Near-CAZAC Preamble Sequences for Initial Synchronization in Spectrally Compact OFDM

Abstract

In practical orthogonal frequency division multi-plexing systems and standards, preamble waveforms are adopted to facilitate initial timing and frequency synchronization. These preamble waveforms are constructed from properly designed preamble sequences which possess exact or near zero periodic autocorrelation (ZAC) property to achieve robust synchronization and consist of exact or near constant amplitude (CA) symbols to achieve low waveform peak-to-average power ratio (PAPR). Unfortunately, preamble waveforms carrying conventional CAZAC sequences (which have ZAC property and consist of CA symbols) or near-CAZAC sequences result in large power spectral sidelobes and thus are not spectrally compact. In this paper, new near-CAZAC sequences are designed to construct spectrally compact OFDM preamble waveforms with robust timing and frequency synchronization and very low waveform PAPR comparable to those constructed from the conventional CAZAC sequences.