  Massive multiple-input multiple-output (MIMO) is becoming a mature
technology, and has been approved for standardization in the 5G ecosystem.
Although there is a large body of papers on the theoretical analysis of massive
MIMO, the majority of relevant work assumes the simplified, yet overly
idealistic, Kronecker-type model for spatial correlation. Motivated by the
deficiencies of the Kronecker model, we invoke a naturally generalized spatial
correlation model, that is the Weichselberger model. For this model, we pursue
a comprehensive analysis of massive MIMO performance in terms of channel
hardening and favorable propagation (FP). We identify a number of scenarios
under which massive MIMO may fail, in terms of channel hardening and FP, and
discuss their relevance from a practical perspective.
