Coarse Time Delay Estimation for Pre-Correction of High Power Amplifiers in OFDM Communications

Orthogonal Frequency Division Multiplexing (OFDM) modulations used in DAB, DVB-T and future 4G communications standards are highly sensitive to the presence of non-linear distortion and synchronization errors between the transmitted and received signals. Digital precorrection schemes can be applied for the compensation of the AM/AM and AM/PM distortion introduced by High Power Amplifiers (HPA). However, this linearization process cannot be realized successfully unless the path delay introduced by the analog chains, required for the observation of the HPA output, is previously estimated. A coarse time delay estimation (TDE) algorithm robust to the presence of unknown non-linearities is presented in this paper. The proposed technique provides the basis for a fast time alignment of base-band signals within a range of several samples with a discrete resolution. Any residual timing offset can be then estimated and compensated by defining some analysis criteria over the obtained TDE spectrum. Keywords— Synchronization, communication systems, nonlinear distortion, orthogonal frequency division multiplexing, multicarrier systems.