Linear Precoding Design for OTFS Systems in Time/Frequency Selective Fading Channels

TL;DR

This paper introduces algebraic number theory-based linear precoding for OTFS systems, ensuring maximal diversity and coding gains in time and frequency selective fading channels without CSI at the transmitter.

Contribution

It proposes novel linear precoding methods for OTFS that guarantee full diversity and improve performance over existing schemes without rate loss or transmitter CSI.

Findings

Proposed precoding guarantees maximal diversity in fading channels.

Simulation shows superior performance over unprecoded and phase-rotated OTFS.

No transmission rate loss or need for channel state information at transmitter.

Abstract

Even orthogonal time frequency space (OTFS) has been shown as a promising modulation scheme for high mobility doubly-selective fading channels, its attainability of full diversity order in either time or frequency selective fading channels has not been clarified. By performing pairwise error probability (PEP) analysis, we observe that the original OTFS system can not always guarantee full exploitation of the embedded diversity in either time or frequency selective fading channels. To address this issue and further improve system performance, this work proposes linear precoding solutions based on algebraic number theory for OTFS systems over time and frequency selective fading channels, respectively. The proposed linear precoded OTFS systems can guarantee the maximal diversity and potential coding gains in time/frequency selective fading channels without any transmission rate loss and do not require the channel state information (CSI) at the transmitter. Simulation results are finally provided to illustrate the superiority of our proposed precoded OTFS over both the original unprecoded and the existing phase rotation OTFS systems in time/frequency selective fading channels.