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Optimal control of aluminum electrolysis production process (AEPP) has long been a challenging industrial issue due to its inherent difficulty in establishing an accurate dynamic model. In this paper, a novel robust optimal control algorithm based on adaptive dynamic programming (ADP) is proposed for the AEPP, where the system subjects to input constraints. First, to establish an accurate dynamic model for the AEPP system, recursive neural network (RNN) is employed to reconstruct the system dynamic using the input-output production data. To ensure input constraints are not to exceed the bound of the actuator, the optimal control problem of the AEPP is formulated under a new nonquadratic form performance index function. Then, considering the perturbation of the AEPP, the robust control problem is effectively converted to the constrained optimal control problem via system transformation. Furthermore, a single critic network framework is developed to obtain the approximate solution of the Hamilton-Jacobi-Bellman (HJB) equation. Finally, the proposed ADP controller is applied to the AEPP system to validate the effectiveness and performance.

Direct detection (DD) systems based on high-order quadrature amplitude modulation (QAM) is promising to provide high spectrum efficiency (SE) for future short-reach data-center applications with next generation standardization of 800 GbE or even 1.6 TbE considering bandwidth limitation. Kramers-Kronig (KK) receiver is recently proposed as an effective method to inherently remove signal-signal beat interference (SSBI) by reconstructing complex optical field in single-sideband (SSB) DD systems. In this paper, we make a detailed system performance assessment of applying a KK receiver in 128, 256 and 512 QAM systems through simulations and experimental demonstrations. 25 GHz-spaced 4 × 140 Gb/s wavelength division multiplexing (WDM) 128 QAM and 4 × 160 Gb/s WDM 256 QAM SSB KK transmissions over 20 km of standard single-mode fiber (SSMF) are successfully achieved. As far as we know, this is the first time that a constellation size as high as 256 QAM with a net SE of 5.12 b/s/Hz is experimentally demonstrated in a WDM system with KK receiver, and the effect of adjusting carrier-to-signal power ratio (CSPR) on the performance of 128, 256 and 512 QAM systems is also investigated with simulation and experimental results.

Desulfurization control of natural gas has long been a challenging industrial issue owing to its inherent difficulty in establishing accurate mathematical model for the nonlinear and strong coupling process. In this paper, a data-based adaptive dynamic programming (ADP) algorithm is presented to solve optimal control for natural gas desulfurization. First, neural network (NN) is used to reconstruct the dynamics of the desulfurization system via the input and output production data. Then, an improved unscented Kalman filter (IUKF) aided ADP method is presented to solve optimal control problem for desulfurization system, where IUKF algorithm is developed as a new weight-updating strategy for the action network and the critic network. The IUKF aided algorithm can improve the convergence speed as well as the anti-interference ability of the ADP controller. Furthermore, the proposed IUKF-ADP algorithm is implemented using the heuristic dynamic programming (HDP) structure. Finally, the effectiveness of the proposed IUKF-ADP algorithm is demonstrated through experiments of the natural gas desulfurization system.

In this paper, we experimentally demonstrate the intensity modulation and direct-detection (IM/DD) 112-Gb/s single carrier pulse amplitude modulation (PAM)-4 transmission system over 80-km standard signal-mode fiber (SSMF) without any optical chromatic dispersion (CD) compensation at the 3.8 × 1 0 − 3 BER threshold for 7% the hard-decision forward error correction (HD-FEC). The training based pre-equalization (pre-EQ) and the nonlinear look-up-table (LUT) based pre-distortion (pre-DT) in the transmitter (Tx)-side are employed to reduce the computation complexity and deal with the modulation bandwidth and the nonlinearity impairments of electro-optical modulators and detectors. On the other hand, the system without optical CD compensation modules is obviously more simple and flexible. Therefore, the nonlinear LUT pre-DT simultaneously used for CD compensation will further simplify the system. The BER is about 20% without any digital signal processing (DSP) such as equalization, pre-distortion, pre-equalization or compensation. After signal recovery, the BERs of BTB and 80-km SSMF system can achieve 3.07 × 10 −5 and 1.50 × 10 −3 respectively. The principle of the LUT based pre-DT and the pre-EQ are introduced in the paper.

In this paper, we propose a joint processing algorithm for carrierless amplitude and phase modulation (CAP) signal to improve the system performance in both short-reach and metro network. Utilizing our proposed method, 112 Gb/s/λ CAP-64 quadrature amplitude modulation (QAM)-based transmission over 50 km of standard single mode fiber (SSMF) is experimentally achieved with a bandwidth-limited direct-detection receiver under the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10–3. Furthermore, we experimentally demonstrate 112 Gb/s/λ CAP-16 QAM transmission over 480 km of SSMF with direct detection. With our proposed joint processing algorithm, both nonlinearity and In-phase/quadrature (IQ) imbalance can be mitigated. More than 3 dB receiver sensitivity gain is achieved at the HD-FEC threshold after 400-km transmission compared with the result using traditional nonlinear compensation.

Metro network, as a medium distance transmission system, poses a special challenge of transmission capacity and cost. In this paper, we present a detailed comparison of applying three advanced modulation formats including pulse amplitude modulation-4 (PAM-4), carrierless amplitude and phase modulation-16 QAM (CAP-16), and discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) with low-cost direct detection for 100-Gb/s/λ metro optical transmission systems. These modulation formats are all experimentally demonstrated with similar digital signal processing algorithms. Three kinds of chromatic dispersion (CD) compensation ways named CD precompensation method, single sideband (SSB), and dispersion compensating fiber (DCF) are also compared. Two types of modulators including an IQ modulator and a dual-drive Mach–Zehnder modulator are employed to generate SSB or CD precompensated signals in this experiment and their transmission performance is also evaluated. To the best of our knowledge, this is the first time that the performance of single-wavelength 100-G signal transmission based on direct detection is evaluated over 480 km of standard single mode fiber with PAM-4, CAP-16, and DFT-S OFDM modulation formats.

We experimentally demonstrate 208-Gb/s/λ discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) transmission over a 40-km standard single-mode fiber without chromatic dispersion compensation using a low-cost direct-detection architecture based on the dual-driver Mach-Zehnder modulator (MZM). One twin-single sideband (SSB) signal is generated by driving the upper and lower arms of a dual-driver MZM with a real signal and its respective Hilbert pair. A MIMO-Volterra equalizer is proposed to mitigate the interference and nonlinearity penalty of the twinSSB signal. Using the Twin-SSB without the MIMO algorithm can only reach 165 Gb/s/λ, and applying a conventional SSB can only achieve 164 Gb/s/λ with a bit error ratio less than 5×10 -3 . However, we achieve a 240-Gb/s/λ twin-SSB DFT-S OFDM signal in the back-to-back (BTB) case using the twin-SSB signal and MIMO-Volterra Equalization method, which implies that double spectral efficiency and more than 45% data rate improvement are obtained.

We propose a hybrid optical spectral efficient mobile fronthaul (MFH) incorporating low-cost light-emitting diode-based visible light communication (VLC) links in the spatial densified network to enable multi-tier cell coordination. With proposed VLC links between multi-tier master remote radio heads (RRHs) and slave RRHs, fiber connection is not necessary for all RRHs, which simplifies the network structure, and reduces the deployment and operation cost. The proposed architecture can increase the flexibility and capability for network extension significantly by adding new RRHs without fiber deployment. Centralized and distributed pre-equalization are proposed and compared with the letter theoretically and experimentally. In the experiment, we demonstrated a MFH network serving one master RRH and six slave RRHs with only single fiber connection, delivering eight independent long term evolution (LTE) streams with multi-tier cell coordination. Experimental results verify the feasibility of the proposed scheme with high performances suitable for LTE and 64-quadratic-amplitude modulation (64-QAM).

In this paper, we proposed a 2×2 imaging Multi-Input Multi-Output (MIMO)-Visible Light Communication (VLC) system by employing Space Balanced Coding (SBC) based on two RGB LEDs and integrated PIN array reception. We experimentally demonstrated 1.4-Gbit/s VLC transmission at a distance of 2.5 m. The proposed imaging system not only overcomes the limitation of bandwidth existing in LEDs, but also can reject the second-order nonlinearity distortion. It turned out to be very promising to use integrated antennas in the VLC system in the future.

We experimentally demonstrated 600G per-wavelength (848-Gbps coded line rate) probabilistically shaped 16QAM coherent WDM transmission over 5,600-km ultra-low-loss fibers with Raman amplification above the 27.5% SD-FEC threshold of 0.8 NGMI, attaining 27% transmission-distance improvement compared with regular-16QAM.

We experimentally demonstrate PS-64QAM outperforms hybrid-32/64QAM by 37.5% in a 400G per channel 50-GHz WDM system, which enables a 990-km transmission link consisting of SSMF and EDFA-only amplification.

We experimentally demonstrate the first single-wavelength 100-Gb/s PAM-4 TDM-PON transmission in C-band using simplified and phase-insensitive heterodyne coherent detection. Power budget of over 32 dB is achieved after 20-/40-km fiber transmission.

Probabilistically-shaped DP-64QAM at record 105 GBd is demonstrated, achieving per-wavelength 1.26- Tbps line rate and 905.8-Gbps net rate after 800-km single-channel and 400-km WDM (SE: 8.05 bits/s/Hz) transmissions, respectively, satisfying the NGMI threshold for a 27.5% FEC.

We experimentally demonstrate an eight-channel WDM coherent system with 50GHz frequency spacing which can realize the transmission of 528-Gb/s/channel probabilistically-shaped 64QAM signal over 3000km fiber in a terrestrial system. Based on the GMI and NGMI results, about 100% transmission-distance improvement can be attained after probabilistic shaping.

We propose quasi-linear preequalization to be used for high speed visible light communication (VLC) system. Compared with zero-forcing preequalization, this kind of preequalization method is more suitable for a real VLC experimental system with peak power limitation. We carry out simulations and experiments to test the performance of quasi-linear preequalization. With this equalizer, the 3 dB bandwidth of the system can be extended from 17 MHz to 450 MHz. We implement 2.32 Gbit/s phosphorescent white light-emitting diode (LED) VLC transmission over 1 m distance with quasi-linear equalizer, bit and power loading OFDM, differential amplification positive intrinsic negative diode (PIN) receivers, and maximum ratio combining algorithm. To our knowledge, this is the highest transmission data rate based on a phosphorescent white LED VLC system.

To meet the increasing bandwidth demand for rapidly growing data flow from the wide spreading multimedia services, broadband Internet, and cloud services, 100G and even beyond data transmission based on compact and low-cost transceivers have been intensively studied in short-reach links, access, inter data-center-interconnections, metro and regional networks. For these systems, direct-detection is more attractive due to the lower system cost and power consumption. In this paper, we review four advanced modulation formats including pulse amplitude modulation-4 (PAM-4), carrier-less amplitude and phase modulation-16 QAM (CAP-16), discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) and Duobinary with low-cost direct detection in 100 Gb/s/λ short-reach and metro optical transmission systems. These modulation formats are all experimentally demonstrated with similar digital signal processing algorithms. Three kinds of chromatic dispersion (CD) compensation ways named pre-CD method, single sideband (SSB) and dispersion compensating fiber (DCF) are also compared. Two types of modulators including IQ modulator and dual-drive Mach-Zehnder modulator (DDMZM) are employed to generate SSB or pre-CD signal in this experiment and their transmission performance is also evaluated. To further to improve the spectrum efficiency and reduce the cost, we also present a detailed comparison of applying three advanced modulation formats including pulse amplitude modulation-8 (PAM-8), carrier-less amplitude and phase modulation-64 QAM (CAP-64), and discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) with a bandwidth-limited direct-detection receiver for 100 Gb/s/λ optical transmission systems. The comparison is carried out to evaluate the performance of each modulation format in terms of nonlinear equalization, received optical power and optical signal to noise ratio (OSNR).

We demonstrate a 112 Gbit/s/λ CAP over 480 km of SSMF with low-cost direct detection. A joint processing algorithm is employed to improve system performance. To the best of our knowledge, this is the first time that single-wavelength 100G signal transmission is experimentally achieved over 480 km of SSMF with CAP-16 and direct detection.

We experimentally demonstrate 506-Gb/s/channel (66.125-Gbaud/channel) eight-channel WDM probabilistically-shaped 16QAM signal coherent transmission using high-bandwidth coherent driver modulator (HB-CDM) over 6000-km fiber with BER under 4.2×10–2. 150% transmission-distance improvement, and 0.216-bit/symbol achievable-information-rate improvement can be attained after probabilistic shaping.

We experimentally demonstrate a 28.95 Gbit/s/λ PS-1024-QAM DFT-S OFDM over 40 km of SSMF in a low-cost IM-DD system. A 1.85 Gbit/s capacity increment is achieved using PS-1024-QAM format. To the best of our knowledge, this is the first time to employ high order PS-QAM format in OFDM modulation.

We experimentally demonstrated a PS-256-QAM OFDM fiber transmission in a low-cost IM-DD system. Compared with uniform 128-QAM, the proposed PS-256-QAM obtains the same entropy of 7 bits/QAM symbol, but higher achievable-information-rate performance and stronger nonlinearity robustness.

We summarized the latest progress on advanced modulation for high speed VLC system including CAP, adaptive bit loading OFDM and super-Nyquist modulation to achieve high speed and high spectrum efficiency.

A 128-Gb/s 20/80-km edge-node compatible mobile fronthaul with single-side-band OQAM-CAP is demonstrated. Digital pre-equalization and power loading are jointly applied to mitigate the ISI and SSBI. Compared with QAM-CAP, spectral and computational efficiencies are improved by 8% and 50% respectively.

Using centralized DSPs and low complexity 10G receiver, we experimentally demonstrated 50 and 64-Gb/s/A PAM4 TDM-PON downstream transmission in C-band. Link budgets of 31 and 29-dB after 20-km SSMF at BER of 3.8E-3 are achieved.

We demonstrate the transmission record of 4 lines of C-band 112-Gb/s PAM-4 signals over 400-km SSMF based on direct-detection without any optical dispersion compensation, thanks to the digital CD pre-compensation and advanced nonlinearity distortion compensations.

We summarized the latest progress on enabling technologies for high speed VLC system beyond Gigabit/s including advanced modulation formats, software and hardware pre-equalization, advanced coding and nonlinear compensation.

We proposed two-staged linear software equalizer to be applied in high speed visible light communication system. Through the experimental demonstration, we implemented 2.32 Gbit/s VLC transmission based on a phosphorescent white LED with 450MHz bandwidth and 1m transmission distance. The other key technologies are adaptive bit and power loading OFDM, differential amplification PINs and maximum ratio combing algorithm. As far as we know, this is the highest data rate implemented based on a phosphorescent white LED in VLC system.

New VLC based wireless backhaul technologies are studied for high data-rate access. In this paper, we summarize the latest progress on VLC systems including pre-/post-equalization hardware, electrical differential receivers, bitloading OFDM, and MRC, which supporting VLC Gigabit capacity over long-range free-space transmission.

Exploiting the increasingly wide use of light emitting diodes (LEDs) lighting, in this paper we propose a reversed indoor positioning system (IPS) based on LED visible light communication (VLC) in order to improve indoor positioning accuracy. Unlike other VLC positioning systems, we employ two annular receivers with multi-photodiodes installed on the ceiling to locate the persons who carry LEDs. The basic idea is using multi-photodiodes to calculate the angle while using the received signal strength (RSS) method to calculate the distance. The experiment results show that the effective positioning range of the proposed system is 1.8 m when the distance between two receivers is 1.2 m. Moreover, a positioning error less than 0.2 m can be achieved under the condition that the radius of the PIN circle is between 0.16 m and 0.2 m, and the distance of the transmitter-receiver plane is less than 1.8 m, which will be effective in practice.

We experimentally demonstrates a VLC downlink based on two LEDs and one mobile user. A self-adaptive STBC is proposed in this work to suppress the interference between VLC nodes, resulting in a significant mobile feasibility.

We present a detailed comparison of applying three advanced modulation formats including pulse amplitude modulation-8 (PAM-8), carrier-less amplitude and phase modulation-64 QAM (CAP-64), and discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S OFDM) with a bandwidth-limited direct-detection receiver for 100 Gb/s/λ optical transmission systems. These modulation formats are all experimentally demonstrated with corresponding digital signal processing (DSP) algorithms. The comparison is carried out to evaluate the performance of each modulation format in terms of nonlinear equalization, received optical power and optical signal to noise ratio (OSNR). Our experimental results show that only 112 Gbit/s DFT-S OFDM is successfully achieved over 50 km of SSMF under the hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10−3.

High-speed multi-user access with high spectral efficiency is one of the key challenges for band-limited visible light communication (VLC) systems. In this paper, we propose a novel scheme for effective multiple-access VLC systems based on multi-band, Nyquist-filtered pulse amplitude modulation (PAM)-8 modulation. Within this scenario, the spectral efficiency can be improved from 1.5 to 2.73 b/s/Hz by implementing an appropriate Nyquist filter to suppress spectral bandwidth. We experimentally demonstrate a multi-band VLC system at 1.2 Gb/s after 1 m indoor free space transmission. The system performances have also been thoroughly investigated for different sub-band numbers, utilizing a rectangular filter in the frequency domain and a Nyquist filter based on square root raised cosine. The results show that the Nyquist-filtered PAM-8 signal can outperform a rectangular filtered signal. The maximum improvement of system capacity is up to 1.67 times for the Nyquist-filtered multi-band system. The results clearly show the advantage and feasibility of multi-band Nyquist PAM for high-speed multiple-access VLC systems.

In this paper, we propose a real-valued interleaved single-carrier frequency-division multiplexing (I-SC-FDM) scheme for intensity-modulation and direct-detection optical interconnects. By simplifying the encoding structure, the computational complexity can be reduced from Nlog2N complex multiplications to N complex multiplications. At the complementary cumulative distribution function of 10-2, a reduction of 10 dB and 7.5 dB for the peak-to-average power ratio (PAPR) of the I-SC-FDM is achieved than that of orthogonal frequency-division multiplexing modulated with QPSK and 16QAM, respectively, when the subcarrier number is set to 4096. We experimentally demonstrate the I-SC-FDM scheme for optical interconnects with data rates of 12 Gbit/s, 24 Gbit/s and 128 Gbit/s transmitted over 22.5-km, 22.5-km and 2.4-km standard single mode fiber, respectively. The I-SC-FDM scheme shows great potential for cost-sensitive and power-sensitive optical interconnects owing to its low computational complexity and low PAPR.

Visible light communication (VLC) has no doubt become a promising candidate for future wireless communications due to the increasing trends in the usage of light-emitting diodes (LEDs). In addition to indoor high-speed wireless access and positioning applications, VLC usage in outdoor scenarios, such as vehicle networks and intelligent transportation systems, are also attracting significant interest. However, the complex outdoor environment and ambient noise are the key challenges for long-range high-speed VLC outdoor applications. To improve system performance and transmission distance, we propose to use receiver diversity technology in an outdoor VLC system. Maximal ratio combining–based receiver diversity technology is utilized in two receivers to achieve the maximal signal-to-noise ratio. A 400-Mb/s VLC transmission using a phosphor-based white LED and a 1-Gb/s wavelength division multiplexing VLC transmission using a red–green–blue LED are both successfully achieved over a 100-m outdoor distance with the bit error rate below the 7% forward error correction limit of 3.8×10−3. To the best of our knowledge, this is the highest data rate at 100-m outdoor VLC transmission ever achieved. The experimental results clearly prove the benefit and feasibility of receiver diversity technology for long-range high-speed outdoor VLC systems.

We propose and experimentally demonstrate time division multiplexed orbital angular momentum (OAM) access system to increase transmission capacity and spectral efficiency. In this system, data carried on different time tributaries share the same OAM mode. Multiple time division multiplexed OAM modes are multiplexed to realize two-dimensional (time dimension and OAM dimension) multiplexing. Therefore, the capacity and spectral efficiency of the access system will increase. The orthogonality between optical time division multiplexing (OTDM) and OAM techniques is also verified in our experiment. In a proof-of-concept experiment, 2×5-Gbps return-to-zero signal over OAM mode +4 is transmitted and investigated. The bit error ratio performance after transmission in this system can be smaller than 1×10−9. Results show that the proposed time division multiplexed OAM access system is suitable for future broadband access network.

We experimentally demonstrated single-lane EML-based IM/DD 106-Gbaud PAM-4 and PS-PAM-8 signals transmission over 1-km NZDSF based on Pre-EQ and clipping technique. 260-Gb/s PS-PAM-8 signal transmission can be achieved.

For APD or SOA pre-amplified receivers with power-dependent non-uniform noise distributions, we demonstrate an enhanced PAM-4 modulation and detection scheme with unequally spaced signal levels, achieving improved receiver sensitivity for 50-b/s/λ PON.