Low-Complexity Equalization for Orthogonal Time and Frequency Signaling (OTFS)

TL;DR

This paper presents a low-complexity equalizer for OTFS that significantly improves performance over OFDM in high-mobility scenarios by utilizing soft-symbol feedback for interference cancellation.

Contribution

The paper introduces a novel low-complexity equalization method with soft-symbol feedback for OTFS, enhancing its practical performance in time- and frequency-selective channels.

Findings

Achieves a 5dB gain over OFDM at BER of 10^-4 at 200 km/h.

Demonstrates effectiveness of equalizer in delay-Doppler and time-frequency domains.

Improves OTFS performance with reduced complexity.

Abstract

Recently, a new precoding technique called orthogonal time-frequency signaling (OTFS) has been proposed for time- and frequency-selective communication channels. OTFS precodes a data frame with a complete set of spreading sequences and transmits the results via orthogonal frequency division multiplexing (OFDM). OTFS uses two dimensional (2D) linear spreading sequences in time and frequency which are the basis functions of a symplectic Fourier transform. OTFS allows the utilization of time- and frequency-diversity but requires maximum likelihood decoding to achieve full diversity. In this paper we show performance results of a low-complexity equalizer using soft-symbol feedback for interference cancellation after an initial minimum-mean square error equalization step. Performance results for an implementation in the delay-Doppler domain and in the time-frequency domain are compared. With our equalizer, OTFS achieves a gain of 5dB compared to OFDM for a bit error rate of $10^{-4}$ and a velocity of $200\,\text{km/h}$.