Efficient Baseband Digital Predistorter Using Lut for Power Amplifier (PA) with Memory Effect

Modern communications systems will have to integrate multiple radio technologies to support a large number of wireless standards (WLAN, WPAN...). This system should operate with third generation (3G) air interface standards, where non constant envelope modulation formats (MQAM, OFDM...) are required. The amplification of a modulated signal with large variation of envelope introduces distortions when the input-output characteristic is nonlinear. These distortions are particularly important when the power amplifier (PA) has non-linear memory effects with a wideband signal. The technique proposed in this paper aims to fight against this phenomenon by optimizing the method developed in the laboratory [7,20] for a real-time implementation. This technique is able to provide exactly the reverse characteristics of a PA modeled by a Hammerstein model in base band. Its principle is to find the largest real root of a polynomial related to the analytical model of the PA and to the input signal to be amplified to calculate a pre-distorted signal. To reduce significantly the computation time, an implementation by the LUT method is proposed. This method uses two pre-distortion principles and can be implemented on a FPGA board with table bases method known for simplicity including in the same way the correction of the memory effect.