Coexistence of OTFS Modulation With OFDM-based Communication Systems

TL;DR

This paper investigates how OTFS modulation can coexist with OFDM-based systems, analyzing the impact of cyclic prefix lengths on channel response and proposing a pilot-aided channel estimation method to improve performance.

Contribution

It derives the input-output relation for coexisting OTFS and OFDM systems considering unequal CP lengths and introduces an effective channel estimation technique.

Findings

Unequal CP lengths reduce DD domain channel sparsity.

Ignoring CP length differences degrades bit error rate performance.

Proposed CE method outperforms existing threshold-based techniques.

Abstract

This study examines the coexistence of orthogonal time-frequency space (OTFS) modulation with current fourth- and fifth-generation (4G/5G) wireless communication systems that primarily use orthogonal frequency-division multiplexing (OFDM) waveforms. We first derive the input-output-relation (IOR) of OTFS when it coexists with an OFDM system while considering the impact of unequal lengths of the cyclic prefixes (CPs) in the OTFS signal. We show analytically that the inclusion of multiple CPs to the OTFS signal results in the effective sampled delay-Doppler (DD) domain channel response to be less sparse. We also show that the effective DD domain channel coefficients for OTFS in coexisting systems are influenced by the unequal lengths of the CPs. Subsequently, we propose an embedded pilot-aided channel estimation (CE) technique for OTFS in coexisting systems that leverages the derived IOR for accurate channel characterization. Using numerical results, we show that ignoring the impact of unequal lengths of the CPs during signal detection can degrade the bit error rate performance of OTFS in coexisting systems. We also show that the proposed CE technique for OTFS in coexisting systems outperforms the state-of-the-art threshold-based CE technique.