Two-Timescale Learning for Pilot-Free ISAC Systems

TL;DR

This paper introduces a novel deep learning-based receiver architecture called T3former for pilot-free ISAC systems, which jointly estimates channels and detects signals without dedicated pilots, significantly improving data throughput and reliability.

Contribution

The paper proposes the T3former, a two-timescale Transformer architecture that eliminates pilot overhead and enhances joint channel estimation and detection in PMCW-NOMA ISAC systems.

Findings

T3former outperforms traditional SIC receivers in bit error rate.

T3former achieves higher Goodput approaching theoretical capacity.

Eliminates pilot overhead by leveraging waveform structure.

Abstract

A pilot-free integrated sensing and communication (ISAC) system is investigated, in which phase-modulated continuous wave (PMCW) and non-orthogonal multiple access (NOMA) waveforms are co-designed to achieve simultaneous target sensing and data transmission. To enhance effective data throughput (i.e., Goodput) in PMCW-NOMA ISAC systems, we propose a deep learning-based receiver architecture, termed two-timescale Transformer (T3former), which leverages a Transformer architecture to perform joint channel estimation and multi-user signal detection without the need for dedicated pilot signals. By treating the deterministic structure of the PMCW waveform as an implicit pilot, the proposed T3former eliminates the overhead associated with traditional pilot-based methods. The proposed T3former processes the received PMCW-NOMA signals on two distinct timescales, where a fine-grained attention mechanism captures local features across the fast-time dimension, while a coarse-grained mechanism aggregates global spatio-temporal dependencies of the slow-time dimension. Numerical results demonstrate that the proposed T3former significantly outperforms traditional successive interference cancellation (SIC) receivers, which avoids inherent error propagation in SIC. Specifically, the proposed T3former achieves a substantially lower bit error rate and a higher Goodput, approaching the theoretical maximum capacity of a pilot-free system.