Rotatable Antenna Meets Multiple Access: NOMA or OMA?
Provides first theoretical comparison of multiple access schemes under RA for power efficiency, clarifying when NOMA or OMA is preferable.
This work compares NOMA and OMA in rotatable antenna (RA) systems for transmit power minimization. Results show RA reduces power vs fixed antennas; RA-NOMA can be worse than TDMA for symmetric users but better for asymmetric scenarios.
Rotatable antenna (RA) technology has emerged as a promising solution to enhance spectrum efficiency by exploiting additional spatial degrees of freedom (DoFs) in multiple access networks. However, the relative performance superiority among different multiple access schemes remains largely unclear due to the unique capability of RA in reconfiguring the directional gain pattern. In this letter, we conduct a theoretical comparison between non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) schemes in RA-assisted communication systems in terms of transmit power minimization, subject to constraints on antenna rotational range and users' target rates. To address the associated non-convex optimization problem, a particle swarm optimization (PSO) algorithm is employed to optimize the rotational angle. Simulation results demonstrate that RA-assisted schemes significantly reduce transmit power compared to fixed-antenna benchmarks. Furthermore, RA-assisted NOMA may perform worse than time-division multiple access (TDMA) for symmetric user deployments, while it exhibits superior robustness and energy efficiency in asymmetric scenarios.