A low complexity underwater sweep-spread communication method within OCDM framework

Leveraging the correlation between the received signal of sweep-spread carrier (SSC) in a multipath channel and the orthogonal chirp division multiplexing (OCDM) symbol, this paper introduces the discrete fractional Fourier transform (DFnT) and proposes a low-complexity SSC demodulator. Within this framework, most multipath components in SSC are treated as subcarriers within the OCDM system and are filtered out using the DFnT. Training symbols are then employed to record the phase shifts caused by residual nearby multipath, and a deflected constellation diagram is utilized for the direct demodulation of data symbols. Compared to the traditional demodulation and equalization methods, the strategy of using DFnT transform in the baseband in this paper reduces the complexity of multipath filtering and channel equalization to near O(1). Simulations and experiments indicate that the proposed demodulator maintains performance comparable to conventional demodulation methods, while significantly reducing complexity.