We propose a coherent optical OFDM (CO-OFDM) system based on 3-dimensional (3-D) OFDM technique in this paper. By using the 3-D signal mapper and 2-D IFFT module, the minimum Euclidean distance (MED) in constellations is increased by 8.7%, and the peak-to-average power ratio of the generated OFDM signal is reduced by 4 dB. The experimental results show that the 3-D OFDM method can improve nonlinearity tolerance by 2 dB for 100-km standard single mode fiber in a 16.27-Gb/s 2-D coherent optical OFDM system without polarization modulation. Theoretical analysis and simulation results show that the OSNR penalty could be attributed to the increased MED, the extended decision boundaries and the coding gain. To further analyze the performance in long haul transmission system, the simulation setup of 1000-km SSMF CO-OFDM system is built up. The results verify that the proposed method could effectively enhance nonlinearity tolerance and transmission performance of the CO-OFDM system.

In this paper, we review the prior works on optical fiber transmission OFDM/OQAM systems, including the coherent optical OFDM/OQAM, and direct detection optical OFDM/OQAM. Besides this, we prospect the future optical communication of OFDM/OQAM.

In a typical intensity-modulated direct-detection optical system, the information is carried on the intensity of the optical signal, and therefore can only be positive. Existing synchronization methods for RF-based OFDM system cannot be used directly in asymmetrically clipped DC biased optical of DM (ADO-OFDM) system. In order to solve the above problem, according to the characteristics of ADO-OFDM signal, the modified training symbol is presented. The simulation results show that the modified synchronization method gives good performance.

Visible Light Communication (VLC) is a short-range optical wireless communication technology that has been gaining attention due to its potential to offload heavy data traffic from the congested radio wireless spectrum. At the same time, wireless communications are becoming crucial to smart manufacturing within the scope of Industry 4.0. Industry 4.0 is a developing trend of high-speed data exchange in automation for manufacturing technologies and is referred to as the fourth industrial revolution. This trend requires fast, reliable, low-latency, and cost-effective data transmissions with fast synchronizations to ensure smooth operations for various processes. VLC is capable of providing reliable, low-latency, and secure connections that do not penetrate walls and is immune to electromagnetic interference. As such, this paper aims to show the potential of VLC for industrial wireless applications by examining the latest research work in VLC systems. This work also highlights and classifies challenges that might arise with the applicability of VLC and visible light positioning (VLP) systems in these settings. Given the previous work performed in these areas, and the major ongoing experimental projects looking into the use of VLC systems for industrial applications, the use of VLC and VLP systems for industrial applications shows promising potential.

Efficient frame synchronization is essential for data recovery in communication systems. In this study, a single pilot sequence is used to achieve both frame synchronization and peak-to-average power ratio (PAPR) reduction. The two systems considered are direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) and asymmetrically clipped O-OFDM (ACO-OFDM). The pilot symbol is allocated to odd indexed subcarriers only. Thus, the synchronization algorithm leverages the mirror symmetric property of the pilot symbol within a frame to detect the start of the pilot signal at the receiver. This scheme has low complexity and gives precise frame synchronization at signal-to-noise ratios as low as 4 dB in an indoor visible light communication (VLC) channel.

We present a review of concepts and challenges to implement the OFDM technique in the all-optical domain so that it may emerge, in a near future, as a technically and economically feasible option to meet, with spectral efficiency and energy saving, the ever-increasing demand of capacity in data transmission systems.

Novel bidirectional architecture on two optical OFDM SSB modulation techniques to mitigate Rayleigh backscattered and reflections interferences in RoF transmission is proposed. The interference effect is analyzed with mathematical model comparing conventional SSB and the modified SSB based on elimination of higher order RB-RE harmonics.

In this paper, optical performance monitoring is presented as enabler to address the key challenges in disaggregated optical networks. In fact, data plane elements for non-intrusive monitoring of different modulation formats will be discussed, reviewing different options based on high resolution spectral analysis. Furthermore, we will report how the information retrieved by these monitoring probes can be used to actually control the transceivers and other data plane elements, emphasizing on the suitable figures of merit to be delivered to the SDN control, orchestration and management planes.

Suppressing the intrinsic imaginary interference (IMI) effect induced by multiple-path fading channel is the key technology for maintaining the good performance of the orthogonal frequency division multiplexing offset-quadrature amplitude modulation (OFDM/OQAM) systems. Recently, both theoretical studies and experimental demonstrations for coherent optical OFDM/OQAM (CO-OFDM/OQAM) system has been studied. A number of works have been conducted to provide effective channel estimation for CO-OFDM/OQAM. However, there are no theoretical discussions on optimal pilot design principles. In this paper, we discuss the system robustness against IMI for the optical OFDM/OQAM with the using of different pilot structure. The pseudo pilot was constructed with three and five consecutive loaded pilot blocks were compared for CO-OFDM/OQAM. As demonstrated in the theoretical analysis and simulation results, triangle loaded pilot blocks were sufficient to combat IMI with moderate complexity.

We demonstrate combined WDM/SDM delivery of mobile fronthaul in PONs, employing SDN-enabled S-BVTs based on adaptive multicarrier modulation. Experiments show successful BBU-RRU connectivity on several deploying strategies while coping with capacities beyond 50Gb/s per flow.

Orthogonal frequency division multiplexing (OFDM) combined with offset quadrature amplitude modulation (OQAM) have aroused wide interest for optical communication recently. With the relaxation of orthogonal condition from the complex field to the real field, optical OFDM/OQAM faced with serious intrinsic imaginary interference (IMI) brought by chromatic dispersion and polarization mode dispersion. As have been discussed in previous publications, frequency domain channel estimation methods utilizing the concept of pseudo pilot have been proved effective in combating IMI. In this paper, we discussed a novel frequency domain channel estimation method based on the using of three consecutive full loaded pilot blocks for optical OFDM/OQAM system. In this approach, the pseudo pilot was constructed with three consecutive loaded pilot blocks. The discussed method can efficiently promote the power of the pseudo-pilot and improve the system robustness against IMI effect significantly. As demonstrated in the Montel Carlo simulation results, 1.8dB advantage in require optical signaI to noise ratio (OSNR) at a BER target of $10^{-3}$ could be achieved with the using of the discussed method, compared with the IAM-C method.

This paper analyses the performance of two advanced modulation techniques for reducing the peak-to-average power ratio (PAPR) of a visible light communication (VLC) system namely, double precoded OFDM which is a variant of DFT precoded OFDM used in 4G LTE-A and optical generalized frequency division multiplexing (OGFDM) which is a variant of one of the proposed 5G waveform (GFDM). The performance of double precoded OFDM and OGFDM is compared against asymmetrically clipped optical OFDM (ACO-OFDM) on the basis of PAPR and SER. The results show that double precoded OFDM and OGFDM reduces the PAPR by 9 and 5 dB respectively, over ACO-OFDM.

International audience; In this paper, we present the orthogonal frequency division multiplexing (OFDM) technique based on discrete multitone modulation (DMT) over multimode fiber (MMF), at length up to 5Km at a bit rate of 20 Gb/s. Through numerical simulations, we investigate the optimal launching conditions of the MMF fiber. The effect of the fiber length on the performances of the system is also studied.