On the Diversity of Uncoded OTFS Modulation in Doubly-Dispersive Channels

Abstract

Orthogonal time frequency space (OTFS) is a 2-dimensional (2D) modulation technique designed in the delay-Doppler domain. A key premise behind OTFS is the transformation of a time varying multipath channel into an almost non-fading 2D channel in delay-Doppler domain such that all symbols in a transmission frame experience the same channel gain. It has been suggested in the recent literature that OTFS can extract full diversity in the delay-Doppler domain, where full diversity refers to the number of multipath components separable in either the delay or Doppler dimension, but without a formal analysis. In this paper, we present a formal analysis of the diversity achieved by OTFS modulation along with supporting simulations. Specifically, we prove that the asymptotic diversity order of OTFS (as SNR $\to \infty$) is one. However, in the finite SNR regime, potential for a higher order diversity is witnessed before the diversity one regime takes over. Also, the diversity one regime starts at lower BER values for increased frame sizes. We also propose a phase rotation scheme for OTFS using transcendental numbers. We show that OTFS with this proposed scheme extracts the full diversity in the delay-Doppler domain.

Accepted in IEEE Trans. Wireless Commun. \c{opyright} 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses. https://www.ieee.org/content/dam/ieee-org/ieee/web/org/pubs/pspb/opsmanual.pdf

References in corpus (4)

• OTFS: A New Generation of Modulation Addressing the Challenges of 5G
• A Simple Two-stage Equalizer With Simplified Orthogonal Time Frequency Space Modulation Over Rapidly Time-varying Channels
• OTFS - Orthogonal Time Frequency Space
• Low-Complexity Iterative Detection for Orthogonal Time Frequency Space Modulation

Cited by in corpus (1)

• Multiple Access in the Delay-Doppler Domain using OTFS modulation