Detection, Synchronization and Doppler Scale Estimation

Three key components in the orthogonal frequency‐division multiplexing (OFDM) receiver design are discussed in this chapter: preamble detection, synchronization and residual Doppler shift estimation. For clarity of presentation, this chapter focuses on detection, synchronization and Doppler scale estimation in the underwater acoustic OFDM system in a linear time‐varying channel with a common Doppler scale factor. The first section discusses several cross‐correlation based methods for detection, synchronization and Doppler scale estimation, based on Doppler‐insensitive or sensitive waveforms. Next, it presents detection, synchronization and Doppler scale estimation for a specifically designed waveform that consists of two identical OFDM symbols preceded by a cyclic prefix (CP). This is followed by a discussion on the zero‐padded (ZP)‐OFDM block structure for synchronization and Doppler scale estimation. Several design examples for practical systems are presented, before the chapter ends with a discussion on the residual Doppler shift estimation methods for ZP‐OFDM.