Enhanced OTFS using Channel Modulation

Orthogonal time frequency space (OTFS) modulation provides robust communication in doubly-selective channels owing to its non-fading nature in the delay-Doppler (DD) domain. In this paper, for the first time in the literature, we propose a novel transmission scheme where the performance of OTFS is further enhanced through the use of channel modulation (a.k.a media-based modulation). In channel modulation (CM), radio frequency (RF) mirrors placed in the near-field of the transmit antenna are controlled by information bits, which create different channel fade realizations that form the CM alphabet. The proposed OTFS-CM scheme is shown to simultaneously offer the benefits of robustness to high-Doppler due to DD signal processing in OTFS and an additional SNR gain due to the improved distance properties of the signal set due to CM. For example, simulation results show that, at a bit error rate (BER) of $10^{-4}$, the proposed OTFS-CM scheme achieves an SNR gain of about 1 to 4 dB compared to OTFS without CM, which is attributed to the enhanced distance profile of the OTFS-CM signal set. For the same reason, the SNR gain increases with increase in the dimensionality of the signal at the receiver and the number of RF mirrors.