Massive MIMO with Max-Min Power Control in Line-of-Sight Propagation Environment

A key component for the success of Massive MIMO is the asymptotic orthogonality of channel vectors. With M service antennas, the expected correlation between a pair of channel vectors in line-of-sight (LoS) propagation environment decreases at least as fast as log(M)/M while its counterpart in independent and identically distributed (iid) Rayleigh fading propagation environment decreases much slower at 1/sqrt(M), but the variance is higher in LoS. This signifies that most likely channel vectors are more nearly orthogonal in LoS than in iid Rayleigh, but in the worst case they can be highly correlated in LoS. Massive MIMO with max-min power control performs comparably in LoS and iid Rayleigh when a simple algorithm is applied to drop a few users with high channel vector correlation from service in LoS.