Recent wireless communication systems demand very high signal to noise ratios (SNR). However, the continuous improvement of power amplifier (PA) efficiencies has led to an increased nonlinearity behavior, severely degrading system's fidelity. One former way to minimize this effect consisted on using constant envelope modulation systems, trading higher spectrum bandwidths for lower distortion. Unfortunately, spectrum bandwidth became a scarce precious good imposing non-constant envelope modulation schemes. Therefore, the PA nonlinearity is nowadays of primordial importance to the maximization of the SNR in this type of telecommunication systems. The main objective of this project is to propose new design PA procedures intended to improve linearity in presence of complex communication signals of non-constant envelope. To fulfill this goal, the time and frequency domain properties of the complex modulation techniques will first be studied. Special attention will be given to the peak to average ratio of the excitation's time description, and to its complex spectral representation, mainly to the correlation between its different spectral lines. The information gathered with this analysis, associated to the previous background of the authors, will inspire improvements to the existing nonlinear RF circuits' simulation tools, or even to the proposal of novel nonlinear analysis methods, specially tailored for the type of modulated signals under study. With the aid of the proposed simulation techniques, and the knowledge of the driving signal statistics, the nonlinear behavior of PA will be studied when in the presence of complex communication signals. The correct understanding of this behavior will end up in the suggestion of a new procedure for the design PAs optimized for linearity. Finally, a PA prototype specially designed for handling multi-tone complex modulated signals will be implemented and tested. That will serve as the practical validation of the proposed theoretical analysis methods and circuit design tools.
|Start Date: 01-07-2002|
|End Date: 30-06-2004|
|Team: Nuno Miguel Gonçalves Borges de Carvalho, José Carlos Esteves Duarte Pedro, João Paulo Martins|
|Groups: Radio Systems – Av|
|Local Coordinator: Nuno Miguel Gonçalves Borges de Carvalho|