Waveform Candidates for 3D Network: A Comparative Study of OTFS, AFDM, ODDM and OFDM

Abstract

Integrating terrestrial (TN) and non-terrestrial (NTN) networks into 3D user-centric cell-free massive multiple-input multiple-output (UC-CFmMIMO) architectures poses significant challenges, including extreme Doppler shifts, spatially diverse delay spreads and dynamic topology changes. This paper provides the first comprehensive comparison of four waveforms — Orthogonal Time-Frequency-Space (OTFS), Affine Frequency-Division-Multiplexing (AFDM), Orthogonal-Delay-Doppler-Multiplexing (ODDM) and Orthogonal-Frequency-Division-Multiplexing (OFDM) — across three deployment scenarios: ground-based UC-CFmMIMO, NTN-dominant UC-CFmMIMO and 3D UC-CFmMIMO. By integrating 3GPP TN (TR 38.901) and NTN (TR 38.811) channel models within a unified framework, we demonstrate the superiority of AFDM in NTN scenarios and the robustness of OTFS in unified space-air-ground networks. ODDM’s staggered pulse shaping reduces ground-level intersymbol interference and OFDM remains optimal for low-mobility deployments. We discuss the need for adaptive waveform switching to balance Doppler/delay robustness, latency and complexity, offering actionable guidelines for 6G system designers.

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