  We analyse the behaviour of a massive multi-user MIMO (MU-MIMO) system
comprising a base station (BS) equipped with one of five different antenna
topologies for which the spatial aperture is either unconstrained, or
space-constrained. We derive the normalized mean interference (NMI) with a
ray-based channel model, as a metric for topology comparison in each of the two
cases. Based on the derivation for a horizontal uniform rectangular array
(HURA) in [1], we provide closed-form NMI equations for the uniform linear
array (ULA) and uniform circular array (UCirA). We then derive the same for a
vertical URA (VURA) and uniform cylindrical array (UCylA). Results for the
commonly-considered unconstrained case confirm the prior understanding that
topologies with wider azimuth footprints aid performance. However, in the
space-constrained case performance is dictated by the angular resolution
afforded by the topology, particularly in elevation. We confirm the behavioural
patterns predicted by the NMI by observing the same patterns in the system SINR
with minimum mean-squared error (MMSE) processing.
