Pedro L. Carro

Efficient feedforward linearization technique using genetic algorithms for OFDM systems

Feedforward is a linearization method that simultaneously offers wide bandwidth and good intermodulation distortion suppression; so it is a good choice for Orthogonal Frequency Division Multiplexing (OFDM) systems. Feedforward structure consists of two loops, being necessary an accurate adjustment between them along the time, and when temperature, environmental, or operating changes are produced. Amplitude and phase imbalances of the circuit elements in both loops produce mismatched effects that lead to degrade its performance. A method is proposed to compensate these mismatches, introducing two complex coefficients calculated by means of a genetic algorithm. A full study is carried out to choose the optimal parameters of the genetic algorithm applied to wideband systems based on OFDM technologies, which are very sensitive to nonlinear distortions. The method functionality has been verified by means of simulation.

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.

Analysis and Synthesis of Double-Sided Parallel-Strip Transitions

Antenna feeders, mixers, and filters made in double-sided parallel-strip technology usually must be adapted to unbalanced lines like the microstrip structure, needing transitions from asymmetric to symmetric waveguides (baluns). In this paper, we propose a new method for the evaluation of a generic tapered balun based on a conformal-mapping technique and an integral equation. This method, along with the use of an optimization technique such as genetic algorithms, allows for quick evaluation of the return losses of any tapered balun and the synthesizing of specific shapes to achieve desired responses in terms of return losses or impedance values.

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.

Ultrawide-Band Antenna Distortion Characterization Using Hermite-Gauss Signal Subspaces

Evaluation of signal distortion produced by antennas in ultrawide-band (UWB) communications has become an important concern due to possible degradation in signal-to-noise ratio (SNR) and furthermore, in system bit-error rate (BER). Fidelity has proved to be a useful method for taking into account distortion involving single-users and single waveforms, that is, unidimensional signal spaces. A new method for evaluating distortion in multiple waveform sets is set forth in this letter. The method is based on a link representation matrix computed by means of Hermite-Gauss signal subspaces and a related Frobenius matrix norm. Proof that this measure allows evaluation of distortion by resorting to a geometrical approach is supplied. Finally, its properties and applications are analyzed, highlighting its differences, advantages, and drawbacks in comparison with the traditional method.

3-D Conformal Spiral Antenna on Elliptical Cylinder Surfaces for Automotive Applications

We propose a new 3-D conformal spiral antenna that is based on the standard equiangular spiral geometry for automotive applications. The impact of its integration when it is placed inside a wing mirror is investigated. The antenna is miniaturized using meandered surface techniques to increase the electrical length and improve its performance. Scattering parameters are numerically estimated with the aid of the commercial code HFSS (finite element method). Experimental measurements show a wide frequency bandwidth that is suitable for several car communication systems.

Memory Behavioral Modeling of RF Power Amplifiers

Power amplifiers (PAs) are the most extended and widely used nonlinear devices in communications. Their non- linearities generate distortion both in amplitude and phase of the PAs output signal. The use of wideband efficient modulations in the last generation systems, such as wideband code-division multiple access (WCDMA) or orthogonal frequency-division multiplexing (OFDM), adds new problems to the use of PAs, due to the memory effects associated with the bandwidth and the increase of distortion by the non-constant envelope. In this paper it is shown the need of taking into account the memory effects in order to get a more accurate model of PA operation. We compare the performance of the memoryless model with some well-known memory models based on memory polynomials and Volterra series using a novel calibration signal.

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.

Polarization Diversity with Genetic Parallel Printed Dipole Antennas for Bluetooth and WiMAX Applications

Multipath propagation effect degrades usually the wireless system performances. Antenna diversity in one of the several methods that have been studied to mitigate this phenomena. This technique can overcome the multipath fading improving the overall performance of communication system. In order to study the impact of the wireless channel and perform antenna diversity, two parameters must be evaluated: the mean effective gain, and the correlation coefficient between the antennas. Parallel printed dipole antennas have been successfully used in mobile base station development, showing either broadband or multiple-band properties besides its low cost. However, polarization diversity parameters have not been analysed since these antennas have not been yet considered in mobile devices and diversity applications. In this paper, a polarization diversity schema comprised of two dual-printed dipole antennas for bluetooth and WIMAX applications operating in 2.4-2.4835 GHz and 3.5 GHz frequency bands are presented. Genetic algorithm optimization (GA) is applied first, to a classical dual band printed dipole antenna schema, second to a pre-fractal tree parallel printed dipole to achieve a more compact radiator. Frequency performance of both antennas is introduced showing a VSWR< 1.5 for a input impedance of 50 Ohms. Later on, a diversity antenna based on the pre-fractal configuration is studied in terms of mean effective gain (MEG) and correlation coefficient for indoor and outdoor scenarios. Results shows that MEG is nearly the same in both environments with a low correlation between the elements which means that diversity gain can be achieved using this schema.