Index modulated OFDM for underwater acoustic communications

Abstract

UWA channels exhibit time-varying multipath characteristics. To this end, OFDM is well known for its robustness against multipath channels but is prone to ICI induced by time variation. More recently, inspired by spatial modulation, the so-called IM-OFDM has also been proposed to provide higher system throughput than plain OFDM under certain conditions. A key feature of IM-OFDM is that partial subcarriers are kept inactive. This could potentially improve system performance in the presence of ICI. Leveraging on this, we are the first to propose IM-OFDM for UWA communications. On the other hand, however, we realize that ICI could potentially lead to energy leakage from active subcarriers to inactive ones, and impair the demodulation of IM-OFDM. In this article, we introduce IM-OFDM for UWA communications and propose a hybrid IM-OFDM scheme with improved spectral efficiency. We then review existing ICI self-cancellation techniques for generic OFDM, and propose a new ICI cancellation method for IM-OFDM.