Why does Massive MIMO show lower beamforming gain in line-of-sight conditions? 

Tech Expert: Hi Mohamed, I have a question for you.

Me: Go ahead.

Tech Expert: Our outdoor LOS cells show lower beamforming gain than NLOS cells. Calibration issue?

Me: Not calibration. It is channel rank and it surprises most engineers.

In NLOS environments:

▪️ Multiple reflections → rich channel → high rank matrix H

▪️ Beamformer focuses precisely → MU-MIMO works well ✅

In strong LOS environments:

▪️ One direct path dominates → rank 1 matrix H

▪️ Spatial multiplexing collapses → single beam ⚠️

Tech Expert: So Massive MIMO is worse outdoors?

Me: Not worse, differently. Per-UE SINR is strong in LOS. But MU-MIMO efficiency drops because channels are too spatially correlated.

💡 Fix: increase minimum angular separation threshold for MU-MIMO pairing. Only pair UEs with sufficient spatial isolation.

Tech Expert: Thanks a lot.