  Cell-Free (CF) Massive MIMO is an alternative topology for future wireless
networks, where a large number of single-antenna access points (APs) are
distributed over the coverage area. There are no cells but all users are
jointly served by the APs using network MIMO methods. Prior works have claimed
that CF Massive MIMO inherits the basic properties of cellular Massive MIMO,
namely channel hardening and favorable propagation. In this paper, we evaluate
if one can rely on these properties when having a realistic stochastic AP
deployment. Our results show that channel hardening only appears in special
cases, for example, when the pathloss exponent is small. However, by using
5--10 antennas per AP, instead of one, we can substantially improve the
hardening. Only spatially well-separated users will exhibit favorable
propagation, but when adding more antennas and/or reducing the pathloss
exponent, it becomes more likely for favorable propagation to occur. The
conclusion is that we cannot rely on channel hardening and favorable
propagation when analyzing and designing CF Massive MIMO networks, but we need
to use achievable rate expressions and resource allocation schemes that work
well also in the absence of these properties. Some options are reviewed in this
paper.
