A simple predistorter in fixed microwave radio system with the transmission power control

This paper presents an orthogonal look up tables (LUTs) based predistorter (PD) whose coefficients are generated adaptively to minimize the out-band distortion power. It has low complexity and high robustness to impairments from the feedback circuit, with the drawback of slow convergence meanwhile. To counteract the performance degradation in the case of fast transmission power control (TPC) due to the slow convergence, a selection mechanism between on-line generated and memorized coefficients is proposed. The orthogonal LUTs based perdistorter and its TPC countermeasure were implemented in a fixed microwave radio system, where 14 dB reduction of adjacent channel leakage ratio (ACLR) was verified relying on experiments. In addition, the performance in the case of 100 dB/s TPC was also confirmed to satisfy the ACLR requirement of -45 dB.