OTFS: A New Generation of Modulation Addressing the Challenges of 5G.

In this paper, we introduce a new 2D modulation scheme referred to as OTFS(Orthogonal Time Frequency & Space) that multiplexes information QAM symbolsover new class of carrier waveforms that correspond to localized pulses in asignal representation called the delay-Doppler representation. OTFS constitutesa far reaching generalization of conventional time and frequency modulationssuch as TDM and FDM and, from a broader perspective, it establishes aconceptual link between Radar and communication. The OTFS waveforms couple withthe wireless channel in a way that directly captures the underlying physics,yielding a high-resolution delay-Doppler Radar image of the constituentreflectors. As a result, the time-frequency selective channel is converted intoan invariant, separable and orthogonal interaction, where all received QAMsymbols experience the same localized impairment and all the delay-Dopplerdiversity branches are coherently combined. The high resolution delay-Dopplerseparation of the reflectors enables OTFS to approach channel capacity withoptimal performance-complexity tradeoff through linear scaling of spectralefficiency with the MIMO order and robustness to Doppler and multipath channelconditions. OTFS is an enabler for realizing the full promise of MUMIMO gainseven in challenging 5G deployment settings where adaptation is unrealistic.