Real Signal DHT-OFDM With Index Modulation for Underwater Acoustic Communication

This article presents orthogonal frequency division multiplexing (OFDM) that is based on discrete Hartley transform (DHT) as a modulation transform for underwater acoustic (UWA) communication instead of the conventional discrete Fourier transform (DFT). The proposed DHT-OFDM scheme has the advantages of reducing the pilot overheads required to track the UWA channel effects by 50%, increasing the robustness against the carrier frequency offset, and relaxing the system complexity. The receiver design of the proposed system is based on DFT instead of DHT to enable low-complexity estimation and equalization tasks and to overcome the issue of intercarrier coupling, which deteriorates up to half of the existed DHT-OFDM data rate. For more spectral efficiency harvesting, the proposed underwater DHT-OFDM has been extended to cooperate with the index modulation. Simulation and real experimental results have been conducted to demonstrate the outperformance of the proposed schemes against the benchmarks in terms of bit error rate, Doppler shift, spectral efficiency, and system complexity.