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

Massive MIMO relies on the asymptotic orthogonality of channel vectors to different users. For <inline-formula> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> service antennas, the expected correlation between a pair of channel vectors under line-of-sight (LoS) conditions decreases at least as fast as <inline-formula> <tex-math notation="LaTeX">$\log (M)/M$ </tex-math></inline-formula>, while in independent and identically distributed (iid) Rayleigh fading, it decreases much slower at <inline-formula> <tex-math notation="LaTeX">$1/\sqrt {M}$ </tex-math></inline-formula>, but the variance is higher under LoS. This signifies that typically channel vectors are more nearly orthogonal under LoS, but with a non-negligible probability, they can have an anomalously large correlation. A single-cell analysis discloses that Massive MIMO with max-min power control performs comparably under LoS and iid Rayleigh, when a simple algorithm is applied under LoS to drop a small number of high-correlation users from service.