Abstract
Predistortion (PD) technique has been proposed to linearize the power amplifier (PA) and improve the power efficiency for non-constant envelope modulation schemes (Cavers, 1990). In this paper a new PD scheme based on block estimation suitable for burst type communications is described. Piecewise linear regression is applied to estimate the AM/AM and AM/PM distortions. The predistortion is simply the inverse of these estimated curves up to a predefined point. The PD is implemented using two cascaded uniform look-up tables (LUT) for amplitude and phase corrections. An adaptation algorithm is proposed to compensate for variations of PA characteristics due to temperature and/or shift of frequency. Simulations are carried out to find the optimum size of the LUT. Simulation results for 16-QAM modulation show significant reduction in adjacent channel interference (ACI) and considerable improvement in constellation quality for a typical class A high power amplifier. The error vector magnitude (EVM) criterion is used to measure the constellation quality. The system set-up to implement the algorithm is presented. Experimental results for 16-QAM modulated signal with the symbol rate of 151.2 kHz are presented. As shown in section V, about 10-15 dB power leakage reduction in adjacent channel and about 13 dB improvement in EVM were obtained.
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