Imbalance Compensation Research Articles

ADAPTIVE COMPLEX FILTERS BASED TRANSMITTER IQ IMBALANCE REJECTION

This paper presents an efficient method for compensation of frequency-dependent (FD) transmitter In-phase Quadrature (IQ) imbalance. Proposed method compensates imbalance by exploiting indirect learning architecture (ILA) and complex filters whose coefficients are determined in an iterative process. Compensation performance is assessed after the method has been implemented in a Software Defined Radio (SDR) platform, capable of transmitting modulations at different central frequencies. Measured results demonstrate that the imbalance related images are reduced down to the noise floor. After applying the proposed IQ imbalance correction method, the transmitter image rejection ratio (IRR) is increased by 15dB in the case of an SDR transmitter operating at central frequency of 1.7 GHz. The ADC/DAC sampling rate is 61.44MS/s, while the signal bandwidth, for which the compensation is performed, is 30.72MHz. The advantage of the proposed method is low complexity in terms of a reduced number of coefficients. The method is generic and can be utilized for IQ imbalance compensation when wideband signals are transmitted.

How does cervical sagittal profile change after the spontaneous compensation of global sagittal imbalance following one- or two-level lumbar fusion.

This study aimed to evaluate the cervical sagittal profile after the spontaneous compensation of global sagittal imbalance and analyze the associations between the changes in cervical sagittal alignment and spinopelvic parameters. In this retrospective radiographic study, we analyzed 90 patients with degenerative lumbar stenosis (DLS) and sagittal imbalance who underwent short lumbar fusion (imbalance group). We used 60 patients with DLS and sagittal balance as the control group (balance group). Patients in the imbalance group were also divided into two groups according to the preoperative PI: low PI group (≤ 50°), high PI group (PI > 50°). We measured the spinal sagittal alignment parameters on the long-cassette standing lateral radiographs of the whole spine. We compared the changes of spinal sagittal parameters between pre-operation and post-operation. We observed the relationships between the changes in cervical profile and spinopelvic parameters. Sagittal vertical axis (SVA) occurred spontaneous compensation (p = 0.000) and significant changes were observed in cervical lordosis (CL) (p = 0.000) and cervical sagittal vertical axis (cSVA) (p = 0.023) after surgery in the imbalance group. However, there were no significant differences in the radiographic parameters from pre-operation to post-operation in the balance group. The variations in CL were correlated with the variations in SVA (R = 0.307, p = 0.041). The variations in cSVA were correlated with the variations in SVA (R=-0.470, p = 0.001). Cervical sagittal profile would have compensatory changes after short lumbar fusion. The spontaneous decrease in CL would occur in patients with DLS after the spontaneous compensation of global sagittal imbalance following one- or two-level lumbar fusion. The changes of cervical sagittal profile were related to the extent of the spontaneous compensation of SVA.

Joint Channel and IQ Imbalance Compensation Method for MIMO-OFDM Using in Coastal Railway

Joint Channel and IQ Imbalance Compensation Method for MIMO-OFDM Using in Coastal Railway

I/Q Imbalance Compensation in Cell-Free Massive MIMO During Uplink Transmission

I/Q Imbalance Compensation in Cell-Free Massive MIMO During Uplink Transmission

A Novel Radio Frequency Fingerprint Concealment Method Based on IQ Imbalance Compensation and Digital Pre-Distortion

A Novel Radio Frequency Fingerprint Concealment Method Based on IQ Imbalance Compensation and Digital Pre-Distortion

INCREASED CATALASE ACTIVITY IN AGING ADULTS WITH DOWN SYNDROME: ASSOCIATIONS WITH AGE AND COGNITIVE DECLINE

AbstractBackgroundThe aging process in Down syndrome (DS) is associated with a high prevalence of dementia, which is regarded as a variant form of early‐onset Alzheimer’s disease (AD). In addition to the central role played by amyloid pathology, DS‐dementia (DS‐D) may also be related to abnormal regulation of oxidative stress. The copper/zinc‐dependent superoxide dismutase (SOD1) gene is also located on chromosome 21, and studies have suggested an association of SOD1 overexpression with disrupted redox homeostasis. We hypothesize that such abnormalities may be further related to cognitive decline in DS.Method30 aging adults with DS were enrolled to the study, of whom 14 were cognitively stable (DS‐S) and 16 had evidence of cognitive decline (DS‐D). Two comparison groups were constituted with euploid volunteers, i.e., 30 age‐matched, cognitively healthy subjects (euploid controls, EU‐C); and 60 MCI and AD patients (EU‐MCI‐AD). We used an enzymatic assay to determine catalase activity.ResultAs compared to euploid controls, catalase activity was increased in DS irrespective of the presence of cognitive decline (p<0.004). This finding was also observed when the DS group was stratified according to the presence of cognitive decline (EU‐C vs. DS‐S, p<0.001; EU‐C vs. DS‐D, p<0.01). Catalase activity was also increased among cognitively stable DS as compared to MCI‐AD (DS‐S vs. EU‐MCI‐AD, p<0.027).When the DS group was stratified by age (18‐34y, 35‐49y, and ≥ 50y), catalase activity was found to be increased in younger and middle‐aged DS‐S as compared to EU‐C (18‐34y, p<0.01; 35‐49y, p<0.01) and in middle‐aged DS‐S as compared to SD‐D (35‐49y: p< 0.03).ConclusionOur preliminary findings suggest a systemic pro‐oxidant status in DS, evidenced by the increased catalase activity, presumably as a physiological compensation for redox imbalance due to the upregulation of SOD1 (data not shown). Furthermore, antioxidant defense functions decline with aging in the DS carrying. Thus, catalase could be a predictive biomarker candidate for AD.

ANALYSIS OF METHODS OF CHANGING VOLUMES OF ELECTRICITY GENERATION AT SOLAR POWER PLANTS

The article examines the methods of changing electricity generation schedules at solar power plants when operating under the central regulator of the power system. An analysis of the existing regulation methods was carried out, and a new method of controlling the generation of solar power plants under the central regulator of the power system was proposed.
 Background. The increase in the share of solar electricity generation in the energy systems of the countries of the world leads to the need to control and manage the process of electricity production to increase the stability and sustainability of the energy system. A significant price for compensation of imbalances in the energy system is included in the tariffs, which affects the end consumers of electricity.
 Objective: increasing the adequacy of the results of the distribution of deficit frequency containment reserves, frequency restoration reserves to compensate for imbalances that arise when generation is changed at solar power plants. Reducing the cost of compensation for imbalances that occur when changing generation at solar power plants. To solve the goal, it is necessary to analyze the existing methods of compensating power system imbalances that arise as a result of changes in generation at solar power plants and to propose a new technical and mathematical solution for the distribution of deficit reserves of support and frequency restoration.
 Methods: the social engineering approach of forecasting and modeling was used to analyze the processes affecting the method of controlling the generation schedule of the solar power plant.
 Results. A new mathematical and technical solution for compensating the imbalance in the power system in the event of a rapid change in the electricity generation schedule at solar power plants is proposed. For the first time, the given task was solved using a new technical and mathematical solution. Such a technical and mathematical solution can be widely used in the management of the electricity generation schedule at solar power plants in many system operators in different countries of the world, where there is a problem of insufficient for frequency containment and restoration reserves, and the amount of solar electricity generation has a significant share in the total amount of electricity generation energy.
 Conclusions. Existing methods of compensating power system imbalances arising as a result of changes in generation at solar power plants are analyzed and a new technical and mathematical solution for the distribution of deficit reserves of frequency containment reserves and frequency restoration reserves is proposed. The proposed technical and mathematical solution makes it possible to predict an event during which there will be a change in the level of electric energy generation at solar power plants, to transmit information to the central regulator of the energy system, which in turn will give a command to change the schedule of electric energy generation in advance within the insensitivity zone, which will lead to the activation of the frequency restoration reserves and will allow to compensate the existing imbalance at the expense of cheaper reserves and not to activate the frequency containment reserves. Such a mathematical and technical solution will make it possible to significantly increase the stability of the energy system against emerging imbalances and make their compensation cheaper, which in general has a positive effect on the energy security of the state.

Joint Estimation and Compensation of CFO, IQ Imbalance and Channel Parameters for Zero Padded OTSM Systems

Joint Estimation and Compensation of CFO, IQ Imbalance and Channel Parameters for Zero Padded OTSM Systems

Persistent Lower Extremity Compensation for Sagittal Imbalance After Surgical Correction of Complex Adult Spinal Deformity: A Radiographic Analysis of Early Impact.

Achieving spinopelvic realignment during adult spinal deformity (ASD) surgery does not always produce ideal outcomes. Little is known whether compensation in lower extremities (LEs) plays a role in this disassociation. The objective is to analyze lower extremity compensation after complex ASD surgery, its effect on outcomes, and whether correction can alleviate these mechanisms. We included patients with complex ASD with 6-week data. LE parameters were as follows: sacrofemoral angle, knee flexion angle, and ankle flexion angle. Each parameter was ranked, and upper tertile was deemed compensation. Patients compensating and not compensating postoperatively were propensity score matched for body mass index, frailty, and T1 pelvic angle. Linear regression assessed correlation between LE parameters and baseline deformity, demographics, and surgical details. Multivariate analysis controlling for baseline deformity and history of total knee/hip arthroplasty evaluated outcomes. Two hundred and ten patients (age: 61.3 ± 14.1 years, body mass index: 27.4 ± 5.8 kg/m2, Charlson Comorbidity Index: 1.1 ± 1.6, 72% female, 22% previous total joint arthroplasty, 24% osteoporosis, levels fused: 13.1 ± 3.8) were included. At baseline, 59% were compensating in LE: 32% at hips, 39% knees, and 36% ankles. After correction, 61% were compensating at least one joint. Patients undercorrected postoperatively were less likely to relieve LE compensation (odds ratio: 0.2, P = .037). Patients compensating in LE were more often undercorrected in age-adjusted pelvic tilt, pelvic incidence, lumbar lordosis, and T1 pelvic angle and disproportioned in Global Alignment and Proportion (P < .05). Patients matched in sagittal age-adjusted score at 6 weeks but compensating in LE were more likely to develop proximal junctional kyphosis (odds ratio: 4.1, P = .009) and proximal junctional failure (8% vs 0%, P = .035) than those sagittal age-adjusted score-matched and not compensating in LE. Perioperative lower extremity compensation was a product of undercorrecting complex ASD. Even in age-adjusted realignment, compensation was associated with global undercorrection and junctional failure. Consideration of lower extremities during planning is vital to avoid adverse outcomes in perioperative course after complex ASD surgery.

Improving visual question answering for remote sensing via alternate-guided attention and combined loss

Visual question answering (VQA) for remote sensing (RS) images offers a typical multi-modal task advanced by natural language processing and computer vision technologies. Still, it remains a problem subjected to two aspects of factors. First, the RS image contains a wealth of visual elements but is rarely involved in the question; therefore, the regions humans choose to look at to answer questions differ from current attention approaches. Second, the class-imbalance problem in the existing RSVQA dataset leads the prediction to drift towards frequent answers. To address these issues, we aim to explore the intrinsic relationship between RS visual elements and text generations with imbalance compensation. Here, we propose a new method called Union Context-wise and Alternate-Guided Attention Network (UCAGAN). Our method uses a cross-modal alternative-guided attention module to map visual and textual features. Moreover, we introduce an improved multi-category loss function to compensate for the model bias caused by sample imbalance. We carried out thorough experimentation on a diverse range of datasets, demonstrating that our approach is effective and efficient, achieving state-of-the-art performance. Our work provides results that are not only correctable but also explainable, ultimately leading to the development of reliable VQA models for RS images.

A Novel MIMO Control for Interleaved Buck Converters in EV DC Fast Charging Applications

This brief proposes a new multiple input multiple output (MIMO) control for off-board electric vehicle (EV) dc fast chargers. The proposed feedback matrix design avoids multiple tuning of controllers in multiple and interconnected loops while improving the performance of interleaved dc buck converters over classical PI/PID controls. The innovative features of the presented strategy are the reference current monotonic tracking from any initial state of charge with an arbitrarily fast settling time and the fast compensation of both load variations and imbalances among the legs. Numerical results validate the performance improvements of the proposed discrete-time MIMO algorithm for interleaved buck converters over classical PI/PID controls. Full-scale hardware-in-the-loop (HIL) and scaled-down prototype experimental results prove the feasibility and effectiveness of the proposal.

Compensation of the Current Imbalance of an Interleaved DC–DC Buck Converter, Sensorless Online Solution Based on Offline Fuzzy Identification and Post-Linearization

This paper presents a new approach to compensate for the current imbalance of an interleaved DC–DC buck converter (IBC), in which the current sensors are not involved in the operation of the converter when it is connected to an invariable load. The current sensors are only used during the offline identification process that builds the universal fuzzy model of the converter’s steady states. Model building involves an upstream identification phase, followed by further dimensionality reduction of the model and error minimization. The method presented here discusses the mathematical complexity of the analytical modelling of hybrid systems and opposes it with a complexity-reduced identification by learning from data. An offline rendered model of the stable and steady states of the IBC is used as a mapping of the required inverter output current to n-fold asymmetric duty cycles, which are distributed among the IBC phases to allow arbitrarily accurate load sharing. The mapping is carried out in the mathematically normalized space of variables or in the physical sense RMS values, achieving the desired robustness in a noisy environment and stability. The final and canonical feedback control is built from the standard and optimized PI controller, which is compensated by the identified IBC model correction. The only measured feedback of the whole controller is the output voltage. Even when applied to the simulation model (physical MATLAB platform) of a two-phase IBC with the built-in system asymmetry, the presented methodology is also applicable to the n-phase IBC without loss of generality.

A General Double-Input Synchronous Signal Processor for Imbalanced Vibration Mitigation in AMB-Rotor Systems

Imbalanced vibration is an urgent yet challenging problem in active magnetic bearings (AMBs) rotor manufacturing due to the rotor mass imbalance effect. The virtue of active control in AMB systems lies in enabling substantial online mitigation of imbalanced vibrations. However, in practice, due to the lack of speed sensors in most of the existing AMB-rotor systems, efficient rotational speed feedback is still on the way. As a remedy, this article proposes a rotational speed sensor-free synchronous signal processor (SSP) with the double inputs: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$</tex-math> </inline-formula> -and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$</tex-math> </inline-formula> -axes direction displacement measurements of radial AMBs. The proposed SSP is capable of estimating the rotational speed and accordingly generating synchronous signals of the imbalanced vibrations by filtering noise in both directions. Such signals are afterward implemented as a feedforward compensator for eliminating the periodical imbalance effects. With the assistance of the Lyapunov theory, the conditions of the proposed SSP method together with the feedforward imbalance compensator are derived to guarantee the stability of the closed-loop AMB-rotor system. Extensive experimental results substantiate the effectiveness and superiority of the proposed SSP method in terms of imbalanced vibration suppression.

A Study on the Operation of a Balancing Group Consisting of PVs and On-site Storage Batteries

The renewable energy resources, such as photovoltaic generation and wind turbine, are rapidly being integrated. In order to compensate for the variable output and imbalance between actual and scheduled outputs, introduction of a battery storage would be one of the promising solutions. In this paper, we focus on the scheduled operation of a balancing group (BG) consisting of the widely distributed photovoltaic generation with storage battery. BG forming would bring reduction of total imbalance due to cancellation of forecast errors among PV stations, and could enable cooperative usage of battery storages for imbalance compensation. This paper proposes a new battery storages operation scheduling for the BG considering the imbalance risk, which are assumed based on the confidence interval forecast for PV output. Effectiveness of the proposed scheduling method is ascertained through year-basis computational simulation of the BG. Advantages of BG forming is also discussed.

Design of imbalance compensator to mitigate circulating currents under master–slave operation of inverters

Design of imbalance compensator to mitigate circulating currents under master–slave operation of inverters

Low-complexity two-stage equalizer for receiver IQ imbalance compensation and polarization demultiplexing for real-time System

Reducing the complexity of adaptive equalizer is significant for realizing real-time hardware systems. In this paper, we propose a low-complexity two-stage equalizer that can be used in real-time systems. The performance of the proposed equalizer was verified through a 112 Gbit/s polarization multiplexing quadrature phase shift keying (PM-QPSK) back-to-back experiment with a receiver IQ impairment emulation module. The results revealed that, as for FIR module, compared with the conventional 2 × 2 MIMO, the number of multipliers in the proposed equalizer can be reduced by approximately 70% by use of 21 taps, while this equalizer is less sensitive to IQ impairment.

Reconfigurable microwave photonic mixer for hybrid macro-micro cellular systems.

Microwave photonic mixing can realize the frequency conversion of microwave signals in the optical domain, breaking through the bandwidth bottleneck and electromagnetic interference problems of traditional microwave mixing methods. In the background of the hybrid macro-micro cellular system, a wideband, large dynamic range and reconfigurable microwave photonic mixer is proposed, theoretically analyzed and experimentally demonstrated in this paper. By adjusting the modulator bias voltages and matching the proper digital domain operations, a microwave photonic mixer with reconfigurable functions including single-ended dispersion immune mixing, I/Q frequency down-conversion, image rejection mixing, and double-balanced mixing are realized, respectively. Meanwhile, optimizing the electrical attenuator using convex optimization can suppress the third-order intermodulation distortion (IMD3), maximize the conversion gain, and finally improve the spur-free dynamic range (SFDR). Experimental results show that the proposed scheme can be operated with a frequency from 5 to 20 GHz, and the SFDR can achieve 118.3 dB·Hz4/5. Over the whole frequency range, I/Q frequency down-conversion can be well conducted with an amplitude imbalance below 0.7 dB and a phase imbalance below ±0.7°. After an I/Q imbalance compensation algorithm, the image rejection ratio of over 60 dB is produced. The power fading caused by fiber dispersion is also compensated successfully. For a vector signal with 16 quadrature amplitude modulation, the best error vector magnitude (EVM) reaches 3.4%.

A Predictive Negative Sequence Current Control Algorithm for Voltage Imbalance Compensation and Power Oscillation Minimization under Unbalanced Conditions

The predictive-based strategy employed in this paper allows an inverter to simultaneously inject positive and negative sequence reactive current to compensate for voltage imbalance, taking into account imbalance adverse effects on power oscillations. A suggested optimization cost function of a predictive-based controller is formulated to solve the trade-off problem between grid voltage support and voltage imbalance compensation by determining the optimal negative sequence reactive power to be injected to the reference current of a generator. The proposed predictive-based control strategy is evaluated under various distributed generation operating conditions in terms of injected active to reactive power ratio. Additionally, its performance is compared with the performance of an active power oscillations minimization (p̃-minimization) control strategy, where the active power oscillations due to reactive power disappear. In contrast with p̃-minimization control strategy, the proposed predictive-based strategy managed to reduce the active power oscillation. The adequacy of the proposed strategy is verified via simulations of a distributed energy resource (DER) grid-connected inverter under voltage imbalance caused by an unbalanced load. The simulation work presented in this paper was conducted using MATLAB/Simulink software. As a part of a smart inverter functions to preserve the energy supply under unbalanced conditions, this research would serve as a platform for studying the inverter optimal control of negative sequence component.

Evaluation of the impact of I/Q imbalance compensation on communication performance

Evaluation of the impact of I/Q imbalance compensation on communication performance

Estimation and Compensation of IQ Imbalance for OTSM Systems

Recently, orthogonal time sequency multiplexing (OTSM) waveform was proposed using Walsh Hadamard transform (WHT) for doubly-dispersive channels at a lower modulation/demodulation complexity than orthogonal time frequency space (OTFS) waveform. At high frequencies, hardware imperfections such as in-phase and quadrature (IQ) imbalance is prominent at the transceiver. In this letter, the input-output (I/O) relation in the delay-sequency domain is derived under these impairments at the receiver. The impairment parameters are estimated in the delay-time domain and are compensated in the time domain using proposed dual pilot approach. The normalized mean square error (NMSE) of the estimated imbalance parameters is evaluated and it is observed that NMSE reduces with increase in SNR and with reduction in mobility. The results are evaluated with OTFS system and it is observed that the NMSE performance of OTSM is similar to OTFS under high pilot power and high SNR at no excess pilot power. The bit error rate performance of the compensated system is evaluated and its performance is close to the ideal system.