Constant-Amplitude Sequences for Spectrally Compact OFDM Training Waveforms

Constant-amplitude (CA) sequences are desirable to construct training waveforms in orthogonal frequency division multiplexing (OFDM) systems in order to achieve accurate channel estimation and robust initial time and frequency synchronization. However, widely adopted CA pseudorandom-noise and Zadoff-Chu sequences suffer from large power spectral sidelobes and thus render low spectral compactness in OFDM training waveforms. This arouses the design of new CA sequences to provide compact spectrum. In this paper, new CA sequences of length $N$ are developed in explicit sequence expressions for all composite sequence lengths and all prime sequence lengths larger than 11 under all parametric conditions, and shown to provide higher spectral compactness than existing CA sequences.