Block based predistortion for amplifier linearization in burst type mobile satellite communications

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.