A Survey on Physical Layer Techniques and Challenges in Underwater Communication Systems

In the past decades, researchers/scientists have paid attention to physical layer of underwater communications (UWCs) due a variety scientific, military, and civil tasks completed beneath water. This includes numerous activities critical for communication, such as survey monitoring oceans, rescue, response disasters under sea. Till end last decade, many review articles addressing history UWC been published which were mostly focused on sensor networks (UWSN), routing protocols, optical communication (UWOC). paper provides an overview acoustic (UWA) techniques including cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), zero padding (ZP-OFDM), time-domain synchronization (TDS-OFDM), multiple input output (MIMO-OFDM), generalized (GFDM), unfiltered (UF-OFDM), continuous phase modulation (CPM-OFDM), filter bank multicarrier (FBMC) modulation, MIMO, spatial technologies (SMTs), index (OFDM-IM). Additionally, this comprehensive UWA channel modeling problems challenges, transmission loss, propagation delay, signal-to-noise ratio (SNR) distance, multipath effect, ambient noise delay spread, Doppler effect modeling, shift estimation. Further, modern discussed. study also discusses different technology in terms spectral efficiency, computational complexity, date rate, bit error rate (BER), energy efficiency along with their merits demerits.