Performance of OTFS and OCDM Schemes in Underwater Acoustic Communication Channels

Signaling schemes robust to large Doppler shifts are needed for reliable underwater acoustic (UWA) communication, and orthogonal time frequency space (OTFS) and orthogonal chirp division multiplexing (OCDM) are two promising schemes in this regard. We evaluate the performance of these schemes in realistic UWA channels. We see that OTFS and OCDM have significantly lower symbol error probability (SEP) compared to orthogonal frequency division multiplexing (OFDM) when perfect channel information is available to the receiver. While OTFS and OCDM still performed better than OFDM with estimated channel information, the reductions in SEPs are comparatively lower. Thus, OTFS and OCDM are seen to be sensitive to estimation errors and the outdated nature of channel information. A simple channel interpolation is then proposed to account for the variations of the channel between channel estimation phases. This is seen to reduce SEP compared to the case where the channel variations are ignored.