Channel Matched Sparse Non-Orthogonal frequency division multiplexing (CM-SNOFDM) Operating in Underwater Acoustic Channels

Underwater acoustic channels (UWAC) are characterized by time-varying frequency selective fading. OFDM technique is suitable for UWAC due to its robustness to channel's frequency selectivity. As acoustic transmission is supported at low frequencies, the channels suffer from low capacity. Using sparse Non-OFDM (S-NOFDM), spectral efficiency of OFDM is improved to overcome capacity limitations. The subcarriers of S-NOFDM are generated from a subset of OFDM orthogonal sub-channels and hence, it requires fewer spectral resources. Then, time shift is used to generate a number of non-orthogonal subcarriers to substitute for the reduction of OFDM sub-channels used in transmission. Channel-Matched S-NOFDM approach is investigated, where the set of selected sub-channels corresponds to maximum transmission through the channel. The results indicate that the proposed scheme has better performance than S-NOFDM and it approaches the performance of OFDM while using less spectral resources.