J. de Mingo

An RF electronically controlled impedance tuning network design and its application to an antenna input impedance automatic matching system

A novel design is proposed for an electronically tunable impedance unit. The prototypes include lumped elements, but no electromechanical control methods. The devices can tune many different complex impedances at minimum manufacture costs. Two antenna input impedance automatic matching systems are also presented, based on the tuning network. One includes a simplified version of the generic tuner, which can achieve good matching levels between the antenna and the power module with low losses. In a more complete version, an application specific integrated circuit control unit is developed including a complex search algorithm. In order to obtain a good matching level, both systems require a control module to select the proper tuner impedance configuration. The measurements and results of both constructed prototypes are presented. The designs were carried on terrestrial trunked radio mobile stations in the 380-400-MHz frequency band and supported high power levels (greater than 40 dBm).

An adaptive digital method of imbalances cancellation in LINC transmitters

The linear amplification using nonlinear components (LINC) technique is a well-known power amplifier linearization method to reduce adjacent channel interference in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method is described which corrects any gain and phase imbalances in LINC transmitters mainly due to the unmatching of the two amplifier paths. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficient to adjust gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator imbalances and loop delay. A computer simulation has been carried out to verify the method functionality.

Nonlinear distortion cancellation using LINC transmitters in OFDM systems

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system, such as Digital Video Broadcasting (DVB) system, which is based on a very sensitive to nonlinear distortions OFDM modulation scheme. The major drawback of LINC transmitters is the inherited sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method, which corrects any gain and phase imbalances in LINC transmitters mainly due to the un-matching of the two amplifier paths, is described. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficients to correct gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator impairments. A computer simulation has been carried out to verify method functionality.

Performance of a new digital baseband predistorter using calibration memory

Digital predistortion of a baseband signal is a well-known method of power amplifier (PA) linearization used to reduce adjacent channel interference (ACI) in a nonconstant envelope modulation system. This paper proposes a specific predistorter configuration based on the estimation of the PA characteristics extracting its linear behavior and comparing with a linear model by means of a calibrating signal. The effects of quadrature modulator and demodulator imbalances are included in our analysis. The effects and requirements of the reconstruction filters are stated and a new method for the loop delay estimation is presented. We also focus our attention in some design considerations and simulation results related to the use of a fixed point digital signal processor (DSP). Simulations show that out-of-band skirts lower than -60 dBc can be obtained for a narrow bandwidth system.

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.

Amplifier linearization using a new digital predistorter for digital mobile radio systems

This paper presents some simulation results based in the well known predistortion technique of the baseband signal to reduce the adjacent channel interference (ACI). This known effect is produced by a typical nonlinear device (power amplifier) when a varying envelope modulation scheme is used.

Analysis of closed loop power control modes in UTRA-FDD under time varying multipath channels

Fast power control is perhaps the most important aspect in a WCDMA system like UTRA-FDD. In this paper, closed loop power control procedures in UTRA-FDD are studied. A physical layer simulator, which has been implemented in the C language from the standard of the UTRA-FDD mode, has been the tool to get the results included in this research. Simulations have been made for different mobile speeds (3, 30, 50 and 120 Km/h) getting very different results. Power control gets worse quickly as the mobile speed grows. The implementation of an adaptive algorithm to predict the received power to try to improve the power control has been studied, but large improvements have not been obtained. The probability distribution of the power control error and influence of SIR estimation error have also been studied.

Input impedance antenna automatic matching system

The paper presents a new design for an antenna input impedance automatic matching system. In order to achieve this main objective, it is necessary to accomplish several intermediate tasks. On the one hand, a study of the implementation of a generic electronically tunable impedance synthesizer is carried out. Then, a prototype based on the research is constructed, and its characteristics and improvements are evaluated. On the other hand, a fully automatic system is developed. The device is integrated inside a commercial mobile radio communications handset, in order to evaluate the improvements achieved with the automatic system. Experimental results about the influence of the human body on the input impedance of helical and monopole antennas are presented for the 380-400 MHz frequency band. Several control methods are studied.

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.

Cartesian loop transmitter for TETRA

This paper presents the design process of a Cartesian loop transmitter and the simulated results include the effects of IQ modulator and demodulator, the requirements for the low-pass filter, open loop gain and loop delay, to verify the TETRA (Terrestrial European Trunked Radio) ACI mask and stability. The Cartesian feedback will suppose an algebraic equation for each sample at the input of the system. The modulator and demodulator errors are simulated using a matricial model for the gain and phase imbalances and DC-offset. The low-pass filter is simulated with a first order infinite impulsional response filter. The AM/AM and AM/PM power amplifier conversion is simulated with polynomic regression from Mitsubishi (M68749) measurements.