Paloma Garcia-Ducar

Design and Applications of a 300–800 MHz Tunable Matching Network

In this paper, the optimized design, characterization and applications of a broadband 300-800 MHz (~ 91% fractional bandwidth) digitally-controlled tunable matching network is presented. The design employs PIN diodes as switching components and a repetitive structure of basic cells using lumped reactive elements. After an intensive and complex optimization process, a Smith chart coverage (return losses better than 10 dB and losses lower than 2 dB) above 60% is obtained in all the bandwidth reaching 75% in the middle of the band (400-700 MHz). The potential of the manufactured tunable matching network for antenna mismatch compensation, antenna bandwidth extension and power amplifier efficiency improvement in back-off is showed.

Performance improvement of mobile DVB-H terminals using a reconfigurable impedance tuning network

DVB-H (digital video broadcasting for handheld) is one of the technology standards for the transmission of digital TV to handheld receivers such as mobile phones or PDAs. Antenna design for DVB-H terminals is challenging due to the size limitation and as a result, the antenna presents large mismatches. To address this issue, we propose the use of a reconfigurable tuning network to reduce the mismatch (or the antenna size for a given mismatch) between the antenna and the RF front-end in a DVB-H terminal. This technique offers some advantages over other proposed alternatives and improves the antenna realized gain, as well as the overall efficiency of the DVB-H receiver.

Dynamic Load Modulation With a Reconfigurable Matching Network for Efficiency Improvement Under Antenna Mismatch

This brief presents the application of a reconfigurable matching network (RMN) to improve the efficiency of an RF power amplifier (PA) using dynamic load modulation techniques under different antenna mismatch conditions. By changing the RMN state, a near-optimal output impedance is presented to the PA, achieving high efficiency for all input-driven levels. Simulations show efficiency enhancement, while nonlinear distortion can be mitigated using digital predistortion. It will be also shown that under severe mismatch conditions, using an RMN, significant efficiency and linearity improvements can be achieved.

Antenna effects in DVB-H mobile rebroadcasters

Digital video broadcasting for handheld (DVBH) is one of the wireless technologies that provide modern digital television services. The main objective of this paper is to propose a method to evaluate the performance of mobile rebroadcaster in terms of symbol error rate, taking into account antenna effects and the angle of arrival statistics. A correction factor is derived from concepts as the mean effective gain, which joined to a closed-form expression for the symbol error probability, allows predictions about the antenna impact on the broadcaster. The quantitative evaluation of the analysis identifies an important SNR reduction from 4 dB to 10 dB, depending on the environment.

Misalignments Feedforward Transmitter Correction Design for Nonlinear Distortion Cancellation in OFDM Systems

The Feedforward linearization technique is a well-known power amplifier linearization method to reduce out-of-band distortion that can approach wideband signals with high efficiency. The Feedforward structure consists of two loops, where an accurate adjustment between them is necessary to ensure a correct behaviour. This adjustment must remain along the time to compensate for temperature, environmental and operating changes. Amplitude and phase imbalances of the circuit elements in both loops produce mismatched effects that lead to degrade the performance of the Feedforward technique. A method is proposed to compensate for these mismatches, introducing two complex gain coefficients calculated by means of a genetic algorithm. The method is applied to broadband systems based on OFDM modulation schemes. The OFDM transmission is an efficient way to deal with multipath, being its implementation less complex than traditional equalizers. This together with an efficient implementation, using the Fast Fourier Transform algorithm, has made it ideal for new technology. However, it is also very sensitive to nonlinear distortions due to its greatly variable envelope and high peak to mean envelope power ratio values. Therefore, Feedforward is a good linearization method for OFDM systems because simultaneously offers wide bandwidth and good nonlinear distortion suppression. The method functionality has been verified by means of simulation.

Synthesis of Hecken-tapered microstrip to Paralell-Strip baluns for UHF frequency band

Microstrip to Parallel-Strip transitions are frequently used for feeding balanced antenna structures, such as dipoles and printed spiral antennas. In this paper, we propose an analytical method to compute the gradual taper using a Hecken approach in order to minimize the return losses and to have continuity. The proposed method is verified experimentally with the aid of three transitions including matching capabilities with different ratios, suitable for spiral antenna structures in, at least, the ranges from 450 MHz to 2 GHz.

Improvement in the Linearity of a LINC Transmitter using Genetic Algorithms

This paper proposes an automatically-adjusted linearization method based on the well-known linearization technique LINC (Linear amplification using Nonlinear Components) applied to the base station transmitter. A correction method of the gain and phase imbalances between both amplifying branches in a LINC transmitter is proposed to reduce the adjacent channel interference. A simple architecture is designed to compensate the unmatching between both branches being the adjusting coefficients calculated by means of a genetic algorithm. Several nonidealities are included in the analysis to deal with a realistic model, such as quadrature modulator imbalances, reconstruction filters and quantization error.

Predistortion Method for Nonlinear Distortion Cancellation in WiMAX Transmitters

A full digital linearization technique based on a predistorter scheme with a look-up table (LUT) is applied to the orthogonal frequency-division multiplexing (OFDM) transmission scheme, such as a WiMAX system. The OFDM transmission is an efficient way to deal with multipath, being its implementation less complex than traditional equalizers. This together with an efficient implementation, using the Fast Fourier Transform algorithm, has made it ideal for using in new technologies. However, it is also very sensitive to nonlinear distortions due to its greatly variable envelope and high peak to mean envelope power ratio values. The proposed method includes also a peak cancellation stage in order to reduce this problem and to improve the efficiency of the power amplifier. The method functionality has been verified by means of simulation, obtaining a reduction in the adjacent channel interference level and also an improvement in the error vector magnitude (EVM) measurement.

Radio-over-fiber linearization with optimized genetic algorithm CPWL model

This article proposes an optimized version of a canonical piece-wise-linear (CPWL) digital predistorter in order to enhance the linearity of a radio-over-fiber (RoF) LTE mobile fronthaul. In this work, we propose a threshold allocation optimization process carried out by a genetic algorithm (GA) in order to optimize the CPWL model (GA-CPWL). Firstly, experiments show how the CPWL model outperforms the classical memory polynomial DPD in an intensity modulation/direct detection (IM/DD) RoF link. Then, the GA-CPWL predistorter is compared with the CPWL model in several scenarios, in order to verify that the proposed DPD offers better performance in different optical transmission conditions. Experimental results reveal that with a proper threshold allocation, the GA-CPWL predistorter offers very promising outcomes.

Modeling and Digital Predistortion based on Zernike polynomial functions for LTE-RoF system

A novel modeling technique is proposed to improve the Radio over Fiber (RoF) modeling and the Predistorter identification. This method is based on an orthogonal basis composed by Zernike polynomials, whose features guarantee numerical stability, a problem present in the classical polynomial model based on Volterra series. The measurements have been carried out with a LTE downlink signal with a bandwith of 3 MHz and QPSK modulation. The DFB laser has been biasing with 40, 70 and 100 mA to compare the distortion effects in each case. The measurements confirm that the RoF and PA modeling has an important improvement in terms of the ACEPR. In order to the DPD, the results show that the new technique reach an improvement of 2.57 dB in order to the ACPR, as well as an increase in the channel power.