Secure RSMA for CF-mMIMO Systems With Low-Resolution DACs

This letter presents an investigation into secure transmission in a downlink rate-splitting-aided cell-free massive multiple-input multiple-output system. In this system, each user equipment (UE) receives both common and private streams from access points, while simultaneously attempting to wiretap the private streams of other UEs. The analysis considers the presence of low-resolution digital-to-analog converters and imperfect channel state information. By incorporating these factors, we derive tight closed-form expressions for the data rate and secrecy rate under Ricean fading channels. Furthermore, we formulate a power control problem with the objective of maximizing the weighted sum data rate, while ensuring a target secrecy rate for all UEs. A path-following optimization algorithm is then proposed to determine its solution numerically. The theoretical analyses, as well as the performance of the proposed power control algorithm, are rigorously validated through extensive simulations.