Separation of time-varying multipath arrivals by converting their time delays into their frequency reallocations

Multipath propagation causes the transmitted signal to take numerous, time-varying different-length paths to receiver. Exploitation of conventional frequency-constant carrier signals for communication over underwater acoustic channels typically shows that intricate mutual time variations of multipath arrivals create a serious problem for equalizers to compensate for non-stable interferences. Communication over such channels can be, however, substantially improved by using not a conventional constant-frequency carrier but a carrier consisting of a sequence of steep sweeps. The method provides significant processing improvement enabling clear separation of multipath arrivals by converting their time delays into their frequency reallocations. When despreading the signal, the best suitable multipath can be filtered not as traditionally in time domains, applying complex equalizers, but in frequency domains via usual band-pass filters. An important aspect is that every multipath is separated together with its individual time-varying phase impairments, obtained with the signal during its propagation over a certain path, whereas signal impairments, specific for a given path, are completely separated from other signal impairments delivered by the signal during its propagation over every different path.