Zak-OTFS Based Coded Random Access for Uplink mMTC

TL;DR

This paper introduces a Zak-OTFS based coded random access scheme for uplink mMTC, improving reliability and scalability in doubly selective channels by enabling accurate channel estimation and interference cancellation.

Contribution

It presents a novel Zak-OTFS based CRA scheme tailored for doubly selective channels, outperforming OFDM-based methods in high mobility and user density scenarios.

Findings

Achieves lower packet loss rates compared to OFDM-based CRA.

Demonstrates robustness over standardized Veh-A channels.

Supports scalability for future mMTC deployments.

Abstract

This paper proposes a grant-free coded random access (CRA) scheme for uplink massive machine-type communications (mMTC), based on Zak-orthogonal time frequency space (Zak-OTFS) modulation in the delay-Doppler domain. The scheme is tailored for doubly selective wireless channels, where conventional orthogonal frequency-division multiplexing (OFDM)-based CRA suffers from unreliable inter-slot channel prediction due to time-frequency variability. By exploiting the predictable nature of Zak-OTFS, the proposed approach enables accurate channel estimation across slots, facilitating reliable successive interference cancellation across user packet replicas. A fair comparison with an OFDM-based CRA baseline shows that the proposed scheme achieves significantly lower packet loss rates under high mobility and user density. Extensive simulations over the standardized Veh-A channel confirm the robustness and scalability of Zak-OTFS-based CRA, supporting its applicability to future mMTC deployments.