Non Linear Distortions introduced by Amplifiers on COFDM signals. Measurements, Effects and Compensation Techniques
Coded Orthogonal Frequency Division Multiplexed (COFDM) techniques, used by terrestrial European broadcasting systems (DAB, DVB-T), could be adopted in the last mile of the downlink channel for Wireless Broadband Communication System to provide Multimedia Services to mobile or nomadic users by cellular coverage techniques, as evinced from the actual research activity. COFDM signals are characterised by non-constant envelope (peak-to-mean power ratio > 10 dB) which forces to project amplifiers with low or well-counteracted non-linear distortion effects. Our aim is to present Itelco experience to characterise non-linear distortions introduced by final amplifiers on COFDM signals (AM/AM, AM/PM and NonLinearities with Memory). Both experimental measurements and simulation results will be shown. Moreover we will point out the improvements achievable by digital baseband predistortion, to counteract for AM/AM and AM/PM non-linearities, and by RF compensation techniques to remove Non Linear Memory effects.
KeywordsMemory Effect Orthogonal Frequency Division Multiplex Signal Digital Video Broadcasting OFDM Signal Memory Distortion
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