Orthogonal Delay Scale Space Modulation: A New Technique for Wideband Time-Varying Channels

TL;DR

This paper introduces ODSS, a novel modulation scheme inspired by OTFS, designed to effectively handle wideband time-varying channels by utilizing delay-scale space transformations, resulting in improved performance and low-complexity receivers.

Contribution

The paper develops ODSS modulation, including transmission and reception schemes, and introduces $mbda$-convolution in delay-scale space, enhancing wideband channel handling over OTFS.

Findings

ODSS outperforms OTFS and OFDM in bit error rate in wideband channels.

The channel matrix in ODSS is nearly diagonal, enabling low-complexity receivers.

ODSS effectively manages frequency-dependent Doppler shifts in wideband channels.

Abstract

Orthogonal Time Frequency Space (OTFS) modulation is a recently proposed scheme for time-varying narrowband channels in terrestrial radio-frequency communications. Underwater acoustic (UWA) and ultra-wideband (UWB) communication systems, on the other hand, confront wideband time-varying channels. Unlike narrowband channels, for which time contractions or dilations due to Doppler effect can be approximated by frequency-shifts, the Doppler effect in wideband channels results in frequency-dependent non-uniform shift of signal frequencies across the band. In this paper, we develop an OTFS-like modulation scheme -- Orthogonal Delay Scale Space (ODSS) modulation -- for handling wideband time-varying channels. We derive the ODSS transmission and reception schemes from first principles. In the process, we introduce the notion of $\omega$-convolution in the delay-scale space that parallels the twisted convolution used in the time-frequency space. The preprocessing 2D transformation from the Fourier-Mellin domain to the delay-scale space in ODSS, which plays the role of inverse symplectic Fourier transform (ISFFT) in OTFS, improves the bit error rate performance compared to OTFS and Orthogonal Frequency Division Multiplexing (OFDM) in wideband time-varying channels. Furthermore, since the channel matrix is rendered near-diagonal, ODSS retains the advantage of OFDM in terms of its low-complexity receiver structure.