Orthogonal Time Frequency Space (OTFS) With Dual-Mode Index Modulation

A Novel Block-Wise Index Modulation Scheme for High-Mobility OTFS Communications

“…Unlike the conventional random IM schemes applied in OTFS systems [32], [33], our proposed DeIM-OTFS and DoIM-OTFS schemes activate a block of delay/Doppler resource bins simultaneously, which can help to further improve the receiver performance and combat the effect of high mobility time-varying channels.…”

“…Specifically, the index bits are transmitted by the indices of the activated OTFS delay-Doppler resources, where the active resource bins are independently randomly selected. To further improve the system performance, OTFS with dual-mode index modulation (OTFS-DM-IM) was proposed in [33], which provides a desired trade-off between transmission reliability and spectral efficiency (SE). To effectively decode the index bits and constellation bits, several detectors have also been proposed in the literature.…”

“…In [32], a minimum mean squared error with maximum likelihood (MMSE-ML) detector was proposed, where the MMSE criterion was employed for the detection of constellation bits and index bits, and the ML principle is utilized to detect the indices information. In [33], a modified log likelihood ratio (LLR) detector based on the minimum Hamming distance was investigated to improve the BER performance. However, the performance analysis for the designed schemes and detectors in [32] and [33] only considers ideal bi-orthogonal OTFS pulses and requires mobile channels exhibiting on-the-grid delays and Doppler shifts, which are unrealistic assumptions in practical OTFS system deployment.…”

“…In [33], a modified log likelihood ratio (LLR) detector based on the minimum Hamming distance was investigated to improve the BER performance. However, the performance analysis for the designed schemes and detectors in [32] and [33] only considers ideal bi-orthogonal OTFS pulses and requires mobile channels exhibiting on-the-grid delays and Doppler shifts, which are unrealistic assumptions in practical OTFS system deployment.…”

“…On the other hand, the channel delay and Doppler shifts will cause severe inter-symbol interference (ISI) in high mobility OTFS communications. The existing IM-OTFS systems [32], [33] only activate independent delay-Doppler resources and cannot determine the active and inactive resources accurately at the receiver, leading to an inevitable performance loss. Therefore, it is necessary to develop more efficient and reliable IM schemes for OTFS transmissions by considering the effects caused by the channel delays and Doppler spreads.…”