User-Centric Multi-Dimensional Modulation for Receiver Operational Cost Minimization in Non-Orthogonal Domains

The perpetual efforts in supporting ever-growing QoS requirements have brought new challenges in 5G advanced and 6G networks such as increased spatial channel correlation, large delaydoppler spread, higher carrier frequency offset, and more complex multi-path signals. As a result, the orthogonality among spatial, time-frequency, and delay-doppler domain radio resources is often destroyed leading to non-orthogonal radio resources a common paradigm for modulation in next-generation networks. Such non-orthogonality degrees have become both transmitter-receiver pair specific and domain specific due to diverse channel conditions perceived by the UE involved. Furthermore, the operational cost of restoring orthogonality and demodulation varies across domains due to different synchronization and interference cancelation capabilities of receiver in different domains. To tackle these issues, we propose user-centric multi-dimensional modulation (UC-MDM) aiming to minimize receiver costs while supporting necessary data rates. Our situation-aware, cost-conscious UC-MDM optimizes resource separation across spatial, time-frequency, and delay-doppler domains, utilizing optimal resource combinations through multidimensional modulation in either spatial-time-frequency or spatial-delay-doppler domains. Simulation results under simultaneously varied domain specific non-orthogonality degrees validate that UC-MDM achieves required data rate with less operational cost from user-device compared to MIMO-OFDM and MIMO-OTFS systems.