OFDM with Minimal PAPR and Non-Coherent Demodulation for Non-Stationary Underwater Acoustic Channels

Non-stationary nature of underwater environment, caused by sea disturbance, movement of a support vessel and underwater robots, significantly complicates the performance of digital communication and navigation systems by the short coherence time of an underwater acoustic (UA) communication channel. Often, the stability of the underwater acoustic path parameters even at short distances (units of km) does not exceed hundreds of milliseconds in some cases, at significant distances (hundreds of km) this value can be up to fractions/units of seconds when using the appropriate frequency band for communication. Possessing a wide range of amplitude-phase parameters, which vary from static, quasi-stationary to absolutely unstable, the underwater acoustics remains the only wireless means of communication in the World Ocean despite all its complexity. Considering all the mentioned challenges of underwater acoustic communications, as well as modern advanced developments in this field, a concept of a new class of multi-frequency (OFDM) multiplexing methods was developed for transmitting digital data using new pseudo-random sequences with incoherent demodulation of symbols in multipath non-stationary underwater medium.