Enhanced OTFS using Channel Modulation and Delay-Doppler Indexing

Discrete Zak transform (DZT) based orthogonal time frequency space (OTFS) modulation provides robustness in high-mobility wireless channels and benefits in implementation complexity. Channel modulation (CM) and index modulation (IM) are promising physical layer techniques that offer improved spectral efficiencies and bit error performance. In this paper, we propose an OTFS-CM-IM scheme that integrates CM and delay-Doppler (DD) domain indexing that enhances the performance of DZT-OTFS. For the proposed OTFS-CM-IM scheme, we derive a compact input-output relation which enables system simulations and the computation of an upper bound on the bit error performance and the distance properties of the signal set. We consider two types of DD indexing, one with constellation indexing and one without. Our simulation results show that the proposed OTFS-CM-IM scheme performs better than the OTFS scheme (without CM and IM) and the OTFS-CM scheme (without IM). This enhanced performance is attributed to the improved distance properties of the proposed OTFS-CM-IM signal set.