Compensation Of Impairments Research Articles

SOA‐based AOWC of 128QAM using Gaussian pulse shaping for transmission system with 227 Gbps

AbstractWe demonstrate an ultra‐high‐speed transmission system‐based, all‐optical wavelength conversion using Gaussian pulse shaping and 128 quadrature amplitude modulation. In this system, the modulated ultra‐high‐speed, photonic‐carrier signals with the modulation format of 128 quadrature amplitude modulation are coupled with the outputs of the double pump lasers, and amplified by nonlinear, all‐optical processing via a semiconductor optical amplifier. The transmission system with the wavelength conversion from 193.4 to 193.19 THz is then achieved. By the compensation of transmission impairments based on the digital signal processing algorithms, the single‐carrier signals with the converted wavelength of 193.19 THz are transmitted over the standard single‐mode fiber with the bit rate of 227 Gbps. In addition, the transmission performances influenced by the optical signal‐to‐noise ratio, injection current of the semiconductor optical amplifier, and the bandwidth of the Gaussian optical filter are analyzed. The relationship curves about bit error rate and error vector magnitude under different conditions are given, and the relationship between bit error rate and error vector magnitude is demonstrated.

Augmented Real-Valued Time-Delay Neural Network for Compensation of Distortions and Impairments in Wireless Transmitters.

A digital predistorter, modeled by an augmented real-valued time-delay neural network (ARVTDNN), has been proposed and found suitable to mitigate the nonlinear distortions of the power amplifier (PA) along with modulator imperfections for a wideband direct-conversion transmitter. The input signal of the proposed ARVTDNN consists of Cartesian in-phase and quadrature phase ( I/Q ) components, as well as envelope-dependent terms. Theoretical analysis shows that the proposed model is able to produce a richer basis function containing both the desired odd- and even-order terms, resulting in improved modeling capability and distortion mitigation. Its actual performance has been validated through extensive simulations and experiments. The results show that the compensation and hardware impairment mitigation capabilities of the ARVTDNN are superior to the existing state-of-the-art real-valued focused time-delay neural network (RVFTDNN) by 3-4 dB for the adjacent channel power ratio and by 2-3 dB in terms of the normalized mean square error. Other important features of the proposed model are its reduced complexity, in terms of the number of parameters and floating-point operations, and its improved numerical stability compared to the RVFTDNN model.

Comparison of Low Complexity Coherent Receivers for UDWDM-PONs ($\lambda$-to-the-User)

It is predicted that demand in future optical access networks will reach multigigabit/s per user. However, the limited performance of the direct detection receiver technology currently used in the optical network units at the customers’ premises restricts data rates per user. Therefore, the concept of coherent-enabled access networks has attracted attention in recent years, as this technology offers high receiver sensitivity, inherent frequency selectivity, and linear field detection enabling the full compensation of linear channel impairments. However, the complexity of conventional (dual-polarization digital) coherent receivers has so far prevented their introduction into access networks. Thus, to exploit the benefits of coherent technology in access networks, low complexity coherent receivers, suitable for implementation in ONUs, are needed. In this paper, the recently proposed low complexity coherent (i.e., polarization-independent Alamouti-coding heterodyne) receiver is, for the first time, compared in terms of its minimum receiver sensitivity with five previously reported receiver designs, including a detailed discussion on their advantages and limitations. It is shown that, of all the configurations considered, the Alamouti-coding based receiver approach allows the lowest number of photons per bit (PPB) transmitted (with a lower bound of 15.5 PPB in an ideal implementation of the system), while requiring the lowest optical receiver hardware complexity (in terms of the optical component count). It also exhibits comparable complexity to the currently deployed direct-detection receivers, which typically require over 1000 PPB. Finally, a comparison of experimentally achieved receiver sensitivities and transmission distances using these receivers is presented. The highest spectral efficiency and longest transmission distance at the highest bit rate (10 Gb/s) was reported using the Alamouti-coding receiver, which is also the only one, to date, to have been demonstrated in a full system bidirectional transmission.

OLS-Based RBF Neural Network for Nonlinear and Linear Impairments Compensation in the CO-OFDM System

For the first time, we propose and experimentally verify a novel low-complexity orthogonal least square (OLS) based radial basis function (RBF) neural network (NN) nonlinear equalizer for high-speed coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Its ability to compensate nonlinear impairments as well as linear impairments is comprehensively evaluated and compared with the linear equalizer. The impact of training overhead on system performance is also investigated. Results show that in a single-channel 40-Gb/s 16-quadrature amplitude modulation CO-OFDM system, with the training overhead of 4%, the maximum transmission distance is extended to 800 km at Q threshold of 8.7 dB, and RBF-NN outperforms the linear equalizer by 2.8 and 5.6 dB Q -factors after 800 and 600 km transmissions, respectively.

Upper Limb Coordination in Individuals With Stroke: Poorly Defined and Poorly Quantified

Background. The identification of deficits in interjoint coordination is important in order to better focus upper limb rehabilitative treatment after stroke. The majority of standardized clinical measures characterize endpoint performance, such as accuracy, speed, and smoothness, based on the assumption that endpoint performance reflects interjoint coordination, without measuring the underlying temporal and spatial sequences of joint recruitment directly. However, this assumption is questioned since improvements of endpoint performance can be achieved through different degrees of restitution or compensation of upper limb motor impairments based on the available kinematic redundancy of the system. Confusion about adequate measurement may stem from a lack a definition of interjoint coordination during reaching. Methods and Results. We suggest an operational definition of interjoint coordination during reaching as a goal-oriented process in which joint degrees of freedom are organized in both spatial and temporal domains such that the endpoint reaches a desired location in a context-dependent manner. Conclusions. In this point-of-view article, we consider how current approaches to laboratory and clinical measures of coordination comply with our definition. We propose future study directions and specific research strategies to develop clinical measures of interjoint coordination with better construct and content validity than those currently in use.

Transmitter Linearization Adaptable to Power-Varying Operation

This paper presents the design of a power-scalable digital predistorter (DPD) for transmitter architectures. The target is to accomplish the joint compensation of impairments due to the I/Q modulator and nonlinearities associated with the power amplifier, and procure a maintained linearization performance in a range of average working operation levels. The identification method for the linearizer parameters enriches the standard least-squares procedure with a synergistic integration with sparsity-based model pruning strategies. The method has been tested with a general complex-valued Volterra model applied to the linearization of two communications transmitters operating at 3.6 GHz. The linearizers designed for the two transmitters effectively provide the joint compensation of the nonlinear behavior. In addition to their good performance in terms of adjacent channel power ratio, the DPDs exhibit a wide range of power-varying adaptation.

Cartesian augmented Hammerstein model for non‐linearity and I/Q impairments compensation in concurrent dual‐band transmitters

In this study, a novel model for the joint compensation of dual-band power amplifier (PA) distortion and in-phase/quadrature (I/Q) imbalance, which are the dominant impairments of wireless signal transmitters, in a complexity reduced structure is proposed. This model is mainly based on the augmented Hammerstein approach in a Cartesian form so that a static block is intended to model the PA non-linearity and the modulator I/Q imbalance while a finite impulse response filter based block is used to model the PA memory effects. The proposed approach reduces significantly the complexity of the proposed model compared with the recently published memory polynomial models. Experiments with and without I/Q modulator impairments have been carried out on a dual-band PA to verify the accuracy and the performance of the linearisation technique based on the proposed model. The experimental results have revealed a good impairments reduction with much less model coefficients compared with the recently published ones.

The interpretation of the amended RAF Act 56 of 1996 and the regulations thereto by the courts with regard to "serious injury" claims.

The RAF Amendment Act 19 of 2005 came into effect on 1 August 2008 and sections 17(1) and 17(1A) introduced the concept of “serious injury”. This entails that a third-party claimant who wishes to claim compensation for non-patrimonial loss suffered after a motor-vehicle accident has to prove that his or her injury is “serious”. If the claimant’s injury is not considered “serious” no compensation will be awarded for the non-patrimonial loss suffered and, furthermore, the claimant will also not be entitled to claim any compensation from the wrongdoer in terms of common law (s 21 of the RAF Act). In a sequence of unreported cases the courts have provided guidelines on the procedure to be followed in serious-injury claims. Firstly, a claimant must submit himself or herself to an assessment by a medical practitioner registered under the Health Professions Act. Secondly, the medical practitioner must assess if the injuries sustained by the claimant fall within the list of “non-serious injuries”, and if so, compensation for non-patrimonial loss will not be awarded. If the injury is not on the list of non-serious injuries, the medical practitioner may assess the injuries and if they result in 30 per cent or more of whole-person impairment (“WPI”) compensation for non-patrimonial loss may be awarded. If the evaluation is that the 30 per cent of WPI cannot be reached, non-patrimonial loss may still be claimed if the injuries fall within the “narrative test”, namely (a) resulting in a serious long-term impairment or loss of a body function; (b) constituting permanent serious disfigurement; (c) resulting in severe long-term mental or severe long-term behavioural disturbance or disorder; or (d) resulting in the loss of a foetus. A plaintiff may use either of the two tests to establish serious injury and in such a manner qualify for compensation for non-patrimonial loss. A medical practitioner must complete and submit a serious-injury assessment report on the RAF 4. If the RAF is not satisfied that the injury has been correctly assessed they must (a) reject the serious-injury assessment report within 60 days and furnish reasons for the rejection; or (b) direct that the third party submit himself or herself, at the cost of the Fund, to a further assessment. Thereafter the RAF must either accept the further assessment or dispute the further assessment within 90 days. An Appeal Tribunal, consisting of three independent medical practitioners, has been created to hear these disputes.

Autophagy compensates impaired energy metabolism in CLPXP-deficient Podospora anserina strains and extends healthspan.

SummaryThe degradation of nonfunctional mitochondrial proteins is of fundamental relevance for maintenance of cellular homeostasis. The heteromeric CLPXP protein complex in the mitochondrial matrix is part of this process. In the fungal aging model Podospora anserina, ablation of CLPXP leads to an increase in healthy lifespan. Here, we report that this counterintuitive increase depends on a functional autophagy machinery. In PaClpXP mutants, autophagy is involved in energy conservation and the compensation of impairments in respiration. Strikingly, despite the impact on mitochondrial function, it is not mitophagy but general autophagy that is constitutively induced and required for longevity. In contrast, in another long‐lived mutant ablated for the mitochondrial PaIAP protease, autophagy is neither induced nor required for lifespan extension. Our data provide novel mechanistic insights into the capacity of different forms of autophagy to compensate impairments of specific components of the complex mitochondrial quality control network and about the biological role of mitochondrial CLPXP in the control of cellular energy metabolism.

System impairment compensation in coherent optical communications by using a bio-inspired detector based on artificial neural network and genetic algorithm

A bio-inspired detector based on the artificial neural network (ANN) and genetic algorithm is proposed in the context of a coherent optical transmission system. The ANN is designed to mitigate 16-quadrature amplitude modulation system impairments, including linear impairment: Gaussian white noise, laser phase noise, in-phase/quadrature component imbalance, and nonlinear impairment: nonlinear phase. Without prior information or heuristic assumptions, the ANN, functioning as a machine learning algorithm, can learn and capture the characteristics of impairments from observed data. Numerical simulations were performed, and dispersion-shifted, dispersion-managed, and dispersion-unmanaged fiber links were investigated. The launch power dynamic range and maximum transmission distance for the bio-inspired method were 2.7dBm and 240km greater, respectively, than those of the maximum likelihood estimation algorithm. Moreover, the linewidth tolerance of the bio-inspired technique was 170kHz greater than that of the k-means method, demonstrating its usability for digital signal processing in coherent systems.

Laser Frequency Noise in Coherent Optical Systems: Spectral Regimes and Impairments

Coherent communication networks are based on the ability to use multiple dimensions of the lightwave together with electrical domain compensation of transmission impairments. Electrical-domain dispersion compensation (EDC) provides many advantages such as network flexibility and enhanced fiber nonlinearity tolerance, but makes the system more susceptible to laser frequency noise (FN), e.g. to the local oscillator FN in systems with post-reception EDC. Although this problem has been extensively studied, statistically, for links assuming lasers with white-FN, many questions remain unanswered. Particularly, the influence of a realistic non-white FN-spectrum due to e.g., the presence of 1/f-flicker and carrier induced noise remains elusive and a statistical analysis becomes insufficient. Here we provide an experimentally validated theory for coherent optical links with lasers having general non-white FN-spectrum and EDC. The fundamental reason of the increased susceptibility is shown to be FN-induced symbol displacement that causes timing jitter and/or inter/intra symbol interference. We establish that different regimes of the laser FN-spectrum cause a different set of impairments. The influence of the impairments due to some regimes can be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided.

Проблемы адаптации основной образовательной программы в вузе для лиц с ограниченными возможностями здоровья по слуху

The article analyzes in detail various features of how learning process participants interact with each other, as well as classifies possible (observed) impairments of cognitive qualities in students, as compared to the normal level. It also determines and scrutinizes mutual connections between certain impairments, along with their effect on perception during learning. The usage of orientated graphs measuring labour-intensiveness during the acquisition of the main educational program (MEP) provided a comparative characteristic of impaired students’ performance (hearing impairments) as compared to unimpaired ones. The solution that allows for MEP adaptation is presented in the form of courses that accompany every profile discipline, along with special cognitive technologies. The account of minimization or/and compensation of certain cognitive impairments in disabled students, as practiced at Bauman Moscow State Technical University, is given. Generalized goals of accompaniment courses are formulated. The examples are given (based on calculus and geometry courses) of using logical matrixes as a universal method of teaching conceptual systems that involve generic and specific relations. The accompaniment courses are shown to meet the metasubjective requirements. Special requirements for teachers working with hearing impaired students are formulated.

Joint Channel and Clipping Level Estimation for OFDM in IoT-based Networks

We consider scenarios such as IoT-based 5G or IoT-based machine type communication, where a low-cost low-power transmitter communicates with a high-quality receiver. Then, digital predistortion of the nonlinear power amplifier may be too expensive. In order to investigate the feasibility of receiver-side compensation of the transmitter RF impairments, we study joint maximum-likelihood estimation of channel and clipping level in multipath fading OFDM systems. In particular, we propose an alternative optimization algorithm, which uses frequency-domain block-type training symbols, and prove that this algorithm always converges, at least to a local optimum point. Then, we calculate the Cramer-Rao lower bound, and show that the proposed estimator attains it for high signal-to-noise ratios. Finally, we perform numerical evaluations to illustrate the performance of the estimator, and show that iterative decoding can be done using the estimated channel and clipping level with almost the same performance as a genie-aided scenario, where the channel and clipping level are perfectly known.

Nonlinear impairment compensation for DFT-S OFDM signal transmission with directly modulated laser and direct detection

We experimentally demonstrate a 16-ary quadrature amplitude modulation (16QAM) DFT-spread optical orthogonal frequency division multiplexing (OFDM) transmission system utilizing a cost-effective directly modulated laser (DML) and direct detection. For 20-Gbaud 16QAM-OFDM signal, with the aid of nonlinear equalization (NLE) algorithm, we respectively provide 6.2-dB and 5.2-dB receiver sensitivity improvement under the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10−3 for the back-to-back (BTB) case and after transmission over 10-km standard single mode fiber (SSMF) case, related to only adopt post-equalization scheme. To our knowledge, this is the first time to use dynamic nonlinear equalizer (NLE) based on the summation of the square of the difference between samples in one IM/DD OFDM system with DML to mitigate nonlinear distortion.

Advances in selective activation of muscles for non-invasive motor neuroprostheses.

Non-invasive neuroprosthetic (NP) technologies for movement compensation and rehabilitation remain with challenges for their clinical application. Two of those major challenges are selective activation of muscles and fatigue management. This review discusses how electrode arrays improve the efficiency and selectivity of functional electrical stimulation (FES) applied via transcutaneous electrodes. In this paper we review the principles and achievements during the last decade on techniques for artificial motor unit recruitment to improve the selective activation of muscles. We review the key factors affecting the outcome of muscle force production via multi-pad transcutaneous electrical stimulation and discuss how stimulation parameters can be set to optimize external activation of body segments. A detailed review of existing electrode array systems proposed by different research teams is also provided. Furthermore, a review of the targeted applications of existing electrode arrays for control of upper and lower limb NPs is provided. Eventually, last section demonstrates the potential of electrode arrays to overcome the major challenges of NPs for compensation and rehabilitation of patient-specific impairments.

Optical Time–Frequency Packing: Principles, Design, Implementation, and Experimental Demonstration

Time-frequency packing (TFP) transmission provides the highest achievable spectral efficiency with a constrained symbol alphabet and detector complexity. In this work, the application of the TFP technique to fiber-optic systems is investigated and experimentally demonstrated. The main theoretical aspects, design guidelines, and implementation issues are discussed, focusing on those aspects which are peculiar to TFP systems. In particular, adaptive compensation of propagation impairments, matched filtering, and maximum a posteriori probability detection are obtained by a combination of a butterfly equalizer and four 8-state parallel Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. A novel algorithm that ensures adaptive equalization, channel estimation, and a proper distribution of tasks between the equalizer and BCJR detectors is proposed. A set of irregular low-density parity-check codes with different rates is designed to operate at low error rates and approach the spectral efficiency limit achievable by TFP at different signal-to-noise ratios. An experimental demonstration of the designed system is finally provided with five dual-polarization QPSK-modulated optical carriers, densely packed in a 100 GHz bandwidth, employing a recirculating loop to test the performance of the system at different transmission distances.

Histamine in the basolateral amygdala promotes inhibitory avoidance learning independently of hippocampus

Recent discoveries demonstrated that recruitment of alternative brain circuits permits compensation of memory impairments following damage to brain regions specialized in integrating and/or storing specific memories, including both dorsal hippocampus and basolateral amygdala (BLA). Here, we first report that the integrity of the brain histaminergic system is necessary for long-term, but not for short-term memory of step-down inhibitory avoidance (IA). Second, we found that phosphorylation of cyclic adenosine monophosphate (cAMP) responsive-element-binding protein, a crucial mediator in long-term memory formation, correlated anatomically and temporally with histamine-induced memory retrieval, showing the active involvement of histamine function in CA1 and BLA in different phases of memory consolidation. Third, we found that exogenous application of histamine in either hippocampal CA1 or BLA of brain histamine-depleted rats, hence amnesic, restored long-term memory; however, the time frame of memory rescue was different for the two brain structures, short lived (immediately posttraining) for BLA, long lasting (up to 6 h) for the CA1. Moreover, long-term memory was formed immediately after training restoring of histamine transmission only in the BLA. These findings reveal the essential role of histaminergic neurotransmission to provide the brain with the plasticity necessary to ensure memorization of emotionally salient events, through recruitment of alternative circuits. Hence, our findings indicate that the histaminergic system comprises parallel, coordinated pathways that provide compensatory plasticity when one brain structure is compromised.

The Deterioration of Spatial Memory and the Role of the Masticatory Function during Aging: A Brief Literature Review

This article reviews the current state of scientific information on the relationship between the deterioration of spatial memory and the role of the masticatory function, both of which are primarily examined during the aging process. The article broadly examines the current notions regarding neuroscientific processing mechanisms of spatial memory. Additionally, some variables that produce alterations in hippocampal function during aging are presented here. Fin ally, the role that mastication fulfills as an emerging physiological mechanism of cognitive impairment compensation is discussed. This article concludes that, despite the recent progress in understanding the concepts presented in this article, evidence su ggests that there are still many questions to be answered. These questions are sustaining the growing interest in the field of neuroscience in examining the underlying mechanisms of the intricate process of spatial orientation and their relation to mastica tory function in aged organisms. Mini - review Article

High-Speed Coherent Transmission Using Advanced Photonics in Terahertz Bands

SUMMARY A terahertz-wave communication system directly connected to an optical fiber network is promising for application to future mobile backhaul and fronthaul links. The possible broad bandwidth in the terahertz band is useful for high-speed signal transmission as well as radio-space encapsulation to the high-frequency carrier. In both cases, the low-latency feature becomes important to enhance the throughput in mobile communication and is realized by waveform transport technology without anydigital-signal-processing-based media conversion. A highlyprecise optical frequency comb signal generated by optical modulation and the vector signal demodulation technology adopted from advanced optical fiber communication technologies help perform modulation and demodulation with impairment compensation at just the edges of the link. Terahertz wave, radio over fiber, waveform transport, coherent detection, multilevel modu

Digital compensation of cross-phase modulation distortions using perturbation technique for dispersion-managed fiber-optic systems

A digital compensation scheme based on a perturbation theory for mitigation of cross-phase modulation (XPM) distortions is developed for dispersion-managed fiber-optic communication systems. It is a receiver-side scheme that uses a hard-decision unit to estimate data for the calculation of XPM fields using the perturbation technique. The intra-channel nonlinear distortions are removed by intra-channel digital backward propagation (DBP) based on split-step Fourier scheme before the hard-decision unit. The perturbation technique is shown to be effective in mitigating XPM distortions. However, wrong estimations in the hard-decision unit result in performance degradation. A hard-decision correction method is proposed to correct the wrong estimations. Numerical simulations show that the hybrid compensation scheme with DBP for dispersion and intra-channel nonlinear impairments compensation and the perturbation technique for XPM compensation brings up to 3.7 dBQ and 1.7 dBQ improvements as compared with the schemes of linear compensation only and intra-channel DBP, respectively. The perturbation technique for XPM compensation requires only one-stage (or two-stage when hard-decision correction is applied) compensation and symbol-rate signal processing.