A Green Coordinated Multi-Cell NOMA System With Fuzzy Logic Based Multi-Criterion User Mode Selection and Resource Allocation

We consider a multi-cell non-orthogonal multiple access (NOMA) system with coordinated base stations and investigate its downlink user coordination mode selection and resource allocation to green the system while maintaining high spectral efficiency, in the presence of inter-cell interference. To the best of our knowledge, this is the first work to consider multiple criteria in user coordination mode selection for coordinated NOMA systems, and a fuzzy logic (FL) based approach is proposed to balance among multiple criteria to achieve higher robustness against the combined effect of shadowing, fading and inter-cell interference, compared to the previous single-criterion-based user coordination mode selection methods. This is also the first known effort to investigate multi-subchannel resource allocation for coordinated NOMA where the previous work on coordinated orthogonal multiple access is not applicable. Two resource allocation algorithms are proposed: first, a serving channel gain based subchannel allocation (SCG-SA) algorithm, based on the theoretical proof that the total transmission power is mono-decreasing with respect to the SCG of the non-coordinated user in each cell with the highest channel gain on the shared subchannel; second, a low-complexity FL user ranking order based joint resource allocation algorithm, which requires no separate user ranking process in subchannel allocation, thanks to the FL ranking list generated from user coordination mode selection. Also, the effects of imperfect channel state information and successive interference cancellation are considered. Numerical results show that the proposed multi-criterion based schemes significantly outperform the previous schemes based on single-criterion user coordination mode selection, in terms of transmission power and energy efficiency, contributing to a greener system.