OSDMA: Orthogonal Signal Division Multiple Access for Downlink Multiuser Underwater Acoustic Networks

The extreme and uncertain underwater environment presents significant challenges in achieving reliable acoustic communications, mainly due to limited bandwidth and time variability. To address these challenges, this work proposes a novel multiple-access technique for downlink multiuser networks, called Orthogonal Signal Division Multiple Access (OSDMA), which enables simultaneous transmission of different data streams from a single transmitter to the corresponding receivers/users by modulating the streams with an orthogonal Inverse Discrete Fourier Transform (IDFT) matrix. In a low-noise environment, each receiver/user can accurately estimate the channel and demodulate the data. Emulations and simulations are conducted based on at-sea channel measurements. The results show that OSDMA offers greater robustness against underwater time-varying channels than Orthogonal Frequency Division Multiple Access (OFDMA) and Non-Orthogonal Multiple Access (NOMA).