This paper investigates multi-user grouping (MUG) to improve energy efficiency (EE) in cell-free massive multiple-input multiple-output systems with access point (AP) switch on/off (ASO). ASO puts those APs into sleep mode which have little contribution with any spatially-multiplexed user equipments (UEs). However, in general, ASO can be less effective especially when spatially-multiplexed UEs are widely distributed in the area. Therefore, it is crucial to systematically integrate ASO and MUG, where UEs are divided into groups for spatial multiplexing. As a concrete procedure, we propose a practical MUG-ASO algorithm utilizing the criteria based on correlations of large-scale fading among UEs for effective EE improvement. The proposed algorithm can effectively select closely locating UEs into the same group for spatial multiplexing, and then it can put comparatively large number of APs into sleep mode at each time slot. Numerical example simulations show the effectiveness of the integration for EE improvement; in a typical case, the proposed algorithm can improve EE by 29.4% at 50-percentile compared to the conventional ASO algorithms with random MUG without severe degradation of spectral efficiency.
Joint Multi-User Grouping and AP Switch On/Off for Energy-Efficient Cell-Free Massive MIMO
2024-06-24
776258 byte
Conference paper
Electronic Resource
English