MIMO capacity in hallways and adjacent rooms

Channel capacity in a waveguide with mode coupling is limited by a keyhole effect caused by the propagation mechanism. The coupling among the propagating modes reduces the channel rank, and at sufficient distances between the transmitter and receiver, the channel rank converges to 1. Measurements of the received power and channel capacity along a hallway and in rooms beside it, show a decrease of capacity with distance, which explained by the keyhole effect in the hallway.