Precompensation Technique Research Articles

Odd-even symbol dispersion pre-compensation technique utilizing interleaved dual-FIR filters in IM-DD systems.

An interleaved odd and even samples electrical dispersion pre-compensation (pre-EDC) scheme with low complexity is proposed to alleviate the severe distortions caused by frequency-selective fading due to chromatic dispersion (CD) in the intensity-modulation and direct-detection (IM-DD) optical transmission systems. This scheme utilizes training-based interleaved dual finite impulse response (FIR) filters for odd and even samples pre-compensation, respectively, referred to as training-based ID FIRs-pre-EDC. Additionally, a Tx and Rx side joint scheme is proposed to enhance the performance of the training-based ID FIRs-pre-EDC by implementing the efficient reduced state maximum likelihood sequence estimation (RS-MLSE) at the receiver side. Experimental validations in a C-band 56 Gbit/s PAM-4 80 km standard single-mode fiber (SSMF) transmission system show that the training-based ID FIRs-pre-EDC achieves over 0.95 dB receiver sensitivity improvement at the 7% hard-decision forward error correction (HD-FEC) threshold compared to traditional FIR-pre-EDC schemes. Employing the proposed joint scheme obtains ∼3 dB receiver sensitivity gain at the 7% HD-FEC threshold compared with only implementing training-based ID FIRs-pre-EDC at the transmitter side. These results indicate the potential and feasibility of the proposed schemes in optical interconnects.

Optical wireless channel reciprocity-based temporal power allocation technique for FSO communications

We propose a temporal power allocation technique for optical transmitting power using the average limiting property of an erbium-doped fiber amplifier to secure the degradation of communication performance due to the turbulence effect of the FSO vertical link. Unlike the existing turbulence degradation prevention technology, the FSO channel reciprocity-based pre-compensation technique proposed in this study can overcome degradation caused by strong channel fading and maintain the quality of the transmission signal through sufficient transmitted power. The proposed technique was demonstrated using simulations and experiments. The transmission performance was effectively enhanced by applying the proposed technique.

High-power linear-polarization burst-mode all-fibre laser and generation of frequency-adjustable microwave signal

Abstract Narrowband microwave generation with tuneable frequency is demonstrated by illuminating a photoconductive semiconductor switch (PCSS) with a burst-mode fibre laser. The whole system is composed of a high-power linearly polarized burst-mode pulsed fibre laser and a linear-state PCSS. To obtain a high-performance microwave signal, a desired envelope of burst is necessary and a pulse pre-compensation technique is adopted to avoid envelope distortion induced by the gain-saturation effect. Resulting from the technique, homogenous peak power distribution in each burst is ensured. The maximum energy of the laser burst pulse reaches 200 μJ with a burst duration of 100 ns at the average power of 10 W, corresponding to a peak power of 4 kW. When the PCSS is illuminated by the burst-mode fibre laser, narrowband microwave generation with tuneable frequency (0.80–1.12 GHz) is obtained with a power up to 300 W. To the best of the authors’ knowledge, it is the first demonstration of frequency-tuneable narrowband microwave generation based on a fibre laser. The high-power burst-mode fibre laser reported here has great potential for generating high-power arbitrary microwave signals for a great deal of applicable demands such as smart adaptive radar and intelligent high-power microwave systems.

Distribution of high-dimensional orbital angular momentum entanglement over a 1 km few-mode fiber

High-dimensional entanglement has demonstrated its potential for increasing channel capacity and resistance to noise in quantum information processing. However, distributing it is a challenging task, imposing severe restrictions on its application. Here we report the first distribution of three-dimensional orbital angular momentum (OAM) entanglement via a 1-km-long few-mode optical fiber. Using an actively stabilizing phase precompensation technique, we successfully transport one photon of a three-dimensional OAM entangled photon pair through the fiber. The distributed OAM entangled state still shows a fidelity up to 71% with respect to the three-dimensional maximally entangled state (MES). In addition, we certify that the high-dimensional quantum entanglement survives the transportation by violating a generalized Bell inequality, obtaining a violation of ∼ 3 standard deviations from the classical limit with I 3 = 2.12 ± 0.04 . The method we developed can be extended to a higher OAM dimension and larger distances in principle. Our results make a significant step towards future OAM-based high-dimensional long-distance quantum communication.

Decentralized Tracking Optimization Control for Partially Unknown Fuzzy Interconnected Systems via Reinforcement Learning Method

In this article, a novel parallel tracking control optimization algorithm is first proposed for partially unknown fuzzy interconnected systems. In the existing standard optimal tracking control, the bounded or nonasymptotic stable reference trajectory will lead the feedback control not converging to zero, which causes the performance index infinite and invalid. By using the precompensation technique, in this article, the working feedback control is considered as a reconstructed dynamic with the virtual control and a new augmented fuzzy interconnected tracking system is built, thus that the performance index is valid for optimal control. Then, combining the integral reinforcement learning (RL) method and decentralized control design, the novel integral RL parallel algorithm is first developed to solve the tracking controls for interconnected systems, which relax the requirements of exact matrices information A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sup> and B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sup> during the solving process. Both the convergence and stability of the designed control optimization scheme are guaranteed by theorems. Finally, the new parallel tracking algorithm for interconnected systems is verified through the dual-manipulator coordination system and simulation results demonstrate the effectiveness.

Lattice Reduction Aided Precoding Design in Downstream G.fast DSL Networks

As a non-linear precoding alternative to Tomlinson-Harashima precoding (THP), in this paper, so-called lattice reduction aided precoding (LRP) is considered as a crosstalk precompensation technique for downstream transmission in G.fast DSL networks. First, a practically achievable bit-rate expression for LRP is proposed in function of the precoder and integer matrix. The problem then consists of a joint precoder and integer matrix design in order to maximize the weighted sum-rate (WSR) under per-line power constraints. For a fixed integer matrix, zero-forcing (ZF) precoder matrix design simplifies to gain scaling optimization with complex gain scalars, for which a successive lower bound maximization method is presented. Additionally, it is established that the achievable ZF-LRP sum-rate is upper bounded by the achievable ZF-THP sum-rate at high SNR. For computing the optimal precoder matrix, on the other hand, an efficient method is developed by leveraging on the equivalence between the WSR maximization and the weighted sum of mean squared error (MSE) minimization, leading to a locally-optimal MMSE-LRP solution. Simulations with a measured G.fast cable binder are provided to compare the proposed LRP schemes with THP schemes.

Fuzzy adaptive dynamic programming-based optimal leader-following consensus for heterogeneous nonlinear multi-agent systems

In this paper, a novel online iterative scheme, based on fuzzy adaptive dynamic programming, is proposed for distributed optimal leader-following consensus of heterogeneous nonlinear multi-agent systems under directed communication graph. This scheme combines game theory, adaptive dynamic programming together with generalized fuzzy hyperbolic model (GFHM). Firstly, based on precompensation technique, an appropriate model transformation is proposed to convert the error system into augmented error system, and an exquisite performance index function is defined for this system. Secondly, on the basis of Hamilton–Jacobi–Bellman (HJB) equation, the optimal consensus control is designed and a novel policy iteration (PI) algorithm is put forward to learn the solutions of the HJB equation online. Here, the proposed PI algorithm is implemented on account of GFHMs. Compared with dual-network model including critic network and action network, the proposed scheme only requires critic network. Thirdly, the augmented consensus error of each agent and the weight estimation error of each GFHM are proved to be uniformly ultimately bounded, and the stability of our method has been verified. Finally, some numerical examples and application examples are conducted to demonstrate the effectiveness of the theoretical results.

Approximate neural optimal control with reinforcement learning for a torsional pendulum device

A torsional pendulum device containing hyperbolic tangent input nonlinearities can be formulated as a nonaffine system. Unlike basic affine systems, the optimal feedback control of complex nonaffine plants is difficult but quite important. In this paper, the approximate optimal control design of continuous-time nonaffine nonlinear systems is investigated with the help of reinforcement learning. For addressing the learning algorithm conveniently, an effective pre-compensation technique is adopted to perform proper system transformation. Then, the integral policy iteration strategy is incorporated to relieve the demand of system dynamics. Moreover, the actor–critic structure is implemented by virtue of neural network approximators. Finally, the experimental verification for the proposed torsional pendulum plant is conducted after a learning process of 20 iterations and the stability performance with basic robustness guarantee can be observed during two case studies.

Adaptive reversible watermarking for authentication and privacy protection of medical records

Medical systems, such as PACS or scanners, are vulnerable to security and forgery attacks. Consequently, medical records, such as patient information and medical imagery, can be easily leaked or forged. Reversible watermarking is an efficient solution used to protect medical records. However, previous studies have not sufficiently addressed medical applications. This study proposes an adaptive reversible watermarking algorithm that is directly applicable to medical systems that preserves the quality of medical imagery. In particular, the characteristics of medical imagery are considered. Once object and background regions are segmented, the reversible watermarking algorithm is applied based on an estimated error expansion approach. The watermark is embedded by expanding the estimated error from adjacent pixels. This watermark can include patient information or a hash code to detect forgery. When the watermark is extracted, original imagery is perfectly reconstructed without any quality degradation. Inherent over- and underflow problems are solved using an error pre-compensation technique. With the use of medical images from MRI, CT, and X-ray scanners, intensive experiments are performed to analyze the performance of the proposed algorithm with respect to capacity, perceptual quality, and reconstruction rate.

Vector Modulation by Laser and Electroabsorption Modulator With Digital Pre-Coding and Pre-Compensation

We present a method to achieve vector modulation of lightwave using an electroabsorption modulator intregrated laser. The laser section is used for direct phase modulation followed by an amplitude modulation of the electroabsorption modulator section in a cascade manner, which is an alternative method to conventional IQ modulator. To allow an improved phase demodulation, we propose a digital pre-compensation technique for a transmitter in optical coherent system for the first time, which includes a phase-balanced differential phase shift keying encoding and a digital domain pre-equalization filtering. The phase-balanced encoding technique applies parallel DC-balance coding with a phase-balanced symbol mapping, which results in a bounded cumulative phase and a constant statistical characteristic of the modulating signal in differential M-ary phase shift keying and M-ary quadrature amplitude modulation formats. The digital pre-equalization filter also compensates for the phase response of the laser section. Experimental results show that the pre-digital compensation technique allows the improved complex signal demodulation compared to conventional DQPSK modulation in a back-to-back setup.

Digital pre-compensation techniques enabling high-capacity bandwidth variable transponders

Digital pre-compensation techniques are among the enablers for cost-efficient high-capacity transponders. In this paper we describe various methods to mitigate the impairments introduced by state-of-the-art components within modern optical transceivers. Numerical and experimental results validate their performance and benefits.

Agile Single- and Dual-Band All-Digital Transmitter Based on a Precompensated Tunable Delta–Sigma Modulator

In this paper, a new architecture for designing tunable single- and dual-band radio-frequency fully digital transmitters is proposed and validated. The proposed architecture excels the state of the art in terms of simplicity and flexibility. While its short critical path leverages the use of equivalent polyphase decomposition techniques to increase the global system’s sampling frequency, the capability of changing the system’s frequency response in real time enables its use in both single- and dual-band transmission scenarios. To mitigate a crosstalk in the dual-band scenario, a precompensation technique is also proposed. This novel concept has been successfully validated in a field-programmable gate array (FPGA) based transmitter. To validate both the proposed transmitter as well as the precompensation mechanism, spectrum and error-vector magnitude (EVM) measurements were obtained for two scenarios with a carrier frequency of 2.5 GHz: 1) single-band, using quadrature phase-shifting keying (QPSK), 16-quadrature amplitude modulation (QAM) and 64-QAM, with no intermediate frequency (IF), for different symbol rate (SR) values (from 3.125 up to 15.625 Msps) and 2) single- and dual-band, using QPSK and 16-QAM, with an SR of 3.125 Msps, for different IF values (from 2 up to 120 MHz). All the experimental results present EVM values below 2.6%, resulting in a well-defined constellation.

Photonic-Assisted Error-Free Wireless Communication With Multipath Precompensation Covering 2–18 GHz

A wireless communication experiment that uses photonic-assisted radio-frequency arbitrary waveform generation (RF-AWG) for precompensation of multipath distortion over a 2-18 GHz frequency band is reported. Photonic-assisted RF-AWG is used both for spread spectrum sounding of the multipath channel and for synthesis of precompensation waveforms that yield pulse compression and distortion suppression at the receiver. By directly encoding the precompensated waveforms in optical hardware, 250 Mbit/s error-free data transmission is achieved experimentally in binary-phase-shift-keying format. For the first time to our knowledge, phase compensation and time reversal precompensation techniques are compared in hardware encoded data transmission experiments; our results confirm predictions that phase compensation outperforms time reversal under intersymbol interference limited conditions.

Analysis of WDM System With Dispersion Compensation Schemes

One of the major factors that limit the performance of a WDM system is dispersion. Use of Dispersion Compensating Fiber (DCF) is the most common method for dispersion compensation in WDM systems. In this work, the performance of a WDM system at 8Gbps employing different dispersion compensation schemes using DCF (pre compensation, post compensation and symmetrical compensation techniques) are analyzed in terms of BER and Q factor. Analysis of WDM system with NRZ and RZ modulation format is also done. It is found that a WDM system using RZ modulation format and employing symmetrical compensation scheme provides best performance.

Bandwidth-constrained digital pre-compensation technique for multi-carrier satellite communications

Summary A wide variety of imperfections impact end-to-end performance in multiple-carrier per transponder transparent satellite links. Analysis of the link architecture leads to the identification of the sources and characteristics of distortion experienced by a typical multi-carrier signal. This paper introduces a new remote pre-compensation technique that takes this analysis into account to compensate for the specific distortion that occurs in the satellite channel. The proposed technique succeeds in compensating both linear and nonlinear channel distortions while overcoming the numerous challenges associated with remote waveform predistortion. Excellent linearisation performance has been observed across a wide range of link scenarios, even for high power amplifiers already linearised in the analogue domain. In addition, through an extensive end-to-end simulation campaign and a field programmable gate array implementation of the new algorithms, feasibility of the technique has been verified. Copyright © 2015 John Wiley & Sons, Ltd.

Two-Dimensional Magnetic Recording With a Novel Write Precompensation Scheme for 2-D Nonlinear Transition Shift

This paper proposes a novel write precompensation scheme that adjusts the current magnitude, not the timing, to mitigate the serious 2-D nonlinear transition shift (NLTS) during the shingled writing process in a two-dimensional magnetic recording (TDMR) system. This scheme calculates the needed optimum write field for the current transition being written by subtracting the demagnetizing field produced by the previous written bits from a fixed write field and determines the optimum writing current based on the minimum mean-squared-error criterion between the needed field and the available fields within an established field library. Such a write precompensation scheme is tested with a micromagnetic writer and exchange coupled composite media, and readback with a rotated reader array combined with a read channel. Simulation indicates that the proposed write precompensation technique can decrease bit error rate compared with the case without write precompensation and approach the performance of a system with negligible NLTS. Correspondingly, the maximum user areal density is increased from 3.2 to 4.1 Tbits/in $^{\mathrm {\mathbf {2}}}$ for a TDMR system with 8 nm Voronoi grains due to the proposed write precompensation.

Digital linear pre‐compensation technique to enhance predistortion performance in multicarrier DVB‐S2 satellite communication systems

Nonlinearity in communication satellite payloads often severely degrades the downlink signal quality in such systems. A digital pre-compensation technique to enhance digital predistortion performance in multicarrier satellite communication systems is presented. The proposed technique has been validated by simulations with an appropriate platform where excellent performance improvements have been measured. In addition, the implementation feasibility of this technique has been briefly demonstrated by means of a real-time FPGA implementation.

Broadband Impairment Compensation in Hybrid Fiber-Wireless OFDM Long-Reach PONs

This paper proposes and demonstrates experimentally the broadband transmission impairment compensation in optical and electrical domain, enabling the provision of a bundle of simultaneous services using orthogonal frequency division multiplexing (OFDM) modulation in hybrid wireless-optic networks. The combination of electrical pre-compensation and fixed optical dispersion compensation is assessed in long-reach passive optical networks (LR-PONs): i) An electrical pre-compensation technique using extra RF-pilots located in the free spectrum of a bundle of OFDM-based services is proposed to evaluate the response of the transmission channel. The impact of the number of extra RF-pilots and the digital signal processing algorithm used for channel estimation is analyzed experimentally for different configurations. Using the proposed electrical pre-compensation technique, an error vector magnitude (EVM) improvement of 5.2 dB in the higher frequency OFDM signal is achieved. The electrical compensation enables the long-reach transmission at 100 km of simultaneous long term evolution (LTE), worldwide interoperability for microwave access (WiMAX) and ultra wideband (UWB) signals and an I/Q OFDM signal providing GbE connectivity. ii) Fixed optical dispersion compensation is used to overcome partly the dispersion-induced impairments of the long-reach transmission. With the combination of electrical and optical impairment compensation approaches, we demonstrate that the electrical compensation technique is able to counterbalance the residual dispersion of the optical access network. An EVM fluctuation below 1 dB is obtained for residual dispersion values ranging from -425 to 425 ps/nm. The EVM of the highest frequency UWB signal centered at 4.49 GHz is improved by 8.8 dB when using the combination of electrical and optical compensation, enabling the simultaneous transmission of the bundle of OFDM-based signals in a 125 km LR-PON.

Simulation and analysis of dispersion compensation schemes for 100 Gbps PDM–OFDM optical communication system

In this paper, the implementation of 100Gbps optical communication system exploiting polarization diversity at transmitter and receiver is developed and investigated with pre-, post- and symmetrical dispersion compensation schemes by using dispersion shifted and dispersion compensated fibers through simulations to optimize high data rate optical transmission. Motivation to the current analysis is to compare all 3 compensation schemes and it's found that the pre compensation technique is superior to post and symmetrical compensation techniques in 100Gbps PDM–OFDM communication system. On examination of symmetrical and post dispersion compensation schemes, it's found that the later is superior to the previous in this case. A 100Gbps coherent optical OFDM workplace has been discovered in which two 50Gbps data streams are combined into one wavelength by polarization beam combiner. By comparing one can get a promising system to the symmetrical high capacity access network with high spectral efficiency, cost effective, good flexibility.

DPSK Modulated (Tbit/s) Transmission Incorporating Dispersion-compensated Hybrid Amplifier

The simulative implementation of differential phase shift keying (DPSK) modulated data transmission incorporating single-pump highly efficient dispersion compensated Raman/EDFA hybrid amplifier is demonstrated. The simulative results are discussed to compare two different types of configurations of dispersion compensated 16-channel wavelength division multiplexing (WDM) system to achieve transmission of Tbit/s data. In pre-compensation technique, dispersion compensated fiber (DCF) is used prior to fiber Raman amplifier (FRA) (Type I) and in post-compensation technique; the DCF is used after FRA (Type II) in a WDM optical communication system. The pumped dispersion shifted fiber (DSF) is in use to act as FRA amplifier. The performance characteristics such as Q factor, BER and eye closure penalty are premeditated to realize the ultra high speed WDM systems by employing DCF based FRA together with DPSK modulation. From simulated results, it is recommended to implement Type I over Type II to realize the feasibility of such high speed WDM systems.