Nonlinear effects in lte downlink signals and application of a compensation technique at the receiver side

This article proposes a nonlinear compensation technique for long-term evolution downlink signals based on the memoryless solid-state power amplifier model, which provides a simple and effective linearization technique at the receiver side, allowing a reduction in the error vector magnitude measured characteristics. The error vector magnitude per subcarrier is analyzed for different appropriate resource blocks allocations in the long-term evolution signal to examine the distortion due to the nonlinear effects produced by a power amplifier in the experimental setup.CICYT TEC2008-06259/TECCICE P07-TIC-0264

Experimental study of two-tone intermodulation products in a communications modulator

This article presents the experimental nonlinear characterization of a quadrature modulator following a two‐tone test approach. The observed intermodulation products show different slopes with respect to the desired carrier level that can be predicted by a simple model. Measurements for two‐tone tests versus carrier level and tone spacing are discussedCICYT TEC2008-06259/TECCICE P07-TIC-0264

Digital predistortion technique with in-band interference optimisation applied to DVB-T2

The efficient transmission and nonlinear modelling of orthogonal frequency division multiplexing (OFDM) signals are difficult to address owing to the special characteristics of this modulation scheme. Proposed is a digital predistortion technique suitable for the implementation in an OFDM transmitter to optimise the in-band interference caused by the nonlinear distortion generated in the amplification chain. The approach is experimentally validated by its application in one of the world's most advanced broadcasting systems, achieving an outstanding linearisation performance in the transmitter; specially for the in-band interference, a modulation error ratio (MER) of 42.1 dB is obtained.CICYT TEC2011-2355

Antenas resonadoras dieléctricas cilíndricas para sistemas MIMO: fundamentos y evaluación

The analysis and preliminary evaluation of different configurations provided by slot-coupled cylindrical dielectric resonator antenna arrays at one side of ground plane for MIMO systems is the main purpose of this paper. Appropriate envelope correlation values are obtained, and therefore spatial diversity, especially when cross polarization is used

Predistorsión digital de un amplificador clase J

The efficient transmission and modeling of Orthogonal Frequency Division Multiplexing signals are difficult to address due to the special characteristics of this modulation scheme. This paper implements a memoryless digital predistorter based on a curve fitting procedure in order to linearize a highly efficient continuous mode class J power amplifier based on a 15 W GaN device at a frequency of 850 MHz. Measurements show that the compensation method obtains improvements up to 18.8 dB in ACPR and 14 dB in MER when combined with a PAPR reduction technique

Modeling and compensation of non-linear effects in wireless communications systems

La Ingeniería de Microondas y Radiofrecuencia ha ido adquiriendo una importancia cada vez mayor en los últimos años, incentivada en particular por el excepcional crecimiento de las comunicaciones móviles digitales. Es evidente una tendencia hacia frecuencias de operación más altas y mayores anchuras de banda. Uno de los principales retos que se plantea en el análisis y diseño asistido por computador de los sistemas de alta frecuencia es el desarrollo de técnicas de modelado y algoritmos de simulación precisos, robustos y eficientes, que tengan en cuenta el comportamiento no lineal de los dispositivos.|Premio Extraordinario de Doctorado U

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 precompensation 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.European Space Agency (ESA

Output-Controllable Partial Inverse Digital Predistortion for RF Power Amplifiers

In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to user's demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.Science Foundation Irelan

Nonlinear effects in lte downlink signals and application of a compensation technique at the receiver side

This article proposes a nonlinear compensation technique for long-term evolution downlink signals based on the memoryless solid-state power amplifier model, which provides a simple and effective linearization technique at the receiver side, allowing a reduction in the error vector magnitude measured characteristics. The error vector magnitude per subcarrier is analyzed for different appropriate resource blocks allocations in the long-term evolution signal to examine the distortion due to the nonlinear effects produced by a power amplifier in the experimental setup.CICYT TEC2008-06259/TECCICE P07-TIC-0264

Weaning from mechanical ventilation in intensive care units across 50 countries (WEAN SAFE): a multicentre, prospective, observational cohort study

Background: Current management practices and outcomes in weaning from invasive mechanical ventilation are poorly understood. We aimed to describe the epidemiology, management, timings, risk for failure, and outcomes of weaning in patients requiring at least 2 days of invasive mechanical ventilation. Methods: WEAN SAFE was an international, multicentre, prospective, observational cohort study done in 481 intensive care units in 50 countries. Eligible participants were older than 16 years, admitted to a participating intensive care unit, and receiving mechanical ventilation for 2 calendar days or longer. We defined weaning initiation as the first attempt to separate a patient from the ventilator, successful weaning as no reintubation or death within 7 days of extubation, and weaning eligibility criteria based on positive end-expiratory pressure, fractional concentration of oxygen in inspired air, and vasopressors. The primary outcome was the proportion of patients successfully weaned at 90 days. Key secondary outcomes included weaning duration, timing of weaning events, factors associated with weaning delay and weaning failure, and hospital outcomes. This study is registered with ClinicalTrials.gov, NCT03255109. Findings: Between Oct 4, 2017, and June 25, 2018, 10 232 patients were screened for eligibility, of whom 5869 were enrolled. 4523 (77·1%) patients underwent at least one separation attempt and 3817 (65·0%) patients were successfully weaned from ventilation at day 90. 237 (4·0%) patients were transferred before any separation attempt, 153 (2·6%) were transferred after at least one separation attempt and not successfully weaned, and 1662 (28·3%) died while invasively ventilated. The median time from fulfilling weaning eligibility criteria to first separation attempt was 1 day (IQR 0-4), and 1013 (22·4%) patients had a delay in initiating first separation of 5 or more days. Of the 4523 (77·1%) patients with separation attempts, 2927 (64·7%) had a short wean (≤1 day), 457 (10·1%) had intermediate weaning (2-6 days), 433 (9·6%) required prolonged weaning (≥7 days), and 706 (15·6%) had weaning failure. Higher sedation scores were independently associated with delayed initiation of weaning. Delayed initiation of weaning and higher sedation scores were independently associated with weaning failure. 1742 (31·8%) of 5479 patients died in the intensive care unit and 2095 (38·3%) of 5465 patients died in hospital. Interpretation: In critically ill patients receiving at least 2 days of invasive mechanical ventilation, only 65% were weaned at 90 days. A better understanding of factors that delay the weaning process, such as delays in weaning initiation or excessive sedation levels, might improve weaning success rates. Funding: European Society of Intensive Care Medicine, European Respiratory Society