Frame and Frequency Acquisition for OFDM

Abstract

Frame timing and carrier frequency offsets in orthogonal frequency division multiplexing (OFDM) may drastically degrade performance if not accurately compensated. In practice, these offsets are estimated by transmitting a training block at the beginning of each frame. By designing this training block to have a repetitive structure, various estimation methods have been proposed in the literature. These existing estimation methods rely on the repetitive structure and not on the actual training block. In other words, these methods are based on some second-order statistics of the received signal. Here, we instead use first-order statistics and two modified versions of the nonlinear least squares method. The proposed methods are shown to provide significantly more accurate frame and frequency synchronization at the expense of a slight increase in implementation complexity. As a by-product, an accurate channel estimate is obtained with the same preamble, thus reducing the resources allocated to training.