Analysis of Doppler and Multipath on Orthogonal Chirp Division Multiplexing in Shallow Water Acoustic Channel

In the scenario of underwater acoustic communication, Orthogonal Frequency Division Multiplexing (OFDM) is widely used for its high spectral efficiency and high transmission rate. However, OFDM is sensitive to Doppler shift, which will generate inter-carrier interference to degrade bit error rate performance. Orthogonal Chirp Division Multiplexing (OCDM) consists of multiplexing a number of chirp waveforms that are mutually orthogonal with each other and share the same bandwidth and time slot, achieving good robustness against multipath and Doppler shift. This study reviews the concepts of Orthogonal Chirp Division Multiplexing and combines this multicarrier communication scheme with an underwater acoustic channel. Unlike previous studies analyzing within the signal domain, this study formulates the mathematical model of OCDM in shallow water acoustic channel and illustrates the reason why OCDM can outperform OFDM in both Doppler robustness and multipath robustness, which is a necessary and solid complement for OCDM in the further development of underwater acoustic communication.