This paper proposes decision-feedback multiple differential detection (DFMDD) employing simple first-order channel prediction for time and frequency selective channels, i.e., double selective channels. For the sake of decision-feedback and simple channel prediction, the computational complexity of the proposed DFMDD is independent of the number of differential detection (DD) operations. Computer simulation results confirm that the proposed DFMDD has excellent bit error rate (BER) performance compared with the conventional DD on double selective fading channels. In addition, the field evaluation results in actual shallow underwater acoustic communications (UWAC) and terrestrial acoustic communications confirm that the proposed DFMDD has better BER performance than the conventional DD on fast time-varying channels.

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Because commensurate transmission line circuits consisting of unit elements (UEs) are expressed using a z-transform, wave digital filters (WDFs) and a transient phenomenon can be obtained. There are two types of WDF, i.e., voltage and current WDFs, and hence the reactive power in the steady state can also be obtained. Moreover, normalized WDFs can be obtained using ideal transformers. By applying the construction method for WDFs to resonant tunneling diodes (RTDs), RTDs can be expressed similarly to WDFs. We show that physical phenomena defined as the wave function of quantum wells and the existence probability of electrons correspond to the voltage standing wave generated along the UEs of WDFs. Note that RTDs can be resonant even if the standing wave exists in the steady state.

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