Power Fading Research Articles

DFT Spread Spectrally Efficient Frequency Division Multiplexing for IM-DD Transmission in C-Band

In this article, we propose and experimentally demonstrate a new discrete Fourier transform spread (DFT-S) spectrally efficient frequency division multiplexing (DFT-S SEFDM) system. DFT-S technique is adopted to reduce the peak-to-average-power-ratio (PAPR) of SEFDM signal in optical intensity modulation and direct detection (IM-DD) system for the first time. The existing detection algorithms for SEFDM signal, such as logarithmic-maximum-a-posterior (log-MAP) Viterbi and cascaded binary-phase-shift-keying iterative detection (CBID), are successfully modified to our DFT-S SEFDM system. Experimental results show that DFT-S SEFDM outperforms conventional SEFDM owing to its lower PAPR. In our test, to verify the benefits of our scheme, a net data rate of beyond 100 Gb/s can be achieved after 2-km standard single mode fiber (SSMF) transmission, and DFT-S SEFDM also can outperform DFT-S DMT owing to its tolerance to bandwidth limitation. We further verify the advantage of DFT-S SEFDM in IM-DD C-band system, and show its resistance to the impact of dispersion-induced power fading.

Irregular Shifting of RF Driving Signal Phase to Overcome Dispersion Power Fading

The main problem with the radio-over-fiber (RoF) link is the decrease in the recovered radio frequency (RF) power due to the chromatic dispersion of the fiber known as dispersion power fading. One of the methods for dealing with dispersion power fading is to use the optical single sideband (OSSB) modulation scheme. The OSSB modulation scheme can be generated by biasing the dual-drive Mach–Zehnder modulator (DD-MZM) to the quadrature bias point (QBP) and shifting the RF drive signal phase (θ) by 90°, which is called the regular θ. However, the OSSB modulation scheme only overcomes dispersion power fading well at the modulation index (m) < 0.2. This paper proposes an irregular θ method to overcome dispersion power fading at all m. There are two irregular θ for every m used. The irregular θ managed to handle dispersion power fading better than OSSB modulation scheme did at every m. Specifically, the irregular θ could handle the dispersion power fading well at m ≤ 1. In sum, the irregular θ could overcome the dispersion power fading at any RF frequency and optical wavelength without having to re-adjust the transmitter.

Photonic Radio Frequency Self-Interference Cancellation and Harmonic Down-Conversion for In-Band Full-Duplex Radio-Over-Fiber System

We report a photonic radio frequency (RF) self-interference cancellation (SIC) and harmonic down-conversion (HDC) scheme based on a dual-parallel dual-drive Mach-Zehnder modulator (DDMZM). The proposed scheme can eliminate the chromatic-dispersion induced power fading (CDIP) effect and thus is very suitable for in-band full-duplex (IBFD) radio-over-fiber (ROF) system. The self-interference RF signal is directly cancelled in optical domain, which overcomes the electronics bottleneck limitation of electrical SIC. Moreover, the HDC allows us to use a cost-effective low frequency local oscillation (LO) source to down-convert a high-frequency RF signal into an intermediate frequency (IF) band. In addition, the harmonic odd-order single-sideband (SSB) down-conversion is naturally free from the CDIP effect. The proposed photonic SIC+HDC system is theoretically analyzed and experimentally verified.

Ring‐modulator‐based RoF system with local SSB modulation and remote carrier reuse

A full-duplex radio-over-fibre (RoF) system based on an integrated silicon ring modulator is proposed and demonstrated. For the downstream link, a coherent dual-wavelength laser source is coupled to a silicon ring modulator in the central office (CO). Since only one of the optical carriers in the dual-wavelength laser source is aligned to the resonance of the ring modulator, a single sideband (SSB) modulated optical downstream signal is obtained, which is able to combat the power fading introduced by the fibre dispersion. Besides, for the upstream link, the unmodulated optical carrier in the SSB-modulated optical downstream signal is reused by using an optical filter in the remote radio head. After being modulated by the upstream data, the optical upstream signal is transmitted back to the CO. A proof-of-concept experiment is carried out. Error vector magnitudes of 21-GHz downstream and 10-GHz upstream signals are measured, which confirms that the proposed architecture is a promising low-cost solution for future high-speed wireless communication systems.

Nyquist four-level pulse amplitude modulation scheme (PAM-4) based on hierarchical modulation in IM/DD-TDM PON with hybrid equalization

In order to achieve higher power margin in the intensity-modulation and direct detection (IM/DD) based time division multiplexed passive optical network (TDM-PON) system, at the optical line terminal (OLT) side, we propose to use a Nyquist pulse shaped four-level pulse amplitude modulation (PAM-4) by using the electric low pass filter(LPF). In addition, we apply the hierarchical modulation (HM) scheme by assigning of most-significant bits (MSBs) and the less-significant bits (LSBs) of the PAM-4 symbol to optical network units (ONUs) located at different link positions. In addition, an overlap frequency domain equalizer (OFDE) and a vestigial-side band (VSB) filter are used to mitigate the linear inter symbol interference (ISI) and power fading (both of which are incurred by chromatic dispersion (CD)), respectively. The system performance, i.e., bit error rate (BER) and receiver sensitivity for both MSB and LSB, are analyzed by varying different system configurations. Simulation results show that increasing the hierarchical power ratio, which determines the significance difference between the points in the Nyquist pulse shaped HM PAM-4 constellation diagram, can increase the MSB’s receiver sensitivity and reduce the LSB’s receiver sensitivity. Furthermore, it has been demonstrated that the electric low pass filter can reduce the system ISI. In addition, the effect of linear ISI and power fading can be migrated by utilizing OFDE and VSB filter, respectively.

Chromatic dispersion immune microwave photonic phase shifter based on double-sideband modulation.

A chromatic dispersion (CD) immune microwave photonic phase shifter (MPPS) based on double-sideband (DSB) modulation is proposed and demonstrated. An optical spectrum processor introduces the phase shift to the MPPS. The DSB signals along two orthogonal polarizations are demodulated to two RF signals with both quadrature amplitude and phase items, transferring the CD-induced power fading to the phase item of the synthetic RF signals. Experimental results show that the RF signals over 14-25GHz obtain random phase shift in 360° range without a power fading point (PFP) after passing through a dispersion compensation fiber with CD of -331 ps/nm. The phase variation and power variation of the phase-shifted signal are <±5.7° and <±0.9 dB, respectively, at the original PFP at 16GHz.

All optical Millimeter-wave signal generation and transmission for radio over fiber (RoF) link

&lt;span&gt;Fiber-based wireless system has become a promising solution as a cost- effective communication and it offers high capacity network with millimeter- wave (mm-wave) signal transmission. The system significantly offers superior possible bandwidths for both fiber and free-space applications. Hence, with the increased capacity as well as wireless mobile network applications particularly at mm-wave signal, radio over fiber (RoF) technology is the utmost option. Nevertheless, when high frequency signal transmission is involved, power fading or dispersion effect limits the performance of RoF link. Therefore, this work proposed a RoF system by integrating remote optical local oscillator (LO) with frequency up-conversion at the base station (BS). All optical mm-wave signals are generated and transmitted for the RoF link. The effects of the changes of fiber loop length, optical power of the continuous wave (CW) optical laser carrier and responsivity value of the p-i-n photodiode (PD) mainly at 40 GHz are investigated and the power fading effects are discussed.&lt;/span&gt;

Symbol Error Rate Analysis of OFDM System with CFO Over TWDP Fading Channel

In this manuscript, an exact symbol error rate analysis of orthogonal frequency division multiplexing system is presented in the presence of carrier frequency offset over two wave with diffuse power (TWDP) fading channel. Both Binary Phase Shift Keying and Quadrature Phase Shift Keying modulation techniques are considered in this study over TWDP channel which contains Rayleigh, Rician and two ray fading as its special cases. The results are validated by means of Monte Carlo simulations and also verified from the benchmark results available in the literature.

Anti-chromatic dispersion transmission of frequency and bandwidth-doubling dual-chirp microwave waveform.

A photonic approach to realizing anti-chromatic dispersion transmission for a frequency and bandwidth-doubling dual-chirp microwave waveform is proposed and experimentally demonstrated. The system has no requirement on polarization devices or optical filters for only the integrated dual-drive dual-parallel Mach-Zehnder modulator employed. To overcome chromatic dispersion, the carrier frequency suppression approach is proposed. The anti-chromatic dispersion process is accomplished in a central station and independent to carrier frequency, fiber length, and dispersion coefficients. An experiment is conducted to verify the analysis. Dual-chirp waveforms at 13GHz with a bandwidth of 0.8GHz and time duration of 1μs are obtained. After 25km fiber transmission, the proposed approach shows a relatively flat curve in a frequency-power diagram, while the normally carrier-suppressed double-sideband modulation method experiences a significant power fading for fiber dispersion.

Lithium-ion battery fast charging: A review

Abstract In the recent years, lithium-ion batteries have become the battery technology of choice for portable devices, electric vehicles and grid storage. While increasing numbers of car manufacturers are introducing electrified models into their offering, range anxiety and the length of time required to recharge the batteries are still a common concern. The high currents needed to accelerate the charging process have been known to reduce energy efficiency and cause accelerated capacity and power fade. Fast charging is a multiscale problem, therefore insights from atomic to system level are required to understand and improve fast charging performance. The present paper reviews the literature on the physical phenomena that limit battery charging speeds, the degradation mechanisms that commonly result from charging at high currents, and the approaches that have been proposed to address these issues. Special attention is paid to low temperature charging. Alternative fast charging protocols are presented and critically assessed. Safety implications are explored, including the potential influence of fast charging on thermal runaway characteristics. Finally, knowledge gaps are identified and recommendations are made for the direction of future research. The need to develop reliable onboard methods to detect lithium plating and mechanical degradation is highlighted. Robust model-based charging optimisation strategies are identified as key to enabling fast charging in all conditions. Thermal management strategies to both cool batteries during charging and preheat them in cold weather are acknowledged as critical, with a particular focus on techniques capable of achieving high speeds and good temperature homogeneities.

Photonic Microwave Up-Conversion Link With Compensation of Chromatic Dispersion-Induced Power Fading

An effective scheme of frequency doubling up-conversion is proposed and demonstrated, which achieves the generation of high-frequency microwave signal and the compensation of chromatic dispersion-induced power fading (CDIPF). The system structure is based on a cascading of a Sagnac loop and a Mach–Zehnder modulator (MZM), where a phase modulator is used in the Sagnac loop. In the loop, only the clockwise propagating light wave is modulated by a small local oscillator signal, leaving the counter-clockwise propagating light wave unmodulated because of the velocity mismatch. The output signal is divided into two parts, one traveling into an MZM and the other entering an optical phase shifter. The intermediate frequency signal is supplied to the MZM, which is biased at its minimum point and then the carrier-suppressed double sideband is achieved. With the adjustment of the optical phase shift, the CDIPF can be compensated at any frequency. In the simulation, by comparing the frequency responses of the proposed link with and without dispersion compensation, we successfully demonstrate the performance of power fading compensation for 60- and 80-km link. Consequently, the spurious-free dynamic range is effectively improved by 13.54 dB at 22.6 GHz for 60-km link.

A Novel Weighted-Counter Method for Simulating Coherent TWDP Fading Channels

New channel simulation models are needed for the study of future wireless networks, 5G and beyond. A novel simulation technique dubbed weighted-counting is proposed. It is used to generate random variates having the two-wave with diffuse power (TWDP) fading amplitude distribution. The TWDP channel model describes high-speed train, femtocell, sea surface, heterogeneous, and other channels having two different dominant line-of-sight waves as well as scatter power components.

Effects of frequency chirping and finite extinction ratio of optical modulators in microwave photonic IFM receivers

Frequency-to-power mapping approach based on chromatic dispersion is frequently used in microwave photonic (MWP) instantaneous frequency measurement (IFM) receivers. In this technique, carrier frequency of an unknown microwave signal is estimated according to a specific relationship between the unknown microwave frequency and the ratio of two optical or microwave power functions which is known as amplitude comparison function (ACF). The ACF can be constructed using chromatic dispersion-induced power fading functions of intensity- or phase-modulated optical signals transmitting through dispersive mediums. Practical non-ideal intensity modulators have finite extinction ratio and suffer from frequency chirping. Despite previously published numerous works, the contribution of these parameter in MWP IFMs have not been already studied. In this paper, effects of chirp parameter and finite extinction ratio of intensity modulators on the performance of chromatic dispersion-based MWP IFM receivers are theoretically investigated. It is shown that in general the ACFs of these MWP IFM receivers depend on the chirp parameter of their intensity modulators which is a function of unknown amplitude of the microwave signal whose frequency is intended to be measured and varies with time. This problem cannot be resolved by calibrations and degrades the measurement accuracy. Besides, it is shown that ACFs are different for different finite extinction ratios which degrades the measurement accuracy. Finally, we propose using Mach–Zehnder interferometer (MZI)- and Sagnac interferometer (SI)-based intensity modulators with zero chirp in these MWF IFMs. Analytical results are verified by computer simulations using OptiSystem software.

IM/DD Beyond Bandwidth Limitation for Data Center Optical Interconnects

Intensity modulation with direct detection (IM/DD) provides a low-cost solution for data center optical interconnects. To achieve higher data rate, Tomlinson–Harashima precoding (THP) is adopted to increase the operating symbol rate beyond the Nyquist rate defined by the system bandwidth. By applying THP, the signal is precoded by a feedback filter at the transmitter for the mitigation of the intersymbol interference caused by the faster-than-Nyquist signaling and the spectral power fading induced by the interaction of chromatic dispersion and direct detection. In this paper, high-performance THP-based IM/DD transmission is demonstrated, increasing the achievable data rate using a limited system bandwidth. In the experimental demonstration, we achieve a net bit rate of 185 Gb/s for up to 2-km fiber link, transmitting 74 GBd precoded eight-level pulse amplitude modulation (PAM-8) using an IM/DD system with 33 GHz brick-wall electrical bandwidth limitation.

Analysis of the Current Electric Battery Models for Electric Vehicle Simulation

Electric vehicles (EVs) are a promising technology to reduce emissions, but its development enormously depends on the technology used in batteries. Nowadays, batteries based on lithium-ion (Li-Ion) seems to be the most suitable for traction, especially nickel-manganese-cobalt (NMC) and nickel-cobalt-aluminum (NCA). An appropriate model of these batteries is fundamental for the simulation of several processes inside an EV, such as the state of charge (SoC) estimation, capacity and power fade analysis, lifetime calculus, or for developing control and optimization strategies. There are different models in the current literature, among which the electric equivalent circuits stand out, being the most appropriate model when performing real-time simulations. However, impedance models for battery diagnosis are considered very attractive. In this context, this paper compares and contrasts the different electrical equivalent circuit models, impedance models, and runtime models for battery-based EV applications, addressing their characteristics, advantages, disadvantages, and usual applications in the field of electromobility. In this sense, this paper serves as a reference for the scientific community focused on the development of control and optimization strategies in the field of electric vehicles, since it facilitates the choice of the model that best suits the needs required.

Simplified Chromatic Dispersion Model Applied to Ultrawide Optical Spectra for 60 GHz Radio-Over-Fiber Systems

Radio-over-fiber systems can be harnessed to generate millimeter-wave (mm-wave) frequencies, but the optical impairments such as optical noise, chromatic dispersion, and nonlinearity can degrade the quality of the generated heterodyne signals. When optical frequency comb sources are employed, chromatic dispersion has a main importance since it causes a phase shift and phase decorrelation between optical lines. These both effects subsequently induce power fading and also optical noise on the beat note carrier. With utilizing ultrawide optical spectra, higher order dispersion coefficients must be considered during the propagation across optical fiber, which introduces a high level of complexity in the analytic model. In this paper, we present a simple and convenient model to analyze the impact of chromatic dispersion on the power of the mm-wave heterodyne carrier. The proposed model manipulates and integrates the higher order dispersion terms into an equivalent second-order dispersion term. This allows to perform the easiest way to calculate the propagation constant. Simulation and experimental results are conducted for fiber distance up to 30 km in order to validate the suggested model in terms of the carrier power. Through the results obtained, the well-known behavior between the signal power and chromatic dispersion can be modified. Optical phase shift results in a diverse power fading and intensity noise while optical phase de-correlation manifests phase noise. Therefore, data transmission over 25 km fiber is carried out to show the impact of chromatic dispersion on optical noise of the beating carrier. RF power and error vector magnitude reveal that the chromatic dispersion can overcome power fading and increase the tolerance to fiber length with limiting the optical noise in the optical heterodyning system.

Chirp Compensation of Directly Modulated 3s-DBR Laser for WDM-RoF-Based Mobile Fronthaul

In this letter, we propose and demonstrate through simulations, a chirp compensation scheme with a directly modulated three section distributed Bragg reflector (3s-DBR) laser, for use in a WDM-RoF-based mobile fronthaul network to eliminate the signal distortion caused by the interplay between laser chirp and fiber dispersion, including RF power fading and the composite second-order (CSO) distortion. Employing the phase section characteristics of the 3s-DBR laser, the frequency chirp of the device is reduced with reverse modulation current injection into the phase section. The simulation results show that with the chirp compensation scheme, reduced DBR laser chirp can be achieved, and error vector magnitude (EVM) of a 12 channel 211-MHz bandwidth filtered-OFDM (f-OFDM) signal with 64-QAM after transmission over 20-km standard single mode fiber (SSMF), can still satisfy the 3rd generation partnership project’s (3GPP) requirement.

Multi-IF-Over-Fiber System With Adaptive Frequency Transmit Diversity for High Capacity Mobile Fronthaul

In this paper, we present and experimentally demonstrate a broadband intermediate frequency-over-fiber (IFoF) system with adaptive frequency transmit diversity for the next generation mobile fronthaul (MFH) applications. We propose to employ an integrated dual-parallel Mach-Zehnder Modulator (DPMZM) with adaptive dc-bias voltage setting for a simplified, efficient, and flexible IFoF communication system. The DPMZM is utilized to compensate the chromatic dispersion (CD) induced deep RF power fading impact, by taking advantage of the frequency transmit diversity of the two parallel modulators and optical paths. Using probe signals and the supervised machine learning (ML) technique, an accurate frequency response of the system is generated and utilized to design a dynamic allocation of IF channels to each DPMZM port. This ML-based link frequency response can capture the accumulated CD-induced power fading frequency region, as well as the random degradation caused by the used RF and optical devices characteristics and bandwidth limitation. Applying our proposed system, we successfully transmitted 15 IF channels with 1.2 GHz bandwidth and 64-QAM-OFDM modulated signals over 20-km fiber length, leading to about 1.18 Tbps CPRI-equivalent data rate. If we assume the maximum spectral efficiency of the LTE-A systems (i.e., 3.75 bit/s/Hz), the user throughput can be higher than 67 Gb/s. The obtained results show the potentials of DPMZM-based multi-IFoF system to satisfy the high capacity requirement of 5G mobile network and beyond.

Iterative Block Decision Feedback Equalization for IM/DD-Based OCDM to Compensate Chromatic-Dispersion-Induced Power Fading

Orthogonal chirp-division multiplexing (OCDM) has recently been proposed as an attractive modulation technique for high-speed fiber-optic systems in virtue of its resilience against system impairments. In this paper, we propose an iterative block (IB) decision feedback equalization (DFE) algorithm for the intensity-modulation and direct-detection (IM/DD) based OCDM system to effectively mitigate the chromatic-dispersion (CD) induced power fading in the fiber. An efficient algorithm is derived to simplify the IB-DFE at the receiver. Analysis is provided to show that the fading effect is compensated by recovering the noisy signals in the vicinity of frequency notches. Simulations were carried out to study the performance of the proposed system. The results show that the proposed system with IB-DFE is able to compensate severe fading effects and improves the bit error rate (BER) by several orders of magnitude. An experiment was implemented to realize 30.3-Gb/s IM/DD-OCDM signal over 50-km fiber, in which power fading due to CD over 20 dB was observed. The experiment results show that the proposed system further reduced the required optical signal-to-noise ratio by 8 dB to achieve a BER of 3 × 10−5.

Compensation of dispersion-induced power fading with adjustment-free operation

A scheme for compensation of dispersion-induced power fading is proposed and experimentally demonstrated. The system transmits two modulated laser lights via a wavelength division multiplexer and a wavelength division demultiplexer. By optimizing the power ratio and the phase difference between the two modulated signals, the dispersion-induced power fading can be adequately compensated. A key significance of our approach is that no adjustments are required when the input radio frequency signal scans over a broad bandwidth of 1 to 12 GHz. We successfully demonstrate the compensation of the power fading for both 20- and 30-km fiber links. An improvement of spurious-free dynamic range is also achieved.