Phase-Shifted Pilot Design for NOMA-Empowered Uplink ISAC Systems

TL;DR

This paper introduces a phase-shifted pilot design for NOMA-enabled uplink ISAC systems, enhancing spectral efficiency and sensing resolution while reducing computational complexity.

Contribution

It proposes a novel phase-shifted pilot scheme and nulling variant that improve resource sharing and interference management in ISAC networks.

Findings

Maintains sensing integrity with phase-shifted pilots.

Reduces receiver computational complexity by over 18%.

Enhances spectral efficiency in NOMA-empowered ISAC systems.

Abstract

The deployment of multiple transmitters (TXs) in integrated sensing and communication (ISAC) networks necessitates efficient resource sharing to overcome the limitations of orthogonal allocation. While conventional interleaved (CI) pilots combined with non-orthogonal multiple access (NOMA) improve spectral efficiency (SE), they inherently compromise sensing resolution due to spectral sparsity, rendering the CI nulling (CIN) extension a strictly limited remedy. This paper proposes a phase-shifted (PS) pilot design and its novel PS nulling (PSN) variant to integrate a communication TX (CTX) over the PS-ISAC framework. The PSN variant strategically punctures sensing signals at CTX pilot locations to preserve initial channel estimates, enabling a dense data overlay. To resolve the resulting multi-TX interference, joint iterative interference cancellation (IIC) is adapted for non-nulling configurations and sequential IIC is adapted for nulling variants, optimizing for both detection robustness and convergence speed. Simulation results across varying STX densities and modulation orders demonstrate that the phase-shifted frameworks maintain sensing integrity while explicitly reducing receiver-side computational complexities by $18.8\%$ and $21.0\%$ against their respective interleaved baselines.