Does 6G Need a New Waveform: Comparing Zak-OTFS with CP-OFDM

TL;DR

This paper compares Zak-OTFS and CP-OFDM waveforms for 6G, highlighting their architectural differences and suitability for various propagation environments, especially in high mobility and large cell scenarios.

Contribution

It provides a comprehensive performance comparison of Zak-OTFS and CP-OFDM across diverse 6G channels, informing waveform selection based on use case and environment.

Findings

Zak-OTFS outperforms in high mobility/high delay spread scenarios.

CP-OFDM offers simpler equalization without ICI.

Performance depends on channel characteristics and architectural choice.

Abstract

Across the world, there is growing interest in new waveforms, Zak-OTFS in particular, and over-the-air implementations are starting to appear. The choice between OFDM and Zak-OTFS is not so much a choice between waveforms as it is an architectural choice between preventing inter-carrier interference (ICI) and embracing ICI. In OFDM, once the Input-Output (I/O) relation is known, equalization is relatively simple, at least when there is no ICI. However, in the presence of ICI the I/O relation is non-predictable and its acquisition is non-trivial. In contrast, equalization is more involved in Zak-OTFS due to inter-symbol-interference (ISI), however the I/O relation is predictable and its acquisition is simple. {Zak-OTFS exhibits superior performance in doubly-spread 6G use cases with high delay/Doppler channel spreads (i.e., high mobility and/or large cells), but architectural choice is governed by the typical use case, today and in the future. What is typical depends to some degree on geography, since large delay spread is a characteristic of large cells which are the rule rather than the exception in many important wireless markets.} This paper provides a comprehensive performance comparison of cyclic prefix OFDM (CP-OFDM) and Zak-OTFS across the full range of 6G propagation environments. The performance results provide insights into the fundamental architectural choice.