User Scheduling in Multi-State Los/NLoS Crowded XL-MIMO Channels.

In this paper, we have derived a closed-form expression for the signal-to-interference-and-noise ratio (SINR) in extra-large multiple-input multiple-output (XL-MIMO) systems with spatially correlated multi-state line-of-sight (LoS)/ non- LoS(NLoS) channels, which is valid for a sufficiently large number of base station (BS) antennas, when least-squares (LS) channel estimation is used and under the absence of pilot reuse among the scheduled user equipments (UEs). The derived SINR expression can be computed based on the channel statistics instead of the instantaneous channel realizations, which makes it valid for hundreds of channel coherence blocks. We also have proposed an expeditious user scheduling (US) algorithm for crowded XL-MIMO systems, which aims to maximize the sum spectral efficiency (SE) with the constraint of assigning mutually orthogonal pilots to all the scheduled UEs, such that their channel estimation accuracy is very high. The numerical results reveal that the proposed SINR expression is very accurate for a relatively large number of BS antennas, and that the proposed US algorithm improves considerably the sum SE in crowded scenarios.