Flexible Rate-Splitting Multiple Access for Near-Field Integrated Sensing and Communications

TL;DR

This paper introduces a flexible rate-splitting multiple access framework for near-field integrated sensing and communications, optimizing system performance by joint beam design and user selection to enhance sensing accuracy and interference management.

Contribution

It proposes a novel, flexible RSMA scheme for NF ISAC that optimizes power and rate allocation, and user selection, to improve sensing and communication performance.

Findings

Significantly reduces distance estimation errors by ~100%.

Reduces angle estimation errors by ~20%.

Outperforms conventional RSMA and SDMA schemes.

Abstract

This letter presents a flexible rate-splitting multiple access (RSMA) framework for near-field (NF) integrated sensing and communications (ISAC). The spatial beams configured to meet the communication rate requirements of NF users are simultaneously leveraged to sense an additional NF target. A key innovation lies in its flexibility to select a subset of users for decoding the common stream, enhancing interference management and system performance. The system is designed by minimizing the Cram\'{e}r-Rao bound (CRB) for joint distance and angle estimation through optimized power allocation, common rate allocation, and user selection. This leads to a discrete, non-convex optimization problem. Remarkably, we demonstrate that the preconfigured beams are sufficient for target sensing, eliminating the need for additional probing signals. To solve the optimization problem, an iterative algorithm is proposed combining the quadratic transform and simulated annealing. Simulation results indicate that the proposed scheme significantly outperforms conventional RSMA and space division multiple access (SDMA), reducing distance and angle estimation errors by approximately 100\% and 20\%, respectively.